Universal Ligand-Field Engineering of Layered Vanadium-Based Cathodes for High-Voltage Aqueous Zinc Ion Batteries

Vanadium oxides are promising cathode materials for aqueous zinc ion batteries (ZIBs), but their practical application is hindered by low operating voltage and poor cycling stability. Here, we establish a universal ligand-field regulation principle for the operating voltage enhancement of layered vanadium oxides by using organic ion preintercalation to modulate the local coordination environment of [VO6] octahedra. Using a series of imidazolium cations as model interlayer species, we identify 1-butyl-3-methylimidazolium (BMIM+) as the optimal pillar to reconstruct the local crystal field and electronic states without sacrificing structural stability. Combined synchrotron spectroscopy and theoretical calculations reveal that BMIM+ preintercalation lowers the V 3d-band center, thereby enlarging the energy separation between V 3d and O 2p states and increasing the energy gap between the V redox couple and Zn2+/Zn. As a result, the BMIM+ preintercalated cathode exhibits higher open-circuit and average operating potential, a high capacity of 505 mAh g-1 at 0.1 A g-1, and excellent cycling stability with 94% capacity retention after 15 000 cycles at 8 A g-1. More importantly, the operating voltage enhancement is successfully extended to V6O13 and KV3O8, demonstrating its broad applicability to layered vanadium oxides.