Synthesis and electrochemical behavior of LiFePO4/C with an air-electrode in an aqueous lithium ion battery

This study investigated the intercalation of lithium ions for carbon-coated LiFePO4 (LiFePO4/C) in an aqueous rechargeable lithium-ion battery. LiFePO4/C was obtained using a sol-gel method, with citric acid as the chelating agent. The phase structures and morphologies confirmed the orthorhombic crystal structure of LiFePO4 surrounded by the carbon layer. The electrochemical behavior of LiFePO4/C vs. an air-electrode as the counter electrode was investigated in a 5 M LiNO3 solution. The well-defined flat plateaus in the charge and discharge curves showed that the intercalation of lithium ions and the reduction of oxygen occurred simultaneously within the electrochemical stability window of water. The LiFePO4/C system showed good rate capabilities even at a higher current density (5 C) with a small capacity loss. The rate capability of the LiFePO4/C system was also compared with the rate capability of a platinum counter electrode; the air-electrode still showed better cycling behavior.