Sustainable WO₃/rGO Nanocomposite Anode for Room and High-Temperature Sodium-Ion Storage

The synthesis, structure, morphology, and electrochemical properties of tungsten trioxide (WO₃) and reduced graphene oxide (rGO) nanocomposites (WO₃/rGO) are investigated for their potential as anode materials in sodium-ion batteries (NIBs). Electrochemical analyses revealed that WO₃/rGO outperformed bare WO₃, demonstrating stable cycling, high-rate capability, and enhanced performance. The composite delivered initial discharge/charge capacities of ≈285/350 mAh g^-1 with an initial Coulombic efficiency of ≈81%, stabilizing at ≈285 mAh g^-1 after 150 cycles. It exhibited a remarkable rate retention of ≈49% at 2000 mA g^-1 and exceptional cycling stability over 600 cycles. High-temperature testing improved ionic conductivity and stability, maintaining ≈99% Coulombic efficiency across all conditions. Further, the high-temperature (70 °C) cycling stability of a cell is evaluated at 100 mA g¹ for 250 cycles, where, after initial stabilization, it maintained consistent performance with ≈180 mAh g¹ reversible capacity and ≈100% Coulombic efficiency. Density Functional Theory (DFT) calculations are carried out to investigate the electronic structure, sodium storage, and ion mobility, showing that rGO incorporation lowers the Na diffusion energy barriers, contributing to the higher Coulombic efficiency and reversibility. These results highlight the potential of WO₃/rGO nanocomposites as efficient, durable anode materials for next-generation NIBs under diverse operating conditions.