Vol.1 No.4 2009

10/79

Research paper : Development of high power and high capacity lithium secondary battery based on the advanced nanotechnology (I. Honma)−227 Synthesiology - English edition Vol.1 No.4 (2009) size dependency of capacity retention, the property increased under high-speed charge-discharge condition of 5 A/g or over when the particle size decreased, and active material with 55 nm size showed best output property (Figure 10). According to AIST’s calculation based on diffusion theory, for particle diameter of 100 nm or less, lithium ion diffusion within the particle would be sufficient for 100 charge-discharge per hour. Looking at the actual prototype cell data, when electrode using active material size of 150 nm or less was used, charge-discharge was possible even at high current density, and it was found that output property improved as active material size decreased. As result of optimizing the active material size in the missing region, best output property was obtain in battery cell using negative electrode (100 nm) of nanocrystal active material Li4Ti5O12 with spinel structure and positive electrode (55 nm) of LiMn2O4. Its high output property was demonstrated at battery cell level using the innovative energy storage mechanism of nanocrystal electrodes. Finding the optimal size for nanocrystal active material to be used in high output battery was the most important issue since the commencement of the project. While the development of high-power battery using nanosize active material is becoming fierce around the world, to find out were the optimal solution lies in the 1 nm ~ 100 nm size range will solidify the foundation of innovation in storage technology.In this R&D, AIST clarified by experiment that nanosize active material was effective for realizing high-capacity and high-power properties through its characteristic lithium storage mechanism. Moreover, by engaging in systematic exploration of missing region through vertical collaborative development for quick practical application, and by evaluating the output and cycle properties of the prototype battery, it was clarified by experiment that optimal solution was active material of size around 50 nm. Currently, while R&D of high-power lithium secondary battery using nanosize active material is accelerating around the world, this was the first R&D that specifically pursued which active material size was optimal for battery products. In the vertical collaboration project lead by the Author, optimal active 050100123Capacity (mAh/g)Voltage (E/V)LiMn2O4 55nm0.1/Ag1.0/Ag5.0/Ag0.2/Ag2.0/Ag050100123Capacity(mAh/g)Voltage (E/V)LiMn2O4 150nm0.1/Ag1.0/Ag5.0/Ag0.2/Ag2.0/AgFig. 10 Output property of lithium battery using nanocrystal electrode.55 nm LiMn2O4 vs 100 nm Li4Ti5O121 A/g (2.4 mA/cm2)Number of cyclesCapacity (mAh/g)020004000600080001000050100150Project goal value3 KW, 30 Wh/KgLithium secondary batteryElectric double-layer capacitorCondenserEnergy density (Wh/Kg)Output density(W/Kg)10610110210310410510110210310-110010-2Commercial Li ion batteryFig. 11 Ragone plot of battery performance of prototype and charge-discharge cycle property (higher performances compared to existing batteries were observed for both items).(7)−

※このページを正しく表示するにはFlashPlayer9以上が必要です