A membrane-free lithium/polysulfide semi-liquid battery for large-scale energy storage

Abstract

Large-scale energy storage represents a key challenge for renewable energy and new systems with low cost, high energy density and long cycle life are desired. In this article, we develop a new lithium/polysulfide (Li/PS) semi-liquid battery for large-scale energy storage, with lithium polysulfide (Li₂S₈) in ether solvent as a catholyte and metallic lithium as an anode. Unlike previous work on Li/S batteries with discharge products such as solid state Li₂S₂ and Li₂S, the catholyte is designed to cycle only in the range between sulfur and Li₂S₄. Consequently all detrimental effects due to the formation and volume expansion of solid Li₂S₂/Li₂S are avoided. This novel strategy results in excellent cycle life and compatibility with flow battery design. The proof-of-concept Li/PS battery could reach a high energy density of 170 W h kg⁻¹ and 190 W h L⁻¹ for large scale storage at the solubility limit, while keeping the advantages of hybrid flow batteries. We demonstrated that, with a 5 M Li₂S₈ catholyte, energy densities of 97 W h kg⁻¹ and 108 W h L⁻¹ can be achieved. As the lithium surface is well passivated by LiNO₃ additive in ether solvent, internal shuttle effect is largely eliminated and thus excellent performance over 2000 cycles is achieved with a constant capacity of 200 mA h g⁻¹. This new system can operate without the expensive ion-selective membrane, and it is attractive for large-scale energy storage.