Preparation of LiFe0.99Mn0.01PO4 Cathode Material with Lower Fe-Li Antisite via Wet-Lithiation Following by Tavorite-Olivine Phase Transition

Abstract

Mn doping is widely used to improve the kinetic properties of LiFePO4 cathode materials. In this work, we synthesized LiFe0.99Mn0.01PO4 cathode material by a novel phase transition from the tavorite LiFePO4OH structure to the olivine LiFePO4 structure at 600 °C. A lower crystallization temperature not only results in a looser lattice for LiFePO4 material but also prevents crystal growth in higher temperatures and shortens the ion diffusion path. Experiments reveal that Mn doping can further broaden the lattice on this basis and thus ameliorate the Li+ diffusion property. The Density-Functional Theory (DFT) calculations not only support the above argument, but also predict that the LiFePO4 cathodes obtained from LiFePO4OH-to-LiFePO4 phase transition own lower Fe-Li antisite concentration (due to the high Fe-Li antisite formation energy of pre-lithiated precursor LiFePO4OH). As a result, the obtained LiFe0.99Mn0.01PO4 yields a discharge capacity close to the theoretical capacity of 169.2 mAh g−1 at a low rate of 0.2 C, 142.9 mAh g−1 at a high rate of 10 C and a capacity retention of 97.8% till 1000 cycles at 1 C. These findings indicate that the LiFePO4OH enabled by prelithiation in liquid provides a new idea for realizing substitution-modified LiFePO4 with optimal electrochemical performance.