All-solid-state lithium secondary batteries using LiCoO2 particles with pulsed laser deposition coatings of Li2S–P2S5 solid electrolytes

Electrode–electrolyte composite materials were prepared by coating a highly conductive Li2S–P2S5 solid electrolyte onto LiCoO2 electrode particles using pulsed laser deposition (PLD). Cross-sections of the composite electrode layers of the all-solid-state cells were observed using a transmission electron microscope to investigate the packing morphology of the LiCoO2 particles and the distribution of solid electrolyte in the composite electrode. All-solid-state cells based on a composite electrode composed entirely of solid-electrolyte-coated LiCoO2 were fabricated, and their performance was investigated. The coating amounts of Li2S–P2S5 solid electrolytes on LiCoO2 particles and the conductivity of the coating material were controlled to increase the capacity of the resulting all-solid-state cells. All-solid-state cells using LiCoO2 with thick solid electrolyte coatings, grown over 120 min, had a capacity of 65 mAh g−1, without any addition of Li2S–P2S5 solid electrolyte particles to the composite electrode. The capacity of the all-solid-state cell increased further after increasing the conductivity of the Li2S–P2S5 solid electrolyte coating by heat treatment at 200 °C. Furthermore, an all-solid-state cell based on a composite electrode using both a solid electrolyte coating and added solid electrolyte particles was fabricated, and the capacity of the resulting all-solid-state cell increased to 95 mAh g−1.