Tungsten Carbide Shell Coated Lithium Iron Phosphate Cathode Material

Cathode materials have been the bottleneck to improve the performance and reduce the cost of lithium-ion batteries. Lithium iron phosphate is the first choice of cathode materials for modern commercial lithium-ion batteries because of its low price, high energy density, long life and good safety. However, the low electronic conductivity of lithium iron phosphate seriously hinders its application in the field of power and energy storage batteries.

Cathode materials have been the bottleneck to improve the performance and reduce the cost of lithium-ion batteries. Lithium iron phosphate has the advantages of low price, high energy density, long service life and good safety. It is one of the effective ways to improve the conductivity of lithium iron phosphate materials by modern commercial surface coating. Some scholars have proposed a kind of tungsten carbide shell coated lithium iron phosphate cathode material with excellent conductivity, which can improve the rate characteristics of lithium iron phosphate. In the preparation process:

Weigh 0.1mol ferrous sulfate, 0.11mol lithium chloride and 0.1mol ammonium dihydrogen phosphate respectively, dissolve them in 200ml deionized water, mix them together and pour them into the hydrothermal reaction tank, add ammonia water, control the pH value to 9.0, seal them and place them in the heater for 24h hydrothermal reaction at 200 ℃. After cooling, the precipitate was washed by deionized water and centrifuged repeatedly, and the separated powder was dried in vacuum at 100 ℃ for 10 hours to obtain lithium iron phosphate. The preferred cathode material for Li-ion batteries. However, the low electronic conductivity of lithium iron phosphate seriously hinders its application in the field of power and energy storage batteries.

The LiFePO₄ sample was placed in the reaction chamber of the plasma enhanced chemical vapor deposition equipment, vacuumized to 1.0 × 10-1pa, and heated to 300 ℃. When the mixture of WF₆ + CH₄ (WF₆: CH₄ = 1:1 by volume) is filled in, the total pressure of the reaction chamber is maintained at 50pA. The output power of RF plasma is 600W, and the reaction time is controlled at 25min. The cathode material of lithium iron phosphate coated with WC shell was obtained, and the thickness of the coating layer was 1.0nm. The first discharge capacity of 1C is 155mah · g-1, and the discharge retention rate of 5C / 1C is 98%.

The cathode material of lithium iron phosphate coated with tungsten carbide shell has excellent rate performance. In the range of 2.5-4.35v, the first discharge capacity of 1C is ≥ 155mah · g-1, and the discharge retention rate of 5C / 1C is above 96%.

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