A high-conductivity lithium iron phosphate material and a preparation method thereof

Abstract

The application relates to a high-conductivity lithium iron phosphate material and a preparation method thereof, and belongs to the technical field of lithium iron phosphate. The high-conductivity lithium iron phosphate material comprises the following components in percentage by mass: 88-92% of lithium iron phosphate, 2-4% of graphene, 0.5-1.5% of vapor-grown carbon fiber, 0.5-1% of a noble metal precursor, 2-5% of carbon nanotubes and 0.1-0.5% of a dopant. The application can form an effective conductive network by introducing graphene, vapor-grown carbon fiber, carbon nanotubes and a noble metal precursor. The network not only enhances the electronic conductivity of the material itself, but also promotes the diffusion rate of lithium ions in the material. Specifically, the graphene and the carbon nanotubes provide a continuous electron conduction path, reduce the charge transfer resistance, and the vapor-grown carbon fiber constructs a stable conductive framework at the micro level, so that the material can maintain good electronic conductivity even under high compaction density. This directly improves the performance of the material under high-rate charging and discharging conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium iron phosphate, and in particular relates to a high-conductivity lithium iron phosphate material and a preparation method thereof. Background Art

[0002] Lithium iron phosphate (LiFePO4), as a positive electrode material for lithium-ion batteries, has a stable crystal structure and can maintain structural integrity during the charge and discharge process, thereby ensuring a long cycle life of the battery. At the same time, lithium iron phosphate has high thermal stability and is not prone to thermal runaway, so it has high safety. In addition, due to its rich composition and non-toxicity, lithium iron phosphate is also environmentally friendly. These characteristics make lithium iron phosphate an ideal choice for applications such as electric vehicles and large-scale energy storage systems.

[0003] However, the electronic conductivity and ion diffusion coefficient of lithium iron phosphate materials are low, which limits their performance under high-rate charge and discharge conditions. Under high-rate discharge conditions, the battery needs to quickly transmit electrons and lithium ions to meet the needs of large currents. However, these properties of lithium iron phosphate limit its performance in fast charge and discharge applications, especially in situations where a large amount of energy needs to be provided in a short period of time, such as the rapid start and acceleration of electric vehicles. Therefore, we propose a high-conductivity lithium iron phosphate material and a preparation method. Summary of the Invention

[0004] (1) Technical problems solved

[0005] In response to the shortcomings of the existing technology, the present invention provides a high-conductivity lithium iron phosphate material and a preparation method. By optimizing the material formula and preparation process, the conductivity of lithium iron phosphate is significantly improved, solving the problem that existing lithium iron phosphate materials often involve complex process steps and require precise control of the type and concentration of doping elements, as well as the thickness and uniformity of carbon coating; these requirements not only increase the difficulty of the production process, but also increase the manufacturing cost.

[0006] (2) Technical solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] A high-conductivity lithium iron phosphate material comprises the following components, calculated by mass percentage: 88% to 92% lithium iron phosphate, 2% to 4% graphene, 0.5% to 1.5% vapor-grown carbon fiber, 0.5% to 1% noble metal precursor, 2% to 5% carbon nanotubes, and 0.1% to 0.5% dopant, with the balance being deionized water.

[0009] Furthermore, the noble metal precursor is palladium chloride.

[0010] Furthermore, the dopant is one of boron, nitrogen, and fluorine, or a mixture of more than one of them.

[0011] A method for preparing a high-conductivity lithium iron phosphate material comprises the following steps:

[0012] S1: lithium iron phosphate, graphene, vapor-grown carbon fiber, noble metal precursor, carbon nanotubes and dopant are fully mixed in deionized water for 2 to 3 hours to obtain a mixed slurry;

[0013] S2: drying the mixed slurry obtained in step S1 by spray drying to obtain a dry precursor material, wherein the air inlet temperature during the spray drying process is 150-250° C. and the atomization pressure is 2-5 bar;

[0014] S3: sintering the dried precursor material at a high temperature in a nitrogen or argon atmosphere to obtain a high-conductivity lithium iron phosphate material, wherein the purity of the nitrogen or argon is not less than 99.99%;

[0015] Furthermore, the high-conductivity lithium iron phosphate material prepared by S3 was subjected to the first discharge capacity test: at a current density of 0.1C, the first discharge capacity was ≥160mAh / g.

[0016] Furthermore, the high-conductivity lithium iron phosphate material prepared by S3 was subjected to a cycle stability test: at a current density of 1C, the discharge capacity retention rate after 100 cycles was ≥95%.

[0017] Furthermore, the rate performance test of the high conductivity lithium iron phosphate material prepared by S3 was carried out:

[0018] At a current density of 0.1C, the first discharge capacity is ≥160mAh / g;

[0019] At a current density of 0.5C, the discharge capacity is not less than 90% of the initial discharge capacity;

[0020] At a current density of 1C, the discharge capacity is not less than 85% of the initial discharge capacity;

[0021] At a current density of 2C, the discharge capacity is not less than 80% of the initial discharge capacity;

[0022] At a current density of 5C, the discharge capacity is not less than 60% of the initial discharge capacity.

[0023] Furthermore, in the step S3, the high temperature sintering temperature is 700-800° C., and the sintering time is 10-12 hours.

[0024] Furthermore, the D50 particle size of the high-conductivity lithium iron phosphate material prepared in step S3 is 10 to 30 μm.

[0025] Furthermore, in S1, the solid content of the mixed slurry is 30% to 50%.

[0026] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0027] 1. The present invention forms an effective conductive network by introducing graphene, vapor-grown carbon fibers, carbon nanotubes, and noble metal precursors into lithium iron phosphate materials. This conductive network not only enhances the electronic conductivity of the material itself but also promotes the diffusion rate of lithium ions in the material. Specifically, graphene and carbon nanotubes provide a continuous electron conduction path, reducing the charge transfer resistance, while the vapor-grown carbon fibers construct a stable conductive skeleton at the microscopic level, ensuring that the material maintains good electronic conductivity even at high compaction density. This directly improves the material's performance under high-rate charge and discharge conditions, meeting the instantaneous high current requirements for rapid starting and acceleration of electric vehicles.

[0028] 2. The present invention adopts a specific high-temperature sintering step in the preparation process and performs sintering at 700-800°C in a nitrogen or argon atmosphere. This not only ensures the purity of the material, but also optimizes the size and morphology of the lithium iron phosphate particles by controlling the sintering conditions, so that the particle size distribution of the final product is concentrated in the range of D50=10-30μm. This particle size range is beneficial to improving the electrochemical properties of the material, especially improving the first discharge capacity and the discharge capacity retention rate at different current densities, thereby improving the cycle stability and rate performance of the material under high-rate charge and discharge conditions.

[0029] 3. The present invention significantly improves the conductivity of lithium iron phosphate material by optimizing the material formula and preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the preparation step of the high-conductivity lithium iron phosphate material of the present invention. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, rather than all embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work are within the scope of protection of the present invention.

[0032] Example 1

[0033] A high-conductivity lithium iron phosphate material comprises the following components, calculated by mass percentage: 90% lithium iron phosphate, 3% graphene, 1% vapor-grown carbon fiber, 0.8% noble metal precursor, 4% carbon nanotubes, and 0.3% dopant, with the balance being deionized water.

[0034] The noble metal precursor is palladium chloride.

[0035] The dopant is boron.

[0036] A method for preparing a high-conductivity lithium iron phosphate material comprises the following steps:

[0037] S1: Lithium iron phosphate, graphene, vapor-grown carbon fiber, noble metal precursor, carbon nanotubes, and dopant were thoroughly mixed in deionized water and stirred for 3 h using a high-speed stirrer to obtain a mixed slurry with a solid content of 45%.

[0038] S2: Dry the mixed slurry obtained in step S1 by spray drying at an air inlet temperature of 180°C and an atomization pressure of 3 bar to obtain a dry precursor material. The spray drying time is 45 minutes.

[0039] The spray drying method in S2 comprises the following steps:

[0040] Q1: Preheat the dryer: Preheat the spray dryer to the set air inlet temperature;

[0041] Q2: Slurry preparation: prepare mixed slurry;

[0042] Q3: Slurry delivery: Use a pump to deliver the mixed slurry from the storage tank to the spray head of the spray dryer;

[0043] Q4: Spray drying: In the preheated dryer, the mixed slurry is atomized through the spray nozzle to form fine droplets;

[0044] Q5: Hot air circulation: The hot air is circulated through the spray tower by a fan, so that the droplets are fully in contact with the hot air, accelerating the evaporation of water and obtaining dry precursor materials;

[0045] Q6: Powder collection: The dried precursor material is collected through a bag filter;

[0046] Q7: Product cooling: Cool the collected precursor material to room temperature.

[0047] S3: The precursor material obtained in step Q7 is subjected to high-temperature sintering in a nitrogen or argon atmosphere to obtain a high-conductivity lithium iron phosphate material. The high-temperature sintering temperature is 750°C and the sintering time is 12 hours. The nitrogen or argon content is 99.99% of the total gas volume in the container. The D50 particle size of the prepared high-conductivity lithium iron phosphate material is 20 μm.

[0048] S4: Use an electrochemical analysis station and a lithium battery testing system to test the electrical properties of the high-conductivity lithium iron phosphate material prepared in S3. Test items include initial discharge capacity, cycle stability, and rate performance.

[0049] The electrical performance test in S4 includes the following steps:

[0050] First discharge capacity: The first discharge capacity of the high-conductivity lithium iron phosphate material prepared by S3 was tested at a current density of 0.1C;

[0051] Cycling stability: 100 cycles were performed at a current density of 1C to test the capacity retention of the high-conductivity lithium iron phosphate material prepared by S3;

[0052] Rate performance: The discharge capacity of the high-conductivity lithium iron phosphate material product prepared by S3 was tested at current densities of 0.1C, 0.5C, 1C, 2C, and 5C.

[0053] The results of the electrical performance test are shown in Table 1.

[0054] Table 1

[0055]

[0056]

[0057] S5: The high conductivity lithium iron phosphate material prepared in S3 was tested for its specific surface area using a surface area analyzer, and then its pore volume and average pore diameter were tested using a porosity analyzer. The test results are shown in Table 2.

[0058] Experimental steps:

[0059] Step 1: Specific surface area analysis: Use a specific surface area analyzer to measure the specific surface area of ​​the sample in this embodiment;

[0060] Step 2: Pore structure analysis: Use a porosity analyzer to measure the pore volume and average pore diameter of the sample.

[0061] Table 2

[0062]

[0063] Example 2:

[0064] A high-conductivity lithium iron phosphate material comprises the following components, calculated by mass percentage: 92% lithium iron phosphate, 2% graphene, 1.5% vapor-grown carbon fiber, 0.5% noble metal precursor, 2% nanotubes, and 0.1% dopant, with the balance being deionized water.

[0065] The noble metal precursor is palladium chloride.

[0066] The dopant is fluorine.

[0067] A method for preparing a high-conductivity lithium iron phosphate material comprises the following steps:

[0068] S1: Lithium iron phosphate, graphene, vapor-grown carbon fiber, noble metal precursor, carbon nanotubes, and dopant were thoroughly mixed in deionized water and stirred for 2 h using a high-speed stirrer to obtain a mixed slurry with a solid content of 30%.

[0069] S2: Dry the mixed slurry obtained in step S1 by spray drying (same as in Example 1) at an air inlet temperature of 150°C and an atomization pressure of 2 bar to obtain a dry precursor material. The spray drying time is min;

[0070] S3: The precursor material obtained in step Q7 is subjected to high-temperature sintering in a nitrogen or argon atmosphere to obtain a high-conductivity lithium iron phosphate material. The high-temperature sintering temperature is 700°C and the sintering time is 10 hours. The nitrogen or argon content is 99.99% of the total gas volume in the container. The D50 particle size of the prepared high-conductivity lithium iron phosphate material is 15 μm.

[0071] S4: The high-conductivity lithium iron phosphate material prepared in S3 was subjected to electrical performance testing using an electrochemical analysis station and a lithium battery testing system. The test items included initial discharge capacity, cycle stability, and rate performance. The testing method was the same as in Example 1. The results are shown in Table 3.

[0072] Table 3

[0073]

[0074]

[0075] S5: The high conductivity lithium iron phosphate material prepared in S3 was tested for its specific surface area using a surface area analyzer, and then its pore volume and average pore diameter were tested using a porosity analyzer. The testing method was the same as in Example 1. The test results are shown in Table 4.

[0076] Table 4

[0077]

[0078] Example 3:

[0079] A high-conductivity lithium iron phosphate material comprises the following components, calculated by mass percentage: 88% lithium iron phosphate, 4% graphene, 0.5% vapor-grown carbon fiber, 1% noble metal precursor, 5% carbon nanotubes, and 0.5% dopant, with the balance being deionized water.

[0080] The noble metal precursor is palladium chloride.

[0081] The dopant is nitrogen.

[0082] A method for preparing a high-conductivity lithium iron phosphate material comprises the following steps:

[0083] S1: Lithium iron phosphate, graphene, vapor-grown carbon fiber, noble metal precursor, carbon nanotubes, and dopant were thoroughly mixed in deionized water and stirred using a high-speed stirrer for 3 h to obtain a mixed slurry with a solid content of 50% recorded;

[0084] S2: Dry the mixed slurry obtained in step S1 by spray drying (same as in Example 1) with an air inlet temperature of 250°C and an atomization pressure of 5 bar to obtain a dry precursor material. The spray drying time is min;

[0085] S3: The precursor material obtained in step Q7 is subjected to high-temperature sintering in a nitrogen or argon atmosphere to obtain a high-conductivity lithium iron phosphate material. The high-temperature sintering temperature is 800°C and the sintering time is 12 hours. The nitrogen or argon content is 99.99% of the total gas volume in the container. The D50 particle size of the prepared high-conductivity lithium iron phosphate material is 25 μm.

[0086] S4: Using an electrochemical analysis station and a lithium battery testing system, the electrical properties of the high-conductivity lithium iron phosphate material prepared in S3 were tested, including the initial discharge capacity, cycle stability, and rate performance. The testing methods were the same as in Example 1. The results are shown in Table 7.

[0087] Table 5

[0088]

[0089] S5: The high conductivity lithium iron phosphate material prepared in S3 was tested for its specific surface area using a surface area analyzer, and then its pore volume and average pore diameter were tested using a porosity analyzer. The testing method was the same as in Example 1. The test results are shown in Table 8.

[0090] Table 6

[0091]

[0092]

[0093] Comparative Example 1

[0094] Different from Example 1, the calcination temperature in step S3 is 600°C.

[0095] A high-conductivity lithium iron phosphate material comprises the following components, calculated by mass percentage: 90% lithium iron phosphate, 3% graphene, 1% vapor-grown carbon fiber, 0.8% noble metal precursor, 4% carbon nanotubes, and 0.3% dopant, with the balance being deionized water.

[0096] The noble metal precursor is palladium chloride.

[0097] The dopant is boron.

[0098] A method for preparing a high-conductivity lithium iron phosphate material comprises the following steps:

[0099] S1: Lithium iron phosphate, graphene, vapor-grown carbon fiber, noble metal precursor, carbon nanotubes, and dopant were thoroughly mixed in deionized water and stirred for 3 h using a high-speed stirrer to obtain a mixed slurry with a solid content of 45%.

[0100] S2: Dry the mixed slurry obtained in step S1 by spray drying at an air inlet temperature of 180°C and an atomization pressure of 3 bar to obtain a dry precursor material. The spray drying time is 45 minutes.

[0101] The spray drying method in S2 comprises the following steps:

[0102] Q1: Preheat the dryer: Preheat the spray dryer to the set air inlet temperature;

[0103] Q2: Slurry preparation: prepare mixed slurry;

[0104] Q3: Slurry delivery: Use a pump to deliver the mixed slurry from the storage tank to the spray head of the spray dryer;

[0105] Q4: Spray drying: In the preheated dryer, the mixed slurry is atomized through the spray nozzle to form fine droplets;

[0106] Q5: Hot air circulation: The hot air is circulated through the spray tower by a fan, so that the droplets are fully in contact with the hot air, accelerating the evaporation of water and obtaining dry precursor materials;

[0107] Q6: Powder collection: The dried precursor material is collected through a bag filter;

[0108] Q7: Product cooling: Cool the collected precursor material to room temperature.

[0109] S3: The precursor material obtained in step Q7 is subjected to high-temperature sintering in a nitrogen or argon atmosphere to obtain a high-conductivity lithium iron phosphate material. The high-temperature sintering temperature is 600°C and the sintering time is 12 hours. The nitrogen or argon content is 99.99% of the total gas volume in the container. The D50 particle size of the prepared high-conductivity lithium iron phosphate material is 12 μm.

[0110] S4: The high conductivity lithium iron phosphate material prepared in S3 was tested for electrical performance using an electrochemical analysis station and a lithium battery test system. The test items included initial discharge capacity, cycle stability, and rate capability. The results of the electrical performance test are shown in Table 7.

[0111] Table 7

[0112]

[0113]

[0114] S5: The high conductivity lithium iron phosphate material prepared in S3 was tested for specific surface area using a surface area analyzer, and then tested for pore volume and average pore diameter using a porosity analyzer. The test results are shown in Table 8.

[0115] Table 8

[0116]

[0117] Comparative Example 2

[0118] Unlike Example 1, the calcination temperature in the S3 step was 900°C.

[0119] A high conductivity lithium iron phosphate material, comprising the following components in terms of mass percentage: 90% lithium iron phosphate, 3% graphene, 1% vapor grown carbon fiber, 0.8% noble metal precursor, 4% carbon nanotube, and 0.3% dopant, with the balance being deionized water.

[0120] The noble metal precursor is palladium chloride.

[0121] The dopant is boron.

[0122] A method for preparing a high conductivity lithium iron phosphate material, comprising the following steps:

[0123] S1: Lithium iron phosphate, graphene, vapor grown carbon fiber, noble metal precursor, and carbon nanotube and dopant were thoroughly mixed in deionized water, stirred for 3h using a high-speed stirrer, to obtain a mixed slurry, and the solid content was recorded as 45%;

[0124] S2: The mixed slurry obtained in S1 was dried by spray drying, with an inlet temperature of 180°C and an atomization pressure of 3bar, to obtain a dried precursor material, and the spray drying time was 45min;

[0125] The spray drying method in S2 comprises the following steps:

[0126] Q1: Preheat the dryer: preheat the spray dryer to the set inlet temperature;

[0127] Q2: Slurry preparation: prepare mixed slurry;

[0128] Q3: Slurry delivery: Use a pump to deliver the mixed slurry from the storage tank to the spray head of the spray dryer;

[0129] Q4: Spray drying: In the preheated dryer, the mixed slurry is atomized through the spray nozzle to form fine droplets;

[0130] Q5: Hot air circulation: The hot air is circulated through the spray tower by a fan, so that the droplets are fully in contact with the hot air, accelerating the evaporation of water and obtaining dry precursor materials;

[0131] Q6: Powder collection: The dried precursor material is collected through a bag filter;

[0132] Q7: Product cooling: Cool the collected precursor material to room temperature.

[0133] S3: The precursor material obtained in step Q7 is subjected to high-temperature sintering in a nitrogen or argon atmosphere to obtain a high-conductivity lithium iron phosphate material. The high-temperature sintering temperature is 900°C and the sintering time is 12 hours. The nitrogen or argon content is 99.99% of the total gas volume in the container. The D50 particle size of the prepared high-conductivity lithium iron phosphate material is 18 μm.

[0134] S4: The high-conductivity lithium iron phosphate material prepared in S3 was subjected to electrical performance testing using an electrochemical analysis station and a lithium battery testing system. The test items included initial discharge capacity, cycle stability, and rate performance. The results of the electrical performance tests are shown in Table 9.

[0135] Table 9

[0136]

[0137]

[0138] S5: The high conductivity lithium iron phosphate material prepared in S3 was tested for its specific surface area using a surface area analyzer, and then its pore volume and average pore diameter were tested using a porosity analyzer. The test results are shown in Table 10.

[0139] Table 10

[0140]

[0141] Comparative Example 3

[0142] Different from Example 1, Comparative Example 3 does not contain a dopant.

[0143] A high-conductivity lithium iron phosphate material comprises the following components, calculated by mass percentage: 90% lithium iron phosphate, 3% graphene, 1% vapor-grown carbon fiber, 0.8% noble metal precursor, and 4% carbon nanotubes, with the balance being deionized water.

[0144] The noble metal precursor is palladium chloride.

[0145] A method for preparing a high-conductivity lithium iron phosphate material comprises the following steps:

[0146] S1: Lithium iron phosphate, graphene, vapor-grown carbon fiber, noble metal precursor, and carbon nanotubes were thoroughly mixed in deionized water and stirred for 3 h using a high-speed stirrer to obtain a mixed slurry with a solid content of 45%.

[0147] S2: Dry the mixed slurry obtained in step S1 by spray drying at an air inlet temperature of 180°C and an atomization pressure of 3 bar to obtain a dry precursor material. The spray drying time is 45 minutes.

[0148] The spray drying method in S2 comprises the following steps:

[0149] Q1: Preheat the dryer: Preheat the spray dryer to the set air inlet temperature;

[0150] Q2: Slurry preparation: prepare mixed slurry;

[0151] Q3: Slurry delivery: Use a pump to deliver the mixed slurry from the storage tank to the spray head of the spray dryer;

[0152] Q4: Spray drying: In the preheated dryer, the mixed slurry is atomized through the spray nozzle to form fine droplets;

[0153] Q5: Hot air circulation: The hot air is circulated through the spray tower by a fan, so that the droplets are fully in contact with the hot air, accelerating the evaporation of water and obtaining dry precursor materials;

[0154] Q6: Powder collection: The dried precursor material is collected through a bag filter;

[0155] Q7: Product cooling: Cool the collected precursor material to room temperature.

[0156] S3: The precursor material obtained in step Q7 is subjected to high-temperature sintering in a nitrogen or argon atmosphere to obtain a high-conductivity lithium iron phosphate material. The high-temperature sintering temperature is 750°C and the sintering time is 12 hours. The nitrogen or argon content is 99.99% of the total gas volume in the container. The D50 particle size of the prepared high-conductivity lithium iron phosphate material is 13 μm.

[0157] S4: Use an electrochemical analysis station and a lithium battery testing system to test the electrical properties of the high-conductivity lithium iron phosphate material prepared in S3. Test items include initial discharge capacity, cycle stability, and rate performance.

[0158] The electrical performance test in S4 includes the following steps:

[0159] First discharge capacity: The first discharge capacity of the high-conductivity lithium iron phosphate material prepared by S3 was tested at a current density of 0.1C;

[0160] Cycling stability: 100 cycles were performed at a current density of 1C to test the capacity retention of the high-conductivity lithium iron phosphate material prepared by S3;

[0161] Rate performance: The discharge capacity of the high-conductivity lithium iron phosphate material product prepared by S3 was tested at current densities of 0.1C, 0.5C, 1C, 2C, and 5C.

[0162] The results of the electrical performance test are shown in Table 1.

[0163] Table 11

[0164]

[0165] S5: The high conductivity lithium iron phosphate material prepared in S3 was tested for its specific surface area using a surface area analyzer, and then its pore volume and average pore diameter were tested using a porosity analyzer. The test results are shown in Table 2.

[0166] Experimental steps:

[0167] Step 1: Specific surface area analysis: Use a specific surface area analyzer to measure the specific surface area of ​​the sample in this embodiment;

[0168] Step 2: Pore structure analysis: Use a porosity analyzer to measure the pore volume and average pore diameter of the sample.

[0169] Table 12

[0170]

[0171] Comparative Example 4

[0172] Different from Example 1, no dopant was added, and the calcination temperature in step S3 was 600°C.

[0173] A high-conductivity lithium iron phosphate material comprises the following components, calculated by mass percentage: 90% lithium iron phosphate, 3% graphene, 1% vapor-grown carbon fiber, 0.8% noble metal precursor, and 4% carbon nanotubes, with the balance being deionized water.

[0174] The noble metal precursor is palladium chloride.

[0175] A method for preparing a high-conductivity lithium iron phosphate material comprises the following steps:

[0176] S1: Lithium iron phosphate, graphene, vapor-grown carbon fiber, noble metal precursor, and carbon nanotubes were thoroughly mixed in deionized water and stirred for 3 h using a high-speed stirrer to obtain a mixed slurry with a solid content of 45%.

[0177] S2: Dry the mixed slurry obtained in step S1 by spray drying at an air inlet temperature of 180°C and an atomization pressure of 3 bar to obtain a dry precursor material. The spray drying time is 45 minutes.

[0178] The spray drying method in S2 comprises the following steps:

[0179] Q1: Preheat the dryer: Preheat the spray dryer to the set air inlet temperature;

[0180] Q2: Slurry preparation: prepare mixed slurry;

[0181] Q3: Slurry delivery: Use a pump to deliver the mixed slurry from the storage tank to the spray head of the spray dryer;

[0182] Q4: Spray drying: In the preheated dryer, the mixed slurry is atomized through the spray nozzle to form fine droplets;

[0183] Q5: Hot air circulation: The hot air is circulated through the spray tower by a fan, so that the droplets are fully in contact with the hot air, accelerating the evaporation of water and obtaining dry precursor materials;

[0184] Q6: Powder collection: The dried precursor material is collected through a bag filter;

[0185] Q7: Product cooling: Cool the collected precursor material to room temperature.

[0186] S3: The precursor material obtained in step Q7 is subjected to high-temperature sintering in a nitrogen or argon atmosphere to obtain a high-conductivity lithium iron phosphate material. The high-temperature sintering temperature is 600°C and the sintering time is 12 hours. The nitrogen or argon content is 99.99% of the total gas volume in the container. The D50 particle size of the prepared high-conductivity lithium iron phosphate material is 9 μm.

[0187] S4: Use an electrochemical analysis station and a lithium battery testing system to test the electrical properties of the high-conductivity lithium iron phosphate material prepared in S3. Test items include initial discharge capacity, cycle stability, and rate performance.

[0188] The electrical performance test in S4 includes the following steps:

[0189] First discharge capacity: The first discharge capacity of the high-conductivity lithium iron phosphate material prepared by S3 was tested at a current density of 0.1C;

[0190] Cycling stability: 100 cycles were performed at a current density of 1C to test the capacity retention of the high-conductivity lithium iron phosphate material prepared by S3;

[0191] Rate performance: The discharge capacity of the high-conductivity lithium iron phosphate material product prepared by S3 was tested at current densities of 0.1C, 0.5C, 1C, 2C, and 5C.

[0192] The results of the electrical performance tests are shown in Tables 13 and 14.

[0193] Table 13

[0194]

[0195] S5: The high conductivity lithium iron phosphate material prepared in S3 was tested for its specific surface area using a surface area analyzer, and then its pore volume and average pore diameter were tested using a porosity analyzer. The test results are shown in Table 2.

[0196] Experimental steps:

[0197] Step 1: Specific surface area analysis: Use a specific surface area analyzer to measure the specific surface area of ​​the sample in this embodiment;

[0198] Step 2: Pore structure analysis: Use a porosity analyzer to measure the pore volume and average pore diameter of the sample.

[0199] Table 14

[0200]

[0201] Result analysis:

[0202] 1. Combining the data in Table 1, Table 3 and Table 5, the electrical performance test results of the high-conductivity lithium iron phosphate materials prepared by Examples 1 to 3 show that the high-conductivity lithium iron phosphate materials prepared by the technical solution have good electrochemical properties, the first discharge capacity is not less than 165 mAh / g, the capacity retention rate after 100 cycles at a current density of 1C is not less than 95%, the discharge capacity at different current densities meets the requirements, and shows excellent cycle stability and rate performance.

[0203] 2. Combining the data in Table 2, Table 4 and Table 6, it can be seen from the physical property test results of the high conductivity lithium iron phosphate materials prepared in Examples 1 to 3 that the high conductivity lithium iron phosphate materials have a high specific surface area, pore volume and suitable average pore diameter. The high conductivity lithium iron phosphate materials prepared by the present invention have excellent physical properties.

[0204] 3. In step S2 of Comparative Example 1 and Comparative Example 2, high-temperature calcination is performed at 600°C and 900°C, respectively. Combined with the data in Tables 7 to 10, the physical property tests and conductive property tests of the high-conductivity lithium iron phosphate materials prepared in Comparative Example 1 and Comparative Example 2 are lower than the test results of the physical property tests and conductive property tests of the high-conductivity lithium iron phosphate material prepared in Example 1, indicating that the appropriate calcination temperature of the precursor material in step S2 improves the electrochemical properties of the high-conductivity lithium iron phosphate material, and that too high or too low a sintering temperature will reduce the electrochemical properties of the high-conductivity lithium iron phosphate material finally prepared.

[0205] At the same time, no dopant was added in Comparative Example 3, and the calcination temperature of step S3 in Comparative Example 4 was 600°C based on Comparative Example 3. Combining the data in Comparative Example 1 and Tables 7, 8, 11, 12, 13 and 14, it can be seen that the dopant can best improve the conductive properties of the prepared lithium iron phosphate when the calcination temperature is greater than 700°C.

[0206] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A high-conductivity lithium iron phosphate material, characterized by: The method for preparing the high-conductivity lithium iron phosphate material comprises the following steps: S1: lithium iron phosphate, graphene, vapor-grown carbon fiber, noble metal precursor, carbon nanotubes and dopant are fully mixed in deionized water for 2 to 3 hours to obtain a mixed slurry, wherein the mixed slurry comprises the following components by mass percentage: 88% to 92% lithium iron phosphate, 2% to 4% graphene, 0.5% to 1.5% vapor-grown carbon fiber, 0.5% to 1% noble metal precursor, 2% to 5% carbon nanotubes and 0.1% to 0.5% dopant, and the balance is deionized water, wherein the dopant is one or a mixture of two or more of boron, nitrogen and fluorine; S2: drying the mixed slurry obtained in step S1 by spray drying to obtain a dry precursor material, wherein the air inlet temperature during the spray drying process is 150-250°C and the atomization pressure is 2-5 bar; S3: sintering the dried precursor material at a high temperature in a nitrogen or argon atmosphere to obtain a high-conductivity lithium iron phosphate material, wherein the purity of the nitrogen or argon atmosphere is not less than 99.99%; In the step S3, the high temperature sintering temperature is 700-800°C and the sintering time is 10-12 hours; The D50 particle size of the high-conductivity lithium iron phosphate material prepared in step S3 is 10-30 μm.

2. The high-conductivity lithium iron phosphate material according to claim 1, characterized in that: The noble metal precursor is palladium chloride.

3. The high-conductivity lithium iron phosphate material according to claim 1, characterized in that: The high-conductivity lithium iron phosphate material prepared by S3 was subjected to the first discharge capacity test: at a current density of 0.1C, the first discharge capacity was ≥160mAh / g.

4. The high-conductivity lithium iron phosphate material according to claim 1, characterized in that: The high-conductivity lithium iron phosphate material prepared by S3 was subjected to a cycle stability test: at a current density of 1C, the discharge capacity retention rate after 100 cycles was ≥95%.

5. The high-conductivity lithium iron phosphate material according to claim 1, characterized in that: The rate performance test of the high conductivity lithium iron phosphate material prepared by S3 was carried out: At a current density of 0.1C, the first discharge capacity is ≥160mAh / g; At a current density of 0.5C, the discharge capacity is not less than 90% of the initial discharge capacity; At a current density of 1C, the discharge capacity is not less than 85% of the initial discharge capacity; At a current density of 2C, the discharge capacity is not less than 80% of the initial discharge capacity; At a current density of 5C, the discharge capacity is not less than 60% of the initial discharge capacity.

6. The high-conductivity lithium iron phosphate material according to claim 1, characterized in that: In S1, the solid content of the mixed slurry is 30%~50%.

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