First-principles study on the Jahn-Teller distortion in trigonal bipyramidal coordinated LiFe1-xMxBO3(M = Mn, Co, and Ni) compounds

The development of new cathode materials with high capacity, good stability, and high safety is important for the future improvement of Li batteries. LiFeBO(3)is considered to be a type of promising electrode materials for Li-ion batteries due to its low cost, high theoretical capacity of 220 mAh/g (about 30% larger than that of LiFePO4), low toxicity, and small volume change of 2% during the Li(+)reversible extraction/insertion process. However, its electronic conductivity and rate performance still need further improvement. To optimize the performance of the LiFeBO3, Mn, Cr, and Ni doping at Fe site have been studied experimentally, while the effect of minor addition of 3d transition metals on the electronic structure of LiFeBO(3)is rarely investigated. Thus, density functional theory calculations corrected by on-site Coulomb interactions have been conducted to study the crystal structure and electronic property of the LiFe1-xMxBO3(M = Mn, Co, and Ni) electrode systems. The results indicate that the coordination geometry about Fe in LiFeBO(3)is a distorted trigonal bipyramid with a distortion which can be attributed to a Jahn-Teller effect. The band gap energy of LiFeBO(3)is calculated to be 3.40 eV, which is in reasonable agreement with the previously computed values. The doping at Fe site with Mn cannot reduce the distortion of Jahn-Teller effect, whereas Co doping intensifies Jahn-Teller distortion of the FeO(5)trigonal bipyramid in LiFeBO3. Ni substitution is predicted to be able to introduce impurity levels, and the Jahn-Teller distortion degree of the trigonal bipyramid decreased from 11.9 of the FeO(5)to 8.7% of the NiO5. Thus, Ni doping is expected to increase stability and the electronic conductivity of the LiFeBO(3)structure.