Comparing Na- and Li-ion diffusion in isostructural disordered rocksalt battery materials - muon

Na-ion and Li-ion batteries are central to the Net Zero agenda, enabling vehicle electrification. However, new battery cathode materials are required which can store charge more densely and enable faster ion diffusion to increase driving range and reduce charging times. We are investigating a new class of cathode materials known as disordered rocksalts, which deliver some of the highest reported energy densities and fast-charging capability despite their intrinsically disordered structure. While theoretical mechanisms to explain the fast ion diffusion in disordered rocksalts have been proposed, this important property has never been investigated experimentally in these new cathode materials. Here, we propose to employ muon spectroscopy to directly measure Na+ and Li+ ion diffusion in two archetypal, isotstructural disordered rocksalts, Li2MnO2F and Na2MnO2F. In combination with polarised neutron QENS, for which we have applied to LET in parallel with this proposal, we will investigate ion diffusion over a range of lengthscales and temperatures and compare how fast Li and Na ions can diffuse through the rocksalt structure. This will reveal new experimental insight into how these materials are able to exhibit fast charging capability and high energy densities as cathode materials for rechargeable batteries.