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Hydro-thermal synthesis method for nano LiFePo4

A lithium iron phosphate, hydrothermal synthesis technology, applied in phosphorus compounds, chemical instruments and methods, inorganic chemistry, etc., can solve problems such as shortening crystal nucleation and growth time, and achieve good batch stability, electrical conductivity and rate. The effect of improved performance and simplified control difficulty

Active Publication Date: 2015-11-18
HEBEI UNIV OF TECH
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  • Abstract
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AI Technical Summary

Problems solved by technology

[0003] The technical problem to be solved by the present invention is to provide a method for hydrothermally synthesizing nanoscale lithium iron phosphate, by controlling the temperature rise rate, an important process parameter that affects the growth of lithium iron phosphate crystals, and using direct steam heating to overcome the indirect heating effect. For the problem of heat transfer area limitation, control the temperature rise rate of the reaction system within the range of 4-8°C / min, shorten the nucleation and growth time of crystals in the low temperature section, and make them nucleate and grow at higher temperatures to reach the crystal particle size. The purpose of fineness and high sphericity is to realize the control of product morphology and particle size, so as to improve the electrochemical performance, rate performance and packing density of the product

Method used

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  • Hydro-thermal synthesis method for nano LiFePo4
  • Hydro-thermal synthesis method for nano LiFePo4

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0024] The first step, hydrothermal synthesis reaction

[0025] Will contain 223.4gFe 2+ (i.e. 4mol) pure ferrous sulfate solution diluted 3.5L (the pH value of this solution is about 1); Dilute 461.2g85% phosphoric acid containing pure phosphoric acid to 1L; 2 O was dissolved in water and diluted to 3L.

[0026] Add all the above-mentioned lithium hydroxide solution and phosphoric acid solution into a 10L autoclave with a sealed feeding tube and a heat exchange coil, after purging the air in the dead volume in the autoclave with an inert gas, seal the autoclave, start stirring, and the rotation speed is 200rpm, Heat from room temperature to 40°C, open the feed valve and exhaust valve, add all of the above-mentioned ferrous sulfate solution, feed for 30 minutes, close the feed valve to seal the autoclave after the feed is complete and continue to stir for 20 minutes.

[0027] Introduce 200°C steam into the reactor, so that the temperature in the reactor rises from 40°C to 16...

Embodiment 2

[0035] The time required for the reactants in Example 1 to be raised from the mixed temperature of 40° C. to 160° C. was changed to 15 minutes (the heating rate was 8° C. / min), and the others were the same as in Example 1.

[0036] After the synthesis is completed, filter, wash, and vacuum-dry the filter cake at 120°C to constant weight to obtain 624g LiFePO 4 Off-white powder.

[0037] The particle morphology of the product is rod-shaped and spherical particles with unclear edges and corners, the minimum dimension of the particles is about 100 nanometers, and there is basically no agglomeration between the particles. The electrochemical performance test results are shown in Table 1. figure 1 b is a scanning electron micrograph of the sample obtained in this example. Compare figure 1 a and figure 1 b It can be seen that when the heating rate is greater than 4 °C / min, the morphology and particle size of the sample basically do not change.

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Abstract

The invention provides a hydro-thermal synthesis method for nano LiFePo4. The method comprises the following steps: step 1, a lithium hydroxide solution and phosphoric acid are added to an autoclave, an iron source solution is then added, and a reaction system is heated to 150-170 DEG C from 40 DEG C at the speed of 4-8 DEG C / min; step 2, heat is preserved for 2 h at the temperature of 150-170 DEG C and reduced to 70-80 DEG C, a filter cake and mother liquor are obtained through filtering, the filter cake is washed and dried in vacuum, and grey white LiFePo4 powder is obtained; step 3, the LiFePo4 powder obtained in the step 2 and a carbon source are mixed uniformly in the mass ratio being 100: (15-20), the mixture is roasted for 4 h at 700 DEG C with inert gas shielding, and a carbon coated LiFePo4 product is obtained. The high-rate discharge ability of the product is improved, the capacity cycling retention rate of the product is increased, equipment investment is little, the process is simple and controllable, and the batch stability of the product is good.

Description

technical field [0001] The invention belongs to the technical field of energy material preparation. In particular, it relates to the synthesis of nanostructured lithium iron phosphate by hydrothermal method, which can be used as the cathode material of lithium ion battery. technical background [0002] Lithium iron phosphate has attracted great attention because of its safety, cheapness, and environmental friendliness. In recent years, due to the low conductivity of the material, this shortcoming has been gradually improved, and batteries with lithium iron phosphate as the positive electrode are being widely used. However, the performance index of its high charge-discharge rate performance still has a certain gap compared with the actual requirements. Particle size reduction and carbon coating are the two most effective methods. In terms of reducing the particle size, the particle size of the material can be prepared into nanoscale, and nanoscale compounds have been prove...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C01B25/45
Inventor 欧秀芹时志翔赵南南郅晓科梁广川
Owner HEBEI UNIV OF TECH
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