Probing Dynamic Sodium Diffusion, Local Charge States and Magnetic Environments in NaNiO2 via Operando Electrochemical, and ex situ Variable Temperature Muon Spectroscopy

We propose to measure operando μSR of NaNiO2 vs. Na metal using EMU, to study dynamic Na diffusion during the first charge cycle from OCV (~2.4 - 2.6 V in test cells) to 4.5 V, and discharges to 1.25 V), utilising the BAM cell developed at ISIS for use on EMU. Additionally, we also propose to measure variable temperature ex situ samples of phases which form throughout cycling, to verify the 300 K operando data, as well as facilitating collection of variable temperature (VT) measurements across a wide temperature range (400 – 100 K). This will allow probing of changes in magnetism as a function of temperature, with cooling to 100K expected to provide a clearer probe of the charge ordering (paramagnetic/diamagnetic Ni). EMU is ideally suited to this experiment, as the operando cell has been developed for use with the EMU CCR. EMU has demonstrated improved performance for these measurements, which is crucial when capturing large amounts of data associated with operando experiments, maximising the number of measurements taken per cycle, improving the counting statistics, allowing greater confidence. Ex situ and operando μSR data will be analysed as part of a combined study on the NaNiO2 system, utilising operando synchrotron XRD (Diamond I-11), operando NPD (POLARIS 2410197), and ex situ NPD (WISH 2410019), these structural studies will allow us to fully contextualise the changes in Na-ion motion investigated in the operando muSR experiment.