Low-Cost and Scalable Synthesis of High-Purity Li₂S for Sulfide Solid Electrolyte

Sulfide solid electrolytes (SSEs) are preferable for all-solid-state lithium batteries (ASSLBs) to achieve high energy densities. However, the development of SSEs is impeded due to the high cost of the key raw material-Li2S. It is of great significance to synthesize high-purity Li2S with a more accessible and economic method. Herein, a new strategy for large-scale synthesis of Li2S with a low cost is developed on the basis of a lithium sulfate carbothermic reduction reaction in this work. A high yield of 81.78% and low raw material cost of $62 kg1- are achieved, significantly lower than that of its commercial counterpart ($10,000-15,000 kg1-). To verify the effectiveness of this method, the as-prepared Li2S is further used to synthesize Li6PS5Cl (LPSC), and the corresponding electrochemical performances are evaluated. Room temperature ionic conductivity of LPSC reaches 2.63 mS cm-1. In the NCM622@Al2O3(NCM622@AlO)//LPSC//Li-In ASSLB system, a high discharge specific capacity of 136 mAh g-1 is maintained after 700 cycles at 1C with an ultrahigh area loading of 35.6 mg cm-2 (calculated according to NCM622@Al2O3, which is almost twice the other works). These performances are comparable to those using LPSC from expensive commercial Li2S in the control group, demonstrating the feasibility of the Li2S preparation strategy proposed in this work.