An Open-Ended Ni₃ S₂ -Co₉ S₈ Heterostructures Nanocage Anode with Enhanced Reaction Kinetics for Superior Potassium-Ion Batteries.

Abstract

Sulfides are perceived as promising anode materials for potassium-ion batteries (PIBs) due to their high theoretical specific capacity and structural diversity. Nonetheless, the poor structural stability and sluggish kinetics of sulfides lead to unsatisfactory electrochemical performance. Herein, Ni₃ S₂ -Co₉ S₈ heterostructures with an open-ended nanocage structure wrapped by reduced graphene oxide (Ni-Co-S@rGO cages) are well designed as the anode for PIBs via a selective etching and one-step sulfuration approach. The hollow Ni-Co-S@rGO nanocages, with large surface area, abundant heterointerfaces, and unique open-ended nanocage structure, can reduce the K⁺ diffusion length and promote reaction kinetics. When used as the anode for PIBs, the Ni-Co-S@rGO exhibits high reversible capacity and low capacity degradation (0.0089% per cycle over 2000 cycles at 10 A g^-1 ). A potassium-ion full battery with a Ni-Co-S@rGO anode and Prussian blue cathode can display a superior reversible capacity of 400 mAh g^-1 after 300 cycles at 2 A g^-1 . The unique structural advantages and electrochemical reaction mechanisms of the Ni-Co-S@rGO are revealed by finite-element-simulation in situ characterizations. The universal synthesis technology of bimetallic sulfide anodes for advanced PIBs may provide vital guidance to design high-performance energy-storage materials.