A long-cycle high-rate negative electrode material and its preparation method and application

Abstract

The present invention provides a long-cycle high-rate negative electrode material and its preparation method and application, which belong to the field of negative electrode material technology. By compounding silicon powder, tin powder and graphene and performing carbon coating, a three-dimensional conductive network is constructed to alleviate volume expansion and improve conductivity, cycle stability and rate performance; tungsten oxide is used as an interface stabilizer to form a protective layer, inhibit side reactions, reduce interface impedance and enhance the conductive network; metaphosphoric acid decomposes to form an inorganic phosphate protective film, which is combined with nitrogen-doped carbon generated by urea decomposition to significantly improve interface stability, conductivity and cycle life; lithium carbide reacts with vinylidene fluoride to generate a lithium fluorocarbon additive, which reduces the initial lithium loss and stabilizes the interface by releasing lithium ions in stages; a vanadium-based metal-organic framework prepared from ammonium metavanadate and terephthalic acid is combined with pre-embedded lithium and graphitized carbon coating to optimize the lithium ion transmission path and improve its performance. These synergistic modification measures improve the long-cycle stability and high-rate performance of the negative electrode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of negative electrode materials and relates to a long-cycle high-rate negative electrode material and a preparation method and application thereof. Background Art

[0002] The selection and optimization of anode materials are crucial in the research and development of lithium-ion batteries. This is because anode materials not only directly impact the battery's energy density, cycle stability, and rate capability, but also largely determine its safety and affordability. The performance of anode materials not only affects the battery's performance but also its reliability and cost-effectiveness in practical applications. Therefore, developing high-performance anode materials is a key factor in improving the overall performance of lithium-ion batteries.

[0003] Traditional graphite anode materials have long been the mainstream choice for lithium-ion batteries due to their excellent conductivity and chemical stability. However, despite graphite's relatively low cost and mature production process, its theoretical specific capacity is low, which is insufficient for the demand for modern high-energy-density batteries. In addition, during high-rate charge and discharge, graphite anodes often experience structural collapse, resulting in a sharp decline in their electrochemical performance. This defect has limited their widespread application in high-performance batteries.

[0004] To address the shortcomings of graphite anode materials, researchers are actively exploring high-capacity anode materials, such as silicon and tin. These materials have significantly higher theoretical specific capacities. However, silicon and tin undergo significant volume changes during lithium ion insertion and extraction, causing the electrode materials to expand and contract during charge and discharge. This volume change not only causes electrode pulverization and structural damage but also impacts the battery's cycle life, leading to a significant decrease in conductivity during high-rate charge and discharge, thus limiting the battery's output power and charge and discharge speed. Summary of the Invention

[0005] In response to the above problems, the purpose of the present invention is to provide a long-cycle high-rate negative electrode material and its preparation method and application. This study constructs a three-dimensional conductive network by compounding silicon powder, tin powder and graphene and coating them with carbon, which alleviates volume expansion and improves conductivity, cycle stability and rate performance; tungsten oxide acts as an interface stabilizer to form a protective layer, inhibits side reactions, reduces interface impedance and enhances the conductive network; metaphosphoric acid decomposes to form an inorganic phosphate protective film, which, combined with nitrogen-doped carbon generated by the decomposition of urea, significantly improves interface stability, conductivity and cycle life; lithium carbide reacts with vinylidene fluoride to form a lithium fluorocarbon additive, which reduces the initial lithium loss and stabilizes the interface by releasing lithium ions in stages; ammonium metavanadate and terephthalic acid prepared vanadium-based metal-organic framework are combined with pre-embedded lithium and graphitized carbon coating to optimize the lithium ion transmission path and improve the initial coulomb efficiency, rate performance and structural stability. These synergistic modification measures significantly improve the long-cycle stability and high-rate performance of the negative electrode material.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a long-cycle high-rate negative electrode material, the method comprising:

[0008] S1: mixing silicon powder, tin powder and graphene and ball-milling to obtain composite powder; reacting the composite powder with polyacrylonitrile in N-methylpyrrolidone, drying and heat-treating the resulting composite powder to obtain carbon-coated composite particles; impregnating the resulting composite powder with an ethanol solution of tungsten hexachloride and reacting the resulting particles, and calcining the resulting particles to obtain first modified carbon-coated composite particles;

[0009] S2: mixing the first modified carbon-coated composite particles with metaphosphoric acid and urea in anhydrous ethanol, drying, and then heat-treating to obtain modified composite particles;

[0010] S3: reacting lithium carbide with vinylidene fluoride in tetrahydrofuran, drying, and then heat-treating to obtain a lithium fluorocarbon additive;

[0011] S4: hydrothermally reacting ammonium metavanadate with terephthalic acid and then heat-treating it to obtain a metal-organic framework; reacting it with lithium carbide in tetrahydrofuran and heat-treating it to obtain a pre-embedded lithium composite powder; and reacting it with polyacrylonitrile to obtain a surface-coated metal-organic polymer;

[0012] S5: The surface-coated metal organic polymer is pre-dispersed with carboxymethyl cellulose, and modified composite particles, lithium fluorocarbon additives and conductive carbon black are added to prepare a long-cycle and high-rate negative electrode material.

[0013] Specifically, S1: silicon powder, tin powder and graphene are mixed and ball-milled to obtain a composite powder, the composite powder and polyacrylonitrile are added to N-methylpyrrolidone for stirring and coating, and after drying, heat-treated under an inert atmosphere to obtain carbon-coated composite particles; the composite powder is immersed in an ethanol solution of tungsten hexachloride for impregnation reaction and calcined to obtain first modified carbon-coated composite particles;

[0014] S2: mixing the first modified carbon-coated composite particles with metaphosphoric acid and urea and uniformly dispersing the mixture in anhydrous ethanol, reacting and drying the mixture, and then heat-treating the mixture under an inert atmosphere to obtain modified composite particles;

[0015] S3: dispersing lithium carbide and vinylidene fluoride in tetrahydrofuran, stirring for reaction, drying, and then heat-treating under an inert atmosphere to obtain a lithium fluorocarbon additive;

[0016] S4: adding ammonium metavanadate and terephthalic acid to a mixed solvent, performing a hydrothermal reaction, filtering, washing, and drying to obtain a precursor substrate, which is then heat-treated under an inert atmosphere to obtain a metal-organic framework; dispersing the precursor substrate with lithium carbide in tetrahydrofuran, stirring the reaction, and drying to obtain a pretreated powder, which is then heat-treated to obtain a pre-embedded lithium composite powder; dispersing the pre-embedded lithium composite powder in a polyacrylonitrile N-methylpyrrolidone solution under an inert atmosphere to obtain a reaction solution, stirring the reaction, and then rotary evaporating to obtain a surface-coated metal organic polymer;

[0017] S5: The surface-coated metal organic polymer and carboxymethyl cellulose are pre-dispersed in deionized water to obtain a pretreatment base liquid, and then the modified composite particles and lithium fluorocarbon additives are added. After uniform dispersion, conductive carbon black is added and defoamed to obtain a long-cycle high-rate negative electrode material.

[0018] As a preferred technical solution of the present invention, in step S1, the mass ratio of the silicon powder to the graphene is 3-4:1, for example, it can be 3.0:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1 or 4.0:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] In some optional embodiments, the mass ratio of tin powder to graphene is 2-3:1, for example, it can be 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1 or 3.0:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0020] In some optional embodiments, the mass ratio of the composite powder to polyacrylonitrile is 1:3-5, for example, it can be 1:3.0, 1:3.2, 1:3.4, 1:3.6, 1:3.8, 1:4.0, 1:4.2, 1:4.4, 1:4.6, 1:4.8 or 1:5.0, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0021] In some optional embodiments, the solid-liquid mass ratio of the composite powder and polyacrylonitrile to N-methylpyrrolidone is 1:3-5, for example, it can be 1:3.0, 1:3.2, 1:3.4, 1:3.6, 1:3.8, 1:4.0, 1:4.2, 1:4.4, 1:4.6, 1:4.8 or 1:5.0, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0022] In some optional embodiments, the temperature of the heat treatment is 500-600°C, for example, it can be 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C or 600°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] In some optional embodiments, the heat treatment time is 2-4h, for example, it can be 2.0h, 2.2h, 2.4h, 2.6h, 2.8h, 3.0h, 3.2h, 3.4h, 3.6h, 3.8h or 4.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] In some optional embodiments, the concentration of the ethanol solution of tungsten hexachloride is 0.05-0.1M, for example, 0.050M, 0.055M, 0.060M, 0.065M, 0.070M, 0.075M, 0.080M, 0.085M, 0.090M, 0.095M or 0.100M, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] In some optional embodiments, the mass ratio of the carbon-coated composite particles to tungsten hexachloride is 100:8-12, for example, it can be 100:8.0, 100:8.4, 100:8.8, 100:9.2, 100:9.6, 100:10.0, 100:10.4, 100:10.8, 100:11.2, 100:11.6 or 100:12.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] In some optional embodiments, the calcination temperature is 500-550°C, for example, it can be 500°C, 505°C, 510°C, 515°C, 520°C, 525°C, 530°C, 535°C, 540°C, 545°C or 550°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] In some optional embodiments, the calcination time is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, in step S2, the mass ratio of the first modified carbon-coated composite particles to metaphosphoric acid is 100:8-10, for example, it can be 100:8.0, 100:8.2, 100:8.4, 100:8.6, 100:8.8, 100:9.0, 100:9.2, 100:9.4, 100:9.6, 100:9.8 or 100:10.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In some optional embodiments, the mass ratio of the first modified carbon-coated composite particles to urea is 100:8-10, for example, it can be 100:8.0, 100:8.2, 100:8.4, 100:8.6, 100:8.8, 100:9.0, 100:9.2, 100:9.4, 100:9.6, 100:9.8 or 100:10.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] In some optional embodiments, the solid-liquid mass ratio of the first modified carbon-coated composite particles, metaphosphoric acid and urea after mixing with anhydrous ethanol is 1:5-6, for example, it can be 1:5.0, 1:5.1, 1:5.2, 1:5.3, 1:5.4, 1:5.5, 1:5.6, 1:5.7, 1:5.8, 1:5.9 or 1:6.0, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0031] In some optional embodiments, the temperature of the heat treatment is 400-450°C, for example, it can be 400°C, 405°C, 410°C, 415°C, 420°C, 425°C, 430°C, 435°C, 440°C, 445°C or 450°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] In some optional embodiments, the heat treatment time is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] As a preferred technical solution of the present invention, in step S3, the mass ratio of lithium carbide to vinylidene fluoride is 1:1-2, for example, it can be 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] In some optional embodiments, the solid-liquid mass ratio of the lithium carbide and vinylidene fluoride to tetrahydrofuran is 1:9-10, for example, it can be 1:9.0, 1:9.1, 1:9.2, 1:9.3, 1:9.4, 1:9.5, 1:9.6, 1:9.7, 1:9.8, 1:9.9 or 1:10.0, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0035] In some optional embodiments, the stirring reaction time is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] In some optional embodiments, the first temperature of the heat treatment is 250-280°C, for example, it can be 250°C, 253°C, 256°C, 259°C, 262°C, 265°C, 268°C, 271°C, 274°C, 277°C or 280°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] In some optional embodiments, the first time of the heat treatment is 1-2h, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] In some optional embodiments, the second temperature of the heat treatment is 400-450°C, for example, it can be 400°C, 405°C, 410°C, 415°C, 420°C, 425°C, 430°C, 435°C, 440°C, 445°C or 450°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In some optional embodiments, the second time of the heat treatment is 30-60 min, for example, it can be 30 min, 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min, 57 min or 60 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] As a preferred technical solution of the present invention, in step S4, the molar ratio of ammonium metavanadate to terephthalic acid is 1:1.5-2, for example, it can be 1:1.50, 1:1.55, 1:1.60, 1:1.65, 1:1.70, 1:1.75, 1:1.80, 1:1.85, 1:1.90, 1:1.95 or 1:2.00, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] In some optional embodiments, the mixed solvent is N,N-dimethylformamide:ethanol:water in a volume ratio of 2:1:1;

[0042] In some optional embodiments, the solid-liquid mass ratio of the ammonium metavanadate and terephthalic acid to the mixed solvent is 1:15-20, for example, it can be 1:15.0, 1:15.5, 1:16.0, 1:16.5, 1:17.0, 1:17.5, 1:18.0, 1:18.5, 1:19.0, 1:19.5 or 1:20.0, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0043] In some optional embodiments, the temperature of the hydrothermal reaction is 100-120°C, for example, it can be 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, 112°C, 114°C, 116°C, 118°C or 120°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] In some optional embodiments, the hydrothermal reaction time is 18-20h, for example, it can be 18.0h, 18.2h, 18.4h, 18.6h, 18.8h, 19.0h, 19.2h, 19.4h, 19.6h, 19.8h or 20.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] In some optional embodiments, the temperature of the precursor substrate under heat treatment in an inert atmosphere is 300-400°C, for example, it can be 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C or 400°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0046] In some optional embodiments, the precursor substrate is heat treated under an inert atmosphere for 3-4 hours, for example, 3.0 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours, 3.5 hours, 3.6 hours, 3.7 hours, 3.8 hours, 3.9 hours or 4.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] In some optional embodiments, the mass ratio of the metal-organic framework to lithium carbide is 1:0.3-0.5, for example, it can be 1:0.30, 1:0.32, 1:0.34, 1:0.36, 1:0.38, 1:0.40, 1:0.42, 1:0.44, 1:0.46, 1:0.48 or 1:0.50, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0048] In some optional embodiments, the solid-liquid mass ratio of the metal-organic framework and lithium carbide to tetrahydrofuran is 1:8-9, for example, it can be 1:8.0, 1:8.1, 1:8.2, 1:8.3, 1:8.4, 1:8.5, 1:8.6, 1:8.7, 1:8.8, 1:8.9 or 1:9.0, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0049] In some optional embodiments, the temperature of the pre-treated powder heat treatment is 400-450°C, for example, it can be 400°C, 405°C, 410°C, 415°C, 420°C, 425°C, 430°C, 435°C, 440°C, 445°C or 450°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0050] In some optional embodiments, the heat treatment time of the pretreated powder is 1-2h, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] In some optional embodiments, the mass ratio of the pre-embedded lithium composite powder to polyacrylonitrile is 1:0.1-0.2, for example, it can be 1:0.10, 1:0.11, 1:0.12, 1:0.13, 1:0.14, 1:0.15, 1:0.16, 1:0.17, 1:0.18, 1:0.19 or 1:0.20, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0052] In some optional embodiments, the mass fraction of the polyacrylonitrile N-methylpyrrolidone solution is 2-3 wt.%, for example, it can be 2.0 wt.%, 2.1 wt.%, 2.2 wt.%, 2.3 wt.%, 2.4 wt.%, 2.5 wt.%, 2.6 wt.%, 2.7 wt.%, 2.8 wt.%, 2.9 wt.% or 3.0 wt.%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0053] In some optional embodiments, the stirring reaction time of the reaction liquid is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0054] As a preferred technical solution of the present invention, in step S5, during pre-dispersion, the solid-liquid mass ratio of the surface-coated metal organic polymer and carboxymethyl cellulose to deionized water is 1:5-6, for example, it can be 1:5.0, 1:5.1, 1:5.2, 1:5.3, 1:5.4, 1:5.5, 1:5.6, 1:5.7, 1:5.8, 1:5.9 or 1:6.0, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0055] In a second aspect, the present invention provides a long-cycle, high-rate negative electrode material comprising a surface-coated metal organic polymer, carboxymethyl cellulose, modified composite particles, a lithium fluorocarbon additive, and conductive carbon black.

[0056] In a third aspect, the present invention provides an application of a long-cycle, high-rate negative electrode material prepared by the above-mentioned preparation method in a lithium-ion battery.

[0057] In the present invention, silicon powder, tin powder and graphene are mixed, and a composite powder is prepared by ball milling. Silicon has become a research hotspot for negative electrode materials due to its extremely high theoretical specific capacity. However, silicon undergoes significant volume expansion during the charge and discharge process. This volume change causes the active particles to gradually pulverize during repeated cycles and causes interface stability problems. Specifically, the contact between the silicon surface and the electrolyte causes repeated rupture and reconstruction of the solid electrolyte interface film, which consumes a large amount of lithium ions and aggravates the occurrence of side reactions, ultimately leading to rapid capacity decay. Therefore, using silicon alone as a negative electrode material is difficult to meet the requirements of long-life cycles.

[0058] Tin is also a high-capacity material. Compared to silicon, its volume expansion problem is slightly smaller, but still significant. In addition, tin's electrochemical performance is easily limited by the increase in interfacial impedance, especially under high-rate charge and discharge conditions, where its interfacial chemical stability is poor, which further deteriorates the overall performance of the electrode. In general, although tin's expansion effect and interfacial stability issues are easier to control than silicon, they still need to be optimized through composite design to achieve practical applications with long cycles and high rates.

[0059] In order to alleviate the structural stability problem of silicon and tin, the present invention adopts graphene as the composite matrix. Graphene is a carbon material with high conductivity and two-dimensional flaky structure. With its large specific surface area and excellent mechanical flexibility, it plays a key role in the composite design. During the ball milling process, graphene can be evenly distributed between the silicon and tin particles to form a three-dimensional conductive network, which significantly improves the overall conductivity of the composite material. At the same time, graphene also serves as a flexible support framework to provide the necessary mechanical buffer for silicon and tin to partially absorb the internal stress caused by their volume expansion, thereby slowing down the destruction of the material structure. In addition, the high specific surface area of ​​graphene provides more embedding and diffusion channels for lithium ions, which helps to optimize the lithium ion transmission path and reduce the polarization effect of the electrode.

[0060] After obtaining the silicon-tin-graphene composite powder, the present invention further performs carbonization and coating modification on the polyacrylonitrile to further improve the structural stability and interface properties of the composite material. Polyacrylonitrile undergoes chemical conversion reactions such as dehydrogenation and denitrification during high-temperature heat treatment, ultimately forming a carbon coating layer with a low degree of graphitization. This carbon coating plays an important role in the composite particles. First, the carbon coating layer can provide effective mechanical constraints for the silicon and tin particles, thereby inhibiting their volume expansion and maintaining the structural integrity of the composite particles. Secondly, the carbon layer, as a medium for electron transmission, together with graphene, constructs an efficient conductive network, greatly improving the electron transmission capacity of the composite material, especially under high-rate charge and discharge conditions, which can significantly reduce the electrochemical polarization of the electrode. In addition, the carbon coating layer can also form a chemically stable protective barrier between the electrolyte and the active particles. This barrier effectively reduces the direct contact between the electrolyte and the silicon and tin particles, thereby inhibiting the occurrence of side reactions on the surface of the material. At the same time, the carbon coating layer can stabilize the formation of the solid electrolyte interface film, reduce the rupture and reconstruction of the solid electrolyte interface film, and significantly reduce the irreversible capacity loss during the first charge and discharge.

[0061] Although the conductivity and structural stability of the composite material can be improved to a certain extent by compounding silicon, tin and graphene and further introducing a carbon coating layer, there are still some key issues that need to be resolved. First, when the carbon coating layer is in direct contact with the electrolyte, uncontrollable side reactions may occur, resulting in the formation of an unstable solid electrolyte interface film. This unstable solid electrolyte interface film is easily broken and regenerated during the charge and discharge process, which not only consumes a large amount of lithium ions and electrolyte, increases irreversible capacity loss, but also further aggravates the increase in interfacial impedance, and has a negative impact on cycle life. Secondly, although the carbon coating layer alleviates the volume expansion problem of silicon and tin to a certain extent, since silicon and tin still undergo significant volume changes during the charge and discharge process, poor contact may occur between local particles. This poor contact will destroy the conductive network in the electrode, further limiting the rate performance and cycle stability of the material.

[0062] To address the aforementioned issues and further optimize the performance of the composite material, the present invention introduces tungsten oxide as an interfacial stabilizer, generating nanoscale tungsten oxide on the surface of carbon-coated particles through a calcination reaction of tungsten hexachloride. Tungsten oxide has high chemical stability and electrochemical activity, and its introduction can modify and optimize the composite material in multiple ways. First, tungsten oxide forms a chemically stable inorganic protective layer on the surface of the negative electrode particles, effectively isolating the direct contact between the electrolyte and the active particles, thereby inhibiting the occurrence of side reactions and reducing the formation of unstable solid electrolyte interface films. This protective layer not only reduces the interfacial impedance of the electrode surface but also significantly improves the interfacial chemical stability of the composite material. Second, tungsten oxide itself has a certain lithium ion storage capacity. By participating in the intercalation and deintercalation reactions of lithium ions during the electrochemical cycle, tungsten oxide can provide additional lithium ion storage sites, thereby increasing the specific capacity of the negative electrode material. In addition, the rigidity and mechanical stability of tungsten oxide can mechanically constrain the volume expansion of silicon and tin during the charge-discharge cycle, alleviating the problems of particle pulverization and poor contact.

[0063] Notably, the introduction of tungsten oxide can also enhance the interfacial bonding between composite particles. Between the carbon coating and graphene, tungsten oxide, through its excellent surface activity and mechanical stability, can further enhance the bonding strength between particles, thereby improving the overall structural stability of the composite. This enhanced interfacial bonding helps maintain the integrity of the conductive network, enabling the composite to maintain excellent performance under long-term cycling and high-rate conditions.

[0064] The performance of the composite material is significantly optimized through the synergistic effect of graphene's high conductivity, the mechanical confinement of the carbon coating, and the surface stability of tungsten oxide. The graphene and carbon coating together create an efficient electron transport network, significantly improving the overall conductivity of the material, particularly under high-rate charge and discharge conditions. Furthermore, the introduction of tungsten oxide not only enhances interfacial stability but also further optimizes the structure and properties of the composite material through its lithium storage capacity and mechanical support.

[0065] Secondly, in order to further improve the interfacial stability and electrochemical performance of the composite material, metaphosphoric acid and urea are introduced in the present invention to perform a second modification on the silicon-tin-graphene composite material. Metaphosphoric acid undergoes a decomposition reaction during high-temperature heat treatment, and its dissociation products can react chemically with the active sites on the surface of the composite particles to generate inorganic phosphates with extremely high chemical stability. These inorganic phosphates form a uniform protective film on the surface of the material and have multiple functions. First, the phosphate protective film has excellent chemical stability and can effectively isolate the direct contact between the electrolyte and the active material (such as silicon, tin or carbon surface), thereby significantly reducing unnecessary side reactions, reducing the decomposition rate of the electrolyte, and inhibiting the excessive growth of the solid electrolyte interface film. Secondly, the inorganic phosphate layer has a high lithium ion conductivity, which allows lithium ions to quickly pass through the protective film, thereby reducing the interfacial impedance and improving the electrochemical performance of the electrode. In addition, the inorganic rigidity of the phosphate layer enables it to play a certain mechanical support role during the volume expansion of the material. This support effect can alleviate the structural damage caused by the expansion of silicon and tin, thereby further improving the cycle stability of the composite material.

[0066] At the same time, the introduction of urea provides additional improvements to the material's conductivity and interfacial activity. Under high temperature conditions, urea decomposes to release ammonia and carbon dioxide. These decomposition products can chemically react with carbon materials in the surrounding environment to form nitrogen-doped carbon-based materials. Nitrogen-doped carbon-based materials have significantly improved electronic structures. The introduction of nitrogen atoms changes the electron distribution within the carbon material, significantly enhancing the conductivity of the carbon layer. Furthermore, nitrogen doping introduces more chemically active sites on the material's surface. These active sites not only promote the adsorption and storage of lithium ions but also improve the material's rate capability and specific capacity. More importantly, nitrogen-doped carbon-based materials stabilize the formation of the solid electrolyte interface film at the interface between the electrolyte and the active particles. This stable solid electrolyte interface film has low impedance and high mechanical integrity, effectively suppressing side reactions caused by repeated rupture and reformation of the solid electrolyte interface film, further reducing the battery's irreversible capacity loss.

[0067] The dual modification with metaphosphoric acid and urea creates a synergistic effect on interfacial chemistry and structural stability. The phosphate film formed by metaphosphoric acid provides a chemical barrier and mechanical support for the composite particles, while the nitrogen-doped carbon generated by urea not only enhances the material's conductivity but also further optimizes the composite's overall performance by improving interfacial stability and lithium storage capacity. This secondary modification method significantly improves the composite's cycle life and rate performance, while providing a more stable interface and structural foundation for subsequent functionalization.

[0068] This invention uses lithium carbide and vinylidene fluoride to produce a lithium fluorocarbon additive, which improves the low initial coulombic efficiency, poor interfacial stability, and irreversible lithium ion loss of high-capacity negative electrode materials. Lithium carbide is a highly chemically active lithium-containing compound that can serve as a pre-insertion source of lithium ions, enabling the phased release of lithium ions during the preparation and formation of the negative electrode material.

[0069] Lithium carbide can partially react with negative electrode powders (such as active ingredients such as silicon and tin) to generate localized lithiated compounds. Since silicon and tin consume a large amount of lithium ions to form alloy phases during the initial lithium insertion process, the pre-reaction mechanism of lithium carbide can complete part of the lithiation process in advance during the material preparation stage, thereby reducing the lithium ion loss of active particles during the initial charge and discharge, and improving the initial coulombic efficiency of the battery. In addition, incompletely reacted lithium carbide can continue to release lithium ions during the battery formation stage. These lithium ions can further react with unlithiated silicon and tin particles, or directly participate in electrochemical reactions, thereby compensating for the irreversible lithium loss during the initial charge and discharge, and further improving the actual capacity and efficiency of the battery.

[0070] At the same time, the reaction between lithium carbide and vinylidene fluoride generates lithium fluoride or lithium-fluorine-carbon composite structure. These chemical products form a uniform interfacial protective layer on the surface of the negative electrode. Lithium fluoride has high chemical inertness and low interfacial impedance. Its presence at the negative electrode-electrolyte interface can effectively inhibit the decomposition of the electrolyte and the occurrence of interfacial side reactions. This not only reduces the irreversible loss of lithium ions, but also significantly reduces the interfacial impedance, providing a lower impedance path for the insertion and deintercalation of lithium ions, thereby optimizing the electrochemical performance of the negative electrode material. In addition, this interfacial protective layer also has high mechanical stability, which can provide a certain buffering effect when the silicon and tin particles expand in volume, further stabilizing the structure of the composite material.

[0071] During the battery formation stage, incompletely reacted lithium carbide continues to react with electrolyte components, the surface of the negative electrode material, and other possible chemical components to release additional lithium ions. These released lithium ions are not only directly embedded in the material to form a lithiated alloy, but can also participate in the formation process of the solid electrolyte interface film, reducing the consumption of lithium ions by electrolyte decomposition, thereby improving the stability and uniformity of the solid electrolyte interface film. Through this staged release of lithium ions mechanism, lithium carbide maximizes the utilization efficiency of lithium ions and effectively reduces the loss of lithium metal negative electrodes or electrolyte lithium salts.

[0072] The present invention synthesizes a vanadium-based metal-organic framework (MOF) using ammonium metavanadate and terephthalic acid under hydrothermal reaction conditions. This MOF material, with its unique high specific surface area and well-developed ion channel structure, shows great potential for application in the design of negative electrodes for lithium-ion batteries. The porous structure of the MOF material not only provides abundant reactive sites but also provides low-impedance transport pathways for the insertion and diffusion of lithium ions, significantly improving the electrochemical performance of the negative electrode material.

[0073] During the preparation process, the metal-organic framework undergoes a chemical reaction with lithium carbide to achieve pre-lithium insertion modification of the metal-organic framework. Lithium carbide is a lithium-containing compound with high chemical activity. After reacting with the metal-organic framework, lithium ions can be introduced into the material to generate a composite material with initial lithium ion activity. This pre-lithium insertion process provides an important source of lithium ions for the first charge and discharge of the negative electrode material, thereby significantly reducing the first irreversible capacity loss and improving the first coulombic efficiency of the battery. In addition, the metal-organic framework material after lithium insertion can further release lithium ions during the battery formation stage, so that the negative electrode material has higher activity and lower lithium ion consumption in the first cycle.

[0074] It is worth noting that the high specific surface area and ordered ion channel structure of the metal-organic framework play a positive role in the pre-lithiation process. On the one hand, the high specific surface area provides more active sites for the insertion of lithium ions, making the lithium insertion process more efficient; on the other hand, the ion channel structure of the framework optimizes the diffusion path of lithium ions and significantly reduces the migration impedance of lithium ions within the material. This structural characteristic promotes the rapid transmission of lithium ions in the subsequent cycle process, thereby improving the rate performance of the battery. In addition, the porous structure of the metal-organic framework can also buffer the stress generated by active particles such as silicon and tin during the volume expansion process, effectively improving the mechanical stability of the composite material.

[0075] In order to further enhance the electrical conductivity and structural stability of the metal-organic framework, the present invention also introduces a graphitized carbon coating layer on its surface. Polyacrylonitrile is used as a carbon source, and chemical reactions such as dehydrogenation and denitrification occur during high-temperature heat treatment, ultimately generating a uniform graphitized carbon layer. This carbon coating layer plays multiple functions in the structure of the metal-organic framework. First, the graphitized carbon layer has high electrical conductivity, and together with the metal-organic framework, it constructs an efficient electron transport network, greatly improving the overall electrical conductivity of the composite material. Secondly, the mechanical stability of the carbon layer can further enhance the structural integrity of the metal-organic framework, providing a guarantee for the stability of the material in long-term cycles. In addition, the carbon layer can also form a chemical protective barrier on the surface of the negative electrode, reducing the direct contact between the electrolyte and the active particles, thereby inhibiting the occurrence of side reactions and further stabilizing the formation of the solid electrolyte interface film.

[0076] The high surface area and ion channel structure of the metal-organic framework (MOF) are combined with the pre-lithiation process of lithium carbide to achieve multiple optimizations of the anode material. The MOF after lithium insertion not only provides an additional source of lithium ions for the anode, but also improves the material's rate capability and cycling stability by optimizing the lithium ion diffusion pathway and active site distribution. Furthermore, the graphitized carbon coating on the surface further enhances the electronic conductivity and structural stability of the composite material.

[0077] There is also a synergistic enhancement effect in the present invention. The synergistic effect between the metal-organic framework and lithium carbide in the material preparation process is mainly reflected in the pre-embedding and diffusion optimization of lithium ions. The metal-organic framework material has a high specific surface area and an ordered ion channel structure, which provides a large number of active sites and low-impedance paths for the embedding and transmission of lithium ions. During the reaction with lithium carbide, these structural characteristics maximize the embedding efficiency of lithium ions. In addition, the structural characteristics of the metal-organic framework material can buffer the volume stress that may be generated during the lithiation process, prevent mechanical damage to the material, and ensure that the lithiation reaction proceeds uniformly. The staged lithium ion release function of lithium carbide further matches the high active sites of the metal-organic framework, making the storage and release process of lithium ions more uniform and efficient. This synergistic effect significantly reduces the irreversible lithium loss during the first charge and discharge, and improves the first coulombic efficiency of the material.

[0078] The synergistic effect between the metal-organic framework and the graphitized carbon coating is mainly reflected in the improvement of electrical conductivity and the enhancement of structural stability. The metal-organic framework material itself has low electrical conductivity, but after its surface is coated with a layer of graphitized carbon, the electron transport performance can be significantly improved. The graphitized carbon layer not only provides an efficient electron transport channel for the metal-organic framework, but also synergizes with the porous structure of the metal-organic framework to provide a faster transmission path for the embedding and diffusion of lithium ions. In addition, the mechanical flexibility of the graphitized carbon layer can further enhance the overall structural stability of the metal-organic framework, effectively alleviating the internal stress caused by the volume expansion of silicon or tin particles during the cycle, thereby inhibiting the pulverization of particles and the collapse of the electrode structure.

[0079] There is also a significant synergistic effect between the pre-lithiation process of lithium carbide and the graphitized carbon coating. The lithium ions released by lithium carbide during the reaction can directly participate in the lithiation of the metal-organic framework, and may also generate stable lithium compounds (such as lithium fluoride or lithiated carbon) on the surface of the graphitized carbon layer. The interface layer formed by these lithium compounds on the electrode surface has high chemical stability and low impedance characteristics, which can further optimize the interface stability between the negative electrode and the electrolyte. In addition, the conductivity of the graphitized carbon layer provides a more efficient electron channel for the transmission of lithium ions released by lithium carbide, thereby promoting the uniform embedding of lithium ions. This synergistic effect simultaneously improves the interface performance and electrochemical activity of the electrode.

[0080] As high-capacity anode materials, silicon and tin face significant volume expansion during charge and discharge, a major challenge that needs to be addressed. The porous structure of the metal-organic framework (MOF) and the mechanical flexibility of the graphitized carbon layer work together to provide a buffer for the expansion of silicon and tin particles. The porosity of the MOF allows the expanding silicon or tin particles to be constrained within the framework, while the graphitized carbon layer further enhances this buffering capacity through mechanical support. This synergistic effect significantly improves the material's cycling stability and extends the battery's lifespan.

[0081] Compared with the prior art, the present invention has the following beneficial effects:

[0082] By combining silicon powder, tin powder, and graphene, and then carbonizing and coating with polyacrylonitrile, a three-dimensional conductive network is constructed, optimizing the lithium-ion transmission path while mitigating the volume expansion and interface stability issues of silicon and tin. The carbon coating further enhances mechanical constraints, stabilizes the interface, and reduces side reactions and irreversible capacity loss. The synergistic effect of graphene and the carbon layer significantly improves the material's conductivity, cycle stability, and rate performance.

[0083] By introducing tungsten oxide as an interfacial stabilizer, a stable protective layer is formed, side reactions are suppressed, interfacial impedance is reduced, and its lithium storage capacity is utilized to increase specific capacity. At the same time, tungsten oxide mitigates the volume expansion of silicon and tin, enhancing the integrity of the conductive network. The high conductivity of graphene, the mechanical confinement of the carbon coating, and the interfacial stability of tungsten oxide work synergistically to give the material excellent electrochemical properties and structural stability.

[0084] Metaphosphoric acid decomposes to form an inorganic phosphate protective film, isolating the electrolyte from the active material, inhibiting side reactions and excessive growth of the solid electrolyte interface film, while also providing mechanical support to alleviate volume expansion. Urea decomposes to form nitrogen-doped carbon, significantly improving the material's conductivity and interfacial activity, while also stabilizing the solid electrolyte interface film and reducing side reactions and irreversible capacity loss. The synergistic effect of these two factors significantly enhances interfacial stability and electrochemical performance, improving cycle life, rate capability, and structural stability.

[0085] Lithium fluorocarbon additives are prepared by reacting lithium carbide with vinylidene fluoride to improve the initial coulombic efficiency and actual capacity of the negative electrode material. Lithium carbide acts as a lithium ion pre-embedding source, releasing lithium ions in stages to reduce initial lithium loss. At the same time, the lithium fluoride or lithium-fluorine-carbon composite protective layer reduces interfacial impedance, inhibits side reactions, provides mechanical buffering, and enhances structural stability. During the formation stage, incompletely reacted lithium carbide continues to release lithium ions, promoting the uniform formation of the solid electrolyte interface film, further optimizing the electrochemical performance and stability.

[0086] A vanadium-based metal-organic framework (MOF) was prepared by the hydrothermal reaction of ammonium metavanadate and terephthalic acid. The framework was pre-lithiated with lithium carbide and a graphitized carbon coating was introduced. The MOF's high surface area and ordered ion channels optimize the lithium-ion transport pathway, improving initial coulombic efficiency and rate performance. Pre-lithiation reduces irreversible capacity loss, while the porous structure mitigates volume expansion and enhances mechanical stability. The graphitized carbon coating further enhances conductivity and structural integrity, suppresses side reactions, and significantly improves the cycle stability and electrochemical performance of the negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] Figure 1 Flowchart of the preparation method of the long cycle and high rate negative electrode material provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0088] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be understood as limiting the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments described herein.

[0089] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products without further purification or treatment.

[0090] Example 1

[0091] This embodiment provides a long-cycle high-rate negative electrode material and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0092] S1: mixing silicon powder, tin powder and graphene and ball-milling to obtain composite powder; reacting the composite powder with polyacrylonitrile in N-methylpyrrolidone, drying and heat-treating the resulting composite powder to obtain carbon-coated composite particles; impregnating the resulting composite powder with an ethanol solution of tungsten hexachloride and reacting the resulting particles, and calcining the resulting particles to obtain first modified carbon-coated composite particles;

[0093] Specifically, S1: silicon powder, tin powder and graphene are mixed and ball-milled to obtain a composite powder, wherein the mass ratio of silicon powder to graphene is 3.6:1, and the mass ratio of tin powder to graphene is 2.7:1, and the composite powder and polyacrylonitrile are added to N-methylpyrrolidone and stirred for coating, wherein the mass ratio of the composite powder to polyacrylonitrile is 1:4.1, and the solid-liquid mass ratio of the composite powder and polyacrylonitrile to N-methylpyrrolidone is 1:3.8. After drying, the composite powder is heat-treated at 530° C. under an inert atmosphere for 2 h to obtain carbon-coated composite particles; the composite particles are immersed in an ethanol solution of tungsten hexachloride with a concentration of 0.08 M for immersion reaction, wherein the mass ratio of the carbon-coated composite particles to tungsten hexachloride is 100:10, and calcined at 520° C. for 2 h to obtain first modified carbon-coated composite particles;

[0094] S2: mixing the first modified carbon-coated composite particles with metaphosphoric acid and urea in anhydrous ethanol, drying, and then heat-treating to obtain modified composite particles;

[0095] Specifically, S2: mixing the first modified carbon-coated composite particles with metaphosphoric acid and urea and uniformly dispersing the mixture in anhydrous ethanol, wherein the mass ratio of the first modified carbon-coated composite particles to the metaphosphoric acid is 100:9, the mass ratio of the first modified carbon-coated composite particles to the urea is 100:8, and the solid-liquid mass ratio of the first modified carbon-coated composite particles, metaphosphoric acid and urea to anhydrous ethanol is 1:5.7. After reaction and drying, the mixture is placed in an inert atmosphere and heat treated at 400°C for 2.4h to obtain modified composite particles;

[0096] S3: reacting lithium carbide with vinylidene fluoride in tetrahydrofuran, drying, and then heat-treating to obtain a lithium fluorocarbon additive;

[0097] Specifically, S3: lithium carbide and vinylidene fluoride are dispersed in tetrahydrofuran at a mass ratio of 1:1.6, and the solid-liquid mass ratio of lithium carbide and vinylidene fluoride to tetrahydrofuran is 1:9.4, stirring and reacting for 2 hours and then drying, and then heat-treating at 250° C. for 1 hour under an inert atmosphere and then heating to 400° C. for 30 minutes to obtain a lithium fluorocarbon additive;

[0098] S4: hydrothermally reacting ammonium metavanadate with terephthalic acid and then heat-treating it to obtain a metal-organic framework; reacting it with lithium carbide in tetrahydrofuran and heat-treating it to obtain a pre-embedded lithium composite powder; and reacting it with polyacrylonitrile to obtain a surface-coated metal-organic polymer;

[0099] Specifically, S4: ammonium metavanadate and terephthalic acid are added to a mixed solvent at a molar ratio of 1:1.8, wherein the solid-liquid mass ratio of ammonium metavanadate and terephthalic acid to the mixed solvent is 1:18, and the volume ratio of N,N-dimethylformamide, ethanol and deionized water in the mixed solvent is 2:1:1, and the precursor substrate is hydrothermally reacted at 100°C for 18 hours, filtered, washed and dried to obtain a precursor substrate, which is heat-treated at 300°C under an inert atmosphere for 3 hours to obtain a metal-organic framework; it is mixed with lithium carbide at a mass ratio of 1:0.4. The method comprises dispersing the pretreated powder in tetrahydrofuran, wherein the solid-liquid mass ratio of the metal-organic framework and lithium carbide to the tetrahydrofuran is 1:8.7, stirring the reaction, and drying the pretreated powder to obtain a pretreated powder, which is then heat-treated at 400° C. for 1 hour to obtain a pre-embedded lithium composite powder; dispersing the pre-embedded lithium composite powder in a 2 wt.% polyacrylonitrile solution in N-methylpyrrolidone under an inert atmosphere to obtain a reaction solution, wherein the mass ratio of the pre-embedded lithium composite powder to the polyacrylonitrile is 1:0.16, stirring the reaction for 2 hours, and then rotary evaporating the reaction solution to obtain a surface-coated metal organic polymer;

[0100] S5: The surface-coated metal organic polymer is pre-dispersed with carboxymethyl cellulose, and modified composite particles, lithium fluorocarbon additives and conductive carbon black are added to prepare a long-cycle and high-rate negative electrode material.

[0101] Specifically, S5: pre-dispersing the surface-coated metal organic polymer and carboxymethyl cellulose in deionized water to obtain a pretreatment base liquid, wherein the solid-liquid mass ratio of the surface-coated metal organic polymer and carboxymethyl cellulose to deionized water is 1:5.7, and then adding modified composite particles and lithium fluorocarbon additives, adding conductive carbon black after uniform dispersion, and defoaming to obtain a long-cycle high-rate negative electrode material, wherein the mass ratio of the surface-coated metal organic polymer, carboxymethyl cellulose, modified composite particles, lithium fluorocarbon additives and conductive carbon black is 4.3:4.2:78:3.6:4.

[0102] Example 2

[0103] This embodiment provides a long-cycle high-rate negative electrode material and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0104] S1: mixing silicon powder, tin powder and graphene and ball-milling to obtain composite powder; reacting the composite powder with polyacrylonitrile in N-methylpyrrolidone, drying and heat-treating the resulting composite powder to obtain carbon-coated composite particles; impregnating the resulting composite powder with an ethanol solution of tungsten hexachloride and reacting the resulting particles, and calcining the resulting particles to obtain first modified carbon-coated composite particles;

[0105] Specifically, S1: silicon powder, tin powder and graphene are mixed and ball-milled to obtain a composite powder, wherein the mass ratio of silicon powder to graphene is 4:1, and the mass ratio of tin powder to graphene is 3:1, and the composite powder and polyacrylonitrile are added to N-methylpyrrolidone for stirring and coating, wherein the mass ratio of the composite powder to polyacrylonitrile is 1:5, and the solid-liquid mass ratio of the composite powder and polyacrylonitrile to N-methylpyrrolidone is 1:4.5. After drying, the composite powder is heat-treated at 600°C under an inert atmosphere for 3 hours to obtain carbon-coated composite particles; the composite powder is immersed in an ethanol solution of tungsten hexachloride with a concentration of 0.05M for immersion reaction, wherein the mass ratio of the carbon-coated composite particles to tungsten hexachloride is 100:11, and the composite particles are calcined at 550°C for 2.5 hours to obtain first modified carbon-coated composite particles;

[0106] S2: mixing the first modified carbon-coated composite particles with metaphosphoric acid and urea in anhydrous ethanol, drying, and then heat-treating to obtain modified composite particles;

[0107] Specifically, S2: mixing the first modified carbon-coated composite particles with metaphosphoric acid and urea and uniformly dispersing the mixture in anhydrous ethanol, wherein the mass ratio of the first modified carbon-coated composite particles to the metaphosphoric acid is 100:9.6, the mass ratio of the first modified carbon-coated composite particles to the urea is 100:9, and the solid-liquid mass ratio of the first modified carbon-coated composite particles, metaphosphoric acid and urea to anhydrous ethanol is 1:6. After reaction and drying, the mixture is placed in an inert atmosphere and heat treated at 420° C. for 2 h to obtain modified composite particles.

[0108] S3: reacting lithium carbide with vinylidene fluoride in tetrahydrofuran, drying, and then heat-treating to obtain a lithium fluorocarbon additive;

[0109] Specifically, S3: lithium carbide and vinylidene fluoride are dispersed in tetrahydrofuran in a mass ratio of 1:2, and the solid-liquid mass ratio of lithium carbide and vinylidene fluoride to tetrahydrofuran is 1:9.8, stirring and reacting for 2.6 hours and then drying, and then heat-treating at 270°C under an inert atmosphere for 2 hours and then heating to 440°C for 50 minutes to obtain a lithium fluorocarbon additive;

[0110] S4: hydrothermally reacting ammonium metavanadate with terephthalic acid and then heat-treating it to obtain a metal-organic framework; reacting it with lithium carbide in tetrahydrofuran and heat-treating it to obtain a pre-embedded lithium composite powder; and reacting it with polyacrylonitrile to obtain a surface-coated metal-organic polymer;

[0111] Specifically, S4: ammonium metavanadate and terephthalic acid are added to a mixed solvent at a molar ratio of 1:1.7, wherein the solid-liquid mass ratio of ammonium metavanadate and terephthalic acid to the mixed solvent is 1:20, and the volume ratio of N,N-dimethylformamide, ethanol and deionized water in the mixed solvent is 2:1:1, and the precursor substrate is hydrothermally reacted at 110°C for 19 hours, filtered, washed and dried to obtain a precursor substrate, which is heat-treated at 350°C under an inert atmosphere for 3.6 hours to obtain a metal-organic framework; it is mixed with lithium carbide at a mass ratio of 1:0.5. The pre-embedded lithium composite powder was dispersed in tetrahydrofuran, wherein the solid-liquid mass ratio of the metal-organic framework and lithium carbide to the tetrahydrofuran was 1:9, and dried after stirring for reaction to obtain a pretreated powder, which was heat-treated at 430° C. for 1.6 hours to obtain a pre-embedded lithium composite powder; the pre-embedded lithium composite powder was dispersed in a 2.7 wt.% polyacrylonitrile solution in N-methylpyrrolidone under an inert atmosphere to obtain a reaction solution, wherein the mass ratio of the pre-embedded lithium composite powder to the polyacrylonitrile was 1:0.2, and the reaction was stirred for 3 hours and then rotary evaporated to obtain a surface-coated metal organic polymer;

[0112] S5: The surface-coated metal organic polymer is pre-dispersed with carboxymethyl cellulose, and modified composite particles, lithium fluorocarbon additives and conductive carbon black are added to prepare a long-cycle and high-rate negative electrode material.

[0113] Specifically, S5: pre-dispersing the surface-coated metal organic polymer and carboxymethyl cellulose in deionized water to obtain a pretreatment base liquid, wherein the solid-liquid mass ratio of the surface-coated metal organic polymer and carboxymethyl cellulose to deionized water is 1:6, and then adding modified composite particles and lithium fluorocarbon additives, adding conductive carbon black after uniform dispersion, and defoaming to obtain a long-cycle high-rate negative electrode material, wherein the mass ratio of the surface-coated metal organic polymer, carboxymethyl cellulose, modified composite particles, lithium fluorocarbon additives and conductive carbon black is 4:5:77:3:3.

[0114] Example 3

[0115] This embodiment provides a long-cycle high-rate negative electrode material and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0116] S1: mixing silicon powder, tin powder and graphene and ball-milling to obtain composite powder; reacting the composite powder with polyacrylonitrile in N-methylpyrrolidone, drying and heat-treating the resulting composite powder to obtain carbon-coated composite particles; impregnating the resulting composite powder with an ethanol solution of tungsten hexachloride and reacting the resulting particles, and calcining the resulting particles to obtain first modified carbon-coated composite particles;

[0117] Specifically, S1: silicon powder, tin powder and graphene are mixed and ball-milled to obtain a composite powder, wherein the mass ratio of silicon powder to graphene is 3:1, and the mass ratio of tin powder to graphene is 2:1, and the composite powder and polyacrylonitrile are added to N-methylpyrrolidone and stirred for coating, wherein the mass ratio of the composite powder to polyacrylonitrile is 1:3, and the solid-liquid mass ratio of the composite powder and polyacrylonitrile to N-methylpyrrolidone is 1:3. After drying, the composite powder is heat-treated at 500° C. for 3.5 h under an inert atmosphere to obtain carbon-coated composite particles; the composite particles are immersed in an ethanol solution of tungsten hexachloride with a concentration of 0.07 M for immersion reaction, wherein the mass ratio of the carbon-coated composite particles to tungsten hexachloride is 100:8, and the composite particles are calcined at 500° C. for 2.8 h to obtain first modified carbon-coated composite particles;

[0118] S2: mixing the first modified carbon-coated composite particles with metaphosphoric acid and urea in anhydrous ethanol, drying, and then heat-treating to obtain modified composite particles;

[0119] Specifically, S2: mixing the first modified carbon-coated composite particles with metaphosphoric acid and urea and uniformly dispersing the mixture in anhydrous ethanol, wherein the mass ratio of the first modified carbon-coated composite particles to the metaphosphoric acid is 100:8, the mass ratio of the first modified carbon-coated composite particles to the urea is 100:10, and the solid-liquid mass ratio of the first modified carbon-coated composite particles, metaphosphoric acid and urea to the anhydrous ethanol is 1:5. After reaction and drying, the mixture is placed in an inert atmosphere and heat treated at 430° C. for 2.7 h to obtain modified composite particles;

[0120] S3: reacting lithium carbide with vinylidene fluoride in tetrahydrofuran, drying, and then heat-treating to obtain a lithium fluorocarbon additive;

[0121] Specifically, S3: lithium carbide and vinylidene fluoride are dispersed in tetrahydrofuran in a mass ratio of 1:1, and the solid-liquid mass ratio of lithium carbide and vinylidene fluoride to tetrahydrofuran is 1:9, stirring and reacting for 2.8 hours and then drying, and then heat-treating at 260° C. for 1.2 hours under an inert atmosphere and then heating to 430° C. for 45 minutes to obtain a lithium fluorocarbon additive;

[0122] S4: hydrothermally reacting ammonium metavanadate with terephthalic acid and then heat-treating it to obtain a metal-organic framework; reacting it with lithium carbide in tetrahydrofuran and heat-treating it to obtain a pre-embedded lithium composite powder; and reacting it with polyacrylonitrile to obtain a surface-coated metal-organic polymer;

[0123] Specifically, S4: ammonium metavanadate and terephthalic acid are added to a mixed solvent at a molar ratio of 1:1.5, wherein the solid-liquid mass ratio of ammonium metavanadate and terephthalic acid to the mixed solvent is 1:15, and the volume ratio of N,N-dimethylformamide, ethanol and deionized water in the mixed solvent is 2:1:1, and the precursor substrate is hydrothermally reacted at 115°C for 18.5h, filtered, washed and dried to obtain a precursor substrate, which is heat-treated at 380°C for 3.8h under an inert atmosphere to obtain a metal-organic framework; it is dispersed with lithium carbide at a mass ratio of 1:0.3 In tetrahydrofuran, wherein the solid-liquid mass ratio of the metal-organic framework and lithium carbide to tetrahydrofuran is 1:8.3, the mixture is stirred and reacted, and then dried to obtain a pretreated powder, which is then heat-treated at 420° C. for 1.8 hours to obtain a pre-embedded lithium composite powder; under an inert atmosphere, the pre-embedded lithium composite powder is dispersed in a 2.4 wt.% polyacrylonitrile solution in N-methylpyrrolidone to obtain a reaction solution, wherein the mass ratio of the pre-embedded lithium composite powder to the polyacrylonitrile is 1:0.1, the mixture is stirred and reacted for 2.3 hours, and then rotary evaporated to obtain a surface-coated metal organic polymer;

[0124] S5: The surface-coated metal organic polymer is pre-dispersed with carboxymethyl cellulose, and modified composite particles, lithium fluorocarbon additives and conductive carbon black are added to prepare a long-cycle and high-rate negative electrode material.

[0125] Specifically, S5: pre-dispersing the surface-coated metal organic polymer and carboxymethyl cellulose in deionized water to obtain a pretreatment base liquid, wherein the solid-liquid mass ratio of the surface-coated metal organic polymer and carboxymethyl cellulose to deionized water is 1:5, and then adding modified composite particles and lithium fluorocarbon additives, adding conductive carbon black after uniform dispersion, and defoaming to obtain a long-cycle high-rate negative electrode material, wherein the mass ratio of the surface-coated metal organic polymer, carboxymethyl cellulose, modified composite particles, lithium fluorocarbon additive and conductive carbon black is 4.7:4.5:75:3.8:3.7.

[0126] Example 4

[0127] This embodiment provides a long-cycle high-rate negative electrode material and a preparation method thereof, wherein the preparation method specifically comprises the following steps:

[0128] S1: mixing silicon powder, tin powder and graphene and ball-milling to obtain composite powder; reacting the composite powder with polyacrylonitrile in N-methylpyrrolidone, drying and heat-treating the resulting composite powder to obtain carbon-coated composite particles; impregnating the resulting composite powder with an ethanol solution of tungsten hexachloride and reacting the resulting particles, and calcining the resulting particles to obtain first modified carbon-coated composite particles;

[0129] Specifically, S1: silicon powder, tin powder and graphene are mixed and ball-milled to obtain a composite powder, wherein the mass ratio of silicon powder to graphene is 3.4:1, and the mass ratio of tin powder to graphene is 2.3:1, and the composite powder and polyacrylonitrile are added to N-methylpyrrolidone and stirred for coating, wherein the mass ratio of the composite powder to polyacrylonitrile is 1:4.5, and the solid-liquid mass ratio of the composite powder and polyacrylonitrile to N-methylpyrrolidone is 1:5. After drying, the composite powder is heat-treated at 580°C under an inert atmosphere for 4 hours to obtain carbon-coated composite particles; the composite particles are immersed in an ethanol solution of tungsten hexachloride with a concentration of 0.1M for immersion reaction, wherein the mass ratio of the carbon-coated composite particles to tungsten hexachloride is 100:12, and the composite particles are calcined at 530°C for 3 hours to obtain first modified carbon-coated composite particles;

[0130] S2: mixing the first modified carbon-coated composite particles with metaphosphoric acid and urea in anhydrous ethanol, drying, and then heat-treating to obtain modified composite particles;

[0131] Specifically, S2: mixing the first modified carbon-coated composite particles with metaphosphoric acid and urea and uniformly dispersing the mixture in anhydrous ethanol, wherein the mass ratio of the first modified carbon-coated composite particles to the metaphosphoric acid is 100:10, the mass ratio of the first modified carbon-coated composite particles to the urea is 100:9.4, and the solid-liquid mass ratio of the first modified carbon-coated composite particles, metaphosphoric acid and urea to anhydrous ethanol is 1:5.3. After reaction and drying, the mixture is placed in an inert atmosphere and heat treated at 450°C for 3h to obtain modified composite particles;

[0132] S3: reacting lithium carbide with vinylidene fluoride in tetrahydrofuran, drying, and then heat-treating to obtain a lithium fluorocarbon additive;

[0133] Specifically, S3: lithium carbide and vinylidene fluoride are dispersed in tetrahydrofuran at a mass ratio of 1:1.2, and the solid-liquid mass ratio of lithium carbide and vinylidene fluoride to tetrahydrofuran is 1:10, stirring and reacting for 3 hours and then drying, and then heat-treating at 280°C for 1.7 hours under an inert atmosphere and then heating to 450°C for 60 minutes to obtain a lithium fluorocarbon additive;

[0134] S4: hydrothermally reacting ammonium metavanadate with terephthalic acid and then heat-treating it to obtain a metal-organic framework; reacting it with lithium carbide in tetrahydrofuran and heat-treating it to obtain a pre-embedded lithium composite powder; and reacting it with polyacrylonitrile to obtain a surface-coated metal-organic polymer;

[0135] Specifically, S4: ammonium metavanadate and terephthalic acid are added to a mixed solvent at a molar ratio of 1:2, wherein the solid-liquid mass ratio of ammonium metavanadate and terephthalic acid to the mixed solvent is 1:16, and the volume ratio of N,N-dimethylformamide, ethanol and deionized water in the mixed solvent is 2:1:1, and the precursor substrate is hydrothermally reacted at 120°C for 20 hours, filtered, washed and dried to obtain a precursor substrate, which is heat-treated at 400°C for 4 hours under an inert atmosphere to obtain a metal-organic framework; it is dispersed with lithium carbide at a mass ratio of 1:0.45 In tetrahydrofuran, wherein the solid-liquid mass ratio of the metal-organic framework and lithium carbide to the tetrahydrofuran is 1:8, the mixture is stirred and reacted, and then dried to obtain a pretreated powder, which is then heat-treated at 450° C. for 2 hours to obtain a pre-embedded lithium composite powder; under an inert atmosphere, the pre-embedded lithium composite powder is dispersed in a 3 wt.% polyacrylonitrile solution in N-methylpyrrolidone to obtain a reaction solution, wherein the mass ratio of the pre-embedded lithium composite powder to the polyacrylonitrile is 1:0.12, the mixture is stirred and reacted for 2.7 hours, and then rotary evaporated to obtain a surface-coated metal organic polymer;

[0136] S5: The surface-coated metal organic polymer is pre-dispersed with carboxymethyl cellulose, and modified composite particles, lithium fluorocarbon additives and conductive carbon black are added to prepare a long-cycle and high-rate negative electrode material.

[0137] Specifically, S5: pre-dispersing the surface-coated metal organic polymer and carboxymethyl cellulose in deionized water to obtain a pretreatment base liquid, wherein the solid-liquid mass ratio of the surface-coated metal organic polymer and carboxymethyl cellulose to deionized water is 1:5.3, and then adding modified composite particles and lithium fluorocarbon additives, adding conductive carbon black after uniform dispersion, and defoaming to obtain a long-cycle high-rate negative electrode material, wherein the mass ratio of the surface-coated metal organic polymer, carboxymethyl cellulose, modified composite particles, lithium fluorocarbon additives and conductive carbon black is 5:4:80:4:5.

[0138] Comparative Example 1

[0139] This comparative example provides a long-cycle, high-rate negative electrode material. The difference from Example 1 is that in S1, the mass ratio of carbon-coated composite particles to tungsten hexachloride is 100:15, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0140] Comparative Example 2

[0141] This comparative example provides a long-cycle, high-rate negative electrode material. The difference from Example 1 is that in S1, the mass ratio of carbon-coated composite particles to tungsten hexachloride is 100:5, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0142] Comparative Example 3

[0143] This comparative example provides a long-cycle, high-rate negative electrode material. The difference from Example 1 is that in S5, the mass ratio of the surface-coated metal organic polymer, carboxymethyl cellulose, modified composite particles, lithium fluorocarbon additive and conductive carbon black is 8:4.2:78:3.6:4, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0144] Comparative Example 4

[0145] This comparative example provides a long-cycle, high-rate negative electrode material. The difference from Example 1 is that in S5, the mass ratio of the surface-coated metal organic polymer, carboxymethyl cellulose, modified composite particles, lithium fluorocarbon additive and conductive carbon black is 2:4.2:78:3.6:4, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0146] Comparative Example 5

[0147] This comparative example provides a long-cycle, high-rate negative electrode material. The difference from Example 1 is that in S5, the mass ratio of the surface-coated metal organic polymer, carboxymethyl cellulose, modified composite particles, lithium fluorocarbon additive and conductive carbon black is 2:4.2:78:5:4, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0148] Comparative Example 6

[0149] This comparative example provides a long-cycle, high-rate negative electrode material. The difference from Example 1 is that in S5, the mass ratio of the surface-coated metal organic polymer, carboxymethyl cellulose, modified composite particles, lithium fluorocarbon additive and conductive carbon black is 2:4.2:78:1:4, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0150] The performance test of the long cycle and high rate negative electrode materials of Examples 1-4 and Comparative Examples 1-6 was carried out, and the specific process is as follows:

[0151] The prepared negative electrode material was evenly coated on copper foil and vacuum dried as the working electrode, metallic lithium was used as the counter electrode, polypropylene microporous membrane was used as the separator, and 1M LiPF6 / DMC:EC:DEC=1:1:1 solution was used as the electrolyte to assemble into a simulated battery.

[0152] At 25°C, the simulated battery is first charged at a constant current of 1C to 4.3V, then further charged at a constant voltage of 4.3V to a current of 0.025C, and then discharged at a constant current of 1C to 3.0V. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. Repeat the above-mentioned charge and discharge test for multiple times to obtain the discharge capacity of the 500th cycle;

[0153] Capacity retention rate (%) after 500 cycles of the battery = [discharge capacity at the 500th cycle / discharge capacity at the 1st cycle] × 100%.

[0154] High rate performance test:

[0155] At 25°C, the simulated battery was charged at a constant current of 1C to 4.3V, and further charged at a constant voltage of 4.3V to a current of 0.025C. Subsequently, it was discharged at high rates (5C, 10C, 20C) to 3.0V, and the discharge capacity under different rate conditions was recorded.

[0156] High-rate capacity retention rate of the simulated battery = [discharge capacity at high rate / discharge capacity at 1 C rate] × 100%.

[0157] The test results are shown in Table 1.

[0158] Table 1: Performance test results of long cycle and high rate negative electrode materials of Examples 1-4 and Comparative Examples 1-6

[0159]

[0160] The test results of Example 1 and Comparative Examples 1 and 2 show that when the mass ratio of carbon-coated composite particles to tungsten hexachloride is too low, excess tungsten oxide accumulates on the surface of the composite particles, forming an agglomerated layer of uneven thickness, resulting in the initial charge and discharge capacity being reduced to 564 mAh / g; at the same time, due to the increase in interface transmission impedance, the cycle capacity retention rate of the battery is reduced to 65.75%, and the rate performance is also attenuated; when the mass ratio is too high, the tungsten oxide protective layer is incompletely covered, causing the active material to be directly exposed to the electrolyte. Although the initial discharge capacity can reach 787 mAh / g, the continuous occurrence of side reactions at the interface causes the cycle capacity retention rate of the battery to drop to 70.31%, and the rate performance is also reduced.

[0161] From the test results of Example 1 and Comparative Examples 3 and 4, it can be seen that when the content of the metal organic polymer coated on the surface is too high, the excess MOF layer provides abundant ion migration channels, but at the same time prolongs the actual transmission path of lithium ions and reduces the relative content of active materials. The first discharge capacity drops to 743 mAh / g, and due to the increase in lithium ion transmission paths, the cycle capacity retention rate of the battery drops to 75.75%, and the high-rate performance is poor. When the content is too low, due to insufficient ion channels and active sites provided by MOF, the pre-lithium embedding effect is weakened, and the volume expansion stress of tin and silicon cannot be effectively buffered. As a result, although the first discharge capacity can reach 840 mAh / g, the cycle capacity retention rate of the battery decays to 68.65%, and the high-rate performance also decreases.

[0162] From the test results of Example 1 and Comparative Examples 5 and 6, it can be seen that when the content of the lithium fluorocarbon additive is too high, the excess lithium fluoride forms a dense passivation layer that hinders the transmission of lithium ions, and the initial charge and discharge capacity drops to 768 mAh / g, and the cycle capacity retention rate drops to 75.38%; when the content is too low, the interface regulation effect is insufficient. Although the initial discharge capacity reaches 800 mAh / g, the poor stability of the solid electrolyte interface film leads to a decrease in the battery cycle capacity and a decrease in high-rate performance.

[0163] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a long cycle and high rate negative electrode material, characterized in that: The preparation method comprises: S1: mixing silicon powder, tin powder, and graphene and ball-milling to obtain a composite powder; reacting the composite powder with polyacrylonitrile in N-methylpyrrolidone, drying, and then heat-treating to obtain carbon-coated composite particles; impregnating the composite particles with an ethanol solution of tungsten hexachloride and reacting, and calcining to obtain first modified carbon-coated composite particles, wherein the mass ratio of the carbon-coated composite particles to tungsten hexachloride is 100:8-12; S2: mixing the first modified carbon-coated composite particles with metaphosphoric acid and urea in anhydrous ethanol, drying, and then heat-treating to obtain modified composite particles; S3: reacting lithium carbide with vinylidene fluoride in tetrahydrofuran, drying, and then heat-treating to obtain a lithium fluorocarbon additive; S4: hydrothermally reacting ammonium metavanadate with terephthalic acid and then heat-treating it to obtain a metal-organic framework; reacting it with lithium carbide in tetrahydrofuran and heat-treating it to obtain a pre-embedded lithium composite powder; and reacting it with polyacrylonitrile to obtain a surface-coated metal-organic polymer; S5: The surface-coated metal-organic polymer is pre-dispersed with carboxymethyl cellulose, and modified composite particles, lithium fluorocarbon additives and conductive carbon black are added to prepare a long-cycle and high-rate negative electrode material.

2. The method for preparing a long cycle and high rate negative electrode material according to claim 1, characterized in that: In S1: The mass ratio of silicon powder to graphene is 3-4:1; The mass ratio of the tin powder to the graphene is 2-3:1; The mass ratio of the composite powder to polyacrylonitrile is 1:3-5; The solid-liquid mass ratio of the composite powder to polyacrylonitrile and N-methylpyrrolidone is 1:3-5.

3. The method for preparing a long cycle and high rate negative electrode material according to claim 1, characterized in that: In S1: The concentration of the tungsten hexachloride ethanol solution is 0.05-0.1M.

4. The method for preparing a long cycle and high rate negative electrode material according to claim 1, wherein: In S2: The mass ratio of the first modified carbon-coated composite particles to metaphosphoric acid is 100:8-10; The mass ratio of the first modified carbon-coated composite particles to urea is 100:8-10.

5. The method for preparing a long cycle and high rate negative electrode material according to claim 1, characterized in that: In S3: The mass ratio of lithium carbide to vinylidene fluoride is 1:1-2; The solid-liquid mass ratio of the lithium carbide, vinylidene fluoride and tetrahydrofuran is 1:9-10.

6. The method for preparing a long cycle and high rate negative electrode material according to claim 1, characterized in that: In S4: The molar ratio of the ammonium metavanadate to terephthalic acid is 1:1.5-2.

7. The method for preparing a long cycle and high rate negative electrode material according to claim 1, characterized in that: In S4: The mass ratio of the metal-organic framework to lithium carbide is 1:0.3-0.5; The solid-liquid mass ratio of the metal-organic framework, lithium carbide and tetrahydrofuran is 1:8-9; The mass ratio of the pre-embedded lithium composite powder to polyacrylonitrile is 1:0.1-0.

2.

8. The method for preparing a long cycle and high rate negative electrode material according to claim 1, characterized in that: In S5: during pre-dispersion, the solid-to-liquid mass ratio of the surface-coated metal organic polymer and carboxymethyl cellulose to deionized water is 1:5-6.

9. A long cycle and high rate negative electrode material prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The mass ratio of the metal organic polymer, carboxymethyl cellulose, modified composite particles, lithium fluorocarbon additive and conductive carbon black coated on the surface of the long-cycle high-rate negative electrode material is: (4-5): (4-5): (75-80): (3-4): (3-5).

10. Use of a long-cycle, high-rate negative electrode material prepared by the preparation method according to any one of claims 1 to 8 in a lithium-ion battery.

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