High performance LiFePO_4/CN cathode material promoted by polyaniline as carbon—nitrogen precursor

摘要

A facile and efficient solid state synthesis of carbon and nitrogen coated lithium iron phosphate (LiFePO_4/ CN) cathode material is achieved via polymer-pyrolysis method using polyaniline-chloride (PANI-CI). The current investigation is comparatively analyzed with the results of the composite of LiFePO_4/C (LFP/C) synthesized using sucrose as carbon precursor. The optimized LiFePO_4/CN (LFP/CN) composite is synthesized at 700℃ using 10 wt.% PANI-CI. The composite exhibits remarkable improvement in capacity, cyclability and rate capability compared to those of LFP/C. The specific discharge capacities as high as 164 mAh g~(-1) (theoretical capacity: 170 mAh g~(-1)) at 0.1 C and 100 mAh g~(-1) at 10 C rates were achieved with LFP/CN. In addition, the composite exhibits a long-term cycling stability with the capacity loss of only 10% after 1000 cycles. PANI-CI shifts the size distribution of the composite to nanometer scale (approximately 150 nm), however the addition of sucrose does not have such an effect. LFP/CN contains 1.6 wt.% nitrogen and 15.8 wt.% carbon. LFP particles are mostly coated with a few nanometers thick C—N layer forming a core—shell structure. The possible crosslinking mechanism of PANI-CI upon pyrolysis on size reduction and formation of uniform carbonitrogen coating on LFP are also discussed.