The electrochemical enhancement effect and synergistic modification mechanism of V-Cl co-doping on carbon coated lithium iron phosphate cathode materials

Abstract

The low electronic conductivity and ion diffusion rate of lithium iron phosphate (LiFePO₄) are the main factors limiting its further development as a positive electrode material for lithium-ion batteries. Element doping is an effective method to improve these limitations. In this study, the method of co-doping with cations and anions has been attempted to improve the electrochemical performance of lithium iron phosphate cathode materials. V-Cl co-doped LiFePO₄/C samples were successfully prepared using the high temperature solid-phase method. The controlled particle size LiFe_0.95V_0.05PO_0.95Cl_0.05/C was characterized using XRD, XPS, SEM, and the band structure changes of the system were calculated using the first-principles calculations. The results show that V-Cl co-doped lithium iron phosphate materials could significantly enhance the electrochemical performance of lithium iron phosphate batteries, especially at 1C and 5C rates (1C = 170 mAh/g), where the capacities of the modified lithium iron phosphate battery electrodes could still maintain 89 % and 83 % after 1000 cycles. The synergistic effect of anions and cations in V-Cl co-doped system has been confirmed by the first-principles calculations, could effectively reduce the energy barrier for electronic band transitions and improve electronic conductivity.