Microwave-induced structural tunability of 3D δ-MnO2 microflowers for high-performance aqueous Zn-ion batteries

Rechargeable aqueous Zn//MnO 2 batteries are the promising alternatives to lithium-ion batteries owing to their high safety, high energy density, low cost, and environmental friendliness. However, the unstable MnO 2 cathode causes poor practical energy density and serious capacity fading. To overcome this issue, herein, a unique 2D nanosheets self-supported 3D δ -MnO 2 microflower hierarchical architecture is rationally designed and synthesized by taking advantage of its microwave-absorbing characteristics. The 2D nanosheets with high surface area could expose numerous active sites for ions/electrons transfer. Also, the 3D assembled structure acting as building blocks would ensure structural stability for long-life cycles. Benefiting from these synergistic merits, the δ -MnO 2 microflowers deliver a high capacity of 287.6 mA h g −1 at 0.5 C, an excellent rate capability of 202.7 mA h g −1 at 5 C, and a superior cycling retention of 76.5% over 1000 cycles at 10 C. Furthermore, a storage mechanism of H + /Zn 2+ co-insertion accompanied by the deposition of zinc sulfate hydroxide hydrate is clarified by the aid of ex-situ XRD and SEM technologies. This work provides a new pathway for developing high capacity and long lifespan ZIBs.