Transformation of P 2 S 5 into a Solid Electrolyte with Ionic Conductivity at the Positive Composite Electrode of All‐Solid‐State Lithium–Sulfur Batteries

Battery performance of an all‐solid‐state lithium–sulfur (Li–S) cell with a P 2 S 5 ‐based positive composite electrode was investigated in the absence of solid electrolyte at the positive composite electrode. In the positive composite electrode, P 2 S 5 without ionic conductivity was transformed into a solid electrolyte with ionic conductivity by incorporating lithium ions into P 2 S 5 during the first charge–discharge cycle. Therefore, the all‐solid‐state Li–S cell with P 2 S 5 ‐based positive composite electrode behaved as a secondary battery. This positive composite electrode is very low cost because it did not use an expensive solid electrolyte. In addition to using a cost‐effective positive composite electrode with a sulfur content of 60 wt %, the all‐solid‐state Li–S cell exhibited an extremely high capacity of 1042 mAh g −1 under 6.4 mA cm −2 at 25 °C.