Effect of post-deposition annealing in oxygen atmosphere on LiCoMnO4 thin films for 5 V lithium batteries

Abstract Thin-filmbatteries are a promising microscale high-capacity energy sources for future micro devices. One possible way to increase the energy density is to use a cathode made of spinel LiCoMnO 4 , which has a theoretical specific energyof 475 Wh/kg and operates at about 5 V. However, one problem of this material is the loss of oxygen in the lattice during the thin- film formationprocess, which causes the loss of capacity at 5 V and the appearance of unexpected peak at around 4 V. In the study reported here, the effect of oxygen loss on the thin-filmbattery performance was investigated using post-deposition annealing of the thin-filmsunder an oxygen flow at different temperatures and for different periods of time. The crystallinity and oxygen deficiency were characterized by the intensity of the X-ray diffraction (XRD) peaks and their shift in position. A clear correlation was found between the discharge capacity and the XRD peak shift (or oxygen content of the thin films). Basedon these results, the optimum combination of conditions for post-deposition annealing of the LiCoMnO 4 thin filmswas determined to be a temperature of 600 °C for 6 h under an oxygen atmosphere.