A high-pressure dense and high-capacity lithium iron phosphate based on high specific surface area iron phosphate

Abstract

The application discloses high-pressure dense and high-capacity lithium iron phosphate based on high specific surface area iron phosphate, and first, an iron source is added into a phosphorus source, and after stirring, dissolving and filtering, a filtrate is prepared; an oxidizing agent is added into the filtrate to prepare a reaction liquid; secondly, a mixture prepared by compounding iron phosphate dihydrate and ammonium dihydrogen phosphate is added into the reaction liquid, and stirring and heating reaction are conducted; after filtration, drying and calcination, high specific surface area anhydrous iron phosphate is prepared; finally, a lithium source, iron phosphate, a carbon source and water are mixed, and after grinding, the mixture is dried by spraying to prepare a lithium iron phosphate precursor; the precursor is calcined, crushed, screened and de-magnetized under a protective atmosphere to prepare high-pressure dense and high-capacity lithium iron phosphate. The specific surface area of the prepared iron phosphate can reach 15-20 m 2 / g, and the 0.1C discharge capacity of a button cell prepared based on the lithium iron phosphate is between 157-165 mAh / g, and the powder compaction density reaches 2.50 g / cm 3 / g.

Description

Technical Field

[0001] This invention belongs to the field of lithium iron phosphate preparation, and particularly relates to a high-density, high-capacity lithium iron phosphate based on high specific surface area iron phosphate. Background Technology

[0002] Currently, new energy batteries mainly consist of lithium iron phosphate batteries, ternary batteries, and high-nickel batteries. Among them, lithium iron phosphate batteries have stable PO bonds in their cathode materials, which are difficult to decompose. Even at high temperatures or when overcharged, they will not collapse and generate heat or form strong oxidizing substances like other cathode materials, thus possessing good safety.

[0003] However, as national requirements for driving range become increasingly stringent, the demand for high-density lithium iron phosphate powder is growing, requiring a powder compaction density of 2.3 g / cm³. 3 In order to meet the international market's demand for higher energy and higher compaction density in lithium-ion battery materials, it is necessary to develop LiFePO4 materials with higher energy and higher density. Therefore, improving the performance of lithium iron phosphate cathode materials, such as compaction density and discharge capacity, while simultaneously reducing the cost of their preparation, is of profound significance to the development of this industry.

[0004] Existing technologies, such as application number 2021116741028 entitled "A Preparation Method for Increasing the Specific Surface Area of ​​Ferric Phosphate", disclose the use of a crystallizing agent composed of seed crystals and dispersant in the preparation of ferric phosphate. The addition of seed crystals avoids the risk of ferric hydroxide colloids acting as crystal nuclei during the preparation process, which would lead to an increase in the particle size of the product. Furthermore, the dispersant used in this preparation method avoids the agglomeration of seed crystals, and the choice of phosphoric acid source is limited to phosphoric acid to avoid the addition of oxidants that would increase the pH value of the system and promote the formation of ferric hydroxide colloidal seed crystals. However, when preparing ferric phosphate by this method, the ferric phosphate particles formed are prone to agglomeration during the preparation process.

[0005] Based on this, a novel method for preparing iron phosphate is provided, which also achieves a high specific surface area. Summary of the Invention

[0006] Objective of the Invention: The technical problem to be solved by this invention is to provide a high-density, high-capacity lithium iron phosphate based on high specific surface area iron phosphate, wherein the specific surface area of ​​the iron phosphate can reach 15-20 m². 2 The powder density is 2.50 g / cm³, and the 0.1C discharge capacity of the coin cell based on this lithium iron phosphate is between 157-165 mAh / g. 3 above.

[0007] Technical solution: This invention is based on high-density, high-capacity lithium iron phosphate with high specific surface area iron phosphate, which is prepared by the following steps:

[0008] (1) Add the iron source to the phosphorus source, stir to dissolve and filter to obtain the filtrate, add the oxidant to the filtrate to obtain the reaction solution;

[0009] (2) Add a mixture of ferric phosphate dihydrate and ammonium dihydrogen phosphate to the reaction solution, stir and react at 150-200℃ for 3-5 hours, and obtain anhydrous ferric phosphate with high specific surface area after filtration, drying and calcination; wherein the mass ratio of ferric phosphate dihydrate to iron source is (0.1-10):100, and the mass ratio of ammonium dihydrogen phosphate to iron source is (0.1-10):100.

[0010] (3) The lithium source, iron phosphate, carbon source and water are mixed, ground and spray dried to obtain the lithium iron phosphate precursor. The precursor is then roasted, crushed, sieved and demagnetized under a protective atmosphere to obtain high pressure density and high capacity lithium iron phosphate.

[0011] This invention uses a mixture of ferric phosphate dihydrate and ammonium dihydrogen phosphate to prepare ferric phosphate. The addition of ferric phosphate dihydrate as a seed crystal effectively avoids the use of ferric hydroxide colloid as a seed crystal during ferric phosphate preparation, resulting in smaller ferric phosphate particles with a larger specific surface area. Crucially, the addition of ammonium dihydrogen phosphate is also important. Under heating reaction conditions, ammonium dihydrogen phosphate decomposes into water vapor, phosphoric acid, and other gases such as ammonia. This water vapor and other gases agitate the entire reaction system, preventing the agglomeration of the prepared ferric phosphate particles. Furthermore, the formed phosphoric acid compensates for the increase in pH value caused by the addition of the oxidant, effectively preventing the formation of ferric hydroxide seed crystals. The weakly alkaline gases, such as ammonia, produced during decomposition have a negligible impact compared to the formed phosphoric acid.

[0012] Furthermore, in step (1) of the preparation method, the iron source is ferrous sulfate, ferrous nitrate or ferrous chloride; the phosphorus source is sodium dihydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium phosphate, potassium phosphate or phosphoric acid; the molar ratio of ferrous ions in the iron source to phosphate ions in the phosphorus source is 1:(1.2-1.5).

[0013] Furthermore, in step (1) of the preparation method, the amount of oxidant added is 1-3 times the molar ratio of the iron source, and the oxidant includes hydrogen peroxide, sodium hypochlorite, potassium hypochlorite, sodium chlorate or potassium chlorate.

[0014] Furthermore, in step (2) of this preparation method, the specific surface area of ​​the prepared anhydrous ferric phosphate is 15-20 m². 2 / g.

[0015] Furthermore, in step (2) of the preparation method, the drying temperature is 100-150℃.

[0016] Furthermore, in step (2) of the preparation method, the calcination is carried out at 500-700℃ for 1-6 hours.

[0017] Furthermore, in step (3) of the preparation method, the lithium source is lithium hydroxide, lithium chloride, lithium oxalate, lithium carbonate, lithium acetate or lithium nitrate; the carbon source is glucose, sucrose or citric acid.

[0018] Furthermore, in step (3) of the preparation method, the molar ratio of lithium ions to iron ions in the lithium source and iron phosphate is 1:(1-1.05), and the amount of carbon source added accounts for 13-16% of the mass of the iron phosphate precursor.

[0019] Furthermore, in step (3) of the preparation method, the spray-dried particle size D50 is 35-40 μm.

[0020] Furthermore, in step (3) of the preparation method, the calcination is carried out at 745-780℃ for 8-12 hours, and the heating rate of the calcination is 5-20℃ / min.

[0021] Beneficial effects: Compared with the prior art, the significant advantage of this invention is that the specific surface area of ​​the iron phosphate prepared by this method can reach 15-20 m². 2 The powder density is 2.50 g / cm³, and the 0.1C discharge capacity of the coin cell based on this lithium iron phosphate is between 157-165 mAh / g. 3 The above features not only high electrical capacity but also high compaction density. Attached Figure Description

[0022] Figure 1 This is a SEM image of the iron phosphate prepared in Example 3 of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0024] It should be noted that all raw materials used in this invention are commercially available. The iron source used in this invention can be ferrous sulfate, ferrous nitrate, or ferrous chloride; the phosphorus source can be sodium dihydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium phosphate, potassium phosphate, or phosphoric acid. The lithium source can be lithium hydroxide, lithium chloride, lithium oxalate, lithium carbonate, lithium acetate, or lithium nitrate.

[0025] Preferably, the spray-dried particle size D50 of the present invention is 36.1-39.2 μm. The specific surface area of ​​the ferric phosphate prepared by the present invention is 15.4-19.4 m².2 / g.

[0026] Example 1

[0027] This embodiment is based on high-density, high-capacity lithium iron phosphate with high specific surface area, and is prepared by the following steps:

[0028] (1) Add ferrous sulfate to sodium dihydrogen phosphate at a molar ratio of 1:1.2 between ferrous ions and phosphate ions in the phosphorus source, stir to dissolve and filter to obtain filtrate, add hydrogen peroxide to the filtrate, and the amount of hydrogen peroxide added is 1 times the molar ratio of ferrous sulfate to obtain reaction solution.

[0029] (2) Add a mixture of ferric phosphate dihydrate and ammonium dihydrogen phosphate to the reaction solution, stir and react at 150°C for 5 hours, filter, dry at 100°C and calcine at 500°C for 6 hours to obtain anhydrous ferric phosphate; wherein the mass ratio of ferric phosphate dihydrate to iron source is 0.1:100 and the mass ratio of ammonium dihydrogen phosphate to iron source is 0.1:100.

[0030] (3) Lithium carbonate and iron phosphate were mixed at a lithium ion to iron ion molar ratio of 1:1, and sucrose accounting for 13% of the mass of the lithium iron phosphate precursor was added for mixing. Then, pure water was added at 130% of the total mass of the materials (iron phosphate, lithium carbonate, sucrose) for grinding. After 2.5 hours, the slurry was taken out and the particle size D50 of the slurry was tested to be 0.48 μm. The spray atomizing wheel speed was 14468 rpm, and the particle size of the lithium iron phosphate precursor powder was 36.7 μm.

[0031] (4) The prepared lithium iron phosphate spray precursor with large spray particle size was heated at a heating rate of 5℃ / min under nitrogen atmosphere protection until it reached 745℃. After being kept at the temperature for 9h, sintered lithium iron phosphate was obtained. The sintered lithium iron phosphate was then crushed, sieved and demagnetized to obtain the final lithium iron phosphate product.

[0032] Example 2

[0033] This embodiment is based on high-density, high-capacity lithium iron phosphate with high specific surface area, and is prepared by the following steps:

[0034] (1) Add ferrous nitrate to disodium hydrogen phosphate at a molar ratio of 1:1.5 between ferrous ions and phosphate ions in the phosphorus source, stir to dissolve and filter to obtain filtrate, add sodium hypochlorite to the filtrate, and the amount of sodium hypochlorite added is 3 times the molar ratio of ferrous nitrate to obtain reaction solution.

[0035] (2) Add a mixture of ferric phosphate dihydrate and ammonium dihydrogen phosphate to the reaction solution, stir and react at 200°C for 3 hours, filter, dry at 150°C and calcine at 700°C for 1 hour to obtain anhydrous ferric phosphate; wherein the mass ratio of ferric phosphate dihydrate to iron source is 1:10 and the mass ratio of ammonium dihydrogen phosphate to iron source is 1:10.

[0036] (3) Lithium hydroxide and iron phosphate were mixed at a lithium ion to iron ion molar ratio of 1:1, and glucose accounting for 15% of the mass of the lithium iron phosphate precursor was added for mixing. Then, pure water was added at 130% of the total mass of the materials (iron phosphate, lithium hydroxide, glucose) for grinding. After 3 hours, the slurry was taken out and the particle size D50 of the slurry was tested to be 0.44 μm. The spray atomizing wheel speed was 14213 rpm, and the particle size of the lithium iron phosphate precursor powder was 37.2 μm.

[0037] (4) The prepared lithium iron phosphate spray precursor with large spray particle size was heated at a heating rate of 10℃ / min under nitrogen atmosphere protection until it reached 760℃. After being kept at the temperature for 10h, sintered lithium iron phosphate was obtained. The sintered lithium iron phosphate was then crushed, sieved and demagnetized to obtain the final lithium iron phosphate product.

[0038] Example 3

[0039] This embodiment is based on high-density, high-capacity lithium iron phosphate with high specific surface area, and is prepared by the following steps:

[0040] (1) Add ferrous chloride to potassium dihydrogen phosphate at a molar ratio of 1:1.3 between ferrous ions and phosphate ions in the phosphorus source, stir to dissolve and filter to obtain filtrate, add potassium hypochlorite to the filtrate, and the amount of potassium hypochlorite added is twice the molar ratio of ferrous nitrate to obtain reaction solution.

[0041] (2) Add a mixture of ferric phosphate dihydrate and ammonium dihydrogen phosphate to the reaction solution, stir and react at 160°C for 4 hours, filter, dry at 120°C, and calcine at 550°C for 3 hours to obtain anhydrous ferric phosphate; wherein the mass ratio of ferric phosphate dihydrate to iron source is 5:100, and the mass ratio of ammonium dihydrogen phosphate to iron source is 5:100.

[0042] (3) Lithium oxalate and iron phosphate were mixed at a lithium ion to iron ion molar ratio of 1:1.02, and citric acid accounting for 14% of the mass of the lithium iron phosphate precursor was added for mixing. Then, pure water was added at 130% of the total mass of the materials (iron phosphate, lithium oxalate, citric acid) for grinding. After 3.5 hours, the slurry was taken out and the particle size D50 of the slurry was tested to be 0.41 μm. The spray atomizing wheel speed was 14014 rpm, and the particle size of the lithium iron phosphate precursor powder was 38.5 μm.

[0043] (4) The prepared lithium iron phosphate spray precursor with large spray particle size was heated at a heating rate of 12℃ / min under nitrogen atmosphere protection until it reached 770℃. After being kept at the temperature for 9.5h, sintered lithium iron phosphate was obtained. The sintered lithium iron phosphate was then crushed, sieved and demagnetized to obtain the final lithium iron phosphate product.

[0044] The iron phosphate prepared in this example was characterized structurally, and the results are as follows: Figure 1 As shown in the figure, the high specific surface area iron phosphate prepared by the above method exhibits a relatively uniform and consistent crystal structure and microstructure.

[0045] Example 4

[0046] This embodiment is based on high-density, high-capacity lithium iron phosphate with high specific surface area, and is prepared by the following steps:

[0047] (1) Ferrous sulfate was added to dipotassium hydrogen phosphate at a molar ratio of 1:1.4 between ferrous ions and phosphate ions in the phosphorus source. The mixture was stirred, dissolved, and filtered to obtain a filtrate. Sodium chlorate was added to the filtrate, and the amount of sodium chlorate added was 1.5 times the molar ratio of ferrous nitrate to obtain a reaction solution.

[0048] (2) Add a mixture of ferric phosphate dihydrate and ammonium dihydrogen phosphate to the reaction solution, stir and react at 170°C for 3.5 h, filter, dry at 130°C and calcine at 600°C for 2 h to obtain anhydrous ferric phosphate; wherein the mass ratio of ferric phosphate dihydrate to iron source is 1:100 and the mass ratio of ammonium dihydrogen phosphate to iron source is 1:100.

[0049] (3) Lithium chloride and iron phosphate were mixed at a lithium ion to iron ion molar ratio of 1:1, and sucrose accounting for 14% of the mass of the lithium iron phosphate precursor was added for mixing. Then, pure water was added at 130% of the total mass of the materials (iron phosphate, lithium chloride, sucrose) for grinding. After 3 hours, the slurry was taken out and the particle size D50 of the slurry was tested to be 0.46 μm. The spray atomizing wheel speed was 14380 rpm, and the particle size of the lithium iron phosphate precursor powder was 36.1 μm.

[0050] (4) The prepared lithium iron phosphate spray precursor with large spray particle size was heated at a heating rate of 15℃ / min under nitrogen atmosphere protection until it reached 780℃. After being kept at the temperature for 8 hours, sintered lithium iron phosphate was obtained. The sintered lithium iron phosphate was then crushed, sieved and demagnetized to obtain the final lithium iron phosphate product.

[0051] Example 5

[0052] This embodiment is based on high-density, high-capacity lithium iron phosphate with high specific surface area, and is prepared by the following steps:

[0053] (1) Add ferrous sulfate to sodium phosphate at a molar ratio of 1:1.5 between ferrous ions and phosphate ions in the phosphorus source, stir to dissolve and filter to obtain filtrate, add potassium chlorate to the filtrate, and the amount of potassium chlorate added is twice the molar ratio of ferrous nitrate to obtain reaction solution.

[0054] (2) Add a mixture of ferric phosphate dihydrate and ammonium dihydrogen phosphate to the reaction solution, stir and react at 180°C for 4 hours, filter, dry at 140°C and calcine at 650°C for 4 hours to obtain anhydrous ferric phosphate; wherein the mass ratio of ferric phosphate dihydrate to iron source is 8:100 and the mass ratio of ammonium dihydrogen phosphate to iron source is 8:100.

[0055] (3) Lithium acetate and iron phosphate were mixed at a lithium ion to iron ion molar ratio of 1:105, and sucrose accounting for 14% of the mass of the lithium iron phosphate precursor was added for mixing. Then, pure water was added at 130% of the total mass of the materials (iron phosphate, lithium acetate, sucrose) for grinding. After 4 hours, the slurry was taken out and the particle size D50 of the slurry was tested to be 0.38 μm. The spray atomizing wheel speed was 13875 rpm, and the particle size of the lithium iron phosphate precursor powder was 39.2 μm.

[0056] (4) The prepared lithium iron phosphate spray precursor with large spray particle size was heated at a heating rate of 20℃ / min under nitrogen atmosphere protection until it reached 755℃. After being kept at the temperature for 11h, sintered lithium iron phosphate was obtained. The sintered lithium iron phosphate was then crushed, sieved and demagnetized to obtain the final lithium iron phosphate product.

[0057] Example 6

[0058] This embodiment is based on high-density, high-capacity lithium iron phosphate with high specific surface area, and is prepared by the following steps:

[0059] (1) Add ferrous sulfate to phosphoric acid at a molar ratio of ferrous ions to phosphate ions in the phosphorus source of 1:1.3, stir to dissolve and filter to obtain filtrate, add hydrogen peroxide to the filtrate, and the amount of hydrogen peroxide added is twice the molar ratio of ferrous nitrate to obtain reaction solution.

[0060] (2) Add a mixture of ferric phosphate dihydrate and ammonium dihydrogen phosphate to the reaction solution, stir and react at 190°C for 4.5 h, filter, dry at 145°C and calcine at 700°C for 5 h to obtain anhydrous ferric phosphate; wherein the mass ratio of ferric phosphate dihydrate to iron source is 6:100 and the mass ratio of ammonium dihydrogen phosphate to iron source is 6:100.

[0061] (3) Lithium nitrate and iron phosphate were mixed at a lithium ion to iron ion molar ratio of 1:1, and sucrose accounting for 16% of the mass of the lithium iron phosphate precursor was added for mixing. Then, pure water was added at 130% of the total mass of the materials (iron phosphate, lithium nitrate, sucrose) for grinding. After 5 hours, the slurry was taken out and the particle size D50 of the slurry was tested to be 0.35 μm. The spray atomizing wheel speed was 14130 rpm, and the particle size of the lithium iron phosphate precursor powder was 38.1 μm.

[0062] (4) The prepared lithium iron phosphate spray precursor with large spray particle size was heated at a heating rate of 10℃ / min under nitrogen atmosphere protection until it reached 755℃. After being kept at the temperature for 12h, sintered lithium iron phosphate was obtained. The sintered lithium iron phosphate was then crushed, sieved and demagnetized to obtain the final lithium iron phosphate product.

[0063] Performance testing: Specific surface area measurement

[0064] The specific surface area of ​​the iron phosphate prepared in Examples 1-6 was measured using a CANTA 4200e (USA), and the results are shown in Table 1 below.

[0065] Table 1. Specific surface area of ​​ferric phosphate prepared in Examples 1-6

[0066] Example <![CDATA[Specific surface area (m 2 / g)]]> Example 1 15.6 Example 2 17.3 Example 3 18.4 Example 4 19.4 Example 5 16.8 Example 6 15.4

[0067] As shown in Table 1, the specific surface area of ​​the iron phosphate prepared by the method of the present invention can reach 15-20 m². 2 / g, with a high specific surface area.

[0068] Comparative Example 1

[0069] Referring to Example 3, the difference is that an existing specific surface area of ​​6.5m² is used. 2 Using existing iron phosphate at a speed of 14931 rpm, lithium iron phosphate precursor powder with a particle size of 31.4 μm was prepared.

[0070] Comparative Example 2

[0071] Referring to Example 3, the difference is that an existing specific surface area of ​​5.8m² is used. 2 Using existing iron phosphate at a speed of 15220 rpm, lithium iron phosphate precursor powder with a particle size of 28.2 μm was prepared.

[0072] Comparative Example 3

[0073] Referring to Example 3, the difference is that an existing specific surface area of ​​6.2 m² is used. 2 Using existing iron phosphate at a speed of 15530 rpm, lithium iron phosphate precursor powder with a particle size of 26.3 μm was prepared.

[0074] Comparative Example 4

[0075] Referring to Example 3, the difference is that an existing specific surface area of ​​7.6m² is used. 2 Using existing iron phosphate at a speed of 15672 rpm, lithium iron phosphate precursor powder with a particle size of 25.2 μm was prepared.

[0076] Performance testing

[0077] I. Preparation of Button Cells

[0078] 1. Preparation of conductive adhesive (NMP:PVDF:SP = 26.5:1:1). Weigh 159±0.005g NMP into a 500ml beaker, pre-stir at 850r / min, then add 6±0.003g PVDF, stir at 2000r / min until transparent and free of particles, then add 6±0.003g SP, and continue stirring for 30min. Add 5.7±0.001g conductive adhesive and 3.6±0.001g sample to a dispersion cup. Place the dispersion cup in a disperser and disperse according to the set dispersion parameters (850rm, 1min; 2000rm, 10min). Disperse the dispersed slurry evenly on the front end of the aluminum foil, set the dispersion thickness (250 micrometers), and begin coating. After coating, place it flat in a 100℃ forced-air drying oven and dry for 2 hours. Remove the electrode sheet from the oven and cool it to room temperature. Cut off a section of the electrode sheet and punch four electrode sheets using a slicing machine. Weigh the plates using a 1 / 100,000 balance. Select a region with uniform thickness and cut four electrode sheets with a width of 4-5 cm. Roll them using a roller press and measure the thickness of the rolled electrode sheets with a micrometer. Before using the punching machine, wipe the upper and lower punches, the feed trough, and other areas that come into contact with the electrode sheets with lint-free paper moistened with anhydrous ethanol. After wiping, punch 8-10 electrode sheets from each sample using the punching machine. Observe whether the edges of the electrode sheets are smooth and free of powder. The punching diameter is 14 mm.

[0079] 2. Vacuum drying. Place the weighed electrode sheets into a vacuum oven and press them down. Dry them at 105℃ and a vacuum of -90KPa for more than 4 hours.

[0080] 3. Pre-assembly preparation: Confirm the specifications of assembly auxiliary materials. Battery casing: CR2430; Electrolyte: FB097; Nickel foam thickness: 2.3mm; Separator diameter: 22mm; Lithium sheet: 0.5mm thick, 18mm diameter. Confirm glove box environmental conditions: Water content < 0.01ppm; Oxygen content < 0.01ppm.

[0081] 4. Polish the lithium sheet. Use a wool brush to polish the convex surface of the lithium sheet until smooth, and place the polished lithium sheet on a clean paper towel.

[0082] 5. Assembly. Place the negative electrode shell on a lint-free paper. Then place the nickel foam, flat side down and convex side up. Place the lithium sheet face up in the center of the nickel foam. Add a drop of electrolyte, place the separator, add another drop of electrolyte, then place the electrode plate, aluminum foil side up, and place the positive electrode shell. Use insulated tweezers to place the assembled battery into a sealing machine and seal it at a sealing pressure of 500 kg for 5 seconds. Carefully wipe the surface of the button cell with lint-free paper, and clamp the battery onto the battery holder in sequence, with the negative electrode facing up.

[0083] 6. After selecting the appropriate test method on the Blue Electric testing software, start the test and input the corresponding active material mass. Prepare coin cells A1-A6, corresponding to the lithium iron phosphate cathode materials prepared in Examples 1-6, respectively. B1-B4 correspond to the lithium iron phosphate cathode materials prepared in Comparative Examples 1-4, respectively.

[0084] II. Battery Performance Testing

[0085] The lithium-ion button batteries A1-A6 and B1-B4 prepared as described above were placed on a test cabinet and placed in a 25℃ constant temperature chamber. The test procedure was as follows: stand for 3 hours; charge at 0.1C until the voltage ≥ 3.75V; charge at 3.75V until the current ≤ 0.05mA; stand for 5 minutes; discharge at 0.1C until the voltage ≤ 2V. The initial discharge capacity of the batteries was recorded, and the specific capacity of the batteries was calculated according to the formula described below. The performance data of the finished batteries obtained from the test are shown in Table 2.

[0086] Specific capacity = initial discharge capacity of battery (mAh) / weight of positive electrode material (g).

[0087] Table 2. Performance of Finished Batteries and Usable Compacted Density of Positive Electrode Sheets

[0088] Example Battery number <![CDATA[Compaction density (g / cm 3 )]]> 0.1C discharge capacity (mAh / g) Example 1 A1 2.523 159.4 Example 2 A2 2.514 161.7 Example 3 A3 2.533 160.4 Example 4 A4 2.535 161.3 Example 5 A5 2.519 163.6 Example 6 A6 2.528 158.8 Comparative Example 1 B1 2.372 150.1 Comparative Example 2 B2 2.384 149.7 Comparative Example 3 B3 2.367 151.2 Comparative Example 4 B4 2.396 148.4

[0089] Analysis of the data in the table above shows that the initial discharge specific capacity and compaction density of coin cells (A1-A6) prepared using the high-compact-density lithium iron phosphate as the cathode nanoscale active material through the preparation method of this invention are significantly higher than those of the comparative examples (B1-B4). Therefore, coin cells made from the lithium iron phosphate nanoscale cathode material produced by the manufacturing method of this invention have higher compaction density and higher specific capacity.

Claims

1. A high-density, high-capacity lithium iron phosphate based on high specific surface area iron phosphate, characterized in that, This lithium iron phosphate is prepared by the following steps: (1) Add the iron source to the phosphorus source, stir to dissolve and filter to obtain the filtrate, add the oxidant to the filtrate to obtain the reaction solution; (2) Add a mixture of ferric phosphate dihydrate and ammonium dihydrogen phosphate to the reaction solution, stir and react at 150-200℃ for 3-5 hours. After filtration, drying and calcination, anhydrous ferric phosphate with a high specific surface area of ​​15-20 m² is obtained. 2 / g; wherein, the mass ratio of ferric phosphate dihydrate to the iron source is (0.1-10):100, and the mass ratio of ammonium dihydrogen phosphate to the iron source is (0.1-10):100; (3) A lithium source, anhydrous iron phosphate, carbon source and water are mixed, ground and then spray-dried to obtain a lithium iron phosphate precursor. The precursor is then roasted, crushed, sieved and demagnetized under a protective atmosphere to obtain high pressure density and high capacity lithium iron phosphate.

2. The high-density, high-capacity lithium iron phosphate based on high specific surface area iron phosphate according to claim 1, characterized in that, In step (1), the iron source is ferrous sulfate, ferrous nitrate or ferrous chloride; the phosphorus source is sodium dihydrogen phosphate, disodium hydrogen phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium phosphate, potassium phosphate or phosphoric acid; the molar ratio of ferrous ions in the iron source to phosphate ions in the phosphorus source is 1:(1.2-1.5).

3. The high-density, high-capacity lithium iron phosphate based on high specific surface area iron phosphate according to claim 1, characterized in that, In step (1), the amount of oxidant added is 1-3 times the molar ratio of the iron source, and the oxidant includes hydrogen peroxide, sodium hypochlorite, potassium hypochlorite, sodium chlorate or potassium chlorate.

4. The high-density, high-capacity lithium iron phosphate based on high specific surface area iron phosphate according to claim 1, characterized in that, In step (2), the drying temperature is 100-150℃.

5. The high-density, high-capacity lithium iron phosphate based on high specific surface area iron phosphate according to claim 1, characterized in that, In step (2), the calcination is carried out at 500-700℃ for 1-6 hours.

6. The high-density, high-capacity lithium iron phosphate based on high specific surface area iron phosphate according to claim 1, characterized in that, In step (3), the lithium source is lithium hydroxide, lithium chloride, lithium oxalate, lithium carbonate, lithium acetate or lithium nitrate; the carbon source is glucose, sucrose or citric acid.

7. The high-density, high-capacity lithium iron phosphate based on high specific surface area iron phosphate according to claim 1, characterized in that, In step (3), the molar ratio of lithium ions to iron ions in the lithium source and iron phosphate is 1:(1-1.05), and the amount of carbon source added accounts for 13-16% of the mass of the iron phosphate precursor.

8. The high-density, high-capacity lithium iron phosphate based on high specific surface area iron phosphate according to claim 1, characterized in that, In step (3), the spray-dried particle size D50 is 35-40 μm.

9. The high-density, high-capacity lithium iron phosphate based on high specific surface area iron phosphate according to claim 1, characterized in that, In step (3), the calcination is carried out at 745-780℃ for 8-12 hours, and the heating rate of the calcination is 5-20℃ / min.

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