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

Thin-film batteries 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 LiCoMnO₄, which has a theoretical specific energy of 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 formation process, 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-film battery performance was investigated using post-deposition annealing of the thin-films under 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). Based on these results, the optimum combination of conditions for post-deposition annealing of the LiCoMnO₄ thin films was determined to be a temperature of 600 °C for 6 h under an oxygen atmosphere.