Amorphous Heterostructure Derived from Divalent Manganese Borate for Ultrastable and Ultrafast Aqueous Zinc Ion Storage.

Aqueous zinc-manganese (Zn-Mn) batteries have promising potential in large-scale energy storage applications since they are highly safe, environment-friendly, and low-cost. However, the practicality of Mn-based materials is plagued by their structural collapse and uncertain energy storage mechanism upon cycling. Herein, this work designs an amorphous manganese borate (a-MnBO x ) material via disordered coordination to alleviate the above issues and improve the electrochemical performance of Zn-Mn batteries. The unique physicochemical characteristic of a-MnBO x enables the inner a-MnBO x to serve as a robust framework in the initial energy storage process. Additionally, the amorphous manganese dioxide, amorphous Zn x MnO(OH) 2 , and Zn 4 SO 4 (OH) 6 ·4H 2 O active components form on the surface of a-MnBO x during the charge/discharge process. The detailed in situ/ex situ characterization demonstrates that the heterostructure of the inner a-MnBO x and surface multicomponent phases endows two energy storage modes (Zn 2+ /H + intercalation/deintercalation process and reversible conversion mechanism between the Zn x MnO(OH) 2 and Zn 4 SO 4 (OH) 6 ·4H 2 O) phases). Therefore, the obtained Zn//a-MnBO x battery exhibits a high specific capacity of 360.4 mAh g -1 , a high energy density of 484.2 Wh kg -1 , and impressive cycling stability (97.0% capacity retention after 10 000 cycles). This finding on a-MnBO x with a dual-energy storage mechanism provides new opportunities for developing high-performance aqueous Zn-Mn batteries.