Synthesis, Characterization, and Electrochemical Cycling Behavior of the Ru-Doped Spinel, Li[Mn[sub 2−x]Ru[sub x]]O[sub 4] (x=0, 0.1, and 0.25)

Pure and Ru-doped ( and 0.25) spinel compounds are prepared by the high temperature solid-state reaction and characterized by X-ray diffraction (XRD), scanning electron microscopy, Brunauer, Emmett, and Teller surface area, density, IR, Raman spectroscopy, and X-ray absorption spectroscopy. XRD studies show single-phase compounds with the cubic spinel structure and a decrease in (Mn–O) and an increase in (Li–O) bond lengths on Ru doping. The electrochemical cycling behavior of is examined by galvanostatic cycling and cyclic voltammetry (CV). The CV shows that the couple lies in the range from and the spinel-to-double-hexagonal (S-DH) transition at in agreement with results in the literature. The redox couple operates at vs Li in the spinel structure. The S-DH phase transition is suppressed on Ru doping. Charge–discharge cycling, up to 25 or , in the voltage ranges 3.5–4.3 and vs Li at 0.14C rate gave initial charge capacities ranging from for various . Compositions with and 0.25 showed smaller initial capacity loss and smaller capacity fading during cycling as compared to . For in the voltage range and , the capacity fade is only 9% thereby showing the beneficial effect of Ru doping, by way of suppression of S-DH transition, participation of Ru-redox couple, and better electronic conductivity of the compound during cycling, in comparison to pure .