Lithium-ion battery anode with high capacity retention derived from zinc vanadate and holey graphene

Several phases of zinc vanadates having different morphologies have been investigated recently for lithium-ion batteries (LIBs), where they suffer from poor electronic conductivity and low mechanical stability resulting in short cycle life, low specific capacity and unsatisfactory rate performance. The issues are resolved here, by directly growing Zn₃V₂O₈ sheets on two dimensional (2D) holey graphene oxide (hGO) nanosheets making an open framework of Zn₃V₂O₈ that allows suitable spacing for Li⁺-ions for (de) intercalation and the holey graphene provides the necessary mechanical strength, permeability and electronic conductivity across the Zn₃V₂O₈ sheets. Consequently, the sheet on sheet morphology has resulted in an impressive rate capability of 851.2 mAh g⁻¹ at 5000 mA g⁻¹ with 67% retention after a 10-fold increase in the current rate, high specific capacity (1465.9 mAh g⁻¹ at 200 mA g⁻¹) and long-term stability (88% retention after 200 cycles). This is due to the crystalline structure of Zn₃V₂O₈/hGO, with a large surface area that can provide more reaction sites and facilitate the fast Li⁺-ion transport as verified by the electrochemical impedance spectroscopy analysis. The ex situ X-ray photoelectron spectrometer reveals the involvement of multiple reaction mechanisms (conversion, (de) insertion and (de) alloying) showing Zn²⁺/Zn⁰ and V⁴⁺/V³⁺/V²⁺ redox couples during the electrochemical process.