Overcharge protection of batteries using current interrupt devices

A battery system includes a main electrochemical cell that includes a cathode and an anode, a cathode tab electrically coupled to the cathode, and an anode tab electrically coupled to the anode. A second electrochemical cell is electrically coupled to the cathode tab and the anode tab. An interrupt device, such as a bi-stable metal disc, is operably coupled to the second electrochemical cell and at least one of the cathode tab or the anode tab. Upon overcharging of the main electrochemical cell, the voltage between the cathode tab and the anode tab causes the second electrochemical cell to generate gases that triggers the interrupt device, which in turn disconnects at least one of the cathode tab or the anode tab, thereby protecting the main electrochemical cell from further damages.

BACKGROUND

Batteries that employ Li-ion cell chemistry may produce gas when they are improperly charged, shorted or exposed to high temperatures. This gas can cause catastrophic failure, explosion, and/or may compromise the reliability and safety of such batteries. Conventional batteries including carbon and a flammable electrolyte may combust when they are improperly charged, shorted, and/or exposed to high temperature. Current interrupt devices (CIDs) in existing Li-ion cells are generally triggered by excessive gas generation within the Li-ion cells. To this end, a small headspace around the jellyroll is usually included in existing Li-ion cells. Once a cell begins to overcharge, excessive gas generated from overcharge can trigger a bi-stable metallic disk so as to disconnect one of the terminals. In some cases, gassing agents can be added to the cell to generate extra gas in an overcharge state, such as adding Li2CO3to the positive electrode. However, these gassing agents can also induce unwanted reactions within the cell, thereby increasing the resistance and decreasing the coulombic efficiency of the cell.

An alternative method is to use a bi-stable metallic strip to cause an intentional short circuit in the presence of excessive gas generation due to overcharge. This approach also relies on gas generation from the storage electrodes and therefore can impose similar tradeoffs between safety and cell performance.

CIDs using the above approaches also suffer from accidental triggers. In general, operations of these devices are more dependent on the temperature and pressure of the cell than on the cell voltage. However, the amount of gas generated by the storage electrodes can change significantly over the lifetime of a cell. At a safe cell voltage, an older cell may generate much more gas than a newer cell does. Therefore, CIDs based on internal cell pressure can accidentally trigger even though the cell is operating safely.

SUMMARY

Apparatus, systems, and methods described herein relate to protection of batteries from over charging. In some embodiments, a battery system includes a main electrochemical cell that includes a cathode and an anode, a cathode tab electrically coupled to the cathode, and an anode tab electrically coupled to the anode. The system also includes a second electrochemical cell electrically coupled to the cathode tab and/or the anode tab and an interrupt device operably coupled to the second electrochemical cell. The interrupt device is also operably coupled to at least one of the cathode tab or the anode tab. Upon overcharging of the main electrochemical cell, the voltage between the cathode tab and the anode tab causes the second electrochemical cell to generate gases that triggers the interrupt device, which in turn disconnects at least one of the cathode tab or the anode tab, thereby protecting the main electrochemical cell from further damages. In some embodiments, upon overcharging of the main electrochemical cell, the voltage between the cathode tab and the anode tab causes the second electrochemical cell to generate gases that triggers the interrupt device, which in turn create a soft short circuit by connecting between anode and cathode through the device, thereby protecting the main electrochemical cell from damage.

DETAILED DESCRIPTION

Embodiments described herein relate generally to protection of electrochemical cells from overcharging using current interrupt devices. In some embodiments, a battery system includes a main electrochemical cell that includes a cathode and an anode, a cathode tab electrically coupled to the cathode, and an anode tab electrically coupled to the anode. A second electrochemical cell (also referred to as a sacrificial cell or a secondary cell) is electrically coupled to the cathode tab and the anode tab. An interrupt device, such as a bi-stable metal disc, is operably coupled to the second electrochemical cell and at least one of the cathode tab or the anode tab. Upon overcharging of the main electrochemical cell, the voltage between the cathode tab and the anode tab causes the second electrochemical cell to generate gases that triggers the interrupt device, which in turn disconnects at least one of the cathode tab or the anode tab, thereby protecting the main electrochemical cell from further damages.

In the battery system, the interrupt device is triggered by the second electrochemical cell, instead of the main electrochemical cell. As a result, the gas generation that triggers the interrupt device can be separated from the functionality of the main electrochemical cell. Accordingly, the second electrochemical cell can be tuned to generate a large volume of gas very rapidly so as to improve the protection while not sacrificing the lifetime and efficiency of the main electrochemical cell.

In some embodiments, a diode can be connected between the second electrochemical cell and the cathode tab (or the anode tab). The diode can adjust the threshold voltage that triggers the interrupt device, thereby decreasing the probability that the interrupt device accidentally triggers.

In some embodiments, the second electrochemical cell and the main electrochemical cell can include the same electrochemical reaction. In some embodiments, the second electrochemical cell can include materials specifically selected for gas generation, while the main electrochemical cell is optimized for other characteristics. In some embodiments, the main electrochemical cell is optimized for energy density. In some embodiments, the main electrochemical cell is optimized for specific energy. In some embodiments, the main electrochemical cell is optimized for power density. In some embodiments, the main electrochemical cell is optimized for specific power. In general, this enables the safety of the electrochemical cell to be decoupled from its performance attributes.

In some embodiments, the electrochemical reaction within the second electrochemical cell can be irreversible, in which case the interrupt device can permanently disconnect the main electrochemical cell from external circuit. In some embodiments, the second electrochemical cell can operate without a separator.

In some embodiments, the second electrochemical cell can be disposed within a casing that also encloses the main electrochemical cell. In some embodiments, the second electrochemical cell can be disposed outside the enclosure of the main electrochemical cell. In some embodiments, the second electrochemical cell and the interrupt device can be replaceable.

In some embodiments, the second electrochemical cell and the interrupt device can be added to the main cell after cell formation and/or during module or system assembly processes and/or after transporting the cells. Adding the device at a later stage of assembly can be advantageous, because this can ensure that the interrupt device is not accidentally triggered during the assembly process. In addition, after formation, if the second cell is not working correctly, the second cell can be replaced by a new one without discarding the main electrochemical cell. Similarly, if the main electrochemical cell is not working properly after formation, the second electrochemical cell and the interrupt device can still be used in another battery system.

As used herein, the term “semi-solid” refers to a material that is a mixture of liquid and solid phases, for example, such as a particle suspension, colloidal suspension, emulsion, gel, slurry or micelle.

As used herein, the terms “condensed ion-storing liquid” or “condensed liquid” refers to a liquid that is not merely a solvent, as in the case of an aqueous flow cell catholyte or anolyte, but rather, that is itself redox-active. Of course, such a liquid form may also be diluted by or mixed with another, non-redox-active liquid that is a diluent or solvent, including mixing with such a diluent to form a lower-melting liquid phase, emulsion or micelles including the ion-storing liquid.

As used in this specification, the terms “about” and “approximately” generally include plus or minus 10% of the value stated. For example, about 5 would include 4.5 to 5.5, approximately 10 would include 9 to 11, and about 100 would include 90 to 110.

As used herein, the terms “activated carbon network” and “networked carbon” relate to a general qualitative state of an electrode. For example, an electrode with an activated carbon network (or networked carbon) is such that the carbon particles within the electrode assume an individual particle morphology and arrangement with respect to each other that facilitates electrical contact and electrical conductivity between particles. Conversely, the terms “unactivated carbon network” and “unnetworked carbon” relate to an electrode wherein the carbon particles either exist as individual particle islands or multi-particle agglomerate islands that may not be sufficiently connected to provide adequate electrical conduction through the electrode.

As used herein, the terms “electrochemical cell,” “battery,” and “capacitor” all relate to a device that undergoes an electrochemical reaction due to reduction/oxidation chemistry, and are used interchangeably. Both the primary battery and the secondary battery (i.e., gas generating battery) can each conceivably be considered an electrochemical cell, a battery, or a capacitor. Other terms of art which are considered interchangeable with these terms are “cell,” “supercapacitor,” “electric double-layer capacitor,” “primary cell,” “secondary cell,” “fuel cell,” and “flow cell.”

FIG. 1Ashows a schematic of a battery system100using a current interrupt device120for overcharging protection, according to embodiments. The battery system100includes a main electrochemical cell110and a current interrupt device120to protect the main electrochemical cell110. The main electrochemical cell110receives and delivers power via a cathode tab112electrically coupled to the cathode (not shown inFIG. 1A) and an anode tab114electrically coupled to the anode (not shown inFIG. 1A). The current interrupt device120includes a second electrochemical cell122and an interrupt device124. The second electrochemical cell122is electrically coupled to the cathode tab112and the anode tab114. More specifically, the cathode of the second electrochemical cell122is electrically coupled to the cathode tab112and the anode of the second electrochemical cell122is electrically coupled to the anode tab114. In some embodiments, the second electrochemical cell122is coupled to the enclosure130.

The interrupt device124is operably coupled to at least one of the cathode tab112or the anode tab114. For illustrative purposes only, the interrupt device124is operably coupled to the anode tab114in this description. In practice, however, the interrupt device124can be coupled to the cathode tab112or both the cathode tab112and the anode tab114. The main electrochemical cell110and the current interrupt device120are substantially contained in an enclosure130(e.g., when the enclosure130includes a metal case or a metal can).

The second electrochemical cell122is configured to generate gas in response to the voltage between the cathode tab112and the anode tab114greater than a threshold voltage (also referred to as the trigger voltage). The trigger voltage can be tuned by the design of the second electrochemical cell122. For example, gas may be generated due to the electrochemical oxidation or reduction of a liquid solvent. The generated gas, in turn, triggers the interrupt device124to disconnect the anode tab115from external circuit. In this manner, the current interrupt device120can protect the main electrochemical cell110from overcharging.

As different liquids usually have different oxidation onset voltages, this trigger voltage can be tuned by the selection of solvents. Solid materials in the second electrochemical cell122may also react to produced gases, and the onset voltage of this reaction is tunable by the choice of solid materials. In general, the trigger voltage can be configured to be greater than the normal maximum operating voltage of the main electrochemical cell110by an appropriate selection of the solid and/or liquid materials comprising the second electrochemical cell122. For example, if the main electrochemical cell operates to a maximum normal voltage of 4.2V, then the second electrochemical cell122may be configured to have a trigger voltage greater than about 4.2V. The exact trigger voltage can be optimized to balance between efficacy of the device and accidental triggering. In some embodiments, the trigger voltage can be greater than about 95% of the maximum normal operating voltage of the main electrochemical cell110, greater than about 96%, greater than about 97%, greater than about 98%, greater than about 99%, greater than about 100%, greater than about 105%, greater than about 110%, greater than about 115%, greater than about 120%, or greater than about 125%, inclusive of all values and ranges therebetween. In some embodiments, the trigger voltage can be less than about 125% of the maximum normal operating voltage of the main electrochemical cell110, less than about 120%, less than about 115%, less than about 110%, less than about 105%, less than about 100%, less than about 99%, less than about 98%, less than about 97%, less than about 96%, or less than about 95%, inclusive of all values and ranges therebetween.

In some embodiments, the device can trigger as quickly as possible after an overcharge condition is reached. In this case, a lower trigger voltage may be beneficial because the device may be triggered more quickly after the main electrochemical cell110reaches the voltage threshold, current surge threshold, temperature threshold, and/or pressure threshold. In some embodiments, it is desirable to reduce accidental triggering. In this case, the device can have a higher trigger voltage.

In some embodiments, the second electrochemical cell122can have a trigger voltage less than twice the normal maximum operating voltage of the main electrochemical cell110. In certain embodiments, the second electrochemical cell122can have a trigger voltage less than 1.5 times the normal maximum operating voltage of the main electrochemical cell110. In certain embodiments, the second electrochemical cell122can have a trigger voltage less than 1.2 times the normal maximum operating voltage of the main electrochemical cell110.

In some embodiments, the second electrochemical cell122can be physically smaller than the main electrochemical cell110to ensure that the energy density of the full battery system100is maximized. In some embodiments, the second electrochemical cell122can occupy less than about 50% of the volume of the main electrochemical cell110. In certain other embodiments, the second electrochemical cell can occupy less than about 25% of the volume of the main electrochemical cell110. In some embodiments, the second electrochemical cell122can occupy less than about 10% of the volume of the main electrochemical cell110. In some embodiments, the second electrochemical cell122can take the form of a cylinder with a diameter of about 10 mm to about 30 mm (e.g., about 10 mm, about 15 mm, about 20 mm, about 25 mm, or about 30 mm, including any values and sub ranges in between). In some embodiments, the electrochemical cell122can have a height of about 1 mm to about 10 mm (e.g., about 1 mm, about 2 mm, about 3 mm, about 4 mm, about 5 mm, about 6 mm, about 7 mm, about 8 mm, about 9 mm, or about 10 mm, including any values and sub ranges in between). In some embodiments, the second electrochemical cell122can take a different form and have a volume of about 1 mL to about 100 mL (e.g., about 1 mL, about 2 mL, about 5 mL, about 10 mL, about 20 mL, about 50 mL, or about 100 mL).

FIG. 1Bshows a schematic of an example interrupt device124, which includes a top disc124a, a bottom disc124b, and an insulator124cdisposed between the top disc124aand the bottom disc124b. The bottom disc124bis electrically coupled to the anode tab114. Under normal operation conditions, the top disc124aand the bottom disc124bare in electric contact via a bulb portion124din the top disc124a, and the top disc124acan be connected to external circuit for charging. Upon overcharging, when a particular voltage threshold or a voltage threshold range is reached, during high current surges, and/or when the temperature within the electrochemical cell exceeds a temperature threshold, gases generated within the cell can push the top disc124aaway from the bottom disc124b, thereby electrically disconnecting the anode tab114from external circuit and protecting the electrochemical cell.

Various embodiments of the battery system100and options of components (e.g., the main electrochemical cell110, the current interrupt device120, and the enclosure130) are described below with reference toFIGS. 2-5.

The Main Electrochemical Cell

FIG. 2shows a side view of an electrochemical cell200that can be used as the main electrochemical cell110shown inFIG. 1A, according to embodiments. The electrochemical cell200includes a cathode210(also referred to as a cathode material) disposed on a cathode current collector212, an anode220(also referred to as an anode material) disposed on an anode current collector222, and a separator230disposed in between. The assembly of the cathode210, the cathode current collector212, the anode220, the anode current collector222, and the separator230is contained substantially in a pouch240. Any cathode tab (not shown inFIG. 2) can be electrically coupled to the cathode current collector212and extends beyond the pouch240for connection with external circuit. Similarly, any anode tab (not shown inFIG. 2) can be electrically coupled to the anode current collector222and extends beyond the pouch240for connection with external circuit.

In some embodiments, the cathode material210can include, for example, Nickel Cobalt Aluminum (NCA), Core Shell Gradient (CSG), Spinel Lithium Manganese Oxide (LMO), High Voltage Spinel (LNMO), Lithium Iron Phosphate (LFP), Lithium Cobalt Oxide (LCO), Nickel Cobalt Manganese (NCM), other lithium-rich materials, and vanadium-based metal hydrides, among others.

The anode material220can be selected from a variety of materials. In some embodiments, the anode material220comprises a carbon-based material, including, but not limited to, graphite, hard carbon, carbon nanotubes, carbon nanofibers, porous carbon, and graphene. In some embodiments, the anode material220comprises a titanium-based oxide including, but are not limited to, spinel Li4Ti5O12(LTO) and titanium dioxide (TiO2, Titania). In some embodiments, the anode material220comprises alloy or de-alloy material including, but not limited to, silicon, silicon monoxide (SiO), germanium, tin, and tin oxide (SnO2). In some embodiments, the anode material220comprises a transition metal compound (e.g., oxides, phosphides, sulphides and nitrides). The general formula of a transition metal compound can be written as MxNy, where M can be selected from iron (Fe), cobalt (Co), copper (Cu), manganese (Mn), and nickel (Ni), and N can be selected from oxygen (O), phosphorous (P), sulfur (S), and nitrogen (N).

In some embodiments, the anode material220comprises an intermetallic compound. An intermetallic compound can be based on a formulation MM′, wherein M is one metal element and M′ is a different metal element. An intermetallic compound can also include more than two metal elements. The M atoms of an intermetallic compound can be, for example, Cu, Li, and Mn, and the M′ element of an intermetallic compound can be, for example, Sb. Exemplary intermetallic compounds include Cu2Sb, Li2CuSb, and Li3Sb, among others. In one example, the intermetallic compound in the anode material can have fully disordered structures in which the M or M′ atoms are arranged in a random manner. In another example, the intermetallic compound in the anode material has partially disordered structures in which the M or M′ atoms in the crystal lattice are arranged in a non-random manner.

In some embodiments, the anode material220can be porous so as to increase the surface area and enhance the rate of lithium intercalation in the resulting electrodes. In one example, the anode material220includes porous Mn2O3, which can be prepared by, for example, thermal decomposition of MnCO3microspheres. In another example, the anode material220includes porous carbon fibers prepared by, for example, electrospinning a blend solution of polyacrylonitrile and poly(l-lactide), followed by carbonization. In some embodiments, the porosity of the anode material220can be achieved or increased by using a porous current collector. For example, the anode material220can include Cu2Sb, which is deposited conformally on a porous foam structure, to have certain degree of porosity.

In some embodiments, at least one of the anode material220or the cathode material210can include a semi-solid or a condensed ion-storing liquid reactant. By “semi-solid” it is meant that the material is a mixture of liquid and solid phases, for example, such as a semi-solid, particle suspension, colloidal suspension, emulsion, gel, slurry or micelle. “Condensed ion-storing liquid” or “condensed liquid” means that the liquid is not merely a solvent as it is in the case of an aqueous flow cell catholyte or anolyte, but rather, that the liquid is itself redox-active. Such a liquid form may also be diluted by or mixed with another, non-redox-active liquid that is a diluent or solvent, including mixing with such a diluent to form a lower-melting liquid phase, emulsion or micelles including the ion-storing liquid. In some embodiments, semi-solid electrode compositions (also referred to herein as “semi-solid suspension” and/or “slurry”) can include a suspension of electrochemically-active agents (anode particulates and/or cathode particulates) and, optionally, electronically conductive particles. The cathodic particles and conductive particles are co-suspended in an electrolyte to produce a cathode semi-solid. The anodic particles and conductive particles are co-suspended in an electrolyte to produce an anode semi-solid. The semi-solids are capable of flowing due to an applied pressure, gravitational force, or other imposed field that exerts a force on the semi-solid, and optionally, with the aid of mechanical vibration. Examples of batteries utilizing semi-solid suspensions are described in U.S. Pat. No. 9,362,583, entitled “Semi-Solid Electrodes Having High Rate Capability,” the entire disclosure of which is hereby incorporated by reference.

In some embodiments, one of both of the current collectors212and222can include a conductive substrate. In one example, the conductive substrate comprises a metal material such as aluminum, copper, lithium, nickel, stainless steel, tantalum, titanium, tungsten, vanadium, or their combinations or alloys. In another example, the conductive substrate comprises a non-metal material such as carbon, carbon nanotubes, or a metal oxide or their combinations of composite (e.g., TiN, TiB2, MoSi2, n-BaTiO3, Ti2O3, ReO3, RuO2, IrO2, etc.)

In some embodiments, one or both of the current collectors212and222can include a base substrate having one or more surface coatings so as to improve the mechanical, thermal, chemical, or electrical properties of the current collector. In one example, the coating(s) on the current collector can be configured to reduce corrosion and alter adhesion characteristics (e.g., hydrophilic or hydrophobic coatings, respectively). In another example, the coating(s) on the current collector can comprise a material of high electrical conductivity to improve the overall charge transport of the base substrate. In yet another example, the coatings can comprise a material of high thermal conductivity to facilitate heat dissipation of the base substrate and protect the battery from overheating. In yet another example, the coatings can comprise a heat-resistant or fire-retardant material to prevent the battery from fire hazards. In yet another example, the coatings can be configured to be rough so as to increase the surface area and/or the adhesion with the anode material. In yet another example, the coatings can include a material with good adhering or gluing properties with the anode material.

In some embodiments, one or both of the current collectors212and222can include a conductive substrate having a roughened surface so as to improve the mechanical, electrical, and thermal contact between the anode material and the current collector. The roughened surface of the current collector can increase the physical contact area between the anode material and the current collector, thereby increasing the adherence of the anode material to the current collector. The increased physical contact area can also improve the electrical and thermal contact (e.g., reduced electrical and thermal resistance) between the current collector and the anode material.

In some embodiments, one or both of the current collectors212and222can include a porous current collector such as a wire mesh. The wire mesh (also referred to herein as mesh) can include any number of filament wires that can be assembled in various configurations using suitable processes, such as a regular pattern or structure produced by weaving, braiding, knitting, etc. or a more random pattern or structure produced by randomly distributing wires and joining them by welding, adhesives, or other suitable techniques. Moreover, the wires comprising the mesh can be any suitable material. For example, in some embodiments, the wires are metallic such as, steel, aluminum, copper, titanium or any other suitable metal. In other embodiments, the wires can be a conductive non-metallic material such as, for example, carbon nanofiber or any other suitable material. In some embodiments, the wires can include coatings. For example, the coatings can be configured to reduce corrosion and enhance or reduce adhesion characteristics (e.g., hydrophilic or hydrophobic coatings, respectively). Examples of porous current collectors are described in U.S. Patent Publication No. U.S. 2013/0065122 A1, entitled “Semi-Solid Electrode Cell Having A Porous Current Collector and Methods of Manufacture,” the entire disclosures of which is hereby incorporated by reference.

In some embodiments, the separator230can be a thin, microporous membrane that electrically separates the anode210from the cathode210but allows ions to pass through the pores between the two electrolytes during discharging and charging. In some embodiments, the separator230includes a thermoplastic polymer, such as polyolefins, polyvinyl chlorides, nylons, fluorocarbons, and polystyrenes, among others. In some embodiments, the separator230includes polyolefins material that comprises, for example, polyethylene, ultra-high molecular weight polyethylene, polypropylene, polybutene, polymethylpentene, polyisoprene, copolymers thereof, and their combinations. Exemplary combinations can include, but are not limited to, mixtures containing two or more of the following polyethylene, ultra-high molecular weight polyethylene, and polypropylene, as well as, mixtures of the foregoing with copolymers such as ethylene-butene copolymer and ethylene-hexene copolymer.

In some embodiments, the separator230can include thermosetting plastics, such as polyimide (PI), poly amide (PA), and poly amide imide (PAI), among others. In some embodiments, the separator230can include a non-woven type separator. In some embodiments, the non-woven type separator can be made of ceramic fibers. In some embodiments, the non-woven type separator can be made of fibrillated fibers. In some embodiments, the non-woven type separator can be made of cellulose nanofibers.

The pouch240in the electrochemical cell200substantially contains the cathode210, the cathode current collector212, the anode220, the anode current collector222, and the separator230. The pouch240can physically separate the electrochemical cell200from adjacent cells so as to mitigate or eliminate defect propagation, and to facilitate easy handling of the electrochemical cell200during battery manufacturing. The pouch240can also reduce the possibility of fire ignition of flammable electrolyte during possible welding processes in battery manufacturing, which at times generates sparks, when working with a semi-solid electrode.

In some embodiments, the cathode210, the cathode current collector212, the anode220, the anode current collector222, and the separator230are sealed in the pouch240(e.g., via vacuum sealing). In these embodiments, the pouch240can still reduce or eliminate chances of exposure to sparking (e.g., from welding processes) that could ignite the electrolyte. A final sealing step can be carried out after the welding process to seal one or more single pouch electrochemical cells into an external pouch or package, in which case the external pouch or package can function as moisture control. Examples of battery architectures utilizing single pouch electrochemical cells are described in U.S. Patent Application Publication No. 2017/0025646, entitled “Single Pouch Battery Cells and Methods of Manufacture,” the entire disclosure of which is hereby incorporated by reference.

In some embodiments, the pouch240includes a three-layer structure, namely an intermediate layer sandwiched by an outer layer and an inner layer, wherein the inner layer is in contact with the electrodes and the electrolyte. For example, the outer layer can include a nylon-based polymer film. The inner layer can include a polypropylene (PP) polymer film, which can be corrosion-resistive to acids or other electrolyte and insoluble in electrolyte solvents. The intermediate layer can include of aluminum (Al) foil. This structure allows the pouch to have both high mechanical flexibility and strength.

In some embodiments, the outer layer of the pouch240includes polymer materials such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), nylon, high-density polyethylene (HDPE), oriented polypropylene (o-PP), polyvinyl chloride (PVC), polyimide (PI), polysulfone (PSU), and their combinations.

In some embodiments, the intermediate layer of the pouch240includes metal layers (foils, substrates, films, etc.) comprising aluminum (Al), copper (Cu), stainless steel (SUS), and their alloys or combinations.

In some embodiments, the inner layer of the pouch240includes materials such as cast polypropylene (c-PP), polyethylene (PE), ethylene vinylacetate (EVA), and their combinations.

In some embodiments, the pouch240includes a two-layer structure, namely an outer layer and an inner layer. In some embodiments, the outer layer can include PET, PBT, or other materials as described above. In some embodiments, the inner layer can include PP, PE, or other materials described above.

In some embodiments, the pouch240can include a water barrier layer and/or gas barrier layer. In some embodiments, the barrier layer can include a metal layer and/or an oxide layer. In some embodiments, it can be beneficial to include the oxide layer because oxide layers tend to be insulating and can prevent short circuits within the battery system.

In some embodiments, there can be only one (or two) unit cell(s) assembly within the pouch240, the pouch240can be substantially thinner than pouches commonly used for multi-stack electrochemical cells. For example, the pouch240can have a thickness less than 200 μm, less than 100 μm, or less than 50 μm. The thickness of the pouch240as used here can be defined as the thickness of the film that forms the pouch240.

In some embodiments, the thickness of the pouch240can depend on at least two aspects. In one aspect, it can be desirable to achieve high energy density in the resulting electrochemical cells, in which case thinner pouches can be helpful since a larger portion of space within a electrochemical cell can be reserved for electrode materials. In another aspect, it can be desirable to maintain or improve the safety advantage of the pouch240. In this case, a thicker pouch can be helpful to, for example, reduce fire hazard. In some embodiments, the pouch thickness can be quantified as a ratio of the volume occupied by the pouch material to the total volume of the electrochemical cell. In some embodiments, the pouch thickness can be about 5% to about 40% in terms of the ratio as defined above. In some embodiments, the pouch thickness can be about 10% to about 30% in terms of the ratio as defined above.

In some embodiments, the thickness of the electrochemical cell200(including the thickness of the pouch240and the thickness of the electrodes) can be about 300 μm to about 3 mm (e.g., about 300 μm, about 400 μm, about 500 μm, about 1 mm, about 2 mm, or about 3 mm, including any values and sub ranges in between).

In some embodiments, the pouch240includes a single layer of lower cost materials that are thinner. For example, these materials can be polypropylene or a combination of polyolefins that can be sealed together using heat or pressure (e.g., thermal fusion or vacuum sealing).

In some embodiments, the pouch240includes a single layer of fire retardant materials so as to prevent the propagation of fire hazard from one single pouch electrochemical cell to another. In some embodiments, the pouch240includes an air-proof material so as to prevent the propagation of gas released by one single pouch electrochemical cell to another, thereby reducing defect propagation.

The Current Interrupt Device

FIGS. 3A-3Bshow schematics of electrochemical cells that can be used as the second electrochemical cell122in the current interrupt device120shown inFIG. 1A. In the battery system100, the second electrochemical cell122is employed to trigger the interrupt device124, instead of storing energy. Therefore, a separator is not needed for the second electrochemical cell122. However, a separator can be still included in the second electrochemical cell122to increase selectivity and/or to provide greater gas generation rate when the interrupt device124is triggered.

FIG. 3Ashows a schematic of an electrochemical cell301without any separator. The electrochemical cell301includes a cathode321disposed on a cathode current collector311, an anode341disposed on an anode current collector351, and an electrolyte331disposed between the cathode current collector311and the anode current collector351.

FIG. 3Bshows a schematic of an electrochemical cell302including a separator to, for example, increase gas generation rates. The electrochemical cell302includes a cathode322disposed on a cathode current collector312, an anode342disposed on an anode current collector352, and a separator362disposed between the cathode322and the anode342. The electrochemical cell302also includes electrolyte332disposed in the space between the cathode current collector312and the anode current collector352.

FIG. 3Cshows a schematic of a capacitor303including a separator to, for example, increase gas generation rates. The capacitor303includes a cathode323disposed on a cathode current collector313, an anode343disposed on an anode current collector353, and a separator363disposed between the cathode323and the anode343. The capacitor303also includes electrolyte333disposed in the space between the cathode current collector313and the anode current collector353. In some embodiments, the capacitor303can be connected to at least one of the cathode323and the anode343.

In some embodiments, components in the electrochemical cells301and302and the capacitor303can be substantially similar to counter components in the electrochemical cell200. For example, the cathodes321,322, and323, the cathode current collectors311,312,313, the anodes341,342, and343, the anode current collectors351,352, and353, and the separators362and363can be substantially similar to the cathode210, the cathode current collector212, the anode220, the anode current collector222, and the separator330, respectively.

In some embodiments, the electrochemical cells301,302, and303can be different from the electrochemical cell200. In some embodiments, the electrochemical cells301,302, and303can use electrochemical reactions that are different from the electrochemical reaction used in the electrochemical cell200. For example, the electrochemical cells301,302, and303can use electrochemical reactions that are otherwise undesirable due to excessive gas generation under high voltages.

In some embodiments, the electrochemical cells301and302can use reversible electrochemical reactions. In this case, the electrochemical cells301and302(and accordingly the current interrupt device including these cells) can be reused. In some embodiments, the electrochemical cells301and302can use irreversible electrochemical reactions. In this case, the current interrupt device including the electrochemical cells301and302can permanently disconnect the battery from external circuit.

In some embodiments, the electrolyte331and332can be selected based on their decomposition window. Typically, battery electrolytes (e.g., the electrolyte used in the main electrochemical cell110) have a wide electrochemical stability window. For the sacrificial electrochemical cells331and332used in current interrupt devices, it can be desirable to choose electrolytes with a tuned decomposition potential for maximum selectivity of gas generation. In some embodiments, the electrolytes331and332can use solvents including, but not limited to, N-Methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), methyl acetate (MA), ethyl acetate (EA), acetonitrile (AN), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, 1-3 dioxolane (DOL), dimethoxyethane (DME), diglyme, triglyme, tetraglyme, gamma-butyrolactone (GBL), methyl propionate (MP), and ethyl propionate (EP). In some embodiments, a lithium salt-based additive can be used to generate gas on purpose above the trigger voltage. In some embodiments, the lithium salt-based additive can be lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), for example to prevent aluminum corrosion, and lithium bis(oxalate) borate (LiBOB), lithium difluoro(oxalate)borate (LiDFOB), or combinations thereof, which can generation gases such as carbon dioxide during oxidation. These solvents can react to formed gas at differing trigger voltages to tune (e.g., to increase) the gas generation capacity of the cells301and302.

In some embodiments, the gas generation trigger voltage can be tuned by modifying the purity level of the solvents; in general, lower purity solvents can have lower decomposition potentials. In some embodiments, the gas generation trigger voltage can be tuned by the use of additives to the solvent. For example, additives including but not limited to, biphenyl (BP), water (H2O), hydrofluoric acid (HF), and fluoroethylene carbonate (FEC) may be incorporated to tune the trigger voltage for gas generation. In some embodiments, the additive can include a salt in a solvent, the solvent having a particular purity.

In some embodiments, the current collectors (i.e.,311and351inFIG. 3A, 312 and 352inFIG. 3B) can be configured to increase gas generation. In some embodiments, the current collectors can include materials that can catalyze gas generation reactions. For example, the current collectors can include carbonaceous, metallic, or an ionic compound. In some embodiments, a non-inert electrode can be used to enhance gas generation. For example, a carbonaceous current collector can be oxidized to produce additional CO2gas.

In some embodiments, the gas generation can be determined by the solvent physical vapor pressure. In some embodiments, the gas-generation device can release gas and/or thermal energy to the CID and increase the internal pressure and/or temperature for both302and200. In some embodiments, the gas generation trigger temperature can be tuned by the use of a highly volatile solvent. For example, additives including but not limited to, benzene, cyclohexane, and petroleum ether with different boiling points can be incorporated to tune the trigger temperature for gas generation.

In some embodiments, the form of the current collectors can be optimized to enhance gas generation. For example, the current collectors can include a dense foil, a porous mesh, or a metal wool (like steel wool). The increased surface area of the porous or wool-type current collector can provide additional surface area for gas generating reactions.

In some embodiments, the current collector can be coated with material that can decompose at a certain onset voltage. For example, the current collector can be coated with a solid such as Li2CO3, LiNO3, and/or Li2O. In some embodiments, the current collector can be coated with a polymer, such as PAN, PAA, or PVDF. These embodiments have the advantage that the liquid solvent does not directly contact the current collector until the coating material is reacted away. If this reaction is triggered at a certain voltage, then the liquid is able to contact the current collector and the gas generation rate is amplified. This provides an additional means by which the trigger voltage and gas generation rates may be independently or collectively tuned. In some embodiments, a supercapacitor that includes carbon electrodes (e.g., a polytetrafluoroethylene-based carbon electrodes without current collectors) can be used as the gas generating device.

In some embodiments, the electrodes321,341,322, and342can include semi-solid electrodes. In some embodiments, the fraction ratio of the liquid phase material to the solid phase material in the semi-solid electrodes can be adjusted to increase gas generation.

In some embodiments, the electrodes321,341,322, and342can include solids that evolve gas under certain electrochemical conditions. In some embodiments, the solids can include materials such as, but not limited to, Li2CO3, Na2CO3, MgCO3, CaCO3, Li3N4, Li2O, and Na2O. In some embodiments, the solids can coat the current collector and in other embodiments they may not. In some embodiments, the coating may be dense and in other embodiments it may be porous.

In some embodiments, the electrodes321,341,322, and342can include materials that are not highly pure. For example, the electrodes321,341,322, and342can include semi-solid electrodes of Na2CO3dissolved in NMP for dual effects of gas generated by the decomposition of a solid and of a liquid solvent. Other combinations of solid and liquid components may be used to achieve similar dual effects of gas generation.

In some embodiments, the electrodes321,341,322, and342can include porous electrodes. In some embodiments, the porous electrodes can include porous Mn2O3and/or porous carbon fibers. In some embodiments, materials of the electrodes321,341,322, and342can be disposed in porous current collectors (e.g. porous foam current collector) so as to construct porous electrodes.

FIG. 4shows a schematic of a battery system400including a diode440to adjust the threshold voltage that triggers the current interrupt device420. The battery system400includes a main electrochemical cell410and a current interrupt device420to protect the main electrochemical cell410. The main electrochemical cell410receives and delivers power via a cathode tab412electrically coupled to the cathode (not shown inFIG. 4) and an anode tab414electrically coupled to the anode (not shown inFIG. 4). The current interrupt device420includes a second electrochemical cell422and an interrupt device414. The second electrochemical cell422is electrically coupled to the cathode tab412and the anode tab414such that the voltage between the cathode tab412and the anode tab414is also applied to the second electrochemical cell422. The interrupt device424is operably to at least one of the cathode tab412or the anode tab414. The main electrochemical cell410and the current interrupt device420are substantially contained in an enclosure430.

A diode440is disposed between the cathode tab412and the second electrochemical cell422. The forward bias voltage of the diode440can be used to adjust the threshold voltage that triggers the interrupt device424. For example, a higher forward bias voltage of the diode440can lead to a higher threshold voltage that can trigger the interrupt device424.

FIG. 4shows that the battery system400includes only one diode440for illustrative purposes. In practice, other numbers of diodes can also be used. For example, the battery system400can include two diodes, with one diode disposed between the cathode tab412and the second electrochemical cell422and the other diode disposed between the anode tab414and the second electrochemical cell422.

In some embodiments, the battery system400can also include one or more resistors disposed between the second electrochemical cell422and the tabs412and414(i.e. in series with the second electrochemical cell422). The resistor(s) can split a portion of the voltage between the cathode tab412and the anode tab414, thereby adjusting the voltage drop across the second electrochemical cell422. In this manner, the resistor(s) can adjust the threshold voltage that triggers the current interrupt device420.

In some embodiments, the battery system400can also include one or more operational amplifiers between the second electrochemical cell422and the tabs412and414. The operational amplifier(s) can amplify the voltage between the cathode tab412and the anode tab414, thereby increasing the sensitivity of the current interrupt device420.

The Enclosure

In some embodiments, the enclosure130inFIG. 1Acan include a pouch. The pouch can be substantially similar to the pouch240in the electrochemical cell200shown inFIG. 2and described above. In some embodiments, the enclosure130can include a metal can, such as the metal can used in coin cell batteries. In some embodiments, the enclosure130can include a plastic case. In some embodiments, the metal can (used as the enclosure130) can be electrically positive or negative. In these cases, the second battery122can be coupled to the metal can.

As described above, the current interrupt device120can be contained in the enclosure130or disposed outside the enclosure130. In some embodiments, the current interrupt device120can be replaceable.

FIG. 5shows a schematic of a battery system500including a replaceable current interrupt device disposed outside the enclosure for the main electrochemical cell. The battery system500includes a main electrochemical cell510substantially contained in an enclosure530. A cathode tab512and an anode tab514connect the main electrochemical cell510with external circuits for power delivery or charging. A current interrupt device520, including a second electrochemical cell522and an interrupt device524, is disposed outside the enclosure530and between the cathode tab512and the anode tab514. The interrupt device524is also operably coupled to at least one of the cathode tab512or the anode tab514so as to disconnect the tab (512and/or514) upon overcharging of the main electrochemical cell510.

As shown inFIG. 5, the current interrupt device520is disposed outside the enclosure530. In this case, the current interrupt device520can be incorporated into the battery system500after the formation and sealing of the main electrochemical cell510. Adding the current interrupt device520at this late stage of assembly can ensure that the current interrupt device520is not accidentally triggered during the assembly process. In addition, after formation, if the second cell522is not working correctly, the second cell522can be replaced by a new one without discarding the main electrochemical cell510. Similarly, if the main electrochemical cell510is not working properly after formation, the second electrochemical cell522and the interrupt device524can still be used in another battery system.

In some embodiments, a diode (e.g., like the diode440shown inFIG. 4) can be used to adjust the threshold voltage that triggers the current interrupt device520. The diode can be coupled to the cathode tab512and/or the anode tab514. In some embodiments, the enclosure530can include a metal enclosure and the second battery522can be electrically coupled to the enclosure530as well. In some embodiments, the metal enclosure530is electrically positive. In some embodiments, the metal enclosure530is electrically negative. In some embodiments, the metal enclosure530can be connected to the ground (e.g., as a ground electrode).

In some embodiments, the battery system500can include a second enclosure (not shown inFIG. 5) that substantially contains both the current interrupt device520and the enclosure530. In this case, the second enclosure can, for example, protect the current interrupt device520from moisture or insulate the current interrupt device520.

FIG. 6shows a schematic of a battery system600using a current interrupt device620for overcharging protection, according to an embodiment. The battery system600includes a main electrochemical cell610and the current interrupt device620to protect the main electrochemical cell610. The main electrochemical cell610receives and delivers power via a cathode tab612electrically coupled to the cathode (not shown inFIG. 6) and an anode tab614electrically coupled to the anode (not shown inFIG. 6). The current interrupt device620includes a second electrochemical cell622and an interrupt device614. The second electrochemical cell622is electrically coupled to the cathode tab612and the anode tab614. More specifically, the cathode of the second electrochemical cell622is electrically coupled to the cathode tab612and the anode of the second electrochemical cell622is electrically coupled to the anode tab614. In some embodiments, the second electrochemical cell622is disposed in an enclosure630.

The interrupt device624is operably coupled to at least one of the cathode tab612or the anode tab614. For illustrative purposes only, as shown inFIG. 6the interrupt device624is operably coupled to the anode tab614. In practice, however, the interrupt device624can be coupled to the cathode tab612or both the cathode tab612and the anode tab614. The main electrochemical cell610and the current interrupt device620are substantially encased in the enclosure630(e.g., when the enclosure630includes a pouch, a metal case, or a metal can).

The second electrochemical cell622is configured to generate gas in response to the voltage between the cathode tab612and the anode tab614exceeding a threshold voltage or within a threshold voltage range (also referred to as the trigger voltage). The trigger voltage can be tuned by the design of the second electrochemical cell622. For example, gas may be generated due to the electrochemical oxidation or reduction of a liquid solvent. The generated gas, in turn, triggers the interrupt device624to at least temporarily disconnect the anode tab615from an external circuit, for example by creating a soft short circuit. In some embodiments, upon overcharging of the main electrochemical cell610, the voltage between the cathode tab612and the anode tab614causes the second electrochemical cell622to generate gas that trigger the interrupt device624. In turn, the interrupt device624can create the soft short circuit by connecting between anode tab615and the cathode tab612through the interrupt device624. In this manner, the current interrupt device620can protect the main electrochemical cell610from overcharging.

FIG. 7shows a schematic of a current interrupt device724for overcharge protection, according to an embodiment. In some embodiments, the current interrupt device724can be operably coupled to an electrochemical cell substantially similar to the main electrochemical cell610. In some embodiments, the current interrupt device can be disposed within an enclosure (e.g.,630). In some embodiments, the electrochemical cell can include a cathode tab712coupled to a cathode (not shown) and an anode tab714coupled to an anode (not shown).

In some embodiments, the current interrupt device724can include a first tab connector725aelectrically coupled to the cathode tab712and a second tab connector725belectrically coupled to the anode tab714. The first tab connector725ais electrically insulated from the second tab connector725bduring normal operation of the electrochemical cell. In some embodiments, the first tab connector725acan be electrically insulated from the second tab connector725busing a first insulator726and a second insulator727. In some embodiments, a gas-tight cavity728can be defined at least in part by the first tab connector725a, the second tab connector725b, the first insulator726, and the second insulator727. In some embodiments, the current interrupt device724can include a liquid solvent configured to generate gas when a voltage threshold or current threshold is reached (or exceeded). In some embodiments, the liquid solvent can be substantially similar to the gas-generating liquid described above with reference toFIGS. 1A-5.

In some embodiments, a portion of the second tab connector725bcan be configured to deform when a force is applied to cause an elongation or expansion of the second tab connector725b. In some embodiments, the force can be applied to the second tab connector725bby gas generated from the liquid solvent in the gas-tight cavity728. The elongation or expansion of the second tab connector725bcan be configured to electrically couple the second tab connector725bto the first tab connector725a. In some embodiments, the electrical coupling of the first tab connector725aand the second tab connector725bcan be configured to cause a soft short circuit between the cathode tab712and the anode tab714. Similarly, the first tab connector725acan be configured to deform when a force is applied to the first tab connector725a. In some embodiments, the first tab connector725aand the second tab connector725bcan both be configured to deform when a force is applied.

In some embodiments, the soft short circuit between the cathode tab712and the anode tab714can help protect the electrochemical cell (e.g.,610) from damage due to overcharging and/or high voltage conditions. In some embodiments, the soft short circuit conditions can discontinue charging/discharging from the electrochemical cell, thereby discontinuing gas generation within the gas-tight cavity728. In some embodiments, the deformed connector may revert substantially back to its original shape and discontinue the soft short circuit after gas generation is discontinued. In some embodiments, the discontinuation of the soft short circuit can return the electrochemical cell to normal operation.

While various embodiments of the system, methods and devices have been described above, it should be understood that they have been presented by way of example only, and not limitation. Where methods and steps described above indicate certain events occurring in certain order, those of ordinary skill in the art having the benefit of this disclosure would recognize that the ordering of certain steps may be modified and such modification are in accordance with the variations of the invention. Certain of the steps may be performed concurrently in a parallel process when possible, as well as performed sequentially as described herein. The embodiments have been particularly shown and described, but it will be understood that various changes in form and details may be made.