CN106315537A - Preparation method of lithium iron phosphate powder - Google Patents

Abstract

A preparation method of lithium iron phosphate, first, the first step: preparation of Li ₂ O-P ₂ O ₅ binary system glass; second step: Li ₂ O-FeO-P ₂ O ₅ ternary system matrix crystallite Preparation of glass; the third step: preparation of LiFePO ₄ powder; the present invention utilizes the method of secondary high-temperature melting and casting to prepare conductive lithium iron phosphate powder, which makes up for the poor electrical conductivity of lithium iron phosphate produced by other processes and the difficulty of industrialization Disadvantages: The lithium iron phosphate powder obtained by the preparation method of the present invention has excellent electrical conductivity, uniform particle size distribution and high crystal purity, and can be used as an excellent lithium ion battery material.

Description

A kind of preparation method of lithium iron phosphate powder

technical field

The invention relates to a method for manufacturing lithium iron phosphate, in particular to a method for preparing lithium iron phosphate powder with conductive function.

Background technique

Lithium iron phosphate has many advantages such as long cycle life, high thermal stability, environmental protection and non-toxicity, and is expected to become an ideal cathode material for the next generation of lithium-ion batteries, especially power batteries. new breakthrough.

Tang Zhiyuan et al. (Tang Zhiyuan, Gao Fei, Xue Jianjun, etc. Preparation and electrochemical performance of lithium-ion battery cathode material LiFePO ₄ [J]. Journal of Tianjin University, 2007, 40 (4): 468-472.) by adding sulfur Mix ferric acid Fe(NH ₄ ) ₂ (SO ₄ ) ₂ ·6H ₂ O with ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ) at a molar ratio of 1:1, dissolve in deionized water, and then add H ₂ O _2. React at 95°C to prepare the precursor of FePO ₄ , then mix it with Li ₂ CO ₃ , calcinate at 600°C for 12 hours, cool and grind to obtain the final product LiFePO ₄ . This method has simple process, easy control of process conditions and easy industrialization, but the product has uneven particle size, wide particle size distribution, irregular crystal shape and long production cycle.

Qu Tao et al. (Qu Tao, Tian Yanwen, Zhong Canyun et al. Preparation of lithium-ion battery cathode material LiFePO ₄ by carbon doping [J]. Materials Herald, 2007, 21(4): 37-41.) synthesized by solid phase method LiFePO ₄ and carbon-doped LiFePO ₄ , and studied the influence of different carbon doping amounts on the electrical properties of LiFePO ₄ materials. The results show that: with the increase of carbon doping, the initial discharge capacity of the obtained samples increases, and when the carbon content is 8.5%, the LiFePO ₄ positive electrode material has the largest initial discharge specific capacity

Li Faxi et al. (Li Faxi, Qiu Weihua, Hu Huanyu, etc. Electrochemical properties of LiFePO ₄ as a cathode material for lithium batteries synthesized by microwave[J]. Research and Design, 2005,29(6):346-348.) used Li ₂ CO ₃ , FeC ₂ O ₄ ·2H ₂ O and NH ₄ H ₂ PO ₄ were used as raw materials, dispersed with acetone, ball milled, briquetted, put into a covered crucible with activated carbon, and heated in a household microwave oven to obtain a LiFePO ₄ sample. This method has simple experimental operation and short synthesis cycle, but it is not suitable for industrial mass production.

Zhang Junling (Zhang Junling. Morphology control of hydrothermally synthesized lithium iron phosphate powder[J]. Chemical New Materials, 2008,36(6):74-75.) Under the protection of N ₂ , H ₃ PO ₄ and Fe SO _4. The solution was moved into an autoclave for stirring, LiOH was added at a set temperature, the autoclave was sealed, and the reaction was carried out at 180° C. for 4 h. The resulting sample was then dried at 120 °C for 2 h and calcined at 600 °C for ₂ h to obtain LiFePO4 material. This method has simple operation process, small product particle size, single and uniform phase, but it is only suitable for preparing a small amount of powder, which is not conducive to large-scale industrial production.

Wang Rui et al. (Wang Rui, Yang Duanfeng. Preparation and electrochemical performance of LiFePO ₄ [J]. Chemical Engineers, 2009, 165(6): 24-26.) used citric acid, ethylenediaminetetraacetic acid (EDTA) and Oxalic acid was used as complexing agent to prepare lithium iron phosphate material by sol-gel method. First, dissolve the complexing agent in water, stir and add Fe(NO ₃ ) ₃ 9H ₂ O to dissolve, then dissolve in LiOH H ₂ O and NH ₄ H ₂ PO ₄ in turn, adjust the pH value to 8.5-9.5, at 60- The solvent was evaporated at 80°C to obtain a gel, dried to obtain a powdery precursor, then heat-treated under nitrogen protection, and cooled to obtain a lithium iron phosphate material. The product has the advantages of small particle size, narrow particle size distribution, easy control, good powder sintering performance, good chemical uniformity, low heat treatment temperature, simple equipment operation, etc., but the drying shrinkage is relatively large, the synthesis cycle is long, and the preparation process is complicated. , not easy to industrialized large-scale production.

Yang Rong et al. (Yang Rong, Zhao Mingshu, Du Baozhong, etc. Study on preparation of cathode material Li Fe PO ₄ by co-precipitation method[J]. Rare Metal Materials and Engineering, 2007,36(2):631-634.) Will (NH ₄ ) ₂ Fe(SO ₄ ) ₂ and (NH ₄ ) ₂ HPO ₄ solutions were mixed, an appropriate amount of ascorbic acid and a certain amount of LiOH solution were added, the pH value was adjusted with ammonia water, stirred for 4-6 hours, and then obtained by suction filtration to obtain lithium iron phosphate The body was calcined at 550°C for 12 hours under an argon atmosphere to obtain a lithium iron phosphate sample. The same method can be used to prepare Co ²⁺ -doped lithium iron phosphate materials with more excellent properties. The preparation process is simple, the synthesis temperature of the precursor is low, and it is easy to industrialize large-scale production, but the raw materials are difficult to obtain, the reaction is difficult to complete, and the reaction cycle is long.

Chen Zhaoyong et al. (Chen Zhaoyong, Zhu Huahua. Preparation and properties of LiFePO ₄ /C composites[J]. Journal of Changsha University of Science and Technology, 2007,4(2):84-88.) prepared LiFePO ₄ by sol-gel method /C composite materials, and using acetylene black, sucrose and glucose as carbon sources respectively, their first discharge specific capacities at 0.1C rate were measured to be 120, 135, 162mAh/g respectively, among which Li The Fe PO ₄ /C composite material has the most excellent high-current charge-discharge performance, and the first discharge specific capacity at 1C and 3C high rate is 90% and 80% of the discharge specific capacity at 0.1C rate, respectively.

Tan Xianyan et al. (Tan Xianyan, Hu Guorong, Gao Xuguang et al. Study on the electrochemical performance of Mg-doped LiFePO ₄ [J]. Battery, 2004,34(5):344-345.) prepared Mg ²⁺ doped LiFePO ₄ material electrochemical performance. The results show that the crystal structure of LiFePO4 doped with Mg ²⁺ does not change, but it has better electrochemical performance than the LiFePO ₄ material without Mg ²⁺ . Doping conductive substances or high-valent metal ions can improve the discharge specific capacity of lithium iron phosphate cathode materials, but this is at the expense of material volume, which hinders the miniaturization process of lithium-ion batteries to a certain extent.

KeitaH et al. (KeitaH, Tsuyoshi H, Yasuhiko B, et al.Glass-ceramics withLiFePO ₄ crystals and crystal line tterning in glass by YAG aser rradition[J].Solid State Ionics,2007,178(11-12):801-807 .) First, mix raw materials such as Li ₂ CO ₃ , FeC ₂ O ₄ 2H ₂ O, Nb ₂ O ₅ and NH ₄ H ₂ PO ₄ , heat to 300°C for 10h under the protection of nitrogen, and then melt at 1200°C 26Li ₂ O-43Fe O-5Nb ₂ O ₅ -26P ₂ O ₅ (mole percent) glass is obtained, and finally the lithium iron phosphate glass is crystallized by two different processes, one is the traditional heat treatment method, the other is One is to use the continuous radiation wave with a wavelength of 1064nm of the yttrium aluminum garnet laser to crystallize the surface of lithium iron phosphate glass. According to XRD analysis, only LiFePO ₄ crystals are precipitated in the samples obtained by the two methods, but the conductivity of LiFePO ₄ glass needs to be improved.

Jozwiak P et al. (Jozwiak P, Garbarczyk JE, Gendron F, et al. Disorder in LixFePO4: From glasses to nanocrystallites [J]. Journal of Non-Crystalline Solids, 2008, 354 (17): 1915-1925.) Li ₂ CO ₃ (LiOH·H ₂ O), H ₄ ) ₂ HPO ₄ (NH ₄ H ₂ PO ₄ ), Fe ₂ O ₃ and other raw materials were mixed evenly, and melted at 1270°C for 1 hour to obtain LixFe PO ₄ (x=0—1) glass , and then heat-treated the resulting glass at 450°C to obtain a crystallized glass whose main crystal phases are LiFePO ₄ and FePO ₄ .

Lee SB et al. (Lee SB, Cho SH, Cho SJ, et al. Synthesis of LiFePO4Material with Improved Cycling Performance Under Harsh Conditions [J]. Electrochemistry Communications, 2008, 10:1219-1221.) Soluble ferrous salt LiOH and H ₃ LiFePO ₄ was synthesized using PO ₄ as a raw material in a short period of time by hydrothermal method at 120°C. XRD analysis and oxidation-reduction titration results showed that the synthesized material was a single LiFePO ₄ phase with an average particle size of about 3 μm. The material is charged and discharged at a current density of 0.14m A·cm-2, and the gram capacitance is 100mAh·g-1. This method uses lithium hydroxide (LiOH) as a precipitating agent and needs to consume 200% more LiOH, which increases the cost of raw materials.

In recent years, with further research and development on the application of lithium iron phosphate, it has been found that lithium iron phosphate has complex processes and extremely low conductivity in terms of raw material cost, preparation process, preparation time, volume, density, and electrical conductivity. The disadvantage of slow ion diffusion coefficient makes it difficult to realize large-scale industrial production. How to prepare low-cost, convenient operation, environmental protection, and large-scale industrial production is an urgent problem to be solved in the production of lithium iron phosphate.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art, and provide a conductive phosphoric acid with low raw material cost, simple preparation process, stable phosphorus content in the raw material, excellent electrical properties, convenient operation, environmental protection and non-toxicity, and suitable for mass production According to the method for preparing lithium iron powder, the lithium iron phosphate prepared according to the method of the invention has excellent electrical conductivity, uniform powder particle size, high crystal purity, and small impurity content, and can be used as a high-performance battery material with high energy density.

In order to achieve the above object, the technical scheme adopted in the present invention is:

Step 1: Preparation of Li ₂ OP ₂ O ₅ binary system glass

1) First, Li ₂ O and P ₂ O ₅ are mixed at a molar ratio of 1:1 until the uniformity is greater than 98%, to obtain a uniformly mixed batch;

2) Next, add the batch material into the platinum crucible that has been heated to 850-900°C, and melt for 30-60 minutes;

3) Then, use a platinum stirring paddle to stir the molten glass melt for 10-30 minutes, and then keep it warm at 850-900°C for 10-20 minutes;

4) Then, pour the molten glass melt rapidly into a rolling mill with water-cooled double rollers, and rapidly cool and roll it into Li ₂ OP ₂ O ₅ binary system glass shards with a size of 1-3mm;

5) Finally, after collecting the rolled glass shards, put them into a ball mill jar and mill them into powders of 50-80 meshes to obtain Li ₂ OP ₂ O ₅ binary system glass powder;

The second step: preparation of Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics

1) First, according to the molar ratio of FeO: Li ₂ O = 2: 1, mix FeO and Li ₂ OP ₂ O ₅ binary system glass powder evenly to obtain batch materials;

2) Then, add iron filings with a mass of 0.1 to 0.01% of the batch to the batch and pass through a 50-mesh standard sieve to obtain a uniform batch;

3) Then, add the batch material into the corundum crucible with a cover that has been heated to 950-1050°C, and melt for 30-60 minutes;

4) Then, the molten glass melt is quickly poured into a rolling mill with water-cooled double rollers, and rapidly cooled and rolled into 1-3mm Li ₂ O-FeO-P ₂ O ₅ ternary system parent glass-ceramic fragments ;

5) Finally, after collecting the rolled glass shards, put them into a polyurethane ball mill jar and grind them into powders with a mesh size of 300-500 meshes to obtain Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics powder;

The third step: preparation of LiFePO ₄ powder

1) First, mix 10-25% glucose with 75-90% Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramic powder according to the mass fraction to obtain a mixture, and then add 10-10% of the mixture mass to it. 30% deionized water, and then put it into a ball mill for 15-30 minutes;

2) Then, air-dry the mixture after ball milling into powder;

3) Finally, put the dry powder into a graphite crucible, raise the temperature to 750-850°C at a heating rate of 5-10°C/min in an atmosphere furnace filled with hydrogen and nitrogen, keep it warm for 2-4 hours, and then With a cooling rate of 10-20°C/min, the temperature is lowered from 750-850°C to below 40°C to obtain lithium iron phosphate powder.

The Li ₂ O is introduced by analytically pure lithium carbonate; the P ₂ O ₅ is introduced by analytically pure phosphorus pentoxide, or (NH ₄ ) ₂ HPO ₄ or (NH ₄ )H ₂ PO ₄ ; the Said FeO is introduced from analytically pure ferrous oxide; said iron powder is introduced from analytically pure iron filings; said glucose is introduced from analytically pure glucose; said ratio of hydrogen and nitrogen is 5:95.

The invention uses the method of secondary high-temperature melting and casting to prepare conductive lithium iron phosphate powder, which makes up for the shortcomings of poor electrical conductivity and difficult industrialization of lithium iron phosphate produced by other processes. The lithium iron phosphate powder obtained according to the preparation method of the invention has excellent electrical conductivity, uniform particle size distribution and high crystal purity, and can be used as an excellent lithium ion battery material.

Description of drawings

Fig. 1 is the diffraction photograph that the lithium iron phosphate powder that makes according to the preparation method of the present invention detects in X-ray diffractometer, and wherein abscissa is diffraction angle 2θ/(°), and ordinate is diffraction intensity.

detailed description

Example 1

Step 1: Preparation of Li ₂ OP ₂ O ₅ binary system glass

1) First, Li ₂ O and P ₂ O ₅ are mixed at a molar ratio of 1:1 until the uniformity is greater than 98%, to obtain a uniformly mixed batch;

2) Next, add the batch material into the platinum crucible that has been heated to 850°C, and melt for 40 minutes;

3) Then, use a platinum stirring paddle to stir the molten glass melt for 20 minutes, and then keep it at 850° C. for 13 minutes;

4) Then, pour the molten glass melt rapidly into a rolling mill with water-cooled _double rollers, and make it into _Li2OP2O5 binary system glass fragments with a size of 1.6mm through rapid cooling and rolling _;

5) Finally, after collecting the rolled glass shards, put them into a ball mill jar and mill them into powders of 50-80 meshes to obtain Li ₂ OP ₂ O ₅ binary system glass powder;

The second step: preparation of Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics

1) First, according to the molar ratio of FeO: Li ₂ O = 2: 1, mix FeO and Li ₂ OP ₂ O ₅ binary system glass powder evenly to obtain batch materials;

2) Then, after adding the iron filings of batch quality 0.03% in the batch, cross 50 mesh standard sieves to obtain a uniform batch;

3) Then, add the batch material into the corundum crucible with a cover that has been heated to 1000°C, and melt for 55 minutes;

4) Then, pour the molten glass melt rapidly into a rolling mill with water-cooled double rollers, and rapidly cool and roll it into 2.4mm _Li2O -FeO _{- P2O5} ternary system parent glass-ceramic fragments;

5) Finally, after collecting the rolled glass shards, put them into a polyurethane ball mill jar and grind them into powders with a mesh size of 300-500 meshes to obtain Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics powder;

The third step: preparation of LiFePO ₄ powder

1) First, mix 13% glucose with 87% Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramic powder according to the mass fraction to obtain a mixture, and then add 21% deionized water of the mixture mass , and then put it into a ball mill for ball milling for 20 minutes;

2) Then, air-dry the mixture after ball milling into powder;

3) Finally, put the dried powder into a graphite crucible, and raise the temperature to 850°C at a heating rate of 8°C/min in an atmosphere furnace with a volume ratio of hydrogen and nitrogen of 5:95, keep it for 3 hours, and then Cool down from 850°C to below 40°C at a cooling rate of 12°C/min to obtain lithium iron phosphate powder.

Referring to accompanying drawing 1, it can be seen that the prepared crystal is LiFePO ₄ crystal with higher purity.

Example 2

Step 1: Preparation of Li ₂ OP ₂ O ₅ binary system glass

1) First, Li ₂ O and P ₂ O ₅ are mixed at a molar ratio of 1:1 until the uniformity is greater than 98%, to obtain a uniformly mixed batch;

2) Next, add the batch material into the platinum crucible that has been heated to 870°C, and melt for 50 minutes;

3) Then, use a platinum stirring paddle to stir the molten glass melt for 15 minutes, and then keep it at 870° C. for 19 minutes;

4) Then, the molten glass melt is poured rapidly into a rolling mill with water-cooled double rollers, and is rapidly cooled and rolled into Li ₂ OP ₂ O ₅ binary system glass shards with a size of 3 mm;

5) Finally, after collecting the rolled glass shards, put them into a ball mill jar and grind them into powders of 50-80 meshes to obtain Li ₂ OP ₂ O ₅ binary system glass powder;

The second step: preparation of Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics

1) First, according to the molar ratio of FeO: Li ₂ O = 2: 1, mix FeO and Li ₂ OP ₂ O ₅ binary system glass powder evenly to obtain batch materials;

2) Then, after adding the iron filings of batch quality 0.07% in the batch, cross the 50 mesh standard sieve to get the batch that mixes homogeneously;

3) Then, add the batch material into the corundum crucible with a cover that has been heated to 1040°C, and melt for 35 minutes;

4) Then, pour the molten glass melt rapidly into a rolling mill with water-cooled double rollers, and quickly cool and roll it into 1.6mm _Li2O -FeO _{- P2O5} ternary system parent glass-ceramic fragments;

5) Finally, after collecting the rolled glass shards, put them into a polyurethane ball mill jar and grind them into powders with a mesh size of 300-500 meshes to obtain Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics powder;

The third step: preparation of LiFePO ₄ powder

1) First, mix 21% glucose with 79% Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramic powder according to the mass fraction to obtain a mixture, and then add 16% deionized water to the mixture , and then put it into a ball mill for ball milling for 15 minutes;

2) Then, air-dry the mixture after ball milling into powder;

3) Finally, put the dry powder into a graphite crucible, and raise the temperature to 780°C at a heating rate of 6°C/min in an atmosphere furnace with a volume ratio of hydrogen and nitrogen of 5:95, and keep it warm for 2.5h. Then, at a cooling rate of 15°C/min, the temperature was lowered from 780°C to below 40°C to obtain lithium iron phosphate powder.

Example 3

Step 1: Preparation of Li ₂ OP ₂ O ₅ binary system glass

1) First, Li ₂ O and P ₂ O ₅ are mixed at a molar ratio of 1:1 until the uniformity is greater than 98%, to obtain a uniformly mixed batch;

2) Next, add the batch material into the platinum crucible that has been heated to 890°C, and melt for 30 minutes;

3) Then, use a platinum stirring paddle to stir the molten glass melt for 28 minutes, and then keep it at 890°C for 20 minutes;

4) Then, pour the molten glass melt rapidly into a rolling mill with water-cooled double rollers, and quickly cool and roll it into Li ₂ OP ₂ O ₅ binary system glass shards with a size of 2.4 mm;

5) Finally, after collecting the rolled glass shards, put them into a ball mill jar and mill them into powders of 50-80 meshes to obtain Li ₂ OP ₂ O ₅ binary system glass powder;

The second step: preparation of Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics

1) First, according to the molar ratio of FeO: Li ₂ O = 2: 1, mix FeO and Li ₂ OP ₂ O ₅ binary system glass powder evenly to obtain batch materials;

2) Then, after adding the iron filings of batch quality 0.05% in the batch, cross the 50 mesh standard sieve to obtain a uniform batch;

3) Then, add the batch material into the corundum crucible with a cover that has been heated to 980°C, and melt for 45 minutes;

4) Then, pour the molten glass melt rapidly into a rolling mill with water-cooled double rollers, and quickly cool and roll it into 1.9mm _Li2O -FeO _{- P2O5} ternary system parent glass-ceramic fragments;

5) Finally, after collecting the rolled glass shards, put them into a polyurethane ball mill jar and grind them into powders with a mesh size of 300-500 meshes to obtain Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics powder;

The third step: preparation of LiFePO ₄ powder

1) First, mix 17% glucose with 83% Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramic powder according to the mass fraction to obtain a mixture, and then add 30% deionized water of the mixture mass , and then put it into a ball mill for ball milling for 23 minutes;

2) Then, air-dry the mixture after ball milling into powder;

3) Finally, put the dried powder into a graphite crucible, and raise the temperature to 820°C at a heating rate of 9°C/min in an atmosphere furnace with a volume ratio of hydrogen and nitrogen of 5:95, and keep it warm for 3.5h. Then, at a cooling rate of 10°C/min, the temperature was lowered from 820°C to below 40°C to obtain lithium iron phosphate powder.

Example 4

Step 1: Preparation of Li ₂ OP ₂ O ₅ binary system glass

1) First, Li ₂ O and P ₂ O ₅ are mixed at a molar ratio of 1:1 until the uniformity is greater than 98%, to obtain a uniformly mixed batch;

2) Next, add the batch material into the platinum crucible that has been heated to 880°C, and melt for 35 minutes;

3) Then, use a platinum stirring paddle to stir the molten glass melt for 10 minutes, and then keep it at 880° C. for 17 minutes;

4) Then, pour the molten glass melt rapidly into a rolling mill with water _- cooled _double rollers, and make _Li2OP2O5 binary system glass shards with a size of 1mm through rapid cooling and rolling;

5) Finally, after collecting the rolled glass shards, put them into a ball mill jar and mill them into powders of 50-80 meshes to obtain Li ₂ OP ₂ O ₅ binary system glass powder;

The second step: preparation of Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics

1) First, according to the molar ratio of FeO: Li ₂ O = 2: 1, mix FeO and Li ₂ OP ₂ O ₅ binary system glass powder evenly to obtain batch materials;

2) Then, after adding iron filings of 0.01% of the batch quality in the batch, cross a 50-mesh standard sieve to obtain a uniform batch;

3) Then, add the batch material into a corundum crucible with a cover that has been heated to 1050°C, and melt for 50 minutes;

4) Then, pour the molten glass melt rapidly into a rolling mill with water-cooled double rollers, and rapidly cool and roll it into 3mm _Li2O -FeO _{- P2O5} ternary system parent glass-ceramic fragments;

5) Finally, after collecting the rolled glass shards, put them into a polyurethane ball mill jar and grind them into powders with a mesh size of 300-500 meshes to obtain Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics powder;

The third step: preparation of LiFePO ₄ powder

1) First, mix 25% glucose with 75% Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramic powder according to the mass fraction to obtain a mixture, and then add 10% deionized water of the mixture mass , and then put it into a ball mill for 30 minutes;

2) Then, air-dry the mixture after ball milling into powder;

3) Finally, put the dry powder into a graphite crucible, and raise the temperature to 800°C at a heating rate of 10°C/min in an atmosphere furnace with a volume ratio of hydrogen and nitrogen of 5:95, keep it for 2 hours, and then Cool down from 800°C to below 40°C at a cooling rate of 17°C/min to obtain lithium iron phosphate powder.

Example 5

Step 1: Preparation of Li ₂ OP ₂ O ₅ binary system glass

1) First, Li ₂ O and P ₂ O ₅ are mixed at a molar ratio of 1:1 until the uniformity is greater than 98%, to obtain a uniformly mixed batch;

2) Next, add the batch material into the platinum crucible that has been heated to 900°C, and melt for 55 minutes;

3) Then, use a platinum stirring paddle to stir the molten glass melt for 25 minutes, and then keep it at 900°C for 15 minutes;

4) Then, the molten glass melt is poured rapidly into a rolling mill with water-cooled double rollers, and is rapidly cooled and rolled into Li ₂ OP ₂ O ₅ binary system glass fragments with a size of 2.1 mm;

5) Finally, after collecting the rolled glass shards, put them into a ball mill jar and mill them into powders of 50-80 meshes to obtain Li ₂ OP ₂ O ₅ binary system glass powder;

The second step: preparation of Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics

1) First, according to the molar ratio of FeO: Li ₂ O = 2: 1, mix FeO and Li ₂ OP ₂ O ₅ binary system glass powder evenly to obtain batch materials;

2) Then, after adding iron filings of 0.1% of the batch quality in the batch, cross a 50-mesh standard sieve to obtain a uniform batch;

3) Then, add the batch material into a corundum crucible with a cover that has been heated to 1020°C, and melt for 60 minutes;

4) Then, pour the molten glass melt rapidly into a rolling mill with water-cooled double rollers, and quickly cool and roll it into 1mm _Li2O -FeO _{- P2O5} ternary system parent glass-ceramic fragments;

5) Finally, after collecting the rolled glass shards, put them into a polyurethane ball mill jar and grind them into powders with a mesh size of 300-500 meshes to obtain Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics powder;

The third step: preparation of LiFePO ₄ powder

1) First, mix 19% glucose with 81% Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramic powder according to the mass fraction to obtain a mixture, and then add 24% deionized water of the mixture mass , and then put it into a ball mill for ball milling for 17 minutes;

2) Then, air-dry the mixture after ball milling into powder;

3) Finally, put the dried powder into a graphite crucible, and raise the temperature to 760°C at a heating rate of 7°C/min in an atmosphere furnace with a volume ratio of hydrogen and nitrogen of 5:95, keep it for 3 hours, and then At a cooling rate of 13°C/min, the temperature was lowered from 760°C to below 40°C to obtain lithium iron phosphate powder.

Example 6

Step 1: Preparation of Li ₂ OP ₂ O ₅ binary system glass

1) First, Li ₂ O and P ₂ O ₅ are mixed at a molar ratio of 1:1 until the uniformity is greater than 98%, to obtain a uniformly mixed batch;

2) Next, add the batch material into the platinum crucible that has been heated to 860°C, and melt for 60 minutes;

3) Then, use a platinum stirring paddle to stir the molten glass melt for 30 minutes, and then keep it at 860°C for 10 minutes;

4) Then, the molten glass melt is poured rapidly into a rolling mill with water-cooled double rollers, and is rapidly cooled and rolled into Li ₂ OP ₂ O ₅ binary system glass shards with a size of 1.9 mm;

5) Finally, after collecting the rolled glass shards, put them into a ball mill jar and mill them into powders of 50-80 meshes to obtain Li ₂ OP ₂ O ₅ binary system glass powder;

The second step: preparation of Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics

1) First, according to the molar ratio of FeO: Li ₂ O = 2: 1, mix FeO and Li ₂ OP ₂ O ₅ binary system glass powder evenly to obtain batch materials;

2) Then, after adding the iron filings of batch quality 0.09% in the batch, cross the 50 mesh standard sieve to get the batch that mixes evenly;

3) Then, add the batch material into the corundum crucible with a cover that has been heated to 950°C, and melt for 40 minutes;

4) Then, pour the molten glass melt rapidly into a rolling mill with water-cooled double rollers, and quickly cool and roll it into 2.1mm _Li2O -FeO _{- P2O5} ternary system parent glass-ceramic fragments;

5) Finally, after collecting the rolled glass shards, put them into a polyurethane ball mill jar and grind them into powders with a mesh size of 300-500 meshes to obtain Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics powder;

The third step: preparation of LiFePO ₄ powder

1) First, mix 10% glucose with 90% Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramic powder according to the mass fraction to obtain a mixture, and then add 19% deionized water to the mixture , and then put it into a ball mill for ball milling for 26 minutes;

2) Then, air-dry the mixture after ball milling into powder;

3) Finally, put the dry powder into a graphite crucible, and raise the temperature to 750°C at a heating rate of 5°C/min in an atmosphere furnace with a volume ratio of hydrogen and nitrogen of 5:95, keep it for 4 hours, and then Cool down from 750°C to below 40°C at a cooling rate of 20°C/min to obtain lithium iron phosphate powder.

Li ₂ O of the present invention is introduced by analytically pure lithium carbonate; P ₂ O ₅ is introduced by analytically pure phosphorus pentoxide, (NH ₄ ) ₂ HPO ₄ or (NH ₄ )H ₂ PO ₄ ; FeO is introduced by analytically pure Ferrous oxide is introduced; iron powder is introduced by analytically pure iron filings; glucose is introduced by analytically pure glucose.

The invention uses the method of secondary high-temperature melting and casting to prepare lithium iron phosphate, which makes up for the shortcomings of poor electrical conductivity and difficult industrialization of lithium iron phosphate produced by other processes. The performance of lithium iron phosphate and the capacity per unit volume are increased. The lithium iron phosphate prepared by the invention may realize large-scale industrial production. The lithium iron phosphate prepared by the invention has good uniformity, low energy consumption, energy saving and environmental protection.

Claims (7)

1. A preparation method for lithium iron phosphate powder, characterized in that: Step 1: Preparation of Li ₂ OP ₂ O ₅ binary system glass 1) First, Li ₂ O and P ₂ O ₅ are mixed at a molar ratio of 1:1 until the uniformity is greater than 98%, to obtain a uniformly mixed batch; 2) Next, add the batch material into the platinum crucible that has been heated to 850-900°C, and melt for 30-60 minutes; 3) Then, use a platinum stirring paddle to stir the molten glass melt for 10-30 minutes, and then keep it warm at 850-900°C for 10-20 minutes; 4) Then, pour the molten glass melt rapidly into a rolling mill with water-cooled double rollers, and rapidly cool and roll it into Li ₂ OP ₂ O ₅ binary system glass shards with a size of 1-3mm; 5) Finally, after collecting the rolled glass shards, put them into a ball mill jar and mill them into powders of 50-80 meshes to obtain Li ₂ OP ₂ O ₅ binary system glass powder; The second step: preparation of Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics 1) First, according to the molar ratio of FeO: Li ₂ O = 2: 1, mix FeO and Li ₂ OP ₂ O ₅ binary system glass powder evenly to obtain batch materials; 2) Then, add iron filings with a mass of 0.1 to 0.01% of the batch to the batch and pass through a 50-mesh standard sieve to obtain a uniform batch; 3) Then, add the batch material into the corundum crucible with a cover that has been heated to 950-1050°C, and melt for 30-60 minutes; 4) Then, the molten glass melt is quickly poured into a rolling mill with water-cooled double rollers, and rapidly cooled and rolled into 1-3mm Li ₂ O-FeO-P ₂ O ₅ ternary system parent glass-ceramic fragments ; 5) Finally, after collecting the rolled glass shards, put them into a polyurethane ball mill jar and grind them into powders with a mesh size of 300-500 meshes to obtain Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramics powder; The third step: preparation of LiFePO ₄ powder 1) First, mix 10-25% glucose with 75-90% Li ₂ O-FeO-P ₂ O ₅ ternary system matrix glass-ceramic powder according to the mass fraction to obtain a mixture, and then add 10-10% of the mixture mass to it. 30% deionized water, and then put it into a ball mill for 15-30 minutes; 2) Then, air-dry the mixture after ball milling into powder; 3) Finally, put the dry powder into a graphite crucible, raise the temperature to 750-850°C at a heating rate of 5-10°C/min in an atmosphere furnace filled with hydrogen and nitrogen, keep it warm for 2-4 hours, and then With a cooling rate of 10-20°C/min, the temperature is lowered from 750-850°C to below 40°C to obtain lithium iron phosphate powder. 2. The preparation method of lithium iron phosphate powder according to claim 1, characterized in that: said _Li2O is introduced from analytically pure lithium carbonate. 3. The preparation method of lithium iron phosphate powder according to claim 1, characterized in that: said P ₂ O ₅ is composed of analytically pure phosphorus pentoxide, (NH ₄ ) ₂ HPO ₄ or (NH ₄ ) _H2PO4 introduced _. 4. The preparation method of lithium iron phosphate powder according to claim 1, characterized in that: the FeO is introduced from analytically pure ferrous oxide. 5. The preparation method of lithium iron phosphate powder according to claim 1, characterized in that: the iron powder is introduced from analytically pure iron filings. 6. The preparation method of lithium iron phosphate powder according to claim 1, characterized in that: the glucose is introduced from analytically pure glucose. 7. The method for preparing lithium iron phosphate powder according to claim 1, characterized in that: the volume ratio of hydrogen and nitrogen is 5:95.