Silicon (Si) is the most promising anode material to increase lithium ion battery energy density. This performance is due in part to the large amount of lithium it can alloy with. However, that amount of (de)lithiation leads to the expansion (or contraction) of particles up to 280%, which induces mechanical degradation at many electrode levels. Our strategy is to buffer this volume expansion with Si particles containing inner porosity. But, it works if the latter is preserved, which is very difficult to assess in working battery conditions. Here we will use X-ray nano-tomography to monitor the Si particles morphological changes down to the nano-scale, as well as possible electrode degradation during cycling (in situ conditions). This will provide unprecedented insight in the role of porosity, providing direction to porous silicon development for the next generation of high energy density batteries. This proposal involves an industrial partner: E-magy, who provides the Si electrodes.