Vol.1 No.4 2009

9/79

Research paper : Development of high power and high capacity lithium secondary battery based on the advanced nanotechnology (I. Honma)−226 Synthesiology - English edition Vol.1 No.4 (2009) (6)−property improved by adding nanoporous property to active material size of several 10 nm in Li4Ti5O12 with high possibility for high-power negative electrode. In titania (TiO2), which is similar titanium oxide, we studied the electrode property to 6 nm size, and clarified the energy storage property characteristic of nanosize material such as high-speed charge-discharge property and pseudo-capacity from the perspective of basic chemistry. On the other hand, existing battery products used bulk (μm level) size electrode, and there was no product realization using such small active material. Therefore, there was no systematic study on active material size for optimizing the battery power property in either industry or academia. Therefore, it is necessary to continue industry-academia-government collaboration research to investigate which nanosize shall be set as goal for nanotech electrode in product realization phase, or to constantly keep in mind what is the optimal active material size for high output property.This was an important technological item for linear connection of R&D by university, AIST, and battery manufacturer. As shown in Fig. 8, there was unexplored area or “missing region” of size between the size regions explored for active materials in basic research by university and AIST and the size regions sought for the products by battery manufacturer. It was imagined that the optimal value for output property lies in this missing region. In vertical collaboration, it was important to study this size region from both basic and practical sides to quickly clarify optimal size, and to investigate the optimal solution in battery cell. In fact, region of active materials of several 10 nm to several 100 nm was not systematically surveyed until now, and R&D in the missing region was an important milestone in this vertical collaboration. In fact, as explained in the following example of Hitachi Maxell, battery prototypes were created using active materials of different sizes from 55 nm ~ 200 nm using spinel structure manganese LiMn2O4 for practical electrode, and the output characteristic was evaluated. Active material size was shifted from bulk range to nanosize range in steps, and actual exploration was done on which size would be optimal for capacity and output within the missing region for intercalation electrode. This R&D project was probably the first systematic investigation of size dependency of electrode property for optimization of active material size for product realization, rather than just synthesis and property clarification of nanosize active material.Next, in vertical collaboration, investigation of quick innovation potential of university and AIST was necessary. To investigate the potential for application to product using the excellent electrode properties of nanocrystal material that were learned from basic research, prototype creation and performance assessment of battery cells were conducted. Prototype fabrication was done by Hitachi Maxell that fabricated and evaluated standard spec laminated cell.First, I shall describe the fabrication of the prototype battery. The electrode body used in the experiment was fabricated by mixing electrode active material, conductivity aid, and PVDF dispersion fluid binder, that were each weighed to target composition, in planetary ball mill, and paint-form electrode sol was fabricated after adjusting the viscosity. This paint-form electrode sol was applied using an applicator on of 15 μm thick aluminum foil so the dried weight would be 5.0~7.0 mg/cm2 for both positive and negative electrodes, and the electrode body was finished by pressing after drying. The structure and photograph of laminated battery cell are shown in Fig. 9.Considering the result of high output property of nanocrystal electrode at AIST, prototype cell with nanosize electrodes for both negative and positive electrode was fabricated. Negative electrode was made of 100 nm Li4Ti5O12 , while positive electrode was made of LiMn2O4 nanocrystal active material of different sizes from 55 nm to 200 nm, for purpose of finding optimal active material size in the missing region.Although there were some variations in LiMn2O4 for active material size 150 nm or less, no significant decrease of discharge capacity occurred to 2 A/g rate. From active material Exploration of missing link → Exploration for optimal nanosize of active materialExploration size region of battery manufacturerExploration size region of university and AISTUnexplored regionParticle diameter of LiCoO2 active materialCapacity (mAh/kg)Output density (W/kg)Nanoporous technology, mass production technologyOptimized nanosizeBattery cell testExploration of nanocrystalline materialsElectrode size that can be commercializedCollaborative R&DUnexplored electrode size1001101006080100120140160110101102105104103106nmµmFig. 8 Exploring active material size in the missing region to optimize the electrode property.SpringPositive electrodeSeparatorNegative electrodeFig. 9 Structure and photograph of laminated battery cell prototype.

※このページを正しく表示するにはFlashPlayer9以上が必要です