Rational design of hierarchical Ni-Mo bimetallic Selenide/N-doped carbon microspheres toward high-performance potassium ion batteries

Potassium ion batteries (KIBs) have received a lot of attention in large-scale energy storage applications because of abundant potassium resources. However, owing to the poor structural durability of electrode materials and sluggish reaction kinetics, the commercialization of KIBs is challenging. Herein, we design a hierarchically structured Ni-Mo bimetallic selenide/N-doped carbon microsphere (NMSe/NC) as an advanced anode material for KIBs. The hierarchical Ni-Mo/polydopamine microsphere precursor, obtained from the spontaneous chemical reaction of NiMoO4 nanorods with dopamine hydrochloride, is converted into heterostructured-Ni-Mo selenide crystals confined in a hierarchical NC matrix via a two-step thermal treatment. The unique hierarchical surface structure and the synergistic effect of Mo and Ni species provide sufficient electrochemical reaction sites and promote the reaction kinetics. Furthermore, the proximate contact between the active materials and the N-doped carbon matrix can facilitate electron transportation and enhance the structural robustness of the electrode. Consequently, the resulting NMSe/NC hierarchical microspheres delivered a high reversible capacity of 332 mA h g(-1) after 200 cycles (current density: 0.5 A g(-1)) and a remarkable rate capability of 206 mA h g(-1) (current density: 2.0 A g(-1)). The excellent electrochemical performance of NMSe/NC indicates their potential for KIB commercialization in large-scale energy storage systems in the future.