Lithium-Sulfur Batteries Employing Hybrid-electrolyte Structure with Li7La3Zr2O12 at Middle Operating Temperature: Effect of Li Salts Concentration on Electrochemical Performance

All solid state Lithium-Sulfur batteries can effectively solve the problem of the conventional Li-S batteries with a liquid electrolyte. However, they still do not achieve sufficient cycle stability and rate capability because of high interfacial resistance between the electrode and the solid electrolyte. Hybrid-electrolyte structure using a liquid electrolyte and a solid electrolyte can efficiency solve the interfacial problem. Here, we demonstrate the effect of Li salt concentration in the liquid electrolyte between the sulfur cathode and the solid electrolyte Li7La3Zr2O12 (LLZ) on the electrochemical properties in Lithium-Sulfur batteries employing hybrid-electrolyte structure. Furthermore, the interfacial reactivity between the liquid electrolyte and LLZ is investigated. With increasing Li salt concentration, the electrochemical performances including the utilization of sulfur, the cycle stability and coulombic efficiency are improved because the dissolution of lithium polysulfides during cycle into the liquid electrolyte at cathode side is inhibited. The interfacial layer is formed on LLZ surface during discharge-charge cycle by a contact of the liquid electrolyte with LLZ, leading to increasing the interfacial resistance. We believe that this study helps to improve the electrochemical properties of Lithium-Sulfur batteries with hybrid electrolyte concepts. (C) The Author(s) 2020. Published by ECSJ. [GRAPHICS]

Automated summary

All solid state Lithium-Sulfur batteries can effectively solve the problem of conventional Li-S batteries with liquid electrolytes by using a hybrid-electrolyte structure. By investigating the effect of Li salt concentration in the liquid electrolyte on the electrochemical properties, it is found that increasing Li salt concentration can improve the performance of the batteries. The study also shows that the formation of an interfacial layer on the solid electrolyte surface during discharge-charge cycles can increase interfacial resistance. This research aims to improve the electrochemical properties of Lithium-Sulfur batteries with hybrid electrolyte concepts.