Layered LiCoO2 （HT-LiCoO2） films were grown on Pt-metalized silicon （PMS） substrates and polished bulk nickel （PBN） substrates by pulsed laser deposition. The effects of substrate temperature, oxygen pressure, a...Layered LiCoO2 （HT-LiCoO2） films were grown on Pt-metalized silicon （PMS） substrates and polished bulk nickel （PBN） substrates by pulsed laser deposition. The effects of substrate temperature, oxygen pressure, and substrate surface roughness on the microstructure of LiCoO2 films were investigated. It has been found that a higher substrate temperature and a higher oxygen pressure favor the formation of better crystallized and less lithium-deficient HT-LiCoO2 films. The HT-LiCoO2 film deposited on PBN substrates consists of large randomly orientated equiaxial grains, whereas on PMS substrate, it is made up of loosely packed highly [001] preferential orientated triangular shaped grains with the average grain size less than 100 nm. Electrochemical measurements show that the highly [001] preferentially orientated nanostructured HT-LiCoO2 thin film grown on PMS substrate has good structural stability upon lithium insertion/extraction and can deliver an initial discharge capacity of approximately 45μA·h·cm^-2·μm^-1 with a cycling efficiency of above 99% at the charge/discharge rate of 0.5 C.展开更多
LiCoO2 thin films, which can be used as a cathode material in microbatteries, were deposited using radio frequency (r.f.) magnetron sputtering system from a LiCoO2 target and in an O2+Ar atmosphere. The films were cha...LiCoO2 thin films, which can be used as a cathode material in microbatteries, were deposited using radio frequency (r.f.) magnetron sputtering system from a LiCoO2 target and in an O2+Ar atmosphere. The films were characterized by various methods such as XRD, SEM and AFM. The LiCoO2 films were annealed in air at 300, 500, 700 and 800 ℃ respectively. The effect of the annealing temperature on the structure, the surface morphology and the electrochemical properties of the films were investigated. The LiCoO2 thin film deposited at room temperature is amorphous and has smaller grain size. With increasing of annealing temperature, the crystallinity of the films is promoted. When the annealing temperature increases to 700 ℃, the films have a perfect crystalline LiCoO2 phase. The LiCoO2 thin film without annealing has no discharge plateau and small discharge capacity (about 27 μAh·cm-2μm). The discharge capacity increases with the increasing of annealing temperature and reaches 47 μAh·cm-2μm for the film annealed with 700 ℃, which also shows the typical discharge plateau of 3.9 V. The cycle performance of LiCoO2 thin films of as grown and annealed at different temperatures were studied. In the case of the film without thermal treatment, the capacity fading is much faster than that of the film annealed at different temperature, showing about 40% capacity loss only after 25 cycles. However, in the case of the film annealed at 700 ℃, the capacity reaches to steady state gradually and maintained constantly with cycling. After 25 times cycling, the discharge capacity of the film annealed at 700 ℃ decreases to about 36.9 μAh·cm-2·μm, only 0.8% capacity loss per cycle.展开更多
基金This work was financially supported by the CERG(Competitive Earmarked Research Grant)grant from Research Grants Council of the Hong Kong Special Administrative Region,China(CityU 1316/03E)the National Natural Science Foundation of China(No.50401015)+1 种基金the Program of the Ministry of Education of China for Changjiang Scholars and Innovative Research Team in Universities(No.1RT 0551)the Natural Science Foundation of Guang-dong Province,China under the Team Project.
文摘Layered LiCoO2 （HT-LiCoO2） films were grown on Pt-metalized silicon （PMS） substrates and polished bulk nickel （PBN） substrates by pulsed laser deposition. The effects of substrate temperature, oxygen pressure, and substrate surface roughness on the microstructure of LiCoO2 films were investigated. It has been found that a higher substrate temperature and a higher oxygen pressure favor the formation of better crystallized and less lithium-deficient HT-LiCoO2 films. The HT-LiCoO2 film deposited on PBN substrates consists of large randomly orientated equiaxial grains, whereas on PMS substrate, it is made up of loosely packed highly [001] preferential orientated triangular shaped grains with the average grain size less than 100 nm. Electrochemical measurements show that the highly [001] preferentially orientated nanostructured HT-LiCoO2 thin film grown on PMS substrate has good structural stability upon lithium insertion/extraction and can deliver an initial discharge capacity of approximately 45μA·h·cm^-2·μm^-1 with a cycling efficiency of above 99% at the charge/discharge rate of 0.5 C.
文摘LiCoO2 thin films, which can be used as a cathode material in microbatteries, were deposited using radio frequency (r.f.) magnetron sputtering system from a LiCoO2 target and in an O2+Ar atmosphere. The films were characterized by various methods such as XRD, SEM and AFM. The LiCoO2 films were annealed in air at 300, 500, 700 and 800 ℃ respectively. The effect of the annealing temperature on the structure, the surface morphology and the electrochemical properties of the films were investigated. The LiCoO2 thin film deposited at room temperature is amorphous and has smaller grain size. With increasing of annealing temperature, the crystallinity of the films is promoted. When the annealing temperature increases to 700 ℃, the films have a perfect crystalline LiCoO2 phase. The LiCoO2 thin film without annealing has no discharge plateau and small discharge capacity (about 27 μAh·cm-2μm). The discharge capacity increases with the increasing of annealing temperature and reaches 47 μAh·cm-2μm for the film annealed with 700 ℃, which also shows the typical discharge plateau of 3.9 V. The cycle performance of LiCoO2 thin films of as grown and annealed at different temperatures were studied. In the case of the film without thermal treatment, the capacity fading is much faster than that of the film annealed at different temperature, showing about 40% capacity loss only after 25 cycles. However, in the case of the film annealed at 700 ℃, the capacity reaches to steady state gradually and maintained constantly with cycling. After 25 times cycling, the discharge capacity of the film annealed at 700 ℃ decreases to about 36.9 μAh·cm-2·μm, only 0.8% capacity loss per cycle.
