Ultrahigh Energy and Power Density in Ni-Zn Aqueous Battery via Superoxide-Activated Three-Electron Transfer

Aqueous Ni-Zn microbatteries are safe, reliable and inexpensive but notoriously suffer from inadequate energy and power densities. Herein, we present a novel mechanism of superoxide-activated Ni substrate that realizes the redox reaction featuring three-electron transfers (Ni ↔ Ni³⁺). The superoxide activates the direct redox reaction between Ni substrate and KNiO₂ by lowering the reaction Gibbs free energy, supported by in-situ Raman and density functional theory simulations. The prepared chronopotentiostatic superoxidation-activated Ni (CPS-Ni) electrodes exhibit an ultrahigh capacity of 3.21 mAh cm^-2 at the current density of 5 mA cm^-2, nearly 8 times that of traditional one-electron processes electrodes. Even under the ultrahigh 200 mA cm^-2 current density, the CPS-Ni electrodes show 86.4% capacity retention with a Columbic efficiency of 99.2% after 10,000 cycles. The CPS-Ni||Zn microbattery achieves an exceptional energy density of 6.88 mWh cm^-2 and power density of 339.56 mW cm^-2. Device demonstration shows that the power source can continuously operate for more than 7 days in powering the sensing and computation intensive practical application of photoplethysmographic waveform monitoring. This work paves the way to the development of multi-electron transfer mechanisms for advanced aqueous Ni-Zn batteries with high capacity and long lifetime.