A positive electrode and a lithium-ion battery

Abstract

This invention provides a positive electrode and a lithium-ion battery. The positive electrode includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer includes a positive electrode active material and an interface modifier. The positive electrode active material includes a nickel-manganese cobalt-free binary material with the chemical formula LiNi. x Mn (1‑x) O2, where x is 0.5~0.9; the interface regulator includes two or three of organic acid anhydride compounds, surface-modifying coupling agents, and phosphate ester compounds. The cathode provided by this invention, utilizing its interface regulator, can effectively solve the problems of poor structural stability, severe interfacial side reactions, and rapid battery performance degradation in nickel-manganese cobalt-free binary cathode materials during high-voltage cycling at 4.45V and above, significantly improving the cycle life and overall electrochemical stability of high-voltage lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a positive electrode and a lithium-ion battery. Background Technology

[0002] As consumer electronics products increasingly demand higher energy density, the operating voltage of lithium-ion batteries has gradually increased to 4.45V or even 4.48V. In the field of cathode materials, nickel-manganese cobalt-free binary layered materials have a significant cost advantage due to their cobalt-free nature, while also maintaining a high specific capacity, making them an important development direction for high-voltage battery cathode materials. However, nickel-manganese cobalt-free binary materials still have stability issues at high voltages. First, due to the lack of cobalt's stabilizing effect on the layered structure, this material is more prone to irreversible phase transitions during high-voltage cycling above 4.45V, leading to lattice distortion and microcrack formation. Second, the material surface has a high residual alkali content, mainly including lithium hydroxide and lithium carbonate. These residual alkalis catalyze electrolyte decomposition at high voltages, accelerating interfacial side reactions. Furthermore, the manganese element in the material is prone to disproportionation reactions at high voltages, generating divalent manganese ions that dissolve in the electrolyte and migrate to the negative electrode, damaging the solid electrolyte interfacial film and further exacerbating performance degradation. Summary of the Invention

[0003] To address the problem of poor stability of nickel-manganese cobalt-free binary cathode materials in high-voltage applications, which leads to poor interfacial film stability and battery cycle stability, a cathode and lithium-ion battery are provided.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: On one hand, the present invention provides a positive electrode, including a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer includes a positive electrode active material and an interface modifier; The positive electrode active material includes a nickel-manganese cobalt-free binary material with the chemical formula LiNi. x Mn (1-x) O2, where x is 0.5~0.9; The interface regulator includes two or three of the following: organic acid anhydride compounds, surface-modifying coupling agents, and phosphate ester compounds.

[0005] Optionally, the interface regulator includes organic acid anhydride compounds, surface-modifying coupling agents, and phosphate ester compounds.

[0006] Optionally, the organic anhydride compound includes one or more of maleic anhydride, phthalic anhydride, succinic anhydride, and glutaric anhydride.

[0007] Optionally, the surface-modified coupling agent includes one of an organosilane coupling agent and a titanate coupling agent; The organosilane coupling agent comprises one or more of γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and vinyltrimethoxysilane; and / or, The titanate coupling agent includes one or more of isopropyl tris(dioctyl pyrophosphoryloxy) titanate and isopropyl tris(dioctyl pyrophosphoryloxy) titanate.

[0008] Optionally, the phosphate ester compound includes one or more of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, dimethyl methylphosphonate, and diethyl ethylphosphonate.

[0009] Optionally, in the positive electrode active material layer, the mass percentage of the organic acid anhydride compound is 0.2% to 1.0% of the positive electrode active material; The surface-modifying coupling agent has a mass percentage of 0.1% to 0.5% of the positive electrode active material; The mass percentage of the phosphate ester compound is 0.3% to 1.0% of the positive electrode active material.

[0010] On the other hand, the present invention provides a lithium-ion battery, including a negative electrode, an electrolyte, and the positive electrode.

[0011] Optionally, the electrolyte includes lithium salt, organic solvent, and functional additives; The lithium salt includes a compound of lithium difluorosulfonylimide and lithium difluorooxalate borate. The total concentration of the lithium salt is 1.0 mol / L to 1.5 mol / L; The molar ratio of lithium difluorosulfonylimide to lithium difluorooxalate borate is 1.5 to 4.

[0012] Optionally, the organic solvent includes a mixture of fluorocarbonate solvents, phosphate ester solvents, and linear carbonate solvents; The fluorocarbonate solvent accounts for 15% to 30% of the total volume of the organic solvent, the phosphate ester solvent accounts for 10% to 25% of the total volume of the organic solvent, and the linear carbonate solvent accounts for 50% to 70% of the total volume of the organic solvent.

[0013] Optionally, the fluorocarbonate solvent includes one or more of fluoroethylene carbonate and difluoroethylene carbonate; and / or, The phosphate ester solvent includes one or more of trimethyl phosphate and triethyl phosphate; and / or, The linear carbonate solvents include one or more of methyl ethyl carbonate, diethyl carbonate, and methyl propyl carbonate.

[0014] Optionally, the functional additive includes a compound of ethylene carbonate and tetrafluoroterephthalonitrile; Based on the total mass of the electrolyte (100%), the mass percentage of ethylene ethylene carbonate is 0.5% to 2.0%. Based on the total mass of the electrolyte (100%), the mass percentage of tetrafluoroterephthalonitrile is 0.5% to 1.5%.

[0015] Optionally, the operating voltage of the lithium-ion battery is ≥4.45V.

[0016] The beneficial effects of this application are as follows: In the positive electrode provided in this application, LiNi is used. x Mn (1-x) O2 nickel-manganese cobalt-free binary material is used as a positive electrode active material. It is compounded with at least two of the following as interface regulators: organic acid anhydride compounds, surface-modifying coupling agents, and phosphate ester compounds, which play a synergistic role. Among them, the surface-modifying coupling agent can effectively coat the surface of the active material particles, reduce the residual alkali content on the surface of the nickel-manganese cobalt-free binary material, inhibit the electrolyte catalytic decomposition side reaction caused by residual alkali, and stabilize the layered crystal structure of the material, alleviating the problems of irreversible phase transition and lattice distortion under high voltage conditions. The organic acid anhydride and phosphate ester components can synergistically optimize the electrode interface environment, inhibit the disproportionation reaction of manganese and reduce the dissolution and migration of divalent manganese ions, and avoid damage to the SEI film of the negative electrode. The combination of multiple interface regulators addresses the problems of poor structural stability, severe interface side reactions, and rapid battery performance degradation of nickel-manganese cobalt-free binary positive electrode materials during high voltage cycling at 4.45V and above from multiple dimensions, such as crystal structure stability, surface impurity passivation, electrolyte interface stabilization, and metal ion dissolution inhibition. This significantly improves the cycle life and overall electrochemical stability of high-voltage lithium-ion batteries. Detailed Implementation

[0017] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0018] This invention provides a positive electrode, comprising a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer comprises a positive electrode active material and an interface modifier; The positive electrode active material includes a nickel-manganese cobalt-free binary material with the chemical formula LiNi. x Mn (1-x) O2, where x is 0.5~0.9; The interface regulator includes two or three of the following: organic acid anhydride compounds, surface-modifying coupling agents, and phosphate ester compounds.

[0019] Specifically, in the positive electrode provided in this application, LiNi is used. x Mn (1-x) O2 nickel-manganese cobalt-free binary material is used as a positive electrode active material. It is compounded with at least two of the following as interface regulators: organic acid anhydride compounds, surface-modifying coupling agents, and phosphate ester compounds, which play a synergistic role. Among them, the surface-modifying coupling agent can effectively coat the surface of the active material particles, reduce the residual alkali content on the surface of the nickel-manganese cobalt-free binary material, inhibit the electrolyte catalytic decomposition side reaction caused by residual alkali, and stabilize the layered crystal structure of the material, alleviating the problems of irreversible phase transition and lattice distortion under high voltage conditions. The organic acid anhydride and phosphate ester components can synergistically optimize the electrode interface environment, inhibit the disproportionation reaction of manganese and reduce the dissolution and migration of divalent manganese ions, and avoid damage to the SEI film of the negative electrode. The combination of multiple interface regulators addresses the problems of poor structural stability, severe interface side reactions, and rapid battery performance degradation of nickel-manganese cobalt-free binary positive electrode materials during high voltage cycling at 4.45V and above from multiple dimensions, such as crystal structure stability, surface impurity passivation, electrolyte interface stabilization, and metal ion dissolution inhibition. This significantly improves the cycle life and overall electrochemical stability of high-voltage lithium-ion batteries.

[0020] Furthermore, organic acid anhydrides can chemically react with lithium hydroxide and lithium carbonate on the surface of the positive electrode active material to generate the corresponding lithium carboxylate salts. First, the in-situ reaction can proceed uniformly on the surface of each positive electrode particle; second, the reaction products are chemically bonded to the particle surface, forming a stable organic-inorganic hybrid interface layer; third, the reaction process is self-limiting, consuming only the residual alkali on the surface and not excessively corroding the bulk material phase. The surface-modified coupling agent molecule contains an alkoxy group at one end, which can undergo a condensation reaction with the hydroxyl groups on the surface of the cathode material to form a strong chemical bond; the other end contains functional groups, such as epoxy and amino groups, which can participate in the formation of the CEI film during subsequent formation processes. In this way, the coupling agent anchors the artificial CEI film to the cathode surface, significantly improving the bonding strength and durability of the interfacial layer; Phosphate esters can form a phosphorus-oxygen bond-rich interfacial layer on the cathode surface, exhibiting excellent lithium-ion conductivity and high-voltage oxidation resistance. Furthermore, phosphate esters show better compatibility with homologous components in the subsequent electrolyte, facilitating the formation of a uniform and dense composite CEI film.

[0021] In some embodiments, the interface modifier includes organic acid anhydride compounds, surface-modifying coupling agents, and phosphate ester compounds.

[0022] Extensive verification in this application has shown that the simultaneous use of the organic acid anhydride compounds, surface-modifying coupling agents, and phosphate ester compounds specified in this application for interface regulation can achieve a better synergistic effect. Specifically, the organic acid anhydride compounds adsorb onto the electrode interface through polar functional groups, neutralizing the local alkaline environment at the interface and inhibiting the oxidative decomposition of the electrolyte; the phosphate esters form complexes with manganese ions through phosphorus-oxygen coordination bonds, effectively inhibiting manganese disproportionation reactions and ion migration. The three types of substances work together to form an integrated protective network from the particle bulk to the surface and then to the solid-liquid interface. Compared with a two-component compound, this can further reduce the incidence of interfacial side reactions under high voltage, reduce manganese dissolution, enhance the anti-phase transition ability of the layered structure, maximize the interface regulation effect, and significantly delay the performance degradation of the battery during high-voltage cycling.

[0023] In some embodiments, the organic anhydride compounds include one or more of maleic anhydride, phthalic anhydride, succinic anhydride, and glutaric anhydride.

[0024] Specifically, one or more of the above-mentioned maleic anhydride, phthalic anhydride, succinic anhydride, and glutaric anhydride can be selected as organic anhydride components. These substances all contain highly active anhydride functional groups, possessing strong polarity and interfacial adsorption capabilities. On one hand, the anhydride groups can neutralize residual alkalis such as LiOH and Li2CO3 on the surface of nickel-manganese binary materials, eliminating the catalytic decomposition effect of alkaline impurities on the electrolyte. On the other hand, the molecules can be directionally adsorbed at the positive electrode interface, forming a thin and dense organic passivation film, blocking direct contact between the electrolyte and the active material under high voltage, and inhibiting electrolyte oxidative decomposition. Furthermore, anhydride molecules with different carbon chain lengths and ring structures can be adapted to active particles with different surface morphologies. For example, succinic anhydride and glutaric anhydride have excellent flexibility due to their chain structure, while maleic anhydride and phthalic anhydride have strong rigidity due to their ring structure. Using them in combination can improve the flexibility and structural stability of the interfacial film, further optimizing the high-voltage interfacial environment.

[0025] In some embodiments, the surface-modified coupling agent includes one of an organosilane coupling agent and a titanate coupling agent; The organosilane coupling agent comprises one or more of γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and vinyltrimethoxysilane; and / or, The titanate coupling agent includes one or more of isopropyl tris(dioctyl pyrophosphoryloxy) titanate and isopropyl tris(dioctyl pyrophosphoryloxy) titanate.

[0026] Specifically, any one of the above-mentioned organosilane coupling agents and titanate coupling agents is selected as the surface modification coupling agent. Both types of coupling agents are typical amphiphilic compounds. One end can chemically bond with the hydroxyl groups and oxygen vacancies on the surface of the nickel-manganese binary material, while the organic groups at the other end extend outward to form a hydrophobic coating layer. Organosilane coupling agents (γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and vinyltrimethoxysilane) are firmly bonded to the material surface via silicon-oxygen bonds, constructing a continuous and uniform inorganic-organic composite coating layer. This not only completely isolates residual alkali on the surface from contact with the electrolyte, but the silicon-oxygen framework can also embed itself into the interstitial spaces of the crystal lattice, enhancing the bonding force of the layered structure and suppressing lattice slip and irreversible phase transitions under high voltage. Titanate coupling agents (isopropyltris(dioctylpyrophosphoryloxy)titanate and isopropyltris(dioctylpyrophosphoryloxy)titanate) contain phosphatoxy functional groups, which can simultaneously generate weak coordination with the material surface and electrolyte components, further improving interfacial compatibility and also assisting in the complexation of free manganese ions. The synergistic effect of these two types of coupling agents achieves multiple effects, including surface coating, structural reinforcement, and interfacial compatibility, maintaining the structural integrity of the material during high-voltage cycling for a long time.

[0027] In some embodiments, the phosphate ester compound includes one or more of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, dimethyl methylphosphonate, and diethyl ethylphosphonate.

[0028] Specifically, one or more of the following listed compounds—trimethyl phosphate, triethyl phosphate, triphenyl phosphate, dimethyl methylphosphonate, and diethyl ethylphosphonate—can be used as phosphate ester interface modifiers. These phosphate ester compounds contain P=O polar coordinating groups. Under high-voltage conditions, these groups can form stable coordination complexes with low-valent manganese ions released from the positive electrode surface, effectively inhibiting manganese disproportionation and blocking the migration path of divalent manganese ions to the negative electrode, thus preventing the negative electrode SEI film from being eroded by manganese ions. Simultaneously, phosphate ester molecules can participate in the construction of the positive electrode interface film, improving the high-voltage resistance and ion conductivity of the interface film, and reducing interfacial impedance. Phosphate esters with different substituents exhibit different properties. Alkyl phosphate esters have good fluidity and excellent ion conductivity, while aryl phosphate esters have stronger thermal stability and oxidation resistance. A combination of multiple substances can address the multiple requirements of interfacial ion transport, high-voltage oxidation resistance, and manganese dissolution inhibition, continuously stabilizing the electrode interface state.

[0029] In some embodiments, the mass percentage of the interface modifier is 0.6% to 2.5% of the positive electrode active material.

[0030] Specifically, the mass percentage of the interface modifier is limited to 0.6% to 2.5% of the positive electrode active material. Within this overall ratio range, the multi-component interface modifier can fully exert its synergistic effect, which is beneficial for long-term improvement of problems such as material phase transition, manganese dissolution, and interface film damage under high voltage conditions, thereby improving the cycle stability and overall electrochemical performance of high-voltage lithium-ion batteries. If the content is less than 0.6%, the interface modifier loading is insufficient, and it is impossible to form a complete coating layer and a uniform interface passivation film on the surface of the active particles. It is difficult to fully passivate the residual alkali on the material surface, inhibit the disproportionation and dissolution of manganese ions and electrolyte side reactions. The problems of positive electrode structural instability and interface degradation under high voltage cannot be effectively improved. If the content is higher than 2.5%, the excessive interface modifier will form an excessively thick coating layer and interface film, increasing the lithium-ion transport resistance and electrode impedance, and aggravating the battery performance degradation.

[0031] In some embodiments, the organic acid anhydride compound in the positive electrode active material layer has a mass percentage content of 0.2% to 1.0% of the positive electrode active material. The surface-modifying coupling agent has a mass percentage of 0.1% to 0.5% of the positive electrode active material; The mass percentage of the phosphate ester compound is 0.3% to 1.0% of the positive electrode active material.

[0032] Specifically, limiting the mass ratio of the three types of interface modifiers based on the positive electrode active material helps to better leverage their synergistic effects. The dosage of surface-modifying coupling agents is relatively low because only a thin coating layer is needed to modify the particle surface; excessive dosage would result in an overly thick coating layer, hindering lithium-ion insertion / extraction and increasing electrode impedance. Organic anhydride compounds, within the 0.2%–1.0% content range, can effectively neutralize residual alkali on the surface and form a uniform interfacial passivation film. If the dosage is less than 0.2%, the residual alkali removal will be incomplete; excessive dosage (above 1.0%) can easily trigger side reactions and increase interfacial impedance. Phosphate ester compounds, at a ratio of 0.3%–1.0%, can fully exert their role in complexing manganese ions and strengthening the interfacial film. Too low a content results in insufficient manganese dissolution inhibition, while too high a content reduces the overall stability of the electrolyte. In other words, precise control of the content ratio ensures that the interfacial modulation functions of each component are fully utilized while avoiding problems such as increased impedance and side reactions caused by excessive additives, achieving a balance between functionality and electrochemical kinetic performance.

[0033] Further, the mass percentage of the organic acid anhydride compound includes, but is not limited to, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%. Furthermore, the mass percentage of the surface-modified coupling agent includes, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%.

[0034] Furthermore, the mass percentage of the phosphate ester compound includes, but is not limited to, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%.

[0035] In another embodiment, the present invention provides a lithium-ion battery, including a negative electrode, an electrolyte, and the positive electrode.

[0036] Specifically, the lithium-ion battery includes the positive electrode provided in this application, which is made of LiNi x Mn (1-x) O2 nickel-manganese cobalt-free binary material serves as the main active material for the positive electrode. Based on this, two or more substances from organic anhydrides, surface-modifying coupling agents, and phosphate esters are added as interface regulators. These multiple components complement each other through their complementary physicochemical properties, creating a synergistic effect. Specifically, the surface-modifying coupling agent can construct a coating layer on the surface of the active particles, passivating residual alkaline impurities on the material surface and blocking the catalytic side reaction pathways between residual alkali and the electrolyte. Simultaneously, it anchors the crystal lattice and reduces layered structure distortion under high voltage. The organic anhydrides and phosphate esters synergistically regulate the physicochemical environment at the solid-liquid interface, and, through functional group complexation, inhibit manganese ion disproportionation and dissolution. This forms a protective system from four dimensions: crystal structure, particle surface impurities, electrode interface reactions, and metal ion dissolution. This specifically addresses the issues of easy interface film damage and rapid cycle decay in this type of binary material under high voltage conditions of 4.45V and above, comprehensively improving the overall electrochemical stability of the positive electrode and the battery.

[0037] In some embodiments, the electrolyte includes lithium salt, organic solvent, and functional additives; The lithium salt includes a compound of lithium difluorosulfonylimide and lithium difluorooxalate borate. The total concentration of the lithium salt is 1.0 mol / L to 1.5 mol / L; The molar ratio of lithium difluorosulfonylimide to lithium difluorooxalate borate is 1.5 to 4.

[0038] Specifically, lithium difluorosulfonylimide has strong dissociation ability and high ionic conductivity, which can improve the lithium-ion transport efficiency of the electrolyte. At the same time, its decomposition products can form a highly stable interface film. Lithium difluorooxalate borate is rich in oxalate and boron-fluorine groups, which can synergistically repair the positive and negative electrode interface films and further inhibit electrolyte decomposition and metal ion dissolution. The combination of lithium difluorosulfonylimide and lithium difluorooxalate borate enables the lithium salt to have better film-forming behavior on the surface modified by the positive electrode interface regulator, and can form an interface film with lower impedance and higher stability.

[0039] Furthermore, limiting the total lithium salt concentration to the range of 1.0 mol / L to 1.5 mol / L ensures that the electrolyte has sufficient current-carrying ions, while avoiding excessive concentration that would lead to increased electrolyte viscosity and hindered lithium ion migration. The specific molar ratio allows the two lithium salts to complement each other, ensuring both high ionic conductivity of the electrolyte and enhanced film-forming ability at high and low voltage interfaces. After being adapted to the modified cathode, this further improves the battery's high voltage tolerance and cycle stability.

[0040] In some embodiments, the organic solvent comprises a mixture of fluorocarbonate solvents, phosphate ester solvents, and linear carbonate solvents; The fluorocarbonate solvent accounts for 15% to 30% of the total volume of the organic solvent, the phosphate ester solvent accounts for 10% to 25% of the total volume of the organic solvent, and the linear carbonate solvent accounts for 50% to 70% of the total volume of the organic solvent.

[0041] Specifically, the composition is defined as 15%–30% fluorocarbonate, 10%–25% phosphate ester, and 50%–70% linear carbonate. Linear carbonate is used as the main solvent due to its low viscosity and good lithium-ion solubility, ensuring the basic ion conductivity of the electrolyte. Fluorocarbonate possesses excellent high-voltage oxidation resistance; the strong electron-withdrawing effect of fluorine atoms can increase the oxidation potential of solvent molecules, making it less prone to decomposition under high voltages of 4.45V and above. It also participates in the construction of the interfacial film, improving the film's weather resistance. Phosphate ester solvents have excellent compatibility with the positive electrode interface regulator components, synergistically complexing manganese ions to inhibit manganese ion dissolution and optimizing the electrolyte's flame retardancy and thermal stability. This combination of three components is beneficial for balancing electrolyte ion conductivity, high-voltage oxidation resistance, thermal safety, and interfacial stability.

[0042] In some embodiments, the fluorocarbonate solvent includes one or more of fluoroethylene carbonate and difluoroethylene carbonate; and / or, The phosphate ester solvent includes one or more of trimethyl phosphate and triethyl phosphate; and / or, The linear carbonate solvents include one or more of methyl ethyl carbonate, diethyl carbonate, and methyl propyl carbonate.

[0043] In some embodiments, the functional additive comprises a combination of ethylene carbonate and tetrafluoroterephthalonitrile; Based on the total mass of the electrolyte (100%), the mass percentage of ethylene ethylene carbonate is 0.5% to 2.0%. Based on the total mass of the electrolyte (100%), the mass percentage of tetrafluoroterephthalonitrile is 0.5% to 1.5%.

[0044] Specifically, the main function of the ethylene ethylene carbonate is to form a uniform polymer film on the surface of the positive electrode modified by the interface regulator. The cyano group in tetrafluoroterephthalonitrile can form a coordinate bond with the dissolved manganese ions, inhibiting the migration of manganese ions to the negative electrode, while the fluorine atoms improve the antioxidant capacity of the molecule, making it stable under high voltage.

[0045] By further limiting the mass percentage of both components, it is beneficial to further ensure film-forming properties, suppress side reactions, and thus achieve better results.

[0046] In some embodiments, the operating voltage of the lithium-ion battery is ≥4.45V.

[0047] This application limits the operating voltage of the lithium-ion battery to ≥4.45V. This voltage range falls within the high-voltage application range of lithium-ion batteries. Under this condition, traditional nickel-manganese cobalt-free binary cathodes are prone to problems such as layered structure phase transition, severe electrolyte oxidation, large-scale dissolution of manganese ions, and interface film failure. The technical solution of this application, through limiting the composition of the cathode active material, compounding and modifying multiple types of interface modifiers, and combining compounded lithium salts, multi-component solvent systems, and functional additives, constructs a high-voltage protection system from the aspects of cathode crystal structure, solid-liquid interface, and electrolyte. Each component synergistically improves the high-voltage oxidation resistance, structural stability, and anti-dissolution ability of the material and electrolyte, thus enabling stable tolerance to high-voltage environments of 4.45V and above. The electrochemical reaction exhibits strong reversibility, effectively solving the technical problems of rapid battery cycle decay and failure under high voltage, and adapting to the practical application requirements of high-voltage lithium-ion batteries.

[0048] The present invention will be further illustrated by the following examples.

[0049] Table 1 Example 1 This embodiment illustrates the positive electrode and lithium-ion battery disclosed in this invention, and includes the following operational steps: Preparation of positive electrode Take LiNi as the positive electrode active material 0.5 Mn 0.5 O2 (96.8%), conductive agent Super-P (1%), binder PVDF (1%) and interface modifier (maleic anhydride, γ-glycidoxypropyltrimethoxysilane, trimethyl phosphate) (1.2%) were mixed and then NMP was added to prepare a positive electrode slurry. The positive electrode slurry was coated onto the surface of the positive electrode current collector and dried to obtain the positive electrode.

[0050] Preparation of negative electrode The negative electrode active material graphite (98%), stabilizer CMC (carboxymethyl cellulose) (1%), and binder SBR (styrene-butadiene rubber) are mixed and deionized water is added to obtain a negative electrode slurry. The negative electrode slurry is coated onto the surface of the negative electrode current collector and dried to obtain the negative electrode.

[0051] Preparation of electrolyte Fluorinated ethylene carbonate, triethyl phosphate, and methyl ethyl carbonate were mixed in a volume ratio of 50:30:20 as an organic solvent. 2.0% ethylene ethylene carbonate and 1.0% tetrafluoroterephthalonitrile were used as functional additives. After mixing, lithium salt (lithium difluorosulfonylimide and lithium difluorooxalate borate in a molar ratio of 2) was added to obtain an electrolyte with a total lithium salt concentration of 1.0 mol / L.

[0052] Preparation of lithium-ion batteries The negative electrode, separator (PE film), and positive electrode are placed in sequence to form a battery cell. The battery cell is placed in a casing, injected with electrolyte, and sealed. After processes such as formation and degassing, a lithium-ion battery is obtained.

[0053] Examples 2-8 Examples 2-8 illustrate the positive electrode and lithium-ion battery disclosed in this invention, and include most of the operations in Example 1, except that: In Examples 2-8, the positive electrode active material, organic acid anhydride compounds, the mass percentage of organic acid anhydride compounds, the surface modified coupling agent, the mass percentage of surface modified coupling agent, the phosphate ester compounds, and the mass percentage of phosphate ester compounds are all based on Table 1.

[0054] Comparative Examples 1-4 Comparative Examples 1-4 are used to compare and illustrate the positive electrode and lithium-ion battery disclosed in this invention, including most of the operations in Example 1, the differences being: The content of positive electrode active material, organic acid anhydride compound, mass percentage of organic acid anhydride compound, surface modified coupling agent, mass percentage of surface modified coupling agent, phosphate ester compound, and mass percentage of phosphate ester compound in Comparative Examples 1-4 are all based on Table 1.

[0055] Performance testing The following performance tests were performed on Examples 1-8 and Comparative Examples 1-4 prepared above: Energy retention rate after 800 cycles: The specific charging and discharging steps are as follows: 1. Place the test cell in a 45-degree Celsius temperature chamber and let it stand for 120 minutes; 2. Charge at 1C constant current and constant voltage to 4.45V, cut off at 0.05C, and let stand for 10 minutes; 3. Discharge at a constant current of 0.5C to 3.0V; 4. Repeat steps 1-2 for 800 cycles; Record the energy retention rate of the battery cell after 800 cycles.

[0056] The test results are entered into Table 2.

[0057] Table 2 As can be seen from the test results in Table 2, the test results of Examples 1 to 8 are significantly better than those of Comparative Examples 1 to 4. Since the interface regulator described in this application was added when preparing the cathode in Examples 1 to 8, the interface regulation system of this invention was verified to improve the cycle stability of high-voltage nickel-manganese cobalt-free binary cathode batteries.

[0058] Specifically, Example 1 combines three interface modifiers: organic acid anhydride compounds, surface-modifying coupling agents, and phosphate ester compounds. After 800 cycles, the energy retention rate of the battery cell reaches 86%, which is good. Examples 2-4 use two different interface modifiers in combination, with energy retention rates of 84%, 85%, and 84%, respectively, indicating that combining two of the interface modifiers specified in this application can also achieve a good interface improvement effect. Compared to Example 1, Examples 5 and 6 adjusted the addition ratios of the three regulators, with Example 5 showing an energy retention rate increased to 86% after optimization. In Example 6, the amount of maleic anhydride added was 1% (upper limit), the amount of γ-glycidyl etheroxypropyltrimethoxysilane added was 0.5% (upper limit), and the amount of trimethyl phosphate added was 0.3% (lower limit). Its energy retention rate was 84%, which further indicates that there is a corresponding preferred addition range for the interface regulator. Excessive or insufficient addition beyond the preferred range will slightly weaken its effect. Compared with Example 1, Example 7 changed the specific type of interface regulator, and the energy retention rate also reached 86%, proving that similar compounds within the scope of this invention can achieve good interface regulation effects. Example 8: The positive electrode active material was replaced with LiNi with a high nickel ratio. 0.8 Mn 0.2 O2's energy retention rate drops to 82% because increasing the nickel content exacerbates the instability of the material structure. Even with a complete control system, its performance degradation will be accelerated under high-pressure cycling.

[0059] Comparative Example 1, without the interface modifiers specified in this application, had an energy retention rate of only 68% and the most severe performance degradation. Comparative Examples 2-4, when individually supplemented with organic acid anhydride compounds, surface-modifying coupling agents, and phosphate ester compounds, showed energy retention rates of 77%, 75%, and 73%, respectively. Although these were improvements over the blank group (Comparative Example 1), the improvement was not significant. This indicates that a single interface regulator cannot provide protection from multiple aspects, such as structural stability, residual alkali passivation, and inhibition of manganese dissolution. It also demonstrates the synergistic effect of the multi-component interface regulator combination specified in this application. That is, the interface regulator can effectively solve the problems of poor structural stability, severe interfacial side reactions, and rapid battery performance degradation of nickel-manganese cobalt-free binary cathode materials during high-voltage cycling at 4.45V and above, significantly improving the cycle life and overall electrochemical stability of high-voltage lithium-ion batteries.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A positive electrode, characterized in that, It includes a positive current collector and a positive active material layer, wherein the positive active material layer includes a positive active material and an interface modifier; The positive electrode active material includes a nickel-manganese cobalt-free binary material with the chemical formula LiNi. x Mn (1-x) O2, where x is 0.5~0.9; The interface regulator includes two or three of the following: organic acid anhydride compounds, surface-modifying coupling agents, and phosphate ester compounds.

2. The positive electrode according to claim 1, characterized in that, The interface modifiers include organic acid anhydride compounds, surface-modifying coupling agents, and phosphate ester compounds.

3. The positive electrode according to claim 1, characterized in that, The organic acid anhydride compounds include one or more of maleic anhydride, phthalic anhydride, succinic anhydride, and glutaric anhydride.

4. The positive electrode according to claim 1, characterized in that, The surface-modified coupling agent includes one of organosilane coupling agents and titanate coupling agents; The organosilane coupling agent comprises one or more of γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and vinyltrimethoxysilane; and / or, The titanate coupling agent includes one or more of isopropyl tris(dioctyl pyrophosphoryloxy) titanate and isopropyl tris(dioctyl pyrophosphoryloxy) titanate.

5. The positive electrode according to claim 1, characterized in that, The phosphate ester compounds include one or more of trimethyl phosphate, triethyl phosphate, triphenyl phosphate, dimethyl methylphosphonate, and diethyl ethylphosphonate.

6. The positive electrode according to claim 1, characterized in that, In the positive electrode active material layer, the organic acid anhydride compound has a mass percentage content of 0.2% to 1.0% of the positive electrode active material; The surface-modifying coupling agent has a mass percentage of 0.1% to 0.5% of the positive electrode active material; The mass percentage of the phosphate ester compound is 0.3% to 1.0% of the positive electrode active material.

7. A lithium-ion battery, characterized in that, It includes a negative electrode, an electrolyte, and a positive electrode as described in any one of claims 1 to 6.

8. The lithium-ion battery according to claim 7, characterized in that, The electrolyte includes lithium salt, organic solvent, and functional additives; The lithium salt includes a compound of lithium difluorosulfonylimide and lithium difluorooxalate borate. The total concentration of the lithium salt is 1.0 mol / L to 1.5 mol / L; The molar ratio of lithium difluorosulfonylimide to lithium difluorooxalate borate is 1.5 to 4.

9. The lithium-ion battery according to claim 8, characterized in that, The organic solvents include a mixture of fluorocarbonate solvents, phosphate ester solvents and linear carbonate solvents; The fluorocarbonate solvent accounts for 15% to 30% of the total volume of the organic solvent, the phosphate ester solvent accounts for 10% to 25% of the total volume of the organic solvent, and the linear carbonate solvent accounts for 50% to 70% of the total volume of the organic solvent.

10. The lithium-ion battery according to claim 9, characterized in that, The fluorocarbonate solvents include one or more of fluoroethylene carbonate and difluoroethylene carbonate; and / or The phosphate ester solvent includes one or more of trimethyl phosphate and triethyl phosphate; and / or, The linear carbonate solvents include one or more of methyl ethyl carbonate, diethyl carbonate, and methyl propyl carbonate.

11. The lithium-ion battery according to claim 8, characterized in that, The functional additives include a compound of ethylene carbonate and tetrafluoroterephthalonitrile; Based on the total mass of the electrolyte (100%), the mass percentage of ethylene ethylene carbonate is 0.5% to 2.0%. Based on the total mass of the electrolyte (100%), the mass percentage of tetrafluoroterephthalonitrile is 0.5% to 1.5%.

12. The lithium-ion battery according to claim 7, characterized in that, The lithium-ion battery has an operating voltage of ≥4.45V.

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