Source: https://patents.google.com/patent/JP5920214B2/en
Timestamp: 2020-01-28 22:18:24
Document Index: 84804269

Matched Legal Cases: ['Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61', 'Application No. 61']

JP5920214B2 - Electrode layer, lithium ion battery, and electrode layer manufacturing method - Google Patents
Electrode layer, lithium ion battery, and electrode layer manufacturing method Download PDF
JP5920214B2
JP5920214B2 JP2012513226A JP2012513226A JP5920214B2 JP 5920214 B2 JP5920214 B2 JP 5920214B2 JP 2012513226 A JP2012513226 A JP 2012513226A JP 2012513226 A JP2012513226 A JP 2012513226A JP 5920214 B2 JP5920214 B2 JP 5920214B2
JP2012513226A
JP2012528464A (en
キュイ、イ
ハン、ソン
ラブネス、ガイルン、イー．
アンプリウス、インコーポレイテッド
2009-06-02 Priority to US18352909P priority
2009-06-02 Priority to US61/183,529 priority
2010-05-26 Application filed by アンプリウス、インコーポレイテッド filed Critical アンプリウス、インコーポレイテッド
2010-05-26 Priority to PCT/US2010/036237 priority patent/WO2010138619A2/en
2012-11-12 Publication of JP2012528464A publication Critical patent/JP2012528464A/en
2016-05-18 Publication of JP5920214B2 publication Critical patent/JP5920214B2/en
This application claims the benefit of US Provisional Patent Application No. 61 / 181,637 (filing date: May 27, 2009, title of invention: “core-shell high capacity nanowires for battery electrodes”). The entire contents of the provisional patent application are incorporated herein by reference. The present application also includes US Provisional Patent Application No. 61 / 183,529 (filing date: June 2, 2009, title of invention: “electrospinning method for producing battery electrodes (electrostatic spinning method)”). Insist on the benefits of. The entire contents of the provisional patent application are incorporated herein by reference.
High-capacity electrochemically active materials are desirable as battery materials. However, there is a problem that the volume change in the battery cycle is large, for example, it expands during lithiation and shrinks during non-lithiation. For example, silicon expands by as much as 400% during lithiation with a theoretical capacity of about 4200 mAh / g, that is, Li 4.4 Si production. When the volume change occurs at such a size, problems such as powdering of the active material structure, intermittent electrical connection, and capacity reduction occur.
Such a problem can be partially addressed by forming a predetermined type of nanostructure from a high-capacity active material. Nanostructures are at least one dimension in nanounits, and expansion / reduction along the nanounit dimension tends to be less damaging than expansion / reduction along larger dimensions. For this reason, the nanostructure is hardly damaged during the battery cycle. However, it is difficult to integrate a plurality of nanostructures while appropriately attaching the active material in the electrode layer of the battery. This integration involves processing to build and maintain electrical connections and mechanical support over many cycles.
An electrode layer used in a storage battery such as a lithium ion battery, and a related manufacturing technique are provided. In such an electrode layer, hollow nanostructures comprising high capacity electrochemical active materials such as silicon, tin and germanium are interconnected. Manufacturing techniques according to certain embodiments include forming a nanoscale coating around a plurality of template structures, removing at least a portion of the structures, and / or shrinking the structures. Forming a cavity. This cavity provides a space for the nanostructured active material to enter as it expands during the battery cycle. Such a configuration can reduce the risk of powdering and maintain electrical contact between the nanostructures. In addition, the surface area that can be used for ion circulation with the electrolyte can be greatly increased. The nanostructure includes a nanoscale shell, but may be much larger for other dimensions. If nanoscale coatings formed around two adjacent template structures overlap each other, it is possible to interconnect the nanostructures in forming the nanoscale coating. According to certain embodiments, the electrode layer further includes a conductive substrate. The conductive substrate may also be interconnected to the nanostructure.
According to certain embodiments, a method is provided for providing an electrode layer comprising interconnected hollow nanostructures. The nanostructure contains a high capacity electrochemical active material. Receiving a template having a plurality of template structures; forming a high-capacity electrochemically active material nanoscale template coating around the plurality of template structures; and removing and / or reducing at least a portion of the templates. Forming an electrode layer. The template may be manufactured using an electrospinning method. For example, an electrospinning method is performed using a polymer material to form template nanofibers that are at least about 5 micrometers in length. The template may comprise polyacryl nitride (PAN), nylon, polyethylene, polyethylene oxide, polyethylene terephthalate, polystyrene, and / or polyvinyl. According to certain embodiments, the template is formed as a layer having a thickness between about 10 micrometers and 150 micrometers and a porosity between about 20% and 80%.
The method according to certain embodiments comprises pre-treating the template by pressing the template, thermally stabilizing the template, and / or carbonizing the template. For example, the thermal stabilization treatment of the template may include heating the template to a temperature between about 150 degrees Celsius and 250 degrees Celsius for at least about 2 hours in an argon atmosphere. The method according to certain embodiments further comprises forming a high-capacity electrochemically active material nanoscale substrate coating on the surface of the conductive substrate adjacent to the template. The nanoscale template coating and the nanoscale substrate coating may be partially overlapped to interconnect the conductive substrate and the plurality of interconnected hollow nanostructures.
According to certain embodiments, the step of forming the nanoscale template coating around the template includes two deposition steps, for example, an initial deposition step and a bulk deposition step. The initial film forming step may be performed under initial processing conditions that avoid a large distortion of the template shape. The bulk film formation stage is performed under bulk processing conditions different from the initial processing conditions. The bulk processing conditions may be set so that the deposition rate of the nanoscale template coating is higher in the bulk deposition step.
According to certain embodiments, removal or reduction of at least a portion of the template is performed while forming the nanoscale template coating around the plurality of template structures. Removing or reducing a portion of the template performs one or more of template firing, template chemical etching, and template annealing at a temperature of at least about 300 degrees Celsius. May include.
The method according to certain embodiments may further comprise forming a second coating over the plurality of interconnected hollow nanostructures. The second coating may increase the conductivity of the electrode layer, improve the solid electrolyte interface (SEI) properties of the electrode layer, and / or limit structural changes in the interconnected hollow nanostructures.
An electrode layer utilized in a storage battery, according to certain embodiments, is interconnected with an aspect ratio of at least about 4, a length of at least about 5 micrometers, and a shell thickness of less than about 100 nanometers. A plurality of hollow nanostructures. The nanostructure may include one or more high capacity electrochemical active materials. The plurality of interconnected hollow nanostructures form a plurality of internal voids that provide space for high capacity electrochemical active material to expand and enter in the battery cycle. The plurality of internal voids may be substantially inaccessible to the storage battery electrolyte. According to certain embodiments, the electrode layer achieves a stable energy capacity of at least about 2000 mAh / g even after at least 100 cycles, depending on the weight of the active material. The electrode layer may further comprise a plurality of bonding structures that interconnect two or more hollow nanostructures. The plurality of bonding structures may include one or more materials of a high capacity electrochemical active material, a metal, and a polymer binder.
The electrode layer according to certain embodiments includes a conductive substrate. The interconnected hollow nanostructures and a portion of the conductive substrate may be interconnected with additional junction structures. According to certain embodiments, the active material includes silicon, tin, and / or germanium. The electrode layer may further comprise an outer layer that substantially covers the outer surface of the interconnected hollow nanostructures. The outer layer may include carbon, titanium, silicon, aluminum, and / or copper. According to certain embodiments, the electrode layer has a porosity between about 20% and 80%. According to certain embodiments, the storage battery is a lithium ion battery and the active material of the electrode layer is a negative electrode active material.
A lithium ion battery according to certain embodiments has a plurality of interconnected hollows having an aspect ratio of at least about 4, a length of at least about 5 micrometers, and a shell thickness of less than about 100 nanometers. An electrode layer having a nanostructure is provided. The plurality of hollow nanostructures may include one or more high capacity electrochemical active materials. The plurality of hollow nanostructures form a plurality of internal voids that provide space for high capacity electrochemically active material to expand and enter in the battery cycle.
In addition, an electrode assembly is provided that includes an electrochemically active material utilized in a battery such as a lithium ion battery. Furthermore, a method for manufacturing the electrode assembly is provided. In the manufacturing method according to the predetermined embodiment, one or more electrospinning processes are performed. For example, an electrospinning process for forming a fiber layer on a conductive substrate is performed. The fiber may include one or more electrochemically active materials. In the same or another embodiment, the fiber or similar fiber can be utilized as a template for depositing one or more electrochemically active materials. Some examples of active materials include silicon, tin, and / or germanium. Further provided is an electrode fiber comprising a core comprising a first active material and a shell comprising a second active material or optionally a second shell (an inner shell provided to surround the periphery). The second active material has electrochemically opposite properties to the first active material (eg, the core includes a negative electrode active material and the shell includes a positive electrode active material. One or more shells include separators and It may function as an electrolyte.
According to certain embodiments, a method of manufacturing an electrode assembly that includes an electrochemically active material is provided. The electrode assembly can be used in a battery such as a lithium ion battery. The method includes a step of preparing a thin film substrate having a first surface and a second surface, and a first layer having a first fiber formed by an electrospinning method, using an electrospinning film forming method. Forming a film on the first surface. Fibers formed by electrospinning include one or more electrochemically active materials. The method may further include depositing a second layer including a second fiber formed by electrospinning using an electrospinning deposition method. According to certain embodiments, the method performs one or more of processes such as annealing, calcination, carbonization, sintering, pressing, and cooling.
According to certain embodiments, a second layer is deposited on the second surface of the substrate. The first layer and the second layer may have approximately the same thickness and approximately the same composition. According to certain embodiments, the first layer includes a negative electrode active material. The second layer may include a positive electrode active material. Furthermore, the thin film substrate may include a permeable membrane, and may include, for example, a battery separator, a battery electrolyte, or a combination of a battery separator and an electrolyte. According to certain embodiments, the first layer and / or the second layer comprise a plurality of separate patches, the patches being between the patches, the first side and / or the second side of the substrate. Is disposed on the substrate so that a part of the substrate is exposed. The plurality of separate patches may be formed using two mechanical stops and / or one electrical shield.
According to certain embodiments, the second layer is deposited over the first layer. The method further includes depositing a third layer including a third fiber formed by an electrospinning method over the second layer, and a fourth layer including a fourth fiber formed by the electrospinning method. Forming the four layers above the third layer, and separating the first layer from the substrate to form four layers, namely, the first layer, the second layer, the third layer, and the fourth layer. Forming a laminate including these layers. The first layer includes a fiber formed by an electrospinning method that includes one or more electrochemically active materials. The third fiber formed by electrospinning includes different active materials. For example, the first layer may include a positive electrode active material, while the third layer may include a negative electrode active material, or vice versa. The fourth layer and the second layer may have substantially the same thickness and may have substantially the same composition, and include a battery separator, a battery electrolyte, or a combination of a battery separator and an electrolyte. Good. The method may further include a step of winding a laminate having four layers to form a jelly roll portion, and disposing the jelly roll portion in the battery casing.
The electrode assembly according to certain embodiments includes an electrolyte material. In the same or other embodiments, the fiber formed by the first layer electrospinning method includes two fiber groups, the first fiber group includes one electrochemically active material, and the second The fiber group contains another electrochemically active material. Examples of electrochemically active materials include silicon, germanium, and tin. As a specific example, the electrochemically active material includes silicon nanowires. According to certain embodiments, the substrate used to deposit the fiber layer formed by electrospinning is copper foil, stainless steel foil, aluminum foil, titanium foil, Mylar® film, polymer paper , Carbon fiber paper, and carbon fiber mesh, a foil that is not interrupted by one or more of a plurality of types. According to certain embodiments, the step of depositing the first layer includes the step of supplying a liquid precursor from an electrospinning nozzle. The liquid precursor includes particles of an active material based on a polymer.
An electrode layer manufacturing method according to a predetermined embodiment includes a step of forming a first layer including a fiber formed by an electrospinning method. The fiber has a core-shell structure and includes one or more electrochemically active materials. In this method, the first layer may be processed to change the shape and / or composition of the fiber formed by electrospinning to form the electrode layer. By processing, the core which is a solid changes into a hollow cylindrical body. Treatment includes drying the solvent from the fiber formed by electrospinning and / or one or more post-deposition treatments such as annealing, calcination, carbonization, sintering, pressing and / or cooling. As good as
In the electrode layer manufacturing method according to a predetermined embodiment, a first layer including a fiber formed by an electrospinning method is formed. A fiber formed by electrospinning may include a polymer material. The method may further include forming an amorphous silicon coating around the fiber formed by electrospinning and processing the first layer to form an electrode layer. A fiber formed by electrospinning may include an electrochemically active material.
An electrode fiber used in a battery electrode according to a predetermined embodiment includes a core having a first electrochemically active material, a shell formed around the core, and a shell formed around the shell. And a second shell containing a second electrochemically active material having electrochemical characteristics opposite to that of the first active material. The inner shell may include a separator material and / or an electrolyte material and may have a function of electronically insulating between the core and the second shell. The shell may be further configured to transport electrochemically active ions between the core and the second shell.
These and other aspects of the invention are further described below with reference to the drawings.
6 is a process flow chart for explaining a method for preparing an electrode layer having an interconnected hollow nanostructure containing a high-capacity electrochemically active material according to a predetermined embodiment.
1 is a schematic perspective view showing an assembly comprising a substrate and a plurality of template patches, according to certain embodiments. FIG.
1 is a schematic side view showing an assembly comprising a substrate and a plurality of template structures, according to certain embodiments. FIG.
FIG. 6 is a schematic diagram illustrating a template comprising two template structures provided close to a substrate and close to each other prior to forming a nanoscale coating comprising a high volume material according to certain embodiments. is there.
FIG. 6 is a schematic diagram illustrating an electrode layer comprising interconnected hollow nanostructures formed on the periphery of two templates and on a substrate surface, including two bonded structures, according to certain embodiments.
It is the schematic which shows the mode of the structure in three different steps of the electrode layer manufacturing process which concerns on predetermined embodiment as an example.
It is a schematic top view which shows the electrode structural example which concerns on predetermined | prescribed embodiment. It is a schematic side view which shows the electrode structural example which concerns on predetermined embodiment.
It is a schematic top view which shows the example of the cell of the structure wound circularly concerning predetermined embodiment. It is a schematic perspective view which shows the example of the cell of the structure wound by the circle which concerns on predetermined embodiment.
It is a schematic top view which shows an example of the cell of the structure wound by the prism shape which concerns on predetermined | prescribed embodiment.
It is a schematic top view which shows an example of the laminated body comprised from the some electrode which concerns on predetermined | prescribed embodiment, and a some separator sheet. It is a schematic perspective view which shows an example of the laminated body comprised from the some electrode which concerns on predetermined | prescribed embodiment, and a some separator sheet.
It is a schematic sectional drawing which shows the example of the cell of the winding structure which concerns on embodiment.
It is a figure which shows an example of the general process which manufactures an electrochemical cell.
It is a figure which shows an example of the electrospinning device for forming one or more layers which comprise the electrode which concerns on predetermined embodiment.
It is a figure which shows an example of the electrospinning apparatus for forming the 1 or more layer which comprises the electrode which concerns on predetermined embodiment.
It is a figure which shows an example of the general process which forms one or more layers which comprise the electrode which concerns on predetermined | prescribed embodiment.
It is a figure which shows an example of the fiber for batteries inject | emitted from the electrospinning nozzle.
It is a figure which shows two examples of the fiber for batteries concerning predetermined embodiment.
FIG. 3 is a top view showing a patch comprising a substrate and four battery layers, according to certain embodiments. 6 is a side view of a patch comprising a substrate and four battery layers, according to certain embodiments. FIG.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be implemented without adopting some or all of the specific and detailed contents described below. Also, detailed descriptions of known processing are omitted to avoid unnecessarily obscuring the present invention. Although the present invention will be described based on specific embodiments, it should be understood that the present invention is not limited to such embodiments.
Nanostructures used in storage batteries can be formed from high capacity electrochemical active materials. Nanostructures tend to degrade very slowly in battery cycles compared to large structures. This is because the nanostructures are less likely to be powdered and thus maintain electrical contact with the conductive current collector of the electrode. However, it is difficult to manufacture an electrode active layer having a nanostructure while appropriately attaching an active material. For example, it is difficult to mechanically place, support and electrically interconnect multiple nanostructures and subsequently maintain this placement and interconnection over multiple cycles. For example, solid nanoparticles with a diameter of only 0.05 to 0.10 micrometers typically have many electrical properties in order to ensure conductivity to the substrate, which is an active layer having a thickness of 50 to 100 micrometers. Connections and intermediate structures must be utilized. For example, the initial electrical connection formed by direct contact between the nanoparticles and the conductive additive is often lost as the nanoparticles expand during lithiation / charging. When the nanoparticles swell, they leave the other components. If the nanoparticles shrink during non-lithiation / discharge, many initial connections may be lost, resulting in “unconnected” active particles that are essentially “inactive” particles. End up. Another type of nanostructure is a nanofilm. Since nanofilms are usually less than 0.1 to 0.25 micrometers in thickness, the amount of active material that can be contained per unit area of the electrode surface becomes very small, and for most battery applications An appropriate capacity cannot be obtained.
The interconnected hollow nanostructures disclosed herein combine some of the beneficial properties of the nanostructures described above to realize new properties and functions that could not be realized with conventional solid structures. An example of a hollow silicon nanostructure utilized in a battery electrode is shown in FIG. 3B. The hollow nanostructure comprises a nanoscale shell, but other dimensions may be much larger. For example, nanotubes may have an inner diameter of up to 5 micrometers and a length of up to 50 micrometers, sometimes longer. Even for such relatively large nanotubes, the nanoscale shell is thin, so it does not cause large-scale powdering in the lithiation / non-lithiation cycle. Such nanotubes are not limited to any particular theory in which the voids that can be accommodated when the active material expands are provided inside, but high capacity materials such as amorphous silicon, When arranged in a hollow structure, it is considered that the expansion / contraction behavior is different from the case of being arranged in another nanostructure. Surprisingly, this difference has been found to contribute to the stability of the new nanostructure during battery cycles. This is evident from the exceptionally long cycle life of batteries incorporating the new electrode layer. For example, according to the experimental results, it has been found that a stable capacity of 2000 mAh / g or more can be obtained even after 140 cycles.
Interconnected hollow nanostructures can be prepared by forming a coating comprising a high volume of material around the template structure. According to certain embodiments, when a plurality of template structures are disposed at positions relatively close to each other or to the substrate, the coating layers overlap to form a bonded structure. After this, the template is partially or entirely removed and / or reduced to form cavities inside the nanostructure. The electrode layers and manufacturing methods are described in more detail below with respect to the above and other aspects.
FIG. 1 is a process flow chart illustrating a method for preparing an electrode layer having interconnected hollow nanostructures containing a high capacity electrochemical active material, according to certain embodiments. Process 100 may begin with receiving a template comprising a plurality of template structures in operation 102. Examples of template structures include high aspect ratio (eg, at least about 4, 10 or 50) fibers and hollow tubes (eg, carbon nanotubes), particles (eg, substantially circular particles), flakes, particles or spheres, And other types of template structures. The template may generally have any shape that provides a suitable surface for forming a coating of high volume material that can subsequently be transformed into a hollow nanostructure. The major cross-sectional dimensions (eg, fiber and particle diameters) of the template structure may be between about 1 nanometer and 5000 nanometers, and more specifically between about 10 nanometers and 1000 nanometers. And more specifically between 100 and 500 nanometers. According to certain embodiments, the template comprises a plurality of randomly oriented fibers. The fiber may be linear (for example, carbon nanotube, carbon fiber) or curved (for example, polymer fiber formed by electrospinning). The fibers may average at least about 100 nanometers in length, more specifically at least about 1 micrometer, or at least about 50 micrometers.
Each of the fibers or other template structures are relatively close to each other such that when a coating layer is deposited on each template structure, at least some of the coating layers overlap to form a coupling structure. It may be arranged. In other words, the distance between the template structures must be at least partially less than twice the thickness of the coating layer. Some template structures may be in direct contact with each other. For example, a plurality of randomly oriented fiber layers can be utilized as a template with each fiber having at least two points of contact with other fibers.
According to certain embodiments, the template has a porosity between about 20% and 80%, more specifically between about 50% and 70%. To increase the thickness of the deposited layer and / or to form a high porosity electrode layer (eg, to improve electrolyte migration), it is necessary to increase the porosity. As good as The porosity of the template should be distinguished from the porosity of the electrode layer which also depends on other factors. According to certain embodiments, a plurality of template structures are attached to another common element, for example a substrate such as a current collector substrate. In such an embodiment, multiple template structures may exist without contacting each other. For example, a metal silicide nanowire can be formed on a metal substrate and used as a template. Examples of such templates are described in US Provisional Patent Application No. 61 / 310,183 (Title of Invention: “Electrochemically Active Silicide-Containing Structure”, Filing Date: March 3, 2010). Yes. The provisional patent application is incorporated herein by reference. Even in such a template, there may be some places where the template structures are accidentally contacted.
The template should be resistant to processing conditions in forming a high volume coating, at least in the initial stages. The template may be tolerated to a certain extent, but may need to be able to provide mechanical support to the formed coating at an early stage. It must be avoided that the shape is greatly distorted until a hollow nanostructure cannot be finally formed. To this end, a robust template material (eg, a heat resistant material) may be selected, or the coating conditions may be controlled in a specific manner. This will be described in detail below.
Examples of template materials include various polymer materials (eg, polyacryl nitride (PAN) (as oxidized PAN fiber), nylon, polyethylene, polyethylene oxide, polyethylene terephthalate, polystyrene and polyvinyl), carbon-based materials ( Examples thereof include graphite, coke, carbon nanotube, and carbon fiber), metal (for example, copper, nickel, aluminum), metal oxide, and metal silicide. Template material that can be provided as a fiber formed by electrospinning or any other form is described in US Provisional Patent Application No. 61 / 183,529 (Invention Name: “Electrospinning Method for Manufacturing Battery Electrodes”. "Application date: June 2, 2009"). This provisional application is incorporated herein by reference.
The layer formed by the template has a thickness between about 1 and 300 micrometers, more specifically between about 10 and 150 micrometers, and more specifically between about 50 and 100 micrometers. May be between micrometers. This layer may later become a layer that delimits the electrode layers. The template layer may be formed as an independent patch that defines the dimensions (eg, length and / or width) of subsequently formed electrodes. This example is further described below with reference to FIG. 2A.
According to certain embodiments, the template layer is placed adjacent to the substrate layer prior to coating. The substrate layer may be, for example, a thin foil having a thickness between about 5 micrometers and 50 micrometers, and more specifically between about 10 micrometers and 30 micrometers. According to other embodiments, the substrate layer is a mesh, perforated sheet, foam or the like. According to such an embodiment, the template may be placed inside the substrate layer. For example, the template structure is a dendrite extending from the mesh wire. Examples of substrate materials include copper, coated and uncoated metal oxides, stainless steel, titanium, aluminum, nickel, chromium, tungsten, metal nitride, metal carbide, carbon, carbon fiber, graphite, Examples include graphene, carbon mesh, conductive polymer, and a multilayer structure in which these materials are combined. According to certain embodiments, the substrate may have a plurality of functional layers and / or protective layers. For example, it may have a catalyst layer, a diffusion barrier layer, and / or an adhesive layer. Various examples of these layers are described in US Provisional Patent Application No. 61 / 260,297 (Title of Invention: “Interlayers Used in Electrode Manufacturing”, Filing Date: November 11, 2009). ing. This provisional application is incorporated herein by reference.
FIG. 2A is a schematic perspective view illustrating an assembly 200 comprising a substrate 202 and a plurality of template patches 204, according to certain embodiments. The assembly 200 is formed, for example, by directly forming a template fiber on the substrate 202 by an electrospinning method, or by depositing a fiber previously formed by an electrospinning method on the substrate 202. As good as Template patches may be provided on both sides of the substrate. Various examples of active layer arrangements are described below in connection with electrodes and batteries. According to certain embodiments, the length of the template patch 204 corresponds to the length or width of the battery electrode that is the final product. The support substrate 202 may be cut at a later stage of the manufacturing process to divide a plurality of template patches for each electrode.
FIG. 2B is a schematic side view illustrating an assembly 210 comprising a substrate 212 and a plurality of template structures 214, according to certain embodiments. A portion of the template structure 214 can be configured to be rooted in the substrate, which can provide a mechanical connection between the template and the substrate 212. If a portion of the template remains in the electrode layer, adopting a configuration rooted in the substrate in this way may lead to at least some mechanical support and / or conduction for the electrode layer. . The configurations rooted in the substrate are various as described in US patent application Ser. No. 12 / 437,529 (invention name: “electrode for storage battery with nanostructure”, filing date: May 7, 2009). Can take form. This application is incorporated herein by reference. According to some embodiments, the template is not bonded to the substrate. As described below in connection with FIGS. 3A and 3B, it may be bonded to the substrate by forming an active material coating. Other bonding processes and / or other materials may be utilized. For example, an adhesive layer can be formed on the substrate to increase the degree of adhesion between the active material structure and the substrate. According to other embodiments, the template structure 214 is temporarily supported on the substrate 212 using, for example, a binder. The binder is later removed before or during the formation of the high volume material. As another example, the template structure 214 is supported on the substrate 212 using electrostatic force or magnetic force.
Returning to FIG. 1, the received template may be pre-processed in process 104 prior to forming the high volume coating. Examples of pre-processing include processing for interconnecting template structures, processing for attaching a template to a substrate, processing for forming a template into a predetermined desired shape, and / or bringing the porosity of the template to a predetermined desired level. Processes, processes that thermally stabilize the template, processes that change the composition of the template (eg, carbonize the polymer) and processes that change conductivity, and processes that are performed for various other purposes. Can be mentioned. According to certain embodiments, the template is pressed to reduce the porosity of the template or to achieve a target thickness. This is for example to strengthen the interconnection between the resulting hollow nanostructures. The template based on the polymer may be heated to at least about 100 degrees Celsius when pressed, more specifically to at least about 150 degrees Celsius.
According to the same or another embodiment, the polymer-based template may be thermally stabilized in process 104. For example, a polymer-based template structure can have a temperature of between about 100 degrees Celsius and 300 degrees Celsius, more specifically, a temperature of between about 150 degrees Celsius and 250 degrees Celsius for about 1 hour. Can be heated in an inert atmosphere (eg, an argon atmosphere) for a period of between 48 hours and 48 hours, and more specifically for a period of between about 12 hours and 28 hours. According to certain embodiments, an oxidant may be added to the chamber to form an oxide layer (eg, to form an oxidized PAN), and a portion of the template structure may be fully fired to dimension the template structure. And / or the composition may be varied.
Polymer based templates may also be partially or wholly pyrolyzed or carbonized. For example, carbonization may lead to improved thermal stability and surface properties for subsequent processing. According to certain embodiments, to carbonize the template, to a temperature between about 300 degrees Celsius and 2000 degrees Celsius, more specifically, to a temperature between about 500 degrees Celsius and 1700 degrees Celsius, The template is heated for a period between 0.25 hours and 4 hours, more specifically, a period between about 0.5 hours and 2 hours. Carbonization or pyrolysis may be performed in a variety of environments, but is usually an inert or reducing environment.
Following the process 100, in operation 106, a nanoscale coating comprising one or more high volume active materials may be formed around the template. The coating may on average have a thickness between about 5 nanometers and 1000 nanometers, more specifically between about 10 nanometers and 500 nanometers, It may be between 20 and 100 nanometers. This thickness may be determined, at least in part, by the composition of the coated material and the cross-sectional dimensions (eg, diameter) of the shell formed by the coated material, and by the dimensions of the template as described above. It may be decided.
A high capacity active material is defined as any electrochemical active material with a theoretical lithiation capacity of at least about 600 mAh / g. Examples of such materials include silicon-containing materials (eg, crystalline silicon, amorphous silicon, other silicides, silicon oxide, silicon suboxide, silicon oxynitride), tin-containing materials (eg, tin, tin oxide), Examples include germanium, carbon-containing materials, metal hydrides (eg, MgH 2 ), metal silicides, metal phosphides, and metal nitrides. Other examples include carbon-silicon mixed materials (eg, carbon coated silicon, silicon coated carbon, silicon doped carbon, carbon doped silicon, and carbon and silicon) Alloys), carbon-germanium mixed materials (eg, carbon-coated germanium, germanium-coated carbon, germanium-doped carbon, carbon-doped germanium), and carbon-tin mixed materials ( For example, tin coated with carbon, carbon coated with tin, carbon doped with tin, and tin doped with carbon). According to certain embodiments, the coating may comprise an active material whose theoretical lithiation capability is less than the above values. Such an active material can be used in combination with a high-capacity active material or can be used alone.
This method may be used to form both the negative electrode layer and the positive electrode layer. Examples of electrochemical active materials for the positive electrode include various lithium metal oxides (eg, LiCoO 2 , LeFePO 4 , LiMnO 2 , LiNiO 2 , LiMn 2 O 4 , LiCoPO 4 , LiNi 1/3 Co 1/3. Mn 1/3 O 2 , LiNi X Co Y Al Z O 2 , LiFe 2 (SO 4 ) 3 ), fluorocarbon, iron fluoride (FeF 3 ) and other metal fluorides, metal oxides, sulfur, and these Combinations are listed. Moreover, what carried out doping to such a positive electrode active material and a negative electrode active material, and a non-stoichiometric thing can also be utilized. Examples of dopants include Group III and Group V elements of the periodic table (eg, boron, aluminum, gallium, indium, thallium, phosphorus, arsenic, antimony, and bismuth) and other suitable dopants (eg, sulfur And selenium).
According to certain embodiments, the coating forms a plurality of bonded structures. In the bonded structure, at least two coating layers covering the template structure adjacent to each other overlap. Further, the coating may be formed on the substrate as long as the substrate is provided in the vicinity of the template. In this case, a bonding structure can also be formed at the substrate interface. In other words, the coating can be described as an interconnect network composed of a plurality of layers formed around a plurality of template structures and, in certain embodiments, further layers formed on the substrate surface. . The layer formed around the template forms an interconnected hollow nanostructure shell or part of the shell that will ultimately be obtained. Specific examples of this process and corresponding structure are described in more detail below with reference to FIGS. 3A and 3B.
FIG. 3A shows an initial assembly 301 comprising a substrate 302 and two template structures 304a and 304b, showing the state prior to forming an active material coating around the template structure. According to certain embodiments, this assembly 301 is provided as a template. Template structures 304a and 304b are illustrated as having a variable gap between them and a variable gap between lower template structure 304a and substrate 302. In some areas, this gap is less than twice the thickness of the high volume coating and a bonded structure will be formed at that location.
FIG. 3B shows the processed assembly 303 after forming a high volume coating composed of three layers 306a, 306b, and 306c. The original template structures 304a and 304b may or may not be present in the processed assembly 303. This coating layer is illustrated as forming two bonding structures 308 and 310. More specifically, the coupling structure 308 is formed at a location where the layers 306a and 306b overlap. As described above, template structures 304a and 304b had a separation distance less than twice the coating thickness at this location. Similarly, the coupling structure 310 was also formed where the layers 306a and 306c overlap due to the distance between the lower template structure 304a and the substrate 302. Such coupling structures 308 and 310 provide mechanical support for the finally obtained hollow nanostructure, while at the same time providing an electron path between the lithiation site and the substrate 302.
According to certain embodiments (not shown), the template may comprise at least two different template structures. One type of template structure may have a large surface area available for coating, i.e. a planar template structure. Such a planar template structure has a relatively large size and a relatively high aspect ratio so that a sufficient surface area can be obtained, and is mainly used in the template. Another type of template structure may be used primarily to increase the number of coupling structures formed in the electrode layer, i.e., an interconnecting template structure. The interconnect template structure may generally be relatively small in size and low in aspect ratio so as to fit between the planar template structures. For example, the above effects may be realized by combining nanofibers and nanoparticles and using them as a composite template.
High volume coatings may be formed using various deposition techniques. For example, a CVD method including a plasma chemical vapor deposition (PECVD) method and a thermal chemical vapor deposition (CVD) method, an electroplating method, an electroless plating, and / or a solvent film forming technique may be used. Hereinafter, an example of the PECVD method will be described in more detail. The template is heated to a temperature between about 200 degrees Celsius and 400 degrees Celsius, specifically to a temperature between about 250 degrees Celsius and 350 degrees Celsius. A processing gas including a silicon-containing precursor (eg, silane) and one or more carrier gases (eg, argon, nitrogen, helium, and carbon dioxide) is introduced into the processing chamber. In a specific example, a combination of silane and helium is used with a silane concentration set between about 5% and 20%, more specifically between about 8% and 15%. The process gas may further include a dopant-containing material such as phosphine. The chamber internal pressure may be maintained at a pressure between about 0.1 Torr and 10 Torr, more specifically between about 0.5 Torr and 2 Torr. A plasma may be generated in the chamber to promote silane decomposition. Utilizing plasma may lead to a reduction in template temperature. This is important in maintaining the integrity of the template. In certain embodiments, a pulsed PECVD method is utilized.
The process parameters (ie, RF power and flow rate) described below are parameters set for the STS MESC Multiplex CVD system manufactured by Surface Technology Systems (Newport, UK). This system can process templates / substrates up to 4 inches in diameter. Those skilled in the art will appreciate that these process parameters can be increased or decreased accordingly as the chamber type and substrate size are changed. The RF power may be maintained at a power between about 10 W and 100 W, and the processing gas flow rate is generally between about 200 sccm and 1000 sccm, more specifically, about 400 sccm and 700 sccm. May be maintained at a flow rate between.
According to one specific embodiment, the formation of the amorphous silicon coating is performed in a processing chamber maintained at a pressure of about 1 Torr. The process gas includes about 50 sccm silane and about 500 sccm helium. When doping the active material, 15% phosphine may be added to the process gas at about 50 sccm. The substrate temperature is maintained at about 300 degrees Celsius. The RF power level is set to about 50 watts.
As described above, it may be necessary to control the processing conditions at least early in the process 106 to avoid significant distortion of the shape of the template structure, particularly the template structure based on the polymer. At a certain point in the coating forming process, the first formed coating can be used as a subsequent mechanical support force, and thereafter, the processing conditions can be adjusted without concern for shape distortion. For example, the processing conditions may be adjusted to increase the deposition rate of the coating.
According to a predetermined embodiment, the process 106 executes two or more stages with different processing conditions. For example, an initial film formation stage and a bulk film formation stage. Also referred to as the first stage and the second stage. In one example, the formation of a high volume coating begins at a low temperature and raises the temperature at some point in process 106. The processing conditions may be changed gradually or stepwise. The change in processing conditions may be performed when at least about 10% of the coating is formed, or more specifically, at least about 25% or at least about 50% of the coating layer is formed. It may be performed at a time (eg, depending on the thickness or weight of the coating). According to certain embodiments, when the template is heated to less than about 250 degrees Celsius, more specifically, less than about 200 degrees Celsius, and even less than about 150 degrees Celsius, an initial deposition step is performed. The temperature may then be increased to at least about 150 degrees Celsius, more specifically at least about 200 degrees Celsius, or at least about 250 degrees Celsius. The initial deposition step is generally performed under conditions that maintain the physical integrity of the template. According to such an embodiment, this condition is maintained until self-supporting of the coating is possible. After that point, more aggressive conditions may be used, for example, to increase the deposition rate. In the bulk deposition stage, more aggressive conditions can be used without concern for the physical integrity of the template. It should be noted that in many embodiments, the template is mostly used at the expense. It is not used after it has played a role in defining the shape of the active material.
FIG. 4 is a schematic diagram showing, as an example, the structure at three different stages of the electrode layer manufacturing process according to a predetermined embodiment. In the figure, an example in which the template is deformed is shown. More specifically, the case where a part of the template is removed in the coating process is shown. It should be noted that the template can generally be partially and wholly deleted and / or reduced during coating formation. Alternatively, the template may be left as it is without being processed in the coating formation process. In such latter embodiments, subsequent processing causes the template to be at least partially or completely removed and / or reduced. In addition to or in place of changing the shape of the template, the template composition may be changed, for example, carbonized, in the processing 106 or the subsequent processing.
In a first stage 401, a template structure 402 without a coating is illustrated. This stage may be seen before the process 106 begins. The template structure 402 may be solid as shown in FIG. 4 or may be hollow (not shown). In the second stage 403, a high-capacity active material is formed around the structure 402 and a thin coating 404 is provided for the same template structure 402. As described above, the processing conditions may be selected so that the shape of the template structure 402 does not significantly deform at this stage. In this stage 403, the initially formed coating 404 may have sufficient strength to support itself, with or without support from the template 402. For this reason, the processing conditions can be changed at this point. New processing conditions may remove and / or reduce the template. As a result, voids 410 are formed in the remaining template structure 408 as shown in the third stage 405. The majority of the coating may be formed between the second and third stages, which may ultimately form the coating 406.
Returning to FIG. 1, the process 100 may subsequently partially or completely remove and / or reduce the template material from the electrode layer at operation 108. This process is optional. As described above, removal and / or reduction may also be performed in the process 106 coating formation. According to certain embodiments, no additional removal and / or reduction need be performed. In other embodiments, removal and / or reduction is performed at process 106 and again at process 108. In yet another embodiment, the removal and / or reduction is performed only in process 108, and the template is left unprocessed in process 106. For example, the metal template used for forming the amorphous silicon layer is not affected by the process for forming the amorphous silicon layer, and may be removed later by etching.
The removal / reduction methods utilized in the process 108 depend in part on the template and coating materials. For example, the polymer template can be fully fired or annealed at elevated temperatures, for example, by heating to at least about 300 degrees Celsius, more specifically at least about 400 degrees Celsius, or even at least about 500 degrees Celsius. It may take at least about 1 hour, and more specifically at least about 4 hours, to fully fire a sufficient amount of the template material. According to certain embodiments, the template (eg, a metal template) is removed by chemical etching. For example, the silicon oxide core template may be removed by etching with a hydrofluoric acid (HF) acid solution. Generally, various metal fibers or silicide fibers used as an initial template can be removed by etching using an acidic solution.
According to certain embodiments, substantially all of the template material is removed from the nanotube structure. In other embodiments, a portion of the template material is left. It should be noted that the material remaining in this way may have a composition different from that of the initial template material (for example, the polymer may change to carbon). In the same or other embodiments, the remaining template material or derivative thereof accounts for less than about 25% of the weight of the electrode layer, more specifically, less than about 10%. Such remaining material is used to improve the conductivity and electrochemical capacity of the electrode layer, protect against unwanted SEI layer formation, suppress structural changes (eg, volume expansion), and other purposes As good as
Process 100 may then form a second coating on the interconnected hollow nanostructures in operation 110. The second coating may be formed on the outer surface of the nanostructure and for this reason may be referred to as the outer coating. In general, the second coating may include carbon, metal (eg, copper, titanium), metal oxide (eg, titanium oxide, silicon oxide), metal nitride, and metal carbide. According to certain embodiments, the carbon content of the outer coating is at least about 50%, and in more specific embodiments, at least about 90% or at least about 99%. According to certain embodiments, the outer coating may include graphite, graphene, graphene oxide, metal oxide (eg, titanium oxide), and / or other materials. The outer coating may coat substantially the entire exposed surface of a plurality of interconnected hollow nanostructures (eg, the entire outer surface, or both the inner and outer surfaces). According to certain embodiments, the thickness of the outer coating is between about 1 nanometer and 100 nanometers, and in a more specific embodiment is between about 2 nanometers and 50 nanometers. Specifically, the outer coating suppresses the high volume coating from coming into direct contact with the electrolyte solution (and does not form a problematic SEI layer), while the electroactive ions are high volume coating. Can be used to be transported between.
In the method of forming the outer coating, annealing may be performed after depositing a carbon-based small molecule (eg, saccharide) or polymer. Another method may be to perform a pyrolysis of a carbon-based gas (eg, using acetylene). For example, the carbon-containing outer coating may use methane, ethane, or any other suitable carbon-containing precursor, nickel, chromium, molybdenum, or any other suitable catalyst (or no catalyst at all). ) To form a layer of carbon on the nanostructure. Other methods include coating the nanostructures with an organic medium and later firing the organic medium to leave a carbon residue. For example, a plurality of interconnected nanostructures may be immersed in a glucose solution or a polymer solution. After the solution enters the nanowire mesh, it is drawn out from the solution and fired. In the case of glucose, a carbon residue remains on the nanostructure. The formation of an outer coating that includes an oxide such as titanium oxide may be initiated by depositing a base material (eg, titanium) from a solution. In this case, an atomic layer deposition (ALD) method or a metal plating method may be used. Thereafter, the base material oxide is formed, for example, by exposing the film to an oxidizing agent at a high temperature. Silicon oxide can be formed, for example, in process 108 and / or other coating processes that utilize CVD, ALD, or other deposition methods.
Other processes included in the process 100 specifically illustrated in FIG. 1 may include a process of pressing the electrode layer, a process of functionalizing the electrode layer, and a process of forming a battery electrode from the electrode layer. . Further downstream processing is described below in relation to electrode and battery configurations.
<Example of electrode layer>
Using the process described above, a plurality of interconnected hollow nanostructured electrode layers comprising a high capacity active material can be prepared. The hollow nanostructure may have a hollow sphere, tube, or other shape, and may be bilaterally symmetric or bilaterally asymmetric. The maximum inner cross-sectional dimension (eg, the inner diameter of the circular structure) of the hollow nanostructure voids may be between about 1 nanometer and 1000 nanometers, and more specifically, about 5 nanometers and 500 nanometers. Or between about 10 and 100 nanometers. The voids provide a space for the active material to enter when the active material expands, avoiding a situation in which other nanostructures become a major obstacle (for example, displace) and the nanostructures themselves are pulverized. According to a specific embodiment, some or all (eg, at least about 50%) of the hollow nanostructures may have a cross-sectional dimension and / or a void opening size that is too small to incorporate the electrode layer into a battery. The electrolyte does not enter and the gap is not filled. For this reason, the voids of the hollow nanostructure may remain substantially free of electrolytes at least during normal battery operation.
According to certain embodiments, the hollow nanostructure has a predetermined shell thickness. Although other dimensions of the nanostructure may be sufficiently large (eg, may be a few micrometers and millimeters), the thickness of the shell is typically less than about 1000 nanometers. As described above, thinning the shell can minimize powdering of the high capacity active material during the cycle. According to certain embodiments, the average thickness of the shell may be between about 5 nanometers and 1000 nanometers, more specifically between about 10 nanometers and 500 nanometers. It may even be between about 50 and 250 nanometers. The porosity of the electrode layer may be between about 20% and 90%, including nanostructured voids. In a more specific embodiment, the porosity is between about 40% and 80%.
According to certain embodiments, the shape of the nanostructure is substantially tubular. Such nanotubes may be at least about 100 nanometers in length, more specifically at least about 1 micrometer, and may be at least about 50 micrometers. The nanotubes may have a bonded structure along the length direction. In the bonding structure, adjacent nanostructures are physically or metal-bonded. Bonded structures typically provide a path for direct electron exchange between adjacent nanostructures and do not require an external conductive portion (eg, carbon black) to provide a conductive path between adjacent nanostructures. .
The electrode layer may be fixed to the conductive substrate. According to certain embodiments, two electrode layers are provided on each side of the conductive substrate. Examples of various substrates are described above. The electrode layer is sometimes called an active layer, and can be used as a positive electrode or a negative electrode of a battery or as a solid electrolyte. This configuration is further described below.
A storage battery incorporating such a new electrode layer should maintain a stable electrochemical capacity of at least about 2000 mAh / g for at least 100 cycles (depending on the total weight of the electrode layer active material). Is possible. According to the same or other embodiments, the battery is capable of maintaining a stable electrochemical capacity of at least about 700 mAh / g for at least about 100 cycles.
<Configuration of electrode and battery>
The electrode layer described above can be used to form a positive electrode and / or a negative electrode for a battery. Usually, a laminated body or a jelly roll type member is formed from the battery electrode. FIG. 5A is a side view showing an aligned laminate including a positive electrode 502, a negative electrode 504, and two sheet-like separators 506a and 506b according to a predetermined embodiment. The positive electrode 502 may include a positive electrode layer 502a and a positive electrode uncoated substrate portion 502b. Similarly, the negative electrode 504 may include a negative electrode layer 504a and a negative electrode uncoated substrate portion 504b. According to many embodiments, the exposed region of the negative electrode layer 504a is slightly larger than the exposed region of the positive electrode layer 502a. This is to capture lithium ions released from the positive electrode layer 502a by the insertion material of the negative electrode layer 504a. According to one embodiment, the negative electrode layer 504a is larger than the positive electrode layer 502a by at least a length between about 0.25 mm and 5 mm in one or more directions (usually in all directions). According to a more specific embodiment, the negative electrode layer is larger than the positive electrode layer by a length between about 1 mm and 2 mm in one or more directions. According to certain embodiments, the edges of the sheet-like separators 506a and 506b extend at least beyond the outer edge of the negative electrode layer 504a to insulate the electrode from other battery components. The uncoated portion 502b for the positive electrode may be used to establish a connection to the positive electrode and may extend beyond the negative electrode 504 and / or the sheet-like separators 506a and 506b. Similarly, the non-coated portion 504b for the negative electrode may be used to establish a connection to the negative electrode and may extend beyond the positive electrode 502 and / or the sheet-like separators 506a and 506b.
FIG. 5B is a top view of the aligned stack. The positive electrode 502 is illustrated as having two positive electrode layers 512a and 512b provided on opposite surfaces of a flat positive current collector 502b. Similarly, negative electrode 504 is illustrated as having two negative electrode layers 514a and 514b provided on opposite surfaces of a flat negative electrode current collector. If there is a gap between the positive electrode layer 512a, the corresponding sheet-like separator 506a, and the corresponding negative electrode layer 514a, it is usually of a size that does not exist from the minimum, especially after the first cycle of the storage battery. . The electrode and the separator are tightly wound as a jelly roll type member or constitute a laminate. The laminate is inserted into a snug housing. The electrodes and separator tend to expand in the housing after the electrolyte is introduced, and in the initial cycle, lithium ions circulate between the two electrodes through the separator, thereby eliminating gaps or dry areas. .
A winding type is a common configuration. A plurality of elongated electrodes are wound together with two sheet-like separators to form an intermediate assembly also called a jelly roll body. The intermediate assembly has a shape and size that matches the inner dimensions of the curved housing, typically a cylindrical housing. FIG. 6A is a top view showing a jelly roll body including a positive electrode 606 and a negative electrode 604. A jelly roll body in which a white portion between the electrodes represents a sheet-like separator is inserted into the housing 602. According to some embodiments, the jelly roll body may have a mandrel 608 inserted in the center, defining a diameter when first wound by the mandrel 608, and the inner winding forms a central axis region Do not. The mandrel 608 may be made of a conductive material, and in some embodiments may be part of the battery terminal. FIG. 6B is a perspective view showing a jelly roll body in which the positive electrode tab 612 and the negative electrode tab 614 are extended. These tabs may be welded to uncoated portions of the electrode substrate.
The length and width of the electrode depend on the overall size of the battery and the thickness of the electrode layer and current collector. For example, a conventional 18650 battery with a diameter of 18 mm and a length of 65 mm may have an electrode length between about 300 mm and 1000 mm. An electrode shortened for low rate / high capacity purposes has a large thickness and a small number of turns.
A cylindrical shape may be desirable for some lithium ion batteries because the electrode expands during cycling and applies pressure to the housing. The circular housing may be sufficiently thin while maintaining sufficient pressure. A prismatic battery may be wound in the same manner, but in this case, the casing may bend along the long side from the internal pressure. Further, the pressure may not be constant in each part of the battery, and in the prismatic battery, the corner may remain vacant. It is not desirable to have a vacant part in the lithium ion battery. This is because when the electrode expands, it is pushed unevenly into the vacant part. In addition, the electrolyte collects and a dry region is formed in the space between the electrodes, which may adversely affect the transport of lithium ions between the electrodes. However, prismatic batteries are appropriate for certain applications where the rectangular form factor is dominant. According to some embodiments, a prismatic battery avoids some of the problems associated with wound prismatic batteries using a stack of rectangular electrodes and sheet separators.
FIG. 7 is a top view showing a wound prismatic jelly roll body. The jelly roll body includes a positive electrode 704 and “a negative electrode 706. A white portion between the electrodes represents a sheet-like separator. The jelly roll body is inserted into a rectangular prismatic casing. FIG. 6A and FIG. Unlike the cylindrical jelly roll body shown in Fig. 6B, the prismatic jelly roll body starts winding from a flat wide portion at the center of the jelly roll body. The body may have a mandrel (not shown) disposed at the center, and an electrode and a separator may be wound around the mandrel.
FIG. 8A is a side view showing a stacked battery including a plurality of sets (801a, 801b, and 801c) in which positive electrodes and negative electrodes are alternately provided and separators are provided between the electrodes. One advantage of the stacked battery is that the stacked body can have any shape, and is particularly suitable for a prismatic battery. However, it is usually necessary to provide a plurality of positive and negative electrode groups in a stacked battery, and the electrode alignment becomes complicated. The current collector tab is typically connected to a total current collector that extends from each electrode and leads to the battery terminals.
When the electrodes are arranged as described above, the battery is filled with an electrolyte. The electrolyte of a lithium ion battery may be a liquid, a solid, or a gel. A lithium ion battery whose electrolyte is solid is also called a lithium polymer battery.
A typical liquid electrolyte includes one or more solvents and one or more salts, at least one of which includes lithium. In the first charge cycle (also called a formation cycle), the organic solvent contained in the electrolyte is partially decomposed on the surface of the negative electrode to form a solid electrolyte interface (SEI) layer. This interface is usually electrically insulating but has ionic conductivity and allows lithium ions to pass through. This interface further inhibits the electrolyte from decomposing in subsequent charging subcycles.
Some examples of non-aqueous solvents suitable for some lithium ion batteries include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and vinyl ethylene carbonate (VEC). Vinylene carbonate (VC)), lactones (eg γ-butyrolactone (GBL), γ-valerolactone (GVL) and α-angelica lactone (AGL)), linear carbonates (eg dimethyl carbonate (DMC), methyl ethyl Carbonate (MEC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC), methyl butyl carbonate (NBC), and dibutyl carbonate (DBC)), ethers (eg Tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane (DME), 1,2-diethoxyethane, and 1,2-dibutoxyethane), nitrites (e.g. Acetonitrile and adiponitrile), linear esters (eg methyl propionate, methyl pivalate, butyl pivalate, octyl pivalate), amides (eg dimethylformamide), organophosphates (eg trimethyl phosphate and trioctyl phosphate) ), And organic compounds containing S═O groups (eg, dimethyl sulfone and divinyl sulfone), and combinations thereof.
Non-aqueous solvents can be used in combination. Examples of combinations include: cyclic carbonate-linear carbonate, cyclic carbonate-lactone, cyclic carbonate-lactone-linear carbonate, cyclic carbonate-linear carbonate-lactone, cyclic carbonate-linear carbonate-ether, and cyclic carbonate -There are combinations such as linear carbonate-linear ester. According to one embodiment, a cyclic carbonate and a linear ester may be combined. Further, a cyclic carbonate may be combined with a lactone and a linear ester. According to a specific embodiment, the volume ratio of cyclic carbonate to linear ester is between about 1: 9 and 10: 0, preferably between 2: 8 and 7: 3.
The salts used for the liquid electrolyte are LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiCF 3 SO 3 , LiC (CF 3 SO 2 ) 3 , LiPF 4 (CF 3 ) 2 , LiPF 3 (C 2 F 5 ) 3 , LiPF 3 (CF 3 ) 3 , LiPF 3 (iso-C 3 F 7 ) 3 , LiPF 5 (iso-C) 3 F 7 ), a lithium salt containing a cyclic alkyl group (eg, (CF 2 ) 2 (SO 2 ) 2x Li and (CF 2 ) 3 (SO 2 ) 2x Li)), and one or more of these combinations May be included. Common combinations include LiPF 6 and LiBF 4 , LiPF 6 and LiN (CF 3 SO 2 ) 2 , LiBF 4 and LiN (CF 3 SO 2 ) 2 .
According to one embodiment, the total salt concentration in the non-aqueous solvent (s) is at least about 0.3M, and in a more specific embodiment is at least about 0.7M. The upper limit of concentration may be determined by the upper limit of solubility, but may be about 2.5M or less. In a more specific embodiment, it is about 1.5M or less.
Since the solid electrolyte normally functions as a separator, the separator is omitted. The solid electrolyte has electrical insulation and ionic conductivity and is electrochemically stable. In the case of a configuration using a solid electrolyte, a lithium-containing salt is used as in the battery using the liquid electrolyte described above, but it is not dissolved in an organic solvent but is held inside the solid polymer composite. . Examples of the solid polymer electrolyte may include an ion conductive polymer prepared from a monomer containing an atom having a lone pair of electrons capable of binding lithium ions of an electrolyte salt and moving during conduction. Copolymers of vinylidene (PVDF) or polyvinylidene chloride or derivatives thereof, poly (chlorotrifluoroethylene), poly (ethylene-chlorotrifluoro-ethylene), or poly (fluorinated ethylene-propylene), polyethylene oxide (PEO) And oxymethylene-linked PEO, PEO-PPO-PEO crosslinked with trifunctional urethane, poly (bis (methoxy-ethoxy-ethoxide))-phosphazene (MEEP), triol type crosslinked with bifunctional urethane PEO, poly ((oligo) oxye Len) methacrylate-co-alkali metal methacrylate, polyacrylonitrile (PAN), polymethyl methacrylate (PNMA), polymethylacrylonitrile (PMAN), polysiloxane and copolymers and derivatives thereof, acrylate-based polymers, and the like May be a solvent-free polymer, another polymer formed by condensing or cross-linking the above polymers, and a physical mixture of any of the above polymers. In addition to this, a relatively low conductive polymer may be used in combination with the above polymer to increase the strength of the thin laminate. Examples include polyester (PET), polypropylene (PP), polyethylene naphthalate (PEN), polyvinylidene fluoride (PVDF), polycarbonate (PC), polyphenylene sulfide (PPS), and polytetrafluoroethylene (PTFE).
FIG. 9 is a cross-sectional view showing a wound and cylindrical battery according to an embodiment. The jelly roll body includes a positive electrode 902 wound in a spiral shape, a negative electrode 904, and two sheet-like separators 906. The jelly roll body is inserted into the battery housing 916, and the battery is sealed using a cap 918 and a gasket 920. It should be noted that in certain embodiments, the battery is not sealed until subsequent processing (ie, processing 208) is completed. The cap 912 or the housing 916 may have a safety device. For example, a safety valve or rupture valve that breaks and opens when the pressure rises to an excessive level in the battery may be used. According to certain embodiments, a one-way gas release valve is provided to release oxygen released when the positive electrode material is activated. Also, a positive temperature coefficient (PTC) device may be incorporated into the conductive path of the cap 918 to reduce damage when a short circuit occurs in the battery. The outer surface of the cap 918 may be used as a positive terminal, and the outer surface of the battery housing 916 may be used as a negative terminal. According to another embodiment, the polarity of the battery may be reversed so that the outer surface of the cap 918 is used as a negative terminal and the outer surface of the battery housing 916 is used as a positive terminal. Tabs 908 and 910 may be used to connect between the positive and negative electrodes and the corresponding terminals. Gaskets 914 and 912 having appropriate insulating properties may be inserted in order to suppress internal short circuit. For example, a Kapton (registered trademark) film may be used for internal insulation. At the time of manufacturing, the battery may be sealed by pressing the cap 918 to the housing 916. However, before performing this process, an electrolyte (not shown) is added to fill the porous space of the jelly roll body.
In general, a lithium ion battery requires a casing having high rigidity, but a lithium polymer battery may be packaged in a casing such as a flexible foil (polymer laminate). Various materials can be selected as the material of the housing. For lithium-ion batteries, Ti-6-4, other Ti alloys, Al, Al alloys, and 300 series stainless steel may be suitable materials for the positive side conductive housing and end cap, and are commercially available Pure titanium, Ti alloy, Cu, Al, Al alloy, Ni, Pb, and stainless steel may be suitable materials for the negative conductive case portion and the end cap.
In addition to use in batteries as described above, metal silicides can be used in fuel cells (eg, negative electrodes, positive electrodes, and electrolytes), heterojunction solar cell active materials, various forms of current collectors, and / or absorbent coatings. But it can be used. Some of these applications benefit from features such as a large surface area of the metal silicide structure, high conductivity of the silicide material, and high speed and low cost deposition techniques.
<Electrospinning method>
A typical process 1000 for manufacturing an electrochemical cell is shown in FIG. In this process, after a plurality of processes for preparing two types of electrodes are performed, the two types of electrodes are combined to complete the battery. The electrode preparation stage 1200 of the manufacturing process is particularly a labor intensive stage. Typically, the process begins with mixing active materials to form a slurry (blocks 1002 and 1102) and coating the slurry on the corresponding substrate (blocks 1004 and 1104). The coated slurry is baked to evaporate the solvent and form a solid coating (blocks 1006 and 1106). The coating process and the firing process are repeated for the other side of each electrode. Thereafter, a pressing process (blocks 1008 and 1108) and a slit forming process (blocks 1100 and 1200) may be performed on the electrodes. Thereafter, the positive and negative electrodes are stacked or wound (block 1202), the electrical connection is attached, and the electrode assembly is placed in the housing to produce an operable battery (block 1204), after which The electrolyte is filled, sealed, and a forming charge / discharge cycle is performed (ie, a battery is formed) (block 1206).
The illustrated process does not include upstream processing to provide the active material, such as processing to form structures (eg, particles, fibers) with the desired size and composition. Such processing further complicates the electrode preparation stage 1200 of the battery manufacturing process. In addition, predetermined materials and shapes (for example, long fibers) are not easily processed by conventional processing techniques.
In the predetermined example, the electrodes are prepared using a process other than the process illustrated in FIG. For example, the nanowires rooted in the substrate may be deposited directly on the substrate from the precursor material. Some of these processes include US patent application Ser. No. 12 / 437,529 (filing date: May 7, 2009), US patent application Ser. No. 61 / 181,637 (filing date: May 27, 2009). Day). The contents of both patent documents are incorporated herein by reference to describe the active material and electrode structure, and the corresponding manufacturing process.
Nanostructures, and more specifically active materials formed as nanofibers, exhibit unique and unexpected electrochemical properties and may be highly desirable for use with a given electrode. For example, silicon nanowires can be formed without applying a stress level exceeding the silicon fracture limit when lithium is inserted into a high capacity anode with good repeatability. In addition, by using a long structure (a structure in which one dimension is significantly larger than the other two dimensions) instead of particles, other characteristics such as predetermined electrical characteristics and mechanical characteristics can be obtained. Can be improved.
<Electrospinning device>
It was an unexpected discovery that the electrospinning technology can be used to manufacture active materials and electrodes for electrochemical cells by appropriately changing the electrospinning technique. In the electrospinning process, a liquid flow of a liquid precursor such as a viscous material or a viscoelastic material is thinly formed by using electric charges. The liquid precursor is later solidified into a fiber. The electrospinning process has predetermined characteristics in common with the electrospray process and the conventional solution-type dry spinning (dry spinning). Electrospinning may utilize both a dissolved precursor and a molten precursor.
FIG. 11 is a diagram illustrating an example of an electrospinning device 2000 according to a predetermined embodiment. The electrospinning device may include a container 2002 for holding a liquid precursor 2004. Container 2002 may be a syringe, supply tube, or any other suitable container. The container 2002 is replenished with a liquid precursor. A given mechanism (not shown) may be used to bring the composition, concentration, viscosity and other parameters of the liquid precursor 2004 to appropriate values. The container 2002 may have one or more nozzles 2006 for diluting the liquid flow from the container 2002. Each nozzle 2006 produces a separate liquid stream of liquid precursor which, when solidified, becomes a fiber. According to certain embodiments, as described further below, the liquid flow and resulting fiber may be a combination of multiple materials. For example, a core shell structure may be included. Such a process utilizes a special composite coaxial nozzle.
The nozzle configuration will influence the liquid flow to be ejected and the resulting fiber dimensions, cross-sectional profile, and other parameters. Process parameters other than nozzle configuration that can be controlled by the electrospinning process include polymer molecular weight, molecular weight distribution and structure, polymer solution properties (eg, viscosity, conductivity, dielectric constant, surface tension), potential, flow rate. , Concentration, distance between the needle and the substrate, ambient temperature, humidity, and the like. Some of the above parameters will be described later.
According to some embodiments, the fiber may form a planarized structure / strip structure by planarization by impact upon striking the collector plate or by forming a bendable polymer film. Examples of polymers and solvents in the flattened form include polyvinyl alcohol and water, polyetherimide and hexafluoro-2-propanol, nylon-6 and hexafluoro-2-propanol, polystyrene and dimethyl-formamide or tetrahydrofuran. . Furthermore, a predetermined polymer (for example, polyvinylidene fluoride, poly-2-hydroxyethyl methacrylate, polystyrene, polyetherimide) can form a branched structure because the liquid flow is unstable.
The deposition rate is determined by various factors including the number of nozzles. A plurality of nozzles provided across the movable web may be used to achieve an appropriate deposition rate and to make the nanofiber distribution uniform throughout the web. According to certain embodiments, the number of nozzles may be between about 1 and 1000, more specifically between 10 and 200, and more specifically 50. And between 150 and 150. Increasing the number of nozzles (assuming the same diameter) increases output and meets the requirements of high speed web deposition processes, but according to some embodiments, increasing the number of fibers increases the placement of each fiber There may be a problem that becomes difficult. For example, in the embodiment of the battery fiber described later, each fiber is handled separately after film formation, which places a limit on the number of nozzles used in parallel processing.
According to certain embodiments, the nozzle 2006 is a metal needle. The nozzle is generally formed from a conductive material. The inner diameter of the nozzle typically depends on the desired fiber diameter and the predetermined processing parameters (eg, viscosity, surface tension, applied voltage, distance). Another parameter of the nozzle configuration is the tip shape. For example, it may be a flat tip. The above parameters are selected and combined so that the Taylor cone that the liquid flow forms at the end of the tip can provide a smooth liquid flow that does not break the resulting fiber.
The nozzle 2006 is connected to a power supply 2008 (for example, 5-50 kV). The power source 2008 is further connected to a collector plate 2100 made of a conductive material. The collector plate 2100 may have a rotating drum, a movable web, or other shape. By moving the collector plate 2100 relative to the nozzle 2006, the fiber distribution and recovery are made uniform. According to certain embodiments, the nozzle 2006 and the collector plate 2100 may move both.
According to certain embodiments, one or more nozzles of the nozzle array may stop (ie, turn off) the liquid flow even though the remaining nozzles each provide liquid flow. For this purpose, the voltage applied to a predetermined nozzle that needs to be controlled to off may be controlled to off. In the nozzle array, in order to obtain a desired fiber distribution on the surface, the liquid flow may be appropriately controlled on / off.
When the voltage applied between the collector plate 2100 and the nozzle 2006 is sufficiently high, the liquid flow of the liquid precursor 2004 may be drawn from the nozzle 2006 (ie, the electrostatic force will exceed the surface tension). . Initially, a droplet is formed at the nozzle. This droplet extends and finally ejects at a critical point to form a liquid stream. The shape of the liquid at the time of ejection is sometimes called a Taylor cone.
The voltage must be high enough to overcome the surface tension of the liquid precursor at the nozzle tip and to draw liquid to form a liquid stream. At the same time, it is generally preferred that the electrostatic force does not exceed the surface tension in the moving liquid flow so that the liquid flow exits the collector plate without interruption. The liquid flow in the precursor may be extended and thinned by being accelerated toward the plate. The liquid stream may also be stretched by a “foaming” process caused by electrostatic repulsion within the liquid stream. The electrostatic repulsion force in the liquid flow is only slightly bent at first, but increases toward the collector.
The parameters generally considered in the electrospinning process are listed below. The average molecular weight of the polymer contained in the liquid precursor (including the distribution and structural properties of the molecular weight of the polymer), solution properties (eg viscosity, conductivity and surface tension), potential, flow rate, nozzle and collector plate Consider the distance between them, the surrounding conditions (temperature, humidity and airflow), collector movement, etc.
FIG. 12 is a diagram showing an example of an apparatus 2200 for forming one or more layers of an electrode material on a moving web substrate by an electrospinning method. The apparatus 2200 includes an unwinding roll 2202 that supplies the substrate web 2206 to the film forming region, and a winding roll 2204 that collects the substrate after the layer is formed. The substrate web 2206 moves so as to pass through the film formation region at a predetermined speed controlled by the system controller 2208. According to certain embodiments, the speed of the substrate web is between about 1 meter / minute and 100 meters / minute, more specifically between about 2 meters / minute and 30 meters / minute.
The apparatus 2200 may include one or more electrospinning units (components 2208 and 2302) and one or more post-deposition processing units (components 2300 and 2304). In FIG. 2, an apparatus including two electrospinning units for forming fibers on opposite surfaces of the substrate and two post-deposition processing units is illustrated, but the number and configuration of both components are as follows. It should be understood that it is optional. Further details will be described later with reference to FIG.
The electrospinning section (components 2208 and 2302) deposits one or more fibers on the substrate 2206. According to certain embodiments, the deposited fiber forms an active layer with the electrode. The electrospinning section is configured so that the layers are uniform throughout and along the substrate web. For example, the electrospinning unit may have a nozzle that moves in the width direction of the substrate. In addition, the apparatus shown in the figure has sensors (for example, laser backscattering, beta ray penetration, gamma ray backscattering) that measure the amount of fibers deposited on the substrate at various locations on the substrate. The film formation parameters may be adjusted accordingly.
The post-deposition processor (components 2300 and 2304) may be used to convert the deposited fiber to a new material and may change the shape and / or function of the deposited fiber. For example, the post-deposition processing unit converts the formed polymer fiber into a ceramic fiber, evaporates the remaining solvent, changes the distribution of the formed layer, and / or is formed. It may be used to perform sintering to press the layer and obtain other effects. Further details of the post-deposition processing will be described later with reference to FIG.
The substrate 2206 may be a metal foil. In this case, one contact of the power supply that is part of the system controller 2306 illustrated in FIG. 12 is electrically coupled to the substrate 2206. For example, an electric brush is provided below the film formation region so that a sufficient voltage gradient is formed between the film formation region and the corresponding nozzle. In some embodiments, one of the rolls may be used to contact the power source. One contact point with respect to the substrate for supporting a plurality of electrospinning portions may be sufficient.
According to other embodiments, the substrate 2206 is an insulating material. For example, the power source may be attached to a conductive member (eg, plate, roll) disposed behind the substrate 2206.
In the electrospinning method, the fiber is usually formed as a nonwoven fabric in which the fibers are randomly oriented. According to certain embodiments, the collector of the electrospinning device includes special features, such as an insulating gap, for uniaxially aligning the deposited fibers.
The system controller 2306 may be further used to control processing parameters of an electrospinning unit that performs a film forming process. Some of these processing parameters are described above in connection with FIG. For more details on electrospinning and electrospinning apparatus, see US Pat. No. 6,713,011 (issue date: March 30, 2004, Chu, B et al.), Ramakrishna, S .; "Electrospinning and Nanofibres," published 2005, World Scientific Publishing Co., and Andrew, A. et al. , "Science and Technology of Polymer Nanofibers", published in 2008, John Wiley & Sons, John Wiley & Sons. These documents are incorporated herein by reference to illustrate the above detailed content.
FIG. 13 illustrates a typical deposition of one or more layers (eg, multiple electrode layers such as anode-separator-cathode, one composite layer, or a combination of the two) according to certain embodiments. It is a figure which shows an example of a process. The process may begin with supplying a substrate to the deposition area (block 3002). The deposition area is usually defined by a collector. The collector may be the substrate itself or another component of the electrospinning device located below the substrate (in the latter case, the substrate is formed of an insulating material). When the substrate functions as a collector (that is, when a voltage is applied between the substrate and the nozzle), the film formation area is a mechanical stop (eg, fiber is not deposited outside the film formation area). Wall) or an electrical shield (eg, a bias ring to reshape the electric field between the nozzle and the substrate).
The substrate may be a separate plate or a continuous web. According to certain embodiments, the substrate is an intermediate carrier (e.g., a foil, the fiber deposited on the foil is later removed). According to another embodiment, the substrate is part of an electrode that permanently attaches the deposited fiber. For example, an electrode current collector disposed between active layers, an already deposited active layer, or any other component. The substrate can be a metal foil (eg, copper foil, stainless steel foil, aluminum foil, titanium foil), polymer foil (eg, Mylar® film), polymer paper (can be converted to carbon after calcination), carbon fiber It may be paper, carbon fiber mesh or the like. The thickness of the substrate may be between about 1 μm and 1000 μm, and in a more specific embodiment is between about 5 μm and 100 μm.
The process continues by forming fibers on the substrate surface by electrospinning to form one or more electrode layers (block 3004). Specific details of the electrospinning method are described above in connection with FIG. According to one embodiment, once the fiber layer is deposited on the substrate, the process continues with another process that is performed only on the fiber layer. According to another embodiment, before proceeding to the next process, fiber layers are deposited on opposite surfaces of the substrate, and two fiber layers are deposited. Of these two layers, for example, one layer may be an anode active material layer and the other layer may be a cathode active material layer. The deposited layer may require post-treatment such as annealing. As an example, a layer formed on one surface may be subjected to a treatment such as annealing before forming a layer on the other surface. As another example, both layers are deposited and then processed together. Specific details of the annealing will be described in association with the process 3006. In some cases, two separate layers are deposited on the same side of the substrate. This is the case, for example, when the first layer is an anode layer or a cathode layer and the second layer is a separator layer.
In general, after one battery layer (for example, a separator layer, an anode layer, or a cathode layer) is formed, the process proceeds to a process for forming another layer. For example, after forming the anode layer, the separator layer is formed, and then the cathode layer is formed. By forming the film in this manner, an electrical short circuit is suppressed from occurring between the anode and the cathode. Certain embodiments are referred to herein as “battery fibers” and are described above or below, but certain components of fibers (ie, separator cores) function as insulators, so that The film forming method may not be generally used.
According to certain embodiments, the battery may further include two types of fibers having different components, and these fibers form what is referred to as a composite electrode layer. These multiple types of fibers may be formed by a single process, or may be formed by a series of sequential processes. For example, the plurality of nozzles provided above one film formation region may include a plurality of nozzles that inject a plurality of different materials. The composition of the layer may be controlled by controlling a given nozzle off or according to the procedure described above. For example, the anode layer may include silicon nanofibers and carbon nanofibers that are deposited in a single process.
The orientation of the fiber deposited on the substrate may be controlled using an electric field. For example, the voltage may be controlled by applying a voltage to the components of the bias ring and other electrospinning devices for changing the electric field by changing the applied voltage. The orientation of the fiber during the deposition process determines the density, porosity, crosslinking and other parameters of the deposited layer. According to certain embodiments, these parameters are changed in one or more post-deposition processes.
In the process, after one or more layers are formed in the process 3004, a process for further processing the formed layers may be optionally performed (process 3006). For example, the deposited layer may be converted into a new material by annealing, calcination, sintering, cooling, or the like. One example used to produce ceramic fibers is to perform sintering at a temperature between about 300 degrees Celsius and 700 degrees Celsius for a period of between about 1 hour and 24 hours. According to another embodiment, the post-deposition treatment (block 3006) was formed by, for example, passing through a roller-type press or placing between two plates for a predetermined period of time. A process of pressing the layer may be included. According to certain embodiments, the press may be heated to a temperature between about 30 degrees Celsius and 300 degrees Celsius, more specifically to a temperature between about 50 degrees Celsius and 150 degrees Celsius. .
According to another embodiment, the post-deposition processing (block 3006) includes depositing another material on the fiber formed by electrospinning. For example, a carbon fiber formed by electrospinning in process 3004 may be coated with amorphous silicon to form a “core shell” structure. More detailed contents of the core-shell structure are described in the above-mentioned US Patent Application No. 61 / 181,637. Note that many core materials described in this reference are deposited using electrospinning. According to certain embodiments, one or more shell materials may be formed with the core using an electrospinning method. The post-deposition treatment is determined according to the material used in the electrospinning method. Such materials will be further described later along with corresponding post-deposition processing.
Process 3004 and optionally process 3006 may be repeated if there are additional layers that need to be deposited (decision block 3008). For example, the first cycle (including process 3004 and, optionally, process 3006) may be used to deposit a separator layer. This cycle may then be repeated to deposit the anode material layer, another separator layer, and the cathode material layer. These layers are also called battery layers. A separator-anode-separator-cathode laminate may be formed by these four battery layers formed in this process, and then processed into a jelly roll or laminate.
According to one embodiment, a stackable battery (including one or more anode-separator-cathode stacks) may be manufactured by repeatedly executing the above-described cycle. The layers constituting the battery may be formed until a desired number is reached. With such a configuration, it is possible to create a battery in which a unique form factor is defined, and omit a given mechanical process that is normally used when placing and handling a laminate. It becomes possible.
According to a predetermined embodiment, one battery layer may be formed by a multi-stage process or a periodic process instead of a single film formation process. For example, when a sub-layer is deposited, it may be necessary to perform an intermediate process (eg, annealing, coating the fiber with another material, pressing) before continuing the deposition process.
Once all the electrospinning layers have been deposited on the substrate, post-deposition processing may be performed on the entire stack, which in certain embodiments consists of only one layer (block 3010). This process is optional, and in some embodiments, the laminate may be available as a battery electrode immediately after process 3004 and optionally process 3006 is completed. This form of processing has already been described above in part in connection with process 3006. This treatment may increase mechanical and electrical contact between the electrospinning layers.
According to certain embodiments, the stack may include a plurality of battery layers, for example, an anode-separator, cathode-separator, anode-separator-cathode, anode-separator-cathode-separator structure. One or more post-deposition processes such as annealing are performed on the entire stack. Annealing may be performed at a temperature between about 300 degrees Celsius and 700 degrees Celsius to convert the materials making up the stack into materials desirable for use as a battery. For example, the separator layer may be converted into an inorganic material such as ceramic.
According to some embodiments, the substrate may be removed from the stack (block 3012). This treatment is optional, and according to some embodiments, the stack may be utilized as an electrode material with the substrate. For example, the active material is formed on the surface of the metal foil using the metal foil as a substrate. The metal foil may remain as an electrode collector on the regenerated electrode.
<Example of battery layer>
The material is supplied in liquid form to an electrospinning device. For example, it is supplied as a solution or a melt containing a base polymer and a solvent. Examples of polymers include nylon 4,6, nylon 6, nylon 6,6, nylon 12, polyacrylic acid, polyacrylonitrile, polyamide-6, poly (benzimidazole), polycarbonate, poly (ether imide), poly (ethylene Oxide), poly (ethylene terephthalate), polystyrene, poly (styrene-butadiene-styrene) triblock copolymer, polysulfone, bisphenol A, poly (trimethylene terephthalate), poly (urethane), poly (urethane urea), poly (vinyl alcohol) ), Poly (vinyl carbazole), poly (vinyl chloride), poly (vinyl pyrrolidone), poly (vinylidene fluoride), poly (vinylidene fluoride-co-hexafluoropropylene), degradable polyester urethane, poly (ε Caprolactone), polydioxanone, polyglycolide, poly (L-lactic acid), poly (D, L-lactide-co-glycolide), poly (L-lactide-co-glycolide), poly (lactic acid-co-glycolic acid), poly (L-lactic acid-co-glycolic acid), fibrinogen arc, gelatin, wheat gluten. Examples of solvents include formic acid, hexafluoro-2-propanol, ethanol, dimethylformamide, dimethylacetamide, dichloromethane, chloroform, tetrahydrofuran, trichloroethane, water, trifluoroacetic acid, t-butylacetic acid, chlorobenzene, ethylacetic acid, methyl ethyl ketone, Examples include tetrahydrofuran, methylene chloride, isopropyl alcohol, hexafluoro-2-propanol, hexafluoroisopropanol, hydrous triethanolamine, methylene chloride, and trifluoroethanol.
According to one embodiment, the liquid precursor utilized in electrospinning is a slurry comprising a base polymer and small rod-like or elongated particles. The particles must be small enough to pass through the nozzle of the electrospinning device. For example, circular particles may be less than about 1 μm, more specifically less than about 100 nm. The diameter of the elongated particles (eg, nanowires) can be between about 5 nm and 1000 nm, and more specifically between about 10 nm and 300 nm. The length of the elongated particles may be less than about 10 μm, more specifically less than about 5 μm, and even less than about 1 μm. In certain embodiments, the elongate particles are provided in US patent application Ser. No. 12 / 437,529 (filing date: May 7, 2009) and US patent application 61 / 181,637 (filing date: 2009). May 27), the nanostructure and / or nanowire. Both applications are incorporated herein by reference for purposes of illustration. These materials may be combined with a polymer substrate. Examples of the polymer substrate are as described above. In a specific example, the nanowires may be coated with carbon before being combined with the polymer substrate.
In another example, the core and one or more shells may be formed in a single electrospinning process. For example, two or more different materials may be simultaneously formed by a spinning method using one special nozzle, and the core-shell structure may be formed at the same time that the nozzle is retracted. A specific example of such an embodiment is called a “battery fiber” and will be described below. Other examples may include an active material core (eg, silicon) and a carbon shell, a carbon core and an active material shell, and a carbon core-active material inner shell-carbon outer shell. In some such structures, the core diameter may be less than about 200 nm. The thickness of the carbon outer shell may be less than about 50 nm. A specific example of such a structure is described in US patent application Ser. No. 61 / 181,637 (filing date: May 27, 2009). The entire contents of this patent document are incorporated herein by reference to illustrate such a multilayer structure. Such a fiber is produced by performing one electrospinning process and then performing one or more post-deposition processes described above (eg, calcination, sintering, annealing, cooling, or carbonization). It's okay.
According to certain embodiments, after forming a homogenous fiber by electrospinning, only a portion of the fiber material is converted to form a core and a shell with different properties such as composition, shape and structure. It may be done.
Examples of materials used for electrospinning of the positive electrode active material layer include LiCoO—MgO, lithium titanate (LTO), and the like. For example, LTO fibers can be produced by using titanium tetraisopropoxide and lithium hydroxide as precursors in a polymer mixture. The resulting polymer fiber may be calcined or sintered to produce a carbon fiber skeleton. In the fiber, the titanium precursor reacts with lithium hydroxide to produce LTO nanoparticles. Using this method, other cathode oxides such as lithium cobalt oxide and lithium manganese oxide, and oxides for inorganic separators such as aluminum oxide and silicon dioxide can be produced. Furthermore, LiFePO 4 fiber may be produced using electrospinning. Various doped LiFePO 4 fibers such as those promoted by A123 Corporation may be included. For example, an active material prior to synthesis using nanoparticles or nanowires can be mixed with a polymer solution to form a nanomaterial / polymer suspension (also referred to as a slurry or paste). By performing the electrospinning method using such a mixed solution, a polymer fiber in which nanoparticles or nanowires are embedded can be generated. A carbonization process may be a process required in order to convert an organic polymer into carbon.
Examples of materials used when the negative electrode active material layer is formed by an electrospinning method include silicon, carbon, germanium, tin, aluminum, tin oxide, alkoxysilane as a Si precursor, and the like. According to certain embodiments, such materials are organized into a core-shell structure such as a silicon core / carbon shell, a carbon core / silicon shell, or a carbon core / silicon inner shell / carbon outer shell. . In the same embodiment or other embodiments, all or part of the layer (eg, core, shell) may be formed of a material in which a plurality of materials are mixed, such as carbon and silicon. For example, carbon and titanium oxide may be mixed.
Other examples of positive and negative electrode active materials are US patent application Ser. No. 12 / 437,529 (filing date: May 7, 2009) and US patent application 61 / 181,637 (filing date: 2009). May 27). The contents of both applications are all incorporated herein by reference to illustrate the positive electrode active material and the negative electrode active material.
Examples of materials utilized in forming the separator layer by electrospinning method, PVDF, polypropylene, inorganic materials (SiO 2, Al 2 O 3 , TiO 2), is modified with organically modified ceramics (silicone and organic polymers And oxides of Al, Si, Ti, and Zr). By using an inorganic material as the separator material, it is possible to combine the separator material with materials of other layers (for example, the cathode and the anode), and it is possible to process the entire laminate together. This is because such inorganic materials continue to acquire and retain ionic conductivity (to some extent) even when exposed to high temperatures during calcination, sintering, annealing, and carbonization.
Table 1 below shows some examples of materials that can be formed using the electrospinning method and treatments performed after the film formation.
According to certain embodiments, the fiber formed by electrospinning is nanoscale in diameter (eg, less than about 1000 nanometers, or less than about 500 nanometers, or less than about 100 nanometers). According to the same or other embodiments, the fiber formed by electrospinning is relatively long (eg, at least about 10 millimeters, or at least about 1 centimeter, or at least about 1 meter).
<Battery fiber>
A battery fiber is a fiber comprising a plurality of shells and, if possible, a core, wherein at least two components (one core and one shell, or two shells) are electrically connected to each other by the core. Have been separated. The core used for electrical separation needs to function as a separator and be configured so that ions can move between the two components that are the subject of separation. One of the separated components includes an anode active material and the other includes a cathode active material. According to certain embodiments, the inner component (of the two separated components) includes the anode active material, and in other examples, the outer component includes the anode active material.
The separated components are sufficiently conductive to pass electrons along the length of the fiber to the current collector. One current collector is attached to the anode of the fiber and another current collector is attached to the cathode. Connections may be made to the inner shell or extension core containing these components, or to the outer shell. The fiber may be formed to a predetermined length by controlling the corresponding portion of the nozzle on or off (eg, 100 μm to 100 mm, more specifically between 1 and 50 mm). This will be further described later. Further, the extension core or inner shell necessary to establish an electrical connection may be formed by synchronizing multiple different parts of the nozzle.
FIG. 14A is a diagram showing a battery fiber 4016 emitted from the electrospinning nozzle 4010. The nozzle 4010 forms a core and at least two shells around the core in an ejected liquid flow. For example, the nozzle 4010 may have a set of three concentric rods. The inner ridge may supply material 4011 for forming the core of the battery fiber. According to certain embodiments, the core may be a hollow cylinder after drying the solvent and performing post-film treatment. According to other embodiments, the inner ridge may not supply material and the resulting battery fiber may be coreless. The second tube from the inside of the nozzle 4010 carries the innermost shell material 4012 of the battery fiber 4016. The next tube carries the next shell material 4014. It should be understood that the nozzle may be configured with more tubes. A given tube, typically the outer tube, protrudes larger than the inner tube to form the outer boundary of the fiber when a jet of multiple materials (eg, 4011, 4012, 4014) is combined. Good (not shown). Further, the longer the tube may be, the longer it may be tapered towards the open end in order to bundle the jets of material. According to the same or other embodiments, multiple materials can be selected together to select multiple polymers with the desired properties (surface tension, viscosity) to combine multiple layers to form a single member. The drying process is controlled to “break” to build a voltage gradient between the tubes of the nozzle 4010.
FIG. 14B is a diagram showing two examples of battery fibers according to a predetermined embodiment. The battery fiber 4030 is illustrated as comprising a core 4032, an inner shell 4034, and an outer shell 4036 that form a set of concentric circular cylinders. It should be understood that other shapes that are not concentric circles or that form a completely closed shape are possible. For example, in the core-shell structure, one or more of the cores may not necessarily cover the inner core or shell. Other shapes and forms of the core-shell structure are described in US patent application Ser. No. 61 / 181,637 (filing date: May 27, 2009).
As described above, in the battery fiber, at least two components are electrically separated. For example, the battery fiber 4030 may include a core 4032 of anode material, an inner shell 4034 of separator material, and an outer shell 4036 of cathode material. Many of these materials are described above. In addition, more shells may be provided in addition, and other components of the core shell structure include anode material, separator material, and cathode material. According to certain embodiments, the battery fiber may comprise a plurality of anode layer-separator layer-cathode layer combinations, for example, anode core-separator shell 1-cathode shell 2-separator shell 3-anode. The shell 4 may be provided.
According to certain embodiments, one or more inner layers of the fiber are stretched to form electrical and mechanical connections and insulate the layers. For example, FIG. 14B illustrates a battery fiber in which a shell 4034 extends beyond the shell 4036 at one end. The core 4032 is further extended. Note that there are similar examples of such a configuration at both ends of the fiber. In examples where the core 4032 includes an anode material, the inner shell 4034 includes a separator material, and the outer shell includes a cathode material, an extension of the core may be used to form an electrical connection to the core 4032 (and the anode). In addition, the separator (inner shell 4034) extends beyond the cathode (outer shell 4036) to ensure electrical insulation between the nanowire cathode and anode.
In a given example, the battery fiber may include a flat portion, for example, a rectangular core-shell fiber 4040 shown in FIG. 14B. The flat portion of this type of battery fiber is formed when forming a liquid flow (eg, a liquid flow defined by a nozzle) or flattened when collected at a collector (eg, impact Alternatively, it may be flattened by pressing after collection), or may be flattened during subsequent post-deposition processing. According to certain embodiments (not shown), flat battery nanofibers can be wound into a jelly roll or laminated.
<Patch-like film formation>
15A and 15B are top and side views showing a patch having a substrate 5002 and four battery layers (5004, 5006, 5007 and 5008), according to certain embodiments. Such a patch may be formed when the battery layer is formed on the substrate using the electrospinning process described above. Each battery layer may be an electrode layer. For example, battery layer 5008 may include a cathode material, battery layers 5004 and 5007 may include a separator material, and battery layer 5006 may include a cathode material. The patch may be formed on the substrate, but once the substrate 5002 is removed by forming a slit, the elongate member is immediately wound without further formation of other electrode or separator components. You may form so that a jelly roll body may be formed. According to other embodiments, other materials such as separator layers may be added to the winding process.
In the multilayer electrode structure as shown in FIGS. 15A and 15B, the layer containing the cathode material and the layer containing the anode material need to form an electrical connection with the terminals of the electrochemical cell. In order to form such an electrical connection, each layer must have an extension that extends beyond the stack. As shown in FIGS. 15A and 15B, the battery layer 5008 has an extended portion 5010, and the battery layer 5006 has an extended portion 5012. Such an extension can be formed by not depositing other layers of the stack in the corresponding region. For example, in a continuous web deposition process, the electrospinning process must be controlled so that other layers of fibers do not enter this region. As described above, the electrospinning process may be stopped by controlling the voltage to the corresponding nozzle off or otherwise. The actions of the nozzles that deposit the different layers are synchronized to obtain the desired structure (and to obtain an open extension for a given layer). In addition, the edge of the already formed layer may be detected using various sensors, and the nozzle for forming the next layer may be driven based on the position of the edge.
While the above description of the invention has been described in some detail for purposes of clarity, it will be apparent that changes and modifications may be practiced within the scope of the claims. There are many other ways to implement the process, system and apparatus according to the present invention. Accordingly, the above-described embodiments are not intended to limit the present invention but to illustrate it, and the present invention is not limited to the detailed contents described in this specification.
A method of preparing a plurality of interconnected hollow nanostructured electrode layers comprising a high capacity electrochemically active material comprising:
Receiving a template having a plurality of template structures;
Forming a nanoscale template coating of the high capacity electrochemical active material around the plurality of template structures;
Performing at least one of removal and reduction of at least a portion of the template to form the electrode layer of the interconnected hollow nanostructures comprising the high capacity electrochemical active material. .
5. The method of item 1, wherein receiving the template comprises forming a polymeric material by electrospinning to form a plurality of template nanofibers that are at least about 5 micrometers in length.
The method of item 1, wherein the template comprises one or more polymeric materials selected from the group consisting of polyacryl nitride (PAN), nylon, polyethylene, polyethylene oxide, polyethylene terephthalate, polystyrene, and polyvinyl.
The method of item 1, wherein the template is formed as a layer having a thickness of between about 10 micrometers and 150 micrometers and a porosity of between about 20% and 80%.
The method of item 1, further comprising pre-treating the template by at least one of pressing the template, thermally stabilizing the template, and carbonizing the template.
Thermally stabilizing the template includes heating the template to a temperature between about 150 degrees Celsius and 250 degrees Celsius for at least about 2 hours in an argon atmosphere. the method of.
Forming a nanoscale substrate coating of the high capacity electrochemically active material on the surface of the conductive substrate adjacent to the template;
The method of item 1, wherein the nanoscale template coating and the nanoscale substrate coating interconnect the conductive substrate and the plurality of interconnected hollow nanostructures to each other by partially overlapping. .
Forming the nanoscale template coating of the high-capacity electrochemically active material around the plurality of template structures comprises:
An initial film formation stage executed under initial processing conditions;
A bulk film formation step performed under a bulk processing condition different from the initial processing condition,
In the initial film formation stage, it is avoided that the shape of the template is greatly distorted,
2. The method according to item 1, wherein the bulk processing conditions are set such that a film forming speed of the nanoscale template coating is higher in the bulk film forming step.
The method of item 1, wherein at least a portion of the template is removed or reduced during formation of the nanoscale template coating of the high volume electrochemically active material around the plurality of template structures.
Removal or reduction of a portion of the template is selected from the group consisting of baking the template in the presence of an oxidant at a temperature of at least about 300 degrees Celsius, chemical etching of the template, and annealing of the template. The method according to item 1, comprising executing one or more processes.
Forming a second coating over the interconnected hollow nanostructures;
The second coating increases at least one of an electrical conductivity of the electrode layer, an improvement in a solid electrolyte interface (SEI) characteristic of the electrode layer, and a restriction on a structural change of the plurality of interconnected hollow nanostructures. 2. The method according to item 1.
An electrode layer used in a storage battery,
A plurality of interconnected hollow nanostructures having an aspect ratio of at least about 4, a length of at least about 5 micrometers, a shell thickness of less than about 100 nanometers, and a high capacity electrochemically active material With structure,
The interconnected hollow nanostructures are electrode layers that form a plurality of internal voids that provide space for the high-capacity electrochemically active material to expand and enter in the storage battery cycle.
13. The electrode layer according to item 12, wherein the plurality of internal voids are substantially inaccessible to the electrolyte of the storage battery.
13. The electrode layer according to item 12, wherein the electrode layer realizes a stable energy capacity of at least about 2000 mAh / g even after at least 100 cycles have elapsed, depending on the weight of the high-capacity electrochemically active material.
A plurality of bonding structures interconnecting two or more interconnected hollow nanostructures;
13. The electrode layer according to item 12, wherein the plurality of bonding structures include one or more materials selected from the group consisting of the high-capacity electrochemically active material, metal, and polymer binder.
16. The electrode layer according to item 15, wherein an additionally provided coupling structure interconnects one or more interconnected hollow nanostructures and the conductive substrate.
13. The electrode layer according to item 12, wherein the high-capacity electrochemically active material includes one or more materials selected from the group consisting of silicon, tin, and germanium.
An outer layer substantially covering an outer surface of the interconnected hollow nanostructures,
13. The electrode layer according to item 12, wherein the outer layer includes one or more materials selected from the group consisting of carbon, titanium, silicon, aluminum, and copper.
Item 13. The electrode layer of item 12, wherein the electrode layer has a porosity between about 20% and 80%.
13. The electrode layer according to item 12, wherein the storage battery is a lithium ion battery, and the high-capacity electrochemical active material is a negative electrode active material.
A plurality of interconnected hollow nanostructures having an aspect ratio of at least about 4, a length of at least about 5 micrometers, a shell thickness of less than about 100 nanometers, and comprising a high capacity electrochemical active material An electrode layer having
The interconnected hollow nanostructures are lithium ion batteries that form a plurality of internal voids that provide space for the high capacity electrochemical active material to expand and enter in a storage battery cycle.
Comprising a plurality of interconnected tubular hollow nanostructures having shells around a plurality of internal voids;
The shell includes a high capacity electrochemical active material;
The plurality of internal voids provide a space for the high-capacity electrochemically active material to expand and enter in the battery cycle;
The electrode layer further comprises a plurality of bonded structures in which two or more interconnected hollow nanostructures are interconnected with two or more first coating layers overlapping ,
The plurality of bonding structures are electrode layers that are part of the first coating layer including one or more materials selected from the group consisting of the high-capacity electrochemically active material and metal.
The electrode layer according to claim 1, wherein the plurality of internal voids cannot reach the electrolyte of the storage battery.
The electrode layer according to claim 1, wherein an additionally provided structure interconnects one or more interconnected hollow nanostructures and the conductive substrate.
The electrode layer according to claim 1, wherein the plurality of bonding structures include nanoparticles.
5. The electrode layer according to claim 1, wherein the high-capacity electrochemically active material includes one or more materials selected from the group consisting of silicon, tin, and germanium.
A second coating layer covering an outer surface of the interconnected hollow nanostructures;
The electrode layer according to any one of claims 1 to 5, wherein the second coating layer includes one or more materials selected from the group consisting of carbon, titanium, silicon, aluminum, and copper.
The electrode layer according to any one of claims 1 to 6, wherein the electrode layer has a porosity of between 20% and 80%.
The electrode layer according to any one of claims 1 to 7, wherein the storage battery is a lithium ion battery, and the high-capacity electrochemical active material is a negative electrode active material.
The electrode layer according to any one of claims 1 to 8, wherein an inner surface of the interconnected hollow nanostructures is coated with a carbon-containing material.
Having a template material inside the shell;
The electrode layer according to claim 1, wherein an internal void is provided inside the template material.
The electrode layer of claim 10, wherein the weight ratio of the template material to the interconnected hollow nanostructures is less than 10%.
The electrode layer according to claim 10 or 11, wherein the template material includes a conductive material.
The second coating layer increases the conductivity of the electrode layer, improves the solid electrolyte interface (SEI) characteristics of the electrode layer, and limits structural changes in the interconnected hollow nanostructures. The electrode layer according to claim 1 , wherein one or more of the above are performed.
The electrode layer according to claim 1 , wherein the second coating layer includes one or more materials selected from the group consisting of carbon, metal, metal oxide, metal nitride, and metal carbide.
A conductive metal substrate on which electrons are transported between two or more interconnected hollow nanostructures;
A plurality of bonding structures between the conductive metal substrate and the two or more interconnected hollow nanostructures;
The plurality of bonded structures provide both mechanical support and electron transport paths between the conductive metal substrate and the two or more interconnected hollow nanostructures;
The electrode layer extending on the surface of the conductive metal substrate has a thickness between 1 and 300 micrometers;
The electrode layer according to claim 1, wherein the high-capacity electrochemically active material includes silicon.
The electrode layer according to claim 15, further comprising a layer of the high-capacity electrochemically active material that coats the conductive metal substrate.
The electrode layer according to any one of claims 1 to 16, wherein the plurality of hollow nanostructures have an aspect ratio of at least 4 and a length of at least 5 micrometers.
The electrode layer according to claim 1, wherein at least some of the plurality of hollow nanostructures have a spherical shape.
The electrode layer according to any one of claims 1 to 18, wherein a maximum inner cross-sectional dimension of the plurality of hollow nanostructures is between 5 nanometers and 500 nanometers.
20. An electrode layer according to any one of the preceding claims, wherein the shell has a thickness between 5 nanometers and 1000 nanometers.
The electrode layer according to any one of claims 1 to 20,
A lithium ion battery comprising an electrolyte in which ions are transported between the electrode layers.
A method of producing a plurality of interconnected tubular hollow nanostructured electrode layers comprising a high capacity electrochemical active material comprising:
Preparing a template having a plurality of templates;
Forming a nanoscale template coating of the high volume electrochemically active material around the plurality of templates;
Performing at least one of removal and reduction of at least a portion of the template to form the electrode layer of the interconnected hollow nanostructures comprising the high capacity electrochemical active material, and
The method of manufacturing an electrode layer, wherein the coating is formed so as to form a plurality of bonded structures in which at least two coating layers covering adjacent templates overlap.
23. The method of manufacturing an electrode layer according to claim 22, wherein the step of preparing the template includes forming a plurality of template nanofibers having a length of at least 5 micrometers by forming a polymer material by an electrospinning method. .
24. The electrode layer according to claim 22 or 23, wherein the template comprises one or more polymer materials selected from the group consisting of polyacrylonitrile (PAN), nylon, polyethylene, polyethylene oxide, polyethylene terephthalate, polystyrene, and polyvinyl. Production method.
25. The template according to any one of claims 22 to 24, wherein the template is formed as a layer having a thickness between 10 and 150 micrometers and a porosity between 20% and 80%. Manufacturing method of electrode layer.
26. The method of any one of claims 22 to 25, further comprising pretreating the template by at least one of pressing the template, thermally stabilizing the template, and carbonizing the template. The manufacturing method of the electrode layer of claim | item.
27. The thermal stabilization of the template includes heating the template to a temperature between 150 degrees Celsius and 250 degrees Celsius in an argon atmosphere for at least 2 hours. Manufacturing method of electrode layer.
Forming a nanoscale substrate coating of the high capacity electrochemically active material on a surface of a conductive substrate adjacent to the template;
28. The nanoscale template coating and the nanoscale substrate coating partially overlap each other to interconnect the conductive substrate and the interconnected hollow nanostructures to each other. The manufacturing method of the electrode layer of any one.
Forming the nanoscale template coating of the high volume electrochemically active material around the template comprises:
And a bulk film forming step executed under a bulk processing condition different from the initial processing condition,
In the initial film formation stage, the shape of the template is not distorted,
29. The bulk processing condition according to any one of claims 22 to 28, wherein the bulk film formation stage is set such that a film formation speed of the nanoscale template coating is higher than that of the initial film formation stage. The manufacturing method of the electrode layer as described in any one of.
30. The removal or reduction of at least a portion of the template is performed while forming the nanoscale template coating of the high volume electrochemically active material around the plurality of templates. The manufacturing method of the electrode layer of claim | item.
Removal or reduction of a portion of the template is selected from the group consisting of firing the template in the presence of an oxidant at a temperature of at least 300 degrees Celsius, chemical etching of the template, and annealing the template. 31. The method for manufacturing an electrode layer according to any one of claims 22 to 30, comprising performing one or more processes.
Forming a second coating layer over the interconnected hollow nanostructures;
The second coating layer increases at least one of conductivity of the electrode layer, improves solid electrolyte interface (SEI) characteristics of the electrode layer, and restricts structural changes of the interconnected hollow nanostructures. The method for producing an electrode layer according to any one of claims 22 to 31, wherein:
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