IMPROVING ELECTROCHEMICAL PERFROMANCE OF IRON TRIFLUORIDE (FeF3) IN SODIUM-ION BATTERIES

Iron trifluoride (FeF3) has been enthusiastically pursued, as one of the most promising conversion materials in sodium-ion batteries (SIBs) due to its high capacity in combination with low cost and environmental benignity of iron. However, the fast degradation and low conductivity strongly affect its electrochemical performance in sodium-ion batteries (SIBs). This thesis systematically explored methods and techniques to improve low conductivity and cycling stability of FeF3-based cathodes. First, active materials were well embedded in conductive carbon matrix by electrospinning followed by carbonization, fluorination, and chemical modification to increase cathode conductivity. Second, atomic layer deposition coatings were utilized as surface coating to decrease the dissolution of active materials and improve cycling performance. Third, introducing new electrolyte systems comprising alternative salts and solvents, including ionic liquids, were shown to benefit formation of favorable cathode electrolyte interphases (CEI) that similarly enhanced the FeF3 cycling stability. The rate of CEI formation and its characteristics influenced the cycling performance at both room temperature and elevated temperatures.Ph.D