Tuning a small electron polaron in FePO 4 by P-site or O-site doping based on DFT+ U and KMC simulation

• Published in: Physical chemistry chemical physics : PCCP 2023-03, Vol.25 (12), p.8734-8742
• Main Authors: Chen, Taowen, Ye, Yaokun, Wang, Ying, Fang, Chi, Lin, Weicheng, Jiang, Yao, Xu, Bo, Ouyang, Chuying, Zheng, Jiaxin
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/D2CP06034E

Due to the existence of a small polaron, the intrinsic electronic conductivity of olivine-structured LiFePO is quite low, limiting its performance as a cathode material for lithium-ion batteries (LIBs). Previous studies have mainly focused on improving intrinsic conductivity through Fe-site doping while P-site or O-site doping has rarely been reported. Herein, we studied the formation and dynamics of the small electron polaron in FeP X O and FePO Z by employing the density functional theory with the on-site Hubbard correction terms (DFT+ ) and Kinetic Monte Carlo (KMC) simulation, where X and Z indicate the doping elements (X = S, Se, As, Si, V; Z = S, F, Cl), and and β indicate the light doping at the P position ( = 0.0625) and O position ( = 0.015625), respectively. We confirmed the small electron polaron formation in pristine FePO and its doped systems, and the polaron hopping rates for all systems were calculated according to the Marcus-Emin-Holstein-Austin-Mott (MEHAM) theory. We found that the hopping process is adiabatic for most cases with the defects breaking the original symmetry. Based on the KMC simulation results, we found that the doping of S at the P site changes the polaron's motion mode, which is expected to increase the mobility and intrinsic electronic conductivity. This study attempts to provide theoretical guidance to improve the electronic conductivity of LiFePO -like cathode materials with better rate performance.