Search

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 2th = 18.48deg with d111 = 4.795 A 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 uAh/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.

A thin-filmed Li-ion rechargeable battery using a carbon nanotube (CNT) anode was realized for the first time. The CNT anode suitable for the thin-filmed battery was successfully fabricated on a SiC surface by using both the SiC surface decomposition technique for growth of an aligned CNT film and the Ar-sputter etching technique for a smooth surface of the CNT film. The present CNT anode battery showed good cell characteristics of a high cell voltage between 3 and 4 V, a large capacity, and long cycle performance over 2000 cycles. Especially, the maximum capacity obtained here reached roughly 1460 mAh/cm3 over the theoretical value of graphite anode.

Nb2O5thin films were prepared using RF magnetron sputtering system. By X-ray diffraction and SEM cross-section analysis, Nb2O5thin film was in an amorphous state and its growth rate is 0.013 nm/s. The electrochemical behaviors of Nb2O5thin films were characterized by capacity measurement and cycling performance. The average capacity of Nb2O5thin films of 630 nm is about 41.8 μAh/cm2for cut-off voltage range of 3.0 and 1.0V (vs. Li/Li+) at a rate of 10 μAh/cm2and the coulombic efficiency reaches to over 98% after the first cycles. In addition, electrochemical characteristics of flexible thin film rechargeable lithium ion batteries composed of LiMn2O4thin films of 720 nm, LiPON electrolyte thin films of ca. 1.0 μm and Nb2O5thin films of 630 nm, fabricated on 30 μm SUS304 substrates, were also investigated. At a discharge current of 50 μA, the maximium discharge capacity of 24.7 μAh/cm2was obtained, and the coulombic efficiency was all over 95% except for the first few cycles, which is due to a large internal resistance of the battery when no Li ion was inserted into Nb2O5thin films. Even at a high discharge current of 500 μA, the thin film battery can still deliver reversible capacity of 18.4 μAh/cm2. The long-term cycle performance of the thin film battery showed steady cycling behaviors with a small decreasing ratio of 0.1% after 20 cycles, and the coulombic efficiency was all over 95% except for the first few cycles.

In this paper, we report on laser modification and characterization of LiMn2O4cathodes 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 LiMn2O4films 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.