A comparative study on electrochemical cycling stability of lithium rich layered cathode materials Li1.2Ni0.13M0.13Mn0.54O2 where M = Fe or Co

In this work we compare electrochemical cycling stability of Fe containing Li rich phase Li1.2Ni0.13Fe0.13Mn0.54O2 (Fe-Li rich) with the well-known Co containing Li rich composition Li1.2Ni0.13Fe0.13Mn0.54O2 (Co-Li rich). During the first charge, the activation plateau corresponding to removal of Li2O from the structure is smaller (removal of 0.6 Li) in the case of Fe-Li rich compared to Co-Li rich composition (0.8 Li removal). Consequently, the Fe compound shows better capacity retention; for example, after 100 cycles Fe-Li rich compound exhibits 20% capacity degradation where as it is about 40% in the case of Co-Li rich phase. The electrochemical and microscopy studies support the fact that compared to Co-Li rich compound, the Fe-Li rich composition display smaller voltage decay and reduced spinel conversion. XPS studies on charged/discharged Fe-Li rich samples show participation of Fe+3/Fe+4 redox during electrochemical cycling which is further supported by our first principles calculations. Also the temperature dependent magnetic studies on charge-discharged samples of Fe-Li rich compound point out that magnetic behavior is sensitive to cation oxidation states and Ni/Li disorder. (C) 2016 Elsevier B.V. All rights reserved.