A Cost‐Effective Sulfide Solid Electrolyte Li 7 P 3 S 7.5 O 3.5 with Low Density and Excellent Anode Compatibility

Abstract The commercialization of all‐solid‐state Li batteries (ASSLBs) demands solid electrolytes with strong cost‐competitiveness, low density (for enabling satisfactory energy densities), and decent anode compatibility (the need for cathode compatibility can be circumvented by the cathode coating techniques that are widely applied in sulfide‐based ASSLBs). However, none of the reported oxide, sulfide, or chloride solid electrolytes meets these requirements simultaneously. Here, we design a Li 7 P 3 S 7.5 O 3.5 (LPSO) solid electrolyte, which shows a combination of all the aforementioned characteristics. The synthesis of this material does not need the expensive Li 2 S, so the raw materials cost is only $14.42/kg, which, unlike most solid electrolytes, lies below the $50/kg threshold for commercialization. The density of LPSO is 1.70 g cm −3 , considerably lower than those of the oxide (typically above 5 g cm −3 ) and chloride (around 2.5 g cm −3 ) solid electrolytes. Besides, LPSO also shows excellent anode compatibility. The Li|LPSO|Li cell cycles stably with a potential of ~50 mV under 0.1 mA cm −2 for over 4200 h at 25 °C, and the all‐solid‐state pouch cell with the Si anode shows a capacity retention of 89.29 % after 200 cycles under 88.6 mA g −1 at 60 °C.