Method for testing high-temperature storage performance of lithium ion battery

Abstract

The invention discloses a method for testing the high-temperature storage performance of a lithium ion battery. The method comprises the following steps: (1) preparing a button type total battery; (2) activating the button type total battery and measuring the initial impedance R0, the thickness L0 of a negative plate and the capacity C0 of the battery; (3) storing a plurality of button type total batteries at high temperature for 6 days, taking out the button type total batteries on the seventh day, and measuring the initial voltage Vi, the discharge capacity Ci, the discharge capacity Cv, the impedance Ri and the thickness Li of a negative plate; and (4) calculating the impedance change rate, the capacity retention rate, the capacity recovery rate and the negative plate expansion rate of the button type total battery. According to the method, the long-term stability and reliability of the battery in a high-temperature environment are predicted according to the performance change condition of the lithium ion battery, important reference is provided for design and application of the battery, and compared with an existing scheme for testing by adopting a soft package type battery or a 18650 battery, the method has the advantages that the test efficiency is improved; the button type total battery provided by the invention has the advantages of lower cost, simpler assembly mode and higher safety performance.

Description

Technical Field

[0001] This invention relates to the field of battery performance testing technology, and in particular to a method for testing the high-temperature storage performance of lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries, as key new energy material devices, possess characteristics such as high operating voltage, high energy density, light weight, and environmental friendliness. The capacity of a lithium-ion battery is primarily determined by the electrode material. Silicon has a theoretical specific capacity of 4200 mAh / g, approximately ten times that of graphite anode materials. Furthermore, silicon has a lower discharge plateau than graphite, effectively meeting the ever-increasing demand for energy density. Meanwhile, silicon (Si) is abundant, existing in the Earth's crust as silicon dioxide or silicates. It is the second most abundant element in the Earth's crust after oxygen, and its mining and processing costs are low, making it a promising anode material with extremely high cost-effectiveness, similar to graphite.

[0003] Most research on silicon-based anodes focuses on standard laboratory conditions, while performance under high temperatures and other non-standard conditions, as well as crucial factors such as calendar aging and storage conditions encountered in actual battery applications, are often overlooked. High-temperature storage can lead to battery capacity degradation, increased internal resistance, and even safety incidents. This poses a significant obstacle to the transition of silicon anode materials from laboratory research to mature products. Therefore, conducting relevant high-temperature tests on silicon anode materials for lithium-ion batteries is essential.

[0004] Patent document CN118376933A discloses a method for evaluating the high-temperature performance of lithium-ion batteries. This method simulates high-temperature operating conditions by continuously storing pouch lithium-ion batteries at a set temperature and voltage. First, the battery capacity and thickness are tested at room temperature. After storing at the set temperature for a certain period, the battery is removed and its immediate hot thickness is measured. Then, after being removed and allowed to stand at room temperature, its cold thickness, capacity retention rate, and capacity recovery rate are measured. By measuring the battery expansion rate, capacity retention rate, and capacity recovery rate, the high-temperature storage test cycle of lithium-ion batteries is effectively shortened, avoiding equipment energy consumption and resource waste. It achieves the same evaluation effect as continuous storage and has certain practical significance.

[0005] Patent document CN104865536A discloses a testing and diagnostic method for the causes of performance degradation in lithium-ion batteries. The method includes measuring the ohmic impedance and relaxation impedance of the battery under test and a reference battery during charging and discharging at a certain state of charge; measuring the temperature entropy coefficients of the battery under test and the reference battery at a certain state of charge; calculating the absolute values ​​of the growth rates of the ohmic impedance and relaxation impedance of the battery under test relative to the reference battery during charging and discharging; and determining the causes of battery performance degradation by comparing the absolute values ​​of the growth rates of the ohmic impedance and relaxation impedance of the battery under test relative to the reference battery.

[0006] However, the aforementioned high-temperature storage performance testing methods all utilize pouch cells or 18650 cells to test the battery materials' high-temperature storage performance. These methods involve significant material and energy consumption and complex operations during battery fabrication and testing. Therefore, it is necessary to develop a high-temperature storage performance testing method for coin cell full cells, achieving simple, low-cost, and highly safe battery material performance testing. Summary of the Invention

[0007] This invention provides a short-process method for preparing vanadium electrolyte that can effectively shorten the process and reduce costs, thereby solving the technical problems mentioned in the background art.

[0008] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A method for testing the high-temperature storage performance of lithium-ion batteries includes the following steps: (1) A coin cell is prepared, wherein the coin cell comprises a positive electrode shell, a positive electrode sheet, a separator, a negative electrode sheet and a negative electrode shell arranged sequentially; the positive electrode sheet comprises an aluminum foil and a positive electrode material layer coated on the aluminum foil, the positive electrode material layer comprising a lithium-containing ternary positive electrode material; the negative electrode sheet comprises a copper foil and a negative electrode material layer coated on the copper foil, the negative electrode material layer comprising a silicon-containing negative electrode material; (2) Activate the coin cell and measure the initial impedance R0, negative electrode thickness L0 and battery capacity C0; (3) Several of the aforementioned button cells were stored at high temperature for 6 days, and on the 7th day, they were taken out and left to stand at room temperature before their initial voltage V was measured. i Discharge capacity C i Discharge capacity C after full charge v and impedance R i Then, remove the button cell and discharge it to 2.5 V, then measure the thickness L of the negative electrode. i ; (4) Calculate the impedance change rate RR, capacity retention rate CR, capacity recovery rate CC and negative electrode expansion rate LR of the button cell, and judge the high temperature storage performance of the lithium-ion battery based on RR, CR, CC and LR.

[0009] The design concept of the above technical solution is that this invention assembles positive and negative electrode materials into a coin cell for subsequent high-temperature storage performance testing. This simulates the high-temperature environment that batteries may encounter in practical applications, providing a more realistic performance evaluation. By measuring capacity retention, capacity recovery, electrode thickness changes, and impedance changes, the performance changes of the lithium-ion battery after high-temperature storage are determined, predicting the long-term stability and reliability of the battery under high-temperature conditions. This provides important reference for battery design and application. Compared to existing solutions using pouch cells or 18650 cells for testing, the coin cell of this invention has lower cost, simpler assembly, and higher safety performance. In constructing the coin cell, this invention replaces the lithium sheet in the coin cell with a multi-element positive electrode material. On the one hand, this allows the lower potential negative electrode material to serve as the negative electrode part of the battery, and the positive electrode material to serve as the positive electrode part, forming a complete battery system. On the other hand, it reduces the side reaction effects caused by abundant lithium in conventional coin half-cells, thus better simulating the internal environment of the complete battery. Meanwhile, in conventional half-cells, the negative electrode is usually larger than the lithium electrode to better accept lithium transferred from the lithium electrode portion. However, in the coin cell of the present invention, the positive and negative electrodes are of the same size, thereby avoiding the phenomenon of lithium plating in the non-overlapping portion caused by selecting positive and negative electrodes of different sizes.

[0010] As a further preferred embodiment of the above technical solution, the coating thickness of the negative electrode material layer and the capacity ratio of the negative electrode material layer to the positive electrode material layer in step (1) are determined based on the material composition and proportion of the silicon-containing negative electrode material. In the design of coin cells, the silicon content of the silicon-containing negative electrode material can be increased to the range of 10-30%. With the increase in the amount added, the designed capacity ratio of the negative electrode material to the positive electrode material also needs to be further improved to prevent the influence of lithium plating. Furthermore, the lower the silicon content, the lower the required coating thickness, thereby reducing the inherent disadvantages of the silicon material itself.

[0011] As a further preferred embodiment of the above technical solution, the designed capacity ratio of the positive electrode material layer to the negative electrode material layer is 1.05 to 1.1. Typically, the designed N / P ratio for pouch cells and 18650 cells is between 1.03 and 1.08. However, due to differences in coating uniformity during the fabrication of coin cells, the actual N / P ratio will fluctuate more significantly compared to pouch cells and 18650 cells. Therefore, the range of N / P should be appropriately increased when designing it, while remaining within the reasonable range of this invention.

[0012] As a further preferred embodiment of the above technical solution, the positive electrode material layer and the negative electrode material layer further include a conductive agent and a binder. Since the silicon-containing negative electrode material has a high capacity, the ratio of silicon-containing negative electrode material: conductive agent: binder can be adjusted between 7:1.5:1.5 and 9:0.5:0.5, depending on the amount of silicon added and the capacity design. The positive electrode material has a relatively low capacity, and its active material: conductive agent: binder ratio is controlled between 8:1:1 and 9:0.5:0.5.

[0013] As a further preferred embodiment of the above technical solution, the preparation method of the positive electrode material layer or negative electrode material layer is as follows: a lithium-containing multi-element positive electrode material or a silicon-containing negative electrode material is mixed with a conductive agent and a binder in a certain mass ratio to obtain a uniform slurry. The slurry is then uniformly coated onto a current collector aluminum foil or copper foil using an automatic coating machine to obtain a positive electrode coating or a negative electrode coating. The obtained positive electrode coating or negative electrode coating is dried and compacted to obtain the positive electrode material layer or negative electrode material layer.

[0014] As a further preferred embodiment of the above technical solution, the mixing method of the lithium-containing multi-element cathode material or silicon-containing anode material with the conductive agent and binder is as follows: rotating forward at 700 rpm for 5 minutes, and then rotating in reverse at 2000 rpm for 20 minutes.

[0015] As a further preferred embodiment of the above technical solution, the membrane is a double-layer membrane. The double-layer membrane further reduces the risk of the membrane being punctured by lithium dendrites while also optimizing the ion transport pathway.

[0016] As a further preferred embodiment of the above technical solution, nickel foam is disposed between the positive electrode shell and the positive electrode sheet. This invention uses nickel foam to replace gaskets and springs to compensate for the extra space occupied by the double-layer separator compared to the single-layer separator, thereby ensuring sufficient space in the coin cell.

[0017] As a further preferred embodiment of the above technical solution, the impedance change rate RR, capacity retention rate CR, capacity recovery rate CC, and negative electrode expansion rate LR are calculated by the following formula: CR=C i / C0;CC=C v / C0;LR=(L i -L0) / L0;RR=(R i -R0) / R0.

[0018] As a further preferred embodiment of the above technical solution, a test cycle is defined as 7 days in step (3). At the end of the test cycle, n sets of coin cells are charged to the storage voltage, and the next test cycle is repeated until 6 test cycles are completed. Compared with the traditional soft-pack test method, which stores the battery until the cold-state thickness expansion rate reaches 10% before conducting the capacity recovery test, the high-temperature storage test method of the present invention can perform capacity recovery tests and impedance change tests for each cycle. Furthermore, without changing the set storage temperature conditions, the continuous storage process is divided into several storage cycles, and the battery is recharged to the storage voltage at the end of each storage cycle. This ensures that the positive electrode remains in a high-voltage oxidized state for a long time during the storage cycle, and the negative electrode remains in a low-voltage reduced state for a long time. This accelerates the side reactions at high temperatures, accelerates storage test failure, shortens the storage test cycle, avoids the energy consumption and resource waste caused by long-term testing, and achieves the same evaluation effect as continuous storage under the set temperature conditions.

[0019] As a further optimization of the above technical solution, groups of coin cells that completed six test cycles with a voltage decay rate of ±5 mV / d and a capacity decay of ±2.00% were selected. The silicon-containing anode materials corresponding to these groups were then assembled into pouch cells or 18650 cells for further testing. Testing the electrode materials of coin cells is a quick and low-cost method for verifying material performance. Further testing of the relevant material properties using pouch cells or 18650 cells is more accurate and better suited to practical application requirements. The national standard (GB / T43092-2023) requires that the voltage decay rate of coin cells during high-temperature storage be within ±1 mV / d and the capacity decay rate within ±3.00%. However, since the lithium sheet was replaced with the cathode material in this test, side reactions will be reduced under high-temperature conditions. Therefore, further testing with pouch cells or 18650 cells is only necessary if the voltage decay rate is within ±5 mV / d and the capacity decay is within ±2.00% during high-temperature storage.

[0020] The present invention has the following beneficial effects: This invention utilizes positive electrode sheets instead of lithium sheets to construct coin cells for high-temperature storage performance testing. This simulates the high-temperature environments batteries may encounter in real-world applications, providing a more realistic performance evaluation. Compared to pouch cells and 18650 batteries, the assembly and testing process of coin cells is relatively simple, allowing for faster acquisition of high-temperature storage performance data. It reduces experimental costs and resource consumption while ensuring safety. Data obtained through high-temperature storage testing can be used to predict the long-term stability and reliability of batteries under high-temperature conditions, providing important references for battery design and application. During high-temperature storage testing, by comparing voltage changes before and after each storage cycle, the voltage decay rate can be calculated, effectively assessing the battery's voltage stability under high-temperature conditions. By comparing the capacity retention rate, capacity recovery rate, and impedance changes in each cycle, the battery's stability under high-temperature conditions can be directly obtained. By comparing the thickness changes and surface elemental composition of the disassembled negative electrode sheet, the causes and influencing factors of high-temperature degradation can be effectively identified. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the button cell of the present invention. Detailed Implementation

[0022] The following detailed description is based on embodiments of the present invention, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0023] Example 1: The method for testing the high-temperature storage performance of lithium-ion batteries in this embodiment includes the following steps: (1) Preparation of button cell: The structure of button cell is as follows Figure 1 As shown ( Figure 1 In the diagram, A represents the positive electrode shell, B represents nickel foam, C represents the positive electrode sheet, D represents the double-layer separator, E represents the negative electrode sheet, and F represents the negative electrode shell. First, NMC532, Super P, and PVDF are dispersed at a mass ratio of 8:1:1 using a degassing mixer at 700 rpm for 5 minutes, followed by stirring at 2000 rpm for 20 minutes to obtain a uniform positive electrode slurry. This slurry is then coated onto aluminum foil using an automatic coating machine to obtain a positive electrode coating. Next, the obtained positive electrode coating is placed in a vacuum drying oven at 80 ℃ for 12 hours to completely remove the solvent and any possible moisture. The electrode sheet is then compacted using a roller press and formed into a 16 mm diameter positive electrode sheet using a stamping machine. Finally, it is dried in a vacuum oven at 80 ℃ for 12 hours.

[0024] Then, according to the designed N / P ratio (1.05) of the battery, graphite and fumed silicon carbide were added to the mortar in a 9:1 ratio and mixed. Then, super P and PAA were added in a ratio of active material: conductive agent: binder = 8:1:1 and mixed. The mixture was stirred in a degassing mixer at 700 rpm for 5 min forward and then at 2000 rpm for 20 min reverse to obtain a uniform slurry. The slurry was then uniformly coated onto copper foil using an automatic coating machine to obtain a negative electrode coating. The negative electrode coating was then transferred to a 60℃ forced-air drying oven and dried for 4 h. After rolling, it was formed into a negative electrode sheet with a diameter of 16 mm using a stamping machine and then dried in an 80℃ vacuum oven for 12 h.

[0025] Finally, the prepared positive and negative electrode sheets are placed in a glove box with an oxygen content of <0.01 ppm. They are then assembled in the following order: positive electrode shell, positive electrode sheet, electrolyte, double-layer separator, electrolyte, negative electrode sheet, nickel foam, and negative electrode shell. The assembled battery is then transferred to a sealing machine for sealing to obtain a CR2430 coin cell. The battery is then left to stand at room temperature for 24 hours.

[0026] (2) The CR2430 coin cell was activated and its impedance data R0 was measured. One cell was removed and placed in a glove box with a water oxygen value of <0.01 ppm for disassembly. The negative electrode was removed and cleaned with DMC electrolyte. After cleaning, it was placed in an 80 ℃ vacuum oven for drying. The electrode thickness L0 was measured. The remaining coin cells were charged to 4.5 V and the battery capacity C0 was recorded.

[0027] (3) Place the CR2430 battery in an environment of 60 ℃ for 6 days. On the 7th day, remove the battery and let it stand at room temperature for 1 day, then place it back in an environment of 60 ℃ for 6 days. On the 14th day, remove the test battery and measure its initial voltage V. i Discharge capacity C i Discharge capacity C after full charge v and impedance R i One electrode was removed and, after being discharged to 2.5 V, placed in a glove box with an oxygen content of <0.01 ppm for disassembly. The negative electrode was removed, and its surface was cleaned with DMC electrolyte. After cleaning, it was placed in an 80 ℃ vacuum oven for drying. The electrode was then removed and its thickness L was measured. i .

[0028] (4) Calculate the impedance change rate RR, capacity retention rate CR, capacity recovery rate CC, and negative electrode expansion rate LR according to the following formulas. The calculation results are shown in Table 1: CR=C i / C0;CC=C v / C0;LR=(L i-L0) / L0;RR=(R i -R0) / R0.

[0029] Comparative Example 1: (1) A soft-pack battery was designed and prepared according to the types of positive and negative electrode materials and N / P=1.05 in Example 1. The capacity of the battery at room temperature was tested, and the battery was charged to the pre-storage voltage of 4.5 V with a current of 0.1 C. The initial capacity and battery thickness before storage were recorded.

[0030] (2) Store the batteries in an environment of 60 °C for 6 days. On the 7th day, take out 2 batteries from each group and let them stand at room temperature for 1 hour before measuring their initial voltage V. i Discharge capacity C i Discharge capacity C after full charge v and impedance R i .

[0031] (3) The impedance change rate RR, capacity retention rate CR, capacity recovery rate CC and negative electrode expansion rate LR were calculated using the same method as in Example 1. The calculation results are shown in Table 1.

[0032] Example 2: The method for testing the high-temperature storage performance of lithium-ion batteries in this embodiment includes the following steps: (1) Preparation of button cell: The structure of button cell is as follows Figure 1 As shown, NMC622, super P, and PVDF were first dispersed at a mass ratio of 9:0.5:0.5 using a degassing mixer at 700 rpm for 5 minutes, followed by stirring at 2000 rpm for 20 minutes to obtain a uniform positive electrode slurry. This slurry was then coated onto aluminum foil using an automatic coating machine to obtain a positive electrode coating. The resulting positive electrode coating was then placed in a vacuum drying oven at 80 ℃ for 12 hours to completely remove the solvent and any remaining moisture. The electrode was then compacted using a roller press and formed into a positive electrode sheet with a diameter of 16 mm using a stamping machine. Finally, it was placed in a vacuum oven at 80 ℃ for 12 hours to dry.

[0033] Then, according to the designed N / P ratio (1.1) of the battery, graphite and lithium titanate-coated silicon-carbon material were added to the mortar in a 9:1 ratio and mixed. Then, super P and PAA were added in a ratio of active material: conductive agent: binder = 8:1:1 and mixed. The mixture was stirred in a degassing mixer at 700 rpm for 5 min forward and then at 2000 rpm for 20 min reverse to obtain a uniform slurry. The slurry was then uniformly coated onto copper foil using an automatic coating machine to obtain a negative electrode coating. The negative electrode coating was transferred to a 60 ℃ forced-air drying oven and dried for 4 h. After rolling, it was formed into a negative electrode sheet with a diameter of 16 mm using a stamping machine and then dried in an 80 ℃ vacuum oven for 12 h.

[0034] Finally, the prepared positive and negative electrode sheets are placed in a glove box with an oxygen content of <0.01 ppm. They are then assembled in the following order: positive electrode shell, positive electrode sheet, electrolyte, double-layer separator, electrolyte, negative electrode sheet, nickel foam, and negative electrode shell. The assembled battery is then transferred to a sealing machine for sealing to obtain a CR2430 coin cell. The battery is then left to stand at room temperature for 24 hours.

[0035] (2) The CR2430 coin cell was activated and its impedance data R0 was measured. One cell was removed and placed in a glove box with a water oxygen value of <0.01 ppm for disassembly. The negative electrode was removed and cleaned with DMC electrolyte. After cleaning, it was placed in an 80 ℃ vacuum oven for drying. The electrode thickness L0 was measured. The remaining coin cells were charged to 4.5 V and the battery capacity C0 was recorded.

[0036] (3) Place the CR2430 battery in an environment of 60 °C for 6 days. On the 7th day, take out two batteries and let them stand at room temperature for 1 hour before measuring their initial voltage V. i Discharge capacity C i Discharge capacity C after full charge v and impedance R i One electrode was removed and, after being discharged to 2.5 V, placed in a glove box with an oxygen content of <0.01 ppm for disassembly. The negative electrode was removed, and its surface was cleaned with DMC electrolyte. After cleaning, it was placed in an 80 ℃ vacuum oven for drying. The electrode was then removed and its thickness L was measured. i .

[0037] (4) Calculate the impedance change rate RR, capacity retention rate CR, capacity recovery rate CC, and negative electrode expansion rate LR according to the following formulas. The calculation results are shown in Table 1: CR=C i / C0;CC=C v / C0;LR=(L i -L0) / L0;RR=(R i-R0) / R0.

[0038] Comparative Example 2: (1) A soft-pack battery was designed and prepared according to the types of positive and negative electrode materials and N / P=1.1 in Example 2. The capacity of the battery at room temperature was tested, and the battery was charged to the pre-storage voltage of 4.5 V with a current of 0.1 C. The thickness of the battery before storage was recorded.

[0039] (2) Store the batteries in an environment of 60 °C for 6 days. On the 7th day, take out 2 batteries from each group and let them stand at room temperature for 1 hour before measuring their initial voltage V. i Discharge capacity C i Discharge capacity C after full charge v and impedance R i .

[0040] (3) The impedance change rate RR, capacity retention rate CR, capacity recovery rate CC and negative electrode expansion rate LR were calculated using the same method as in Example 1. The calculation results are shown in Table 1.

[0041] Table 1. Test results of each embodiment and comparative example

[0042] A comparison of the data in the examples and comparative examples reveals that, for the same materials, coin cells and pouch cells exhibit consistent high-temperature performance, showing good consistency over short cycles. Coin cells can be used for preliminary screening of materials during high-temperature performance testing, thereby reducing experimental testing costs while ensuring testing accuracy.

[0043] The above are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and modifications obtained without departing from the inventive concept should also be considered within the scope of protection of the present invention.

[0044] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for testing the high-temperature storage performance of lithium-ion batteries, characterized in that, Includes the following steps: (1) A coin cell is prepared, wherein the coin cell comprises a positive electrode shell, a positive electrode sheet, a separator, a negative electrode sheet and a negative electrode shell arranged sequentially; the positive electrode sheet comprises an aluminum foil and a positive electrode material layer coated on the aluminum foil, the positive electrode material layer comprising a lithium-containing ternary positive electrode material; the negative electrode sheet comprises a copper foil and a negative electrode material layer coated on the copper foil, the negative electrode material layer comprising a silicon-containing negative electrode material; (2) Activate the coin cell and measure the initial impedance R0, negative electrode thickness L0 and battery capacity C0; (3) Several of the aforementioned button cells were stored at high temperature for 6 days, and on the 7th day, they were taken out and left to stand at room temperature before their initial voltage V was measured. i Discharge capacity C i Discharge capacity C after full charge v and impedance R i Then, remove the button cell and discharge it to 2.5 V, then measure the thickness L of the negative electrode. i ; (4) Calculate the impedance change rate RR, capacity retention rate CR, capacity recovery rate CC and negative electrode expansion rate LR of the button cell, and judge the high temperature storage performance of the lithium-ion battery based on RR, CR, CC and LR.

2. The test method for the high-temperature storage performance of lithium-ion batteries according to claim 1, characterized in that, The coating thickness of the negative electrode material layer and the capacity ratio of the negative electrode material layer and the positive electrode material layer in step (1) are determined according to the material composition and proportion of the silicon-containing negative electrode material.

3. The test method for the high-temperature storage performance of lithium-ion batteries according to claim 2, characterized in that, The design capacity ratio of the negative electrode material layer to the positive electrode material layer is 1.05~1.

1.

4. The test method for the high-temperature storage performance of lithium-ion batteries according to claim 1, characterized in that, The positive electrode material layer and the negative electrode material layer also include conductive agents and binders.

5. The test method for the high-temperature storage performance of lithium-ion batteries according to claim 4, characterized in that, The preparation method of the positive electrode material layer or negative electrode material layer is as follows: lithium-containing multi-element positive electrode material or silicon-containing negative electrode material is mixed with conductive agent and binder in a certain mass ratio to obtain a uniform slurry. The slurry is uniformly coated onto current collector aluminum foil or copper foil using an automatic coating machine to obtain a positive electrode coating or a negative electrode coating. The obtained positive electrode coating or negative electrode coating is dried and compacted to obtain the positive electrode material layer or negative electrode material layer.

6. The test method for the high-temperature storage performance of lithium-ion batteries according to claim 5, characterized in that, The mixing method of the lithium-containing multi-element positive electrode material or silicon-containing negative electrode material with the conductive agent and binder is as follows: rotate forward at 700 rpm for 5 minutes, and then rotate in reverse at 2000 rpm for 20 minutes.

7. The method for testing the high-temperature storage performance of lithium-ion batteries according to claim 1, characterized in that, The diaphragm is a double-layer diaphragm.

8. The method for testing the high-temperature storage performance of lithium-ion batteries according to claim 1, characterized in that, The impedance change rate RR, capacity retention rate CR, capacity recovery rate CC, and negative electrode expansion rate LR are calculated by the following formulas: CR=C i / C0;CC=C v / C0;LR=(L i -L0) / L0;RR=(R i -R0) / R0。 9. The test method for the high-temperature storage performance of a lithium-ion battery according to any one of claims 1-8, characterized in that, The test cycle is 7 days in step (3). At the end of the test cycle, n groups of button cells are charged to the storage voltage and the next test cycle is repeated until 6 test cycles are completed.

10. The method for testing the high-temperature storage performance of a lithium-ion battery according to claim 9, characterized in that, Among the coin cells that have completed 6 test cycles, the groups with a voltage decay rate of ±5 mV / d and a capacity decay of ±2.00% were selected. The silicon-containing anode materials corresponding to these groups were then assembled into pouch cells or 18650 cells for further testing.

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