After the Great East Japan Earthquake, the importance of Business Continuity Plans (BCP) were debated, resulting in strong demands for stable electricity supplies, energy savings and leveling of electric power. Hence, there are now even greater expectations for battery technologies that have high energy density. For these reasons, research is ongoing into lithium-air secondary batteries as a potential new secondary battery technology that can charge and discharge with larger energy densities per weight and volume than lead-acid or lithium ion batteries.
Figure 1 illustrates the structure and the operation mechanism of lithium-air secondary batteries. Unlike the conventional lithium-ion batteries used to power mobile telephones, etc. that contain positive and negative electrode reactants within themselves, Lithium-air secondary batteries have the advantage of always taking in oxygen from the air as the positive electrode (the air electrode) reactant, which means most of the battery can be taken up by the negative metal electrode, giving these batteries extremely high energy density, and enabling long discharge time.
Although lithium-air secondary batteries have great potential in this area, technical issues have been clarified such as low discharge-charge cycle performance, in other words, subsequent discharge after charging finishing in a short time, and difficulty in delivering large currents.
To respond to these issues, in particular by focusing on the positive electrode, we are developing solid-phase catalysts for high-activity air electrodes (Figure 2 (a)), liquid-phase electrolyte catalysts and high-specific surface area, high-porosity carbon carriers (Figure 2 (b)) to enable a solid catalyst.
Lithium-air batteries have a theoretical energy density 5 to 8 times that of a lithium ion battery. For this reason, if used with terminals such as smartphones, these devices would only require charging at intervals greater than 1 week, and if included in electric vehicles would provide longer driving distances.