A negative electrode sheet, its preparation method, and a lithium-ion battery

Abstract

This invention provides a negative electrode sheet, its preparation method, and a lithium-ion battery. The negative electrode sheet includes a silicon-containing negative electrode and a gel polymer layer covering one side of the silicon-containing negative electrode. The gel polymer layer comprises a dual-network structure formed by the physical entanglement of an ionic crosslinking network of a copolymer containing guluronic acid and an ion-conducting polymer. The crosslinking network of the copolymer containing guluronic acid includes metal salt cations; the metal salts include calcium and / or aluminum salts. The gel polymer layer on the surface of the negative electrode sheet can complex transition metal ions dissolved from the positive electrode, inhibiting their damage to the SEI on the electrode surface and reducing side reactions in the electrolyte. The gel polymer layer has excellent mechanical properties, which can suppress the peeling of active material from the electrode sheet due to volume changes in the silicon-based negative electrode during cycling. The Ca introduced during the preparation of the gel protective layer... 2+ Al 3+ Plasma can form an alloying reaction with silicon-based anodes during the formation stage, improving the cycle performance of the battery cell.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and relates to a negative electrode sheet, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] With the development of the new energy industry, the demand for high specific energy lithium ion batteries is becoming more and more urgent. Common high specific energy cells mainly use lithium-rich manganese-based layered oxides and high-nickel ternary materials as positive electrode materials, and silicon-carbon composite graphite or lithium metal as negative electrode materials. At present, high specific energy positive electrode materials such as lithium-rich manganese-based layered oxides (Li 1+x [NiMnCo] 1-x O2, LMR-NMC) or ternary materials (NCM) are prone to transition metal ion dissolution during the cycle process, especially under high temperature or high voltage conditions, due to irreversible phase transition of the bulk material, ion mixing, or HF corrosion in the electrolyte. Transition metal ions have strong catalytic activity and can accelerate the decomposition of electrolyte, destroy the SEI structure on the surface of the electrode sheet, increase the interface impedance, and increase the possibility of cell swelling.

[0003] Therefore, the influence of transition metal ions generated by high specific energy positive electrode materials of lithium ion batteries on battery performance, and the performance degradation and safety risk of the cell caused by the volume change of high specific energy negative electrodes are problems that need to be solved. SUMMARY

[0004] In view of the problems in the prior art, the present application provides a negative electrode sheet with a high molecular gel polymer layer on the surface. The gel polymer layer on the surface of the negative electrode sheet can complex transition metal ions dissolved from the positive electrode, inhibit the destruction of the SEI on the surface of the electrode sheet, and reduce the side reactions of the electrolyte. At the same time, the gel polymer layer has excellent mechanical properties and can inhibit the peeling of active materials from the electrode sheet due to the volume change of silicon-based negative electrodes during the cycle process. In addition, the gel polymer layer introduces Ca 2+ , Al 3+ ions during the preparation process, which can form an alloying reaction with the silicon-based negative electrode during the formation stage, further improving the cycle performance of the cell.

[0005] To achieve this purpose, the present application adopts the following technical solutions:

[0006] In a first aspect, the present application provides a negative electrode sheet, which comprises a silicon-containing negative electrode and a gel polymer layer covering one side of the silicon-containing negative electrode, wherein the gel polymer layer comprises a double network structure formed by an ionically cross-linked network of a guluronic acid-containing copolymer and a physically entangled ion-conducting polymer, and the ionically cross-linked network of the guluronic acid-containing copolymer comprises cations of a metal salt; and the metal salt comprises a calcium metal salt and / or an aluminum metal salt.

[0007] In a preferred embodiment of the present application, the thickness of the gel polymer layer is 0.1 μm to 5 μm.

[0008] In a preferred embodiment of the present application, the mass ratio of the guluronic acid-containing copolymer, the metal salt and the ion-conducting polymer is (1-10):(0.1-1):(1-5).

[0009] In a preferred embodiment of the present application, the mass content of guluronic acid in the guluronic acid-containing copolymer is 10 wt% to 80 wt%.

[0010] In a preferred embodiment of the present application, the weight average molecular weight of the ion-conducting polymer is 800 to 200000.

[0011] In a preferred embodiment of the present application, the guluronic acid-containing copolymer comprises sodium alginate and / or fucoidan.

[0012] In a preferred embodiment of the present application, the ion-conducting polymer comprises any one or a combination of at least two of polyethylene oxide, polyacrylonitrile, polymethyl methacrylate or polyvinylidene fluoride and a copolymer thereof.

[0013] In a preferred embodiment of the present application, the calcium metal salt comprises any one or a combination of at least two of calcium chloride, calcium nitrate, calcium sulfate or calcium bis(fluorosulfonyl)imide.

[0014] In a preferred embodiment of the present application, the aluminum metal salt comprises aluminum nitrate and / or aluminum chloride.

[0015] In a second aspect, the present application provides a preparation method of the aforementioned negative electrode sheet, when the ion-conducting polymer is water-soluble, the preparation method comprises:

[0016] (1) configuring the ion-conducting polymer and the guluronic acid-containing copolymer into a solution A, and configuring a metal salt solution B;

[0017] (2) coating the solution A and the metal salt solution B on the surface of the silicon-containing negative electrode in sequence, standing, drying to obtain the negative electrode sheet.

[0018] In a preferred embodiment of the present application, the mass ratio of the ion-conducting polymer and the guluronic acid-containing copolymer in step (1) is (1-5):1.

[0019] As a preferred scheme of the present application, the solid content of solution A in step (1) is 0.6wt%-4wt%.

[0020] As a preferred scheme of the present application, the solvent of solution A in step (1) is water.

[0021] As a preferred scheme of the present application, the concentration of metal salt solution B in step (1) is 0.01mol / L-2mol / L.

[0022] As a preferred scheme of the present application, the solvent of metal salt solution B in step (1) is water.

[0023] As a preferred scheme of the present application, the mass ratio of solution A and metal salt solution B in step (2) is (2-5):1

[0024] As a preferred scheme of the present application, the coating method in step (2) includes spraying and / or doctor blading.

[0025] As a preferred scheme of the present application, the overall thickness of solution A and metal salt solution B after coating in step (2) is 0.1μm-5μm.

[0026] As a preferred scheme of the present application, the standing time in step (2) is 10h-48h.

[0027] As a preferred scheme of the present application, the pressure of drying in step (2) is < -0.1MPa.

[0028] As a preferred scheme of the present application, the temperature range of drying in step (2) is 75℃-95℃.

[0029] As a preferred scheme of the present application, the time of drying in step (2) is 20h-48h.

[0030] In a third aspect, the present application provides a preparation method of the aforementioned negative electrode tab, when the ion-conducting polymer is water-insoluble, the preparation method comprises:

[0031] (a) preparing a solution containing a guluronate-containing copolymer, an ion-conducting polymer solution and a metal salt solution, respectively;

[0032] (b) coating the solution containing a guluronate-containing copolymer and the metal salt solution on the surface of the silicon-containing negative electrode in turn, performing first drying, coating the ion-conducting polymer solution, standing, performing second drying, and obtaining the negative electrode tab.

[0033] As a preferred scheme of the present application, the concentration of the solution containing a guluronate-containing copolymer in step (a) is 0.2wt%-2wt%.

[0034] As a preferred scheme of the present application, the solvent in the solution of the guluronic acid-containing copolymer in step (a) is water.

[0035] As a preferred scheme of the present application, the concentration of the solution of the ion-conducting polymer in step (a) is 0.5wt%-2wt%.

[0036] As a preferred scheme of the present application, the solvent of the solution of the ion-conducting polymer in step (a) is an oily solvent, including N-methyl pyrrolidone (NMP) and / or N,N-dimethylformamide (DMP).

[0037] As a preferred scheme of the present application, the concentration of the solution of the metal salt in step (a) is 0.01mol / L-2mol / L.

[0038] As a preferred scheme of the present application, the solvent of the solution of the metal salt in step (a) is water.

[0039] As a preferred scheme of the present application, the mass ratio of the guluronic acid-containing copolymer, the metal salt and the ion-conducting polymer in step (a) is (1-10):(0.1-1):(1-5).

[0040] As a preferred scheme of the present application, the coating method in step (b) includes spraying and / or doctor blading.

[0041] As a preferred scheme of the present application, the temperature of the first-time drying in step (b) is 95℃-100℃, and the time of the first-time drying is 7h-10h.

[0042] As a preferred scheme of the present application, the overall coating thickness of the solution of the guluronic acid-containing copolymer, the solution of the metal salt and the solution of the ion-conducting polymer in step (b) is 0.1μm-5μm.

[0043] As a preferred scheme of the present application, the standing time in step (b) is 10h-12h.

[0044] As a preferred scheme of the present application, the pressure of the second-time drying in step (b) is <-0.1MPa.

[0045] As a preferred scheme of the present application, the temperature range of the second-time drying in step (b) is 75℃-95℃.

[0046] As a preferred scheme of the present application, the time of the second-time drying in step (b) is 20h-48h.

[0047] In a fourth aspect, the present application provides a lithium ion battery, wherein the negative electrode sheet of the lithium ion battery is the aforementioned negative electrode sheet.

[0048] Compared with the prior art, the present application has the following beneficial effects:

[0049] During the cycling of the battery cell, the gel polymer layer has excellent elasticity and toughness due to its special network structure, can inhibit the volume expansion of the silicon-containing negative electrode sheet, and avoid the active particles from being separated from the current collector. The ion-conducting polymer in the gel polymer layer helps the lithium ion transmission, and the copolymer containing guluronate can adsorb transition metal ions dissolved from the positive electrode. In addition, the copolymer containing guluronate can form an elastic "egg box" structure with the cations of the metal salt, and the metal multivalent cations in the "egg box" structure can form an alloy reaction with the silicon-based active material in the formation stage, thereby improving the electrochemical performance of the active material. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 The negative electrode sheet structure described in Example 1 of the present application;

[0051] Figure 2 The schematic diagram of the interaction between the copolymer containing guluronate and metal ions in the present application;

[0052] Figure 3 The schematic diagram of the interaction between the gel polymer and the ion-conducting polymer in the present application;

[0053] In the figure, 1 is a silicon-containing negative electrode, and 2 is a gel polymer layer. DETAILED DESCRIPTION

[0054] In order to better illustrate the present application and facilitate the understanding of the technical solutions of the present application, the present application will be further described in detail below. However, the following examples are only simple examples of the present application, and do not represent or limit the protection scope of the present application. The protection scope of the present application is subject to the claims.

[0055] In a first aspect, the detailed description part of the present application provides a negative electrode sheet, which comprises a silicon-containing negative electrode and a gel polymer layer covering one side of the silicon-containing negative electrode. The gel polymer layer comprises a double network structure formed by an ionically cross-linked network of a copolymer containing guluronate and a physical entanglement of an ion-conducting polymer. The ionically cross-linked network of the copolymer containing guluronate comprises cations of a metal salt. The metal salt comprises a calcium metal salt and / or an aluminum metal salt.

[0056] The silicon-containing negative electrode is a conventional silicon-containing negative electrode in a lithium ion battery. The thickness of the silicon-containing negative electrode can be 80 μm-110 μm.

[0057] In the present application, the copolymer containing guluronate (G unit) is cross-linked to form a gel polymer with an "egg box" structure under the action of metal ions (such as Ca 2+ , Al 3 + ) in a metal salt. Figure 2As shown, the gel polymer physically entangles with the ion-conductive polymer to form a network of interpenetrating gel polymer network structure. The Na + In addition to replacing Ca 2+ , Al 3+ , the copolymer containing guluronic acid (G unit) can also complex the Mn ions precipitated during the cycle of lithium ion battery, as shown. The copolymer containing guluronic acid is sensitive to the transition metal ions generated during the cycle of high-energy positive electrode material, and can complex the transition metal ions dissolved from the positive electrode material under high temperature and high pressure conditions to avoid triggering the side reactions on the negative electrode side. Figure 3

[0058] The multivalent metal ions M (such as Ca 2+ , Al 3+ ) in the gel polymer layer can form Li-M-Si ternary phases in situ during the charge and discharge process of the battery. These phases have lower chemical reactivity, can stabilize the Si anion, reduce the electrolyte side reaction, and thus improve the cycle stability, for example: Ca 2+ dominates surface passivation, Ca 2+ is more likely to react with the interface to form CaF2, forming a high-strength inorganic layer. And, as the calcium bisfluorosulfonylimide is used, the bisfluorosulfonylimide anion decomposes on the silicon negative electrode side to form an inorganic-rich SEI film, which helps to improve the cycle life of the lithium ion battery.

[0059] The ion-conductive polymer swells when it encounters electrolyte, which is conducive to lithium ion migration.

[0060] As a preferred scheme of the present application, the thickness of the gel polymer layer is 0.1 μm-5 μm, for example, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, etc., but not limited to the listed values, other values not listed in this range are also applicable.

[0061] ​As a preferred scheme of the present application, the mass ratio of the guluronic acid-containing copolymer, the metal salt and the ion-conducting polymer is (1-10):(0.1-1):(1-5), for example, 2:(0.1-1):(1-5), 3:(0.1-1):(1-5), 4:(0.1-1):(1-5), 5:(0.1-1):(1-5), 6:(0.1-1):(1-5), 7:(0.1-1):(1-5), 8:(0.1-1):(1-5), 9:(0.1-1):(1-5), (1-10):0.2:(1-5), (1-10):0.4:(1-5), (1-10):0.6:(1-5), (1-10):0.8:(1-5), (1-10):(0.1-1):2, (1-10):(0.1-1):3 or (1-10):(0.1-1):4, etc., but not limited to the listed values, and other values not listed in the range are also applicable. The mass of the guluronic acid-containing copolymer refers to the mass of such copolymers as sodium alginate and / or fucoidan.

[0062] As a preferred scheme of the present application, the mass content of guluronic acid in the guluronic acid-containing copolymer is 10wt%-80wt%, for example, 15wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, 70wt% or 80wt%, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0063] As a preferred scheme of the present application, the weight average molecular weight of the ion-conducting polymer is 800-200000, for example, 800, 900, 1000, 3000, 5000, 7000, 10000, 30000, 50000, 100000, 150000 or 200000, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0064] In the present application, if the molecular weight of the ion-conducting polymer is too low, the molecular chains are poorly entangled, and lack of toughness, and cannot protect the negative electrode sheet; if the molecular weight is too high, the lithium ion migration is difficult, and the number of lithium ion migration is reduced.

[0065] As a preferred scheme of the present application, the guluronic acid-containing copolymer includes sodium alginate and / or fucoidan. Both the sodium alginate and the fucoidan are composed of two structural units, guluronic acid (G unit) and mannuronic acid (M unit), and the G unit plays a role in the present application.

[0066] As a preferred scheme of the present application, the ion-conducting polymer comprises any one or a combination of at least two of polyethylene oxide, polyacrylonitrile, polymethyl methacrylate or polyvinylidene fluoride and a copolymer thereof.

[0067] As a preferred scheme of the present application, the metal calcium salt comprises any one or a combination of at least two of calcium chloride, calcium nitrate, calcium sulfate or calcium bisfluorosulfonylimide. Among them, the calcium chloride can be anhydrous calcium chloride or calcium chloride dihydrate.

[0068] As a preferred scheme of the present application, the metal aluminum salt comprises aluminum nitrate and / or aluminum chloride. Among them, the aluminum nitrate can be aluminum nitrate nonahydrate.

[0069] In the second aspect, the detailed description part provides a preparation method of the foregoing negative electrode tab. When the ion-conducting polymer is water-soluble, the preparation method comprises:

[0070] (1) configuring the ion-conducting polymer and the copolymer containing guluronic acid into solution A, and configuring a metal salt solution B;

[0071] (2) coating solution A and the metal salt solution B on the surface of the silicon-containing negative electrode in sequence, standing, drying to obtain the negative electrode tab.

[0072] As a preferred scheme of the present application, the mass ratio of the ion-conducting polymer and the copolymer containing guluronic acid in step (1) is (1-5):1, for example 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, etc., but not limited to the listed values, and other values not listed in the value range are also applicable.

[0073] In the present application, if the content of the ion-conducting polymer is too low, the formed gel polymer layer has poor elasticity, which is not conducive to inhibiting the volume expansion of the silicon negative electrode tab; if the content of the ion-conducting polymer is too high, the crosslinking degree is large, the impedance is large, and too high ion-conducting polymer will destroy the gel structure.

[0074] As a preferred scheme of the present application, the solid content of solution A in step (1) is 0.6wt%-4wt%, for example 0.6wt%, 0.8wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt% or 4wt%, etc., but not limited to the listed values, and other values not listed in the value range are also applicable.

[0075] As a preferred scheme of the present application, the solvent in solution A in step (1) is water.

[0076] As a preferred scheme of the present application, the concentration of the metal salt solution B in step (1) is 0.01 mol / L-2 mol / L, for example, 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L or 2 mol / L, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0077] In the present application, when the concentration of the metal salt solution is too low, the copolymer containing guluronic acid (such as sodium alginate and / or fucoidan) cannot be effectively crosslinked; when the concentration of the metal salt solution is too high, a gel polymer with high molecular weight is formed, which increases the migration resistance of lithium ions and degrades the performance of lithium ion batteries.

[0078] As a preferred scheme of the present application, the solvent of the metal salt solution B in step (1) is water.

[0079] As a preferred scheme of the present application, the mass ratio of solution A and metal salt solution B in step (2) is (2-5):1, for example, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0080] As a preferred scheme of the present application, the coating method in step (2) includes spraying and / or blade coating. Immersion method cannot be used, and for water-based solvents, immersion will damage the pole piece.

[0081] As a preferred scheme of the present application, the overall thickness of solution A and metal salt solution B after coating in step (2) is 0.1 μm-5 μm, for example, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0082] As a preferred scheme of the present application, the standing time in step (2) is 10 h-48 h, for example, 10 h, 12 h, 14 h, 16 h, 20 h, 24 h, 26 h, 30 h, 34 h, 36 h, 40 h, 44 h or 48 h, etc., but not limited to the listed values, and other values not listed in the range are also applicable. The purpose of standing is to fully gel the copolymer containing guluronic acid and the metal salt.

[0083] As a preferred scheme of the present application, the pressure for drying in step (2) is < -0.1 MPa, for example, -0.3 MPa, -0.5 MPa, -0.7 MPa, or -1 MPa, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0084] In the present application, drying is performed under the pressure range, aiming to accelerate water vaporization and volatilization.

[0085] As a preferred scheme of the present application, the temperature range for drying in step (2) is 75-95℃, for example, 75℃, 77℃, 80℃, 83℃, 85℃, 87℃, 90℃, 93℃, or 95℃, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0086] As a preferred scheme of the present application, the time for drying in step (2) is 20-48 h, for example, 20 h, 22 h, 24 h, 26 h, 28 h, 30 h, 32 h, 34 h, 36 h, 38 h, 40 h, 42 h, 44 h, 46 h, or 48 h, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0087] Further, drying in step (2) is segmented drying, including first-stage drying and second-stage drying, the temperature for first-stage drying is 50-60℃, and the drying time is 2-4 h; the temperature for second-stage drying is 80-95℃, and the drying time is 24-48 h. Segmented drying can prevent the negative electrode surface film from being condensed too fast due to too fast drying speed.

[0088] In a third aspect, the detailed description part of the present application provides a preparation method of the aforementioned negative electrode sheet, when the ion-conducting polymer is non-water-soluble, the preparation method comprises:

[0089] (a) preparing a solution containing a guluronic acid-containing copolymer, a solution of an ion-conducting polymer, and a solution of a metal salt, respectively;

[0090] (b) coating the solution containing the guluronic acid-containing copolymer and the solution of the metal salt on the surface of the silicon-containing negative electrode in sequence, performing first-stage drying, coating the solution of the ion-conducting polymer, standing, performing second-stage drying, and obtaining the negative electrode sheet.

[0091] In the present application, when the solution containing the guluronic acid-containing copolymer, the solution of the metal salt, and the solution of the ion-conducting polymer are coated in sequence, the solution containing the guluronic acid-containing copolymer first reacts with metal ions in the solution of the metal salt to form a gel polymer with an “egg box” structure, and then physically entangles with the ion-conducting polymer at the interface to form a double-network structure with network interpenetration.

[0092] As a preferred embodiment of the present application, the solution concentration of the guluronic acid-containing copolymer in step (a) is 0.2 wt% to 2 wt%, such as 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, or 2 wt%, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0093] As a preferred embodiment of the present application, the solvent in the guluronic acid-containing copolymer solution in step (a) is water.

[0094] As a preferred embodiment of the present application, the concentration of the ionic polymer solution in step (a) is 0.5 wt% to 2 wt%, such as 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, or 2.0 wt%, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0095] As a preferred embodiment of the present application, the solvent of the ionic polymer solution in step (a) is an oily solvent, including N-methyl pyrrolidone (NMP) and / or N,N-dimethylformamide (DMP).

[0096] As a preferred embodiment of the present application, the concentration of the metal salt solution in step (a) is 0.01 mol / L to 2 mol / L, such as 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, or 2 mol / L, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0097] As a preferred embodiment of the present application, the solvent of the metal salt solution in step (a) is water.

[0098] As a preferred scheme of the present application, the mass ratio of the guluronic acid-containing copolymer, the metal salt and the ion-conducting polymer in step (a) is (1-10):(0.1-1):(1-5), such as 2:(0.1-1):(1-5), 3:(0.1-1):(1-5), 4:(0.1-1):(1-5), 5:(0.1-1):(1-5), 6:(0.1-1):(1-5), 7:(0.1-1):(1-5), 8:(0.1-1):(1-5), 9:(0.1-1):(1-5), (1-10):0.2:(1-5), (1-10):0.4:(1-5), (1-10):0.6:(1-5), (1-10):0.8:(1-5), (1-10):(0.1-1):2, (1-10):(0.1-1):3 or (1-10):(0.1-1):4, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0099] In the present application, when the concentration of the metal salt solution is too low, the guluronic acid-containing copolymer (such as sodium alginate and / or oligo-fucoidan) cannot effectively form cross-linking; when the concentration of the metal salt solution is too high, a gel polymer with high molecular weight is formed, which increases the migration resistance of lithium ions and deteriorates the performance of the lithium ion battery.

[0100] As a preferred scheme of the present application, the coating method in step (b) includes spraying and / or blade coating.

[0101] As a preferred scheme of the present application, the temperature of the first drying in step (b) is 95-100°C, such as 95°C, 96°C, 97°C, 98°C, 99°C or 100°C, etc., but not limited to the listed values, and other values not listed in the range are also applicable; the time of the first drying is 7-10h, such as 7h, 8h, 9h or 10h, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0102] As a preferred scheme of the present application, the overall coating thickness of the guluronic acid-containing copolymer solution, the metal salt solution and the ion-conducting polymer solution in step (b) is 0.1-5μm, such as 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 4μm or 5μm, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0103] As a preferred scheme of the present application, the standing time in step (b) is 10h-12h, such as 10h, 10.5h, 11h, 11.5h or 12h, etc., but is not limited to the listed values, and other values not listed within the range are also applicable.

[0104] As a preferred scheme of the present application, the pressure of the second drying in step (2) is <-0.1MPa, such as -0.3MPa, -0.5MPa, -0.7MPa or -1MPa, etc., but is not limited to the listed values, and other values not listed within the range are also applicable.

[0105] In the present application, the drying is performed under the pressure range, aiming to accelerate the vaporization of water.

[0106] As a preferred scheme of the present application, the temperature range of the second drying in step (b) is 75℃-95℃, such as 75℃, 77℃, 80℃, 83℃, 85℃, 87℃, 90℃, 93℃ or 95℃, etc., but is not limited to the listed values, and other values not listed within the range are also applicable.

[0107] As a preferred scheme of the present application, the drying time in step (b) is 20h-48h, such as 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h, 42h, 44h, 46h or 48h, etc., but is not limited to the listed values, and other values not listed within the range are also applicable.

[0108] Further, the drying in step (b) is segmented drying, including first-stage drying and second-stage drying, the temperature of the first-stage drying is 50℃, and the drying time is 2h; the temperature of the second-stage drying is 80℃, and the drying time is 24h.

[0109] In the fourth aspect, the embodiment part provides a lithium ion battery, and the negative electrode sheet of the lithium ion battery is the aforementioned negative electrode sheet.

[0110] For example, the lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the negative electrode sheet is the aforementioned negative electrode sheet; the positive electrode material in the positive electrode sheet comprises a lithium-rich manganese-based layered oxide (Li 1+x [NiMnCo] 1-x O2 or LMR-NMC) positive electrode material or a ternary NCM positive electrode material;

[0111] The electrolyte in the electrolyte solution includes one or more of lithium salts such as LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium bis-trifluoromethanesulfonylimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluoro(oxalato)borate), LiBOB (lithium bis(oxalato)borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluoro(oxalato)phosphate), and LiTFOP (lithium tetrafluoro(oxalato)phosphate); and solvents in the electrolyte solution include one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethylene carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), and fluorinated versions of each of them, with preference given to one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethylene carbonate (EMC), ethylene carbonate (EC), fluorinated ethylene carbonate (FEC), propylene carbonate (PC), and trifluoro methyl ethylene carbonate (TFMEC).

[0112] The separator includes a base film and / or a base film coated with a coating layer; wherein the base film is any one of a polyethylene film, a polypropylene film, a polyethylene-polypropylene double-layer film, a polyethylene-polypropylene-polyethylene triple-layer film, a glass cellulose separator, or a non-woven fabric film, or a combination of at least two of them.

[0113] The coating layer of the base film is a high molecular material coating layer and / or a composite material coating layer; wherein the high molecular material coating layer includes any one of a natural high molecular material and / or a synthetic high molecular material; the natural high molecular material includes any one of cellulose, lignin, starch, chitin, chitosan, silk protein and its derivatives, chitin and its derivatives, collagen and its derivatives, alginic acid and its derivatives, starch and its derivatives, dextrin and its derivatives, carrageenan, pectin gelatin, or hyaluronic acid, or a combination of at least two of them; the synthetic high molecular material includes any one of polyvinyl alcohol, polylactic acid, polyamide, polycaprolactone, poly(lactic-co-glycolic acid), polyvinylpyrrolidone, polyethylene glycol, or poly(2-hydroxyethyl methacrylate), or a combination of at least two of them.

[0114] The composite material coating is a composite material coating composed of polymer materials and inorganic fillers; wherein, the inorganic fillers include nonionic conductor fillers and / or ionic conductor fillers; the nonionic conductor fillers include any one or at least two combinations of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate; the ionic conductor fillers include any one or at least two combinations of lithium phosphorus oxy nitrogen and its modified derivatives, lithium lanthanum zirconium oxide and its modified derivatives, lithium lanthanum zirconium titanium oxide and its modified derivatives, lithium titanium aluminum phosphate and its modified derivatives, or lithium germanium aluminum phosphate and its modified derivatives.

[0115] The polymeric material in the composite coating includes any combination of at least two of the following: polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0116] The following are typical but non-limiting embodiments of the present invention:

[0117] Example 1:

[0118] This embodiment provides a negative electrode sheet and its preparation method, such as... Figure 1 As shown, the negative electrode sheet includes a silicon-containing negative electrode 1 and a gel polymer layer 2 coated on one side of the silicon-containing negative electrode. The gel polymer layer includes a dual-network structure formed by the physical entanglement of an ionic crosslinking network containing sodium alginate and polyethylene oxide. The ionic crosslinking network containing sodium alginate includes calcium ions. The thickness of the gel polymer layer is 1.0 µm. The weight-average molecular weight of the polyethylene oxide is 100,000 (MW).

[0119] The methods for preparing silicon-containing anodes include:

[0120] (1) A slurry was prepared by mixing graphite, nano-silicon, CMC, SBR and CNT in a weight ratio of 80:16.72:0.40:0.88:2 using the following steps: CMC was added to deionized water and stirred for 4 hours until the CMC was completely and evenly mixed; CNT was added to the above solution and stirred for 30 minutes until the CNT was completely and evenly dispersed; graphite powder was added (in two batches) and stirred for 6 hours until the graphite powder was evenly dispersed; nano-silicon particles were added and stirred for 6 hours until the silicon particles were evenly dispersed; finally, SBR was added and stirred for 2 hours until it was evenly dispersed to obtain the slurry.

[0121] (2) The obtained slurry is coated onto copper foil, dried at 100℃~110℃, and after rolling, the compaction density is 1.4g / cm³. 3, to obtain the silicon-containing negative electrode sheet.

[0122] The preparation method of the gel polymer layer comprises:

[0123] (1) a polyethylene oxide and sodium alginate are mixed according to a mass ratio of 1:1 to prepare a solution A (solid content of 1 wt%) in water, and a calcium chloride aqueous solution with a concentration of 0.1 mol / L is prepared;

[0124] (2) the solution A and the calcium chloride aqueous solution are sprayed on the surface of the silicon-containing negative electrode sheet in sequence; after being left to stand at room temperature for 12 h, the sodium alginate is fully gelled, and then the negative electrode sheet is placed in a vacuum state with a vacuum degree less than -0.1 MPa, dried at 50 DEG C for 2 h, and then dried at 80 DEG C, with a total drying time of 24 h, to obtain the negative electrode sheet.

[0125] Examples 2-9:

[0126] Examples 2-9 respectively provide a negative electrode sheet and a preparation method thereof, the structure and the preparation method of the negative electrode sheet are the same as those of Example 1, and the only difference is that the material usage is different, and the specific embodiments are shown in Table 1.

[0127] Example 10:

[0128] The present embodiment provides a negative electrode sheet and a preparation method thereof, the negative electrode sheet comprises a silicon-containing negative electrode and a gel polymer layer coated on one side of the silicon-containing negative electrode, the gel polymer layer comprises a double-network structure formed by an ionic cross-linked network containing sodium alginate and polyacrylonitrile physically entangled, the ionic cross-linked network containing sodium alginate comprises calcium ions; the thickness of the gel polymer layer is 1 µm; and the weight average molecular weight of the polyacrylonitrile is 50000 (MW).

[0129] The preparation method of the silicon-containing negative electrode is the same as that of Example 1.

[0130] The preparation method of the gel polymer layer comprises:

[0131] (1) a sodium alginate aqueous solution with a concentration of 1 wt%, a polyacrylonitrile solution PAN with a concentration of 2 wt% (wherein the solvent is N, N-dimethylformamide (DMF)), and a calcium chloride aqueous solution with a concentration of 0.2 mol / L are prepared;

[0132] (2) the sodium alginate aqueous solution and the calcium chloride aqueous solution are sprayed on the surface of the silicon-containing negative electrode in sequence, and dried at 100 DEG C for 7 h, so that the sodium alginate is fully gelled, and then the polyacrylonitrile solution is sprayed, so that the thickness of the gel polymer layer is 1 µm; after being left to stand at room temperature for 10 h, the negative electrode sheet is placed in a vacuum state with a vacuum degree less than -0.1 MPa, dried at 50 DEG C for 2 h, and then dried at 80 DEG C, with a total drying time of 24 h.

[0133] Example 11:

[0134] Example 11 provides a negative electrode sheet and a method for manufacturing the same, the structure and the method for manufacturing the same of which are the same as those of Example 10, except that the ionically conductive polymer is polymethyl methacrylate (PMMA), as shown in Table 1.

[0135] Example 12:

[0136] Example 11 provides a negative electrode sheet and a method for manufacturing the same, the structure and the method for manufacturing the same of which are the same as those of Example 1, except that the kinds and amounts of the metal salts and the amount of the ionically conductive polymer are different, as shown in Table 1.

[0137] Example 13:

[0138] Example 13 provides a negative electrode sheet and a method for manufacturing the same, the structure and the method for manufacturing the same of which are the same as those of Example 10, except that the kinds of the metal salts are different, as shown in Table 1.

[0139] Comparative Example 1:

[0140] The present comparative example provides a silicon-containing negative electrode, the method for manufacturing the same of which is the same as that of Example 1.

[0141] Comparative Example 2:

[0142] The present comparative example provides a negative electrode sheet and a method for manufacturing the same, the negative electrode sheet of which includes a silicon-containing negative electrode and a gel polymer layer coated on one side of the silicon-containing negative electrode, the gel polymer layer of which does not include polyethylene oxide, and the remaining components are shown in Table 1.

[0143] The method for manufacturing the silicon-containing negative electrode is the same as that of Example 1.

[0144] The method for manufacturing the gel polymer layer is the same as that of Example 1, except that polyethylene oxide is not added, as shown in Table 1.

[0145] Comparative Example 3:

[0146] The present comparative example provides a negative electrode sheet and a method for manufacturing the same, the negative electrode sheet of which includes a silicon-containing negative electrode and a polymer layer coated on one side of the silicon-containing negative electrode, the polymer layer of which does not include sodium alginate, and the remaining components are shown in Table 1.

[0147] The method for manufacturing the silicon-containing negative electrode is the same as that of Example 1.

[0148] The method for manufacturing the polymer layer is the same as that of Example 1, except that the amounts of the components are different, as shown in Table 1.

[0149] Comparative Example 4:

[0150] The comparative example 1 provides a negative electrode sheet and a preparation method thereof, the negative electrode sheet comprising a silicon-containing negative electrode and a gel polymer layer coated on one side of the silicon-containing negative electrode, wherein the gel polymer layer is the same as that of the example 1 except that the amounts of polyethylene oxide, sodium alginate and calcium chloride are different.

[0151] The preparation method of the silicon-containing negative electrode is the same as that of the example 1.

[0152] The preparation method of the polymer layer is the same as that of the example 1, except that the amounts of the components are different, as shown in Table 1.

[0153] The comparative example 5 provides a negative electrode sheet and a preparation method thereof, the negative electrode sheet comprising a silicon-containing negative electrode and a gel polymer layer coated on one side of the silicon-containing negative electrode, wherein the gel polymer layer is the same as that of the example 1 except that the amounts of polyethylene oxide, sodium alginate and calcium chloride are different.

[0154] The comparative example 6 provides a negative electrode sheet and a preparation method thereof, the negative electrode sheet comprising a silicon-containing negative electrode and a gel polymer layer coated on one side of the silicon-containing negative electrode, wherein the gel polymer layer is the same as that of the example 1 except that the amounts of polyethylene oxide, sodium alginate and calcium chloride are different.

[0155] The preparation method of the silicon-containing negative electrode is the same as that of the example 1.

[0156] The preparation method of the polymer layer is the same as that of the example 1, except that the amounts of the components are different, as shown in Table 1.

[0157] The comparative example 6 provides a negative electrode sheet and a preparation method thereof, the negative electrode sheet comprising a silicon-containing negative electrode and a gel polymer layer coated on one side of the silicon-containing negative electrode, wherein the gel polymer layer is the same as that of the example 1 except that the amounts of polyethylene oxide, sodium alginate and calcium chloride are different.

[0158] The comparative example 6 provides a negative electrode sheet and a preparation method thereof, the negative electrode sheet comprising a silicon-containing negative electrode and a gel polymer layer coated on one side of the silicon-containing negative electrode, wherein the gel polymer layer is the same as that of the example 1 except that the amounts of polyethylene oxide, sodium alginate and calcium chloride are different.

[0159] The preparation method of the silicon-containing negative electrode is the same as that of the example 1.

[0160] The preparation method of the polymer layer is the same as that of the example 1, except that the amounts of the components are different, as shown in Table 1.

[0161] Lithium ion batteries are prepared using the negative electrode sheets described in the examples 1-13 and the comparative examples 1-6, the lithium ion batteries comprising a positive electrode sheet, an electrolyte, a negative electrode sheet and a separator, wherein the negative electrode sheet is obtained by cutting the negative electrode sheets prepared in the examples 1-13 and the comparative examples 1-5, and the separator is a polyethylene-polypropylene film with a thickness of 10 μm.

[0162] The preparation method of the positive electrode sheet is as follows:

[0163] (1) The positive electrode ternary active material NMC811, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 90:5:5, N-methyl pyrrolidone (NMP) was added as a solvent, and a slurry with a solid content of 70wt% was prepared by mixing and stirring uniformly;

[0164] (2) The slurry was uniformly coated on an aluminum foil, and the positive electrode sheet was obtained by drying, rolling, and cutting.

[0165] The preparation method of the electrolyte is as follows:

[0166] In a dry argon glove box, 1M lithium hexafluorophosphate was dissolved in a solution containing fluoroethylene carbonate, vinyl carbonate (concentration 10.7wt%), wherein the volume ratio of fluoroethylene carbonate and vinyl carbonate was 3:7, to obtain the electrolyte.

[0167] After the negative electrode sheet was packaged with a separator, the positive electrode sheet and the negative electrode sheet were stacked into a designed 6Ah battery, the battery was packaged in an aluminum plastic film, electrolyte was injected, and then the processes of sealing, standing, formation, and exhaust were sequentially carried out to obtain a lithium ion secondary battery.

[0168] The safety performance test of the lithium ion battery was carried out, and the test steps were as follows:

[0169] (1) Single cell charging: constant current charging at 1C current to 4.25V charging termination voltage, then constant voltage charging, stopping charging when the charging current drops to 0.05C, and standing for 1h after charging;

[0170] (2) Single cell heating: the temperature box was raised from the test environment temperature to 130±2℃ at a rate of 5℃ / min and kept at this temperature for 30min, then stopped heating;

[0171] (3) After the above steps were completed, the test was observed for 1 hour under the test conditions.

[0172] The cycle performance test of the lithium ion battery was carried out, and the test steps were as follows:

[0173] (1) Charging to the upper limit voltage 4.25V at 1C rate, then constant voltage charging, and stopping charging when the current is 0.05C;

[0174] (2) Discharging to the lower limit voltage 2.5V at 1C rate;

[0175] (3) The above 1-1C rate was used for cycle test.

[0176] The performance test results of the lithium ion batteries prepared by using the negative electrode sheets of Examples 1-13 and Comparative Examples 1-6 are shown in Table 1.

[0177] Table 1: Performance test table of lithium ion battery

[0178] Spraying solution 130°C hot box pass / fail Cycles to pass First coulombic efficiency Example 1 Solution A: (1 wt% sodium alginate + 1 wt% PEO) solution CaCl2 solution: 0.1 M CaCl2 solution 20 min, pass 691 85.53 Example 2 Solution A: (1 wt% sodium alginate + 1 wt% PEO) solution CaCl2 solution: 0.2 M CaCl2 solution 30 min, pass 720 85.66 Example 3 Solution A: 1 wt% sodium alginate + 1 wt% PEO + water CaCl2 solution: 1 M CaCl2 solution 23 min, pass 705 85.87 Example 4 Solution A: 1 wt% sodium alginate + 1 wt% PEO + water CaCl2 solution: 2 M CaCl2 solution 25 min, pass 700 86.02 Example 5 CaCl2 solution: 0.2 M CaCl2 solution Solution A: (1 wt% sodium alginate + 0.25 wt% PEO) solution 40 min, pass 701 85.74 Example 6 CaCl2 solution: 0.2 M CaCl2 solution Solution A: (1 wt% sodium alginate + 0.5 wt% PEO) solution 35 min, pass 710 85.64 Example 7 CaCl2 solution: 0.2 M CaCl2 solution Solution A: (1 wt% sodium alginate + 1 wt% PEO) solution 38 min, pass 750 85.79 Example 8 CaCl2 solution: 0.1 M CaCl2 solution Solution A: (1 wt% sodium alginate + 2 wt% PEO) solution 1 hour, pass 790 85.98 Example 9 CaCl2 solution: 0.1 M CaCl2 solution Solution A: (1 wt% sodium alginate + 5 wt% PEO) solution 30 min, pass 685 85.67 Example 10 CaCl2 solution: 0.2 M CaCl2 solution Solution A: 1 wt% sodium alginate solution Solution B: 2 wt% PAN in DMP solution 1 hour, pass 795 85.97 Example 11 CaCl2 solution: 0.2 M CaCl2 solution Solution A: 1 wt% sodium alginate solution Solution B: 2 wt% PMMA + DMP solution 1 hour, pass 791 85.89 Example 12 Aluminum nitrate solution: 0.1 M aluminum nitrate solution Solution A: (1 wt% sodium alginate + 2 wt% PEO) solution 20 min, pass 698 85.85 Example 13 Aluminum nitrate solution: 0.2 M aluminum nitrate solution Solution A: 1 wt% sodium alginate solution Solution B: 2 wt% PAN DMP solution 1 hour, pass 701 85.84 Comparative Example 1 - Failed 650 85.94 Comparative Example 2 CaCl2 solution: 0.2 M CaCl2 solution Solution A: 1 wt% sodium alginate solution Pass 570 85.47 Comparative Example 3 CaCl2 solution: 0.1 M CaCl2 solution Solution A: 1 wt% PEO in water Pass 580 85.35 Comparative Example 4 CaCl2 solution: 2.5 M CaCl2 solution Solution A: 1 wt% sodium alginate + PEO: 2 wt% + water 30 min pass 500 84.32 Comparative Example 5 CaCl2 solution: 0.2 M CaCl2 solution Solution A: sodium alginate 1 wt% + 6 wt% PEO + water 50 min pass 532 85.45 Comparative Example 6 CaCl2 solution: 0.2 M CaCl2 solution Solution A: 11 wt% sodium alginate + PEO: 2 wt% + water 40 min by 540 84.54

[0179] As can be seen from Table 1, compared with Comparative Example 1, the positive electrode side transition metal ions were dissolved during the heating test due to the lack of protection of the negative electrode tab surface, which induced the decomposition of the negative electrode SEI film to generate a large amount of gas; compared with Comparative Example 2, the impedance of the entire gel protective layer was too large due to the lack of PEO, which deteriorated the cycle life of the battery; compared with Comparative Example 3, PEO could not complex transition metal ions, so after the battery was heated, the transition metal ions dissolved from the positive electrode side induced the decomposition of the SEI film of the negative electrode, so it could not effectively protect the negative electrode side; compared with Comparative Example 4, the excess calcium chloride increased the amount of divalent calcium ions on the negative electrode side, which formed lithium-silicon-calcium alloy with lithium ions during formation, and the lithium ions in this alloy phase could not be completely removed, resulting in the loss of part of the active lithium ions and affecting the cycle performance; compared with Comparative Example 5, the excess PEO had a large molecular weight and strong intermolecular interaction, so the viscosity was large during the experiment, which made it impossible to operate during the experiment, and on the other hand, the large molecular weight led to a large tab internal resistance, which affected the battery performance; compared with Comparative Example 6, the excess sodium alginate had a large molecular weight, which increased the tab internal resistance, and the protective film formed by the excess sodium alginate lacked toughness, so the gel film formed on the surface was easy to fall off during the cycle due to the expansion of the negative electrode, which deteriorated the performance of the battery.

[0180] The applicant declares that the detailed process equipment and process flow of the present application are illustrated by the above examples, but the present application is not limited to the above detailed process equipment and process flow, that is, it does not mean that the present application must rely on the above detailed process equipment and process flow to be implemented. It should be understood by those skilled in the art that any improvement on the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific modes, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A negative electrode sheet, characterized by, The negative electrode sheet comprises a silicon-containing negative electrode and a gel polymer layer covering one side of the silicon-containing negative electrode, wherein the gel polymer layer comprises a double network structure formed by physical entanglement of an ionically cross-linked network of a guluronic acid-containing copolymer and an ion-conducting polymer, and the ionically cross-linked network of the guluronic acid-containing copolymer comprises cations of a metal salt; and the metal salt is selected from a calcium metal salt and / or an aluminum metal salt. The mass ratio of the guluronic acid-containing copolymer, the metal salt and the ion-conducting polymer is (1-10):(0.1-1):(1-5).

2. The negative electrode sheet according to claim 1, characterized by, The thickness of the gel polymer layer is 0.1-5 μm. The mass content of guluronic acid in the guluronic acid-containing copolymer is 10wt%-80wt%. The weight average molecular weight of the ion-conducting polymer is 800-200000.

3. The negative electrode sheet according to claim 1, wherein The guluronic acid-containing copolymer is selected from sodium alginate and / or fucoidan; the ion-conducting polymer is selected from any one or a combination of at least two of polyethylene oxide, polyacrylonitrile, polymethyl methacrylate or polyvinylidene fluoride and a copolymer thereof; the calcium metal salt is selected from any one or a combination of at least two of calcium chloride, calcium nitrate, calcium sulfate or calcium bisfluorosulfonylimide; and the aluminum metal salt is selected from aluminum nitrate and / or aluminum chloride.

4. A method of producing the negative electrode sheet according to any one of claims 1 to 3, characterized by, When the ion-conducting polymer is water-soluble, the preparation method comprises: (1) configuring the ion-conducting polymer and the guluronic acid-containing copolymer into a solution A, and configuring a metal salt solution B; (2) coating the solution A and the metal salt solution B on the surface of the silicon-containing negative electrode in sequence, standing, drying to obtain the negative electrode sheet.

5. The production method according to claim 4, characterized by, The mass ratio of the ion-conducting polymer and the guluronic acid-containing copolymer in step (1) is (1-5):

1. The solid content of the solution A in step (1) is 0.6wt%-4wt%. The solvent in the solution A in step (1) is water. The concentration of the metal salt solution B in step (1) is 0.01mol / L-2mol / L. The solvent of the metal salt solution B in step (1) is water.

6. The preparation method according to claim 4, characterized in that, The mass ratio of the solution A and the metal salt solution B in step (2) is (2-5):

1. The coating method in step (2) comprises spraying and / or doctoring. The overall thickness of the solution A and the metal salt solution B after the coating in step (2) is 0.1-5 μm. The standing time in step (2) is 10h-48h. The pressure of the drying in step (2) is < -0.1MPa. The temperature range of the drying in step (2) is 75-95℃. The time of the drying in step (2) is 20h-48h.

7. A method of producing the negative electrode sheet according to any one of claims 1 to 3, characterized by, When the ion-conducting polymer is water-insoluble, the preparation method comprises: (a) preparing a guluronic acid-containing copolymer solution, an ion-conducting polymer solution and a metal salt solution respectively; (b) coating the guluronic acid-containing copolymer solution and the metal salt solution on the surface of the silicon-containing negative electrode in sequence, performing first drying, coating the ion-conducting polymer solution, standing, performing second drying to obtain the negative electrode sheet.

8. The production method according to claim 7, characterized by, The concentration of the guluronic acid-containing copolymer solution in step (a) is 0.2wt%-2wt%. The solvent in the solution of the guluronic acid-containing copolymer in step (a) is water; The concentration of the ionic conductive polymer solution in step (a) is 0.5wt%-2wt%; The solvent of the ionic conductive polymer solution in step (a) is an oily solvent, including N-methyl pyrrolidone and / or N,N-dimethylamide; The concentration of the metal salt solution in step (a) is 0.01mol / L-2mol / L; The solvent of the metal salt solution in step (a) is water; The mass ratio of the guluronic acid-containing copolymer, the metal salt and the ionic conductive polymer in step (a) is (1-10):(0.1-1):(1-5).

9. The preparation method according to claim 7, characterized in that, The coating method in step (b) includes spraying and / or doctoring; The temperature of the first drying in step (b) is 95℃-100℃, and the time of the first drying is 7h-10h; The overall coating thickness of the solution of the guluronic acid-containing copolymer, the metal salt solution and the ionic conductive polymer solution in step (b) is 0.1μm-5μm; The standing time in step (b) is 10h-12h; The pressure of the second drying in step (b) is <-0.1MPa; The temperature range of the second drying in step (b) is 75℃-95℃; The time of the second drying in step (b) is 20h-48h.

10. A lithium-ion battery, characterized by, The negative electrode sheet of the lithium ion battery is the negative electrode sheet according to any one of claims 1-3.

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