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

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. NaVOPO 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-NaVOPO with controlled morphologies. The electrochemical properties of the NaVOPO 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 high-energy ball milling, taking KB as the conductive carbon, the as-prepared NaVOPO/5%KB exhibits superior Na-storage performance (140.2 mA h g at 0.1 C and a capacity retention of 84.8% over 1000 cycles at 10 C) to the original NaVOPO (128.5 mA h g at 0.1 C and a capacity retention of 83.1% over 1000 cycles at 10 C). Moreover, the aqueous full cell with NaTi(PO) as the anode delivers a capacity of 114.7 mA h g at 0.2 C (141 W h kg 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 NaVOPO cathode for NIBs.