Boosting high-loading zinc-ion battery performance: Zn-Doped δ-MnO2 cathodes to promote Zn2+ storage

Abstract

Rechargeable aqueous zinc-ion batteries (AZIBs) have emerged as a leading contender for stationary energy storage systems due to their low cost, safety, and environmental sustainability. However, their widespread practical application is hindered by the limited stability and capacity of current AZIB cathodes, such as manganese oxide (MnO₂), which affects their long-term cost-effectiveness. To overcome this limitation, we introduce zinc (Zn) doping in δ-MnO₂, which modulates the electronic states of Mn atoms, suppresses Jahn–Teller distortion, and enhances structural stability. Additionally, the use of a binder-free, self-supported porous electrode without current collectors facilitates three-dimensional ion diffusion, further improving electrochemical performance. As a result, the assembled AZIBs demonstrate outstanding rate capability, delivering 440 mAh∙g^-1 at 0.2 A∙g^-1 and retaining 118 mAh∙g^-1 at 24 A∙g^-1 for Zn-doped δ-MnO₂, outperforming the bare δ-MnO₂ with 356 mAh∙g^-1 at 0.2 A∙g^-1 and 80 mAh∙g^-1 at 24 A∙g^-1. Additionally, the Zn-doped δ-MnO₂ exhibits excellent cycling performance with ∼100 % capacity retention after 6000 cycles at 150 mAh∙g^-1 at 10 A∙g^-1. Furthermore, Zn-doped MnO₂ electrodes integrated with carbon nanotubes achieve a high capacity of ∼210 mAh∙g^-1, even at an ultrahigh mass loading (∼20 mg∙cm^-2) at 0.6 mA∙g^-1. While energy storage in MnO₂ involves the reaction and insertion of H⁺, Mn²⁺, and Zn²⁺ cations, density functional theory calculations reveal that Zn intercalation is the dominant storage mechanism in these cells. Overall, this study highlights the potential of Zn-doped MnO₂ cathodes as a promising strategy for advancing the stability, capacity, and rate performance of next-generation AZIBs.