Interface Instability in LiFePO4–Li3+xP1–xSixO4 All-Solid-State Batteries

Abstract

All-solid-state batteries (ASSBs) based on noncombustible solid electrolytes are promising candidates for safe and high energy storage systems, but it remains a challenge to prepare systems with stable interfaces between the various solid components that survive both the synthesis conditions and electrochemical cycling. We have investigated cathode mixtures based on a carbon-coated LiFePO4 active material and Li3+xP1–xSixO4 solid electrolyte for potential use in all-solid-state batteries. Half-cells were constructed by combining both compounds into pellets by spark plasma sintering (SPS). We report the fast and quantitative formation of two solid solutions (LiFePO4–Fe2SiO4 and Li3PO4–Li2FeSiO4) for different compositions and ratios of the pristine compounds, as tracked by powder X-ray diffraction and solid-state nuclear magnetic resonance; X-ray absorption near-edge spectroscopy confirms the formation of iron silicates similar to Fe2SiO4. Scanning electron microscopy and energy dispersive X-ray spectrosco...