Real‐Time Imaging of Intercalation–Conversion Li Storage in MXenes for Solid‐State Batteries

ABSTRACT 2D transition metal carbides and nitrides (MXenes) are promising electrode materials for next‐generation energy storage devices. However, their charge‐storage mechanisms in solid‐state systems remain poorly understood, hindering further performance optimization. Here, Li‐ion intercalation and conversion reactions in Ti ₃ C ₂ T _x are directly visualized in sulfide‐based solid‐state Li batteries using operando scanning transmission electron microscopy combined with electron energy‐loss spectroscopy. The real‐time observations reveal three distinct reaction pathways: (i) Li (de)intercalation within the interlayer spacings of Ti ₃ C ₂ T _x accompanied by Ti redox reactions; (ii) partially reversible formation and decomposition of Li ₂ O on the Ti ₃ C ₂ T _x surface; and (iii) electrochemical decomposition of the sulfide solid electrolyte. The Li‐intercalation behavior is strongly governed by the surface terminations of Ti ₃ C ₂ T _x : O‐terminated MXenes enable efficient Li accommodation and redox activity at room temperature, whereas F‐ and Cl‐terminated MXenes require elevated temperatures for sufficient Li penetration. These findings provide direct nanoscale evidence of intercalation and conversion processes and highlight surface‐termination engineering as an effective strategy to enhance Li accommodation and improve their redox utilization in all‐solid‐state battery systems.