A binder, a negative electrode slurry, a negative electrode sheet, a battery

Abstract

The application provides a binder, a negative electrode slurry, a negative electrode sheet and a battery. The binder comprises a polymer, the polymer comprises acrylic structural units, quaternary ammonium salt-containing structural units, phenolic ether structural units and flexible structural units, and the mass ratio of the acrylic structural units, the quaternary ammonium salt-containing structural units, the phenolic ether structural units and the flexible structural units is (30-70):(1-10):(0.5-5):(5-20); the phenolic ether structural units comprise at least one of aromatic phenolic structural units and aromatic ether structural units. The binder provided by the application can provide a triple dispersion mechanism of static stability, surface adsorption and hydrophobic anchoring through the cooperation of the acrylic structural units, the quaternary ammonium salt-containing structural units and the phenolic ether structural units, so that the negative electrode slurry can form a long-term stable water-based slurry system without relying on an external dispersant. The binder forms a bactericidal and bacteriostatic barrier in the slurry, has a stable anti-corrosion structure network and stable electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a binder, a negative electrode slurry, a negative electrode sheet, and a battery. Background Art

[0002] Batteries have become the main power source of choice for modern portable electronic devices, electric vehicles and energy storage systems due to their advantages such as high energy density, long cycle life and low self-discharge rate.

[0003] Aqueous binders are usually added to the negative electrode slurry of the battery to improve its dispersibility and film-forming ability. However, due to its high hydrophilicity and rich hydrophilic structure, aqueous binders easily absorb environmental moisture and breed microorganisms, causing the slurry to become moldy and deteriorate after long-term storage, which not only causes material waste, but also affects the stability of the electrode and battery performance.

[0004] The existing technology is to add additional isothiazolinone small molecule preservatives to the negative electrode slurry, but such substances are potentially toxic and easy to migrate and volatilize, posing a threat to the long-term performance of the battery and environmental safety.

[0005] Therefore, there is an urgent need for a new type of negative electrode binder to extend the storage period of the negative electrode slurry. Summary of the Invention

[0006] Aiming at the problem that the existing negative electrode binder easily causes the negative electrode slurry to become moldy and deteriorate, the present invention provides a binder, a negative electrode slurry, a negative electrode sheet and a battery.

[0007] To solve the above technical problems, the present invention provides a binder, comprising a polymer, wherein the polymer comprises an acrylic acid structural unit, a structural unit containing a quaternary ammonium salt, a phenol ether structural unit, and a flexible structural unit, wherein the mass ratio of the acrylic acid structural unit, the structural unit containing a quaternary ammonium salt, the phenol ether structural unit, and the flexible structural unit is (30-70):(1-10):(0.5-5):(5-20); the phenol ether structural unit comprises at least one of an aromatic phenol structural unit and an aromatic ether structural unit.

[0008] Preferably, the antibacterial rate of the adhesive is greater than 96%, and the mildew resistance level is greater than or equal to level 4.

[0009] Preferably, the viscosity of the adhesive is 2500-5000 mPa·s.

[0010] Preferably, the glass transition temperature of the binder is 30-90°C.

[0011] Preferably, the elongation at break of the adhesive is ≥110%.

[0012] Preferably, the flexible structural unit is a structural unit obtained by polymerization of a flexible monomer, and the flexible monomer includes at least one of butyl acrylate, isooctyl acrylate, and polyethylene glycol dimethacrylate.

[0013] Preferably, the structural unit containing a quaternary ammonium salt comprises an olefin structural unit containing a quaternary ammonium salt;

[0014] The olefin structural unit containing a quaternary ammonium salt is a structural unit obtained by polymerization of an olefin monomer containing a quaternary ammonium salt, and the olefin monomer containing a quaternary ammonium salt includes at least one of methacryloyloxyethyltrimethylammonium chloride, acryloyloxypropyltrimethylammonium chloride, and diallyldimethylammonium chloride.

[0015] In a second aspect, the present application provides a negative electrode slurry, comprising the binder as described in any one of the above items, wherein the 24-hour viscosity change rate of the negative electrode slurry is less than 3%.

[0016] Preferably, the 24-hour solid content change rate of the negative electrode slurry is less than 0.6%.

[0017] In a third aspect, the present application provides a negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer is formed by coating, drying, and rolling the negative electrode slurry as described above.

[0018] In a fourth aspect, the present application provides a battery comprising the negative electrode sheet as described above.

[0019] In this application, the synergistic effect of acrylic acid structural units, structural units containing quaternary ammonium salts, and phenol ether structural units gives the binder anti-corrosion properties and a shelf life of ≥6 months. It can also improve the dispersibility of the conductive agent and negative electrode material in the negative electrode slurry. The carboxyl groups in the acrylic acid structural units give the polymer good water solubility and negative charge density, which helps form a stable electrostatic repulsion layer in the negative electrode slurry, preventing the agglomeration and sedimentation of graphite or active materials in the negative electrode slurry and improving the rheological stability of the system.

[0020] By introducing structural units containing quaternary ammonium salts into the binder, the binder assumes a cationic state in the aqueous phase. This allows for electrostatic adsorption to the surface of the conductive agent in the negative electrode slurry, forming a double-layer structure that provides both a charge barrier and adsorption stabilization. This inhibits aggregation of the conductive agent and improves its uniform dispersion in the aqueous environment. Simultaneously, the structural units containing the quaternary ammonium salts electrostatically adsorb to the negatively charged bacterial cell membranes, disrupting the membrane structure and achieving rapid sterilization. The structural units containing the quaternary ammonium salts are covalently embedded in the polymer chain, preventing migration or inactivation, thus endowing the binder with long-lasting antimicrobial properties.

[0021] The binder incorporates phenolic ether structural units with hydrophobic aromatic structures, enabling the binder to form non-polar interactions with the graphite or active material surface through π-π stacking. In particular, because the binder is also hydrophilic, it effectively reduces interfacial tension between particles, improving particle wettability and suspension. The aromatic phenol or aromatic ether structures within the phenolic ether structural units provide the binder with antioxidant and antifungal properties, inhibiting intracellular oxidase activity in microorganisms, blocking spore growth pathways, and reducing biofilm formation.

[0022] Therefore, the binder provides a triple dispersion mechanism of electrostatic stabilization, surface adsorption, and hydrophobic anchoring through the synergistic combination of acrylic acid structural units, structural units containing quaternary ammonium salts, and phenolic ether structural units, enabling the negative electrode slurry to form a long-term stable aqueous slurry system without relying on the addition of an external dispersant. The synergistic effect of the structural units containing quaternary ammonium salts and phenolic ether structural units enables the binder to form a bactericidal and antibacterial barrier in the slurry, providing a stable anticorrosive structural network that is not eluted with water evaporation or electrolyte, and has stable electrochemical performance. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0024] An embodiment of the present application provides a binder, which includes a polymer, wherein the polymer includes an acrylic structural unit, a structural unit containing a quaternary ammonium salt, a phenol ether structural unit, and a flexible structural unit, wherein the mass ratio of the acrylic structural unit, the structural unit containing a quaternary ammonium salt, the phenol ether structural unit, and the flexible structural unit is (30-70):(1-10):(0.5-5):(5-20); the phenol ether structural unit includes at least one of an aromatic phenol structural unit and an aromatic ether structural unit.

[0025] In this embodiment, the synergistic effects of acrylic acid structural units, structural units containing quaternary ammonium salts, and phenolic ether structural units impart corrosion resistance to the binder while also improving the dispersibility of the conductive agent and negative electrode material in the negative electrode slurry. The carboxyl groups in the acrylic acid structural units impart good water solubility and negative charge density to the polymer. This negative charge density helps form a stable electrostatic repulsion layer in the negative electrode slurry, preventing the aggregation and sedimentation of graphite or active materials in the negative electrode slurry and improving the rheological stability of the system.

[0026] By introducing structural units containing quaternary ammonium salts into the binder, the binder assumes a cationic state in the aqueous phase. This allows for electrostatic adsorption to the surface of the conductive agent in the negative electrode slurry, forming a double-layer structure that provides both a charge barrier and adsorption stabilization. This inhibits aggregation of the conductive agent and improves its uniform dispersion in the aqueous environment. Simultaneously, the structural units containing the quaternary ammonium salts electrostatically adsorb to the negatively charged bacterial cell membranes, disrupting the membrane structure and achieving rapid sterilization. The structural units containing the quaternary ammonium salts are covalently embedded in the polymer chain, preventing migration or inactivation, thus endowing the binder with long-lasting antimicrobial properties.

[0027] The binder incorporates phenolic ether structural units with hydrophobic aromatic structures, enabling the binder to form non-polar interactions with the graphite or active material surface through π-π stacking. In particular, because the binder is also hydrophilic, it effectively reduces interfacial tension between particles, improving particle wettability and suspension. The aromatic phenol or aromatic ether structures within the phenolic ether structural units provide the binder with antioxidant and antifungal properties, inhibiting intracellular oxidase activity in microorganisms, blocking spore growth pathways, and reducing biofilm formation.

[0028] Therefore, the binder provides a triple dispersion mechanism of electrostatic stabilization, surface adsorption, and hydrophobic anchoring through the synergistic combination of acrylic acid structural units, structural units containing quaternary ammonium salts, and phenolic ether structural units, enabling the negative electrode slurry to form a long-term stable aqueous slurry system without relying on the addition of an external dispersant. The synergistic effect of the structural units containing quaternary ammonium salts and phenolic ether structural units enables the binder to form a bactericidal and antibacterial barrier in the slurry, providing a stable anticorrosive structural network that is not eluted with water evaporation or electrolyte, and has stable electrochemical performance.

[0029] Compared with adding isothiazolinone, phenol and other potentially toxic and volatile small molecule preservatives to the negative electrode slurry, the binder of the present application has stable, safe and environmentally friendly anti-corrosion and antibacterial properties.

[0030] By regulating the mass ratio of acrylic acid structural units, structural units containing quaternary ammonium salts, phenolic ether structural units, and flexible structural units in the polymer, the adhesive is made to have good dispersibility and bactericidal and antibacterial properties while ensuring adhesion. Specifically, the mass ratio of acrylic acid structural units, structural units containing quaternary ammonium salts, phenolic ether structural units, and flexible structural units includes but is not limited to 30:1:0.5:5, 30:1:3:5, 30:1:5:10, 30:5:0.5:10, 30:10:0.5:15, 70:5:0.5:15, 50:5:0.5:15, 50:5:3:20, 70:5:3:15, 70:1:0.5:20, or 70:10:5:20.

[0031] When the mass ratio of acrylic acid structural units is less than 30, the skeleton strength of the binder is insufficient and the tensile modulus decreases. When used, the binder lacks sufficient carboxyl adsorption on the surface of graphite or silicon particles, resulting in a decrease in the thickening ability of the negative electrode slurry, low viscosity, stratification of the negative electrode slurry, and difficulty in forming a stable coating. When the mass ratio of acrylic acid structural units is greater than 70, there are too many polar structures in the negative electrode slurry system, resulting in a decrease in the affinity of the binder to graphite or carbon tubes (insufficient oleophobicity), and the slurry system is unstable. When the proportion of quaternary ammonium salt structural units is low, that is, the mass ratio is less than 1, the antibacterial / antibacterial ability of the binder is weak, and the risk of mold / deterioration increases. When the proportion of quaternary ammonium salt structural units is high, that is, the mass ratio is greater than 10, the stability of the binder in water decreases, phase separation occurs during the polymerization process, and the negative ions in the electrolyte (such as PF6 - TFSI - ) reactions, triggering side reactions or increasing membrane impedance. When the mass ratio of phenol ether structural units is less than 0.5, the binder lacks aromatic π-π stacking or van der Waals adsorption capacity, hindering its anchoring on the graphite surface. It also causes discontinuity in the antifungal structure, leading to unstable antifungal performance. When the mass ratio of phenol ether structural units is greater than 5, the overall hydrophilicity of the binder is reduced, affecting the dissolution and wetting of the slurry in water.

[0032] By introducing flexible structural units, the flexibility and toughness of the adhesive are adjusted to increase the film-forming performance of the adhesive.

[0033] In some embodiments, the antibacterial rate of the adhesive is greater than 96%, and the mildew resistance level is greater than or equal to level 4.

[0034] In some embodiments, the binder has a glass transition temperature of 30-90°C. The polymer has a glass transition temperature (Tg) of 30-90°C. The polymer's molecular weight and the content of each structural unit in the polymer are controlled to adjust the polymer's glass transition temperature to ensure the adhesive strength of the binder. Specifically, the glass transition temperature is measured by differential thermal analysis (DSC).

[0035] In some embodiments, the adhesive has an elongation at break of ≥ 110%.

[0036] In some embodiments, the viscosity of the adhesive is 2500-5000 mPa·s.

[0037] In some embodiments, the flexible structural unit is a structural unit obtained by polymerization of a flexible monomer, wherein the flexible monomer includes at least one of butyl acrylate (BA), isooctyl acrylate, and polyethylene glycol dimethacrylate (PEGMA). It is understood that the flexible structural unit in the polymer may also be formed by polymerization of other monomers with modifiable flexibility.

[0038] In some embodiments, the structural unit containing a quaternary ammonium salt comprises an olefin structural unit containing a quaternary ammonium salt;

[0039] The quaternary ammonium salt-containing olefin structural unit is a structural unit obtained by polymerization of an olefin monomer containing a quaternary ammonium salt. The olefin monomer containing a quaternary ammonium salt includes at least one of methacryloyloxyethyltrimethylammonium chloride (DMC), acryloyloxypropyltrimethylammonium chloride (MAPTAC), and diallyldimethylammonium chloride (DMDAAC). The selection of an olefin structural unit containing a quaternary ammonium salt facilitates the covalent bonding of the quaternary ammonium salt within the polymer chain. Furthermore, the quaternary ammonium salt carries a permanent positive charge, which can kill bacteria, fungi, and even viruses by disrupting bacterial cell membranes and interfering with cellular metabolism, thereby imparting antimicrobial properties to the adhesive. The cations in the quaternary ammonium salt can form ionic bonds with inorganic molecules, enhancing the adhesive's cohesive strength.

[0040] In some embodiments, the aromatic phenol structural unit is a structural unit obtained by polymerization of an aromatic phenol monomer containing a double bond, and the aromatic phenol monomer containing a double bond includes p-hydroxystyrene;

[0041] And / or, the aromatic ether structural unit is a structural unit obtained by polymerization of an aromatic ether monomer containing a double bond, and the aromatic ether monomer containing a double bond includes at least one of p-methoxystyrene, p-methoxystyrene, 4-tert-butoxystyrene, 2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate, bisphenol-A diglycidyl methacrylate, and bisphenol A glycerol dimethacrylate.

[0042] By selecting the above-mentioned aromatic phenol monomers containing double bonds and aromatic ether monomers containing double bonds to participate in polymerization, aromatic phenol structures or aromatic ether structures are introduced into the polymer chain, so that the adhesive maintains bonding strength while having excellent corrosion resistance and excellent dispersibility.

[0043] In some embodiments, the acrylic acid structural unit is a structural unit obtained by polymerization of acrylic acid monomers, and the acrylic acid monomers include methacrylic acid, sodium acrylate, lithium acrylate, sodium methacrylate, lithium methacrylate, methyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-acrylamide-2-methyl-1-propanesulfonic acid, 2-(methacryloyloxy)ethanesulfonic acid, 2-methacrylate-2-(phosphoryloxy)ethyl ester, maleic anhydride, and at least one of itaconic acid. Specifically, the acrylic acid structural unit dissociates into –COO⁻ under neutral or weak alkaline conditions, so that the polymer molecules have good water solubility and negative charge density, which helps to improve the rheological stability of the negative electrode slurry system.

[0044] In some embodiments, the polymer has a weight average molecular weight of 50,000-500,000 g / mol.

[0045] The solid content of the binder is 20%-40%, making the binder suitable for the preparation of high-solid slurry;

[0046] The pH of the binder is 6.5-8, which is convenient for maintaining the stability of the binder system and making the binder system stable without gelation.

[0047] Furthermore, an embodiment of the present application provides a method for preparing an adhesive, comprising the following steps:

[0048] Deionized water, acrylic monomers, olefin monomers containing quaternary ammonium salts, aromatic phenol monomers / aromatic ether monomers, and acrylic ester monomers are mixed to obtain a mixed solution. The pH of the mixed solution is adjusted to 6.5-8, the temperature is raised to 60-85°C, nitrogen is introduced, an initiator is added dropwise, and the reaction is carried out for 6-8 hours to obtain a light yellow emulsion, namely the adhesive. The adhesive is free of precipitation upon centrifugation and is stable and transparent after dilution.

[0049] The initiator includes at least one of ammonium persulfate (APS), hydrogen peroxide, potassium persulfate, sodium persulfate, sodium bisulfite, azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azobisisopropylimidazoline, and azobiscyanovaleric acid.

[0050] As known to those skilled in the art, the reactions in the above steps are conventional free radical polymerization, etc., and the specific methods and reaction conditions are free radical polymerization methods commonly used in the prior art, which will not be described in detail in the present invention.

[0051] In the present invention, each of the aforementioned structural units represents the structural moiety present in the resulting polymer after the corresponding monomer participates in the polymerization reaction. The mass ratio of each structural unit is based on the mass content of the corresponding monomer in the total amount of monomers participating in the polymerization.

[0052] One embodiment of the present application also provides a negative electrode slurry comprising the binder described in any of the above items. By using the binder, the negative electrode slurry system is stable, has good dispersibility, and exhibits oxygen and mold inhibition capabilities. Specifically, the binder is particularly suitable for difficult-to-disperse systems such as carbon nanotubes, graphite, and silicon-carbon.

[0053] Furthermore, the 24-hour viscosity change rate of the negative electrode slurry is less than 3%, and the 24-hour solid content change rate is less than 0.6%.

[0054] Furthermore, the negative electrode slurry prepared using the aforementioned binder showed no mold or odor after 90 days of storage in a sealed environment at 25°C, with stable viscosity and excellent coating properties. Existing CMC / SBR slurry, under the same conditions, showed significant deterioration after 30 days, with a viscosity drop of over 40% and the formation of mold films and sediment.

[0055] Furthermore, in the negative electrode slurry, the mass percentage of the binder is 1.5%-2.2%.

[0056] An embodiment of the present application further provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer is formed by coating the negative electrode slurry as described above.

[0057] Furthermore, the negative electrode active material layer further includes a negative electrode active material and a conductive agent.

[0058] Specifically, the mass ratio of the negative electrode active material, the binder, and the conductive agent is (97-98.5):(1.5-2.2):(0.05-0.15).

[0059] An embodiment of the present application further provides a battery comprising the negative electrode sheet as described above. The negative electrode sheet containing the binder has excellent electrochemical performance and temperature, so that the battery has excellent rate and cycle performance.

[0060] The present invention is further described below with reference to the following examples.

[0061] The negative electrode binder, negative electrode slurry, negative electrode sheet and battery disclosed in the present invention are specifically described.

[0062] Example 1

[0063] 1. Binder

[0064] Add 350 g of deionized water to the flask, and then add 50 g of acrylic acid (AA), 5 g of DMC, 2 g of p-methoxystyrene, and 15 g of butyl acrylate in sequence. Adjust the pH to 7.0, raise the temperature to 75°C, and after passing nitrogen for 30 minutes, add 1.5 g of APS dropwise. React at 75°C for 6 hours to obtain a light yellow emulsion adhesive.

[0065] 2. Anode slurry

[0066] The binder was mixed with graphite and CNT in a mass ratio of 1.9:98:0.1 to prepare a slurry to obtain a negative electrode slurry. The solid content of the negative electrode slurry was 48%.

[0067] 3. Negative electrode

[0068] The negative electrode slurry is coated on the copper foil, dried, rolled into shape, and cut into electrodes.

[0069] 4. Battery

[0070] After the negative electrode sheet, LiCoO2 positive electrode sheet and separator stack are assembled into a dry battery cell, the electrolyte is injected to obtain a lithium battery. The volume ratio of the electrolyte is 1M LiPF6, ethylene carbonate EC and ethyl methyl carbonate EMC is 3:7.

[0071] Example 2 to Example 12

[0072] Most of the steps of Examples 2 to 12 are the same as those of Example 1, except that the formula in Table 1 is used.

[0073] Comparative Example 1 to Comparative Example 9

[0074] Most of the steps of Comparative Examples 1 to 9 are the same as those of Example 1, except that the formula in Table 1 is used.

[0075] Comparative Example 10

[0076] Most of the steps of Comparative Example 10 are the same as those of Example 1, except that the negative electrode slurry is prepared as follows:

[0077] CMC, SBR, graphite, and CNT were mixed in a mass ratio of 0.6:1.4:97.9:0.1 to produce a negative electrode slurry with a solids content of 48%. The CMC used was CMC2200 from Dasero. The SBR used was 451B from Ruiong, which contains a small molecule fungicide.

[0078] Table 1

[0079]

[0080] Performance testing:

[0081] The binders, negative electrode slurries, negative electrode sheets, and batteries prepared in the above examples and comparative examples were subjected to the following tests.

[0082] 1. Solid content test:

[0083] Measurements were performed according to GB / T 2793-1995. Samples were taken from different locations on the adhesive and weighed to the nearest 0.0001g within a 1.5 ± 0.5g range. Five samples were weighed and baked in an oven at 160 ± 2°C for 180 ± 5 minutes. The samples were removed, cooled to room temperature in a desiccator, and weighed.

[0084] 2. Glass transition temperature test:

[0085] The glass transition temperature (Tg) of the negative electrode binders in the examples and comparative examples was measured using a differential scanning calorimeter (DSC-100, Shanghai Qunhong Instruments Co., Ltd.). The following steps were used: High-purity nitrogen was supplied at a flow rate of 0.5-0.6 L / min, the DSC was powered on, and the tabletop was operated. The temperature was set to 0°C, held constant for 10 minutes, within a temperature range of 0°C to 120°C, and at a heating rate of 10 K / min. After completing the setup, the prepared samples were placed in a heating furnace, the furnace cover was secured, and an appropriate amount of liquid nitrogen was added to the thermostat. The test was then run when the sample temperature reached -60°C.

[0086] 3. Viscosity test:

[0087] The viscosity is measured according to GB / T 10247. The viscosity of the adhesive is tested at 25°C using a 3# rotor (i.e., rotor model) at 12 revolutions.

[0088] 4. Dilute the binder emulsion (30% solid content) to 15% with deionized water and automatically coat it on a frosted glass plate with a wet film thickness of 150µm. Dry it in a vacuum oven at 60°C for 30 minutes and 80°C for 2 hours to produce a self-supporting film with a thickness of 19µm to 21µm. The resulting 19µm to 21µm self-supporting film was subjected to the following tests:

[0089] (1) Dynamic modulus and elongation at break obtained by ASTM D882 tensile test.

[0090] (2) Wrap the film (or coating) to be tested around a cylindrical mandrel with a diameter of 2 mm and make a sharp bend of 180°. Then observe the bend with a 40x microscope to check whether there are any cracks. If there are no cracks or peeling, the film / adhesive film is judged to have the required flexibility.

[0091] 5. Adhesive antibacterial rate test: Test in accordance with GB / T21866.

[0092] 6. Adhesive mildew resistance test: Test in accordance with GB / T 1741-2007 "Determination of mildew resistance of paint films" and QB / T2591-2003 "Adhesive mildew test method" (applicable to adhesives). The above standards use a 0-5 (the higher the level, the stronger the mildew resistance) as a mold growth coverage evaluation system, which is commonly used in battery slurry, glue, and coating fields.

[0093] The specific test results for the adhesive are entered in Table 2.

[0094] Table 2

[0095]

[0096] 7. Negative electrode slurry solid content test:

[0097] Measurements were performed according to GB / T 2793-1995. Samples were taken from different locations of the negative electrode slurry and weighed to the nearest 0.0001g within a 1.5 ± 0.5g range. Five samples were weighed and baked in an oven at 160 ± 2°C for 180 ± 5 minutes. The samples were removed, cooled to room temperature in a desiccator, and weighed.

[0098] 8. Negative electrode slurry solid content change rate test:

[0099] After the negative electrode slurry has been allowed to rest for 24 hours, it is measured according to the GB / T 2793-1995 measurement standard. The formula for calculating the 24-hour change in the negative electrode slurry solids content is: |(24-hour slurry solids content - initial slurry solids content)| / initial slurry solids content * 100%.

[0100] 9. Negative electrode slurry viscosity test:

[0101] The viscosity was measured according to GB / T 10247. The viscosity of the negative electrode slurry was tested at 25°C using a 3# rotor at 12 revolutions.

[0102] After the negative electrode slurry has been allowed to stand for 24 hours, it is measured according to GB / T 10247. The viscosity is measured at 25°C using a 3# rotor (i.e., rotor model) at 12 revolutions. This represents the 24-hour viscosity. The slurry viscosity change rate is calculated as: |(initial slurry viscosity - 24-hour slurry viscosity) / initial slurry | * 100%. A viscosity change greater than 5% indicates unstable slurry viscosity.

[0103] 10. Negative electrode peeling force test: After compacting the coated single-sided negative electrode according to 2.4g / cm3, a tensile testing machine with a range of 20N is used. The electrode is cut into 20cm long and 3cm wide. 3M double-sided tape is affixed to the steel plate. The electrode is fixed on the tape on the steel plate with the coating side facing down. After rolling back and forth 6 times with a 2.5kg roller, the coating and copper foil are torn off. The upper plate clamps the copper foil side and stretches at a speed of 50mm / min and 180°C. The data of the tensile plate is recorded as the peeling strength (N / m).

[0104] 11. Cycle test: After placing the battery in a constant temperature test room at 25℃±2℃ for 1h, charge it to 3.65V with 1C constant current and constant voltage, and the cut-off current is 0.05C; discharge it to 2.5V with 1C constant current, and record the discharge capacity; repeat the above steps 300 times, and calculate the capacity retention rate.

[0105] The test results of the negative electrode slurry, negative electrode sheet and battery are entered in Table 3.

[0106] Table 3

[0107]

[0108] From the test results of the embodiments and comparative examples in Tables 2 and 3, it can be seen that when the binder contains acrylic structural units, structural units containing quaternary ammonium salts, phenol ether structural units and flexible structural units at the same time, the binder has a good antibacterial rate and mildew resistance level, while ensuring that the negative electrode sheet using the binder has good peel strength.

[0109] The test results for Examples 1 to 9, Comparative Examples 1, and Comparative Examples 4 to 9 in Tables 2 and 3 indicate that when the mass ratio of acrylic acid structural units, structural units containing quaternary ammonium salts, phenolic ether structural units, and flexible structural units is within the range of (30-70):(1-10):(0.5-5):(5-20), the binder exhibits excellent dynamic modulus, tensile elongation, antibacterial rate, and mildew resistance, resulting in good dispersibility of the negative electrode slurry. Furthermore, as shown by the change in solids content and viscosity after 24 hours of storage, a binder composed of structural units within this range improves the storage stability of the negative electrode slurry. This also results in good peel strength for the negative electrode sheet, further enhancing the battery's cycling performance. Furthermore, by introducing a certain content range of flexible monomer structural units into the binder, the binder's flexibility can be increased, further improving the peel strength of the negative electrode sheet.

[0110] It can be seen from the test data of Examples 10 to 12 in Tables 2 to 3 that when the binder prepared using other monomers in this application is used, the binder also has good dynamic modulus, tensile elongation, antibacterial rate and mildew resistance level, and the negative electrode slurry has good dispersibility and storage stability, and the negative electrode sheet has good peel strength.

[0111] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A binder, characterized in that: The binder includes a polymer, the polymer includes an acrylic structural unit, a structural unit containing a quaternary ammonium salt, a phenol ether structural unit and a flexible structural unit, the mass ratio of the acrylic structural unit, the structural unit containing a quaternary ammonium salt, the phenol ether structural unit and the flexible structural unit is 50: (1-10): (0.5-5): (5-20); the phenol ether structural unit includes at least one of an aromatic phenol structural unit and an aromatic ether structural unit; The acrylic acid structural unit is a structural unit obtained by polymerization of acrylic acid monomers, wherein the acrylic acid monomers include at least one of methacrylic acid, sodium acrylate, lithium acrylate, sodium methacrylate, lithium methacrylate, and itaconic acid; The flexible structural unit is a structural unit obtained by polymerization of a flexible monomer, wherein the flexible monomer includes at least one of butyl acrylate, isooctyl acrylate, and polyethylene glycol dimethacrylate; The structural unit containing a quaternary ammonium salt comprises an olefin structural unit containing a quaternary ammonium salt; The olefin structural unit containing a quaternary ammonium salt is a structural unit obtained by polymerization of an olefin monomer containing a quaternary ammonium salt, and the olefin monomer containing a quaternary ammonium salt includes at least one of methacryloyloxyethyltrimethylammonium chloride, acryloyloxypropyltrimethylammonium chloride, and diallyldimethylammonium chloride; The aromatic phenol structural unit is a structural unit obtained by polymerization of an aromatic phenol monomer containing a double bond, and the aromatic phenol monomer containing a double bond includes p-hydroxystyrene; The aromatic ether structural unit is a structural unit obtained by polymerization of an aromatic ether monomer containing a double bond, and the aromatic ether monomer containing a double bond includes at least one of p-methoxystyrene, p-methoxystyrene, 4-tert-butoxystyrene, 2-phenoxyethyl acrylate, 2-phenoxyethyl methacrylate, bisphenol-A diglycidyl methacrylate, and bisphenol A glycerol dimethacrylate.

2. The adhesive according to claim 1, characterized in that The viscosity of the binder is 2500-5000 mPa·s.

3. The adhesive according to claim 1, characterized in that The glass transition temperature of the binder is 30-90°C.

4. The adhesive according to claim 1, characterized in that The elongation at break of the adhesive is ≥110%.

5. A negative electrode slurry, characterized in that: Comprising the binder according to any one of claims 1 to 4, the 24-hour viscosity change rate of the negative electrode slurry is less than 3%.

6. The negative electrode slurry according to claim 5, characterized in that The 24-hour solid content change rate of the negative electrode slurry is less than 0.6%.

7. A negative electrode sheet, characterized in that: The invention comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode active material layer is formed by coating, drying and rolling the negative electrode slurry according to claim 5 or 6.

8. A battery, characterized in that: Including the negative electrode sheet according to claim 7.

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