Unveiling the Interfacial and Bulk‐Structural Failures of TiS 2 Anodes Under Deep Sodiation

ABSTRACT Transition metal dichalcogenides (TMDs) suffer from severe capacity degradation during deep sodiation, yet the fundamental failure mechanisms remain elusive. Using titanium disulfide (TiS 2 ) as a model anode, we unravel the interfacial and bulk‐structural failures triggered by extending the discharge cutoff voltage to 0.01 V. Specifically, the interfacial failure is driven by the massive precipitation of highly reactive metallic Ti, which aggressively reacts with the electrolyte to form inactive Ti–O compounds, irreversibly consuming active Ti and preventing Ti–S bond reconstruction. Meanwhile, the bulk‐structural degradation originates from severe accumulation of internal stress, leading to the irreversible disintegration of the layered framework. To circumvent these coupled challenges, we propose a robust carbon‐sphere encapsulation strategy, confining TiS 2 nanosheets within dense spherical carbon matrices (TiS 2 @C). This dual‐functional architecture effectively redistributes localized stress to mechanically buffer severe volume expansion and physically isolates the precipitated active Ti from the electrolyte, thereby suppressing the detrimental parasitic oxidation. Consequently, the TiS 2 @C composite unlocks its full conversion capacity, achieving exceptional long‐term stability with a 98.5% capacity retention over 1800 cycles within an expanded 0.01–3.0 V window. This work elucidates the intrinsic degradation mechanisms of TMDs at extreme sodiation and establishes a highly effective structural engineering paradigm.