All-solid-state lithium secondary batteries using sulfide-based glass–ceramic electrolytes

Highly lithium ion conducting glass–ceramics in the system Li2Ssingle bondP2S5 were successfully prepared by a heat treatment of the mechanochmically prepared sulfide glasses. The 80Li2S·20P2S5 (mol.%) glass–ceramic mainly composed of the crystal analogous to the highly conductive thio-LISICON II phase in the system Li4−xGe1−xPxS4 showed conductivity as high as 10−3 S cm−1 at room temperature. The 70Li2S·30P2S5 glass–ceramic, in which the highly ion conductive new metastable phase was formed on heating, showed the highest conductivity of 3.2 × 10−3 S cm−1 and the lowest activation energy of 12 kJ mol−1 for conduction. The all-solid-state battery In/80Li2S·20P2S5 glass–ceramic/LiCoO2 exhibited excellent cycling performance of over 500 times with no decrease in the charge–discharge capacity (100 mAh g−1). The SnSsingle bondP2S5 glasses as active materials were mechanochemically prepared from SnS and P2S5. High performance of these glassy electrode materials was observed in the rechargeable cell of 80SnS·20P2S5/80Li2S·20P2S5 glass–ceramic/LiCoO2, in which a continuous sulfide network between electrode and electrolyte was successfully formed. The effects of conductive additives in composite electrodes on charge–discharge behavior of all-solid-state cells with Li2Ssingle bondP2S5 glass–ceramics as a solid electrolyte were investigated. Under a current density over 1 mA cm−2, the cell with vapor grown carbon fiber kept larger discharge capacities during 50 cycles than the cell with acetylene black. The design of continuous electron conducting path from a point of view of morphology for conductive additives is important to improve cell performances of all-solid-state lithium secondary batteries.