Polymer materials developed and tested at the universities of Surrey and Bristol appear to have better energy storage properties than lithium ion batteries and could be used in supercapacitors
Materials originally developed for soft contact lenses have energy storage properties that could rival the best lithium ion batteries currently available, according to its developer. A series of serendipitous results led Dr Donald Highgate, director of research for Superdielectrics Ltd and alumnus of Surrey University, to realise that material originally developed for quite different applications was outperforming energy storage materials currently on the market, and he now believes these materials could form a vital link in systems to charge large numbers of electric cars.
“I started this about 40 years ago with materials that went on to form the basis of extended wear contact lenses,” Highgate told The Engineer. “So it’s an aqueous hydrocarbon polymer. But we then wondered whether we could use this material as the basis for membranes in fuel cells. Conventional wisdom then said you could only use fluorocarbons because they were more resistant to corrosion. But we found that if you cross-linked all the polymer chains together the material became corrosion resistant because there are no loose ends. I put some sulphonyl into the mix so that it became electrically active and that material now forms the basis for the membranes and electrolysers produced by ITM Power, of which I was a founder.”
“The next step was to determine whether we could make the material electronically active, and we found that we could. We were trying to make a biocompatible material that could be used to link prosthetics directly into the nervous system, and we sent samples to the University of Bristol for testing. They came back to us and said ‘do you realise you’ve got dielectric properties a thousand times better than our best electrolytes?’ At that point, which was at the end of 2016, we changed our focus away from biocompatibles and towards supercapacitors.”
At the testing point, Highgate was only producing quantities around the size of a rice grain. Production has now been scaled up to the point where the polymer can be coated onto metal foil electrodes in simple demonstration devices. Single-layer cells can be charged to 1.5V for two-to-five minutes and then run a small electric fan. A three cell series stack can be rapidly charged to 5V and run an LED light.
The material achieves practical capacitance values of up to 4F/cm2 with a smooth electrode; existing supercapacitors typically only reach 0.3F/cm2 and rely on complex extended surface area materials. Moreover, the researchers claim, using a specially treated stainless steel electrode – the details of which are classified pending a patent application – the material achieves results of 11 to 20F/cm2. Bristol University is working on a complex series-parallel cell structure in which total capacitance and operating voltage can be controlled separately
If these capacitance values can be achieved in production, the resulting supercapacitors could achieve any densities up to 180Whr/kg – better than lithium ion batteries.
Supercapacitors have different charge and discharge characteristics to batteries. While batteries charge and discharge slowly, supercapacitors charge and discharge very fast. Until now they have only had around a 20th of the energy density per kilogram of battery technology and have not been able to compete with batteries. Supercapacitors currently power electric buses in China, but need to be charged at almost every bus stop.
High capacity supercapacitors could be a vital component in charging electric cars. “If you’re charging a lot of cars, that puts a lot of strain on the grid,” Highgate said. “If you have a buffer between the grid that can accept charge and release it quickly, you take that strain away. Supercapacitors can form that buffer.”
Highgate also believes these supercapacitors have potential in grid level energy storage to balance out the intermittency of renewables.
“The advantage is, it is based on an aqueous material with nothing toxic, no rare earths and no reliance on scarce minerals,” he told The Engineer. In a statement, he added: “This new work would transform the energy system which underpins our entire way of life – it is the necessary development before we and our children can have a genuinely sustainable, environmentally safe energy supply.”
The wins just keep piling up….the questions is how long (I suspect not very long) before this goes commercial?
…I thought you were going to say…how long before this tech is taken up by an overseas investor……my answer would be very soon…..
If this and the recent news from ITER turn out to be reliable, we’re finally onto something. The business of switching cells to modulate voltage and current is a critical area.
How long does it hold it’s charge? Electrolytic capacitors loose their charge over a few minutes. They would still be useful to cope with fluctuating loads and supply, but to replace batteries, they would need to need to keep their charge for days.
We’ve asked the researchers and will add this detail when we get a response.
The team says that they’ve charged the one-cell device, waited an hour and been able to run the fan, but they’re still experimenting so can’t fully answer the question yet.
Sorry to correct you but an electrolytic capacitor in good condition can hold charge for way longer than that – days, even weeks.
S Erin Dipity -that amazing researcher who both thinks and acts outside the box -indeed in this case outside a whole cube of boxes…strikes again! I have always believed that whatever your issue, someone elsewhere has at least pointed you into a new direction: and indeed often been there before. Thinking forwards with inspiration as opposed to backwards for precedent?
We can do it! whatever it is, as long as we stand on those shoulders of giants to see the future.
As a capacitor, it is prey to the relationship of Q = 0.5 C*V*V This means that the voltage declines in direct proportion to the charge drained. This is analogous to the Carnot limitations on a heat engine. A lithium cell also changes the charge state of the lithium ion IN THE BULK, at a constant voltage. This means an intrinsically greater amount of charge in flux than the surface area based storage of a capacitor.
This will mean that it will encounter great difficulty in delivering the amount of wattage as the lithium battery. Of course the nature of a capacitor in terms of charge/discharge rate will exceed that of any lithium battery, and this will allow this design to advance into new applications based on this.
Think of a capacitor as a ‘spring’ in terms of energy storage, and why we have few spring powered cars.
…and the human frame cannot withstand speeds greater than 30mph …
How about using the capacitors to solve the charge duration issue, in conjunction with the Lithium Ion batteries? Drive up to a charging station, charge the capacitor in a few minutes, then drive off and charge the battery from the capacitor while you’re driving, or not driving.
If the capacitors will hold enough energy to charge the batteries . . . you don’t need the batteries.
This is in no way analogous to the Carnot efficiency, which refers to the ratio between input and exhaust temperatures of a heat engine. Yes, the voltage of a capacitor declines more rapidly than that of a battery as current is withdrawn, but as the equation you cite makes clear, three quarters of the energy is obtained by the time the voltage has declined to half its original value. Modern electronic control systems can cope with that range of voltage and more with ease.
With regard to volume vs. area, actual capacitors consist of many stacked (or rolled) layers of thin material, building up to 3 dimensional solid structures with energy stored throughout that bulk every bit as effectively as a chemical battery.
I doubt that will be a problem that can’t be overcome. I’m sure current day processors could manage circuitry to distribute charge and sequence discharging easily enough to spin a flywheel.
I was also (as Ian Downle asks) wondering what the self-discharge rate of these capacitors was.
Typically super capacitors have a very high self-discharge.
Of course it’s early days for the technology and I expect there are opportunities to trade between high Capacitance and low self-discharge.
Looks very exciting R&D. Wish them luck, and please keep us up to date with their work.
Once again and in a completely different field to several recently blogged, we are blessed with comments and proposals from individual Engineers who are clearly ‘well versed in their particular art’ and can increase the knowledge and understanding of the rest of us. Thank you. I have always found analogies and examples from elsewhere in the broad church which is Engineering particularly valuable. There is usually some aspect to a comment with which I can identify from my own experience (relatively narrow as it is) and this leads to a greater understanding of areas presently unknown but important to the future.
The real problem will arrise when you need the finance to defend the Patent against the world.
Gosh – 4F/cm^2 – but I presume that degrades with life charge cycles?
Ken is right: “leeches on the jugular of innovation” -a comment about patents and ‘agents’ from a former President of the I Mech Eng: presumably the theft of intellectual property (surely a contradiction if ever there was one: like military intelligence and legal profession) should be apprehended just like the theft of goods and chattels. Of course most intellectual theft is conducted by lawyers and/or their clients? Sorry Stuart if this is a repeat of past views: but again, I believe it is the very essence of what ails us in this field. If intellectual property is so important (as it is so described by those who make their living from granting such) then let those who offer such, provide their ‘services’ up front: and take a share of the eventual profits.
Pigs may fly?
Forgive my ignorance but the best Lithium Ion batteries are currently 240Whr/kg with plans to double this over the next 5 years.
TF is spot-on, well pretty-much once promise is cautioned with caveat on lifetime limitation from continuously cycled high charge density at fixed fractional depletion. Of course electropolymeric membranes derived from NASA-DOD needs for fuel-cells & electrolysers since 60s, & UK inputs via prepiratisation ARE-DRA on metalised monolayers & sonicated accelerant as recalled from firsthand familiarity during the decade spanning coldwar closure.
“Bristol University is working on a complex series-parallel cell structure in which total capacitance and operating voltage can be controlled separately” – I believe this is the key statement.
And we’ll report on it when they publish.
In my humble opinion, the supercapacitor is one of the best energy storage devices. It can deliver very fast response to the power grid during transient event. The issue has always been its lower energy density. If new material can enhance the energy density that will be a step forward. However, biggest advantage is high power delivery . Hybridised system (e.g: supercapacitor-batteries) can be the best solution.