Kinetics enhancement of hierarchical hollow boride microspheres for double-high aqueous Zn-based batteries

Abstract

The unsatisfactory kinetics of the cathode electrode material are the key factor hampering the achievement of double-high performance (both high energy and high power) in aqueous Zn-based batteries. In this work, an amorphous Co-doped Ni₂B hollow microsphere has been successfully constructed by a controllable etching process using a bimetallic MOF precursor. The unique hierarchical hollow structure and amorphous phase can provide more accessible active centers, abundant channels and a shortened diffusion path for enhanced redox kinetics. Therefore, the obtained CNB sample exhibits an ultra-high capacity of 2173 F g⁻¹ (301.8 mA h g⁻¹) at a current density of 1 A g⁻¹ and can still maintain an initial value of 87.0% when the current density increases to 10 A g⁻¹, achieving outstanding rate performance of CNB. Furthermore, a CNB//rGO–Zn aqueous zinc battery device is fabricated, which exhibits a high energy density of 454.7 W h kg⁻¹ at a high power density of 0.46 kW kg⁻¹. In addition, the CNB//rGO–Zn device can maintain 80.01% of its initial value at a current density of 6 A g⁻¹ after 6600 cycles, revealing outstanding stability. Meanwhile, the energy storage mechanism is explored using ex situ XPS spectroscopy and ex situ TEM mapping, demonstrating that the energy storage mechanism of the CNB//rGO–Zn device involves a mixed process of the Faraday redox reaction of Co/Ni elements and the adsorption and desorption of Zn species. The CNB//rGO–Zn soft-packed device can operate an electronic thermometer for over 8 hours after several seconds of charging time, revealing its outstanding application prospect.