δ-VOPO4 nanosheet with intrinsic V4+ defective as high-performance cathode for sodium-ion battery
2021
Abstract Transition metal phosphates have become of great interest as cathode materials for rechargeable ion batteries because of their low cost and environmental friendliness, but suffer from low-intrinsic conductivity. Here, we report that a δ phase VOPO4 (δ-VPO) nanosheets with intrinsic V4+ defect, can deliver a specific capacity of 130 mA h/g at 0.2 C (1 C = 166 mA/g) with 75% capacity retention after 500 cycles as a cathode of sodium-ion batteries (SIBs), which is superior to previously reported α-VPO as well as sodiated VPO counterparts. Our results demonstrate that the high V4+ defect concentration of VPO is responsible for the better high-rate performance due to enhanced conductivity and reduced redox polarization, while δ-VPO enabling high cycling stability resulting from the limited expansion of the lateral size. This work offers a potentially alternative cathode material with controllable phases and defects towards high-performance SIBs.
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