Supercapacitor material with energy density 2.7 times higher than conventional materials

A research team led by Tohoku University in Japan has developed new materials for supercapacitors with higher voltage and better stability than other materials. Their research was recently published in the journal Energy and Environmental Science.

Supercapacitors are rechargeable energy storage devices with a broad range of applications, from machinery to smart meters. They offer many advantages over batteries, including faster charging and longer lifespans, but they are not so good at storing lots of energy.

Scientists have long sought high-performance materials for supercapacitors that can meet the requirements for energy-intensive applications such as cars. “It is very challenging to find materials that can both operate at high-voltage and remain stable under harsh conditions,” says Hirotomo Nishihara, materials scientist at Tohoku University and co-author of the paper.

Nishihara and his colleagues collaborated with the supercapacitor production company TOC Capacitor Co. to develop a new material that exhibits extraordinarily high stability under conditions of high voltage and high temperature.

Activated carbons are used for the electrodes in capacitors, but these are limited by low voltage in single cells, the building blocks that make up capacitors. This means that a large number of cells must be stacked together to achieve the required voltage. Crucially, the new material has higher single-cell voltage, reducing the stacking number and allowing devices to be more compact.

The new material is a sheet made from a continuous three-dimensional framework of graphene mesosponge, a carbon-based material containing nanoscale pores. A key feature of the materials is that it is seamless—it contains a very small number of carbon edges, the sites where corrosion reactions originate, and this makes it extremely stable.

The researchers investigated the physical properties of their new material using electron microscopy and a range of physical tests, including X-ray diffraction and vibrational spectroscopy techniques. They also tested commercial graphene-based materials, including single-walled carbon nanotubes, reduced graphene oxides, and 3-D graphene, using activated carbons as a benchmark for comparison.

They showed that the material had excellent stability at high temperatures of 60 °C and high voltage of 3.5 volts in a conventional organic electrolyte. Significantly, it showed ultra-high stability at 25°C and 4.4 volts—2.7 times higher than conventional activated carbons and other graphene-based materials. “This is a world record for voltage stability of carbon materials in a symmetric supercapacitor,” says Nishihara.

The new material paves the way for development of highly durable, high-voltage supercapacitors that could be used for many applications, including motor vehicles.

Provided by: Tohoku University 

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The warp and weft of wearable electronics

One of today’s challenges for materials scientists is wearable electronics — smart materials that monitor ailments, harvest energy, track performance or communicate. These remain expensive and hard to produce in bulk, and are often unattractive. Polymer scientist Zijian Zheng takes inspiration from his designer and business colleagues at Hong Kong Polytechnic University’s Institute of Textiles and Clothing. His solution: lightweight electronic yarns that can be made into textiles by adapting existing production processes.


 How do you create wearable electronics?

People need to feel like they’re not wearing electronics, so the materials must be lightweight and flexible. They must also be high-performance, as devices have to charge rapidly, last for a long time and be sweat-proof. Applying all these criteria, we create electronic textiles in which the fabrics themselves form the sensors and devices – from light-emitting diodes, photovoltaics, organic transistors and supercapacitors to batteries. We can make a supercapacitor using conductive yarn, made by coating cotton with nickel, and penetrating it with a form of graphene oxide. If you put a pair of these strands together in parallel, and fill the space between with an electrolyte gel, you can make it work as a supercapacitor storing energy as positively and negatively charged ions collect at the different wires. You could use that to power other devices, such as sensors, or store energy generated from photovoltaics. We’re working on making lithium batteries using the same principles.

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Why doesn’t glass get the same flak as plastic? Glass is also not easily degradable

What is glass?

Glass is made primarily of silicon dioxide. The most common type of glass is known as soda-lime glass, which makes up the bulk of consumer glass products. It is mostly silicon dioxide, aluminum oxide and sodium oxide with about 1% boron trioxide. Silicon dioxide, or silica, makes up 59% of the Earth’s crust, and about 95% of the rocks on Earth. Almost every sandy beach or desert, whether it’s pink sand, white sand, black sand, you’re looking at silica. Most mountains you see are mostly silica.

Glass is recyclable indefinitely. It can be crushed into useful aggregates, abrasives, spun into insulating wools, and remelted into glass. It is non-toxic, does not require toxic chemicals for production or contain any toxic chemicals. If a bottle is floating in the ocean it may endanger whales and marine life that may try to eat it, but it does not contaminate the water with anything toxic. Glass is denser than water, and sinks to the bottom of any body of water. Over time it is broken up and tumbled by waves or currents, and becomes rounded like any other pebble.


What are plastics?

Plastics are man-made synthetic polymers. A polymer is a molecular chain of monomers. Plastics are mostly hydrocarbon monomers. Some of the polymers, like polyvinyl-chloride (PVC), are chlorine-based, and are made from petroleum distillates and various salts. Plastics have a lot in common with gasoline, diesel, synthetic and mineral motor oil, they’re just polymerized into chains of hydrocarbons.

Hydrocarbons are a finite resource. We will run out of useful petroleum, before which the economic cost of using hydrocarbons in general will rise exponentially.

If you’ve ever seen an oil slick, or a gas spill, you’ll know that hydrocarbons are LESS dense than water. If you pour a glass of water into a barrel of oil, it will sink to the bottom. Plastic density or specific gravity varies. Some plastics, like PVC, typically sink in water. Others are less dense and will float on or near the surface of water. So plastic doesn’t JUST float, it can be found floating throughout the water column, AND on the bottom of oceans and lakes. Plastic products also tend to be found in forms and shapes that are dangerous to marine life. Plastic bags look like jellyfish and are often eaten by turtles, sunfish, whales and other jellyfish eaters.

Plastics are not just made up of the hydrocarbon or chlorine polymers. Chemical modifiers are added to polymers to provide whatever desirable characteristics are needed. The modifiers or plasticizers provide things like strength, rigidity, flexibility, stretchiness, flame and heat resistance, optical qualities, resistance to radiation, increase impact strength, wear resistance, etc… These chemicals are not molecularly bonded to the polymers (non-covalent bonds). Most plasticizer are toxic solvents that leak out of the plastic as gasses for months or years after production. Most are phthalates like DEHP Bis(2-ethylhexyl) phthalate. Most of the modifiers have bio-accumulative effects on the endocrine systems of mammals and fish and birds. Animals and humans that are exposed to the chemicals show altered gene expression and endocrine system disruption. Plastics, especially PVC, also release dioxins into the environment during manufacture and during the lifetime of the plastic. PVC that is exposed to too much heat can release harmful amounts of dioxins into the air and as falling solids that contaminate surfaces. Dioxins are among the most toxic chemicals, and are not safe in any amount. The physical presence of plastics in dangerous forms like nets, rings and micro-beads is not the biggest danger. The biggest danger is the accumulation of impossible to remove chemicals in greater and greater amounts in the environment every day, contaminating our water, food and bodies in very negative ways that we may never fully understand.

By: Brian Madigan


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