Operando Elucidation of All Six Reversible Li–Ga Phase Transitions, Inverted Hysteresis, and Interfacial Dynamics in a Nanoconfined CMK-3/Ga Anode

Abstract

Stabilizing phase transitions in alloy-type anodes remains a critical challenge for advancing high-performance lithium-ion batteries (LIBs). Herein, we present a gallium-infused mesoporous carbon composite (CMK-3/Ga), synthesized via a facile ball-milling method, as a promising anode material for LIBs. Leveraging the intrinsic properties of gallium (Ga) and its nanoscale confinement within CMK-3, we unveil unprecedented electrochemical and structural insights into Li–Ga alloying dynamics. For the first time in a carbon-confined system, comprehensive operando cyclic voltammetry (CV) combined with in situ X-ray diffraction (XRD) enables complete identification of all six Li–Ga alloying and dealloying phases (L1–L6 and D1–D6), with direct structural validation. This high-resolution mapping significantly advances the understanding of complex alloy electrochemistry. Notably, we observe a unique inverted hysteresis behavior, where delithiation initiates at lower potentials than lithiation, converging at a distinct low-voltage “pinning point” (~0.05 V). This kinetically favorable pathway is directly correlated with pronounced structural rearrangements observed via in situ XRD, providing new mechanistic insights into lithium extraction processes. Furthermore, we identified the spontaneous formation of a reversible CuGa2 interphase at the current collector. This self-regulating buffer layer, validated by operando CV-EIS through suppressed Cu2O/CuO formation and enhanced kinetics, effectively maintains electrode contact and reduces capacity degradation. The optimized CMK-3/Ga anode delivered a high reversible capacity of 527 mAh/g over 100 cycles, exhibiting enhanced rate capability and significantly lower irreversible capacity loss, outperforming pristine CMK-3. This work provides real-time mechanistic understanding for robust alloy anodes, advancing the rational design of high-performance, self-protective energy storage materials.