A strategy to enhance rate capability by doping Titanium into Na2FeP2O7@C cathode materials for Na-ion batteries

Abstract

We have significantly improved the rate performance of the Na2FeP2O7@C system through the Ti-doping strategy. A series of Ti-doped composites are prepared by the solid-state method. It is found that the Ti-doped sample displays a pair of redox platforms near 2 V, which can contribute a small amount of capacity. In addition, we are surprised to find that an appropriate amount of Ti-doped sample can enhance the rate performance of the raw material. Density functional theory (DFT) calculations reveal the enhanced Na ions diffusion performance in Ti-doped Na2FeP2O7@C, which is consistent with experimental observations. The high current density of 40 C is investigated for the first time in the solid-state synthesis reports, corresponding to a capacity of 50 mAh g−1. This high-rate performance can maintain 1000 cycles with almost no decline, demonstrating that the Ti-doped strategy can retain the excellent structural stability of the pyrophosphates.