Negative electrode binder for silicon-based negative electrode, negative electrode plate and lithium ion battery

Abstract

The invention provides a negative electrode binder for a silicon-based negative electrode, a negative electrode plate and a lithium ion battery, the negative electrode binder comprises a linear main chain and a high-branching-degree branch chain grafted on the main chain through an amido bond, and nitrogen and hydrogen functional groups are arranged in the chain segment and at the tail end of the branch chain. The main chain has an active group capable of forming an intermolecular hydrogen bond and / or an ionic bond with the nitrogen-hydrogen functional group, and the active group comprises at least one of carboxyl, carbonyl, ester group, epoxy group and phenyl; hydrogen bonds and / or ionic bonds formed between the nitrogen-hydrogen functional groups of the same branch chain or different branch chains and between the nitrogen-hydrogen functional groups and the active groups form a dynamic physical cross-linked network. A flexible high-branching-degree branch chain is grafted to a rigid linear main chain, a porous dynamic physical cross-linked network with high cross-linking density is constructed, the expansion stress of silicon particles is efficiently dispersed, meanwhile, the ion transmission efficiency is improved, a conductive network and mechanical flexibility are synergistically optimized, the rate performance is remarkably improved, and the cycle life is remarkably prolonged.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a negative electrode binder, a negative electrode sheet, and a lithium-ion battery for silicon-based negative electrodes. Background Technology

[0002] With the increasing demand for high energy density from new energy vehicles and portable electronic devices, silicon, due to its extremely high theoretical specific capacity (4200 mAh / g), is considered an ideal choice for next-generation lithium-ion battery anodes. However, silicon materials exhibit volume expansion of up to 300% during charge and discharge, which easily leads to electrode structure pulverization, interface debonding, and repeated rupture of the SEI film, resulting in a sharp decline in battery capacity and a significant reduction in cycle life. This inherent volume effect problem severely restricts the large-scale commercial application of silicon-based anodes.

[0003] To address these issues, developing high-performance polymer binders has become a key research direction. Traditional binders, such as polyvinylidene fluoride (PVDF) or sodium carboxymethyl cellulose (CMC), have linear structures and primarily provide adhesion through van der Waals forces, making it difficult to effectively confine the large volume changes of silicon particles. In recent years, researchers have focused on developing novel binder systems by constructing dynamic cross-linked networks (including dynamic covalent or non-covalent bonds). These dynamic networks can reversibly break and recombine under stress, effectively dissipating energy, thereby buffering volume expansion and maintaining the integrity of the electrode structure. However, existing dynamic network designs still face challenges: the response rate and reversibility of dynamic covalent bonds are limited, while non-covalent networks based on simple linear polymers often suffer from uneven cross-linking density, insufficient mechanical strength, or insufficient ionic conductivity.

[0004] Therefore, there is an urgent need in this field for an innovative binder molecular structure design that can provide both strong and rapid stress dissipation capabilities and simultaneously ensure excellent mechanical stability, ion transport efficiency, and electrochemical performance of the electrode. Summary of the Invention

[0005] To address the aforementioned problems and improve the mechanical stability and ion transport efficiency of silicon-based anode structures, a first aspect of this application provides an anode binder comprising a three-dimensional polymer. The three-dimensional polymer includes a linear main chain and highly branched branches grafted onto the main chain via amide bonds. The highly branched branches have nitrogen-hydrogen functional groups within their segments and at their ends. The main chain has active groups capable of forming intermolecular hydrogen bonds and / or ionic bonds with the nitrogen-hydrogen functional groups. The active groups include at least one of carboxyl, carbonyl, ester, epoxy, and phenyl groups. The hydrogen bonds and / or ionic bonds formed between the nitrogen-hydrogen functional groups within the highly branched branches, between the nitrogen-hydrogen functional groups on the highly branched branches and the active groups on the main chain, and between different nitrogen-hydrogen functional groups of the highly branched branches constitute a dynamic physical cross-linking network.

[0006] In some alternative embodiments, the negative electrode binder further includes metal cations crosslinked to the dynamic physical crosslinking network via ionic and / or coordination bonding, the metal cations carrying two or more positive charges.

[0007] In some alternative embodiments, the highly branched branch is a hyperbranched polyamide-amine, the highly branched branch has a generation number of 2.0-4.0 and a number average molecular weight of 2000-10000 g / mol.

[0008] In some alternative embodiments, the grafting rate of the three-dimensional polymer is 10%-40%, and the grafting rate is the percentage of the number of moles of the highly branched side chains to the total number of moles of the active groups in the linear backbone.

[0009] In some optional embodiments, the metal cation is Ca²⁺, Cu²⁺, Mg²⁺, Zn²⁺, Ni²⁺, Fe³⁺, Cr³⁺, Co³⁺, Al³⁺, and Zr. 4+ One or more of the above, wherein the amount of the metal cation added accounts for 0.5-5 wt% of the mass of the three-dimensional polymer.

[0010] In some optional embodiments, the swelling ratio of the negative electrode binder in a 1.0 M LiPF6 electrolyte containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1 is ≤4%, and the ionic conductivity in the symmetrical cell is ≥10. -4 S / cm.

[0011] The second aspect of this application provides a method for preparing a negative electrode binder as described in any of the preceding claims. The method for preparing the three-dimensional polymer in the negative electrode binder includes the following steps: S1: using a main-chain monomer containing the active group to carry out a free radical polymerization reaction in an aqueous solution to synthesize a linear main-chain polymer with a number average molecular weight of 200,000-500,000 g / mol, and using it as the linear main chain; S2: taking a highly branched polymer with nitrogen and hydrogen functional groups inside and at the ends of the chain segments, amiding one end of it, and then adding it to the aqueous solution of the linear main-chain polymer obtained in step S1, reacting at 60-80°C for 4-12 hours, grafting the highly branched polymer onto the linear main-chain polymer through an amidation reaction to form the highly branched branch chain, and obtaining the aqueous solution of the three-dimensional polymer. The physicochemical interactions within and between the three-dimensional polymer molecules form the dynamic physical cross-linking network.

[0012] In some optional embodiments, the method further includes the following step: S3: adding a water-soluble metal salt solution to the aqueous solution of the three-dimensional polymer, stirring and mixing, wherein the metal salt solution is ionized to obtain metal cations with two or more positive charges, and the metal cations are crosslinked into the dynamic physical crosslinking network through ionic and / or coordination binding.

[0013] In some optional embodiments, the highly branched chain is a hyperbranched polyamide-amine, the hyperbranched polyamide-amine having a generation number of 2.0-4.0, and the synthesis method of the hyperbranched polyamide-amine includes a one-step method or an iterative synthesis method; the one-step method includes the following steps: S211: using methyl acrylate and ethylenediamine as monomers, the feeding ratio of methyl acrylate to ethylenediamine is calculated according to the target generation range of the hyperbranched polyamide-amine; S212: dissolving ethylenediamine in anhydrous methanol, and slowly adding an anhydrous methanol solution of methyl methacrylate dropwise under an ice-water bath and a nitrogen protective atmosphere, after the addition is complete, Remove the ice bath and continue the reaction at room temperature with stirring for 12-24 hours; S213: Raise the reaction temperature to 40-50°C and continue the reaction for 24-48 hours, then remove the solvent and unreacted monomers by vacuum distillation to synthesize hyperbranched polyamide-amines with 2.0-4.0 generation branched structures; The iterative synthesis method includes the following steps: S221: Weigh ethylenediamine and methyl methacrylate in a molar ratio of 1:2, dissolve ethylenediamine in anhydrous methanol, and slowly add anhydrous methanol solution of methyl methacrylate dropwise under an ice-water bath and a nitrogen protective atmosphere. After the addition is complete, remove the ice bath and continue the reaction at room temperature with stirring for 12-24 hours; Continue stirring the reaction for 12-24 hours; S222: Remove anhydrous methanol and excess methyl methacrylate by vacuum distillation to obtain the G0.5 product; S223: Dissolve the G0.5 product in anhydrous methanol, and slowly add excess ethylenediamine dropwise under an ice-water bath and nitrogen atmosphere. After the addition is complete, allow the reaction solution to rise to room temperature, then heat to 40°C and stir the reaction for 24-48 hours; S224: Remove anhydrous methanol and excess ethylenediamine by vacuum distillation to obtain the G1.0 product; S225: Dissolve the G1.0 product in anhydrous methanol, and weigh out a portion of the G1.0 product... Twice the molar amount of methyl methacrylate is reacted according to steps S221 and S222 to obtain the G1.5 generation product; S226: The G1.5 generation product is dissolved in anhydrous methanol, excess ethylenediamine is weighed, and reacted according to steps S223 and S224 to obtain the G2.0 generation product; S227: According to steps S225 and S226, the process is continued iteratively to prepare the G2.5, G3.0, G3.5, or G4.0 generation products; The hyperbranched polyamide-amine is any one or a mixture of multiple generations of the G2.0, G2.5, G3.0, G3.5, and G4.0 generation products.

[0014] A third aspect of this application provides a negative electrode sheet using a negative electrode binder prepared by any of the above-described negative electrode binders or by any of the above-described preparation methods, wherein the negative electrode active material layer of the negative electrode sheet comprises a silicon-based active material, a negative electrode conductive agent, and the negative electrode binder, wherein the negative electrode binder accounts for 1-8 wt% of the total mass of the negative electrode active material layer, and the silicon-based active material accounts for 10-50 wt% of the total mass of the negative electrode active material layer.

[0015] In some optional embodiments, after the negative electrode is charged and discharged 100 times at a 1C rate, the peel strength between the negative electrode active material layer and the negative electrode current collector is ≥45N / m, and the electrode thickness expansion rate is ≤12%.

[0016] The fourth aspect of this application provides a lithium-ion battery, including a housing, a core disposed within the housing and formed by winding a positive electrode, a separator, and a negative electrode, and an electrolyte injected into the housing to wet the core. The negative electrode includes a negative current collector and a negative active material layer coated on at least one side of the negative current collector. The negative electrode is any of the negative electrode described above, and the negative electrode binder used in the negative electrode is any of the negative electrode binders described above or a negative electrode binder prepared by any of the preparation methods described above. The lithium-ion battery retains ≥80% of its capacity after 300 cycles at 1C rate.

[0017] This application has at least the following technical effects:

[0018] 1) The first aspect of this application provides a negative electrode binder for silicon-based negative electrodes, which adopts a three-dimensional polymer with a network structure. Flexible, highly branched branches containing more nitrogen and hydrogen functional groups are grafted onto a rigid linear main chain. The two are bonded by amide bonds to form a unique "rigid main chain-flexible branch chain" structure. The branch chains grafted onto the main chain act as "molecular anchors". A dense dynamic physical cross-linking network of hydrogen bonds and / or ionic bonds is formed between the numerous nitrogen and hydrogen functional groups on their surface, between the nitrogen and hydrogen functional groups and the active groups on the main chain, and between the nitrogen and hydrogen functional groups on multiple different branch chains. This allows the negative electrode structure to efficiently dissipate the stress generated by the volume change of silicon particles during charging and discharging through the reversible breaking and recombination of cross-linking bonds. At the same time, the three-dimensional structure formed by the isotropic growth of the highly branched branches in space also provides a continuous channel for lithium ion transport, ensuring the ion transport efficiency and electrochemical performance of the negative electrode.

[0019] 2) The second aspect of this application also provides a method for preparing a negative electrode binder, wherein a linear main chain polymer is synthesized by free radical polymerization with a number average molecular weight of 200,000-500,000 g / mol, balancing the length, rigidity, and reactivity of the main chain, and one end of the highly branched polymer is aminated to graft onto the main chain through an amidation reaction, and covalent cross-linking ensures the connection strength, thereby constituting a negative electrode binder system capable of forming a dynamic physical cross-linking network.

[0020] 3) In a third aspect, this application provides a negative electrode sheet that uses the aforementioned negative electrode binder and combines it with silicon-based active materials to form a rigid-flexible negative electrode active material layer structure, thereby improving the battery's capacity density and mechanical structural stability.

[0021] 4) The fourth aspect of this application provides a lithium-ion battery. Due to the beneficial effects of the negative electrode sheet as described above, the interface material system of the negative electrode sheet of the lithium-ion battery provided by this application is more stable during the charging and discharging process, the cycle performance is improved, the battery capacity decay is effectively suppressed, and the service life is extended. Detailed Implementation

[0022] The embodiments of this implementation are described in detail below. In the description of this implementation, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. If "first" and "second" are mentioned, they are only used to distinguish technical features and should not be construed as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the order of the indicated technical features.

[0023] In the description of this embodiment, unless otherwise explicitly limited, terms such as setting, installing, and connecting should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this embodiment in conjunction with the specific content of the technical solution.

[0024] In this embodiment, the lithium-ion battery includes a core, an electrolyte, and a casing. The core is formed by winding a positive electrode sheet, a separator, and a negative electrode sheet stacked together. The positive electrode sheet includes a positive current collector and a positive active material layer formed on at least one surface of the positive current collector. The positive active material layer includes a positive active material, a positive conductive agent, and a positive binder. The negative electrode sheet includes a negative current collector and a negative active material layer formed on at least one surface of the negative current collector. The negative active material layer includes a silicon-based active material, a negative conductive agent, and a negative binder. The electrolyte includes a lithium salt, a solvent, and additives. The lithium salt is selected from any one or more combinations of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide. The solvent is selected from any one or more combinations of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and methyl ethyl carbonate. The casing is cylindrical, with the inside used to house the winding core. The top is the positive terminal and the bottom is the negative terminal. The casing can be made of steel or aluminum, and the ratio of the battery's diameter to its height is greater than 1.6.

[0025] In the current lithium-ion battery industry, silicon-based anode materials expand by more than 300% in volume during charge and discharge, easily causing electrode structure pulverization, interface debonding, and repeated SEI film rupture. Traditional linear binders such as polyvinylidene fluoride (PVDF) or sodium carboxymethyl cellulose (CMC) are ineffective at confining the large volume changes of silicon particles when faced with highly expanding host materials. Furthermore, existing dynamic network designs suffer from limitations in the response rate and reversibility of dynamic covalent bonds, uneven cross-linking density of non-covalent networks based on simple linear polymers, and insufficient mechanical strength and ionic conductivity. Therefore, this application proposes a method of grafting highly branched branches onto a linear backbone. Utilizing the high mechanical flexibility of the highly branched branches to graft a rigid linear backbone with strong structural support, a densely cross-linked dynamic physical cross-linking network is constructed, both intramolecularly and externally. The reversible breaking and recombination of cross-links efficiently dissipates the stress generated by the volume changes of silicon particles. Simultaneously, the three-dimensional structure formed by the isotropic growth of the highly branched branches in space provides a continuous channel for lithium-ion transport, ensuring the ion transport efficiency and electrochemical performance of the anode electrode.

[0026] A first aspect of this application provides a negative electrode binder for silicon-based negative electrodes, comprising a three-dimensional polymer. The three-dimensional polymer includes a linear main chain and highly branched branches grafted onto the main chain via amide bonds. The highly branched branches have nitrogen-hydrogen functional groups within their segments and at their ends. The main chain has active groups capable of forming intermolecular hydrogen bonds and / or ionic bonds with the nitrogen-hydrogen functional groups. The active groups include at least one of carboxyl, carbonyl, ester, epoxy, and phenyl groups. The hydrogen bonds and / or ionic bonds formed between the nitrogen-hydrogen functional groups within the highly branched branches, between the nitrogen-hydrogen functional groups on the highly branched branches and the active groups on the main chain, and between different nitrogen-hydrogen functional groups of the highly branched branches constitute a dynamic physical cross-linking network.

[0027] It is understood that the nitrogen-hydrogen functional groups include amino-NH2 and imino-NH-, and the nitrogen-hydrogen functional group located at the end of the highly branched branch is amino-NH2.

[0028] The linear backbone can be made of traditional binders such as polyvinylidene fluoride derivatives, carboxymethyl cellulose derivatives, polyacrylic acid and its derivatives, polyamide and its derivatives, etc. Since the backbone and the side chains are connected by amide bonds, the linear backbone polymer should simultaneously have at least one carboxyl group and more of the active groups. The active groups can be derivatives formed by simple substitution of the aforementioned exemplary backbone polymers.

[0029] Taking polyacrylic acid (PAA) as an example, polyacrylic acid itself has a large number of carboxyl groups. Some of these carboxyl groups can be used to react with amino groups on highly branched polymers to form amide bonds and graft the highly branched chains. Other carboxyl groups can be used as active groups to dynamically crosslink with nitrogen and hydrogen functional groups on highly branched chains. They can also be used to replace carbonyl groups, ester groups, epoxy groups, phenyl groups, and other groups with lone pairs of electrons on polyacrylic acid to form polyacrylic acid derivatives, thereby enhancing the strength of hydrogen bonds and / or ionic bonds.

[0030] Furthermore, highly branched chains are composed of highly branched polymers, meaning polymers with a high number of branched layers. These polymers grow through random polymerization mechanisms, forming isotropic random coil conformations. Specifically, highly branched chains can be selected from hyperbranched polyamide-amine, hyperbranched polyethyleneimine-amide, hyperbranched poly(propyleneimine-amide), hyperbranched poly(amide-imide-amine), hyperbranched polylysine, hyperbranched melamine-formaldehyde-amine, chitosan-grafted-polyethyleneimine, etc.

[0031] This embodiment optimizes the topological conformation and function of the crosslinking network by designing a unique branched structure, forming a three-dimensional polymer capable of forming a network structure. Flexible, highly branched branches with numerous nitrogen and hydrogen functional groups are grafted onto a rigid linear main chain. These branches are bonded together via amide bonds to form a unique "rigid main chain-flexible branched chain" structure. The branches grafted onto the main chain act as "molecular anchors," forming a dense, dynamic physical crosslinking network with hydrogen bonds and / or ionic bonds between numerous nitrogen and hydrogen functional groups on their surfaces, between these nitrogen and hydrogen functional groups and the active groups on the main chain, and between nitrogen and hydrogen functional groups on multiple different branches. Hydrogen bonds, as sacrificial bonds, preferentially break under external force to dissipate energy, prevent crack propagation, and improve the toughness and tear resistance of the material system. When the material is damaged, the hydrogen bonds at the breakage points can reform with the movement of chain segments, achieving self-repair. During charging and discharging, the negative electrode structure efficiently dissipates the stress generated by the volume change of silicon particles through the reversible breaking and recombination of cross-linked bonds. At the same time, the three-dimensional structure formed by the isotropic growth of highly branched chains in space also provides a continuous channel for lithium ion transport, ensuring the ion transport efficiency and electrochemical performance of the negative electrode.

[0032] In some alternative embodiments, the negative electrode binder further includes metal cations crosslinked to the dynamic physical crosslinking network via ionic and / or coordination bonding, the metal cations carrying two or more positive charges.

[0033] Metal cations are introduced into the existing three-dimensional polymer molecular system with a three-dimensional network structure. These metal cations, carrying two or more positive charges, can directly coordinate and complex with active groups and nitrogen-hydrogen functional groups, forming new cross-linking bonds and constructing a tertiary network structure with a strength gradient. Specifically, the amide bonds formed covalently by the linear backbone and highly branched branches, as well as the covalent bonds connecting the branches and backbone of the highly branched branches in three dimensions, form a permanent and stable primary polymer backbone network, ensuring the basic structural integrity of the negative electrode binder. The nitrogen-hydrogen functional groups (amide bonds (-C(O)NH-) and amino groups (-NH2)) in the three-dimensional polymer system form a dense secondary dynamic hydrogen bond network with the active groups, which can break and recombine freely, providing high toughness and self-healing ability to the material. The introduced metal cations can ionically or coordinately bind with the active groups on the linear backbone, or coordinate and complex with the nitrogen-hydrogen functional groups on the highly branched branches, forming a point-like distribution in the three-dimensional polymer molecule, creating a tertiary ionic cross-linking point network, further enhancing structural strength and dynamic recombination ability.

[0034] By introducing metal cations, a smart soft material with multiple dynamic cross-linked networks is formed, whose performance far exceeds the simple sum of the components themselves, achieving the effect of "1+1+1>>3".

[0035] As a further example, the active group is a carboxyl group (-COOH), and the metal cation is an aluminum ion (Al). 3+ For example, the carboxyl group partially or completely dissociates into a carboxylate anion (-COO⁻), at which point Al 3+ It undergoes ionic coordination with a carboxylate group, an Al 3+ It can coordinate with two or more carboxylate ions simultaneously, forming "ion bridges" that crosslink different linear backbones together. Additionally, Al... 3+ It can also interact with nitrogen and hydrogen functional groups (-NH2or) on highly branched branches. The coordination of -NH-) can significantly improve the cohesive strength and modulus of the negative electrode binder system. At the same time, under the action of external force or heat, the metal cations can also undergo "coordination bond breaking-reorganization", thereby further enhancing the material's energy dissipation capacity and self-healing ability.

[0036] In some alternative embodiments, the highly branched chain is a hyperbranched polyamide-amine HPAMAM, wherein the hyperbranched polyamide-amine has a generation number of 2.0-4.0 and a number-average molecular weight of 2000-10000 g / mol.

[0037] Branches in generations 2.0-4.0 are sufficient to form relatively complete three-dimensional spherical structures, achieving a balance between the number of functional groups and molecular size. They also exhibit better performance in terms of water solubility and compatibility with other materials compared to generations 4 and above. Furthermore, from a preparation perspective, obtaining hyperbranched polyamide-amine products with generation numbers higher than 4.0 is extremely difficult, whether using a one-step synthesis or an iterative synthesis method. Reaction time and purification costs increase exponentially, resulting in low yields.

[0038] Furthermore, the grafting rate of the three-dimensional polymer is 10%-40%, and the grafting rate is the percentage of the number of moles of the highly branched side chains to the total number of moles of the active groups in the linear main chain.

[0039] When the grafting rate is less than 10%, the amount of highly branched branches introduced is too small to form an effective dynamic cross-linking network, and the gains in mechanical strength, self-healing ability, and buffering effect on volume expansion are almost zero. When the grafting rate is greater than 40%, the main chain and branches are excessively cross-linked, the molecular chain segments are spatially confined, the mobility is severely restricted, the elongation at break decreases, and the material becomes brittle. It is unable to effectively adapt to volume changes during subsequent charging and discharging and is prone to cracking.

[0040] In some optional embodiments, the metal cation is Ca²⁺, Cu²⁺, Mg²⁺, Zn²⁺, Ni²⁺, Fe³⁺, Cr³⁺, Co³⁺, Al³⁺, and Zr. 4+ One or more of the following are used, wherein the amount of the metal cation added accounts for 0.5-5 wt% of the mass of the three-dimensional polymer. The use of divalent or higher metal cations enhances the coordination ability to lone pairs of electrons, enabling simultaneous complexation with multiple main chains or branches, or multiple functional groups, facilitating the formation of a dynamic network structure with multiple chain crosslinks.

[0041] In some optional embodiments, the swelling ratio of the negative electrode binder in a 1.0 M LiPF6 electrolyte containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1 is ≤4%, and the ionic conductivity in the symmetrical cell is ≥10. -4 S / cm. The low swelling ratio of the negative electrode binder ensures the structural stability and safety of the electrode, and maintains a high level of ionic conductivity, thus guaranteeing the power density, energy density, and cycle life of the battery.

[0042] Furthermore, a second aspect of this application provides a method for preparing a negative electrode binder as described in any of the preceding claims, wherein the method for preparing the three-dimensional polymer includes the following steps:

[0043] S1: A linear main-chain polymer with a number-average molecular weight of 200,000-500,000 g / mol is synthesized by free radical polymerization of a main-chain monomer containing the active group in an aqueous solution, and is used as the linear main chain;

[0044] S2: Take a highly branched polymer with nitrogen and hydrogen functional groups inside and at the end of the chain segment, aminate one end of it, and then add it to the aqueous solution of the linear main chain polymer obtained in step S1. React at 60-80℃ for 4-12 hours. The highly branched polymer is grafted onto the linear main chain polymer through an amidation reaction to form the highly branched branch chain and obtain the aqueous solution of the three-dimensional polymer. The physicochemical interactions within and between the molecules of the three-dimensional polymer form the dynamic physical cross-linking network.

[0045] Taking a hyperbranched polyamide-amine (G2.0 HPAMAM) with polyacrylic acid (PAA) as the main chain and highly branched branches with amino groups at both ends as an example, the grafting reaction is: PAA-COOH + H2N-HPAMAM-NH2→ PAA-C(O)-NH-HPAMAM-NH2 + H2O;

[0046] PAA-COOH: Only one carboxyl group on the polyacrylic acid chain is shown as an example;

[0047] H2N-HPAMAM-NH2: Represents a hyperbranched polyamide-amine molecule with amino groups at both ends.

[0048] The simplified structural formula of PAA-C(O)-NH-HPAMAM-NH2 is shown below: .

[0049] In some optional implementations, the method further includes the following steps:

[0050] S3: Add a water-soluble metal salt solution to the aqueous solution of the three-dimensional polymer and stir to mix. The metal salt solution is ionized to obtain metal cations with two or more positive charges. The metal cations are cross-linked into the dynamic physical cross-linking network through ionic and / or coordination binding.

[0051] In some optional embodiments, the highly branched chain is a hyperbranched polyamide-amine HPAMAM, the hyperbranched polyamide-amine has a generation number of 2.0-4.0, and the hyperbranched polyamide-amine includes a one-step or iterative synthesis method; the one-step method includes the following steps: S211: using methyl acrylate and ethylenediamine as monomers, the feed ratio of methyl acrylate to ethylenediamine is calculated according to the target generation range of the hyperbranched polyamide-amine; S212: ethylenediamine is dissolved in anhydrous methanol, and methyl methacrylate is slowly added dropwise under an ice-water bath and a nitrogen protective atmosphere. Anhydrous methanol solution was added dropwise, and after the ice bath was removed, the reaction was continued at room temperature with stirring for 12-24 hours; S213: The reaction temperature was raised to 40-50°C, and the reaction was continued for 24-48 hours. Subsequently, the solvent and unreacted monomers were removed by vacuum distillation to synthesize hyperbranched polyamide-amines with 2.0-4.0 generation branched structures; The iterative synthesis method includes the following steps: S221: Ethylenediamine and methyl methacrylate were weighed in a molar ratio of 1:2. Ethylenediamine was dissolved in anhydrous methanol, and methyl methacrylate was slowly added dropwise under an ice-water bath and a nitrogen protective atmosphere. After the anhydrous methanol solution of methyl methacrylate is added dropwise, the ice bath is removed, and the reaction is continued at room temperature with stirring for 12-24 hours; S222: Anhydrous methanol and excess methyl methacrylate are removed by vacuum distillation to obtain the G0.5 product; S223: The G0.5 product is dissolved in anhydrous methanol, and excess ethylenediamine is slowly added dropwise under an ice-water bath and a nitrogen protective atmosphere. After the addition is complete, the reaction solution is allowed to rise to room temperature, then heated to 40°C and stirred for 24-48 hours; S224: Anhydrous methanol and excess ethylenediamine are removed by vacuum distillation to obtain G1 S225: Dissolve the G1.0 generation product in anhydrous methanol, weigh methyl methacrylate in twice the molar amount of the G1.0 generation product, and react according to steps S221 and S222 to obtain the G1.5 generation product; S226: Dissolve the G1.5 generation product in anhydrous methanol, weigh excess ethylenediamine, and react according to steps S223 and S224 to obtain the G2.0 generation product; S227: Continue iterating according to steps S225 and S226 to prepare G2.5, G3.0, G3.5 or G4.0 generation products.

[0052] In some alternative embodiments, the hyperbranched polyamide-amine is any one or a mixture of multiple generations of the G2.0, G2.5, G3.0, G3.5 and G4.0 generation products.

[0053] Understandably, the molecular weight, size, and degree of branching of the product synthesized in a one-step process for hyperbranched polyamide-amine HPAMAM are not uniform. Multiple molecules from low to high generation may coexist in the reaction system, and the average generation and degree of branching of the final product can be characterized by proton nuclear magnetic resonance spectroscopy.

[0054] A third aspect of this application provides a negative electrode sheet, wherein the negative electrode active material layer comprises a silicon-based active material, a negative electrode conductive agent, and a negative electrode binder, and the negative electrode binder accounts for 1-8 wt% of the total mass of the negative electrode active material layer, and the silicon-based active material accounts for 10-50 wt% of the total mass of the negative electrode active material layer.

[0055] In some optional embodiments, after 100 charge-discharge cycles at 1C, the peel strength between the negative electrode active material layer and the negative electrode current collector is ≥45 N / m, and the electrode thickness expansion rate is ≤12%. The abundant active groups and polar amino or imino groups on the three-dimensional polymer can tightly bond with the surfaces of the negative electrode active material, conductive agent, and negative electrode current collector through hydrogen bonds and ionic bonds, improving interfacial adhesion and thus enhancing peel strength.

[0056] A fourth aspect of this application provides a lithium-ion battery, comprising a casing, a core disposed within the casing and formed by winding a positive electrode, a separator, and a negative electrode, and an electrolyte injected into the casing to wet the core. The negative electrode comprises a negative current collector and a negative active material layer coated on at least one side of the negative current collector. The negative electrode is any of the negative electrode described above, and the negative electrode binder used in the negative electrode is any of the negative electrode binders described above or a negative electrode binder prepared by any of the preparation methods described above.

[0057] In some alternative embodiments, the lithium-ion battery retains ≥80% of its capacity after 300 cycles at 1C rate.

[0058] In some alternative embodiments, the diameter of the battery ranges from 20 mm to 50 mm, and the height ranges from 60 mm to 180 mm, wherein the ratio of the battery's diameter to its height is greater than 1.6.

[0059] The technical solution of this application will be described below with reference to Examples 1-6 and Comparative Examples 1-3.

[0060] Example 1

[0061] 1. Method for manufacturing positive electrode plates:

[0062] Take positive electrode active material (LiNi) 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black, carbon nanotubes, and polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:1:1:2 to form a stable positive electrode slurry (70% solid content). The positive electrode slurry was then uniformly coated onto a positive electrode current collector (12μm thick aluminum foil), and then dried and cold-pressed to obtain a positive electrode sheet (compacted density of approximately 3.4 g / cm³).

[0063] 2. Preparation of electrolyte:

[0064] An electrolyte was prepared by mixing lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and vinylene carbonate (VC) in a mass percentage ratio of 10:20:55:2:8:5.

[0065] 3. Adhesive preparation:

[0066] S1: Weigh 1.0 g of polyacrylic acid (PAA) with a number average molecular weight of approximately 300,000 g / mol, dissolve it in 100 mL of deionized water, and stir until completely dissolved to obtain a transparent PAA aqueous solution.

[0067] S2: Weigh 0.25 g of 2.0 generation hyperbranched polyamide-amine (HPAMAM) with a number average molecular weight of approximately 2800 g / mol and add it to the above PAA solution. Stir the reaction at 75°C for 8 hours to graft HPAMAM branches onto the PAA backbone via amidation reaction, obtaining an aqueous solution of the graft copolymer PAA-g-HPAMAM (grafting rate of approximately 20%).

[0068] S3: No ionic cross-linking is performed to reflect the performance of the physical cross-linking network itself.

[0069] 4. Negative electrode sheet fabrication:

[0070] Artificial graphite, silicon-based active material (silicon-carbon material), conductive agent (SuperP), and binder gel prepared by the above method (based on solid content) are mixed in a mass ratio of 75:15:5:5. Deionized water is added and stirred to form a uniform and stable negative electrode slurry (solid content 40-45%). The negative electrode slurry is uniformly coated onto an 8μm copper foil of the negative electrode current collector, and then dried and cold-pressed to obtain a negative electrode sheet (compacted density approximately 1.6 g / cm³). 3 ).

[0071] 5. Assembly of lithium-ion batteries:

[0072] After the positive and negative electrode sheets are rolled and slit, they are wound together with the separator to obtain a 21700 cylindrical battery core. Then, the battery core is welded to the connecting piece and installed into the battery casing. After completing the liquid injection, sealing and formation processes, the lithium-ion battery of Example 1 is obtained.

[0073] Example 2

[0074] The difference between Example 2 and Example 1 is that ionic crosslinking was performed after step S2:

[0075] S3: To the PAA-g-HPAMAM aqueous solution obtained in S2, slowly add 9.26 mL of aluminum nitrate nonahydrate (Al(NO3)3·9H2O) aqueous solution with a concentration of 0.1 mol / L (the amount of Al³⁺ added accounts for about 2.0 wt% of the total mass of the three-dimensional polymer), stir and mix at room temperature for 2 hours to form ionic coordination crosslinking sites. Everything else is the same as in Example 1.

[0076] Example 3

[0077] The difference between Example 3 and Example 1 is that the HPAMAM branch used in step S2 is HPAMAM of generation 4.0 with a number average molecular weight of about 9000 g / mol, and the amount is adjusted to 0.35 g with a grafting rate of about 20%. Everything else is the same as in Example 1.

[0078] Example 4

[0079] The difference between Example 4 and Example 1 is that the amount of HPAMAM (Generation 2.0) used in step S2 is 0.4g, and the grafting rate is about 32%. Everything else is the same as in Example 1.

[0080] Example 5

[0081] The difference between Example 5 and Example 1 is that the ratio of each component in the negative electrode slurry is: artificial graphite: silicon carbon material: SuperP: binder = 80:10:5:5, while all other aspects are the same as in Example 1.

[0082] Example 6

[0083] The difference between Example 6 and Example 1 is that the proportion of each component in the negative electrode slurry is: artificial graphite: silicon carbon material: SuperP: binder = 75:15:8:2, while all other aspects are the same as in Example 1.

[0084] Comparative Example 1

[0085] The difference between Comparative Example 1 and Example 1 is that step S2 is omitted, and the pure PAA aqueous solution prepared in step S1 is used directly as the binder. Everything else is the same as in Example 1.

[0086] Comparative Example 2

[0087] The difference between Comparative Example 2 and Example 1 is that the amount of HPAMAM used in step S2 is 0.8g (grafting rate of about 65%), while all other aspects are the same as in Example 1.

[0088] Comparative Example 3

[0089] The difference between Comparative Example 3 and Example 1 is that in step S2, an equimolar amount of single-terminated amino polyethylene glycol (mPEG-NH2, Mn=2000g / mol) was used instead of HPAMAM for the grafting reaction; all other aspects were the same as in Example 1.

[0090] Experimental Examples:

[0091] The lithium-ion batteries prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to the following tests:

[0092] Electrode expansion rate test

[0093] First, after 100 charge-discharge cycles at 1C, the lithium-ion battery was constant-current discharged to 2.5V to ensure it was in a safe state, reducing the risk of short circuits or thermal runaway during disassembly. The battery was carefully disassembled inside a glove box (protected by argon or other inert atmosphere), and the negative electrode sheet of the battery core was removed. The electrode sheet was peeled off using plastic tweezers, taking care not to damage the negative electrode active material layer. Next, the removed negative electrode sheet was cut to an appropriate size and immersed in anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove residual electrolyte and possible byproducts. After removing the negative electrode sheet, the surface was gently wiped with lint-free paper, and then the DMC solution was replaced. This immersion-wiping process was repeated three times to ensure no residual contaminants remained on the negative electrode sheet surface. Subsequently, the negative electrode sheet was rinsed with anhydrous ethanol and wiped again to further remove solvent and impurities. After cleaning, the negative electrode sheet was placed in a glove box and left to stand for 48 hours to ensure it was completely dry, preventing interference from residual solvent in subsequent testing. Negative electrode expansion rate: electrode thickness after cycling / initial electrode thickness × 100%.

[0094] Electrode peel strength test

[0095] Cut the aforementioned negative electrode sheet into sample strips 15.0 mm ± 0.1 mm wide and 100 mm long. Take a piece of high-strength double-sided tape and attach it to the rigid substrate. With the side of the sample strip containing the negative electrode current collector (copper foil) facing down, firmly adhere it to the double-sided tape, ensuring there are no air bubbles between the negative electrode current collector and the substrate. Apply even pressure using a small roller or your fingers to ensure a firm bond. Carefully pry the negative electrode active material layer from the copper foil at one end of the sample strip using tweezers, about 10-15 mm. Securely fix the rigid substrate to the lower clamping platform of the material testing machine. Bend the peeled active material layer vertically upwards at 90° and clamp it with the upper clamp, ensuring sufficient clamping area to prevent slippage. The peeling angle is 90°, the upper clamp moves vertically upwards at a peeling speed of 50 mm / min, and the peeling length is at least 50 mm. Start the testing machine to perform the peel test; the software records the peeling force and displacement curves in real time. From the peel force-displacement curve, select a stable peel segment of at least 30 mm in the middle and calculate the average peel force (F, in N) of this stable segment. Calculate the peel strength using the following formula: Peel strength = F / 0.015.

[0096] Electrolyte swelling rate test

[0097] First, a pure adhesive film was prepared using a casting method. 5.0 g of the adhesive solutions prepared in Examples 1-6 and Comparative Examples 1-3 were poured into a polytetrafluoroethylene (PTFE) petri dish and dried in a vacuum drying oven at 40°C for 24 hours to completely remove moisture, resulting in a uniform solid adhesive film. Circular samples with a diameter of 16.0 mm ± 0.1 mm were punched from the film, and their initial mass was weighed using an analytical balance with an accuracy of 0.01 mg, recorded as W0 (unit: mg). Subsequently, the samples were placed in an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm) and immersed in a sealed glass bottle containing 5.0 mL of commercial lithium-ion battery electrolyte (1.0 M LiPF6 in EC / DMC / EMC, 1:1:1 vol%). The glass bottle was stored in a constant temperature incubator at 25°C for 48 hours to ensure that swelling reached equilibrium.

[0098] After soaking, carefully remove the sample from the electrolyte using PTFE tweezers. Quickly and gently wipe away any residual electrolyte on the surface with lint-free paper. Immediately weigh the swollen sample within 30 seconds of removal and record the mass as W. t (Unit: mg). Each sample was tested in triplicate. The electrolyte swelling rate was calculated using the following formula:

[0099] Swelling rate = (W t -W0) / W0×100%

[0100] The final result is the average of the three tests.

[0101] Ion conductivity test

[0102] The ionic conductivity of the binder gel was tested using electrochemical impedance spectroscopy (EIS). The binder solutions (without drying) prepared in Examples 1-6 and Comparative Examples 1-3 were directly dropped between two parallel blocking electrodes (e.g., stainless steel, SS) to assemble a symmetrical cell structure of SS|binder gel|SS. The cell was placed in a constant temperature environment of 25°C and tested using an electrochemical workstation. The test frequency range was 1 MHz to 0.1 Hz, and the applied AC perturbation amplitude was 10 mV. The obtained impedance spectrum typically appears as a curve consisting of a semicircle and a diagonal line. The spectrum corresponding to the high-frequency and mid-frequency regions is the aforementioned semicircle, and the spectrum corresponding to the low-frequency region is the aforementioned diagonal line. The intercept of the starting point of the semicircle with the real axis in the high-frequency region is the bulk impedance (R). b (Unit: Ω). Accurately measure the distance between the two electrodes (d, unit: cm) and the effective contact area of ​​the electrodes (A, unit: cm²).

[0103] Calculate the ionic conductivity (σ) using the following formula. ionic (Unit: S / cm)

[0104] σ ionic =d / (R b ×A)

[0105] Each sample was tested in parallel three times, and the final result was the average.

[0106] Cyclic performance test

[0107] Place the battery in a 25°C constant temperature chamber for 6 hours and test it according to the following steps:

[0108] (1) First round of constant current and constant voltage charging: charge at a constant current of 0.1C to 4.2V, then switch to constant voltage charging until the current drops to 0.01C.

[0109] (2) Let it stand for 30 minutes after charging is complete.

[0110] (3) Perform constant current discharge, and discharge to 2.5V at a rate of 0.1C.

[0111] (4) Cyclic charge and discharge process: Charge at a constant current rate of 1C to 4.2V. Let stand for 30 minutes again. Discharge at a constant current rate of 1C to 2.5V.

[0112] (5) Repeat the above charging and discharging process for a total of 300 cycles.

[0113] Statistical analysis of battery discharge capacities Q1 and Q2 after 1 and 300 cycles. 300Statistical analysis of battery capacity retention rate: Q 300 / Q1×100%.

[0114] The measured data are shown in Table 1 below:

[0115] Table 1

[0116] project Swelling rate (%) Ionic conductivity (S / cm) Peel strength (N / m) Expansion rate (%) Capacity retention rate (%) Example 1 3.2 <![CDATA[2.1×10 -4 ]]> 48 11.5 81.5 Example 2 2.5 <![CDATA[1.8×10 -4 ]]> 55 9.8 83.0 Example 3 2.8 <![CDATA[2.5×10 -4 ]]> 51 10.2 82.0 Example 4 2.9 <![CDATA[1.5×10 -4 ]]> 53 11.0 80.8 Example 5 3.0 <![CDATA[2.2×10 -4 ]]> 50 6.5 88.0 Example 6 3.5 <![CDATA[2.3×10 -4 ]]> 38 13.0 80.0 Comparative Example 1 8.5 <![CDATA[3.8×10 -5 ]]> - >20 <60 Comparative Example 2 1.8 <![CDATA[5.0×10 -5 ]]> 45 12.0 72.0 Comparative Example 3 6.0 <![CDATA[9.0×10 -4 ]]> 40 16.5 75.0

[0117] As shown in Table 1, the core of the negative electrode binder proposed in this application lies in the unique "rigid main chain - flexible highly branched branch chain" structure formed by the combination of hyperbranched polyamide-amine (HPAMAM) branches with a large number of nitrogen and hydrogen functional groups (-NH2 or -NH-) in the middle and end segments of the chain and linear polyacrylic acid (PAA) main chain containing a large number of active groups (carboxyl-COOH) through amide bonds. The HPAMAM branches act like countless "molecular anchors," and the large number of nitrogen and hydrogen functional groups (amino and amide groups) on their surface form a dense dynamic physical cross-linking network (hydrogen bonds and / or ionic bonds) with the carboxyl groups on the PAA main chain and the amino and amide groups on other HPAMAM branches. During charging and discharging, this network efficiently dissipates the stress generated by the volume change of silicon particles through the reversible breaking and recombination of bonds, while its three-dimensional structure provides a continuous channel for ion transport.

[0118] The swelling rates of Examples 1-6 in this application, ranging from 2.5% to 3.5%, are significantly lower than the 8.5% swelling rate in Comparative Example 1 using only pure PAA as the negative electrode binder, and the 6.0% swelling rate in Comparative Example 3 using PAA grafted with linearly branched amino polyethylene glycol as the negative electrode binder. This demonstrates that the dense hydrogen / ionic bond network formed between the HPAMAM branches and the PAA backbone constitutes a stable three-dimensional network structure, which greatly restricts the free movement and expansion of the three-dimensional polymer molecular chains in the electrolyte solvent, thereby effectively resisting swelling. In Comparative Example 1, the pure PAA relies solely on the linear chain entanglement between straight-chain molecules, resulting in weak forces and easy solvation and swelling. In Comparative Example 3, the linear PEG branches provide far fewer crosslinking points than the hyperbranched structure, leading to insufficient network strength and thus poor resistance to swelling.

[0119] Examples 1-6 of this application maintain a high ionic conductivity: 1.5-2.5 × 10⁻⁶. -4 S / cm, while in Comparative Example 2, excessive grafting of HPAMAM led to excessive cross-linking of the negative electrode binder system, blocking ion migration pathways and thus causing a significant decrease in ionic conductivity (5.0 × 10⁻⁶ S / cm). -5S / cm). The -COOH group in PAA and the -NH2 and -CO(NH)- groups in HPAMAM are both strongly polar groups, exhibiting a strong solvation effect on lithium ions (Li⁺), effectively promoting the desolvation and transport of Li⁺, which is beneficial for improving ionic conductivity. Comparative Example 2 formed an overly rigid and dense network, severely restricting the local movement of polymer chains and the channels for ion transitions, leading to a significant decrease in ionic conductivity. This demonstrates that the degree of crosslinking needs optimization, rather than simply being as high as possible.

[0120] Examples 1-6 of this application exhibit excellent peel strength (38-55 N / m), while Comparative Example 1 failed and Comparative Example 3 showed a lower strength (40 N / m). When silicon particles expand, stress first causes the low-energy dynamic physical cross-linking bonds (hydrogen bonds, ionic bonds) to reversibly break, thereby dissipating most of the energy and avoiding permanent damage to the entire network structure caused by stress concentration, such as polymer chain breakage or desorption from the current collector. After the silicon particles shrink, these dynamic bonds can adaptively and reversibly reform, restoring the adhesive force. The carboxyl groups of the PAA backbone can form strong chemical adsorption with the oxide layer on the surface of the current collector, while the HPAMAM branches penetrate deep into the negative electrode active material particles (silicon particles), "wrapping" and "anchoring" the silicon particles through multiple forces, providing strong overall adhesive force. The pure PAA in Comparative Example 1 lacks this energy dissipation mechanism, and stress directly destroys the linear molecular chain, leading to pulverization failure. The linear branches in Comparative Example 3 have fewer cross-linking points and limited energy dissipation capacity, hence the lower strength.

[0121] Examples 1-6 of this application effectively suppressed electrode expansion (9.8-13.0%), while Comparative Examples 1 and 3 showed severe expansion (>16.5%). The aforementioned dense dynamic cross-linked network tightly wraps and constrains the silicon particles, transforming the radial expansion of the silicon particles into uniform pressure on the three-dimensional polymer network, which is borne by the entire network, thus macroscopically exhibiting lower electrode thickness expansion. Comparative Examples 1 and 3 lack a dense cross-linked network and therefore cannot constrain silicon expansion; contact failure easily occurs between particles, creating porosity, resulting in a loose overall electrode structure and a significant increase in thickness.

[0122] Examples 1-6 of this application achieve high capacity retention (78.0-83.0%), while comparative examples 1-3 are significantly worse. High peel strength and low swelling ratio ensure good electrical contact between the active material, conductive agent, and binder, as well as between the active layer and the current collector. The low swelling ratio of the binder network structure is stable, reducing the possibility of cracking due to repeated volume changes, exposing fresh silicon surface, and generating a new SEI film through side reactions, thereby reducing the continuous consumption of active lithium and electrolyte.

[0123] In summary, by grafting flexible, highly branched branches with numerous nitrogen and hydrogen functional groups onto a rigid linear main chain, a unique "rigid main chain-flexible branch chain" structure is formed through amide bonds. The branch chains grafted onto the main chain act as "molecular anchors," forming a dense, dynamic physical cross-linking network of hydrogen and / or ionic bonds between numerous nitrogen and hydrogen functional groups on their surfaces, between these functional groups and the active groups on the main chain, and between nitrogen and hydrogen functional groups on multiple different branch chains. This allows the negative electrode structure to efficiently dissipate stress caused by silicon particle volume changes during charging and discharging through the reversible breaking and recombination of cross-linking bonds, suppressing electrode expansion. Simultaneously, the three-dimensional structure formed by the isotropic growth of the highly branched branches provides a continuous channel for lithium-ion transport, ensuring the ion transport efficiency and electrochemical performance of the negative electrode, significantly improving the rate performance and cycle life of the final battery, and achieving high-performance synergistic optimization of silicon-based negative electrodes.

[0124] Although embodiments of this implementation have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this implementation, the scope of which is defined by the claims and their equivalents.

Claims

1. A negative electrode binder for silicon-based negative electrodes, characterized in that, The negative electrode binder comprises a three-dimensional polymer, which includes a linear main chain and highly branched branches grafted onto the main chain via amide bonds. The highly branched branches have nitrogen-hydrogen functional groups both internally and at their ends. The main chain has active groups capable of forming intermolecular hydrogen bonds and / or ionic bonds with the nitrogen-hydrogen functional groups. These active groups include at least one of carboxyl, carbonyl, ester, epoxy, and phenyl groups. The hydrogen bonds and / or ionic bonds formed between the nitrogen-hydrogen functional groups within the highly branched branches, between the nitrogen-hydrogen functional groups on the highly branched branches and the active groups on the main chain, and between different nitrogen-hydrogen functional groups of the highly branched branches constitute a dynamic physical cross-linking network.

2. The negative electrode binder according to claim 1, characterized in that, The negative electrode binder also includes metal cations that are cross-linked to the dynamic physical cross-linking network by ionic and / or coordination bonding, the metal cations carrying two or more positive charges.

3. The negative electrode binder according to claim 1, characterized in that, The highly branched branch is a hyperbranched polyamide-amine, and the highly branched branch has a generation number of 2.0-4.0 and a number average molecular weight of 2000-10000 g / mol.

4. The negative electrode binder according to claim 1, characterized in that, The grafting rate of the three-dimensional polymer is 10%-40%, and the grafting rate is the percentage of the number of moles of the highly branched side chains to the total number of moles of the active groups in the linear main chain.

5. The negative electrode binder according to claim 2, characterized in that, The metal cations are Ca²⁺, Cu²⁺, Mg²⁺, Zn²⁺, Ni²⁺, Fe³⁺, Cr³⁺, Co³⁺, Al³⁺, and Zr. 4 One or more of ⁺, wherein the amount of the metal cation added accounts for 0.5-5 wt% of the mass of the three-dimensional polymer.

6. The negative electrode binder according to claim 1, characterized in that, The swelling rate of the negative electrode binder in a 1.0 M LiPF6 electrolyte containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 1:1:1 is ≤4%, and the ionic conductivity in the symmetrical cell is ≥10. -4 S / cm.

7. A method for preparing a negative electrode binder as described in any one of claims 1-6, characterized in that, Method for preparing the three-dimensional polymer in the negative electrode binder Includes the following steps: S1: A linear main-chain polymer with a number-average molecular weight of 200,000-500,000 g / mol is synthesized by free radical polymerization of the main-chain monomer containing the active group in an aqueous solution, and this polymer is used as the linear main chain. S2: A highly branched polymer with nitrogen and hydrogen functional groups inside and at the ends of the chain segments is subjected to amylation treatment at one end, and then added to the aqueous solution of the linear main-chain polymer obtained in step S1. The reaction is carried out at 60-80°C for 4-12 hours. The highly branched polymer is grafted onto the linear main-chain polymer through an amidation reaction to form the highly branched branch chain, and the aqueous solution of the three-dimensional polymer is obtained. The physicochemical interactions within and between the molecules of the three-dimensional polymer form the dynamic physical cross-linking network.

8. The method for preparing the negative electrode binder according to claim 7, characterized in that, The method also Includes the following steps: S3: Add a water-soluble metal salt solution to the aqueous solution of the three-dimensional polymer and stir to mix. The metal salt solution is ionized to obtain metal cations with two or more positive charges. The metal cations are cross-linked into the dynamic physical cross-linking network through ionic and / or coordination binding.

9. The method for preparing the negative electrode binder according to claim 7, characterized in that, The highly branched chain is a hyperbranched polyamide-amine, the hyperbranched polyamide-amine having a generation number of 2.0-4.0, and the synthesis method of the hyperbranched polyamide-amine includes a one-step method or an iterative synthesis method; the one-step method The process includes the following steps: S211: Using methyl acrylate and ethylenediamine as monomers, the feed ratio of methyl acrylate to ethylenediamine is calculated based on the target generation range of the hyperbranched polyamide-amine; S212: Ethylenediamine is dissolved in anhydrous methanol, and an anhydrous methanol solution of methyl methacrylate is slowly added dropwise under an ice-water bath and a nitrogen protective atmosphere. After the addition is complete, the ice bath is removed, and the reaction is continued at room temperature with stirring for 12-24 hours; S213: The reaction temperature is raised to 40-50°C, and the reaction is continued for 24-48 hours. Subsequently, the solvent and unreacted monomers are removed by vacuum distillation to synthesize a hyperbranched polyamide-amine with a 2.0-4.0 generation branched structure; the iterative synthesis method... The process includes the following steps: S221: Weigh ethylenediamine and methyl methacrylate in a molar ratio of 1:

2. Dissolve the ethylenediamine in anhydrous methanol. Slowly add the anhydrous methanol solution of methyl methacrylate dropwise under an ice-water bath and a nitrogen atmosphere. After the addition is complete, remove the ice bath and continue stirring at room temperature for 12-24 hours; S222: Remove anhydrous methanol and excess methyl methacrylate by vacuum distillation to obtain the G0.5 product; S223: Dissolve the G0.5 product in anhydrous methanol. Slowly add excess ethylenediamine dropwise under an ice-water bath and a nitrogen atmosphere. After the addition is complete, allow the reaction solution to reach room temperature, then heat to 40°C and stir for 24-48 hours; S224: Remove anhydrous methanol and excess methyl methacrylate by vacuum distillation. S225: Dissolve the G1.0 product in anhydrous methanol, weigh methyl methacrylate in twice the molar amount of the G1.0 product, and react with it according to steps S221 and S222 to obtain the G1.5 product; S226: Dissolve the G1.5 product in anhydrous methanol, weigh excess ethylenediamine, and react with it according to steps S223 and S224 to obtain the G2.0 product; S227: Continue iterating according to steps S225 and S226 to prepare G2.5, G3.0, G3.5, or G4.0 products; The hyperbranched polyamide-amine is any one or a mixture of multiple generations of the G2.0, G2.5, G3.0, G3.5, and G4.0 products.

10. A negative electrode sheet using the negative electrode binder as described in any one of claims 1-6 or the negative electrode binder prepared by the preparation method as described in any one of claims 7-9, characterized in that, The negative electrode active material layer of the negative electrode sheet includes a silicon-based active material, a negative electrode conductive agent and a negative electrode binder, wherein the negative electrode binder accounts for 1-8 wt% of the total mass of the negative electrode active material layer and the silicon-based active material accounts for 10-50 wt% of the total mass of the negative electrode active material layer.

11. The negative electrode sheet according to claim 10, characterized in that, After the negative electrode is charged and discharged 100 times at a 1C rate, the peel strength between the negative electrode active material layer and the negative electrode current collector is ≥45N / m, and the electrode thickness expansion rate is ≤12%.

12. A lithium-ion battery, comprising a casing, a core disposed within the casing and formed by winding a positive electrode, a separator, and a negative electrode, and an electrolyte injected into the casing to wet the core, wherein the negative electrode comprises a negative current collector and a negative active material layer coated on at least one surface of the negative current collector, characterized in that, The negative electrode sheet is the negative electrode sheet as described in claim 10 or 11, and the negative electrode binder used in the negative electrode sheet is the negative electrode binder as described in any one of claims 1-6 or the negative electrode binder prepared by the preparation method as described in any one of claims 7-9. After the lithium-ion battery is cycled 300 times at 1C rate, the capacity retention rate is ≥80%.