Conductivity and electrochemical behavior of Li1-x Fe1-2x (MIIMIII) x PO4 with olivine structure
Lithium iron phosphates with olivine structure doped by trivalent cations and co-doped by divalent and trivalent cations of the compositions Li1-x Fe1-x MIII x PO4 (MIII = Al, Cr, Ga, Y, In) and Li1-x Fe1-2x (NiMIII) x PO4 (MIII = Al, In) were prepared by the sol-gel method. Structure, morphology, and conductivity of the prepared materials were studied by the X-ray diffraction analysis, scanning electron microscopy, and impedance spectroscopy. The solubility of M3+ cations in LiFePO4 with olivine structure was estimated. Single-phase samples were shown to be preserved at x ≤ 0.05 for Cr3+ and Al3+ cations, at x ≤ 0.02 for In3+, and at x ≤ 0.005 for Ga3+ and Y3+ cations. The materials doped with M3+ and co-doped with both M2+ and M3+ cations were characterized by a higher ionic conductivity and by a lower activation energy of ionic conductivity. Carbon-coated materials Li0.995Fe0.99(NiM)0.005PO4/C (MIII = Al, In) were prepared, and their electrochemical behavior was studied using the charge/discharge tests. Due to LiFePO4 co-doping with M2+ and M3+ cations, capacity slightly decreases but the charge/discharge rate increases.
KeywordsCathode materials Lithium ion battery Lithium iron phosphate Doping Ion conductivity Rate capability
This research was supported by the Ministry of Education and Science of the Russian Federation (Project no. 14.604.21.0126, unique identifier RFMEFI60414X0126).
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