Electrochemical and structural investigation of NaCrCb as a positive electrode for sodium secondary battery using inorganic ionic liquid NaFSA-KFSA

摘要

The electrochemical performance of NaCrO_2 as a positive electrode material for an intermediate-temperature sodium secondary battery was evaluated in an inorganic ionic liquid, NaFSA-KFSA (FSA = bis(fluorosulfonyl)amide), at 363 K. The positive electrode using NaCrO_2, acetylene black, and polytetrafluoroethylene exhibited a stable discharge capacity of 113 mA h g~(-1) at a current density of 125 mA g~(-1). The Coulombic efficiency and the capacity retention at the 100th cycle were 99.6% and 98.5%, respectively. Even at the very high current density of 2000 mA g~(-1) the discharge capacity was maintained at 63 mA h g~(-1). X-ray diffraction analyses revealed that the deintercalation of Na~+ ion from NaCrO_2 was associated with several phase transitions in the following sequence: rhombohedral O3, monoclinic O'3, and monoclinic P'3.