Cyclic voltammetry studies on 4 V and 5 V plateaus of non-stoichiometric spinel Li1+xMn2−yO4

Abstract Li 1+ x Mn 2− y O 4 spinels with various Li/Mn ratios were synthesized by a solid-state reaction. By X-ray diffraction analysis, Li 2 MnO 3 was detected as a second phase with increasing the Li/Mn ratio; and the role of Li 2 MnO 3 in Li 1+ x Mn 2− y O 4 spinel was discussed. A slow scanning cyclic voltammetry(CV) at the rate of 0.1 mV/s was adopted to characterize the evolutions of 4 V and 5 V plateaus of Li 1-x Mn 2− y O 4 spinels. An additional Li + insertion in 4 V region was observed in both Li-lack and Li-rich spinels at 3.95 V, which is different from the general Li + insertion with weak Li-Li interaction and strong Li-Li interaction; and this plateau disappeared in the subsequent cycles. The 4.4 V/3.8 V plateaus correspondent to Li + insertion and extraction of Li 2 MnO 3 were discussed, and these plateaus have a high reversibility with cycling. The 5 V plateau was found only in the Li-rich samples, and this plateau has a tendency to emerge at higher voltage region with increasing Li/Mn ratio.