Stop-start problems could lead to rise of ultracapacitors

The proliferation of start-stop systems in today's cars and trucks is pretty simple to explain. With these systems, manufacturers have an easy, mostly unobtrusive way of boosting a vehicle's fuel economy. As with just about anything though, there are drawbacks to modern start-stop tech.

In particular, they're not great when paired with today's lead-acid batteries. These batteries limit the ability of the start-stop function to operate based on factors like charge level and temperature. If the battery is outside the parameters, the stop-start system won't function, curbing any potential fuel economy gains. Obviously, this problem will only become more noticeable as the battery ages.

Ultracapacitors could solve this problem, though, according to a new report from Ward's Auto. Becauseultracapacitors can be cycled rapidly and they can store quite a lot of energy – they don't function via chemical reactions, like standard batteries – they could handle the stop-start duties when the battery isn't up to snuff.

There are other applications for the high-powered capacitors too, including regenerative braking functions, where their ability to harness energy can really be taken advantage of. Ward's has a great breakdown of the pros and cons in a fairly extensive feature on the future of this potentially big automotive technology.

News Source: Ward's Auto

Image Credit: AndyArmstrong/Flickr - CC 2.0

New Toyota Supra and BMW Z4 Could Get AWD, Supercapacitors

The next Toyota Supra and BMW Z4 could use the same hybrid drivetrain in the Yaris Hybrid-R, paired with supercapacitors and all-wheel drive. But whether it will be a six-figure supercar or something a little more attainable hasn’t been settled just yet.

Rumors have been circulating for years that Toyota and BMW are teaming up on a hybrid sports car, and with the reveal of the Toyota FT-1 Concept, the return of the Supra as a performance hybrid seems all but certain. The blurry details are starting to come into focus, and the picture they paint a very different vehicle from the classic Supra or Z4.

The new car will utilize an all-wheel drive system paired with a plug-in hybrid drivetrain similar to the one the Yaris Hybrid-R Concept, but with one key difference. Instead of a 1.6 liter Toyota gas engine, a BMW motor no bigger than 2.0 liters will be used alongside a pair of electric motors. Engineers are drawing from knowledge gained from the Toyota TS030, the hybrid Le Mans endurance racer that has been nipping at Audi’s heels for the past couple of years.

This is where the supercapacitors come in. Unlike lihtium-ion batteries, which more energy but also a lot longer longer to recharge and discharge, supercapacitors store a little bit of kinetic energy for a big (but brief) boost in power. They recharge with kinetic energy (mostly from braking) just as quickly as they discharge, making supercapacitors a better option than standard lithium-ion batteries. High-strength steel and aluminum will be used to keep weight down, further improving performance. With no hard numbers to pin down right now though, it’s hard to tell where in the supercar hierarchy the next Supra/Z4 will fall.

So where does this leave the in-demand BMW i8? Hard to say; the current BMW Z4 and BMW i8 are distinctly different vehicles, and the ‘i’ brand is being touted as somewhat separate (but not TOO separate) from the regular BMW lineup. While Toyota’s lineup is noticeably devoid of any high-end performance cars, is there room in the BMW lineup for another hybrid supercar?

I don’t see why not.

Source: AutoCar

Study: Most Efficient Car Is A Supercapacitor Hydrogen Hybrid

Automakers are going every which way trying to figure out what the future of the automobile is, embracing everything from pure electrics to hydrogen fuel cells, turbocharged gas engines and super-efficient diesels. A recent study suggests that the most efficient car is something nobody has yet considered; a hydrogen fuel cell hybrid using supercapacitors instead of batteries.

While supercapacitors are being using in some public transit projects, as well as by Mazda’s new i-Eloop system, I can’t recall a project combining them with a hydrogen fuel cell hybrid. Despite the extra weight of such a system, researchers claim that a hybrid using hydrogen and supercapacitors would provide the cleanest, most-efficient mode of transportation.

The study points out the shortcomings of current fuel cell systems, which lack adequate power and response under load. A supercapacitor system would allow for rapid delivery of extra power when the fuel system needed it, and could be quickly recharged as well. Whether or not this paper influences any major automaker’s decisions remains to be seen, but it sounds like a pretty good idea to us.

Source: Green Car Congress

South Korean engineers find graphene electrodes can recharge in 16 seconds

Yes, one day, you too may be able to fully recharge your plug-in vehicle's battery in the amount of time it takes to decelerate down one of those runaway truck ramps. Assuming your brakes actually work, of course.

Engineers at South Korea's Gwangju Institute of Science and Technology are researching the concept ofgraphene supercapacitors and how they can be applied to plug-in vehicle technology, Technology Reviewsays. A simplified explanation is that the engineers have created an extremely porous version of graphene, turned it into a powder (which makes its surface area larger) and packed the powder into a cell.

The fun part is that the new graphene electrode was tested to provide almost as much charge as a fully recharged lithium-ion battery, with the amazing benefit of only needing about 16 seconds to recharge, raising interesting possibilities for applying the technology to a regenerative braking system. And the electrode was tested 10,000 times and didn't suffer capacity reduction. Cornell University published a version of the studyhere.

The idea of using graphene, a crystalline form of carbon, for automotive technology, is continuously being researched. Earlier this year, researchers from South Korea, Case Western University and University of North Texas said they discovered that a graphene-coated cathode may generate a greater battery current than a cathode covered with the more expensive but more traditional platinum. And in 2011, University of Technology Sydney researchers created a type of graphene "paper" that is stronger, lighter and less dense than steel. Such widespread use would enable automakers to cut vehicle weight and boost fuel efficiency as a result.

News Source: Technology Review

Image Credit: Flickr

Monash University team develops graphene-based supercapacitor with energy density of 60 Wh/L

A research team at Monash University (Australia) led by Professor Dan Li of the Department of Materials Engineering has developed a new strategy to engineer graphene-based supercapacitors (SC), resulting in an energy density of 60 Wh/liter—comparable to lead-acid batteries and around 12 times higher than commercially available SCs.

The approach could make SCs more viable for widespread use in renewable energy storage, portable electronics and electric vehicles. A paper on the work is published in Science.

SCs are generally made of highly porous carbon impregnated with a liquid electrolyte to transport the electrical charge. Known for their almost indefinite lifespan and the ability to re-charge in seconds, the drawback of existing SCs is their low energy density. With a low energy density of 5-8 Wh/liter, SCs are unfeasibly large or must be re-charged frequently.

It has long been a challenge to make SCs smaller, lighter and compact to meet the increasingly demanding needs of many commercial uses.

—Professor Li

Graphene, which is formed when graphite is broken down into layers one atom thick, is very strong, chemically stable and an excellent conductor of electricity.

To make the compact electrode, Professor Li’s team exploited an adaptive graphene gel film they had developed previously. They used liquid electrolytes—generally the conductor in traditional SCs—to control the spacing between graphene sheets on the sub-nanometer scale. In this way the liquid electrolyte played a dual role: maintaining the minute space between the graphene sheets and conducting electricity. Unlike in traditional hard porous carbon, where space is wasted with unnecessarily large pores, density is maximized without compromising porosity.

Porous yet densely packed carbon electrodes with high ion-accessible surface area and low ion transport resistance are crucial to the realization of high-density electrochemical capacitive energy storage but have proved to be very challenging to produce. Taking advantage of chemically converted graphene’s intrinsic micro-corrugated two-dimensional configuration and self-assembly behavior, we show that such materials can be readily formed by capillary compression of adaptive graphene gel films in the presence of a nonvolatile liquid electrolyte. This simple soft approach enables sub-nanometer scale integration of graphene sheets with electrolytes to form highly compact carbon electrodes with a continuous ion transport network. Electrochemical capacitors based on the resulting films can obtain volumetric energy densities approaching 60 watt-hours per liter.

—Yang et al.

To create their material, the research team used a method similar to that used in traditional paper making, meaning the process could be easily and cost-effectively scaled up for industrial use.

We have created a macroscopic graphene material that is a step beyond what has been achieved previously. It is almost at the stage of moving from the lab to commercial development.

—Professor Li

The work was supported by the Australian Research Council.

Resources

• Xiaowei Yang, Chi Cheng, Yufei Wang, Ling Qiu, and Dan Li (2013) Liquid-Mediated Dense Integration of Graphene Materials for Compact Capacitive Energy Storage. Science 341 (6145), 534-537 doi: 10.1126/science.1239089
  
  
  
  
  Source: Green Car Congress

Georgia Tech team develops high-capacity supercapacitor using cobalt oxide nanonets; design approach suited for other supercap and battery application

Specific capacitances of CFP-supported Co3O4 nanonet (mass loading of 0.4, 0.7, and 1.4 mg/cm2) and nanocube electrodes (a mass loading of 0.7 mg/cm2) at different current densities. Credit: ACSA, Yang et al. Click to enlarge.

A team at Georgia Tech has developed a high-capacity supercapacitor based on a hierarchical network architecture consisting of a cobalt oxide (Co₃O₄) nanowire network (nanonet) coated on a carbon fiber paper (CFP). With this tailored architecture, the electrode shows ideal capacitive behavior and large specific capacitance (1124 F/g) at high charge/discharge rate (25.34 A/g), still retaining 94% of the capacitance at a much lower rate of 0.25 A/g.

In a paper published in the ACS journal Nano Letters, the team attributed the much-improved capacity, rate capability, and cycling stability to the unique hierarchical network structures, which improves electron/ion transport, enhances the kinetics of redox reactions, and facilitates facile stress relaxation during cycling.

It has been well established that electrodes with proper nanostructures may enhance not only power density (or rate capability) but also cycling stability. While a wide variety of nanostructures have been created and tested, it still represents a grand challenge to identify the most promising structure or architecture that dramatically enhance the capacity while maintaining the excellent rate capability and charge−discharge cycling life. For example, cobalt oxides with a broad range of morphologies were successfully fabricated, including three-dimensional (3D) oval-shaped microparticles, 2D nanosheets, and 1D needlelike nanorods. It was demonstrated that these porous Co3O4 structures exhibit enhanced initial specific capacity (∼111 F/g), yet the rate capability and capacitance retention are still unsatisfactory.

Nanonet, a random network of nanotubes, nanowires, or nanofibers, has been recently proposed as an advantageous architecture for transparent electrodes in optoelectronic devices due primarily to high transparency, better network conductance and fault tolerance. Considering the similar requisite characteristics of electrodes in optoelectronic devices and in supercapacitors, we introduced oxide thin films with nanonet structures into supercapacitors in order to effectively enhance the specific capacitance and charge−discharge kinetics because the improved electron and ion percolation may enhance ionic and electronic transport through the electrode system.

...In this report, we present our findings on fabrication of a cobalt oxide nanonet thin film supported on a conductive carbon fiber network paper and demonstrate that such hierarchical nano/micro network architectures dramatically enhanced redox kinetics at high charge/discharge rates while maintaining electrochemical and structural stability.

—Yang et al.

They deposited Co₃O₄ with various morphologies directly onto CFP using a hydrothermal synthesis route; this deposition technique produced thin, uniform coatings of Co₃O₄ on CFP, thereby retaining the network structure of the CFP. The researchers found that the directly grown thin films can ensure good mechanical adhesion and electrical connection to the carbon fiber paper, avoiding the use of polymer binders and conducting additives (carbon or metal).

The Co₃O₄ nanonet, similar to the carbon fiber network, creates an electron and ion percolation path with high fault tolerance as well as numerous suitable pores for efficient ion access; these, the authors found, are more advantageous than the properties of Co₃O₄ nanocube coatings.

To test the CFP-supported Co₃O₄ nanonet and nanocube electrodes for electrical energy storage, they performed cyclic voltammetry measurements at different potential scan rates. They also characterized the charge−discharge behaviors of the cobalt oxide nanonet and nanocube electrodes under galvanostatic conditions.

The nanonet electrode yielded substantially higher specific capacitances than nanocube electrode. At a mass loading of 0.4 mg/cm², the specific capacitance for the nanonet electrode was 1190 F/g at 0.25 A/g, which was more than twice that of the nanocube electrode (540 F/g at 0.28 A/g) and much higher than the values reported in the literatures. Also, the capacitance of the nanocube electrode dropped to 255 F/g when the current density was increased to 14.07A/g.

However, the specific capacitance of the nanonet electrode was not kinetically limited and remained relatively constant at very high current densities, for example, reaching 1124 F/g at 25.34 A/g, which was ∼94.4% of the value at 0.25A/g. The excellent rate capability is superior to those of Co₃O₄ electrodes ever reported, even better than that of the Co₃O₄−Ag hybrid electrode...The results suggest that this hierarchical architecture is flexible in areal capacity and is ideally suited for fast and efficient energy storage.

...With this tailored architecture, the electrode shows high specific capacitance while maintaining an ideal capacitive behavior: high rate capability and excellent cycling stability, making it one of the best electrode systems for high-performance, lightweight supercapacitors. Further, the electrode design concept can be readily applied to other electrode materials (e.g., MnO₂ and V₂O₅) for supercapacitor and battery applications.

—Yang et al.

Source: Green Car Congress

Graphene-based supercapacitor offers energy density comparable to NiMH battery, but with rapid charge and discharge

Ragone plot of graphene supercapacitor. Credit: ACS, Liu et al. Click to enlarge.

Researchers from Nanotek Instruments and Angstron Materials have developed a graphene-based supercapacitor that exhibits a specific energy density of 85.6 Wh/kg at room temperature and 136 Wh/kg at 80 °C (all based on the total electrode weight), measured at a current density of 1 A/g. These values are comparable to those of NiMH batteries, the researchers note, but the new supercapacitor offers the ability to be charged or discharged within seconds or minutes. A paper on their work was published online in the ACS journal Nano Letters.

These are the highest energy density values ever reported with carbon electrodes without the pseudocapacitance contributions from a conducting polymer or metal oxide, the authors said, further stating that “We believe that this is truly a breakthrough in energy technology.”

The group, led by Bor Jang of Nanotek Instruments, reported in 2006 that graphene can be used as a supercapacitor electrode material. Despite a number of efforts to improve the specific capacitance of graphene-based electrodes, however, results fell sort of the theoretical capacitance of 550 F/g due to the high tendency for graphene sheets to re-stack together.

The team determined that the best strategy to achieve a high capacitance in such graphene-based electrodes is to use curved graphene sheets rather than flat sheets to prevent the sheets from sticking to one another face-to-face. The curved morphology enables the formation of mesopores accessible to and wettable by environmentally benign ionic liquids capable of operating at a voltage >4 V.

With the total electrode weight of a supercapacitor system being typically one-fourth to one-half of the total system weight, the system-level specific energy of graphene-based supercapacitors can exceed 21.4-42.8 Wh/kg, which is comparable to that of a modern nickel metal hydride battery used in a hybrid vehicle. This breakthrough energy storage device is made possible by the high intrinsic capacitance and the exceptionally high specific surface area that can be readily accessed and wetted by an ionic liquid electrolyte capable of operating at a high voltage.

—Liu et al.

Source: Green Car Congress