Advantages, Disadvantages and Future Applications of Supercapacitors

    Now, when it comes to electric vehicle powertrain design, "battery" is no longer the only word that comes to our mind. With the development of energy storage technology, the birth of "supercapacitor" has opened a new chapter for electric/hybrid vehicles. Supercapacitor is the third generation of energy storage after mechanical energy storage and chemical energy storage - physical energy storage.

    The biggest advantage of supercapacitors is that they can be charged and discharged quickly, and their power density is much higher than that of nickel-hydrogen batteries. Thanks to this, supercapacitors can not only store and supply energy, but also increase the power of electric vehicles in a short time.

    Cosmin Laslau, an analyst at Lux Research, a high-tech research company, said that supercapacitors not only have ultra-high charging and discharging efficiency, but also have a positive effect on the brake energy regeneration system and the start-stop system. Some European and Japanese automakers use supercapacitors in their micro-hybrid cars because these models are mainly designed for urban road conditions that often require starting and stopping, and supercapacitors can better recover energy. At this year's Frankfurt Motor Show, Toyota Yaris Hybrid-R used supercapacitors.

    Lux Research says global consumer electronics revenues, which include components such as superconductors and turbine blade controllers, are now about $366 million. The company expects that figure to grow 18% annually. By 2018, supercapacitors will be widely used in heavy commercial vehicles, with revenues of $323 million, while passenger cars will be designed with supercapacitors to generate $152 million.

    The company recently released a research report titled "Growth Trends of Supercapacitors in Transportation and Electronics."

    Traditional batteries generate electricity through slow chemical reactions, while supercapacitors generate electricity by moving electrons at high speed on the surface of electrodes, which means that supercapacitors can generate electricity more efficiently. Each supercapacitor contains a pair of metal plates with activated carbon on them.

    Activated carbon has a porous structure, so its surface area is very large, and it can firmly "lock" the charge whether by chemical or physical means.

    The electrode pairs are immersed in an organic electrolyte that accelerates the charge flow. When the supercapacitor is fully charged, each carbon electrode has two layers of charge carrier coating the surface. This is one of the reasons why supercapacitors are called double-layer capacitors.

Supercapacitors in cars

    Honda pioneered the use of ultracapacitors in automobiles. The 2002 FCX fuel cell test vehicle was equipped with an ultracapacitor that Honda called an "ultracapacitor."

    However, it was not until a few years ago that Peugeot Citroen signed a contract with Maxwell Technologies to purchase a batch of supercapacitors for its Peugeot and Citroen micro-hybrid vehicles for use in e-HDI systems that supercapacitors officially entered the mass production application stage. Similarly, Mazda uses similar capacitor technology in its i-ELOOP system, allowing the battery to achieve the function of braking energy recovery while ensuring the start-stop function.

    Supporters of supercapacitor technology say that supercapacitors are more suitable for long-term operation than traditional batteries because they are more stable. However, in general micro-hybrid vehicles, car companies still prefer traditional batteries because supercapacitors will be accompanied by a series of other components, including DC-AC converters, generators, etc. These components will increase the cost of the car, and in addition, the weight of the car body will also increase.

    Automakers are mainly considering using supercapacitors in hybrid vehicles, or as a component that can increase peak power. Lux analyst Laslau said: "Several OEM engineers have shown interest in the application of supercapacitors, such as using 30-50 supercapacitors to form a capacitor bank in a hybrid vehicle. This will achieve energy savings of about 7%."

    Prinz团队的研究重点是解决现有燃料电池在燃烧过程中一系列问题，氧离子在高温下的移动速度远高于低温，这就意味着如果想获得高的工作效能，则必须让燃料电池保持在高温环境，原有的技术所要求的工作温度往往高于500摄氏度，但这样的高温足以融化电池中经常使用的锌材料。像熔炉或由电池功能的加热器可以用来为燃料电池提供反应初始热量，以加快氧离子穿越薄膜的速度；一旦氧气和燃料开始发生反应，所产生的热量能够反过来为薄膜加热，让它始终保持在合适的工作温度。当降低燃料电池工作温度的时候，氧化还原反应产生能量中用于加热薄膜的热量供应将会明显的降低，但同时氧离子流动速度也会显著减缓，这种情况下工程师们开始研发适用燃料电池结构的更多材料，希望新型材料既要有高的性价比，还要有过硬的质量保证。

    Lower operating temperatures mean slower reaction rates and lower oxygen ion transfer rates. The original approach was to make a trade-off between speed and temperature, but Prinz's team hopes that in a lower temperature working environment, the fuel cell they developed will neither slow down the movement of oxygen ions nor reduce the efficiency of the system. The core work they carried out was to redesign the structure of the solid oxide film so that it has better oxygen ion transfer efficiency at low temperatures. Oxygen is the bottleneck restricting the development of fuel cells, which is why Prinz's team focused most of their efforts and innovative research on the oxygen side of the film.

    Traditional solid oxide fuel cell membranes are flat structures. Flat membranes are easy to process and produce, but they fail to make the best use of space, so Prinz's team has made a series of improvements to this membrane. First, the membrane they designed and manufactured is bumpy and uneven, thereby increasing the surface area that can be used to transfer oxygen ions; secondly, a micro-particle protrusion structure is designed on the wrinkled surface, which looks similar to sandpaper, further increasing the potential contact points between solid oxide and oxygen; then the thickness of the membrane has also been significantly reduced, making it easier and more convenient for oxygen ions to move to the fuel side. This innovative membrane is only 60 nanometers thick, about two hundredths the thickness of cellophane.

    Prinz's team also mentioned an innovative technology to improve the efficiency of fuel cells, that is, they sprayed a new catalyst on the membrane, but the specific material has not yet been announced. Finally, the engineers also used a nano-scale particle protrusion structure for the catalyst layer, which has the same effect as the sandpaper-like membrane surface structure: oxygen ions have more opportunities to be absorbed to participate in the subsequent redox reaction.

    Prinz believes that their new technology will effectively advance the research and development of solid oxidant fuel cells in low-temperature environments. The low-temperature and high-efficiency characteristics will lay a solid foundation for future promotion to the commercial power supply field.