Low-strain layered Zn0.56VOPO4∙2H2O as a high-voltage and long-lifespan cathode material for Zn-ion batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) have been regarded as a potential competitor in grid-scale energy storage scenarios due to the merits of high safety, easy manufacturing and cost-efficiency. However, the lack of suitable robust hosts to accommodate Zn2+ with high electrostatic repulsion remains the major obstacle to the development of ZIBs. The exploration of low-strain Zn-storage cathode materials is a critical strategy to address the challenges. In this work, we developed a layered phyllo-oxovanadophosphate Zn0.56VOPO4∙2H2O as a structurally stable cathode material for the first time. Benefiting from the "inductive effect" of strong P–O covalent bonds and the single-phase reaction mechanism with tiny lattice volume distortion of 1.9%, the Zn0.56VOPO4∙2H2O cathode manifests a high operating voltage of 1.46 V and ultralong cycle life (capacity retention of 70.5% after 8000 cycles). Importantly, the versatility and practicability of this layered cathode is verified in both "rocking-chair" ZIBs and anode-free ZIBs, all of which demonstrate outstanding cycling performance. The low-strain structural superiority and prominent electrochemical performance are expected to inspire more efforts in the research of Zn-storage polyanionic cathode materials and revitalize the development of rechargeable ZIBs towards energy storage applications.