Lithium iron phosphate composite modified lithium ion battery cathode material and preparation method thereof

Abstract

The invention discloses a lithium iron phosphate composite modified lithium ion battery cathode material and a preparation method thereof. The chemical formula of the cathode material is LiFe1-xRExPO4-REPO4 / (C+Fe2P), and a multi-phase structure with LiFe1-xRExPO4, REPO4 and Fe2P exists; REPO4, C and Fe2P are coated on the surface of the LiFe1-xRExPO4; and x ranges from 0.01 to 0.04. The method comprises the following steps of: uniformly mixing a lithium source compound, a phosphorus source compound, inorganic and organic mixed iron source compound and rare earth oxide RE2O3 so as to prepare a reaction precursor; and forging the reaction precursor so as to obtain the lithium iron phosphate composite modified lithium ion battery cathode material. The preparation method is simple and feasible and low in production cost; the prepared material has relatively high electrochemical performance and tap density; and the method is favorable for industrial production.

Description

technical field [0001] The invention belongs to the technical field of lithium ion batteries, and specifically refers to a lithium iron phosphate composite modified lithium ion battery cathode material and a preparation method thereof. Background technique [0002] Lithium iron phosphate (LiFePO 4 ) has the advantages of stable structure, large discharge specific capacity, good safety performance, cheap and easy-to-obtain raw materials, and environmental friendliness. Its thermal stability and high-temperature cycle performance are particularly outstanding. One of the best cathode materials for low-cost lithium-ion power batteries. [0003] However, some inherent shortcomings of lithium iron phosphate materials have seriously hindered its commercialization process: First, the lithium ion migration rate and electronic conductivity of this material are both low, and the high-current charge-discharge performance is poor, and the prepared battery cannot meet the requirements. ...

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Problems solved by technology

[0005] 1. Although methods such as hydrothermal synthesis, liquid-phase co-precipitation, and sol-gel methods can prepare powder materials with smaller particle sizes and reduce the migration path of lithium ions, the particle size reduction increases The contact area between the material particles is reduced, and the tap density, volume specific capacity and volume specific power of the material are reduced. At the same time, there are disadvantages such as high equipment requirements or complicated preparation processes, making it difficult to carry out industrialized mass production;

[0006] 2. Although the doping of transition metal elements can improve the bulk electronic conductivity of the material, it has little effect on the particle size of the material and cannot improve the lithium ion diffusion rate of the material, so the improvement effect on the electrochemical performance of the material is very limited ;

[0007] 3. Carbon coating not only improves the electronic conductivity of the material, but also significantly reduces the particle size of the material, reduces the migration path of lithium ions, and has a very prominent effect on improving the electrical properties of the material, but the tap density of carbon is lower than that of LiFePO 4 Low, pure carbon-coated materials reduce the volume specific energy, which seriously affects the practicability of the material

[0008] 4. Although the controlled crystallization method and the liquid phase co-precipitation method can synthesize LiFePO with a spherical structure with high tap density 4 materials, but the synthesis process needs to strictly control the temperature, pH value, stirring rate, coprecipitation rate and other factors of the reaction system, the operation steps are complicated, and the industrialization is difficult

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