Structural Evolution of State-Dependent Kinetics during Potassium Storage in Layered CrSe2

Abstract Layered CrSe2 reversibly accommodates approximately one potassium (K) per formula unit, but the structural origin of its rate-dependent capacity remains unresolved. Operando synchrotron X-ray diffraction (SXRD) reveals the sequential P-3m1-R3m-C2/m phase pathway during cycling at different current rates. The P-3m1/R3m transformation exhibits the lattice discontinuity and becomes incomplete when increasing the current rate, as directly observed by operando SXRD. Chemical K deintercalation and state-resolved impedance measurements provide complementary evidence for sluggish kinetics near the fully deintercalated regime. Restricting the upper cutoff voltage will sacrifice some capacity but will improve electrochemical cycling capacity retention. These findings identify a particularly rate-sensitive structural region and show how phase-resolved characterization can guide voltage-window selection for layered potassium-storage electrodes.