Challenges and Breakthroughs Towards the Development and Optimisation of a Zero Excess Li-S Battery

Abstract

There is currently a large demand to produce batteries and energy storage devices offering both improved volumetric and gravimetric energy densities to help prevent the catastrophic effects of climate change. One promising candidate is the lithium-sulfur (Li-S) chemistry due to the high theoretical capacity and abundance of sulfur. However, current designs require a 1000% excess of Li metal which impedes their commercialisation. An area gaining momentum is the development of “anode-free” or zero excess lithium (ZEL) cells which minimise inactive materials and mitigate the challenges of handling Li metal foils during fabrication. So far, most studies involving anode-free have been based on the Li-ion chemistry and there are significantly fewer systematic studies concerning ZEL Li-S cell fabrication and optimisation. However, nearly all fall short of targets required for commercialisation.Here we present the development of an Li2S ZEL cell composed of a Li2S/C65/SBR positive electrode material paired with a metallic current collector. The design allows for a Li-limited LiS battery where Li-ions are reversibly plated and stripped to a metallic current collector surface. We initially investigate the effects of electrolyte volume :Li2S mg (ES) ratio, conductive carbon loading, C-rate capacity dependency, various current collector materials and positive electrode substrates. The optimised cell achieves good capacity retention with a Coulombic efficiency of over 98% after 50 cycles, and a final capacity of 400 mAh g-1.Previous studies have shown difficulties in achieving consistent results and are often distorted by a large volume of conductive carbon present in the cathode substrate [1, 2]. Therefore, investigations into capacity losses stemming from the cathode are presented using a range of air-tight characterisation techniques. The performance is also closely correlated to the efficiency of reversible Li deposition onto the metallic current collector, as evaluated by comparison to the use of Li negative electrodes. In the ZEL set up, losses from dead Li formation and SEI instability result in permanent loss of Li inventory with no reservoir to replenish. To counter this, initial investigations attempting to apply an ionically conductive coating to the metal current collector surface are shown.[1]. S. Nanda, A. Gupta and A. Manthiram, Adv. Energy Mater., 2018, 8, 2–7.[2]. S. Nanda, A. Bhargav and A. Manthiram, Joule, 2020, 4, 1121–1135.