Defective MnO2 nanosheets based free-standing and high mass loading electrodes for high energy density aqueous zinc ion batteries

Abstract

Aqueous zinc ion batteries (ZIBs) hold great promises for large-scale energy storage and wearable devices due to their low cost and high safety, but suffer from the low capacity and energy density of cathodes for practical applications. Herein, defective MnO₂ (d-MnO₂) nanosheets based free-standing and high mass loading electrodes (H-d-MnO₂) were successfully developed via an interfacial synthesis of MnO₂ nanosheets, phosphorization, and phase inversion procedure combined with a freeze-drying process. Benefiting from the ultrathin thickness of ∼4.2 nm for highly exposed surface with electrolytes, abundant defects (e.g., oxygen vacancies) in d-MnO₂ nanosheets for high capacity and long cycling performance, and porous film electrodes without current collectors for fast ion transfer and high energy density, the d-MnO₂ nanosheets loaded on a carbon cloth delivered a high capacity of 241.3 mA h g⁻¹ at 1 C after 250 cycles, superior to MnO₂ (84.5 mA h g⁻¹). Importantly, the H-d-MnO₂ film electrodes exhibited a high specific capacity of 221.4 mA h g⁻¹ at 0.2 C, a high energy density of 265 W h kg⁻¹, and a remarkable initial areal capacity of ∼2.73 mA h cm⁻² with an ultrahigh mass loading of 10 mg cm⁻². In addition, the H-d-MnO₂ based quasi-solid-state devices were demonstrated to withstand mechanical deformations and power an electronic watch for dozens of hours, suggesting their great potentials in practical applications.