UCLA researchers (University of California-Los Angeles) were able to produce graphene supercapacitor electrodes using a simple DVD burner sold commercially.
The method is based on a DVD disc coated with a thin plastic film (PET) which has been removed from the graphite oxide. The DVD is inserted into a standard DVD burner (LightScribe) then treated with infrared laser engraver to produce graphene electrodes.
The infrared laser DVD burner causes the reduction and simultaneous exfoliation of graphite oxide and produces isolated graphene monolayers but tangled called "Laser Scribed Graphene" (LSG). Graphene LSG is taken off and placed on a flexible substrate and then sliced to form electrodes. Two electrodes are sandwiched with an electrolyte layer in the middle. The result is a high density electrochemical capacitor, said supercapacitor.
Demonstration in the video below:
The surface of the graphene electrodes thus created is 1,520 square meters per gram, 3 to 5 times the surface of activated carbon electrodes in supercapacitors used commercially. It's hard to do better because the intrinsic surface of a graphene layer is 2,630 square meters per gram.
This new technique using a DVD burner makes it easy to create graphene micro-supercapacitors and also achieves exceptional performance.
A graphene LSG micro-supercapacitor with high performance
Generally, the performance of energy storage devices was evaluated by two main characteristics: the energy density and power density. For an electric car, for example, the energy density tells us how far the car can travel on a single charge whereas the power density tells us how fast the car can go.
On the search supercapacitors LSG is supervised by Richard B. Kaner, a professor of chemistry and materials science and engineering at UCLA, who said that graphene supercapacitor can "store a large amount of energy than conventional batteries but can be charged and discharged 100 to 1,000 times faster. "supercapacitors Laser Scribed Graphene (LSG) are the ones capable of discharging 20 watts per cm3, about 20 times more than standard ultracapacitors with activated carbon, and 1000 times the lithium-ion batteries thin film of 500 mAh.
In terms of energy density, the research team expects to obtain 1.36 milliwatt-hours per cm3, about 2 times the energy density of activated carbon ultracapacitors and a density comparable to lithium-ion thin layer high power.
A micro-supercapacitor LSG with exceptional power
The electrodes Laser Scribed Graphene (LSG) exhibit ultrahigh energy density values with different electrolytes tested while maintaining a high power density and excellent stability during charge / discharge cycles of the supercapacitor. In addition, micro-supercapacitors LSG maintain excellent electrochemical characteristics when subjected to a high mechanical stress. A very interesting feature for flexible electronics.
The open network structure of the electrodes LSG minimizes the diffusion path of electrolyte ions, which is crucial for the charging capacity of the supercapacitor. This can be explained by the fact that the graphene sheets are flat and therefore easily accessible, while the surface of the activated carbon consists of very small pores which limit the diffusion of ions. This means that LSG supercapacitors have the ability to deliver extremely high power in a short time.
A supercapacitor sturdy, pliable and not very expensive to produce
LSG electrodes are mechanically robust and show high conductivity (> 1700 S / m) compared to activated carbon electrodes (10-100 S / m). This means that RSV electrodes may be directly used as electrodes for supercapacitor without the need for binders or current collector as is the case for conventional supercapacitors using activated carbon.
These properties allow the electrodes LSG to act both as an active material and as current collector in the supercapacitor. Combining the two functions in a single layer leads to a simplified architecture and provides a cost-effective interesting for supercapacitors LSG.
Ultracapacitors commercially available consist of a separator sandwiched between two electrodes with liquid electrolyte, which is wound spirally and packed into a cylindrical container, is stacked in a button cell. Unfortunately, these supercapacitors architectures not only suffer from possible adverse electrolyte leakage, but the design also makes it difficult to use them for practical reasons in the flexible electronics field.
The research team replaced the liquid electrolyte with a polymer gel electrolyte also acts as a separator, which reduces the thickness and weight of the device and simplifies the manufacturing process because it does not require materials special packaging.
To assess in real conditions the potential of LSG supercapacitors for flexible storage, the research team placed a supercapacitor prototype LSG under constant mechanical stress to analyze its performance. Curiously, this had almost no effect on device performance. Only minor loss of 1% of the electrical resistance was observed after 1000 flex cycles.
"We attribute the performance and durability to the high mechanical flexibility of the electrodes and the interpenetrating network structure between the electrodes and the electrolyte gel LSG" said Kaner. "The electrolyte solidifies on the entire device and acts like a glue that holds the components of the assemblies supercapacitor."
The method improves the mechanical integrity and increases the life cycle of the device even when tested under extreme conditions.
This remarkable performance has never been made from commercial devices. These supercapacitors LSG could pave the way for energy storage systems ideal for the next generation of flexible and portable electronic devices.
Due to their enormous power density and better energy density ultracapacitors could revolutionize electric vehicles that could then be fully recharged in record time. Charging stations for high-speed electric car and also equipped with super capacitors should provide an equivalent cooldown time that we put to refuel.