E-Mobility Engineering 014 l InoBat Auto dossier l In Conversation: Brandon Fisher l Battery monitoring focus l Supercapacitor applications insight l Green-G ecarry digest l Lithium-sulphur batteries insight l Cell-to-pack batteries focus

electrode in the cell and allows more effective use of the sulphur. Combining the cathode and electrolyte into one liquid, called a catholyte, can help save weight in the battery, as well as offer faster charging and better power capabilities. “You take the aerogel, which is a long thin tube, and then you slice it,” says Carmen Cavallo of the Department of Physics at Chalmers, and lead researcher on the study. “You take that slice and compress it to fit into the battery. Then a sulphur- rich solution, the catholyte, is added and the porous aerogel acts as the support. “The aerogel’s porous structure is key. It soaks up a lot of the catholyte, giving you a high enough sulphur loading to make the catholyte concept worthwhile. “This kind of semi-liquid catholyte is really essential here. It allows the sulphur to cycle back and forth without any losses. It is not lost through dissolution, because it is already dissolved into the catholyte solution.” Some of the catholyte solution is applied to the separator as well, to maximise the battery’s sulphur content. The resulting cell showed 85% capacity retention after 350 cycles, but the challenge is to improve the capacity and the cycle life. The project includes Volkswagen as well as materials company Johnson Matthey, which acquired the technology developed by LiS cell pioneer Oxis Energy. The research aims to develop all the steps for producing a commercial battery cell, starting from material synthesis and characterisation, and using nanotechnology for improving the charging rate before building and testing large-scale prototypes, with scaling up the manufacturing process with industrial partners. It will also make sure the cells can be recycled. Conclusion Sulphur is an intriguing material for e-mobility batteries. Combined with a lithium metal anode, it has the potential to provide lightweight, high-capacity battery packs at half the cost of present lithium-ion packs without the safety risks, even with liquid electrolytes. With solid electrolytes the risks are reduced even further, and this reduces the need for many of the safety-related aspects of a battery pack that are designed to limit the impact of thermal runaway, making packs lighter still. The high energy density makes it a strong candidate for powering the motors of electric aircraft, but the challenges of the relatively short cycle life remain. Many research projects around the world are looking to overcome the challenge of the polysulphide shuttle problem, with different architectures and materials such as graphene aerogels and Kevlar nanoparticles. These are showing highly promising results, boosting the lifetime of LiS cells from under 50 to over 4000 charge- discharge cycles. The challenge being addressed now is to commercialise the technology for volume production. The lower cost of sulphur, and the elimination of nickel and cobalt gives battery makers more headroom for reducing costs, even with smaller manufacturing volumes. Some manufacturers are now emerging from years of quiet development with high-capacity prototype LiS battery packs with long lifetimes that are now being tested by lead customers in the US. As these gain traction in niche applications, e-mobility designers will be able to adopt the technology in existing lithium-ion manufacturing lines, boosting the range and operating times of vehicles. That then leads to the potential for high-performance battery cells that eliminate the use of lithium metal anodes. Cells with silicon or magnesium anodes and sulphur cathodes offer the potential for more rugged battery packs with even higher energy densities that sidestep the challenges of thermal runaway entirely. Deep insight | Lithium-sulphur batteries :ulphur oɈers a way to eliminate lithium from high-performance EV batteries (Courtesy of Chalmers <ni]ersity) 62 Summer 2022 | E-Mobility Engineering