Formation and air exhaust method of soft package battery after positive electrode lithium supplementation

Abstract

The invention discloses a formation and air exhaust method of a soft package battery after positive electrode lithium supplement. According to the invention, through the design of the cell airbag area, the airbag size of three times of vacuum air extraction sealing is reserved, so that the state of the flexible package cell pole piece group is not influenced by each time of vacuum air extraction sealing. And by matching with a proper formation and air exhaust device, the battery cell can be kept fixed in the clamping plate, and the formed battery cell is subjected to air exhaust and sealing under the condition that the test fixture is not changed. Besides, through step-by-step formation under different multiplying powers and combination of shelving of the battery cell under a fixed voltage, gas generated by the pre-lithiation battery cell added with the positive electrode lithium supplementing agent during first charging is fully generated and discharged in time; the adverse influence on the electrochemical performance of an electrode plate and a battery cell caused by residual gas generated by a solid electrolyte interface film in a battery cell system in the lithium supplement agent decomposition and formation stages is reduced, and the normal exertion of the service life performance of the long-service-life battery cell is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery preparation technology and processes, and particularly to a formation and gas extraction method for a soft-pack battery after positive electrode lithium supplementation. Background Art

[0002] Due to advantages such as high working voltage, high energy density, and long cycle life, lithium-ion batteries have currently been widely used in fields such as new energy vehicles, portable electronic devices, smart grids, and energy storage. The rapid development of the above application fields has put forward higher requirements for performance indicators such as the long endurance ability and high specific energy of lithium-ion batteries. During the first charge and discharge process of a lithium-ion battery, the electrolyte will undergo irreversible decomposition, and a solid electrolyte interface (SEI film) formed on the negative electrode surface will cause irreversible loss of active lithium, resulting in capacity loss of the battery, manifested as a low first Coulomb efficiency and energy density, and affecting the cycle performance of the battery. Based on the lithium supplementation strategy of additionally supplementing active lithium to compensate for the irreversible loss of active lithium in the battery, it helps to exert the energy density of a high-capacity electrode and achieve an improvement in the Coulomb efficiency and cycle life performance of the battery.

[0003] According to different battery manufacturing processes, lithium-ion battery lithium supplementation technologies can be divided into negative electrode lithium supplementation technology and positive electrode lithium supplementation technology. Although the development of negative electrode prelithiation started earlier, the negative electrode lithium supplementation method based on metal lithium materials still has safety risks. The positive electrode lithium supplementation technology can directly add a positive electrode lithium supplement during the slurry preparation process of the positive electrode slurry, and the positive electrode lithium supplement decomposes to release active lithium, thereby achieving compensation for the irreversible loss of active lithium caused by the growth of the negative electrode SEI. The positive electrode lithium supplementation technology has a high compatibility with the existing lithium-ion battery manufacturing process flow, providing a new idea for the large-scale application of lithium-ion battery prelithiation technology.

[0004] Although the positive electrode lithium supplementation technology has gradually started industrial application, the decomposition products, especially gas products, of the positive electrode lithium supplement after the first charge of the battery will remain in the battery system. The gas discharge process technology during battery formation and charge and discharge is still worthy of attention, and the existing technology does not involve the subsequent formation steps of the battery cell. Based on this, it is necessary to propose a series of methods for the formation and gas discharge of positive electrode lithium-supplemented battery cells. Summary of the Invention

[0005] During the first charge and discharge or formation process of a lithium-ion battery using the positive electrode lithium supplementation technology, gas by-products are generated, and the gas products in the battery need to be discharged. In view of this, the present invention provides a formation and gas extraction method for a soft-pack battery after positive electrode lithium supplementation. By optimizing the formation process, carrying out the design of the airbag of the soft-pack battery, and introducing the gas extraction process, it is ensured that the gas products generated after the decomposition of the positive electrode lithium supplement can be discharged from the battery system, avoiding the influence of the remaining gas molecules on the battery electrode sheets and the electrochemical performance of the battery, and improving the cycle life of the battery product.

[0006] In a first aspect, a formation and gas extraction method for a soft-pack battery after lithium supplementation of the positive electrode is provided, including:

[0007] S1. Assemble a positive electrode sheet prepared by using a positive electrode lithium supplementation technique, a negative electrode sheet, and a separator into a cell electrode sheet group, and encapsulate it with an aluminum-plastic film;

[0008] S2. Inject electrolyte. The electrolyte does not fill the entire space inside the aluminum-plastic film to reserve an airbag area inside the aluminum-plastic film. The airbag area can accommodate the gases generated during the formation stage of the soft-pack cell and the decomposition stage of the positive electrode lithium supplement agent. Then, encapsulate the aluminum-plastic film at the first sealing position of the airbag area. The distance from the first sealing position to the cell electrode sheet group is the farthest;

[0009] S3. After the soft-pack cell is statically fixed for a fixed time t1, place the soft-pack cell in a clamping plate for fixation, perform a first constant-current charge on the soft-pack cell. After charging to the cut-off voltage V1, perform a first vacuum gas extraction on the soft-pack cell, and then perform a second sealing on the aluminum-plastic film at the second sealing position of the airbag area. The second sealing position is closer to the cell electrode sheet group than the first sealing position;

[0010] S4. Perform a second constant-current charge on the soft-pack cell. After charging to the cut-off voltage V2, statically fix the soft-pack cell for a fixed time t2, where V2 < V1. Then, perform a second vacuum gas extraction on the battery, and subsequently perform a third sealing on the aluminum-plastic film at the third sealing position of the airbag area. The third sealing position is closer to the cell electrode sheet group than the second sealing position;

[0011] S5. Perform a third constant-current charge on the soft-pack cell to the voltage upper limit V3, statically fix the soft-pack cell for a fixed time t3, where V3 ≤ V2. Then, perform a first constant-current discharge on the soft-pack cell to the voltage lower limit V4, where V4 < V1. Subsequently, change the constant-current charge rate and perform a fourth constant-current charge to the voltage upper limit V2, and then perform a second constant-current discharge to the voltage lower limit V4. Perform three vacuum gas extractions on the soft-pack cell, and then perform a fourth sealing on the aluminum-plastic film at the fourth sealing position of the airbag area. The fourth sealing position is closer to the cell electrode sheet group than the third sealing position.

[0012] Combined with the first aspect, in some implementation manners of the first aspect, the cell electrode sheet group, the positive electrode tab, and the negative electrode tab are encapsulated with an aluminum-plastic film. The positive electrode tab and the negative electrode tab are placed on one side of the aluminum-plastic film and extend out of the aluminum-plastic film, and an airbag area is reserved on the side inside the aluminum-plastic film and away from the positive electrode tab or the negative electrode tab.

[0013] Combined with the first aspect, in some implementation manners of the first aspect, in step S3, the static fixed time t1 is 12 - 24 h, the rate of the first constant-current charge is 0.01 - 0.05 C, and the cut-off voltage V1 of the first constant-current charge is 3.8 - 3.9 V.

[0014] In combination with the first aspect, in certain implementations of the first aspect, in step S4, the second constant current charging rate is 0.02 - 0.05C, the cut-off voltage V2 for the second constant current charging is 4.0 - 4.2V, and the standing fixed time t2 is 6 - 12h.

[0015] In combination with the first aspect, in certain implementations of the first aspect, in step S5, the third constant current charging rate is 0.02 - 0.05C, the third charging cut-off voltage V3 is 4.3 - 4.35V, the standing fixed time t3 is 2 - 4h, the first constant current discharging rate is 0.05C, and the lower limit of the discharging cut-off voltage V4 is 2.75V.

[0016] In combination with the first aspect, in certain implementations of the first aspect, in step S5, the fourth constant current charging rate is 0.1 - 0.2C, and the second constant current discharging rate is 0.1 - 0.2C.

[0017] In combination with the first aspect, in certain implementations of the first aspect, the active material of the positive electrode sheet is one or more composites including lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium manganate, and lithium nickelate.

[0018] In combination with the first aspect, in certain implementations of the first aspect, the positive electrode lithium supplementing agent added to the positive electrode slurry and used to prepare the lithium - supplemented positive electrode sheet is one or more composite ternary lithium - containing lithium supplementing agents including original or surface - coated and modified Li 5 FeO 4 ,Li 2 NiO 2 ,Li 6 CoO 4 ,Li 2 MoO 3 ,Li 8 ZrO 6 and one or more composite organic lithium - containing lithium supplementing agents including lithium oxalate Li 2 C 2 O 4 ,squaric acid lithium Li 2 C 4 O 4 ,organic lithium salt Li 2 DHBN after being original or coated and modified or compounded with a conductive agent.

[0019] In combination with the first aspect, in certain implementations of the first aspect, the active material of the negative electrode sheet is graphite, silicon - oxygen / graphite composite, silicon - carbon / graphite composite, lithium titanate, or metallic lithium negative electrode material.

[0020] In combination with the first aspect, in certain implementations of the first aspect, the electrolyte is composed of a lithium salt, a carbonate solvent, and an additive; among them, the lithium salt is lithium hexafluorophosphate LiPF6 One or more mixtures of lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethanesulfonyl)imide LiTFSI, and lithium difluoro(oxalato)borate LiODFB; the carbonate solvent is one or more mixtures of ethylene carbonate EC, propylene carbonate PC, ethyl methyl carbonate EMC, diethyl carbonate DEC, and dimethyl carbonate DMC; the additive consists of vinylene carbonate VC, 1,3 - propane sultone PS, fluoroethylene carbonate FEC, ethylene sulfate DTD, and lithium difluorophosphate LiPO 2 F 2 One or more mixtures of lithium difluoro(oxalato)phosphate LiDFOP.

[0021] Compared with the prior art, the solution provided by the present invention has at least the following beneficial technical effects:

[0022] Through the design of the airbag area of the battery cell, the size of the airbag for three - time vacuum pumping and sealing is reserved, ensuring that each vacuum pumping and sealing has no impact on the state of the electrode sheet group of the soft - packaged battery cell. In cooperation with an appropriate formation and pumping device, the battery cell can be fixed within the clamping plate, and the formation battery cell can be pumped and sealed under the condition that the test fixture remains unchanged. In addition, through step - by - step formation at different rates, combined with the shelving of the battery cell at a fixed voltage, the gas generated during the first charge of the prelithiated battery cell with a positive - electrode lithium supplement is fully generated and discharged in a timely manner, reducing the decomposition of the lithium supplement and the gas generated by the solid - electrolyte interface film during the formation stage remaining in the battery cell system, which has an adverse impact on the electrode sheet and the electrochemical performance of the battery cell, and ensuring the normal performance of the long - life battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Shows the schematic diagram of the airbag area reserved in the soft - package battery and the sealing position in the present invention.

[0024] Figure 2 Is the flow chart of the formation and pumping method of a positive - electrode lithium - supplemented long - cycle battery of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0026] Refer to Figure 1 and Figure 2 , the present invention provides a method for forming and pumping air of a soft - package battery after positive - electrode lithium supplementation, which is as follows.

[0027] S1. Assemble the positive - electrode sheet prepared by the positive - electrode lithium - supplementation technology, the negative - electrode sheet, and the separator into a battery - cell electrode sheet group, and encapsulate it with an aluminum - plastic film.

[0028] In step S1, the cell electrode assembly consists of a positive electrode plate after adding a lithium supplement agent, a negative electrode plate, and a separator disposed between the positive electrode plate and the negative electrode plate. The cell electrode assembly is prepared by winding or laminating the positive electrode plate, the negative electrode plate, and the separator. The cell electrode assembly is encapsulated with an aluminum-plastic film together with a positive electrode tab and a negative electrode tab. The positive electrode tab and the negative electrode tab are placed on one side of the aluminum-plastic film and protrude from the aluminum-plastic film. A gasbag area is reserved on the side inside the aluminum-plastic film and away from the positive electrode tab or the negative electrode tab. That is to say, the positive electrode tab and the negative electrode tab are arranged on one side in the longitudinal direction of the cell, and the reserved gasbag area is on the other side in the longitudinal direction of the cell.

[0029] S2. Inject electrolyte into the cell, reserve a gasbag area in the cell, and then seal the edge to obtain a soft-packaged cell.

[0030] Inject an appropriate amount of electrolyte into the aluminum-plastic film containing the cell electrode assembly to fully soak the entire cell (both the cell electrode assembly and the lithium supplement source are immersed in the electrolyte). The electrolyte does not fill the entire internal space of the aluminum-plastic film so that gas can be stored in the reserved gasbag area. That is to say, the gasbag area can accommodate the gas generated during the formation stage of the cell and the decomposition stage of the positive lithium supplement agent. Then, the aluminum-plastic film is encapsulated at the first sealing position of the gasbag area. After encapsulation, the cell after electrolyte injection is left standing. As Figure 1 shown, the distance from the first sealing position to the cell electrode assembly is the farthest.

[0031] S3. After the soft-packaged cell is left standing for a fixed time t1, the soft-packaged cell is placed in a clamping plate for fixation, and the soft-packaged cell is subjected to the first constant-current charging. After charging to the cut-off voltage V1, the soft-packaged cell is subjected to the first vacuum pumping, and then the soft-packaged cell is secondarily sealed at the second sealing position of the gasbag area. As Figure 1 shown, the second sealing position is closer to the cell electrode assembly than the first sealing position.

[0032] S4. The soft-packaged cell is subjected to the second constant-current charging. After charging to the cut-off voltage V2, the soft-packaged cell is left standing for a fixed time t2, where V2 < V1. Then, the cell is subjected to the second vacuum pumping, and subsequently, the soft-packaged cell is thirdly sealed at the third sealing position of the gasbag area. As Figure 1 shown, the third sealing position is closer to the cell electrode assembly than the second sealing position.

[0033] S5. The soft-packaged cell is subjected to the third constant-current charging to the voltage upper limit V3, and the soft-packaged cell is left standing for a fixed time t3, where V3 ≤ V2. Then, the soft-packaged cell is first subjected to the first constant-current discharging to the voltage lower limit V4, where V4 < V1. Subsequently, the constant-current charging rate is changed and the fourth constant-current charging is performed to the voltage upper limit V2, and then the second constant-current discharging is performed to the voltage lower limit V4. The soft-packaged cell is subjected to three vacuum pumpings, and then the soft-packaged cell is fourthly sealed at the fourth sealing position of the gasbag area. AsFigure 1 As shown, the fourth sealing position is closer to the electrode group of the battery cell than the third sealing position. Thus, the formation and gas extraction process of the battery cell based on the positive electrode lithium supplement technology is completed.

[0034] In some embodiments, in step S3, the static fixed time t1 is 12 - 24 h.

[0035] In some embodiments, in step S3, the rate of the first constant current charging is 0.01 - 0.05 C, and the cut-off voltage V1 of the first constant current charging is 3.8 - 3.9 V.

[0036] In some embodiments, in step S4, the rate of the second constant current charging is 0.02 - 0.05 C, the cut-off voltage V2 of the second constant current charging is 4.0 - 4.2 V, and the static fixed time t2 is 6 - 12 h.

[0037] In some embodiments, in step S5, the rate of the third constant current charging is 0.02 - 0.05 C, the cut-off voltage V3 of the third charging is 4.3 - 4.35 V, and the static fixed time t3 is 2 - 4 h. Then, the rate of the first constant current discharging is 0.05 C, and the lower limit of the discharging cut-off voltage V4 is 2.75 V; subsequently, the constant current charging / discharging rate is changed to 0.1 - 0.2 C, charged to the voltage V2 and then discharged to the voltage V4, and the soft-packaged battery cell is subjected to vacuum gas extraction, and the formation is completed.

[0038] In some embodiments, the active material of the positive electrode sheet is one or more composites including lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganate, lithium nickelate, etc.

[0039] In some embodiments, the positive electrode lithium supplement agent added to the positive electrode slurry and used to prepare the lithium-supplemented positive electrode sheet is one or more composite ternary lithium-containing lithium supplement agents including original or surface-coated and modified Li 5 FeO 4 , Li 2 NiO 2 , Li 6 CoO 4 , Li 2 MoO 3 , Li 8 ZrO 6 etc., and one or more composite organic lithium-containing lithium supplement agents including original or coated and modified or conductive agent-combined lithium oxalate (Li 2 C 2 O 4 ), lithium squarate (Li 2 C 4 O 4 ), organic lithium salt (Li 2 DHBN), etc.

[0040] In some embodiments, the negative electrode active material is a negative electrode material such as graphite, silicon oxide / graphite composite, silicon carbide / graphite composite, lithium titanate, metallic lithium, etc.

[0041] In some embodiments, the electrolyte is composed of a lithium salt, a carbonate solvent, and an additive. Among them, the lithium salt is one or more mixtures of lithium hexafluorophosphate LiPF 6 , lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethanesulfonyl)imide LiTFSI, lithium difluoro(oxalato)borate LiODFB, etc. The carbonate solvent is one or more mixtures of ethylene carbonate EC, propylene carbonate PC, ethyl methyl carbonate EMC, diethyl carbonate DEC, dimethyl carbonate DMC, etc. The additive is one or more mixtures of vinylene carbonate VC, 1,3 - propane sultone PS, fluoroethylene carbonate FEC, vinylene sulfate DTD, lithium difluorophosphate LiPO 2 F 2 , lithium difluoro(oxalato)phosphate LiDFOP, etc.

[0042] Example 1

[0043] Prepare the battery cell according to the following method and complete the formation and gas extraction steps, and test the initial capacity and cycle performance of the battery cell.

[0044] S1. Assemble the positive electrode sheet prepared by the positive electrode lithium supplement technology, the negative electrode sheet, and the separator into a battery cell electrode sheet group, and encapsulate it with an aluminum-plastic film together with the positive electrode tab and the negative electrode tab. The positive electrode tab and the negative electrode tab are placed on one side of the aluminum-plastic film and protrude from the aluminum-plastic film, and an airbag area is reserved on the side inside the aluminum-plastic film and away from the positive electrode tab or the negative electrode tab.

[0045] S2. Inject an appropriate amount of electrolyte into the aluminum-plastic film containing the battery cell electrode sheet group to fully soak the entire battery cell, and then encapsulate the aluminum-plastic film at the first sealing position of the reserved airbag area. After encapsulation, leave the battery cell after injecting the electrolyte to stand. As Figure 1 shown, the distance from the first sealing position to the battery cell electrode sheet group is the farthest.

[0046] S3. After standing and fixing the soft-packaged battery cell for 12 h, place the soft-packaged battery cell in a clamping plate for fixing, perform the first constant-current charging on the soft-packaged battery cell, the charging rate is 0.05C, the charging cut-off voltage is 3.8V, then perform the first vacuum gas extraction on the soft-packaged battery cell, and perform the second sealing on the soft-packaged battery cell at the second sealing position.

[0047] S4. Continue to perform constant-current charging on the soft-packaged battery cell, the charging rate is 0.05C. After charging to the cut-off voltage of 4.2V, leave the soft-packaged battery cell to stand for 6 h, then perform vacuum gas extraction on the battery, and perform heat sealing on the soft-packaged battery cell at the third sealing position;

[0048] S5. Continue to perform constant-current charging on the soft-packaged battery cell at a charging rate of 0.05C, with the upper limit of the charging voltage being 4.3V. Subsequently, let the soft-packaged battery cell stand for 2h, and then discharge it at a rate of 0.05C until the lower limit voltage of 2.75V. Then change the battery cell rate to 0.1C, perform constant-current charging until the upper limit voltage of 4.2V, and then discharge it at a constant current until the lower limit voltage of 2.75V. After that, perform vacuum pumping on the soft-packaged battery cell and heat-seal it at the fourth sealing position. From this point, completely cut off the airbag area. The free electrolyte and residual gas inside the battery cell are pumped out, and the formation and gas extraction process of the battery cell based on the positive lithium supplement technology are completed.

[0049] In step S1, the positive electrode plate is preferably lithium nickel cobalt aluminate, and the size of the positive electrode plate is 60×100mm. The negative electrode plate is preferably graphite, and the size of the negative electrode plate is 62×104mm. Preferably, a polypropylene separator is used, and the positive electrode, negative electrode, and separator are assembled into a battery cell electrode group by a stacking process. In step S2, the components of the injected electrolyte are: LiPF 6 , EC, PC, EMC, DMC, VC, PS. The molar concentration of LiPF 6 in the electrolyte is 1M. Both the battery cell and the lithium supplement source are immersed in the electrolyte and encapsulated by an aluminum-plastic film.

[0050] Comparative Example 1

[0051] A soft-packaged battery is prepared by a conventional formation and gas extraction process. The specific method is as follows: Prepare the battery cell according to steps S1 and S2 in the embodiment, and reserve the same airbag area. Subsequently, in the formation stage, perform constant-current charge and discharge once at 0.05C, with the voltage range being 2.75 - 4.2V. Then adjust the current rate to 0.1C and perform charge and discharge once in the voltage range of 2.75 - 4.2V. After that, perform vacuum pumping and sealing on the soft-packaged battery cell. The positive electrode plate is preferably lithium nickel cobalt aluminate, and the size of the positive electrode plate is 60×100mm. The negative electrode plate is preferably graphite, and the size of the negative electrode plate is 62×104mm. Preferably, a polypropylene separator is used, and the positive electrode, negative electrode, and separator are assembled into a battery cell electrode group by a stacking process. In step S2, the components of the injected electrolyte are: LiPF 6 , EC, PC, EMC, DMC, VC, PS. The molar concentration of LiPF 6 in the electrolyte is 1M. Both the battery cell and the lithium supplement source are immersed in the electrolyte and encapsulated by an aluminum-plastic film. The battery cell preparation process is the same as that in the embodiment, except for the difference in the formation and gas extraction process flow.

[0052] Test the initial capacity and cycle performance of the battery cell.

[0053] The battery cell capacities and cycle performances obtained from the tests of Example 1 and Comparative Example 1 are shown in Table 1. From the result comparison in Table 1, it can be seen that the cycle performance of the battery cell using the formation and gas extraction process flow in the present invention has been significantly improved.

[0054] Table 1 Test Results of Examples and Comparative Examples

[0055]

[0056] The present invention provides a method for forming and gas extraction of a lithium-ion battery based on a cathode lithium supplement technology. By optimizing the forming process, combining with the airbag design of a soft-pack battery, and introducing a gas extraction process, it is ensured that the gas products generated after the decomposition of the cathode lithium supplement agent can be discharged from the battery system, avoiding the influence of residual gas molecules on the battery electrode sheets and the electrochemical performance of the battery, and improving the cycle life of the battery product. Through the design of the airbag area of the battery cell, the airbag size for three-time vacuum gas extraction and sealing is reserved to ensure that each vacuum gas extraction and sealing has no influence on the state of the electrode sheet group of the soft-pack battery cell. With an appropriate forming and gas extraction device, the battery cell can be fixed within the clamping plate, and the gas extraction and sealing of the formed battery cell can be carried out without changing the test fixture. In addition, through step-by-step forming at different rates, combined with the shelving of the battery cell at a fixed voltage, the battery polarization is further eliminated, and at the same time, the gas generated by the prelithiated battery cell added with the cathode lithium supplement agent during the first charge is fully generated and discharged in time, reducing the adverse effects of the gas remaining in the battery cell system due to the decomposition of the lithium supplement agent and the generation of gas in the solid electrolyte interface film during the forming stage on the electrode sheet and the electrochemical performance of the battery cell, ensuring the normal performance of the long-life battery cell.

[0057] Although the present invention is disclosed above in preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the scope defined in the claims of the present invention.

Claims

1. A formation and evacuation method for a soft-pack battery after positive lithium supplementation, characterized in that: Including: S1. Assemble the positive electrode sheet prepared by the positive electrode lithium supplement technology, the negative electrode sheet and the separator into a battery cell electrode sheet group, and package it with an aluminum-plastic film; S2. Inject the electrolyte. The electrolyte does not fill the entire space inside the aluminum-plastic film, so as to reserve an airbag area inside the aluminum-plastic film. The airbag area can accommodate the gas generated during the formation stage of the soft-packaged battery cell and the decomposition stage of the positive electrode lithium supplement agent. Then, seal the aluminum-plastic film at the first sealing position of the airbag area to prepare a soft-packaged battery cell. The distance from the first sealing position to the battery cell electrode sheet group is the farthest; S3. After the soft-packaged battery cell is left standing for a fixed time t1, place the soft-packaged battery cell in a clamping plate for fixation, perform the first constant current charging on the soft-packaged battery cell. After charging to the cut-off voltage V1, perform the first vacuum pumping on the soft-packaged battery cell. Then, perform the second sealing on the aluminum-plastic film at the second sealing position of the airbag area. The second sealing position is closer to the battery cell electrode sheet group than the first sealing position; S4. Perform the second constant current charging on the soft-packaged battery cell. After charging to the cut-off voltage V2, leave the soft-packaged battery cell standing for a fixed time t2, where V2 < V1. Then, perform the second vacuum pumping on the battery. Subsequently, perform the third sealing on the aluminum-plastic film at the third sealing position of the airbag area. The third sealing position is closer to the battery cell electrode sheet group than the second sealing position; S5. Perform the third constant current charging on the soft-packaged battery cell to the voltage upper limit V3, leave the soft-packaged battery cell standing for a fixed time t3, where V3 ≤ V2. Then, perform the first constant current discharging on the soft-packaged battery cell to the voltage lower limit V4, where V4 < V1. Subsequently, change the constant current charging rate and perform the fourth constant current charging to the voltage upper limit V2, and then perform the second constant current discharging to the voltage lower limit V4. Perform three vacuum pumpings on the soft-packaged battery cell. Then, perform the fourth sealing on the aluminum-plastic film at the fourth sealing position of the airbag area. The fourth sealing position is closer to the battery cell electrode sheet group than the third sealing position.

2. The method according to claim 1, characterized in that The battery cell electrode sheet group, the positive electrode tab and the negative electrode tab are packaged with an aluminum-plastic film. The positive electrode tab and the negative electrode tab are placed on one side of the aluminum-plastic film and protrude from the aluminum-plastic film. An airbag area is reserved on the side inside the aluminum-plastic film and away from the positive electrode tab or the negative electrode tab.

3. The method according to claim 1, characterized in that In step S3, the fixed standing time t1 is 12 - 24 h, the rate of the first constant current charging is 0.01 - 0.05 C, and the cut-off voltage V1 of the first constant current charging is 3.8 - 3.9 V.

4. The method according to claim 1, characterized in that: In step S4, the rate of the second constant current charging is 0.02 - 0.05 C, the cut-off voltage V2 of the second constant current charging is 4.0 - 4.2 V, and the fixed standing time t2 is 6 - 12 h.

5. The method according to claim 1, characterized in that In step S5, the rate of the third constant current charging is 0.02 - 0.05 C, the cut-off voltage V3 of the third charging is 4.3 - 4.35 V, the fixed standing time t3 is 2 - 4 h, the rate of the first constant current discharging is 0.05 C, and the lower limit of the discharging cut-off voltage V4 is 2.75 V.

6. The method according to claim 1, characterized in that In step S5, the rate of the fourth constant current charging is 0.1 - 0.2 C, and the rate of the second constant current discharging is 0.1 - 0.2 C.

7. The method according to claim 1, characterized in that The active material of the positive electrode sheet is one or more complexes including lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium manganate, lithium nickelate.

8. The method according to claim 1, characterized in that The positive electrode lithium replenisher added into the positive electrode slurry to prepare the lithium replenishing positive electrode sheet includes one or more composite ternary lithium-containing replenishers of original or surface-coated modified Li5FeO4, Li2NiO2, Li6CoO4, Li2MoO3, Li8ZrO6, and one or more composite organic lithium-containing replenishers of original or coated modified or conductive agent composite lithium oxalate Li2C2O4), lithium squarate Li2C4O4, and organic lithium salt Li2DHBN.

9. The method according to claim 1, characterized in that: The active materials of the negative electrode sheet are graphite, silicon oxygen / graphite composite, silicon carbon / graphite composite, lithium titanate, and metallic lithium negative electrode materials.

10. The method according to claim 1, characterized in that The electrolyte is composed of lithium salt, carbonate solvent and additives; wherein the lithium salt is a mixture of one or more of lithium hexafluorophosphate LiPF6, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(trifluoromethanesulfonyl)imide LiTFSI and lithium difluorooxalatoborate LiODFB; the carbonate solvent is a mixture of one or more of vinyl carbonate EC, propylene carbonate PC, ethyl methyl carbonate EMC, diethyl carbonate DEC and dimethyl carbonate DMC; the additive is a mixture of one or more of vinylene carbonate VC, 1,3-propanesulfonate PS, fluoroethylene carbonate FEC, vinyl sulfate DTD, lithium difluorophosphate LiPO2F2 and lithium difluorobis(oxalato)phosphate LiDFOP.

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