Microstructure Control of LiCoO2-Li10GeP2S12 Composite Cathodes by Adjusting the Particle Size Distribution for the Enhancement of All-Solid-State Batteries

Abstract

Microstructure control of composite electrodes comprising active materials and solid electrolytes is imperative to achieve sufficient ion- and electron-conductive pathways for the development of all-solid-state Li ion batteries. Here, we synthesized Li10GeP2S12 solid electrolytes with various particle size distributions by milling and filtering. Impedance spectroscopy revealed that the ionic conductivities in the bulk were hardly changed by the synthetic processes. This enabled us to investigate only the microstructure effects on the electrochemical properties of the composite electrodes. Microscopic and electrochemical tests of the LiCoO2-Li10GeP2S12 composite cathodes clarified that the size distributions of the Li10GeP2S12 drastically affected the microstructures in the composite cathodes, such as contacts at interfaces and voids between particles. The size distributions also contributed to the appropriate ratio of LiCoO2 to Li10GeP2S12 for superior charge/discharge properties. The (de)intercalation reversibly proceeded in the composite cathode using the filtered Li10GeP2S12 even though the ratio of Li10GeP2S12 decreased from 50 % to 30 % in volume. This study demonstrated the possibility of high-energy-density composite cathodes for all-solid-state batteries by control of microstructures in composite electrodes.