A lithium-ion battery anode and its preparation method

Abstract

This invention provides a lithium-ion battery negative electrode and its preparation method. The negative electrode includes a negative electrode active material layer, which comprises a negative electrode active material, a binder, and a conductive agent. The binder is added at an amount of 0.5-1.5 wt% of the negative electrode active material layer. The binder comprises 65-70 wt% polyacrylonitrile and 30-35 wt% of one or a mixture of two of polyacrylic acid and / or polyphthalamide. By compounding the polyacrylonitrile binder, which has a certain thickening effect, with polyacrylic acid and polyphthalamide, the amount of binder used is significantly reduced, thereby improving the low-temperature performance and cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium batteries, and more particularly to a lithium-ion battery anode and its preparation method. Background Technology

[0002] Since their commercialization, lithium-ion batteries have been widely used in various portable consumer electronics products due to their numerous advantages, including high energy density, high operating voltage, long cycle life, no memory effect, environmental friendliness, and the ability to be flexibly designed in size and shape according to actual needs. The new energy vehicle market has enormous potential, and as an important chemical power source, lithium-ion batteries are widely used in mobile communication devices, power tools, and electric vehicles, leading to a growing demand for lithium-ion batteries and related supporting industries.

[0003] For use in electric vehicles or related energy storage devices, batteries need to have a long service life and high safety performance. However, in actual use, the battery capacity deteriorates due to repeated charging and discharging over a long period. One possible reason is that the expansion of the active material during charging and discharging causes the current collector and active material layer to detach. To solve this problem, increasing the binder content can improve the adhesion between the current collector and the active material layer. However, excessive binder content can easily lead to increased internal resistance and decreased energy density. For the CMC+SBR negative electrode binder system used in daily applications, an excessively high CMC ratio not only makes the electrode too brittle but also increases the battery's internal resistance. In addition, the low-temperature performance of CMC+SBR negative electrode binder system batteries is generally poor.

[0004] Therefore, it is essential to provide a new type of adhesive combination. Summary of the Invention

[0005] To address the existing problems of current negative electrode binder systems, one objective of this invention is to provide a lithium-ion battery negative electrode. The negative electrode includes a negative electrode active material layer, which comprises a negative electrode active material, a binder, and a conductive agent. The binder is added at an amount of 0.5-1.5 wt% of the negative electrode active material layer and comprises 65-70 wt% polyacrylonitrile and 30-35 wt% polyacrylic acid and / or a mixture of one or two of polyphthalamide.

[0006] In the traditional SBR+CMC anode binder system, CMC (carboxymethyl cellulose) mainly acts as a thickener, while SBR (styrene-butadiene rubber) mainly acts as a binder. Adding CMC helps maintain the anode slurry at a suitable viscosity, allowing the anode active material, such as graphite, to be uniformly dispersed in the slurry. Currently, the known amount of binder added to the SBR+CMC system is more than 5 wt% of the anode active material layer. If the amount added is too low, it can easily lead to the shedding of the current collector and the anode active material layer. If the amount added is too high, it will lead to a decrease in battery energy density and an increase in resistance.

[0007] Polyacrylonitrile has both thickening and binding properties, which makes it surprisingly effective as a binder. A complete negative electrode binder system can be obtained by combining polyacrylonitrile as the main component with specific amounts of polyacrylic acid and polyphthalamide. Compared with the SBR+CMC system, it has a lower addition amount, which can be as low as 0.5wt%, greatly improving the performance of the battery.

[0008] The negative electrode of the present invention also includes a current collector. Without departing from the concept of the present invention, any known current collector can be used in the present invention. Preferably, the current collector is a metal foil, preferably a metal element or alloy. More preferably, the metal element in the current collector includes any one or at least two of aluminum, copper, nickel and zinc.

[0009] Particularly preferred is that the current collector is copper foil.

[0010] Preferably, the negative electrode active material in the negative electrode active material layer includes any one or a combination of at least two of the following: metal active material, carbon active material, and oxide active material.

[0011] Preferably, the metal active material includes any one or a combination of at least two of Si metal, Sn metal, In metal, Si-Al alloy, and Si-In alloy.

[0012] Preferably, the carbon-active material includes any one or a combination of at least two of graphite, hard carbon, and soft carbon.

[0013] Preferably, the oxide active material includes Li4Ti5O. 12 .

[0014] In the negative electrode active material layer, the proportion of the negative electrode active material is 85-99 wt%, preferably 90-99 wt%, and particularly preferably 95-98 wt%.

[0015] The conductive agent includes, but is not limited to, one or more of graphite, acetylene black, Ketjen black, super-P, carbon nanotubes and carbon fibers. The mass percentage of the conductive agent in the negative electrode active material layer is 0.5-10 wt%, preferably 1-5 wt%, and more preferably 1-3 wt%.

[0016] A second aspect of the present invention is to provide a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode is the negative electrode described in the first aspect of the present invention.

[0017] The positive electrode includes a positive electrode current collector and a positive electrode active material layer;

[0018] The selection of the positive electrode current collector is not particularly limited. Any known current collector can be used in this invention without departing from the inventive concept. Preferably, the current collector is a metal foil, preferably an elemental metal or an alloy. More preferably, the metal element in the current collector includes any one or a combination of at least two of aluminum, copper, nickel, and zinc. Preferably, the positive electrode current collector is aluminum foil.

[0019] The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0020] This application does not limit the type of positive electrode active material. Any conventional positive electrode active material that does not contradict the innovative concept of this invention can be used in this invention. Known positive electrode active materials are selected from LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMn2O4, LiTi5O 12 Li(Ni) 0.5 Mn 1.5 Any one or at least two combinations of O4, LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4 and LiNbO3.

[0021] Among them, LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 has a rock salt layered structure, LiMn2O4, LiTi5O 12 Li(Ni) 0.5 Mn 1.5 LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, and LiNbO3 have spinel structures, while LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, and LiNbO3 have olivine structures. Furthermore, coating the surface of positive electrode active materials is also known, for example, with LiNbO3.

[0022] The positive electrode active material accounts for 85-99 wt% of the mass of the positive electrode active material layer, preferably 90-98 wt%, and more preferably 95-98 wt%.

[0023] The conductive agent includes, but is not limited to, one or more of graphite, acetylene black, Ketjen black, super-P, carbon nanotubes and carbon fibers. The mass percentage of the conductive agent in the negative electrode active material layer is 0.5-10 wt%, preferably 1-5 wt%, and more preferably 1-3 wt%.

[0024] The binder may be selected from, but is not limited to, one or more of polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose, and polyvinyl alcohol. The binder accounts for 1-10 wt% of the positive electrode active material layer by mass, preferably 1-5 wt%, and more preferably 2-3 wt%.

[0025] The electrolyte can be a liquid electrolyte, a solid electrolyte, or a solid-liquid mixture electrolyte.

[0026] The liquid electrolyte, i.e., non-aqueous electrolyte system lithium battery, preferably, the non-aqueous electrolyte includes lithium salt and non-aqueous solvent, and the non-aqueous electrolyte system lithium battery further includes a separator, the separator being located between the positive electrode and the negative electrode;

[0027] Preferably, the non-aqueous solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl carbonate, butenyl carbonate, γ-butyrolactone, sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran.

[0028] Preferably, the lithium salt is one or more of LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2;

[0029] In particular, the non-aqueous electrolyte may also include various other additives, such as flame retardant additives and overcharge protection additives. These additives are common knowledge in the art and will not be described in detail here.

[0030] The separator is disposed between the positive and negative electrodes and has electrical insulation and liquid retention properties. The separator can be selected from various separators used in lithium-ion batteries, such as one or more of polyolefin microporous membranes, polypropylene, polyethylene felt, glass fiber felt, or ultrafine glass fiber paper. The separator is well known to those skilled in the art.

[0031] The preparation of the non-aqueous electrolyte system lithium battery includes preparing the positive electrode, negative electrode and electrolyte of the battery, separating the positive electrode and negative electrode by a separator to form an electrode assembly, placing the electrode assembly into the battery case, adding electrolyte, and then sealing the battery case, wherein the negative electrode is the negative electrode provided by the present invention.

[0032] Solid electrolytes are solid materials that conduct lithium ions. Known solid electrolytes can be crystalline or amorphous. Furthermore, solid electrolyte materials can be glass or crystallized glass (glass-ceramic). Examples of solid electrolyte material shapes include particles.

[0033] Preferably, the solid electrolyte is one of oxide solid electrolyte, sulfide solid electrolyte, and polymer solid electrolyte.

[0034] The oxide solid electrolyte, as an oxide-based solid electrolyte, can specifically be exemplified by LiPON (lithium oxyphosphate nitride), Li 1.3 Al 0.3 Ti 0.7 (PO4)3, La 0.51 Li 0.34 TiO 0.74 Li3PO4, Li2SiO2, Li2SiO4, etc.

[0035] Polymer electrolytes typically contain a metal salt and a polymer. In the case of a lithium battery according to the present invention, a lithium salt can be used as the metal salt. As the lithium salt, at least any one of the aforementioned inorganic and organic lithium salts can be used. As for the polymer, there are no particular limitations as long as it forms a complex with the lithium salt; examples include polyethylene oxide.

[0036] Examples of sulfide solid electrolytes include Li₂S-P₂S₅, Li₂S-P₂S₅-LiI, Li₂S-P₂S₅-Li₂O, Li₂S-P₂S₅-Li₂O-LiI, Li₂S-SiS₂, Li₂S-SiS₂-LiI, Li₂S-SiS₂-LiBr, Li₂S-SiS₂-LiCl, Li₂S-SiS₂-B₂S₃-LiI, Li₂S-SiS₂-P₂S₅-LiI, Li₂S-B₂S₃, and Li₂S-P₂S₅-Z. m S n (Where m and n are positive numbers, and Z is any one of Ge, Zn, or Ga), Li₂S-GeS₂, Li₂S-SiS₂-Li₃PO₄, Li₂S-SiS₂-Li x MO y(Where x and y are positive numbers. M is any one of P, Si, Ge, B, Al, Ga, and In.) It should be noted that the above description of "Li2S-P2S5" refers to a sulfide solid electrolyte material made using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions.

[0037] In addition to the aforementioned ion conductors, sulfide solid electrolyte materials may also contain lithium halides. Examples of lithium halides include LiF, LiCl, LiBr, and LiI, with LiCl, LiBr, and LiI being preferred. The proportion of LiX (X = F, I, Cl, Br) in the sulfide solid electrolyte material is, for example, in the range of 5 mol% to 30 mol%, and may be in the range of 15 mol% to 25 mol%.

[0038] In addition to the above, examples of solid electrolytes used in this invention include Li2Ti(PO4)3-AlPO4 (Ohara glass).

[0039] Solid-liquid mixed electrolytes refer to the combination of liquid and solid electrolytes. Any known solid-liquid mixed system can be used in this invention without departing from the concept of this invention, and will not be elaborated here.

[0040] A third aspect of the present invention is to provide a method for preparing the lithium-ion battery negative electrode according to the first aspect of the present invention, comprising the following steps:

[0041] S1. Weigh out one or a mixture of two of polyacrylonitrile, polyacrylic acid and / or polyphthalamide according to the stoichiometric ratio and dissolve them in a solvent, then slurry them to form a suspension.

[0042] S2. Add a measured amount of conductive agent and negative electrode active material to the suspension obtained in step S1, and mix to form a negative electrode slurry.

[0043] S3. Coating and drying yield the negative electrode sheet.

[0044] Preferably, the pulping time in step S1 is 1-5 hours, preferably 2-3 hours. Since CMC is no longer used as a thickener, and polyacrylonitrile itself has both thickening and binding properties, the entire binder can be pulped as a whole, eliminating the CMC pulping step, greatly improving the preparation efficiency of the negative electrode slurry, and increasing the production line capacity.

[0045] Preferably, the choice of solvent is not particularly limited, and any known solvent such as polyacrylonitrile, polyacrylic acid, or polyphthalamide can be used in this invention without departing from the concept of this invention; preferably, the solvent is deionized water.

[0046] In a preferred embodiment of the present invention, during the pulping process in step S1, 10-15 wt% of polyethylene oxide is added. The number average molecular weight of the polyethylene oxide is 200,000-300,000. The polyethylene oxide has certain adhesive properties and good hydrophilicity. The addition of polyethylene oxide within a specific range has a promoting effect on the polyacrylonitrile / (polyacrylic acid and / or polyphthalamide) system involved in this application. Detailed Implementation

[0047] Example 1

[0048] Copper foil is used as the current collector. Each material is weighed according to the metering ratio of 1 wt% binder, 1 wt% conductive agent, and 98 wt% negative electrode active material. The binder is composed of 70 wt% polyacrylonitrile and 30 wt% polyacrylic acid. The conductive agent is Super-P and the negative electrode active material is graphite.

[0049] Polyacrylonitrile and polyacrylic acid were poured into deionized water and mixed for 30 minutes to obtain a suspension. A metric ratio of negative electrode active material and conductive agent was added to the obtained suspension and stirred for 3 hours to obtain a negative electrode slurry.

[0050] The obtained negative electrode slurry is coated onto copper foil, dried to obtain a negative electrode sheet, and then stacked with a positive electrode and a solid electrolyte to obtain a solid-state lithium battery.

[0051] Example 2

[0052] Copper foil is used as the current collector. Each material is weighed according to the metering ratio of 1 wt% binder, 1 wt% conductive agent, and 98 wt% negative electrode active material. The binder is composed of 70 wt% polyacrylonitrile and 30 wt% polyphthalamide. The conductive agent is super-P and the negative electrode active material is graphite.

[0053] Polyacrylonitrile and polyphthalamide were poured into deionized water and mixed for 30 minutes to obtain a suspension. A metric ratio of negative electrode active material and conductive agent was added to the obtained suspension and stirred for 3 hours to obtain a negative electrode slurry.

[0054] The obtained negative electrode slurry is coated onto copper foil, dried to obtain a negative electrode sheet, and then stacked with a positive electrode and a solid electrolyte to obtain a solid-state lithium battery.

[0055] Example 3

[0056] Copper foil is used as the current collector. Each material is weighed according to the metering ratio of 1 wt% binder, 1 wt% conductive agent, and 98 wt% negative electrode active material. The binder is composed of 70 wt% polyacrylonitrile, 30 wt% (5 wt% polyphthalamide and 25 wt% polyacrylic acid), the conductive agent is super-P, and the negative electrode active material is graphite.

[0057] Polyacrylonitrile, polyphthalamide, and polyacrylic acid were poured into deionized water and mixed for 30 minutes to obtain a suspension. A metric ratio of negative electrode active material and conductive agent was added to the obtained suspension and stirred for 3 hours to obtain a negative electrode slurry.

[0058] The obtained negative electrode slurry is coated onto copper foil, dried to obtain a negative electrode sheet, and then stacked with a positive electrode and a solid electrolyte to obtain a solid-state lithium battery.

[0059] Example 4

[0060] Copper foil is used as the current collector. Each material is weighed according to the metering ratio of 1 wt% binder, 1 wt% conductive agent, and 98 wt% negative electrode active material. The binder is composed of 70 wt% polyacrylonitrile and 30 wt% (25 wt% polyphthalamide and 5 wt% polyacrylic acid). The conductive agent is super-P and the negative electrode active material is graphite.

[0061] Polyacrylonitrile, polyphthalamide, and polyacrylic acid were poured into deionized water and mixed for 30 minutes to obtain a suspension. A metric ratio of negative electrode active material and conductive agent was added to the obtained suspension and stirred for 3 hours to obtain a negative electrode slurry.

[0062] The obtained negative electrode slurry is coated onto copper foil, dried to obtain a negative electrode sheet, and then stacked with a positive electrode and a solid electrolyte to obtain a solid-state lithium battery.

[0063] Example 5

[0064] Copper foil is used as the current collector. Each material is weighed according to the following metering ratio: 1 wt% binder, 1 wt% conductive agent, and 98 wt% negative electrode active material. The binder consists of 70 wt% polyacrylonitrile, 30 wt% (25 wt% polyphthalamide and 5 wt% polyacrylic acid), the conductive agent is super-P, and the negative electrode active material is graphite. 12 wt% polyethylene oxide is also added to the polyacrylonitrile.

[0065] Polyacrylonitrile, polyphthalamide, and polyacrylic acid were poured into deionized water and mixed for 30 minutes to obtain a suspension. A metric ratio of negative electrode active material and conductive agent was added to the obtained suspension and stirred for 3 hours to obtain a negative electrode slurry.

[0066] The obtained negative electrode slurry is coated onto copper foil, dried to obtain a negative electrode sheet, and then stacked with a positive electrode and a solid electrolyte to obtain a solid-state lithium battery.

[0067] Comparative Example 1

[0068] Copper foil is used as the current collector. The materials are weighed according to the metering ratio of 5 wt% binder, 1 wt% conductive agent and 94 wt% negative electrode active material. The binder is composed of 40 wt% CMC and 60 wt% SBR. The conductive agent is super-P and the negative electrode active material is graphite.

[0069] First, CMC is pulped for 5 hours. After the CMC is completely dissolved, a CMC slurry is obtained. A metered ratio of negative electrode active material and conductive agent is added to the obtained CMC slurry. After high-speed mixing for 5 hours, SBR is added and the mixture is slowly stirred for 1 hour to obtain the negative electrode slurry.

[0070] The obtained negative electrode slurry is coated onto copper foil, dried to obtain a negative electrode sheet, and then stacked with a positive electrode and a solid electrolyte to obtain a solid-state lithium battery.

[0071] Comparative Example 2

[0072] Copper foil is used as the current collector. Each material is weighed according to the metering ratio of 1 wt% binder, 1 wt% conductive agent, and 98 wt% negative electrode active material. The binder is polyacrylonitrile, the conductive agent is Super-P, and the negative electrode active material is graphite.

[0073] Polyacrylonitrile was added to deionized water and stirred for 30 minutes to obtain a suspension. A metric ratio of negative electrode active material and conductive agent was added to the obtained suspension and stirred for 3 hours to obtain a negative electrode slurry.

[0074] The obtained negative electrode slurry is coated onto copper foil, dried to obtain a negative electrode sheet, and then stacked with a positive electrode and a solid electrolyte to obtain a solid-state lithium battery.

[0075] Comparative Example 3

[0076] Copper foil is used as the current collector. Each material is weighed according to the metering ratio of 1 wt% binder, 1 wt% conductive agent, and 98 wt% negative electrode active material. The binder is polyphthalamide, the conductive agent is super-P, and the negative electrode active material is graphite.

[0077] Add polyphthalamide to deionized water and beat for 30 minutes to obtain a suspension; add the stoichiometric ratio of negative electrode active material and conductive agent to the obtained suspension and stir for 3 hours to obtain negative electrode slurry.

[0078] Comparative Example 4

[0079] Copper foil is used as the current collector. Each material is weighed according to the metering ratio of 1 wt% binder, 1 wt% conductive agent, and 98 wt% negative electrode active material. The binder is polyacrylic acid, the conductive agent is super-P, and the negative electrode active material is graphite.

[0080] Polyacrylic acid was added to deionized water and stirred for 30 minutes to obtain a suspension. A metric ratio of negative electrode active material and conductive agent was added to the obtained suspension and stirred for 3 hours to obtain a negative electrode slurry.

[0081] Test methods and conditions

[0082] 1. Test method for peel strength:

[0083] ① First, use a flat paper cutter to cut the graphite negative electrode sheet into strips with a length of 170mm and a width of 20mm. Then, wipe the unmarked steel ruler clean with lint-free paper to remove stains and dust.

[0084] ② Next, attach a 25mm wide double-sided tape to the unmarked steel ruler, 70mm in length, and center it;

[0085] ③ Next, paste the test sample onto the double-sided tape, with the end face flush, and use a pressure roller (2kg) with a diameter of 84mm and a height of 45mm to roll back and forth on the electrode surface 3 times;

[0086] ④ After folding the free end of the negative electrode sheet in the experimental sample 180°, clamp it on the upper clamp of the tensile testing instrument, and clamp the ungraded steel ruler on the lower clamp. Under the conditions of 22-28℃ and humidity less than 25%, prepare several negative electrode sheets with a width of 20mm. The electrode sheet is stretched at a speed of 200mm / min. The average value of the stretching is taken as 25-80mm (total stretching distance 100mm). Peel the negative electrode sheet. When the current collector and coating of the electrode sheet are completely separated, read the test result of the peel strength of the electrode sheet coating.

[0087] 2. Test method for low-temperature discharge performance:

[0088] ① Charge using standard charging method, store at room temperature for 1 hour, then discharge at 1C at the same temperature to the termination voltage, and record the discharge capacity;

[0089] ② After storing at room temperature for 24 hours, charge using the standard charging method. After storing at -20±2℃ for 24 hours, discharge at 1C to 80% of the termination voltage at that temperature and record the discharge capacity.

[0090] 3. Method for room temperature cycling test:

[0091] ① Charge at room temperature with 1C or specified current to the termination voltage, cut-off current 0.05C, and let stand for 30 minutes;

[0092] ② Discharge at 1C until the final discharge voltage, record the discharge capacity, and let stand for 30 minutes;

[0093] ③ Repeat steps ① to ②.

[0094] The test results are shown in Tables 1 and 2:

[0095] Table 1

[0096] Peel strength (N / m) -20℃ low-temperature discharge performance (%) Capacity retention rate after 500 cycles at room temperature (%) Example 1 15.1 92 96 Example 2 12.3 89 95 Example 3 14.6 86 96 Example 4 13.1 90 96 Example 5 15.6 94 96

[0097] Table 2

[0098] Peel strength (N / m) -20℃ low-temperature discharge performance (%) Capacity retention rate after 500 cycles at room temperature (%) Comparative Example 1 8.6 65 96 Comparative Example 2 9.3 90 95 Comparative Example 3 Severe sedimentation of slurry / / Comparative Example 4 Severe sedimentation of slurry / /

[0099] As can be seen from Tables 1 and 2, the use of polyphthalamide or polyacrylic acid alone results in severe sedimentation of the slurry due to the lack of thickener, making it impossible to obtain a stable electrode slurry. On the other hand, the use of polyacrylonitrile alone results in too low electrode peel strength. The use of polyacrylonitrile in combination with polyphthalamide or polyacrylic acid can significantly improve battery performance. In addition, the addition of polyethylene oxide has the greatest effect on the overall battery performance.

Claims

1. A lithium-ion battery anode, characterized by, The negative electrode includes a negative electrode active material layer, which includes a negative electrode active material, a binder, and a conductive agent; the amount of the binder added is 0.5-1.5 wt% of the negative electrode active material layer, and the binder includes 65-70 wt% polyacrylonitrile and 30-35 wt% polyphthalamide. Alternatively, the adhesive may comprise a mixture of 65-70 wt% polyacrylonitrile, 30-35 wt% polyacrylic acid, and polyphthalamide.

2. The lithium-ion battery anode of claim 1, wherein, The binder accounts for 1-1.5 wt% of the negative electrode active material layer.

3. The lithium-ion battery anode of claim 1 or 2, wherein, The negative electrode active material includes any one or a combination of at least two of the following: metal active material, carbon active material, and oxide active material.

4. The lithium-ion battery anode of claim 3, wherein the carbon-based material is selected from the group consisting of graphite, graphene, carbon nanotubes, carbon nanofibers, and combinations thereof. The carbon-active material is graphite.

5. A lithium-ion battery negative electrode according to claim 1 or 2, wherein the negative electrode active material accounts for 95-98 wt% of the negative electrode active material layer.

6. A method for preparing a lithium-ion battery negative electrode as described in claim 1, characterized in that, The method includes the following steps: S1. Weigh out one or a mixture of two of polyacrylonitrile, polyacrylic acid and / or polyphthalamide according to the stoichiometric ratio and dissolve them in a solvent, then slurry them to form a suspension. S2. Add a measured amount of conductive agent and negative electrode active material to the suspension obtained in step S1, and mix to form a negative electrode slurry. S3. Coating and drying yield the negative electrode sheet.

7. The method according to claim 6, characterized in that, In step S1, the pulping time is 1-5 hours.

8. The method according to claim 7, characterized in that, The solvent is deionized water.