Positive electrode binder with chelating function as well as preparation method and application of positive electrode binder

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a positive electrode binder with a chelating function and a preparation method and application thereof. A positive electrode binder with a chelating function comprises a copolymer main chain formed through free radical polymerization, and the copolymer main chain is grafted with a functional group with transition metal chelating ability. According to the present invention, the chelating group is introduced into the binder through the molecular design, such that the free metal ions are effectively captured, the transition metal impurities in the electrolyte are reduced, the SEI film is prevented from being invaded or the invasion is reduced, and the cycle life of the battery is prolonged. Through functional group design and synthesis process innovation, multi-functionalization of the binder is realized, the binder has high bonding strength (the peel strength is greater than or equal to 10 N / m) and ion adsorption capacity (the concentration of transition metal ions in an electrolyte is reduced by greater than or equal to 50% after 100 cycles of a lithium ion battery), the cycle life of the battery is remarkably prolonged (the capacity retention rate is greater than or equal to 90% after 500 cycles of the lithium ion battery), and the safety is remarkably improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a positive electrode binder with a chelating function, and a preparation method and application thereof. Background Art

[0002] Existing lithium-ion battery cathode materials (such as LFP, NCM, and LMO) are prone to transition metal dissolution during cycling, leading to electrolyte contamination and damage to the negative electrode SEI film, resulting in capacity decay. Traditional binders (such as PVDF) only provide bonding properties and cannot inhibit metal dissolution. Summary of the Invention

[0003] In the current cathode material, due to the collapse of crystal structure or side reaction of electrolyte during the cycle, transition metals (such as Fe, Mn, Ni, Co, etc.) are dissolved into the electrolyte, forming free metal ion impurities, causing electrolyte contamination and the dissolved metal ions migrate to the negative electrode surface through the electrolyte, and react with Li in the SEI film. + Replacement reaction occurs, destroying the SEI film structure and blocking the Li + Transmission channels lead to increased internal resistance and capacity attenuation. This application provides a positive electrode binder with chelating function, its preparation method and application. Through molecular design, chelating groups are introduced into the binder to effectively capture free metal ions, reduce transition metal impurities in the electrolyte, ensure that the SEI film is protected from or reduced from invasion, and improve the battery cycle life. This application realizes the multifunctionality of the binder through functional group design and synthesis process innovation, with both high bonding strength (peel strength ≥ 10N / m) and ion adsorption capacity (the concentration of transition metal ions in the electrolyte is reduced by ≥ 50% after 100 cycles of lithium-ion batteries), significantly improving the battery cycle life (capacity retention rate ≥ 90% after 500 cycles of lithium-ion batteries) and safety.

[0004] In a first aspect, the present application provides a positive electrode binder with a chelating function, which adopts the following technical solution: A positive electrode binder with chelating function comprises a copolymer main chain formed by free radical polymerization, onto which a functional group with transition metal chelating ability is grafted; the functional group is selected from at least one of carboxyl, amino, mercapto, phosphonic acid and pyridyl.

[0005] By adopting the above technical solution, (1) transition metal ions are chelated and fixed, and functional groups such as carboxyl, amino, and thiol grafted on the copolymer backbone form stable coordination bonds (such as OM, NM, and SM bonds) with dissolved Fe, Mn, Ni, and Co ions to form insoluble complexes. The transition metal ions are anchored on the surface of the positive electrode active material, significantly reducing their free concentration in the electrolyte (concentration reduction ≥50% after 100 cycles), blocking subsequent chain reactions. (2) The positive electrode structure stability is enhanced, and the bonding and interface are strengthened: the binder network with high peel strength (≥10N / m) tightly coats the positive electrode particles, inhibiting particle breakage and crystal structure collapse caused by volume expansion during the cycle, and reducing the shedding of active materials. In-situ repair effect: dynamic polymer chains redistribute when local stress is concentrated through reversible coordination-dissociation behavior, delaying crack propagation. (3) SEI film protection and lithium ion transport optimization, chelation action blocks the migration of metal ions into the electrolyte, and prevents them from depositing on the negative electrode surface and Li in SEI + Replacement reaction occurs (such as Fe 2+ +2Li→Fe+2Li +), maintaining the integrity of the SEI structure. The intact SEI film ensures efficient Li+ transmission and inhibits the growth of internal resistance (capacity retention rate ≥90% after 500 cycles). Synergistic mechanism: (1) Synergy between functional groups and polymer structures, spatial adaptability: Select large-volume monomers containing pyridine groups, phosphonic acid groups, etc. (such as 3-(2-methoxypyridin-3-yl) acrylic acid), enhance coordination selectivity through steric hindrance effects, and preferentially bind to transition metal ions with high charge density. Multidentate coordination design: For example, acrylamide ethoxyphosphonate simultaneously provides O and P electron-donating atoms to form a multidentate chelate structure (such as a six-membered ring complex), which significantly improves the complex stability. (2) Balance between adhesion and ion adsorption, flexible chain segment regulation: By introducing (meth)acrylate monomers to adjust the glass transition temperature (Tg) of the copolymer, while ensuring mechanical strength, providing chain segment mobility, and achieving dynamic adsorption-release balance. Cross-link density optimization: Benzenesulfonic acid catalyzes the free radical polymerization reaction, controls the density of cross-linking sites, and forms a three-dimensional network with both high bonding strength and ion permeation channels. (3) Cooperative stabilization of the electrochemical interface and surface charge regulation: Acidic functional groups such as carboxyl groups dissociate in the electrolyte to form a negatively charged surface, which inhibits the release of transition metal ions from the positive electrode through electrostatic repulsion. Passivation layer construction: Some chelating groups (such as thiol groups) are oxidized under high pressure to form a sulfur-containing passivation film covering the positive electrode surface, inhibiting the oxidative decomposition of the electrolyte. In short, this positive electrode binder with chelating function breaks through the single function limitation of traditional binders through a multi-level synergistic mechanism of chemical chelation (coordination bond) → physical anchoring (high adhesion) → interface regulation (charge / passivation), achieving: electrolyte purification (transition metal contamination reduction ≥50%), stable electrode structure and long cycle life (500-cycle capacity retention rate ≥90%). This design provides a key material solution for positive electrode systems with easily soluble metals such as high nickel and lithium-rich manganese.

[0006] Preferably, the functional group is grafted to the main chain of the copolymer through a condensation reaction, wherein the condensation reaction includes at least one of forming an ester bond between a carboxyl group and a hydroxyl group, forming an amide bond between a carboxyl group and an amino group, and forming an ester bond between a carboxyl group and a hydroxyl group and an amide bond between a carboxyl group and an amino group.

[0007] Preferably, the main chain of the copolymer is formed by free radical polymerization of at least two of acrylonitrile, acrylic acid, and acrylate monomers.

[0008] Preferably, the monomer composition of the main chain of the copolymer is as follows by mass: 10-15 parts of acrylonitrile, 25-35 parts of acrylic acid, and 25-35 parts of acrylate monomer.

[0009] In a second aspect, the present application provides a method for preparing a positive electrode binder having a chelating function, which adopts the following technical solution: As a general technical concept, the present application also provides a method for preparing the above-mentioned positive electrode binder with chelating function, comprising the following steps: S51, dispersing acrylonitrile, acrylic acid, acrylate monomers and anionic surfactant in an aqueous solution, introducing protective gas to replace the air, and then heating with stirring to 75-85° C., adding an initiator to carry out free radical polymerization for 2-3 hours to form a copolymer backbone; S52. Heat the reaction system to 83-88° C., then dropwise add a mixture of a monomer containing a chelating functional group and a catalyst into the reaction system within 1 hour, continue the reaction for 5-7 hours, cool to room temperature, and filter to obtain a positive electrode binder with a chelating function.

[0010] By adopting the above technical solution, step S51: construction of the main chain of the copolymer, acrylonitrile: provides a rigid skeleton to enhance the mechanical strength and thermal stability of the copolymer. Acrylic acid / acrylate monomers: introduce carboxyl / ester flexible chain segments, adjust the glass transition temperature, and optimize the binder's coating ability on the positive electrode particles (peel strength ≥ 10N / m). Anionic surfactant: forms a micellar structure to promote uniform dispersion of the monomer in the aqueous phase, avoid agglomeration, and ensure the uniformity of the polymerization reaction. Protective gas (such as N2): eliminates the quenching effect of oxygen on free radicals and ensures a polymerization reaction conversion rate of >95%. Heating at 75-85℃: activates the initiator (such as ammonium persulfate) to generate primary free radicals to start chain growth, while avoiding high temperature-induced chain transfer side reactions. 2-3 hours reaction time: controls the molecular weight of the copolymer and balances the film-forming and processability of the binder. The rigidity of acrylonitrile and the flexibility of acrylate synergistically form a three-dimensional network with both high bonding strength and elastic deformation ability. Anionic surfactants orient the monomers, regulate the distribution of copolymer segments, and provide an ordered interface for subsequent functional group grafting. Step S52: Grafting of chelating functional groups. Heating the temperature to 83-88°C: This increases reaction activity and accelerates the free radical grafting reaction (grafting efficiency >80%), while preventing degradation of the main chain due to excessive temperature. Add the mixed solution dropwise over 1 hour: This controls the monomer / catalyst concentration gradient, inhibits homopolymer formation, and ensures uniform distribution of functional groups. Catalysts such as benzenesulfonic acid activate monomers containing chelating functional groups (such as pyridyl acrylic acid) through protonation, promoting their copolymerization with main chain free radicals. Functional group design and multiple coordination site selection: For example, 3-(2-methoxypyridin-3-yl) acrylic acid provides N / O bidentate coordination, while acrylamidoethoxyphosphonate provides P / O coordination, forming a highly stable chelate ring. Dynamic adsorption capacity: The thiol (-SH) group dynamically captures and releases metal ions through reversible redox reactions, avoiding functional group saturation and failure. Synergy is reflected in the gradient reaction design: the main chain polymerization and functional group grafting are carried out in steps to avoid the premature participation of functional group monomers in the main chain formation and to ensure the density of chelating sites. Catalyst-directed activation: benzenesulfonic acid preferentially activates the monomers containing chelating groups to ensure the selectivity of the grafting reaction. Synergistic effect between steps: (1) Structural-functional integrated construction, the main chain provides a mechanical skeleton: the copolymer main chain generated by S51 serves as a carrier, and its carboxyl / ester group is combined with the hydroxyl group on the surface of the positive electrode material (such as NCM) through hydrogen bonds to enhance the interfacial adhesion (peel strength ≥ 10N / m). The functional group imparts chemical activity: the chelating group grafted by S52 "anchors" the dissolved transition metal ions (such as Ni) through coordination bonds 2 +、Co 3+), forming a surface passivation layer to inhibit further dissolution. (2) Coordinated optimization of process parameters, temperature gradient control: S51 moderate temperature polymerization (75-85℃) ensures the integrity of the main chain, S52 moderate temperature increase (83-88℃) improves the grafting efficiency, and the two work together to achieve a balance between high grafting rate and low side reactions. Dispersion system continuity: Anionic surfactants maintain micelle stability in both steps to ensure that the main chain and grafted monomers are uniformly dispersed at the nanoscale. (3) Synergistic performance improvement, mechanical-chemical coupling: The high bonding strength of the main chain inhibits the rupture of positive electrode particles (volume expansion rate reduction> 60%), while the chelation effect of the functional group blocks the migration of metal ions, forming a "physical barrier + chemical adsorption" dual protection mechanism. Dynamic adaptive interface: The flexible chain segment (acrylate) allows the binder to expand and contract with the change of electrode volume during charging and discharging, and the chelating group dynamically adjusts the coordination state to achieve cycle stability (500-cycle capacity retention rate ≥ 90%). In summary, through step-by-step polymerization (S51 backbone → S52 functional group grafting) and process-structure collaborative design, this preparation method achieves: 1. High-density chelating sites; 2. Balanced mechanical-chemical properties (peel strength ≥ 10 N / m, transition metal adsorption rate ≥ 50%); and 3. Scalable production feasibility (aqueous reaction, no organic solvents, and environmental compliance).

[0011] Preferably, in step S51, the initiator is ammonium persulfate, and the added amount is 0.5-1.5wt% of the total mass of the acrylonitrile, acrylic acid and acrylate monomers; the anionic surfactant is at least one of sodium dodecylbenzenesulfonate, dioctyl sodium sulfosuccinate and sodium lauryl sulfate.

[0012] Preferably, in step S52, the monomer containing a chelating functional group is selected from at least one of an acrylic acid (pyridyl) monomer, an acrylic amine monomer, a sulfur-containing acrylic acid monomer, an acrylamide phosphonic acid monomer, a (meth) acrylic acid phosphate monomer and a vinyl phosphonic acid monomer; and the catalyst is benzenesulfonic acid.

[0013] Preferably, the monomer containing a chelating functional group is selected from at least one of 3-(2-methoxypyridin-3-yl) acrylic acid, dimethylaminoethyl (meth)acrylate, 2-acrylamide-2-methylpropanesulfonic acid, 2-mercaptoethyl acrylate, (2-methylthio)ethyl methacrylate, acrylamidoethoxyphosphonate, (meth)acrylate phosphate, and vinylphosphonate.

[0014] In a third aspect, the present application provides a positive electrode plate, which adopts the following technical solution: As a general technical concept, the present application also provides a positive electrode sheet, which is obtained by coating a positive electrode slurry on a current collector, drying, and roll-pressing; the positive electrode slurry includes the above-mentioned positive electrode binder with chelating function, positive electrode active material, conductive agent and solvent; the mass proportion of the positive electrode binder with chelating function is 1-5%; the positive electrode active material is at least one of lithium iron phosphate (LFP), lithium nickel cobalt manganese oxide (NCM) or lithium manganese oxide (LMO); the conductive agent is selected from at least one of Super P, Ketjen black, and acetylene black; the current collector is selected from one of aluminum foil and carbon-containing aluminum foil.

[0015] In a fourth aspect, the present application provides a lithium-ion battery, which adopts the following technical solution: As a general technical concept, the present application also provides a lithium-ion battery comprising the above-mentioned positive electrode plate, wherein the capacity retention rate of the lithium-ion battery is ≥90% after 500 cycles, and the concentration of transition metal ions in the electrolyte is reduced by ≥50% after 100 cycles.

[0016] In summary, this application includes at least one of the following beneficial technical effects: 1. Electrolyte purification and transition metal suppression Highly efficient chelating ability: Functional groups such as carboxyl, amino, and thiol form stable complexes with dissolved Fe, Mn, Ni, and Co ions through multidentate coordination (such as OM, NM, and SM bonds), reducing the concentration of transition metal ions in the electrolyte by ≥50% (after 100 cycles), significantly reducing electrolyte pollution.

[0017] Dynamic adsorption mechanism: Sulfur-containing groups (such as 2-mercaptoethyl acrylate) achieve dynamic capture and release of metal ions through reversible redox reactions, avoiding functional group saturation failure and extending adsorption life.

[0018] 2. Improved electrode structure stability High-strength bonding network: Acrylonitrile and acrylate copolymerize to form a three-dimensional network that is both rigid and flexible, with a peel strength of ≥10N / m, effectively inhibiting the volume expansion of positive electrode particles and the shedding of active materials during cycling.

[0019] In-situ repair function: The flexible part of the copolymer chain (acrylate) allows dynamic deformation, which relieves local stress concentration through hydrogen bond reorganization and chain segment slippage, thereby delaying crack propagation.

[0020] 3. Interface protection and lithium ion transport optimization SEI film protection: Chelation blocks the migration of transition metal ions to the negative electrode, reducing their replacement reaction with Li+ in SEI (such as Fe 2+ +2Li→Fe+2Li + ), maintaining the structural integrity of the SEI film.

[0021] Unimpaired lithium ion channels: Undamaged SEI film and low-impurity electrolyte ensure Li + Efficient transmission, suppressing the increase of internal resistance.

[0022] 4. Enhanced security performance Improved thermal stability: The rigid acrylonitrile skeleton and the flame retardant properties of phosphonic acid groups (such as vinyl phosphonate) work synergistically to make the thermal decomposition temperature of the binder >200°C, reducing the risk of thermal runaway.

[0023] Side reaction inhibition: Pyridine groups (such as 3-(2-methoxypyridin-3-yl) acrylic acid) inhibit the decomposition of the electrolyte by adsorbing acidic substances (such as HF) in the electrolyte.

[0024] 5. Advantages of the preparation process: Environmentally friendly and efficient: The aqueous reaction system (without organic solvent) and benzenesulfonic acid catalysis process achieve atom economy and meet the requirements of green chemistry.

[0025] Scale compatibility: The step-by-step polymerization strategy (S51 main chain → S52 grafting) ensures uniform distribution of functional groups and is compatible with existing electrode coating processes without the need for additional equipment investment.

[0026] 6. Multifunctional synergy breakthrough Balance of mechanical and chemical properties: Breaking through the single functional limitations of traditional adhesives, achieving both high bonding strength and strong ion adsorption capacity.

[0027] Wide temperature adaptability: By adjusting the proportion of acrylate monomers, the adhesive can maintain stable bonding performance in the range of -20-60°C (peel strength fluctuation <15%), making it suitable for applications in extreme environments.

[0028] In summary, this application utilizes a trinity of molecular design, process innovation, and performance synergy to achieve: 1) high-purity electrolyte maintenance (≥50% reduction in transition metal contamination); 2) long-term stability of the electrode-electrolyte interface (≥90% capacity retention after 500 cycles); and 3) high safety and wide temperature range compatibility. This binder provides key material support for the commercial application of high-energy-density lithium-ion batteries (such as NCM811 and lithium-rich manganese-based batteries). DETAILED DESCRIPTION

[0029] The embodiments of the present application will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0030] In the following examples, 1 portion means 10 g.

[0031] Example 1 10 parts of acrylonitrile, 30 parts of acrylic acid, 30 parts of acrylic acid ester and 1 part of anionic surfactant (sodium lauryl sulfate) are dispersed in 500 parts of deionized water solution and placed in a reactor, and high-purity nitrogen as a protective gas is introduced to replace the air in the reactor; then, the mixture is heated and stirred, and when the temperature in the reactor reaches 75°C, 0.7 parts of initiator (ammonium persulfate) is added, and the reaction is carried out at 75°C for 3 hours; then 20 parts of dimethylaminoethyl acrylate, 10 parts of 2-acrylamide-2-methylpropanesulfonic acid and 0.2 parts of benzenesulfonic acid are uniformly mixed to obtain a mixed solution; the reaction system is heated to 85°C, and the mixed solution is then dripped into the reactor at a uniform speed, the dripping time is 60 minutes, the dripping reaction time is 6 hours, and then the temperature is cooled to room temperature and filtered to obtain a positive electrode binder with chelating function.

[0032] Example 2 15 parts of acrylonitrile, 35 parts of acrylic acid, 35 parts of acrylic acid ester and 1 part of anionic surfactant (sodium dodecylbenzenesulfonate) are dispersed in 500 parts of deionized water solution and placed in a reactor, and high-purity nitrogen as a protective gas is introduced to replace the air in the reactor; then, 1.5 parts of initiator (ammonium persulfate) are added while heating and stirring, and when the temperature in the reactor reaches 85°C, 1.5 parts of initiator (ammonium persulfate) are added, and the reaction is carried out at 85°C for 2 hours; then 22 parts of dimethylaminoethyl acrylate, 11 parts of 2-acrylamide-2-methylpropanesulfonic acid and 0.3 parts of benzenesulfonic acid are uniformly mixed to obtain a mixed solution; the reaction system is heated to 88°C, and the mixed solution is then dripped into the reactor at a uniform speed, the dripping time is 60 minutes, the dripping reaction time is 5 hours, and then the temperature is cooled to room temperature and filtered to obtain a positive electrode binder with chelating function.

[0033] Example 3 10 parts of acrylonitrile, 30 parts of acrylic acid, 30 parts of acrylic acid ester and 1 part of anionic surfactant (sodium dioctyl succinate sulfonate) are dispersed in 500 parts of deionized water solution and placed in a reactor, and high-purity nitrogen as a protective gas is introduced to replace the air in the reactor; then, the mixture is heated and stirred, and when the temperature in the reactor reaches 80°C, 0.5 parts of initiator (ammonium persulfate) is added, and the reaction is carried out at 80°C for 2.5 hours; then 20 parts of dimethylaminoethyl acrylate, 10 parts of 2-acrylamide-2-methylpropanesulfonic acid and 0.2 parts of benzenesulfonic acid are uniformly mixed to obtain a mixed solution; the reaction system is heated to 83°C, and the mixed solution is then dripped into the reactor at a uniform speed, the dripping time is 60 minutes, the dripping reaction time is 7 hours, and then the temperature is cooled to room temperature and filtered to obtain a positive electrode binder with chelating function.

[0034] Example 4 10 parts of acrylonitrile, 30 parts of acrylic acid, 30 parts of acrylic ester and 1 part of anionic surfactant (sodium dioctyl succinate sulfonate) are dispersed in 500 parts of deionized water and placed in a reactor. High-purity nitrogen as a protective gas is introduced to replace the air in the reactor. Then, the mixture is heated and stirred. When the temperature in the reactor reaches 80°C, 0.8 parts of initiator (ammonium persulfate) is added and the reaction is carried out at 78°C for 2.5 hours. Then, 20 parts of dimethylaminoethyl acrylate, 12 parts of 3-(2-methoxypyridin-3-yl) acrylic acid and 0.25 parts of benzenesulfonic acid are uniformly mixed to obtain a mixed solution. The reaction system is heated to 85°C, and the mixed solution is then dripped into the reactor at a uniform rate. The dripping time is 60 minutes and the dripping reaction time is 6 hours. Then, the temperature is cooled to room temperature and filtered to obtain a positive electrode binder with chelating function.

[0035] Example 5 10 parts of acrylonitrile, 30 parts of acrylic acid, 30 parts of acrylic ester and 1 part of anionic surfactant (sodium dioctyl succinate sulfonate) are dispersed in 500 parts of deionized water solution and placed in a reactor, and high-purity nitrogen as a protective gas is introduced to replace the air in the reactor; then, the mixture is heated and stirred, and when the temperature in the reactor reaches 80°C, 0.7 parts of initiator (ammonium persulfate) is added, and the reaction is carried out at 80°C for 2.5 hours; then 20 parts of dimethylaminoethyl acrylate, 8 parts of 2-mercaptoethyl acrylate and 0.25 parts of benzenesulfonic acid are uniformly mixed to obtain a mixed solution; the reaction system is heated to 84°C, and the mixed solution is then dripped into the reactor at a uniform speed, the dripping time is 60 minutes, the dripping reaction time is 6 hours, and then the temperature is cooled to room temperature and filtered to obtain a positive electrode binder with chelating function.

[0036] Example 6 10 parts of acrylonitrile, 30 parts of acrylic acid, 30 parts of acrylic acid ester and 1 part of anionic surfactant (sodium dioctyl succinate sulfonate) are dispersed in 500 parts of deionized water solution and placed in a reactor, and high-purity nitrogen as a protective gas is introduced to replace the air in the reactor; then, the mixture is heated while stirring, and when the temperature in the reactor reaches 80°C, 0.5 parts of initiator (ammonium persulfate) is added, and the reaction is carried out at 80°C for 2.5 hours; then 20 parts of dimethylaminoethyl acrylate, 15 parts of (2-methylthio)ethyl methacrylate and 0.25 parts of benzenesulfonic acid are uniformly mixed to obtain a mixed solution; the reaction system is heated to 85°C, and the mixed solution is then dripped into the reactor at a uniform speed, the dripping time is 60 minutes, the dripping reaction time is 6 hours, and then the temperature is cooled to room temperature and filtered to obtain a positive electrode binder with chelating function.

[0037] Example 7 10 parts of acrylonitrile, 30 parts of acrylic acid, 30 parts of acrylic ester and 1 part of anionic surfactant (sodium dioctyl succinate sulfonate) are dispersed in 500 parts of deionized water solution and placed in a reactor, and high-purity nitrogen as a protective gas is introduced to replace the air in the reactor; then, the mixture is heated and stirred, and when the temperature in the reactor reaches 80°C, 0.6 parts of initiator (ammonium persulfate) is added, and the reaction is carried out at 80°C for 2.5 hours; then 20 parts of dimethylaminoethyl acrylate, 14 parts of vinyl phosphonate and 0.2 parts of benzenesulfonic acid are uniformly mixed to obtain a mixed solution; the reaction system is heated to 85°C, and the mixed solution is then dripped into the reactor at a uniform speed, the dripping time is 60 minutes, the dripping reaction time is 6 hours, and then the temperature is cooled to room temperature and filtered to obtain a positive electrode binder with chelating function.

[0038] Example 8 10 parts of acrylonitrile, 30 parts of acrylic acid, 30 parts of acrylic acid ester and 1 part of anionic surfactant (sodium dioctyl succinate sulfonate) are dispersed in 500 parts of deionized water solution and placed in a reactor, and high-purity nitrogen as a protective gas is introduced to replace the air in the reactor; then, the mixture is heated while stirring, and when the temperature in the reactor reaches 80°C, 0.6 parts of initiator (ammonium persulfate) is added, and the reaction is carried out at 80°C for 2.5 hours; then, 20 parts of dimethylaminoethyl acrylate, 15 parts of (methyl)acrylic acid phosphate and 0.2-0.3 parts of benzenesulfonic acid are uniformly mixed to obtain a mixed solution; the reaction system is heated to 86°C, and the mixed solution is then dripped into the reactor at a uniform rate, the dripping time is 60 minutes, the dripping reaction time is 7 hours, and then the temperature is cooled to room temperature and filtered to obtain a positive electrode binder with chelating function.

[0039] Comparative Example 1 Polyvinylidene fluoride (Solvay PVDF5130) was used as the positive electrode binder.

[0040] Performance testing Preparation of the battery: 1. The positive electrode binders with chelating function prepared in Examples 1 to 8 were added to pure water to prepare a solution with a solid content of 3% as a binder. Lithium manganese oxide and Super P were then added to control the mass ratio of active material, binder, and Super P to be 92:3:5 (the binder was calculated based on its solute mass). The mixture was fully stirred using a homogenizer to obtain a positive electrode slurry. The positive electrode slurry was scraped onto a carbon-containing aluminum foil and vacuum-dried at 80°C for 12 hours, pressed into sheets, and sliced ​​to obtain a positive electrode sheet. The above-mentioned positive electrode sheet and lithium sheet were used as electrodes, Celgard2500 as a diaphragm, and LS-009 as an electrolyte. A lithium-ion battery was assembled in an argon-filled glove box. Comparative Example 1 was also prepared into a corresponding lithium-ion battery according to the above method.

[0041] 2. Peel strength test: The positive electrode sheet (sheet surface density 300mg / cm2, compaction 3.0g / cm 3 ) were cut into 30 mm wide and 50 mm long laminates, then attached to 3M tape. The peel strength was tested using a universal tensile tester at a speed of 5 mm / min, with the tape torn at a 180° angle. The test results are shown in Table 1.

[0042] 3. Cycling performance test: Using a Bluetron electrochemical workstation, the battery was cycled at 1C / 1C at room temperature with a voltage range of 2.5-3.8V. The capacity retention after cycling was calculated. The test results are shown in Table 2.

[0043] 4. Metal ion test: ICP was used to test the transition metal element content in the electrolyte after 100 cycles. The test results are shown in Table 3.

[0044] Table 1 Peel strength Table 2 Cycle performance Table 3 Transition metal ion solubility From the data in Tables 1 to 3, it can be seen that the positive electrode binder with chelating function prepared by this application introduces chelating groups into the binder through molecular design, effectively capturing free metal ions, reducing transition metal impurities in the electrolyte, ensuring that the SEI film is protected from or reduced from invasion, and improving the battery cycle life. This application realizes the multifunctionalization of the positive electrode binder with chelating function through functional group design and synthesis process innovation, combining high bonding strength (peel strength ≥ 10N / m) and ion adsorption capacity (the transition metal ion concentration in the electrolyte is reduced by ≥ 50% after 100 cycles of lithium-ion batteries), significantly improving the battery cycle life (capacity retention rate ≥ 90% after 500 cycles of lithium-ion batteries) and safety.

[0045] The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the above embodiments provide a detailed description of the present application, relevant technical personnel should understand that the specific implementation methods of the present application may still be modified or replaced by equivalents. Any modifications and equivalent replacements that do not depart from the spirit and scope of the present application should be included in the scope of protection of the present application.

Claims

1. A positive electrode binder with chelating function, characterized in that: The invention comprises a copolymer main chain formed by free radical polymerization, wherein a functional group with transition metal chelating ability is grafted onto the copolymer main chain; the functional group is selected from at least one of carboxyl, amino, thiol, phosphonic acid and pyridyl.

2. The positive electrode binder having a chelating function according to claim 1, characterized in that: The functional group is grafted to the main chain of the copolymer through a condensation reaction, wherein the condensation reaction includes at least one of forming an ester bond between a carboxyl group and a hydroxyl group, forming an amide bond between a carboxyl group and an amino group, and forming an ester bond between a carboxyl group and a hydroxyl group and an amide bond between a carboxyl group and an amino group.

3. The positive electrode binder with chelating function according to claim 1, characterized in that: The main chain of the copolymer is formed by free radical polymerization of at least two of acrylonitrile, acrylic acid and acrylate monomers.

4. The positive electrode binder with chelating function according to claim 3, characterized in that: The monomer composition of the main chain of the copolymer is calculated as follows by mass: 10-15 parts of acrylonitrile, 25-35 parts of acrylic acid, and 25-35 parts of acrylate monomers.

5. A method for preparing a positive electrode binder with a chelating function according to any one of claims 1 to 4, characterized in that: The following steps are involved: S51, dispersing acrylonitrile, acrylic acid, acrylate monomers and anionic surfactant in an aqueous solution, introducing protective gas to replace the air, and then heating with stirring to 75-85° C., adding an initiator to carry out free radical polymerization for 2-3 hours to form a copolymer backbone; S52. Heat the reaction system to 83-88° C., then dropwise add a mixture of a monomer containing a chelating functional group and a catalyst into the reaction system within 1 hour, continue the reaction for 5-7 hours, cool to room temperature, and filter to obtain a positive electrode binder with a chelating function.

6. The method for preparing a positive electrode binder with a chelating function according to claim 5, characterized in that: In step S51, the initiator is ammonium persulfate, and the added amount is 0.5-1.5wt% of the total mass of the acrylonitrile, acrylic acid and acrylate monomers; the anionic surfactant is at least one of sodium dodecylbenzenesulfonate, dioctyl sodium sulfosuccinate and sodium lauryl sulfate.

7. The method for preparing a positive electrode binder with a chelating function according to claim 5, characterized in that: In step S52, the monomer containing a chelating functional group is selected from at least one of acrylic acid (pyridyl) monomers, acrylic amine monomers, sulfur-containing acrylic acid monomers, acrylamide phosphonic acid monomers, (meth) acrylic acid phosphate monomers and vinyl phosphonic acid monomers; and the catalyst is benzenesulfonic acid.

8. The method for preparing a positive electrode binder with a chelating function according to claim 7, characterized in that: The monomer containing a chelating functional group is selected from at least one of 3-(2-methoxypyridin-3-yl) acrylic acid, dimethylaminoethyl (meth)acrylate, 2-acrylamide-2-methylpropanesulfonic acid, 2-mercaptoethyl acrylate, (2-methylthio)ethyl methacrylate, acrylamidoethoxyphosphonate, (meth)acrylate phosphate, and vinylphosphonate.

9. A positive electrode plate, characterized in that: The positive electrode slurry is coated on a current collector, dried, and roll-pressed; the positive electrode slurry comprises the positive electrode binder with a chelating function according to any one of claims 1 to 4, a positive electrode active material, a conductive agent, and a solvent; the mass proportion of the positive electrode binder with a chelating function is 1-5%; the positive electrode active material is at least one of lithium iron phosphate (LFP), lithium nickel cobalt manganese oxide (NCM), or lithium manganese oxide (LMO); the conductive agent is selected from at least one of Super P, Ketjen black, and acetylene black; and the current collector is selected from one of aluminum foil and carbon-containing aluminum foil.

10. A lithium ion battery, characterized in that: The positive electrode sheet according to claim 9 is included, wherein the capacity retention rate of the lithium-ion battery after 500 cycles is ≥90%, and the concentration of transition metal ions in the electrolyte is reduced by ≥50% after 100 cycles.

Images