A B-doped layered VOPO4·2H2O cathode for high-performance zinc-ion batteries with an H+/Zn2+ co-insertion mechanism

Abstract

The state of V in a vanadium-based cathode is considered a key factor in improving its electrochemical energy storage characteristics for zinc-ion batteries. Herein, we innovatively developed a B-doping strategy to strengthen the V–O bond in a vanadium oxophosphate (VOPO₄·2H₂O) cathode. B was pre-inserted into the interlayer of VOPO₄·2H₂O and it bound to the oxygen atoms, forming V–O–B bonds, decreasing the positive charge distribution of V. The increased amount of V⁴⁺ and the interlayer separation of VOPO₄·2H₂O are beneficial for modified B-doped VOPO₄·2H₂O. Experimentally, the optimal B-doped VOPO₄·2H₂O delivers a high discharge capacity of 234.5 mA h g⁻¹ at 0.1 A g⁻¹ and a good rate performance, and the percentage of intercalated pseudocapacitance rose from 83% to 98% caused by the H⁺/Zn²⁺ co-intercalation after B-doping. Based on the ex situ XRD characterization in the charging and discharging process, the stability of the layered structure of B-doped VOPO₄·2H₂O was verified, which enables it to act as a promising cathode for high-performance ZIBs.