Patent Publication Number: US-2022216453-A1

Title: Lithiation of electrodes for energy storage devices and method for making same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application relates to and claims the benefit of U.S. Provisional Patent Application Ser. No. 62/925,682 filed Oct. 24, 2019 and entitled “LITHIATION OF ELECTRODES FOR ENERGY STORAGE DEVICES AND METHOD OF MAKING SAME,” the entire disclosure of which is hereby incorporated by reference. 
    
    
     STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
     Not Applicable 
     BACKGROUND 
     1. Technical Field 
     Apparatuses and methods consistent with the present inventive concept relate to energy storage devices, and more particularly to electrodes for energy storage devices. 
     2. Description of the Related Art 
     Lithium (Li) pre-doped electrodes, or lithiated electrodes, are widely used in energy storage devices, for example, lithium-ion (Li-ion) batteries and Li-ion capacitors. 
     In the external Li attachment and pre-dope method, an electrode pack is constructed with at least one positive electrode, at least one separator, at least one Li film laminated on a current collector, and at least one negative electrode. The negative electrode is connected to the Li film through welding of the current collector tabs. The electrode pack is immersed in electrolyte that contains Li ions. Through the pre-dope process, the Li film is converted into Li ions and the Li ions migrate and are doped into the negative electrode. 
     In the external Li attachment and pre-dope method, thin Li metal films are normally provided on the uppermost and lowermost layers of an electrode package. During the Li pre-dope process, the Li ions have to travel through the electrode and separator layers. One of the requirements is that the current collectors inside the electrodes needs to be in a mesh or perforation format, which is costly, and the Li may be non-uniformly doped into the stacked negative electrode layers even though the current collectors in the center of the electrodes are made porous. Long manufacture time is reported to uniformly dope lithium to the negative electrode inside the electrode laminates. Further, as Li metal is very sensitive to moisture, the entire operation of the manufacture of the electrodes attached to Li metal, the electrode packs, and the energy storage devices must be carried out in a full scale dry room, which requires high capital investment and high energy consumption. Therefore, the long manufacture cycle time plus the dry room operation requirements, makes this high cost method less competitive in the energy storage device industry. 
     In order to improve the long manufacture time and high cost necessary for the external Li attachment and pre-dope method, direct contact methods were proposed by different inventors as described, for example, in U.S. Patent Application Pub. No. 2017/0062815, the entire contents of which is incorporated by reference herein. In the direct contact methods, Li powder or Li film with patterns were pressed directly onto the electrode surface layer. The direct contact methods largely shortened the Li pre-dope time. However, Li metal powder or foils may remain on the electrode surface after completion of the pre-doping process, which again presents a high safety issue for the energy storage devices. More detrimentally, instantaneous electrical shorting between the Li metal and the negative electrode active layer materials (i.e., the surface of the electrode) induced by immersing the electrode pack into electrolyte caused severe reactions. These severe reactions resulted in damage to the electrode and separator, resulting in sub-par batteries and capacitors. Further, the direct contact method still requires the whole manufacture process being carried out in a full-scale dry room environment, which again, requires high capital investment and high energy consumption in operations. 
     In order to reduce the energy storage device manufacture time and cost, to eliminate the need for expensive full scale dry room operations, and to prevent the damage caused to the electrode by direct contact, new lithiation methods to produce Li pre-doped electrodes for energy storage devices have been newly developed as set forth herein. 
     BRIEF SUMMARY 
     Various embodiments provide lithiated or pre-doped electrodes and methods for fabricating lithiated or pre-doped electrodes. Lithiation can be introduced to the electrode at the different assembly stages of an energy storage device. 
     Steps and corresponding stages of a typical large scale energy storage device assembly process are listed below: 
     1. Prepare an electrode in a roll to roll format (Stage 1) 
     2. Prepare an electrode pack, e.g., wound or stacked electrode(s) and separator(s) (Stage 2) 
     3. Insert the electrode pack into a case (e.g. a cylindrical or prismatic container or a pouch), the cell assembly (Stage 3) 
     4. Vacuum dry the cell assembly 
     5. Impregnation of the electrolyte 
     6. Seal the case 
     According to various embodiments there is provided a method for lithiation, or Li pre-doping, of an electrode. In some embodiments, the method may include a Step 1 of preparing an electrode to be lithiated. The electrode may be a single electrode (i.e. a Stage 1 roll also referred to as an electrode roll). Alternatively, the electrode may be part of an electrode pack including wound or stacked electrode(s) and separator(s), which may consist of at least one negative electrode, at least one separator, and at least one positive electrode (i.e. a Stage 2 electrode pack). Alternatively, the electrode may be part of an unfinished battery or ultracapacitor with an electrode pack including wound or stacked electrode(s) and separator(s) inside a case and with or without an unsealed lid (i.e. a Stage 3 cell assembly). Step 1 may include preparing the electrode roll, electrode pack, or cell assembly in a normal air environment, drying it in a vacuum oven, and moving it into a dry box or a small dry room. The method may further include a Step 2 of preparing a piece of Li metal with predetermined weight separately in the dry box or the small dry room and, optionally, attaching the piece of Li metal to a conductive material with high conductivity, such as copper or nickel foil. The method may further include a Step 3 of attaching the piece of Li metal or the conductive material to a current collector of the electrode to be lithiated or to a metal tab connected to or from a current collector of the electrode to be lithiated, a Step 4 of placing at least one such electrode roll, electrode pack, or cell assembly into a container, and a Step 5 of filling the container with electrolyte containing Li salts. The order of the steps can be changed. For example, Step 4 and Step 5 can be reversed. The Li metal may be located anywhere in relation to the electrode. In some embodiments, the container inner wall may be made conductive and the lithium metal can be attached on or be a part of the inner wall. In that case, Steps 3 and 4 can be reversed. 
     In the case of lithiation of the Stage 3 cell assembly, one of the options is that the cell packaging case containing the electrode pack may itself serve as the container of Steps 4 and 5, if the case is a metal or other conductive material. The most significant advantage of this approach is that the large dry room for the electrode preparation and the cell manufacture is not needed. Lithium is not introduced during the processes of preparing the electrode or electrode pack, e.g. jellyroll. It is introduced only during the later steps of the cell assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a view of a roll with a metal tab, a piece of lithium, electrolyte, and a container according to various example embodiments. 
         FIG. 2  is a diagram illustrating a roll with a metal tab attached to a piece of lithium. 
         FIG. 3  is a diagram illustrating a Stage 2 electrode pack consisting of a positive electrode, a separator, and a negative electrode. 
         FIG. 4  is another diagram illustrating a Stage 2 electrode pack. 
         FIG. 5  shows an example operational flow of a lithiation method for producing Li pre-doped electrodes. 
     
    
    
     DETAILED DESCRIPTION 
     While certain embodiments are described, these embodiments are presented by way of example only, and are not intended to limit the scope of protection. The apparatuses, methods, and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions, and changes in the form of the example methods and systems described herein may be made without departing from the scope of protection. 
     Various embodiments provide a lithiation method for producing Li pre-doped electrodes. The lithiation method may reduce the manufacture time and cost compared to the conventional Li attachment and pre-dope methods, and may further prevent electrode and separator damage caused during the pre-dope process in the direct contact methods. In some cases, it may reduce, minimize or eliminate the usage of a production scale dry room. The lithiated electrodes may be incorporated into energy storage devices, for example, but not limited to, lithium-ion batteries, lithium-ion capacitors, etc. 
       FIG. 1  is a diagram illustrating a view of a roll  110  with a metal tab  120 , a piece of lithium  130 , electrolyte  150 , and a container  160  according to various example embodiments. Referring to  FIG. 1 , at least one metal tab  120  of the roll  110  may come from or be connected to a current collector  117   b  (see  FIG. 3 ) of the electrode to be lithiated. The roll  110  may consist of a single electrode (i.e. a Stage 1 roll also referred to as an electrode roll) or a jellyroll consisting of at least one negative electrode  116 , one separator  114 , and one positive electrode  112  as shown in  FIGS. 3 and 4  (Stage 2 electrode pack for the example of a cylindrical cell); or an unfinished battery or ultracapacitor with an electrode pack inside and with a case and with or without an unsealed lid (Stage 3 cell assembly for the example of a cylindrical cell). 
     A piece of Li metal  130  with predetermined weight, attached to a conductive material  140  with high conductivity, such as copper or nickel foil, may be attached to the metal tab  120  or directly to the current collector  117   b  (in which case the metal tab  120  may be omitted) of the roll  110 . The roll  110  with optional metal tab  120  and the piece of Li metal  130  with conductive material  140  are placed inside a container  160  filled with electrolytes  150  according to various embodiments. One roll  110  with metal tab  120  may be connected to one or more pieces of Li metal  130  with conductive material(s)  140 . Conversely, one piece of Li metal  130 , optionally with conductive material  140 , may be connected to one or more rolls  110  with metal tab(s)  120 . Alternatively, the piece of Li metal  130  with predetermined weight can be attached to the metal tab  120  or current collector  117   b  of the roll  110  directly, without being attached to a conductive material  140 . The metal tab  120  or current collector  117   b  may be attached either to the piece of Li metal  130  or a conductive material  140  attached to the piece of Li metal  130 . Thus, the element labeled “ 130 ,  140 ” in  FIGS. 2-4  may be either or both of the piece of Li metal  130  and the conductive material  140 . 
     The roll  110  and the piece of Li metal  130  may be connected to each other through the metal tab  120  or directly through the current collector  117   b  of the roll  110  (in which case the metal tab  120  may be omitted as noted above) and the optional conductive material  140  attached to the piece of Li metal  130 . The piece of Li metal  130  and optional conductive material  140  can be located anywhere relative to the roll  110 , within the bounds and flexibility of the metal tab  120  or current collector  117   b . This includes the piece of Li metal  130  and optional conductive material  140  being above, next to, or below the roll  110 . However, for a fast lithiation process, the piece of Li metal  130  and optional conductive material  140  should be placed as close to the roll  110  as possible, preferably on the top or at the bottom of the roll  110  (e.g. on a longitudinal axis L of a cylindrical jellyroll), as shown in  FIGS. 2 and 3 , where the lithiation paths  118  are along the surfaces of the negative electrode active layers  117   a . Therefore, the lithiation paths  118  are along the surfaces of the negative electrode active layers  117   a . As such, Li ions don&#39;t need to pass through the electrode  116 , and a low cost solid metal foil can be used as the current collector  117   b  inside the electrode  116 . 
     Another relative location of the piece of Li metal  130  and optional conductive material  140  to the roll  110  is shown in  FIG. 4 , which illustrates the Stage 2 roll  110  of  FIG. 3 , consisting of the positive electrode  112 , separator  114 , and negative electrode  116 , along with another separator  114 . As in  FIG. 3 , the piece of Li metal  130  with predetermined weight, attached to the conductive material  140  with high conductivity, such as copper or nickel, is attached to the metal tab  120  or directly to the current collector  117   b  (in which case the metal tab  120  may be omitted) of the roll  110 . However, in the example of  FIG. 4 , the piece of Li metal  130  with conductive material  140  is placed not above or below the roll  110  but to the side of the roll  110  (e.g. off the longitudinal axis L of  FIG. 2 ). Therefore, the lithiation paths  118  are perpendicular to the surfaces of the negative electrode active layers  117   a , which may also be referred to as vertical to the roll  110 . As such, Li ions need to pass through the electrode  116 , and a high cost mesh type metal foil or a high cost perforated metal foil must be used as the current collector  117   b  inside the electrode  116 . Alternatively, if a solid metal foil is used inside the electrode  116  as the current collector  117   b , the electrode  116  may be perforated before making the Stage 2 roll  110 . 
       FIG. 5  shows an example operational flow of a lithiation method for producing Li pre-doped electrodes. The operational flow may begin with preparing the roll  110  in a normal air environment (step  510 ), drying the roll  110  in a vacuum oven (step  520 ), and moving the roll  110  into a dry box or small dry room (step  530 ). The roll  110  may consist of a single electrode such as the negative electrode  116  (Stage 1 roll also referred to as an electrode roll). Alternatively, the roll  110  may consist of an electrode pack, e.g. a jellyroll, consisting of at least one negative electrode  116 , at least one separator  114 , and at least one positive electrode  112  (Stage 2 electrode pack for the example of a cylindrical cell). Alternatively, the roll  110  may consist of an unfinished battery or ultracapacitor with an electrode pack, e.g. a jellyroll, inside a case and with or without an unsealed lid (Stage 3 cell assembly for the example of a cylindrical cell). In any case, at least one metal tab  120  may be connected to or from the negative electrode  116  to be lithiated (e.g. connected to or from a current collector  117   b  thereof). 
     The operational flow may continue with preparing the piece of Li metal  130  with predetermined weight separately in the dry box or the small dry room (step  540 ) and, optionally, attaching the piece of Li metal  130  to a conductive material  140  with high conductivity, such as copper or nickel foil (Step  550 ), for example, by mechanical press. The piece of Li metal  130  or, optionally, the conductive material  140  attached thereto, may then be attached to the metal tab  120  or directly to the current collector  117   b  of the roll  110  (step  560 ), that is, the metal tab  120  or current collector  117   b  of the negative electrode  116  to be lithiated (or metal tab  120  or current collector  113   b  of positive electrode  112  to be lithiated), for example, by welding (e.g. laser welding, ultrasonic welding, cold welding). In this way, a single roll  110 , optionally with metal tab  120 , may be connected to one or more pieces of lithium metal  130 . Conversely, a single piece of lithium metal  130  may be attached to one or more rolls  110  with metal tab(s)  120 . 
     The operational flow may further include placing at least one roll  110  and piece of Li metal  130  in the container  160  (step  570 ) and filling the container  160  with electrolyte  150  containing Li salts (step  580 ). The electrolyte  150  may be reusable during a process of lithiating multiple electrodes. The order of the steps is not limited to the example shown in  FIG. 5 . For example, steps  570  and  580  can be reversed, with the container  160  first being filled with the electrolyte  150  and thereafter the roll(s)  110  and piece(s) of Li metal  130  being placed in the container  160 . The container  160  is a container for holding the electrolyte  150 . Lithiation or pre-doping may begin immediately after the roll(s)  110  and Li metal  130  (with optional conductive material) are connected (via metal tab(s)  120  or directly via current collector(s)  117   b ) and placed inside the electrolyte  150  in the container  160 . 
     The Li metal  130  may be located anywhere in relation to the roll  110  as described above. In some embodiments, the inner wall of the container  160  may be made conductive and serve as the conductive material  140  and the piece of Li metal  130  can be installed on or be a part of the inner wall of the container  160 . In that case, steps  560  and  570  can be reversed or occur substantially simultaneously, as the roll  110  is placed inside the container  160  and attached to the inner wall thereof. 
     The container  160  of electrolyte  150  may contain one or more multiple rolls  110  with optional metal tab(s)  120  and may contain one or more multiple pieces of Li metal  130  with optional conductive material(s)  140 . When the lithiation or pre-doping process is finished, the roll(s) with metal tab(s)  120  may be removed from the container  160 . 
     In the case of lithiation of a Stage 3 cell assembly, one of the options is that the cell packaging case, i.e. the can in the example of a cylindrical cell, outside of the electrode pack may itself serve as the container  160 . In this situation, the electrode pack, e.g. jellyroll, inside the can, may be regarded as the roll  110 , and a piece of Li metal  130  (and optional conductive material  140 ) may be connected to the electrode pack and inserted into the can serving as the container  160 . The can may then be filled with the electrolyte  150  to begin the lithiation or pre-doping process. In this case, excess Li metal  130  may be removed from the can serving as the container  160  when the lithiation is complete. The most significant advantage of this approach is that the large dry room for the electrode preparation and the cell manufacture is not needed. Lithium is not introduced during the electrode or electrode pack preparation process. It is introduced only during the late steps of the cell assembly. 
     This lithiation methods disclosed herein may need a longer lithiation time than the direct contact method. However, the disclosed methods may prevent the electrode, separator and cell damage caused by the shorting and strong reactions between the Li metal and the electrode being lithiated. The method disclosed herein also provides lithiation paths along the electrode surfaces such that a low cost solid current collector can be used inside the electrodes. 
     Depending on whether a Stage 1, Stage 2, or Stage 3 roll  110  is to be lithiated, the assembly of the electrodes or electrode packs (e.g. jellyrolls) or complete energy storage devices, such as battery and Ultracapacitor, can be conducted in a normal air environment before the Li metal  130  is introduced and connected to the rolls  110 . Thus, in the case of a Stage 2 or Stage 3 roll  110 , the dry room size requirements may be reduced. For Stage 3 roll lithiation, no dry room is necessary, since the lithium is introduced only at the last steps of cell assembly. After the electrodes, electrode packs (e.g. jellyrolls), or energy storage devices are prepared, the rolls  110  can be dried and moved into a dry box or a small dry room and then connected to the piece of Li metal  130  and immersed in a container  160  filled with electrolytes  150  containing Li salts. This eliminates the need for a full scale dry room, which can be very expensive to build, maintain, and operate. 
     In the above example embodiments of  FIGS. 1-5 , the disclosed methods are described in relation to a cylindrical cell. However, the disclosed subject matter is not intended to be so limited. As noted above, the innovations describe herein apply equally in the case of non-cylindrical cells including, for example, pouch cells, button cells, or prismatic cells. Thus, throughout the description of  FIGS. 1-5 , the roll  110  may more generally refer to an electrode roll, electrode pack, or cell assembly for any type of electrode cell, including, for example, a pouch cell in which the electrode pack comprises stacked rather than would electrodes. Along the same lines, the container  160  is not limited to a can and may be, for example, a pouch of a pouch cell. 
     Although the present disclosure provides certain example embodiments and applications, other embodiments that are apparent to those of ordinary skill in the art, including embodiments which do not provide all of the features and advantages set forth herein, are also within the scope of this disclosure. Accordingly, the scope of the present disclosure is intended to be defined only by reference to the appended claims.