A method for preparing a silicon-based soft-pack lithium-ion battery

Abstract

The present application relates to the field of battery preparation, and in particular to a method for preparing a silicon-based soft-pack lithium-ion battery; the method comprises: obtaining a low-temperature battery cell; injecting a first electrolyte into the low-temperature battery cell, and then performing formation and aging to obtain a first battery; draining the first battery, and then charging and discharging to obtain a primary battery; injecting a second electrolyte into the primary battery, and then performing formation and aging to obtain a second battery; draining the second battery, and then charging and discharging to obtain a secondary battery; injecting a third electrolyte into the secondary battery, and then performing a capacity test, draining and final sealing to obtain a silicon-based soft-pack lithium-ion battery with high cycle performance; wherein the first electrolyte comprises a negative electrode film-forming additive, the second electrolyte comprises a positive electrode film-forming additive, and the third electrolyte comprises a negative electrode film-forming additive; by adding electrolytes in batches before and after forming and aging the battery, and then draining, the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the field of battery preparation, and in particular to a method for preparing a silicon-based soft-pack lithium-ion battery. Background Art

[0002] With the continuous advancement of lithium-ion battery cell technology and the increasing demand for electrical performance and energy density, the graphite batteries currently used in the market have reached their energy density limit, so it is difficult to have room for further improvement; while silicon-based batteries have obvious advantages in energy density, and as new energy vehicles continue to increase their requirements for driving range in actual applications, silicon-based batteries will gradually become the best choice for battery companies due to the abundant reserves of silicon negative electrode materials and the advantages of ultra-high theoretical specific capacity. It is the most promising next-generation lithium-ion battery.

[0003] However, since the specific surface area of ​​silicon-based negative electrode materials is larger than that of carbon negative electrode materials, more Li+ is consumed to form the solid electrolyte interface film (SEI film), and the electrolyte will undergo strong decomposition on the Si surface, which will produce irreversible capacity. At the same time, there are also problems such as electrical performance deterioration and pole piece expansion caused by the reaction between silicon materials and HF components in the electrolyte; and in the "discharge-charge" cycle of lithium-ion batteries, the stress caused by lithium insertion and extraction causes the SEI film of the negative electrode to be continuously destroyed and continuously generated. In the above-mentioned destruction and generation process, the film-forming additives will be continuously consumed, resulting in a rapid decay of the cycle capacity, thereby affecting the battery life. Therefore, how to improve the cycle performance of the battery is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application provides a method for preparing a silicon-based soft-pack lithium-ion battery to solve the technical problem in the prior art that it is difficult to improve the cycle performance of the battery.

[0005] In a first aspect, the present application provides a method for preparing a silicon-based soft-pack lithium-ion battery, the method comprising:

[0006] A low-temperature battery cell is obtained;

[0007] Injecting a first electrolyte into the low-temperature battery cell, and then performing formation and aging to obtain a first battery;

[0008] The first battery is drained, and then charged and discharged to obtain a primary battery;

[0009] Injecting a second electrolyte into the primary battery, followed by formation and aging to obtain a second battery;

[0010] The second battery is drained, and then charged and discharged to obtain a secondary battery;

[0011] The third electrolyte is injected into the secondary battery, and then a capacity test, liquid extraction and final sealing are performed to obtain a silicon-based soft-pack lithium-ion battery with high cycle performance; wherein the first electrolyte includes a negative electrode film-forming additive, the second electrolyte includes a positive electrode film-forming additive, and the third electrolyte includes a negative electrode film-forming additive.

[0012] Optionally, the negative electrode film-forming additive includes one or two of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilyl)borate, tris(2,2,2-trifluoroethyl)boric acid and lithium difluorobis(oxalate)phosphate;

[0013] The positive electrode film-forming additive includes one or two of tris(trimethylsilyl)phosphate, dimethyldimethoxysilane, tris(2,2,2-trifluoroethyl)phosphite, trimethyl phosphate, tris(pentafluorophenyl)phosphine and 1,2-dimethoxy-4-nitrobenzene.

[0014] Optionally, the first electrolyte, the second electrolyte and the third electrolyte all include lithium salt, and the molar concentration of lithium ions in the lithium salt is 1.0 mol / L to 1.5 mol / L.

[0015] Optionally, in terms of mass fraction, the first electrolyte comprises 3% to 8% of anode film-forming additives, the second electrolyte comprises 0.2% to 3% of cathode film-forming additives, and the third electrolyte comprises 10% to 15% of cathode film-forming additives.

[0016] Optionally, the solvents of the first electrolyte, the second electrolyte and the third electrolyte are all a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate;

[0017] Or, the solvents of the first electrolyte, the second electrolyte and the third electrolyte are all a mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate;

[0018] Alternatively, the solvents of the first electrolyte, the second electrolyte and the third electrolyte are all a mixture of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.

[0019] Optionally, the injection amount of the first electrolyte accounts for 40% to 60% of the total injection amount of the lithium-ion battery, the injection amount of the second electrolyte accounts for 40% to 60% of the total injection amount of the lithium-ion battery, and the injection amount of the third electrolyte accounts for 40% to 60% of the total injection amount of the lithium-ion battery.

[0020] Optionally, the formation includes forming in a three-stage charging system, wherein the first stage formation includes: charging at a first preset temperature and a first preset pressure with a first preset rate constant current for a first preset time;

[0021] The second formation includes: charging at a second preset temperature and a second preset pressure for a second preset time with a second preset rate of current constant current;

[0022] The third formation includes: under the conditions of a third preset temperature and a third preset pressure, constant current charging with a third preset rate for a third preset time.

[0023] Optionally, the first preset temperature is 35°C to 40°C, the second preset temperature is 45°C to 55°C, and the third preset temperature is 60°C to 65°C;

[0024] The first preset pressure is 0.3MPa to 0.6MPa, the second preset pressure is 0.6MPa to 0.8MPa, and the third preset pressure is 0.8MPa to 1.0MPa;

[0025] The first preset magnification is 0.05C to 0.1C, the second preset magnification is 0.1C to 0.2C, and the third preset magnification is 0.2C to 0.5C;

[0026] The first preset time is 30 minutes to 60 minutes, the second preset time is 15 minutes to 45 minutes, and the third preset time is 60 minutes to 120 minutes.

[0027] Optionally, the aging temperature is 35° C. to 45° C., the aging pressure is 0.8 MPa to 1.0 MPa, and the aging time is 18 h to 26 h.

[0028] Optionally, the charging includes charging to 4.2V at a constant current and constant voltage at a current rate of 0.5C;

[0029] The discharging includes discharging at a constant current of 0.5C to 3V.

[0030] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0031] A method for preparing a silicon-based soft-pack lithium-ion battery provided in an embodiment of the present application adopts the method of adding electrolyte in batches before and after the formation and aging of the battery, thereby promoting the battery to form a stable and dense SEI film at the positive and negative electrodes of the battery without being interfered by too many additive components by adding electrolyte multiple times, and then by pumping liquid from the battery, it can be ensured or controlled that no side reaction occurs in the electrolyte added each time, and then the impurities generated by some side reactions can be diluted or removed, and the stability of the SEI film can be further maintained, thereby effectively improving the stability of the battery cycle and improving the cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0034] Figure 1 A schematic diagram of a process for a method provided in an embodiment of the present application;

[0035] Figure 2 A comparison chart of the average cycle efficiency of batteries provided in the embodiments of the present application. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0037] The creative thinking of the present application is: since the specific surface area of ​​silicon-based negative electrode materials is larger than that of carbon negative electrode materials, more Li+ is consumed to form the SEI film, and the electrolyte will undergo strong decomposition on the Si surface, thereby generating irreversible capacity, and the Si material and the HF impurities in the electrolyte will react with Si, thereby causing problems of deterioration of electrical performance and expansion of the electrode sheet; and during the cycle of lithium-ion batteries, the stress caused by lithium insertion and extraction causes the SEI film of the negative electrode to be continuously destroyed and generated, and the film-forming additives will be continuously consumed, resulting in a rapid decay of the cycle capacity.

[0038] Therefore, during the formation stage, when the positive and negative electrode materials react with the electrolyte, they can form a moderately thick, stable and dense low-impedance SEI film at the solid-liquid interface, which plays an important role in improving the life of lithium-ion batteries. However, the close contact between the electrode and the electrolyte will cause side reactions, especially under high temperature conditions. The impurities such as HF produced by these side reactions will cause capacity decay and structural degradation, thereby affecting the performance of lithium-ion batteries. Therefore, on the basis of forming a dense SEI film, it is necessary to remove the side reaction impurities in the electrolyte to improve the battery's cycle performance.

[0039] In one embodiment of the present application, Figure 1 A method for preparing a silicon-based soft-pack lithium-ion battery is provided, the method comprising:

[0040] S1. Obtaining a low-temperature battery cell;

[0041] S2. Injecting a first electrolyte into the low-temperature battery cell, followed by formation and aging to obtain a first battery;

[0042] S3. The first battery is drained, and then charged and discharged to obtain a primary battery;

[0043] S4. Injecting a second electrolyte into the primary battery, followed by formation and aging to obtain a second battery;

[0044] S5. The second battery is drained, and then charged and discharged to obtain a secondary battery;

[0045] S6. Inject the third electrolyte into the secondary battery, then perform capacity test, liquid extraction and final sealing to obtain a silicon-based soft-pack lithium-ion battery with high cycle performance; wherein the first electrolyte includes a negative electrode film-forming additive, the second electrolyte includes a positive electrode film-forming additive, and the third electrolyte includes a negative electrode film-forming additive.

[0046] In some optional embodiments, the negative electrode film-forming additive includes one or two of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilyl)borate, tris(2,2,2-trifluoroethyl)boric acid and lithium difluorobis(oxalate)phosphate;

[0047] The positive electrode film-forming additive includes one or two of tris(trimethylsilyl)phosphate, dimethyldimethoxysilane, tris(2,2,2-trifluoroethyl)phosphite, trimethyl phosphate, tris(pentafluorophenyl)phosphine and 1,2-dimethoxy-4-nitrobenzene.

[0048] In the present application, by limiting the types of negative electrode film-forming additives and positive electrode film-forming additives, the low content of impurities in the components of the negative electrode film-forming additives and the positive electrode film-forming additives can be ensured, thereby controlling the generation of HF in the side reaction and ensuring that the negative and positive electrodes of the battery generate a dense SEI film.

[0049] In some optional embodiments, the first electrolyte, the second electrolyte and the third electrolyte all include a lithium salt, the molar concentration of lithium ions of the lithium salt is 1.0 mol / L to 1.5 mol / L, and the lithium salt may be LiPF6.

[0050] In the present application, the positive effect of the molar concentration of lithium ions in the lithium salt being 1.0 mol / L to 1.5 mol / L is that within this concentration range, a SEI film of moderate thickness and compactness can be formed, while ensuring stable decomposition of the electrolyte on Si, avoiding the generation of irreversible capacity, and thus improving the cycle performance of the battery; when the concentration value is greater than the maximum value of the endpoint of the range, the adverse effect that will result is that although the excessively high lithium ion concentration can ensure the formation of the SEI film, too much lithium ions will not only increase the production cost but also lead to aggravated side reactions of the electrolyte, generate a large amount of HF impurities, and affect the cycle performance of the battery; when the concentration value is less than the minimum value of the endpoint of the range, the adverse effect that will result is that too few lithium ions will result in the inability to form a SEI film of moderate thickness and compactness.

[0051] In some optional embodiments, the first electrolyte comprises 3% to 8% of anode film-forming additives, the second electrolyte comprises 0.2% to 3% of cathode film-forming additives, and the third electrolyte comprises 10% to 15% of cathode film-forming additives, by mass fraction.

[0052] In the present application, the positive effect of the first electrolyte including 3% to 8% of the negative electrode film-forming additive is that within the mass fraction range, it can ensure that after the first electrolyte is added, the negative electrode on the battery cell can initially form a SEI film of moderate thickness and density, thereby ensuring the formation of the SEI film of the negative electrode; when the mass fraction value is greater than the maximum value of the endpoint of the range, the adverse effect that will result is that too much negative electrode film-forming additive is added, which will increase the impurities produced by side reactions, leading to battery capacity attenuation and structural degradation, thereby affecting the battery's cycle performance; when the mass fraction value is less than the minimum value of the endpoint of the range, the adverse effect that will result is insufficient negative electrode film-forming additive, which will cause the negative electrode of the battery cell to be unable to form a SEI film of moderate thickness and density, affecting the battery capacity, thereby causing battery structural degradation and affecting the performance of the lithium-ion battery.

[0053] The positive effect of the second electrolyte including 0.2% to 3% of the positive electrode film-forming additive is that within the range of this mass fraction, it can ensure that after the second electrolyte is added, the SEI film initially formed on the negative electrode can further form a SEI film of moderate thickness and density on the positive electrode, thereby ensuring the cycle performance of the battery; when the mass fraction value is greater than the maximum value of the endpoint of the range, the adverse effect that will result is that the amount of positive electrode film-forming additive added is too much, which will increase the impurities produced by side reactions and affect the battery capacity. When the mass fraction value is less than the minimum value of the endpoint of the range, the adverse effect that will result is insufficient positive electrode film-forming additive, which will cause the positive electrode of the battery cell to be unable to form a SEI film of moderate thickness and density, affecting the battery capacity, and then causing the battery structure to degrade and affect the performance of the lithium-ion battery.

[0054] The positive effect of the third electrolyte including 10% to 15% of the negative electrode film-forming additive is that within the range of this mass fraction, it can ensure that after the third electrolyte is added, a stable and dense SEI film can be further formed on the negative electrode, ensuring that the thickness of the SEI film at the negative electrode of the battery is moderate and stable; when the mass fraction value is greater than the maximum value of the endpoint of this range, the adverse effect will be that too much negative electrode film-forming additive is added, which will increase the impurities produced by side reactions and affect the battery capacity. When the mass fraction value is less than the minimum value of the endpoint of this range, the adverse effect will be insufficient negative electrode film-forming additive, which will cause the negative electrode of the battery cell to be unable to form a SEI film of moderate thickness and density, affecting the battery capacity, and then causing the battery structure to degrade and affect the performance of the lithium-ion battery.

[0055] In some optional embodiments, the solvents of the first electrolyte, the second electrolyte and the third electrolyte are all a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate;

[0056] Or, the solvents of the first electrolyte, the second electrolyte and the third electrolyte are all a mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate;

[0057] Alternatively, the solvents of the first electrolyte, the second electrolyte and the third electrolyte are all a mixture of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.

[0058] In the present application, by respectively limiting the composition of the first electrolyte, the second electrolyte and the third electrolyte, and then using substances with lower impurity content or risk of producing side reactions, the occurrence of side reactions can be effectively reduced, thereby ensuring the formation of a stable and dense low-resistance SEI film, increasing the battery capacity, and at the same time increasing the film formation speed.

[0059] In some optional embodiments, the injection amount of the first electrolyte accounts for 40% to 60% of the total injection amount of the lithium-ion battery, the injection amount of the second electrolyte accounts for 40% to 60% of the total injection amount of the lithium-ion battery, and the injection amount of the third electrolyte accounts for 40% to 60% of the total injection amount of the lithium-ion battery.

[0060] In the present application, the positive effect of the injection amount of the first electrolyte accounting for 40% to 60% of the total injection amount of the lithium-ion battery is that within the range of the proportion, the first electrolyte can be guaranteed to react fully, and a SEI film can be initially formed at the negative electrode of the battery cell, thereby providing a basis for the subsequent stable formation of the SEI film; when the value of the proportion is greater than the maximum value of the endpoint of the range, the adverse effect that will result is that too much electrolyte injection will lead to excessive consumption of the electrolyte, and at the same time, too much electrolyte will increase the risk of side reactions, resulting in impurities corroding the subsequent positive electrode and affecting the film-forming effect. When the value of the proportion is less than the minimum value of the endpoint of the range, the adverse effect that will result is that too little electrolyte will not be able to initially form a SEI film at the negative electrode of the battery cell.

[0061] The positive effect of the injection amount of the second electrolyte accounting for 40% to 60% of the total injection amount of the lithium-ion battery is that within the range of this proportion, the second electrolyte reaction liquid can be guaranteed to react fully and a SEI film can be formed at the positive electrode of the battery cell, thereby providing a basis for the subsequent stable formation of the SEI film; when the proportion is greater than the maximum value of the endpoint of the range, the adverse effect will be that too much electrolyte will lead to excessive consumption of the electrolyte, and at the same time, too much electrolyte will increase the risk of side reactions, causing impurities to corrode the formed positive electrode and affect the film-forming effect. When the proportion is less than the minimum value of the endpoint of the range, the adverse effect will be that too little electrolyte will not be able to form a SEI film at the positive electrode of the battery cell.

[0062] The positive effect of the injection amount of the third electrolyte accounting for 40% to 60% of the total injection amount of the lithium-ion battery is that within the range of this proportion, the third electrolyte reaction liquid can be fully reacted to form a moderately thick and dense SEI film on the battery cell that has formed the negative electrode again, and the SEI film of the battery cell can be more evenly distributed; when the proportion is greater than the maximum value of the endpoint of the range, the adverse effect will be that too much electrolyte will lead to excessive consumption of the electrolyte, and at the same time, too much electrolyte will increase the risk of side reactions, causing impurities to corrode the already formed positive electrode and affect the film-forming effect. When the proportion is less than the minimum value of the endpoint of the range, the adverse effect will be that too little electrolyte will ensure that the already formed SEI film is evenly distributed and dense.

[0063] In some optional embodiments, the formation includes forming in a three-stage charging system, wherein the first stage formation includes: charging at a first preset temperature and a first preset pressure with a first preset rate constant current for a first preset time;

[0064] The second formation includes: charging at a second preset temperature and a second preset pressure for a second preset time with a second preset rate of current constant current;

[0065] The third formation includes: under the conditions of a third preset temperature and a third preset pressure, constant current charging with a third preset rate for a third preset time.

[0066] In some optional embodiments, the first preset temperature is 35°C to 40°C, the second preset temperature is 45°C to 55°C, and the third preset temperature is 60°C to 65°C;

[0067] The first preset pressure is 0.3MPa to 0.6MPa, the second preset pressure is 0.6MPa to 0.8MPa, and the third preset pressure is 0.8MPa to 1.0MPa;

[0068] The first preset magnification is 0.05C to 0.1C, the second preset magnification is 0.1C to 0.2C, and the third preset magnification is 0.2C to 0.5C;

[0069] The first preset time is 30 minutes to 60 minutes, the second preset time is 15 minutes to 45 minutes, and the third preset time is 60 minutes to 120 minutes.

[0070] In the present application, the positive effect of the first preset temperature of 35°C to 40°C is that within this temperature range, the SEI film can be initially formed at the negative electrode of the battery cell; when the temperature value is greater than the maximum value of the endpoint of the range, the adverse effect will be that the excessively high temperature will cause the SEI film formed at the negative electrode of the battery cell to be unstable and uneven in thickness, thereby affecting the capacity of the battery and further affecting the cycle performance of the battery; when the temperature value is less than the minimum value of the endpoint of the range, the adverse effect will be that the excessively low temperature will cause the negative electrode of the battery cell to be unable to form a SEI film of sufficient thickness, thereby causing the SEI film to be unstable, thereby affecting the capacity of the battery.

[0071] The positive effect of the second preset temperature of 45°C to 55°C is that within this temperature range, the SEI film can be formed at the positive electrode of the battery cell; when the temperature value is greater than the maximum value of the endpoint of the range, the adverse effect will be that the excessively high temperature will cause the SEI film formed at the positive electrode of the battery cell to be unstable and uneven in thickness, thereby affecting the capacity of the battery and further affecting the cycle performance of the battery; when the temperature value is less than the minimum value of the endpoint of the range, the adverse effect will be that the excessively low temperature will cause the positive electrode of the battery cell to be unable to form a SEI film of sufficient thickness, thereby causing the SEI film to be unstable, thereby affecting the capacity of the battery.

[0072] The positive effect of the third preset temperature of 60°C to 65°C is that within this temperature range, it can ensure that the negative electrode of the battery cell can further form a SEI film, ensure that the thickness of the SEI film is uniform and dense, and at the same time stabilize the SEI film already formed at the positive electrode to ensure the capacity of the battery; when the temperature value is greater than the maximum value of the endpoint of the range, the adverse effect will be that the excessively high temperature will cause the SEI film formed again at the negative electrode of the battery cell to be unstable and uneven in thickness, thereby affecting the capacity of the battery, and then affecting the cycle performance of the battery; when the temperature value is less than the minimum value of the endpoint of the range, the adverse effect will be that the excessively low temperature will cause the negative electrode of the battery cell to be unable to form a SEI film of sufficient thickness again, and the SEI film already formed at the positive electrode cannot be stabilized, thereby affecting the capacity of the battery.

[0073] The positive effect of the first preset pressure of 0.3MPa to 0.6MPa is that within this pressure range, it can ensure that the SEI film is initially formed at the negative electrode of the battery cell; when the pressure value is greater than the maximum value of the endpoint of the range, the adverse effect will be that the excessively high pressure will cause the SEI film formed at the negative electrode of the battery cell to be unstable and uneven in thickness, thereby affecting the capacity of the battery and further affecting the cycle performance of the battery; when the pressure value is less than the minimum value of the endpoint of the range, the adverse effect will be that the excessively low pressure will cause the negative electrode of the battery cell to be unable to form a SEI film of sufficient thickness, thereby causing the SEI film to be unstable, thereby affecting the capacity of the battery.

[0074] The positive effect of the second preset pressure of 0.6MPa to 0.8MPa is that within this pressure range, the SEI film can be formed at the positive electrode of the battery cell; when the pressure value is greater than the maximum value of the endpoint of the range, the adverse effect is that the excessively high pressure will cause the SEI film formed at the positive electrode of the battery cell to be unstable and uneven in thickness, thereby affecting the capacity of the battery and further affecting the cycle performance of the battery; when the pressure value is less than the minimum value of the endpoint of the range, the adverse effect is that the excessively low pressure will cause the positive electrode of the battery cell to be unable to form a SEI film of sufficient thickness, thereby causing the SEI film to be unstable, thereby affecting the capacity of the battery.

[0075] The positive effect of the third preset pressure of 0.8MPa to 1.0MPa is that within this pressure range, it can ensure that the negative electrode of the battery cell can further form a SEI film, ensure that the thickness of the SEI film is uniform and dense, and at the same time stabilize the SEI film already formed at the positive electrode to ensure the capacity of the battery; when the pressure value is greater than the maximum value of the endpoint of the range, the adverse effect will be that the excessively high pressure will cause the SEI film formed again at the negative electrode of the battery cell to be unstable and uneven in thickness, thereby affecting the capacity of the battery, and further affecting the cycle performance of the battery; when the pressure value is less than the minimum value of the endpoint of the range, the adverse effect will be that the excessively low pressure will cause the negative electrode of the battery cell to be unable to form a SEI film of sufficient thickness again, and the SEI film already formed at the positive electrode cannot be stabilized, thereby affecting the capacity of the battery.

[0076] The positive effect of the first preset rate of 0.05C to 0.1C is that within the current rate range, it can ensure that the SEI film is initially formed at the negative electrode of the battery cell; when the current rate value is greater than the maximum value of the endpoint of the range, the adverse effect will be that the excessively high current rate will cause the SEI film formed at the negative electrode of the battery cell to be unstable and uneven in thickness, thereby affecting the capacity of the battery and further affecting the cycle performance of the battery; when the current rate value is less than the minimum value of the endpoint of the range, the adverse effect will be that the excessively low current rate will cause the negative electrode of the battery cell to be unable to form a SEI film of sufficient thickness, thereby causing the SEI film to be unstable, thereby affecting the capacity of the battery.

[0077] The positive effect of the second preset rate of 0.1C to 0.2C is that within the current rate range, the SEI film can be ensured to be formed at the positive electrode of the battery cell; when the current rate value is greater than the maximum value of the endpoint of the range, the adverse effect will be that the excessively high current rate will cause the SEI film formed at the positive electrode of the battery cell to be unstable and uneven in thickness, thereby affecting the capacity of the battery and further affecting the cycle performance of the battery; when the current rate value is less than the minimum value of the endpoint of the range, the adverse effect will be that the excessively low current rate will cause the positive electrode of the battery cell to be unable to form a SEI film of sufficient thickness, thereby causing the SEI film to be unstable, thereby affecting the capacity of the battery.

[0078] The positive effect of the third preset rate of 0.2C to 0.5C is that within the current rate range, it can ensure that the negative electrode of the battery cell can further form a SEI film, ensure that the thickness of the SEI film is uniform and dense, and stabilize the SEI film already formed at the positive electrode to ensure the capacity of the battery; when the current rate value is greater than the maximum value of the endpoint of the range, the adverse effect will be that the excessively high current rate will cause the SEI film formed again at the negative electrode of the battery cell to be unstable and uneven in thickness, thereby affecting the capacity of the battery and further affecting the cycle performance of the battery; when the current rate value is less than the minimum value of the endpoint of the range, the adverse effect will be that the excessively low current rate will cause the negative electrode of the battery cell to be unable to form a SEI film of sufficient thickness again, and the SEI film already formed at the positive electrode cannot be stabilized, thereby affecting the capacity of the battery.

[0079] The first preset time is 30min to 60min. The positive effect is that within this time range, the SEI film can be initially formed at the negative electrode of the battery cell; when the time value is greater than the maximum value of the endpoint of the range, the adverse effect will be that too high a time will cause the SEI film formed at the negative electrode of the battery cell to be unstable and uneven in thickness, thereby affecting the capacity of the battery, and further affecting the cycle performance of the battery; when the time value is less than the minimum value of the endpoint of the range, the adverse effect will be that too low a time will cause the negative electrode of the battery cell to be unable to form a SEI film of sufficient thickness, thereby causing the SEI film to be unstable, thereby affecting the capacity of the battery.

[0080] The positive effect of the second preset time of 15min to 45min is that within this time range, the SEI film can be guaranteed to be formed at the positive electrode of the battery cell; when the time value is greater than the maximum value of the endpoint of the range, the adverse effect will be that too high a time will cause the SEI film formed at the positive electrode of the battery cell to be unstable and uneven in thickness, thereby affecting the capacity of the battery, and further affecting the cycle performance of the battery; when the time value is less than the minimum value of the endpoint of the range, the adverse effect will be that too low a time will cause the positive electrode of the battery cell to be unable to form a SEI film of sufficient thickness, thereby causing the SEI film to be unstable, thereby affecting the capacity of the battery.

[0081] The positive effect of the third preset time of 60min to 120min is that within this time range, it can ensure that the negative electrode of the battery cell can further form a SEI film, ensure that the thickness of the SEI film is uniform and dense, and at the same time stabilize the SEI film already formed at the positive electrode to ensure the capacity of the battery; when the time value is greater than the maximum value of the endpoint of the range, the adverse effect that will result is that too high a time will cause the SEI film formed again at the negative electrode of the battery cell to be unstable and uneven in thickness, thereby affecting the capacity of the battery, and then affecting the cycle performance of the battery; when the time value is less than the minimum value of the endpoint of the range, the adverse effect that will result is that too low a time will cause the negative electrode of the battery cell to be unable to form a SEI film of sufficient thickness again, and the SEI film already formed at the positive electrode cannot be stabilized, thereby affecting the capacity of the battery.

[0082] In some optional embodiments, the aging temperature is 35° C. to 45° C., the aging pressure is 0.8 MPa to 1.0 MPa, and the aging time is 18 h to 26 h.

[0083] In the present application, the positive effect of the aging temperature of 35°C to 45°C is that within this temperature range, the aging stability of the SEI film of the negative electrode and the SEI film of the positive electrode that have been formed is guaranteed, thereby forming a dense SEI film, and at the same time ensuring that the electrolyte fully infiltrates the battery; when the temperature value is greater than the maximum value of the endpoint of the range, the adverse effect that will result is that the excessively high temperature will cause side reactions in the electrolyte, thereby forming HF impurities and corroding the SEI film of the positive electrode; when the temperature value is less than the minimum value of the endpoint of the range, the adverse effect that will result is that the excessively low temperature will lead to the inability to stabilize the aging of the SEI film, and at the same time, it is impossible to ensure that the electrolyte is fully infiltrated in the battery, and the stability of the battery components cannot be achieved.

[0084] In some optional embodiments, the charging includes charging to 4.2V at a constant current and constant voltage at a current rate of 0.5C;

[0085] The discharging includes discharging at a constant current of 0.5C to 3V.

[0086] In the present application, the positive effect of charging including constant current and constant voltage charging to 4.2V at a current rate of 0.5C is that under the conditions of this current and voltage, by carrying out sufficient charging and discharging processes, the formed SEI film can be fully stabilized, thereby ensuring the excellent performance of the formed battery.

[0087] The positive effect of discharging including constant current discharge at a rate of 0.5C to 3V is that under the conditions of this current and voltage, the battery can be stably charged and discharged, thereby ensuring that the SEI film in the battery can work stably.

[0088] Example 1

[0089] like Figure 1 As shown, a method for preparing a silicon-based soft-pack lithium-ion battery comprises:

[0090] S1. Obtain a low-temperature battery cell, wherein the temperature of the low-temperature battery cell is ≤45°C;

[0091] S2. Inject the first electrolyte into the low-temperature battery cell, let it stand for 8 hours at 35°C, and then perform formation and aging to obtain a first battery;

[0092] S3. The first battery is drained, and then charged and discharged to obtain a primary battery;

[0093] S4. Injecting a second electrolyte into the primary battery, followed by formation and aging to obtain a second battery;

[0094] S5. The second battery is drained, and then charged and discharged to obtain a secondary battery;

[0095] S6. Inject the third electrolyte into the secondary battery, then perform capacity test, liquid extraction and final sealing to obtain a silicon-based soft-pack lithium-ion battery with high cycle performance; wherein the first electrolyte includes a negative electrode film-forming additive, the second electrolyte includes a positive electrode film-forming additive, and the third electrolyte includes a negative electrode film-forming additive.

[0096] The negative electrode film-forming additive of the first electrolyte is fluoroethylene carbonate;

[0097] The positive electrode film-forming additive of the second electrolyte includes tris(trimethylsilyl)phosphate;

[0098] The negative electrode film-forming additive of the third electrolyte is fluoroethylene carbonate.

[0099] The first electrolyte, the second electrolyte and the third electrolyte all include lithium salt LiPF6, and the molar concentration of lithium ions in the lithium salt is 1.2 mol / L.

[0100] In terms of mass fraction, the first electrolyte includes 5% of the negative electrode film-forming additive, the second electrolyte includes 1% of the positive electrode film-forming additive, and the third electrolyte includes 10% of the negative electrode film-forming additive.

[0101] The solvents of the first electrolyte, the second electrolyte and the third electrolyte are all a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and the volume ratio thereof is 1:1:1;

[0102] The injection amount of the first electrolyte accounts for 50% of the total injection amount of the lithium-ion battery, the injection amount of the second electrolyte accounts for 50% of the total injection amount of the lithium-ion battery, and the injection amount of the third electrolyte accounts for 50% of the total injection amount of the lithium-ion battery, wherein the total injection amount of the lithium-ion battery is 8mL.

[0103] The formation includes forming in a three-stage charging system, wherein the first stage formation includes: charging at a first preset temperature and a first preset pressure for a first preset time with a first preset rate of current constant current;

[0104] The second formation includes: charging at a second preset temperature and a second preset pressure for a second preset time with a second preset rate of current constant current;

[0105] The third formation includes: under the conditions of a third preset temperature and a third preset pressure, constant current charging with a third preset rate for a third preset time.

[0106] The first preset temperature is 35°C, the second preset temperature is 45°C, and the third preset temperature is 60°C;

[0107] The first preset pressure is 0.4MPa, the second preset pressure is 0.6MPa, and the third preset pressure is 0.8MPa;

[0108] The first preset magnification is 0.05C, the second preset magnification is 0.1C, and the third preset magnification is 0.2C;

[0109] The first preset time is 60 minutes, the second preset time is 30 minutes, and the third preset time is 80 minutes.

[0110] The aging temperature is 45°C, the aging pressure is 1.0MPa, and the aging time is 24h.

[0111] Charging includes constant current and constant voltage charging at a current rate of 0.5C to 4.2V;

[0112] The discharge includes constant current discharge at a rate of 0.5C to 3V.

[0113] Example 2

[0114] Comparing Example 2 with Example 1, the difference between Example 2 and Example 1 is:

[0115] The negative electrode film-forming additive of the first electrolyte includes a mixture of tris(trimethylsilyl)borate and lithium difluorobisoxalate phosphate, wherein the mass fractions of tris(trimethylsilyl)borate and lithium difluorobisoxalate phosphate are both 3%;

[0116] The cathode film-forming additive of the second electrolyte is dimethyldimethoxysilane;

[0117] The negative electrode film-forming additive of the third electrolyte is fluoroethylene carbonate.

[0118] The first electrolyte, the second electrolyte and the third electrolyte all include lithium salt, and the molar concentration of lithium ions in the lithium salt is 1.0 mol / L.

[0119] In terms of mass fraction, the first electrolyte includes 3% of the negative electrode film-forming additive, the second electrolyte includes 0.5% of the positive electrode film-forming additive, and the third electrolyte includes 15% of the negative electrode film-forming additive.

[0120] The solvents of the first electrolyte, the second electrolyte and the third electrolyte are all a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate, wherein the volume ratio of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate is 3:4:3;

[0121] The injection amount of the first electrolyte accounts for 40% of the total injection amount of the lithium-ion battery, the injection amount of the second electrolyte accounts for 40% of the total injection amount of the lithium-ion battery, and the injection amount of the third electrolyte accounts for 50% of the total injection amount of the lithium-ion battery, wherein the total injection amount of the lithium-ion battery is 8mL.

[0122] The first preset temperature is 40°C, the second preset temperature is 55°C, and the third preset temperature is 65°C;

[0123] The first preset pressure is 0.6MPa, the second preset pressure is 0.8MPa, and the third preset pressure is 1.0MPa;

[0124] The first preset magnification is 0.05C, the second preset magnification is 0.2C, and the third preset magnification is 0.5C;

[0125] The first preset time is 30 minutes, the second preset time is 15 minutes, and the third preset time is 60 minutes.

[0126] The aging temperature is 45°C, the aging pressure is 1.0MPa, and the aging time is 24h.

[0127] Example 3

[0128] Comparing Example 3 with Example 1, the difference between Example 3 and Example 1 is:

[0129] The negative electrode film-forming additive of the first electrolyte is fluoroethylene carbonate;

[0130] The positive electrode film-forming additive of the second electrolyte is a mixed solution of tri(pentafluorophenyl)phosphine and 1,2-dimethoxy-4-nitrobenzene;

[0131] The negative electrode film-forming additive of the first electrolyte is a mixed solution of fluoroethylene carbonate and tris(2,2,2-trifluoroethyl)boric acid.

[0132] The first electrolyte, the second electrolyte and the third electrolyte all include lithium salt, and the molar concentration of lithium ions in the lithium salt is 1.0 mol / L to 1.5 mol / L.

[0133] In terms of mass fraction, the first electrolyte includes 5% of the negative electrode film-forming additive, the second electrolyte includes 0.2% of the positive electrode film-forming additive, and the third electrolyte includes 15% of the negative electrode film-forming additive.

[0134] The solvents of the first electrolyte, the second electrolyte and the third electrolyte are all a mixed solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate, wherein the volume ratio of ethylene carbonate, diethyl carbonate and dimethyl carbonate is 1:1:1.

[0135] The injection amount of the first electrolyte accounts for 60% of the total injection amount of the lithium-ion battery, the injection amount of the second electrolyte accounts for 50% of the total injection amount of the lithium-ion battery, and the injection amount of the third electrolyte accounts for 40% of the total injection amount of the lithium-ion battery, wherein the total injection amount of the lithium-ion battery is 8mL.

[0136] The first preset temperature is 35°C, the second preset temperature is 50°C, and the third preset temperature is 60°C;

[0137] The first preset pressure is 0.3MPa, the second preset pressure is 0.7MPa, and the third preset pressure is 0.8MPa;

[0138] The first preset magnification is 0.1C, the second preset magnification is 0.2C, and the third preset magnification is 0.3C;

[0139] The first preset time is 60 minutes, the second preset time is 45 minutes, and the third preset time is 90 minutes.

[0140] The aging temperature is 40°C, the aging pressure is 0.8MPa, and the aging time is 24h.

[0141] Comparative Example 1

[0142] Comparing Comparative Example 1 with Example 1, the difference between Comparative Example 1 and Example 1 is:

[0143] Only the first electrolyte is used, the negative electrode film-forming additive of the first electrolyte is a mixture of fluoroethylene carbonate and tris(trimethylsilyl)phosphate, and the injection volume is 8 mL;

[0144] The first electrolyte includes a lithium salt LiPF6, and the molar concentration of lithium ions in the lithium salt is 1.2 mol / L.

[0145] The first electrolyte includes 10% of fluoroethylene carbonate and 1% of tris(trimethylsilyl)phosphate by mass.

[0146] The solvent of the first electrolyte is a mixed solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate, wherein the volume ratio of ethylene carbonate, diethyl carbonate and dimethyl carbonate is 1:1:1.

[0147] After standing at room temperature for 24 hours, the reaction is carried out.

[0148] The first preset temperature, the second preset temperature and the third preset temperature are all 25° C.; the first preset pressure, the second preset pressure and the third preset pressure are all 0.4 MPa;

[0149] The first preset magnification is 0.05C, the second preset magnification is 0.1C, and the third preset magnification is 0.2C;

[0150] The first preset time is 120 minutes, the second preset time is 180 minutes, and the third preset time is 120 minutes.

[0151] The aging temperature is 45°C, the aging pressure is 0.8MPa, and the aging time is 48h.

[0152] Comparative Example 2

[0153] Comparing Comparative Example 2 with Example 1, the difference between Comparative Example 2 and Example 1 is:

[0154] The negative electrode film-forming additive includes one or two of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilyl)borate, tris(2,2,2-trifluoroethyl)boric acid and lithium difluorobis(oxalate)phosphate;

[0155] The positive electrode film-forming additive includes one or two of tris(trimethylsilyl)phosphate, dimethyldimethoxysilane, tris(2,2,2-trifluoroethyl)phosphite, trimethyl phosphate, tris(pentafluorophenyl)phosphine and 1,2-dimethoxy-4-nitrobenzene.

[0156] The first electrolyte, the second electrolyte and the third electrolyte all include lithium salt LiPF6, and the molar concentration of lithium ions in the lithium salt is 1.0 mol / L.

[0157] The solvent of the first electrolyte is ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, wherein the volume ratio of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate is 1:1:1.

[0158] The injection amount of the first electrolyte solution was 8 mL.

[0159] The first preset temperature, the second preset temperature and the third preset temperature are all 25° C.; the first preset pressure, the second preset pressure and the third preset pressure are all 0.4 MPa;

[0160] The first preset magnification is 0.1C, the second preset magnification is 0.2C, and the third preset magnification is 0.3C;

[0161] The first preset time is 60 minutes, the second preset time is 120 minutes, and the third preset time is 90 minutes.

[0162] The aging temperature is 45°C, the aging pressure is 1.0MPa, and the aging time is 48h.

[0163] Related experiments:

[0164] The batteries obtained in Examples 1-3 and Comparative Examples 1-2 were collected and subjected to cycle performance tests. The results are shown in Table 1.

[0165] Test methods for related experiments:

[0166] Testing method for average coulombic efficiency: Coulombic efficiency refers to the ratio of battery discharge capacity to charging capacity during the same cycle. The average coulombic efficiency of 2-10 cycles refers to the average value of the coulombic efficiency of all cycles in the 2nd to 10th cycle. The same calculation is used for others.

[0167] Table 1

[0168]

[0169]

[0170] Detailed analysis of Table 1:

[0171] The average coulombic efficiency is the ratio of the discharge capacity of the battery to the charge capacity during the same cycle. As the battery charge and discharge cycle proceeds, the faster the coulombic efficiency of the battery reaches a relatively high coulombic efficiency, the less irreversible capacity loss and the lower the battery capacity decay. From the data of Examples 1-3, it can be seen that:

[0172] By the method of the present application, the electrolyte is added in batches before and after the formation and aging of the battery, thereby ensuring that the battery forms a stable and dense SEI film at the positive and negative electrodes of the battery respectively without being interfered by excessive additive components, and then by pumping liquid from the battery, it is possible to ensure or control that no side reactions or a small amount of side reactions occur in the electrolyte in the battery, and then the impurities generated by some side reactions can be diluted or removed, thereby further maintaining the stability of the SEI film, and then effectively improving the stability of the battery cycle and improving the cycle performance of the battery.

[0173] The method of the present application can effectively improve the coulombic efficiency of the battery.

[0174] From the data of Comparative Examples 1-2, it can be seen that:

[0175] If the method of multiple electrolyte injections of the present application is not adopted, or if the conditions within the process parameter range specified in the present application are not adopted, the average cycle efficiency of the resulting battery is low and the number of cycles is small.

[0176] One or more technical solutions in the embodiments of the present application also have at least the following technical effects or advantages:

[0177] (1) The method provided in the embodiments of the present application, by injecting electrolyte into the battery before and after formation and aging, and extracting the electrolyte from the battery after injection, can form a stable and dense SEI film on the positive and negative electrodes of the battery, thereby avoiding the impurities produced by the side reactions in the electrolyte from corroding the SEI film of the positive electrode, thereby effectively improving the cycle performance of the battery.

[0178] (2) According to the method provided in the embodiment of the present application, the average coulombic efficiency of the obtained battery is stably maintained at more than 99.7% within 50 cycles, and the battery capacity can be maintained at 80% after 596 cycles.

[0179] (3) The method provided in the embodiments of the present application can effectively form an SEI film on the positive electrode of the battery by graded injection of the electrolyte, thereby significantly inhibiting the oxidative decomposition of the electrolyte on the high-nickel positive electrode and the high-voltage lithium nickel manganese cobalt oxide positive electrode, and further effectively improving the high temperature and cycle problems of the fluoroethylene carbonate electrolyte in high-nickel or high-voltage lithium nickel manganese cobalt oxide batteries.

[0180] Explanation of the attached figure:

[0181] Figure 2 A comparison chart of the average cycle efficiency of the batteries provided in the embodiments of the present application; Figure 2 It can be seen that the battery prepared in comparative example 1 maintains a capacity of 80% when it is cycled 427 times at room temperature, while the battery prepared in example 1 maintains a capacity of 80% when it is cycled 596 times at room temperature, which indicates that the electrolyte injection method and formation method of the present application can improve the room temperature cycle performance of lithium batteries.

[0182] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0183] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a silicon-based soft-pack lithium-ion battery, characterized in that: The method comprises: A low-temperature battery cell is obtained; Injecting a first electrolyte into the low-temperature battery cell, and then performing formation and aging to obtain a first battery; The first battery is drained, and then charged and discharged to obtain a primary battery; Injecting a second electrolyte into the primary battery, followed by formation and aging to obtain a second battery; The second battery is drained, and then charged and discharged to obtain a secondary battery; Injecting a third electrolyte into the secondary battery, and then performing a capacity test, extracting liquid, and final sealing to obtain a silicon-based soft-pack lithium-ion battery with high cycle performance; wherein the first electrolyte includes a negative electrode film-forming additive, the second electrolyte includes a positive electrode film-forming additive, and the third electrolyte includes a negative electrode film-forming additive; The negative electrode film-forming additive includes one or two of vinylene carbonate, fluoroethylene carbonate, tris(trimethylsilyl)borate, tris(2,2,2-trifluoroethyl)boric acid and lithium difluorobis(oxalate)phosphate; The positive electrode film-forming additive includes one or two of tris(trimethylsilyl)phosphate, dimethyldimethoxysilane, tris(2,2,2-trifluoroethyl)phosphite, trimethyl phosphate, tris(pentafluorophenyl)phosphine and 1,2-dimethoxy-4-nitrobenzene; In terms of mass fraction, the first electrolyte includes 3% to 8% of a negative electrode film-forming additive, the second electrolyte includes 0.2% to 3% of a positive electrode film-forming additive, and the third electrolyte includes 10% to 15% of a negative electrode film-forming additive; The injection amount of the first electrolyte accounts for 50% to 60% of the total injection amount of the lithium-ion battery, the injection amount of the second electrolyte accounts for 50% to 60% of the total injection amount of the lithium-ion battery, and the injection amount of the third electrolyte accounts for 50% to 60% of the total injection amount of the lithium-ion battery; The formation includes forming in a three-stage charging system, wherein the first stage formation includes: charging at a first preset temperature and a first preset pressure with a first preset rate constant current for a first preset time; The second formation includes: charging at a second preset temperature and a second preset pressure for a second preset time with a second preset rate of current constant current; The third formation includes: charging at a third preset temperature and a third preset pressure for a third preset time with a third preset rate of current constant current; The first preset temperature is 35°C to 40°C, the second preset temperature is 45°C to 55°C, and the third preset temperature is 60°C to 65°C; The first preset pressure is 0.3MPa~0.6MPa, the second preset pressure is 0.6MPa~0.8MPa, and the third preset pressure is 0.8MPa~1.0MPa; The first preset magnification is 0.05C to 0.1C, the second preset magnification is 0.1C to 0.2C, and the third preset magnification is 0.2C to 0.5C; The first preset time is 30 minutes to 60 minutes, the second preset time is 15 minutes to 45 minutes, and the third preset time is 60 minutes to 120 minutes; The aging temperature is 35° C. to 45° C., the aging pressure is 0.8 MPa to 1.0 MPa, and the aging time is 18 h to 26 h.

2. The method according to claim 1, characterized in that The first electrolyte, the second electrolyte and the third electrolyte all include lithium salt, and the molar concentration of lithium ions in the lithium salt is 1.0 mol / L.

3. The method according to claim 1, characterized in that The solvents of the first electrolyte, the second electrolyte and the third electrolyte are all a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate; Or, the solvents of the first electrolyte, the second electrolyte and the third electrolyte are all a mixture of ethylene carbonate, diethyl carbonate and dimethyl carbonate; Alternatively, the solvents of the first electrolyte, the second electrolyte and the third electrolyte are all a mixture of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.

4. The method according to claim 1, characterized in that: The charging includes charging to 4.2V at a constant current and constant voltage of 0.5C rate; The discharging includes discharging at a constant current of 0.5C to 3V.

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