Available online at www.sciencedirect.com ScienceDirect Materials Today: Proceedings 4 (2017) 12333–12342 www.materialstoday.com/proceedings EMRSH_2017 Recent progress of thermoelectric devices or modules in Japan Yoshikazu Shinohara* *National Institute for Materials Science, Tsukuba 305-0047, Japan Abstract The Japanese government has promoted the thermoelectric research and development as one possible technology for raising the energy usage efficiency since 1978. The 1st application of thermoelectric power generation in Japan was a candle radio using β-FeSi2 modules, which was commercialized in 1990. Development of thermoelectric devices or modules was reactivated in 2002, when the 5-year NEDO project titled by “Development of thermoelectric energy conversion system with high efficiency” started. The Bi-Te devices with high energy conversion efficiency of 7.2% under a temperature gradient of 303-553K was reported. Ministry of Economy, Trade and Industry (MITI) of Japan has launched the 10-year project of "Development on the innovative utilization technologies of unused heat energy" since 2013. The administrator of this project has been changed from MITI to NEDO since 2015. Prototype devices of Mg-Si, skutterudite and organic polymers have been developed for power generation. In this paper, the recent progress of thermoelectric devices or modules in Japan is reviewed. © 2017 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or Peer-review under responsibility of EMRS Spring Meeting, symposium H. Keywords: thermoelectric device; thermoelectric module; * Corresponding author. Tel.: 81-29859-2649; fax: +81-29859-2601 E-mail address: [email protected] 2214-7853 © 2017 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or Peer-review under responsibility of EMRS Spring Meeting, symposium H. 12334 Yoshikazu Shinohara / Materials Today: Proceedings 4 (2017) 12333–12342 1. Introduction Japan started thermoelectric research and development in 1960’s [1]. The government has promoted these activities as one possible technology to raise the energy usage efficiency since 1978 [2]. The 1st national project from 1978 to 1993 was called as Moon Light Project. st The 1 general application of thermoelectric power generation in Japan was a candle radio using β-FeSi2 devices that was commercialized by YOUTES Co. in 1990 [3]. The 2nd one was a thermoelectric wrist watch using Bi-Te modules by CITIZEN WATCH Co., Ltd. in 1999 [4]. Development of thermoelectric devices or modules had been activated since 2002, when the 5-year NEDO project titled by “Development of thermoelectric energy conversion system with high efficiency” started [5]. The so much activities on devices or modules, however, has not been reported in the scientific journals or on the English website, since Japanese private companies paid almost no attention to the foreign markets of power generation. Ministry of Economy, Trade and Industry (MITI) of Japan started the 10-year project of "Development on the innovative utilization technologies of unused heat energy" in 2013 [6]. The main target is automobile applications, and the research association consists of Furukawa Co., Ltd., Hitachi, Ltd. Fijifilm Co., Furukawa Electric Co., Ltd., Nippon Thermostat Co., Ltd. and National Institute of Advanced Industrial Science and Technology (AIST). The administrator of this project has been changed from MITI to New Energy and Industrial Technology Development Organization (NEDO) since 2015. Figure 1 shows the history of typical applications of thermoelectric power generation. The spacecrafts such as the Voyger and the Pionner are the 1st touch of power generation, followed by the power generator for gas pipe line monitoring [7-8]. Only the prototypes were manufactured for a codeless fun heater in 1988 and a liquid crystal projector in 2006, which were not in the market. The 3rd application in Japan is a thermoelectric pot using Bi-Te and oxide modules that was commercialized by TES New Energy Co. The most recent product is a cassette fan heater with Bi-Te modules by Iwatani Co.,[9]. There are many kinds of thermoelectric devices or modules developed by Japanese companies; β-FeSi2, Bi-Te, skutterudite, Heusler, half-Heusler, oxide, organic polymer, and so on. In this article, the recent progress of thermoelectric devices or modules in Japan is reviewed. Fig.1 Typical thermoelectric power applications. Red circled ones are Japanese applications. Yoshikazu Shinohara / Materials Today: Proceedings 4 (2017) 12333–12342 12335 2. Showcase of Japanese device or modules In this chapter, typical Japanese thermoelectric devices or modules are shown in chronological order. 2.1. In 1990 A candle radio was manufactured and commercialized by YOUTES Co. in 1990 [3]. A U-shape β-FeSi2 module was applied to the product. The top of the module is a joint of p-type Mn-doped β-FeSi2 and n-type Co-doped one. This type of module was developed by National Institute for Materials Science. The advantages of β-FeSi2 are 1) the common constituent elements that are abundant on earth, 2) high oxidation resistance, and 3) low price. The modules were fabricated by sintering techniques. The generated power by 5 pairs is 30mW directly heated by a candle flame, which is enough to work a radio. 2.2. In 1999 A thermoelectric wrist watch was developed and commercialized by CITIZEN WATCH Co., Ltd. in 1999 [4]. A small size of Bi-Te module shown in Fig.2 was applied as a body-temperature power generator. The number of p-n pairs is 1242 in the 7.5x7.5mm size module. The leg size of pairs is 0.09x0.11mm. The module was fabricated by the sintering and semiconductor processing techniques. The generated power s 14μW at ΔT=1K. This power is enough to μ work a watch movement, since the required power is 1 W. Fig.2 Small Bi-Te module installed in the wrist watch by CITIZEN WATCH 2.3. In 2004 Co., Ltd. A high power density module named by Giga Topaz was developed and commercialized by Toshiba Co. in 2004 [10]. The material is half-heusler (Ti, Zr, Hf) Ni (Sn,Sb). The power density was 1W/cm2 at ΔT=480K (773K-293K) in 2004. The material was modified to reach 4.1W/cm2 at ΔT=644K (984K-339K) in 2012. The maximum ZT was over 1.5 at 673K. This module is a top runner of power density in Japan. 2.4. In 2006 An excellent Bi-Te module was developed as a power source of a liquid crystal projector, and commercialized by Yamaha Co. in 2006 [11]. The module dimensions are from 8mm to 14mm, and the ZT is ~1.2 at 300K. Rapid cooling technology was applied to preparation of the Bi-Te powders for sintering. The power density is 0.5W/cm2 at ΔT=100K (398K-298K). This module presents a high power density at ΔT=100K (398K-298K). The NEDO’s 5- year project from 2002 to 2007 contributed to development of this module. This company has been developing the sensing system of body information using this module as an energy harvester. The temperature sensing system for a human body and the temperature and humidity sensing system for factories were developed in 2013. 2.5. In 2009 A reliable common Bi-Te module for power generation was developed and commercialized by KELK Ltd. in 2009 [12]. This company is a leading company of the sintered Bi-Te modules in Japan. The dimensions are 50x50x4.2mm, and the weight is 47g. The maximum output power is 24W at ΔT=250K (553K-303K). The power density is 1W/cm2 and the efficiency is 7.2% at the maximum output power. This module is regarded as a benchmark in Japan regarding thermoelectric performance and reliability. This company has tested the power generation system of 10kW class at the iron continuous casting process in corporation with JFE Steel Co. A new NEDO project on demonstration of that system by KELK Ltd. and JFE Steel Co. started in 2017[13]. 12336 Yoshikazu Shinohara / Materials Today: Proceedings 4 (2017) 12333–12342 2.6. In 2011 A practical multilayer module shown in Fig. 3 was developed by Murata manufacturing Co. Ltd. in 2011 [14]. The p-type material is Ni doped with Mo, and the n-type one is SrTiO3 substituted by La. The grey layer in Fig.3 is p-type, and the black one is n-type. The manufacturing process is as follows; 1) Thin thermoelectric green sheets were fabricated by doctor blade method for p-type (0.03mm) and n-type (0.12mm). 2) The insulating layer 6μm thick of partially stabilized ZrO2 was formed on the green sheets by screen printing method. 3) The green sheets with the insulating layers were stacked layer by layer, and then sintered at 1573K in the air. This module consists of 50 pairs of the p-n junctions. The power Fig.3 Multilayer module by Murata μ 2 Δ density is 100 W/cm at T=10K (303K-293K). This company has manufacturing Co. Ltd. been developing the sensing system for factories and plants by applying this module. A prototype of the integrated wireless sensor node was developed in 2015. A new concept of Bi-Te tubular module shown in Fig.4 was developed by Panasonic Co. in 2011 [15]. This is a one-leg module composed of Bi-Sb-Te and Ni. Ni is an electrode material. This module is made of a laminate structure of Bi0.5Sb1.5Te3/Ni. Power generation is achieved from the temperature difference between the outer and inner surfaces of the module by the transverse thermoelectric effect.