First-Principles Calculations on the LiMSO4F/MSO4F (M = Fe, Co, and Ni) Systems

Systematic first-principles calculations based on the density functional theory are carried out to discuss the crystal and electronic structures of the LiMSO4F/MSO4F (M = Fe, Co, and Ni) systems. It is shown that all of the LiMSO4F compounds are in a high spin antiferromagnetic ground state. However, they transform to different ground states with Li+ extraction. LiFeSO4F is a typical Mott-Hubbard insulator and then transforms to a charge-transfer insulator with Li+ extraction. The theoretical intercalation voltages of LiMSO4F are 3.54 (Fe), 4.73 (Co), and 5.16 V (Ni), respectively, which are close to corresponding LiMPO4 phosphates. First-principles calculations show that a significant amount of electron-charge transfer takes place on the oxygen anions with Li+ extraction, especially for LiCoSO4F and LiNiSO4F. This will lead to significant loss of oxygen from the material lattice which is an intrinsic drawback of LiMSO4F due to the concerns of structural and thermal stabilities.