Revealing the Dynamic Lithiation Process of Copper Disulfide by in Situ TEM

Abstract Transition metal oxides, fluorides, and sulfides are extensively studied as candidate electrode materials for lithium‐ion batteries driven by the urgency of developing next‐generation higher energy density lithium batteries. These conversion‐type electrode materials often require nanosized active materials to enable a “smooth” lithiation and de‐lithiation process during charge/discharge cycles, determined by their size, structure, and phase. Herein, the structural and chemical changes of Copper Disulfide (CuS 2 ) hollow nanoparticles during the lithiation process through an in situ transmission electron microscopy (TEM) method are investigated. The study finds the hollow structure of CuS 2 facilitates the quick formation of fluidic Li 2 S “drops,” accompanied by a de‐sulfurization to the Cu 7 S 4 phase. Meanwhile, the metallic Cu phase emerges as fine nanoparticles and grows into nano‐strips, which are embedded in the Li 2 S/Cu 7 S 4 matrix. These complex nanostructured phases and their spatial distribution can lead to a low de‐lithiation barrier, enabling fast reaction kinetics.