Mo Doping-Induced Synthesis of Hierarchical Γ-Mno2 Microspheres Assembled by Ultrathin Nanosheets as a Highly Stable Cathode for Aqueous Zinc Ion Batteries

Abstract

MnO2 is one of the most widely researched cathode materials for aqueous zinc-ion batteries. This is attributed to its high theoretical specific capacity, competitive cost, safety, and non-toxicity. However, its structural instability and inferior electronic conductivity lead to suboptimal zinc-ion storage performance. Herein, a simple one-step hydrothermal method is utilized to prepare Mo-doped hierarchical γ-MnO2 microspheres, which are composed of ultrathin nanosheets. The results show that Mo doping has a multifunctional effect. On one hand, it induces the formation of hierarchical structures for γ-MnO2, thereby providing a large contact area between the electrode material and the electrolyte. At the same time, this hierarchical structure helps alleviate the collapse of the MnO2 structure during the charge/discharge process. In addition, Mo doping enhances the transport rate of ions and electrons. Thus, it can be concluded that the Mo-doped γ-MnO2 exhibits enhanced cycling stability and rate capability. For example, the discharge specific capacity of Mo-doped γ-MnO2 is maintained at 108.2 mAh g−1 for 1000 cycles at a current density of 2,000 mA g−1, which is significantly higher than that of undoped γ-MnO2 (21.5 mAh g−1) under the same test conditions.

Keywords: γ-MnO2, hierarchicalmicrospheres, Mo doping, nanosheet, aqueous zinc ion battery