(Invited) In situ muon spin relaxation for probing ion diffusion in lithium batteries

All solid-state batteries present highly promising opportunities for safer energy storage. High ionic conducting solid electrolytes may overcome some of the limitations of organic polymer electrolytes, where safety concerns limit the electrochemical stability window, to provide a way to increase energy densities in a safe manner. However, resistance to ion mobility across the solid-solid electrode-electrolyte interface remains a bottle-neck to be overcome in realising this technology. The synthetic approach employed can potentially influence conductivities (and hence battery performance) exhibited by solid electrolytes and this talk will detail our efforts to maximise these properties through developments in our synthetic and characterisation approaches. Recent synthetic results on systems such as the NASICONs and perovskites where electrodes and electrolytes with similar crystal structures are applied in an effort to lattice match across the interface, will be discussed. Comprehensive characterisation methods which employ multiple experimental techniques to simultaneously probe lithium-ion diffusion on different length and time scales will be presented, with particular attention to recently developed in situ muon spin relaxation measurements aimed at interrogating ion diffusion across the electrode-electrolyte interface. These results will showcase how careful synthetic design can enable performance and a comprehensive analysis provides greater insight into materials properties.