MEM Charge Density Study of Olivine LiMPO4 and MPO4 (M = Mn, Fe) as Cathode Materials for Lithium-Ion Batteries

Abstract

We have investigated the electron-density distributions in LiMPO4 and MPO4 (M = Mn, Fe) by analyzing high-energy synchrotron-radiation powder-diffraction data using the maximum entropy method (MEM)/Rietveld method to deepen understanding of the electrochemical properties in designing a promising cathode material. The Jahn–Teller Mn3+ ion in a high electric field induced by the adjacent (PO4)3– ion in MnPO4 forms anisotropic chemical bonding with the neighboring oxide ions. The net charge analysis shows that the electrons assigned to both the Mn and P atoms influence the delithiation for LiMnPO4, while the electrons of the Fe atom in LiFePO4 mainly contribute to the delithiation. The effects of the anisotropy of the d-electron density of the Mn3+ ion and the role played by the charge transfer of the P atom are discussed on the instability at high temperature and the metastability at room temperature, respectively.