Accumulative Delocalized Mo 4d Electrons to Bound the Volume Expansion and Accelerate Kinetics in Mo₆S₈ Cathode for High-Performance Aqueous Cu²⁺ Storage

Electronic structure defines the conductivity and ion absorption characteristics of a functional electrode, significantly affecting the charge transfer capability in batteries, while it is rarely thought to be involved in mesoscopic volume and diffusion kinetics of the host lattice for promoting ion storage. Here, we first correlate the evolution in electronic structure of the Mo6S8 cathode with the ability to bound volume expansion and accelerate diffusion kinetics for high-performance aqueous Cu2+ storage. Operando synchrotron energy-dispersive X-ray absorption spectroscopy reveals that accumulative delocalized Mo 4d electrons enhance the Mo-Mo interaction with distinctly contracting and uniformizing Mo-6 clusters during the reduction of Mo6S8, which potently restrain lattice expansion and release space to promote Cu2+ diffusion kinetics. Operando synchrotron X-ray diffraction and comprehensive characterizations further validate the structural and electrochemical properties induced by the Cu2+ intercalation electronic structure, endowing the Mo6S8 cathode a high specific capacity with small volume expansion, fast ions diffusion, and long-term cycling stability.