Fabrication and charge-discharge reaction of all solid-state lithium battery using Li4-2xGe1-xSxO4 electrolyte

Bulk-type solid-state batteries using a LIthium Super Ionic CONductor (LISICON)-based oxide electrolyte, Li4-2xGe1-xSxO4, were assembled by spark plasma sintering (SPS) and electric furnace sintering (FS), and their charge-discharge performances were investigated. Li4-2xGe1-xSxO4, which has a γ-Li3PO4-type structure, was synthesized by conventional solid-state reaction. The total ionic conductivity of the Li3.6Ge0.8S0.2O4 sample sintered at 600 °C by SPS was 2 × 10−5 S cm−1 at room temperature, which is comparable to the bulk conductivity of the material sintered at 800-1100 °C by FS. No impurity peaks were observed in the X-ray diffraction patterns of the LiNi1/3Mn1/3Co1/3O2-Li3.6Ge0.8S0.2O4 mixture even after high-temperature sintering at 900 °C by FS. The solid-state cells of laminated LiNi1/3Mn1/3Co1/3O2 cathode and Li3.6Ge0.8S0.2O4 electrolyte co-sintered by SPS at 600 °C and FS at 900 °C exhibited first discharge capacities of 130 and 92 mAh g−1, respectively, at 60 °C. These experimental results confirm that the LISICON-based material, Li4-2xGe1-xSxO4, exhibits thermal compatibility to the active material and relatively high lithium ion conductivity, which lead to the high charge-discharge performance of the bulk-type all-solid-state cell.