The work of material scientists in the discovery, understanding, and development of Li-ion batteries largely depends on the techniques available to observe the relevant processes on the appropriate time and length scales. This chapter aims at demon­strating the role and use of different neutron-scattering techniques in gaining insight into Li-ion battery electrode and electrolyte function. This is not an exhaustive review of the neutron-scattering work on Li-ion battery materials or on the materials themselves, but an attempt to demonstrate the range of possibilities of neutron scattering in Li-ion battery materials research.

The role of neutron scattering in battery research is mainly based on the sen­sitivity of neutrons to Li compared to X-rays and electrons. The coherent neutron­scattering cross section of Li often allows the determination of the Li positions, atomic displacement parameters (ADPs), and occupancies using diffraction where X-rays do not, making it possible to elucidate Li-ion insertion/extraction mecha­nisms. The relatively-large coherent neutron-scattering cross section of Li provides sufficient contrast that Li distributions can be studied using imaging and, in thin — films, reflectometry. The incoherent neutron-scattering cross section of Li allows examination of Li mobility. Measuring Li diffusion directly is difficult as Li has only a moderate incoherent neutron-scattering cross section, so each material has to be considered individually to determine if the neutron-scattering signal originates from Li. Often measuring host material dynamics, e. g. anion and hydrogen group dynamics or lattice vibrations using quasi-elastic neutron scattering (QENS) and inelastic neutron scattering (INS), can provide information on Li dynamics. The diffusion pathway can be additionally corroborated or even independently obtained using the abovementioned large coherent cross-section of Li by considering the anisotropic contribution in the displacement parameter because of the deviation from harmonicity due to thermal motion at elevated temperatures. The relatively large neutron absorption cross-section of Li enables neutron depth profiling to determine Li distributions in materials. In these neutron-based techniques used to study Li-ion battery materials, the effective cross-sections of samples under study can be tuned through the isotopic composition. Naturally occurring Li is composed of 7.5 % 6Li and 92.5 % 7Li. The larger coherent neutron-scattering cross section and lower incoherent neutron-scattering and absorption cross-section of 7Li make it possible to improve data quality by tuning compositionally (isotopically) samples according to the neutron investigation technique being used.