Ultrafast and reversible anion storage of spinel nanoarchitecture for high-performance alkaline zinc full cells

Rechargeable alkaline zinc batteries are considered to be potential energy-storage systems owing to their natural abundance, low toxicity, and high capacity. However, their performance and efficiency are limited by the sluggish kinetics and irreversibility of the anode and cathode. In particular, high-capacity binary transition metal-based spinel materials that can store OH⁻ anions are expected to replace commercial MnO cathodes owing to their abundant active sites of two or more transition metals. Herein, we report an ultrafast and reversible anion storage mechanism of spinel NiCo₂O₄ nanoarchitectures decorated onto N-doped reduced graphene oxide (NCO@N-rGO) for high-performance rechargeable alkaline zinc full cells. The NCO@N-rGO electrode exhibits high specific and rate capacities of 191 mA h g⁻¹ at 1000 mA g⁻¹ and 151 mA h g⁻¹ even at 20 000 mA g⁻¹, respectively, much higher than those of NCO@rGO and NCO. The as-designed cells achieve a record-high volumetric power density (7.20 W cm⁻³) among alkaline zinc full cells, along with a high energy density (14.93 mW h cm⁻³) and a capacity retention of 77% over 3000 cycles at 6000 mA g⁻¹. These results are attributed to the facile charge-storage kinetics of the spinel framework, multiple Ni³⁺/Ni²⁺ and Co³⁺/Co²⁺ redox couples with OH⁻, and structural integrity of N-rGO as verified by electrochemical, ex situ XRD and XPS, and postmortem analyses. This work proposes a rational design of nanoarchitectured electrode materials for high volumetric performances and long-cycle life of rechargeable alkaline zinc batteries.