RESUMO
The realizing of high-performance rechargeable aqueous zinc-ion batteries (ZIBs) with high energy density and long cycling life is promising but still challenging due to the lack of suitable layered cathode materials. The work reports the excellent zinc-ion storage performance as-observed in few-layered ultrathin VSe2 nanosheets with a two-step Zn2+ intercalation/de-intercalation mechanism verified by ex situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) characterizations. The VSe2 nanosheets exhibit a discharge plateau at 1.0-0.7 V, a specific capacity of 131.8 mAh g-1 (at 0.1 A g-1 ), and a high energy density of 107.3 Wh kg-1 (at a power density of 81.2 W kg-1 ). More importantly, outstanding cycle stability (capacity retention of 80.8% after 500 cycles) without any activation process is achieved. Such a prominent cyclic stability should be attributed to its fast Zn2+ diffusion kinetics (DZn 2+ ≈ 10-8 cm-2 s-1 ) and robust structural/crystalline stability. Density functional theory (DFT) calculation further reveals a strong metallic characteristic and optimal zinc-ion diffusion pathway with a hopping energy barrier of 0.91 eV. The present finding implies that 2D ultrathin VSe2 is a very promising cathode material in ZIBs with remarkable battery performance superior to other layered transitional metal dichalcogenides.
RESUMO
Aqueous zinc ion secondary batteries (ZIBs) have recently attracted considerable attention and global interest due to their low cost, aqueous-based nature and great safety. Unfortunately, the intrinsic properties of poor cycle life, low energy density and uncontrolled dendrite growth during the charge/discharge process for metallic Zn anodes significantly hinder their practical application. In this work, we rationally designed two-dimensional (2D) δ-MnO2 nanofluidic channels by the ordered restacking of exfoliated MnO2 single atomic layers, which exhibited a high zinc ion transport coefficient (1.93 × 10-14 cm2 s-1) owing to their appropriate d-spacing and the negative charge of the inner channel walls. More importantly, we found that Zn dendrite growth was prevented in the as-assembled ZIBs, resulting in superior stability compared with the bulk-MnO2 sample. Our design sheds light on developing high-performance ZIBs from two-dimensional nanofluidic channels, and this strategy might be applicable to the storage of other metal ions (Mg2+, Ca2+, Al3+, etc.) in next-generation electrochemical energy storage devices.
RESUMO
Rechargeable aqueous Zn-ion batteries (ZIBs) have recently attracted much attention due to their low cost and superior safety. Unfortunately, their low capacity and poor cycle life still hinder their practical application. Here, we have developed a general synthesis strategy for ultrasmall spinel oxide nanodots (Mn3O4, CoMn2O4, MnCo2O4.5, Co3O4, and ZnMn2O4) with abundant oxygen vacancies and highly active surface. Among them, 6.0-nanometer-sized Mn3O4 nanodots deliver the best Zn-ion storage ability with a high reversible capacity of 386.7 mA h g-1 at 0.1 A g-1, excellent rate performance, and a long-term stability of 500 cycles at 0.5 A g-1. Taking advantage of the highly activated surficial atoms, shortened transfer pathway, and introduction of numerous oxygen vacancies, an ultrahigh Zn2+ diffusion coefficient of 2.4 × 10-10 cm2 s-1 has been detected during the discharge process. This value is more than 2 orders of magnitude higher than that of other spinel oxide nanostructures in previous reports and also the highest one in all of the as-reported ZIB cathode materials to date. Our finding offers promising opportunities for the development of ZIB cathode materials with high energy density, long-term cycling stability, excellent flexibility, and wearability.