K-buserite manganese oxide nanosheets enabling high-efficiency energy storage in aqueous Zn-ion batteries and hybrid supercapacitors

Mn-based cathode materials are promising for aqueous Zn-ion batteries (AZIBs) and hybrid supercapacitors (AZHSCs) because of their high theoretical capacity, low costs, and environmental benignity. However, sluggish reaction kinetics and robust electrostatic interaction often weaken their electrochemical performances, limiting their widespread application. Herein, novel potassium buserite manganese oxide nanosheets (MnOx NSs) are reported as a cathode material for AZIBs and AZHSCs. In-/Ex-situ characterizations and theoretical calculations demonstrate that MnOx NSs consist of K-buserite units which are irreversibly transformed into Zn-buserite units during the first cycle. In subsequent cycles, Zn-buserite serves as an active material with high activity/stability, enabling excellent energy storage. Notably, in full cells of MnOx NSs//PrGO-PTCDI (Perylene-3,4,9,10-tetracarboxylic diimide), a desirable capacity is achieved at 3.0 A g−1, and 103 mAh g−1 is retained at 0.5 A g−1 after 2000 cycles. Meanwhile, hybrid supercapacitors of MnOx NSs//PAC (porous activated carbon) achieve a capacitance of 212.9 F g−1 at 3.0 A g−1 with an energy (power) density of 180.3 Wh kg−1 (2094.2 W kg−1), and surprisingly long stability of 235 F g−1 remains after 53,000 cycles at 2.0 A g−1 with 88 % capacitance retention. This work offers new insights into deep understanding and creative designing of Mn-based materials for high-efficiency Zn-storage.