One distinct feature of modern life is a seemingly unlimited demand for more energy, including electrical energy, and a corresponding demand for better ways of storing it. ‘Better’ in this case often boils down to higher energy density – expressed as energy per unit mass and or volume – charge/discharge rates and cycle life. The advent of hybrid and all-electric vehicles is emblematic of this trend. The short range of electric vehicles is due to the fact that there are practical limits to how much room and weight can be allotted to the storage devices in a passenger car. Higher energy density storage equates to longer range. Also, slow charging rates limit auto utility, and the storage device must withstand multiple charge/discharge cycles to be economically viable.
Additionally, the move towards green energy production comes with a new need for grid storage solutions to better address consumer demands. Heavy investments in advancements in energy storage are primarily in two areas: batteries and capacitors. The leading technology contenders, Li-ion batteries and Electric Double Layer Capacitors (also known as super-capacitors or ultra-capacitors), can both be improved with the incorporation of CNTs. Although advances in capacitor technology are reducing the distinction, in broad terms, the difference is that batteries can hold more total energy and capacitors can charge and discharge at a high rate and survive much greater cycling. Lead-acid, along with Li-ion batteries is the key development component for energy grid storage demands. Fuel cells are another area where CNTs can provide catalyst support and increased performance.
Application developers for CNT in the energy market have been specifically focusing on batteries and supercapacitors. CNTs will enable significant performance improvements in both technologies, specifically for supercapacitor and battery electrodes, by providing structural, thermal, and electrical benefits. These benefits can be realized in incremental improvements, where CNTs are used as an additive material, or by direct replacement of a component material. The requirements for Li-ion batteries for most of the major applications including electric vehicles (EVs) are as follows:
- High energy density and power capacity
- Higher charge and discharge rates
- Longer cycle life
- Intrinsically safe
- Lower cost
More specifically, CNTs can significantly improve performance when incorporated into Li-ion battery cathodes by providing both improved electrical conductivity and ionic conductivity. The diagram provided illustrates electrodes with carbon black and MWCNT conductive fillers. It can be seen that the CNTs allow for a much more robust network that can handle the changes to the structure caused by the charge/discharge cycle.
It is proposed that replacing the current carbon powders commonly used commercially with “high aspect ratio” CNTs in cathode materials will enhance cyclability of Li-ion batteries.
Our multi-wall CNT material, (now under license to 3DNB) will enhance the performance of Li-ion batteries in several ways. These batteries typically use 6 weight % carbon black in cathodes. This could be replaced by 1% of our MWCNT material, allowing for an additional 5% of active materials for increased storage. More importantly, this modification resulted in a doubling (2x) of cycle life, a critical issue for major applications such as cell phones, and especially automobiles, for improved performance in cold conditions. The specialty MWCNT material had distinct advantages over competing CNT’s due to its long, largely defect-free structure and 98% purity value. With knowledge of this battery storage breakthrough 3D Nano Batteries (3DNB), has effectively been able to secure the exclusive and world-wide licensing rights from our strategic equity partner, CSS Nanotech Inc., (CSSN), to integrate this specialty MWCNT material into our own battery and capacitor products and/or distribute and sell this material to any third party OEM or battery manufacturer around the world through our licensing business model.
In addition, our licensing agreement also gives 3DNB the global distribution and licensing rights to utilize and sell the only commercially scalable 3 dimensional CNT material in the world today, our strategic equity partner, CSSN’s, patented 3D NanoSponge™. This “game changer” battery material does more than incrementally increase battery and capacitor storage, but will redefine industry standards for energy storage and recharge capabilities on a monumental scale. This is truly the unicorn breakthrough in battery technology that the industry has been striving for over the last 15 years of research (Reference article). 3DNB can now power us into our energy future!
With respect to capacitors, studies have also shown that CNT’s like our licensed MWCNT’s could replace the use of platinum in capacitors by 60% or more. Other university studies have proven that using braided carbon nano wire in capacitors help make a superior capacitor then capacitors using other precious metal materials on the market today. Here again, is where our new licensed and patented NanoSponge™ material comes into play, since its 3 dimensional scalable matrix makes it better than braided nano wire as far as strength and conductivity is concerned. This alone will revolutionize the capacitor market.
Some other highlights of how CNTs have improved battery performance are provided below:
- Smaller, nano-sized materials allow for shorter diffusion length of the Li-ions and it has been shown that short CNTs have a higher lithium extraction capacity than long CNTs
- Shorter CNTs have shown lower electrical resistance, allowing for better rate performance at high current densities.
- When used as an additive in Li-ion batteries, CNTs help connect the isolated graphite powder particles to form a better conductive network.
- When comparing MWCNTs to carbon black, both used as conductive additives for Liion battery electrodes, the MWCNT electrodes demonstrated: lower impedance (105 Ω versus 154 Ω), higher initial C/10 discharge capacity (~155 mA/Hg versus ~146 mA/Hg), and a higher capacity retention ratio after 50 cycles (95% versus 90%). The SEM images below show the MWCNT networks that are formed, connecting the LiFePO4 particles. This network improved the electron transfer between the active material and the current collector, as well as the electrochemical performance.
- It was also seen that the discharge capacity was higher for Li-ion battery cathodes containing CNT as an additive material.
- Using CNT as an additive in Li-ion batteries has been shown to increase the reversible capacity, enhance the rate capability, and improve cyclability. Additionally, it is expected that further advancement is possible by opening the nanotube ends and by chiral separation.
- CNT’s can increase the charge acceptance of lead acid batteries by >200%. CNT batteries have 8 times the reserve capacity of typical lead-acid batteries, which will allow cars to travel up to an estimated 380 miles per charge.
These performance attributes contribute to fundamental improvements in cell performance including boosting energy density, power and cycle life.