E-Mobility Engineering 019 | In conversation: Stephen Lambert l WAE EVR l Battery case materials focus l Quality control insight l Clipper Automotive Clipper Cab digest l Optimising battery chemistries insight l Powertrain testing focus

58 May/June 2023 | E-Mobility Engineering With the move towards solid-state cells, Nick Flaherty reports on the latest research into improving their performance as well as that of other chemistries Solid state of play T here are many materials involved in the optimisation of battery cells beyond the anode, cathode and electrolyte, and researchers around the world are working on a wide range of additives to boost the performance of cells. The move to solid-state cells for example is driving the development of materials ranging from ceramic and polymer layers throughout a cell to materials such as silicon disulphide (SiS 2 ). The additives, frompolymer coatings for electrodes to flame-retardant materials in the electrolyte, are also pointing theway tomaking lithiummetal and lithiumsulphur cellsmore viable, providing a route to cells withmuch higher energy densities. Solid-state materials Researchers in Korea have developed a low-cost SiS 2 production technology to boost all-solid-state battery (ASSB) performance. A team led by Dr Ha Yoon-Cheol, a Principal Researcher in the Next Generation Battery Research Centre at the Korea Electrotechnology Research Institute (KERI), and Dr Cheol-Min Park, a Professor at the School of Materials Science and Engineering at Kumoh National Institute of Technology (KIT), have developed the technique for producing SiS 2 for argyrodite-type solid- state batteries based on Li6PS5Cl. They replace the liquid-state electrolytes that transfer ions between the anode and cathode with a solid that is less prone to fire or explosion. However, there remain many challenges to achieving commercialisation, such as difficulties in processing and mass production, and high material costs. Adding SiS 2 to solid-state electrolytes for ASSBs helps improve ionic conductivity andmoisture stability. Thematerial also helps boost the performance of layeredmaterials with tuneable bandgaps, valley polarisation, and weak van der Waals interlayer forces. However, the synthesis of SiS 2 from sulphur and silicon requires a high reaction temperature, which leads to surges in the vapour pressure of sulphur, making the production of SiS 2 particularly tricky. For this reason, SiS 2 is very expensive, currently costing about $1300 for 20g. The chemical synthesis process optimises the arrangement of sulphur, silicon and carbon powders in a sealed environment to withstand the vapour pressure of sulphur at 800 oC. The quality of the resulting product is comparable to commercially available products but with a simpler production process and lower costs. The SiS 2 is fabricated using amorphous carbon in a simple mechanical process. It has a high Investigating lithium sulphur materials at the University of Coventry (Courtesy of Nyobol)