Correlation Between Li‐Fe Anti‐Site and Memory Effect of LiFePO4 in Li‐Ion Batteries

Abstract In Li‐ion batteries, the origin of memory effect in Al‐doped Li 4 Ti 5 O 12 has been revealed as the reversible Al‐ion switching between 8a and 16c sites in the spinel structure, but it is still not clear about that for olivine LiFePO 4 , which is one of the most important cathode materials. In this work, a series of Na‐doped and Ti‐doped LiFePO 4 are prepared in a high‐temperature solid‐state method, electrochemically investigated in Li‐ion batteries and characterized by X‐Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Magic‐Angle‐Spinning Nuclear Magnetic Resonance (MAS NMR). Compared with non‐doped LiFePO 4 , the Ti doping can simultaneously suppress the memory effect and the Li−Fe anti‐site, while they are simultaneously enhanced by the Na doping. Meanwhile, the Ti doping improves the electrochemical performance of LiFePO 4 , opposite to the Na doping. Accordingly, a schematic diagram of phase transition is proposed to interpret the memory effect of LiFePO 4 , in which the memory effect is attributed to the defect of Li−Fe anti‐site.