Figure 1 shows comparison of energy densities of various batteries. It clearly shows Lithium ion battery possesses higher energy density compared with other batteries, indicating that it is possible to fabricate small battery with high power and capacity. Therefore, the lithium ion batteries have been widely applied for mobile phones and laptop computers as a power source.
In the lithium ion battery, Li ion migrates from positive to negative electrodes during charge process. At discharge process, the Li ion in the negative electrodes moves to the positive electrode. In this way, battery reaction is going quite simply, only movement of the Li ion as shown in fig. 2. Mainly, present lithium ion batteries have been made up of LiCoO2 cathode and graphite anode.
Present issue and effort
A flammable organic liquid electrolyte has been one of the components of present lithium ion battery construction. This sometimes causes serious safety problems like explosion and electrolyte leakage. Especially, for fabrication of large scale battery, this flammable electrolyte should be removed. In our group, we have been tried to fabricate all-solid-state battery with ultimate safely and reliability. Also, to improve power density of the lithium ion battery, development of high capacity electrode materials has been performed.