A secondary battery and an electric device

Abstract

The application discloses a secondary battery and a power utilization device, and relates to the field of electrochemical energy storage. The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode active layer, the negative electrode active layer comprises a negative electrode binder, the negative electrode binder comprises structural unit 1 and structural unit 2, the structural unit 1 is a polyaniline cross-linked skeleton, and the structural unit 2 is a side chain formed after polymerization of thioctic acid. The negative electrode binder of the application adopts a conductive polymer with a side chain with a dynamic disulfide bond reaction site, the conductive polymer contains rich active groups which can form strong hydrogen bond interactions with hydroxyl groups of active material particles and the like, so that the interface adhesion is improved, and the dynamic disulfide bond and the hydrogen bond are used to synergistically and efficiently dissipate expansion stress, so that the electrode structure stability is improved; in addition, the chemical stability of the negative electrode binder is excellent, the swelling rate of the electrode sheet can be reduced, the interface stability can be improved, and the cycle life of the secondary battery can be effectively prolonged.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage, and more particularly to a secondary battery and an electrical device. Background Technology

[0002] To meet the demands of fast charging for electric vehicles, high-rate discharge for consumer electronics, and efficient operation of energy storage systems, developing lithium-ion battery electrodes with ultra-low internal resistance has become a core industry objective. The internal resistance of the electrode directly determines the battery's power performance, energy efficiency, and temperature rise control. Excessive internal resistance leads to limited charging speed, a decreased discharge voltage plateau, and increased energy loss, and may even cause overheating risks, severely restricting battery performance and safety. While silicon-based anodes can significantly improve energy density, their inherent volume expansion characteristics further deteriorate interfacial contact, increasing internal resistance and becoming a fundamental bottleneck in achieving integrated high-energy-high-power designs.

[0003] Currently, electrodes are typically fabricated using a physical blending strategy, where insulating linear binders (such as styrene-butadiene rubber (SBR) and polyacrylic acid (PAA), conductive agents (such as carbon black and carbon nanotubes), and active materials are simply mixed in a solvent and then coated. This physical blending approach suffers from weak interfacial bonding, with the components relying solely on weak van der Waals forces for adhesion. Under the volume expansion stress of repeated charge-discharge cycles, the bonding interface is prone to creep, relaxation, and even peeling, leading to separation of the active material from the conductive network. Secondly, traditional binders (such as SBR) only provide passive adhesive force and lack electronic or ion conduction capabilities, becoming a bottleneck for ion transport and increasing interfacial impedance. Traditional conductive agents only provide electronic pathways and cannot actively enhance interfacial bonding or buffer stress, resulting in limited functionality. Furthermore, the entire electrode structure is a static, rigid system, unable to dissipate stress through internal structural adjustments, lacking dynamic adaptability. This leads to the irreversible generation and propagation of microcracks, causing the conductive network to break down, resulting in a sharp increase in battery internal resistance and rapid capacity decay during cycling. Therefore, there is an urgent need for a new approach that can actively construct a robust, adaptive, and highly efficient integrated electrode structure at the molecular level. Summary of the Invention

[0004] This application provides a secondary battery and an electrical device that aims to overcome the limitations of traditional physical blending of electrodes. It provides a negative electrode with a robust, adaptive, and highly efficient conductive structure actively constructed at the molecular level. The negative electrode uses a polymer with reactive sites on its side chains as a binder. This polymer has a stable and dense three-dimensional network structure and abundant carboxyl and amino groups. It can form strong hydrogen bond interactions with hydroxyl groups on the surface of active materials and other particles, thereby improving the interfacial adhesion. In conjunction with the self-healing function of dynamic disulfide bonds, it effectively buffers the volume expansion stress of the negative electrode during charging and discharging, maintains the structural stability of the electrode, and thus extends the cycle life of the secondary battery.

[0005] To address the aforementioned technical problems, one objective of this application is to provide a secondary battery, comprising a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode binder, and the negative electrode binder includes structural unit 1 and structural unit 2, wherein the general structural formula of structural unit 1 is as follows: In the formula, R is at least one of substituted or unsubstituted alkyl, phenyl, benzyl, and cycloalkyl groups; The general structural formula of structural unit 2 is as follows: .

[0006] In some embodiments, the negative electrode binder further includes structural unit 3, the general structural formula of which is: .

[0007] In some embodiments, the molar ratio of structural unit 1 to structural unit 2 is 1:(0.12-0.50).

[0008] In some embodiments, the molar ratio of structural unit 1 to structural unit 3 is 1:(0.18-0.36).

[0009] In some embodiments, the molar ratio of structural unit 1, structural unit 2 and structural unit 3 is 1:(0.15-0.25):(0.25-0.3).

[0010] In some embodiments, in the general formula of the structural unit 1, 160≤n≤590.

[0011] In some embodiments, the negative electrode active layer further includes a negative electrode active material and a negative electrode conductive agent, wherein the negative electrode conductive agent is an MXene material with a coupling agent grafted onto its surface, and the coupling agent contains unsaturated carbon-carbon double bonds.

[0012] In some embodiments, the swelling rate of the negative electrode sheet after immersion in the electrolyte for 48 h is ≤15%.

[0013] In some embodiments, the peeling force of the negative electrode active layer in the negative electrode sheet is ≥14 N / m.

[0014] In some embodiments, the negative electrode active material includes at least one of silicon-based materials, silicon-carbon materials, carbon-based materials, silicon-oxygen materials, and silicon-nitrogen materials.

[0015] In some embodiments, the mass ratio of the negative electrode active material, the negative electrode conductive agent and the negative electrode binder is 90:(3-8):(1-6).

[0016] To address the aforementioned technical problems, the second objective of this application is to provide an electrical device, including a secondary battery.

[0017] Compared with the prior art, this application has the following beneficial effects: 1. The negative electrode binder of this application uses conductive polyaniline as a rigid skeleton. The side chain contains dynamic disulfide bonds and multiple reaction sites, and has a stable and dense three-dimensional cross-linked network. Its abundant active groups can form strong hydrogen bond interactions with the hydroxyl groups of the active material, improve the interfacial adhesion, and utilize the synergistic effect of dynamic disulfide bonds and hydrogen bonds to efficiently dissipate expansion stress, reduce the electrode expansion rate and the structural stability of the electrode, and extend the cycle life of the secondary battery.

[0018] 2. The negative electrode conductive agent of this application uses MXene material treated with unsaturated bond coupling agent, which has high electronic conductivity and can effectively reduce the internal resistance of the electrode by adsorbing harmful gases generated during the cycle to suppress chemical factors that cause the internal resistance to increase cyclically. Moreover, the negative electrode binder and negative electrode conductive agent can trigger an in-situ click chemical reaction between them during the electrode forming process, realizing covalent bonding between the conductive network and the bonding skeleton, making the electrode structure dense and stable, greatly reducing the contact resistance, realizing the active construction of a strong, self-adaptive and highly efficient conductive electrode integrated structure at the molecular level, and jointly ensuring the low resistance and long life of the electrode throughout its entire life cycle. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the synthetic route of functionalized polyaniline in step (1) of the preparation method of a secondary battery in Example 1 of this application; Figure 2 This is a schematic diagram of the synthesis route of lithium thiocate in step (2) of the preparation method of a secondary battery in Example 1 of this application; Figure 3 This is a schematic diagram of the synthesis route of polymer PAL in step (3) of the preparation method of a secondary battery in Example 1 of this application; Figure 4 This is a schematic diagram of the synthesis route of MXene material with KH-570 grafted on its surface in step (4) of the preparation method of a secondary battery in Example 1 of this application. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] It should be understood that the terminology used in this application is merely for describing particular implementations and is not intended to limit the application. Furthermore, for numerical ranges in this application, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0022] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art described herein. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0023] This application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet including a negative electrode active layer, the negative electrode active layer including a negative electrode binder, and the negative electrode binder including structural unit 1 and structural unit 2. The general formula of structural unit 1 is as follows: In the formula, R is at least one of substituted or unsubstituted alkyl, phenyl, benzyl, and cycloalkyl groups; The general structural formula of structural unit 2 is: .

[0024] This application uses a polymer with reactive sites on the side chain as the negative electrode binder. The polymer uses conductive polyaniline as a rigid backbone, and CS bonds are cross-linked to form a three-dimensional network. Its large π conjugated backbone can provide an electron transport highway through the electrode. Through thermally initiated self-polymerization, thioctic acid containing dynamic disulfide bonds is covalently grafted onto the backbone side chain. When heated, thioctic acid can reversibly open the ring to generate free radicals, which can serve as the initiator of the polymerization reaction. The dynamic disulfide bonds (-SS-) in its polymerization product can also give the material the property of adaptive stress buffering. Moreover, the covalent network of this polymer is structurally stable at high temperatures, which can effectively constrain the huge volume expansion of silicon particles at high temperatures and prevent electrode collapse. This polymer possesses a stable and dense three-dimensional cross-linked network and abundant active groups such as carboxyl and amino groups. It can form strong hydrogen bonds with the hydroxyl groups on the surface of active materials and other particles, providing strong interfacial adhesion and improving the peel strength of the electrode. Furthermore, the dynamic disulfide bonds can consume strain energy during the volume expansion of the electrode, and work in synergy with hydrogen bonds to efficiently dissipate expansion stress. Moreover, the dynamic disulfide bonds in the network can be reversibly broken and recombined, and can autonomously repair microcracks without external interference. This effectively buffers the volume expansion stress of the negative electrode during charging and discharging, maintains the structural stability of the electrode, avoids the rapid capacity decay of the secondary battery during long cycles, and extends the cycle life of the secondary battery.

[0025] In some embodiments, the negative electrode binder further includes structural unit 3, the general formula of which is: .

[0026] The negative electrode binder of this application also contains structural unit 3 containing dynamic disulfide bonds and lithium carboxyl groups (-COOLi). The lithium carboxyl groups (-COOLi) contained therein construct continuous lithium ion coordination and migration channels in the polymer network, which, together with the polyaniline skeleton, ensures high-speed electron transport. This significantly optimizes the ion transport kinetics inside the electrode, especially at the interface of active particles, directly reduces electrochemical polarization and charge transfer impedance (Rct), and improves the first coulombic efficiency of the battery.

[0027] In some implementations, the molar ratio of structural unit 1 to structural unit 2 is 1:(0.1-0.7).

[0028] In some embodiments, the molar ratio of structural unit 1 and structural unit 2 in the negative electrode binder is any one of 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7 or a range between any two.

[0029] In some embodiments, the molar ratio of structural unit 1 to structural unit 2 in the negative electrode binder is 1:(0.2-0.5).

[0030] In some embodiments, the molar ratio of structural unit 1 to structural unit 3 is 1:(0.18-0.36). In some embodiments, the molar ratio of structural unit 1 to structural unit 3 in the negative electrode binder is any one of 1:0.18, 1:0.20, 1:0.25, 1:0.30, 1:0.35, 1:0.36, or a range between any two of them.

[0031] In some embodiments, the molar ratio of structural unit 1, structural unit 2 and structural unit 3 is 1:(0.15-0.25):(0.25-0.3).

[0032] The molar ratio of structural unit 1, structural unit 2, and structural unit 3 in this application is controlled within the aforementioned range. In the negative electrode binder, structural unit 2 is derived from thioctic acid, and structural unit 1 is derived from functionalized polyaniline. After ring opening, thioctic acid adds to the double bonds of functionalized polyaniline to form crosslinking points. Therefore, the content of structural unit 2 needs to match the number of double bonds in polyaniline. This ratio range can avoid excessive free small molecules precipitating and contaminating the interface, and the coating thickness of structural unit 2 does not hinder lithium-ion transport or reduce impedance. At the same time, it avoids insufficient crosslinking density and incomplete network, which would not effectively constrain the volume expansion of the silicon-based material, and ensures a sufficient number of carboxyl groups to form hydrogen anchors at the interface of the active material, thereby improving peel strength. In addition, structural unit 3 is derived from lithium thiocate, which mainly plays a role in promoting lithium-ion transport and stabilizing the interface. This ratio range can avoid excessive hydrophilicity and electrode swelling due to excessive amounts, while avoiding insufficient lithium-ion transport promoting effect, which would affect the electrode's stability.

[0033] In some implementations, in the general formula of structural unit 1, 160≤n≤590.

[0034] In some implementations, in the general formula of structural unit 1, n is any one of 160, 200, 250, 300, 350, 400, 450, 500, 550, 590, or a range between any two of them.

[0035] In some implementations, n is 215-537 in the general formula of structural unit 1.

[0036] The structural unit 1 of the negative electrode binder in this application serves as a rigid framework. A smaller n value indicates a lower polymer molecular weight, while a larger n value indicates a larger polymer molecular weight. Controlling the n value within the range of 215-537 avoids the problems of insufficient crosslinking points and incomplete network structure caused by shorter polymer molecular chains. This ensures that the polymer molecular weight guarantees sufficient chain entanglement, improving its cohesive strength and mechanical properties as a negative electrode binder. Simultaneously, it avoids the problem of poor solubility caused by excessively high molecular weight, improving processability and coating uniformity. Furthermore, the appropriate crosslinking density and network strength of the polymer provide sufficient reaction sites to construct a complete and dense three-dimensional network, preventing excessive entanglement or steric hindrance due to excessively long molecular chains, which could hinder the efficient crosslinking reaction.

[0037] In some embodiments, in the general formula of structural unit 1, R is at least one of substituted or unsubstituted alkyl, phenyl, benzyl, and cycloalkyl groups, and the substituted groups are each independent and include at least one of alkyl, alkoxy, nitro, halogen atom, and halogen-containing groups.

[0038] In some embodiments, the negative electrode active layer further includes a negative electrode active material and a negative electrode conductive agent, wherein the negative electrode conductive agent is an MXene material with a coupling agent grafted onto its surface, and the coupling agent contains unsaturated carbon-carbon double bonds.

[0039] The MXene material used as the negative electrode conductive agent in this application provides high electronic conductivity, and its surface properties can adsorb trace amounts of harmful gases such as HF generated during cycling. This helps to mitigate electrolyte side reaction decomposition and abnormal thickening of the solid electrolyte interphase (SEI) film, thereby suppressing chemical factors that lead to increased internal resistance during cycling. Moreover, after modification with KH silane coupling agent, the abundant functional groups on the surface of MXene can form covalent bonds or strong hydrogen bonds with amine and carboxyl groups in the negative electrode binder, constructing a three-dimensional cross-linked network between the active material, conductive agent, and binder, maintaining interfacial contact. Meanwhile, during the baking process of the electrode preparation process, the dynamic disulfide bonds in the negative electrode binder break due to heat, generating a large number of active sulfur free radicals. These free radicals will instantly undergo an addition reaction with the unsaturated bonds on the MXene surface to form strong CS covalent bonds, which crosslink the negative electrode conductive agent in situ to the binder network. This ensures that the conductive pathway does not detach due to the shrinkage of the active material during high-temperature cycling, resulting in a dense and stable electrode structure. This greatly reduces the contact resistance. The electrode is integrated into a covalent network, resulting in high mechanical strength. It can maintain structural integrity during rolling and cycling, and integrates conductivity, ion conduction, buffering, and adsorption functions, which together ensure the low resistance and high-temperature cycling life of the electrode throughout its entire life cycle.

[0040] In some implementations, the intrinsic electronic conductivity of the MXene material is >10000 S / cm.

[0041] In some embodiments, the MXene material is a transition metal carbide and / or a transition metal nitride.

[0042] In some embodiments, the transition metal carbide includes Ti3C2T x , Ti3AlC2, Ti2C, Ti2AlC, Nb2C, Nb2AlC, Nb4C3, Nb4AlC3, Ta4C3T x At least one of Ta4AlC3, V4C3Tx, V4AlC3, V2AlC, TiVAlC, TiNbAlC, TiTaAlC, VNbAlC, Ti2VAlC2, Ti2TaAlC2, Mo2TiAlC2, Ti3AlCN, and Mo2Ti2AlC3.

[0043] In some embodiments, the transition metal nitrides include Ti2AlN and / or Ti4AlN3.

[0044] In some embodiments, the swelling rate of the negative electrode sheet after immersion in the electrolyte for 48 hours is ≤15%.

[0045] In some implementations, the swelling rate of the negative electrode sheet after immersion in the electrolyte for 48 hours is 7%-15%.

[0046] In some embodiments, the swelling rate of the negative electrode sheet after immersion in the electrolyte for 48 h is any one or a range between any two of 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15%.

[0047] The polymer used in the negative electrode binder of the secondary battery in this application has excellent chemical stability and stronger intermolecular forces, which can more effectively resist the penetration and erosion of solvents and reduce the swelling rate of the electrode in the electrolyte. Moreover, the polymer matrix has strong interfacial compatibility with the MXene sheet material of the negative electrode conductive agent, making the electrode structure more compact and effectively improving the interfacial stability, so that the swelling rate of the electrode can be kept at a low level.

[0048] It should be noted that the method for testing the swelling rate of the negative electrode sheet includes the following steps: The negative electrode sheet was cut into electrode sheets of a specific size (length * width * thickness = 20 mm * 20 mm * 1.5 mm) and immersed in an electrolyte solution. The electrolyte solution specifically included 1 mol / L LiPF6, 10% fluoroethylene carbonate (FEC), 1% ethylene carbonate (VC), and the remainder organic solvent, which included vinyl ethylene carbonate (VEC) and VDEC in a 1:1 mass ratio. After 48 h, the sample was removed, the surface electrolyte was wiped dry, and the sample was weighed. The mass of the negative electrode sheet before and after swelling was recorded, and the swelling rate was calculated. The formula for calculating the swelling rate is: Swelling rate = (M... 后 -M 前 ) / M 前 *100%.

[0049] In some embodiments, the peeling force of the negative electrode active layer in the negative electrode sheet is ≥14 N / m.

[0050] In some embodiments, the peeling force of the negative electrode active layer in the negative electrode sheet is 14 N / m-25 N / m.

[0051] In some embodiments, the peeling force of the negative electrode active layer in the negative electrode sheet is a range of any one or any two of 14 N / m, 15 N / m, 16 N / m, 17 N / m, 18 N / m, 19 N / m, 20 N / m, 21 N / m, 22 N / m, 23 N / m, 24 N / m, and 25 N / m.

[0052] It should be noted that the peel force test method for the negative electrode active layer in the negative electrode sheet includes the following steps: After cutting the negative electrode sheet into a rectangle (length * width = 50 mm * 20 mm), stick the tape to the negative electrode active layer coating surface of the negative electrode sheet, then place it in the upper and lower clamps of the testing machine, set the speed to 15 mm / min, and pull it evenly until the negative electrode active layer coating surface of the negative electrode sheet is completely peeled off, and record the test data.

[0053] In some embodiments, the negative electrode active material includes at least one of silicon-based materials, silicon-carbon materials, carbon-based materials, silicon-oxygen materials, and silicon-nitrogen materials.

[0054] In some embodiments, the carbon-based material includes at least one of natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, and mesophase carbon microspheres.

[0055] In some embodiments, the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder is 90:(3-8):(1-6).

[0056] In some embodiments, the negative electrode sheet further includes a negative current collector, and the negative active layer is disposed on the surface of the negative current collector.

[0057] In some embodiments, the negative electrode current collector is a metal foil or a composite metal foil, preferably a copper foil.

[0058] In some implementations, the secondary battery also includes a positive electrode.

[0059] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active layer, wherein the positive active layer includes a positive active material, a positive binder, and a positive conductive agent.

[0060] In some embodiments, the positive electrode active material includes LiCoO2, LiNiO2, LiNixMnyO2, and Li 1+ z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al z At least one of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, and LiMnPO4, wherein each x is independently from 0.2 to 0.9; each y is independently from 0.1 to 0.45; and each z is independently from 0 to 0.2.

[0061] In some embodiments, the positive electrode active material contains a dopant element selected from at least one of Fe, Ni, Mn, Al, Mg, Zn, Ti, La, Ce, Sn, Zr, Ru, Si, and Ge.

[0062] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer.

[0063] In some embodiments, the positive electrode conductive agent includes at least one of carbon, carbon black, graphite, expanded graphite, graphene, superconducting carbon, acetylene black, Ketjen black, carbon dots, carbon fibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon.

[0064] In some embodiments, the positive current collector is a metal foil or a composite metal foil, preferably an aluminum foil.

[0065] In some implementations, the secondary battery also includes a separator.

[0066] In some embodiments, the diaphragm is a porous substrate, which includes at least one of polyolefin, polyester, polyacetal, polyamide, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate.

[0067] In some embodiments, the secondary battery also includes an electrolyte.

[0068] In some embodiments, the electrolyte includes lithium salts and organic solvents.

[0069] In some embodiments, the lithium salt includes at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.

[0070] In some embodiments, the organic solvent includes at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0071] In some embodiments, the carbonate compound includes at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0072] In some embodiments, the carboxylic acid ester compound includes at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate.

[0073] In some embodiments, the ether compound includes at least one selected from dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran.

[0074] In some embodiments, the secondary battery includes a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0075] This application also provides a method for preparing a negative electrode binder, including the following steps: S1. Polyaniline is dissolved in solvent A under inert gas protection, acid-binding agent and functionalizing reagent are added, and electrophilic substitution reaction is carried out by heating. After the reaction is completed, the precipitate is filtered, washed and dried to obtain functionalized polyaniline. S2. Lithium hydroxide was dissolved in solvent B, thioctic acid was added, and the mixture was heated and stirred. After being evaporated under reduced pressure and dried, lithium thioctic acid was prepared. S3. Functionalized polyaniline, thioctic acid, and lithium thiocate are mixed to obtain a mixture. The mixture is dissolved in solvent C and heated under inert gas protection to carry out a polymerization reaction, thereby preparing a polymer, which is the negative electrode binder.

[0076] In some embodiments, in S1, the structural formula of polyaniline is: In the formula, 160≤n≤590.

[0077] In some embodiments, n in the structural formula of polyaniline is a range of any one or any two of 160, 200, 250, 300, 350, 400, 450, 500, 550, and 590.

[0078] In some embodiments, n in the structural formula of polyaniline is 215-537.

[0079] It should be noted that in S1, the n value in the structural formula of polyaniline can be determined by MALDI-TOF mass spectrometry. The test uses gentian acid (DHB) as the matrix, the sample is prepared by evaporation and grinding, and the mass spectrum is acquired in positive ion reflection mode. Then, according to the difference in mass-to-charge ratio between adjacent mass peaks in the mass spectrum, which corresponds to the molecular weight of the polyaniline repeating unit, the degree of polymerization n of each peak can be directly assigned.

[0080] In some embodiments, in S1, the number average molecular weight of polyaniline is 15,000-55,000.

[0081] In some embodiments, in S1, the number average molecular weight of polyaniline is any one or a range between any two of 15,000, 20,000, 25,000, 30,000, 35,000, 40,000, 45,000, 50,000, and 55,000.

[0082] It should be noted that the number-average molecular weight of polyaniline was determined by gel permeation chromatography (GPC); the polyaniline sample was reduced to a colorless emerald green imine base with phenylhydrazine, then dissolved in N-pyrrolidone, and determined by gel permeation chromatography.

[0083] In some embodiments, in S1, the molar ratio of polyaniline to functionalizing agent is (1-1.5):1.

[0084] In some embodiments, in S1, the molar ratio of the functionalizing agent to the acid-binding agent is 1:(0.8-1.5).

[0085] In some embodiments, in S1, the heating temperature is 55-65 °C and the electrophilic substitution reaction time is 20-28 h.

[0086] In some embodiments, in S1, solvent A is a polar solvent, and solvent A includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, N-ethyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-methyl-3- or 4-pyrrolidone, and 1,3-dimethyl-2-imidazolium ketone.

[0087] In some embodiments, in S1, the acid-binding agent includes at least one of potassium carbonate, pyridine, triethylamine, sodium carbonate, sodium acetate, DIEA, sodium hydroxide, magnesium oxide, and N-methylpyrazole.

[0088] In some embodiments, in S1, the functionalizing agent includes at least one of allyl bromide, allyl chloride, acryloyl chloride, methacryloyl chloride, and 4-vinylbenzyl chloride.

[0089] In some embodiments, the drying temperature in S1 is 50-80 °C.

[0090] In some embodiments, in S2, the heating temperature is 50-70 °C and the stirring time is 4-6 h.

[0091] In some embodiments, in S2, solvent B includes at least one of ethanol, methanol, isopropanol, n-propanol, ethylene glycol, and propylene glycol.

[0092] In some embodiments, in S2, the molar ratio of lipoic acid to lithium hydroxide is 1:(0.8-1.2).

[0093] In some embodiments, in S3, the molar ratio of functionalized polyaniline, lipoic acid, and lithium lipoate is 1:(0.12-0.50):(0-0.3).

[0094] In some embodiments, in S3, the heating temperature is 80-120 °C and the polymerization reaction time is 4-8 h.

[0095] In some embodiments, in S3, solvent C is a polar solvent, and solvent C includes at least one of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, N-ethyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-methyl-3- or 4-pyrrolidone, and 1,3-dimethyl-2-imidazolium ketone.

[0096] In some embodiments, in S1 and S3, the inert gas includes at least one of nitrogen, argon, and neon.

[0097] This application also provides a method for preparing a secondary battery, including the following steps: (1) After mixing the positive electrode active material, positive electrode conductive agent and positive electrode binder in proportion, add them to the solvent and stir evenly to prepare a positive electrode slurry. Coat the positive electrode slurry on the surface of the positive electrode current collector, dry, roll, slit and cut into sheets to obtain a positive electrode sheet. (2) After mixing the negative electrode active material, negative electrode conductive agent and negative electrode binder in proportion, add them to the solvent and stir evenly to prepare a negative electrode slurry. Coat the negative electrode slurry on the surface of the negative electrode current collector, dry, roll, slit and cut into sheets to obtain a negative electrode sheet. (3) The positive electrode, separator and negative electrode are stacked in sequence, then wound into a bare cell, packaged and baked, injected with electrolyte and sealed, and after standing, formation and capacity testing, a secondary battery is prepared.

[0098] In some embodiments, in step (2), the negative electrode conductive agent is an MXene material with a coupling agent grafted on its surface. The preparation method of the negative electrode conductive agent includes the following steps: dispersing MXene in a solvent, adding a coupling agent, adjusting the pH to 4.5-5.5, heating and stirring to react, centrifuging, washing, and drying to obtain the negative electrode conductive agent.

[0099] In some embodiments, in the preparation method of the negative electrode conductive agent, the coupling agent is 5%-15% by mass of MXene.

[0100] In some embodiments, in the preparation method of the negative electrode conductive agent, the coupling agent contains unsaturated bonds, and the coupling agent includes at least one of silane coupling agents, titanate coupling agents, aluminate coupling agents, bimetallic coupling agents, phosphate coupling agents, and borate coupling agents.

[0101] In some embodiments, in the preparation method of the negative electrode conductive agent, the silane coupling agent includes at least one of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(2-methoxyethoxy)silane, and γ-glycidoxypropyltrimethoxysilane.

[0102] In some embodiments, the solvent in the preparation method of the negative electrode conductive agent includes water and / or ethanol.

[0103] In some embodiments, the heating temperature is 60-80 °C and the reaction time is 6-10 h in the preparation method of the negative electrode conductive agent.

[0104] This application also provides an electrical device, including a secondary battery.

[0105] The electrical device used in this application is not particularly limited and can be any electronic device known in the prior art. Electrical devices include, but are not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robotic dogs, industrial robots, and android robots.

[0106] To further illustrate this application, the following detailed description is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of this application. Unless otherwise specified, the raw materials used in the following embodiments and comparative examples are all commercially available, and the same raw materials were used in parallel experiments.

[0107] Example 1 A secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes an aluminum foil and a positive active layer on both sides of the aluminum foil. The positive active layer includes LiFePO4 (LFP) in a mass ratio of 88:6:6, a positive conductive agent, and a positive binder. The positive conductive agent is conductive carbon black, and the positive binder is polyvinylidene fluoride. The negative electrode includes a copper foil and a negative active layer on both sides of the copper foil. The negative active layer includes silicon-carbon material in a mass ratio of 90:6:3, a negative conductive agent, and a negative binder. The silicon-carbon material includes silicon and carbon in a mass ratio of 10:90. The separator is a porous PE film. The electrolyte includes 1 mol / L LiPF6, 10% fluoroethylene carbonate (FEC), 1% vinylene carbonate (VC), and the balance organic solvent. The organic solvent includes vinyl ethylene carbonate (VEC) and diethyl carbonate (DEC) in a mass ratio of 1:1. The negative electrode conductive agent is an MXene material with KH-570 grafted onto its surface. MXene is a multilayer Ti3C2T material. x abbreviated as Ti3C2T x -KH, the negative electrode conductive agent contains Ti-O-Si covalent bonds; The negative electrode binder is a polymer, which includes structural unit 1, structural unit 2, and structural unit 3 with a molar ratio of 1:0.2:0.28; the general formula of structural unit 1 is... In the formula, R is —CH2CH2CH2—, and n is 376; the general structural formula of structural unit 2 is The general structural formula of structural unit 3 is: .

[0108] The above-mentioned method for preparing a secondary battery includes the following steps: (1) Synthesis of allyl-functionalized polyaniline: The synthetic route is as follows Figure 1 As shown, conductive polyaniline with a number-average molecular weight of 35000 g / mol, abbreviated as PANI, was selected, and its structural formula is as follows: , where n is a repeating unit, under nitrogen protection, it was dissolved in anhydrous N-methylpyrrolidone at a concentration of 5% by mass, mixed with potassium carbonate as an acid-binding agent, and then a functionalizing agent, allyl bromide, was added. The molar ratio of polyaniline to functionalizing agent was 1.3:1, and the molar ratio of allyl bromide to potassium carbonate was 1:1.1. The electrophilic substitution reaction was carried out at 60 °C for 24 h. After the reaction was completed, it was precipitated in ethanol, filtered and washed thoroughly, and dried under vacuum at 60 °C to obtain functionalized polyaniline, abbreviated as PANI-A; (2) Preparation of lithium lipoate: The synthetic route is as follows Figure 2 As shown, lithium hydroxide was dissolved in an ethanol solution, and then thioctic acid was added. The mixture was heated and stirred at 60 °C for 5 h. The molar ratio of thioctic acid to lithium hydroxide was 1:1.05, and the concentration of lithium hydroxide in the solution was 0.5 mol / L. After rotary evaporation under reduced pressure and drying, a pale yellow powder was obtained, and lithium thiocate, abbreviated as LA-Li, was prepared. (3) Preparation of negative electrode binder: The synthesis route is as follows Figure 3 As shown, functionalized polyaniline, lipoic acid, and lithium lipoate were mixed in a molar ratio of 1:0.2:0.28 to obtain a mixture. The mixture was dissolved in anhydrous N,N-dimethylformamide (DMF) at a mass fraction of 5%, and heated to 100 °C under nitrogen protection for 6 h. During this process, lipoic acid and lithium lipoate underwent ring-opening self-polymerization and graft copolymerization with the double bonds of the polyaniline side chain to obtain a polymer containing a three-dimensional network, abbreviated as PAL, which is the negative electrode binder. (4) Preparation of negative electrode conductive agent: The synthesis route is as follows Figure 4As shown, MXene was dispersed in an ethanol aqueous solution with a volume concentration of 90%. In this embodiment, MXene is specifically a multilayered Ti3C2T x Add a coupling agent, which is silane coupling agent KH-570, at a dosage of 10% of MXene mass. Adjust the pH to about 5 with glacial acetic acid. Stir the reaction at 70 ℃ for 8 h. After the reaction, centrifuge, wash and dry to obtain the negative electrode conductive agent. (5) After mixing LiFePO4, positive electrode conductive agent and positive electrode binder in proportion, add them to N-methylpyrrolidone (NMP) and stir evenly to prepare a positive electrode slurry with a solid content of 55%. The positive electrode slurry is extruded and coated on both sides of aluminum foil, dried at 80 °C, rolled, slit and cut to obtain a positive electrode sheet. (6) After mixing silicon carbon material, negative electrode conductive agent and negative electrode binder in proportion, add water and stir evenly to prepare a negative electrode slurry with a solid content of 35%. The negative electrode slurry is extruded and coated on both sides of copper foil, dried at 80 ℃, rolled, slit and cut to obtain a negative electrode sheet. (7) The positive electrode, separator and negative electrode are stacked in sequence, with the separator between the positive electrode and the negative electrode. After being wound into a square bare cell, it is installed in the aluminum shell of the battery. Then, it is baked at 80 °C to remove moisture, electrolyte is injected and sealed. After standing, formation and capacity testing, a secondary battery is prepared.

[0109] Example 2 A secondary battery, the preparation method of which differs from that of Example 1, is that in step (1), the number-average molecular weight of polyaniline and the n value in the structural formula are adjusted to achieve different n values ​​in the structural unit 1 of the negative electrode binder. In step (3), the molar ratio of functionalized polyaniline, thioctic acid, and lithium thiocate is adjusted to achieve different molar ratios of structural unit 1, structural unit 2, and structural unit 3 in the negative electrode binder. In step (4), the composition of MXene is adjusted to Ti3AlC2 to achieve different negative electrode conductive agents. Specifically, the negative electrode conductive agent is a Ti3AlC2 material with KH-570 grafted on its surface, referred to as Ti3AlC2-KH.

[0110] Example 3 A secondary battery, the preparation method of which differs from that of Example 1, is that in step (1), the number-average molecular weight of polyaniline and the n value in the structural formula are adjusted to achieve different n values ​​in the structural unit 1 of the negative electrode binder. In step (3), the molar ratio of functionalized polyaniline, thioctic acid, and lithium thiocate is adjusted to achieve different molar ratios of structural unit 1, structural unit 2, and structural unit 3 in the negative electrode binder. In step (4), the composition of MXene is adjusted to Nb2C to achieve different negative electrode conductive agents. Specifically, the negative electrode conductive agent is an Nb2C material with KH-570 grafted on its surface, referred to as Nb2C-KH.

[0111] Examples 4-7 A secondary battery is prepared in a way that differs from that in Example 1. In step (3), the molar ratio of functionalized polyaniline, thioctic acid, and lithium thiocate is adjusted to achieve different molar ratios of structural unit 1, structural unit 2, and structural unit 3 in the negative electrode binder.

[0112] Examples 8-11 A secondary battery is prepared in a way that differs from that in Example 1. In step (1), the number-average molecular weight of polyaniline and the n value in the structural formula are adjusted to achieve different n values ​​in the structural unit 1 of the negative electrode binder.

[0113] Examples 12-14 A secondary battery is prepared in a way that differs from that in Example 1. In step (3), the molar ratio of functionalized polyaniline, thioctic acid, and lithium thiocate is adjusted to achieve different molar ratios of structural unit 1, structural unit 2, and structural unit 3 in the negative electrode binder.

[0114] Examples 15-16 A secondary battery is prepared in a way that differs from that in Example 1. In step (6), the molar ratio of silicon-carbon material, negative electrode conductive agent and negative electrode binder is adjusted to achieve different molar ratios of silicon-carbon material, negative electrode conductive agent and negative electrode binder in the negative electrode active layer.

[0115] Example 17 A secondary battery, the preparation method of which differs from that of Example 1, is that in step (6), the negative electrode conductive agent is adjusted to be conductive carbon black with KH-570 grafted on the surface, referred to as SP-KH, so as to achieve different negative electrode conductive agents in the negative electrode active layer; the preparation method of conductive carbon black with KH-570 grafted on the surface includes the following steps: the conductive carbon black is dispersed in an ethanol aqueous solution with a volume concentration of 90%, silane coupling agent KH-570 is added, the amount of KH-570 is 10% of the mass of the conductive carbon black, the pH is adjusted to about 5 with glacial acetic acid, the reaction is stirred at 70 ℃ for 8 h, and after the reaction, it is centrifuged, washed and dried to obtain modified conductive carbon black.

[0116] Example 18 A secondary battery, the preparation method of which differs from that of Example 1, is that in step (6), the negative electrode conductive agent is adjusted to be carbon nanotubes grafted with KH-570, referred to as CNT-KH, so as to achieve different negative electrode conductive agents in the negative electrode active layer; the preparation method of carbon nanotubes grafted with KH-570 includes the following steps: dispersing carbon nanotubes in an ethanol aqueous solution with a volume concentration of 90%, adding silane coupling agent KH-570, the amount of KH-570 being 10% of the mass of carbon nanotubes, adjusting the pH to about 5 with glacial acetic acid, stirring and reacting at 70 ℃ for 8 h, and after the reaction, centrifuging, washing and drying to obtain modified carbon nanotubes.

[0117] Example 19 A secondary battery, the preparation method of which differs from that of Example 1, is that in step (6), the negative electrode conductive agent is adjusted to be a multilayer Ti3C2T without KH-570 grafted on the surface. x To achieve different negative electrode conductive agents in the negative electrode active layer.

[0118] Examples 20-21 A secondary battery is prepared in a way that differs from that in Example 1 in that, in step (1), the composition of the functionalized reagent is adjusted to achieve different R values ​​for structural unit 1 in the negative electrode binder.

[0119] Comparative Example 1 A secondary battery is prepared in a way that differs from that in Example 1. In step (6), the negative electrode binder is adjusted to be polyvinylidene fluoride to achieve a different negative electrode binder in the negative electrode active layer.

[0120] Comparative Example 2 A secondary battery is prepared in a way that differs from that in Example 1 in that, in step (6), the negative electrode binder is adjusted to be styrene-butadiene rubber to achieve a different negative electrode binder in the negative electrode active layer.

[0121] Comparative Example 3 A secondary battery, the preparation method of which differs from that of Example 1, is that in step (6), the negative electrode binder is adjusted to the functionalized polyaniline obtained in step (1), abbreviated as PANI-A, so as to achieve a different negative electrode binder in the negative electrode active layer.

[0122] Comparative Example 4 A secondary battery is prepared in a way that differs from that in Example 1. In step (3), the molar ratio of functionalized polyaniline, thioctic acid, and lithium thiocate is adjusted to achieve different molar ratios of structural unit 1, structural unit 2, and structural unit 3 in the negative electrode binder.

[0123] In the above examples and comparative examples of secondary battery preparation methods, the molar ratio of functionalized polyaniline, thioctic acid, and lithium thiocate in step (2), the n value in the polyaniline structural formula in step (1), the number-average molecular weight of polyaniline in step (1), and the functionalizing reagents in step (1) are all shown in Table 1 below.

[0124] In the above embodiments and comparative examples of secondary battery negative electrode sheets, the composition of the negative electrode binder, the molar ratio of structural unit 1, structural unit 2 and structural unit 3, the R in structural unit 1, the composition of the negative electrode conductive agent, the silicon-carbon material, and the mass ratio of the negative electrode conductive agent and the negative electrode binder are all shown in Table 2 below.

[0125] Table 1 - Parameter settings for process components and content in the preparation method of secondary batteries in this application. Table 2 - Parameter settings of the negative electrode in the secondary battery of this application Performance testing 1. Negative Electrode Swelling Test: The negative electrode sheets prepared in the examples and comparative examples were cut into electrode sheets of the same size (length * width * thickness = 20 mm * 20 mm * 1.5 mm) and immersed in the same electrolyte, which included 1 mol / L LiPF6, 10% fluoroethylene carbonate (FEC), 1% ethylene carbonate (VC), and the balance organic solvent, which included vinyl ethylene carbonate (VEC) and diethyl carbonate (DEC) in a 1:1 mass ratio. After 48 h, the samples were removed, the surface electrolyte was wiped dry, and the samples were weighed. The mass of the negative electrode sheet before and after swelling was recorded, and the swelling rate of the electrode sheet was calculated. The formula for calculating the swelling rate is: Swelling rate = (M 后 -M 前 ) / M 前 *100%, the test results are shown in Table 3 below.

[0126] 2. Peel strength test of negative electrode sheet: After cutting the negative electrode sheets prepared in the examples and comparative examples into rectangles (length * width = 50mm * 20mm), tape was attached to the negative electrode active layer coating surface of the negative electrode sheet, and then placed in the upper and lower clamps of the testing machine. The speed was set to 15 mm / min, and the sheet was pulled evenly until the negative electrode active layer coating surface of the negative electrode sheet was completely peeled off. The test data was recorded. Five parallel samples were tested in each group, and the average value was taken. The average peel strength of the test is shown in Table 3 below.

[0127] 3. DC resistance (DCR) test at room temperature: Under the condition of 25±2 ℃, the secondary batteries prepared in the examples and comparative examples were charged to 3.65 V with a constant current of 1 C, then discharged with a constant current of 1 C for 30 min, adjusted to 50% SOC, and then pulsed discharged with a constant current of 2 C for 30 s and charged for 30 s. The DCR result was calculated according to the formula DCR=(voltage before pulse discharge-voltage after pulse discharge) / discharge current. The test results are shown in Table 3 below.

[0128] 4. Cyclic performance test: The secondary batteries prepared in the examples and comparative examples were subjected to charge-discharge cycle tests at a charge rate of 2 C and a discharge rate of 2 C within the range of 2.5-3.65 V under temperature adjustment of 25±2 ℃ and 45±2 ℃ respectively. The number of cycles in which the battery capacity retention rate was 80% was recorded. The test results are shown in Table 3 below.

[0129] Table 3 - Performance test results of secondary batteries in the embodiments and comparative examples of this application As shown in Table 3, in the negative electrode sheet of the secondary battery of Example 1 of this application, the negative electrode binder uses conductive polyaniline as a rigid skeleton. Through thermally initiated self-polymerization, thioctic acid containing dynamic disulfide bonds and lithium thiocate providing lithium ion transport sites are covalently grafted onto the side chains of the skeleton to form a stable and dense three-dimensional cross-linked network. Its molecular structure contains abundant active groups such as carboxyl and amino groups, which can interact with the negative electrode active material and the -OH on the surface of MXene to form strong hydrogen bonds, thereby improving the interfacial adhesion and electrode peel strength. Furthermore, the dynamic disulfide bonds can consume strain energy during volume expansion, and they, together with hydrogen bonds, efficiently dissipate expansion stress, thereby improving the stability of the electrode structure. In addition, the negative electrode conductive agent uses MXene material with KH-570 grafted on its surface, which has high electronic conductivity and can adsorb trace amounts of harmful gases generated during cycling to improve interfacial stability and reduce internal resistance. Moreover, during the electrode baking stage, the dynamic disulfide bonds of the negative electrode binder break due to heat, generating a large number of active sulfur free radicals. These free radicals can undergo addition reactions with the unsaturated bonds on the MXene surface to form covalent bonds, achieving covalent bonding between the conductive network and the binder skeleton. The cross-linked network forms a more efficient electron transport path, reducing interfacial contact resistance and improving the mechanical strength of the electrode. It can simultaneously possess high ion conductivity and expansion buffering functions, effectively reducing the low resistance of the electrode and improving the cycle life and high-temperature cycle performance of the secondary battery.

[0130] Compared to Example 1, the negative electrode in Comparative Examples 1-2 uses traditional binder materials such as polyvinylidene fluoride and styrene-butadiene rubber. This traditional binder does not contain dynamic disulfide bonds and cannot form strong hydrogen bonds with the negative electrode active material and MXene material. It only relies on weak van der Waals forces to bind. During the electrode baking process, the traditional binder cannot generate active sulfur free radicals. Therefore, it cannot undergo an addition reaction with the unsaturated carbon-carbon double bonds on the MXene surface to form CS covalent bonds. The components are only physically mixed, and a three-dimensional dense cross-linked network cannot be formed in the electrode. Moreover, the insulating properties of the traditional binder will hinder electron conduction and destroy the continuity of the conductive network, resulting in a significant increase in the internal resistance of the electrode. Under the volume expansion stress of repeated charging and discharging, the bonding interface is prone to creep, relaxation, or even peeling. The peeling force of the negative electrode is low, and the cycling stability at room temperature and high temperature decreases.

[0131] In Example 12, the polymer in the negative electrode binder was formed by thermally initiated self-polymerization of functionalized polyaniline and thioctic acid. Compared to Example 12, the negative electrode binder in Comparative Example 3 used functionalized polyaniline, which did not polymerize thioctic acid to form side chains. The reduced carboxyl content affected the strong hydrogen bonding ability of the binder with the active material and MXene. At the same time, since no dynamic disulfide bonds were introduced, the expansion stress could not be dissipated by the synergistic effect of dynamic disulfide bonds and hydrogen bonds. The large expansion stress of the electrode led to a decrease in structural stability. Moreover, during the electrode baking stage, active sulfur free radicals could not be generated, so they could not undergo an addition reaction with the unsaturated carbon-carbon double bonds on the MXene surface to form CS covalent bonds. The negative electrode binder and negative electrode conductive agent could not form a cross-linked conductive network through covalent bonds, resulting in a large interfacial contact resistance and low electrode mechanical strength. Therefore, its DC impedance and electrode peel force were lower than those of Example 1.

[0132] Compared to Example 1, the polymer in the negative electrode binder of Comparative Example 4 only polymerizes lithium thiocate and does not polymerize thioctic acid. The lithium carboxyl groups cannot form strong hydrogen bonds with the active material, and the ring-opening addition activity of disulfide bonds is reduced. The three-dimensional cross-linked network is difficult to construct, and the constraint force on the volume expansion of silicon-based materials is insufficient, affecting cycle stability. Secondly, the lack of free carboxyl groups to provide hydrogen bond anchoring sites leads to a decrease in interfacial adhesion, and the binder is easy to peel off during high-temperature cycling. Moreover, excessive lithium groups will make the hydrophilicity too strong, the electrode is easy to swell and the density is reduced. In addition, the lack of carboxyl anchoring sites makes the lithium groups uniformly distributed and unable to form a concentration gradient, which is not conducive to the efficient desolvation of lithium ions at the interface.

[0133] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit the scope of protection of this application. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application for those skilled in the art.

Claims

1. A secondary battery, characterized in that, The negative electrode includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active layer, the negative electrode active layer includes a negative electrode binder, the negative electrode binder includes structural unit 1 and structural unit 2, and the general structural formula of structural unit 1 is as follows: In the formula, R is at least one of substituted or unsubstituted alkyl, phenyl, benzyl, and cycloalkyl groups; The general structural formula of structural unit 2 is as follows: .

2. The secondary battery as described in claim 1, characterized in that, The negative electrode binder also includes structural unit 3, the general structural formula of which is: .

3. The secondary battery as described in claim 2, characterized in that, The molar ratio of structural unit 1 to structural unit 2 is 1:(0.12-0.50). And / or, the molar ratio of the structural unit 1 and the structural unit 3 is 1:(0.18-0.36).

4. The secondary battery as described in claim 3, characterized in that, The molar ratio of structural unit 1, structural unit 2 and structural unit 3 is 1:(0.15-0.25):(0.25-0.3).

5. The secondary battery as described in claim 1, characterized in that, In the general formula of the structural unit 1, 160≤n≤590.

6. The secondary battery as described in claim 1, characterized in that, The negative electrode active layer also includes a negative electrode active material and a negative electrode conductive agent. The negative electrode conductive agent is an MXene material with a coupling agent grafted on its surface. The coupling agent contains unsaturated carbon-carbon double bonds.

7. The secondary battery as described in claim 1, characterized in that, The swelling rate of the negative electrode sheet after soaking in the electrolyte for 48 hours is ≤15%.

8. The secondary battery as described in claim 1, characterized in that, The peeling force of the negative electrode active layer in the negative electrode sheet is ≥14 N / m.

9. The secondary battery as described in claim 6, characterized in that, The negative electrode active material includes at least one of silicon-based materials, silicon-carbon materials, carbon-based materials, silicon-oxygen materials, and silicon-nitrogen materials.

10. The secondary battery as described in claim 6, characterized in that, The mass ratio of the negative electrode active material, the negative electrode conductive agent and the negative electrode binder is 90:(3-8):(1-6).

11. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1-10.

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