Effective enhancement of the electrochemical properties for Na2FeP2O7/C cathode materials by boron doping

In recent years, the composite materials based on polyanionic frameworks as secondary sodium ion battery electrode material have been developed in large-scale energy storage applications due to its safety and stability. The Na2FeP2O7/C (theoretical capacity 97 mA·h·g−1) is recognized as optimum Na-storage cathode materials with a trade-off between electrode performance and cost. In the present work, The Na2FeP2O7/C and boron-doped Na2FeP2−xBxO7/C composites were synthesized via a novel method of liquid phase combined with high temperature solid phase. The non-metallic element B doping not only had positive influence on the crystal structure stability, Na+ diffusion and electrical conductivity of Na2FeP2O7/C, but also contributed to the high-value recycling of B element in waste borax. The structure and electrochemical properties of the cathode material were investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM), The X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and charge/discharge cycling. The results showed that different amounts of boron doping had positive effects on the structure and electrochemical properties of the material. The initial charge/discharge performances of born doped materials were improved in comparison to the bare Na2FeP2O7/C. The cycle performance of the Na2FeP1.95B0.05O7/C showed an initial reversible capacity of 74.8 mA·h·g−1 and the high capacity retention of 91.8% after 100 cycles at 1.0 C, while the initial reversible capacity of the bare Na2FeP2O7/C was only 66.2 mA·h·g−1. The improvement of apparent Na+ diffusion and electrical conductivity due to B doping were verified by the EIS test and CVs at various scan rate. The experimental results from present work is useful for opening new insight into the contrivance and creation of applicable sodium polyanionic cathode materials for high-performance.