In situ construction of hollow Ni3S2-Co9S8 heterostructures with enhanced reaction kinetics for potassium ion storage

Owing to high theoretical capacity, nickel sulfide and cobalt sulfide were highly competitive anode materials for potassium ion batteries (PIBs). However, the slow reaction kinetics and poor structural stability during the cycle hinder its application in the anode materials of PIBs. An exquisite heterogeneous structure of bimetal sulfide Ni3S2-Co9S8 nanotube wrapped with a nitrogen-doped carbon layer is prepared by in situ growth and solvothermal strategies. Such a well-designed structural provides a channel for the rapid diffusion of potassium ions, promotes charge transfer at the heterojunction interface and effectively improves the reaction kinetics. When used as the anode for PIBs, the Ni3S2-Co9S8@NSC exhibits an excellent capacity of 419 mA h g−1 after 200 cycles at 0.1 A g−1 and an excellent rate performance of 220 mA h g−1 at 5 A g−1. And after 200 cycles at 1 A g−1 and 2 A g−1, there are 285 mA h g−1 and 238 mA h g−1 high reversible capacities, respectively. Moreover, potassium ion hybrid capacitor can provide good energy density (148 Wh kg−1), power density (6639.3 W kg−1) and excellent cycle reversibility. Based on experiments and DFT calculations, the heterojunction structure in the composite can not only optimize the electronic structure and distribution to improve the conductivity, but also improve the potassium ion adsorption energy to accelerate the reaction kinetics. The excellent electrochemical properties reveal the advantages of reasonably designing carbon coated hollow heterostructures for energy storage.