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

62 lithium-ion,” says Larry Curtiss, a Distinguished Fellow at Argonne. In previous lithium-air designs, the lithium in a lithiummetal anodemoves through a liquid electrolyte to combine with oxygen during the discharge, yielding lithiumperoxide (Li 2 O 2 ) or superoxide (LiO 2 ) at the cathode. The peroxide/ superoxide is then broken back down into its lithiumand oxygen components during the charge. This chemical sequence stores and releases energy on demand. The solid electrolyte is a Li 10 GeP 2 S 12 ceramic polymer material built fromnanoparticles embedded in amodified polyethylene oxide polymer matrix that enables the chemical reactions that produce lithiumoxide (Li 2 O) on discharge. “The chemical reaction for lithium superoxide or peroxide involves only one or two electrons stored per oxygen molecule, whereas that for lithium oxide involves four electrons,” says Argonne chemist Rachid Amine. This gives the higher theoretical energy density. The design is the first lithium-air battery to achieve a four-electron reaction at room temperature and with oxygen from ambient air rather than pressurised tanks. To confirm the four- electron discharge operation, the team used transmission electron microscopy of the discharge products on the cathode surface. Previous lithium-air test cells have also suffered fromvery short cycle lives. The newdesign has been tested over 1000 cycles, demonstrating its stability over repeated charging and discharging cycles. “With further development, we expect our new design for the lithium-air battery to also reach a record energy density of 1200 Wh/kg,” says Curtiss. ​ “That is nearly four times better than lithium-ion batteries.” Polymer coatings Scientists at Lawrence Berkeley National Laboratory have developed a conductive polymer coating for lithium- ion cells that conducts electrons and ions at the same time. This ensures battery stability and high charge/ discharge rates while enhancing battery life. The coating also shows promise as a battery adhesive that could extend the lifetime of a lithium-ion battery from an average of 10 years to about 15. Silicon and aluminium are promising electrode materials for lithium-ion batteries because of their potentially high energy storage capacity and lightweight profiles. But these cheap and abundant materials quickly wear down after multiple charge/discharge cycles. The coating is a conductive binder made froma non-toxic polymer that transforms at the atomic level in response to heat. At room temperature, alkyl end-chains on the (9,9-dioctylfluorene- co-fluorenonecomethylbenzoic ester, PFM) polymer chain limit themovement of lithium ions. However, when heated to about 450 oC, the alkyl end-chains melt away, creating vacant ‘sticky’ sites that ‘grab’ onto silicon or aluminiummaterials at the atomic level. The polymer chains then self- assemble into spaghetti-like strands called hierarchically ordered structures, or HOS. The resulting strands of material, now called HOS- PFM, allow lithium ions to move along with the electrons aligned to the conductive polymer chains, boosting the energy transfer. Scanning electron microscopy shows the improvement in the electrode material’s surface using the HOS-PFM polymer (Courtesy of Berkeley Labs) Testing out a fluorosulphate material as a flame-retardant additive (Courtesy of ETRI) May/June 2023 | E-Mobility Engineering