A method for preparing a porous composite current collector using a template method, a porous composite current collector prepared using the same, and applications thereof

Abstract

The application discloses a method for preparing a porous composite current collector by using a template method and a porous composite current collector prepared by using the method and application thereof, and belongs to the technical field of current collectors. The method comprises the following steps: (1) preparation of a precursor solution, (2) pretreatment of a silicon wafer, (3) PI film treatment, (4) preparation of a PS microsphere and ethanol mixed solution, (5) silicon wafer film coating, (6) annealing treatment, (7) re-laminating, (8) attaching copper oxide to the other side of the PI film, and (9) reduction treatment. The method has the beneficial effects that: by using the template method and through special process steps, the prepared porous current collector has high specific area, can effectively reduce local current density, inhibit the formation of lithium dendrites, and thus improve the safety of the current collector; the porous current collector reduces the current density and has higher cycle stability, and thus the stability of the battery is maintained.

Description

Technical Field

[0001] This invention belongs to the field of current collector technology, specifically relating to a method for preparing porous composite current collectors using a template method, and the porous composite current collectors prepared therefrom and their applications. Background Technology

[0002] Current collectors are an indispensable component of lithium-ion batteries. Their main function is to collect the current generated by the battery's active materials to form a larger current output. Currently, the negative electrode current collectors used in cell production mainly use electrolytic copper foil with a thickness of 6-8 μm.

[0003] With the development of new energy lithium battery technology, the processing thickness of traditional electrolytic copper foil is nearing its limit. Furthermore, during the lithium insertion / extraction process of the negative electrode material, the rapid volume change causes deformation of the copper foil, generating internal stress that leads to the separation of the negative electrode material from the copper foil, further accelerating the decline in battery capacity. Traditional electrolytic copper foil is insufficient to meet the demands of high-capacity, high-power, and high-safety lithium-ion batteries.

[0004] Three-dimensional porous current collectors can significantly increase battery capacity due to the ability to fill more active materials with their hollow internal space. The porous structure, to a certain extent, restricts the drastic volume changes of the new alloy anode material during battery charging and discharging. Its surface area is significantly increased compared to two-dimensional copper foil, which can reduce current density and inhibit the formation of lithium dendrites to a certain extent. Furthermore, the porous hollow structure can provide space for lithium dendrite growth, greatly reducing the probability of battery short circuits, failures, and other safety issues, and effectively improving the battery's cycle stability and rate performance.

[0005] In recent years, composite copper foil has attracted much attention. Currently, composite copper foil uses PET or PP as the substrate. A 20-80nm copper layer is first pre-deposited on both sides of a 2-4μm plastic film using magnetron sputtering. Then, the copper layer thickness is increased to 1μm using electroplating technology. Composite copper foil can save about half of the copper, significantly reducing material costs. Moreover, the polymer film in the middle of the composite copper foil can act as a barrier between the positive and negative electrodes, avoiding thermal runaway problems caused by short circuits between the positive and negative electrodes.

[0006] While composite copper foil current collectors have saved costs and improved safety to some extent, they have not solved the safety problems caused by lithium dendrite growth and cannot improve the cycle stability and rate performance of batteries.

[0007] Chinese patent application CN105186006A discloses a composite porous current collector, its preparation method, and its application. The composite porous current collector comprises a porous electronically conductive layer with through-holes and an electronically insulating layer. The porosity of the through-holes in the porous electronically conductive layer is not less than that in the electronically insulating layer. The locations corresponding to the through-holes in the electronically insulating layer are always through-holes, while the non-through-hole locations in the electronically insulating layer can be through-holes, blind holes, or rough surfaces. The electronically insulating layer is adjacent to the separator, which prevents lithium dendrites from piercing the separator and avoids direct contact between the electronically conductive layer and the separator, improving battery safety. The corresponding through-hole structure facilitates lithium-ion transport and reduces battery internal resistance. The pore structure and homogeneous rough surface of the porous electronically conductive layer facilitate sufficient contact between the electrode active material and the current collector, uniformly distributing current and improving current collection efficiency. The airflow punching method is simple, clean, energy-saving, and has multiple other implementation methods, making it convenient for production and application. However, the current collector prepared by this method still has poor safety, requiring further improvement. Summary of the Invention

[0008] The technical problem to be solved by this invention is how to address the poor safety of existing current collectors and the poor performance of lithium-ion batteries made with them.

[0009] The present invention solves the above-mentioned technical problems through the following technical means:

[0010] A method for preparing porous composite current collectors using a template method includes the following steps:

[0011] (1) Preparation of precursor solution: Prepare copper nitrate solution with copper nitrate and deionized water, i.e., precursor solution;

[0012] (2) Silicon wafer pretreatment: The silicon wafer is washed with ethanol and water in sequence and then dried. The silicon wafer is then treated under ultraviolet light and ozone conditions to obtain pretreated silicon wafer.

[0013] (3) PI film treatment: The surface of the PI film is treated with a thin film corona treatment machine, and then the PI film is bonded to a pre-treated silicon wafer.

[0014] Note: PI film specifically refers to polyimide film.

[0015] (4) Preparation of PS microspheres and ethanol mixture: PS microspheres and ethanol are prepared into a mixture in a certain proportion, and then ultrasonically mixed evenly to obtain PS microspheres and ethanol mixture;

[0016] Note: PS microspheres specifically refer to polystyrene microspheres.

[0017] (5) Silicon wafer coating: A water film is laid on another pretreated silicon wafer, and the PS microspheres and ethanol mixture obtained in step (3) are injected to form a single PS film; the PS film is transferred to the precursor liquid obtained in step (1), and after a period of time, the PS film is picked up with the pretreated silicon wafer with PI film obtained in step (3), left to stand and then dried to obtain a coated silicon wafer.

[0018] (6) Annealing: The coated silicon wafer obtained in step (5) is heated and then cooled to room temperature;

[0019] (7) Re-lamination: After annealing, the side of the PI film containing copper oxide is laminated to the silicon wafer;

[0020] (8) Apply copper oxide to the other side of the PI film: Repeat steps (4) to (7) to cover the other side of the PI film with copper oxide;

[0021] (9) Reduction treatment: The coated silicon wafer treated in step (8) is heated again, CO is introduced during the heating process, and then cooled to room temperature to obtain the final product.

[0022] Beneficial effects: This invention uses a template method and special process steps to produce a porous current collector with a high specific area, which can effectively reduce local current density and suppress the formation of lithium dendrites, thereby improving the safety of the current collector. The porous current collector reduces current density and has higher cycle stability, thus maintaining the stability of the battery.

[0023] Preferably, in step (1), the mass ratio of copper nitrate to deionized water is 3g:35-45mL.

[0024] Preferably, the processing time for the silicon wafer in step (2) is 10-20 minutes.

[0025] Preferably, the thickness of the PI film in step (3) is 2.0-3.0 μm.

[0026] Preferably, in step (4), the volume ratio of PS microspheres to ethanol is 1:0.5-1.5.

[0027] Preferably, the diameter of the PS microspheres in step (4) is 0.02-1 μm.

[0028] Preferably, the heating in step (6) is specifically to heat to 250-350°C at an average heating rate of 2°C / min for 1.5-2.5 hours.

[0029] Preferably, the heating temperature in step (9) is 200-300℃ and the heating time is 1-3h.

[0030] The present invention also provides a porous composite current collector prepared by the above method.

[0031] The present invention also provides an application of the porous composite current collector prepared by the above method in lithium batteries.

[0032] The advantages of this invention are:

[0033] This invention utilizes a template method and special process steps to produce a porous current collector with a high specific area, which can effectively reduce local current density and suppress the formation of lithium dendrites, thereby improving the safety of the current collector. The porous current collector reduces current density and has higher cycle stability, thus maintaining the stability of the battery. Attached Figure Description

[0034] Figure 1 This is a side view of the porous composite current collector of the present invention;

[0035] Figure 2 This is a top view of the porous composite current collector of the present invention.

[0036] In the figure, 1-PI film, 2-porous copper foil. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The PI film used in this invention was purchased from Jiangsu Yabao Insulation Materials Co., Ltd.

[0039] Example 1:

[0040] A method for preparing porous composite current collectors using a template method includes the following steps:

[0041] (1) Preparation of precursor solution

[0042] Weigh 3.75g of copper nitrate and place it in a beaker. Add 30mL of deionized water to dissolve it. Transfer the copper nitrate solution in the beaker to a 50mL volumetric flask. Rinse the beaker three times with deionized water. Pour the rinsing solution into the volumetric flask as well. Finally, use a dropper to make up to the mark to obtain the copper nitrate solution, which is the precursor solution.

[0043] (2) Silicon wafer pretreatment

[0044] Two silicon wafers with a thickness of 10 μm and a diameter of 1 inch and two silicon wafers with a thickness of 525 μm and a diameter of 4 inches were sequentially cleaned with ethanol and deionized water for 15 min and then dried. The silicon wafers were then surface-treated under ultraviolet light and ozone conditions for 15 min to obtain pretreated silicon wafers.

[0045] (3) PI film treatment

[0046] First, the 2.5μm polyimide (PI) film is treated with a thin film corona treatment machine. After treatment, it is cut into the shape of a 1-inch silicon wafer. The PI film is then bonded to the 1-inch silicon wafer with an organosilicon adhesive.

[0047] (4) Preparation of PS microspheres and ethanol mixture

[0048] Take 0.4 ml of PS microspheres with a diameter of 20 nm and mix them with ethanol at a volume ratio of 1:1. After mixing, sonicate for 15 min to obtain a mixture of PS microspheres and ethanol.

[0049] (5) Silicon wafer coating

[0050] A water film is laid on a 4-inch diameter silicon wafer. The PS microspheres and ethanol mixture obtained in step (4) are injected to form a PS monolayer. The PS monolayer is then transferred to the copper nitrate solution (i.e., the precursor solution) obtained in step (1). After 30 minutes, the PS film is retrieved using a 1-inch silicon wafer with a PI film attached. After standing and drying, a coated silicon wafer is obtained.

[0051] (6) Annealing treatment

[0052] The coated silicon wafer obtained in step (5) is placed in a muffle furnace and heated to 300°C at an average heating rate of 2°C / min. It is then kept at this temperature for 2 hours and allowed to cool naturally to room temperature to attach porous copper oxide to one side of the PI film.

[0053] (7) Re-lamination: After annealing, the side of the PI film containing copper oxide is laminated to the silicon wafer;

[0054] (8) Copper oxide is attached to the other side of the PI film.

[0055] Repeat steps (4) to (7) to cover the other side of the PI film with copper oxide;

[0056] (9) Reduction process

[0057] The coated silicon wafer processed in step (8) is placed in a tubular muffle furnace quartz tube, CO is introduced into the quartz tube, the temperature is maintained at 250°C for 2 hours, and then it is naturally cooled to room temperature to obtain the final product.

[0058] The application of the porous composite current collector prepared in this embodiment in a lithium-ion battery involves stamping the prepared porous current collector into a circular electrode with a diameter of 12 mm on a stamping machine. Commercially available graphite and silicon-carbon alloy are used as the negative electrode materials, lithium metal sheets are used as the symmetrical electrodes, and porous composite copper foil (i.e., the circular electrode) is used as the current collector. The electrolyte is 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in the solvent EC+DMC+EMC. 20 μL of electrolyte is added to both the negative electrode and the separator, for a total electrolyte volume of 40 μL. The separator is made of polypropylene, and the gaskets and springs are made of 304 stainless steel. The battery is prepared in an argon-filled glove box, sealed, and allowed to stand for 24 hours before being removed.

[0059] Example 2:

[0060] The difference between this embodiment and embodiment 1 is that the diameter of the PS microspheres in step (4) is 500 nm, while the other steps are the same as in embodiment 1.

[0061] Example 3:

[0062] The difference between this embodiment and embodiment 1 is that the diameter of the PS microspheres in step (4) is 1 μm, while the other steps are the same as in embodiment 1.

[0063] Example 4:

[0064] A method for preparing porous composite current collectors using a template method includes the following steps:

[0065] (1) Preparation of precursor solution

[0066] Weigh 3.75g of copper nitrate and place it in a beaker. Add 30mL of deionized water to dissolve it. Transfer the copper nitrate solution in the beaker to a 43.75mL volumetric flask. Rinse the beaker three times with deionized water. Pour the rinsing solution into the volumetric flask as well. Finally, use a dropper to make up to the mark to obtain the copper nitrate solution, i.e., the precursor solution.

[0067] (2) Silicon wafer pretreatment

[0068] Two silicon wafers with a thickness of 10 μm and a diameter of 1 inch and two silicon wafers with a thickness of 525 μm and a diameter of 4 inches were sequentially cleaned with ethanol and deionized water for 15 min and then dried. The silicon wafers were then surface-treated under ultraviolet light and ozone for 10 min to obtain pretreated silicon wafers.

[0069] (3) PI film treatment

[0070] First, the 2.0μm polyimide (PI) film is treated with a thin film corona treatment machine. After treatment, it is cut into the shape of a 1-inch silicon wafer. The PI film is then bonded to the 1-inch silicon wafer with an organosilicon adhesive.

[0071] (4) Preparation of PS microspheres and ethanol mixture

[0072] Take 0.4 ml of PS microspheres with a diameter of 20 nm and mix them with ethanol at a volume ratio of 1:0.5. After mixing, sonicate for 15 min to obtain a mixture of PS microspheres and ethanol.

[0073] (5) Silicon wafer coating

[0074] A water film is laid on a 4-inch diameter silicon wafer. The PS microspheres and ethanol mixture obtained in step (4) are injected to form a PS monolayer. The PS monolayer is then transferred to the copper nitrate solution (i.e., the precursor solution) obtained in step (1). After 30 minutes, the PS film is retrieved using a 1-inch silicon wafer with a PI film attached. After standing and drying, a coated silicon wafer is obtained.

[0075] (6) Annealing treatment

[0076] The coated silicon wafer obtained in step (5) is placed in a muffle furnace and heated to 250°C at an average heating rate of 2°C / min. It is then kept at this temperature for 2.5 hours and allowed to cool naturally to room temperature to attach porous copper oxide to one side of the PI film.

[0077] (9) Re-lamination: After annealing, the side of the PI film containing copper oxide is laminated to the silicon wafer;

[0078] (10) Copper oxide is attached to the other side of the PI film.

[0079] Repeat steps (4) to (7) to cover the other side of the PI film with copper oxide;

[0080] (9) Reduction process

[0081] The coated silicon wafer processed in step (8) is placed in a tubular muffle furnace quartz tube, CO is introduced into the quartz tube, the temperature is maintained at 200℃ for 3 hours, and then it is naturally cooled to room temperature to obtain the final product.

[0082] The application of the porous composite current collector prepared in this embodiment in a lithium-ion battery involves stamping the prepared porous current collector into a circular electrode with a diameter of 12 mm on a stamping machine. Commercially available graphite and silicon-carbon alloy are used as the negative electrode materials, lithium metal sheets are used as the symmetrical electrodes, and porous composite copper foil (i.e., the circular electrode) is used as the current collector. The electrolyte is 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in the solvent EC+DMC+EMC. 20 μL of electrolyte is added to both the negative electrode and the separator, for a total electrolyte volume of 40 μL. The separator is made of polypropylene, and the gaskets and springs are made of 304 stainless steel. The battery is prepared in an argon-filled glove box, sealed, and allowed to stand for 24 hours before being removed.

[0083] Example 5:

[0084] A method for preparing porous composite current collectors using a template method includes the following steps:

[0085] (1) Preparation of precursor solution

[0086] Weigh 3.75g of copper nitrate and place it in a beaker. Add 30mL of deionized water to dissolve it. Transfer the copper nitrate solution in the beaker to a 56.25mL volumetric flask. Rinse the beaker three times with deionized water. Pour the rinsing solution into the volumetric flask as well. Finally, use a dropper to make up to the mark to obtain the copper nitrate solution, which is the precursor solution.

[0087] (2) Silicon wafer pretreatment

[0088] Two silicon wafers with a thickness of 10 μm and a diameter of 1 inch and two silicon wafers with a thickness of 525 μm and a diameter of 4 inches were cleaned with ethanol and deionized water for 15 min in sequence and then dried. The silicon wafers were then surface-treated under ultraviolet light and ozone for 20 min to obtain pretreated silicon wafers.

[0089] (3) PI film treatment

[0090] First, the 3.0μm polyimide (PI) film is treated with a thin film corona treatment machine. After treatment, it is cut into the shape of a 1-inch silicon wafer. The PI film is then bonded to the 1-inch silicon wafer with an organosilicon adhesive.

[0091] (4) Preparation of PS microspheres and ethanol mixture

[0092] Take 0.4 ml of PS microspheres with a diameter of 20 nm and mix them with ethanol at a volume ratio of 1:1.5. After mixing, sonicate for 15 min to obtain a mixture of PS microspheres and ethanol.

[0093] (5) Silicon wafer coating

[0094] A water film is laid on a 4-inch diameter silicon wafer. The PS microspheres and ethanol mixture obtained in step (4) are injected to form a PS monolayer. The PS monolayer is then transferred to the copper nitrate solution (i.e., the precursor solution) obtained in step (1). After 30 minutes, the PS film is retrieved using a 1-inch silicon wafer with a PI film attached. After standing and drying, a coated silicon wafer is obtained.

[0095] (6) Annealing treatment

[0096] The coated silicon wafer obtained in step (5) is placed in a muffle furnace and heated to 350°C at an average heating rate of 2°C / min. It is then kept at this temperature for 1.5 hours and allowed to cool naturally to room temperature to attach porous copper oxide to one side of the PI film.

[0097] (11) Re-lamination: After annealing, the side of the PI film containing copper oxide is laminated to the silicon wafer;

[0098] (12) Copper oxide is attached to the other side of the PI film.

[0099] Repeat steps (4) to (7) to cover the other side of the PI film with copper oxide;

[0100] (9) Reduction process

[0101] The coated silicon wafer processed in step (8) is placed in a tubular muffle furnace quartz tube, CO is introduced into the quartz tube, the temperature is maintained at 300℃ for 1 hour, and then it is naturally cooled to room temperature to obtain the final product.

[0102] The application of the porous composite current collector prepared in this embodiment in a lithium-ion battery involves stamping the prepared porous current collector into a circular electrode with a diameter of 12 mm on a stamping machine. Commercially available graphite and silicon-carbon alloy are used as the negative electrode materials, lithium metal sheets are used as the symmetrical electrodes, and porous composite copper foil (i.e., the circular electrode) is used as the current collector. The electrolyte is 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in the solvent EC+DMC+EMC. 20 μL of electrolyte is added to both the negative electrode and the separator, for a total electrolyte volume of 40 μL. The separator is made of polypropylene, and the gaskets and springs are made of 304 stainless steel. The battery is prepared in an argon-filled glove box, sealed, and allowed to stand for 24 hours before being removed.

[0103] Comparative Example 1:

[0104] Commercially available graphite and silicon-carbon alloy were used as the negative electrode materials, lithium metal sheets as the symmetrical electrodes, and ordinary composite copper foil (a 2.5 μm PI film with 1 μm copper plating on both sides) as the current collector. The electrolyte was 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in the solvent EC+DMC+EMC. 20 μL of electrolyte was added to both the negative electrode and the separator, for a total electrolyte volume of 40 μL. The separator was made of polypropylene, and the gaskets and springs were made of 304 stainless steel. The battery was prepared in an argon-filled glove box, sealed, and allowed to stand for 24 hours before being removed.

[0105] Battery performance test:

[0106] The batteries prepared in Examples 1-3 and Comparative Example 1 were subjected to rate performance and cycle life performance tests. The testing equipment was the Xinwei CT-4008T-5V10mA battery monitoring device.

[0107] Rate performance test conditions: Tests were conducted within a voltage range of 0–3V, at different currents (1C and 5C), and at a room temperature of 25°C. Cycle life test conditions: Tests were conducted within a voltage range of 0–3V, at a current of 1C, and at a room temperature of 25°C. The test results are shown in the table below:

[0108] Table 1: Battery performance test results of Examples 1-3 and Comparative Example 1

[0109] 5C / 1C Capacity Retention Rate 1C cycle 500 cycles capacity retention Example 1 97.30％ 96.72％ Example 2 98.12％ 97.10％ Example 3 99.43％ 98.61％ Comparative Example 1 91.38％ 92.50％

[0110] Figure 1 This is a side view of the porous composite current collector of the present invention; Figure 2 This is a top view of the porous composite current collector of the present invention.

[0111] As shown in Table 1, the porous composite current collector improves the stability and chemical stability of the battery under high current density. This is because the porous current collector has a high specific area, which can effectively reduce the local current density and suppress the formation of lithium dendrites. Simultaneously, the larger pore size provides more space for lithium dendrites to expand. Furthermore, the porous current collector exhibits higher cycle stability. This is because the porous current collector reduces the current density, thus suppressing side reactions between metallic lithium and the electrolyte, thereby maintaining battery stability.

[0112] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing porous composite current collectors using a template method, characterized in that, Includes the following steps: (1) Preparation of precursor solution: Prepare copper nitrate solution with copper nitrate and deionized water, i.e., precursor solution; (2) Silicon wafer pretreatment: The silicon wafer is washed with ethanol and water in sequence and then dried. It is then treated under ultraviolet light and ozone conditions to obtain pretreated silicon wafers. (3) PI film treatment: The surface of the PI film is treated with a thin film corona treatment machine, and then the PI film is bonded to a pre-treated silicon wafer. (4) Preparation of PS microspheres and ethanol mixture: PS microspheres and ethanol are prepared into a mixture in a certain proportion, and then ultrasonically mixed evenly to obtain PS microspheres and ethanol mixture; (5) Silicon wafer coating: A water film is laid on another pretreated silicon wafer, and the PS microspheres and ethanol mixture obtained in step (4) are injected to form a single layer of PS film; The PS film is transferred onto the precursor liquid obtained in step (1). After a period of time, the PS film is picked up with the pretreated silicon wafer with PI film obtained in step (3), left to stand, and then dried to obtain the coated silicon wafer. (6) Annealing treatment: The coated silicon wafer obtained in step (5) is heated and then cooled to room temperature; the heating is specifically heated to 250-350℃ at an average heating rate of 2℃ / min. (7) Re-lamination: After annealing, the side of the PI film containing copper oxide is laminated to the silicon wafer; (8) Apply copper oxide to the other side of the PI film: Repeat steps (4) to (7) to cover the other side of the PI film with copper oxide; (9) Reduction treatment: The coated silicon wafer treated in step (8) is heated again, CO is introduced during the heating process, and then cooled to room temperature to obtain the final product.

2. The method for preparing porous composite current collectors using the template method according to claim 1, characterized in that, In step (1), the mass ratio of copper nitrate to deionized water is 3g:35-45mL.

3. The method for preparing porous composite current collectors using the template method according to claim 1, characterized in that, The processing time for the silicon wafer in step (2) is 10-20 minutes.

4. The method for preparing porous composite current collectors using the template method according to claim 3, characterized in that, The thickness of the PI film in step (3) is 2.0-3.0 μm.

5. The method for preparing porous composite current collectors using the template method according to claim 4, characterized in that, In step (4), the volume ratio of PS microspheres to ethanol is 1:0.5-1.

5.

6. The method for preparing porous composite current collectors using the template method according to claim 1, characterized in that, In step (4), the diameter of the PS microspheres is 0.02-1 μm.

7. The method for preparing porous composite current collectors using the template method according to claim 1, characterized in that, The heating time in step (6) is 1.5-2.5 hours.

8. The method for preparing porous composite current collectors using the template method according to claim 1, characterized in that, The heating temperature in step (9) is 200-300℃, and the heating time is 1-3h.

9. A porous composite current collector prepared by the method according to any one of claims 1-8.

10. The application of the porous composite current collector prepared by the method according to any one of claims 1-8 in lithium batteries.

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