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

Highly lithium ion conducting glass-ceramics in the system Li2S-P2S5 were successfully prepared by a heat treatment of the mechanochmically prepared sulfide glasses. The 80Li(2)S center dot 20P(2)S(5) (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 70Li(2)S center dot 30P(x)S(5) glass-ceramic, in which the highly ion conductive new metastable phase was formed on heating, showed the highest conductivity of 3.2 x 10(-3) S cm(-1) and the lowest activation energy of 12kJ mol(-1) for conduction. The all-solid-state battery In/80Li(2)S center dot 20P(2)S(5) glass-ceramic/LiCoO2 exhibited excellent cycling performance of over 500 times with no decrease in the charge-discharge capacity (100 mAh g(-1)). The SnS-P2S5 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 center dot 20P(2)S(5)/80Li(2)S center dot 20P(2)S(5) 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 Li2S-P2S5 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. (c) 2006 Elsevier B.V. All rights reserved.