E-Mobility Engineering 017 l ECE Doosan electric excavators dossier l In Conversation: Matt Faulks l Battery testing focus l Battery Show North America 2022 report l Ariel Hipercar digest l Cathode materials insight l Thermal management focus

to polyanion oxides led to polyanion oxides with phosphate groups being investigated in the late 1980s. LiTi 2 (PO 4 ) 3 , LiZrTi(PO 4 ) 3 , NbTi(PO 4 ) 3 and SbTi(PO 4 ) 3 all had an operating voltage of 2-3V, with the LixSbTi(PO 4 ) 3 system displaying the highest voltage of 3V compared with about 1.5V for the Ti3+/4+ couple in a simple oxide such as TiO 2 . The ability to increase the voltage to as high as about 5V in polyanion oxide cathodes, for example in LiMnPO 4 , has led to a range of sulphates, phosphates and silicates being used in lithium-ion cells as well as sodium-ion cells with Li 3 V 2 (PO 4 ) 3 , Na 3 V 2 (PO 4 ) 3 , and Na 3 V 2 (PO 4 ) 2 F 3 and LiFePO 4 . After Sony commercialised lithium- ion batteries with LiCoO 2 cathodes and graphite anodes in 1991, researchers focused on polyanion oxides, says Prof Manthiram, driving the identification of olivine LiFePO 4 as a cathode material in 1997. LFP materials such as PLFP02113 from Targray have a high specific capacity of C0.2 discharge (more than 150 mAh/g) with a C10 discharge rate and low-temperature performance for applications such as electric buses. Pros and cons Layered and spinel classes of oxides offer good electronic conductivity, while the polyanion oxide class suffers from poor electronic conductivity. That means polyanion oxide cathodes require the particles to be synthesised small and coated with conductive carbon, which often increases the processing cost and introduces inconsistencies in performances. Layered and spinel oxides have close-packed structures with high densities, while the polyanion class of oxides generally have lower densities, which is further reduced by that need to make them as small particles coated with carbon, leading to a lower volumetric energy density and more suited to e-mobility applications with lower peak power requirements, such as trucks. However, the polyanion cathodes have high thermal stability and better safety than the layered and spinel oxide cathodes. The small carbon- coated particles can also sustain higher charge/discharge rates thanks to their good structural integrity, despite their lower volumetric energy density. Using abundant transition metals such as iron rather than cobalt also offers sustainability advantages. Between the layered and spinel oxides, layered oxides are more Top: schematic illustration of the dissolution and migration of transition-metal ions from the cathode to the graphite anode; bottom: making the lattice robust by perturbing the long-range metal-to-metal interaction and increasing the metal-oxygen bond strength (Courtesy of Arumugam Manthiram) Scanning electron microscopy images reveal the sphere-like morphology of the powder particles of NMC622 (Courtesy of Skoltech) 60 January/February 2023 | E-Mobility Engineering