Self-generated hollow NaTi2(PO4)3 nanocubes decorated with graphene as a large capacity and long lifetime anode for sodium-ion batteries

Abstract

NaTi₂(PO₄)₃ is a promising anode material for sodium-ion batteries due to its sodium-super-ion-conductor type structure. However, the inherent low conductivity of the NaTi₂(PO₄)₃ limits its cyclability and rate capability. Herein, to overcome these shortcomings, an electrode material that combines the hollow NaTi₂(PO₄)₃ nanocubes with the reduced graphene oxide is synthesized by a simple hydrothermal method. The as-synthesized products demonstrate a high specific capacity of 128 mA h g⁻¹, nearly achieving its theoretical capacity of the NaTi₂(PO₄)₃ electrode at 0.1C; even when the discharging rate reached 50C, it still achieved a capacity retention of 60%. Simultaneously, the sample also shows stable cycling performance with a discharge capacity of 60 mA h g⁻¹ after 500 cycles at a high rate of 20C. This excellent electrochemical performance of the NaTi₂(PO₄)₃@rGO is attributed to the large surface area of the hollow structure and high conductivity of the three-dimensional reduced graphene oxide that facilitate the electrolyte to soak in, increase the contact area between the nanocubes and electrolyte, and speed up Na⁺/e⁻ transfer in the nanocomposites. In addition, the unique hollow structure and the combination with the graphene could effectively accommodate the volume variation during repeated sodiation/desodiation processes.