All-solid-state lithium secondary battery with Li₂ S-C composite positive electrode prepared by spark-plasma-sintering process

Electrochemically active lithium sulfide-carbon (Li₂ S-C) composite positive electrodes, prepared by the spark plasma sintering process, were applied to all-solid-state lithium secondary batteries with a _Li3 PO₄ - Li₂ S- SiS₂ glass electrolyte. The electrochemical tests demonstrated that In/ Li₂ S-C cells showed the initial charge and discharge capacities of ca. 1010 and 920 mAh g-1 - Li₂ S, respectively, which showed higher discharge capacity and coulombic efficiency (ca. 91%) than the Li/ Li₂ S-C cells with nonaqueous liquid electrolytes (ca. 200-380 mAh g^-1 - Li₂ S and ca. 27%, respectively). The ex situ S K-edge X-ray absorption fine structure measurements suggested the appearance and disappearance of elemental sulfur in the positive electrodes after charging and discharging, respectively, indicating that the ideal electrochemical reaction Li₂S 2Li+S proceeded in the present all-solid-state cells. Such ideal electrochemical reaction, due probably to the suppression of the dissolution of Li₂ S in the form of polysulfides into the electrolytes, would result in higher coulombic efficiency and discharge capacity as compared with those of the liquid-electrolyte cells.