In situ characterization of Si-based anodes by coupling synchrotron X-ray tomography and diffraction

In the present work, combined synchrotron X-ray tomography/diffraction analyses are performed along the 1st and 10th cycles of a Si-based anode made with nanocrystalline/amorphous Si particles synthesized by ballmilling. We are using a porous C paper as a current collector instead of a conventional Cu foil and graphene nanoplatelets as a conducive additive instead of usual carbon black. It is shown that this specific formulation has a major impact on the structural changes of the electrode occurring upon cycling by (i) preventing its macroscopic cracking and related electrical disconnections, (ii) limiting its volume expansion and improving its reversibility, indicative of limited permanent damage in the electrode architecture, (iii) preventing the formation of c-Li15Si4 which is known to be detrimental for the electrode cyclability. However, the capacity fade with cycling remains significant. It can result from the accumulation of SEI products with cycling, progressively obstructing the porous network of the electrode, as supported by a significant decrease of the electrode porosity from 48% to 21% between the 1st and 10th cycle. The displacement and/or micro-cracking of the Si particles can also induce some electrical disconnections and irreversibility of the lithiation reaction. However, this degradation process occurring at the particle scale cannot be clearly identified from the present in-situ XRCT measurements due to spatial resolution limitation.