Unusual crystal-structure behaviour of Li₂CO₃under static compression

Li₂CO₃ is the largest natural source of lithium (82,000 tonnes extracted in 2020), used as a precursor in the synthesis of lithium-ion battery cathode materials. Partially due to the large quantities involved, this is a field where the use of high-pressure has yet to be fully investigated. It can, for example, be used to stabilise unusually doped cathode materials which can then be recovered to ambient conditions, [1] or to control particle size, or alter synthesis efficiency for existing materials. Despite its industrial significance, there is little known about the crystallography of Li₂CO₃ at high-pressure [2]. Current work has found that the relatively simple structure shows unusual high-pressure behaviour, such as negative linear compressibility. This leads to a distortive first-order phase-transition to a hexagonal structure above ~8 GPa, with a change to octahedral Li⁺ coordination. Additionally, the material is shown to be highly affected by non-hydrostatic pressure conditions, forming a new structure altogether. I will present a combination of neutron powder-diffraction data, Raman spectroscopy and computational analysis, building our understanding of why this material behaves in this way.

[1] Stoyanova, R. et al. (2002). Journal of Materials Chemistry 12, 2501-2506.

[2] Grzechnik, A. et al. (2003). Journal of Solid State Chemistry 173, 13-19.