A coated and modified ternary cathode material, its preparation method, and its application.

Abstract

This invention discloses a coated and modified ternary cathode material, its preparation method, and its applications, belonging to the field of cathode material technology. The coated and modified ternary cathode material comprises: a ternary cathode active material core, and a composite material coating at least a portion of the core's surface. This invention uses high specific surface area WO3 and C3N4 to co-coat the ternary cathode material. The high specific surface area WO3 surface is rich in active sites and oxygen vacancies, which can react with residual lithium on the cathode surface, enhancing the chemical bonding between the coating layer and the cathode, providing lithium-ion conduction channels, and reducing interfacial impedance. C3N4 has good flexibility and abundant nitrogen-containing functional groups, which can buffer charge-discharge volume changes and neutralize acidic substances, inhibiting transition metal dissolution. The two materials complement each other, with WO3 providing structural support and an ion conduction framework, and C3N4 filling gaps and inhibiting crack propagation. Through different mechanisms, they synergistically suppress interfacial side reactions, achieving dual chemical protection.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery cathode material technology, specifically relating to a coated and modified ternary cathode material, its preparation method, and its application. Background Technology

[0002] High-nickel ternary cathode materials (such as NCM811 and NCA) have become the mainstream choice for power batteries due to their high specific capacity, but they face many problems during high-voltage charging and long-cycle operation. The surface of high-nickel cathodes exhibits high chemical activity, making them prone to side reactions with the electrolyte, leading to continuous growth of the cathode-electrolyte interface (CEI) film and a continuous increase in interfacial impedance. Simultaneously, the high oxidation state of transition metal ions (especially Ni)... 4+ Lithium readily dissolves and migrates to the negative electrode, catalyzing electrolyte decomposition, damaging the SEI film on the negative electrode surface, and accelerating irreversible lithium consumption. Furthermore, high-nickel cathodes, under deep delithiation, are prone to irreversible reconstruction of layered-rock-salt phases, resulting in loss of surface electrochemical activity and capacity decay. These problems severely restrict the cycle life and safety performance of high-nickel ternary batteries. Surface coating modification is currently recognized as one of the effective strategies. By constructing a uniform and stable coating layer on the surface of cathode particles, direct contact between the electrolyte and the positive electrode active material can be effectively isolated, interfacial side reactions can be suppressed, transition metal dissolution and surface phase transitions can be slowed down, and charge transfer impedance can be reduced.

[0003] Among numerous coating materials, metal oxides such as Al2O3, TiO2, ZrO2, MoO3, and WO3 have been extensively studied. Research indicates that they can improve the interfacial stability of cathode materials and promote lithium-ion migration at the interface through physical barrier effects and chemical interactions. Tungsten trioxide (WO3), in particular, stands out due to its unique layered structure and variable valence state (W... 6+ / W 5+ WO3, with its ability to neutralize residual alkali on the surface, is considered a promising cathode coating material. However, single WO3 coating has significant shortcomings: firstly, most WO3 used in research is a commercial product with a typically low specific surface area (commercial bulk WO3 has a specific surface area of ​​only 1-15 m²). 2 The limited number of surface active sites makes it difficult to form a uniform and dense nanoscale coating layer on the surface of cathode particles. On the other hand, metal oxide coatings are rigid and have poor toughness. When cathode particles repeatedly undergo anisotropic volume changes during charge and discharge, they are prone to microcracks or even local detachment, causing the protective effect of the coating layer to gradually diminish with cycling. In addition, some studies have found that excessive WO3 coating may introduce additional electrochemical inert phases, which may increase interfacial impedance and affect the rate performance of the battery.

[0004] Graphitic carbon nitride (C3N4) is a two-dimensional layered inorganic semiconductor material formed by covalent bonds between carbon and nitrogen elements. Its structure is similar to graphite, with highly conjugated two-dimensional planes formed by triazine or heptaazine rings connected by nitrogen bridge atoms within the layers, and the layers stacked by van der Waals forces. C3N4 exhibits good chemical stability and abundant nitrogen-containing functional groups on its surface (such as —NH2, —NH—, C=N, etc.), and has attracted widespread attention in recent years in the fields of photocatalysis, electrocatalysis, and energy storage. In the modification of lithium-ion battery cathodes, the nitrogen-containing functional groups on the C3N4 surface can undergo acid-base reactions with residual lithium on the cathode surface, helping to reduce the content of alkaline residues on the surface; its flexible layered structure also holds promise for buffering volume changes in cathode particles. However, single C3N4 coating also has limitations: its own electronic and ion conductivity is poor, and when used alone as a coating layer, it is not conducive to interfacial charge transfer and may increase electrode polarization; at the same time, the C3N4 layers are mainly bonded by van der Waals forces, and the interlayer forces are weak. During long-term cycling, the layered structure may peel off, affecting the integrity of the coating layer. Summary of the Invention

[0005] In view of at least one problem existing in the prior art, the purpose of the present invention is to provide a coated and modified ternary cathode material, its preparation method, and its application.

[0006] In a first aspect, the present invention provides a coated and modified ternary cathode material, comprising a ternary cathode active material core and a composite material coating at least a portion of the surface of the core, wherein the composite material is composed of high specific surface area WO3 and C3N4, and the specific surface area of ​​the high specific surface area WO3 is not less than 28 m². 2 / g.

[0007] Secondly, this invention provides a method for preparing a coated and modified ternary cathode material, comprising the following steps: S1. High specific surface area WO3, C3N4 and solvent are mixed and ultrasonically dispersed. After the solvent is removed by evaporation, a mixture is obtained. The mixture is sintered under an inert atmosphere to obtain a composite material. S2. After mixing the ternary cathode active material with the composite material, sintering is carried out under an inert atmosphere to obtain the coated and modified ternary cathode material.

[0008] Thirdly, the present invention provides a positive electrode sheet comprising the aforementioned coated and modified ternary positive electrode material.

[0009] Fourthly, the present invention provides a lithium battery, including the aforementioned positive electrode.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs a blend coating of high-specific-surface-area WO3 and C3N4 onto a ternary cathode material. The high-specific-surface-area WO3 surface possesses abundant active sites and oxygen vacancies, allowing for thorough reaction with residual lithium on the cathode surface, enhancing the chemical bonding between the coating layer and the cathode, while simultaneously providing a high-density lithium-ion conduction channel and effectively reducing interfacial impedance. C3N4 exhibits good flexibility and abundant nitrogen-containing functional groups, buffering volume changes during cathode charging and discharging, neutralizing acidic substances generated by electrolyte decomposition, and inhibiting transition metal dissolution. After blending, the rigid WO3 provides structural support and an ion conduction framework for the coating layer, while the flexible C3N4 fills the interparticle gaps and inhibits crack propagation, forming a complementary rigid-flexible composite coating structure. Simultaneously, the WO of WO3... 6+ / W 5+ Redox pairs synergistically suppress interfacial side reactions through different chemical mechanisms with the nitrogen-containing functional groups of C3N4, achieving dual chemical protection. Furthermore, the high specific surface area of ​​WO3, with its high surface energy and strong adsorption capacity, facilitates the formation of a dense and uniform coating layer on the surface of the cathode particles by the blended components. This allows for efficient interfacial protection even with a relatively low coating amount, minimizing the impact on battery energy density. Attached Figure Description

[0011] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 The process flow diagram for preparing high specific surface area WO3 in Examples 1-3 is shown.

[0012] Figure 2 XRD pattern of high specific surface area WO3 prepared for Example 1.

[0013] Figure 3 SEM image of WO3 with high specific surface area prepared in Example 1.

[0014] Figure 4 SEM image of WO3 with high specific surface area prepared for Example 2.

[0015] Figure 5 SEM image of WO3 with high specific surface area prepared in Example 3.

[0016] Figure 6 SEM images of WO3 prepared in Preparation Example 1 are shown for comparison.

[0017] Figure 7 SEM images of WO3 prepared in Preparation Example 2 are shown for comparison.

[0018] Figure 8 SEM images of WO3 prepared in Preparation Example 3 are shown for comparison.

[0019] Figure 9 This is a TEM image of the coated and modified ternary cathode material prepared in Example 1. Detailed Implementation

[0020] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0021] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0022] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0023] In a first aspect, the present invention provides a coated and modified ternary cathode material, comprising a ternary cathode active material core and a composite material coating at least a portion of the surface of the core, wherein the composite material is composed of high specific surface area WO3 and C3N4, and the specific surface area of ​​the high specific surface area WO3 is not less than 28 m². 2 / g.

[0024] This invention recycles waste tungsten wire, obtaining sodium tungstate through oxidation and alkaline leaching. High specific surface area WO3 is then prepared using a hydrogen peroxide and oxalic acid dual-coordination system, and subsequently blended with C3N4 to coat and modify ternary cathode materials. The high specific surface area WO3 exposes a large number of active functional groups such as W=O bonds, bridging oxygen bonds (WOW), and terminal hydroxyl groups (W-OH), and has abundant surface oxygen vacancies (W... 5+ The concentration of defect states is significantly higher than that of ordinary commercial WO3. These abundant surface active sites can fully react with the residual Li2CO3 and LiOH on the ternary cathode surface during the coating heat treatment process, generating a Li2WO4 interface phase with good lithium-ion conductivity in situ, effectively reducing the alkalinity residue on the cathode surface. At the same time, the more dangling bonds and defect sites on the WO3 surface are conducive to forming WOM (M=Ni, Co, Mn) chemical bonds with the -OH and -O groups on the cathode surface, significantly enhancing the bonding force between the coating layer and the cathode particles, and preventing the coating layer from falling off and failing during long-term cycling. In addition, in the unique layered / tunnel-like crystal structure of WO3, the interlayer and tunnel gaps can serve as fast channels for lithium-ion migration. The high specific surface area means more exposed interlayer surfaces, and lithium ions can be rapidly transported along the exposed interlayer channels. Combined with the abundant oxygen vacancies on the surface, the ion migration energy barrier is further reduced, providing a high-density lithium-ion conduction channel for the composite coating layer and effectively reducing the interfacial impedance.

[0025] C3N4, a two-dimensional layered inorganic semiconductor material composed of carbon and nitrogen covalent bonds, exhibits good chemical stability. Its two-dimensional layered structure endows it with a certain degree of flexibility, effectively buffering the internal stress generated by anisotropic volume changes during the charging and discharging of the ternary cathode, and inhibiting the cracking and delamination of the coating layer. The abundant nitrogen-containing functional groups (-NH2, -NH-, C=N, etc.) on the surface of C3N4 can chemically react with acidic substances such as HF produced by electrolyte decomposition, neutralizing the acidic environment at the interface and inhibiting the growth of transition metal ions (especially Ni). 4+ The dissolution of ) reduces the corrosion of the positive electrode surface and the irreversible reconstruction of the rock salt phase.

[0026] In this invention, the blending of high specific surface area WO3 and C3N4 exhibits a significant synergistic effect. Rigid WO3 provides structural support and an ion-conducting framework for the composite coating layer, while flexible C3N4 sheets fill the gaps between WO3 particles and cover the uncovered areas, inhibiting crack initiation and propagation. The two form a complementary rigid-flexible composite coating structure, significantly improving the mechanical integrity and structural stability of the coating layer during long-term cycling.

[0027] W of high specific surface area WO3 6+ / W 5+ Redox pairs absorb excess electrons at the ternary cathode interface, inhibiting the reductive decomposition of the electrolyte; nitrogen-containing functional groups on the C3N4 surface consume acidic products generated by electrolyte decomposition through acid-base reactions, inhibiting the dissolution of transition metals. These two mechanisms address different harmful reactions at the interface through different chemical mechanisms, forming a complementary dual chemical protection system, which offers superior protection compared to single WO3 or single C3N4 coatings.

[0028] WO3, with its high specific surface area, has high surface energy and strong adsorption capacity. During blending with C3N4, the contact between the two is closer. The abundant surface active sites of WO3 with high specific surface area can generate strong interaction forces (such as hydrogen bonds and Lewis acid-base interactions) with the nitrogen-containing functional groups on the surface of C3N4, making the two components more tightly bound in the blend system. This is conducive to forming a dense, uniform, and complete composite coating layer on the surface of the ternary cathode particles, effectively blocking the direct contact between the electrolyte and the cathode active material, and minimizing the coverage blind zone.

[0029] WO3 with high specific surface area has a high density of active sites, which can play a significant role in surface protection and ion conduction even at a low mass fraction. When blended with C3N4, the two-dimensional sheets of C3N4 further extend the coverage area, achieving efficient interface protection with low coating amount and minimizing the negative impact of inactive materials on battery energy density.

[0030] In some embodiments, the mass ratio of the composite material to the ternary cathode active material core is 0.2:99.8 to 1:99, including but not limited to: 0.2:99.8, 0.3:99.7, 0.4:99.6, 0.5:99.5, 0.6:99.4, 0.7:99.3, 0.8:99.2, 0.9:99.1, 1:99, etc.

[0031] In some embodiments, the mass ratio of high specific surface area WO3 to C3N4 in the composite material is 1:(0.05~0.1), including but not limited to: 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, etc.

[0032] In some embodiments, the specific surface area of ​​the high specific surface area WO3 is 28~35m². 2 / g, including but not limited to: 28m 2 / g、29m 2 / g、30m 2 / g、31m 2 / g、32m 2 / g、33m 2 / g、34m 2 / g、35m 2 / g etc.

[0033] In some embodiments, the chemical formula of the ternary cathode material is LiNi. x Co y Mn z O2, where: x+y+z=1, 0.6≤x<1, 0<y≤0.3, 0<z≤0.3.

[0034] Secondly, this invention provides a method for preparing a coated and modified ternary cathode material, comprising the following steps: S1. High specific surface area WO3, C3N4 and solvent are mixed and ultrasonically dispersed. After the solvent is removed by evaporation, a mixture is obtained. The mixture is sintered under an inert atmosphere to obtain a composite material. S2. After mixing the ternary cathode active material with the composite material, sintering is carried out under an inert atmosphere to obtain the coated and modified ternary cathode material.

[0035] This invention involves ultrasonically dispersing high-specific-surface-area WO3 and C3N4 in a solvent, followed by solvent evaporation to remove the solvent. The ultrasonic cavitation effect breaks up particle agglomerates, allowing WO3 nanoparticles to be uniformly dispersed and in close contact between C3N4 sheets. Subsequently, sintering is performed at an appropriate temperature under an inert atmosphere, promoting chemical interactions at the WO3-C3N4 interface to enhance bonding strength. During this process, C3N4 sheets coat the surface of the WO3 particles and are distributed between them, providing spatial isolation and preventing direct contact between WO3 particles. This inhibits agglomeration and growth of WO3 particles during sintering, preserving the high specific surface area and abundant surface active sites of WO3 in the composite material. Simultaneously, the inert atmosphere effectively prevents the oxidative decomposition of C3N4 at high temperatures, maintaining the integrity of its layered structure and nitrogen-containing functional groups. Furthermore, the resulting composite material is mixed with a ternary cathode active material and sintered again under an inert atmosphere, allowing the composite material to fully spread on the surface of the cathode particles and undergo interfacial chemical bonding, forming a uniform, dense, and firmly bonded composite coating layer. The two-step sintering process separates and controls the preparation and coating of the composite material, facilitating independent optimization of process parameters for each step and offering high process flexibility. This method is simple, involving only routine operations such as ultrasonic dispersion, solvent evaporation, and two-step sintering, making it easy to scale up for industrial production.

[0036] The waste tungsten wires are derived from industrial waste generated in fields such as diamond cutting wire, electric light sources, and electronic packaging, and their main component is metallic tungsten. Using waste tungsten wires as raw materials not only realizes the resource utilization of solid waste and reduces raw material costs, but also ensures that the waste tungsten wires have high purity, which is beneficial for the subsequent preparation of high-purity tungsten oxide products.

[0037] In some embodiments, in step S1, the solvent is ethanol, and the mass ratio of high specific surface area WO3 to the solvent is 1:(10~12), including but not limited to: 1:10, 1:10.5, 1:11, 1:11.5, 1:12, etc.; the ultrasonic dispersion time is 2~5h, including but not limited to: 2h, 3h, 4h, 5h, etc.; the sintering temperature is 400~500℃, including but not limited to: 400℃, 420℃, 450℃, 480℃, 500℃, etc.; the sintering time is 3~5h, including but not limited to: 3h, 3.5h, 4h, 4.5h, 5h, etc.

[0038] In some embodiments, in step S2, the sintering process is as follows: first, pre-sintering at 200~300℃ for 2~4h, then raising the temperature to 450~500℃ and sintering for 5~8h, including but not limited to: 5h, 6h, 7h, 8h, etc.

[0039] In some embodiments, in steps S1 and S2, the inert atmosphere is independently either a nitrogen atmosphere or an argon atmosphere.

[0040] In some embodiments, step S1, the method for preparing the high specific surface area WO3, includes the following steps: (1) Oxidize the waste tungsten wire to obtain crude tungsten oxide, then add the crude tungsten oxide to an alkaline solution to dissolve it, and filter it to obtain a sodium tungstate solution; (2) Add hydrogen peroxide and oxalic acid to the sodium tungstate solution obtained in step (1) for dual coordination complexation treatment. After the treatment is completed, add inorganic acid and reducing agent to the obtained solution for acid precipitation treatment. After the acid precipitation treatment is completed, perform solid-liquid separation and heat treatment of the filter cake to obtain high specific surface area WO3.

[0041] This invention uses waste tungsten wire as raw material and obtains sodium tungstate solution through oxidation and alkali dissolution, realizing the high-value recycling and utilization of waste tungsten wire as a secondary resource. Compared with the traditional process route of alkali leaching to recover ammonium paratungstate, it eliminates high-energy-consuming steps such as evaporation and crystallization, and the process flow is shorter and the energy consumption is lower.

[0042] This invention involves simultaneously adding hydrogen peroxide and oxalic acid to a sodium tungstate solution for dual-coordination complexation before acid precipitation. Hydrogen peroxide reacts with tungstate ions, with oxygen atoms binding to the tungsten center via η²-coordination to form a soluble peroxytungstate complex. The peroxy ligand, being relatively large, occupies multiple coordination sites on the tungsten center through chelation. Oxalic acid, acting as a bidentate ligand, further coordinates with the tungsten center, forming an oxalic acid-peroxy dual-ligand complex. This synergistic encapsulation by the dual ligands ensures that each tungsten center is fully encapsulated and isolated by an organic-inorganic hybrid ligand shell, effectively blocking the polymerization and condensation reaction of tungstate ions in solution. This avoids the problem of rapid condensation of tungstate ions to form large-sized polytungstate clusters, resulting in dense and coarse precipitates, which is common in traditional direct acid precipitation methods. Meanwhile, the dual-coordination complex constructs each tungsten species into a uniform and independent molecular-level precursor, fundamentally changing the reaction starting point of subsequent acid precipitation. This causes the precipitate to aggregate in a loose and porous manner during acid precipitation, rather than in a dense manner, laying the foundation for the formation of a rich pore structure inside the final product.

[0043] During acid precipitation, the peroxy ligand decomposes to generate a large number of oxygen microbubbles, which are encapsulated within the precipitate, acting as an in-situ pore-forming agent and creating a rich microporous and mesoporous structure within the product particles. Oxalic acid and its decomposition products are completely combusted and released during subsequent calcination, their original space forming interconnected pore structures, thus acting as a sacrificial template for pore formation. The synergy of these two processes results in the final WO3 particles exhibiting a sponge-like, loose, and porous microstructure with abundant and interconnected internal pores, significantly increasing the specific surface area.

[0044] The reducing agent will partially release W during the acid precipitation process. 6+ Restore to W 5+This generates oxygen vacancy defects, further increasing the surface defect concentration and chemical activity of the product, providing more active binding sites for subsequent composite coating with C3N4.

[0045] Although the WO3 prepared by this invention has a particle size in the micrometer range, the particles have a rich, loose porous structure, resulting in a specific surface area of ​​not less than 28 m². 2 / g, far exceeding the traditional commercial block WO3 (1~15m) 2 While maintaining the fluidity of micron-sized particles, it achieves the advantage of high specific surface area, which is beneficial for fully utilizing the functions of residual lithium neutralization, ion conduction and chemical protection in the ternary cathode blending and coating modification.

[0046] In some embodiments, in step (1), the oxidation temperature is 700~800℃, including but not limited to: 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, etc.; the oxidation time is 6~10h, including but not limited to: 6h, 7h, 8h, 9h, 10h, etc.

[0047] When the oxidation temperature is below 700℃, the oxidation of the tungsten wire is incomplete, and the residual metallic tungsten is difficult to dissolve in the subsequent alkaline dissolution process; when the oxidation temperature is above 800℃, the crude tungsten oxide may sinter, the particles become dense, and the efficiency of the subsequent alkaline dissolution is reduced.

[0048] In some embodiments, in step (1), the alkaline solution is a sodium hydroxide solution, and the pH of the solute is controlled to be 12±0.5.

[0049] In some embodiments, during step (1), the tungsten content is controlled to be 200~300g / L, including but not limited to: 200g / L, 220g / L, 250g / L, 280g / L, 300g / L, etc.

[0050] In some embodiments, in step (1), the dissolution temperature is 80~100℃, including but not limited to: 80℃, 85℃, 90℃, 95℃, 100℃, etc.; the dissolution time is 5~8h, including but not limited to: 5h, 6h, 7h, 8h, etc.

[0051] In some embodiments, in step (2), the WO4 in the sodium tungstate solution 2- The molar ratio with H2O2 is 1:(1~3), including but not limited to: 1:1, 1:1.5, 1:2, 1:2.5, 1:3, etc.; WO4 in sodium tungstate solution 2- The molar ratio with oxalic acid is 1:(0.75~1.25), including but not limited to: 1:0.75, 1:1, 1:1.25, etc.

[0052] In some embodiments, the time for the dual coordination complexation treatment in step (2) is 1 to 2 hours, including but not limited to: 1 hour, 1.5 hours, 2 hours, etc.

[0053] In some embodiments, in step (2), the inorganic acid is one of sulfuric acid, nitric acid, or hydrochloric acid, and the H2O of the solution is controlled during the acid precipitation treatment. + The concentration is 2~3 mol / L, including but not limited to: 2 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L, 3 mol / L, etc.

[0054] When H + When the concentration is too low, the complex decomposes incompletely, resulting in a low tungstic acid precipitation rate; when H... + When the concentration is too high, the acid precipitation reaction is too vigorous, and the generated tungstic acid particles agglomerate severely, reducing the specific surface area.

[0055] In some embodiments, in step (2), the reducing agent is one of sodium sulfite, sodium metabisulfite, or sodium thiosulfate.

[0056] The role of the reducing agent is to reduce and decompose residual hydrogen peroxide in the solution, preventing the violent decomposition of hydrogen peroxide under strongly acidic conditions that would generate a large number of bubbles, thus affecting the precipitation and filtration of tungstic acid. The introduction of the reducing agent makes the acid precipitation process more controllable.

[0057] In some embodiments, in step (2), when sodium sulfite is used, the molar ratio of sodium sulfite to H2O2 is (2~2.5):1; when sodium metabisulfite is used, the molar ratio of sodium metabisulfite to H2O2 is (1~1.25):1; when sodium thiosulfate is used, the molar ratio of sodium thiosulfate to H2O2 is (1~1.25):1.

[0058] In some embodiments, in step (2), the heat treatment temperature is 250~350℃, including but not limited to: 250℃, 280℃, 300℃, 320℃, 350℃, etc.; the heat treatment time is 10~15h, including but not limited to: 10h, 11h, 12h, 13h, 14h, 15h, etc.

[0059] Thirdly, the present invention provides a positive electrode sheet comprising the aforementioned coated and modified ternary positive electrode material.

[0060] Fourthly, the present invention provides a lithium battery, including the aforementioned positive electrode.

[0061] The process flow diagrams for preparing high specific surface area WO3 in Examples 1-3 of this invention are as follows: Figure 1 As shown 。

[0062] Preparation Example 1 (1) 1 kg of waste tungsten wire was placed in a muffle furnace and sintered at 750°C for 8 hours to produce crude tungsten oxide.

[0063] (2) Add crude tungsten oxide to sodium hydroxide solution for alkaline dissolution, control the tungsten content in the solution to be 250 g / L, the pH of the solution to be 12.5, stir in a water bath at 90℃ for 6 h, filter out impurities, and obtain sodium tungstate solution.

[0064] (3) At room temperature, add 27% hydrogen peroxide and 40% oxalic acid to a sodium tungstate solution, where WO4 2- The molar ratio of H2O2 to H2C2O4 is 1:2:1. After stirring for 1.5 h, a sodium peroxyoxalate tungstate solution is obtained.

[0065] (4) Add sulfuric acid to the sodium peroxatate tungstate solution obtained in step (3) to control the H+ concentration in the solution. + The concentration was 2.5 mol / L, and then sodium sulfite was added. The molar ratio of sodium sulfite to H2O2 added in step (2) was 2.2:1. After stirring and reacting in a water bath at 55℃ for 4 hours, the mixture was filtered. After filtering the mother liquor, pure water was added to wash the filter cake. The amount of water used for washing was 250 g / time, and the mixture was washed 3 times to obtain wet tungstic acid. The wet tungstic acid was placed in an oven and dried at 300℃ for 12 hours to obtain WO3 with high specific surface area.

[0066] The specific surface area of ​​the high specific surface area WO3 prepared in Example 1 was tested to be 32.5 m². 2 / g, XRD indicates that it has an amorphous structure (see g), Figure 2 SEM analysis showed that it exhibited a loose, sponge-like morphology (see...). Figure 3 SEM analysis showed that it has an amorphous structure.

[0067] Preparation Example 2 (1) 1 kg of waste tungsten wire was placed in a muffle furnace and sintered at 700°C for 6 hours to produce crude tungsten oxide.

[0068] (2) Add crude tungsten oxide to sodium hydroxide solution for alkaline dissolution, control the tungsten content in the solution to be 200 g / L, the pH of the solution to be 12, stir in a water bath at 80℃ for 5 h, and then filter out impurities to obtain sodium tungstate solution.

[0069] (3) At room temperature, add 27% hydrogen peroxide and 40% oxalic acid to a sodium tungstate solution, where WO4 2- The molar ratio of H2O2 to H2C2O4 is 1:2:0.75. After stirring for 1 hour, a sodium peroxyoxalate tungstate solution is obtained.

[0070] (4) Add sulfuric acid to the sodium peroxyoxalate tungstate solution obtained in step (3) to control the H+ concentration in the solution. +The concentration was 2 mol / L, followed by the addition of sodium metabisulfite. The molar ratio of sodium metabisulfite to H2O2 was 1.2:1. The mixture was stirred and kept in a water bath at 50°C for 3 hours before being filtered. The mother liquor was filtered and the filter cake was washed with pure water at a rate of 200 g per wash, for a total of 3 washes, to obtain wet tungstic acid. The wet tungstic acid was then placed in an oven and heat-treated at 250°C for 15 hours to obtain WO3 with a high specific surface area.

[0071] The specific surface area of ​​the high specific surface area WO3 prepared in Preparation Example 2 was tested to be 31.9 m². 2 / g, SEM showed that it exhibited a loose, sponge-like morphology (see Figure 4 SEM analysis showed that it has an amorphous structure.

[0072] Preparation Example 3 (1) 1 kg of waste tungsten wire was placed in a muffle furnace and sintered at 800°C for 10 h to produce crude tungsten oxide.

[0073] (2) Add crude tungsten oxide to sodium hydroxide solution for alkaline dissolution, control the tungsten content in the solution to be 300 g / L, the pH of the solution to be 13, stir in a water bath at 100℃ for 8 h, filter out impurities, and obtain sodium tungstate solution.

[0074] (3) At room temperature, add 27% hydrogen peroxide and 40% oxalic acid to a sodium tungstate solution, where WO4 2- The molar ratio of H2O2 to H2C2O4 is 1:2:1.25. After stirring for 2 hours, a sodium peroxyoxalate tungstate solution is obtained.

[0075] (4) Add concentrated sulfuric acid to the sodium peroxyoxalate tungstate solution obtained in step (3) to control the H+ concentration in the solution. + The concentration was 3 mol / L, and sodium thiosulfate was added simultaneously, with a molar ratio of sodium thiosulfate to H2O2 of 1.25:1. After stirring and reacting in a water bath at 60℃ for 5 hours, the mixture was filtered. The mother liquor was filtered and the filter cake was washed with pure water at a rate of 300 g per wash, for a total of 3 washes, to obtain wet tungstic acid. The wet tungstic acid was placed in an oven and dried at 350℃ for 15 hours to obtain WO3 with a high specific surface area.

[0076] The high specific surface area WO3 prepared in Preparation Example 3 was tested and found to have a specific surface area of ​​32.1 m². 2 / g. SEM showed that it exhibited a loose, spongy morphology (see Figure 5 SEM analysis showed that it has an amorphous structure.

[0077] Comparative Preparation Example 1 The difference between this comparative preparation example and preparation example 1 is that step (3) is not performed.

[0078] (1) Same as step (1) in Preparation Example 1.

[0079] (2) Same as step (2) in Preparation Example 1.

[0080] (3) Same as step (4) in Preparation Example 1.

[0081] Testing showed that the specific surface area of ​​WO3 prepared in Comparative Preparation Example 1 was 7.9 m². 2 / g; SEM showed that it exhibited an irregular particle morphology (see...). Figure 6 ).

[0082] Comparative Preparation Example 2 The difference between this comparative preparation example and preparation example 1 is that in step (3), only hydrogen peroxide is used for coordination, and oxalic acid is not added.

[0083] (1) Same as step (1) in Preparation Example 1.

[0084] (2) Same as step (2) in Preparation Example 1.

[0085] (3) Add 27% hydrogen peroxide by mass to the sodium tungstate solution at room temperature, where WO4 2- The molar ratio of H2O2 is 1:3. After stirring for 1.5 h, a sodium peroxytungstate solution is obtained.

[0086] (4) Same as step (4) in Preparation Example 1.

[0087] Testing showed that the specific surface area of ​​WO3 prepared in Comparative Preparation Example 2 was 26.7 m². 2 / g. SEM showed that it exhibited an irregular particle morphology (see [link]). Figure 7 ).

[0088] Comparative preparation example 3 The difference between this comparative preparation example and preparation example 1 is that only oxalic acid is used for coordination in step (3), and hydrogen peroxide is not added.

[0089] (1) Same as step (1) in Preparation Example 1.

[0090] (2) Same as step (2) in Preparation Example 1.

[0091] (3) Add 40% oxalic acid (by mass) to a sodium tungstate solution at room temperature, where WO4 2- The molar ratio of H2C2O4 was 1:3, and the mixture was stirred for 1.5 h to obtain a sodium oxalate tungstate solution.

[0092] (4) Same as step (4) in Preparation Example 1.

[0093] Tests showed that the specific surface area of ​​WO3 prepared in Comparative Preparation Example 3 was 23.7 m². 2 / g. SEM showed that it exhibited an irregular particle morphology (see [link]). Figure 8 ).

[0094] The comparison between the above preparation examples and comparative preparations shows that the tungsten oxide prepared using the hydrogen peroxide and oxalic acid dual coordination system (preparation examples 1-3) has a significantly higher specific surface area (31-33 m²). 2 / g), without the use of any ligands, direct acid precipitation (Comparative Preparation Example 1) yielded a specific surface area of ​​only 7.9 m². 2 / g, using only the hydrogen peroxide single-coordination system (comparative preparation example 2), the specific surface area was significantly reduced (26.7m²). 2 / g), using only the oxalic acid single-coordination system (comparative preparation example 3), the specific surface area was significantly reduced (23.7m). 2 / g); the results showed that the dual coordination system of hydrogen peroxide and oxalic acid played a key role in the preparation of high specific surface area WO3.

[0095] Preparation Example 4 Preparation of NCM622: A mixed salt solution with a total metal ion concentration of 2 mol / L was prepared by mixing NiSO4, CoSO4, and MnSO4 in a molar ratio of Ni:Co:Mn = 0.6:0.2:0.2. Under N2 protection, this solution was co-precipitated by pumping three parallel streams of the solution (Ni, Co, and Mn) into a reactor along with 2 mol / L NaOH solution and 30 wt% ammonia solution. The pH was controlled at 10.5–11.5, the reaction temperature at 55℃, the stirring speed at 800 rpm, and the reaction time at 15 h. After the reaction was completed, the solution was aged, filtered, washed, and vacuum dried to obtain Ni. 0.6 Co 0.2 Mn 0.2 (OH)₂ precursor; the precursor and LiOH were mixed uniformly at a molar ratio of Li / (Ni+Co+Mn) = 1.04, and the mixture was heated to 500℃ at 5℃ / min and held for 5 h in an oxygen atmosphere, and then heated to 850℃ and held for 12 h for high-temperature solid-state sintering. The sintered product was subjected to air jet milling and classification, water washing to remove residual lithium on the surface, and drying to obtain LiNi. 0.6 Co 0.2 Mn 0.2 O2.

[0096] Preparation Example 5 Preparation of NCM811: NiSO4, CoSO4, and MnSO4 were prepared into a mixed salt solution with a total metal ion concentration of 2 mol / L at a molar ratio of Ni:Co:Mn = 0.8:0.1:0.1. Under N2 protection, this solution was co-precipitated by pumping three parallel streams of NiSO4, CoSO4, and MnSO4 into a reactor. The pH was controlled at 10.5–11.5, the reaction temperature at 55℃, the stirring speed at 800 rpm, and the reaction time at 20 h. After the reaction was completed, the solution was aged, filtered, washed, and vacuum dried to obtain Ni. 0.8 Co 0.1 Mn 0.1(OH)₂ precursor; the precursor and LiOH were mixed uniformly at a molar ratio of Li / (Ni+Co+Mn) = 1.04, and the mixture was heated to 500℃ at 5℃ / min and held for 6 h in an oxygen atmosphere, and then heated to 800℃ and held for 15 h for high-temperature solid-state sintering. The sintered product was subjected to air jet milling and classification, water washing to remove residual lithium on the surface, and drying to obtain LiNi. 0.8 Co 0.1 Mn 0.1 O2.

[0097] Example 1 S1. The high specific surface area WO3, C3N4 and ethanol prepared in Preparation Example 1 were mixed at a ratio of 1:0.08:11 and ultrasonically dispersed for 4 hours. Then, the ethanol solvent was evaporated at 80°C to obtain the mixture. The mixture was heated to 450°C under a nitrogen atmosphere and sintered for 4 hours to obtain the composite material.

[0098] S2. The NCM622 prepared in Preparation Example 4 and the composite material were mixed evenly at a ratio of 99.2:0.8. The mixture was then heated to 250°C and held for 3 hours under a nitrogen atmosphere. The temperature was then increased to 480°C and sintered for 6 hours to obtain the coated and modified ternary cathode material.

[0099] TEM images of the coated and modified ternary cathode material prepared in this embodiment are shown below. Figure 9 As shown, there is a distinct coating layer on the ternary cathode material, and the coating layer is tightly bonded to the ternary cathode material.

[0100] Comparative Example 1 The NCM622 prepared in Example 4 was directly used as the cathode material.

[0101] Comparative Example 2 Only WO3 with high specific surface area is used as the coating material. The specific preparation method is as follows: The NCM622 prepared in Preparation Example 4 and the high specific surface area WO3 prepared in Preparation Example 1 were mixed evenly at a ratio of 1:0.008. The mixture was then heated to 250°C and held for 3 hours under a nitrogen atmosphere, and then heated to 480°C and sintered for 6 hours to obtain the coated and modified ternary cathode material.

[0102] Comparative Example 3 Only C3N4 is used as the coating material, and the specific preparation method is as follows: The NCM622 and C3N4 prepared in Preparation Example 4 were mixed evenly at a ratio of 1:0.008, and then heated to 250°C and held for 3 hours under a nitrogen atmosphere. The temperature was then increased to 480°C and sintered for 6 hours to obtain the coated and modified ternary cathode material.

[0103] Comparative Example 4 The process is basically the same as in Example 1, except that in step S1, the high specific surface area WO3 prepared in Preparation Example 1 is replaced by WO3 prepared in Comparative Preparation Example 1.

[0104] Comparative Example 5 The process is basically the same as in Example 1, except that in step S1, the high specific surface area WO3 prepared in Preparation Example 1 is replaced by WO3 prepared in Comparative Preparation Example 2.

[0105] Comparative Example 6 The process is basically the same as in Example 1, except that in step S1, the high specific surface area WO3 prepared in Preparation Example 1 is replaced by WO3 prepared in Comparative Preparation Example 3.

[0106] Example 2 The preparation method is basically the same as that in Example 1, except that in step S1, the mass ratio of the high specific surface area WO3 and C3N4 prepared in Example 1 is 1:0.05.

[0107] Example 3 The preparation method is basically the same as that in Example 1, except that in step S1, the mass ratio of the high specific surface area WO3 and C3N4 prepared in Example 1 is 1:0.1.

[0108] Example 4 The process is basically the same as in Example 1, except that in step S2, the mass ratio of NCM622 to the composite material is 99.8:0.2.

[0109] Example 5 It is basically the same as Example 1, except that in step S2, the mass ratio of NCM622 to the composite material is 99:1.

[0110] Example 6 S1. The high specific surface area WO3, C3N4 and ethanol prepared in Preparation Example 2 were mixed at a ratio of 1:0.06:11 and ultrasonically dispersed for 2 hours. Then, the ethanol solvent was evaporated at 80°C to obtain the mixture. The mixture was heated to 400°C under a nitrogen atmosphere and sintered for 5 hours to obtain the composite material.

[0111] S2. The NCM811 prepared in Preparation Example 5 and the composite material were mixed evenly at a ratio of 99.5:0.5. The mixture was then heated to 300°C and held for 2 hours under a nitrogen atmosphere. The temperature was then increased to 450°C and sintered for 8 hours to obtain the coated and modified ternary cathode material.

[0112] Example 7 S1. The high specific surface area WO3, C3N4 and ethanol prepared in Preparation Example 3 were mixed at a ratio of 1:0.07:11 and ultrasonically dispersed for 5 hours. Then, the ethanol solvent was evaporated at 80°C to obtain the mixture. The mixture was heated to 500°C under a nitrogen atmosphere and sintered for 3 hours to obtain the composite material.

[0113] S2. The NCM811 prepared in Preparation Example 5 and the composite material were mixed evenly at a ratio of 99.3:0.7. The mixture was then heated to 200°C and held for 4 hours under a nitrogen atmosphere. The temperature was then increased to 500°C and sintered for 5 hours to obtain the coated and modified ternary cathode material.

[0114] The positive electrode materials prepared in the examples and comparative examples were mixed with Super-P, PVDF, and NMP in a ratio of 8:1:1 to form a slurry. This slurry was then uniformly coated onto aluminum foil using a 200μm scraper and dried in a vacuum oven at 100℃ for 2 hours to obtain the positive electrode sheet. The positive electrode sheet was cut into round pieces (12mm in diameter) suitable for button batteries, and then assembled into button batteries in an Ar atmosphere glove box. A lithium metal sheet was used as the negative electrode; a lithium-ion secondary electrolyte LB-037 (1M LiPF6 in DEC:EC:EMC (volume ratio) = 1:1:1) was used as the electrolyte, and Celgard 2325 was used as the separator to assemble the button battery. Charge-discharge tests were performed on the Blue Electric testing system at a temperature of 25℃ and a voltage range of 3~4.3V. After activation by two cycles at a 0.1C rate, 200 charge-discharge cycles at a 1C rate were performed, and the capacity retention rate was calculated. The results are shown in Table 1.

[0115] Table 1 As can be seen from the data in Table 1, in Comparative Example 1, NCM622 was directly used as the cathode material without any coating treatment, resulting in poor initial specific capacity and cycle stability of the prepared battery. In Example 1, after coating modification using a composite material composed of high specific surface area WO3 and C3N4, the initial specific capacity and cycle stability of the battery assembled with the corresponding cathode material were significantly improved compared to Comparative Example 1. In Comparative Example 2, only high specific surface area WO3 was used for coating (without adding C3N4), and the initial specific capacity and cycle stability of the battery assembled with the corresponding cathode material were improved compared to Comparative Example 1, but significantly worse than in Example 1. This may be because the single WO3 coating lacks flexibility, and the coating layer is prone to cracking and falling off during long cycles. In Comparative Example 3, only C3N4 was used for coating (without adding WO3), and the initial specific capacity and cycle stability of the battery assembled with the corresponding cathode material were improved compared to Comparative Example 1, but significantly worse than in Example 1. This may be because single C3N4 lacks a lithium-ion conductive framework, resulting in increased interfacial impedance. In Comparative Example 4, a composite coating material composed of WO3 and C3N4 with a lower specific surface area was used. The initial specific capacity and cycle stability of the battery assembled with the corresponding cathode material were improved compared to Comparative Example 1, but significantly lower than those of Example 1. This may be because the low specific surface area WO3 has insufficient surface active sites, resulting in weaker chemical bonding and ion conduction capabilities with the cathode surface. In Comparative Examples 5 and 6, WO3 with a medium specific surface area was used instead of high specific surface area WO3. The initial specific capacity and cycle stability of the battery assembled with the corresponding cathode material were further improved compared to Comparative Example 4, but still lower than those of Example 1. This indicates that the higher the specific surface area of ​​WO3, the better the composite coating effect. In Example 2, reducing the amount of C3N4 resulted in a certain decrease in the initial specific capacity and cycle stability of the battery assembled with the corresponding cathode material compared to Example 1. In Example 3, increasing the amount of C3N4 resulted in the initial specific capacity and cycle stability of the battery assembled with the corresponding cathode material being basically the same as those of Example 1. This indicates that the composite coating can maintain excellent performance over a wide range of C3N4 dosages. In Example 4, reducing the amount of coating material resulted in a slight decrease in the initial specific capacity and cycle stability of the battery assembled with the corresponding cathode material compared to Example 1, but overall, it still exhibited superior electrochemical performance. In Example 5, increasing the amount of coating material resulted in a slight decrease in the initial specific capacity of the battery assembled with the corresponding cathode material compared to Example 1, but the cycle stability remained essentially the same. In Examples 6 and 7, NCM811 was composite-coated under different preparation conditions. The initial specific capacity and cycle stability of the batteries assembled with the corresponding cathode materials were very close to those of Example 1, and all exhibited superior electrochemical performance, indicating that this composite coating scheme has good universal applicability to different ternary cathode materials.

[0116] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the present invention.

Claims

1. A coated and modified ternary cathode material, characterized in that, include: The ternary cathode active material core and the composite material coating at least a portion of the surface of the core, wherein the composite material is composed of high specific surface area WO3 and C3N4, and the specific surface area of ​​the high specific surface area WO3 is not less than 28 m². 2 / g.

2. The coated and modified ternary cathode material according to claim 1, characterized in that, The mass ratio of the composite material to the ternary cathode active material core is 0.2:99.8~1:99; And / or, the mass ratio of high specific surface area WO3 to C3N4 in the composite material is 1:(0.05~0.1); And / or, the specific surface area of ​​the high specific surface area WO3 is 28~35m². 2 / g; And / or, the chemical formula of the ternary cathode material is LiNi x Co y Mn z O2, where: x+y+z=1, 0.6≤x<1, 0<y≤0.3, 0<z≤0.

3.

3. The method for preparing the coated and modified ternary cathode material according to claim 1 or 2, characterized in that, Includes the following steps: S1. After mixing high specific surface area WO3, C3N4 and solvent, ultrasonic dispersion is performed, and the solvent is removed by evaporation to obtain a mixture; the mixture is sintered under an inert atmosphere to obtain a composite material. S2. After mixing the ternary cathode active material with the composite material, sintering is carried out under an inert atmosphere to obtain the coated and modified ternary cathode material.

4. The method for preparing the coated and modified ternary cathode material according to claim 3, characterized in that, In step S1, the solvent is ethanol, the mass ratio of high specific surface area WO3 to solvent is 1:(10~12), the ultrasonic dispersion time is 2~5h, the sintering temperature is 400~500℃, and the sintering time is 3~5h. And / or, in step S2, the sintering process is as follows: first, pre-sintering at 200~300℃ for 2~4h, then raising the temperature to 450~500℃ and sintering for 5~8h; And / or, in steps S1 and S2, the inert atmosphere is independently either a nitrogen atmosphere or an argon atmosphere.

5. The method for preparing the coated and modified ternary cathode material according to claim 3, characterized in that, In step S1, the method for preparing the high specific surface area WO3 includes the following steps: (1) Oxidize the waste tungsten wire to obtain crude tungsten oxide, then add the crude tungsten oxide to an alkaline solution to dissolve it, and filter it to obtain a sodium tungstate solution; (2) Add hydrogen peroxide and oxalic acid to the sodium tungstate solution obtained in step (1) for dual coordination complexation treatment. After the treatment is completed, add inorganic acid and reducing agent to the obtained solution for acid precipitation treatment. After the acid precipitation treatment is completed, perform solid-liquid separation and heat treatment of the filter cake to obtain high specific surface area WO3.

6. The method for preparing the coated and modified ternary cathode material according to claim 5, characterized in that, In step (1), the oxidation temperature is 700~800℃ and the oxidation time is 6~10h; And / or, the alkaline solution is a sodium hydroxide solution, and the pH of the solution is controlled to be 12±0.5 during dissolution; And / or, during dissolution, control the tungsten content in the solution to be 200~300g / L; And / or, the dissolution temperature is 80~100℃, and the dissolution time is 5~8h.

7. The method for preparing the coated and modified ternary cathode material according to claim 5, characterized in that, In step (2), the WO4 in the sodium tungstate solution 2- The molar ratio of WO4 to H2O2 is 1:(1~3); the WO4 in the sodium tungstate solution 2- The molar ratio with oxalic acid is 1:(0.75~1.25); And / or, the duration of the dual-coordination complexation treatment is 1-2 hours; And / or, the inorganic acid is one or more of sulfuric acid, nitric acid, and hydrochloric acid, and the H2O of the solution is controlled during the acid precipitation treatment. + The concentration is 2~3 mol / L; And / or, the heat treatment temperature is 250~350℃, and the heat treatment time is 10~15h.

8. The method for preparing the coated and modified ternary cathode material according to claim 5, characterized in that, In step (2), the reducing agent is one or more of sodium sulfite, sodium metabisulfite, and sodium thiosulfate; When using sodium sulfite, the molar ratio of sodium sulfite to H2O2 is (2~2.5):1; when using sodium metabisulfite, the molar ratio of sodium metabisulfite to H2O2 is (1~1.25):1; when using sodium thiosulfate, the molar ratio of sodium thiosulfate to H2O2 is (1~1.25):

1.

9. A positive electrode plate, characterized in that, Includes the coated and modified ternary cathode material as described in claim 1 or 2, or the coated and modified ternary cathode material prepared by the method described in any one of claims 3 to 8.

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

Images