Aqueous binder, process for its preparation and use thereof

Abstract

The present disclosure relates to a water-based binder, a preparation method and application thereof, the water-based binder comprising modified polyvinyl alcohol, the modified polyvinyl alcohol having repeating units as shown in formula (1) and formula (2), wherein R1 is selected from one or more of -Ph and -Ph-(R3)n1, each R3 is the same or different, and each is independently selected from one or more of a halogen atom and a C1-C3 halogenated hydrocarbon group, and the n1 is any integer between 1 and 5. The modified polyvinyl alcohol water-based binder of the present disclosure has good dispersion performance on electrode materials and conductive agents, maintains good compatibility with electrolyte, has excellent adhesion and green environmental protection advantages, and further enables the lithium ion battery to have excellent cycle stability and high rate performance, thereby improving the service life of the lithium battery.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery binders, specifically to an aqueous binder, its preparation method, and its application. Background Technology

[0002] Binders are a crucial component of lithium-ion batteries, primarily serving to tightly bond active materials and conductive agents to the electrode current collectors, maintaining the integrity of the electrode structure. Although the amount of binder used is small, its performance directly affects the electrochemical performance and lifespan of the lithium-ion battery.

[0003] Replacing oil-based binders such as PVDF with water-based binders to make lithium battery manufacturing processes meet environmental protection requirements is one of the current development trends for battery electrodes. Currently, commercial lithium batteries use PVDF with 1-methyl-2-pyrrolidone (NMP) as a solvent as a binder. PVDF as a binder has the following drawbacks: First, the connection between PVDF and the active material is through weak van der Waals forces, which may lead to separation between the active material and the current collector during cycling. Second, PVDF is expensive, and NMP is a high-boiling-point, toxic, and flammable solvent, resulting in high recycling costs and significant environmental pollution.

[0004] Researching novel aqueous binders to meet the development needs of lithium-ion batteries has significant practical application value. Currently reported aqueous binders mainly include polyacrylic acid (PAA), carboxymethyl cellulose (CMC), and sodium alginate. CMC has generally poor bonding performance, high brittleness, and the electrode is prone to cracking during charging and discharging. PAA has a high glass transition temperature and is relatively hard at room temperature, easily leading to hard and brittle electrodes. Furthermore, PAA has poor viscosity and needs to be used in conjunction with thickeners. CN115172752A reports a tannic acid and its derivatives as an aqueous binder, which significantly improves the bonding strength and structural stability of silicon-based anodes. However, while the battery exhibits a high first-cycle discharge specific capacity, its capacity retention is low, meaning that the first-cycle discharge specific capacity and capacity retention cannot be simultaneously optimized. In addition, natural polymer materials such as sodium alginate and chitosan, as binders, perform well in terms of environmental protection and have good water solubility. However, they have many shortcomings in electrochemical performance and bonding performance, making it difficult to meet the application requirements of batteries. Summary of the Invention

[0005] The purpose of this disclosure is to provide an aqueous binder, its preparation method and application. This aqueous binder has good dispersibility for electrode materials and conductive agents, maintains good compatibility with electrolytes, and also has the advantages of excellent adhesion and environmental friendliness.

[0006] To achieve the above objectives, a first aspect of this disclosure provides an aqueous adhesive comprising modified polyvinyl alcohol having repeating units as shown in formulas (1) and (2).

[0007]

[0008] Wherein, R1 is selected from one or more of -Ph and -Ph-(R3)n1, each R3 may be the same or different, and each is independently selected from one or more of halogen atoms and C1 to C3 halogenated hydrocarbon groups, and n1 is any integer between 1 and 5.

[0009] Optionally, the modified polyvinyl alcohol has a weight-average molecular weight of 50,000 to 300,000; and the molar content of ester groups in the modified polyvinyl alcohol is 5% to 15%.

[0010] Optionally, the water-based adhesive is obtained by modifying polyvinyl alcohol with an anhydride, wherein the anhydride has the structural formula shown in formula (3).

[0011]

[0012] Wherein, R2 is selected from one or more of -Ph and -Ph-(R4)n2, each R4 may be the same or different, and each is independently selected from one or more of halogen atoms and C1 to C3 halogenated hydrocarbon groups, and n2 is any integer between 1 and 5; preferably, R4 is selected from one or more of F and Cl, preferably F; the C1 to C3 halogenated hydrocarbon groups are selected from one or more of -CF3, -CHF2 and -CH2F, preferably -CF3.

[0013] Optionally, R3 is selected from one or more of F and Cl, preferably F; the halogenated hydrocarbon group of C1 to C3 is selected from one or more of -CF3, -CHF2 and -CH2F, preferably -CF3.

[0014] A second aspect of this disclosure provides a method for preparing an aqueous adhesive, the method comprising:

[0015] Polyvinyl alcohol and acid anhydride are reacted in the presence of a eutectic solvent; the acid anhydride has the structural formula shown in formula (3).

[0016]

[0017] Wherein, R1 is selected from one or more of -Ph and -Ph-(R3)n1, each R3 may be the same or different, and each is independently selected from one or more of halogen atoms and C1 to C3 halogenated hydrocarbon groups, and n1 is any integer between 1 and 5;

[0018] R2 is selected from one or more of -Ph and -Ph-(R4)n2, where each R4 may be the same or different, and each is independently selected from one or more of halogen atoms and C1 to C3 halogenated hydrocarbon groups, where n2 is any integer between 1 and 5;

[0019] R1 and R2 may be the same or different.

[0020] Optionally, the degree of alcoholysis of the polyvinyl alcohol is 88% to 99%, and the weight-average molecular weight of the polyvinyl alcohol is 50,000 to 300,000, preferably 100,000 to 200,000.

[0021] The acid anhydride is one or more of benzoic anhydride, tetrafluorobenzoic anhydride and 4-trifluoromethylbenzoic anhydride; preferably one or more of tetrafluorobenzoic anhydride and 4-trifluoromethylbenzoic anhydride.

[0022] The mass ratio of polyvinyl alcohol to acid anhydride is 1 to 5:1, preferably 1.5 to 3:1.

[0023] Optionally, the eutectic solvent includes a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor is a quaternary ammonium salt, which is selected from one or more of choline chloride and benzyltriethylammonium chloride, preferably choline chloride;

[0024] The hydrogen bond donor is selected from one or more of amides, carboxylic acids, urea, thiourea, and imidazoles, preferably amides and urea; the amide is selected from one or more of formamides, benzamides, and trifluoroacetamides, preferably benzamides; the carboxylic acid is selected from one or more of oxalic acid and levulinic acid, preferably oxalic acid;

[0025] The molar ratio of hydrogen bond acceptors to hydrogen bond donors in the eutectic solvent is 1:1 to 5, preferably 1:1 to 3.

[0026] Optionally, the conditions for the contact reaction include: the reaction is carried out in an organic solvent, the temperature of the contact reaction is 30–70°C, preferably 40–60°C, and the contact reaction time is 2–6 h, preferably 3–5 h; the organic solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0027] A third aspect of this disclosure provides an aqueous adhesive prepared by the method described in the second aspect of this disclosure.

[0028] This fourth aspect of the disclosure provides the application of the aqueous binders described in the first or third aspects of the disclosure in lithium-ion batteries.

[0029] Optionally, the aqueous binder is used for the positive electrode and / or negative electrode of a lithium-ion battery.

[0030] Through the above technical solution, this disclosure discloses a modified polyvinyl alcohol aqueous binder obtained by grafting anhydride with polyvinyl alcohol in the presence of a eutectic solvent. This aqueous binder can enhance the bonding performance between the active material and the conductive agent, as well as between the active material and the current collector, ensuring the integrity of the electrode structure. It also maintains good compatibility with the electrolyte, which is beneficial for the transport of electrons and ions inside the electrode, greatly reducing the internal impedance of the battery and improving the high-rate performance and cycle stability of the positive and negative electrode materials of the lithium battery.

[0031] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Detailed Implementation

[0032] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this disclosure.

[0033] A first aspect of this disclosure provides an aqueous adhesive comprising modified polyvinyl alcohol having repeating units as shown in formulas (1) and (2).

[0034]

[0035] Wherein, R1 is selected from one or more of -Ph and -Ph-(R3)n1, each R3 may be the same or different, and each is independently selected from one or more of halogen atoms and C1 to C3 halogenated hydrocarbon groups, and n1 is any integer between 1 and 5.

[0036] This disclosure uses polyvinyl alcohol (PVA) modification to improve the dispersibility and suspension of the slurry, which is beneficial for improving the slurry quality and uniformity. The aqueous binder of this disclosure has a large number of active hydroxyl groups, which can form strong hydrogen bonds with the active material and the current collector, thereby improving their bonding strength. The aqueous binder of this disclosure has a large number of benzene rings, which can generate π-π stacking interactions with the conductive agent, which is beneficial for improving the dispersibility of the conductive agent in the aqueous solution system, improving the conductivity of the electrode, and thus improving the high-rate performance of the battery. The introduction of hydrophobic groups can reduce the hydrophilicity of the binder, improve the compatibility between the binder and the electrolyte, improve the interfacial compatibility problem, and at the same time reduce the polarity of PVA, allowing the electrolyte to enter the electrode quickly, improving the conductivity of lithium ions, and further enabling the lithium-ion battery to have excellent cycle stability and high-rate performance. This disclosure uses water-soluble polymer material PVA for modification, which is green and environmentally friendly, low in cost, and easier to implement in engineering design.

[0037] According to one embodiment of this disclosure, the modified polyvinyl alcohol has a weight-average molecular weight of 50,000 to 300,000; and the molar content of ester groups in the modified polyvinyl alcohol is 5% to 15%.

[0038] According to one embodiment of this disclosure, the aqueous adhesive is obtained by modifying polyvinyl alcohol with an anhydride, wherein the anhydride has the structural formula shown in formula (3).

[0039]

[0040] Wherein, R2 is selected from one or more of -Ph and -Ph-(R4)n2, each R4 may be the same or different, and each is independently selected from one or more of halogen atoms and C1 to C3 halogenated hydrocarbon groups, and n2 is any integer between 1 and 5; preferably, R4 is selected from one or more of F and Cl, preferably F; the C1 to C3 halogenated hydrocarbon groups are selected from one or more of -CF3, -CHF2 and -CH2F, preferably -CF3.

[0041] According to one embodiment of this disclosure, R3 is selected from one or more of F and Cl, preferably F; the halogenated hydrocarbon group of C1 to C3 is selected from one or more of -CF3, -CHF2 and -CH2F, preferably -CF3. The above-mentioned preferred embodiment is beneficial for the aqueous binder to have excellent bonding strength, swelling properties, and lithium-ion conductivity, further improving the cycle performance and high-rate performance of the battery.

[0042] A second aspect of this disclosure provides a method for preparing an aqueous adhesive, the method comprising:

[0043] Polyvinyl alcohol and acid anhydride are reacted in the presence of a eutectic solvent; the acid anhydride has the structural formula shown in formula (3).

[0044]

[0045] Wherein, R1 is selected from one or more of -Ph and -Ph-(R3)n1, each R3 may be the same or different, and each is independently selected from one or more of halogen atoms and C1 to C3 halogenated hydrocarbon groups, and n1 is any integer between 1 and 5; R2 is selected from one or more of -Ph and -Ph-(R4)n2, each R4 may be the same or different, and each is independently selected from one or more of halogen atoms and C1 to C3 halogenated hydrocarbon groups, and n2 is any integer between 1 and 5; R1 and R2 may be the same or different.

[0046] The method disclosed herein modifies polyvinyl alcohol by chemical grafting with acid anhydride in the presence of a eutectic solvent to obtain an aqueous binder. This method is beneficial for the aqueous binder to have excellent bonding strength, swelling properties and lithium-ion conductivity, thereby further improving the cycle performance and high-rate performance of the battery.

[0047] According to one embodiment of this disclosure, the degree of hydrolysis of the polyvinyl alcohol is 88%–99%, and the weight-average molecular weight of the polyvinyl alcohol is 50,000–300,000, preferably 100,000–200,000. In this disclosure, the degree of hydrolysis of polyvinyl alcohol refers to the maximum amount of polyvinyl alcohol that can dissolve in water under specific conditions. The above embodiments are beneficial for enabling water-based binders to possess excellent bonding strength, swelling properties, and lithium-ion conductivity, further improving the cycle performance and high-rate performance of lithium batteries, and extending the service life of lithium-ion batteries.

[0048] According to one embodiment of this disclosure, the acid anhydride is one or more selected from benzoic anhydride, tetrafluorobenzoic anhydride, and 4-trifluoromethylbenzoic anhydride, more preferably one or more selected from tetrafluorobenzoic anhydride and 4-trifluoromethylbenzoic anhydride. The above embodiment is beneficial in enabling the aqueous binder to possess excellent bonding strength, swelling properties, and lithium-ion conductivity, further improving the cycle performance and high-rate performance of lithium batteries, and extending the service life of lithium-ion batteries.

[0049] According to one embodiment of this disclosure, the mass ratio of polyvinyl alcohol to acid anhydride is 1 to 5:1, preferably 1.5 to 3:1. This embodiment helps to give the aqueous binder excellent bonding strength, swelling properties, and lithium-ion conductivity, further improving the cycle performance and high-rate performance of lithium batteries and extending their service life.

[0050] According to one embodiment of this disclosure, the eutectic solvent includes a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor is a quaternary ammonium salt, selected from one or more of choline chloride and benzyltriethylammonium chloride, preferably choline chloride; the hydrogen bond donor is selected from one or more of amides, carboxylic acids, urea, thiourea, and imidazoles, preferably amides and urea; the amide is selected from one or more of formamide, benzamide, and trifluoroacetamide, preferably benzamide; the carboxylic acid is selected from one or more of oxalic acid and levulinic acid, preferably oxalic acid. This disclosure does not impose specific limitations on the amount of the eutectic solvent used, and it can be a conventional amount used in the art, for example, the mass ratio of the eutectic solvent to polyvinyl alcohol can be 1:5. The above preferred embodiments are beneficial for giving the aqueous binder excellent bonding strength, swelling properties, and lithium-ion conductivity, further improving the cycle performance and high-rate performance of lithium batteries, and extending the service life of lithium-ion batteries.

[0051] According to one embodiment of this disclosure, the molar ratio of hydrogen bond acceptor to hydrogen bond donor in the eutectic solvent is 1:(1-5), preferably 1:(1-3). In a further embodiment, the method includes mixing the hydrogen bond acceptor and hydrogen bond donor at a first temperature to obtain the eutectic solvent. The first temperature is 60-80°C, preferably 65-75°C. The above embodiments are beneficial for giving the aqueous binder excellent bonding strength, swelling properties, and lithium-ion conductivity, further improving the cycle performance and high-rate performance of lithium batteries, and extending the service life of lithium-ion batteries.

[0052] According to one embodiment of this disclosure, the contact reaction conditions include: the reaction is carried out in an organic solvent; the contact reaction temperature is 30–70°C, preferably 40–60°C; the contact reaction time is 2–6 hours, preferably 3–5 hours; and the organic solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone. The above embodiment is beneficial for giving the aqueous binder excellent bonding strength, swelling properties, and lithium-ion conductivity, further improving the cycle performance and high-rate performance of lithium batteries, and extending the service life of lithium-ion batteries.

[0053] According to one embodiment of this disclosure, the method includes: mixing polyvinyl alcohol with an organic solvent at a second temperature; the second temperature is 60–90°C, preferably 70–90°C. In a further embodiment, polyvinyl alcohol is dissolved in a contact solvent under oil bath conditions. The above embodiments are advantageous in giving the aqueous binder excellent bonding strength, swelling properties, and lithium-ion conductivity, further improving the cycle performance and high-rate performance of lithium batteries, and extending the service life of lithium-ion batteries.

[0054] A third aspect of this disclosure provides an aqueous adhesive prepared by the method described in the second aspect of this disclosure.

[0055] The fourth aspect of this disclosure provides the application of the aqueous binders described in the first or third aspects of this disclosure in lithium-ion batteries.

[0056] According to one embodiment of this disclosure, the aqueous binder is used for positive and / or negative electrode sheets of a lithium-ion battery.

[0057] In one embodiment, the aqueous binder is used in a lithium-ion battery negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode solid coating loaded on the negative electrode current collector; the negative electrode solid coating comprises a negative electrode active material, a conductive agent, and the modified polyvinyl alcohol aqueous binder described in the third aspect of this disclosure. This disclosure does not specifically limit the negative electrode current collector, which can be a material conventional in the art, such as copper foil. This disclosure does not specifically limit the negative electrode active material, which can be graphite, silicon dioxide, and silicon conventional in the art. This disclosure does not specifically limit the conductive agent, which can be conductive carbon black, carbon nanotubes, and graphene conventional in the art, such as carbon black.

[0058] In one embodiment, the aqueous binder is used for a positive electrode sheet of a lithium-ion battery. The positive electrode sheet includes a positive current collector and a positive solid coating loaded on the positive current collector. The positive solid coating includes a positive active material, a conductive agent, and the modified polyvinyl alcohol aqueous binder described in the third aspect of this disclosure. This disclosure does not specifically limit the positive current collector; it can be a material conventional in the art, such as aluminum foil. This disclosure also does not specifically limit the positive active material; it can be conventional lithium iron phosphate or lithium cobalt oxide.

[0059] The present invention will be further illustrated by the following examples, but the present invention is not limited thereto.

[0060] The polyvinyl alcohol used in this disclosure was purchased from Aladdin, product designation P434371. Unless otherwise specified, all other reagents are commercially available products.

[0061] The electrochemical performance of the battery was tested using a Blue Electric testing system, model CT2001A.

[0062] Example 1

[0063] (1) Take appropriate amounts of choline chloride and urea in a molar ratio of 1:2, stir and heat at 74°C until the solid dissolves and becomes a transparent liquid to obtain a eutectic solvent;

[0064] (2) Take 1g of polyvinyl alcohol (weight average molecular weight of 200,000, degree of alcoholysis of 99%) in 10ml of dimethyl sulfoxide solution, heat and stir at 80℃ until dissolved; after complete dissolution, add 0.5g of benzoic anhydride and 1ml of eutectic solvent, heat and stir at 50℃ for 4h; the mass ratio of benzoic anhydride to polyvinyl alcohol is 1:2. After the reaction is completed, wash the product with ethanol to obtain a white flocculent substance, dry at 80℃ for 12h to obtain modified polyvinyl alcohol water-based binder.

[0065] Example 2

[0066] The method in this embodiment is the same as that in Embodiment 1, except that benzoic anhydride is replaced with tetrafluorobenzoic anhydride.

[0067] Example 3

[0068] The method in this embodiment is the same as that in Embodiment 1, except that benzoic anhydride is replaced with tetra-trifluorobenzoic anhydride.

[0069] Example 4

[0070] The method in this embodiment is the same as that in Example 1, except that the amount of benzoic anhydride added is 1g and the molar ratio of benzoic anhydride to polyvinyl alcohol is 1:1.

[0071] Example 5

[0072] The method in this embodiment is the same as that in Example 1, except that the amount of benzoic anhydride added is 0.25g and the mass ratio of benzoic anhydride to polyvinyl alcohol is 1:4.

[0073] Example 6

[0074] This embodiment uses the same method as Embodiment 1, except that the eutectic solvents choline chloride and urea are replaced with choline chloride and formamide.

[0075] Example 7

[0076] This embodiment uses the same method as Embodiment 1, except that the eutectic solvents choline chloride and urea are replaced with choline chloride and benzamide.

[0077] Example 8

[0078] This embodiment uses the same method as Embodiment 1, except that the eutectic solvents choline chloride and urea are replaced with choline chloride and imidazole.

[0079] Example 9

[0080] The method in this embodiment is the same as that in Example 1, except that the weight-average molecular weight of polyvinyl alcohol is 50,000 and the degree of alcoholysis is 99%.

[0081] Example 10

[0082] The method in this embodiment is the same as that in Example 1, except that the weight-average molecular weight of polyvinyl alcohol is 100,000 and the degree of alcoholysis is 99%.

[0083] Example 11

[0084] The method in this embodiment is the same as that in Example 1, except that the weight-average molecular weight of polyvinyl alcohol is 200,000 and the degree of alcoholysis is 95%.

[0085] Example 12

[0086] The method in this embodiment is the same as that in Example 1, except that the weight-average molecular weight of polyvinyl alcohol is 200,000 and the degree of alcoholysis is 89%.

[0087] Example 13

[0088] The method in this embodiment is the same as that in Embodiment 1, except that the temperature of the contact reaction is 90°C.

[0089] Example 14

[0090] The method in this embodiment is the same as that in Example 1, except that the amount of benzoic anhydride is 0.75g and the mass ratio of benzoic anhydride to polyvinyl alcohol is 1:1.3.

[0091] Example 15

[0092] This embodiment uses the same method as Embodiment 1, except that the molar ratio of the eutectic solvent hydrogen bond acceptor to hydrogen bond donor is 1:6.

[0093] Comparative Example 1

[0094] A water-based adhesive, specifically a commercially available CMC adhesive (Aladdin, AR).

[0095] Comparative Example 2:

[0096] An oil-based adhesive, specifically a commercially available PVDF adhesive (Aladdin, AR).

[0097] Comparative Example 3

[0098] The method used in this comparative example is the same as in Example 1, except that the eutectic solvent is replaced with dimethyl sulfoxide.

[0099] Comparative Example 4

[0100] The method used in this comparative example is the same as in Example 1, except that benzoic anhydride is replaced with 0.5g of maleic anhydride.

[0101] Application examples

[0102] The preparation of a positive electrode sheet for a lithium-ion battery includes a current collector (Al foil) and a coating loaded on the current collector. The coating material includes lithium iron phosphate, a positive electrode active material, a conductive agent (carbon black SP), and a binder. The binders are the binders provided in Examples 1-12 and Comparative Examples 1-4, respectively.

[0103] The preparation method of the positive electrode sheet is as follows: the positive active material (lithium iron phosphate material), conductive agent carbon black and binder are mixed in a mass ratio of 8:1:1, solvent (water or NMP) is added and stirred thoroughly to make a uniform positive electrode slurry. The slurry is coated on the positive current collector Al foil with a thickness of 60μm using a coater and dried in a drying oven to obtain the positive electrode sheet.

[0104] Test Example 1

[0105] The adhesive bonding strength is reflected by testing the peel strength of the positive electrode sheet. The test method is as follows: a sample 20 mm wide and 10 mm long is taken from the positive electrode sheet; the coated side of the sample is fixed to a stainless steel plate with double-sided tape, and the end of the sample being peeled is fixed to a tensile probe; peeling is performed at a constant speed of 20 mm / min at a 180° angle. The peel force during the peeling process is tested, and the test results are shown in Table 1.

[0106] Test Example 2

[0107] The swelling performance of the binder was characterized by the amount of electrolyte absorbed by the positive electrode sheet. The test method was as follows: the positive electrode sheet was cut into circular pieces with a diameter of 25 mm, immersed in the electrolyte for 3 days, and the mass of the positive electrode sheet before and after immersion was measured. The difference between the two masses was the amount of electrolyte absorbed, and the ratio of the absorbed mass to the original weight of the positive electrode sheet was the swelling performance of the positive electrode sheet. The test results are shown in Table 1.

[0108] Table 1

[0109] Example 1 9.43 9.8 Example 2 9.61 9.5 Example 3 9.76 9.6 Example 4 9.23 9.1 Example 5 9.41 8.8 Example 6 8.12 8.6 Example 7 8.67 8.2 Example 8 9.11 9.2 Example 9 9.36 8.7 Example 10 8.55 10.1 Example 11 8.01 9.8 Example 12 8.88 9.2 Example 13 9.32 9.7 Example 14 9.46 9.6 Example 15 9.35 9.7 Comparative Example 1 6.11 8.8 Comparative Example 2 2.12 12.3 Comparative Example 3 9.22 9.5 Comparative Example 4 9.38 9.1

[0110] According to the data in Table 1, the modified polyvinyl alcohol aqueous binder disclosed herein has good bonding and swelling properties. When applied to the preparation process of lithium-ion battery electrodes, it can improve the stability and dispersibility of the slurry, form a uniform and complete film on the current collector, prevent the electrode from falling off during battery charging and discharging, and further improve the cycle stability and rate performance of lithium-ion battery cathode materials, thereby extending the battery's service life.

[0111] Test Example 3

[0112] Electrochemical performance was tested using cyclic voltammetry and electrochemical impedance spectroscopy to assess the cycle performance, high-rate performance, and rate performance of the lithium-ion battery. The test results are shown in Table 2. The specific methods are as follows:

[0113] Cyclic performance: The assembled battery was left to stand for 10 hours; it was then charged at 0.5C constant current to 4.2V, charged at 4.2V constant voltage until the current was less than 0.05mA, and left to stand for 5 minutes; it was then discharged at 0.5C constant current to 2.4V and left to stand for 5 minutes; the cycle was completed after 200 cycles.

[0114] High performance: Let the assembled battery stand for 10 hours; charge at 5C constant current to 4.2V, charge at 4.2V constant voltage until the current is less than 0.05mA, and let stand for 5 minutes; discharge at 5C constant current to 2.4V, and let stand for 5 minutes; cycle 300 times to finish.

[0115] Rate performance: The prepared positive electrode half-cell was charged to 4.2V at different rates (0.5C, 1C, 2C, 3C, 5C, 0.5C) using a constant current, then switched to a constant voltage charge of 4.2V, rested for 5 minutes, and then discharged at a constant current to the termination voltage of 2.4V. Each rate was cycled 10 times.

[0116] Cyclic voltammetry: Tests were performed using an electrochemical workstation with a scanning voltage range of 2.4–4.2 V and a scanning speed of 1 mV / s.

[0117] Electrochemical impedance: The test was conducted using an electrochemical workstation with an applied perturbation voltage amplitude of 10mV and a frequency range of 0.01Hz-10000Hz.

[0118] Table 2

[0119]

[0120] According to the data in Table 2, the aqueous binder of this disclosure exhibits high discharge specific capacity, good cycle stability, and high-rate performance when used in the positive electrode of a lithium battery. A comparison of Examples 1 and 3 shows that, under the preferred anhydride conditions of this disclosure, the aqueous binder, when used in the positive electrode of a lithium battery, has an even higher discharge specific capacity, better cycle stability, and high-rate performance. A comparison of Examples 1, 6, 7, and 8 shows that, under the preferred hydrogen bond donor conditions of this disclosure, the aqueous binder, when used in the positive electrode of a lithium battery, has an even higher discharge specific capacity, better cycle stability, and high-rate performance. A comparison of Examples 1 and 13 shows that, within the temperature range of the contact reaction of this disclosure, the aqueous binder, when used in the positive electrode of a lithium battery, has an even higher discharge specific capacity, better cycle stability, and high-rate performance. A comparison of Examples 1, 4, 5, and 14 shows that, within the preferred mass ratio range of polyvinyl alcohol to anhydride of this disclosure, the aqueous binder, when used in the positive electrode of a lithium battery, has an even higher discharge specific capacity, better cycle stability, and high-rate performance. A comparison of Example 1 and Example 15 shows that, within the molar ratio range of hydrogen bond acceptor to hydrogen bond donor in the eutectic solvent disclosed in this invention, the aqueous binder prepared for use in the positive electrode of a lithium battery exhibits higher discharge specific capacity, better cycle stability, and high-rate performance.

[0121] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0122] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0123] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A water-based adhesive, characterized in that, Including modified polyvinyl alcohol, said modified polyvinyl alcohol having repeating units as shown in formulas (1) and (2), Equation (1), Equation (2), Wherein, R1 is selected from one or more of -Ph and -Ph-(R3)n1, each R3 may be the same or different, and each is independently selected from one or more of halogen atoms and C1~C3 haloalkyl groups, and n1 is any integer between 1 and 5; The method for preparing the water-based adhesive includes reacting polyvinyl alcohol with an acid anhydride in the presence of a eutectic solvent; The eutectic solvent includes hydrogen bond acceptors and hydrogen bond donors; The hydrogen bond acceptor is a quaternary ammonium salt; The hydrogen bond donor is selected from one or more of amides, carboxylic acids, urea, thiourea, and imidazoles.

2. The water-based adhesive according to claim 1, wherein, The modified polyvinyl alcohol has a weight-average molecular weight of 50,000 to 300,000; the molar content of ester groups in the modified polyvinyl alcohol is 5% to 15%.

3. The water-based adhesive according to claim 1, wherein, Each R3 may be the same or different, and each is independently selected from one or more of F and Cl.

4. The water-based adhesive according to claim 1, wherein, Each R3 is F.

5. The water-based adhesive according to claim 1, wherein, The C1-C3 haloalkyl groups are selected from one or more of -CF3, -CHF2 and -CH2F.

6. The water-based adhesive according to claim 1, wherein, The halogenated hydrocarbon groups of C1 to C3 are -CF3.

7. A method for preparing an aqueous adhesive according to any one of claims 1 to 6, characterized in that, The method includes: Polyvinyl alcohol and acid anhydride are reacted in the presence of a eutectic solvent; the acid anhydride has the structural formula shown in formula (3). Equation (3), Wherein, R1 is selected from one or more of -Ph and -Ph-(R3)n1, each R3 may be the same or different, and each is independently selected from one or more of halogen atoms and C1~C3 haloalkyl groups, and n1 is any integer between 1 and 5; R2 is selected from one or more of -Ph and -Ph-(R4)n2, where each R4 may be the same or different, and each is independently selected from one or more of halogen atoms and C1~C3 halogenated hydrocarbon groups, where n2 is any integer between 1 and 5; R1 and R2 may be the same or different; The eutectic solvent includes hydrogen bond acceptors and hydrogen bond donors; The hydrogen bond acceptor is a quaternary ammonium salt; The hydrogen bond donor is selected from one or more of amides, carboxylic acids, urea, thiourea, and imidazoles.

8. The method according to claim 7, wherein, The degree of alcoholysis of the polyvinyl alcohol is 88%~99%, and the weight-average molecular weight of the polyvinyl alcohol is 50,000~300,000. The acid anhydride is one or more of benzoic anhydride, tetrafluorobenzoic anhydride and 4-trifluoromethylbenzoic anhydride; The mass ratio of polyvinyl alcohol to acid anhydride is 1~5:

1.

9. The method according to claim 7, wherein, The weight-average molecular weight of the polyvinyl alcohol is 100,000 to 200,000.

10. The method according to claim 7, wherein, The acid anhydride is one or more of tetrafluorobenzoic anhydride and 4-trifluoromethylbenzoic anhydride.

11. The method according to claim 7, wherein, The mass ratio of polyvinyl alcohol to acid anhydride is 1.5~3:

1.

12. The method according to claim 7, wherein, The quaternary ammonium salt is selected from one or more of choline chloride and benzyltriethylammonium chloride; The amide is selected from one or more of formamide, benzamide, and trifluoroacetamide; the carboxylic acid is selected from one or more of oxalic acid and levulinic acid. The molar ratio of hydrogen bond acceptors to hydrogen bond donors in the eutectic solvent is 1:1~5.

13. The method according to claim 7, wherein, The quaternary ammonium salt is choline chloride.

14. The method according to claim 7, wherein, The hydrogen bond donors are amide and urea.

15. The method according to claim 7, wherein, The amide is benzamide.

16. The method according to claim 7, wherein, The carboxylic acid is oxalic acid.

17. The method according to claim 7, wherein, The molar ratio of hydrogen bond acceptors to hydrogen bond donors in the eutectic solvent is 1:1 to 3.

18. The method according to claim 7, wherein, The conditions for the contact reaction include: the reaction is carried out in an organic solvent, the temperature of the contact reaction is 30~70℃, the contact reaction time is 2~6h, and the organic solvent is one or more of dimethyl sulfoxide, N,N-dimethylformamide and N-methylpyrrolidone.

19. The method according to claim 7, wherein, The temperature of the contact reaction is 40~60℃.

20. The method according to claim 7, wherein, The contact reaction time is 3-5 hours.

21. The method according to claim 7, wherein, Each R4 may be the same or different, and each is independently selected from one or more of F and Cl.

22. The method according to claim 7, wherein, Each R4 is F.

23. The method according to claim 7, wherein, When R4 is selected from one or more of the C1-C3 halogenated hydrocarbon groups, the C1-C3 halogenated hydrocarbon groups are selected from one or more of -CF3, -CHF2 and -CH2F.

24. The method according to claim 7, wherein, When R4 is selected from one or more of the C1-C3 halogenated hydrocarbon groups, the C1-C3 halogenated hydrocarbon group is -CF3.

25. The application of the aqueous binder according to any one of claims 1 to 6 in lithium-ion batteries.

26. The application according to claim 25, wherein, The aqueous binder is used for the positive and / or negative electrode sheets of lithium-ion batteries.

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