Olivine-type phosphates LiMnxFe1−xPO4 are attracting increasing interest as positive electrode materials for lithium-ion batteries due to their low cost and good electrochemical performance. However, the effects of the mixed Mn/Fe composition on lithium intercalation and ion transport are not fully characterised, especially in Mn-rich compositions. In this study, the electrochemical, structural and ion transport properties of Mn-rich LiMnxFe1−xPO4 (x = 0.6, 0.7, 0.8) (LMFP) are investigated using a combination of experimental and materials modelling techniques. Considerable asymmetry in charge/discharge profiles is found, which highlights the complexity of the mixed-metal system. An intricate lithium intercalation mechanism is observed, including both solid solution and two-phase regions. While the Fe/Mn cation disorder causes the oxidation to proceed mostly via a solid solution mechanism, the Mn plateau remains associated with a two-phase process. Ab initio simulations indicate that Li+ diffusion occurs along one-dimensional channels parallel to the crystallographic b-axis following a curved trajectory, and find favourable Li/Fe and Li/Mn anti-site defect formation. Analysing the band gaps of the lithiated and delithiated phases revealed that Mn substitution of Fe can improve the electronic conductivity, suggesting asymmetric electronic behaviour.
Electrode
,Electronics
,Nanoarchitectures for lithium-ion batteries
,Electrochemistry
