Investigation of LiMn2O4 cathodes for use in rechargeable lithium batteries by linear sweep voltammetry (LSV): Part II. Experimental study using thin films, single particles and composite electrodes

Thin films, single particles and a composite electrode of the cathode material LiMn2O4 in the lithium battery system were investigated by linear sweep voltammetry (LSV) in 1 M LiClO4+PC:EC. The experimental data were compared to and analysed by mathematical models described in Part I of this work. Analysis of the measured peak potential, Ep, showed clearly that the larger the characteristic length, the larger is the potential peak shift, at a given sweep rate. From the observations of the measured peak current behaviour, Ip, it seems that the composite electrode and the single particles are semi-infinite diffusion limited at all sweep rates applied. For the thin films, when increasing the sweep rate, a transition from finite to semi-infinite mass transfer limitation is indicated. A model based on solid-phase diffusion, interfacial charge transfer and an external IR-drop could fairly well be fitted to the experimental data measured on a single electrode system at a given sweep rate. It was found that the determined parameter values, i.e. solid-phase diffusion coefficient and the IR-drop, vary greatly with sweep rate and characteristic length. These results indicate that the physical description used is an oversimplification for describing the reaction mechanism in LiMn2O4.