Rate Balance Design and Construction of a Conductive Ni_0.5Co_0.5MoO₄ Solid-Solution Microspherical Superstructure toward Advanced Hybrid Supercapacitors

The modest rate behaviors of pseudo-capacitive positive electrodes always restrict the realization of advanced hybrid supercapacitors (HSpCs). The purposeful exploration of highly conductive metal oxides with porous nano-/microstructures is an efficient approach to obtain a rate balance between the positive and negative electrodes of HSpCs. Herein, we develop a bottom-up synthetic strategy to fabricate 2D nanosheet-assembled hierarchical Ni0.5Co0.5MoO4 solid-solution microspheres (NCMO-SS MSs) and further evaluate its electrochemical performance as a positive electrode toward HSpCs. Density functional theory calculations reveal the optimal electronic conductivity of NCMO-SS in the NixCo1–xMoO4 family. Such a unique hierarchical architecture and composition guarantee fast electron/ion transport and abundant electroactive sites for efficient charge storage of the NCMO-SS MSs at high rates. The resulting porous NCMO-SS MSs are endowed with exceptional specific capacitances (SCs) of ∼1188.2 and ∼625.6 F g–1 at 2.0 and 8.0 A g–1, respectively. More encouragingly, the hybrid device delivers an SC of ∼81.7 F g–1 at 6.0 A g–1 (i.e., 81.0 mA cm–2), along with an energy density of ∼40.1 W h kg–1 at 363.6 W kg–1 and 93.4% capacitance retention at 2.0 A g–1 after 9700 consecutive cycles. Our NCMO-SS MSs are highlighted promisingly as a competitive electrode for advanced next-generation HSpCs.