Preparation method of high-rate capacity lithium iron phosphate material

Abstract

The invention discloses a preparation method of a high-rate capacity lithium iron phosphate material, which comprises the steps of: weighing FePO4.xH2O and a lithium source compound as raw materials according to the mol ratio of Li to Fe of (1-1.05) :1, adding a carbon source compound and a catalyst (nitrate or acetate of Fe, Co, Ni and the like), ball-grinding for 0.5-24h by using deionized water, absolute ethyl alcohol or acetone as a ball grinding medium to obtain slurry, spraying and drying the slurry and then thermally treating under the protection of an inert gas, and in the process, with the thermal cracking of the carbon source compound, promoting the carbon source compound to form a carbon cladding cover with higher graphitization crystallinity under a lower temperature through mutual action of the catalyst and the carbon source compound. The lithium iron phosphate cathode material prepared by adopting the preparation method has higher electronic conductivity and higher specific capacity under the condition of lower carbon content, greatly improved high-rate performance especially, and better application value in the field of power batteries.

Description

technical field [0001] The invention belongs to the technical field of energy materials, and relates to a preparation method of a high-rate lithium iron phosphate / carbon composite material. Background technique [0002] Lithium-ion battery is a high-efficiency and compact energy storage device. The development trend of lithium-ion battery technology is to pursue higher mass-to-volume specific energy, higher specific power, longer cycle and service life, and lower cost of use. At the same time, more emphasis is placed on the environmental adaptability and safety of devices. Its application fields have expanded from mobile phones and notebooks to power tools, light electric vehicles, hybrid electric vehicles, telecom backup power, space and aerospace and other fields. The safety issue of lithium-ion batteries has always been the focus of attention in the industry and scientific research circles. From the perspective of the chemical reaction mechanism of safety issues, the sele...

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Problems solved by technology

[0005] In fields that have higher requirements for discharge rate, such as electric tools, it is generally required to discharge continuously at 10C (1C=170mA / g). Because the particles prepared by the traditional solid-state reaction method are too large (the average size of primary particles is about 0.5um), In addition, due to the poor electronic conductivity and ion diffusivity of lithium iron phosphate, the application range of lithium iron phosphate batteries has been restricted. The batteries made of lithium iron phosphate materials currently available on the market have two significant problems under high current. Defects: one is that the voltage is reduced due to the polarization effect of discharge at a large rate. Generally, the average voltage after 10C discharge does not exceed 2.85V, so that the energy density of the battery is reduced by more than 10% compared with the conventional one; the other aspect is Severe heating occurred during the high-rate discharge. In the LFP18650 battery test, the temperature of the battery surface reached above 50°C when it was discharged at 10C, and the temperature reached about 70°C when it was discharged at 20C. Due to the phenomenon of iron ion dissolution in high temperature , so it has an adverse effect on the cycle life and safety of the battery

[0012] In the traditional preparation method, in order to obtain higher sp 2 / sp 3 Compared with the electrode material, it needs heat treatment at 750°C and above. Such high temperature can easily make the grain size grow, so that LiFePO 4 The diffusion of Li+ in the medium is more difficult, and the cost of preparation is virtually increased. Therefore, adding an appropriate catalyst during the reaction can achieve higher graphitization of carbon (that is, higher sp 2 / sp 3 Compare)

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