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

• LiFe1−xMIIxPO4/C (MII = Co, Ni, Mg) cathode materials for LIBs were studied.
• LiFePO4 doping results in the charge/discharge rate increase.
• LiFe0.9Ni0.1PO4 retains 62 mAh/g capacity at discharge current 3000 mA/g.
• MII ion ordering takes place in LiFe1−xMIIxPO4/C (MII = Co, Ni) materials.

LiFe1−xMIIxPO4/C (MII = 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 Mössbauer 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. Mössbauer spectroscopy has shown that MII ions in the LiFe1−xMIIxPO4/C (MII = Co, Ni) materials are orderly distributed both in charged and discharged states, each iron ion has no more than one MII 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 Mössbauer spectroscopy and XRD data.