LiFe1−xMIIxPO4/C (MII=Co, Ni, Mg) as cathode materials for lithium-ion batteries

LiFe 1− x M II x PO 4 /C (M II  = Co, Ni, Mg) composites had been obtained by sol–gel method. Structure and morphology of the obtained materials have been studied with the use of the XRD-analysis, SEM and Mossbauer spectroscopy. Their electrochemical behavior has been investigated with the use of charge/discharge tests. The materials doped by cobalt and nickel were shown to be characterized by an increased lithium intercalation and deintercalation rates, and retain a high capacity during charge and discharge the battery at high currents densities (LiFe 0.9 Ni 0.1 PO 4 capacity amounts to 145 and 62 mAh/g at a discharge current 50 and 3000 mA/g). Mg 2+ incorporation into LiFePO 4 /C cathode material results in the slight increase of charge/discharge rate and significant capacity decrease. Mossbauer spectroscopy has shown that M II ions in the LiFe 1− x M II x PO 4 /C (M II  = Co, Ni) materials are orderly distributed both in charged and discharged states, each iron ion has no more than one M II ion in the nearest environment. In the case of Ni-doped samples the ordering is less pronounced. The reasons of the changes observed in the electrochemical performances and charge/discharge rate have been discussed on the base of Mossbauer spectroscopy and XRD data.