Neutron and muon characterisation techniques for battery materials

Neutron and muon characterisation techniques offer unique capabilities for investigating the complex structure and dynamics of rechargeable battery systems. Whilst the non-monotonic interaction of the neutron with the nuclei of atoms makes it sensitive to light and neighbouring elements in the periodic table, its weakly interacting nature allows it to penetrate deep into the sample without damaging it, enabling the flexible use of complex sample environments such as in situ/in operando cells. Meanwhile, the also non-invasive nature of an implanted positive muon allows it to be used as a probe to study bulk ionic diffusion phenomena within materials at different depths by tuning the energy of the incident muons. This review discusses the application of relevant neutron and muon characterisation techniques to the study of specific phenomena in ion batteries, highlighting key literature cases that serve as the archetypal example for the utility of each technique. Furthermore, this review includes an accessible overview of the working principles of each technique that has been condensed and optimised to provide a basic understanding of their relevance to the particular challenges they can address.