Method for preparing high-density lithium ferric phosphate

Abstract

The invention relates to a method for preparing high-density lithium ferric phosphate, which comprises the following steps of: adding a lithium salt, a ferric salt, a phosphorus-containing compound and doping metal-containing elements into a dispersing agent by the conventional method, and performing ball mill twice; performing drying and predecomposition for 3 to 10 hours; crushing, adding at least one of lithium dihydrogen phosphate or potassium dihydrogen phosphate as a bonding agent in an amount which is 1 to 5 percent based on the weight of a predecomposition product, performing ball mill for 1 to 5 hours, and processing according to the prior art to obtain the high-density lithium ferric phosphate. In the method, the ball mill is performed twice in the first step, so that granules are fine; the grain size can be controlled within the range of between 300 and 2,000 nanometers, so that raw materials are mixed uniformly; more importantly, due to the addition of the bonding agent, the bonding among the granules is enhanced, the stacking density of products is improved, and contact conductivity among the granules is reduced; and the prepared products have good crystallization, simple structure and uniform grain fineness distribution and do not contain impure phases, the tap density is between 1.4 and 1.8 g/cm<3>, the specific surface area is between 5 and 11m<2>/g, the compaction density of pole pieces is between 2.4 and 2.8 g/cm<3>, and the specific capacity of first discharging at the room temperature is between 140 and 160 mAh/g.

Description

technical field [0001] The invention relates to a preparation method of lithium iron phosphate, a cathode material of a lithium ion secondary battery. Background technique [0002] Lithium iron phosphate has been widely used as the cathode material of lithium-ion secondary batteries. In order to improve the low conductivity of lithium iron phosphate, people have engaged in various work and made significant progress. The main measures are: (1) in phosphoric acid Doping metal ions or non-metal ions in the lithium iron phosphate lattice, (2) adding conductive carbon to the lithium iron phosphate material or coating the conductive carbon material on the surface of the lithium iron phosphate particles, usually in the process of doping metal ions One-time ball milling; the particles can only reach the micron level, which causes the problem of uniform mixing of raw materials; there is another disadvantage in the existing preparation method that the binding force between the particl...

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Problems solved by technology

[0002] Lithium iron phosphate has been widely used as the cathode material of lithium-ion secondary batteries. In order to improve the low conductivity of lithium iron phosphate, people have engaged in various work and made significant progress. The main measures are: (1) in phosphoric acid Doping metal ions or non-metal ions in the lithium iron phosphate lattice, (2) adding conductive carbon to the lithium iron phosphate material or coating the conductive carbon material on the surface of the lithium iron phosphate particles, usually in the process of doping metal ions One-time ball milling; the particles can only reach the micron level, which causes the problem of uniform mixing of raw materials; there is another disadvantage in the existing preparation method that the binding force between the particles is not very good. The current method to improve the binding force between the particles is to increase the temperature. But the raising of temperature can cause the danger that particle grows up, and brings product capacity to decline; On carbon coating layer and lithium iron phosphate surface combination, some are to adopt inorganic conductive carbon to carry out lithium iron phosphate coating, as disclosed in CN101112979 is Inorganic conductive carbon is used in the one-step carbon coating process; this method is due to simple physical contact, resulting in incomplete coating, resulting in poor conductivity of lithium iron phosphate; due to poor mixing uniformity and poor inter-particle bonding , the carbon coating layer and the surface of lithium iron phosphate are not well bonded, which will lead to poor processing of lithium iron phosphate pole pieces, as well as poor control of lithium iron phosphate battery performance and product quality consistency

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