Phase relations of Li2O-FeO-SiO2 ternary system and electrochemical properties of Li (x) Si (y) O (z) compounds

摘要

Phase equilibria in the ternary Li2O-FeO-SiO2 system have been studied by means of X-ray powder diffraction. The experimental results show that no new lithium ferrous silicate compounds can be found in our experimental condition which may be a candidate cathode material for LIBs. The Li2O-FeO-SiO2 system can be characterized by the existence of 9 three-phase regions. In Li2O-SiO2 binary system, Li2SiO3 and Li4SiO4 are purely synthesized by solid-state reactions; other new information includes the electrochemical properties of Li2SiO3 and Li4SiO4 compounds, where the electrochemical test indicated that initial discharge-specific capacities can reach to 136 and 129 mAhg(-1), respectively. Enhanced performance was exhibited after carbon coating. The initial discharge-specific capacities of carbon-coated Li2SiO3 and carbon-coated Li4SiO4 compound can reach to 230 and 220 mAhg(-1) respectively. Our results show that Li2SiO3 and Li4SiO4 samples have better capacity retention except for the first discharge. No significant change can be seen in ex situ XRD patterns for Li2SiO3/C, while the lithium-ion insertion/extraction reaction may exist in Li4SiO4/C as forming solid solutions (nominated Li4+x SiO4).