Published on November 7th, 2014 | by Tina Casey13
Energy Storage Slam-Dunk: Graphene + Carbon Nanotubes + Li-ion EV Batteries
November 7th, 2014 by Tina Casey
Holy gilding the lily, Batman! Researchers at Australia’s Queensland University of Technology are hot on the trail of a new energy storage concept that melds our two favorite next-millennium nanomaterials, graphene and carbon nanotubes, and combines them with the current gold standard in electric vehicle technology, which would be a lithium-ion battery.
The end result would be an EV with extra souped-up energy storage integrated into its body panels, enabling it to charge much more quickly, and travel much farther, than current technology allows.
Naturally that got us to thinking that the new breakthrough could also be applied to fuel cell EVs as well as battery EVs, but we digress.
Graphene And Carbon Nanotubes
For those of you new to the topic, graphene and carbon nanotubes are two forms of the element carbon. Coal and diamonds are two other forms, which just goes to show how far carbon can go in terms of the diversity its properties.
Graphene comes in sheets of carbon just one atom thick. Carbon nanotubes, as the name indicates, consist of carbon atoms arranged in a tube shape.
Both graphene and carbon nanotubes have emerged relatively recently, with seemingly limitless application for energy storage and many other new energy technologies. Since carbon is cheap and abundant, teasing out its unique properties on the nanoscale level has been the focus of literally thousands of research papers in just the past few years.
Researchers are already beginning to combine the two forms. Just last May, for example, we took note of a new energy storage device under development by a US-China-Singapore team based on a combination of graphene and carbon nanotubes.
So, here’s where it starts to get interesting. Researchers are also beginning to incorporate graphene into a class of powerful energy storage devices called supercapacitors, with enormous potential for application to electric vehicle technology.
While supercapacitors store energy like batteries, in the current state of technology there are two distinct points of difference. One is an advantage: unlike your typical lithium-ion EV battery, a supercapacitor charges in just a few minutes.
The other difference, though, is a disadvantage. Supercapacitors have a relatively low energy density, so the next challenge for EV technology is to build up the ability of supercapacitors to store more energy.
With that in mind, let’s get to the new QUT (Queensland University of Technology) research.
Jacking Up Lithium-Ion EV Batteries
Partnering in the new research is Rice University, which has been doing a deep dive into next-generation nano-carbon energy storage technology.
The team found that they could construct a supercapacitor “sandwich” in the form of a super-strong, super-thin film. Here’s the money quote:
The film could be embedded in a car’s body panels, roof, doors, bonnet and floor – storing enough energy to turbocharge an electric car’s battery in just a few minutes.
The findings have been published online in the upcoming January 2015 issue of the Journal of Power Sources.
The supercapacitor uses all-carbon electrodes, which the team created by mixing graphene sheets with clusters of carbon nanotubes. That combination resulted in a large surface area, which is a desirable trait for electrodes. In a battery, the two electrodes are the two points at which the current enters and leaves, so you can get more punch by packing as much surface area into the smallest possible space.
Integrating the electrodes into a thin film required a series of additional steps, as described in the team’s abstract:
This electrode is transferred onto a plastic-paper-supported double-wall carbon nanotube film used as current collector. These all-carbon thin films are combined with plastic paper and gelled electrolyte to produce solid-state bendable thin film supercapacitors.
The team also found that the shape of the film had a significant impact on its ability to store a charge, with an in-line arrangement of rectangular sheets yielding the best results.
The team foresees that if the energy density angle can be improved, their supercapacitor film could provide enough storage to enable the development of EVs that run entirely off the charge stored in their film-integrated body panels.
Supercapacitor development using other materials is also under way (here’s a recent example from Rice), but carbon has the advantage when it comes to abundance, cost, toxicity (or rather, lack thereof), and amenability to low-cost manufacturing techniques.
A Turbo-Charged Fuel Cell Electric Vehicle
In terms of EV manufacturing carbon also has a supply chain advantage over lithium, in addition to lower costs. While Li-ion battery EVs dominate right now, the future EV market could diversify into both batteries and fuel cells (check out California for fuel cell activity), or even vehicles that combine both.
The supercapacitor film adds yet another new angle, which is why we’re thinking that another technology to emerge in the future EV market could be a combination of body-integrated supercapacitors and fuel cells.
Before we go to the comment thread, yes we’ve noted many times that the current practice of sourcing hydrogen for fuel cells from fossil natural gas is a deal-breaker, but when renewable hydrogen sources go mainstream, that will provide another option for sustainable personal mobility.
So, any thoughts?