A method for pre-lithiation of a negative electrode sheet of a lithium-ion battery and a negative electrode sheet of a lithium-ion battery

Abstract

The present invention provides a method for pre-lithiation of a negative electrode sheet of a lithium ion battery and a negative electrode sheet of a lithium ion battery. The method comprises the following steps: calculating and obtaining the required lithium foil area; laying the lithium foil on the surface of the negative electrode sheet, and rolling the lithium foil so that the lithium foil is embedded in the pores of the negative electrode sheet; adding an electrolyte to the negative electrode sheet, and then sealing and standing; applying a planar pressure to the sealed negative electrode sheet so that the lithium foil and the negative electrode sheet react completely to obtain a pre-lithiation negative electrode sheet. The pre-lithiation of the negative electrode is achieved by self-discharge generated by a potential difference, without the need for battery assembly and disassembly steps, simplifying the difficulty of pre-lithiation operation, and the degree of pre-lithiation can be controlled by adjusting the lithium foil capacity and pre-lithiation time, and it has good compatibility with the existing electrode preparation process; the pre-lithiation effect is regulated by controlling the pre-lithiation pressure, the variable is simple and easy to control and no additional energy consumption is required, the process route is simple, and it is conducive to controlling and reducing the production cost of electrode pre-lithiation.

Description

Technical Field

[0001] The invention relates to the technical field of chemical power sources, and in particular to a pre-lithiation method for a negative electrode sheet of a lithium ion battery and a negative electrode sheet of a lithium ion battery. Background Art

[0002] Lithium-ion batteries (LIBs) are widely used in consumer electronics, electric vehicles, and energy storage systems. However, the improvement of their electrochemical efficiency and lifespan still faces challenges. Pre-lithiation technology is an important method for improving the efficiency and extending the service life of LIBs, and is particularly suitable for the development of high energy density batteries. This technology mainly targets the problem of irreversible loss in the first charge and discharge, that is, a large capacity loss (called irreversible capacity loss) will occur in the first cycle, resulting in a decrease in the initial coulombic efficiency of the battery. Therefore, by pre-supplementing the lithium source in the electrode material before the first cycle, the initial coulombic efficiency and the overall cycle stability of the battery can be effectively improved. In LIBs, especially when new negative electrode materials such as silicon-based and graphene are used, the first charge and discharge process will consume a large amount of lithium ions to form a solid electrolyte interface (SEI) film, resulting in low initial coulombic efficiency.

[0003] Pre-lithiation can replenish the lithium source and reduce the irreversible capacity loss in the first cycle, thereby improving the initial coulombic efficiency. In addition, pre-lithiation technology can effectively reduce the lithium loss caused by the formation of SEI film, which is especially important for batteries with large volume changes in negative electrode materials (such as high-capacity silicon negative electrode batteries). The pre-replenished lithium source can help maintain stability in subsequent cycles, thereby extending the service life of the battery. Pre-lithiation technology can also significantly improve the available capacity and energy density of the battery, especially in high energy density application scenarios, by reducing initial cycle losses to achieve higher battery energy output.

[0004] In the prior art, traditional pre-lithiation methods mainly include electrochemical pre-lithiation and chemical pre-lithiation. Electrochemical pre-lithiation requires the negative electrode and lithium metal to be assembled into a half-cell for pre-lithiation, followed by disassembly and reassembly into a full cell. This process is cumbersome and easy to introduce pollution; chemical pre-lithiation usually uses lithium powder, lithium slurry, etc. to directly contact the negative electrode, but there are problems such as the intensity of the reaction is difficult to control and lithium residues affect the electrode structure. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a lithium-ion battery negative electrode sheet pre-lithiation method and a lithium-ion battery negative electrode sheet, aiming to solve the technical problem of poor traditional pre-lithiation effect in the prior art.

[0006] In order to achieve the above object, the present invention is implemented by the following technical scheme: a method for pre-lithiation of a negative electrode sheet of a lithium-ion battery, comprising the following steps: S1, calculating the required lithium foil area according to the type of active material, lithium insertion capacity and lithium foil thickness of the negative electrode sheet of the lithium-ion battery; S2, in an inert atmosphere, laying a lithium foil corresponding to the area of ​​the lithium foil on the surface of the negative electrode sheet; S3, applying pressure to the negative electrode sheet covered with the lithium foil so that the lithium foil contacts the negative electrode sheet, and rolling the lithium foil so that the lithium foil is embedded in the pores of the negative electrode sheet; S4, in an inert atmosphere environment, adding electrolyte to the negative electrode sheet according to the lithium insertion capacity, and then sealing the negative electrode sheet containing the electrolyte through a sealing film and leaving it to stand, so that the lithium ions are evenly diffused; S5, applying a planar pressure to the sealed negative electrode sheet, and leaving the sealed negative electrode sheet to stand under a constant pressure condition to allow the lithium foil to react completely with the negative electrode sheet; S6, cleaning the surface of the negative electrode with a solvent to obtain a pre-lithiated negative electrode sheet.

[0007] According to one aspect of the above technical solution, in step S1, the types of active materials include graphite, carbon silicon alloy and silicon oxide.

[0008] According to one aspect of the above technical solution, in step S1, the calculation expression of the lithium foil area is: ; In the formula, is the area of ​​the lithium foil, is the surface capacity of lithium foil, is the lithium insertion capacity required for pre-lithiation.

[0009] According to one aspect of the above technical solution, in step S2, the step of laying the lithium foil corresponding to the area of ​​the lithium foil on the surface of the negative electrode sheet specifically includes: If the area of ​​lithium foil required for pre-lithiation is smaller than the area of ​​the negative electrode sheet, place the lithium foil in the center of the negative electrode sheet to ensure that there is no overhang at the edge of the lithium foil; If the lithium foil area required for pre-lithiation is larger than the negative electrode sheet area, the lithium foil is cut into a plurality of lithium foil sub-sheets of the same shape, and the lithium foil sub-sheets are stacked layer by layer and placed at the center of the negative electrode sheet.

[0010] According to one aspect of the above technical solution, the step of laying the lithium foil corresponding to the area of ​​the lithium foil on the surface of the negative electrode sheet specifically includes: A lithium foil corresponding to the area of ​​the lithium foil is laid on the surface of the negative electrode sheet through a vacuum adsorbent.

[0011] According to one aspect of the above technical solution, in step S3, the step of rolling the lithium foil specifically includes: The lithium foil is rolled using a horizontal double-roll cold press, wherein the roller spacing is 75%-85% of the total thickness of the negative electrode sheet and the lithium foil.

[0012] According to one aspect of the above technical solution, in step S4, the electrolyte includes a lithium salt, an organic solvent and an additive, the lithium salt is lithium fluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate or lithium diimide; the organic solvent is a carbonate solvent, an ether solvent or an ester solvent, the carbonate solvent is ethylene carbonate, dimethyl carbonate, diethyl carbonate or propylene carbonate, the ether solvent is dimethoxyethane or 1,3-dioxolane, the ester solvent is methyl formate or ethyl acetate, and the additive includes a flame retardant, an overcharge protection additive and a conductive salt additive.

[0013] According to one aspect of the above technical solution, in step S5, the sealing film is an aluminum-plastic film, and the sealing method is heating and melting sealing at normal pressure in an argon atmosphere, the standing temperature is 0°C-28°C, the plane pressure is 0.02Mpa-1Mpa, and the standing time is 6h-72h.

[0014] According to one aspect of the above technical solution, the solvent is a carbonate solvent, an ether solvent or an ester solvent, the carbonate solvent is ethylene carbonate, dimethyl carbonate, diethyl carbonate or propylene carbonate, the ether solvent is dimethoxyethane or 1,3-dioxolane, and the ester solvent is methyl formate or ethyl acetate.

[0015] On the other hand, the present invention further provides a lithium-ion battery negative electrode sheet, which is obtained by pre-lithiation treatment of the lithium-ion battery negative electrode sheet pre-lithiation method described in the above technical solution.

[0016] Compared with the prior art, the beneficial effects of the present invention are: a direct contact pre-lithiation method is adopted. Compared with the traditional pre-lithiation method, this method realizes the pre-lithiation of the negative electrode through self-discharge generated by the potential difference, and does not require battery assembly and disassembly steps, which simplifies the difficulty of pre-lithiation operation. The degree of pre-lithiation can be controlled by adjusting the lithium foil capacity and the pre-lithiation time, and it has good compatibility with the existing electrode preparation process; the pre-lithiation effect is regulated by controlling the pre-lithiation pressure, the variables are simple and easy to control and no additional energy consumption is required, the process route is simple, and it is conducive to controlling and reducing the production cost of electrode pre-lithiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart of a method for pre-lithiation of a negative electrode sheet of a lithium-ion battery according to an embodiment of the present invention; Figure 2 This is a SEM scan of the negative electrode sheet before pre-lithiation in one embodiment of the present invention; Figure 3This is a SEM scan of the negative electrode sheet after pre-lithiation in one embodiment of the present invention; Figure 4 A comparison chart of battery performance of a negative electrode sheet with and without pre-lithiation in one embodiment of the present invention; The following specific implementation manner will further illustrate the present invention in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0018] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0019] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0021] See also Figure 1 , which is a flow chart of a method for pre-lithiation of a negative electrode sheet of a lithium-ion battery in one embodiment of the present invention. Figure 1 As shown, the method comprises the following steps: S1, according to the type of active material, lithium insertion capacity and thickness of lithium foil of the negative electrode sheet of the lithium-ion battery, the required lithium foil area is calculated. Specifically, the type of active material includes graphite, carbon silicon alloy and silicon oxide; the calculation expression of the lithium foil area is: ; In the formula, is the area of ​​the lithium foil, is the surface capacity of lithium foil, The lithium insertion capacity required for pre-lithiation. According to the type of active material of the negative electrode of the selected lithium-ion battery and the theoretical lithium insertion capacity of the negative electrode, the required lithium foil area under a specified thickness is calculated. After the required lithium foil area is calculated, single-layer lithium foil is preferred to meet the lithium insertion capacity requirements, and the use of laminated structures is avoided as much as possible.

[0022] Preferably, in this embodiment, the active material of the negative electrode sheet is graphite, and the required lithium foil capacity is obtained by multiplying the mass of the active material by the pre-lithiation specific capacity (65 mAh / g), and the required 10 um thick lithium foil is cut.

[0023] S2, in an inert atmosphere, laying a lithium foil corresponding to the area of ​​the lithium foil on the surface of the negative electrode sheet. The inert atmosphere is preferably argon, and during laying, it is necessary to ensure that the lithium foil has no wrinkles or damage.

[0024] Specifically, in this embodiment, in step S2, the step of laying the lithium foil corresponding to the area of ​​the lithium foil on the surface of the negative electrode sheet specifically includes: If the area of ​​lithium foil required for pre-lithiation is smaller than the area of ​​the negative electrode sheet, place the lithium foil in the center of the negative electrode sheet to ensure that there is no overhang at the edge of the lithium foil; If the lithium foil area required for pre-lithiation is larger than the negative electrode sheet area, the lithium foil is cut into a plurality of lithium foil sub-sheets of the same shape, and the lithium foil sub-sheets are stacked layer by layer and placed at the center of the negative electrode sheet.

[0025] Preferably, the step of laying the lithium foil corresponding to the area of ​​the lithium foil on the surface of the negative electrode sheet specifically includes: Lithium foil corresponding to the area of ​​the lithium foil is laid on the surface of the negative electrode sheet through a vacuum adsorbent. When the lithium foil area to be covered is large or requires stacking, in order to ensure the integrity of the lithium foil and the uniformity of the coverage, a special tool such as a vacuum adsorbent can be used for covering and laying.

[0026] S3, applying pressure to the negative electrode sheet covered with the lithium foil to make the lithium foil contact with the negative electrode sheet, and rolling the lithium foil to make the lithium foil embedded in the pores of the negative electrode sheet.

[0027] Preferably, in this embodiment, in step S3, the step of rolling the lithium foil specifically includes: The lithium foil is rolled using a horizontal double-roll cold press, wherein the roller spacing is 75%-85% of the total thickness of the negative electrode sheet and the lithium foil.

[0028] After the lithium foil is laid, a certain mechanical pressure is applied to the negative electrode sheet covered with lithium foil to make the lithium foil in close contact with the electrode sheet. The magnitude of the pressure is determined by the characteristics of the negative electrode active material and the lithium foil; then, in an inert atmosphere, the negative electrode sheet covered with lithium foil is sent to a roller press for rolling. The roller spacing of the roller press is adjusted to be slightly smaller than the sum of the thicknesses of the negative electrode sheet and the lithium foil. Repeated rolling is performed to make the lithium foil further in close contact with the electrode sheet and embedded in the surface pores. The rolling process should be carried out at a suitable roller speed and roller spacing to prevent damage to the electrode caused by excessive compression. In this embodiment, the roller spacing of the roller press is 175um.

[0029] S4, in an inert atmosphere, adding electrolyte to the negative electrode sheet according to the lithium insertion capacity, and then sealing the negative electrode sheet containing the electrolyte through a sealing film and leaving it to stand, so that the lithium ions diffuse evenly.

[0030] Preferably, in this embodiment, in step S4, the electrolyte includes a lithium salt, an organic solvent and an additive, the lithium salt is lithium fluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate or lithium diimide; the organic solvent is a carbonate solvent, an ether solvent or an ester solvent, the carbonate solvent is ethylene carbonate, dimethyl carbonate, diethyl carbonate or propylene carbonate, the ether solvent is dimethoxyethane or 1,3-dioxolane, the ester solvent is methyl formate or ethyl acetate, and the additive includes a flame retardant, an overcharge protection additive and a conductive salt additive.

[0031] S5, applying a planar pressure to the sealed negative electrode sheet, and leaving the sealed negative electrode sheet to stand under a constant pressure condition to allow the lithium foil to react completely with the negative electrode sheet.

[0032] In this embodiment, the sealing film is an aluminum-plastic film, and the sealing method is heating and melting sealing at normal pressure in an argon atmosphere, the standing temperature is 0°C-28°C, the plane pressure is 0.02Mpa-1Mpa, and the standing time is 6h-72h. The standing temperature is preferably 0°C, 15°C, 25°C, and 28°C; the standing pressure is preferably 0.02MPa, 0.2MPa, 0.5MPa, and 1Mpa; and the standing time is preferably 6h, 12h, 24h, 36h, 48h, and 72h.

[0033] In this step, 300uL of electrolyte is added to the graphite negative electrode sheet covered with lithium foil and rolled. The electrolyte composition is 1 M LiTFSI in EC:DMC=1:1. The negative electrode sheet containing the electrolyte is sealed with a special membrane to ensure that there is no leakage, gas leakage, etc., and then the sealed negative electrode sheet is placed in a 25°C environment, and then a pressure of 0.02MPa is applied to the packaged graphite negative electrode and kept constant for 36 hours to ensure sufficient insertion and diffusion of lithium ions.

[0034] S6, cleaning the surface of the negative electrode with a solvent to obtain a pre-lithiated negative electrode sheet.

[0035] Preferably, the above-mentioned solvent includes carbonate solvents, ether solvents or ester solvents according to different electrolyte components. The carbonate solvent is ethylene carbonate, dimethyl carbonate, diethyl carbonate or propylene carbonate, the ether solvent is dimethoxyethane or 1,3-dioxolane, and the ester solvent is methyl formate or ethyl acetate.

[0036] Specifically, the graphite negative electrode sheet after lithium insertion is taken out and thoroughly cleaned with ethylene carbonate (EC) to obtain a pre-lithiation-completed graphite negative electrode sheet.

[0037] It should be noted that Figure 2 This is a SEM scan image of the surface morphology of the graphite negative electrode before pre-lithiation. Before pre-lithiation, a loose and porous structure can be observed on the surface of the graphite negative electrode. The layered graphite particles can be clearly observed, and there are clear boundaries between different particles. After pre-lithiation, the surface of the graphite negative electrode ( Figure 3 ) It can be observed that there is obvious layered material coverage. At this time, the surface of the negative electrode becomes smoother and the boundary lines between the graphite particles are no longer as clear as before pre-lithiation.

[0038] The pre-lithiation electrodes were assembled into full batteries and compared with the electrodes before pre-lithiation. Figure 4 The results show that the first-cycle coulombic efficiency of the full battery assembled with pre-lithiation electrodes is significantly higher than that of the battery assembled with non-pre-lithiation electrodes, and the cycle stability is greatly improved, indicating that the pre-lithiation of the negative electrode has achieved ideal results.

[0039] Embodiment 2 The second embodiment of the present invention provides a method for pre-lithiation of a negative electrode sheet of a lithium-ion battery. The principle of the method is basically similar to that of the pre-lithiation method in the first embodiment, except that: In step S1, SiC is selected as the active material of the negative electrode of the lithium-ion battery, and the required lithium foil capacity is obtained by multiplying the mass of the active material by the pre-lithiation specific capacity (300 mAh / g). The corresponding required lithium foil area is 25 um thick lithium foil.

[0040] In step S2, lithium foil is laid in a stacking manner, the lithium foil is cut into a plurality of lithium foil sub-sheets of the same shape, and the lithium foil sub-sheets are stacked layer by layer and placed at the center of the negative electrode sheet.

[0041] In step S3, in an argon atmosphere, a certain pressure is applied to the SiC negative electrode sheet covered with lithium foil in advance to ensure that the lithium foil is in close contact with the negative electrode sheet, and the negative electrode sheet covered with lithium foil is sent to a roller press for roller pressing. The roller spacing of the roller press is adjusted to 255um, which is slightly smaller than the sum of the thickness of the negative electrode sheet and the lithium foil. Repeated roller pressing is performed to make the lithium foil further in close contact with the SiC negative electrode and embedded in the surface pores.

[0042] In steps S4-S5, in an argon atmosphere, 1400uL of electrolyte is added to the SiC negative electrode sheet covered with lithium foil and rolled, and the composition of the electrolyte is 1.5M LiTFSI in EC:DEC=2:1. For ease of understanding, the above 1.5M means that the concentration of LiTFSI in the electrolyte is 1.5 moles per liter, LiTFSI is lithium bis(trifluoromethanesulfonyl imide), EC is ethylene carbonate, and DEC is diethyl carbonate. A special membrane is used to seal the negative electrode sheet containing the electrolyte to ensure that there is no leakage, gas leakage, etc., and then the sealed negative electrode sheet is placed in a 25°C environment; a pressure of 0.5MPa is applied to the packaged SiC negative electrode and maintained constant, and it is left to stand for 72h to ensure that lithium ions are fully embedded and diffused.

[0043] In step S6, the SiC negative electrode sheet after lithium insertion is taken out and is fully cleaned with ethylene carbonate (EC) to obtain a pre-lithiation SiC negative electrode sheet.

[0044] Embodiment 3 The third embodiment of the present invention provides a method for pre-lithiation of a negative electrode sheet of a lithium-ion battery. The principle of the method is basically similar to that of the pre-lithiation method in the first embodiment, except that: In step S1, nano silicon (Si) is selected as the negative electrode active material of the lithium-ion battery, and the required lithium foil capacity is obtained by multiplying the mass of the active material by the pre-lithiation specific capacity (600 mAh / g), and the required 25 um thick lithium foil is cut.

[0045] In step S2, in an argon atmosphere, the lithium foil is cut into a plurality of lithium foil sub-sheets of the same shape by laminating, and each cut lithium foil sub-sheet is evenly and completely laid on the negative electrode surface to ensure that the lithium foil is free of wrinkles and damage during the laying process.

[0046] In step S3, in an argon atmosphere, a certain pressure is applied to the Si negative electrode sheet covered with lithium foil in advance to ensure that the lithium foil is in close contact with the negative electrode sheet, and the negative electrode sheet covered with lithium foil is sent to a roller press for rolling. The roller spacing of the roller press is adjusted to 180um, which is slightly smaller than the sum of the thickness of the negative electrode sheet and the lithium foil. Rolling is repeated to make the lithium foil further in close contact with the Si negative electrode and embedded in the surface pores.

[0047] In steps S4-S5, in an argon atmosphere, add 700uL of electrolyte to the Si negative electrode sheet covered with lithium foil and rolled, and the composition of the electrolyte is 1.5 M LiTFSI in EC:DEC=1:1. Use a special membrane to seal the negative electrode sheet containing the electrolyte to ensure that there is no leakage, gas leakage, etc., and then place the sealed negative electrode sheet in a 25℃ environment; apply a pressure of 1MPa to the packaged Si negative electrode and keep it constant, and let it stand for 48h to ensure sufficient insertion and diffusion of lithium ions.

[0048] In step S6 , the Si negative electrode sheet after lithium insertion is taken out and is fully cleaned with ethylene carbonate (EC) to obtain a pre-lithiation Si negative electrode sheet.

[0049] Embodiment 4 A fourth embodiment of the present invention provides a negative electrode sheet for a lithium-ion battery. The negative electrode sheet for a lithium-ion battery is obtained by a pre-lithiation treatment of the negative electrode sheet pre-lithiation method for a lithium-ion battery described in the above embodiment.

[0050] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0051] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for pre-lithiation of a negative electrode sheet of a lithium-ion battery, characterized in that: The following steps are involved: S1, calculating the required lithium foil area according to the type of active material, lithium insertion capacity and lithium foil thickness of the negative electrode sheet of the lithium-ion battery; S2, in an inert atmosphere, laying a lithium foil corresponding to the area of ​​the lithium foil on the surface of the negative electrode sheet; S3, applying pressure to the negative electrode sheet covered with the lithium foil so that the lithium foil contacts the negative electrode sheet, and rolling the lithium foil so that the lithium foil is embedded in the pores of the negative electrode sheet; S4, in an inert atmosphere environment, adding electrolyte to the negative electrode sheet according to the lithium insertion capacity, and then sealing the negative electrode sheet containing the electrolyte through a sealing film and leaving it to stand, so that the lithium ions are evenly diffused; S5, applying a planar pressure to the sealed negative electrode sheet, and leaving the sealed negative electrode sheet to stand under a constant pressure condition to allow the lithium foil to react completely with the negative electrode sheet; S6, cleaning the surface of the negative electrode with a solvent to obtain a pre-lithiated negative electrode sheet.

2. The method for pre-lithiation of a negative electrode sheet of a lithium-ion battery according to claim 1, characterized in that: In step S1, the active material types include graphite, carbon silicon alloy and silicon oxide.

3. The method for pre-lithiation of a negative electrode sheet of a lithium-ion battery according to claim 1, characterized in that: In step S1, the calculation expression of the lithium foil area is: ； In the formula, is the area of ​​the lithium foil, is the surface capacity of lithium foil, is the lithium insertion capacity required for pre-lithiation.

4. The method for pre-lithiation of a negative electrode sheet of a lithium-ion battery according to claim 1, characterized in that: In step S2, the step of laying the lithium foil corresponding to the area of ​​the lithium foil on the surface of the negative electrode sheet specifically includes: If the area of ​​lithium foil required for pre-lithiation is smaller than the area of ​​the negative electrode sheet, place the lithium foil in the center of the negative electrode sheet to ensure that there is no overhang at the edge of the lithium foil; If the lithium foil area required for pre-lithiation is larger than the negative electrode sheet area, the lithium foil is cut into a plurality of lithium foil sub-sheets of the same shape, and the lithium foil sub-sheets are stacked layer by layer and placed at the center of the negative electrode sheet.

5. The method for pre-lithiation of a negative electrode sheet of a lithium-ion battery according to claim 4, characterized in that: The step of laying the lithium foil corresponding to the area of ​​the lithium foil on the surface of the negative electrode sheet specifically includes: A lithium foil corresponding to the area of ​​the lithium foil is laid on the surface of the negative electrode sheet through a vacuum adsorbent.

6. The method for pre-lithiation of a negative electrode sheet of a lithium-ion battery according to claim 1, characterized in that: In step S3, the step of rolling the lithium foil specifically includes: The lithium foil is rolled using a horizontal double-roll cold press, wherein the roller spacing is 75%-85% of the total thickness of the negative electrode sheet and the lithium foil.

7. The method for pre-lithiation of a negative electrode sheet of a lithium-ion battery according to claim 1, characterized in that: In step S4, the electrolyte includes a lithium salt, an organic solvent and an additive, the lithium salt is lithium fluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate or lithium diimide; the organic solvent is a carbonate solvent, an ether solvent or an ester solvent, the carbonate solvent is ethylene carbonate, dimethyl carbonate, diethyl carbonate or propylene carbonate, the ether solvent is dimethoxyethane or 1,3-dioxolane, the ester solvent is methyl formate or ethyl acetate, and the additive includes a flame retardant, an overcharge protection additive and a conductive salt additive.

8. The method for pre-lithiation of a negative electrode sheet of a lithium-ion battery according to claim 1, characterized in that: In step S5, the sealing film is an aluminum-plastic film, and the sealing method is heating and melting sealing at normal pressure in an argon atmosphere, the standing temperature is 0°C-28°C, the plane pressure is 0.02Mpa-1Mpa, and the standing time is 6h-72h.

9. The method for pre-lithiation of a negative electrode sheet of a lithium-ion battery according to claim 1, characterized in that: The solvent is a carbonate solvent, an ether solvent or an ester solvent. The carbonate solvent is ethylene carbonate, dimethyl carbonate, diethyl carbonate or propylene carbonate. The ether solvent is dimethoxyethane or 1,3-dioxolane. The ester solvent is methyl formate or ethyl acetate.

10. A negative electrode sheet for a lithium-ion battery, characterized in that: The lithium-ion battery negative electrode sheet is obtained by pre-lithiation treatment of the lithium-ion battery negative electrode sheet pre-lithiation method according to any one of claims 1 to 9.

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