Orbital Occupancy Engineering of Co d-Band Centers via Interfacial Electron Injection Enables High-Efficiency Alkaline Zinc Batteries

Abstract The high theoretical capacity of cobalt sulfide makes it a compelling cathode material for aqueous alkaline zinc batteries (AAZBs). Nevertheless, they still fall short of the performance requirements for practical AAZBs due to the unfavorable OH– adsorption capability and low electrical conductivity, which originate from an intrinsically unfavorable d-orbital configuration of Co centers. Herein, we propose a strategy to precisely modulate the d-orbital configuration of Co centers via spontaneous interfacial electron transfer from a Ti3C2Tx MXene substrate into a mixed-phase CoS/Co9S8 (CS@MXene). This electronic perturbation shifts the Co d-band center upward and improves the metallic character, thus strengthening its OH– binding affinity, enhancing electrical conductivity, and accelerating the redox kinetics. Consequently, the battery assembled with the CS@MXene cathode delivers a high areal capacity of 1.69 mAh cm–2 and superior rate capability. It also exhibits outstanding cycling performance with only 0.0065% of capacity fading after 1700 cycles and an average coulombic efficiency of ~97%. Moreover, the CS@MXene//Zn battery achieves a peak energy density of 2.95 mWh cm–2 with a peak power density of 17.5 mW cm–2. This work offers a valuable perspective on designing advanced electrodes via electronic structure modulation for energy storage devices.