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

the boundaries and improve the mechanical integrity during battery cycling. Testing small cells with such single-crystal cathodes showed a 25% increase in energy storage per unit volume, with almost no loss of performance over 100 cycles of testing. By contrast, over the same cycle life, the capacity declined by 60-88% in NMC cathodes composed of single crystals with many internal boundaries or with coated polycrystals. “We now have guidelines that battery manufacturers can use to prepare cathode material that is boundary- free and works at high voltages,” says Khalil Amine, an Argonne Distinguished Fellow who worked on the project. “And the guidelines should apply to other cathode materials besides NMC.” These show how the structure of the cathode depends on a combination of materials and the manufacturing process. The processes for manufacturing cathodes are also coming under scrutiny for the cost of the energy to create the high temperatures needed, the greenhouse gases produced as a result, and the cost of materials such as cobalt. synthesis on the other hand, there’s really not much you can do to affect morphology.” The team identified the salt parameters that promoted spherical particle formation. Tests confirmed that the resulting material had the same energy storage capacity per unit mass as the commercial analogues but had greater energy density, enabling more power to be packed into the same limited space. The researchers are now experimenting with particle size, combining smaller and larger spheres for denser packing. The team will also pursue layered transition-metal oxides that would replace even more cobalt and manganese atoms with nickel, further enhancing energy storage capacity. However, there is a drive to retain cobalt. Researchers at Stanford University, in the US, have shown that cobalt’s thermodynamic stability in layered structures is essential in enabling access to higher energy densities without sacrificing performance or safety, effectively lowering battery costs per kWh despite increasing raw material costs. The supply growth required to support intermediate cobalt-content cathodes for 1.3 billion EVs by 2050 is within historical trends for major industrial metals, says Professor William Gent at Stanford, although providing sufficient supply from unstable economies – or what he calls “challenging jurisdictions” – is likely to remain a problem. Cathode cracks Researchers at the US Department of Energy’s Argonne National Laboratory have also been working on single- crystal cathodes. “The present-day NMC cathode has posed a major barrier to operation at high voltage,” says Guiliang Xu, assistant chemist at Argonne. “During the charge/discharge cycles, performance rapidly declines owing to cracks forming in the cathode particles. For several decades, battery researchers have been seeking ways to eliminate those cracks. Xu and his team had previously developed a protective polymer coating around each polycrystalline particle to minimise cracking at the grain boundaries. They also looked at a different approach to avoid this cracking that involves using single- crystal particles; however this material still formed cracks with cycling, so they looked at the reason for that. “When we look at the surface morphology of these particles; they look like single crystals,” says Argonne physicist Wenjun Liu. “But when we use synchrotron X-ray diffraction microscopy and other techniques, we find boundaries hiding inside.” The team developed a method for producing boundary-free single crystals by focusing on the oxygen redox instability from the domain boundaries in single-crystalline cathode particles. By investigating single-crystalline cathodes with different domain boundaries structures, they could eliminate A patented ‘one-pot’ process combines all input components in a single reaction to produce a precursor that forms quickly into a single-crystal cathode material simultaneously with its protective coating (Courtesy of Nano One Materials) 62 January/February 2023 | E-Mobility Engineering