Zinc hexacyanoferrate polyhedra coating at separator for a long-lasting LiV3O8 nanorods-based Zn-ion battery

Abstract

We report herein on the use of a zinc hexacyanoferrate (ZnHCF) overlayer at the separator to obtain a long-lived non-aqueous zinc-ion battery (ZIB). The ZIB cathode is a composite of lithium vanadate (LiV3O8) nanorods and carbon flakes (CFs) derived from sugarcane fibers. The LiV3O8/CFs-ZnHCF-based ZIB delivers an outstanding capacity of 254 mAh g−1 (at 25 mA g−1) with ca. 91% capacity retention after 100 charge–discharge cycles and an energy density of 110 Wh kg−1, significantly enhanced compared to a cell without the ZnHCF layer (215 mAh g−1). The CFs additive not only improves the electrical conductivity of the LiV3O8 cathode and promotes ion/electron transport and kinetics, but, by virtue of its sheet-like structure, also accommodates the volume change to which LiV3O8 is subjected, thus restricting the pulverization/detachment of active material and to some extent suppressing capacity fade during cycling. However, the durability of the ZIB is more effectively enhanced by inclusion of the ZnHCF@separator. The ZnHCF layer efficiently confines the Zn2+ ions at the cathode, that is, blocks their uncontrolled diffusion into the electrolyte or towards the anode during discharge, but also allows the facile transport of Zn2+ ions during charging due to the presence of open channels in the rhombohedral lattice, which is confirmed by a high Zn2+ ion diffusion coefficient (>10−6 cm2 s−1). The ZIB LiV3O8/CFs-ZnHCF@separator/Zn(CF3SO3)2-acetonitrile/Zn outperforms its analogue devoid of a ZnHCF layer in terms of cycling stability, capacity, and rate performance. About 71% of initial capacity is retained at 125 mA g−1 after 500 charge–discharge cycles. The stable performance paves the way for the implementation of this new design involving the application of cost-effective, easy-to-apply, Zn2+-ion-conducting layers for developing high-performance ZIBs.