Carbon-coated titanium-based polyanion composite material for lithium ion battery and preparation method of carbon-coated titanium-based polyanion composite material

Abstract

The invention provides a carbon-coated titanium-based polyanion composite material for a lithium ion battery and a preparation method of the carbon-coated titanium-based polyanion composite material, and the carbon-coated titanium-based polyanion composite material for the lithium ion battery consists of derivative carbon and a titanium-based polyanion material, the mass percentage of the derived carbon in the carbon-coated titanium-based polyanion composite material for the lithium ion battery is 1.5-24.4%, and the balance is the titanium-based polyanion material. Compared with the prior art, the carbon-coated titanium-based polyanion composite material for the lithium ion battery is obtained by adopting the components, and the titanium-based polyanion material has a stable crystal structure and three-dimensional skeleton characteristics, so that volume deformation caused by lithium ion intercalation / deintercalation in the charging and discharging process can be effectively relieved. After the carbon coating layer is overlaid, a protective layer with excellent conductivity and high mechanical strength is formed on the surface of the material, so that pulverization and falling of active substances in circulation are inhibited, corrosion of electrolyte to the electrode material is blocked, and the cycle life of the battery is remarkably prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and more particularly to a carbon-coated titanium-based polyanion composite material for lithium ion batteries and a preparation method thereof. Background Art

[0002] With the increasing anxiety about the range of electric vehicles and the demand for lightweight portable electronic devices, improving the energy density of lithium batteries has become a global research hotspot. As the core component of the battery, the performance of the negative electrode material is crucial to the endurance of the device. Although the current commercial graphite negative electrode is low in cost, its 372 mAh g −1 The theoretical specific capacity of lithium-ion batteries has reached its physical limit and is unlikely to meet future demands. This situation has prompted researchers to look into new high-capacity material systems, among which titanium-based compounds have shown great potential due to their unique advantages.

[0003] Titanium-based materials can be divided into two major systems: oxides and polyanion compounds, and their properties show significant differences. Among them, titanium-based oxides (such as TiO2 and Li4Ti5O 12 ) due to its relatively high Li + The insertion / extraction voltage and small volume change make it a potential negative electrode material for lithium-ion batteries. However, the practical application of TiO2 negative electrodes is seriously hindered by its poor rate capability and low theoretical capacity. The successful application of polyanionic positive electrode materials (such as LiFePO4) has stimulated the research interest of transition metal phosphates with polyanionic structures as negative electrodes for lithium batteries. Titanium-based phosphates, such as TiP2O7 and Ti2O(PO4)2, are promising because of their open framework that allows Li + Multi-directional diffusion, while the strong electronegativity of the PO bond can reduce the Ti 3+ / Ti 4+ The redox potential of TiP2O7 / rGO micro-flower-like composites is low, which leads to excellent performance, including high specific capacity, excellent cycle stability and fast charge and discharge capability. For example, the TiP2O7 / rGO micro-flower-like composites can be used even at 2000 mA g −1 After 4000 cycles at an ultra-high rate, the material still showed a capacity of 353.6 mAh g −1 Chen et al. reported that TiP2O7 / rGO composites can achieve a high capacity of 1000 mA g −1 After 700 cycles, it can still maintain 411.7 mAh g −1 In addition, titanium-based polyanion anodes, such as Ti2O(PO4)2(H2O) and its dehydrated form Ti2O(PO4)2, are considered to be promising lithium-ion battery anode materials due to their open ion transport framework.

[0004] However, titanium-based polyanion materials have problems such as low electronic conductivity and complex preparation process, which limit their application in lithium-ion batteries. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the existing titanium-based polyanion materials have problems such as low electronic conductivity and complex preparation process. In order to overcome the above defects of the existing technology, the present invention is expected to overcome these defects in the future through the development of carbon composite materials and optimization of the preparation process, providing solutions for extending battery life and achieving fast charging and discharging, thereby promoting the further development of lithium battery technology.

[0006] The present invention provides a carbon-coated titanium-based polyanion composite material for lithium-ion batteries. The negative electrode is composed of derived carbon and titanium-based polyanion material. In terms of mass percentage, the mass percentage of the derived carbon in the carbon-coated titanium-based polyanion composite material for lithium-ion batteries is 1.5-24.4%, and the balance is the titanium-based polyanion material.

[0007] Compared to existing technologies, the present invention utilizes the aforementioned composition to produce a negative electrode material for lithium-ion batteries. The titanium-based polyanion material possesses a stable crystal structure and three-dimensional framework, effectively mitigating volume deformation caused by lithium ion insertion and extraction during charge and discharge. The addition of a carbon coating creates a protective layer with excellent conductivity and high mechanical strength on the surface of the material, which not only inhibits the pulverization and shedding of the active material during cycling, but also blocks electrolyte corrosion on the electrode material, significantly extending the battery's cycle life.

[0008] In one possible embodiment, the chemical formula of the titanium-based polyanion material is Ti2O 1.3 (PO4) 1.6 .

[0009] Compared with the prior art, the titanium-based polyanion material Ti2O 1.3 (PO4) 1.6 Through its unique crystal structure and chemical composition, combined with the synergistic effect of the carbon coating, it exhibits excellent lithium ion insertion / extraction kinetics. While maintaining the material's high theoretical specific capacity and stable skeleton structure, it effectively alleviates the volume deformation during charging and discharging, and inhibits the pulverization and shedding of the electrode material. The introduction of the carbon layer further enhances the conductivity of the composite material and optimizes the interfacial charge transfer efficiency. Combined with the rich reserves of titanium and the environmentally friendly properties of polyanionic compounds, it provides important technical support for the development of lithium-ion battery negative electrodes with high energy density, long cycle life and sustainability.

[0010] The second object of the present invention is to provide a method for preparing a carbon-coated titanium-based polyanion composite material for lithium-ion batteries, the preparation method specifically comprising the following steps: S1. Preparation of 1-butyl-3-methylimidazolium hexafluorophosphate: using 1-butyl-3-methylimidazolium bromide and potassium hexafluorophosphate as raw materials, and obtaining 1-butyl-3-methylimidazolium hexafluorophosphate after ion exchange reaction; S2. Preparing a precursor: using isopropyl titanate, 1-butyl-3-methylimidazolium hexafluorophosphate prepared in step S1, and glucose as raw materials, and subjecting the raw materials to a hydrothermal reaction to prepare a precursor; S3. Product preparation: heat-treating the precursor prepared in step S2 to obtain a carbon-coated titanium-based polyanion composite material.

[0011] Compared with existing technologies, the preparation method described in this invention achieves uniform carbon coating on the surface of titanium-based polyanionic materials and precise control of the interface structure through ionic liquid-assisted hydrothermal synthesis and controllable heat treatment. The ionic liquid, acting as a green solvent and structure-directing agent, promotes the efficient recombination of the titanium source and carbon source. The hydrothermal reaction conditions are mild and controllable, which facilitates the formation of a carbon-titanium-based composite structure with high conductivity and stable chemical bonding. Subsequent heat treatment further optimizes the graphitization degree and pore distribution of the carbon layer, improving the electron transport efficiency of the electrode material and alleviating the volume stress during lithium ion insertion and extraction through the flexible protection mechanism of the carbon layer. The overall process is simple and efficient, combining environmental protection with the potential for large-scale production.

[0012] In one possible embodiment, in step S1, the molar ratio of 1-butyl-3-methylimidazolium bromide to potassium hexafluorophosphate is 1:1.01.

[0013] Compared with the prior art, step S1 of the present invention ensures the high efficiency and selectivity of the ion exchange reaction by precisely controlling the stoichiometric ratio of the reactants, thereby promoting the full reaction of 1-butyl-3-methylimidazolium bromide and potassium hexafluorophosphate to generate the target ionic liquid, while suppressing the formation of by-products. This ratio optimizes the balance of reaction kinetics, ensuring the high purity and low impurity content of the product, and simplifying the subsequent purification process, thereby laying a clean and stable raw material foundation for the preparation of high-quality carbon-coated titanium-based polyanion negative electrode materials.

[0014] In a possible embodiment, in step S1, the parameters of the ion exchange reaction are as follows: temperature is 65-75° C., and time is 2-3 days.

[0015] Compared with the prior art, step S1 of the present invention achieves efficient synthesis and structural controllability of ionic liquids through mild ion exchange reaction conditions, which not only avoids the damage to the reaction system caused by high temperature and high pressure, but also ensures the functional stability of ionic liquids as green solvents and structure-directing agents, laying the foundation for the uniform recombination of titanium source and carbon source in subsequent hydrothermal reactions, while reducing the generation of by-products and improving the purity and uniformity of the precursor.

[0016] In one possible embodiment, the specific operation of step S1 is as follows: 1-butyl-3-methylimidazolium bromide and potassium hexafluorophosphate are introduced into acetonitrile, and then an ion exchange reaction is carried out at 65-75° C. for 2-3 days; after the ion exchange reaction is completed, the obtained solution is filtered to remove the potassium bromide salt, and then the filtrate is evaporated using a rotary evaporator to finally obtain 1-butyl-3-methylimidazolium hexafluorophosphate.

[0017] Step S1 of the present invention utilizes acetonitrile as a green solvent to promote the directional synthesis of ionic liquids through a mild ion exchange reaction and an efficient purification process, accurately removes the by-product potassium bromide salt, and ensures the high purity and low impurity content of the product; the reaction conditions are mild and controllable, which not only avoids the damage to the ionic liquid structure caused by high temperature and high pressure, but also simplifies the post-processing process, improves the synthesis efficiency and product stability, and lays a clean and controllable raw material foundation for the subsequent uniform preparation of carbon-coated titanium-based polyanion materials.

[0018] In a possible embodiment, in step S2, the molar ratio of isopropyl titanate to 1-butyl-3-methylimidazolium hexafluorophosphate is (1.45-1.55):1, and the molar ratio of glucose to 1-butyl-3-methylimidazolium hexafluorophosphate is (0.47-1.89):1.

[0019] Compared to the prior art, step S2 of the present invention achieves uniform compounding of the titanium-based polyanion material and the carbon precursor under mild hydrothermal reaction conditions through the synergistic effect of a titanium source, a carbon source, and an ionic liquid. The ionic liquid, acting as a green solvent and structure-directing agent, promotes the molecular dispersion of isopropyl titanate and glucose, forming a uniform composite structure. The hydrothermal reaction precisely regulates the material's micromorphology and interfacial bonding through a self-assembly mechanism, ensuring close contact between the titanium-based active component and the carbon layer. Furthermore, through the in-situ conversion of the carbon source, a continuous conductive network is constructed, providing a structurally controllable, defect-free, and highly conductive precursor foundation for the subsequent high-temperature pyrolysis to form a high-performance carbon-coated structure.

[0020] In a possible embodiment, in step S2, the parameters of the hydrothermal reaction are as follows: temperature is 120-180° C., and time is 11-13 h.

[0021] Compared to existing technologies, step S2 of the present invention achieves efficient self-assembly of the titanium-based polyanion material and the carbon precursor under mild and controllable reaction conditions by precisely controlling the temperature and time parameters of the hydrothermal reaction. These suitable reaction conditions not only avoid the damage to the material structure caused by high temperature and high pressure, but also promote the full dispersion and interfacial fusion of the titanium source, carbon source, and ionic liquid, forming a uniform composite structure through the self-assembly mechanism. Furthermore, the rational setting of the reaction time ensures the integrity of grain growth and the continuity of the conductive network, laying the foundation for the uniform coating of the subsequent carbon layer and the high conductivity and structural stability of the final negative electrode material.

[0022] In one possible embodiment, the specific operation of step S2 is as follows: after stirring and mixing isopropyl titanate and 1-butyl-3-methylimidazolium hexafluorophosphate obtained in step S1, H2O is gradually added to immediately form a white precipitate, and after stirring for 2 minutes, H2O and glucose are added to obtain a mixture, and the mixture is stirred at room temperature for 0.8-1.2 hours to obtain a mixed solution; the mixed solution is transferred to a high-temperature and high-pressure stainless steel reactor for hydrothermal reaction to obtain a reaction solution; the reaction solution is subjected to high-speed centrifugation to extract a powder reactant, and the powder reactant is vacuum dried at 65-75°C for 11-13 hours to obtain a precursor.

[0023] Compared to the prior art, step S2 of the present invention achieves efficient composite and structural control of titanium-based polyanionic materials and carbon precursors through step-by-step mixing and hydrothermal self-assembly. The ionic liquid, acting as a green solvent and structure-directing agent, promotes uniform dispersion and interfacial fusion of the titanium and carbon sources. The hydrothermal reaction forms a uniform composite structure through a mild self-assembly mechanism. The centrifugation and vacuum drying processes precisely control the purity and morphology of the precursor, avoiding damage to the material structure caused by high temperature and high pressure while ensuring close contact between the titanium-based active component and the carbon layer and the continuity of the conductive network. This provides a precursor foundation with uniform structure, few defects, and stable interface for the efficient construction of the subsequent carbon coating layer.

[0024] In a possible embodiment, in step S3, the heat treatment is performed in an atmosphere-protected tube furnace, and the parameters are as follows: the protective atmosphere is nitrogen, and the temperature is 600-900°C.

[0025] Compared to existing technologies, step S3 of the present invention achieves controlled graphitization and structural densification of the carbon layer through a high-temperature heat treatment process under nitrogen protection. The inert atmosphere effectively prevents oxidative loss of active components during high-temperature processes, ensuring the chemical stability of the material. The gradient temperature ramp precisely regulates carbon layer growth and interfacial bonding, improving conductivity to accelerate lithium-ion transport and enhancing structural toughness through optimized interface between the carbon layer and the titanium-based polyanion material. Ultimately, a highly conductive, low-expansion-stress composite electrode material is formed, providing a key guarantee for the battery's long cycle life and high-rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 XRD patterns of the carbon-coated titanium-based polyanion composite materials prepared in Examples 1-5 and the composite material prepared in Comparative Example 1; Figure 2 TG graphs of the carbon-coated titanium-based polyanion composite materials prepared in Examples 1-5 and the composite material prepared in Comparative Example 1; Figure 3 This is a charge and discharge curve diagram of the button-type lithium battery of Application Example 1 of the present invention; Figure 4 This is a cycle curve diagram of the button-type lithium battery of Application Example 1 of the present invention; Figure 5 This is a charge and discharge curve diagram of the button-type lithium battery of Application Example 2 of the present invention; Figure 6 This is a cycle curve diagram of the button-type lithium battery of Application Example 2 of the present invention; Figure 7 This is a charge and discharge curve diagram of the button-type lithium battery of Application Example 3 of the present invention; Figure 8 This is a cycle curve diagram of the button-type lithium battery of Application Example 3 of the present invention; Figure 9 This is a charge and discharge curve diagram of the button-type lithium battery of Application Example 4 of the present invention; Figure 10 This is a cycle curve diagram of the button-type lithium battery of Application Example 4 of the present invention; Figure 11 This is a charge and discharge curve diagram of a button-type lithium battery in Application Example 5 of the present invention; Figure 12 This is a cycle curve diagram of the button-type lithium battery of Application Example 5 of the present invention; Figure 13 This is a charge and discharge curve diagram of the button-type lithium battery of Application Example 6 of the present invention; Figure 14 This is a cycle curve diagram of the button-type lithium battery of Application Example 6 of the present invention. DETAILED DESCRIPTION

[0027] To make the above-mentioned objects, features and advantages of the present invention more clearly understood, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only intended to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter ranges described in the present invention. Reasonable variations derived therefrom are still within the scope of protection of the claims of the present invention.

[0028] It should be noted that the endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0029] Unless otherwise defined, all terms, symbols and other scientific terms used herein are intended to have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. In some cases, terms with conventional meanings are defined herein for the purpose of clarification or ease of reference, and such definitions herein should not be construed as indicating significant differences from conventional understandings in the art. The technical methods described or cited herein are generally well understood by those skilled in the art and are adopted by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents and instruments was carried out in accordance with the protocols and parameters given by the manufacturers.

[0030] Example 1 This embodiment provides a carbon-coated titanium-based polyanion composite material, which is prepared by the following preparation steps: A1: 1-Butyl-3-methylimidazolium bromide [Bmim]Br (21.9 g, 100 mmol) and potassium hexafluorophosphate (KPF6) (18.6 g, 101 mmol) were introduced into 50 mL of acetonitrile and then heated at 70°C for 2 days. After completion, the solution was filtered to remove the potassium bromide (KBr). Subsequently, the filtrate was further evaporated using a rotary evaporator to obtain a transparent liquid of imidazolium ions. After testing, the ionic liquid was found to be 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim]PF6.

[0031] A2: Stir and mix isopropyl titanate (1.5 g, 5.27 mmol) and 1-butyl-3-methylimidazolium hexafluorophosphate (1 g, 3.52 mmol). Then, gradually add H₂O (1 mL). A white precipitate immediately forms. After stirring for 2 minutes, add H₂O (11 mL) and glucose (0.3 g, 1.67 mmol). Stir the mixture at room temperature for 1 hour to obtain a mixed solution.

[0032] The reaction solution was transferred into a 50 mL polytetrafluoroethylene-lined autoclave and reacted at 150 °C for 12 h in a conventional oven to obtain a reaction solution; The reaction solution was centrifuged at high speed to extract the powdered reactant, which was then vacuum dried at 70 °C for 12 h to obtain the precursor. A3: The precursor was heat treated in a tube furnace at a rate of 3 °C / min under nitrogen N2 and maintained at 600 °C for two hours to obtain a carbon-coated titanium-based polyanion composite material; After testing, the carbon-coated titanium-based polyanion negative electrode is C@Ti2O 1.3 (PO4) 1.6 Composite materials.

[0033] Example 2 This embodiment provides a carbon-coated titanium-based polyanion composite material, which differs from Example 1 only in that, in step A2 of this embodiment, the amount of glucose added is 0.6 g. The rest is the same as in Example 1 and will not be repeated here.

[0034] Example 3 This embodiment provides a carbon-coated titanium-based polyanion composite material, which differs from Example 1 only in that, in step A2 of this embodiment, the amount of glucose added is 0.9 g. The rest is the same as in Example 1 and will not be repeated here.

[0035] Example 4 This embodiment provides a carbon-coated titanium-based polyanion composite material, which differs from Example 1 only in that, in step A2 of this embodiment, the amount of glucose added is 1.2 g. The rest is the same as in Example 1 and will not be repeated here.

[0036] Example 5 This embodiment provides a carbon-coated titanium-based polyanion composite material, which differs from Example 1 only in that the specific operation of step A3 of this embodiment is as follows: the precursor is heat-treated in nitrogen N2 at a rate of 3 ° C / min in a tube furnace, and after being maintained at 900 ° C for two hours, a carbon-coated titanium-based polyanion composite material is obtained; the rest is the same as Example 1 and will not be repeated here.

[0037] Comparative Example 1 This comparative example provides a composite material, which differs from Example 1 only in that the specific operation of step A3 of this comparative example is as follows: the precursor is heat-treated in nitrogen N2 at a rate of 3 ° C / min in a tube furnace, and after maintaining it at 450 ° C for two hours, a composite material is obtained; the rest is the same as Example 1 and will not be repeated here.

[0038] The inventors conducted phase structure tests on the carbon-coated titanium-based polyanion composite materials obtained in Examples 1-5 and the composite material obtained in Comparative Example 1. The test results are as follows: Figure 1-Figure 2 As shown, Figure 1 XRD patterns of the carbon-coated titanium-based polyanion composite materials prepared in Examples 1-5 and the composite material prepared in Comparative Example 1; Figure 2TG graphs of the carbon-coated titanium-based polyanion composite materials prepared in Examples 1-5 and the composite material prepared in Comparative Example 1.

[0039] Depend on Figure 1 It can be seen that the composite materials of Examples 1 to 5 and Comparative Example 1 of the present application all exhibit Ti2O 1.3 (PO4) 1.6 The diffraction peaks of the titanium-based polyanion composite material for lithium batteries are proved to be Ti2O 1.3 (PO4) 1.6 This shows that the increase of glucose content is beneficial to the titanium-based polyanion material Ti2O 1.3 (PO4) 1.6 The crystallinity of the carbon-coated titanium-based polyanion composite material is enhanced, and the crystallinity is highest at 0.6 g glucose in Example 2. In addition, the heat treatment temperature will also greatly affect the crystallinity and purity of the carbon-coated titanium-based polyanion composite material. Among them, the pure phase titanium-based polyanion material obtained at 900 ° C in Example 5 has the highest crystallinity. Figure 2 It can be seen that the composite materials of Examples 1 to 5 of the present application and Comparative Example 1 all contain carbon materials derived from glucose and excess ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, proving that the carbon material content of the high-performance carbon-coated titanium-based polyanion negative electrode for lithium batteries is in the range of 1.5 wt% to 24.4 wt%. This shows that as the glucose content increases, the carbon content gradually increases. Among them, the carbon-coated titanium-based polyanion material prepared at 1.2 g of glucose in Example 5 has the highest carbon content, approximately 24.4 wt%. Similarly, the heat treatment temperature also affects the carbon content of the carbon-coated titanium-based polyanion composite material, wherein the higher the temperature, the lower the carbon content. The carbon-coated titanium-based polyanion composite material obtained at 900 ° C in Example 5 has the lowest carbon content, only 1.5 wt%.

[0040] Application Example 1 This application example provides a button-type lithium battery, the preparation method of which includes the following steps: A1: The carbon-coated titanium-based polyanion composite material (80 wt%) prepared in Example 1 was mixed with AB (10 wt%) and PVDF (10 wt%) in NMP solvent to form a uniform slurry. The slurry was then coated on copper foil and dried under vacuum at 90 °C for 3 h. Finally, the dried coating was cut into 12 mm diameter discs to obtain a carbon-coated titanium-based polyanion anode with a loading mass of approximately 1 mg.

[0041] A2: Based on the carbon-coated titanium-based polyanion negative electrode in step A1, a lithium metal sheet is used as the positive electrode, 1 molLiPF6 / EC:DMC (volume ratio 1:1; EC: ethylene carbonate; DMC: dimethyl carbonate) is used as the electrolyte, and a button-type lithium battery is assembled under an argon protective atmosphere.

[0042] Application Example 2 This application example provides a button-type lithium battery, the preparation method of which includes the following steps: A1: The carbon-coated titanium-based polyanion composite material (80 wt%) prepared in Example 2 was mixed with AB (10 wt%) and PVDF (10 wt%) in NMP solvent to form a uniform slurry. The slurry was then coated on copper foil and dried under vacuum at 90 °C for 3 h. Finally, the dried coating was cut into 12 mm diameter discs to obtain a carbon-coated titanium-based polyanion anode with a loading mass of approximately 1 mg.

[0043] A2: Based on the carbon-coated titanium-based polyanion negative electrode in step A1, a lithium metal sheet is used as the positive electrode, 1 molLiPF6 / EC:DMC (volume ratio 1:1; EC: ethylene carbonate; DMC: dimethyl carbonate) is used as the electrolyte, and a button-type lithium battery is assembled under an argon protective atmosphere.

[0044] Application Example 3 This application example provides a button-type lithium battery, the preparation method of which includes the following steps: A1: The carbon-coated titanium-based polyanion composite material (80 wt%) prepared in Example 3 was mixed with AB (10 wt%) and PVDF (10 wt%) in NMP solvent to form a uniform slurry. The slurry was then coated on copper foil and dried under vacuum at 90 °C for 3 h. Finally, the dried coating was cut into 12 mm diameter discs to obtain a carbon-coated titanium-based polyanion anode with a loading mass of approximately 1 mg.

[0045] A2: Based on the carbon-coated titanium-based polyanion negative electrode in step A1, a lithium metal sheet is used as the positive electrode, 1 molLiPF6 / EC:DMC (volume ratio 1:1; EC: ethylene carbonate; DMC: dimethyl carbonate) is used as the electrolyte, and a button-type lithium battery is assembled under an argon protective atmosphere.

[0046] Application Example 4 This application example provides a button-type lithium battery, the preparation method of which includes the following steps: A1: The carbon-coated titanium-based polyanion composite material (80 wt%) prepared in Example 4 was mixed with AB (10 wt%) and PVDF (10 wt%) in NMP solvent to form a uniform slurry. The slurry was then coated on copper foil and dried under vacuum at 90 °C for 3 h. Finally, the dried coating was cut into 12 mm diameter discs to obtain a carbon-coated titanium-based polyanion anode with a loading mass of approximately 1 mg.

[0047] A2: Based on the carbon-coated titanium-based polyanion negative electrode in step A1, a lithium metal sheet is used as the positive electrode, 1 molLiPF6 / EC:DMC (volume ratio 1:1; EC: ethylene carbonate; DMC: dimethyl carbonate) is used as the electrolyte, and a button-type lithium battery is assembled under an argon protective atmosphere.

[0048] Application Example 5 This application example provides a button-type lithium battery, the preparation method of which includes the following steps: A1: The carbon-coated titanium-based polyanion composite material (80 wt%) prepared in Example 5 was mixed with AB (10 wt%) and PVDF (10 wt%) in NMP solvent to form a uniform slurry. The slurry was then coated on copper foil and dried under vacuum at 90 °C for 3 h. Finally, the dried coating was cut into 12 mm diameter discs to obtain a carbon-coated titanium-based polyanion anode with a loading mass of approximately 1 mg.

[0049] A2: Based on the carbon-coated titanium-based polyanion negative electrode in step A1, a lithium metal sheet is used as the positive electrode, 1 molLiPF6 / EC:DMC (volume ratio 1:1; EC: ethylene carbonate; DMC: dimethyl carbonate) is used as the electrolyte, and a button-type lithium battery is assembled under an argon protective atmosphere.

[0050] Application Example 6 This application example provides a button-type lithium battery, the preparation method of which includes the following steps: A1: The composite material prepared in Comparative Example 1 (80 wt%) was mixed with AB (10 wt%) and PVDF (10 wt%) in NMP solvent to form a uniform slurry. The slurry was then coated on copper foil and dried under vacuum at 90 °C for 3 h. Finally, the dried coating was cut into 12 mm diameter discs to obtain a negative electrode with a loading mass of approximately 1 mg.

[0051] A2: Based on the negative electrode prepared in step A1, a lithium metal sheet was used as the positive electrode, 1 mol LiPF6 / EC:DMC (volume ratio 1:1; EC: ethylene carbonate; DMC: dimethyl carbonate) was used as the electrolyte, and a button-type lithium battery was assembled under an argon protective atmosphere.

[0052] The button batteries assembled in Application Examples 1 to 6 of this application were tested for charge and discharge specific capacity, cycle performance, and coulombic efficiency using a constant current charge and discharge method. The test method is as follows: Constant current charge and discharge method: At a constant current (20 mA g −1 ) using a suitable voltage window (0.05–3.0 V) and recording the voltage variation over time. This method can be used to study the specific capacity, cycling stability, and Coulombic efficiency of electrode materials.

[0053] The specific capacity of the battery can be calculated by the following formula.

[0054] C=I∆t / m Where: C - specific capacity, unit: mAh g −1 ; I ——Charge-discharge current, unit: mA; m——mass of active material of carbon-coated titanium-based polyanion negative electrode sheet, unit: g; Δt——Charge and discharge time, unit: h.

[0055] The battery cycle capacity retention rate can be calculated by the following formula.

[0056] Capacity retention rate% = final capacity value / initial capacity value*100 The coulombic efficiency of the battery can be calculated by the following formula.

[0057] Coulombic efficiency%=discharge specific capacity / charge specific capacity*100 Test results such as Figure 3-Figure 14 As shown. Figure 3 and Figure 4 It can be seen that the button battery of Application Example 1 shows 467.8mAh g −1 The reversible charge and discharge capacity of the battery is 355 mAh g in the first 200 cycles. −1 After more than 200 cycles, the discharge capacity-cycle number curve showed some fluctuations and dropped sharply after 400 cycles, finally dropping to 230.1 mAh g at 500 cycles. −1 The capacity retention rate is 49.2% after 500 cycles. In addition, the coulombic efficiency also fluctuates significantly after 300 cycles. Figure 5 and Figure 6 It can be seen that the button battery of Application Example 2 exhibits a similar reversible capacity, but the capacity continues to decrease during the 250-cycle process, and the discharge capacity drops to 190.3 mAh g at 250 cycles. −1 , showing a cycle stability performance worse than that of Application Example 1. Figure 7 and8 It can be seen that the reversible discharge capacity of the button battery in Application Example 3 is as high as 655.3 mAh g −1 , which is much higher than the capacity values ​​of Application Example 1 and Application Example 2. In addition, the discharge capacity of the button battery in Application Example 3 is stable at 517.7 mAh g in the first 200 cycles. −1 After more than 200 cycles, the discharge capacity-cycle number curve showed fluctuations, but remained basically stable. The coulombic efficiency was also relatively stable during this process. At 500 cycles, the discharge capacity still maintained 528.3 mAh g −1 , and the corresponding capacity retention rate is 80.6%. This result shows that the cycle stability performance of application example 3 is much higher than that of application examples 1 and 2. Figure 9 and Figure 10 It can be seen that the reversible discharge capacity of the button battery in Application Example 4 is 433.6 mAh g −1 , which is comparable to Application Examples 1 and 2. The discharge capacity of the button battery in Application Example 4 decreased to 263.5 mAh g after 500 cycles. −1 . The corresponding capacity retention rate is 60.8%, which is slightly better than Application Example 1 and Application Example 2, but significantly worse than Application Example 3. This shows that in the total raw materials for preparing the high-performance carbon-coated titanium-based polyanion negative electrode for the lithium battery of this application, when the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim] PF6 is mixed with glucose in a molar ratio of 1:1.42 (the mass of glucose is 0.9 g), the obtained carbon-coated titanium-based polyanion negative electrode exhibits the largest reversible capacity and excellent cycle performance. In addition, after testing, the charge and discharge performance of Application Examples 1 and 4 are close.

[0058] Depend on Figure 11 and Figure 12 It can be seen that the reversible discharge capacity of the button battery in Application Example 5 is only 179.9 mAh g −1 , and the capacity after 500 cycles decreased to 138.7 mAh g −1 , showing the lowest reversible capacity and poor cycling performance. Figure 13 and Figure 14 It can be seen that the reversible discharge capacity of the button battery in Application Example 6 is 449.6 mAh g −1 , which is comparable to the first three cycles of the button cell batteries in Application Examples 1, 2, and 3. The capacity after 200 cycles steadily decreases to 319.6 mAh g −1, exhibiting slightly inferior cycling performance compared to Application Example 1. This demonstrates that, under the preparation conditions for the carbon-coated titanium-based polyanion composite material of this application, a heat treatment temperature of 600°C yields the best battery performance. Meanwhile, Application Example 5 exhibits the worst charge-discharge performance, which may be due to the low content of the conductive carbon layer and the narrow lithium ion diffusion path in the high crystallinity.

[0059] This shows that in the preparation of the high-performance carbon-coated titanium-based polyanion negative electrode for the lithium battery of the present application, an appropriate molar ratio of ionic liquid and glucose, and an appropriate heat treatment temperature facilitate the synthesis of an appropriate lattice structure of the titanium-based polyanion, as well as the derivation of an appropriate carbon coating layer, thereby significantly improving the reversible charge and discharge capacity, optimizing the long cycle performance, and achieving high performance of the lithium-ion battery negative electrode material.

[0060] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A carbon-coated titanium-based polyanion composite material for lithium-ion batteries, characterized in that: The carbon-coated titanium-based polyanion composite material is composed of derived carbon and titanium-based polyanion material, and in terms of mass percentage, the mass percentage of the derived carbon in the carbon-coated titanium-based polyanion composite material for lithium-ion batteries is 1.5-24.4%, and the balance is titanium-based polyanion material.

2. The carbon-coated titanium-based polyanion composite material for lithium-ion batteries according to claim 1, wherein: The chemical formula of the titanium-based polyanion material is Ti2O 1.3 (PO4) 1.6 .

3. A method for preparing a carbon-coated titanium-based polyanion composite material for lithium-ion batteries, characterized in that: The preparation method specifically comprises the following steps: S1. Preparation of 1-butyl-3-methylimidazolium hexafluorophosphate: using 1-butyl-3-methylimidazolium bromide and potassium hexafluorophosphate as raw materials, and obtaining 1-butyl-3-methylimidazolium hexafluorophosphate after ion exchange reaction; S2. Preparing a precursor: using isopropyl titanate, 1-butyl-3-methylimidazolium hexafluorophosphate prepared in step S1, and glucose as raw materials, and subjecting the raw materials to a hydrothermal reaction to prepare a precursor; S3. Product preparation: heat-treating the precursor prepared in step S2 to obtain a carbon-coated titanium-based polyanion composite material.

4. The preparation method according to claim 3, wherein In the step S1, the molar ratio of 1-butyl-3-methylimidazolium bromide to potassium hexafluorophosphate is 1:1.

01.

5. The preparation method according to claim 3, wherein In step S1, the parameters of the ion exchange reaction are as follows: temperature is 65-75° C., and time is 2-3 days.

6. The preparation method according to claim 4 or 5, characterized in that The specific operation of step S1 is as follows: 1-butyl-3-methylimidazolium bromide and potassium hexafluorophosphate are introduced into acetonitrile, and then an ion exchange reaction is carried out at 65-75° C. for 2-3 days; after the ion exchange reaction is completed, the obtained solution is filtered to remove the potassium bromide salt, and then the filtrate is evaporated using a rotary evaporator to finally obtain 1-butyl-3-methylimidazolium hexafluorophosphate.

7. The preparation method according to claim 3, wherein In step S2, the molar ratio of isopropyl titanate to 1-butyl-3-methylimidazolium hexafluorophosphate is (1.45-1.55):1, and the molar ratio of glucose to 1-butyl-3-methylimidazolium hexafluorophosphate is (0.47-1.89):

1.

8. The preparation method according to claim 3, wherein In step S2, the parameters of the hydrothermal reaction are as follows: temperature is 120-180° C., and time is 11-13 hours.

9. The preparation method according to claim 7 or 8, characterized in that The specific operation of step S2 is as follows: after stirring and mixing isopropyl titanate and 1-butyl-3-methylimidazolium hexafluorophosphate prepared in step S1, H2O is gradually added to immediately form a white precipitate. After stirring for 2 minutes, H2O and glucose are added to obtain a mixture, and the mixture is stirred at room temperature for 0.8-1.2 hours to obtain a mixed solution; the mixed solution is transferred to a high-temperature and high-pressure stainless steel reactor for hydrothermal reaction to obtain a reaction solution; the reaction solution is subjected to high-speed centrifugation to extract a powdered reactant, and the powdered reactant is vacuum dried at 65-75°C for 11-13 hours to obtain a precursor.

10. The preparation method according to claim 3, wherein In step S3, the heat treatment is performed in a tube furnace with protective atmosphere, and the parameters are as follows: the protective atmosphere is nitrogen, and the temperature is 600-900°C.

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