New energy storage device could recharge electric vehicles in minutes
August 19, 2011 by Lisa Zyga
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(PhysOrg.com) -- It has all the appearances of a breakthrough in battery technology, except that it’s not a battery. Researchers at Nanotek Instruments, Inc., and its subsidiary Angstron Materials, Inc., in Dayton, Ohio, have developed a new paradigm for designing energy storage devices that is based on rapidly shuttling large numbers of lithium ions between electrodes with massive graphene surfaces. The energy storage device could prove extremely useful for electric vehicles, where it could reduce the recharge time from hours to less than a minute. Other applications could include renewable energy storage (for example, storing solar and wind energy) and smart grids.
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The researchers call the new devices "graphene surface-enabled lithium ion-exchanging cells," or more simply, "surface-mediated cells" (SMCs). Although the devices currently use unoptimized materials and configurations, they can already outperform Li-ion batteries and supercapacitors. The new devices can deliver a power density of 100 kW/kgcell, which is 100 times higher than that of commercial Li-ion batteries and 10 times higher than that of supercapacitors. The higher the power density, the faster the rate of energy transfer (resulting in a faster recharge time). In addition, the new cells can store an energy density of 160 Wh/kgcell, which is comparable to commercial Li-ion batteries and 30 times higher than that of conventional supercapacitors. The greater the energy density, the more energy the device can store for the same volume (resulting in a longer driving range for electric vehicles).
“Given the same device weight, the current SMC and Li-ion battery can provide an electric vehicle (EV) with a comparable driving range,” Bor Z. Jang, co-founder of Nanotek Instruments and Angstron Materials, told PhysOrg.com. “Our SMCs, just like the current Li-ion batteries, can be further improved in terms of energy density [and therefore range]. However, in principle, the SMC can be recharged in minutes (possibly less than one minute), as opposed to hours for Li-ion batteries used in current EVs.”
Jang and his coauthors at Nanotek Instruments and Angstron Materials have published the study on the next-generation energy storage devices in a recent issue of Nano Letters. Both companies specialize in nanomaterial commercialization, with Angstron being the world’s largest producer of nano graphene platelets (NGPs).
As the researchers explain in their study, batteries and supercapacitors each have their respective strengths and weaknesses when it comes to energy storage. While Li-ion batteries provide a much higher energy density (120-150 Wh/kgcell) than supercapacitors (5 Wh/kgcell), the batteries deliver a much lower power density (1 kW/kgcell compared to 10 kW/kgcell). Many research groups have made efforts to increase the power density of Li-ion batteries and increase the energy density of supercapacitors, but both areas still have significant challenges. By providing a fundamentally new framework for energy storage devices, the SMCs could enable researchers to bypass these challenges.
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“The development of this new class of energy storage devices bridges the performance gap between a Li-ion battery and a supercapacitor,” Jang said. “More significantly, this fundamentally new framework for constructing energy storage devices could enable researchers to achieve both the high energy density and high power density without having to sacrifice one to achieve the other.”
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