Fabrication and Characterization of LiMn2O4 Thin Films for Flexible Thin Film Lithium-ion Batteries: Effect of thermal Annealing

Rongbin Ye, Koji Ohta, Mamoru Baba

Thin film, Sputtering technique, Cathode material, Annealing, Thin film battery

In this paper, we report on effect of thermal annealing on LiMn₂O₄ thin films for flexible thin film lithium-ion batteries. The as-deposited film was in amorphous state. When the annealing temperature is over 300 °C, a peak at 2θ = 18.657° with d₁₁₁ = 4.75 Å was observed, which suggests that the LiMn₂O₄ films were restructured and crystalline spinel films were formed. Increasing the annealing temperature, the full width at half maximum (FWHM) of the (111) peak was decreased, which implies that the annealing temperature significantly improves the crystal quality of the films. While the annealing temperature is over 500 °C, some small impurity phases such as Mn₂O₃ were observed. The film with the single-phase spinel structure could be gained at the optimized annealing temperature of 400 °C. On the other hand, increasing the annealing temperature, the discharge capacity of the cathode film is increased. At the annealing temperature of 400 °C, the maximum discharge capacity is 22.75 μAh/cm², which is twice larger than that of the battery with as-deposited cathode film. Unfortunately, the coulombic efficiency is lower than that of the device for the as-deposited cathode film after the first cycle, which is due to higher internal resistance. Thus, it is necessary to further improve the annealing process for fabrication of flexible thin film battery.

https://dx.doi.org/10.31873/IJEAS.8.5.02