Tetsuya Yamada

Abstract:

Development of high-power density battery is one of important issues for managing high-performance energetic applications including electric vehicles, rescue robots, elevating machines, and so on. Lithium cobalt oxide, LiCoO2, is one of the most popular active materials in lithium ion secondary batteries because of exhibiting good conductivities with reasonable capacity. Toward the application of LiCoO2 as high-output uses, there are still some issues to be solved. Usually, LiCoO2 was prepared by solid-state reaction, which provided a few micron-size polycrystals with inhomogeneous distribution in shapes. Under high loading rate, it is presumed that the usual LiCoO2 particles undergo local overcurrent and volume changes during lithiation / delithiation caused by aggregation and inhomogeneous natures of them. Since these electrochemical overloads would lead serious degradation in the cycle abilities, improvements of LiCoO2 are inevitable. There are two kinds of approaches for the improvement. The first one is modification of chemical compositions, including doping with other elements, coating with inactive materials, and the second one is control of crystallographic characteristics, such as crystal habits, particle dispersibility, and sizes. Combining them, synergetic improvement of LiCoO2 toward high-output battery would be possible. Recently, we have grown LiCoO2 single crystals by using flux method, which is one of liquid-phase crystal growth techniques. Exhibiting submicron-size, dispersed, low-aspect ratio with rich a, b faces, and high crystalline natures, which commonly provide efficient electron and Li+ transportations, it is expected that the flux grown LiCoO2 crystals inhibit the unfavorable electrochemical degradations at high electrochemical load. In this report, we applied the flux grown LiCoO2 crystals to the active materials for high-output batteries. The effects of crystallographic characteristics of the LiCoO2 to the battery performances were examined at 10C rate, coupled with their degradation manners in terms of morphologies and chemical phases.