Recent progress in Mn and Fe-rich cathode materials used in Li-ion batteries

Rechargeable Li-ion battery has been regarded as the most effective electrochemical energy storage device because of its high energy density and power density of 3 and 6 magnitudes respectively higher than the conventional Ni-Cd and Ni-MH batteries. Amongst the cathode materials, used in LIBs, layered Li2MnO3, spinel LiMn2O4, olivine-type LiMnPO4, LiFePO4 and LiMnFePO4 have generated a great interest due to their enhanced electrochemical activities, high theoretical capacity, low cost, high discharge potential, good thermal stability, high natural abundance, and low toxicity. However, these materials have their own limitations which include poor rate capability and decrease in electrochemical performance due to low electronic conductivity and ionic diffusivity. In addressing these challenges, various modification strategies were employed by researchers. Herein, we present a detailed review on these cathode materials. These include a comprehensive study of the structural and electrochemical properties of layered Li2MnO3, spinel LiMn2O4, olivine-type LiMnPO4, LiFePO4, and LiMnFePO4 cathode materials for LIB applications. Limitations to their electrochemical performances based on structural, morphological, and chemical modifications were presented. We highlighted some modification techniques such as Mn- and Fe-ion substitution, surface coating, surface treatment, and co-doping, that have been carried out to overcome some of the limitations inherent in the materials. Finally, an overview of prospects in using these materials is given.