Regulated Synthesis of α-NaVOPO₄ with an Enhanced Conductive Network as a High-Performance Cathode for Aqueous Na-Ion...

The low-cost and profusion of sodium reserves make Na-ion batteries (NIBs) a potential candidate to lithium-ion batteries for grid-scale energy storage applications. NaVOPO₄ has been recognized as one of the most promising cathodes for high-energy NIBs, owing to their high theoretical capacity and energy density. However, their further application is hindered by the multiphase transition and conductivity confinement. Herein, we proposed a feasible, one-step hydrothermal synthesis to regulate the synthesis of α-NaVOPO₄ with controlled morphologies. The electrochemical properties of the NaVOPO₄ electrode can be significantly enhanced taking Ketjen black (KB) as the optimized conductive carbon. Besides, combining with the nanocrystallization and construction of the conductive framework via high-energy ball milling, taking KB as the conductive carbon, the as-prepared NaVOPO₄/5%KB exhibits superior Na-storage performance (140.2 mA h g^-1 at 0.1 C and a capacity retention of 84.8% over 1000 cycles at 10 C) to the original NaVOPO₄ (128.5 mA h g^-1 at 0.1 C and a capacity retention of 83.1% over 1000 cycles at 10 C). Moreover, the aqueous full cell with NaTi₂(PO₄)₃ as the anode delivers a capacity of 114.7 mA h g^-1 at 0.2 C (141 W h kg^-1 energy density) and 80.6% capacity retention over 300 cycles at 5 C. The excellent electrochemical performance can be attributed to the nanosized structural and enhanced interfacial effect, which could be rewarding to construct electron transportation tunnels, thus speeding up the Na⁺-diffusion kinetics. The modified strategy provides an efficient approach to intensify the electrochemical performance, which exhibits potential application of the NaVOPO₄ cathode for NIBs.