Method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on joule heat
By using Joule thermal synthesis technology to form carbon vapor-coated nanocrystalline lithium iron phosphate under vacuum conditions, the problem of uneven carbon distribution is solved, the conductivity and lithium ion diffusion rate of the material are improved, and energy consumption and cost are reduced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHAANXI UNIV OF SCI & TECH
- Filing Date
- 2026-02-04
- Publication Date
- 2026-05-29
AI Technical Summary
In the preparation of lithium iron phosphate materials, the carbon element is unevenly distributed, resulting in low conductivity and lithium-ion diffusion rate, as well as high energy consumption and cost.
Joule thermal synthesis technology is used to mix porous carbon materials with lithium iron phosphate under vacuum conditions. Joule heating is generated by applying current and voltage to form carbon vapor that coats the surface of nanocrystalline lithium iron phosphate particles, forming a uniform carbon layer.
This method achieves uniform coating of carbon layer on the surface of lithium iron phosphate, improves conductivity and lithium-ion diffusion rate, reduces energy consumption and cost, and is simple and environmentally friendly.
Smart Images
Figure CN122102084A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to new energy battery materials, specifically a method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on Joule thermal synthesis. Background Technology
[0002] Lithium iron phosphate (LFP) is a cathode material for lithium-ion batteries, characterized by high safety and long lifespan, and is widely used in new energy batteries. However, the low conductivity and lithium-ion diffusion rate of pure LFP materials limit its application.
[0003] To overcome the above challenges, some researchers have attempted to shorten the diffusion path of lithium ions in materials by reducing the particle size, thereby increasing the diffusion rate of lithium ions. For example, Chinese invention patent CN 101546830A discloses a lithium iron phosphate material coated with carbon nanotubes (CNTs). This method directly disperses carbon nanotubes into the reactant solution for reaction and coating, resulting in carbon nanotube-coated lithium iron phosphate material with good rate capability and cycle performance. However, this method, which directly adds carbon nanotubes to the lithium iron phosphate reactant solution, is prone to uneven distribution and agglomeration. Chinese invention patent CN105789620A discloses a method for preparing lithium iron phosphate cathode material, which uses a solid-phase synthesis method to prepare lithium iron phosphate material. Acetylene is introduced into the inert atmosphere during calcination, forming carbon nanotubes inside and between the generated lithium iron phosphate particles to obtain a highly conductive lithium iron phosphate cathode material. However, this method has high energy consumption, high operational difficulty, and relatively high cost.
[0004] It is evident that there is an urgent need to propose a novel method for preparing nanoscale lithium iron phosphate materials, which can improve the uniformity of carbon distribution in lithium iron phosphate with low energy consumption and low cost. Summary of the Invention
[0005] The purpose of this invention is to provide a method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on Joule thermal synthesis, which not only enables the carbon layer to be uniformly coated on the surface of nanocrystalline lithium iron phosphate, but also reduces energy consumption and cost.
[0006] This invention is achieved through the following technical solution: A method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on Joule heating includes the following steps: Step 1: Take nano-sized iron phosphate and lithium compound and mix them according to the molar ratio of Li, Fe and P (1.02 ~ 1.3): 1: 1 to obtain a mixture; Step 2: The mixture is subjected to wet ball milling and drying in sequence, and then sieved to obtain a small particle size mixture; Step 3: Press the small particle size mixture into sheets, wrap the sheet-like mixture around the porous carbon material to ensure close contact between the sheet-like mixture and the porous carbon material, then transfer the porous carbon material wrapped with the sheet-like mixture into the Joule thermal synthesis apparatus and clamp it between two electrodes. Next, evacuate the Joule thermal synthesis apparatus, then turn on the power switch to apply current and voltage to the two electrodes to generate Joule heat, raise the temperature inside the Joule thermal synthesis apparatus to 700~1600℃, hold it at that temperature for 10 s~5 min, and after the reaction is complete, grind it to obtain powdered carbon-coated nanocrystalline lithium iron phosphate. Alternatively, the small-particle mixture is placed on top of porous carbon material in a quartz tube, with both ends of the quartz tube plugged with graphite plugs, ensuring close contact between the mixture and the graphite plugs. The quartz tube containing the mixture is then transferred to the Joule thermal synthesis apparatus and clamped between two electrodes. The apparatus is then evacuated, and the power switch is turned on to apply current and voltage to the electrodes, generating Joule heating. The temperature inside the Joule thermal synthesis apparatus is raised to 700~1600 ℃ and held for 10 s~5 min. After the reaction is complete, the mixture is ground to obtain powdered carbon-coated nanocrystalline lithium iron phosphate.
[0007] Furthermore, the lithium compound in step 1 is lithium carbonate or lithium hydroxide.
[0008] Furthermore, in step 2, the wet ball milling is carried out by placing the mixture into a planetary ball mill with anhydrous ethanol as the ball milling medium at a mass ratio of 1:5:(1.1~1.4) for 6~16 hours.
[0009] Furthermore, the drying in step 2 is carried out at 80~140℃ for 4~12 hours.
[0010] Furthermore, the particle size of the small-particle mixture in step 2 is 0.1~1.5 μm.
[0011] Furthermore, in step 3, the pressing into sheets involves pressing the small particle size mixture into round sheets with a thickness of 2-5 mm and a diameter of 10-15 cm using a pressure of 5-20 MPa.
[0012] Furthermore, the porous carbon material in step 3 is graphite felt, graphite paper, or carbon paper.
[0013] Furthermore, in step 3, the vacuuming inside the Joule thermal synthesis instrument involves reducing the vacuum level inside the instrument to 10. -2 Pa.
[0014] Furthermore, the grinding in step 3 is carried out using a planetary ball mill at a speed of 300 r / min for 3 to 8 hours to obtain carbon-coated nanocrystalline lithium iron phosphate with a particle size of 500 nm to 1.5 μm.
[0015] The present invention has the following beneficial technical effects: This invention utilizes Joule thermal ultrafast synthesis technology to synthesize carbon-coated nanocrystalline lithium iron phosphate materials, offering the following advantages: First, by directly applying voltage and current to the electrodes of the Joule thermal synthesis instrument, a temperature of 1600℃ can be reached within 10 seconds, significantly shortening the synthesis time and contributing to reduced energy consumption; second, in a vacuum-sealed environment, the porous carbon material provides a strong reducing atmosphere, enabling rapid and efficient synthesis of Fe... 3+ Reduced to Fe 2+ First, it eliminates the need for hydrogen or other reducing gases, making the process simpler and safer. Second, at high temperatures, the carbon vapor volatilized from the porous carbon material is deposited in situ on the surface of newly grown lithium iron phosphate particles, forming a coating layer. This carbon layer, naturally formed during the reaction, typically exhibits stronger and more uniform bonding with the lithium iron phosphate particle surface, and its conductivity is superior to the amorphous carbon formed by traditional sucrose pyrolysis. In short, this invention can effectively suppress grain growth in a very short time, directly synthesizing carbon-coated nanocrystalline lithium iron phosphate, significantly shortening the lithium-ion diffusion path, and effectively reducing energy consumption and costs. Furthermore, the process is simple and easy to operate, reducing environmental pollution and achieving green production. Attached Figure Description
[0016] Figure 1 This is a flowchart illustrating the synthesis of powdered carbon-coated nanocrystalline lithium iron phosphate in Examples 1-4 of the present invention; Figure 2 This is a diagram showing the placement of the sheet-like mixture in graphite felt in Embodiment 4 of the present invention; Figure 3 The image shows the XRD pattern of the powdered carbon-coated nanocrystalline lithium iron phosphate prepared in Example 4 of this invention. Detailed Implementation
[0017] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.
[0018] refer to Figure 1 As shown in Examples 1-4 of this invention, in the process of preparing carbon-coated nanocrystalline lithium iron phosphate based on Joule thermal synthesis, iron phosphate and lithium compounds are first mixed, then sequentially subjected to wet ball milling, drying, sieving, and tableting. The mixture is then wrapped with porous carbon material and placed inside a Joule thermal synthesis apparatus under vacuum conditions. Figure 2As shown, current and voltage are applied to porous carbon materials, and the generated Joule heat is used to create a high-temperature environment inside the Joule thermal synthesis instrument. The carbon vapor generated by the volatilization of porous carbon materials is deposited in situ on the surface of newly grown lithium iron phosphate (LFP) particles to form a coating layer, thus obtaining carbon-coated nanocrystalline lithium iron phosphate.
[0019] Example 1 Step 1: Take nano-sized iron phosphate and lithium carbonate and mix them according to the molar ratio of Li, Fe and P of 1.02:1:1 to obtain a mixture; Step 2: Using anhydrous ethanol as the ball milling medium, the mixture is placed in a planetary ball mill at a mass ratio of 1:5:1.1 for 6 hours. After milling, it is dried at 80°C for 4 hours and then sieved to obtain a small particle size mixture with a particle size of 0.3 μm. Step 3: Press the small particle size mixture into a disc with a thickness of 5 mm and a diameter of 10 cm at a pressure of 5 MPa to obtain a disc-shaped mixture. Wrap the disc-shaped mixture in two layers of graphite felt to ensure close contact between the disc-shaped mixture and the graphite felt. Then transfer the graphite felt containing the disc-shaped mixture into the Joule thermal synthesis apparatus and clamp it between two electrodes. Next, evacuate the Joule thermal synthesis apparatus and turn on the power switch to apply current and voltage to the graphite felt to generate Joule heat. Raise the temperature inside the Joule thermal synthesis apparatus to 1600℃ and hold it for 10 s. After the reaction is complete, use a planetary ball mill at a speed of 300 r / min for dry grinding for 5 h to obtain powdered carbon-coated nanocrystalline lithium iron phosphate with a particle size of 1 μm.
[0020] Example 2 Step 1: Take nano-sized iron phosphate and lithium carbonate and mix them according to the molar ratio of Li, Fe and P of 1.05:1:1 to obtain a mixture; Step 2: Using anhydrous ethanol as the ball milling medium, the mixture is placed in a planetary ball mill according to the mass ratio of material, grinding stone and ball milling medium of 1:5:1.2, and ball milled for 12 h. Then it is dried at 120℃ for 12 h and then sieved to obtain a small particle size mixture with a particle size of 0.5 μm. Step 3: Press the small particle size mixture into a disc with a thickness of 4 mm and a diameter of 11 cm at a pressure of 10 MPa to obtain a disc-shaped mixture. Wrap the disc-shaped mixture in two layers of graphite paper to ensure close contact between the disc-shaped mixture and the graphite paper. Then transfer the graphite paper containing the disc-shaped mixture into the Joule thermal synthesis apparatus and clamp it between two electrodes. Next, evacuate the Joule thermal synthesis apparatus and turn on the power switch to apply current and voltage to the graphite paper to generate Joule heat. Raise the temperature inside the Joule thermal synthesis apparatus to 1200℃ and hold it for 3 min. After the reaction is complete, use a planetary ball mill at a speed of 300 r / min for dry grinding for 8 h to obtain powdered carbon-coated nanocrystalline lithium iron phosphate with a particle size of 500 nm.
[0021] Example 3 Step 1: Take nano-sized iron phosphate and lithium carbonate and mix them according to the molar ratio of Li, Fe and P of 1.3:1:1 to obtain a mixture; Step 2: Using anhydrous ethanol as the ball milling medium, the mixture is placed in a planetary ball mill according to the mass ratio of material, grinding stone and ball milling medium of 1:5:1.3, and milled for 10 h. Then, it is dried at 140℃ for 10 h and then sieved to obtain a small particle size mixture with a particle size of 0.8 μm. Step 3: Press the small particle size mixture into discs with a thickness of 2 mm and a diameter of 15 cm at a pressure of 20 MPa to obtain a disc-shaped mixture. Wrap the disc-shaped mixture in two layers of carbon paper to ensure close contact between the disc-shaped mixture and the carbon paper. Then transfer the carbon paper wrapped with the disc-shaped mixture into the Joule thermal synthesis apparatus and clamp it between two electrodes. Next, evacuate the Joule thermal synthesis apparatus and turn on the power switch to apply current and voltage to the carbon paper to generate Joule heat. Raise the temperature inside the Joule thermal synthesis apparatus to 700 °C and hold it for 5 min. After the reaction is complete, use a planetary ball mill at a speed of 300 r / min for dry grinding for 7 h to obtain powdered carbon-coated nanocrystalline lithium iron phosphate with a particle size of 0.6 μm.
[0022] Example 4 Step 1: Take nano-sized iron phosphate and lithium hydroxide and mix them according to the molar ratio of Li, Fe and P of 1.2:1:1 to obtain a mixture; Step 2: Using anhydrous ethanol as the ball milling medium, the mixture was placed in a planetary ball mill at a mass ratio of 1:5:1.4 of material, grinding stone and ball milling medium. The mixture was ball milled for 16 h, dried at 80℃ for 8 h, and then sieved to obtain a small particle size mixture with a particle size of 0.1 μm. Step 3: Press the small particle size mixture into a disc with a thickness of 3 mm and a diameter of 14 cm at a pressure of 15 MPa to obtain a disc-shaped mixture. First, wrap the disc-shaped mixture in graphite paper, and then place the graphite paper on two layers of graphite felt to ensure close contact between the disc-shaped mixture and the graphite paper. Then, transfer the graphite felt containing the disc-shaped mixture into the Joule thermal synthesis apparatus and clamp it between two electrodes. Next, evacuate the Joule thermal synthesis apparatus and then turn on the power switch to apply current and voltage to the graphite felt to generate Joule heat. Raise the temperature inside the Joule thermal synthesis apparatus to 1000℃ and hold it for 4 min. After the reaction is complete, use a planetary ball mill at a speed of 300 r / min for dry grinding for 6 h to obtain powdered carbon-coated nanocrystalline lithium iron phosphate with a particle size of 0.8 μm.
[0023] See Figure 3 The characteristic peaks of the sample prepared in Example 4 completely match the PDF card of LiFePO4, indicating that Example 4 successfully prepared powdered carbon-coated nanocrystalline lithium iron phosphate.
[0024] Example 5 Step 1: Take nano-sized iron phosphate and lithium hydroxide and mix them according to the molar ratio of Li, Fe and P of 1.15: 1: 1 to obtain a mixture; Step 2: Using anhydrous ethanol as the ball milling medium, the mixture is placed in a planetary ball mill according to the mass ratio of material, grinding stone and ball milling medium of 1:5:1.3. The mixture is ball milled for 14 h, dried at 100℃ for 6 h, and then sieved to obtain a small particle size mixture with a particle size of 1.5 μm. Step 3: Place the small-particle mixture on the carbon paper inside the quartz tube. Plug both ends of the quartz tube with graphite plugs, ensuring the mixture is in close contact with the graphite plugs. Transfer the quartz tube containing the mixture into the Joule thermal synthesis apparatus and clamp it between two electrodes. Then, evacuate the inside of the Joule thermal synthesis apparatus. Turn on the power switch to apply current and voltage to the electrodes, generating Joule heat. Raise the temperature inside the Joule thermal synthesis apparatus to 1400℃ and hold for 1 min. After the reaction is complete, use a planetary ball mill at a speed of 300 r / min for dry grinding for 3 h to obtain powdered carbon-coated nanocrystalline lithium iron phosphate with a particle size of 1.5 μm.
Claims
1. A method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on Joule thermal synthesis, characterized in that, Includes the following steps: Step 1: Take nano-sized iron phosphate and lithium compound and mix them according to the molar ratio of Li, Fe and P (1.02 ~ 1.3): 1: 1 to obtain a mixture; Step 2: The mixture is subjected to wet ball milling and drying in sequence, and then sieved to obtain a small particle size mixture; Step 3: Press the small particle size mixture into sheets, wrap the sheet-like mixture with porous carbon material to ensure close contact between the sheet-like mixture and the porous carbon material, then transfer the porous carbon material wrapped with the sheet-like mixture into the Joule thermal synthesis apparatus and clamp it between two electrodes. Next, evacuate the Joule thermal synthesis apparatus, then turn on the power switch to apply current and voltage to the two electrodes to generate Joule heat, raise the temperature inside the Joule thermal synthesis apparatus to 700~1600 ℃, hold it at that temperature for 10 s~5 min, and after the reaction is complete, grind it to obtain powdered carbon-coated nanocrystalline lithium iron phosphate. Alternatively, the small-particle mixture is placed on top of porous carbon material in a quartz tube, with both ends of the quartz tube plugged with graphite plugs, ensuring close contact between the mixture and the graphite plugs. The quartz tube containing the mixture is then transferred to the Joule thermal synthesis apparatus and clamped between two electrodes. The apparatus is then evacuated, and the power switch is turned on to apply current and voltage to the electrodes, generating Joule heating. The temperature inside the Joule thermal synthesis apparatus is raised to 700~1600 ℃ and held for 10 s~5 min. After the reaction is complete, the mixture is ground to obtain powdered carbon-coated nanocrystalline lithium iron phosphate.
2. The method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on Joule thermal synthesis according to claim 1, characterized in that, The lithium compound in step 1 is lithium carbonate or lithium hydroxide.
3. The method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on Joule thermal synthesis according to claim 1, characterized in that, The wet ball milling in step 2 involves placing the mixture into a planetary ball mill with anhydrous ethanol as the ball milling medium, according to a mass ratio of material, grinding stone, and grinding media of 1:5:(1.1~1.4), and milling for 6~16 hours.
4. The method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on Joule thermal synthesis according to claim 1, characterized in that, The drying in step 2 is carried out at 80~140℃ for 4~12 hours.
5. The method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on Joule thermal synthesis according to claim 1, characterized in that, The particle size of the small-particle mixture in step 2 is 0.1~1.5 μm.
6. The method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on Joule thermal synthesis according to claim 1, characterized in that, The pressing process in step 3 involves pressing the small particle size mixture into round sheets with a thickness of 2-5 mm and a diameter of 10-15 cm at a pressure of 5-20 MPa.
7. The method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on Joule thermal synthesis according to claim 1, characterized in that, The porous carbon material in step 3 is graphite felt, graphite paper, or carbon paper.
8. The method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on Joule thermal synthesis according to claim 1, characterized in that, In step 3, evacuating the Joule heating instrument involves reducing the vacuum level inside the instrument to 10. -2 Pa.
9. The method for synthesizing carbon-coated nanocrystalline lithium iron phosphate based on Joule heating according to claim 1, characterized in that, The grinding in step 3 is carried out using a planetary ball mill at a speed of 300 r / min for 3 to 8 hours to obtain carbon-coated nanocrystalline lithium iron phosphate with a particle size of 500 nm to 1.5 μm.