Study on operating mechanism for all-solid-state Li-sulfur battery

Abstract

Recently, sulfur is chosen as a cathode material for Li ion rechargeable battery (LIB) with its high theoretical capacity, environmental friendliness and low cost. However, shuttle mechanism (reduction in discharge capacity, overcharge) caused by dissolved lithium polysulfides is the main obstacle for practical use. In this thesis, solid electrolyte is used for Li-sulfur battery to eliminate the shuttle mechanism. Thio-LiSICON II analogue Li2S-P2S5 solid electrolyte was adopted as a solid electrolyte with high lithium ionic conductivity, low temperature synthesizing process, and stable interface with Li metal. To begin with, construction of all-solid-state Li-sulfur battery was carried out to evaluate performance. Afterwards, Raman spectroscopy and XPS were used to find out intermediates and mechanism of all-solid-state Li-sulfur battery. During charging, Li2S was oxidized to defective Li2S and later on to short-chain lithium polysulfide and finally to sulfur. During discharging, reverse reaction was occurred. Examined defective Li2S after 1st charge might be correlated to irreversible capacity and poor cycle life. Solid electrolyte-Li2S-carbon composite can be a solution to control interfaces among cell components.