In recent years, as a battery anticipated to have small size, light weight, and high capacity, a non-aqueous electrolytic solution-based secondary battery such as a lithium ion battery has been proposed and put into practical use.
The lithium ion battery is constituted of a cathode and an anode which allow the reversible insertion and removal of lithium ions, and a non-aqueous electrolyte.
Regarding an anode material for lithium ion batteries, as an anode active material, generally, a lithium-containing metal oxide allowing the reversible insertion and removal of lithium ions such as a carbon-based material or lithium titanate (Li4Ti5O12) is used.
On the other hand, regarding a cathode material for lithium ion batteries, as a cathode active material, generally, a lithium-containing metal oxide allowing the reversible insertion and removal of lithium ions such as lithium iron phosphate (LiFePO4) or an electrode material mixture is used. In addition, the cathode in the lithium ion battery is formed by applying the electrode material mixture to the surface of a metal foil called a current collector.
Compared with secondary batteries of the related art such as lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries, lithium ion batteries have a lighter weight, a smaller size, and higher energy, and thus are used not only as small-size power supplies but also as large-size stationary emergency power supplies in portable electronic devices such as mobile phones and notebook personal computers.
In addition, recently, studies have been underway regarding the use of lithium ion batteries as high-output power supplies for plug-in hybrid vehicles, hybrid vehicles, and electric power tools, and batteries used as the high-output power supplies are required to have high-speed charge and discharge characteristics.
However, electrode materials including an electrode active material, for example, a lithium phosphate compound allowing the reversible insertion and removal of lithium ions have a problem of low electron conductivity. Therefore, as electrode materials having increased electron conductivity, an electrode material in which particle surfaces of an electrode active material are uniformly coated with a chemically-deposited carbonaceous material, and the current density of the electrode active material is improved (Japanese Laid-open Patent Publication No. 2001-15111), an electrode material including a carbon black complex obtained by conjugating fibrous carbon and carbon black and olivine-type lithium iron phosphate (Japanese Laid-open Patent Publication No. 2011-108522), and the like have been proposed.