Mitigating effects of polysulphide shuttle in lithium polysulphide flow batteries

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Energy storage is seen as a crucial component of a net zero energy landscape, and redox flow batteries have particular advantages over other battery types to enable flexible, long-lasting and long-duration storage. This project will work with flow battery manufacturer StorTera Ltd to develop a lithium polysulphide single-liquid flow battery, which promises to be a very low cost, sustainable solution thanks to the high abundance of sulphur and ability to use recycled lithium. Lithium-sulphur batteries have been under development for many years, with the promise of 10x higher energy density (2600 W h kg-1) than Li-ion batteries (up to 260 W h kg-1). There are major challenges to commercialise the Li-S cell such as a low coulombic efficiency due to the transport and reduction of polysulphides, known as polysulphide shuttle. Polymers of lithium and sulphur (Li2Sn , n=3-8), which get shorter as the battery discharges, should stay on the cathode side but can diffuse to the anode and cause self-discharge. A variety of technologies have been applied to inhibit the shuttle such as making new electrode constructions and formulations as well as the addition of lithium passivating agents (LiNO3) to inhibit the shuttle by forming a solid electrolyte interphase (SEI) on the anode. An alternative option is to configure a battery where the cathode consists of a solution of the soluble polysulphide compounds and is kept separate from the electrodes. This configuration has a lithium metal anode and graphite cathode with the polysulphide solution (catholyte) being pumped through the cell, known as a single liquid redox flow battery (SLIQ).The aim of this project is to seek a greater understanding of the polysulphide shuttle effect and the speciation of sulphur at different states of charge by analysis of the lithium polysulphide SLIQ. This will be achieved by utilising a variety of techniques, such as; spectroelectrochemistry to monitor the speciation of sulphur in the catholyte during a discharge/charge cycle; electrochemical quartz crystal microbalance to determine the deposition rates and composition of the SEI layer formed on the lithium anode. A combination of these techniques alongside typical electrochemical characterisations such as cyclic voltammetry and impedance spectroscopy will create a toolkit for analysis of future materials that will be considered for use in the system.