In situ Scanning Electron Microscopy (SEM) observation of interfaces within plastic lithium batteries

Cross-sections of plastic rechargeable Li-cells were observed in a quasi in situ mode by means of a scanning electron microscope. All cells were composed of a composite cathode, containing LiMn2O4 as active material, and of a hybrid polymer electrolyte consisting of a polymer matrix embedded with a solution of lithium salt. At the negative side, three kinds of anodes (Li, Cu and graphite) were successively used. The influence of the current density on the morphology of the lithium deposit was studied from these three different configurations. Scanning Electron Microscopy (SEM) evidences for (1) the accumulation of mossy lithium, and (2) the Li-dendrites growth at the interface between Li and electrolyte are given, and correlated to the poor cell cyclability. This deterioration of the interface was confirmed by AC-impedance measurements.