A Cost-Effective Sulfide Solid Electrolyte Li₇P₃S_7.5O_3.5 with Low Density and Excellent Anode Compatibility

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 Li₇P₃S_7.5O_3.5 (LPSO) solid electrolyte, which shows a combination of all the aforementioned characteristics. The synthesis of this material does not need the expensive Li₂S, 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.