Method for synthesizing tungsten-doped lithium iron phosphate carbon nano composite fiber by solvothermal method
Tungsten-doped lithium iron phosphate carbon nanocomposite fibers were prepared by electrospinning and solvothermal methods, which solved the problems of conductivity and slow lithium-ion transport of lithium iron phosphate materials, and achieved improved high capacity and high rate performance, making them suitable for lithium-ion batteries.
Patent Information
- Application Number
- CN202511381752.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-25
- Publication Date
- 2026-01-23
AI Technical Summary
Lithium iron phosphate materials suffer from poor conductivity and slow lithium-ion transport rate, which limits their application in lithium-ion batteries.
Carbon nanofibers were prepared using electrospinning technology, and tungsten doping was introduced through a solvothermal method to form lithium iron phosphate carbon nanocomposite fibers, thereby improving the conductivity and lithium-ion diffusion performance of the material.
It significantly improves the conductivity and lithium-ion diffusion rate of the material, enhances the battery's capacity utilization and rate performance, and is suitable for industrial production.
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Figure CN121381349A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of lithium ion battery cathode material, and particularly relates to a method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers by a solvothermal method. BACKGROUND
[0002] "Green electricity" generated by renewable energy such as solar energy, wind energy, geothermal energy and hydroelectric power through zero-carbon power conversion processes is gradually replacing traditional coal-fired "thermal power", which not only helps to achieve sustainable transformation of energy structure, but also effectively alleviates climate change problems. However, intermittent renewable energy such as wind power and photovoltaic power has the characteristics of power fluctuation, and efficient energy storage solutions are urgently needed to balance supply and demand fluctuations.
[0003] Therefore, building an efficient, environmentally friendly and economically viable clean energy system has become a key issue in global energy transformation. Among many energy storage technologies, secondary battery technology based on electrochemical principles is driving innovation and development in the fields of portable electronic devices, electric vehicles and smart grids due to its environmental friendliness, application flexibility, long cycle life and other advantages.
[0004] Among them, lithium ion batteries (LIB) have become the preferred technology in the current energy storage field due to their high operating voltage, good environmental compatibility, no memory effect, high volume energy density and other outstanding characteristics. Its significant advantages in promoting sustainable energy development have enabled it to be widely used in electronic devices, new energy vehicles and renewable energy grid-connected fields, and continues to lead the direction of energy storage technology innovation.
[0005] Olivine-structured lithium iron phosphate (LiFePO4) as a cathode material for lithium ion batteries has attracted widespread attention and shown great development potential due to its high theoretical capacity (170 mAh g -1 However, its low energy density and low specific capacity are major limiting factors for its widespread application in batteries due to its low conductivity and low lithium diffusion rate. Therefore, the development of lithium iron phosphate (LFP) materials has significant strategic significance, and the development of sustainable synthesis processes with low cost, high efficiency and environmental friendliness has always been the long-term goal of the scientific community.
[0006] To achieve this goal, researchers have developed a variety of synthesis pathways, such as high-temperature solid-phase method (such as), carbon thermal reduction method, microwave-assisted synthesis method, mechanical chemical method, hydrothermal / solvothermal method, co-precipitation method, sol-gel method, spray pyrolysis method and emulsion drying method.
[0007] However, the inherent structural defects of lithium iron phosphate result in technical bottlenecks such as insufficient conductivity, low tap density, poor high-rate discharge performance and limited ion diffusion rate.
[0008] To address these key scientific questions, the research team proposed a multi-dimensional modification strategy. For example, by precisely controlling the particle size of the material to the nanoscale, not only is the specific surface area significantly increased, but the lithium-ion transport kinetics at the LiFePO4 / FePO4 two-phase interface in the electrode material can also be optimized. The nanostructure can effectively shorten the lithium-ion insertion / extraction path and the electron conduction distance, while the mesoporous structure formed between particles can enhance electrolyte wettability and significantly reduce ion migration resistance.
[0009] In addition to conventional carbon coating and morphology manipulation, ion doping technology exhibits unique advantages in improving intrinsic conductivity. Addressing the core issue of limited lithium-ion diffusion at high rates, selective ion substitution at Li, Fe, or O sites can significantly improve the charge transport characteristics of materials. Li-site doping and Fe-site doping have been proven to have outstanding effects on improving charge-discharge performance. These innovative modification methods provide important technical pathways for breaking through the performance boundaries of lithium iron phosphate materials.
[0010] Therefore, combining highly conductive materials with lithium iron phosphate and modifying them with metal element doping is one of the main strategies for obtaining high-performance electrode materials. Developing feasible and efficient new high-efficiency lithium-ion battery LiFePO4 materials remains an urgent need. Summary of the Invention
[0011] This invention aims to provide a solvothermal method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers. The method employs a simple and convenient electrospinning technique to prepare a support polymer fiber membrane, which is then calcined at high temperature to obtain carbon nanofibers. Finally, the tungsten-doped lithium iron phosphate carbon nanocomposite fiber electrode material is obtained through a solvothermal method, thus solving the problems of poor conductivity and slow ion transport rate of LiFePO4 material.
[0012] The method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers by solvothermal method includes the following steps: S1. Using nitrogen, dimethylformamide (DMF) as a solvent, a polyacrylonitrile (PAN) spinning solution was prepared for electrospinning to obtain a fiber membrane; S2. The fiber membrane described in step S1 is calcined at high temperature to obtain carbon nanofiber material. S3. Dissolve the iron source, lithium source, phosphorus source and tungsten source in a solvent, add the carbon nanofiber material prepared in step S2, soak it to better wet the fiber membrane, carry out a high-temperature solvothermal reaction, cool to room temperature and wash with ethanol to wash away the salt substances precipitated on the surface, and dry to obtain carbon nanocomposite fiber material. S4. The carbon nanocomposite fiber material prepared in step S3 is calcined at high temperature under a nitrogen atmosphere to obtain tungsten-doped lithium iron phosphate carbon nanocomposite fiber material.
[0013] This invention uses a simple and convenient electrospinning technique to prepare a support polymer fiber membrane, which is then calcined at high temperature to obtain carbon nanofibers. Finally, a tungsten-doped lithium iron phosphate carbon nanocomposite fiber electrode material is obtained by a solvothermal method to solve the shortcomings of poor conductivity and slow ion transport rate of LiFePO4 material.
[0014] The fibrous structure of carbon nanofibers can anchor tungsten-doped LiFePO4 particles, preventing structural damage caused by particle agglomeration or volume expansion during charging and discharging. Simultaneously, the nanoscale fiber diameter (typically tens to hundreds of nanometers in electrospun products) increases the material's specific surface area, enhancing the contact area between the electrolyte and the active material, reducing interfacial impedance, and improving stability and wettability. The introduction of tungsten optimizes the olivine lattice structure of LiFePO4, reducing lattice distortion; the encapsulation by carbon nanofibers further protects the active particles from electrolyte erosion. The synergistic effect of these two elements enhances the material's conductivity.
[0015] Metal ion doping of lithium iron phosphate (LFP) can improve its electrochemical performance. The mechanism mainly involves two aspects: first, the introduction of foreign metal ions can generate controllable structural defects in the crystal lattice. These defects act as additional charge carrier channels, significantly enhancing the intrinsic electronic conductivity of the material; second, doping-induced lattice distortion can reduce the lithium-ion migration barrier, thereby effectively improving the lithium-ion diffusion coefficient. This atomic-scale structural control fundamentally solves the core problem of poor conductivity in LFP materials, resulting in a significant improvement in their rate performance and cycle stability.
[0016] In a preferred embodiment, the mass fraction of polyacrylonitrile in the precursor solution described in step S1 is 7% to 9%.
[0017] In the preferred embodiment, the acrylonitrile in step S1 has a Mw of 80000.
[0018] In the preferred embodiment, the high-temperature calcination in step S2 specifically includes: pre-oxidation at 200~300 ℃ for 1.5~2.5 h under a nitrogen atmosphere, followed by high-temperature calcination at 400~500 ℃ for 1~3 h.
[0019] In the preferred embodiment, the iron source mentioned in step S3 is selected from ferrous sulfate.
[0020] In the preferred embodiment, the lithium source mentioned in step S3 is selected from lithium hydroxide.
[0021] In a preferred embodiment, the phosphorus source in step S3 is selected from ammonium dihydrogen phosphate.
[0022] In a preferred embodiment, the tungsten source mentioned in step S3 is selected from ammonium metatungstate.
[0023] In a preferred embodiment, the solvent in step S3 is a mixed solution of water and polyethylene glycol.
[0024] In the preferred embodiment, the soaking time in step S3 is 35~45 min.
[0025] In the preferred embodiment, the temperature of the high-temperature solvothermal reaction in step S3 is 180~200 ℃, and the duration is 7.5~8.5 h.
[0026] In the preferred embodiment, the high-temperature calcination in step S4 is carried out at a temperature of 700~750 ℃ for a duration of 1.5~2.5 h.
[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The tungsten-doped lithium iron phosphate carbon nanocomposite fiber material provided by this invention exhibits high specific capacity, reaching 154.33 mAh / g at a discharge rate of 0.1 C, far exceeding that of existing conventional lithium iron phosphate materials (typically below 140 mAh / g), and approaching the theoretical capacity of LiFePO4 (170 mAh / g), resulting in a significant improvement in capacity utilization. Even at high rates (0.5C, 1C), it maintains a high capacity, and compared to the problem of rapid capacity decay at high rates in existing technologies, the rate adaptability of the material of this invention is significantly superior.
[0028] 2. In the tungsten-doped lithium iron phosphate carbon nanocomposite fiber material provided by this invention, tungsten doping enhances intrinsic conductivity and ion migration efficiency. Tungsten doping can generate controllable structural defects in the LiFePO4 lattice. These defects serve as additional charge carrier channels, directly enhancing the intrinsic electronic conductivity of the material. Simultaneously, the doping-induced lattice distortion can reduce the lithium-ion migration barrier, significantly improving the lithium-ion diffusion coefficient, thus fundamentally solving the problem of inefficient electron-ion transport. Carbon nanofibers construct a three-dimensional conductive network.
[0029] 3. The carbon nanofibers prepared by electrospinning in this invention have excellent conductivity. When combined with LiFePO4, they can form a three-dimensional continuous conductive network. On the one hand, this avoids the breakage of conductive pathways caused by the agglomeration of active particles. On the other hand, the high specific surface area of the nanofibers can enhance the wettability of the electrolyte and further reduce the ion migration resistance, which is something that existing bulk or micron-sized lithium iron phosphate cannot achieve.
[0030] 4. The solvothermal method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers provided by the present invention has the advantages of low energy consumption, convenient operation, no need for complex equipment, strong process repeatability, and suitability for industrial mass production compared with existing lithium iron phosphate synthesis methods (such as high-temperature solid-phase method with high energy consumption, microwave-assisted method with poor repeatability, and sol-gel method with complicated steps). Attached Figure Description
[0031] Figure 1 This is a flowchart illustrating the preparation process of tungsten-doped lithium iron phosphate carbon nanocomposite fiber electrode material. Detailed Implementation
[0032] The technical solution of the present invention will be further described and illustrated below through examples. All raw materials used in the examples are commercially available or prepared using conventional methods.
[0033] Example 1 A method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers using a solvothermal method includes the following steps: S1. Weigh 0.85 g of polyacrylonitrile (Mw=80000) and add it to 9.15 g of nitrogen, nitrogen dimethylformamide (DMF). Stir and dissolve for 12 h until the solution is homogeneous. Prepare a polyacrylonitrile (PAN) spinning solution and perform electrospinning to obtain a fiber membrane. S2. The fiber membrane described in step S1 is transferred to a tube furnace for high-temperature calcination. Under a nitrogen atmosphere, it is pre-oxidized at 250°C for 2 hours and then calcined at 450°C for 2 hours. After natural cooling to room temperature, carbon nanofiber material is obtained. S3. Ferrous sulfate, lithium hydroxide, ammonium dihydrogen phosphate, and ammonium metatungstate are dissolved in a mixed solution of water and the organic solvent polyethylene glycol. After being fully dissolved, the solution is transferred to a high-temperature and high-pressure reactor. The carbon nanofiber material prepared in step S2 is added and soaked for 30 min. The reactor is then transferred to an oven and subjected to a high-temperature solvothermal reaction at 200 °C for 8 h. After cooling to room temperature, the material is cleaned and dried to obtain the carbon nanocomposite fiber material. S4. The carbon nanocomposite fiber material prepared in step S3 is transferred to a tube furnace and calcined at 700°C for 2 h under a nitrogen atmosphere to obtain tungsten-doped lithium iron phosphate carbon nanocomposite fiber material (labeled as LFP-1).
[0034] Example 2 A method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers using a solvothermal method includes the following steps: S1. Weigh 0.85 g of polyacrylonitrile (Mw=80000) and add it to 9.15 g of nitrogen, nitrogen dimethylformamide (DMF). Stir and dissolve for 12 h until the solution is homogeneous. Prepare a polyacrylonitrile (PAN) spinning solution and perform electrospinning to obtain a fiber membrane. S2. The fiber membrane described in step S1 is transferred to a tube furnace for high-temperature calcination. Under a nitrogen atmosphere, it is pre-oxidized at 250°C for 2 hours and then calcined at 450°C for 2 hours. After natural cooling to room temperature, carbon nanofiber material is obtained. S3. Ferrous sulfate, lithium hydroxide, ammonium dihydrogen phosphate, and ammonium metatungstate are dissolved in a mixed solution of water and the organic solvent polyethylene glycol. After being fully dissolved, the solution is transferred to a high-temperature and high-pressure reactor. The carbon nanofiber material prepared in step S2 is added and soaked for 30 min. The reactor is then transferred to an oven and subjected to a high-temperature solvothermal reaction at 200 °C for 10 h. After cooling to room temperature, the material is cleaned and dried to obtain the carbon nanocomposite fiber material. S4. The carbon nanocomposite fiber material prepared in step S3 is transferred to a tube furnace and calcined at 700°C for 2 h under a nitrogen atmosphere to obtain tungsten-doped lithium iron phosphate carbon nanocomposite fiber material (labeled as LFP-2).
[0035] Example 3 A method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers using a solvothermal method includes the following steps: S1. Weigh 0.85 g of polyacrylonitrile (Mw=80000) and add it to 9.15 g of nitrogen, nitrogen dimethylformamide (DMF). Stir and dissolve for 12 h until the solution is homogeneous. Prepare a polyacrylonitrile (PAN) spinning solution and perform electrospinning to obtain a fiber membrane. S2. The fiber membrane described in step S1 is transferred to a tube furnace for high-temperature calcination. Under a nitrogen atmosphere, it is pre-oxidized at 250°C for 2 hours and then calcined at 450°C for 2 hours. After natural cooling to room temperature, carbon nanofiber material is obtained. S3. Ferrous sulfate, lithium hydroxide, ammonium dihydrogen phosphate, and ammonium metatungstate are dissolved in a mixed solution of water and the organic solvent polyethylene glycol. After being fully dissolved, the solution is transferred to a high-temperature and high-pressure reactor. The carbon nanofiber material prepared in step S2 is added and soaked for 30 min. The reactor is then transferred to an oven and subjected to a high-temperature solvothermal reaction at 200 °C for 12 h. After cooling to room temperature, the material is cleaned and dried to obtain the carbon nanocomposite fiber material. S4. The carbon nanocomposite fiber material prepared in step S3 is transferred to a tube furnace and calcined at 700°C for 2 h under a nitrogen atmosphere to obtain tungsten-doped lithium iron phosphate carbon nanocomposite fiber material (labeled as LFP-3).
[0036] Example 4 A method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers using a solvothermal method includes the following steps: S1. Weigh 0.85 g of polyacrylonitrile (Mw=80000) and add it to 9.15 g of nitrogen, nitrogen dimethylformamide (DMF). Stir and dissolve for 12 h until the solution is homogeneous. Prepare a polyacrylonitrile (PAN) spinning solution and perform electrospinning to obtain a fiber membrane. S2. The fiber membrane described in step S1 is transferred to a tube furnace for high-temperature calcination. Under a nitrogen atmosphere, it is pre-oxidized at 250°C for 2 hours and then calcined at 450°C for 2 hours. After natural cooling to room temperature, carbon nanofiber material is obtained. S3. Ferrous sulfate, lithium hydroxide, ammonium dihydrogen phosphate, and ammonium metatungstate are dissolved in a mixed solution of water and the organic solvent polyethylene glycol. After complete dissolution, the solution is transferred to a high-temperature and high-pressure reactor. The carbon nanofiber material prepared in step S2 is added and soaked for 30 min. The reactor is then transferred to an oven and subjected to a high-temperature solvothermal reaction at 200 °C for 14 h. After cooling to room temperature, the material is cleaned and dried to obtain the carbon nanocomposite fiber material. S4. The carbon nanocomposite fiber material prepared in step S3 is transferred to a tube furnace and calcined at 700°C for 2 h under a nitrogen atmosphere to obtain tungsten-doped lithium iron phosphate carbon nanocomposite fiber material (labeled as LFP-4).
[0037] Comparative Example 1 A solvothermal method for synthesizing lithium iron phosphate carbon nanocomposite fibers is basically the same as that in Example 3, except that ammonium metatungstate is not added in step S3.
[0038] Testing and Analysis According to GB / T 33822-2025 "Nano Lithium Iron Phosphate", samples LFP-1~LFP-4, Comparative Example 1, and lithium iron phosphate (as blank control group) were tested, and their electrical performance at 0.1 C, 0.5 C, and 1 C rates was tested, as shown in Table 1.
[0039] Table 1. Charge-discharge specific capacity of samples at 0.1 C, 0.5 C, and 1 C rates.
[0040] As shown in Table 1, the synthesis method provided by this invention effectively improves the electrical performance and conductivity of lithium iron phosphate. At 0.1 C, the discharge specific capacity is as high as 154.33 mAh / g. The electrical performance of the prepared LFP-3 is optimal when the hydrothermal temperature is 200 ℃ and the hydrothermal time is 12 h.
[0041] It should be understood that the above embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.
Claims
1. A method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers by a solvothermal method, characterized in that, Includes the following steps: S1. Using nitrogen, N,N-dimethylformamide as a solvent, a polyacrylonitrile spinning solution was prepared and electrospinned to obtain a fiber membrane. S2. The fiber membrane described in step S1 is calcined at high temperature to obtain carbon nanofiber material. S3. Dissolve the iron source, lithium source, phosphorus source and tungsten source in a solvent, add the carbon nanofiber material prepared in step S2, soak, carry out a high-temperature solvothermal reaction, cool to room temperature for cleaning, and dry to obtain carbon nanocomposite fiber material. S4. The carbon nanocomposite fiber material prepared in step S3 is calcined at high temperature under a nitrogen atmosphere to obtain tungsten-doped lithium iron phosphate carbon nanocomposite fiber material.
2. The method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers by solvothermal method according to claim 1, characterized in that, The mass fraction of polyacrylonitrile in the precursor solution in step S1 is 7%~9%; the Mw of acrylonitrile in step S1 is 80000.
3. The method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers by solvothermal method according to claim 1, characterized in that, The high-temperature calcination mentioned in step S2 specifically includes: pre-oxidation at 200~300 ℃ for 1.5~2.5 h under a nitrogen atmosphere, followed by high-temperature calcination at 400~500 ℃ for 1~3 h.
4. The method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers by solvothermal method according to claim 1, characterized in that, The iron source mentioned in step S3 is selected from ferrous sulfate.
5. The method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers by solvothermal method according to claim 1, characterized in that, The lithium source mentioned in step S3 is selected from lithium hydroxide.
6. The method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers by solvothermal method according to claim 1, characterized in that, The phosphorus source mentioned in step S3 is selected from ammonium dihydrogen phosphate.
7. The method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers by solvothermal method according to claim 1, characterized in that, The tungsten source mentioned in step S3 is selected from ammonium metatungstate.
8. The method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers by solvothermal method according to claim 1, characterized in that, The solvent mentioned in step S3 is a mixed solution of water and polyethylene glycol.
9. The method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers by solvothermal method according to claim 1, characterized in that, The soaking time in step S3 is 35~45 min; the temperature of the high-temperature solvothermal reaction in step S3 is 180~200 ℃, and the duration is 7.5~8.5 h.
10. The method for synthesizing tungsten-doped lithium iron phosphate carbon nanocomposite fibers by solvothermal method according to claim 1, characterized in that, The high-temperature calcination in step S4 is carried out at a temperature of 700~750 ℃ for a duration of 1.5~2.5 h.