A negative electrode, a method for manufacturing the same, and a battery

Abstract

The application relates to the new energy field, in particular to a negative electrode and a preparation method thereof and a battery, the negative electrode comprising a current collector, a first negative electrode active material layer arranged on the surface of the current collector and a second negative electrode active material layer arranged on the surface of the first negative electrode active material layer; wherein the first negative electrode active material layer comprises a first negative electrode active substance, a first liquid absorbent and a first composite binder; the second negative electrode active material layer comprises a second negative electrode active substance, a second liquid absorbent and a second composite binder; the first liquid absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde groups, and the first composite binder comprises a first hydroxyl-containing water-based binder; the second liquid absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde groups, and the second composite binder comprises a second hydroxyl-containing water-based binder. The negative electrode sheet of the application can quickly absorb liquid and has a good infiltration effect, and the battery applying the negative electrode sheet has obviously improved electrical performance.

Description

Technical Field

[0001] This invention relates to the field of new energy batteries, specifically to a negative electrode, its preparation method, and a battery. Background Technology

[0002] Compared to traditional processes, double-layer coating technology for battery electrodes can effectively improve battery rate capability, energy density, and cycle life. Existing double-layer coating technologies enhance the cell's electrical performance, including high and low temperature performance, rate cycling, DCR (damping rate response), and storage capacity, by adjusting the layering structure of the binder, conductive agent, porosity, active particles, particle size distribution, and the thickness of the two film layers. However, because the active material in double-layer coating technology consists of two layers, it also presents challenges such as difficulty in achieving proper electrode wettability. Batteries prepared using normal wettability times, upon disassembly, showed numerous black and purple spots on the negative electrode surface. Furthermore, trace water and byproducts in the battery also contributed to the appearance of these spots, collectively impacting the cell's capacity and overall electrical performance.

[0003] Therefore, how to improve the wetting rate in double coating is a problem that urgently needs to be solved in this field. Summary of the Invention

[0004] In view of this, the present invention aims to provide a negative electrode, its preparation method and battery, to solve the problem in the prior art that a large number of black spots and purple spots appear on the surface of the negative electrode sheet due to excessive immersion time.

[0005] To solve the above-mentioned technical problems, this application is implemented as follows:

[0006] The first aspect of the present invention provides a negative electrode, the negative electrode comprising a current collector, a first negative electrode active material layer disposed on the surface of the current collector, and a second negative electrode active material layer disposed on the surface of the first negative electrode active material layer;

[0007] The first negative electrode active material layer includes a first negative electrode active substance, a first liquid absorbent, and a first composite binder; the second negative electrode active material layer includes a second negative electrode active substance, a second liquid absorbent, and a second composite binder.

[0008] The first absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the first composite adhesive comprises a first aqueous adhesive containing hydroxyl groups; the second absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the second composite adhesive comprises a second aqueous adhesive containing hydroxyl groups.

[0009] Optionally, in the first negative electrode active material layer, the mass ratio of the first negative electrode active material, the first absorbent, and the first composite binder is (70-90):(0.5-1.5):(1.0-2.5); preferably (75-85):(0.7-1.2):(1.2-2.4); and / or, in the second negative electrode active material layer, the mass ratio of the second negative electrode active material, the second absorbent, and the second composite binder is (80-98):(0.2-0.6):(0.5-1.5); preferably (85-95):(0.3-0.5):(0.6-1.3); preferably, the masses of the first absorbent and the second absorbent satisfy the following formula:

[0010] x = -5y 2 +6.5y-0.8,

[0011] Where x represents the mass of the first absorbent and y represents the mass of the second absorbent.

[0012] Optionally, the mass density of the first negative electrode active material in the first negative electrode active material layer is 60–100 mg / cm³. 3 Preferably 70–90 mg / cm³ 3 Optionally, the first negative electrode active material is selected from at least one of natural graphite, artificial graphite, soft carbon, and hard carbon; and / or, the mass density of the second negative electrode active material in the second negative electrode active material layer is 40–90 mg / cm³. 3 Preferably 50-80 mg / cm³ 3 Optionally, the second negative electrode active material is selected from at least one of natural graphite, artificial graphite, soft carbon, and hard carbon.

[0013] Optionally, the first composite adhesive further includes styrene-butadiene rubber; optionally, the mass ratio of the hydroxyl-containing first aqueous adhesive to the styrene-butadiene rubber is (0.5-3):(0.1-0.5), preferably (1-2):(0.2-0.4); optionally, the hydroxyl-containing first aqueous adhesive is selected from at least one of cellulose acetate, hydroxyethyl cellulose, methyl cellulose, polyvinyl alcohol, and polyacrylamide; and / or, the second composite adhesive further includes styrene-butadiene rubber; optionally, the mass ratio of the hydroxyl-containing second aqueous adhesive to the styrene-butadiene rubber is (0.3-1.2):(0.1-0.5), preferably (0.5-1):(0.1-0.3); optionally, the hydroxyl-containing second aqueous adhesive is selected from at least one of cellulose acetate, hydroxyethyl cellulose, methyl cellulose, polyvinyl alcohol, and polyacrylamide.

[0014] Optionally, the first negative electrode active material layer further includes a first conductive agent; optionally, in the first negative electrode active material layer, the mass ratio of the first negative electrode active material to the first conductive agent is (70-90):(1.5-4.5), preferably (75-85):(2-4); optionally, the first conductive agent is selected from at least one of graphite, carbon black, graphene, conductive carbon black, and acetylene black; and / or, the second negative electrode active material layer further includes a second conductive agent; optionally, the mass ratio of the second conductive agent to the second conductive agent in the second negative electrode active material layer is (80-98):(3.2-5.5); preferably (85-95):(3-5); optionally, the second conductive agent is selected from at least one of graphite, carbon black, graphene, conductive carbon black, and acetylene black.

[0015] Optionally, the thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer is 1:2 to 4, preferably 1:2 to 3; optionally, the thickness of the first negative electrode active material layer is 90 to 150 μm, preferably 100 to 120 μm; optionally, the thickness of the second negative electrode active material layer is 50 to 90 μm, preferably 65 to 75 μm.

[0016] A second aspect of the present invention provides a method for preparing a negative electrode, the method comprising the following steps:

[0017] S1. The inner layer slurry is coated onto the surface of the current collector and a first drying process is performed to obtain a current collector with a first negative electrode active material layer.

[0018] S2. The outer layer slurry is coated onto the surface of the current collector where the first negative electrode active material layer is provided, and a second drying process is performed.

[0019] The inner layer slurry comprises a first negative electrode active material, a first liquid absorbent, and a first composite binder; wherein the first liquid absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the first composite binder comprises a first water-based binder containing hydroxyl groups.

[0020] The outer slurry comprises a second negative electrode active material, a second liquid absorbent, and a second composite binder; wherein the second liquid absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the second composite binder comprises a second water-based binder containing hydroxyl groups.

[0021] Optionally, the preparation step of the inner layer slurry includes: first mixing a first negative electrode active material, a first conductive agent, a first composite binder, and a first solvent to obtain a first material; adding a first absorbent to the first material and performing a second mixing; wherein the first absorbent includes potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the first composite binder includes a first aqueous binder containing hydroxyl groups; optionally, the first solvent is water; and / or, the preparation step of the outer layer slurry includes: third mixing a second negative electrode active material, a second conductive agent, a second composite binder, and a second solvent to obtain a second material; adding a second absorbent to the second material and performing a third mixing; wherein the second absorbent includes potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the second composite binder includes a second aqueous binder containing hydroxyl groups; optionally, the second solvent is water.

[0022] Optionally, the inner layer slurry comprises: 75-80 parts by weight of the first negative electrode active material, 2-4 parts by weight of the first conductive agent, 1.2-2.4 parts by weight of the first composite binder, 0.7-1.2 parts by weight of the first liquid absorbent, and 20-30 parts by weight of the first solvent; and / or, the outer layer slurry comprises: 85-95 parts by weight of the second negative electrode active material, 3-5 parts by weight of the second conductive agent, 0.6-1.3 parts by weight of the second composite binder, 0.3-0.5 parts by weight of the second liquid absorbent, and 35-45 parts by weight of the second solvent.

[0023] A third aspect of the present invention provides a battery comprising the above-described negative electrode and / or a negative electrode prepared according to the above method.

[0024] The beneficial technical effects of the present invention through the above technical solution are as follows:

[0025] (1) The negative electrode in this invention includes a first negative electrode active material layer (inner layer) disposed on the surface of the current collector and a second negative electrode active material layer (outer layer) disposed on the surface of the first negative electrode active material layer away from the current collector. The first negative electrode active material layer includes a first absorbent and a first aqueous binder containing hydroxyl groups; the second negative electrode active material layer includes a second absorbent and a second aqueous binder containing hydroxyl groups; the first and second absorbents each contain aldehyde groups, and the aldehyde groups of the absorbent polymerize with the hydroxyl groups in the binder, enabling the absorbent to be dispersed more uniformly, which is beneficial for the rapid absorption of liquid by the entire electrode.

[0026] (2) The negative electrode sheet of the present invention improves the wetting effect and speed, while also improving the overall electrical performance of the battery. Furthermore, the preparation process of the negative electrode sheet of the present invention is simple and easy to industrialize.

[0027] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0028] This invention discloses a negative electrode, its preparation method, and a battery. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0029] In the description of this invention, the list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0030] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0031] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0032] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0033] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0034] To address the problem of numerous black and purple spots appearing on the surface of the negative electrode sheet due to excessively long immersion time in existing technologies, the present invention adopts the following technical solution:

[0035] The first aspect of the present invention provides a negative electrode, the negative electrode comprising a current collector, a first negative electrode active material layer disposed on the surface of the current collector, and a second negative electrode active material layer disposed on the surface of the first negative electrode active material layer;

[0036] The first negative electrode active material layer includes a first negative electrode active substance, a first liquid absorbent, and a first composite binder; the second negative electrode active material layer includes a second negative electrode active substance, a second liquid absorbent, and a second composite binder.

[0037] The first absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the first composite adhesive comprises a first aqueous adhesive containing hydroxyl groups; the second absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the second composite adhesive comprises a second aqueous adhesive containing hydroxyl groups.

[0038] The negative electrode of this invention includes a first negative electrode active material layer (inner layer) disposed on the surface of the current collector and a second negative electrode active material layer (outer layer) disposed on the surface of the first negative electrode active material layer away from the current collector. This invention adds an aldehyde-containing absorbent and a hydroxyl-containing aqueous binder to the inner and outer layers of the negative electrode, respectively. The aldehyde group of the absorbent polymerizes with the hydroxyl group in the aqueous binder, making the absorbent more uniformly dispersed, which is beneficial to the rapid absorption of liquid by the entire electrode sheet, and can improve the wetting effect and speed, which is conducive to improving the overall electrical performance of the battery.

[0039] In a preferred embodiment of the present invention, the first and second absorbents each comprise potassium formate. In this embodiment, potassium formate undergoes an exothermic reaction with water, effectively removing harmful trace water from inside the battery and improving the overall electrochemical performance of the battery. Furthermore, the exothermic reaction allows the battery to be used in low-temperature environments (e.g., -30°C), increasing the cell temperature so that the cell can function normally at low temperatures, effectively improving the poor performance of lithium iron phosphate batteries at low temperatures. In addition, potassium formate can react with acids, removing acidic substances generated by side reactions in the electrolyte, further improving battery performance; and through polymerization, the absorbent and binder are effectively combined, improving wettability while significantly optimizing battery performance.

[0040] According to the present invention, since the absorbent in the second negative electrode active material layer (outer layer) can directly contact the electrolyte and absorb liquid more quickly, the amount of absorbent added in the first negative electrode active material layer (inner layer) is higher than that in the second negative electrode active material layer (outer layer) to facilitate rapid wetting of the electrode sheet. For example, in the first negative electrode active material layer, the mass ratio of the first negative electrode active material, the first absorbent, and the first composite binder can be (70-90):(0.5-1.5):(1.0-2.5); in the second negative electrode active material layer, the mass ratio of the second negative electrode active material, the second absorbent, and the second composite binder can be (80-98):(0.2-0.6):(0.5-1.5).

[0041] Preferably, in the first negative electrode active material layer, the mass ratio of the first negative electrode active substance, the first liquid absorbent and the first composite binder can be (75-85):(0.7-1.2):(1.2-2.4); and in the second negative electrode active material layer, the mass ratio of the second negative electrode active substance, the second liquid absorbent and the second composite binder can be (85-95):(0.3-0.5):(0.6-1.3).

[0042] In a preferred embodiment of the present invention, the masses of the first absorbent and the second absorbent satisfy the following formula:

[0043] x = -5y 2 +6.5y-0.8,

[0044] Where x represents the mass of the first absorbent and y represents the mass of the second absorbent. In this embodiment, the mass of the first absorbent first increases and then decreases with the mass of the second absorbent, thereby ensuring rapid wetting of the electrode sheet; when the two layers of absorbent reach a certain amount, further increasing the amount of absorbent added does not significantly change the wetting speed or the amount added, and the trend of decreasing wetting time weakens.

[0045] According to the present invention, a suitable mass density of the first negative electrode active material can ensure both the diffusion effect of lithium ions in the inner layer and the lithium intercalation effect in the outer layer. In the present invention, the mass density of the first negative electrode active material in the first negative electrode active material layer can be 60–100 mg / cm³. 3 For example, the mass density of the first negative electrode active material can be 60 mg / cm³. 3 70mg / cm 3 80mg / cm 3 90mg / cm 3 and 100mg / cm 3The value can be any value in the range or any value within the range formed by any two of the above values. In this invention, if the mass density of the first negative electrode active material is too high, it can provide more lithium intercalation sites, which may result in less second negative electrode active material and hinder lithium ion diffusion in the inner layer; if the mass density of the first negative electrode active material is too low, it may result in too few lithium intercalation sites in the outer layer, which is not conducive to fast charging. Preferably, the mass density of the first negative electrode active material can be 70-90 mg / cm³. 3 .

[0046] For example, the first negative electrode active material may be selected from at least one of natural graphite, artificial graphite, soft carbon, and hard carbon.

[0047] According to the present invention, a suitable mass density of the second negative electrode active material can ensure both the diffusion effect of lithium ions in the inner layer and the lithium intercalation effect in the outer layer. In the present invention, the mass density of the second negative electrode active material in the second negative electrode active material layer can be 40–90 mg / cm³. 3 For example, the mass density of the second negative electrode active material can be 40 mg / cm³. 3 50mg / cm 3 60mg / cm 3 70mg / cm 3 80mg / cm 3 and 90mg / cm 3 The value can be any value within the range of any two of the above values. In this invention, if the mass density of the second negative electrode active material is too high, it may result in too few lithium intercalation sites in the outer layer, which is detrimental to fast charging; if the mass density of the second negative electrode active material is too low, it may result in less second negative electrode active material, which is detrimental to lithium ion diffusion in the inner layer. Preferably, the mass density of the second negative electrode active material can be 50–80 mg / cm³. 3 .

[0048] For example, the second negative electrode active material may be selected from at least one of natural graphite, artificial graphite, soft carbon, and hard carbon.

[0049] According to the present invention, the first composite adhesive may further include styrene-butadiene rubber; optionally, the mass ratio of the hydroxyl-containing first aqueous adhesive to the styrene-butadiene rubber may be (0.5-3):(0.1-0.5). A suitable ratio of the hydroxyl-containing first aqueous adhesive to the styrene-butadiene rubber in the present invention can improve the absorption rate of the first absorbent in the first negative electrode active material layer while ensuring the bonding effect. Preferably, the mass ratio of the hydroxyl-containing first aqueous adhesive to the styrene-butadiene rubber may be (1-2):(0.2-0.4).

[0050] For example, the hydroxyl-containing first aqueous binder may be selected from at least one of cellulose acetate, hydroxyethyl cellulose, methyl cellulose, polyvinyl alcohol, and polyacrylamide.

[0051] For example, the second composite adhesive also includes styrene-butadiene rubber.

[0052] According to the present invention, the mass ratio of the hydroxyl-containing second aqueous binder to the styrene-butadiene rubber can be (0.3-1.2):(0.1-0.5). A suitable ratio of the hydroxyl-containing second aqueous binder to the styrene-butadiene rubber in the present invention can improve the absorption rate of the second absorbent in the second negative electrode active material layer while ensuring the bonding effect. Preferably, the mass ratio of the hydroxyl-containing second aqueous binder to the styrene-butadiene rubber can be (0.5-1):(0.1-0.3).

[0053] For example, the hydroxyl-containing second aqueous binder may be selected from at least one of cellulose acetate, hydroxyethyl cellulose, methyl cellulose, polyvinyl alcohol, and polyacrylamide.

[0054] According to the present invention, the first negative electrode active material layer may further include a first conductive agent; optionally, in the first negative electrode active material layer, the mass ratio of the first negative electrode active material to the first conductive agent is (70-90):(1.5-4.5), preferably (75-85):(2-4).

[0055] For example, the first conductive agent may be selected from at least one of graphite, carbon black, graphene, conductive carbon black and acetylene black.

[0056] According to the present invention, the second negative electrode active material layer may further include a second conductive agent; optionally, the mass ratio of the second negative electrode active material layer to the second conductive agent may be (80-98):(3.2-5.5); preferably (85-95):(3-5).

[0057] For example, the second conductive agent may be selected from at least one of graphite, carbon black, graphene, conductive carbon black and acetylene black.

[0058] According to the present invention, a suitable thickness ratio of the first negative electrode active material layer and the second negative electrode active material layer is beneficial to improving the overall electrical performance of the battery. In this invention, the thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer can be 1:2 to 4. Exemplarily, the thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer can be any value from 1:2, 1:2.5, 1:3, 1:3.5, and 1:4, or any value within the range formed by any two of the above values. In this invention, if the thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer is too high, i.e., the thickness of the first negative electrode active material layer is relatively large, it may result in a longer time required for lithium ions to intercalate into the inner layer; if the thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer is too low, i.e., the thickness of the second negative electrode active material layer is relatively large, it may be detrimental to the rapid intercalation of lithium ions. Preferably, the thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer can be 1:2 to 3.

[0059] According to the present invention, the thickness of the first negative electrode active material layer can be 90–150 μm. Exemplarily, the thickness of the first negative electrode active material layer can be any value selected from 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, and 150 μm, or any value within the range formed by any pair of the above values. Preferably, the thickness of the first negative electrode active material layer can be 100–120 μm.

[0060] According to the present invention, the thickness of the second negative electrode active material layer can be 50–90 μm. Exemplarily, the thickness of the second negative electrode active material layer can be any value selected from 50 μm, 60 μm, 70 μm, 80 μm, and 90 μm, or any value within the range formed by any pair of the above values. Preferably, the thickness of the second negative electrode active material layer can be 65–75 μm.

[0061] A second aspect of the present invention provides a method for preparing a negative electrode, the method comprising the following steps:

[0062] S1. The inner layer slurry is coated onto the surface of the current collector and a first drying process is performed to obtain a current collector with a first negative electrode active material layer.

[0063] S2. The outer layer slurry is coated onto the surface of the current collector where the first negative electrode active material layer is provided, and a second drying process is performed.

[0064] The inner layer slurry comprises a first negative electrode active material, a first liquid absorbent, and a first composite binder; wherein the first liquid absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the first composite binder comprises a first water-based binder containing hydroxyl groups.

[0065] The outer slurry comprises a second negative electrode active material, a second liquid absorbent, and a second composite binder; wherein the second liquid absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the second composite binder comprises a second water-based binder containing hydroxyl groups.

[0066] In one embodiment of the present invention, the preparation step of the inner layer slurry may include: mixing a first negative electrode active material, a first conductive agent, a first composite binder and a first solvent to obtain a first material; adding a first liquid absorbent to the first material and mixing it a second time.

[0067] For example, the first absorbent may include potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the first composite adhesive may include a first aqueous adhesive containing hydroxyl groups.

[0068] For example, the first solvent may be water.

[0069] In another embodiment of the present invention, the preparation step of the outer layer slurry may include: mixing the second negative electrode active material, the second conductive agent, the second composite binder and the second solvent in a third mixing to obtain a second material; adding a second liquid absorbent to the second material and mixing in a third mixing.

[0070] For example, the second absorbent may include potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the second composite adhesive may include a second water-based adhesive containing hydroxyl groups.

[0071] For example, the second solvent may be water.

[0072] According to the present invention, the inner layer slurry may include: 75-80 parts by weight of the first negative electrode active material, 2-4 parts by weight of the first conductive agent, 1.2-2.4 parts by weight of the first composite binder, 0.7-1.2 parts by weight of the first liquid absorbent, and 20-30 parts by weight of the first solvent.

[0073] According to the present invention, the outer slurry may include: 85-95 parts by weight of the second negative electrode active material, 3-5 parts by weight of the second conductive agent, 0.6-1.3 parts by weight of the second composite binder, 0.3-0.5 parts by weight of the second liquid absorbent, and 35-45 parts by weight of the second solvent.

[0074] A third aspect of the present invention provides a battery comprising the above-described negative electrode and / or a negative electrode prepared according to the above method.

[0075] The present invention will be further described in detail below through examples. All raw materials used in the examples are commercially available.

[0076] Example 1

[0077] (1) Preparation of inner and outer layer slurries: 75 parts natural graphite, 2 parts conductive carbon black (SP), 1 part cellulose acetate, 0.2 parts styrene-butadiene rubber and 20 parts deionized water were stirred for 120 min to obtain the first material; 0.7 parts potassium formate were added to the first material and stirred for 30 min to obtain the inner layer slurry. 85 parts artificial graphite, 3 parts SP, 0.5 parts cellulose acetate, 0.1 parts styrene-butadiene rubber and 35 parts deionized water were stirred for 120 min to obtain the second material; 0.3 parts potassium formate were added to the second material and stirred for 30 min to obtain the outer layer slurry.

[0078] (2) Preparation of negative electrode sheet: The inner layer slurry is coated on the surface of aluminum foil and subjected to a first drying treatment at a temperature of 90°C to obtain an aluminum foil with a first negative electrode active material layer, wherein the thickness of the first negative electrode active material layer is 100 μm; the outer layer slurry is coated on the surface of the aluminum foil with the first negative electrode active material layer and subjected to a second drying treatment at a temperature of 90°C to obtain a negative electrode sheet, wherein the thickness of the second negative electrode active material layer is 80 μm.

[0079] (3) Preparation of positive electrode sheet: Lithium iron phosphate, conductive carbon black (SP), and binder polyvinylidene fluoride (PVDF) are mixed with an appropriate amount of N-methylpyrrolidone (NMP) in a ratio of 95:3:2 to prepare a positive electrode slurry, which is coated on aluminum foil, dried by blowing at 100°C, and then cold-pressed and cut into positive electrode sheets.

[0080] (4) Battery preparation: The positive electrode, separator, and negative electrode are wound into a core, wherein the separator completely covers the positive and negative electrode. The core is then placed in a metal shell or wrapped in an aluminum-plastic film and injected with electrolyte. Finally, the lithium iron phosphate battery is produced through processes such as settling, formation, and capacity testing.

[0081] Example 2

[0082] (1) Preparation of inner and outer layer slurries: 80 parts of natural graphite, 3 parts of conductive carbon black (SP), 1.5 parts of cellulose acetate, 0.3 parts of styrene-butadiene rubber and 25 parts of deionized water were stirred for 120 min to obtain the first material; 1 part of potassium formate was added to the first material and stirred for 30 min to obtain the inner layer slurry. 90 parts of artificial graphite, 4 parts of SP, 0.7 parts of cellulose acetate, 0.2 parts of styrene-butadiene rubber and 40 parts of deionized water were stirred for 120 min to obtain the second material; 0.4 parts of potassium formate was added to the second material and stirred for 30 min to obtain the outer layer slurry.

[0083] (2) Preparation of negative electrode sheet: The inner layer slurry is coated on the surface of aluminum foil and subjected to a first drying treatment at a temperature of 90°C to obtain an aluminum foil with a first negative electrode active material layer, wherein the thickness of the first negative electrode active material layer is 100 μm; the outer layer slurry is coated on the surface of the aluminum foil with the first negative electrode active material layer and subjected to a second drying treatment at a temperature of 90°C to obtain a negative electrode sheet, wherein the thickness of the second negative electrode active material layer is 80 μm.

[0084] The preparation method of the positive electrode sheet and the preparation method of the battery in this embodiment are the same as in Embodiment 1.

[0085] Example 3

[0086] (1) Preparation of inner and outer layer slurries: 85 parts natural graphite, 4 parts conductive carbon black (SP), 2 parts cellulose acetate, 0.4 parts styrene-butadiene rubber, and 30 parts deionized water were stirred for 120 min to obtain the first material; 1.2 parts potassium formate were added to the first material and stirred for 30 min to obtain the inner layer slurry. 95 parts artificial graphite, 5 parts SP, 1 part cellulose acetate, 0.3 parts styrene-butadiene rubber, and 30 parts deionized water were stirred for 120 min to obtain the second material; 0.5 parts potassium formate were added to the second material and stirred for 30 min to obtain the outer layer slurry.

[0087] (2) Preparation of negative electrode sheet: The inner layer slurry is coated on the surface of aluminum foil and subjected to a first drying treatment at a temperature of 90°C to obtain an aluminum foil with a first negative electrode active material layer, wherein the thickness of the first negative electrode active material layer is 100 μm; the outer layer slurry is coated on the surface of the aluminum foil with the first negative electrode active material layer and subjected to a second drying treatment at a temperature of 90°C to obtain a negative electrode sheet, wherein the thickness of the second negative electrode active material layer is 80 μm.

[0088] The preparation method of the positive electrode sheet and the preparation method of the battery in this embodiment are the same as in Embodiment 1.

[0089] Example 4

[0090] (1) Preparation of inner and outer layer slurries: 85 parts of natural graphite, 4 parts of conductive carbon black (SP), 2 parts of cellulose acetate, 0.4 parts of styrene-butadiene rubber, and 30 parts of deionized water were stirred for 120 min to obtain the first material; 1.2 parts of aldehyde-based polyethylene glycol aldehyde were added to the first material and stirred for 30 min to obtain the inner layer slurry. 95 parts of artificial graphite, 5 parts of SP, 1 part of cellulose acetate, 0.3 parts of styrene-butadiene rubber, and 45 parts of deionized water were stirred for 120 min to obtain the second material; 0.5 parts of aldehyde-based polyethylene glycol aldehyde were added to the second material and stirred for 30 min to obtain the outer layer slurry.

[0091] (2) Preparation of negative electrode sheet: The inner layer slurry is coated on the surface of aluminum foil and subjected to a first drying treatment at a temperature of 90°C to obtain an aluminum foil with a first negative electrode active material layer, wherein the thickness of the first negative electrode active material layer is 100 μm; the outer layer slurry is coated on the surface of the aluminum foil with the first negative electrode active material layer and subjected to a second drying treatment at a temperature of 90°C to obtain a negative electrode sheet, wherein the thickness of the second negative electrode active material layer is 80 μm.

[0092] The preparation method of the positive electrode sheet and the preparation method of the battery in this embodiment are the same as in Embodiment 1.

[0093] Comparative Example 1

[0094] (1) Preparation of inner and outer layer slurries: 75 parts natural graphite, 2 parts conductive carbon black (SP), 1 part cellulose acetate, 0.2 parts styrene-butadiene rubber and 20 parts deionized water were stirred for 120 min to obtain the inner layer slurry. 85 parts artificial graphite, 3 parts SP, 0.5 parts cellulose acetate, 0.1 parts styrene-butadiene rubber and 35 parts deionized water were stirred for 120 min to obtain the second material; 0.3 parts potassium formate were added to the second material and stirred for 30 min to obtain the outer layer slurry.

[0095] (2) Preparation of negative electrode sheet: The inner layer slurry is coated on the surface of aluminum foil and subjected to a first drying treatment at a temperature of 90°C to obtain an aluminum foil with a first negative electrode active material layer, wherein the thickness of the first negative electrode active material layer is 100 μm; the outer layer slurry is coated on the surface of the aluminum foil with the first negative electrode active material layer and subjected to a second drying treatment at a temperature of 90°C to obtain a negative electrode sheet, wherein the thickness of the second negative electrode active material layer is 80 μm.

[0096] The preparation method of the positive electrode sheet and the battery of this comparative example are the same as those in Example 1.

[0097] Comparative Example 2

[0098] (1) Preparation of inner and outer layer slurries: 75 parts natural graphite, 2 parts conductive carbon black (SP), 1 part cellulose acetate, 0.2 parts styrene-butadiene rubber and 20 parts deionized water were stirred for 120 min to obtain the first material; 0.7 parts potassium formate were added to the first material and stirred for 30 min to obtain the inner layer slurry. 85 parts artificial graphite, 3 parts SP, 0.5 parts cellulose acetate, 0.1 parts styrene-butadiene rubber and 35 parts deionized water were stirred for 120 min to obtain the outer layer slurry.

[0099] (2) Preparation of negative electrode sheet: The inner layer slurry is coated on the surface of aluminum foil and subjected to a first drying treatment at a temperature of 90°C to obtain an aluminum foil with a first negative electrode active material layer, wherein the thickness of the first negative electrode active material layer is 100 μm; the outer layer slurry is coated on the surface of the aluminum foil with the first negative electrode active material layer and subjected to a second drying treatment at a temperature of 90°C to obtain a negative electrode sheet, wherein the thickness of the second negative electrode active material layer is 80 μm.

[0100] The preparation method of the positive electrode sheet and the battery of this comparative example are the same as those in Example 1.

[0101] Comparative Example 3

[0102] (1) Preparation of inner and outer layer slurries: 75 parts natural graphite, 2 parts conductive carbon black (SP), 1 part cellulose acetate, 0.2 parts styrene-butadiene rubber and 20 parts deionized water were stirred for 120 min to obtain the inner layer slurry. 85 parts artificial graphite, 3 parts SP, 0.5 parts cellulose acetate, 0.1 parts styrene-butadiene rubber and 35 parts deionized water were stirred for 120 min to obtain the outer layer slurry.

[0103] (2) Preparation of negative electrode sheet: The inner layer slurry is coated on the surface of aluminum foil and subjected to a first drying treatment at a temperature of 90°C to obtain an aluminum foil with a first negative electrode active material layer, wherein the thickness of the first negative electrode active material layer is 100 μm; the outer layer slurry is coated on the surface of the aluminum foil with the first negative electrode active material layer and subjected to a second drying treatment at a temperature of 90°C to obtain a negative electrode sheet, wherein the thickness of the second negative electrode active material layer is 80 μm.

[0104] The preparation method of the positive electrode sheet and the battery of this comparative example are the same as those in Example 1.

[0105] The compositional analysis of the inner and outer slurries in Examples 1-4 and Comparative Examples 1-3 is shown in Table 1.

[0106] Table 1

[0107]

[0108]

[0109] Test Example 1

[0110] The batteries prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to cycle tests and battery capacity verification tests. The test results are shown in Table 2.

[0111] The cycle test method includes: charging the battery at 0.5C constant current and constant voltage to 3.65V at 25℃, with a cutoff condition of 0.05C; discharging at 0.5C to 2.5V after standing for 60 minutes, and continuing the above process until the capacity decays to 80% of the initial test capacity, and recording the number of cycles.

[0112] The method for verifying the battery capacity interface includes: after verifying the battery capacity, charging the battery to 3.65V at a full charge of 0.5C, and then disassembling the battery to verify the interface.

[0113] Low temperature performance test: At -30℃, the battery is charged to 4.0V with a constant current and constant voltage of 0.05C, and the cutoff condition is 0.05C; after standing for 60 minutes, it is discharged to 1.5V at 0.3C. The above process is continued until the capacity decays to 80% of the initial capacity, and the number of cycles is recorded.

[0114] Table 2

[0115]

[0116] As can be seen from Table 2, in the embodiments of the present invention, an aldehyde-containing absorbent and a hydroxyl-containing aqueous binder are added to the inner and outer layers of the negative electrode, respectively. By using the aldehyde-containing absorbent and the hydroxyl-containing aqueous binder together, the number of black spots can be effectively reduced and the number of battery cycles can be increased.

[0117] Specifically, data from Examples 1-3 show that appropriately increasing the content of absorbent in both the inner and outer layers results in a cycle count greater than 3200 cycles in the cycle test, demonstrating good cycle performance; the low-temperature performance test results in a cycle count greater than 1500 cycles, demonstrating good low-temperature performance; and the number of black spots on the negative interface is significantly reduced. Data from Example 1 and Comparative Example 1 show that when absorbent is added only to the outer layer additive, the cycle count in the cycle test is reduced to 2467 cycles, the low-temperature performance test results to 1428 cycles, and the number of black spots on the negative interface reaches 6. Data from Example 1 and Comparative Example 2 show that when absorbent is added only to the inner layer additive, the cycle count in the cycle test is reduced to 2619 cycles, the low-temperature performance test results to 1443 cycles, and the number of black spots on the negative interface reaches 2. Therefore, the present invention, by simultaneously adding absorbent to both the inner and outer layers of the negative electrode, can effectively reduce the number of black spots and improve the cycle count and low-temperature performance of the battery.

[0118] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A negative electrode, characterized in that, The negative electrode includes a current collector, a first negative electrode active material layer disposed on the surface of the current collector, and a second negative electrode active material layer disposed on the surface of the first negative electrode active material layer; The first negative electrode active material layer includes a first negative electrode active substance, a first liquid absorbent, and a first composite binder; the second negative electrode active material layer includes a second negative electrode active substance, a second liquid absorbent, and a second composite binder. The first absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the first composite adhesive comprises a first aqueous adhesive containing hydroxyl groups; the second absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the second composite adhesive comprises a second aqueous adhesive containing hydroxyl groups.

2. The negative electrode according to claim 1, characterized in that, In the first negative electrode active material layer, the mass ratio of the first negative electrode active substance, the first liquid absorbent, and the first composite binder is (70~90):(0.5~1.5):(1.0~2.5). And / or, In the second negative electrode active material layer, the mass ratio of the second negative electrode active substance, the second liquid absorbent and the second composite binder is (80~98):(0.2~0.6):(0.5~1.5).

3. The negative electrode according to claim 2, characterized in that, In the first negative electrode active material layer, the mass ratio of the first negative electrode active substance, the first liquid absorbent, and the first composite binder is (75~85):(0.7~1.2):(1.2~2.4). And / or, In the second negative electrode active material layer, the mass ratio of the second negative electrode active substance, the second liquid absorbent and the second composite binder is (85~95):(0.3~0.5):(0.6~1.3).

4. The negative electrode according to claim 1, characterized in that, The mass density of the first negative electrode active material in the first negative electrode active material layer is 60~100 mg / cm³. 3 ; And / or, The mass density of the second negative electrode active material in the second negative electrode active material layer is 40~90 mg / cm³.

5. The negative electrode according to claim 4, characterized in that, The mass density of the first negative electrode active material in the first negative electrode active material layer is 70~90 mg / cm³. 3 ; And / or, The mass density of the second negative electrode active material in the second negative electrode active material layer is 50~80 mg / cm³. 3 .

6. The negative electrode according to claim 4, characterized in that, The first negative electrode active material is selected from at least one of natural graphite, artificial graphite, soft carbon, and hard carbon; And / or, The second negative electrode active material is selected from at least one of natural graphite, artificial graphite, soft carbon, and hard carbon.

7. The negative electrode according to claim 1, characterized in that, The first composite adhesive also includes styrene-butadiene rubber; And / or, The second composite adhesive also includes styrene-butadiene rubber.

8. The negative electrode according to claim 7, characterized in that, The first composite adhesive further includes styrene-butadiene rubber, and the mass ratio of the hydroxyl-containing first aqueous adhesive to the styrene-butadiene rubber is (0.5~3):(0.1~0.5). And / or, The second composite adhesive further includes styrene-butadiene rubber, and the mass ratio of the hydroxyl-containing second aqueous adhesive to the styrene-butadiene rubber is (0.3~1.2):(0.1~0.5).

9. The negative electrode according to claim 8, characterized in that, The first composite adhesive further includes styrene-butadiene rubber, and the mass ratio of the hydroxyl-containing first aqueous adhesive to the styrene-butadiene rubber is (1~2):(0.2~0.4). And / or, The second composite adhesive further includes styrene-butadiene rubber, and the mass ratio of the hydroxyl-containing second aqueous adhesive to the styrene-butadiene rubber is (0.5~1):(0.1~0.3).

10. The negative electrode according to claim 1, characterized in that, The hydroxyl-containing first aqueous binder is selected from at least one of cellulose acetate, hydroxyethyl cellulose, methyl cellulose, and polyvinyl alcohol; And / or, The hydroxyl-containing second aqueous binder is selected from at least one of cellulose acetate, hydroxyethyl cellulose, methyl cellulose, and polyvinyl alcohol.

11. The negative electrode according to claim 1, characterized in that, The first negative electrode active material layer also includes a first conductive agent; And / or, The second negative electrode active material layer also includes a second conductive agent.

12. The negative electrode according to claim 11, characterized in that, In the first negative electrode active material layer, the mass ratio of the first negative electrode active material to the first conductive agent is (70~90):(1.5~4.5). And / or, In the second negative electrode active material layer, the mass ratio of the second negative electrode active material to the second conductive agent is (80~98):(3.2~5.5).

13. The negative electrode according to claim 12, characterized in that, In the first negative electrode active material layer, the mass ratio of the first negative electrode active material to the first conductive agent is (75~85):(2~4). And / or, In the second negative electrode active material layer, the mass ratio of the second negative electrode active material to the second conductive agent is (85~95):(3.2~5).

14. The negative electrode according to claim 11, characterized in that, The first conductive agent is selected from at least one of graphite, carbon black, graphene, conductive carbon black, and acetylene black; And / or, The second conductive agent is selected from at least one of graphite, carbon black, graphene, conductive carbon black, and acetylene black.

15. The negative electrode according to claim 1, characterized in that, The thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer is 1:(2~4).

16. The negative electrode according to claim 15, characterized in that, The thickness ratio of the first negative electrode active material layer to the second negative electrode active material layer is 1:(2~3).

17. The negative electrode according to claim 1, characterized in that, The thickness of the first negative electrode active material layer is 90~150μm.

18. The negative electrode according to claim 17, characterized in that, The thickness of the first negative electrode active material layer is 100~120μm.

19. The negative electrode according to claim 1, characterized in that, The thickness of the second negative electrode active material layer is 50~90μm.

20. The negative electrode according to claim 19, characterized in that, The thickness of the second negative electrode active material layer is 65~75μm.

21. A method for preparing the negative electrode according to any one of claims 1 to 20, characterized in that, The preparation method includes the following steps: S1. The inner layer slurry is coated onto the surface of the current collector and a first drying process is performed to obtain a current collector with a first negative electrode active material layer. S2. The outer layer slurry is coated onto the surface of the current collector where the first negative electrode active material layer is provided, and a second drying process is performed. The inner layer slurry comprises a first negative electrode active material, a first liquid absorbent, and a first composite binder; wherein the first liquid absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the first composite binder comprises a first water-based binder containing hydroxyl groups. The outer slurry comprises a second negative electrode active material, a second liquid absorbent, and a second composite binder; wherein the second liquid absorbent comprises potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the second composite binder comprises a second water-based binder containing hydroxyl groups.

22. The preparation method according to claim 21, characterized in that, The preparation steps of the inner layer slurry include: mixing a first negative electrode active material, a first conductive agent, a first composite binder and a first solvent to obtain a first material; adding a first liquid absorbent to the first material and mixing it a second time; wherein the first liquid absorbent includes potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the first composite binder includes a first water-based binder containing hydroxyl groups; And / or, The preparation steps of the outer layer slurry include: mixing the second negative electrode active material, the second conductive agent, the second composite binder and the second solvent in a third mixing to obtain the second material; adding the second liquid absorbent to the second material and mixing in a third mixing; wherein the second liquid absorbent includes potassium formate and / or aldehyde-based polyethylene glycol aldehyde, and the second composite binder includes a second water-based binder containing hydroxyl groups.

23. The preparation method according to claim 22, characterized in that, The first solvent is water; And / or, The second solvent is water.

24. The preparation method according to claim 22, characterized in that, The inner layer slurry comprises: 75-80 parts by weight of the first negative electrode active material, 2-4 parts by weight of the first conductive agent, 1.2-2.4 parts by weight of the first composite binder, 0.7-1.2 parts by weight of the first liquid absorbent, and 20-30 parts by weight of the first solvent; And / or, The outer slurry comprises: 85-95 parts by weight of the second negative electrode active material, 3-5 parts by weight of the second conductive agent, 0.6-1.3 parts by weight of the second composite binder, 0.3-0.5 parts by weight of the second liquid absorbent, and 35-45 parts by weight of the second solvent.

25. A battery, characterized in that, The battery includes a negative electrode as described in any one of claims 1 to 20 or a negative electrode prepared by the method described in any one of claims 21 to 24.

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