Prediction of New Phase and Electrochemical Properties of Li2S2 for the Application of Li-S Batteries

The intermediate product Li2S2 plays a pivotal role in the charge/discharge process of lithium-sulfur batteries. However, the structural configuration and relevant properties of Li2S2 are unclear. In this work, by using ab initio calculations, we present results of novel phases, average open circuit voltages ( Vocs), and electronic properties of the stable Li2S2. Two new Li2S2 phases are predicted: orthorhombic ( Cmca) and orthorhombic ( Immm) structures. The calculated Vocs of hexagonal ( P63/ mmc), orthorhombic ( Cmca), and orthorhombic ( Immm) are 3.91, 3.95, and 3.88 V, respectively. In particular, the calculated band gap of the Immm structure is about 0.225 eV, which is smaller than that of Li2S. The narrow band gap of Li2S2 derives from the electronic lump between the Li s state and S 3p state for the orthorhombic structure. Therefore, the electronic properties of Li2S2 are markedly influenced by the structural configuration.