Operando electrode-scale stress characterization revealing the Li+ insertion mechanism of graphite anode

As a preferred anode material for lithium-ion batteries, a deeper understanding of the lithiation mechanism in graphite is essential for advancing novel optimization strategies. In this study, the lattice evolution information traditionally obtained through techniques such as X-ray diffraction and neutron powder diffraction is innovatively translated into stress signals for analysis, providing mechanical insights into the Li⁺ intercalation mechanism in graphite. The dynamic lithiation behavior of graphite particle assemblies is simulated using the Monte Carlo method, and combined with in situ X-ray diffraction and high-resolution transmission electron microscopy, the mechanical–electrochemical mapping relationship during lithiation is systematically elucidated. The lithiation process of graphite exhibits three distinct mechanical stages: C→LiC₃₀, LiC₃₀→LiC₁₂, and LiC₁₂→LiC₆. Notably, during the transitions between the first/second and second/third stages, significantly differentiated mechanical signatures are observed, which deviate from theoretical predictions. Further analysis reveals that the former originates from a rapid phase separation process, while the latter is driven by lattice reconstruction induced by lithium intercalation. These two phenomena can be well explained by the Rüdorff–Hofmann interlayer intercalation model and the Daumas–Herold domain wall migration mechanism, respectively. The presence of such stage-specific mechanical responses suggests that distinct intercalation mechanisms govern different stages of graphite lithiation. The experimental findings presented in this work contribute to a multidimensional and comprehensive understanding of the graphite lithiation mechanism.