Composite binder containing PVMPT ionic liquid, lithium battery electrode and preparation method of lithium battery electrode

Abstract

The invention relates to the technical field of lithium battery production, and provides a composite binder containing PVMPT ionic liquid, a lithium battery electrode and a preparation method of the lithium battery electrode. The composite binder comprises an ionic liquid A and a polymer binder B which are used for increasing conductivity, wherein the ionic liquid A is 3-vinyl-N-methylphenothiazine polymer ionic liquid (PVMPT ionic liquid); the preparation method comprises the following steps: preparing PVMPT with a pi-pi conjugated skeleton structure, carrying out ion doping on the PVMPT to prepare a PVMPT ionic liquid with an electron-ion dual-conduction characteristic, and finally blending the PVMPT ionic liquid with a common polymer binder B to construct a functionalized composite binder system which can be applied to preparation of a lithium battery electrode in electrode slurry. Compared with a traditional binder, after the composite binder is applied to the lithium battery, the electrode interface impedance of the lithium battery can be effectively reduced, the electrode reaction uniformity can be improved, the dosage of the conductive agent can be reduced, the charge-discharge performance and the cycle performance of the lithium battery can be greatly improved, and meanwhile the electrical insulation problem of the traditional binder can be solved.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery production technology, and specifically relates to a composite binder containing PVMPT ionic liquid, a lithium battery electrode using the composite binder, and a method for preparing the same. Background Technology

[0002] With rapid socio-economic development, global energy demand continues to rise, and the large-scale consumption of fossil fuels has triggered severe environmental pollution and ecological crises. In order to achieve a green transformation of the energy structure, building a new energy system dominated by clean and renewable energy has become a global consensus. Against this backdrop, secondary battery technology with high-efficiency energy storage and conversion characteristics has become a key infrastructure supporting the development of the new energy industry.

[0003] Among numerous electrochemical energy storage devices, lithium-ion batteries dominate the market due to their significant energy density advantage (>180Wh / kg) and are widely used in consumer electronics, electric vehicles, and smart grids due to their memory-free properties, wide temperature range adaptability, and environmental friendliness. However, existing lithium-ion battery systems still face the core challenge of cycle life degradation. Research shows that interfacial failure between electrode active materials and current collectors is a key factor leading to capacity decay. As the "mechanical framework" and "charge bridge" of the electrode microstructure, binders play a decisive role in maintaining electrode integrity and constructing conductive networks, but their functional design has not yet broken through the performance boundaries of traditional material systems.

[0004] Currently, commercial binders mainly employ a binary technology approach: ① Organic solvent-based binders, represented by polyvinylidene fluoride (PVDF), while possessing excellent chemical stability, suffer from significant electron / ion transport barriers within the electrode due to their inherent insulating properties; ② Water-based binders, represented by carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) composite systems, while reducing production costs, exhibit inherent drawbacks such as insufficient mechanical strength and poor resistance to swelling in high-voltage electrolytes. More critically, neither type of traditional binder can simultaneously meet the requirements of high-energy-density electrodes for dual electron-ion conductivity.

[0005] Theoretical analysis and experimental studies show a strong correlation between the intrinsic conductivity of the binder system and electrode polarization loss. When the binder exhibits dual electronic / ionic insulation properties, it forces charge carriers to circumvent the non-functional phase region, significantly increasing interfacial impedance and exacerbating reaction kinetic lag. This contradiction is particularly pronounced in advanced battery systems with high areal density and thick electrodes, and has become a common technical bottleneck restricting the development of high-energy-density lithium-ion batteries. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned problems by proposing a composite binder containing PVMPT ionic liquid, a lithium battery electrode, and a method for preparing the same.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A composite adhesive containing a PVMPT ionic liquid includes an ionic liquid A that increases conductivity and a polymeric binder B, wherein the mixing ratio of ionic liquid A to polymeric binder B is 1:1 to 1:9; wherein the ionic liquid A is a 3-vinyl-N-methylphenthiazide polymeric ionic liquid (PVMPT ionic liquid).

[0009] Preferably, the ionic liquid A is a 3-vinyl-N-methylphenothiazine polymer ionic liquid (PVMPT ionic liquid) obtained by polymerizing 3-vinyl-N-methylphenothiazine monomer, oxidizing it to generate free radical cations, doping it with temporary anions, and then exchanging it with target anions.

[0010] Preferably, the polymer binder B is one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylpyrrolidone (PVP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyvinyl alcohol (PVA), sodium alginate (Alg), β-cyclodextrin polymer (β-CDp), polypropylene emulsion (LA132), and polytetrafluoroethylene (PTFE), or any combination thereof.

[0011] This invention also provides a method for preparing a composite adhesive containing PVMPT ionic liquid, comprising the following steps:

[0012] Step S1: Prepare compound one, 3-formyl-N-methylphenthiazine;

[0013] Step S2: Prepare compound 2,3-vinyl-N-methylphenthiazide;

[0014] Step S3: The compound 2 obtained in step S2 is polymerized and ion-doped sequentially to obtain ionic liquid A, 3-vinyl-N-methylphenthiazide polymer ionic liquid;

[0015] Step S4: Mix the ionic liquid A obtained in step S3 with the polymer binder B in a certain proportion to obtain a composite binder containing PVMPT ionic liquid.

[0016] More preferably, compound one is prepared by the following method:

[0017] Step A1: Mix phosphorus oxychloride and N,N-dimethylformamide at room temperature for 2 hours;

[0018] Step A2: Add anhydrous dichloroethane solution containing 10-methylphenthiazide, stir at ambient temperature for 1 hour, then heat to 90°C and heat for 24 hours, with the ambient temperature range being 25±5°C.

[0019] Step A3: After the above reaction is completed, the product is extracted with dichloromethane and purified by column chromatography to obtain compound 1 (3-formyl-N-methylphenthiazide).

[0020] More preferably, compound two is prepared by the following method:

[0021] Step B1: Add methyltriphenylphosphine iodide and sodium hydride sequentially to anhydrous tetrahydrofuran solution, stir for 1 hour at ambient temperature, and then cool to 0°C. The ambient temperature range is 25±5°C.

[0022] Step B2: Add the compound I obtained in step S1 to a round-bottom flask, then add anhydrous tetrahydrofuran solution under an inert gas atmosphere, and sonicate for 10 min until compound I is completely dissolved; then add the anhydrous tetrahydrofuran solution containing compound I to the reaction system of step B1, then heat to ambient temperature and stir for 24 h, with the ambient temperature range being 25±5℃.

[0023] Step B3: After the above reaction is completed, the compound is extracted with dichloromethane and purified by column chromatography to obtain compound bis(3-vinyl-N-methylphenthiazide).

[0024] More preferably, the ionic liquid A is prepared by the following method:

[0025] Step C1: Add the compound 2 and azobisisobutyronitrile obtained in step S2 to anhydrous tetrahydrofuran solution, stir at 60-70°C for 1 week, then precipitate in methanol 3 times, and purify to obtain 3-vinyl-N-methylphenthiazide polymer (PVMPT).

[0026] Step C2: Nitrosine hexafluorophosphate and the 3-vinyl-N-methylphenothiazine polymer obtained in step C1 are added to anhydrous dichloromethane. Partial oxidation is carried out under an inert atmosphere to generate free radical cations via ion doping. Simultaneously, temporary anions are introduced through ion doping to form a charge transfer complex. The introduced temporary anion is hexafluorophosphate ion, with an ion doping degree >2%. Sodium trifluoromethanesulfonylimide is introduced into the partially doped polymer solution to induce ion exchange. The target anion for exchange is trifluoromethanesulfonylimide ion. The solution is then washed and purified with deionized water and vacuum dried to obtain a 3-vinyl-N-methylphenothiazine polymer ionic liquid (PVMPT ionic liquid).

[0027] The present invention also provides a lithium battery electrode comprising a composite binder containing the PVMPT ionic liquid, the lithium battery electrode comprising an electrode slurry and a current collector, the electrode slurry comprising an electrode active material, a composite binder containing the PVMPT ionic liquid, a conductive medium and a solvent.

[0028] The present invention also provides a method for preparing a lithium battery electrode, comprising the following steps: mixing an electrode active material, a composite binder containing a PVPPT ionic liquid and a conductive medium and dispersing them in a solvent to obtain an electrode slurry; then coating the electrode slurry onto a current collector and heating and drying it to obtain a lithium battery electrode.

[0029] Preferably, the mass ratio of the electrode active material, the composite binder containing PVMPT ionic liquid, and the conductive medium is 40–98:30–1:30–1.

[0030] Preferably, the amount of solvent used is 1 to 30 times the total weight of the electrode active material, the composite binder containing PVMPT ionic liquid, and the conductive medium.

[0031] Preferably, the conductive medium is selected from one or more of conductive graphite, carbon black, carbon nanorods, and carbon nanotubes, or any combination thereof.

[0032] Preferably, the solvent is selected from one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, ethanol, acetone, isopropanol, and deionized water.

[0033] Preferably, the current collector is selected from one of copper foil, aluminum foil, carbon-coated copper foil, carbon-coated aluminum foil, nickel mesh, copper mesh, aluminum mesh, stainless steel mesh, nickel foam, and carbon cloth.

[0034] Preferably, the electrode active material includes a positive electrode material and a negative electrode material, respectively selected from layered materials such as LiCoO2, ternary composite materials such as LiNi0.8 / Mn0.1 / Co0.1 / O2, spinel materials such as LiMn2O4, olivine structures such as LiFePO4, organic molecules such as anthraquinone, S, Li2S, O2, Si, Sn, graphite, metal sulfides such as FeS2, and metal oxides such as CuO.

[0035] More preferably, the electrode active material is selected from one of the high-nickel layered ternary material NCM811 and lithium iron phosphate.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] (1) The present invention achieves innovation through three levels: “molecular structure design - controllable doping - functional composite”. It designs and synthesizes phenothiazine polymers with π-π conjugated structure and dopable units, laying the foundation for “dual conductivity”. It adopts the strategy of “partial doping + ion exchange” to balance conductivity and mechanical properties, so that PVMPT ionic liquid has both electronic and ionic dual conductivity characteristics. By combining conductive polymer ionic liquid with traditional binders to form composite binders, the intrinsic conductivity of composite binders is given without sacrificing the bonding performance, breaking through the functional limitations of traditional binders.

[0038] (2) Compared with traditional binders, the composite binder containing PVMPT ionic liquid of the present invention can effectively reduce the interface impedance of lithium battery electrodes, improve the uniformity of electrode reaction, reduce the amount of conductive agent, and maintain the mechanical integrity of the electrode structure. While greatly improving the charge-discharge performance and cycle performance of lithium battery electrodes, enabling lithium batteries to have a longer charge-discharge cycle life, it can also effectively improve the electrical insulation problem of traditional binders, providing key material support for the development of high specific energy and long life lithium-ion batteries. Attached Figure Description

[0039] Figure 1 The PVMPT obtained in the embodiments of the present invention 1 H-NMR spectrum;

[0040] Figure 2 The CV curves of the half-cells of Example 1 and Comparative Example 1 of the present invention are shown in the third cycle.

[0041] Figure 3 The graph shows the cycling performance of the half-cells of Example 1 and Comparative Example 1 of the present invention at a current of 0.2C.

[0042] Figure 4 The graph shows the cycling performance of the half-cells of Example 2 and Comparative Example 2 of the present invention at a current of 0.2C.

[0043] Figure 5 The graph shows the cycling performance of the half-cells of Example 3 and Comparative Example 3 of the present invention at a current of 1C.

[0044] Figure 6 This is a comparison chart of the first discharge curves of the half-cell in Example 4 and Comparative Example 4 of the present invention. Detailed Implementation

[0045] To better illustrate the objectives, technical solutions, and advantages of this invention, the following embodiments are provided. Obviously, the following embodiments are only a part of the embodiments of this invention, and not all of them; it should be understood that the embodiments of this invention are only used to illustrate the technical effects of this invention, and not to limit the scope of protection of this invention.

[0046] This invention provides a composite binder containing a PVMPT ionic liquid, comprising an ionic liquid A that increases conductivity and a polymer binder B, wherein the mixing ratio of ionic liquid A to polymer binder B is 1:1 to 1:9; wherein the ionic liquid A is a 3-vinyl-N-methylphenthiazide polymer ionic liquid (PVMPT ionic liquid).

[0047] The higher the proportion of polymer binder B, the stronger the bonding effect; and the higher the proportion of ionic liquid A, the stronger the conductivity of the composite binder. Therefore, it is necessary to control the mixing ratio of the two between 1:1 and 1:9, while balancing the conductivity and viscosity of the composite binder system.

[0048] The ionic liquid A is a 3-vinyl-N-methylphenothiazine polymer ionic liquid (PVMPT ionic liquid) obtained by polymerizing 3-vinyl-N-methylphenothiazine monomers, oxidizing them to generate free radical cations, doping them with temporary anions, and then exchanging them with target anions.

[0049] The polymer binder B is one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylpyrrolidone (PVP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyvinyl alcohol (PVA), sodium alginate (Alg), β-cyclodextrin polymer (β-CDp), polypropylene emulsion (LA132), and polytetrafluoroethylene (PTFE), or any combination thereof.

[0050] This invention also provides a method for preparing a composite adhesive containing PVMPT ionic liquid, comprising the following steps:

[0051] Step S1: Prepare compound one, 3-formyl-N-methylphenthiazine;

[0052] Step S2: Prepare compound 2,3-vinyl-N-methylphenthiazide;

[0053] Step S3: The compound 2 obtained in step S2 is polymerized and ion-doped sequentially to obtain ionic liquid A, 3-vinyl-N-methylphenthiazide polymer ionic liquid;

[0054] Step S4: Mix the ionic liquid A obtained in step S3 with the polymer binder B in a certain proportion to obtain a composite binder containing PVMPT ionic liquid.

[0055] Specifically, compound one is prepared by the following method:

[0056] Step A1: Mix and stir phosphorus oxychloride (POCl3) and N,N-dimethylformamide (DMF) at room temperature for 2 hours;

[0057] Step A2: Add anhydrous dichloroethane solution (DCE) containing 10-methylphenothiazine, stir at ambient temperature for 1 hour, then heat to 90°C and heat for 24 hours, with the ambient temperature range being 25±5°C.

[0058] Step A3: After the above reaction is completed, the product is extracted with dichloromethane and purified by column chromatography to obtain compound 1 (3-formyl-N-methylphenthiazide).

[0059] In the presence of phosphorus oxychloride (POCl3) and N,N-dimethylformamide (DMF), 10-methylphenthiazide undergoes formylation at the C3 position to generate an aldehyde-modified compound (3-formyl-N-methylphenthiazide); the synthetic reaction equation for the preparation of compound one is as follows:

[0060]

[0061] Specifically, compound two is prepared by the following method:

[0062] Step B1: Add methyltriphenylphosphine iodide (Ph3PMeI) and sodium hydride (NaH) sequentially to anhydrous tetrahydrofuran solution (THF), stir for 1 hour at ambient temperature, and then cool to 0°C. The ambient temperature range is 25±5°C.

[0063] Step B2: Add the compound I obtained in step S1 to a round-bottom flask, then add anhydrous tetrahydrofuran solution under an inert gas atmosphere, and sonicate for 10 min until compound I is completely dissolved; then add the anhydrous tetrahydrofuran solution containing compound I to the reaction system of step B1, then heat to ambient temperature and stir for 24 h, with the ambient temperature range being 25±5℃.

[0064] Step B3: After the above reaction is completed, the compound is extracted with dichloromethane and purified by column chromatography to obtain compound bis(3-vinyl-N-methylphenthiazide).

[0065] Compound 1 (3-formyl-N-methylphenthiazine) reacts with methyltriphenylphosphine iodide (Ph3PMeI) in the presence of sodium hydride (NaH) via a Wittig ylide reaction to generate a vinyl-substituted compound 2 (3-vinyl-N-methylphenthiazine); the synthetic reaction equation for the preparation of compound 2 is as follows:

[0066]

[0067] Specifically, the ionic liquid A is prepared by the following method:

[0068] Step C1: Compound II and azobisisobutyronitrile (AIBN) obtained in step S2 were added to anhydrous tetrahydrofuran solution (THF) and stirred for 1 week at an ambient temperature of 70°C. Then, the mixture was precipitated three times in methanol and purified to obtain 3-vinyl-N-methylphenthiazide polymer (PVMPT).

[0069] Step C2: Nitrosine hexafluorophosphate (NOPF6) and the 3-vinyl-N-methylphenthiazide polymer obtained in step C1 are added to anhydrous dichloromethane. Partial oxidation is carried out under an inert atmosphere via ion doping to generate free radical cations. Simultaneously, temporary anions are introduced through ion doping to form a charge-transfer complex. The introduced temporary anion is the hexafluorophosphate ion (PF6). - The ion doping degree is >2%; sodium trifluoromethanesulfonyl imide (NaTFSI) is introduced into the partially doped polymer solution to induce ion exchange, with the target anion being trifluoromethanesulfonyl imide ions (TFSI). - The product was then washed and purified with deionized water and dried under vacuum to obtain 3-vinyl-N-methylphenthiazine polymer ionic liquid (PVMPT ionic liquid).

[0070] The chemical formula of the 3-vinyl-N-methylphenthiazine polymer is (C 15 H 13 NS) n n represents the degree of aggregation, which ranges from 50 to 100.

[0071] In step C1 above, the anhydrous tetrahydrofuran solution can be replaced with anhydrous benzene solution.

[0072] More specifically, in step C1 above, compound two undergoes free radical polymerization initiated by azobisisobutyronitrile (AIBN) to form a polymer with a vinyl backbone and N-methylphenathiazide side chains; the synthetic reaction equation for obtaining PVMPT is as follows:

[0073]

[0074] refer to Figure 1 PVMPT 1 The H-NMR spectrum matches the structure of the 3-vinyl-N-methylphenthiazide polymer. Key supporting evidence includes: characteristic peaks of aromatic ring hydrogen (δ7-8 ppm), with integral values ​​corresponding to the number of hydrogen atoms, proving the retention of the aromatic ring conjugated system; characteristic peaks of N-methyl hydrogen (δ≈2.95 ppm), with integral values ​​corresponding to the number of hydrogen atoms, proving the presence of the N-CH3 group; and a broad cluster of low-field peaks (δ0.5-2.5 ppm), corresponding to the hydrogen atoms in the saturated main chain after polymerization, which may overlap with some solvent peaks on this spectrum. Therefore, this NMR result proves the successful synthesis of PVMPT in step C1 above.

[0075] More specifically, in step C2 above, PVMPT is partially oxidized and ion-doped: NOPF6 selectively oxidizes some MPT units (approximately 26-50%) to generate PVMPT. + PF6 - , forming [MPT-MPT] + Pimer complex, enhances charge jumping;

[0076] Ion exchange: Sodium trifluoromethanesulfonyl imide (NaTFSI) was used to replace hexafluorophosphate ions (PF6). - ), trifluoromethanesulfonyl imide ion (TFSI) - The soft anion properties of ) maintain low T g (Glass transition temperature) and improve stability;

[0077] The ion doping reaction equation for the preparation of PVMPT ionic liquid is as follows:

[0078]

[0079] The mechanism of action in step C2 above is: constructing an "electron-ion" dual-conductivity network.

[0080] (1) Electron conduction mechanism

[0081] π-π conjugation and hole hopping conduction: The phenothiazine unit in the PVMPT ionic liquid possesses a rigid π-π conjugated framework, in which the lone pair electrons of the nitrogen and sulfur heteroatoms participate in delocalization, providing pathways for charge transport. Neutral PVMPT acts as an insulator. After oxidative doping, the phenothiazine forms a radical cation (MPT). + Through intermolecular π-π stacking, hole delocalization channels are formed, enabling electron hopping and conduction between polymer chains.

[0082] Formation of the charge transfer complex (pimer): By controlling partial doping (approximately 26%–50% oxidation), neutral MPT and oxidized MPT are formed. + To form an optimal ratio of charge-transfer complexes (pimers), thereby significantly improving the electron hopping rate while avoiding the pmer structure disruption (chain stiffness) and decreased charge mobility (conductivity) caused by complete doping; simultaneously, anions (such as PF6) - The introduction of electrons can maintain charge balance, and their migration can contribute to ionic conductivity. Through the synergistic effect of ensuring the continuous progress of redox reactions, dual electron-ion conductivity is achieved.

[0083] (2) Ion conduction mechanism

[0084] Counterion migration mechanism: The introduction of anions (such as TFSI) -Under the influence of an electric field, they can migrate and contribute to ionic conductivity.

[0085] Plasticizing effect: TFSI - Large-volume soft anions have a certain plasticizing effect, which can inhibit electrostatic hardening between polymer chains, maintain the flexibility of materials and the ability of chain segments to move, and facilitate ion transport.

[0086] (3) Synergistic effect

[0087] PVMPT ionic liquids possess both electron-ion dual conductivity properties, enabling the construction of a "dual conductivity network" within the electrode. This simultaneously promotes the transport of electrons and lithium ions, significantly reduces electrode polarization, and improves reaction kinetics.

[0088] In particular, the ion doping degree of the PVMPT ionic liquid is >2%, which means that a sufficient number of phenothiazine units are oxidized to free radical cations (PTZ). + However, the doping degree cannot be too high, because ion intercalation will swell the polymer and generate mechanical stress. Therefore, in order to achieve the best balance between charge transport efficiency and material mechanical properties, this invention adopts partial doping (about 26-50% oxidation) rather than complete doping in the polymer solution, and effectively controls it through the strategy of "partial doping" and "low proportion blending".

[0089] In addition, partial doping can maintain the flexibility of the material and increase the glass transition temperature only slightly. This is due to the plasticizing effect of trifluoromethanesulfonyl imide ions (TFSI-) which inhibits interchain electrostatic hardening. In contrast, complete doping may cause a significant increase in Tg, leading to brittleness of the material.

[0090] This invention achieves innovation through three levels: "molecular structure design, controllable doping, and functional compositing." It designs and synthesizes phenothiazine polymers with π-π conjugated structures and dopable units, laying the foundation for dual conductivity. It adopts a "partial doping + ion exchange" strategy to balance conductivity and mechanical properties, enabling PVMPT ionic liquids to possess both electronic and ionic dual conductivity characteristics. By combining conductive polymer ionic liquids with traditional binders to form composite binders, intrinsic conductivity is imparted to the composite binders without sacrificing adhesive performance, thus breaking through the functional limitations of traditional binders.

[0091] The present invention also provides a lithium battery electrode comprising a composite binder containing the PVMPT ionic liquid, the lithium battery electrode comprising an electrode slurry and a current collector, the electrode slurry comprising an electrode active material, a composite binder containing the PVMPT ionic liquid, a conductive medium and a solvent.

[0092] Specifically, the preparation method of the lithium battery electrode includes the following steps: mixing and dispersing the electrode active material, the composite binder containing PVMPT ionic liquid and the conductive medium in a solvent to obtain an electrode slurry, then coating the electrode slurry onto a current collector, heating and drying to obtain the lithium battery electrode.

[0093] The heating and drying process involves vacuum heating to 60°C or 70°C and drying at an ambient temperature of 60°C or 70°C for 24 hours.

[0094] The mass ratio of the electrode active material, the composite binder containing PVMPT ionic liquid, and the conductive medium is 40–98:30–1:30–1.

[0095] The amount of solvent used is 1 to 30 times the total weight of the electrode active material, the composite binder containing PVMPT ionic liquid, and the conductive medium.

[0096] The conductive medium is selected from one or more of conductive graphite, carbon black, carbon nanorods, and carbon nanotubes, or any combination thereof, wherein the carbon black includes acetylene black.

[0097] The solvent is selected from one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, ethanol, acetone, isopropanol, and deionized water.

[0098] The current collector is selected from one of the following: copper foil, aluminum foil, carbon-coated copper foil, carbon-coated aluminum foil, nickel mesh, copper mesh, aluminum mesh, stainless steel mesh, nickel foam, and carbon cloth.

[0099] The electrode active materials include positive electrode materials and negative electrode materials, which are respectively selected from layered materials such as LiCoO2, ternary composite materials such as LiNi0.8 / Mn0.1 / Co0.1 / O2, spinel materials such as LiMn2O4, olivine structures such as LiFePO4, organic molecules such as anthraquinone, S, Li2S, O2, Si, Sn, graphite, metal sulfides such as FeS2, and metal oxides such as CuO.

[0100] Specifically, the electrode active material is selected from one of the high-nickel layered ternary material NCM811 and lithium iron phosphate (LFP).

[0101] The lithium battery electrode is one of the high-nickel ternary material NCM cathode and lithium iron phosphate cathode used as the positive electrode of the lithium battery.

[0102] The present invention will be further described below with reference to specific embodiments.

[0103] Example 1

[0104] Fabrication of NCM / PVDF-PVMPT lithium battery electrodes:

[0105] High-nickel layered ternary material NCM811 was selected as the electrode active material, carbon black was selected as the conductive medium, and PVDF-PVMPT composite binder, prepared by mixing the above-prepared PVMPT ionic liquid with PVDF in a ratio of 1:9, was used as the binder in the electrode slurry.

[0106] The electrode active material, composite binder and carbon black were mixed in a mass ratio of 80:10:10, and after being mixed evenly, they were dispersed in N-methylpyrrolidone solvent to obtain the electrode slurry.

[0107] The electrode slurry was then coated onto aluminum foil, vacuum heated, and dried at 60°C for 24 hours to obtain a lithium battery electrode (NCM / PVDF-PVMPT) containing PVDF-PVMPT composite binder, which can be used as the NCM811 positive electrode for lithium batteries.

[0108] Compare with Example 1

[0109] Fabrication of NCM / PVDF lithium battery electrodes:

[0110] The PVDF-PVMPT composite binder used above was replaced with pure PVDF binder, and the lithium battery electrode was prepared according to the method of preparing lithium battery electrode in Example 1 above, to obtain a lithium battery electrode (NCM / PVDF) containing pure PVDF binder.

[0111] 1. Comparison of battery performance tests of lithium battery electrodes prepared in Example 1 and Comparative Example 1

[0112] (1) The lithium battery electrodes obtained in Example 1 and Comparative Example 1 were respectively made into half cells containing the lithium battery electrodes, namely NCM / PVDF-PVMPT half cells and NCM / PVDF half cells.

[0113] (2) See Figure 2 The CV curve shows three pairs of redox peaks, which correspond to...

[0114] Ni 2+ / Ni 3+ Ni 3+ / Ni 4+ and Co 3+ / Co 4+ The redox reaction, where the black line corresponds to...

[0115] The CV curves of the NCM / PVDF half-cell are shown, with the red line corresponding to the CV curve of the NCM / PVDF-PVMPT half-cell. The graph shows that the oxidation peak intensity is relatively weakened around 4.1V in the PVMPT-doped half-cell, indicating that using a composite binder containing PVMPT ionic liquid is beneficial for suppressing the phase transition of the cathode material. Simultaneously, after doping, the three pairs of redox peaks show virtually no change, indicating that the introduction of PVMPT ionic liquid does not participate in the electrochemical reaction and affect the electrochemical stability of the cathode.

[0116] (3) See Figure 3 The battery material cycle performance graph, with the horizontal axis representing the number of cycles, the left vertical axis representing the specific capacity (mAh / g), and the right vertical axis representing the coulombic efficiency (%), is used to compare the electrochemical performance of electrode materials using PVDF and PVDF-PVMPT binders:

[0117] (3.1) Specific capacity (left curve, mAh / g)

[0118] Compare with Example 1, NCM / PVDF half-cell (black curve):

[0119] The initial specific capacity of the NCM / PVDF half-cell was 161.7 mAh / g, which was lower than that of the NCM / PVDF-PVMPT half-cell. Furthermore, the specific capacity decayed rapidly during cycling, and by the time of 80 cycles, the capacity had dropped significantly to 120.2 mAh / g. This indicates that the electrode structure of the NCM / PVDF half-cell (Comparative Example 1) has relatively poor cycling stability.

[0120] Example 1, NCM / PVDF-PVMPT half-cell (red curve):

[0121] The NCM / PVDF-PVMPT half-cell exhibits a high initial discharge specific capacity of 176.9 mAh / g. Furthermore, its specific capacity decays very slowly over approximately 80 cycles, remaining at a consistently high level. After 80 cycles, the discharge specific capacity is 148.4 mAh / g (the final NCM / PVDF-PVMPT capacity is still significantly higher than that of NCM / PVDF). This indicates that the electrode structure of the NCM / PVDF-PVMPT half-cell (Example 1) demonstrates better high-voltage cycling stability and can continuously provide high capacity.

[0122] (3.2) Coulomb efficiency (right-hand implied trend, %)

[0123] Coulombic efficiency reflects the "match between discharge capacity and charge capacity" during the charge and discharge process (the higher the efficiency, the better the reversibility); combined with the curve trend: the half-cell charge and discharge reversibility of lithium battery electrodes using pure PVDF binder and PVDF-PVMPT composite binder are both good, and the coulombic efficiency is almost close to 100%.

[0124] Conclusion: Compared with using pure PVDF as a binder in the electrode slurry, the resulting NCM811 cathode is used for assembling lithium batteries. The present invention uses a mixture of PVMPT ionic liquid and PVDF as a binder in the electrode slurry, and the resulting NCM811 cathode is used for assembling lithium batteries, which greatly improves the battery cycle performance and electrode stability.

[0125] Example 2

[0126] Fabrication of NCM / PAA-PVMPT lithium battery electrodes:

[0127] High-nickel layered ternary material NCM811 was selected as the electrode active material, carbon black was selected as the conductive medium, and PAA-PVMPT composite binder, prepared by mixing the PVMPT ionic liquid obtained above with PAA in a ratio of 1:9, was used as the binder in the electrode slurry.

[0128] The electrode active material, composite binder and carbon black were mixed in a mass ratio of 80:10:10. After being mixed evenly, the mixture was dispersed in a deionized water solvent to obtain the electrode slurry.

[0129] The electrode slurry was then coated onto aluminum foil, vacuum heated, and dried at 70°C for 24 hours to obtain a lithium battery electrode (NCM / PAA-PVMPT) containing PAA-PVMPT composite binder, which can be used as the NCM811 positive electrode for lithium batteries.

[0130] Compare with Example 2

[0131] Fabrication of NCM / PAA lithium battery electrodes:

[0132] The PAA-PVMPT composite binder used above was replaced with pure PAA binder, and the lithium battery electrode was prepared according to the method of preparing lithium battery electrode in Example 2 above, to obtain a lithium battery electrode (NCM / PAA) containing pure PAA binder.

[0133] 2. Comparison of battery performance tests between lithium battery electrodes prepared in Example 2 and Comparative Example 2

[0134] (1) The lithium battery electrodes obtained in Example 2 and Comparative Example 2 were respectively made into half cells containing the lithium battery electrodes, namely NCM / PAA-PVMPT half cells and NCM / PAA half cells.

[0135] (2) See Figure 4 The battery material cycle performance graph, with the horizontal axis representing the number of cycles, the left vertical axis representing the specific capacity (mAh / g), and the right vertical axis representing the coulombic efficiency (%), is used to compare the electrochemical performance of electrode materials using PAA and PAA-PVMPT binders:

[0136] (2.1) Specific capacity (left curve, mAh / g)

[0137] Compare with Example 2, NCM / PAA half-cell (black curve):

[0138] The initial specific capacity of the NCM / PAA half-cell was 103 mAh / g, which was lower than that of the NCM / PAA-PVMPT half-cell. Furthermore, the specific capacity decayed rapidly during cycling, and by the time of 200 cycles, the capacity had dropped significantly to 93 mAh / g. This indicates that the NCM / PAA half-cell (Control Example 2) has relatively poor cycling stability.

[0139] Example 2, NCM / PAA-PVMPT half-cell (red curve):

[0140] The NCM / PAA-PVMPT half-cell exhibits a high initial discharge specific capacity of 129 mAh / g. Although its specific capacity decreases somewhat over approximately 200 cycles, it remains at a high level overall, with a discharge specific capacity of 112 mAh / g after 200 cycles (the final NCM / PAA-PVMPT is still much higher than NCM / PAA). This indicates that the NCM / PAA-PVMPT half-cell (Example 2) has good electrode structure stability and exhibits better charge and discharge performance.

[0141] (2.2) Coulomb efficiency (right-hand implied trend, %)

[0142] Coulombic efficiency reflects the "match between discharge capacity and charge capacity" during charge and discharge (higher efficiency indicates better reversibility). Based on the curve trends: lithium battery electrodes using PAA-PVMPT composite binders exhibit better half-cell charge-discharge reversibility, with coulombic efficiency approaching 100%. Lithium battery electrodes using pure PAA binders show poorer half-cell charge-discharge reversibility, with particularly low and unstable coulombic efficiency in the first 50 cycles. While subsequent changes occur, the overall efficiency remains significantly lower than the PAA-PVMPT system. Conclusion: Compared to using pure PAA as a binder in the electrode slurry, the resulting NCM811 cathode is suitable for assembling lithium batteries. This invention uses a mixture of PVPPT ionic liquid and PAA as a binder in the electrode slurry, resulting in an NCM811 cathode that significantly improves battery cycle performance when used in lithium battery assembly.

[0143] Example 3

[0144] Preparation of LFP / PVDF-PVMPT lithium battery electrodes:

[0145] Lithium iron phosphate was selected as the electrode active material, carbon black was selected as the conductive medium, and PVDF-PVMPT composite binder, prepared by mixing the above-prepared PVMPT ionic liquid and PVDF in a ratio of 1:9, was used as the binder in the electrode slurry.

[0146] The electrode active material, composite binder and carbon black were mixed in a mass ratio of 80:10:10, and after being mixed evenly, they were dispersed in N-methylpyrrolidone solvent to obtain the electrode slurry.

[0147] The electrode slurry was then coated onto aluminum foil, vacuum heated, and dried at 60°C for 24 hours to obtain a lithium battery electrode (LFP / PVDF-PVMPT) containing PVDF-PVMPT composite binder, which can be used as a lithium iron phosphate cathode for lithium batteries.

[0148] Compare with Example 3

[0149] Fabrication of LFP / PVDF lithium battery electrodes:

[0150] The PVDF-PVMPT composite binder used above was replaced with pure PVDF binder, and the lithium battery electrode was prepared according to the method of preparing lithium battery electrode in Example 3 above, to obtain a lithium battery electrode (LFP / PVDF) containing pure PVDF binder.

[0151] 3. Comparison of battery performance tests between the lithium battery electrodes prepared in Example 3 and Comparative Example 3

[0152] (1) The lithium battery electrodes obtained in Example 3 and Comparative Example 3 were respectively made into half cells containing the lithium battery electrodes, namely LFP / PVDF-PVMPT half cells and LFP / PVDF half cells.

[0153] (2) See Figure 5 The battery material cycle performance graph, with the horizontal axis representing the number of cycles, the left vertical axis representing the specific capacity (mAh / g), and the right vertical axis representing the coulombic efficiency (%), is used to compare the electrochemical performance of electrode materials using PVDF and PVDF-PVMPT binders:

[0154] (2.1) Specific capacity (left curve, mAh / g)

[0155] Compare with Example 3, LFP / PVDF half-cell (black curve):

[0156] The initial specific capacity of the LFP / PVDF half-cell was 138 mAh / g, which was lower than that of the LFP / PVDF-PVMPT half-cell. Furthermore, the specific capacity decayed rapidly during cycling, and by the time of 200 cycles, the capacity had dropped significantly to 115 mAh / g. This indicates that the LFP / PVDF half-cell (Control Example 2) has relatively poor cycling stability.

[0157] Example 3, LFP / PVDF-PVMPT half-cell (red curve):

[0158] The LFP / PVDF-PVMPT half-cell exhibits a high initial discharge specific capacity of 148 mAh / g, and its specific capacity decays very slowly over approximately 200 cycles, remaining at a high level. After 200 cycles, the discharge specific capacity is 125 mAh / g (the final LFP / PVDF-PVMPT is still much higher than LFP / PVDF). This indicates that the LFP / PVDF-PVMPT half-cell (Example 3) has good electrode structure stability, can continuously provide high capacity, and exhibits better cycle performance.

[0159] (2.2) Coulomb efficiency (right-hand implied trend, %)

[0160] Coulombic efficiency reflects the "match between discharge capacity and charge capacity" during the charge and discharge process (the higher the efficiency, the better the reversibility); combined with the curve trend: the half-cell charge and discharge reversibility of lithium battery electrodes using pure PVDF binder and PVDF-PVMPT composite binder are both good, and the coulombic efficiency is almost close to 100%.

[0161] Conclusion: Compared to using pure PVDF as a binder in the electrode slurry, the resulting lithium iron phosphate cathode is used for assembling lithium batteries. The present invention uses a mixture of PVMPT ionic liquid and PVDF as a binder in the electrode slurry, and the resulting lithium iron phosphate cathode is used for assembling lithium batteries, which has a significantly improved battery cycle performance.

[0162] Example 4

[0163] Fabrication of LFP / PVMPT lithium battery electrodes:

[0164] Lithium iron phosphate (LFP) was selected as the electrode active material, carbon black was selected as the conductive medium, and the PVMPT ionic liquid prepared above was used as the binder in the electrode slurry.

[0165] The electrode active material, binder and carbon black were mixed in a mass ratio of 80:10:10, and after being mixed evenly, they were dispersed in N-methylpyrrolidone solvent to obtain the electrode slurry.

[0166] The electrode slurry was then coated onto aluminum foil, vacuum heated, and dried at 60°C for 24 hours to obtain a lithium battery electrode (LFP / PVMPT) containing PVMPT binder, which can be used as a lithium iron phosphate cathode for lithium batteries.

[0167] Compare with Example 4

[0168] Fabrication of LFP / PVDF lithium battery electrodes:

[0169] The PVMPT binder used above was replaced with pure PVDF binder, and the lithium battery electrode was prepared according to the method of preparing lithium battery electrode in Example 4 above, to obtain a lithium battery electrode (LFP / PVDF) containing pure PVDF binder.

[0170] 4. Comparison of battery performance tests between the lithium battery electrodes prepared in Example 4 and Comparative Example 4

[0171] (1) The lithium battery electrodes obtained in Example 4 and Comparative Example 4 were respectively made into half cells containing the lithium battery electrodes, namely LFP / PVMPT half cells and LFP / PVDF half cells.

[0172] (2) See Figure 6 The graph shows a comparison of the first-cycle discharge curves of the batteries. The horizontal axis represents the number of cycles, the horizontal axis represents the specific capacity (mAh / g), and the vertical axis represents the voltage (V). This graph is used to compare the discharge voltage characteristics of electrode materials using PVDF and PVMPT binders.

[0173] The initial discharge specific capacities of the LFP / PVDF half-cell (Comparative Example 4) and the LFP / PVMPT half-cell (Example 4) were 138 mAh / g and 152 mAh / g, respectively.

[0174] From the capacity range covered by the curve, the LFP / PVMPT half cell (Example 4) can release more capacity in the higher voltage range (the capacity covered by the "plateau segment + subsequent drop segment" of the discharge curve is wider), while the LFP / PVDF half cell (Comparative Example 4) not only drops voltage quickly, but also releases a larger proportion of capacity in the low voltage range, which means that its energy efficiency is relatively low.

[0175] Furthermore, the discharge curve of the LFP / PVMPT half-cell (Example 4) showed relatively better voltage stability, a longer stable discharge plateau, and a higher cutoff voltage, indicating that when PVMPT ionic liquid is used as a related component (such as a binder), it can improve the discharge characteristics of the battery and enhance the reversibility of the electrochemical reaction and energy output efficiency. In contrast, the LFP / PVDF half-cell (Control Example 4) showed weaker discharge voltage stability and energy output performance.

[0176] Conclusion: Compared with using pure PVDF as a binder in the electrode slurry, the resulting lithium iron phosphate cathode is used to assemble lithium batteries. Using PVMPT ionic liquid as a binder in the electrode slurry, the resulting lithium iron phosphate cathode is used to assemble lithium batteries, and the battery charge and discharge performance is greatly improved.

[0177] In summary, compared with lithium batteries obtained using traditional pure polyvinylidene fluoride (PVDF) binders or pure polyacrylic acid (PAA) binders, lithium batteries obtained using the composite binder containing PVMPT ionic liquid of the present invention exhibit significantly improved charge-discharge performance and cycle performance, which also demonstrates that it can effectively improve the electrical insulation problem of traditional binders.

[0178] The effect of the composite binder containing PVMPT ionic liquid of the present invention on lithium battery electrodes:

[0179] (1) Reduce interface impedance

[0180] Traditional insulating binders (such as PVDF) create an electron / ion transport barrier between the active material and the conductive agent, leading to increased interfacial impedance. However, the composite binder containing PVMPT ionic liquid of the present invention can form a conductive coating layer on the surface of the active material particles, providing additional electron / ion transport paths and effectively reducing the internal impedance of the electrode.

[0181] (2) Improve the uniformity of electrode reaction

[0182] The "electron-ion" dual conductive network of the composite binder containing PVMPT ionic liquid of the present invention helps to uniformly distribute current and lithium ions in the electrode thickness direction, avoiding excessive local current or lithium ion concentration polarization, which is particularly advantageous in high areal density thick electrodes.

[0183] (3) Reduce the amount of conductive agent used

[0184] Traditional electrodes require a large amount of conductive agents (such as carbon black) to build a conductive network, while the composite binder containing PVMPT ionic liquid of the present invention is itself conductive and can partially replace conductive agents, thereby increasing the proportion of active material in the electrode and improving energy density.

[0185] The embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A composite adhesive containing PVMPT ionic liquid, characterized in that, It includes an ionic liquid A that increases conductivity and a polymer binder B, with the mixing ratio of ionic liquid A to polymer binder B being 1:1 to 1:9; the ionic liquid A is a 3-vinyl-N-methylphenthiazide polymeric ionic liquid (PVMPT ionic liquid).

2. The composite binder containing PVMPT ionic liquid according to claim 1, characterized in that, The ionic liquid A is a 3-vinyl-N-methylphenothiazine polymer ionic liquid (PVMPT ionic liquid) obtained by polymerizing 3-vinyl-N-methylphenothiazine monomers, oxidizing them to generate free radical cations, doping them with temporary anions, and then exchanging them with target anions.

3. The composite binder containing PVMPT ionic liquid according to claim 1, characterized in that, The polymer binder B is one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylpyrrolidone (PVP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyvinyl alcohol (PVA), sodium alginate (Alg), β-cyclodextrin polymer (β-CDp), polypropylene emulsion (LA132), and polytetrafluoroethylene (PTFE), or any combination thereof.

4. A method for preparing a composite adhesive containing PVMPT ionic liquid, characterized in that, Includes the following steps: Step S1: Prepare compound one, 3-formyl-N-methylphenthiazine; Step S2: Prepare compound 2,3-vinyl-N-methylphenthiazide; Step S3: The compound 2 obtained in step S2 is polymerized and ion-doped sequentially to obtain ionic liquid A, 3-vinyl-N-methylphenthiazide polymer ionic liquid; Step S4: Mix the ionic liquid A obtained in step S3 with the polymer binder B in a certain proportion to obtain a composite binder containing PVMPT ionic liquid.

5. The method for preparing the composite adhesive containing PVMPT ionic liquid according to claim 4, characterized in that, The compound one is prepared by the following method: Step A1: Mix phosphorus oxychloride and N,N-dimethylformamide at room temperature for 2 hours; Step A2: Add anhydrous dichloroethane solution containing 10-methylphenthiazide, stir at ambient temperature for 1 hour, then heat to 90°C and heat for 24 hours, with the ambient temperature range being 25±5°C. Step A3: After the above reaction is completed, the product is extracted with dichloromethane and purified by column chromatography to obtain compound 1 (3-formyl-N-methylphenthiazide).

6. The method for preparing the composite binder containing PVMPT ionic liquid according to claim 4, characterized in that, Compound 2 was prepared by the following method: Step B1: Add methyltriphenylphosphine iodide and sodium hydride sequentially to anhydrous tetrahydrofuran solution, stir for 1 hour at ambient temperature, and then cool to 0°C. The ambient temperature range is 25±5°C. Step B2: Add the compound I obtained in step S1 to a round-bottom flask, then add anhydrous tetrahydrofuran solution under an inert gas atmosphere, and sonicate for 10 min until compound I is completely dissolved; then add the anhydrous tetrahydrofuran solution containing compound I to the reaction system of step B1, then heat to ambient temperature and stir for 24 h, with the ambient temperature range being 25±5℃. Step B3: After the above reaction is completed, the compound is extracted with dichloromethane and purified by column chromatography to obtain compound bis(3-vinyl-N-methylphenthiazide).

7. The method for preparing the composite binder containing PVMPT ionic liquid according to claim 4, characterized in that, The ionic liquid A is prepared by the following method: Step C1: Add the compound 2 and azobisisobutyronitrile obtained in step S2 to anhydrous tetrahydrofuran solution, stir at 60-70°C for 1 week, then precipitate in methanol 3 times, and purify to obtain 3-vinyl-N-methylphenthiazide polymer (PVMPT). Step C2: Nitrosine hexafluorophosphate and the 3-vinyl-N-methylphenothiazine polymer obtained in step C1 are added to anhydrous dichloromethane and partially oxidized in an inert atmosphere to generate free radical cations. Simultaneously, ion doping is performed to introduce temporary anions to form a charge transfer complex. The temporary anion introduced by doping is hexafluorophosphate ion, and its ion doping degree is >2%. Sodium trifluoromethanesulfonylimide is introduced into the partially doped polymer solution to induce ion exchange. The target anion for exchange is trifluoromethanesulfonylimide ion. Subsequently, the solution is washed and purified with deionized water and dried under vacuum to obtain 3-vinyl-N-methylphenothiazine polymer ionic liquid (PVMPT ionic liquid).

8. A lithium battery electrode comprising a composite binder containing a PVMPT ionic liquid as described in any one of claims 1-7, characterized in that, The lithium battery electrode includes an electrode slurry and a current collector. The electrode slurry includes an electrode active material, a composite binder containing PVMPT ionic liquid, a conductive medium, and a solvent.

9. A method for preparing a lithium battery electrode according to claim 8, characterized in that, The preparation method includes the following steps: mixing and dispersing the electrode active material, the composite binder containing PVMPT ionic liquid and the conductive medium in a solvent to obtain an electrode slurry; then coating the electrode slurry onto a current collector and heating and drying it to obtain a lithium battery electrode.

10. The method for preparing a lithium battery electrode according to claim 9, characterized in that, The mass ratio of the electrode active material, the composite binder containing PVMPT ionic liquid, and the conductive medium is 40–98:30–1:30–1; the amount of solvent used is 1–30 times the total weight of the electrode active material, the composite binder containing PVMPT ionic liquid, and the conductive medium.

11. The method for preparing a lithium battery electrode according to claim 9, characterized in that, The conductive medium is selected from one or more of conductive graphite, carbon black, carbon nanorods, and carbon nanotubes, or any combination thereof; the solvent is selected from one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, ethanol, acetone, isopropanol, and deionized water; the current collector is selected from one of copper foil, aluminum foil, carbon-coated copper foil, carbon-coated aluminum foil, nickel mesh, copper mesh, aluminum mesh, stainless steel mesh, nickel foam, and carbon cloth.

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