LiFe1-xMxIIPO4/C (MII = Co, Ni, Mg) as cathode materials for lithium-ion batteries

(LiFe1-xMxPO4)-P-II/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 (LiFe0.9Ni0.1PO4 capacity amounts to 145 and 62 mAh/g at a discharge current 50 and 3000 mA/g). Mg2+ incorporation into LiFePO4/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 (LiFe1-xMxPO4)-P-II/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. (C) 2013 Elsevier Ltd. All rights reserved.