Phase relations of Li₂O–FeO–SiO₂ ternary system and electrochemical properties of Li _x Si _y O _z compounds

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 Li_4+x SiO₄).