Temperature-driven structural evolution of carbon modified LiFePO4 in air

Lithium iron phosphate (LiFePO4) is an appealing cathode material for lithium ion batteries. However, the degradation of LiFePO4 in air presents an unavoidable challenge, due to the vulnerability of divalent Fe against oxygen attack. In this work, we have carried out comprehensive research on the thermal stability and temperature-driven evolution of nanocarbon modified LiFePO4 in air. The results show that LiFePO4 retains structural stability up to 250 degrees C for short periods of exposure to air. At long exposure times, structural evolution occurs at a much lower temperature, 150 degrees C. The structural evolution proceeds as the temperature increases, and finishes at 400 degrees C. The final products are monoclinic Li3Fe2(PO4)(3) and alpha-Fe2O3. A quantitative evolution map has been developed through electrochemical cyclic voltammetry and galvanostatic tests. The results show that the largest changes take place between 200 and 250 degrees C.