Laser Modification and Characterization of LiMn2O4 Cathodes for Thin Film Lithium　Ion Battery

In this paper, we report on laser modification and characterization of LiMn2O4 cathodes for thin film lithium ion battery. The as-deposited film was in amorphous state. When the laser power is over 60W, a peak at 2θ = 18.48° with d111 = 4.795 Å was observed, which suggests that the LiMn2O4 films were restructured and crystalline spinel films were formed. Increasing the laser power the full width at half maximum (FWHM) of the (111) peak was decreased and the intensity was increased, which implies that the laser power significantly improves the crystal quality of the films, and the smallest FWHM was gained at the laser power of between 80 W and 100 W. In electrochemical analysis of the cathode laser annealed at 80 W, the maximum discharge capacity is 25.3 μAh/cm2, which is twice larger than that of the battery with amorphous cathode films. Due to higher internal resistance, which originates from the difficult absorption reaction of the electrolyte and the cathode film melted or hardened in the laser annealing process, the coulombic efficiency was only 23.6% at the 1st cycle. Thus it is necessary to further improve the laser annealing process for fabrication of thin film battery.