Method for synthesizing a defective niobium tungsten oxide negative electrode and applications thereof

Abstract

A method for synthesizing defective niobium tungsten oxide anodes and its applications belong to the field of lithium-ion battery anode material preparation technology. The method, by precisely controlling the valence ratio of niobium ions in the raw materials and combining it with a specific annealing process, directly synthesizes niobium tungsten oxide materials with abundant and controllable cation vacancies (Nb vacancies or W vacancies) under an inert atmosphere. This method is simple, low-cost, and can effectively optimize the ion diffusion channels and structural stability of the material, reconstructing the bulk structure of niobium tungsten oxide, making it particularly suitable for preparing high-power, low-temperature resistant lithium-ion battery anode materials. This invention controls the valence ratio of niobium ions in the raw materials and combines it with a specific annealing process. 5+ / Nb 4+ The ratio allows for precise control over the type and concentration of Nb or W vacancies; the resulting material has abundant cation defects and open ion diffusion pathways, making it suitable for high-rate and low-temperature environments.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material preparation technology, specifically relating to a method for synthesizing defective niobium tungsten oxide anodes and their applications. Background Technology

[0002] The electrification of electronic devices and vehicles has placed higher demands on the performance of lithium-ion batteries, requiring them to adapt to complex environments such as high power output and low-temperature operation. Wadsley-Roth compounds with crystalline shear phases, due to the open, shared-corner pathways formed within their shared-edge octahedral frameworks, possess both structural stability and rapid ion diffusion capabilities, making them a research hotspot for lithium-ion battery anode materials. In recent years, researchers have focused on the electrochemical lithium-ion intercalation behavior of various Wadsley-Roth compounds with crystalline shear phases, covering binary H-Nb₂O₅ systems and ternary systems such as niobium titanium oxides (TiNb₂O₇, Ti₂Nb₂O₅, etc.). 10 O 29 TiNb 24 O 62 ), niobium tungsten oxide (including Nb) 12 WO 33 、Nb 14 W3O 44 、Nb 16 W5O 55 、Nb 18 W8O 69 ), niobium molybdenum oxide (Nb) 12 MoO 33 、Nb 14 Mo3O 44 These Wadsley-Roth compounds with crystalline shear phases are all formed by MO6 octahedra connected by edge conjugation, creating an m×n×∞ blocky structure. In some niobium-tungsten systems, tetrahedral sites appear at the vertices of the blocky structure, achieving structural connection. Among various Wadsley-Roth compounds with crystalline shear phases, the niobium-tungsten oxide family has attracted widespread attention due to the fact that some phases can achieve multi-electron redox reactions of each transition metal cation, and possess excellent volumetric capacity due to high density characteristics. This characteristic makes it particularly suitable for space-constrained applications, such as electric vehicles, where battery mass and volume constraints are equally critical. At the same time, niobium-tungsten oxides are also suitable for high-rate performance requirements at both room temperature and low temperature environments. Despite the promising prospects, current research on Wadsley-Roth compounds with crystalline shear phases is still significantly insufficient. Existing studies mostly focus on composition-related bronze structures or single-phase states, with limited exploration of their low-temperature electrochemical performance, failing to meet the application requirements of lithium-ion batteries under high-power conditions.

[0003] Therefore, there is an urgent need for a novel material design and preparation method that can overcome the limitations of traditional modification approaches. Defective niobium-tungsten oxides, due to their abundant ion transport channels and excellent structural stability, have become ideal materials for anodes in high-rate, extreme-environment lithium-ion batteries. Based on practical application scenarios, by precisely controlling the metal cation vacancies in niobium-tungsten oxides, a next-generation niobium-tungsten oxide anode material with excellent overall performance, especially outstanding low-temperature fast-charging performance, can be developed. Summary of the Invention

[0004] The purpose of this invention is to solve the problem that traditional niobium tungsten oxide anodes have poor low-temperature electrochemical performance and cannot be adapted to the application of lithium-ion batteries under high-power conditions, and to provide a method for synthesizing defective niobium tungsten oxide anodes and their applications.

[0005] This invention provides a low-cost, controllable synthesis method for niobium tungsten oxide anode materials with cation defects. The method directly synthesizes niobium tungsten oxide materials with abundant and controllable cation vacancies (Nb vacancies or W vacancies) under an inert atmosphere by precisely controlling the valence ratio of niobium ions in the raw materials and combining it with a specific annealing process. This method is simple, low-cost, and effectively optimizes the ion diffusion channels and structural stability of the material, reconstructing the bulk structure of niobium tungsten oxide. It is particularly suitable for preparing high-power, low-temperature resistant lithium-ion battery anode materials.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for synthesizing defective niobium tungsten oxide anodes, the method comprising:

[0008] Step 1: Mix the niobium compound and tungsten compound evenly, place them in a ball mill jar, add anhydrous ethanol or deionized water as a dispersion medium, and perform wet ball milling for 4 to 12 hours to ensure uniform mixing at the atomic scale. Then dry the mixture and grind it to obtain a uniform precursor powder.

[0009] Step 2: After compacting the precursor powder, place it in an alumina boat, center it in a tube furnace, seal the furnace tube, and then purge with an inert protective gas (such as high-purity argon (Ar, 99.999%) or nitrogen) at a flow rate of 200 mL / min for 30 minutes to purge air and create a reaction environment with extremely low oxygen partial pressure. Subsequently, under continuous argon protection, raise the furnace temperature to a sintering temperature of 800-1200℃ at a heating rate of 2-5℃ / min, and hold at this temperature for 2-10 hours. During this process, the raw materials undergo a solid-state reaction, forming niobium-tungsten oxide with a preliminary crystal structure. Simultaneously, due to the reducing atmosphere and valence imbalance (Nb... 4+ W 4+ The presence of cation vacancies begins to be introduced;

[0010] Step 3: After the sintering process, under an inert atmosphere, adjust the furnace temperature to an annealing temperature of 500~700℃ and hold at this temperature for 1~4 hours to allow the atoms in the crystal lattice to fully relax, making the vacancy distribution generated at high temperature more uniform and releasing some internal stress. After annealing, perform rapid cooling: rapidly cool the sample to 100~200℃ at a cooling rate of not less than 50℃ / min, then turn off the heating and allow the sample to cool naturally to room temperature in an argon flow. This rapid cooling process aims to "freeze" the optimized defect configuration at the annealing temperature, preventing it from annihilating or becoming ordered during slow cooling, thereby maximizing the preservation of beneficial vacancy defects.

[0011] Step 4: Post-processing of the product: After mechanical crushing and grinding, the annealed block material is sieved (e.g., through a 400-mesh sieve) to obtain niobium tungsten oxide anode material powder with uniform particle size distribution and controllable cation defects.

[0012] Through the above steps, this invention achieves low-cost synthesis that can be completed in a conventional inert atmosphere furnace, with well-defined and controllable process parameters, facilitating large-scale production. The prepared material exhibits excellent ionic conductivity and structural stability due to its unique controllable cation defect structure.

[0013] Furthermore, in step one, the molar ratio of the niobium compound to the tungsten compound is 8:5.

[0014] Furthermore, in step one, there are three possible raw materials: (1) Nb₂O₅, NbO₂, and WO₃; (2) Nb₂O₅, WO₃, and WO₂; (3) Nb₂O₅, NbO₂, WO₃, and WO₂. Based on the general chemical formula of the target niobium tungsten oxide (e.g., Nb₂O₅, NbO₂, WO₃, and WO₂), 12 WO 33 、Nb 14 W3O 44 (etc.) Calculate the total molar ratio. The core of this invention lies in controlling the Nb content in the niobium source. 5+ With Nb 4+ The initial molar ratio. This ratio directly affects the type and concentration of cation vacancies during sintering. Ratio range: Nb 5+ With Nb 4+ The molar ratio is controlled between 1:0.1 and 10, preferably between 1:0.5 and 4. Within this range, the optimal balance between defect concentration and structural stability can be achieved while ensuring the electrochemical activity of the material. Mechanism of action: When Nb... 5+ When the proportion is relatively high, it tends to form a structure rich in Nb vacancies; when Nb 4+ When the ratio is relatively high, it tends to form a structure rich in W vacancies. By precisely adjusting this ratio, it is possible to achieve targeted design of the types of defects in the material.

[0015] Furthermore, in step three, the annealing process involves holding at 550–650°C for 1.5–3 hours, followed by rapid cooling to approximately 150°C at a rate of 60–100°C / min. This condition has been proven to most effectively stabilize Nb vacancies and form continuous channels conducive to rapid lithium-ion transport.

[0016] Furthermore, to obtain materials dominated by W vacancies, higher Nb levels can be selected. 4+ Ratio (e.g., Nb) 5+ :Nb 4+ = 1:3~10), and with a slightly higher annealing temperature (such as 650~700℃).

[0017] An application of a defective niobium tungsten oxide anode synthesized by the above method in a lithium-ion battery: the niobium tungsten oxide anode material is dispersed in a solvent with a conductive agent and a binder in a certain mass ratio to obtain an anode slurry. The slurry is coated on a negative electrode current collector, dried, rolled, and punched to obtain a negative electrode sheet, which is then assembled into a coin cell.

[0018] Furthermore, the binder is polyvinylidene fluoride (PVDF), the conductive agent is acetylene black, and the solvent is N-methylpyrrolidone (NMP); the mass ratio of niobium tungsten oxide anode material: conductive agent: binder is 80%:10%:10%.

[0019] The advantages of this invention over the prior art are as follows:

[0020] (1) Defect structure is controllable: by adjusting Nb 5+ / Nb 4+ The ratio enables precise control over the type and concentration of Nb or W vacancies;

[0021] (2) Low synthesis cost: raw materials are widely available, the process is simple, and no complex equipment is required;

[0022] (3) Excellent electrochemical performance: The obtained material has abundant cation defects and open ion diffusion pathways, making it suitable for high-rate and low-temperature environments;

[0023] (4) Strong process adaptability: The material structure can be further optimized by adjusting the annealing temperature and cooling rate, making it suitable for different application scenarios. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a defective NWO structure;

[0025] Figure 2 The topographic image of an NWO with a defective structure;

[0026] Figure 3This is a comparison chart of the rate performance of the original NWO and different examples at 0℃. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0028] Example 1:

[0029] A method for synthesizing defective niobium tungsten oxide anodes at low cost for use in lithium-ion battery anodes, the method comprising the following steps:

[0030] Step 1: Mix Nb₂O₅, NbO₂, and WO₃ in a molar ratio of 5:3:5 as raw materials. Place the weighed raw materials into a polyurethane ball mill jar, add an appropriate amount of anhydrous ethanol as a dispersion medium, and then add zirconia balls. Ball mill the mixture at 300 rpm for 8 hours on a planetary ball mill. Then dry the slurry in an 80°C oven for 12 hours. After drying, manually grind the slurry to obtain a uniform light gray precursor powder.

[0031] Step 2: After compacting the precursor powder, place it into an alumina boat and center it in a tube furnace. Seal the furnace tube and purge with high-purity argon (Ar, 99.999%) at a flow rate of 200 mL / min for 30 minutes to purge air. Then, under continuous argon protection, heat to 1150℃ at a heating rate of 3℃ / min and hold at this temperature for 6 hours to complete the solid-state reaction and preliminary crystallization. During this process, the raw materials undergo a solid-state reaction to form niobium-tungsten oxide with a preliminary crystal structure. Simultaneously, due to the reducing atmosphere (Nb... 4+ W 4+ The presence of cation vacancies and valence imbalance lead to the introduction of cation vacancies.

[0032] Step 3: After the sintering process is completed, while maintaining argon gas flow, rapidly reduce the furnace temperature to 600℃ (this process is program-controlled and takes approximately 15 minutes). Once 600℃ is reached, maintain this temperature for annealing for 2 hours to allow the atoms in the crystal lattice to fully relax and the vacancy distribution to become uniform. After annealing, perform rapid cooling: quickly move the sample from 600℃ to the low-temperature zone of the furnace (using a pre-designed pull-out mechanism or quenching device), cooling it to approximately 150℃ within 1-2 minutes, with an estimated cooling rate of approximately 80℃ / min. Then, turn off the heating and allow the sample to cool naturally to room temperature in the argon gas flow.

[0033] Step 4: Remove the annealed sintered block, gently crush it in an agate mortar, and then mechanically ball-mill it (200 rpm, 2 hours) to refine the particles. Finally, pass it through a 400-mesh (approximately 38 μm) nylon sieve to obtain a uniform, grayish-black niobium-tungsten-oxygen anode material powder;

[0034] Step 5: The obtained niobium-tungsten oxide heterojunction material is dispersed in a solvent with a conductive agent and a binder at a certain mass ratio to obtain a negative electrode slurry. The slurry is coated onto the negative electrode current collector, dried, rolled, and punched to obtain the negative electrode sheet, which is then assembled into a coin cell. The binder is polyvinylidene fluoride (PVDF), the conductive agent is acetylene black, and the solvent is N-methylpyrrolidone (NMP). The mass ratio of negative electrode active material: conductive agent: binder is 80%:10%:10%.

[0035] like Figure 1 As shown, a schematic diagram of an NWO crystal with a defective structure is presented, and the presence of some metal cations does indeed cause the crystal structure to become incomplete.

[0036] like Figure 2 As shown, the NWO material with defective structure has a micron-sized rod-like structure.

[0037] Example 2

[0038] The difference between this embodiment and Embodiment 1 is that the molar ratio of Nb2O5, WO3, and WO2 in step one is 8:4:1.

[0039] Example 3

[0040] The difference between this embodiment and Embodiment 1 is that the molar ratio of Nb2O5, WO3, and WO2 in step one is 8:3:2.

[0041] like Figure 3 As shown, the discharge specific capacity of NWO electrodes and different examples at different rates was tested at 0℃. It can be seen that the NWO electrode with defective structure exhibits excellent electrochemical performance.

Claims

1. A method for synthesizing defective niobium tungsten oxide anodes, characterized in that: The method is as follows: Step 1: Mix the niobium compound and tungsten compound evenly, place them in a ball mill jar, add anhydrous ethanol or deionized water as a dispersion medium, and perform wet ball milling for 4 to 12 hours to ensure uniform mixing at the atomic scale. Then dry the mixture and grind it to obtain a uniform precursor powder. Step 2: After compacting the precursor powder, place it into an alumina boat, put it in the center of a tube furnace, seal the furnace tube, and introduce inert protective gas at a flow rate of 200 mL / min to purge the air. Then, under continuous argon protection, raise the furnace temperature to a sintering temperature of 800-1200℃ at a heating rate of 2-5℃ / min, and hold at this temperature for 2-10 hours. Step 3: After the sintering process is completed, under the condition of maintaining an inert atmosphere, adjust the furnace temperature to an annealing temperature of 500~700℃ and hold it at this temperature for 1~4 hours. After annealing, perform rapid cooling: cool the sample rapidly to 100~200℃ at a cooling rate of not less than 50℃ / min, then turn off the heating and let the sample cool naturally to room temperature in an argon flow. Step 4: Post-processing of the product: After mechanical crushing and grinding, the annealed block material is sieved to obtain niobium tungsten oxide anode material powder with uniform particle size distribution and controllable cation defects.

2. The method for synthesizing defective niobium tungsten oxide anodes according to claim 1, characterized in that: In step one, the molar ratio of the niobium compound to the tungsten compound is 8:

5.

3. The method for synthesizing defective niobium tungsten oxide anodes according to claim 1, characterized in that: In step one, there are three types of raw materials: (1) Nb2O5, NbO2 and WO3; (2) Nb2O5, WO3 and WO2; (3) Nb2O5, NbO2, WO3 and WO2.

4. The method for synthesizing defective niobium tungsten oxide anodes according to claim 1, characterized in that: In step three, the annealing process is as follows: hold at 550~650℃ for 1.5~3 hours, and then rapidly cool to 145~155℃ at a rate of 60~100℃ / min.

5. The method for synthesizing defective niobium tungsten oxide anodes according to claim 1, characterized in that: Nb 5+ :Nb 4+ =1:3~10, annealing temperature is 650~700℃.

6. The application of a defective niobium tungsten oxide anode synthesized by the method according to any one of claims 1 to 5 in a lithium-ion battery, characterized in that: The niobium tungsten oxide anode material is dispersed in a solvent with a conductive agent and a binder to obtain an anode slurry. The slurry is coated on the anode current collector, dried, rolled, and punched to obtain the anode sheet, and then assembled into a coin cell.

7. The application according to claim 6, characterized in that: The binder is polyvinylidene fluoride (PVDF), the conductive agent is acetylene black, and the solvent is N-methylpyrrolidone; the mass ratio of niobium tungsten oxide anode material, conductive agent, and binder is 80%:10%:10%.

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