Kirkendall Growth and Ostwald Ripening Induced Hierarchical Morphology of Ni–Co LDH/MMoSx (M = Co, Ni, and Zn) Heteronanostructures as Advanced Electrode Materials for Asymmetric Solid-State Supercapacitors

By changing the mixed metal sulfide composition, morphology tuning of an active electrode material can be possible, which can have a huge impact on its electrochemical performance. Here, effective morphology tuning of Ni-Co layered double hydroxide (LDH)/MMoS x (M = Co, Ni, and Zn) heteronanostructures is demonstrated by varying the composition of MMoS x. Taking advantage of the benefits associated with Kirkendall growth and Ostwald ripening, tunable morphologies were successfully achieved. Among the Ni-Co LDH/MMoS x (M = Co, Ni, and Zn) heteronanostructures, a Ni-Co LDH/NiMoS x core-shell structured electrode delivered a high specific capacity of 404 mAh g-1 at 3 mA cm-2 and an extraordinary cycling stability (after 10 000 cycles) of 93.2% at 50 mA cm-2. In addition, an asymmetric supercapacitor (ASC) device coupled with Ni-Co LDH/NiMoS x as the cathode and Fe2O3/reduced graphene oxide as the anode exhibited excellent cell capacity and extraordinary cycling stability. Moreover, the ASC device provided a very high specific energy of 72.6 Wh kg-1 at a specific power of 522.7 W kg-1 and maintained the specific power of 23.5 Wh kg-1 at 5357.6 W kg-1, demonstrating its high applicability to energy storage devices.