Preparation method of modified lithium titanate battery negative electrode material

Abstract

The invention discloses a preparation method of a modified lithium titanate battery negative electrode material. The preparation method comprises the following steps: S1, weighing zirconium chloride and benzoic acid, dissolving the zirconium chloride and benzoic acid in N, N-dimethylformamide, and mixing to obtain a first solution; s2, weighing 2, 2 '-bipyridine-5, 5'-dicarboxylic acid formic acid, dissolving the 2, 2 '-bipyridine-5, 5'-dicarboxylic acid formic acid into N, N-dimethylformamide, and mixing to obtain a second solution; s3, adding the first solution into the second solution, uniformly mixing, and reacting to obtain a third solution; s4, the third solution is subjected to suction filtration, washing and drying, and powdery UiO-bpy is obtained; s5, weighing lithium titanate powder and UiO-bpy, dissolving the weighed lithium titanate powder and UiO-bpy in ethanol to obtain a fourth solution, and drying the fourth solution to obtain an intermediate sample; and S6, heating the intermediate sample in a tubular furnace under the protection of Ar atmosphere, and cooling to obtain the battery negative electrode material UiO-bpy (LTO), thereby solving the problems of low electronic conductivity, poor rate capability and insufficient energy density of the lithium titanate (LTO) negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of lithium titanate technology, and in particular to a method for preparing a modified lithium titanate battery anode material. Background Technology

[0002] As the global energy structure shifts towards cleaner and lower-carbon energy, the performance requirements for power batteries and electrochemical energy storage systems, as key energy storage carriers, continue to increase. In particular, their performance in terms of cycle stability, safety and reliability, wide temperature range adaptability, and fast charge and discharge capabilities has become a core bottleneck driving the development of electric vehicles, large-scale energy storage power stations, and other fields.

[0003] Lithium titanate (Li4Ti5O) 12 Lithium-ion batteries (hereinafter referred to as LTO) are anode materials for lithium-ion batteries. With their unique "zero-strain" crystal structure (lattice volume change rate during lithium-ion insertion / extraction <1%), they exhibit excellent cycle stability, with a cycle life that can easily exceed 20,000 cycles, far exceeding that of traditional graphite anodes (approximately 1,000-2,000 cycles). At the same time, their high lithium insertion potential (approximately 1.55V vs Li⁺ / Li) can effectively prevent the precipitation of lithium dendrites, fundamentally solving safety hazards such as battery short circuits and thermal runaway. In addition, LTO can maintain stable electrochemical performance in a wide temperature range of -30~60℃ and supports high-rate charging of 10C~20C, giving it a natural advantage in scenarios such as low-temperature start-up and fast-charging energy storage. Therefore, it has received widespread attention in the fields of power batteries, special energy storage, and backup power.

[0004] However, the inherent defects of LTO severely limit its commercial application: on the one hand, LTO has extremely low electronic conductivity (only 10). -13 ~10 -9 The low charge-to-charge ratio (S / cm) of LTO hinders charge transport within the electrode, affecting not only the battery's rate discharge performance but also increasing polarization losses and reducing energy conversion efficiency. Furthermore, the higher operating potential of LTO (approximately 1V higher than graphite anodes) lowers the overall voltage plateau of the battery. Combined with its relatively low theoretical specific capacity (175mAh / g), this ultimately results in insufficient energy density for the battery system, making it difficult to meet the demands of electric vehicles and other applications requiring long driving ranges. Therefore, improving the electronic conductivity of LTO and optimizing lithium-ion transport kinetics through material modification to enhance its energy density and rate performance has become the core research direction for LTO anode materials.

[0005] Therefore, there is an urgent need to design a method for preparing modified lithium titanate battery anode materials to solve the problems mentioned above. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a modified lithium titanate battery anode material, which has the advantages of continuous conduction path, shortened lithium ion diffusion distance and suppression of interfacial side reactions, and solves the problems of low electronic conductivity, poor rate performance and insufficient energy density of lithium titanate (LTO) anode material.

[0007] To achieve the above objectives, the specific technical solution of the preparation method of the modified lithium titanate battery anode material of the present invention is as follows: A method for preparing a modified lithium titanate battery anode material includes the following steps: S1: Weigh zirconium chloride and benzoic acid and dissolve them in N,N-dimethylformamide, then mix to obtain the first solution; S2: Weigh 2,2'-bipyridine-5,5'-dicarboxycarboxycarboxylic acid and dissolve it in N,N-dimethylformamide, then mix to obtain a second solution; S3: After adding the first solution to the second solution and mixing them evenly, the reaction yields the third solution; S4: The third solution is filtered, washed and dried to obtain powdered UiO-bpy; S5: Weigh lithium titanate powder and the UiO-bpy, dissolve them in ethanol to obtain a fourth solution, and dry the fourth solution to obtain an intermediate sample; S6: The intermediate sample was heated in a tube furnace under the protection of Ar atmosphere and then cooled to obtain the battery anode material UiO-bpy@LTO.

[0008] Further, in step S1, the molar ratio of zirconium chloride and benzoic acid is weighed as 1:19 to 1:30.

[0009] Further, the molar ratio of zirconium chloride weighed in step S1 to 2,2'-bipyridine-5,5'-dicarboxycarboxylic acid weighed in step S2 is 1:0.9 to 1:1.2.

[0010] Furthermore, equal amounts of N,N-dimethylformamide are used in steps S1 and S2.

[0011] Furthermore, step S3 also includes the following steps: adding the first solution to the second solution and mixing them evenly to obtain a mixed solution; then reacting the mixed solution in a thick-walled, pressure-resistant glass bottle at 80-150°C for 12-72 hours using a solvothermal method; and finally cooling the solution to obtain the third solution.

[0012] Further, in step S4, the third solution is filtered to obtain a first solid, and the first solid is washed sequentially with N,N-dimethylformamide and acetone to obtain a second solid. The second solid is then cooled and dried to obtain the powdered UiO-bpy.

[0013] Further, in step S5, the mass ratio of the lithium titanate powder to UiO-bpy is 5:1 to 10:1.

[0014] Further, in step S5, lithium titanate powder and the UiO-bpy are weighed, dissolved in ethanol, and stirred for 12-72 hours to obtain a fourth solution.

[0015] Further, in step S6, the intermediate sample is heated to 600-1000°C at a heating rate of 5-10°C / min under the protection of Ar atmosphere in a tube furnace, and then held at that temperature for 2-5 hours. After the holding period is completed, it is cooled to obtain the battery negative electrode material UiO-bpy@LTO.

[0016] Furthermore, the mixing in steps S1, S2 and S3 is performed using ultrasonic mixing.

[0017] The preparation method of the modified lithium titanate battery anode material of the present invention has the following advantages: 1. Simple process and easy to mass-produce: This invention adopts a process that combines hydrothermal method, liquid phase mixing method and high temperature carbonization method. Each step is a mature chemical unit operation with low equipment requirements (such as ultrasonic instrument, tube furnace, oven, etc.). The operation process is simple and does not require complicated special equipment, which is convenient for industrial scale-up production.

[0018] 2. Raw materials are readily available and environmentally friendly: The raw materials used (zirconium chloride, benzoic acid, 2,2'-bipyridine-5,5'-dicarboxylic acid, DMF, and ethanol) are all commercially available chemicals, and the cost is controllable; ethanol, as a green solvent, can be recycled and reused, reducing environmental pollution; the carbonization process is protected by an Ar atmosphere, with no harmful gas emissions, which meets the requirements of green production.

[0019] 3. High parameter controllability: The process parameters of each step (such as raw material molar ratio, reaction temperature, stirring time, carbonization temperature, etc.) have clear and reasonable ranges, which can be precisely adjusted according to actual needs (such as target rate performance, specific capacity) to ensure stable and controllable product performance.

[0020] 4. Porous core-shell structure enhances conductivity: N-doped porous carbon formed after UiO-bpy carbonization uniformly coats LTO particles, constructing a porous core-shell structure. On one hand, the continuous carbon layers form a highly efficient electronic conduction network, increasing the electronic conductivity from 10 times that of LTO itself. -13 ~10 -9 S / cm increased to 10 -2 ~10 0The S / cm ratio significantly reduces interface resistance; on the other hand, the porous structure provides abundant lithium-ion diffusion channels, shortening the Li⁺ diffusion distance (from the micrometer level to the nanometer level), and significantly improving rate performance. According to test data, UiO-bpy@LTO maintains a capacity retention rate of 61.98% at a 15C high-rate charge, which is 10.24 percentage points higher than pure LTO (51.74%); and a capacity retention rate of 66.76% at a 15C rate discharge, which is 5.42 percentage points higher than pure LTO (61.34%).

[0021] 5. Nitrogen doping suppresses side reactions: The pyridine nitrogen and graphitic nitrogen in UiO-bpy derived carbon can adsorb Li⁺ in the electrolyte, enhancing the storage capacity of lithium ions. Simultaneously, it promotes the formation of a uniform and stable solid electrolyte interphase (SEI) film on the electrode surface, preventing direct reaction between the electrolyte and the LTO surface, reducing the generation of byproducts (such as Li₂CO₃ and LiOH), and improving the cycle stability of the battery. Tests show that UiO-bpy@LTO retains over 90% of its capacity after 2000 cycles, a significant improvement over pure LTO (approximately 80%).

[0022] 6. Strong structural stability: UIO-bpy has high Zr-O bond strength, and can still maintain a porous structure after carbonization. Furthermore, a tight interface bond is formed between the carbon layer and LTO, which prevents the carbon layer from falling off or LTO particles from agglomerating during charge-discharge cycles, thus ensuring the long-term stability of the material structure. Attached Figure Description

[0023] Figure 1 This is a schematic flowchart of the preparation method of the modified lithium titanate battery anode material of the present invention; Figure 2 The charge-discharge curves of the UiO-bpy@LTO and LTO negative electrode batteries of Embodiment 1 of the present invention are shown at 7C. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, in the claims, any of the claimed embodiments can be used in any combination.

[0026] The following is a reference to the appendix. Figure 1 To be continued Figure 2 This invention describes a method for preparing a modified lithium titanate battery anode material.

[0027] A method for preparing a modified lithium titanate battery anode material, such as Figure 1 As shown, it includes the following steps: S1: Weigh zirconium chloride and benzoic acid and dissolve them in N,N-dimethylformamide, then mix to obtain the first solution; Specifically, zirconium chloride (ZrCl4) and benzoic acid (C7H6O2) were weighed and dissolved together in N,N-dimethylformamide (DMF) solvent. A specific mixing method was used to ensure the raw materials were fully dissolved and evenly dispersed, yielding the first solution. Zirconium chloride serves as the metal center source for UIO-bpy, while benzoic acid acts as a regulator, controlling the crystal growth rate and morphological integrity of UIO-bpy. DMF, as a polar aprotic solvent, possesses excellent dissolving power, ensuring the complete dissolution of both raw materials and preventing undissolved particles from affecting subsequent reactions.

[0028] S2: Weigh 2,2'-bipyridine-5,5'-dicarboxycarboxycarboxylic acid and dissolve it in N,N-dimethylformamide, then mix to obtain a second solution; Specifically, 2,2'-bipyridine-5,5'-dicarboxylic acid (as the organic ligand of UIO-bpy) is weighed and dissolved in N,N-dimethylformamide (DMF). The ligand is completely dissolved using the same mixing method as in step S1 to obtain a second solution. The carboxyl group in 2,2'-bipyridine-5,5'-dicarboxylic acid can react with Zr in zirconium chloride. 4+ Forming coordination bonds is a key component in constructing the UIO-bpy framework, and the bipyridine groups it contains also provide a nitrogen source for the subsequent carbonization process.

[0029] S3: After adding the first solution to the second solution and mixing them evenly, the reaction yields the third solution; Specifically, the first solution prepared in step S1 is slowly added to the second solution prepared in step S2, and the two solutions are fully mixed to form a homogeneous mixed solution. This mixed solution is then transferred to a thick-walled, pressure-resistant glass bottle, where a solvothermal reaction is carried out under specific temperature conditions. After the reaction, the solution is naturally cooled to room temperature to obtain the third solution. The solvothermal reaction provides a closed, high-temperature reaction environment for the crystal growth of UIO-bpy, which promotes the full coordination of the metal center and the organic ligand, resulting in UIO-bpy crystals with a complete structure and regular morphology.

[0030] S4: The third solution is filtered, washed and dried to obtain powdered UiO-bpy; Specifically, the third solution obtained in step S3 is subjected to vacuum filtration to separate the solid product generated by the reaction (the first solid). Subsequently, the first solid is washed multiple times with a specific solvent to remove unreacted raw materials, impurities, and solvent residues from the solid surface, yielding a purified second solid. Finally, the second solid is dried to remove residual moisture and washing solvent, resulting in a fluffy white powder, UiO-bpy. The vacuum filtration, washing, and drying steps ensure the purity of UiO-bpy and prevent impurities from affecting its subsequent recombination with LTO and its final electrochemical performance.

[0031] S5: Weigh lithium titanate powder and the UiO-bpy, dissolve them in ethanol to obtain a fourth solution, and dry the fourth solution to obtain an intermediate sample; Specifically, lithium titanate (LTO) powder and UiO-bpy powder prepared in step S4 were weighed and mixed in a specific mass ratio, then added to an ethanol solvent. The mixture was stirred to ensure thorough dispersion and initial composite of the LTO and UiO-bpy powders in the ethanol, yielding a fourth solution. This fourth solution was then transferred to an oven and dried at a suitable temperature to remove the ethanol solvent, resulting in a mixed solid of LTO and UiO-bpy, i.e., the intermediate sample. Ethanol, as a green solvent, has the advantages of high volatility and easy removal, ensuring that LTO and UiO-bpy remain uniformly dispersed after drying, laying the foundation for uniform carbon layer coating during subsequent carbonization.

[0032] S6: The intermediate sample was heated in a tube furnace under the protection of Ar atmosphere and then cooled to obtain the battery anode material UiO-bpy@LTO.

[0033] Specifically, the intermediate sample obtained in step S5 is placed in a ceramic boat, which is then placed in a tube furnace. Argon gas (Ar) is introduced into the tube furnace to purge the air inside and create an inert protective atmosphere. Subsequently, the temperature inside the tube furnace is raised to the target carbonization temperature at a specific heating rate and held at this temperature for a specific time to allow UiO-bpy to undergo a carbonization reaction, forming N-doped porous carbon that uniformly coats the surface of LTO particles. After the holding time is completed, the heating device is turned off, and the tube furnace is allowed to cool naturally to room temperature. The solid product in the ceramic boat is then removed, which is the modified lithium titanate battery anode material UiO-bpy@LTO. The inert atmosphere prevents the intermediate sample from being oxidized during the high-temperature carbonization process. Precise control of the heating rate, carbonization temperature, and holding time ensures that UiO-bpy is fully carbonized and maintains its porous structure, while preventing the LTO crystal structure from being destroyed.

[0034] Further, in step S1, the molar ratio of zirconium chloride and benzoic acid is weighed as 1:19 to 1:30.

[0035] Specifically, in step S1, the molar ratio of zirconium chloride and benzoic acid is weighed to be 1:19 to 1:30. This molar ratio range is determined based on the requirements for UIO-bpy crystal growth: benzoic acid, as a regulator, cannot effectively control Zr when its dosage is too low. 4+ The hydrolysis rate of benzoic acid can easily lead to disordered growth and irregular morphology of UIO-bpy crystals. Excessive benzoic acid can adsorb onto the surface of UIO-bpy crystals, hindering further coordination between the metal center and organic ligands, resulting in an incomplete crystal structure and increasing the burden on subsequent washing steps. When the molar ratio is controlled between 1:19 and 1:30, it ensures that benzoic acid effectively regulates crystal growth without causing excessive residue, ultimately forming an octagonal pyramidal structure with a high specific surface area of ​​UiO-bpy. For example, when the amount of zirconium chloride is 0.5 mmol, the amount of benzoic acid can be selected between 9.5 mmol (1:19) and 15 mmol (1:30), which can be finely adjusted according to the morphological requirements of the target UiO-bpy.

[0036] Further, the molar ratio of zirconium chloride weighed in step S1 to 2,2'-bipyridine-5,5'-dicarboxycarboxylic acid weighed in step S2 is 1:0.9 to 1:1.2.

[0037] Specifically, the molar ratio of zirconium chloride weighed in step S1 to 2,2'-bipyridine-5,5'-dicarboxylic acid weighed in step S2 is 1:0.9 to 1:1.2. This ratio is determined based on the stoichiometric ratio of the UIO-bpy coordination structure: Zr in zirconium chloride 4 ⁺ forms a coordinate bond with the carboxyl group in 2,2'-bipyridine-5,5'-dicarboxylic acid. Theoretically, the two can react in a specific stoichiometric ratio to form a structurally stable UIO-bpy. When the molar ratio of 2,2'-bipyridine-5,5'-dicarboxylic acid is less than 0.9, the amount of ligand is insufficient and cannot react with Zr. 4+ Sufficient coordination can easily lead to the formation of defective UIO-bpy, resulting in discontinuous carbon layers after subsequent carbonization. When the molar ratio is higher than 1.2, excess ligands cannot participate in the coordination reaction and remain in the solution, increasing the difficulty of subsequent washing. Furthermore, excess ligands may form free carbon after carbonization, affecting the conductivity of the composite material. Controlling the molar ratio between 1:0.9 and 1:1.2 ensures the optimal conductivity of Zr. 4+ It fully coordinates with the ligand to form a structurally complete UIO-bpy, ensuring uniform coating of LTO in the subsequent process. For example, when the amount of zirconium chloride is 0.5 mmol, the amount of 2,2'-bipyridine-5,5'-dicarboxylic acid can be adjusted between 0.45 mmol (1:0.9) and 0.6 mmol (1:1.2).

[0038] Furthermore, equal amounts of N,N-dimethylformamide are used in steps S1 and S2.

[0039] Specifically, equal amounts of N,N-dimethylformamide (DMF) are used in steps S1 and S2. The purpose of using equal amounts of DMF is to ensure that the concentrations of the two raw materials in the first solution (zirconium chloride + benzoic acid + DMF) and the second solution (2,2'-bipyridine-5,5'-dicarboxylic acid + DMF) are similar before mixing. This avoids localized aggregation of raw materials due to excessively high concentrations in one solution, which could affect the uniform growth of UIO-bpy crystals. For example, 10 mL of DMF is used to dissolve zirconium chloride and benzoic acid in step S1, and the same 10 mL of DMF is used to dissolve the organic ligand in step S2. The mixture forms a homogeneous reaction system, reducing the problem of uneven crystal morphology caused by localized concentration differences. Furthermore, equal amounts of DMF simplify solvent calculations in experimental operations, reduce process complexity, and facilitate subsequent industrial scale-up.

[0040] Furthermore, step S3 also includes the following steps: adding the first solution to the second solution and mixing them evenly to obtain a mixed solution; then reacting the mixed solution in a thick-walled, pressure-resistant glass bottle at 80-150°C for 12-72 hours using a solvothermal method; and finally cooling the solution to obtain the third solution.

[0041] Specifically, in step S3, the first solution is added to the second solution and mixed thoroughly to obtain a mixed solution. This mixed solution is then reacted in a thick-walled, pressure-resistant glass bottle at 80–150°C for 12–72 hours. After cooling, a third solution is obtained. The temperature and time of the solvothermal reaction directly affect the crystal growth quality of UIO-bpy. Temperature control: 80℃ is the minimum temperature at which the effective coordination reaction of UIO-bpy begins. Below this temperature, the reaction rate is too slow, and the metal center and ligands cannot fully coordinate, easily forming an amorphous solid. 150℃ is the upper limit of the suitable reaction temperature for DMF in a closed system. Above this temperature, DMF is prone to decomposition, producing impurity gases. At the same time, excessively high temperatures may lead to excessive crystal growth and agglomeration. The temperature range of 80~150℃ ensures efficient reaction and the formation of a uniformly sized and regularly shaped octagonal pyramidal structure of UIO-bpy.

[0042] Time control: 12 hours is the minimum time required for the basic formation of UIO-bpy crystals. Insufficient reaction time leads to incomplete coordination reactions, incomplete crystal structure, and low specific surface area. 72 hours is the maximum time for complete reaction. Beyond this time, crystal growth reaches saturation; further extending the time not only fails to improve crystal quality but also increases energy consumption and production cycle. A time range of 12-72 hours allows for both ensuring crystal quality and production efficiency. For example, reacting at 120℃ for 30 hours yields UIO-bpy crystals with a complete structure and good dispersibility.

[0043] Further, in step S4, the third solution is filtered to obtain a first solid, and the first solid is washed sequentially with N,N-dimethylformamide and acetone to obtain a second solid. The second solid is then cooled and dried to obtain the powdered UiO-bpy.

[0044] Specifically, in step S4, the third solution is filtered to obtain a first solid. The first solid is then washed sequentially with N,N-dimethylformamide (DMF) and acetone to obtain a second solid. The second solid is then freeze-dried to obtain powdered UiO-bpy. The functions of each step are as follows: Vacuum filtration: Vacuum filtration under reduced pressure can quickly separate the solid product (first solid) in the third solution. Compared with natural filtration, it is more efficient and can reduce the amount of solution remaining in the solid. Washing: First, wash with DMF to dissolve and remove unreacted zirconium chloride, benzoic acid, and excess organic ligands remaining on the surface of the first solid, preventing impurities from affecting the purity of UIO-bpy; then wash with acetone to further remove residual DMF (acetone and DMF are miscible), and acetone's high volatility facilitates solvent removal in subsequent drying steps; usually, the washing is repeated 3 to 5 times until the washing solution is colorless and transparent, ensuring thorough removal of impurities; Drying: Freeze-drying is employed. The washed second solid is placed in a freeze dryer and subjected to low temperature (-50~-30℃) and vacuum conditions to allow the moisture and solvent in the solid to sublimate. This avoids the collapse or agglomeration of the UIO-bpy crystal structure caused by high temperatures during conventional drying (such as oven drying). The final product is a fluffy, well-dispersed white powder of UiO-bpy, with a specific surface area that can be maintained at a high level (typically >1000m²). 2 / g).

[0045] Further, in step S5, the mass ratio of the lithium titanate powder to UiO-bpy is 5:1 to 10:1.

[0046] Specifically, in step S5, the mass ratio of lithium titanate powder to UiO-bpy is 5:1 to 10:1. This mass ratio range is determined based on the balance between the conductivity and specific capacity of the composite material. Excessive use of UiO-bpy (mass ratio < 5:1): Although it can form a thicker carbon layer and improve electronic conductivity, the specific capacity of UiO-bpy itself is much lower than that of LTO. Excessive UiO-bpy will lead to a decrease in the overall specific capacity of the composite material, which in turn will affect the energy density of the battery. Insufficient UiO-bpy dosage (mass ratio > 10:1): The carbon layer coating is incomplete, unable to form a continuous electron conduction network, and the porous structure is insufficient, making it difficult to effectively shorten the lithium-ion diffusion distance, resulting in limited modification effect; A mass ratio of 5:1 to 10:1 ensures that the carbon layer formed after UiO-bpy carbonization can completely coat the LTO particles, constructing a continuous conductive network, without excessively occupying the mass ratio of the composite material, thus achieving a balance between conductivity and specific capacity. For example, when the amount of LTO powder is 500mg, the amount of UiO-bpy can be selected between 50mg (10:1) and 100mg (5:1), which can be adjusted according to the target rate performance requirements.

[0047] Further, in step S5, lithium titanate powder and the UiO-bpy are weighed, dissolved in ethanol, and stirred for 12-72 hours to obtain a fourth solution.

[0048] Specifically, in step S5, lithium titanate powder and UiO-bpy are weighed, dissolved in ethanol, and stirred for 12-72 hours to obtain the fourth solution. The stirring time is limited based on the requirement for uniform dispersion of LTO and UiO-bpy in ethanol. Stirring time less than 12h: LTO and UiO-bpy are difficult to disperse fully in ethanol, and local agglomeration is likely to occur, resulting in uneven carbon layer coating after subsequent carbonization, and some LTO particles are exposed, affecting electrochemical performance. Stirring time exceeds 72 hours: The dispersion effect has reached saturation. Continuing to stir will not further improve the dispersion uniformity, but will instead increase energy consumption and production time and reduce production efficiency. Stirring time of 12~72h: This ensures that LTO and UiO-bpy form a uniform suspension in ethanol, and that they remain uniformly mixed after drying, thus guaranteeing uniform carbon coating during subsequent carbonization. For example, using magnetic or mechanical stirring at a speed of 300~500rpm for 24h can achieve good dispersion.

[0049] Further, in step S6, the intermediate sample is heated to 600-1000°C at a heating rate of 5-10°C / min under the protection of Ar atmosphere in a tube furnace, and then held at that temperature for 2-5 hours. After the holding period is completed, it is cooled to obtain the battery negative electrode material UiO-bpy@LTO.

[0050] Specifically, in step S6, the intermediate sample is heated to 600-1000℃ in a tube furnace under an Ar atmosphere at a heating rate of 5-10℃ / min, held at that temperature for 2-5 hours, and then cooled to obtain the battery anode material UiO-bpy@LTO. The reasons for the limitations of each parameter are as follows: Heating rate (5~10℃ / min): A heating rate that is too slow (<5℃ / min) will prolong the heating time, increasing the production cycle and energy consumption; a heating rate that is too fast (>10℃ / min) will result in an excessively large internal temperature gradient in the intermediate sample, preventing the timely discharge of gases (such as CO2 and H2O) generated during the UiO-bpy carbonization process, which can easily cause carbon layer cracking or LTO particle agglomeration, damaging the porous structure. A heating rate of 5~10℃ / min ensures a uniform temperature rise and a stable carbonization reaction. Carbonization temperature (600~1000℃): Below 600℃, UiO-bpy carbonization is insufficient, the organic ligands cannot be completely converted into carbon materials, the resulting carbon layer has poor conductivity and low nitrogen doping content; above 1000℃, the porous structure of UiO-bpy will collapse due to carbon layer sintering, the specific surface area will decrease significantly, and the LTO crystal structure may be destroyed, leading to a decrease in specific capacity. The temperature range of 600~1000℃ can ensure that UiO-bpy is fully carbonized, forming highly conductive N-doped porous carbon, while maintaining the integrity of the porous structure and the LTO crystal. Holding time (2~5h): If the holding time is less than 2h, the carbonization reaction is incomplete, and the residual organic components may undergo side reactions during subsequent battery charging and discharging. If the holding time exceeds 5h, the carbon layer may be over-graphitized, resulting in a reduction in porous structure, obstruction of lithium-ion diffusion channels, and increased energy consumption. A holding time of 2~5h ensures complete carbonization reaction while avoiding excessive graphitization of the carbon layer.

[0051] Furthermore, the mixing in steps S1, S2 and S3 is performed using ultrasonic mixing.

[0052] Specifically, the mixing in steps S1, S2, and S3 all employs ultrasonic mixing. Ultrasonic mixing was chosen because of its unique dispersion advantages: Ultrasonic mixing principle: When ultrasound propagates in a liquid, it generates alternating compressive and tensile stresses, forming a large number of tiny bubbles (cavitation bubbles). When the cavitation bubbles burst, they generate local high temperature, high pressure and strong shock waves, which can effectively break up agglomerated particles in the liquid and promote the dissolution and dispersion of raw materials. Advantages compared to conventional stirring: Conventional stirring is difficult to achieve uniform dispersion of nano-sized particles, while ultrasonic mixing can ensure that zirconium chloride and benzoic acid are fully dissolved in step S1, 2,2'-bipyridine-5,5'-dicarboxylic acid is completely dispersed in step S2, and the first solution and the second solution are rapidly fused in step S3, avoiding UIO-bpy crystal morphology defects caused by local concentration unevenness. Ultrasonic parameter control: The ultrasonic power is usually controlled at 100~300W, and the ultrasonic time is 5~10min (steps S1, S2) or 5min (step S3). This can ensure the mixing effect while avoiding solvent overheating or raw material decomposition caused by prolonged high-power ultrasonication.

[0053] The present invention will now be described in detail with reference to specific embodiments, but the scope of the present invention is not limited to these examples.

[0054] Example 1 Step S1: Prepare the first solution Weigh 0.5 mmol of zirconium chloride (ZrCl4) and 12.3 mmol of benzoic acid, and add them together to 10 mL of N,N-dimethylformamide (DMF). Use 200 W power to sonicate for 8 min to completely dissolve and disperse the raw materials evenly, and obtain the first solution.

[0055] Step S2: Prepare the second solution Weigh 0.51 mmol of 2,2'-bipyridine-5,5'-dicarboxylic acid and add it to 10 mL of LDM. Mix the solution with sonication at 200 W for 8 min to completely dissolve the ligand and obtain the second solution.

[0056] Step S2: Prepare the third solution The first solution was slowly poured into the second solution, and the mixture was ultrasonically mixed at 200W for 5 minutes to obtain a homogeneous mixed solution. The mixed solution was then transferred to a 50mL thick-walled pressure-resistant glass bottle, sealed, and placed in an oven for a solvothermal reaction at 120℃ for 30 hours. After the reaction was completed, the oven was turned off and the solution was allowed to cool naturally to room temperature to obtain the third solution.

[0057] Step S4: Prepare UiO-bpy powder The third solution was subjected to vacuum filtration to separate a white solid product (first solid). The first solid was washed three times with 10 mL of LDM, followed by three times with 10 mL of acetone to remove residual impurities and solvent, yielding the second solid. The second solid was then freeze-dried at -40°C and 10 Pa for 24 hours to obtain a fluffy white powder, UiO-bpy, with a standard octagonal pyramidal structure and a specific surface area of ​​approximately 1200 m². 2 / g.

[0058] Step S5: Prepare intermediate samples Weigh 500 mg of LTO powder and 100 mg of UiO-bpy powder prepared in step S4, add them to 200 mL of ethanol, and mechanically stir at 400 rpm for 12 h to obtain a homogeneous fourth solution; transfer the fourth solution to a 60 °C oven and dry for 8 h to remove the ethanol solvent and obtain an intermediate sample.

[0059] Step S6: Preparation of UiO-bpy@LTO composite anode material The intermediate sample was placed in an alumina ceramic boat, and then the ceramic boat was placed in a tube furnace. Ar gas (flow rate 50 mL / min) was introduced into the tube furnace for 30 min to remove air from the furnace. Then, the temperature of the tube furnace was raised to 700℃ at a heating rate of 5℃ / min and held at this temperature for 3 h. After the holding period, the Ar gas and heating device were turned off, and the furnace was allowed to cool naturally to room temperature. The solid product in the ceramic boat was then removed, which is the UiO-bpy@LTO composite anode material.

[0060] Electrochemical performance tests were performed on the UiO-bpy@LTO prepared in this embodiment. The results showed that the capacity was 2.033 Ah at 1C, the capacity retention rate was 61.98% at 15C charging, 66.76% at 15C discharging, and 92.3% after 2000 cycles. All performance characteristics were better than those of pure LTO.

[0061] like Figure 2 As shown, UiO-bpy@LTO exhibits smaller electrode polarization, indicating that using UiO-bpy as a precursor to coat LTO can effectively improve the conductivity and ion diffusion capability of the electrode material.

[0062] Table 1 compares the charging capacity and capacity retention of UiO-bpy@LTO and pure LTO at different charging rates. Data shows that at 1C, the capacities of the two are similar (UiO-bpy@LTO is 2.033 Ah, LTO is 2.097 Ah). As the charging rate increases, the capacity retention of UiO-bpy@LTO is consistently higher than that of pure LTO. At 15C, the capacity retention of UiO-bpy@LTO is 61.98%, an increase of 10.24 percentage points compared to pure LTO (51.74%), demonstrating the advantages of the material of this invention in high-rate charging performance.

[0063] Table 1 shows the charging capacity and capacity retention of UiO-bpy@LTO and pure LTO at different charging rates. Table 2 compares the discharge capacity and capacity retention of UiO-bpy@LTO and pure LTO at different discharge rates. The results show that at 1C, the capacity of UiO-bpy@LTO is 2.073 Ah, while that of LTO is 2.142 Ah. At 15C, the discharge capacity retention of UiO-bpy@LTO is 66.76%, an improvement of 5.42 percentage points compared to pure LTO (61.34%), further validating the improved performance of UiO-bpy@LTO at high discharge rates. Table 2 shows the discharge capacity and capacity retention of UiO-bpy@LTO and pure LTO at different discharge rates. Example 2 Step S1: Prepare the first solution Weigh 0.5 mmol of zirconium chloride and 10 mmol of benzoic acid, add them to 10 mL of LDM, and sonicate at 250 W for 10 min to obtain the first solution.

[0064] Step S2: Prepare the second solution Weigh 0.55 mmol of 2,2'-bipyridine-5,5'-dicarboxylic acid and add it to 10 mL of LDM. Mix the solution by sonication at 250 W for 10 min to obtain the second solution.

[0065] Step S3: Prepare the third solution The first solution was poured into the second solution and ultrasonically mixed at 250W for 5 minutes. The mixed solution was then transferred to a thick-walled, pressure-resistant glass bottle and subjected to a solvothermal reaction at 130°C for 24 hours. After cooling to room temperature, the third solution was obtained.

[0066] Step S4: Prepare UiO-bpy powder The first solid was obtained by filtration of the third solution, washed four times with DMF and four times with acetone; then freeze-dried at -35°C and 8 Pa for 20 h to obtain UiO-bpy powder with an octagonal pyramidal structure and a specific surface area of ​​approximately 1150 m². 2 / g.

[0067] Step S5: Prepare intermediate samples Weigh 700 mg of LTO powder and 100 mg of UiO-bpy powder, add 300 mL of ethanol, stir at 350 rpm for 20 h; dry in an oven at 65 °C for 6 h to obtain an intermediate sample.

[0068] Step S6: Preparation of UiO-bpy@LTO composite anode material The intermediate sample was placed in a ceramic boat and Ar gas was passed through the tube furnace (flow rate 60 mL / min) for 25 min; the temperature was increased to 600℃ at 5℃ / min and held for 4 h; after cooling, UiO-bpy@LTO was obtained.

[0069] Performance tests show that the material has a 1C capacity of 2.011Ah, a 15C charging capacity retention rate of 60.5%, a 15C discharging capacity retention rate of 65.3%, and a capacity retention rate of 90.1% after 2000 cycles, demonstrating excellent performance.

[0070] Example 3 Step S1: Prepare the first solution Weigh 0.5 mmol of zirconium chloride and 15 mmol of benzoic acid (molar ratio 1:30, within the range of 1:19 to 1:30), add 20 mL of LDM, and sonicate at 180 W for 12 min to obtain the first solution.

[0071] Step S2: Prepare the second solution Weigh 0.6 mmol of 2,2'-bipyridine-5,5'-dicarboxylic acid (molar ratio 1:1.2, within the range of 1:0.9 to 1:1.2), add 20 mL of LDM, and sonicate at 180 W for 12 min to obtain the second solution.

[0072] Step S3: Prepare the third solution The first solution was poured into the second solution and sonicated at 180W for 5 minutes. The mixed solution was then transferred to a thick-walled bottle and reacted solvothermically at 90℃ for 72 hours. After cooling to room temperature, the third solution was obtained.

[0073] Step S4: Prepare UiO-bpy powder The first solid was obtained by filtration, washed five times with DMF and five times with acetone; then freeze-dried at -45°C and 5 Pa for 28 h to obtain UiO-bpy powder with a specific surface area of ​​approximately 1250 m². 2 / g.

[0074] Step S5: Prepare intermediate samples Weigh 500 mg of LTO powder and 100 mg of UiO-bpy powder (mass ratio 5:1), add 200 mL of ethanol, stir at 450 rpm for 36 h; dry at 55 °C for 10 h to obtain intermediate sample.

[0075] Step S6: Preparation of UiO-bpy@LTO composite anode material The intermediate sample was placed in a ceramic boat and Ar gas was passed through the tube furnace (flow rate 40 mL / min) for 35 min; the temperature was increased to 900℃ at 10℃ / min and held for 2 h; after cooling, UiO-bpy@LTO was obtained.

[0076] Performance tests show that the material has a 1C capacity of 2.055Ah, a 15C charging capacity retention rate of 62.8%, a 15C discharging capacity retention rate of 67.5%, and a capacity retention rate of 93.5% after 2000 cycles, exhibiting the best overall performance.

[0077] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a modified lithium titanate battery anode material, characterized in that, The method comprises the following steps: S1: weighing zirconium chloride and benzoic acid, and dissolving them in N,N-dimethylformamide to obtain a first solution; S2: weighing 2,2'-bipyridine-5,5'-dicarboxylic acid, and dissolving it in N,N-dimethylformamide to obtain a second solution; S3: adding the first solution into the second solution, and mixing to obtain a third solution; S4: performing suction filtration, washing and drying on the third solution to obtain a powder-shaped UiO-bpy; S5: weighing lithium titanate powder and the UiO-bpy, and dissolving them in ethanol to obtain a fourth solution, and drying the fourth solution to obtain an intermediate sample; S6: heating the intermediate sample in a tube furnace under the protection of an Ar atmosphere, and cooling to obtain a battery anode material UiO-bpy@LTO.

2. The method for preparing the modified lithium titanate battery anode material according to claim 1, characterized in that, In the step S1, the molar ratio of zirconium chloride to benzoic acid is 1:19-1:

30.

3. The method of claim 1, wherein the modified lithium titanate battery anode material is prepared by the steps of: mixing a lithium titanate powder with a solvent to form a mixture; and adding a dispersant to the mixture to form a slurry. In the step S1, the molar ratio of zirconium chloride to 2,2'-bipyridine-5,5'-dicarboxylic acid in the step S2 is 1:0.9-1:1.

2.

4. The method of claim 1, wherein the modified lithium titanate battery anode material is prepared by the steps of: mixing a lithium titanate powder with a solvent to form a mixture; and adding a dispersant to the mixture to form a slurry. In the steps S1 and S2, equal amounts of N,N-dimethylformamide are used.

5. The method of claim 1, wherein the modified lithium titanate battery anode material is prepared by the steps of: mixing a lithium titanate powder with a solvent to form a mixture; and adding a dispersant to the mixture to form a slurry. The step S3 further comprises the following steps: after the first solution is added into the second solution and mixed uniformly, a mixed solution is obtained, the mixed solution is subjected to a solvothermal reaction at 80-150 DEG C for 12-72 hours in a thick-walled pressure-resistant glass bottle, and the third solution is obtained after cooling.

6. The method of claim 1, wherein the modified lithium titanate battery anode material is prepared by the steps of: mixing a lithium titanate powder with a solvent to form a mixture; and adding a dispersant to the mixture to form a slurry. In the step S4, a first solid is obtained after the third solution is subjected to suction filtration, a second solid is obtained after the first solid is washed with N,N-dimethylformamide and acetone in sequence, and the powder-shaped UiO-bpy is obtained after the second solid is cooled and dried.

7. The method of claim 1, wherein the modified lithium titanate battery anode material is prepared by the steps of: mixing a lithium titanate powder with a solvent to form a mixture; and adding a dispersant to the mixture to form a slurry. In the step S5, the mass ratio of lithium titanate powder to UiO-bpy is 5:1-10:

1.

8. The method of claim 1, wherein the modified lithium titanate battery anode material is prepared by a process comprising: mixing a lithium titanate powder with a solvent to form a mixture; and adding a dispersant to the mixture to form a slurry. In the step S5, the fourth solution is obtained after the lithium titanate powder and the UiO-bpy are stirred in ethanol for 12-72 hours.

9. The method of claim 1, wherein the modified lithium titanate battery anode material is prepared by a process comprising: mixing a lithium titanate powder with a solvent to form a mixture; and adding a dispersant to the mixture to form a slurry. In the step S6, the intermediate sample is heated to 600-1000 DEG C at a heating rate of 5-10 DEG C / min under the protection of an Ar atmosphere in a tube furnace, and is kept at a constant temperature for 2-5 hours, and the battery anode material UiO-bpy@LTO is obtained after cooling.

10. The method of claim 1, wherein the modified lithium titanate battery anode material is prepared by a process comprising: In the steps S1, S2 and S3, ultrasonic mixing is used for mixing. ​

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