High performance LiFePO4/CN cathode material promoted by polyaniline as carbon–nitrogen precursor

Abstract

A facile and efficient solid state synthesis of carbon and nitrogen coated lithium iron phosphate (LiFePO4/CN) cathode material is achieved via polymer-pyrolysis method using polyaniline-chloride (PANI-Cl). The current investigation is comparatively analyzed with the results of the composite of LiFePO4/C (LFP/C) synthesized using sucrose as carbon precursor. The optimized LiFePO4/CN (LFP/CN) composite is synthesized at 700 °C using 10 wt.% PANI-Cl. 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-Cl 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-Cl upon pyrolysis on size reduction and formation of uniform carbon/nitrogen coating on LFP are also discussed.