Vol.1 No.4 2009

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Research paper : Development of high power and high capacity lithium secondary battery based on the advanced nanotechnology (I. Honma)−232 Synthesiology - English edition Vol.1 No.4 (2009) inside the electrode solid, and I think it is a good example of application of nanosizing of active material. Although it is described that in surface pseudo-capacity, “the surface becomes metallic as lithium concentration increases and voltage decreases,” it may be helpful if the author explain the reaction mechanism and specific image of the surface related to the pseudo-capacity.Answer (Itaru Honma)To provide simple explanation, as shown in Fig. 7, lithium ion causes intercalation (insertion of ion) inside the solid in bulk reaction, and at the same time, oxidation reduction of the compositional metal occurs to store electric energy. It arises from the essential (perhaps standard?) electrochemical reaction of the material. Therefore, no matter who conducts experiment anywhere in the world, as long as material with same stoichiometric composition is used, same amount of lithium ion is stored in equilibrium voltage. However, the storage mechanism at surface is different from the essential (bulk) property unique to the material, and it is non-unique property that manifests because a surface exists. Therefore, difference occurs in capacity property due to change in specific surface area or plane direction (crystal morphology) (that is, data will differ according to experiment group).In Figure 7, it is described as surface reaction where electron enters the titania surface layer and causes single-electron reduction of Ti4+/Ti3+ at same time as adsorption of lithium ion to the surface in the fast charge transfer process. That is, regardless of crystal structure, it is thought that pseudo-capacity originates from surface reaction. Moreover, the two-electron reduction of Ti4+/Ti2+ that does not occur in bulk becomes possible in nanocrystal surface with special chemical bond status for lithium ion, and that produces large capacity. The lithium ion shown in red in Fig. 7 is presenting special surface reaction, and shows that the lithium is stored at higher concentration than bulk. If two-electron reduction takes place, Ti2+ will appear, so voltage decreases and the surface becomes more metallic as shown in bottom figure.In addition, grid expansion occurs in nanocrystal and crystal structure (phase) different from bulk becomes stable, and the surface is not necessarily same as surface of bulk. These are extremely interesting research subject. In other words, there is possibility that new storage mechanism may appear, and we intend to pursue this basic research further.3 Collaboration of AIST with battery manufacturer and automobile manufacturerQuestion and Comment (Akira Ono)I think this research demonstrates advantages of the vertical collaboration of industry-academia-government. Then, I ask the Author, who was the project leader, about the collaboration. In this project, what specific suggestions did AIST receive from the battery manufacturer, and how were they reflected in the project? Also, what specific suggestions did AIST or the battery manufacturer receive from the automobile manufacturer, and how were they reflected in the project? Please answer from the standpoint of project leader.Answer (Itaru Honma)It has been found that high output can be obtained using nanosize active material and basic research is accelerating in this area, but I was surprised that there was absolutely no research on which nanosize materials were optimal for LiMn2O4 and Li4Ti5O12 that are practical electrode materials. As shown in Fig. 8, there is missing range in active material size, and the battery manufacturer suggested that we should seek physicochemical knowledge of nanosizing effect by exploring this unexplored range, and search for sizes that generate highest capacity and output properties, as most important items of development. It is important from perspective of basic research to systematically investigate the size effect of active materials in nano range, and the surface effect that becomes clear in the process and size effect of charge transfer process of ion and electron in that process become very important guides for material design in developing high-power electrode. AIST set direction of basic research to respond to the expectation of the battery manufacturer, and studied the nanosizing effect of metal oxide materials such as titania, as described in the paper. The automobile manufacturer indicated that low cost and productivity are important issues in actual commercialization, and we worked simultaneously on mass production process of nanosize active material based on this suggestion. Although not included in this paper, we developed new active material synthesis process where nanocrystal active material could be mass-produced in kilogram level using molten salt method.4 Collaboration of AIST and universityQuestion (Akira Ono)What specifically was the collaboration between Nagasaki University and AIST? Rather than transferring just the technological potential of Nagasaki University to AIST, can you talk specifically about the interaction and coordination between the two organizations from the standpoint of project leader?Answer (Itaru Honma)Nagasaki University (NU) made major contribution in developing the basic chemical process. AIST has been studying the nanosizing effect of active material, and NU selected the reaction process appropriate for synthesis of the material. Specifically, they conducted reaction kinetic investigation for the hydrothermal synthesis and molten salt synthesis methods used in this project, and we received basic but very important advices on starting material and solvent types. Moreover, they conducted basic research on low cost synthesis that was requested by the automobile manufacturer. Particularly NU investigated the practical process where synthesis could be accomplished as a one-step firing process for carbon high-capacity electrode material. The result is being utilized in battery development by the automobile manufacturer.In the collaboration of AIST and NU, to maximize each other’s research potential in extremely short period of three years, the development of nanocrystal active material of metal oxides was done by AIST, while the development of nanoporous and high-power carbon materials that are essential as conductivity aid in actual battery electrode was done by NU. By doing so, we were able to design innovative high-capacity high-power electrode through combining the two results during the course of project.(12)−

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