Low-cost synthesis of high-purity Li2S for sulfide solid state electrolytes enabled by polyvinyl alcohol

Sulfide solid electrolytes (S-SEs) are widely preferred for their high ionic conductivity and processability. However, the further development of S-SEs is hindered by the excessive price of its critical raw materials of Li 2 S. Herein, a low-cost and environmentally friendly method is proposed to synthesize Li 2 S by the carbothermal reduction reaction of Li 2 SO 4 in one step, and the effects of various factors are also discussed. As a result, a purity of 99.67% is obtained over the self-prepared Li 2 S. More importantly, the cost of the self-prepared Li 2 S is only about 50 $/kg, which is significantly lower than that of the commercial counterpart (10000–15000 dollar/kg). Moreover, the ionic conductivity of Li 5.5 PS 4.5 Cl 1.5 prepared using self-prepared Li 2 S as raw materials is 4.19 mS/cm at room temperature, which is a little higher than that of Li 5.5 PS 4.5 Cl 1.5 using commercial Li 2 S (4.05 mS/cm). And the all-solid-state lithium batteries (ASSLBs) with the as-prepared electrolytes could maintain a discharge capacity of 109.9 mA·h/g with an average coulombic efficiency (CE) of 98% after 100 cycles at 0.2 C , which is equivalent to that using commercial Li 2 S, demonstrating that the preparation strategy of Li 2 S proposed in this work is feasible.