Lithium supplementing negative electrode sheet and preparation method and application thereof

Abstract

This invention provides a lithium-supplemented anode sheet, its preparation method, and its application. The preparation method includes the following steps: uniformly mixing and fiberizing anode powder to obtain a fiberized mixture; pre-rolling the fiberized mixture to obtain anode preforms; placing the preforms on both sides of a lithium metal foil to form a laminated composite preform; thinning the composite preform by rolling to obtain a composite film; and combining a current collector with the composite film to obtain the lithium-supplemented anode sheet. The composite film comprises two adjacent layers of lithium-supplemented anode active material. This preparation method completely incorporates the lithium foil into the anode active material layers, forming lithium-supplemented anode active material layers. The resulting composite film no longer contains a lithium metal layer, thus solving the lithium residue problem in the prior art and ensuring the production quality of the lithium-supplemented anode sheet.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a lithium-added negative electrode sheet, its preparation method and application. Background Technology

[0002] Lithium foil replenishment is an easily mass-producible method that can improve battery initial efficiency, capacity, energy density, and cycle performance. In existing technologies, to save on battery processing costs, the negative electrode is prepared separately, typically with a thickness of 100–200 μm. Then, lithium foil is stacked on one side of the negative electrode and rolled together with it to form a lithium-replenished negative electrode. For example, CN 112786971A discloses a method for preparing a pre-lithiated lithium-ion battery and the battery itself. The method includes: preparing a negative electrode, a positive electrode, and a separator; and composite lithium metal onto at least one surface of the negative electrode to obtain a composite negative electrode. The lithium metal composite method involves first preparing a negative electrode that can be directly used in a battery system, and then directly pressing purchased lithium metal foil onto the surface of the negative electrode active material layer of the negative electrode to obtain the composite negative electrode.

[0003] However, since the prepared negative electrode sheet has virtually no ductility, on the one hand, if the lithium foil is more ductile than the electrode sheet, it is prone to wrinkling, affecting the production quality of the negative electrode sheet; on the other hand, the thickness of commercial lithium foil is generally 500μm. Directly pressing it with a virtually non-ductile negative electrode sheet makes it difficult to reduce the thickness of the lithium foil, which would lead to excessive lithium replenishment, resulting in lithium source waste and the risk of lithium dendrite growth. Therefore, thinner lithium foil is required for negative electrode lithium replenishment. Currently, the commercially available thickness of lithium foil specifically for battery lithium replenishment is usually around 50-100μm, which is already relatively high in terms of cost and equipment requirements, while 10μm thick lithium foil is already quite expensive.

[0004] However, according to known reports and research, even using 5μm lithium foil for lithium replenishment can lead to over-lithiation and the formation of lithium dendrites. Therefore, it is necessary to further thin the lithium foil, reducing its thickness to below 5μm. However, while lithium metal has good ductility, its strength is poor, and it easily sticks to equipment during the rolling process. Currently, the maximum thickness of lithium foil achievable with existing equipment and processes is only 5–10μm, making it difficult to obtain commercially viable lithium foils below 5μm. This also results in a significant problem of over-lithiation in lithium-replenishing anodes obtained through conventional methods of directly combining the anode sheet and lithium foil. Although existing technologies reduce the amount of lithium replenishment by creating gaps in the lithium foil layer, this leads to uneven lithium replenishment.

[0005] Based on the above research, there is a need to provide a method for preparing a lithium-replenished anode sheet, which can produce a higher quality lithium-replenished anode sheet with sufficient lithium replenishment and no residual lithium metal foil. Summary of the Invention

[0006] The purpose of this invention is to provide a lithium-filled anode sheet, its preparation method, and its application. The preparation method involves co-rolling a thicker anode preform film and a thinner lithium foil. Utilizing the ductility of the thicker anode preform film and the thinner lithium foil, both are rolled together without wrinkles, and the lithium foil can be completely incorporated into the anode sheet, resulting in a high-quality lithium-filled anode sheet. This solves the problems of high cost, high process requirements, and wrinkles caused by rolling of thin lithium foil.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a lithium-added negative electrode sheet, the method comprising the following steps:

[0009] (1) The negative electrode powder is uniformly mixed and fiberized to obtain a fiberized mixture; the fiberized mixture is pre-rolled to obtain a negative electrode preform film;

[0010] (2) The negative electrode preform is disposed on both sides of the lithium metal foil to form a laminated composite preform; the composite preform is rolled thinned to obtain a composite film.

[0011] (3) Combine the current collector with the composite film described in step (2) to obtain the lithium-supplemented negative electrode sheet;

[0012] The composite membrane comprises two adjacent layers of lithium-supplementing anode active material.

[0013] Preferably, the thickness ratio of the negative electrode preform film to the lithium metal foil in step (1) is ≥15.

[0014] Preferably, the thickness ratio of the negative electrode preform film to the lithium metal foil in step (1) is 20-50.

[0015] Preferably, the thickness of the negative electrode membrane in step (1) is >800 μm.

[0016] Preferably, the thickness of the negative electrode membrane in step (1) is 1000-5000 μm.

[0017] Preferably, the thickness of the composite film in step (2) is <500μm.

[0018] Preferably, the thickness of the composite film in step (2) is ≤300μm.

[0019] Preferably, the thickness of the lithium metal foil in step (2) is ≤100μm;

[0020] Preferably, the thickness of the lithium metal foil in step (2) is ≤80μm.

[0021] Preferably, in the negative electrode embryo membrane described in step (1), the areal density of the negative electrode active material is 15-200 mg / cm³. 2 .

[0022] Preferably, the areal density of the lithium foil in step (2) is 0.26-11 mg / cm³. 2 .

[0023] Preferably, the thickness ratio of the negative electrode embryo film to the lithium-supplemented negative electrode active material layer in step (1) is ≥3.

[0024] Preferably, the thickness ratio of the negative electrode embryo film to the lithium-supplemented negative electrode active material layer in step (1) is ≥8.

[0025] Preferably, uniformly mixing and fiberizing the negative electrode powder includes mixing and fiberizing the negative electrode active material, the conductive agent, and the fiberizable binder.

[0026] Preferably, the fiberization method includes any one or a combination of at least two of air jet milling, high-speed mixing, mechanical fusion, or twin-screw extrusion.

[0027] Preferably, the negative electrode active material includes any one or a combination of at least two of the following: graphite, silicon, silicon-graphene, silicon-aluminum alloy, tin-based materials, graphene, pitch carbon microspheres, activated carbon, carbon fiber, graphene, carbon nanotubes, carbon aerogel, transition metal oxides, conductive polymers, lithium-containing compounds, hard carbon materials, or soft carbon materials.

[0028] Preferably, the conductive agent includes any one or a combination of at least two of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0029] Preferably, the fiberizable adhesive comprises any one or a combination of at least two of polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyamide, acrylic plastics, polysulfone, polyphenylene ether, or carboxymethyl cellulose.

[0030] As a preferred embodiment of the preparation method of the present invention, the preparation method includes the following steps:

[0031] (1) The negative electrode powder is uniformly mixed and fiberized to obtain a fiberized mixture; the fiberized mixture is pre-rolled to obtain a negative electrode preform film;

[0032] The thickness of the negative electrode preform film is >800μm, and the areal density of the negative electrode active material in the negative electrode preform film is 15-200mg / cm³. 2 ;

[0033] (2) The negative electrode preform is disposed on both sides of the lithium metal foil to form a laminated composite preform; the composite preform is rolled thinned to obtain a composite film.

[0034] The thickness ratio of the negative electrode preform film to the lithium metal foil is ≥15;

[0035] The thickness of the composite film is <500μm, and the composite film includes two adjacent lithium-supplemented negative electrode active material layers. The ratio of the thickness of the negative electrode preform film to the thickness of the lithium-supplemented negative electrode active material layer in step (1) is ≥3.

[0036] The thickness of the lithium foil is ≤100μm, and the areal density of the lithium foil is 0.26-11mg / cm³. 2 ;

[0037] (3) Combine the current collector with the composite film described in step (2) to obtain the lithium-supplemented negative electrode.

[0038] In a second aspect, the present invention provides a lithium-replenishing anode sheet, which is prepared by the preparation method described in the first aspect.

[0039] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the lithium-filled negative electrode sheet as described in the second aspect.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The present invention stacks a thick negative electrode preform and a lithium foil together. The negative electrode preform has a thicker thickness and thus has better ductility. It can be rolled synchronously with the thinner lithium foil, so that the lithium foil, which is difficult to be further thinned on existing ordinary rolling equipment, can be further stretched. As the negative electrode preform is rolled, the already thin lithium foil is further thinned to the target lithium replenishment thickness and areal density, reducing the limitation on the thickness and areal density of the lithium foil material and achieving lithium replenishment with a lower areal density.

[0042] (2) In this invention, the thick negative electrode preform and the lithium foil are rolled together. Since the negative electrode preform has better mechanical strength, it can provide sufficient mechanical support and connection strength for the lithium foil during the synchronous rolling process, so that the lithium foil can maintain continuity even when it is continuously thinned. This avoids the situation where the lithium foil is crushed or stuck to the roller when the lithium foil is directly rolled in the prior art, thus ensuring the quality of the lithium foil. At the same time, since the thicker negative electrode preform and the thinner lithium foil have better ductility, the electrode sheet is not easy to wrinkle when rolled together.

[0043] (3) Therefore, according to the method for preparing the lithium-replenishing negative electrode sheet of the present invention, by controlling the thickness ratio of the negative electrode preform film to the lithium foil, even under existing ordinary equipment and process conditions, an extremely thin metallic lithium layer with a thickness of less than 5 μm can still be obtained. Since the metallic lithium layer is very thin, it can be completely added into the negative electrode active material layer during the co-rolling process to form a lithium-replenishing negative electrode active material layer. The obtained composite film no longer contains a metallic lithium layer, thereby solving the problem of lithium residue in the prior art and ensuring the production quality of the lithium-replenishing negative electrode sheet. Detailed Implementation

[0044] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0045] In a first aspect, the present invention provides a method for preparing a lithium-added negative electrode sheet, the method comprising the following steps: (1) uniformly mixing and fiberizing negative electrode powder to obtain a fiberized mixture; pre-rolling the fiberized mixture to obtain a negative electrode preform film;

[0046] (2) The negative electrode preform is disposed on both sides of the lithium metal foil to form a laminated composite preform; the composite preform is rolled thinned to obtain a composite film.

[0047] (3) Combine the current collector with the composite film described in step (2) to obtain the lithium-supplemented negative electrode sheet;

[0048] The composite membrane comprises two adjacent layers of lithium-supplementing anode active material.

[0049] This invention, by stacking the negative electrode preform film and lithium foil together, can achieve synchronous rolling with the lithium foil, reducing the limitations on the thickness and areal density of the lithium foil material and achieving lithium replenishment with a lower areal density; and during the co-rolling process, the lithium foil can be completely replenished into the negative electrode active material layer to form a lithium-replenished negative electrode active material layer. The resulting composite film no longer contains a metallic lithium layer, thus solving the problem of lithium residue in the prior art and ensuring the production quality of the lithium-replenished negative electrode sheet.

[0050] In some specific embodiments, the ratio of the thickness of the negative electrode preform film to the thickness of the lithium metal foil in step (1) is ≥15, for example, it can be 15, 20, 40, 60 or 70, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0051] In some specific embodiments, the thickness ratio of the negative electrode preform film to the lithium metal foil in step (1) is 20-50, for example, it can be 20, 30, 40 or 50, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] In some specific embodiments, the thickness of the negative electrode film in step (1) is >800μm, for example, it can be 850μm, 900μm, 1000μm, 2000μm, 4000μm or 6000μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] In some specific embodiments, the thickness of the negative electrode film in step (1) is 1000-5000μm, for example, it can be 1000μm, 2000μm, 3000μm, 4000μm or 5000μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] In some specific embodiments, the thickness of the composite film in step (2) is <500μm, for example, it can be 450μm, 400μm, 300μm, 200μm, 100μm or 50μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] In some specific embodiments, the thickness of the composite film in step (2) is ≤300μm, for example, it can be 300μm, 200μm, 100μm, 50μm or 30μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0056] In some specific embodiments, the thickness of the lithium metal foil in step (2) is ≤100μm, for example, it can be 100μm, 90μm, 80μm, 70μm or 60μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0057] In some specific embodiments, the thickness of the lithium metal foil in step (2) is ≤80μm, for example, it can be 80μm, 70μm, 60μm, 50μm or 40μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0058] In some specific embodiments, the areal density of the negative electrode active material in the negative electrode embryo film described in step (1) is 15-200 mg / cm³. 2 For example, it could be 20 mg / cm³ 2 50mg / cm 2 80mg / cm 2 100mg / cm 2 130mg / cm 2 150mg / cm 2 180mg / cm 2 Or 200mg / cm 2However, this does not limit the listed values; other unlisted values ​​within the range also apply.

[0059] In some specific embodiments, the areal density of the lithium metal foil in step (2) is 0.26-11 mg / cm³. 2 For example, it could be 1 mg / cm³ 2 5mg / cm 2 10mg / cm 2 Or 11mg / cm 2 However, this does not limit the listed values; other unlisted values ​​within the range also apply.

[0060] In order to ensure that the negative electrode preform and lithium foil are easy to roll, the present invention, based on the use of a negative electrode preform and lithium foil of a specific thickness, preferably uses the above-mentioned areal density, thereby further ensuring the ductility of the negative electrode film and lithium foil and ensuring that the thinning can be effectively achieved.

[0061] In some specific embodiments, the ratio of the thickness of the negative electrode preform film to the thickness of the lithium-supplemented negative electrode active material layer in step (1) is ≥3, for example, it can be 3, 5, 8, 10, 12, 15, 18 or 20, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0062] In some specific embodiments, the ratio of the thickness of the negative electrode preform film to the thickness of the lithium-supplemented negative electrode active material layer in step (1) is ≥8, for example, it can be 8, 10, 12, 15, 18 or 20, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0063] In some specific embodiments, uniformly mixing and fiberizing the negative electrode powder includes mixing and fiberizing the negative electrode active material, the conductive agent, and the fiberizable binder.

[0064] In some specific embodiments, the fiberization method includes any one or a combination of at least two of air jet milling, high-speed mixing, mechanical fusion, or twin-screw extrusion.

[0065] In some specific embodiments, the negative electrode active material includes any one or a combination of at least two of the following: graphite, silicon, silicon-graphene, silicon-aluminum alloy, tin-based materials, graphene, pitch carbon microspheres, activated carbon, carbon fiber, graphene, carbon nanotubes, carbon aerogel, transition metal oxides, conductive polymers, lithium-containing compounds, hard carbon materials, or soft carbon materials.

[0066] In some specific embodiments, the conductive agent includes any one or a combination of at least two of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0067] In some specific embodiments, the fiberizable adhesive includes any one or a combination of at least two of polytetrafluoroethylene, polyvinylidene fluoride, polypropylene, polyvinyl chloride, polystyrene, polyoxymethylene, polycarbonate, polyamide, acrylic plastics, polysulfone, polyphenylene ether, or carboxymethyl cellulose.

[0068] As a preferred embodiment of the preparation method, the preparation method includes the following steps:

[0069] (1) The negative electrode powder is uniformly mixed and fiberized to obtain a fiberized mixture; the fiberized mixture is pre-rolled to obtain a negative electrode preform film;

[0070] The thickness of the negative electrode preform film is >800μm, and the areal density of the negative electrode active material in the negative electrode preform film is 15-200mg / cm³. 2 ;

[0071] (2) The negative electrode preform is disposed on both sides of the lithium metal foil to form a laminated composite preform; the composite preform is rolled thinned to obtain a composite film.

[0072] The thickness ratio of the negative electrode preform film to the lithium metal foil is ≥15;

[0073] The thickness of the composite film is <500μm, and the composite film includes two adjacent lithium-supplemented negative electrode active material layers. The ratio of the thickness of the negative electrode preform film to the thickness of the lithium-supplemented negative electrode active material layer in step (1) is ≥3.

[0074] The thickness of the lithium foil is ≤100μm, and the areal density of the lithium foil is 0.26-11mg / cm³. 2 ;

[0075] (3) The current collector is combined with the composite film described in step (2) to obtain the lithium-replenishing anode sheet. In a second aspect, the present invention provides a lithium-replenishing anode sheet, which is prepared by the method described in the first aspect.

[0076] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the lithium-filled negative electrode sheet as described in the second aspect.

[0077] Example 1

[0078] This embodiment provides a method for preparing a lithium-added negative electrode sheet, the method comprising the following steps:

[0079] (1) The negative electrode active material, conductive agent and fiberizable binder are mixed and fiberized, and then pre-pressed to obtain a negative electrode preform film;

[0080] The fiberization method is air jet milling; the negative electrode active material is graphite, the conductive agent is carbon black, and the fiberizable binder is polytetrafluoroethylene;

[0081] (2) The lithium foil is placed between the two negative electrode preforms obtained in step (1), and then rolled together to obtain a composite film, the composite film comprising two layers of lithium-supplementing negative electrode active material layers that are bonded to each other;

[0082] The negative electrode film obtained in step (1) has a thickness of 2000 μm and an areal density of 183 mg / cm³. 2 The lithium foil has a thickness of 100 μm and an areal density of 5.31 mg / cm³. 2 The thickness ratio of the negative electrode preform film to the lithium metal foil is 20;

[0083] (3) The copper foil is combined with the composite film described in step (2) to obtain the lithium-filled negative electrode sheet;

[0084] The composite film has a thickness of 165 μm, with no metallic lithium residue between the two lithium-supplemented anode active material layers. The thickness of a single lithium-supplemented anode active material layer is 82.5 μm, and the ratio of the thickness of the anode preform film to the thickness of the lithium-supplemented anode active material layer is 24.2.

[0085] Example 2

[0086] This embodiment provides a method for preparing a lithium-added negative electrode sheet. The difference between this method and the previous embodiment is that the thickness of the negative electrode preform film in step (1) is 2800 μm and the areal density is 196 mg / cm³. 2 The lithium foil has a thickness of 100 μm and an areal density of 5.31 mg / cm³. 2 ;

[0087] The composite film was prepared with a thickness of 165 μm and contained no residual metallic lithium.

[0088] Example 3

[0089] This embodiment provides a method for preparing a lithium-added negative electrode sheet. The difference between this method and the previous embodiment is that the thickness of the negative electrode preform film in step (1) is 1200 μm and the areal density is 109 mg / cm³. 2 The lithium foil has a thickness of 80 μm and an areal density of 4.17 mg / cm³. 2 ;

[0090] The composite film was prepared with a thickness of 140 μm and contained no residual metallic lithium.

[0091] Example 4

[0092] This embodiment provides a method for preparing a lithium-added negative electrode sheet. The difference between this method and the previous embodiment is that the thickness of the negative electrode preform obtained in step (1) is 2500 μm and the areal density is 190 mg / cm³. 2 The lithium foil has a thickness of 50 μm and an areal density of 2.54 mg / cm³. 2 ;

[0093] The composite film was prepared with a thickness of 170 μm and contained no residual metallic lithium.

[0094] Example 5

[0095] This embodiment provides a method for preparing a lithium-added negative electrode sheet. The difference between this method and the previous embodiment is that the thickness of the negative electrode preform film obtained in step (1) is 900 μm and the areal density is 71 mg / cm³. 2 The lithium foil has a thickness of 30 μm and an areal density of 1.56 mg / cm³. 2 ;

[0096] The composite film was prepared with a thickness of 130 μm and contained no residual metallic lithium.

[0097] Comparative Example 1

[0098] The negative electrode active material, conductive agent and fiberizable binder are mixed and fiberized, and then rolled to obtain a negative electrode film with a thickness of 130 μm.

[0099] A current collector with a thickness of 20 μm is composited onto one side of the negative electrode film obtained in step (1) to obtain a negative electrode sheet;

[0100] A 50 μm thick lithium metal foil is composited onto the other side of the negative electrode film in step (2) to obtain a lithium-replenished negative electrode sheet.

[0101] Among them, the thickness of the lithium metal foil in the lithium-added negative electrode is 49μm, with no significant thinning.

[0102] The thickness of the composite film and the thickness of the lithium foil in the lithium-added anode sheets obtained in the above embodiments and comparative examples are shown in the following table:

[0103] Table 1

[0104]

[0105] As can be seen from the above embodiments and comparative examples:

[0106] The preparation method described in this invention can completely incorporate lithium foil into the negative electrode active material layer, resulting in a negative electrode sheet without any lithium foil residue. Conventional preparation methods cannot effectively reduce the thickness of the lithium foil. Therefore, this invention effectively solves the problem of residual metallic lithium foil and ensures the production quality of lithium-filled negative electrode sheets.

[0107] In summary, this invention provides a lithium-added anode sheet, its preparation method, and its application. The preparation method involves co-rolling a thicker anode preform film and a thinner lithium foil. Utilizing the ductility of both the thicker anode preform film and the thinner lithium foil, they are both rolled without wrinkling after co-rolling. The lithium foil can be stretched to an extremely thin thickness, allowing it to be completely incorporated into the anode active material layer, resulting in a high-quality lithium-added anode sheet with no lithium metal foil residue. This solves the problems of high cost and process requirements in thin lithium foil preparation, wrinkling during rolling, and lithium dendrite formation caused by excessive lithium metal residue.

[0108] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A preparation method of a lithium supplementing negative electrode sheet, characterized by comprising the steps of: 2 ​ (1) uniformly mixing and fiberizing the negative electrode powder to obtain a fiberized mixture; and pre-rolling the fiberized mixture to obtain a negative electrode embryo film; The thickness of the negative electrode embryo film in step (1) is 1000-5000 μm; (2) arranging the negative electrode embryo film on both sides of a metal lithium foil to form a laminated composite embryo film; and rolling and thinning the composite embryo film to obtain a composite film sheet; The thickness of the metal lithium foil in step (2) is ≤100 μm; (3) combining a current collector with the composite film sheet in step (2) to obtain the lithium supplementing negative electrode sheet. The composite film sheet comprises two adjacent lithium supplementing negative electrode active material layers. The thickness of the composite film sheet is ≤300 μm.

2. The production method according to claim 1, characterized by, The ratio of the thickness of the negative electrode embryo film to the thickness of the metal lithium foil in step (1) is ≥15.

3. The preparation method according to claim 2, characterized in that, The ratio of the thickness of the negative electrode embryo film to the thickness of the metal lithium foil in step (1) is 20-50.

4. The method of claim 1, wherein, The thickness of the metal lithium foil in step (2) is ≤80 μm.

5. The preparation method according to claim 1, characterized in that, In the negative electrode precursor film of step (1), the surface density of the negative electrode active material is 15 to 200 mg / cm 2 .

6. The method of claim 1, wherein, The metal lithium foil of step (2) has an area density of 0.26 to 11 mg / cm 2 .

7. The preparation method according to claim 1, characterized in that, The ratio of the thickness of the negative electrode embryo film to the thickness of the lithium supplementing negative electrode active material layer in step (1) is ≥3.

8. The preparation method according to claim 7, characterized in that, The ratio of the thickness of the negative electrode embryo film to the thickness of the lithium supplementing negative electrode active material layer in step (1) is ≥8.

9. The method of claim 1, wherein, The preparation method comprises the following steps: (1) uniformly mixing and fiberizing the negative electrode powder to obtain a fiberized mixture; and pre-rolling the fiberized mixture to obtain a negative electrode embryo film; The thickness of the negative electrode embryonic film is > 800 μm, and the surface density of the negative electrode active material in the negative electrode embryonic film is 15-200 mg / cm 2 ; (2) arranging the negative electrode embryo film on both sides of a metal lithium foil to form a laminated composite embryo film; and rolling and thinning the composite embryo film to obtain a composite film sheet; The ratio of the thickness of the negative electrode embryo film to the thickness of the metal lithium foil is ≥15; The thickness of the composite film sheet is <300 μm, the composite film sheet comprises two adjacent lithium supplementing negative electrode active material layers, and the ratio of the thickness of the negative electrode embryo film to the thickness of the lithium supplementing negative electrode active material layer in step (1) is ≥3; The thickness of the metal lithium foil is ≤ 100 μm, and the area density of the metal lithium foil is 0.26-11 mg / cm 2 ; (3) combining a current collector with the composite film sheet in step (2) to obtain the lithium supplementing negative electrode sheet.

10. A lithium supplementing negative electrode sheet, characterized by comprising: The lithium supplementing negative electrode sheet is prepared by the preparation method in any one of claims 1-9.

11. A lithium-ion battery, characterized by The lithium ion battery comprises the lithium supplementing negative electrode sheet in claim 10. The lithium supplementing negative electrode sheet is prepared by the preparation method in any one of claims 1-9. The lithium ion battery comprises the lithium supplementing negative electrode sheet in claim 10.

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