Bridging Particle-Scale Lithiation Mechanisms and Macroscopic Performance in High-Energy Density Si Anodes via Time-resolved Full 3D Visualisation

Anodes with high silicon (Si) content, paired with nickel-manganese-cobalt (NMC) cathodes, enable interesting prospects for Li-ion batteries well beyond the state of the art. However, when Si alloys with lithium (Li), it undergoes significant volume changes, raising the critical question of how exactly the electrode and individual particles respond to the lithiation dynamics and thus impacting the battery performance. Here, we provide enhanced insights into the chemo-mechanical processes for cells with an 89 wt% Si anode paired with an NMC cathode. Electrode-scale deformation is linked with particle-scale mechanics by incorporating correlative multiscale 3D in situ investigations. Indeed, the combination of a sophisticated in situ cell setup, with high-resolution synchrotron X-ray computed nano-tomography, together with AI-driven segmentation and 4D strain mapping, allows us to detect pronounced spatial deformation and strain heterogeneities from the electrode to the single particle level. We observe diverse lithiation behaviours, anisotropic strain evolution and mechanically distinct transformation modes across hundreds of particles. Stress concentrators and fracture nucleation sites steer the transformation, generating localized strain fields decoupled from bulk electrode swelling. Indeed, many particles lithiate via complex internal network-like transformation routes. These 4D multiscale observations highlight key design levers for silicon-rich anodes, including defect screening, particle size optimization and electrode architecture engineering.