The development of energy storage and conversion devices demanded to generate clean and sustainable energy relies on the design, synthesis, and characterisation of novel materials with suitable properties in terms of ionic or electronic conductivity, ionic insertion capabilities, redox activity, catalytic properties, etc. The structure of the materials used in energy may condition these properties and their overall good performance, and its knowledge is essential for proper understanding and optimising of these materials. To define the crystalline structure, Neutron powder diffraction (NPD) is a powerful tool that, combined with the Rietveld refinement method, is able to provide detailed structural information. This way, properties closely related to the structure and its evolution with external factors (temperature, pressure, cycling in in-operando systems, etc.) can be assessed with greater certainty. Well-known applications of neutron diffraction are the location of oxygen atoms and oxygen vacancies in oxide ion conductors, Li ions in solid electrolytes or Li-ion battery cathodes, protons in fast H⁺ conductors, etc. The ionic conductivity of these diverse materials is partly conditioned by the structure, composition, atomic radii, and formal charges of each atom, among others. An inexpensive and relatively efficient way to exploit these data in order to determine properties such as ionic percolation activation energy is the use of Bond‑Valence Energy Landscape (BVEL), which relies on structural data that can be determined by NPD. In this way, NPD and BVEL form a synergistic tandem that is useful in the assessment of ionic conductors. In this talk, we will present some recent results obtained for different types of energy-related materials, including Li-ion battery electrodes, electrolytes in Na batteries, and H⁺ conductors.

As Li cathode example, an N-doped LiFePO₄-type material, where nitrogen partially replaces an oxygen atom of the olivine tetrahedra lattice at 4c Wyckoff site in the Pnma space group. The structure was correctly determined by the Rietveld method from NPD data, and a subsequent calculation by BVEL confirms the decrease in activation energy (Ea) by about 6 % with respect to the pristine structure upon N-doping. As a solid electrolyte example, collaborative work is presented, in which the structures of Mg-doped NZSP NASICON-type electrolytes were determined at different temperatures from neutron data. A decrease in the activation energy concerning the undoped sample and its temperature dependency is assessed by BVEL. Finally, an example of a proton conductor used as a catalyst is presented, the so-called antimonic acid, where the presence and location of two different H⁺ are verified and identified by means of Fourier density difference maps. In this talk, a brief review of these different materials will be made, with emphasis on the specific structural features determined by the neutrons that explain the desired properties of the materials applied to energy.