Local Spin-State Tuning Enables High-Efficiency Nickel Sulfide Cathode for Stable Alkaline Zn Batteries

Nickel sulfide (Ni 3 S 2 ) has shown great promise as advanced cathode in alkaline nickel -zinc batteries (ANZBs) for its good electrochemical reversibility and electronic conductivity. However, due to the unfavorable OHadsorption capability and low intrinsic activity of Ni sites originated from the unsuitable d -electron spin state, the overall performances of Ni 3 S 2 are yet unsatisfactory for practical ANZBs. Herein, we demonstrate the engineering of local spit state of Ni sites via a facile electrochemical activation in Ni 3 S 2 to significantly boost its comprehensive energy storage capability. After electrochemical treatment, the spit state of fractional Ni 2+ ( e 4 g t 42 g ) sites of Ni 3 S 2 is successfully transformed into high -valence Ni 3+ ( e 4 g t 32 g ), which considerably enhances the OHadsorption capability and redox reactivity. The optimal Ni 3 S 2 electrode exhibits a high capacity of 1.11 mAh cm -2 at 1 mA cm -2 and no capacity decay after 3000 cycles, which are far greater than the pristine Ni 3 S 2 (0.39 mAh cm -2 ) electrode and also comparable to the best ever -reported alkaline cathodes. Furthermore, the assembled full ANZB can afford a peak energy density of 1.59 mWh cm - 2 and power density of 33.92 mW cm - 2 . This work affords valuable insights into local electronic structure modulation of electrode materials for aqueous energy storage devices.