Paper EH-TuE7
High-Resolution Observation of Electronic Properties of a Cathode Material in a Li-ion Battery

Tuesday, December 13, 2016, 7:40 pm, Room Lehua

Li-ion batteries are widely used in many portable electronic devices and are recognized to be energy storage devices for mass-produced electric vehicles. However, to improve of power density, durability and safety, it is crucial to optimize the structure of the electrode as well as exploring new materials because the kinetics of the electrode reaction depends on the structure of the composite electrode.

The main elements are positive electrodes, negative electrodes, separators, and electrolytes. The electrolyte is typically a nonaqueous mixture of organic carbonates containing complexes of Li ions, which are noncoordinating anion salts such as Li hexafluorophos phate (LiPF₆). The separator is, for example, monolayer polypropylene. The electrode materials hold the key to determine the performance of the batteries. They are generally intercalated lithium compounds. Depending on the materials, the voltages, capacities, and lifetimes of the batteries greatly change. Therefore, they have been actively investigated.

The cathode material is also an oxide such as lithium cobalt oxide (LiCoO₂). Concerning the cathode materials, some materials, Li₂MnO₃, Li_1.2Mn_0.4Fe_0.4O₂, LiNi_0.3Mn_0.3-Co_0.3O₂, etc., have been proposed, developed, and investigated. Redox of the transition metal oxides or valence fluctuation of transition metals play important roles of charge neutral. Therefore, not only ionic conductivity but also electronic conductivity is important for battery operation. However, electric conductivity varies with valence fluctuation of the transition metals due to extraction or insertion of Li ions. We present results on a change in band structure of LiCoO₂ corresponding to the Li-ion concentrations, which were obtained via a scanning probe microscope.