Preparation method for lithium iron phosphate material of positive electrode of lithium ion secondary battery

Abstract

The invention provides a preparation method for a lithium iron phosphate material of a positive electrode of a lithium ion secondary battery. The preparation method comprises the following steps of: evenly mixing an iron source, a carbon source, a lithium source, a phosphate radial source and doping ions, conducting a drying procedure to obtain lithium iron phosphate precursor mixture, warming and heating the mixture in reducing atmosphere at the speed of 0.5-10 DEG C / min, preserving heat at 300-400 DEG C for 2-5hours, calcining at 500-850 DEG C for 3-28 hours, conducting furnace cooling to room temperature, smashing and classifying to obtain the lithium iron phosphate material of the positive electrode. The preparation method realizes the adoption of the low-cost ferric iron source, and achieves the doping of metal ions and further synthesis of the lithium iron phosphate composite material, and the prepared lithium iron phosphate material of the positive electrode is good in rate capability, easy for the synthesis process to control, and suitable for industrialized production, the prepared material is even in particles, high in crystallinity degree, good in discharge capacity, and stable in recycling property.

Description

Technical field: [0001] The invention belongs to a preparation method of a lithium ion battery cathode material, in particular to a method for preparing a high-rate lithium iron phosphate cathode material by multi-element doping. technical background: [0002] Olivine-type lithium iron phosphate is considered to be one of the best cathode materials for power batteries because of its low cost, environmental friendliness, long cycle life, good thermal stability and high safety performance. [0003] Although LiFePO 4 It has many advantages, but it also has the following two shortcomings that hinder its practical application process: (1), electronic conductivity and lithium ion diffusion rate are low, resulting in initial capacity loss and poor high-rate charge and discharge performance; ( 2), LiFePO during the synthesis process 4 It is difficult to control the purity of Fe, even if the synthesis conditions are strictly controlled, it is still impossible to completely avoid Fe...

AI Technical Summary

Problems solved by technology

[0003]Although LiFePO4 has many advantages, it still has the following two shortcomings that hinder its practical application process: (1), Electronic conductivity and lithium ion diffusion rate are low, resulting in initial capacity loss and poor high-rate charge-discharge performance; (2), it is difficult to control the purity of LiFePO4 during the synthesis process, even if the synthesis conditions are strictly controlled , it is still unavoidable to completely avoid the oxidation of Fe3+. At present, most researches often use expensive Fe3+ compounds as iron sources, which increases the preparation cost

(3) The tap density of LiFePO4 is low, resulting in low volume specific energy

However, it is difficult to design and manufacture large-scale high-temperature and high-pressure reactors, and the cost is high, and it is often necessary to add twice as much Li salt as a precipitant during the synthesis process, which increases the preparation cost

[0007]Patent CN200410017382.5 adopts low-priced ferric iron source and one-step solid phase synthesis of carbon-coated lithium iron phosphate simplifies the process and reduces the cost. Coating can well solve the problem of poor conductivity of lithium iron phosphate. The 0.2C discharge capacity is 157mAh / g, but the conductivity inside the lithium iron phosphate lattice has not changed. The 1C discharge capacity is 124 mAh / g. Industrialization is still a long way off

Images