A Novel Codoping Approach for Enhancing the Performance of LiFePO4 Cathodes

By combining experimental and theoretical studies, we have demonstrated that donor‐acceptor charge‐compensating codoping is a promising approach to significantly enhance the rate performance of LiFePO4 cathodes. Our density‐functional theory calculation predicts that codoping with Si on the P site and F on the O site modifies the nature of the conduction band edge of LiFePO4 from localized Fe 3d derived states to more delocalized F s and cation s derived states. This effect, thus changes the carrier transport from a poloron‐like to a band‐like mechanism, and consequently leads to significant improvement in the electrical conductivity of LiFePO4. Most importantly, our comparative doping experiments show that the electrical conductivity of Si P ‐FO codoped LiFePO4 exhibits at least 2 to 3 orders of magnitude increase in electrical conductivity as compared to that of un‐doped LiFePO4. Because of the dramatic improvement of electrical conductivity, the optimal Si‐F codoped LiFePO4 shows both a much higher rate‐capability than un‐doped LiFePO4 or LiFePO4 solely doped with either Si or F. Furthermore, we also believe that the charge‐compensating codoping approach may be employed to improve the performance of other cathode materials suffering from inferior electrical conductivities due to localized conduction band states.