Lithium iron phosphate cathode material and preparation method thereof

Abstract

The invention discloses a lithium iron phosphate cathode material and a preparation method thereof. The cathode material comprises 30-450nm of small particle size lithium iron phosphate accounting for 25-50% of the total volume, 450-3000nm of large particle size lithium iron phosphate accounting for 50-75% of the total volume and conductive carbon. In the preparation, lithium phosphate and iron phosphate are firstly prepared; then, the lithium phosphate and the iron phosphate are mixed according to the mol ratio of 2 / 3-2:1 and then added with phosphorus source compound, ferric iron source compound and lithium source compound; afterwards, absolute ethyl alcohol is added into the mixture for ball milling, and the lithium iron phosphate cathode material is obtained after the processing. The invention adopts a coprecipitation method to prepare the spherical iron phosphate and lithium phosphate which have controllable particle sizes, and then uses a solid state sintered technology to synthesize the lithium iron phosphate, so that the tap density reaches 1.6g / cm; the source of the raw materials is wide, and the requirements for the equipment and the cost are low, so that large-scale production can be realized.

Description

technical field [0001] The invention relates to a lithium ion battery cathode material, in particular to a lithium iron phosphate cathode material and a preparation method thereof. Background technique [0002] Lithium-ion batteries have been widely used in many fields since their commercial production in 1990. Olivine LiFePO 4 As a new lithium-ion battery cathode material, it has the following unique advantages compared with common transition metal oxide cathode materials: the theoretical specific capacity can reach 170mAh / g, and the actual specific capacity in industrial production can reach more than 145mAh / g; Stable discharge voltage platform; long cycle life, which can reach more than 1000 times; good high temperature performance and thermal stability; wide working temperature range (-20°C ~ 75°C); stable structure, O and P are firmly combined with strong covalent bonds, It is difficult to decompose the material by oxygen evolution, and has excellent safety performanc...

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Problems solved by technology

[0003] However, so far, there are still two obvious shortcomings of lithium iron phosphate: one is low conductivity, large polarization during high-rate charge and discharge, and the actual specific capacity is low; the other is low tap density, and its theoretical tap density is only 3.6g / cm 3 , the actual tap density is only 1.0g / cm 3 around, less than LiCoO 2 half of the tap density

[0007] 1. Using mechanical metallurgy, molten salt method, ultrasonic thermal decomposition method, continuous hydrothermal method, etc., although lithium iron phosphate with fine particle size and uniform crystal phase can be synthesized, the tap density and electrical conductivity of the material can be improved. performance, but these methods have higher requirements on equipment and increase production costs, and are only suitable for small batch production

[0008] 2. Although the metal ion crystal phase doping method can improve the conductivity of the material, the tap density of the material has not been significantly improved, and the volume specific capacity and volume specific power of the material cannot be effectively improved, and it also increases Cost of production

This method improves the electrical conductivity and tap density of the material by introducing a metal powder conductive agent between the lithium iron phosphate grains, but the cost is high, the process is more complicated, the uniform distribution of the metal powder is difficult to control, and the operability is poor. Poor, difficult to carry out large-scale industrial production

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