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)−222 Synthesiology - English edition Vol.1 No.4 (2009) of lithium battery technology is moving from small to large devices, and higher power, higher capacity, and lower cost are important issues assuming application as power source for automobiles. As shown in Fig. 1, the frontline of battery technology application is shifting from lower right to upper left. The middle- and large-size, highly reliable lithium battery is expected to become central energy technology for robots, HEVs, and recyclable energy in the future. To accomplish this, it is necessary to develop high-power cell of several kW/kg level as mentioned above, and innovative technological development using nanotechnology is drawing great expectation and investments.In fact, assuming use as auxiliary power for clean vehicles represented by hybrid and fuel cell cars that are key technologies to counter global warming, power source with both sufficient energy and output densities is necessary. Figure 2 is a Ragone plot of target performance values of auxiliary power source for HEV of Japanese automobile manufacturers and U.S. Department of Energy (DOE). When targeting energy regeneration for general-use automobile, about 30 Wh/kg energy density and 3 kW/kg output density are required for battery cell, and such performance is intermediate level for lithium secondary battery and electric double-layer capacitor (EDLC). This performance (30 Wh/kg, 3 kW/kg) is equivalent to charge-discharge rate of 100 times per hour (completely charged in only 36 sec), and it is impossible to construct a storage device with such energy and output densities using bulk size intercalation electrode materials currently available. If ion intercalation mechanism was used for secondary battery active material, charge-transfer rate must be improved 100 times. That is, if storage mechanism that is midway between secondary battery and EDLC is used to obtain both energy and output densities, dramatic acceleration of ion dispersal within electrode and electronic conductivity must be achieved simultaneously.This paper is a report of the result of the industry-academia-government vertical collaboration project where the goal was development of nanoporous electrode composed of nanospace and nanocrystal active material, to create power source that enables high-speed input/output of electric energy, and to create high-power battery that can charge and discharge 100 times faster compared to ordinary lithium secondary battery. Particularly, I shall explain the original concept of the National Institute of Advanced Industrial Science and Technology (AIST) that conducted application of nanocrystal electrode material to high-power battery, and describe how nanotechnology can greatly contribute to the innovation of electric power storage. In the vertical collaboration R&D, automobile manufacturer who was end user participated from the planning stage of the project. For electrode material development that enabled high-output power source performance (strategic goal value in Fig. 2 about 3 kW/kg) required for plug-in HEV, we had the automaker indicate the direction of basic research at university and AIST, to maintain sufficient market competitiveness in terms of safety and low cost. To demonstrate the efficacy of vertical collaboration R&D that lead to product realization in shortest distance without major changes in specification due to result of core technology development, we conducted industry-academia-government collaboration product by four organizations with support from New Energy and Industrial Technology Development Organization (NEDO).First, I shall explain the physicochemical basis of how high-power battery that is an innovation of storage technology using nanotechnology can be realized. The storage mechanism originates from electrochemical reaction accompanied by charge transfer by ion diffusion and electronic conduction. Here, diffusion length L in certain time can be expressed by the following equation, when diffusion coefficient of lithium ion in solid is DLi and diffusion time is . L =(DLi )1/2 (1)If the diffusion coefficient of lithium ion in active material is estimated to be about 10-13 cm2/s, time required for ion (2)−Fig. 1 Industrial products realized by innovations in battery technology.Nanocrystalline active materialsLithium ion batteryNickel hydride & nickel cadmiumElectric double-layer capacitor (EDLC)Energy density (Wh/kg)power density (W/kg)For HEVFor robotsFor power toolsFor powered bicycleLaptop PCLIB of industrial useHigh-power secondary battery02040601208014016018020022024010050010001500,2000250030003500400045000LeadTechnological limit of the electrical energy storageStrategic target CondenserLead acid batteryElectrical double layer capacitorLithium secondary battery30 Wh/kg,3kW/kgRagone plot of various battery performance10-210-1103102101100103102101106105104Energy density (Wh/kg)Output density (W/kg)Fig. 2 Frontier in battery performance.

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