Nanoporous carbon leading to the high performance of a Na3V2O2(PO4)2F@carbon/graphene cathode in a sodium ion battery

Abstract

The Na₃V₂O₂(PO₄)₂F/graphene sandwich cathode has attracted great attention as a potential candidate for sodium-ion batteries in view of its high capacity and good cycling ability. However, a big issue for Na₃V₂O₂(PO₄)₂F/graphene is its extremely poor electronic conductivity due to the multilayer structure in which Na₃V₂O₂(PO₄)₂F particles are located between the graphene layers. We introduced carbon in the Na₃V₂O₂(PO₄)₂F/graphene sandwich to form a 3D architecture – Na₃V₂O₂(PO₄)₂F@carbon/graphene (NVPF@C/G). A battery with the NVPF@C/G cathode presents good electrochemical properties, a high capacity, 135.8 mAh g⁻¹ at 0.1C, with a capacity retention of 96.8% at 2C for fifty cycles. NVPF@C/G showed obvious advantage in the rate performance and cycle stability compared with the NVPF/G sandwich, which indicated that the nanoporous carbon integrated in the 3D structure plays a crucial role in improving the electrochemical performance. It is anticipated that such a new method of introducing nanoporous carbon for battery performance enhancement can be extended to other graphene-based sandwich structure electrodes.