Batteries will be key in our efforts to reduce CO2 emissions but require major progress in sustainability, cost, and energy density. Liquid-electrolyte metal-sulfur batteries, in particular lithium-sulfur (Li–S) systems, would be game-changers in many respects: a theoretical capacity amongst the highest of all batteries paired with the low cost and sustainability of sulfur. However, intrinsic obstacles are imposed by the electronically and ionically insulating nature of sulfur. Converting sulfur during discharge/charge is fundamentally different from mixed-conducting storage materials. While Li-ion battery materials transform in the solid-state, sulfur converts to metal sulfides in a solid-liquid-solid process. This causes poor cycle life and insufficient energy densities.
In the SOLIDCON project, we aim to redirect sulfur conversion towards a high-rate, bulk solid-state mechanism, combining high capacity with improved cycle life, reduced parasitic dissolution, and a higher packing density of active material. To achieve this, we develop advanced characterization methods, such as cryo-transmission electron microscopy (cryo-TEM) and operando scattering techniques, supported by machine-learning-based stochastic modelling to monitor and understand conversion processes at nanometer length scales, ranging from approximately 1 to 1000 nm. We systematically study three mechanistic regimes of electrochemical sulfur/sulfide conversion: (i) conventional solid-liquid-solid conversion in solvating electrolytes; (ii) quasi solid state conversion in sparingly solvating systems; and (iii) true solid state conversion in carbon confinement and with carbonate based electrolytes.
Based on these insights, we design composite cathodes, incorporating structured conductive hosts (nanoporous carbons) and ion/electron transport networks, targeting high rate, high density solid state sulfur conversion. The expected impact is the development of battery materials and methods that push metal-sulfur systems closer to practical, high energy, sustainable storage solutions, contributing to climate mitigation and enabling next generation electrochemical energy storage.
