Diffusion-driven fabrication of yolk-shell structured K-birnessite@mesoporous carbon nanospheres with rich oxygen vacancies for high-energy and high-power zinc-ion batteries

ABSTRACT Structural unsteadiness and limited electrochemical kinetics upon cycling seriously impede further applications of birnessite cathodes for rechargeable aqueous zinc‑ion batteries (ZIBs), even though they have high voltage platforms and distinctively layered structures for preferable (de)intercalation of zinc ions. Herein, yolk-shell structured K-birnessite (K0.48Mn2O4·0.49H2O)@mesoporous carbon nanospheres (KMOH@C) with rich oxygen vacancies are synthesized for the first time with a two-step diffusion-driven strategy of hydrothermal synthesis followed by etching with KOH. The transport of reaction ions is regulated by surface charge and pore structure of the carbon shells, thus K-birnessite is preciously transferred into the hollow mesoporous carbon (HMC) nanospheres. Furthermore, the etching effect of KOH and the confinement effect of HMC nanospheres generate intercalated K+ and abundant oxygen vacancies into KMOH, leading to an excellent electrochemical kinetics. Meanwhile, HMC nanospheres also endow rapid electron/ion transport and stabilize the crystal structure of K-birnessite. Therefore, KMOH@C exhibits superior electrochemical performances with high reversible capacities of 412.7 and 122.2 mA h g‒1 at 0.5 and 10.0 A g‒1 than reported cathodes, respectively. Moreover, an exceptional cyclability of 129.6 mA h g‒1 even after 6000 cycles at 3.0 A g‒1 is achieved, making the KMOH@C cathode highly competitive for eco-friendly aqueous ZIBs.