Phosphorus-Doped FeOF Nanoparticle-Based Cathodes for Lithium Storage

Iron oxyfluoride (FeOF), an intercalation-conversion material, offers high energy density as a cathode in Li-ion batteries. Unfortunately, sluggish reaction kinetics and irreversible structural degradation impede FeOF application. Here, a controllable P-doping strategy is used to develop P-doped FeOF with a nanorod morphology, and the optimal doping ratio is reached by adjusting the phosphating time. Comprehensive research demonstrates that P doping can broaden the Li+ transport channels and storage sites, optimize the electronic structure, improve the Li+ migration rate and pseudocapacitive properties, and thus enhance the Li+ transport kinetics. When the phosphating time is 60 min, the cycle stability of the electrode significantly improves due to the alleviation of local structural change. In addition, the nano-size of the P-F6 electrode reduces the Li+ diffusion distance and improves the diffusion kinetics. Therefore, the FeOF cathode after 60 min of phosphating exhibits superior rate performance (104.8 mA h g–1 at 1000 mA g–1) and cycle performance (209.1 mA h g–1 after 200 cycles at 100 mA g–1). Furthermore, the electrochemical reaction mechanism of P-doped FeOF electrodes is investigated by in situ X-ray diffraction and ex situ characterization. The proposed P-doping strategy provides a feasible way to improve the electrochemical performance of other intercalation-conversion materials.