Method for preparing high-performance lithium iron phosphate cathode material by using compound type reducing agent

Abstract

The invention relates to a method for preparing high-performance lithium iron phosphate cathode material by using compound type reducing agent, belonging to the technical field of preparation of a lithium ion battery cathode material. The invention has the technical point that the method comprises the following steps: carrying out uniform compound ball-milling on an iron source, a lithium source, a phosphorous source and a compound carbon source for 1-3 hours, wherein the stoichiometric ratio of the lithium source to the iron source to the phosphorous is (1-1.1): 1: 1, and the compound carbon source accounts for 6-10% of the total mass of the materials; drying size obtained by the compound ball-milling at the temperature of 100-120 DEG C and smashing the dried size; heating the smashed size to 650-800 DEG C in nitrogen atmosphere at the heating rate of 2-5 DEG C / min, insulating for 3-15 hours, and cooling to room temperature to obtain lithium iron phosphate powder. A method combining compound carbon thermal reduction and mechanical activation is adopted, cheap iron oxide is taken as the iron source, the doped compound carbon source is taken as reducing agent and conductive agent, and lithium iron phosphate cathode material with stable structure and high electrochemical activity is synthesized by one-step reaction.

Description

Method for preparing high-performance lithium iron phosphate cathode material with composite reducing agent technical field The invention relates to a method for preparing a high-performance lithium iron phosphate positive electrode material with a composite reducing agent, and belongs to the technical field of lithium ion battery positive electrode material preparation. Background technique The long cycle life and good safety performance of lithium-ion batteries make them have broad application prospects in portable electronic devices, electric vehicles, space technology, defense industry, etc. Electric bicycles, hybrid vehicles, etc. are the first choice for providing low-cost clean energy, which requires this lithium-ion battery not only to have high capacity, but also to have high power. Judging from the current usage situation, although LiXC6 / Li1-XCoO2 lithium-ion batteries can meet the requirements of most mobile electronic products and the existing improvement of th...

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Problems solved by technology

However, the classic synthetic route in the liquid phase method is to use ferrous salt, phosphoric acid and lithium hydroxide as raw materials. In this reaction process, the loss of lithium salt is large, and the utilization rate is only about 33.3% (taking ferrous sulfate as an example). Lithium is left in the solution after the reaction, the waste of lithium is serious, and the waste liquid is also very serious to environmental pollution

Compared with the commonly used divalent iron source route, the main problem of ferric iron is that the reduction is relatively difficult, especially in the process of using iron oxide as the iron source. Due to the stable iron oxide lattice and the large mass of iron ions, the diffusion is difficult. , which will cause a large difference in the concentration of iron between the surface and the interior of the sample. At the same time, the decomposition temperature of a single organic carbon source such as sucrose is relatively low. It is difficult to completely reduce ferric iron to ferrous iron under high temperature reaction conditions. The common solutions are: Two, one is to increase the amount used; the other is to prolong the sintering time

The former method will cause the carbon content of the finished product to be too high, the volumetric energy density will decrease, and the processing performance will deteriorate; although the latter method is conducive to ion diffusion and crystal growth, the obtained material has good crystallinity and complete crystal form, but the material The size of the particles will grow, and the agglomeration phenomenon will be aggravated, which will affect the electrochemical performance

Generally speaking, the discharge capacity of materials prepared by the current inorganic ferric salt route is not high enough, and it still lacks certain competitiveness compared with the classic oxalate sub-iron route.

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