Lithium battery positive electrode slurry and preparation method thereof, positive plate and lithium battery

Abstract

The invention provides lithium battery positive electrode slurry and a preparation method thereof, a positive plate and a lithium battery, and belongs to the field of lithium batteries. The positive electrode slurry comprises a positive electrode active material, a conductive agent, a binder and a solvent, the mass ratio of the positive active material to the conductive agent to the binder is (94-97.5): (1-2): (1.5-3); the positive active material is a high-nickel ternary lithium oxide coated with lithium phosphate and a carbon layer on the surface; the conductive agent is composed of carboxylated carbon nanotubes, aminated conductive carbon black and carbon quantum dots with epoxy groups on the surfaces; the binding agent is a polyvinylidene fluoride-graft-polyamide imide copolymer; the solvent is prepared from N-methyl pyrrolidone and 1-ethyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt. According to the invention, through collaborative design of multiple components in molecule and microstructure levels, the core contradiction that the electron / ion transmission efficiency and the long-term stability of the electrode structure in a high-nickel positive electrode system are difficult to achieve at the same time is systematically solved.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a lithium battery positive electrode slurry and its preparation method, a positive electrode sheet, and a lithium battery. Background Technology

[0002] In the current development of high-energy-density lithium-ion batteries, the use of high-nickel cathode materials is the mainstream approach to improve energy density. However, their inherent characteristics make the electron / ion transport efficiency of the cathode electrode and the long-term cycle stability of the electrode structure two goals that are difficult to achieve simultaneously within the framework of traditional technologies.

[0003] On the one hand, to achieve higher electron / ion transport efficiency and improve rate performance, it is typically necessary to construct a highly permeable conductive network and maintain open ion transport channels. This often leads to strategies such as increasing the content of conductive agents, reducing electrode compaction density, or using thinner interface layers. However, these methods can directly or indirectly weaken the mechanical integrity of the electrode: excessive conductive agents may disrupt the continuity of the binder network; excessively low compaction density or excessively thin interface protective layers make the active material particles more susceptible to direct friction and cracking during long-term cycling volume changes, and they are more likely to undergo continuous side reactions with the electrolyte, resulting in accelerated electrode structure failure and rapid capacity decay. On the other hand, to enhance the long-term cycling stability of the electrode structure and extend its lifespan, conventional methods involve strengthening the physical constraint and chemical protection of the active material particles. For example, using thicker and stronger coating layers, or increasing the amount of binder to form a more robust adhesive network. However, these reinforcement measures often introduce new problems: excessively thick coatings may hinder lithium-ion insertion / extraction kinetics; while excessive binders or overly dense electrode structures can encapsulate active materials and conductive agents, blocking electron transport paths and ion diffusion channels, increasing electrode internal resistance, and severely sacrificing the battery's power characteristics and fast-charging capability. Therefore, under traditional material systems and processes, there is a significant trade-off between transport efficiency and structural stability, making simultaneous optimization difficult. Summary of the Invention

[0004] This application provides a lithium battery cathode slurry and its preparation method, a cathode sheet, and a lithium battery to solve the following technical problem: how to simultaneously improve the electron / ion transport efficiency of the cathode electrode and the long-term cycle stability of the electrode structure in a high-energy-density system using high-nickel cathode materials.

[0005] In a first aspect, embodiments of this application provide a positive electrode slurry for a lithium-ion battery, the positive electrode slurry comprising: a positive electrode active material, a conductive agent, a binder, and a solvent;

[0006] The mass ratio of the positive electrode active material, conductive agent, and binder is (94-97.5):(1-2):(1.5-3);

[0007] The solid content of the positive electrode slurry is 35-45%;

[0008] The positive electrode active material is a high-nickel ternary lithium oxide with a surface coated with lithium phosphate and a carbon layer;

[0009] The conductive agent is composed of carboxylated carbon nanotubes, aminated conductive carbon black, and carbon quantum dots with epoxy groups on their surface.

[0010] The adhesive is a polyvinylidene fluoride-grafted-polyamide-imide copolymer;

[0011] The solvent consists of N-methylpyrrolidone and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0012] Optionally, the mass ratio of the carboxylated carbon nanotubes, the aminated conductive carbon black, and the epoxy-containing carbon quantum dots on the surface is (0.5-1.5):(0.5-1.5):(0.1-0.5).

[0013] Optionally, the mass of the 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is 0.5 to 5% of the total mass of the solvent.

[0014] Optionally, the preparation method of the positive electrode active material includes the following steps:

[0015] S101. High-nickel ternary lithium oxide is dispersed in a solution of lithium hydroxide and ammonium dihydrogen phosphate, and then dried to obtain the precursor.

[0016] S102. The precursor is sintered at 400-600°C for 2-6 hours to form a lithium phosphate coating layer on the surface of the high-nickel ternary lithium oxide, thereby obtaining a coating.

[0017] S103. Under an inert atmosphere, the coating material is mixed with glucose and then heat-treated at 500-700°C for 1-4 hours to form a carbon layer on the outside of the lithium phosphate coating layer, thereby obtaining the positive electrode active material.

[0018] Optionally, the molar ratio of lithium hydroxide to ammonium dihydrogen phosphate is (3.0-3.5):1;

[0019] The mass of the ammonium dihydrogen phosphate is 0.5% to 3.0% of the mass of the high-nickel ternary lithium oxide;

[0020] The glucose content is 0.5% to 2.0% of the coating material.

[0021] Optionally, the method for preparing the adhesive includes the following steps:

[0022] S201. Polyvinylidene fluoride is dissolved in N-methylpyrrolidone, then potassium hydroxide and tetrabutylammonium bromide are added, and the reaction is carried out at 60-90℃ for 0.5-3h to defluorinate the polyvinylidene fluoride main chain and obtain a functionalized polyvinylidene fluoride solution.

[0023] S202. Under nitrogen protection, trimellitic anhydride, 4,4'-diaminodiphenyl ether and triethylamine are added to the functionalized polyvinylidene fluoride solution, and then the mixture is stirred and reacted at 80-120°C for 4-12 hours to allow polyamide imide to be grafted onto the functionalized polyvinylidene fluoride. The adhesive is obtained after post-treatment.

[0024] Optionally, the mass ratio of the polyvinylidene fluoride, the potassium hydroxide, and the tetrabutylammonium bromide is 1:(0.05-0.20):(0.005-0.10);

[0025] The molar ratio of trimellitic anhydride to 4,4'-diaminodiphenyl ether is 1:(0.9-1.1);

[0026] The ratio of the total mass of the trimellitic anhydride and the 4,4'-diaminodiphenyl ether to the mass of the polyvinylidene fluoride is (0.10-0.50):1;

[0027] The mass ratio of triethylamine to trimellitic anhydride is (0.05–0.20):1.

[0028] Secondly, embodiments of this application provide a method for preparing the positive electrode slurry of a lithium-ion battery according to any one of the first aspects, the method comprising the following steps:

[0029] S1. The carboxylated carbon nanotubes, the aminated conductive carbon black, and the carbon quantum dots with epoxy groups on their surface are mixed with a portion of the solvent and subjected to a first dispersion treatment to obtain a conductive agent dispersion.

[0030] S2. Mix the polyvinylidene fluoride-grafted-polyamide-imide copolymer adhesive with the remaining portion of the solvent to obtain an adhesive solution;

[0031] S3. The positive electrode active material is added to the binder solution for a second dispersion treatment, and then the conductive agent dispersion is added for a third dispersion treatment to obtain the initial positive electrode slurry.

[0032] S4. The initial positive electrode slurry is vacuum stirred and degassed, and the viscosity is adjusted to 2500-6000 mPa·s to obtain the positive electrode slurry of the lithium-ion battery.

[0033] Thirdly, embodiments of this application provide a positive electrode sheet, wherein the raw material for the positive electrode coating layer of the positive electrode sheet includes the positive electrode slurry described in any one of the first aspects.

[0034] Fourthly, embodiments of this application provide a lithium battery, which includes the positive electrode sheet described in the third aspect.

[0035] The technical solutions provided in this application have the following advantages compared with the prior art:

[0036] This application provides a positive electrode slurry for lithium-ion batteries. Through the synergistic design of multiple components at the molecular and microstructure levels, it systematically solves the core contradiction in high-nickel positive electrode systems where it is difficult to simultaneously achieve electron / ion transport efficiency and long-term stability of the electrode structure.

[0037] Firstly, to improve electron / ion transport efficiency, this approach does not simply increase the amount of traditional conductive agent (which would sacrifice energy density and stability), but rather constructs a highly efficient and robust dual-pathway transport network. For electron transport, the conductive agent consists of carboxylated carbon nanotubes, aminated conductive carbon black, and carbon quantum dots with epoxy groups on their surface. These three components undergo chemical reactions during processing (such as amidation and epoxy ring opening) through their surface functional groups (-COOH, -NH2, epoxy groups), forming a three-dimensional conductive network connected by covalent bonds. Compared to traditional carbon black with physical contact, this chemically bonded network exhibits extremely low contact resistance and excellent mechanical stability, achieving highly efficient electron percolation with a very low addition amount (only 1-2% of the total solid mass). For ion transport, the lithium phosphate coating on the surface of the active material is a fast ion conductor, providing a high-speed interfacial channel for lithium ions to enter and exit the active particles; simultaneously, a small amount of ionic liquid in the solvent remains in the electrode pores after the electrode is dried, which can improve solid-solid interface wettability and enhance local ionic conductivity. These designs collectively ensure that even with a high proportion of active materials (94–97.5%), the electrode still possesses excellent electronic and ion mixing conductivity, thus supporting high-rate performance.

[0038] Secondly, to ensure the long-term cycling stability of the electrode structure, this solution works synergistically from three levels: particle body reinforcement, strong interfacial anchoring, and overall stress buffering. First, the dual coating of lithium phosphate and carbon stabilizes the high-nickel active material from the source: the lithium phosphate layer inhibits interfacial side reactions and transition metal dissolution, while the carbon layer constrains particle volume changes and improves mechanical strength. Second, the core innovation lies in the use of a polyvinylidene fluoride-grafted-polyamide-imide copolymer as a binder. The highly polar polyamide-imide segments, through abundant amide bonds, form strong hydrogen bonds, dipole bonds, and even coordination bonds with the active material coating layer and the conductive agent surface, achieving molecular-level anchoring and providing exceptional adhesion to prevent component stripping during cycling. Third, this graft copolymer, with flexible polyvinylidene fluoride as the main chain, intertwines with the aforementioned three-dimensional conductive network to form a rigid-flexible elastic framework. Under the volume change stress of long-term charge-discharge cycles, this framework can effectively buffer stress through elastic deformation, avoiding brittle fracture, thereby maintaining the integrity of the conductive network and the overall unity of the electrode structure.

[0039] Ultimately, the solution proposed in this application lies in: using a chemically bonded rigid conductive network to ensure efficient electron transport, and using a fast ion conductor coating layer and ionic liquid to optimize ion transport; simultaneously, using molecularly anchored strong interfacial bonding and a rigid-flexible elastic framework to ensure structural stability. These two systems are not independent, but are deeply coupled through a multifunctional binder and an active coating layer, thereby unifying the open structure required for high transport efficiency and the robust structure required for high stability, thus simultaneously achieving the goals of high energy density, high rate capability, and long cycle life. Attached Figure Description

[0040] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0041] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 A schematic flowchart illustrating the preparation method of the positive electrode slurry for a lithium-ion battery provided in this application embodiment;

[0043] Figure 2 This is a SEM image of the positive electrode active material provided in Example 1 of this application;

[0044] Figure 3 This is a TEM image of the positive electrode active material provided in Example 1 of this application. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0046] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1 to 6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0047] This application provides a positive electrode slurry for a lithium-ion battery, the positive electrode slurry comprising: a positive electrode active material, a conductive agent, a binder, and a solvent;

[0048] The mass ratio of the positive electrode active material, conductive agent, and binder is (94-97.5):(1-2):(1.5-3);

[0049] The solid content of the positive electrode slurry is 35-45%;

[0050] The positive electrode active material is a high-nickel ternary lithium oxide with a surface coated with lithium phosphate and a carbon layer;

[0051] The conductive agent is composed of carboxylated carbon nanotubes, aminated conductive carbon black, and carbon quantum dots with epoxy groups on their surface.

[0052] The adhesive is a polyvinylidene fluoride-grafted-polyamide-imide copolymer;

[0053] The solvent consists of N-methylpyrrolidone and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0054] The core of this application lies in constructing a stable electrode microstructure with strong internal bonding, strong interfacial anchoring, and multiple transport paths, systematically solving the core challenges faced by high-energy-density cathodes. Specifically, the roles of each component of the cathode slurry are as follows:

[0055] (1) Positive electrode active material: a capacity core with a stable interface and dual-channel transport capability, whose main body is a high-nickel layered oxide (such as LiNi). 0.8 Co 0.1 Mn 0.1 O2), providing electrochemical capacity. The key surface double coating layer endows it with stability and high transport properties at the molecular level: the inner layer is lithium phosphate (Li3PO4): as a fast ion conductor, its crystal structure contains (PO4). 3- The tetrahedral structure, through which oxygen atoms form a one-dimensional fast ion channel, allows for rapid lithium-ion migration. This layer constructs a stable chemical barrier between the active material and the electrolyte, and its strong PO covalent bonds effectively suppress the release of lattice oxygen and transition metal ions (such as Ni) from the high-nickel surface under high voltage. 4+ Dissolution. Outer amorphous carbon: mainly composed of short-range sp. 2 It consists of an amorphous carbon network composed of clusters. This layer, acting as a "skin" for electron collection and transport, greatly improves the intrinsic electronic conductivity of the active particle surface and provides an ideal interface for subsequent connection with macroscopic conductive networks.

[0056] (2) Conductive agent: The intrinsic three-dimensional electron percolation network is constructed through covalent bonds. This scheme abandons physical mixing and actively constructs the network through the chemical reaction of surface functional groups: Carboxylated carbon nanotubes (-COOH) and amino-modified conductive carbon black (-NH2): During the preparation or drying of the slurry, the functional groups of the two can undergo amidation condensation reaction to form strong amide bonds (-CO-NH-), covalently bonding the one-dimensional CNT "wires" with the zero-dimensional SP "nodes". Carbon quantum dots with epoxy groups (-CH(O)CH-) on the surface: As a multifunctional "nano solder", its epoxy groups can undergo epoxy ring-opening reaction with the -NH2 at the defects of amino-modified carbon black or CNTs to form CN or COC covalent connections, further strengthening the network nodes. This design realizes covalent bonding between heterogeneous carbon materials at the molecular scale, constructing a "three-dimensional highway" with extremely low electron transport resistance, overcoming the defects of high contact resistance and easy network destruction in traditional physical mixing.

[0057] (3) Binder: A graft copolymer that achieves strong interfacial anchoring and mechanical buffering, polyvinylidene fluoride-grafted-polyamide-imide (PVDF-g-PAI) is a molecular-level hybrid material: PVDF backbone (-CH2-CF2-): provides basic chemical stability and chain segment flexibility, ensuring the macroscopic flexibility of the electrode. PAI grafted segments: the regularly arranged amide bonds (-NH-CO-) and rigid imide five-membered rings on its molecular chain are the functional core. These polar groups can generate strong dipole-dipole interactions, hydrogen bonds (NH…O, C=O…HO) and possible coordination effects with the PO bonds, O atoms of the lithium phosphate coating layer on the surface of the active material and the oxygen-containing groups at the carbon layer defects. This multiple and strong intermolecular interaction achieves the "molecular anchoring" of the polymer to the surface of the active particles, providing exceptional bonding strength.

[0058] (4) Solvent: A composite medium with both dissolving and interface modification functions, N-methylpyrrolidone (NMP): Its highly polar lactam structure is an ideal solvent for dissolving PVDF and PAI segments, ensuring that the binder molecular chains are fully extended. Ionic liquids [EMIM][TFSI]: Its cationic [EMIM] + It possesses organic characteristics and is an anionic [TFSI] - They exhibit charge delocalization and structural stability. They preferentially adsorb onto the surface of carbon materials and coatings, improving the dispersion of nano-components through steric hindrance and electrostatic repulsion; the residual ionic liquid after drying can fill the electrode micropores, and its intrinsic ionic conductivity provides an additional pathway for lithium ion transport in the solid-solid interface region.

[0059] At the same time, the synergy among the components is not a simple superposition, but a systematic optimization based on molecular interactions.

[0060] (1) Mechanical Synergy of "Rigid-Flexible Interlocking" between Conductive Network and Binder: The covalently bonded rigid conductive network provides a stable mechanical framework and electronic pathway for the electrode. The flexible PVDF-g-PAI binder "weaves" itself into the network through chain segment entanglement and physical adsorption with the conductive agent surface (such as the interaction between PAI and carbon black), forming an interpenetrating structure. Under the volume change stress of battery cycling, the elasticity of the binder can buffer the stress and prevent the rigid conductive network from breaking due to brittleness; at the same time, the stable network also prevents excessive plastic flow of the binder. The two support each other and jointly maintain the long-term mechanical integrity of the electrode structure, thereby keeping the electronic pathway unobstructed for a long time.

[0061] (2) Synergistic “molecular anchoring-stress transmission” interface between binder and active material: The strong molecular anchoring of PAI segments to the surface of the active material forms a super strong interfacial bond. This ensures that the active material and the current collector will not debond under the micro-strain of particles caused by repeated lithium-ion intercalation and deintercalation. More importantly, this strong interfacial bond allows the volume change stress of the active material particles to be effectively transferred through the binder layer and dispersed throughout the flexible polymer matrix, avoiding particle breakage or coating peeling caused by stress concentration in local areas. The binder plays a dual role as a “stress buffer” and a “stress transmission network”.

[0062] (3) Synergistic effect of ionic liquid's "interfacial bridging" and "local plasticization" transport: Bridging effect: The residual ionic liquid is located at the three-phase interface of the active material / conductive agent / binder. Its ionic properties can improve the wettability between the phases and reduce interfacial contact voids. Local plasticization and ion transport: Ionic liquid can slightly swell adjacent polymer chain segments (local plasticization effect), which may improve the chain segment mobility in local areas of the binder. At the same time, as an ionic conductor, it provides a bypass transport channel for lithium ions to bypass the low conductivity region in the solid-solid interface region of the electrode. This, combined with the anchoring effect of the binder and the electron transport of the conductive network, jointly optimizes the ion-electron dual continuous transport efficiency inside the electrode, which is particularly beneficial for high rate performance.

[0063] (4) Orderly assembly and functional multiplication effect of the overall system: This scheme guides the components to undergo ordered assembly towards the lowest energy during the electrode drying and forming process through molecular design (functional groups, polarity) and preparation process (such as pre-dispersion of conductive agents and stepwise mixing). The active material is strongly anchored by PAI segments, the covalently bonded conductive network is uniformly wrapped around it, and the ionic liquid fills and modifies the remaining interface. This ordered structure at the molecular scale makes the functions of conductivity, bonding, ion transport, and structural stability no longer isolated contributions, but mutually reinforcing, ultimately achieving a unity of high energy density, long cycle life and excellent rate performance.

[0064] In some embodiments, the mass ratio of the carboxylated carbon nanotubes, the aminated conductive carbon black, and the epoxy-containing carbon quantum dots on the surface is (0.5-1.5):(0.5-1.5):(0.1-0.5).

[0065] In the design of the conductive agent system, carboxylated carbon nanotubes (CNT-COOH), amino-modified conductive carbon black (SP-NH2), and carbon quantum dots (CQDs) with epoxy groups on their surface are compounded in a specific mass ratio (0.5–1.5):(0.5–1.5):(0.1–0.5). The core purpose of this ratio is to guide the three components to construct a stable three-dimensional conductive network through chemical reactions during slurry processing or electrode drying. Specifically, the carboxyl groups of CNT-COOH and the amino groups of SP-NH2 can undergo an amidation condensation reaction to form covalent amide bonds (-CO-NH-), thereby firmly bonding the one-dimensional CNTs to the zero-dimensional SPs. At the same time, the epoxy groups (-CH(O)CH-) on the surface of CQDs can act as "nano-soldering points," undergoing epoxy ring-opening reactions with the amino groups at SP-NH2 or CNT defects to form COC or CNC bonds, further strengthening the network nodes. This parameter range ensures that the host conductive material can form an effective permeation network and provides an appropriate ratio of crosslinking agent, optimizing the matching of reaction sites, ultimately leading to a hybrid conductive architecture with low electronic transport resistance and high mechanical stability, connected by covalent bonds.

[0066] In some embodiments, the mass of the 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is 0.5 to 5% of the total mass of the solvent.

[0067] For the solvent system, the addition amount of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][TFSI]) is set at 0.5–5% of the total solvent mass. The cations of [EMIM][TFSI] are surface-active and can preferentially adsorb onto the surfaces of hydrophobic carbon materials and active substances. Through steric hindrance and electrostatic repulsion, it significantly improves the dispersion stability of nanocomponents in N-methylpyrrolidone (NMP) and prevents agglomeration. This addition range effectively improves the rheological properties and uniformity of the slurry without excessively increasing costs or significantly altering the solvent polarity. After the electrode is dried, trace amounts of residual ionic liquid are distributed at the electrode pore interface, and its intrinsic ionic conductivity helps to enhance the lithium-ion transport capacity in localized areas within the electrode.

[0068] In some embodiments, the preparation method of the positive electrode active material includes the following steps:

[0069] S101. High-nickel ternary lithium oxide is dispersed in a solution of lithium hydroxide and ammonium dihydrogen phosphate, and then dried to obtain the precursor.

[0070] S102. The precursor is sintered at 400-600°C for 2-6 hours to form a lithium phosphate coating layer on the surface of the high-nickel ternary lithium oxide, thereby obtaining a coating.

[0071] S103. Under an inert atmosphere, the coating material is mixed with glucose and then heat-treated at 500-700°C for 1-4 hours to form a carbon layer on the outside of the lithium phosphate coating layer, thereby obtaining the positive electrode active material.

[0072] In some embodiments, the molar ratio of lithium hydroxide to ammonium dihydrogen phosphate is (3.0-3.5):1;

[0073] The mass of the ammonium dihydrogen phosphate is 0.5% to 3.0% of the mass of the high-nickel ternary lithium oxide;

[0074] The glucose content is 0.5% to 2.0% of the coating material.

[0075] The positive electrode active material is prepared using a stepwise coating method to construct a dual protective and conductive interface of "lithium phosphate inner layer - carbon outer layer". First, in the lithium phosphate coating step, the high-nickel material is dispersed in a solution of lithium hydroxide (LiOH) and ammonium dihydrogen phosphate (NH4H2PO4), dried, and then sintered at 400–600 °C for 2–6 h. Under these conditions, NH4H2PO4 decomposes and reacts with LiOH to form a stable fast-ion conductor lithium phosphate (Li3PO4) crystal coating layer on the material surface. The molar ratio of LiOH to NH4H2PO4 is controlled at (3.0–3.5):1 to provide a slight excess of lithium source, ensuring the formation of stoichiometric Li3PO4. The amount of NH4H2PO4 used is 0.5–3.0% of the mass of the high-nickel material, aiming to precisely control the thickness of the coating layer so that it effectively suppresses interfacial side reactions without excessively hindering lithium-ion transport. Subsequently, a carbon coating is applied. Under an inert atmosphere, the coating material is mixed with glucose and heat-treated at 500–700°C for 1–4 hours to allow the glucose to pyrolyze and carbonize, forming a uniform amorphous carbon layer on the particle surface. The amount of glucose used is 0.5–2.0% of the coating material's mass. This ratio can form a continuous and dense conductive carbon film, significantly improving the electronic conductivity of the particle surface and establishing good contact with the external conductive network.

[0076] In some embodiments, the method for preparing the adhesive includes the following steps:

[0077] S201. Polyvinylidene fluoride is dissolved in N-methylpyrrolidone, then potassium hydroxide and tetrabutylammonium bromide are added, and the reaction is carried out at 60-90℃ for 0.5-3h to defluorinate the polyvinylidene fluoride main chain and obtain a functionalized polyvinylidene fluoride solution.

[0078] S202. Under nitrogen protection, trimellitic anhydride, 4,4'-diaminodiphenyl ether and triethylamine are added to the functionalized polyvinylidene fluoride solution, and then the mixture is stirred and reacted at 80-120°C for 4-12 hours to allow polyamide imide to be grafted onto the functionalized polyvinylidene fluoride. The adhesive is obtained after post-treatment.

[0079] In some embodiments, the mass ratio of the polyvinylidene fluoride, the potassium hydroxide, and the tetrabutylammonium bromide is 1 : (0.05–0.20) : (0.005–0.10);

[0080] The molar ratio of trimellitic anhydride to 4,4'-diaminodiphenyl ether is 1:(0.9-1.1);

[0081] The ratio of the total mass of the trimellitic anhydride and the 4,4'-diaminodiphenyl ether to the mass of the polyvinylidene fluoride is (0.10-0.50):1;

[0082] The mass ratio of triethylamine to trimellitic anhydride is (0.05–0.20):1.

[0083] The highly polar segments of polyamide-imide (PAI) are introduced into the polyvinylidene fluoride (PVDF) backbone via chemical grafting. This process consists of two steps: the first step is the functionalization of PVDF. PVDF is dissolved in NMP, followed by the addition of potassium hydroxide (KOH) and the phase-transfer catalyst tetrabutylammonium bromide (TBAB), and the reaction is carried out at 60–90 °C for 0.5–3 h. During this process, the PVDF backbone undergoes a defluorination (E2 elimination) reaction, forming carbon-carbon double bonds (-CH=CF-) active sites. The raw material mass ratio of PVDF:KOH:TBAB is 1:(0.05–0.20):(0.005–0.10). KOH provides a moderately alkaline environment to drive the reaction, while TBAB ensures the presence of OH groups. -Effective transfer to the reaction interface enables controllable functionalization. The second step is the graft copolymerization of PAI. Under nitrogen protection, trimellitic anhydride (TMA), 4,4'-diaminodiphenyl ether (ODA), and the catalyst triethylamine (TEA) are added to the functionalized PVDF solution, and the reaction is stirred at 80–120 °C for 4–12 h. The molar ratio of TMA to ODA is 1:(0.9–1.1) to ensure the polycondensation to generate high molecular weight PAI segments; the mass ratio of the total mass of both to the mass of PVDF is controlled at (0.10–0.50):1. This "grafting rate" range effectively regulates the balance of polarity, bonding strength, and flexibility of the final binder; the mass ratio of TEA to TMA is (0.05–0.20):1, providing sufficient catalytic activity for the polycondensation and grafting reactions. Under these conditions, the active end groups (such as amino groups) of PAI oligomers or segments can react with the double bonds on PVDF through mechanisms such as Mygl addition to achieve covalent grafting of PAI segments and obtain graft copolymers with well-defined structures.

[0084] Figure 1 This is a schematic flowchart illustrating the preparation method of the positive electrode slurry for a lithium-ion battery provided in this application embodiment.

[0085] Based on a general inventive concept, such as Figure 1 As shown in the figure, this application provides a method for preparing the positive electrode slurry of a lithium-ion battery according to any one of the above-mentioned embodiments, the method comprising the following steps:

[0086] S1. The carboxylated carbon nanotubes, the aminated conductive carbon black, and the carbon quantum dots with epoxy groups on their surface are mixed with a portion of the solvent and subjected to a first dispersion treatment to obtain a conductive agent dispersion.

[0087] S2. Mix the polyvinylidene fluoride-grafted-polyamide-imide copolymer adhesive with the remaining portion of the solvent to obtain an adhesive solution;

[0088] S3. The positive electrode active material is added to the binder solution for a second dispersion treatment, and then the conductive agent dispersion is added for a third dispersion treatment to obtain the initial positive electrode slurry.

[0089] S4. The initial positive electrode slurry is vacuum stirred and degassed, and the viscosity is adjusted to 2500-6000 mPa·s to obtain the positive electrode slurry of the lithium-ion battery.

[0090] The preparation method of this positive electrode slurry, through carefully designed steps and process control, aims to achieve highly uniform dispersion and effective composite of various nano-components, thereby constructing an ideal multifunctional microstructure within the electrode. The specific functions of each step are as follows:

[0091] Step S1 (conductive agent pre-dispersion) aims to actively construct the initial three-dimensional conductive network prototype. Carboxylated carbon nanotubes, amino-modified conductive carbon black, and carbon quantum dots with epoxy groups on their surface are mixed with a portion of the solvent and subjected to a first dispersion treatment. The core purpose is to achieve a highly uniform dispersion of the three nano-carbon materials with active functional groups in the solvent using high-intensity mechanical dispersing forces (such as high-speed shearing) before introducing the high-density active material. This process not only breaks up the aggregation of nanoparticles but also promotes the initial contact and reaction between carboxyl and amino groups, and between epoxy and amino groups. This lays the structural foundation for the subsequent formation of a stable conductive network with covalent bonds through amidation and epoxy ring-opening reactions within the slurry system or during electrode drying. This step ensures that the conductive network exists as an independent and uniform "pre-formed" structure, avoiding uneven dispersion problems caused by competitive adsorption and steric hindrance during subsequent mixing with the active material.

[0092] Step S2 (binder dissolution) ensures the full extension and solubility of the functional polymer chains. Mixing the polyvinylidene fluoride-grafted-polyamide-imide copolymer binder with the remaining solvent aims to completely dissolve and extend the molecular chains of the graft copolymer in a good solvent. This process fully exposes the functional groups, such as amide bonds and imide rings, abundant in the polymer segments, especially the highly polar polyamide-imide (PAI) segments. This "activation" prepares the polymer for subsequent strong intermolecular interactions (such as hydrogen bonding and dipole-dipole interactions) with the surface of the active material, and is a key prerequisite for achieving strong interfacial adhesion.

[0093] Step S3 (stepwise mixing) guides the formation of an optimal "core-shell-network" composite structure. This step employs a specific sequence of adding the active material first, followed by the conductive agent dispersion, providing clear microstructure guidance. First, the positive electrode active material is added to the binder solution for a second dispersion treatment. This allows the "activated" binder molecules to preferentially and fully wet, adsorb, and coat the surface of each active material particle, forming a uniform polymer binder layer. Subsequently, the pre-constructed conductive agent dispersion is added for a third dispersion treatment. This enables the initially formed conductive network to effectively adhere to and bridge the periphery of the binder-coated active material particles. This sequence effectively avoids the risk of the conductive agent losing conductivity due to excessive binder coating, ultimately guiding the formation of an ideal coating structure with "active material as the core, binder as the intermediate layer, and a three-dimensional conductive network as the outer shell," maximizing the contact efficiency and functional synergy between the components.

[0094] Step S4 (homogenization and degassing) aims to obtain an engineered slurry that meets coating requirements. Vacuum stirring and degassing of the initial positive electrode slurry eliminates air microbubbles introduced during the initial high-speed dispersion process. If these bubbles remain in the slurry, they will form defects within the electrode after coating and drying, impairing the electrode's uniformity and mechanical integrity. Simultaneously, adjusting the slurry viscosity to the range of 2500–6000 mPa·s ensures the slurry possesses ideal rheological properties suitable for processes such as slot extrusion or blade coating. This viscosity range ensures good suspension stability, appropriate flowability, and leveling properties, thereby forming a uniformly thick, smooth, and crack-free wet film on the current collector—essential process conditions for obtaining high-performance electrode sheets.

[0095] Based on a general inventive concept, embodiments of this application provide a positive electrode sheet, wherein the raw material for the positive electrode coating layer of the positive electrode sheet includes any of the positive electrode slurries described above.

[0096] Based on a general inventive concept, embodiments of this application provide a lithium battery, which includes the positive electrode sheet described above.

[0097] The positive electrode sheet and lithium battery obtained by coating the positive electrode slurry onto the surface of the positive electrode current collector provided in this application have the following advantages:

[0098] (1) Constructing a highly stable and highly conductive electrode framework to achieve simultaneous performance improvement: A robust internal structure of the electrode is actively constructed through chemical methods. Traditional slurry mixing is a physical process with weak inter-component bonding. In this scheme, the conductive agent forms a three-dimensional network with covalent bonds through the amidation of surface functional groups and the ring-opening reaction of epoxy; the binder is grafted copolymerized to anchor the highly polar polyamide-imide (PAI) segments to the polyvinylidene fluoride (PVDF) main chain with covalent bonds. Together, these two provide the electrode with a "framework" that combines excellent electronic conductivity and extraordinary mechanical strength. As a result, while the electrode has extremely low internal resistance (which is beneficial for fast charging and rate performance), its structure can still remain intact under the volume change stress of long-term charge and discharge, thus simultaneously achieving high rate performance and ultra-long cycle life, breaking the usual dilemma of "it is difficult to have both".

[0099] (2) Achieving superior interfacial stability and fundamentally alleviating the degradation of high-nickel materials: This scheme "reinforces" the most vulnerable electrode interface from three dimensions. First, the double coating of lithium phosphate (fast ion conductor) and carbon (electronic conductor) on the surface of the active material physically isolates the direct contact between the electrolyte and the highly active high-nickel core, and provides a fast ion / electron inlet / outlet channel, suppressing side reactions and transition metal dissolution. Second, the polar groups such as amide bonds on the PAI segments of the graft copolymer binder form strong hydrogen bonds and dipole interactions with the active material coating layer and the surface of the conductive agent, achieving "molecular-level anchoring," making the various components of the electrode tightly bound during cycling and less prone to pulverization and detachment. Finally, trace amounts of ionic liquid remain at the interface, which can play the role of local "plasticization" and ion transport bridge. This triple interfacial protection synergistically improves the chemical and mechanical stability of the high-nickel cathode under high voltage, which is the key to breaking through its cycle life bottleneck.

[0100] (3) Achieving "low addition, high efficiency" material utilization directly improves energy density:

[0101] The conductive and binding systems in this design aim for "maximum functionality and minimum dosage." The covalently bonded 3D conductive network optimizes the electron transport path, allowing the total amount of conductive agent added to be reduced to an extremely low level, while maintaining superior performance compared to traditional systems with higher addition amounts. This means a significant reduction in the proportion of "inactive materials" that do not contribute capacity in the electrode. Similarly, the graft copolymer binder, due to its stronger bonding efficiency per unit mass, is also expected to reduce its dosage while maintaining the electrode structure. The lower proportion of inactive materials directly translates into higher electrode compaction density and volumetric energy density, which has an immediate effect on improving the energy density of individual battery cells.

[0102] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards / industry standards / the disclosure herein; if there are no corresponding national standards / industry standards / the disclosure herein, they are performed according to generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer. Example 1

[0103] This embodiment details the preparation method of lithium-ion battery cathode slurry and its components. The specific preparation steps are as follows:

[0104] (1) Preparation of positive electrode active material

[0105] Take 1000g of commercial high-nickel ternary lithium oxide LiNi 0.8 Co 0.1 Mn 0.1Using O2 (NCM811) powder as a matrix, it was dispersed in a deionized aqueous solution containing 6.2 g of lithium hydroxide (LiOH•H2O) and 6.9 g of ammonium dihydrogen phosphate (NH4H2PO4). After thorough mixing, the mixture was dried at 120 °C for 12 h to obtain a precursor. The precursor was then sintered at 500 °C for 4 h in an air atmosphere and allowed to cool naturally to obtain a coating material with lithium phosphate (Li3PO4) on its surface. Subsequently, this coating material was mixed uniformly with 15 g of glucose in a high-speed mixer, transferred to a tube furnace, and heat-treated at 600 °C for 2 h under an argon atmosphere. After natural cooling, the mixture was sieved to obtain a double-coated positive electrode active material with lithium phosphate and carbon layers sequentially coated on its surface, wherein the glucose accounted for 1.5% of the coating material by mass.

[0106] Figure 2 This is a SEM image of the positive electrode active material provided in Example 1 of this application; Figure 3 This is a TEM image of the positive electrode active material provided in Example 1 of this application.

[0107] Depend on Figure 2 and Figure 3 It is known that the average particle size of the positive electrode active material in Example 1 is about 15 μm, the particle surface is smooth and the outline is soft, the sharp edges and clear boundaries between the original primary particles are covered and filled by a uniform and dense coating layer, and the total thickness of the coating layer is about 20 nm.

[0108] (2) Preparation of conductive agent

[0109] Weigh out carboxylated multi-walled carbon nanotubes (CNT-COOH), amino-modified conductive carbon black (SP-NH2), and carbon quantum dots (CQDs) with epoxy groups on their surface in a mass ratio of 1:1:0.3. Mix the three components evenly before use to ensure the dispersion and synergistic conductivity of the conductive components.

[0110] Among them, the CAS number of the carboxylated multi-walled carbon nanotubes is 308068-56-6, which was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0111] The preparation method of aminated conductive carbon black includes the following steps: Take 10.0 g of conductive carbon black (Super P), add 100 mL of 65% concentrated nitric acid, and reflux at 80 °C for 4 h. After cooling, centrifuge to separate the solid, wash repeatedly with deionized water until neutral, and vacuum dry at 80 °C for 12 h to obtain carbon black oxide (CB-COOH). Take 2.0 g of CB-COOH, disperse it in 200 mL of water, and sonicate for 30 min. Add 100 mL of polyethyleneamine (PVAm) aqueous solution (containing 2.0 g PVAm, molecular weight 10,000) under stirring, adjust the pH to 11.0 with sodium hydroxide solution, and react at 50 °C for 4 h. Amide bonds can be formed between the surface -COOH and the primary amine, and the remaining amine groups are adsorbed on the carbon black surface by electrostatic / hydrogen bonding. After the reaction, centrifuge to collect the solid, wash with water until the filtrate is clear, vacuum dry at 70 °C overnight, and grind to obtain aminated conductive carbon black (CB-NH2) with a total nitrogen content of 2.0 mmol g. -1 .

[0112] The preparation method of carbon quantum dots with epoxy groups on the surface includes the following steps: 10 mL of carbon quantum dot stock solution (purchased from Xi'an Ruixi Biotechnology Co., Ltd.) was taken, 1 mL of epichlorohydrin was added, and the pH was adjusted to 10 with sodium hydroxide solution. The reaction was stirred at 60℃ for 6 h. After the reaction, the product was purified by dialysis for 3 days using a dialysis bag (molecular weight cutoff 1000 Da) to remove unreacted ions and small molecules. Finally, the product was freeze-dried to obtain a solid powder of carbon quantum dots with epoxy groups on the surface. The epoxy value was determined to be 0.45 mmol g using the hydrochloric acid-acetone method. -1 .

[0113] (3) Synthesis of adhesive (PVDF-g-PAI)

[0114] In a three-necked flask equipped with a stirrer, thermometer, and nitrogen inlet, 100 g of N-methylpyrrolidone (NMP) was added, followed by 10 g of polyvinylidene fluoride (PVDF) powder. The mixture was heated to 70 °C and stirred continuously until the PVDF was completely dissolved. Then, 1.0 g of potassium hydroxide (KOH) and 0.2 g of tetrabutylammonium bromide (TBAB) were added sequentially to the solution. The reaction was carried out at 70 °C under nitrogen protection for 1.5 h to functionalize the PVDF backbone with defluorination, yielding a functionalized PVDF solution. Maintaining the system temperature at 70 °C, 2.0 g of trimellitic anhydride (TMA), 1.99 g of 4,4'-diaminodiphenyl ether (ODA), and 0.3 g of triethylamine (TEA) were added sequentially to the functionalized PVDF solution. The system temperature was raised to 105℃, and the reaction was continued to be stirred for 8 hours under nitrogen protection. After the reaction was completed, the reaction solution was cooled to room temperature, poured into a large amount of anhydrous ethanol to precipitate, filtered to collect the solid and washed three times with ethanol, and then vacuum dried at 80℃ for 24 hours. After grinding, polyvinylidene fluoride-grafted-polyamide-imide (PVDF-g-PAI) copolymer powder was obtained, which is the target binder.

[0115] (4) Preparation of positive electrode slurry and electrode sheet

[0116] First, prepare the mixed solvent: Add 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIM][TFSI]) at 2% of the total mass of NMP to NMP, and stir until homogeneous. Prepare the conductive agent dispersion: Take 1 / 3 of the total volume of the above mixed solvent, add all the prepared conductive agent mixture, and disperse using a high-speed homogenizer at 2000 rpm for 60 min to obtain a homogeneous conductive agent dispersion. Prepare the binder solution: Take the remaining 2 / 3 of the mixed solvent, add the synthesized PVDF-g-PAI binder, and stir in a planetary mixer at 400 rpm for 120 min until completely dissolved to obtain a homogeneous binder solution.

[0117] The initial slurry was prepared by stepwise mixing: all the double-coated positive electrode active material was added to the binder solution. The material was first wetted by low-speed stirring at 100 rpm for 30 minutes in a planetary mixer, then fully dispersed by high-speed stirring at 600 rpm for 90 minutes. Subsequently, the pre-prepared conductive agent dispersion was slowly added, and stirring continued at 800 rpm for 60 minutes to obtain the initial positive electrode slurry. The mass ratio of positive electrode active material, conductive agent, and binder was 96.2:1.0:2.0. Finally, vacuum degassing and viscosity adjustment were performed: the initial slurry was transferred to a vacuum mixing vessel and degassed and stirred at 100 rpm for 45 minutes under a vacuum of -0.095 MPa. A small amount of mixed solvent was added to adjust the final viscosity of the slurry to 4000 mPa·s (25℃). The resulting slurry had a solid content of 40%, thus obtaining a qualified lithium-ion battery positive electrode slurry. Example 2

[0118] This embodiment details the preparation method of lithium-ion battery cathode slurry and its components. The specific preparation steps are as follows:

[0119] (1) Preparation of positive electrode active material

[0120] 1000g of commercially available high-nickel ternary lithium oxide NCM811 powder was used as the matrix and dispersed in a deionized aqueous solution containing 8.5g of lithium hydroxide and 15.0g of ammonium dihydrogen phosphate. After thorough mixing, the mixture was dried at 110℃ for 14h to obtain a precursor. The precursor was then sintered at 550℃ for 3h in an air atmosphere and allowed to cool naturally to obtain a coating material with lithium phosphate on the surface. Subsequently, the coating material was mixed evenly with 10g of glucose in a high-speed mixer, transferred to a tube furnace, and heat-treated at 650℃ for 3h under an argon atmosphere. After natural cooling, the mixture was sieved to obtain a double-coated positive electrode active material with lithium phosphate and carbon layers sequentially coated on the surface, wherein the glucose accounted for 1.0% of the coating material by mass.

[0121] (2) Preparation of conductive agent

[0122] Weigh out carboxylated multi-walled carbon nanotubes, amino-modified conductive carbon black, and carbon quantum dots with epoxy groups on the surface in a mass ratio of 1.2:0.8:0.4. Mix the three together thoroughly before use to ensure the dispersion and synergistic conductivity of the conductive components.

[0123] (3) Synthesis of adhesive (PVDF-g-PAI)

[0124] In a three-necked flask equipped with a stirrer, thermometer, and nitrogen inlet, 120 g of N-methylpyrrolidone was added, followed by 10 g of polyvinylidene fluoride powder. The mixture was heated to 75 °C and stirred continuously until the PVDF was completely dissolved. Then, 1.5 g of potassium hydroxide and 0.15 g of tetrabutylammonium bromide were added to the solution sequentially. The reaction was carried out at 75 °C under nitrogen protection for 2 hours to functionalize the PVDF backbone with defluorination, yielding a functionalized PVDF solution. Maintaining the system temperature at 75 °C, 2.2 g of trimellitic anhydride, 2.1 g of 4,4'-diaminodiphenyl ether, and 0.44 g of triethylamine were added sequentially to the functionalized PVDF solution. The system temperature was raised to 110℃, and the reaction was continued to be stirred for 7 hours under nitrogen protection. After the reaction was completed, the reaction solution was cooled to room temperature, poured into a large amount of anhydrous ethanol to precipitate, the solid was collected by filtration and washed three times with ethanol, and then vacuum dried at 85℃ for 20 hours. After grinding, polyvinylidene fluoride-graft-polyamide-imide copolymer powder was obtained, which is the target binder.

[0125] (4) Preparation of positive electrode slurry and electrode sheet

[0126] First, prepare the mixed solvent: Add 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt to NMP at 3% of the total mass of NMP, and stir until homogeneous. Prepare the conductive agent dispersion: Take 1 / 3 of the total volume of the above mixed solvent, add all the prepared conductive agent mixture, and disperse using a high-speed homogenizer at 2200 rpm for 50 min to obtain a homogeneous conductive agent dispersion. Prepare the binder solution: Take the remaining 2 / 3 of the mixed solvent, add the synthesized PVDF-g-PAI binder, and stir in a planetary mixer at 450 rpm for 100 min until completely dissolved to obtain a homogeneous binder solution.

[0127] The initial slurry was prepared by stepwise mixing: all the double-coated positive electrode active material was added to the binder solution. The material was first wetted by low-speed stirring at 120 rpm for 25 minutes in a planetary mixer, then fully dispersed by high-speed stirring at 650 rpm for 80 minutes. Subsequently, the pre-prepared conductive agent dispersion was slowly added, and stirring continued at 850 rpm for 50 minutes to obtain the initial positive electrode slurry. The mass ratio of positive electrode active material, conductive agent, and binder was 95.5:1.5:3.0. Finally, vacuum degassing and viscosity adjustment were performed: the initial slurry was transferred to a vacuum mixing vessel and degassed and stirred at 120 rpm for 40 minutes under a vacuum of -0.092 MPa. A small amount of mixed solvent was added to adjust the final viscosity of the slurry to 4500 mPa·s (25℃). The resulting slurry had a solid content of 42%, thus obtaining a qualified lithium-ion battery positive electrode slurry. Example 3

[0128] This embodiment details the preparation method of lithium-ion battery cathode slurry and its components. The specific preparation steps are as follows:

[0129] (1) Preparation of positive electrode active material

[0130] 1000g of commercially available high-nickel ternary lithium oxide NCM811 powder was used as the matrix and dispersed in a deionized aqueous solution containing 5.8g of lithium hydroxide and 25.0g of ammonium dihydrogen phosphate. After thorough mixing, the mixture was dried at 125℃ for 10h to obtain a precursor. The precursor was then sintered at 480℃ for 5h in air and allowed to cool naturally to obtain a lithium phosphate-coated material. Subsequently, the coated material was mixed uniformly with 8g of glucose in a high-speed mixer, transferred to a tube furnace, and heat-treated at 580℃ for 2.5h under argon as a protective atmosphere. After natural cooling, the mixture was sieved to obtain a double-coated positive electrode active material with lithium phosphate and carbon layers sequentially coated on the surface, wherein the glucose accounted for 0.8% of the coating mass.

[0131] (2) Preparation of conductive agent

[0132] Weigh out carboxylated multi-walled carbon nanotubes, amino-modified conductive carbon black, and carbon quantum dots with epoxy groups on the surface in a mass ratio of 1.4:0.6:0.2. Mix the three together thoroughly and set aside to ensure the dispersion and synergistic conductivity of the conductive components.

[0133] (3) Synthesis of adhesive (PVDF-g-PAI)

[0134] In a three-necked flask equipped with a stirrer, thermometer, and nitrogen inlet, 90 g of N-methylpyrrolidone was added, followed by 10 g of polyvinylidene fluoride powder. The mixture was heated to 68 °C and stirred continuously until the PVDF was completely dissolved. Then, 0.8 g of potassium hydroxide (KOH) and 0.08 g of tetrabutylammonium bromide were added sequentially to the solution. The reaction was carried out at 68 °C under nitrogen protection for 1 h to functionalize the PVDF backbone with defluorination, yielding a functionalized PVDF solution. While maintaining the system temperature at 68 °C, 1.8 g of trimellitic anhydride, 1.85 g of 4,4'-diaminodiphenyl ether, and 0.18 g of triethylamine were added sequentially to the functionalized PVDF solution. The system temperature was raised to 95℃, and the reaction was continued to be stirred for 9 hours under nitrogen protection. After the reaction was completed, the reaction solution was cooled to room temperature, poured into a large amount of anhydrous ethanol to precipitate, filtered to collect the solid and washed three times with ethanol, and then vacuum dried at 78℃ for 26 hours. After grinding, polyvinylidene fluoride-grafted-polyamide-imide (PVDF-g-PAI) copolymer powder was obtained, which is the target binder.

[0135] (4) Preparation of positive electrode slurry and electrode sheet

[0136] First, prepare the mixed solvent: Add 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt to NMP at 1% of the total mass of NMP, and stir until homogeneous. Prepare the conductive agent dispersion: Take 1 / 3 of the total volume of the above mixed solvent, add all the prepared conductive agent mixture, and disperse using a high-speed homogenizer at 1800 rpm for 70 min to obtain a homogeneous conductive agent dispersion. Prepare the binder solution: Take the remaining 2 / 3 of the mixed solvent, add the synthesized PVDF-g-PAI binder, and stir in a planetary mixer at 380 rpm for 130 min until completely dissolved to obtain a homogeneous binder solution.

[0137] The initial slurry was prepared by stepwise mixing: all the double-coated positive electrode active material was added to the binder solution. The material was first wetted by low-speed stirring at 90 rpm for 35 minutes in a planetary mixer, then fully dispersed by high-speed stirring at 580 rpm for 100 minutes. Subsequently, the pre-prepared conductive agent dispersion was slowly added, and stirring continued at 750 rpm for 70 minutes to obtain the initial positive electrode slurry. The mass ratio of positive electrode active material, conductive agent, and binder was 97.0:1.2:1.8. Finally, vacuum degassing and viscosity adjustment were performed: the initial slurry was transferred to a vacuum mixing vessel and degassed and stirred at 90 rpm for 50 minutes under a vacuum of -0.098 MPa. A small amount of mixed solvent was added to adjust the final viscosity of the slurry to 3500 mPa·s (25℃). The resulting slurry had a solid content of 38%, thus obtaining a qualified lithium-ion battery positive electrode slurry.

[0138] Comparative Example 1

[0139] This comparative example provides a positive electrode slurry, using NCM811 as the active material, a 1:1 mass ratio of ordinary conductive carbon black (Super P) and ordinary carbon nanotubes as the conductive agent, ordinary PVDF (HSV900) as the binder, and pure NMP as the solvent. The active material ratio is Super P:PVDF = 96.5:1.5:2.0 (solid mass ratio), with a solid content of 40%.

[0140] Comparative Example 2

[0141] This comparative example is modified from the one disclosed in Example 1 as follows:

[0142] Commercially available NCM811 powder without any surface coating was used instead of the active material with double coating of lithium phosphate and carbon layer in Example 1.

[0143] Comparative Example 3

[0144] This comparative example is modified from the one disclosed in Example 1 as follows:

[0145] Ordinary conductive carbon black (Super P) and ordinary carbon nanotubes were physically mixed at a mass ratio of 1:1 to replace the covalent bonding system of carboxylated CNT / aminolated SP / epoxy carbon quantum dots in Example 1.

[0146] Comparative Example 4

[0147] This comparative example is modified from the one disclosed in Example 1 as follows:

[0148] A conventional polyvinylidene fluoride (PVDF) binder was used instead of the polyvinylidene fluoride-grafted-polyamide-imide copolymer in Example 1.

[0149] Comparative Example 5

[0150] This comparative example is modified from the one disclosed in Example 1 as follows:

[0151] The solvent is only pure N-methylpyrrolidone (NMP), without the addition of any ionic liquids ([EMIM][TFSI]). Example 4

[0152] The positive electrode slurries obtained in Examples 1-3 and Comparative Examples 1-5 were coated onto one side of the positive electrode current collector (15 μm aluminum foil). After coating, the positive electrode slurry was vacuum dried at 100 °C for 16 h. The positive electrode sheet was then rolled to obtain a positive electrode sheet with a coating thickness of 12 μm.

[0153] Meanwhile, the positive electrode sheets of each example were assembled into CR2032 coin cells using lithium metal sheets as the counter electrode for testing. The electrolyte was a 1M LiPF6 EC / DEC / EMC (1:1:1 vol%) mixture, and the separator was Celgard 2325.

[0154] The physical properties of the positive electrode slurry, electrode sheets, and batteries prepared in Examples 1-3 and Comparative Examples 1-5, as well as the electrochemical properties of the batteries, were measured. The performance test results are shown in Tables 1 and 2. All tests were conducted at a constant temperature of 25°C.

[0155] (1) Physical property testing of slurry and electrode

[0156] Slurry stability (48h viscosity change rate): The viscosity of the slurry was measured using a Brookfield DV2T viscometer when it was prepared and after standing for 48 hours, and the change rate was calculated.

[0157] Electrode peel strength (N / m): The dried electrode was cut into strips and its adhesion to aluminum foil was tested using an Instron 3365 universal testing machine with a 180° peel test.

[0158] Electrode volume resistivity (Ω·cm): The resistance of the electrode under a specific pressure was measured and the volume resistivity was calculated using a four-probe resistance meter (RTS-9) in conjunction with a compaction density meter.

[0159] Table 1 Physical properties of slurry and electrode

[0160]

[0161] As shown in Table 1, Examples 1-3 exhibited excellent and consistent physical properties: the viscosity change rate of the slurry remained at a low level of 2.5%-3.1% after 48 hours, indicating excellent slurry stability; the electrode peel strength was as high as 41.5-44.2 N / m, demonstrating super strong electrode adhesion; and the electrode volume resistivity was as low as 18.5-20.1 Ω·cm, confirming the excellent electronic conductivity inside the electrode.

[0162] Comparative Example 1 (complete conventional technology) has the worst performance in all aspects because none of the components have been optimized. It has a surge in viscosity, weak adhesion and high resistivity, and constitutes the performance benchmark.

[0163] Comparative Example 2 (without active material coating) lacked a stable interface of lithium phosphate / carbon layer, resulting in a weakened adhesive anchoring effect and a peel strength (24.8 N / m) that was significantly lower than that of the Example.

[0164] Comparative Example 3 (traditional physical mixed conductive agent) could not construct a covalently bonded three-dimensional network, and the conductive agent was prone to agglomeration, resulting in poor slurry stability (viscosity change rate of 12.7%) and a significant increase in electrode resistivity (32.5 Ω·cm).

[0165] Comparative Example 4 (ordinary PVDF adhesive) had the lowest peel strength (19.1 N / m) due to the lack of strong interfacial interactions of polyamide-imide segments, directly demonstrating the decisive role of graft copolymers in improving adhesion.

[0166] Comparative Example 5 (without ionic liquid) showed a significantly higher viscosity change rate (8.2%) than the Example due to the lack of ionic liquid to disperse and stabilize the nano-components.

[0167] This demonstrates that the four major innovations in this application—double coating of active materials, covalently bonded conductive network, graft copolymer binder, and ionic liquid additive—are all indispensable, and their synergistic effect is the fundamental reason for achieving a highly stable, highly adhesive, and highly conductive positive electrode slurry.

[0168] (2) Battery electrochemical performance testing

[0169] First charge / discharge efficiency (%): The ratio of the first discharge capacity to the charge capacity at a rate of 0.1C (1C=200 mA / g).

[0170] 1C rate discharge capacity retention (%): After activation by cycling at 0.2C rate for 3 weeks, the percentage of 1C discharge capacity relative to 0.2C discharge capacity is measured.

[0171] 5C rate discharge capacity retention (%): After activation by cycling at 0.2C rate for 3 weeks, the percentage of 5C discharge capacity relative to 0.2C discharge capacity is measured.

[0172] 1C / 1C 500-cycle capacity retention (%): The ratio of the capacity of the last discharge cycle to the capacity of the third discharge cycle after 500 constant current charge-discharge cycles at a 1C rate within a voltage window of 2.8 to 4.3V.

[0173] Table 2 Battery Electrochemical Performance

[0174]

[0175] As shown in Table 2, Examples 1-3 all exhibited excellent and balanced electrochemical performance: the initial charge-discharge efficiency was as high as 92.8%-93.5%, and the capacity retention rate at 1C rate was 96.5%-97.2%, indicating that it has excellent charge-discharge reversibility and medium-rate performance; at 5C rate, which reflects fast charging capability, the capacity retention rate can still reach 87.3%-89.7%; more importantly, after 500 cycles under harsh 1C / 1C conditions, the capacity retention rate is stable at a high level of 90.5%-92.1%, which proves its excellent long cycle life.

[0176] Comparative Example 1 (complete conventional technology) had the worst performance across all categories, with severe degradation in its cycle retention (76.8%) and 5C rate performance (72.4%), establishing the performance baseline for conventional technology.

[0177] Comparative Example 2 (without active substance coating) showed a significant decrease in initial efficacy (89.0%) and long-term cycling stability (82.5%) due to aggravated interfacial side reactions, highlighting the core role of dual coating in stabilizing the interface.

[0178] Comparative Example 3 (traditional physical mixed conductive agent) had the worst 5C rate performance (78.9%) among all groups due to the inefficiency of the electron transport network, which also affected the cycle life (80.2%). This directly proves the criticality of the covalently bonded three-dimensional conductive network in supporting high-rate operation and maintaining structural stability.

[0179] Comparative Example 4 (ordinary PVDF binder) suffered from insufficient adhesion, leading to gradual pulverization of the electrode during long-term cycling. Its cycle retention rate (81.2%) dropped significantly, demonstrating the irreplaceable role of the graft copolymer binder in maintaining the structural integrity of the electrode.

[0180] The high-rate performance (85.4%) of Comparative Example 5 (without ionic liquid) was slightly lower than that of the Example, indicating that ionic liquid has a clear auxiliary synergistic effect on improving interfacial ion transport and optimizing fast charging performance.

[0181] In summary, the data in Table 2 clearly demonstrate that this invention successfully achieves a balance between high initial efficiency, excellent rate performance, and ultra-long cycle life through multi-component synergy. The absence of any single innovative point would lead to a significant decline in the overall performance of the battery.

[0182] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A positive electrode slurry for a lithium-ion battery, characterized in that, The positive electrode slurry includes: positive electrode active material, conductive agent, binder and solvent; The mass ratio of the positive electrode active material, conductive agent, and binder is (94-97.5):(1-2):(1.5-3); The solid content of the positive electrode slurry is 35-45%; The positive electrode active material is a high-nickel ternary lithium oxide with a surface coated with lithium phosphate and a carbon layer; The conductive agent is composed of carboxylated carbon nanotubes, aminated conductive carbon black, and carbon quantum dots with epoxy groups on their surface. The adhesive is a polyvinylidene fluoride-grafted-polyamide-imide copolymer; The solvent consists of N-methylpyrrolidone and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

2. The positive electrode slurry for a lithium-ion battery according to claim 1, characterized in that, The mass ratio of the carboxylated carbon nanotubes, the aminated conductive carbon black, and the epoxy-containing carbon quantum dots on the surface is (0.5-1.5):(0.5-1.5):(0.1-0.5).

3. The positive electrode slurry for a lithium-ion battery according to claim 1, characterized in that, The mass of the 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt is 0.5 to 5% of the total mass of the solvent.

4. The positive electrode slurry for a lithium-ion battery according to claim 1, characterized in that, The preparation method of the positive electrode active material includes the following steps: S101. High-nickel ternary lithium oxide is dispersed in a solution of lithium hydroxide and ammonium dihydrogen phosphate, and then dried to obtain the precursor. S102. The precursor is sintered at 400-600°C for 2-6 hours to form a lithium phosphate coating layer on the surface of the high-nickel ternary lithium oxide, thereby obtaining a coating. S103. Under an inert atmosphere, the coating material is mixed with glucose and then heat-treated at 500-700°C for 1-4 hours to form a carbon layer on the outside of the lithium phosphate coating layer, thereby obtaining the positive electrode active material.

5. The positive electrode slurry for a lithium-ion battery according to claim 4, characterized in that, The molar ratio of lithium hydroxide to ammonium dihydrogen phosphate is (3.0-3.5):1; The mass of the ammonium dihydrogen phosphate is 0.5% to 3.0% of the mass of the high-nickel ternary lithium oxide; The glucose content is 0.5% to 2.0% of the coating material.

6. The positive electrode slurry for a lithium-ion battery according to claim 1, characterized in that, The method for preparing the adhesive includes the following steps: S201. Polyvinylidene fluoride is dissolved in N-methylpyrrolidone, then potassium hydroxide and tetrabutylammonium bromide are added, and the reaction is carried out at 60-90℃ for 0.5-3h to defluorinate the polyvinylidene fluoride main chain and obtain a functionalized polyvinylidene fluoride solution. S202. Under nitrogen protection, trimellitic anhydride, 4,4'-diaminodiphenyl ether and triethylamine are added to the functionalized polyvinylidene fluoride solution, and then the mixture is stirred and reacted at 80-120°C for 4-12 hours to allow polyamide imide to be grafted onto the functionalized polyvinylidene fluoride. The adhesive is obtained after post-treatment.

7. The positive electrode slurry for a lithium-ion battery according to claim 6, characterized in that, The mass ratio of the polyvinylidene fluoride, the potassium hydroxide, and the tetrabutylammonium bromide is 1 : (0.05-0.20) : (0.005-0.10). The molar ratio of trimellitic anhydride to 4,4'-diaminodiphenyl ether is 1:(0.9-1.1); The ratio of the total mass of the trimellitic anhydride and the 4,4'-diaminodiphenyl ether to the mass of the polyvinylidene fluoride is (0.10-0.50):1; The mass ratio of triethylamine to trimellitic anhydride is (0.05–0.20):

1.

8. A method for preparing the positive electrode slurry of a lithium-ion battery according to any one of claims 1 to 7, characterized in that, The method includes the following steps: S1. The carboxylated carbon nanotubes, the aminated conductive carbon black, and the carbon quantum dots with epoxy groups on their surface are mixed with a portion of the solvent and subjected to a first dispersion treatment to obtain a conductive agent dispersion. S2. Mix the polyvinylidene fluoride-grafted-polyamide-imide copolymer adhesive with the remaining portion of the solvent to obtain an adhesive solution; S3. The positive electrode active material is added to the binder solution for a second dispersion treatment, and then the conductive agent dispersion is added for a third dispersion treatment to obtain the initial positive electrode slurry. S4. The initial positive electrode slurry is vacuum stirred and degassed, and the viscosity is adjusted to 2500-6000 mPa·s to obtain the positive electrode slurry of the lithium-ion battery.

9. A positive electrode plate, characterized in that, The raw material for the positive electrode coating layer of the positive electrode sheet includes the positive electrode slurry as described in any one of claims 1 to 7.

10. A lithium battery, characterized in that, The lithium battery includes the positive electrode as described in claim 9.

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