Multilevel carbon composite construction of NASICON-type NaVPO4F/C/CNT cathode material for enhanced-performance sodium-ion batteries

Abstract

NaVPO₄F (NVPF) holds significant promise for advancing the commercialization of sodium-ion batteries owing to its high voltage of 3.4 V, impressive theoretical capacity of 143 mA h g⁻¹, and low vanadium content. However, its further development is hindered by its limited internal electronic conductivity. To address this issue, herein, an additional network of highly conductive carbon nanotube (CNT) was applied onto a layer of reduced carbon to form a multilevel carbon structure. The introduction of 3D tubular network increased the specific surface area of the material, inhibited the growth of the particle size of the sample, and accelerated the transport of sodium ions, which provided a stabilizing barrier to mitigate structural degradation. The prepared NaVPO₄F/C/CNT10% (NVPF/C/CNT10%) cathode demonstrated a discharge specific capacity of 125.6 mA h g⁻¹ at 0.2C, achieving impressive capacity retention of 98.4% after 100 cycles. Furthermore, after 1000 cycles at 5C, it exhibited the capacity retention of 78%. Notably, the fabricated full battery demonstrated an exceptionally high capacity retention of 86.2% after 300 cycles at the same rate. Through ex situ XRD and XPS analyses of the NVPF/C/CNT10% sample, the mechanism of sodium-ion intercalation/deintercalation was disclosed during the charging/discharging processes. This study paves the way for the development of highperformance cathode materials for sodium-ion batteries.