Strategies of Enhancing Ionic Conductivity in Model Solid‐State Electrolyte Li₁₅P₄S₁₆Cl₃

High ionic conductivity is the key point in the development of new solid‐state electrolytes. Herein, a combining strategy of anion (O 2− ) doping and structure distortion is applied to enhance the Li + ion conductivity in Li 15 P 4 S 16 Cl 3 , thus converting the nonionic conductor into fast ionic conductor. Solid‐state 6 Li nuclear magnetic resonance analysis shows redistribution of Li + ions in Li 15 P 4 S 16 Cl 3 with O 2− doping or local structure distortion via ball milling, indicating energy changes at different lithium sites. As a result, the activation energy is reduced from 0.50 to 0.35 eV for the ball‐milled Li 15 P 4 S 15.6 O 0.4 Cl 3 , and the ionic conductivity is enhanced from 10 −9 to 10 −4 S cm −1 . The electrochemical stability of Li 15 P 4 S 15.6 O 0.4 Cl 3 is broadened at the anode side as well. The symmetric cell Li|Li 15 P 4 S 15.6 O 0.4 Cl 3 |Li can cycle more than 1000 h with negligible voltage increase. The LiCoO 2 |Li 15 P 4 S 15.6 O 0.4 Cl 3 |Li‐Si all‐solid‐state battery demonstrates an initial capacity of 106 mA h g −1 and retains 92% capacity after 200 cycles at 0.5 C, highlighting excellent rate performance and electrochemical stability.