Effect of Ni and Cu Substitution in Mn Oxide Spinel Cathode Electrodes: An Electrochemical and In situ Synchrotron Spectroscopic Study

摘要

Partial substitution of Mn in lithium manganese oxide spinel materials by Cu and Ni greatly affects the electrochemistry and the cycle life characteristics of the cathode. Substitution with either metal or a combination of both shortens the 4.2 V plateau associated with the conversion of Mn~(3+) to Mn~(4+). A higher voltage plateau associated with oxidation of the substituted transition element is also observed. There substituent also significantly alter the onset of Jahn Teler distortions in the 3V plateau. Synchrotron based in situ x-ray absorption (XAS) is used to determine the exact nature of the oxidation state changes in order to explain the overall capacities at the different voltage plateaus. Synchrotron based in situ x-ray diffraction (XRD) studies on LiCu_(0.5)Mn_(1.5)O_4 shows single phase behavior in the 4-5 V region and a good cycle life. Lower cycle life characteristics for LiNi_(0.5)Mn_(1.5)O_4 and LiNi_(0.25)Cu_(0.25)Mn_(1.5)O_4 are accounted for on the basis of several phase coexistence in this potential region. In the 3 V plateau however, the LiCu_(0.5)Mn_(1.5)O_4 shows onset of the Jahn Teller distortions, in contrast to the LiNi_(0.5)Mn_(1.5)O_4 and LiNi_(0.25)Cu_(0.25)Mn_(1.5)O_4.