A heterostructure of NiMn-LDH nanosheets assembled on ZIF-L-derived ZnCoS hollow nanosheets with a built-in electric field enables boosted electrochemical energy storage

Abstract

Supercapacitors (SCs) have emerged as an efficient technology toward the utilization of renewable energy, which demands high-performance electrode materials. Transition-metal sulfides (TMSs) and layered double hydroxides (LDHs) rich in active sites and valence states are very promising electrode materials, but they still suffer from inherent defects, such as low electric conductivity, sluggish reaction kinetics and large volume change during electrochemical reactions. In this work, NiMn-LDH nanosheets are assembled on the surfaces of ZnCoS hollow nanosheet arrays derived from a zeolitic imidazolate framework-L (ZIF-L) to form a ZnCoS@NiMn-LDH heterostructure (ZCS@LDH) with a built-in electric field. The unique structure gives rise to abundant exposed active sites and improved ion diffusion. More importantly, the built-in electric field can enhance conductivity and charge transfer by modulating the electronic structures. With these merits, the optimal ZCS@LDH-6 electrode displays outstanding specific capacitance (2102.2 F g⁻¹ at 1 A g⁻¹) and remarkable rate performance (68.1% at 10 A g⁻¹). The assembled asymmetric supercapacitor (ASC) using the ZCS@LDH-6 electrode shows high energy storage capacity (41.7 W h kg⁻¹ at 850.0 W kg⁻¹), satisfactory cycle life (92.2% capacitance retention after 10 000 cycles) and high coulombic efficiency (95.8%). This work will shed light on designing high-performance electrode materials via heterostructure and morphology engineering.