δ-VOPO4 nanosheet with intrinsic V4+ defective as high-performance cathode for sodium-ion battery

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 con-ductivity. Here, we report that a delta phase VOPO4 (delta-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 a-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 because of enhanced conductivity and reduced redox polarization, while delta-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 toward high-performance SIBs. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Transition metal phosphates, specifically delta phase VOPO4 (delta-VPO) nanosheets with intrinsic V4+ defect, demonstrated superior performance as cathode materials for sodium-ion batteries (SIBs) in terms of specific capacity and cycling stability. The high V4+ defect concentration of VPO resulted in enhanced conductivity and reduced redox polarization, while delta-VPO enabled high cycling stability due to limited lateral size expansion. This work offers a potentially alternative cathode material with controllable phases and defects toward high-performance SIBs.