In situ diffraction studies can capture transient crystalline phases forming during chemical reactions. Whether the reaction is a chemical solid-state synthesis, or an electrochemical intercalation process within typical active compounds used as battery electrodes, proper sample environments allow nowadays to perform in situ diffraction experiments with high temporal and angular resolution at large scale facilities, and even when using laboratory diffractometers. In both cases, the time-resolved nature of the experiments allows to obtain a greatly increased amount of information. For example, in the synthesis of inorganic materials, reactions often yield non-equilibrium kinetic byproducts instead of the thermodynamic equilibrium phase ^[1]. On the other hand, often stable compounds cannot be synthesized. To rationalize that, the competition between thermodynamics and kinetics occurring during the process need to be investigated in real time. Fully determining the reaction pathway is a key requirement to achieve the rational synthesis of target materials ^{[2, 3].} In this presentation, I will highlight recent examples from our work applying in situ xray/synchrotron/neutron diffraction to understand the synthesis of relevant industrial compounds such as LiNiO₂^[4], LiCoO₂^[5] and doped versions thereof ^[6,7], as well as some promising positive electrode for sodium-ion batteries. These will be both layered compounds, as well as fluorophosphates of the Na₃V₂(PO₄)₂F₃-_yO_y family [8].