Enhanced electrochemical performance of carbon and aluminum oxide co-coated Na3V2(PO4)2F3 cathode material for sodium ion batteries

Abstract

Carbon and aluminum oxide co-coated Na3V2(PO4)2F3 cathode material has been successfully prepared via a wet chemistry method. The effects of the hybrid layer coating of C and Al2O3 on crystalline structure, morphology and electrochemical performance have been investigated. It is found that C and Al2O3 co-coating can stabilize the structure and improve the conductivity of NVPF. As a cathode material for sodium-ion batteries, the co-coated NVPF electrode shows a significant enhancement in rate capability and cycling performance, i.e., compared with bare NVPF, C-coated NVPF and Al2O3-coated NVPF, the NVPF/C-Al electrode delivers the highest capacity of 122.8 mAh g−1 with a superior capacity retention ratio of 95.6% after 100 cycles at 1 C. This enhancement in cycling performance and rate capability can be ascribed to the protective effect of this hybrid coating layer of C and Al2O3 on NVPF from electrolyte attack and the facilitated electron/ion transmission caused by the hybrid coating layer. This modification method of co-coating with electronic conductor C and sodium ionic conductivity Al2O3 provides an effective way to improve the electrochemical properties of NVPF and other cathode materials with low electron/ion conductivity for sodium/lithium ion batteries.