Composite binders and their preparation methods and lithium-ion batteries

Abstract

This invention belongs to the field of lithium-ion battery technology, specifically relating to a composite binder, its preparation method, and a lithium-ion battery. The composite binder comprises carboxymethylated tamarind polysaccharide gum and a water-based binder—a crosslinked product of polyethylene glycol dimethacrylate. The water-based binder comprises at least one of an olefinically unsaturated monomer polymer and an epoxy alkane monomer polymer, and its side chain or end group contains at least one of N and O elements. The composite binder provided by this invention, by comprising carboxymethylated tamarind polysaccharide gum and a water-based binder—a crosslinked product of polyethylene glycol dimethacrylate—possesses strong adhesive strength and can be used in the preparation of silicon-based anodes for lithium batteries, resulting in excellent cycle stability performance of the silicon-based lithium battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to a composite binder, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] To meet the increasing energy density demand of future electric power storage and electric vehicle applications, high specific capacity electrode materials are urgently needed. Silicon has become a promising anode material due to its high theoretical specific capacity. In addition, silicon anodes also have the advantages of low operating voltage, environmental friendliness and abundance. However, the practical application of silicon anodes still faces severe challenges, mainly because the volume of silicon expands dramatically during lithiation, and silicon particles are prone to cracking and pulverization, which affects the structural integrity of the electrode and leads to rapid capacity decay and poor cycle stability. To solve the problems faced by silicon anodes, existing methods include structural modification of silicon materials (such as nanowires, nanosheets and layered structures), introduction of additives and development of new binders. Among these strategies, the use of advanced binders has been proven to be a simple and effective method without affecting the energy density of the battery. For example, the patent with publication number CN112322223A discloses a modification method of a lithium ion battery silicon-based anode material binder and its application. The commonly used binder for silicon-based materials, sodium carboxymethyl cellulose (CMC), is modified through amidation reaction and used as a lithium ion battery silicon anode material binder. The modified binder contains a catechol structure in its molecule, which can form a double hydrogen bond with the surface of silicon particles, increasing the adhesion to active materials and current collectors. The first efficiency and reversible cycle capacity of lithium ion batteries are significantly improved. The main function of the binder in lithium ion batteries is to connect the electrode active material, conductive agent and current collector, so that they have overall connectivity, thereby reducing the electrode impedance and at the same time making the electrode sheet have good mechanical properties and processability to meet the needs of actual production.

[0003] In the prior art, the silicon-based material type binder still has the problem of low adhesion, which leads to poor cycle performance of the silicon anode during the cycle process. For example, the adhesion of carboxymethylated tamarind polysaccharide glue type binder is poor, which leads to poor cycle stability of the lithium ion battery prepared therefrom. Therefore, it is a technical problem to be solved in the field to develop a binder with strong adhesion so that the lithium ion battery has excellent cycle stability. SUMMARY

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a composite binder, a preparation method thereof and a lithium ion battery. The composite binder provided by the present application comprises carboxymethylated tamarind polysaccharide gum and a water-based binder-polyethylene glycol dimethyl acrylate (PEGDMA) crosslinking product, so that the binder has strong adhesion and can be used for the preparation of a silicon-based negative electrode of a lithium battery, so that the silicon-based lithium battery has excellent cycle stability.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] In the first aspect, the present application provides a composite binder, which comprises carboxymethylated tamarind polysaccharide gum and a water-based binder-polyethylene glycol dimethyl acrylate crosslinking product, wherein the water-based binder comprises at least one of an olefinic unsaturated monomer polymer, an alkylene oxide monomer polymer, and has at least one of N and O elements in the side chain or end group.

[0007] The composite binder provided by the present application comprises carboxymethylated tamarind polysaccharide gum and a water-based binder-polyethylene glycol dimethyl acrylate (PEGDMA) crosslinking product, so that the binder has strong adhesion and can be used for the preparation of a silicon-based negative electrode of a lithium battery, so that the silicon-based lithium battery has excellent cycle stability.

[0008] In the above-mentioned composite binder, as a preferred embodiment, the water-based binder comprises at least one of an olefinic amide monomer polymer, an olefinic cyan monomer polymer, an olefinic acid monomer polymer, an olefinic alcohol monomer polymer, and a polyoxyalkylene polymer.

[0009] In the above-mentioned composite binder, as a preferred embodiment, the water-based binder comprises at least one of polyacrylamide (PAM), polyacrylonitrile, polyacrylic acid, polyvinyl alcohol and polyoxyethylene. When the water-based binder is polyacrylamide, the adhesion and processability of the binder are optimal.

[0010] In the above-mentioned composite binder, as a preferred embodiment, the water-based binder-polyethylene glycol dimethyl acrylate crosslinking product is obtained by crosslinking polymerization of the water-based binder and the polyethylene glycol dimethyl acrylate in an aqueous solution in the presence of an iron salt.

[0011] In the above-mentioned composite binder, as a preferred embodiment, the mass ratio of the carboxymethylated tamarind polysaccharide gum to the water-based binder-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 1:(8-20), for example, it can be 1:8, 1:10, 1:12, 1:14, 1:18 or 1:20, etc., preferably 1:(12-18). If the content of the crosslinking product is too high, the stability of the electrode paste prepared from it will decrease, the paste will easily settle, affecting the subsequent coating performance and the processing performance will be poor; if the content of the crosslinking product is too low, the adhesion of the obtained composite binder will be poor.

[0012] In the above-mentioned composite adhesive, as a preferred embodiment, the raw materials for preparing the water-based adhesive-polyethylene glycol dimethacrylate crosslinking product include a water-based adhesive, polyethylene glycol dimethacrylate, and an iron salt. The mass ratio of the water-based adhesive, polyethylene glycol dimethacrylate, and the iron salt is (50-80):(1-5):(3-7), for example, it can be 60:1:4, 60:5:4, 50:1:3, 70:3:6, or 80:5:7, etc.

[0013] In the above-mentioned composite adhesive, as a preferred embodiment, the raw materials for preparing the aqueous adhesive-polyethylene glycol dimethacrylate crosslinking product further include an oxidant. The mass ratio of the aqueous adhesive, polyethylene glycol dimethacrylate, iron salt, and oxidant is (50-80):(1-5):(3-7):(1-10), for example, 60:1:4:2, 60:5:4:10, 50:1:3:2, 70:3:6:6, or 80:5:7:8, etc. Preferably, the mass ratio of the aqueous adhesive, polyethylene glycol dimethacrylate, iron salt, and oxidant is 60:1:4:2 or 60:5:4:10, in which the aqueous adhesive and polyethylene glycol dimethacrylate have the best crosslinking effect and form a good bonding skeleton.

[0014] In the above-mentioned composite binder, as a preferred embodiment, the iron salt includes at least one of ferric nitrate, ferric chloride, and ferric sulfate.

[0015] In the above-mentioned composite adhesive, as a preferred embodiment, the carboxymethylated tamarind polysaccharide gum has a weight-average molecular weight of 500,000 to 1,200,000, for example, 500,000, 800,000, 1,000,000 or 1,200,000.

[0016] In the above-mentioned composite adhesive, as a preferred embodiment, the weight-average molecular weight of the water-based adhesive is 200,000 to 2,000,000, for example, it can be 200,000, 400,000, 600,000, 800,000, 1,000,000, 1,500,000, or 2,000,000.

[0017] In the above-mentioned composite adhesive, as a preferred embodiment, the weight-average molecular weight of the polyethylene glycol dimethacrylate is 50,000 to 200,000, for example, it can be 50,000, 100,000, 150,000 or 200,000.

[0018] In the above-mentioned composite adhesive, as a preferred embodiment, the weight-average molecular weight of the water-based adhesive-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 200,000 to 1,000,000.

[0019] In the above-mentioned composite adhesive, as a preferred embodiment, the composite adhesive further includes water, and the solid content of the composite adhesive is 2 to 10 wt% (for example, it can be 2 wt%, 4 wt%, 6 wt%, 8 wt% or 10 wt%, etc.), preferably 4 to 6 wt%, at which time the adhesive has better processing performance.

[0020] In a second aspect, the present invention provides a method for preparing a composite adhesive as described in the first aspect, the method comprising the following steps:

[0021] Preparation of water-based adhesive-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product:

[0022] In an inert atmosphere, an aqueous binder and polyethylene glycol dimethacrylate (PEGDMA) were added to water, followed by the addition of an oxidant to carry out a crosslinking reaction, thereby obtaining an aqueous binder-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product.

[0023] Preparation of composite adhesive:

[0024] The composite adhesive was prepared by dissolving carboxymethylated tamarind polysaccharide gum and the crosslinking product of the water-based adhesive - polyethylene glycol dimethacrylate (PEGDMA) in water.

[0025] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, in the preparation step of the aqueous adhesive-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product, the aqueous adhesive and the polyethylene glycol dimethacrylate (PEGDMA) are added to an aqueous solution of iron salt.

[0026] In the above-mentioned method for preparing composite adhesives, as a preferred embodiment, the method for preparing carboxymethylated tamarind polysaccharide gum includes: reacting tamarind collagen powder (TKP) and a monosubstituted organic acid in a reaction solvent in the presence of a base to obtain the carboxymethylated tamarind polysaccharide gum. For example, the reaction formula can be as follows:

[0027]

[0028] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, the oxidant includes at least one of ferric toluenesulfonate, ammonium persulfate, potassium persulfate, sodium persulfate, and hydrogen peroxide.

[0029] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, the temperature of the crosslinking reaction is 20-60℃ (e.g., 20℃, 40℃, 50℃ or 60℃, etc.). If the reaction temperature is too high, explosive polymerization is likely to occur, the colloid will be unstable, and stratification and flocculent matter will appear. The time of the crosslinking reaction is 8-12h (e.g., 8h, 10h or 12h, etc.).

[0030] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, the inert atmosphere is any one or both of nitrogen and argon.

[0031] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, in the preparation step of the water-based adhesive-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product, after the crosslinking reaction is completed, the product is obtained by filtration and freeze-drying.

[0032] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, the mass fraction of iron salt in the aqueous solution of iron salt is 0.1% to 5%, for example, it can be 0.1%, 0.8%, 1%, 3% or 5%.

[0033] In the above-mentioned method for preparing the composite adhesive, as a preferred embodiment, in the preparation step of the water-based adhesive-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product, the oxidant is added at a rate of 2-5 g / min. When the rate is too low, the crosslinking reaction proceeds slowly, and bulk polymerization will occur locally in the system, leading to an increase in cohesion rate, and sometimes even stratification.

[0034] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, the monosubstituted organic acid includes at least one of monochloroacetic acid, monobromoacetic acid, chloropropionic acid, and bromopropionic acid.

[0035] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, the alkali includes at least one of sodium hydroxide, lithium hydroxide, and potassium hydroxide, preferably lithium hydroxide.

[0036] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, the reaction solvent includes at least one of isopropanol, anhydrous ethanol, and methanol.

[0037] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, in the preparation process of carboxymethylated tamarind polysaccharide gum, after the reaction is completed, the gum is washed with ethanol to remove impurities, filtered, and then freeze-dried to obtain the carboxymethylated tamarind polysaccharide gum.

[0038] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, the mass ratio of tamarind collagen powder (TKP) to the reaction solvent is 1:(10-20), for example, it can be 1:10, 1:15 or 1:20, etc. Preferably, the mass ratio is 1:(14-15). Within the preferred range, tamarind collagen powder has better dispersion effect and reaction efficiency.

[0039] In the above-mentioned method for preparing the composite adhesive, as a preferred embodiment, the mass ratio of the tamarind collagen powder, the alkali, and the monosubstituted organic acid is (25-35):(4-25):(5-30). More preferably, when the mass ratio of the tamarind collagen powder, the alkali, and the monosubstituted organic acid is 3:1:1, the macromolecular network structure of the carboxymethylated tamarind polysaccharide gum has more abundant and uniform polar hydroxyl and carboxyl groups, and the hydrogen bonds between the silicon anode and the adhesive are stronger.

[0040] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, in the preparation process of carboxymethylated tamarind polysaccharide gum, the alkali is added to the reaction solvent in the form of an aqueous solution.

[0041] In the above-mentioned method for preparing composite adhesive, as a preferred embodiment, the reaction time is 5-8 hours during the preparation of carboxymethylated tamarind polysaccharide gum.

[0042] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material, a conductive agent, a binder and a current collector, the binder comprising a composite binder as described in the first aspect or a composite binder prepared by the preparation method described in the second aspect.

[0043] In the aforementioned lithium-ion battery, as a preferred embodiment, the negative electrode active material comprises at least one of soft carbon, hard carbon, mesophase carbon microspheres, artificial graphite, natural graphite, silicon-carbon, silicon-oxygen, micron-sized silicon particles, silicon nanowires, carbon-encapsulated silicon particles, silicon-based alloy powder, and tin dioxide particles.

[0044] In the aforementioned lithium-ion battery, as a preferred embodiment, the conductive agent includes at least one of the following: metal-based conductive agents (e.g., silver powder, copper powder, nickel powder), metal oxide-based conductive agents (e.g., tin oxide, iron oxide, zinc oxide), particulate conductive agents (e.g., conductive graphite, conductive carbon black), fibrous conductive agents (e.g., carbon nanotubes, VGCF), sheet-like conductive agents (e.g., graphene), and composite conductive agents (e.g., composite powder, composite fiber).

[0045] In the above-mentioned lithium-ion battery, as a preferred embodiment, the mass ratio of the negative electrode active material, the conductive agent and the binder is (90-97):(2-3):(1-8).

[0046] In the aforementioned lithium-ion battery, as a preferred embodiment, the preparation method of the negative electrode sheet includes: mixing the negative electrode active material and conductive agent evenly, adding a portion of the binder, kneading for 20-60 minutes, continuing to add the remaining binder and deionized water for high-speed dispersion for 1-2 hours, finally adding deionized water for high-speed dispersion for 2-3 hours, discharging and sieving to obtain a negative electrode slurry, uniformly coating the negative electrode slurry onto copper foil, and obtaining the negative electrode sheet through baking and rolling. The negative electrode sheet preparation method of the present invention is simple, feasible, and efficient. It includes the composite binder (aqueous binder) provided by the present invention, the slurry is uniform and has good processability, which is beneficial for electrolyte wetting and absorption. Combined with a matched areal density design, it has superior peel strength and electrochemical performance, and can be applied to both high-power and high-energy systems.

[0047] In the above-mentioned lithium-ion battery, as a preferred embodiment, the kneaded solid content is 65-70%.

[0048] In the above-mentioned lithium-ion battery, as a preferred embodiment, the viscosity of the negative electrode slurry is 5000-10000 mPa·S.

[0049] In the aforementioned lithium-ion battery, as a preferred embodiment, the single-sided areal density of the negative electrode sheet is 40–100 g / m². 2 .

[0050] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0051] (1) The composite binder provided by the present invention comprises a crosslinking product of carboxymethylated tamarind polysaccharide gum and water-based binder-polyethylene glycol dimethacrylate (PEGDMA), which makes the binder have strong adhesion and can be used to prepare silicon-based anodes for lithium batteries, thus enabling silicon-based lithium batteries to have excellent cycle stability.

[0052] (2) The composite binder provided by this invention is an aqueous dual-network binder, comprising a carboxymethylated tamarind polysaccharide network constructed by elongating the molecular chain of tamarind collagen powder (TKP) and introducing a large number of carboxymethyl groups, and an amphiphilic copolymer network composed of an aqueous binder and polyethylene glycol dimethacrylate (PEGDMA). The composite binder provided by this invention, on the one hand, forms more and stronger bonds with silicon-based materials through the large number of polar hydroxyl and carboxyl groups in the carboxymethylated tamarind polysaccharide network; on the other hand, it utilizes the supramolecular interaction between the aqueous binder-PEGDMA crosslinked product (amphiphilic copolymer) network and the carboxymethylated tamarind polysaccharide network to form a hybrid network. This not only suppresses excessive volume expansion of the silicon-based electrode during cycling with good mechanical strength, but also eliminates stress caused by silicon volume changes, stabilizes the formation of the SEI film, and helps stabilize the electrode interface during volume contraction and expansion of the silicon electrode during cycling, reducing electrolyte decomposition caused by mechanical damage, thereby improving the cycle performance stability of the battery. Simultaneously, through Fe... 3+ The dynamic cross-linking framework is formed by ionic dipole or hydrogen bonding between the Si electrode and the carboxylic acid and hydroxyl functional groups, which induces the formation of a solid electrolyte interface layer rich in lithium nitride / lithium fluoride. This inhibits the continuous decomposition of the electrolyte, which not only gives the Si electrode strong adhesion, but also gives it high self-healing ability. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0054] The embodiments of the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally in accordance with conventional conditions.

[0055] The endpoints and any values ​​of the ranges disclosed in this invention 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 and 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 in this invention.

[0056] In this invention, unless otherwise specified and / or stated, all parts are by weight. Process parameters not specifically described in the following examples are generally performed under conventional conditions. Unless otherwise specified, the experimental reagents used in the following examples are conventional biochemical reagents; and unless otherwise specified, the amounts of experimental reagents used are the amounts used in conventional experimental operations.

[0057] In a first aspect, the present invention provides a composite adhesive comprising carboxymethylated tamarind polysaccharide gum and a water-based adhesive-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product, wherein the water-based adhesive-polyethylene glycol dimethacrylate crosslinking product is obtained by crosslinking polymerization of the water-based adhesive and polyethylene glycol dimethacrylate in an aqueous solution in the presence of iron salts, wherein the water-based adhesive comprises at least one of an olefinically unsaturated monomer polymer and an epoxy alkane monomer polymer, and the side chain or end group contains at least one of N and O elements, wherein the water-based adhesive comprises at least one of polyacrylamide (PAM), polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, and polyoxyethylene, and the mass ratio of the carboxymethylated tamarind polysaccharide gum to the water-based adhesive-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 1:(8-20), and the water-based adhesive-polyethylene glycol dimethacrylate crosslinking product is prepared by crosslinking polymerization. The raw materials for the crosslinking product of polyethylene glycol dimethacrylate include an aqueous binder, polyethylene glycol dimethacrylate, an iron salt, and an oxidant. The mass ratio of the aqueous binder, polyethylene glycol dimethacrylate, and the iron salt and oxidant is (50-80):(1-5):(3-7):(1-10). The iron salt includes at least one of ferric nitrate, ferric chloride, and ferric sulfate. The weight-average molecular weight of the carboxymethylated tamarind polysaccharide gum is 500,000-1,200,000. The weight-average molecular weight of the aqueous binder is 200,000-2,000,000. The weight-average molecular weight of the polyethylene glycol dimethacrylate is 50,000-200,000. The weight-average molecular weight of the aqueous binder-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 200,000-10,000,000. The composite binder also includes water, and the solid content of the composite binder is 2-10 wt%.

[0058] Currently, many synthetic and natural polymers with linear or cross-linked backbones have been developed and applied as silicon anode binders, such as polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), sodium alginate (Alg), and blended polymers (CMC / PAA). These binders can improve the cycle stability of the battery to some extent. However, they are difficult to achieve mechanical stability of the silicon electrode during cycling because existing binders, including so-called self-healing binders, are difficult to guarantee stable cycling of the Si electrode: (1) PAA-based polymers with supramolecular interactions (such as hydrogen bonds and ion dipole interactions) can promote the recovery of the electrode film during wear, but it is difficult to restore it to the original state (i.e., bonding position) before the last lithiation; (2) Pectin-based polymers are prone to deformation during cycling. Therefore, it is urgent to develop a functional binder that combines rigidity and flexibility to achieve stable cycling of the Si electrode.

[0059] The composite binder provided by this invention is an aqueous dual-network binder. On the one hand, it forms more and stronger bonds with silicon-based materials through the large number of polar hydroxyl and carboxyl groups in the carboxymethylated tamarind polysaccharide gum network. On the other hand, it forms a hybrid network by utilizing the supramolecular interaction between the aqueous binder-polyethylene glycol dimethacrylate (PEGDMA) crosslinked product (amphiphilic copolymer) network and the carboxymethylated tamarind polysaccharide gum network. This not only suppresses the excessive volume expansion of silicon-based electrodes during cycling with good mechanical strength, but also eliminates the stress caused by silicon volume changes, stabilizes the formation of the SEI film, and helps stabilize the electrode interface when the silicon electrode shrinks and expands during cycling, reducing electrolyte decomposition caused by mechanical damage, thereby improving the cycle performance stability of the battery.

[0060] In this invention, the water-based adhesive and polyethylene glycol dimethacrylate undergo a crosslinking reaction via the oxidation of -CC- to obtain a crosslinked product containing -CCOCC-. For example, the crosslinking reaction between polyacrylamide and polyethylene glycol dimethacrylate can be as follows:

[0061]

[0062] Amphiphilic copolymers have an amphiphilic epoxy ether (-CH2-CH2-O-) structure, which has the effects of blurring the phase interface (good solubility), improving compatibility, and increasing solubility.

[0063] In a second aspect, the present invention provides a method for preparing a composite adhesive as described in the first aspect, the method comprising the following steps:

[0064] S1. Tamarind collagen powder (TKP) and a monosubstituted organic acid are reacted in a reaction solvent in the presence of an alkali. After the reaction is completed, the mixture is washed with ethanol to remove impurities, filtered, and freeze-dried to obtain the carboxymethylated tamarind polysaccharide gum. The alkali includes at least one of sodium hydroxide, lithium hydroxide, and potassium hydroxide. The reaction solvent includes at least one of isopropanol, anhydrous ethanol, and methanol. The monosubstituted organic acid includes at least one of monochloroacetic acid, monobromoacetic acid, chloropropionic acid, and bromopropionic acid. The mass ratio of tamarind collagen powder (TKP) to the reaction solvent is 1:(10-20). The mass ratio of tamarind collagen powder, alkali, and the monosubstituted organic acid is (25-35):(4-25):(5-30). The reaction time is 5-8 hours.

[0065] S2. Under an inert atmosphere, an aqueous binder and polyethylene glycol dimethacrylate (PEGDMA) are added to an aqueous solution of iron salts, followed by the addition of an oxidant to initiate a crosslinking reaction. After the crosslinking reaction is complete, the product is filtered and freeze-dried to obtain the aqueous binder-polyethylene glycol dimethacrylate (PEGDMA) crosslinked product. The oxidant includes at least one of ferric toluenesulfonate, ammonium persulfate, potassium persulfate, sodium persulfate, and hydrogen peroxide. The crosslinking reaction temperature is 20–60°C, the reaction time is 8–12 h, the inert atmosphere is any one or both of nitrogen and argon, the mass fraction of iron salts in the aqueous solution is 0.1–5%, and the oxidant addition rate is 2–5 g / min.

[0066] S3. Dissolve carboxymethylated tamarind polysaccharide gum and the water-based binder - polyethylene glycol dimethacrylate (PEGDMA) crosslinking product in water to prepare the composite binder.

[0067] Thirdly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material, a conductive agent, a binder and a current collector, the binder comprising a composite binder as described in the first aspect or a composite binder prepared by the preparation method described in the second aspect.

[0068] In the following embodiments and comparative examples:

[0069] The room temperature is 20-30℃.

[0070] To further understand the present invention, the composite binder, its preparation method, and lithium-ion battery provided by the present invention will be described in detail below with reference to the embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0071] Example 1

[0072] The composite adhesive provided in this embodiment includes carboxymethylated tamarind polysaccharide gum and polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product. The mass ratio of carboxymethylated tamarind polysaccharide gum to polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 1:14. The raw materials for preparing the polyacrylamide-polyethylene glycol dimethacrylate crosslinking product include polyacrylamide, polyethylene glycol dimethacrylate, ferric nitrate, and ammonium persulfate. The mass ratio of polyacrylamide, polyethylene glycol dimethacrylate, ferric nitrate, and ammonium persulfate is 60:1:4:2.

[0073] The method for preparing the composite adhesive provided in this embodiment includes the following steps:

[0074] S1. At room temperature, 6 parts by weight of tamarind collagen powder (TKP) were dispersed in 84 parts by weight of isopropanol and stirred for 30 min. Then, 20 parts by weight of 10 wt% lithium hydroxide aqueous solution were added and stirred for another 30 min. Then, 40 parts by weight of 5 wt% monochloroacetic acid solution (solvent is isopropanol) were added and stirred for another 6 h. The mixture was washed with ethanol to remove impurities, filtered, and the filter cake was freeze-dried to obtain carboxymethylated tamarind polysaccharide gum (weight average molecular weight of 800,000).

[0075] S2. Under a nitrogen atmosphere, 4 parts by weight of ferric nitrate [Fe(NO3)3] were dispersed in 496 parts by weight of water. Then, 60 parts by weight of polyacrylamide (PAM, Mw = 500,000) and 1 part by weight of polyethylene glycol dimethacrylate (PEGDMA, Mw = 100,000) were added. The mixture was stirred until completely dissolved. 2 parts by weight of ammonium persulfate were added at a rate of 3 g / min. The temperature was raised to 50 °C and the reaction was carried out for 10 h. After filtration, the filtrate was freeze-dried to obtain a polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinked product (amphiphilic copolymer, Mw = 1,000,000).

[0076] S3. Dissolve 1 part by weight of the carboxymethylated tamarind polysaccharide gum obtained in step S1 and 14 parts by weight of the amphiphilic copolymer obtained in step S2 in 360 parts by weight of deionized water to obtain a composite adhesive (waterborne dual-network adhesive) with a solid content of 4 wt%.

[0077] Example 2

[0078] The composite adhesive provided in this embodiment includes carboxymethylated tamarind polysaccharide gum and polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product. The mass ratio of carboxymethylated tamarind polysaccharide gum to polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 1:14. The raw materials for preparing the polyacrylamide-polyethylene glycol dimethacrylate crosslinking product include polyacrylamide, polyethylene glycol dimethacrylate, ferric nitrate, and ammonium persulfate. The mass ratio of polyacrylamide, polyethylene glycol dimethacrylate, ferric nitrate, and ammonium persulfate is 60:5:4:10.

[0079] The method for preparing the water-based adhesive provided in this embodiment includes the following steps:

[0080] S1. At room temperature, 6 parts by weight of tamarind collagen powder (TKP) were dispersed in 84 parts by weight of isopropanol and stirred for 30 min. Then, 60 parts by weight of 10 wt% lithium hydroxide aqueous solution were added, and stirring was continued for another 30 min. Next, 120 parts by weight of 5 wt% monochloroacetic acid solution (solvent: isopropanol) were added, and stirring was continued for 6 h. The mixture was washed with ethanol to remove impurities, filtered, and the filter cake was freeze-dried to obtain carboxymethylated tamarind polysaccharide gum (weight average molecular weight of 1,000,000).

[0081] S2. Under a nitrogen atmosphere, 4 parts by weight of ferric nitrate [Fe(NO3)3] were dispersed in 496 parts by weight of water. Then, 60 parts by weight of polyacrylamide (PAM, Mw = 500,000) and 5 parts by weight of polyethylene glycol dimethacrylate (PEGDMA, Mw = 100,000) were added. The mixture was stirred until completely dissolved. 10 parts by weight of ammonium persulfate were added at a rate of 3 g / min. The temperature was raised to 50 °C and the reaction was carried out for 10 h. After filtration, the filtrate was freeze-dried to obtain a polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinked product (amphiphilic copolymer, Mw = 1,800,000).

[0082] S3. Dissolve 1 part by weight of the carboxymethylated tamarind polysaccharide gum obtained in step S1 and 14 parts by weight of the amphiphilic copolymer obtained in step S2 in 360 parts by weight of deionized water to obtain a composite adhesive (waterborne dual-network adhesive) with a solid content of 4 wt%.

[0083] Example 3

[0084] The composite adhesive provided in this embodiment includes carboxymethylated tamarind polysaccharide gum and polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product. The mass ratio of carboxymethylated tamarind polysaccharide gum to polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 1:14. The raw materials for preparing the polyacrylamide-polyethylene glycol dimethacrylate crosslinking product include polyacrylamide, polyethylene glycol dimethacrylate, and ammonium persulfate. The mass ratio of polyacrylamide, polyethylene glycol dimethacrylate, and ammonium persulfate is 60:1:2.

[0085] The method for preparing the composite adhesive provided in this embodiment includes the following steps:

[0086] S1 is the same as step S1 in Example 1.

[0087] S2 is basically the same as step S2 in Example 1, except that ferric nitrate is not added. Specifically, under a nitrogen atmosphere, 60 parts by weight of polyacrylamide (PAM, Mw = 500,000) and 1 part by weight of polyethylene glycol dimethacrylate (PEGDMA, Mw = 100,000) are added to 496 parts by weight of water, mixed evenly and sonicated until completely dissolved. 2 parts by weight of ammonium persulfate are added at a rate of 3 g / min, the temperature is raised to 50°C, and the reaction is carried out for 10 h. After filtration, the filtrate is freeze-dried to obtain a polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinked product (amphiphilic copolymer, Mw = 800,000).

[0088] S3. Dissolve 1 part by weight of the carboxymethylated tamarind polysaccharide gum obtained in step S1 and 14 parts by weight of the amphiphilic copolymer obtained in step S2 in 360 parts by weight of deionized water to obtain a composite adhesive (waterborne dual-network adhesive) with a solid content of 4 wt%.

[0089] Example 4

[0090] The composite adhesive provided in this embodiment is basically the same as that in Example 1, except that "polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product" is replaced with "polyacrylic acid-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product".

[0091] The preparation method of the composite adhesive provided in this embodiment is basically the same as that in Example 1. The difference is that in step S2, polyacrylamide is replaced with polyacrylic acid (Mw = 800000), and the weight average molecular weight of the obtained polyacrylic acid-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 5,000,000.

[0092] Example 5

[0093] The composite adhesive provided in this embodiment is basically the same as that in Example 1, except that "polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product" is replaced with "polyacrylonitrile-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product".

[0094] The preparation method of the composite adhesive provided in this embodiment is basically the same as that in Example 1. The difference is that in step S2, polyacrylamide is replaced with polyacrylonitrile (Mw = 300000), and the weight average molecular weight of the resulting polyacrylonitrile-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 600000.

[0095] Example 6

[0096] The composite adhesive provided in this embodiment is basically the same as that in Example 1, except that the mass ratio of carboxymethylated tamarind polysaccharide gum to polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 1:24.

[0097] The preparation method of the composite binder provided in this embodiment is basically the same as that in Example 1, except that in step S3, 1 part by weight of the carboxymethylated tamarind polysaccharide gum obtained in step S1 and 24 parts by weight of the amphiphilic copolymer obtained in step S2 are dissolved in 600 parts by weight of deionized water to obtain a composite binder (waterborne dual-network binder) with a solid content of 4 wt%. If the content of crosslinking products is too high, the stability of the electrode paste prepared from it will decrease, the paste will easily settle, affecting the subsequent coating performance and the processing performance will be poor.

[0098] Example 7

[0099] The composite adhesive provided in this embodiment is basically the same as that in Example 1, except that the mass ratio of carboxymethylated tamarind polysaccharide gum to polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 1:6.

[0100] The preparation method of the composite adhesive provided in this embodiment is basically the same as that in Example 1, except that in step S3, 1 part by weight of the carboxymethylated tamarind polysaccharide gum obtained in step S1 and 6 parts by weight of the amphiphilic copolymer obtained in step S2 are dissolved in 168 parts by weight of deionized water to obtain a composite adhesive (waterborne dual-network adhesive) with a solid content of 4 wt%. If the content of the crosslinking product is too low, the adhesive strength of the obtained composite adhesive will be poor.

[0101] Example 8

[0102] The composite adhesive provided in this embodiment is basically the same as that in Example 1, except that the mass ratio of carboxymethylated tamarind polysaccharide gum to polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 1:8.

[0103] The preparation method of the composite adhesive provided in this embodiment is basically the same as that in Example 1. The difference is that in step S3, 1 part by weight of the carboxymethylated tamarind polysaccharide gum obtained in step S1 and 8 parts by weight of the amphiphilic copolymer obtained in step S2 are dissolved in 216 parts by weight of deionized water to obtain a composite adhesive (waterborne dual-network adhesive) with a solid content of 4 wt%.

[0104] Example 9

[0105] The composite adhesive provided in this embodiment includes carboxymethylated tamarind polysaccharide gum and polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product. The mass ratio of carboxymethylated tamarind polysaccharide gum to polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 1:14. The raw materials for preparing the polyacrylamide-polyethylene glycol dimethacrylate crosslinking product include polyacrylamide, polyethylene glycol dimethacrylate, ferric nitrate, and ammonium persulfate. The mass ratio of polyacrylamide, polyethylene glycol dimethacrylate, ferric nitrate, and ammonium persulfate is 60:1:4:2.

[0106] The method for preparing the composite adhesive provided in this embodiment includes the following steps:

[0107] S1. At room temperature, 6 parts by weight of tamarind collagen powder (TKP) were dispersed in 84 parts by weight of isopropanol and stirred for 30 min. Then, 20 parts by weight of 10 wt% sodium hydroxide aqueous solution were added and stirred for another 30 min. Then, 40 parts by weight of 5 wt% monochloroacetic acid solution (solvent is isopropanol) were added and stirred for another 6 h. The mixture was washed with ethanol to remove impurities, filtered, and the filter cake was freeze-dried to obtain carboxymethylated tamarind polysaccharide gum (weight average molecular weight of 800,000).

[0108] S2-S3 are the same as S2-S3 in Example 1.

[0109] Comparative Example 1

[0110] The binder in this comparative example consists of carboxymethylated tamarind polysaccharide gum and deionized water, with a solid content of 4 wt%. The carboxymethylated tamarind polysaccharide gum is prepared in step S1 of Example 1. Compared with Example 1, the 4 wt% aqueous binder in this comparative example does not contain polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking products.

[0111] Comparative Example 2

[0112] The binder in this comparative example consists of a polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product and deionized water, with a solid content of 4 wt%. The polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is prepared in step S2 of Example 1. Compared to Example 1, this 4 wt% aqueous binder does not contain carboxymethylated tamarind polysaccharide gum.

[0113] Comparative Example 3

[0114] The composite adhesive provided in this comparative example includes carboxymethyl cellulose (CMC) (Mw = 90000), polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product, and deionized water. The mass ratio of carboxymethyl cellulose (CMC) to polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is 1:14, and the solid content of the composite adhesive is 4 wt%. The polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product is prepared by step S2 in Example 1.

[0115] Comparative Example 4

[0116] The method for preparing the composite adhesive provided in this comparative example includes the following steps:

[0117] S1 is the same as step S1 in Example 1.

[0118] S2. Under a nitrogen atmosphere, 4 parts by weight of ferric nitrate [Fe(NO3)3] were dispersed in 496 parts by weight of water. Then, 60 parts by weight of polyacrylamide (PAM, Mw = 500,000) and 1 part by weight of polyethylene glycol dimethacrylate (PEGDMA, Mw = 100,000) were added. The mixture was stirred until completely dissolved by sonication. After filtration, the filtrate was freeze-dried to obtain a mixture of polyacrylamide (PAM) and polyethylene glycol dimethacrylate (PEGDMA).

[0119] S3. Dissolve 1 part by weight of the carboxymethylated tamarind polysaccharide gum obtained in step S1 and 14 parts by weight of the mixture obtained in step S2 in 360 parts by weight of deionized water to obtain a composite adhesive with a solid content of 4 wt%.

[0120] Comparative Example 5

[0121] The method for preparing the composite adhesive provided in this embodiment includes the following steps:

[0122] S1 is the same as step S1 in Example 1.

[0123] S2. Under a nitrogen atmosphere, 4 parts by weight of ferric nitrate [Fe(NO3)3] were dispersed in 496 parts by weight of water, followed by the addition of 61 parts by weight of polyacrylamide (PAM, Mw = 500,000), and sonicated until completely dissolved. Then, 2 parts by weight of ammonium persulfate were added at a rate of 3 g / min, the temperature was raised to 50°C, and the reaction was carried out for 10 h. After filtration, the filtrate was freeze-dried to obtain the copolymer (Mw = 2,500,000).

[0124] S3. Dissolve 1 part by weight of the carboxymethylated tamarind polysaccharide gum obtained in S1 and 14 parts by weight of the copolymer obtained in step S2 in 360 parts by weight of deionized water to obtain a composite adhesive (waterborne dual-network adhesive) with a solid content of 4 wt%.

[0125] Comparative Example 6

[0126] The method for preparing the composite adhesive provided in this embodiment includes the following steps:

[0127] S1 is the same as step S1 in Example 1.

[0128] S2. Under a nitrogen atmosphere, 4 parts by weight of ferric nitrate [Fe(NO3)3] were dispersed in 496 parts by weight of water, followed by the addition of 61 parts by weight of polyethylene glycol dimethacrylate (PEGDMA, Mw = 100000). The mixture was stirred until completely dissolved, and then 2 parts by weight of ammonium persulfate were added at a rate of 3 g / min. The temperature was raised to 50°C and the reaction was carried out for 10 h. After filtration, the filtrate was freeze-dried to obtain the copolymer (Mw = 500000).

[0129] S3. Dissolve 1 part by weight of the carboxymethylated tamarind polysaccharide gum obtained in step S1 and 14 parts by weight of the copolymer obtained in step S2 in 360 parts by weight of deionized water to obtain a composite adhesive (waterborne dual-network adhesive) with a solid content of 4 wt%.

[0130] Assembly and performance testing of lithium-ion batteries:

[0131] Preparation of negative electrode sheets: Negative electrode sheets were prepared using the aqueous binders from Examples 1-9 and Comparative Examples 1-6, respectively. Specifically, 95 parts by weight of silicon-based graphite active material (wherein the mass ratio of silicon-based material to graphite is 12:88) and 2 parts by weight of conductive agent Super P were uniformly mixed for 30 min. Then, 1.9 parts by weight (based on solid content) of 4 wt% aqueous binder were added, and the kneading solid content was controlled at 68%–69%. Kneading was continued for 60 min, followed by the addition of 1.1 parts by weight (based on solid content) of 4 wt% aqueous binder and 28 parts by weight of deionized water for high-speed dispersion for 3 h. The discharged material was sieved through a 200-mesh sieve to obtain a negative electrode slurry with a solid content of 48–52%. The negative electrode slurry was uniformly coated onto copper foil, with a single-sided coating surface density of 50 g / m². 2The negative electrode sheet is obtained after baking and rolling. The thickness of the negative electrode sheet is measured and recorded as the rolling thickness. According to the ASTM-D903 test method, the electrode sheet is peeled off at a rate of 10 mm / min and an angle of 180° to test the peel strength of the negative electrode sheet. The test results are shown in Table 1.

[0132] The aforementioned negative electrode sheets are assembled with positive electrode sheets to form battery cells, wherein the positive electrode sheets use NCMA positive electrode material, and a soft-pack lithium-ion battery is manufactured using a soft-pack stacking process. The NCMA positive electrode sheet, silicon-based graphite negative electrode sheet, and polyethylene separator (e.g., PE+OBS separator) are stacked and assembled, then baked until the moisture content is within acceptable limits, electrolyte is injected, and after hot-pressing formation and high-temperature settling, they are packaged. After capacity testing, they are settling at room temperature to obtain the finished soft-pack battery.

[0133] Cyclic expansion rate test: The rolled negative electrode sheet was assembled with lithium sheet to form a button cell with a voltage range of 2.75 to 4.2V. After 100 cycles of 1C / 1C, the cell was disassembled and the full-charge thickness of the negative electrode was tested. The 100-cycle expansion rate = (100-cycle full-charge thickness - rolled thickness) / rolled thickness. The results are shown in Table 1.

[0134] Cyclic performance testing: The finished pouch cells were subjected to 3C / 3C cycle testing at 25℃, with a voltage range of 2.75–4.2V. The number of cycles at 80% SOH is shown in Table 1. SOH, or State of Health, refers to the ratio of the battery's actual capacity to its theoretical capacity.

[0135] Table 1

[0136] Group Peeling strength N / m 100 cycle expansion rate % 80% SOH cycle number Example 1 8.04 28.56 1180 Example 2 8.15 28.43 1185 Example 3 7.64 29.32 942 Example 4 7.57 28.94 1033 Example 5 7.64 28.81 1065 Example 6 8.13 29.28 966 Example 7 5.85 33.71 839 Example 8 6.77 32.28 878 Example 9 8.02 28.51 1091 Comparative Example 1 3.13 38.46 574 Comparative Example 2 7.29 31.07 693 Comparative Example 3 7.61 30.94 905 Comparative Example 4 6.32 33.29 846 Comparative Example 5 5.19 35.84 762 Comparative Example 6 5.49 33.85 799

[0137] At least the following points can be observed from Table 1:

[0138] (1) As can be seen from Examples 1-9 and Comparative Example 1, the peel strength of the adhesive provided by the present invention is 5.85-8.15 N / m, the 100-cycle expansion rate is 28.43-33.71%, and the number of cycles with capacity below 80% SOH can reach more than 1185 cycles. In contrast, the peel strength of the adhesive provided by Comparative Example 1 is 3.13 N / m, the 100-cycle expansion rate is 38.46%, and the capacity is below 80% SOH after more than 574 cycles. This indicates that the composite adhesive provided by the present invention, through the inclusion of carboxymethylated tamarind polysaccharide... The adhesive and water-based binder - polyethylene glycol dimethacrylate (PEGDMA) crosslinking product - has a large number of polar hydroxyl and carboxyl groups in its dual network structure that form more and stronger bonds with the negative electrode active material and the current collector copper foil. This gives the binder strong adhesion, which can suppress excessive volume expansion of silicon-based electrodes during cycling with good mechanical strength. It can also eliminate the stress caused by silicon volume change, avoid electrolyte decomposition caused by the volume change of active material, thereby improving the stability of electrode structure and improving the cycle performance of silicon-based lithium-ion batteries.

[0139] (2) As can be seen from Examples 1 and 3, when the raw materials for preparing the polyacrylamide (PAM)-polyethylene glycol dimethacrylate (PEGDMA) crosslinking product do not include ferric nitrate, the peel strength, the performance in inhibiting silicon-based electrode expansion, and the cycle performance are all significantly reduced. The reason may be that: the present invention uses Fe 3+ The dynamic cross-linking framework formed by ionic dipole or hydrogen bonding between the Si electrode and the carboxylic acid and hydroxyl functional groups suppresses the continuous side reactions between the Si electrode and the electrolyte. This not only gives the Si electrode strong adhesion but also high self-healing ability.

[0140] (3) Compared with Example 1 and Example 6, if the content of crosslinking products in the composite binder is too high, the cycle performance will decrease significantly. The reason may be that if the content of crosslinking products is too high, the stability of the electrode slurry prepared by it will decrease, the slurry will easily settle, affecting the subsequent coating performance, the processing performance will be poor, resulting in poor electrode consistency and damage to some negative electrode structures, thereby affecting the cycle performance of the battery.

[0141] (4) As can be seen from Example 1 and Comparative Example 2, when the composite binder does not contain carboxymethyl tamarind polysaccharide gum, the cycle performance is significantly reduced. The reason may be that: when carboxymethyl tamarind polysaccharide gum is not present, on the one hand, the negative electrode particles are poorly dispersed, the processing performance of the slurry deteriorates, resulting in poor electrode consistency and damage to some negative electrode structures, causing the cell to drop in performance during later cycles; on the other hand, during the lithium insertion / extraction process, due to the poor flexibility of the binder, it is difficult for the binder to return to its original state, thus causing the lithium battery to drop in performance during the cycle.

[0142] (5) As can be seen from Example 9 and Comparative Example 3, when the carboxymethylated tamarind polysaccharide gum was replaced with carboxymethyl cellulose (CMC), the cycle performance decreased significantly, indicating that the crosslinking product and the carboxymethylated tamarind polysaccharide gum have a better interaction in suppressing the volume expansion of silicon electrodes and improving the cycle performance of silicon-based lithium batteries.

[0143] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A composite binder, characterized by, The composite binder comprises carboxymethylated tamarind polysaccharide gum and water-based binder-polyethylene glycol dimethacrylate crosslinking product, wherein the water-based binder comprises at least one of olefinic unsaturated monomer polymer, alkylene oxide monomer polymer, and side chains or end groups contain at least one of N, O elements; The raw materials for preparing the water-based binder-polyethylene glycol dimethacrylate crosslinking product comprise the water-based binder, the polyethylene glycol dimethacrylate, the iron salt and the oxidizing agent; The mass ratio of the water-based binder, the polyethylene glycol dimethacrylate, the iron salt and the oxidizing agent is 50-80:1-5:3-7:1-10; The mass ratio of the carboxymethylated tamarind polysaccharide gum and the water-based binder-polyethylene glycol dimethacrylate crosslinking product is 1:(8-20).

2. The composite binder of claim 1, wherein, The water-based binder-polyethylene glycol dimethacrylate crosslinking product is obtained by crosslinking polymerization of the water-based binder and the polyethylene glycol dimethacrylate in an aqueous solution in the presence of the iron salt; And / or, the water-based binder comprises at least one of olefinic amide monomer polymer, olefinic cyan monomer polymer, olefinic acid monomer polymer, olefinic alcohol monomer polymer, polyoxyalkylene polymer.

3. The composite binder of claim 1, wherein, The water-based binder comprises at least one of polyacrylamide, polyacrylonitrile, polyacrylic acid, polyvinyl alcohol, polyoxyethylene; And / or, the weight average molecular weight of the carboxymethylated tamarind polysaccharide gum is 500000-1200000; And / or, the weight average molecular weight of the water-based binder is 200000-2000000; And / or, the weight average molecular weight of the polyethylene glycol dimethacrylate is 50000-200000; And / or, the weight average molecular weight of the water-based binder-polyethylene glycol dimethacrylate crosslinking product is 200000-10000000; And / or, the composite binder further comprises water, and the solid content of the composite binder is 2-10wt%.

4. The composite binder of claim 1, wherein, The iron salt comprises at least one of ferric nitrate, ferric chloride, ferric sulfate.

5. A method of preparing the composite binder as claimed in any one of claims 1 to 4, characterized in that, The preparation method comprises the following steps: Preparation of water-based binder-polyethylene glycol dimethacrylate crosslinking product: Under an inert atmosphere, the water-based binder and the polyethylene glycol dimethacrylate are added to an aqueous solution of the iron salt, and then the oxidizing agent is added to perform crosslinking reaction, thereby obtaining the water-based binder-polyethylene glycol dimethacrylate crosslinking product; Preparation of composite binder: The carboxymethylated tamarind polysaccharide gum and the water-based binder-polyethylene glycol dimethacrylate crosslinking product are dissolved in water to prepare the composite binder.

6. The method of claim 5, wherein the composite binder is prepared by mixing the components in the following order: the binder resin, the curing agent, the curing accelerator, the filler, the coupling agent, and the dispersant. In the preparation step of the water-based binder-polyethylene glycol dimethacrylate crosslinking product, the water-based binder and the polyethylene glycol dimethacrylate are added to an aqueous solution of the iron salt; And / or, the preparation method of the carboxymethylated tamarind polysaccharide gum comprises: reacting tamarind gum powder and monosubstituted organic acid in a reaction solvent in the presence of alkali to obtain the carboxymethylated tamarind polysaccharide gum. And / or, the oxidizing agent comprises at least one of ferric methylbenzenesulfonate, ammonium persulfate, potassium persulfate, sodium persulfate, and hydrogen peroxide; And / or, the temperature of the cross-linking reaction is 20-60℃, and the time of the cross-linking reaction is 8-12h; And / or, the inert atmosphere is any one or both of nitrogen and argon.

7. The method of claim 5, wherein the composite binder is prepared by mixing the components in the following order: the binder resin, the curing agent, the curing accelerator, the filler, the coupling agent, and the dispersant. In the preparation step of the water-based adhesive-polyethylene glycol dimethacrylate cross-linking product, after the cross-linking reaction is completed, the water-based adhesive-polyethylene glycol dimethacrylate cross-linking product is obtained by freeze-drying after suction filtration. And / or, in the preparation step of the water-based adhesive-polyethylene glycol dimethacrylate cross-linking product, the addition rate of the oxidizing agent is 2-5g / min.

8. The method of claim 6, wherein the composite binder is prepared by mixing the components in the following order: the binder resin, the curing agent, the curing accelerator, the filler, the coupling agent, and the dispersant. The mass fraction of the iron salt in the aqueous solution of the iron salt is 0.1-5%; And / or, the monosubstituted organic acid comprises at least one of monochloroacetic acid, monobromoacetic acid, chloropropionic acid, and bromopropionic acid; And / or, the base comprises at least one of sodium hydroxide, lithium hydroxide, and potassium hydroxide; And / or, the reaction solvent comprises at least one of isopropyl alcohol, anhydrous ethanol, and methanol; And / or, in the preparation process of the carboxymethylated tamarind polysaccharide gum, after the reaction is completed, the carboxymethylated tamarind polysaccharide gum is obtained by freeze-drying after washing and removing impurities with ethanol and suction filtration; And / or, the mass ratio of the tamarind gum powder to the reaction solvent is 1:(10-20); And / or, the mass ratio of the tamarind gum powder, the base, and the monosubstituted organic acid is (25-35):(4-25):(5-30); And / or, in the preparation process of the carboxymethylated tamarind polysaccharide gum, the base is added to the reaction solvent in the form of an aqueous solution.

9. The method for preparing the composite adhesive according to claim 6, characterized in that, In the preparation process of the carboxymethylated tamarind polysaccharide gum, the reaction time is 5-8h.

10. A lithium-ion battery, characterized by, The lithium ion battery comprises a negative electrode sheet, and the negative electrode sheet comprises a negative electrode active material, a conductive agent, a binder, and a current collector, wherein the binder comprises the composite binder according to any one of claims 1-4 or the composite binder prepared by the preparation method according to any one of claims 5-9.

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