Phase relations of Li2O–FeO–SiO2 ternary system and electrochemical properties of LixSiyOz compounds

Phase equilibria in the ternary Li 2 O–FeO–SiO 2 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 Li 2 O–FeO–SiO 2 system can be characterized by the existence of 9 three-phase regions. In Li 2 O–SiO 2 binary system, Li 2 SiO 3 and Li 4 SiO 4 are purely synthesized by solid-state reactions; other new information includes the electrochemical properties of Li 2 SiO 3 and Li 4 SiO 4 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 Li 2 SiO 3 and carbon-coated Li 4 SiO 4 compound can reach to 230 and 220 mAhg −1 respectively. Our results show that Li 2 SiO 3 and Li 4 SiO 4 samples have better capacity retention except for the first discharge. No significant change can be seen in ex situ XRD patterns for Li 2 SiO 3 /C, while the lithium-ion insertion/extraction reaction may exist in Li 4 SiO 4 /C as forming solid solutions (nominated Li 4+ x SiO 4 ).