Electrochemical performances of 0.9Li2MnO3-0.1Li(Mn0.375Ni0.375Co0.25)O2 cathodes: Role of the cycling induced layered to spinel phase transformation

In the present work, we have reported that as compared to Li2MnO3 lean compositions, the electrochemical properties of Li2MnO3 rich integrated cathodes (viz. 0.9Li2MnO3-0.1Li(Mn0.375Ni0.375Co0.25)O2) are singular in three different ways. First, unlike its Li2MnO3 lean counterparts, the oxygen and concomitant lithium extraction in Li2MnO3 rich composition (viz. Li(Li0.31Mn0.646Ni0.026Co0.017)O2) continues beyond first charging cycle. Second, for Li2MnO3 rich compositions, layered to spinel phase transformation seems to be unavoidable with repeated charge-discharge cycling. Formation of spinel phase triggers capacity fading in these cathodes. We have found that for these cathodes, galvanostatic cycling at relatively higher rate (> 20 mA g− 1) retards the spinel formation with concomitant improvement of capacity retention with cycling. Finally, for Li2MnO3 rich integrated cathodes the major capacity contribution is found to be due to the reversible manganese redox (~ 3 V and ~ 2.6 V). Therefore, the energy densities of these cathodes are less as compared to Li2MnO3 lean compositions.