People first used capacitors to store electricity. Then, when electrical engineering went beyond laboratory experiments, batteries were invented, which became the main means of storing electrical energy. But at the beginning of the 21st century, it is again proposed to use capacitors to power electrical equipment. How possible is this and will batteries finally become a thing of the past?
The reason why capacitors were replaced by batteries was due to the significantly greater amounts of electricity that they are capable of storing. Another reason is that during discharge the voltage at the battery output changes very little, so that a voltage stabilizer is either not required or can be of a very simple design.
The main difference between capacitors and batteries is that capacitors directly store electrical charge, while batteries convert electrical energy into chemical energy, store it, and then convert the chemical energy back into electrical energy.
During energy transformations, part of it is lost. Therefore, even the best batteries have an efficiency of no more than 90%, while for capacitors it can reach 99%. The intensity of chemical reactions depends on temperature, so batteries perform noticeably worse in cold weather than at room temperature. In addition, chemical reactions in batteries are not completely reversible. Hence the small number of charge-discharge cycles (on the order of thousands, most often the battery life is about 1000 charge-discharge cycles), as well as the “memory effect”. Let us recall that the “memory effect” is that the battery must always be discharged to a certain amount of accumulated energy, then its capacity will be maximum. If, after discharging, more energy remains in it, then the battery capacity will gradually decrease. The “memory effect” is characteristic of almost all commercially produced types of batteries, except acid ones (including their varieties - gel and AGM). Although it is generally accepted that lithium-ion and lithium-polymer batteries do not have it, in fact they also have it, it just manifests itself to a lesser extent than in other types. As for acid batteries, they exhibit the effect of plate sulfation, which causes irreversible damage to the power source. One of the reasons is that the battery remains in a state of charge of less than 50% for a long time.
With regard to alternative energy, the “memory effect” and plate sulfation are serious problems. The fact is that the supply of energy from sources such as solar panels and wind turbines is difficult to predict. As a result, the charging and discharging of batteries occurs chaotically, in a non-optimal mode.
For the modern rhythm of life, it turns out to be absolutely unacceptable that batteries have to be charged for several hours. For example, how do you imagine driving a long distance in an electric vehicle if a dead battery keeps you stuck at the charging point for several hours? The charging speed of a battery is limited by the speed of the chemical processes occurring in it. You can reduce the charging time to 1 hour, but not to a few minutes. At the same time, the charging rate of the capacitor is limited only by the maximum current provided by the charger.
The listed disadvantages of batteries have made it urgent to use capacitors instead.
Using an electrical double layer
For many decades, electrolytic capacitors had the highest capacity. In them, one of the plates was metal foil, the other was an electrolyte, and the insulation between the plates was metal oxide, which coated the foil. For electrolytic capacitors, the capacity can reach hundredths of a farad, which is not enough to fully replace the battery.
Large capacitance, measured in thousands of farads, can be obtained by capacitors based on the so-called electrical double layer. The principle of their operation is as follows. An electric double layer appears under certain conditions at the interface of substances in the solid and liquid phases. Two layers of ions are formed with charges of opposite signs, but of the same magnitude. If we simplify the situation very much, then a capacitor is formed, the “plates” of which are the indicated layers of ions, the distance between which is equal to several atoms.
Capacitors based on this effect are sometimes called ionistors. In fact, this term not only refers to capacitors in which electrical charge is stored, but also to other devices for storing electricity - with partial conversion of electrical energy into chemical energy along with storing the electrical charge (hybrid ionistor), as well as for batteries based on double electrical layer (so-called pseudocapacitors). Therefore, the term “supercapacitors” is more appropriate. Sometimes the identical term “ultracapacitor” is used instead.
Technical implementation
A supercapacitor consists of two plates of activated carbon filled with electrolyte. Between them there is a membrane that allows the electrolyte to pass through, but prevents the physical movement of activated carbon particles between the plates.
It should be noted that supercapacitors themselves have no polarity. In this way, they fundamentally differ from electrolytic capacitors, which, as a rule, are characterized by polarity, failure to comply with which leads to failure of the capacitor. However, polarity is also applied to supercapacitors. This is due to the fact that supercapacitors leave the factory assembly line already charged, and the marking indicates the polarity of this charge.
Supercapacitor parameters
The maximum capacity of an individual supercapacitor, achieved at the time of writing, is 12,000 F. For mass-produced supercapacitors, it does not exceed 3,000 F. The maximum permissible voltage between the plates does not exceed 10 V. For commercially produced supercapacitors, this figure, as a rule, lies within 2. 3 – 2.7 V. Low operating voltage requires the use of a voltage converter with a stabilizer function. The fact is that during discharge, the voltage on the capacitor plates changes over a wide range. Building a voltage converter to connect the load and charger is a non-trivial task. Let's say you need to power a 60W load.
To simplify the consideration of the issue, we will neglect losses in the voltage converter and stabilizer. If you are working with a regular 12 V battery, then the control electronics must be able to withstand a current of 5 A. Such electronic devices are widespread and inexpensive. But a completely different situation arises when using a supercapacitor, the voltage of which is 2.5 V. Then the current flowing through the electronic components of the converter can reach 24 A, which requires new approaches to circuit technology and a modern element base. It is precisely the complexity of building a converter and stabilizer that can explain the fact that supercapacitors, the serial production of which began in the 70s of the 20th century, have only now begun to be widely used in a variety of fields.
Supercapacitors can be connected into batteries using series or parallel connections. In the first case, the maximum permissible voltage increases. In the second case - capacity. Increasing the maximum permissible voltage in this way is one way to solve the problem, but you will have to pay for it by reducing the capacitance.
The dimensions of supercapacitors naturally depend on their capacity. A typical supercapacitor with a capacity of 3000 F is a cylinder with a diameter of about 5 cm and a length of 14 cm. With a capacity of 10 F, a supercapacitor has dimensions comparable to a human fingernail.
Good supercapacitors can withstand hundreds of thousands of charge-discharge cycles, exceeding batteries by about 100 times in this parameter. But, like electrolytic capacitors, supercapacitors face the problem of aging due to the gradual leakage of electrolyte. So far, no complete statistics on the failure of supercapacitors for this reason have been accumulated, but according to indirect data, the service life of supercapacitors can be approximately estimated at 15 years.
Accumulated energy
The amount of energy stored in a capacitor, expressed in joules:
where C is the capacitance, expressed in farads, U is the voltage on the plates, expressed in volts.
The amount of energy stored in the capacitor, expressed in kWh, is:
Hence, a capacitor with a capacity of 3000 F with a voltage between the plates of 2.5 V is capable of storing only 0.0026 kWh. How does this compare to, for example, a lithium-ion battery? If we take its output voltage to be independent of the degree of discharge and equal to 3.6 V, then an amount of energy of 0.0026 kWh will be stored in a lithium-ion battery with a capacity of 0.72 Ah. Alas, a very modest result.
Application of supercapacitors
Emergency lighting systems are where using supercapacitors instead of batteries makes a real difference. In fact, it is precisely this application that is characterized by uneven discharge. In addition, it is desirable that the emergency lamp is charged quickly and that the backup power source used in it has greater reliability. A supercapacitor-based backup power supply can be integrated directly into the T8 LED lamp. Such lamps are already produced by a number of Chinese companies.
As already noted, the development of supercapacitors is largely due to interest in alternative energy sources. But practical application is still limited to LED lamps that receive energy from the sun.
The use of supercapacitors to start electrical equipment is actively developing.
Supercapacitors are capable of delivering large amounts of energy in a short period of time. By powering electrical equipment at startup from a supercapacitor, peak loads on the electrical grid can be reduced and, ultimately, the inrush current margin can be reduced, achieving huge cost savings.
By combining several supercapacitors into a battery, we can achieve a capacity comparable to the batteries used in electric cars. But this battery will weigh several times more than the battery, which is unacceptable for vehicles. The problem can be solved by using graphene-based supercapacitors, but they currently only exist as prototypes. However, a promising version of the famous Yo-mobile, powered only by electricity, will use new generation supercapacitors, which are being developed by Russian scientists, as a power source.
Supercapacitors will also benefit the replacement of batteries in conventional gasoline or diesel vehicles - their use in such vehicles is already a reality.
In the meantime, the most successful of the implemented projects for the introduction of supercapacitors can be considered the new Russian-made trolleybuses that recently appeared on the streets of Moscow. When the supply of voltage to the contact network is interrupted or when the current collectors “fly off”, the trolleybus can travel at a low speed (about 15 km/h) for several hundred meters to a place where it will not interfere with traffic on the road. The source of energy for such maneuvers is a battery of supercapacitors.
In general, for now supercapacitors can displace batteries only in certain “niches”. But technology is rapidly developing, which allows us to expect that in the near future the scope of application of supercapacitors will expand significantly.
Alexey Vasiliev
The requirement to reduce the size of radio components while increasing their technical characteristics led to the emergence of a large number of devices that are used everywhere today. This fully affected capacitors. The so-called ionistors or supercapacitors are elements with a high capacity (the range of this indicator is quite wide from 0.01 to 30 farads) with a charging voltage of 3 to 30 volts. Moreover, their sizes are very small. And since the subject of our conversation is a do-it-yourself ionistor, it is necessary first of all to understand the element itself, that is, what it is.
Design features of the ionistor
In essence, this is an ordinary capacitor with a large capacity. But ionistors have a high resistance, because the element is based on an electrolyte. This is the first. The second is the low charging voltage. The thing is that in this supercapacitor the plates are located very close to each other. This is precisely the reason for the reduced voltage, but it is precisely for this reason that the capacitance of the capacitor increases.
Factory ionizers are made from different materials. The covers are usually made of foil, which is separated by a dry substance with a separating effect. For example, activated carbon (for large plates), metal oxides, polymer substances that have high electrical conductivity.
Assembling the ionizer with your own hands
Assembling an ionizer with your own hands is not the easiest thing, but you can still do it at home. There are several designs where different materials are present. We offer one of them. To do this you will need:
- metal coffee jar (50 g);
- activated carbon, which is sold in pharmacies, can be replaced with crushed carbon electrodes;
- two circles of copper plate;
- cotton wool
First of all, you need to prepare the electrolyte. To do this, you first need to crush the activated carbon into powder. Then make a saline solution, for which you need to add 25 g of salt to 100 g of water, and mix it all well. Next, activated carbon powder is gradually added to the solution. Its quantity is determined by the consistency of the electrolyte; it should be as thick as putty.
After which the finished electrolyte is applied to copper circles (on one side). Please note that the thicker the electrolyte layer, the greater the capacity of the ionistor. And one more thing, the thickness of the applied electrolyte on the two circles should be the same. So, the electrodes are ready, now they need to be separated by a material that would pass electric current, but would not allow carbon powder to pass through. For this, ordinary cotton wool is used, although there are many options here. The thickness of the cotton layer determines the diameter of the metal coffee jar, that is, this entire electrode structure should fit comfortably into it. Hence, in principle, you will have to select the dimensions of the electrodes themselves (copper circles).
All that remains is to connect the electrodes themselves to the terminals. That’s it, the ionistor, made with your own hands, and even at home, is ready. This design does not have a very large capacity - no higher than 0.3 farads, and the charging voltage is only one volt, but this is a real ionistor. 
Conclusion on the topic
What else can be said about this element in addition? If we compare it, for example, with a nickel-metal hydride battery, then the ionistor can easily hold a supply of electricity up to 10% of the battery power. In addition, its voltage drop occurs linearly, and not abruptly. But the level of charge of the element depends on its technological purpose.
The buzz surrounding Elon Musk's construction of a “Battery Gigafactory” for the production of lithium-ion batteries has not yet died down, when a message appeared about an event that could significantly adjust the plans of the “billionaire revolutionary”.
This is a recent press release from the company. Sunvault Energy Inc., which together with Edison Power Company managed to create the world's largest graphene supercapacitor with a capacity of 10 thousand (!) Farads.
This figure is so phenomenal that it raises doubts among domestic experts - in electrical engineering even 20 Microfarads (that is, 0.02 Millifarads), this is a lot. There is no doubt, however, that the director of Sunvault Energy is Bill Richardson, the former governor of New Mexico and former US Secretary of Energy.
Bill Richardson is a well-known and respected man: he served as the US ambassador to the UN, worked for several years at the Kissinger and McLarty think tank, and was even nominated for a Nobel Prize for his successes in freeing Americans captured by militants in various “hot spots” peace. In 2008, he was one of the Democratic Party candidates for the presidency of the United States, but lost to Barack Obama.
Today, Sunvault is growing rapidly, having created a joint venture with the Edison Power Company called Supersunvault, and the board of directors of the new company includes not only scientists (one of the directors is a biochemist, another is an enterprising oncologist), but also famous people with good business acumen. I note that in just the last two months the company has increased the capacity of its supercapacitors tenfold - from a thousand to 10,000 Farads, and promises to increase it even more so that the energy accumulated in the capacitor is enough to power an entire house, that is, Sunvault is ready to act directly competitor of Elon Musk, who plans to produce Powerwall-type superbatteries with a capacity of about 10 kWh.
The benefits of graphene technology and the end of the Gigafactory. Here we need to recall the main difference between capacitors and batteries - if the former quickly charge and discharge, but accumulate little energy, then batteries - on the contrary. Notemain advantages of graphene supercapacitors.
1. Fast charging— capacitors charge approximately 100-1000 times faster than batteries.
2. Cheapness: if conventional lithium-ion batteries cost about $500 per 1 kWh of accumulated energy, then a supercapacitor costs only $100, and by the end of the year the creators promise to reduce the cost to $40. In terms of its composition, it is ordinary carbon - one of the most common chemical elements on Earth.
3. Compactness and energy density and. The new graphene supercapacitor amazes not only with its fantastic capacity, which exceeds known samples by about a thousand times, but also with its compactness - it is the size of a small book, that is, one hundred times more compact than the 1 Farad capacitors currently used.
4. Safety and environmental friendliness. They are much safer than batteries, which heat up, contain dangerous chemicals, and sometimes even explode. Graphene itself is a biodegradable substance, that is, in the sun it simply disintegrates and does not spoil the environment. It is chemically inactive and does not harm the environment.
5. The simplicity of the new technology for producing graphene. The vast territory and capital investment, the mass of workers, the toxic and dangerous substances used in the technological process of lithium-ion batteries - all this contrasts sharply with the amazing simplicity of the new technology. The fact is that graphene (that is, the thinnest, monatomic carbon film) is produced at Sunvault... using an ordinary CD disk onto which a portion of a graphite suspension is poured. Then the disc is inserted into a regular DVD drive and burned with a laser using a special program - and the graphene layer is ready! It is reported that this discovery was made by accident - by student Maher El-Kadi, who worked in the laboratory of chemist Richard Kaner. He then burned the disk using LightScribe software to produce a layer of graphene.
Moreover, as Sunvault CEO Gary Monahan said at a Wall Street conference, the firm is working to graphene energy storage devices could be produced by conventional printing on a 3D printer- and this will make their production not only cheap, but also practically universal. And in combination with inexpensive solar panels (today their cost has dropped to $1.3 per W), graphene supercapacitors will give millions of people the chance to gain energy independence by completely disconnecting from the power grid, and even more so - to become their own electricity suppliers and, by destroying “ natural" monopolies.
Thus, there is no doubt: graphene supercapacitors are revolutionary breakthrough in the field of energy storage and
. And this is bad news for Elon Musk - the construction of a plant in Nevada will cost him about $5 billion, which would be difficult to recoup even without such competitors. It seems that while construction of the Nevada plant is already underway and is likely to be completed, then the other three that Musk has planned are unlikely to be completed.
Access to the market? Not as soon as we would like.
The revolutionary nature of such technology is obvious. Another thing is unclear - when will it hit the market? Already today, Elon Musk’s bulky and expensive lithium-ion Gigafactory project looks like a dinosaur of industrialism. However, no matter how revolutionary, necessary and environmentally friendly a new technology may be, this does not mean that it will come to us in a year or two. The world of capital cannot avoid financial shocks, but it is quite successful in avoiding technological ones. In such cases, behind-the-scenes agreements between large investors and political players come into play. It is worth recalling that Sunvault is a company located in Canada, and the board of directors includes people who, although they have extensive connections in the political elite of the United States, are still not part of its petrodollar core, a more or less obvious struggle against which, apparently it has already begun.
What is most important to us is Opportunities offered by emerging energy technologies: energy independence
for the country, and in the future - for each of its citizens. Of course, graphene supercapacitors are more of a “hybrid”, transitional technology; it does not allow direct generation of energy, unlike magneto-gravitational technologies, which promise to completely change the scientific paradigm itself and the appearance of the whole world. Finally there is revolutionary financial technologies, which are actually taboo by the global petrodollar mafia. Still, this is a very impressive breakthrough, all the more interesting because it is happening in the “lair of the petrodollar Beast” - in the United States.
Just six months ago I wrote about the successes of the Italians in cold fusion technology, but during this time we learned about the impressive LENR technology of the American company SolarTrends, and about the breakthrough of the German Gaya-Rosch, and now about the truly revolutionary technology of graphene storage devices. Even this short list shows that the problem is not that our or any other government does not have the ability to reduce the bills we receive for gas and electricity, and not even in the non-transparent calculation of tariffs.
The root of evil is the ignorance of those who pay the bills and the reluctance of those who issue them to change anything
. Only for ordinary people, energy is electricity. In reality, the energy of the self is power.
The scientific publication Science reported on a technological breakthrough made by Australian scientists in the field of creating supercapacitors.
Employees of Monash University, located in Melbourne, managed to change the production technology of supercapacitors made from graphene in such a way that the resulting products are more commercially attractive than previously existing analogues.
Experts have long been talking about the magical qualities of graphene-based supercapacitors, and laboratory tests have more than once convincingly proven the fact that they are better than conventional ones. Such capacitors with the prefix “super” are expected by the creators of modern electronics, automobile companies and even builders of alternative sources of electricity, etc.
The extremely long life cycle, as well as the ability of a supercapacitor to charge in the shortest possible period of time, allow designers to use them to solve complex problems when designing various devices. But until that time, the triumphal march of graphene capacitors was blocked by their low specific energy and... On average, an ionistor or supercapacitor had a specific energy indicator of the order of 5–8 Wh/kg, which, against the background of rapid discharge, made the graphene product dependent on the need to very often provide recharging.
Australian employees of the Department of Materials Manufacturing Research from Melbourne, led by Professor Dan Lee, managed to increase the specific energy density of a graphene capacitor by 12 times. Now this figure for the new capacitor is 60 W*h/kg, and this is already a reason to talk about a technical revolution in this area. The inventors managed to overcome the problem of fast discharge of the graphene supercapacitor, ensuring that it now discharges more slowly than even a standard battery.
A technological discovery helped the scientists achieve such an impressive result: they took an adaptive graphene-gel film and created a very small electrode from it. The inventors filled the space between the graphene sheets with liquid electrolyte so that a subnanometer distance was formed between them. This electrolyte is also present in conventional capacitors, where it acts as a conductor of electricity. Here it became not only a conductor, but also an obstacle to the contact of graphene sheets with each other. It was this move that made it possible to achieve a higher density of the capacitor while maintaining the porous structure.
The compact electrode itself was created using technology that is familiar to manufacturers of the paper we are all familiar with. This method is quite cheap and simple, which allows us to be optimistic about the possibility of commercial production of new supercapacitors.
Journalists hastened to assure the world that humanity has received an incentive to develop completely new electronic devices. The inventors themselves, through the mouth of Professor Lee, promised to help the graphene supercapacitor very quickly cover the path from the laboratory to the factory.
Like it or not, the era of electric cars is steadily approaching. And currently, only one technology is holding back the breakthrough and takeover of the market by electric vehicles, electric energy storage technology, etc. Despite all the achievements of scientists in this direction, most electric and hybrid cars have lithium-ion batteries in their design, which have their positive and negative sides, and can only provide a vehicle mileage on one charge for a short distance, sufficient only to travel in city limits. All the world's leading automakers understand this problem and are looking for ways to increase the efficiency of electric vehicles, which will increase the driving range on a single battery charge.
One of the ways to improve the efficiency of electric cars is to collect and reuse energy that turns into heat when the car brakes and when the car moves over uneven road surfaces. Methods for returning such energy have already been developed, but the efficiency of its collection and reuse is extremely low due to the low operating speed of batteries. Braking times are typically measured in seconds, which is too fast for batteries that take hours to charge. Therefore, to accumulate “fast” energy, other approaches and storage devices are required, the role of which is most likely to be high-capacity capacitors, the so-called supercapacitors.
Unfortunately, supercapacitors are not yet ready to hit the big road; despite the fact that they can charge and discharge quickly, their capacity is still relatively low. In addition, the reliability of supercapacitors also leaves much to be desired; the materials used in the electrodes of supercapacitors are constantly destroyed as a result of repeated charge-discharge cycles. And this is hardly acceptable given the fact that over the entire life of an electric car, the number of operating cycles of supercapacitors should be many millions of times.
Santhakumar Kannappan and a group of his colleagues from the Institute of Science and Technology, Gwangju, Korea, have a solution to the above problem, the basis of which is one of the most amazing materials of our time - graphene. Korean researchers have developed and manufactured prototypes of highly efficient graphene-based supercapacitors, the capacitive parameters of which are not inferior to those of lithium-ion batteries, but which are capable of very quickly accumulating and releasing their electrical charge. In addition, even prototypes of graphene supercapacitors can withstand many tens of thousands of operating cycles without losing their characteristics. 
The trick to achieving such impressive results is to obtain a special form of graphene, which has a huge effective surface area. The researchers made this form of graphene by mixing graphene oxide particles with hydrazine in water and crushing it all using ultrasound. The resulting graphene powder was packaged into disc-shaped pellets and dried at a temperature of 140 degrees Celsius and a pressure of 300 kg/cm for five hours.
The resulting material turned out to be very porous; one gram of such graphene material has an effective area equal to the area of a basketball court. In addition, the porous nature of this material allows the ionic electrolytic liquid EBIMF 1 M to completely fill the entire volume of the material, which leads to an increase in the electrical capacity of the supercapacitor.
Measurements of the characteristics of experimental supercapacitors showed that their electrical capacity is about 150 Farads per gram, the energy storage density is 64 watts per kilogram, and the electric current density is 5 amperes per gram. All these characteristics are comparable to those of lithium-ion batteries, whose energy storage density ranges from 100 to 200 watts per kilogram. But these supercapacitors have one huge advantage: they can fully charge or release all their stored charge in just 16 seconds. And this time is the fastest charge-discharge time to date.
This impressive set of characteristics, plus the simple manufacturing technology of graphene supercapacitors, may justify the claim of the researchers, who wrote that their “graphene supercapacitor energy storage devices are now ready for mass production and could appear in the coming generations of electric cars.”
A group of scientists from Rice University have adapted a method they developed to produce graphene using a laser to make supercapacitor electrodes.
Since its discovery, graphene, a form of carbon whose crystal lattice is monatomically thick, has, among other things, been considered as an alternative to activated carbon electrodes used in supercapacitors, capacitors with high capacitance and low leakage currents. But time and research have shown that graphene electrodes do not work much better than microporous activated carbon electrodes, and this caused a decrease in enthusiasm and the curtailment of a number of studies.
Nevertheless, graphene electrodes have some undeniable advantages compared to porous carbon electrodes.
Graphene supercapacitors can operate at higher frequencies, and the flexibility of graphene makes it possible to create extremely thin and flexible energy storage devices based on it, which are ideally suited for use in wearable and flexible electronics.
The two aforementioned advantages of graphene supercapacitors prompted further research by a group of scientists from Rice University. They adapted the laser-assisted graphene production method they developed to make supercapacitor electrodes.
“What we have achieved is comparable to the performance of microsupercapacitors that are available in the electronics market,” says James Tour, the scientist who led the research team. “With our method, we can produce supercapacitors that have any spatial form. When we need to pack graphene electrodes into a small enough area, we simply fold them like a sheet of paper.”
To produce graphene electrodes, scientists used laser method(laser-induced grapheme, LIG), in which a powerful laser beam is aimed at a target made of an inexpensive polymer material.
The parameters of the laser light are selected in such a way that it burns out all elements from the polymer except carbon, which is formed in the form of a porous graphene film. This porous graphene has been shown to have a sufficiently large effective surface area, making it an ideal material for supercapacitor electrodes.
What makes the Rice University team's findings so compelling is the ease of producing porous graphene.
“Graphene electrodes are very simple to make. This does not require a clean room and the process uses conventional industrial lasers, which work successfully on factory floors and even outdoors,” says James Tour.
In addition to ease of production, graphene supercapacitors have shown very impressive characteristics. These energy storage devices have withstood thousands of charge-discharge cycles without loss of electrical capacity. Moreover, the electrical capacitance of such supercapacitors remained virtually unchanged after the flexible supercapacitor was deformed 8 thousand times in a row.
“We have demonstrated that the technology we have developed can produce thin and flexible supercapacitors that can become components of flexible electronics or power sources for wearable electronics that can be built directly into clothing or everyday items,” said James Tour.
People first used capacitors to store electricity. Then, when electrical engineering went beyond laboratory experiments, batteries were invented, which became the main means of storing electrical energy. But at the beginning of the 21st century, it is again proposed to use capacitors to power electrical equipment. How possible is this and will batteries finally become a thing of the past?
The reason why capacitors were replaced by batteries was due to the significantly greater amounts of electricity that they are capable of storing. Another reason is that during discharge the voltage at the battery output changes very little, so that a voltage stabilizer is either not required or can be of a very simple design.
The main difference between capacitors and batteries is that capacitors directly store electrical charge, while batteries convert electrical energy into chemical energy, store it, and then convert the chemical energy back into electrical energy.
During energy transformations, part of it is lost. Therefore, even the best batteries have an efficiency of no more than 90%, while for capacitors it can reach 99%. The intensity of chemical reactions depends on temperature, so batteries perform noticeably worse in cold weather than at room temperature. In addition, chemical reactions in batteries are not completely reversible. Hence the small number of charge-discharge cycles (on the order of thousands, most often the battery life is about 1000 charge-discharge cycles), as well as the “memory effect”. Let us recall that the “memory effect” is that the battery must always be discharged to a certain amount of accumulated energy, then its capacity will be maximum. If, after discharging, more energy remains in it, then the battery capacity will gradually decrease. The “memory effect” is characteristic of almost all commercially produced types of batteries, except acid ones (including their varieties - gel and AGM). Although it is generally accepted that lithium-ion and lithium-polymer batteries do not have it, in fact they also have it, it just manifests itself to a lesser extent than in other types. As for acid batteries, they exhibit the effect of plate sulfation, which causes irreversible damage to the power source. One of the reasons is that the battery remains in a state of charge of less than 50% for a long time.
With regard to alternative energy, the “memory effect” and plate sulfation are serious problems. The fact is that the supply of energy from sources such as solar panels and wind turbines is difficult to predict. As a result, the charging and discharging of batteries occurs chaotically, in a non-optimal mode.
For the modern rhythm of life, it turns out to be absolutely unacceptable that batteries have to be charged for several hours. For example, how do you imagine driving a long distance in an electric vehicle if a dead battery keeps you stuck at the charging point for several hours? The charging speed of a battery is limited by the speed of the chemical processes occurring in it. You can reduce the charging time to 1 hour, but not to a few minutes. At the same time, the charging rate of the capacitor is limited only by the maximum current provided by the charger.
The listed disadvantages of batteries have made it urgent to use capacitors instead.
Using an electrical double layer
For many decades, electrolytic capacitors had the highest capacity. In them, one of the plates was metal foil, the other was an electrolyte, and the insulation between the plates was metal oxide, which coated the foil. For electrolytic capacitors, the capacity can reach hundredths of a farad, which is not enough to fully replace the battery.
Comparison of designs of different types of capacitors (Source: Wikipedia)
Large capacitance, measured in thousands of farads, can be obtained by capacitors based on the so-called electrical double layer. The principle of their operation is as follows. An electric double layer appears under certain conditions at the interface of substances in the solid and liquid phases. Two layers of ions are formed with charges of opposite signs, but of the same magnitude. If we simplify the situation very much, then a capacitor is formed, the “plates” of which are the indicated layers of ions, the distance between which is equal to several atoms.
Supercapacitors of various capacities produced by Maxwell
Capacitors based on this effect are sometimes called ionistors. In fact, this term not only refers to capacitors in which electrical charge is stored, but also to other devices for storing electricity - with partial conversion of electrical energy into chemical energy along with storing the electrical charge (hybrid ionistor), as well as for batteries based on double electrical layer (so-called pseudocapacitors). Therefore, the term “supercapacitors” is more appropriate. Sometimes the identical term “ultracapacitor” is used instead.
Technical implementation
A supercapacitor consists of two plates of activated carbon filled with electrolyte. Between them there is a membrane that allows the electrolyte to pass through, but prevents the physical movement of activated carbon particles between the plates.
It should be noted that supercapacitors themselves have no polarity. In this way, they fundamentally differ from electrolytic capacitors, which, as a rule, are characterized by polarity, failure to comply with which leads to failure of the capacitor. However, polarity is also applied to supercapacitors. This is due to the fact that supercapacitors leave the factory assembly line already charged, and the marking indicates the polarity of this charge.
Supercapacitor parameters
The maximum capacity of an individual supercapacitor, achieved at the time of writing, is 12,000 F. For mass-produced supercapacitors, it does not exceed 3,000 F. The maximum permissible voltage between the plates does not exceed 10 V. For commercially produced supercapacitors, this figure, as a rule, lies within 2. 3 – 2.7 V. Low operating voltage requires the use of a voltage converter with a stabilizer function. The fact is that during discharge, the voltage on the capacitor plates changes over a wide range. Building a voltage converter to connect the load and charger is a non-trivial task. Let's say you need to power a 60W load.
To simplify the consideration of the issue, we will neglect losses in the voltage converter and stabilizer. If you are working with a regular 12 V battery, then the control electronics must be able to withstand a current of 5 A. Such electronic devices are widespread and inexpensive. But a completely different situation arises when using a supercapacitor, the voltage of which is 2.5 V. Then the current flowing through the electronic components of the converter can reach 24 A, which requires new approaches to circuit technology and a modern element base. It is precisely the complexity of building a converter and stabilizer that can explain the fact that supercapacitors, the serial production of which began in the 70s of the 20th century, have only now begun to be widely used in a variety of fields.
Schematic diagram of an uninterruptible power supply
voltage on supercapacitors, the main components are implemented
on one microcircuit produced by LinearTechnology
Supercapacitors can be connected into batteries using series or parallel connections. In the first case, the maximum permissible voltage increases. In the second case - capacity. Increasing the maximum permissible voltage in this way is one way to solve the problem, but you will have to pay for it by reducing the capacitance.
The dimensions of supercapacitors naturally depend on their capacity. A typical supercapacitor with a capacity of 3000 F is a cylinder with a diameter of about 5 cm and a length of 14 cm. With a capacity of 10 F, a supercapacitor has dimensions comparable to a human fingernail.
Good supercapacitors can withstand hundreds of thousands of charge-discharge cycles, exceeding batteries by about 100 times in this parameter. But, like electrolytic capacitors, supercapacitors face the problem of aging due to the gradual leakage of electrolyte. So far, no complete statistics on the failure of supercapacitors for this reason have been accumulated, but according to indirect data, the service life of supercapacitors can be approximately estimated at 15 years.
Accumulated energy
The amount of energy stored in a capacitor, expressed in joules:
E = CU 2 /2,
where C is the capacitance, expressed in farads, U is the voltage on the plates, expressed in volts.
The amount of energy stored in the capacitor, expressed in kWh, is:
W = CU 2 /7200000
Hence, a capacitor with a capacity of 3000 F with a voltage between the plates of 2.5 V is capable of storing only 0.0026 kWh. How does this compare to, for example, a lithium-ion battery? If we take its output voltage to be independent of the degree of discharge and equal to 3.6 V, then an amount of energy of 0.0026 kWh will be stored in a lithium-ion battery with a capacity of 0.72 Ah. Alas, a very modest result.
Application of supercapacitors
Emergency lighting systems are where using supercapacitors instead of batteries makes a real difference. In fact, it is precisely this application that is characterized by uneven discharge. In addition, it is desirable that the emergency lamp is charged quickly and that the backup power source used in it has greater reliability. A supercapacitor-based backup power supply can be integrated directly into the T8 LED lamp. Such lamps are already produced by a number of Chinese companies.
Powered LED ground light
from solar panels, energy storage
in which it is carried out in a supercapacitor
As already noted, the development of supercapacitors is largely due to interest in alternative energy sources. But practical application is still limited to LED lamps that receive energy from the sun.
The use of supercapacitors to start electrical equipment is actively developing.
Supercapacitors are capable of delivering large amounts of energy in a short period of time. By powering electrical equipment at startup from a supercapacitor, peak loads on the electrical grid can be reduced and, ultimately, the inrush current margin can be reduced, achieving huge cost savings.
By combining several supercapacitors into a battery, we can achieve a capacity comparable to the batteries used in electric cars. But this battery will weigh several times more than the battery, which is unacceptable for vehicles. The problem can be solved by using graphene-based supercapacitors, but they currently only exist as prototypes. However, a promising version of the famous Yo-mobile, powered only by electricity, will use new generation supercapacitors, which are being developed by Russian scientists, as a power source.
Supercapacitors will also benefit the replacement of batteries in conventional gasoline or diesel vehicles - their use in such vehicles is already a reality.
In the meantime, the most successful of the implemented projects for the introduction of supercapacitors can be considered the new Russian-made trolleybuses that recently appeared on the streets of Moscow. When the supply of voltage to the contact network is interrupted or when the current collectors “fly off”, the trolleybus can travel at a low speed (about 15 km/h) for several hundred meters to a place where it will not interfere with traffic on the road. The source of energy for such maneuvers is a battery of supercapacitors.
In general, for now supercapacitors can displace batteries only in certain “niches”. But technology is rapidly developing, which allows us to expect that in the near future the scope of application of supercapacitors will expand significantly.
An ionistor is a capacitor whose plates are a double electrical layer between the electrode and the electrolyte. Another name for this device is supercapacitor, ultracapacitor, double-layer electrochemical capacitor or ionix. It has a large capacity, which allows it to be used as a current source.
Supercapacitor device
The principle of operation of an ionistor is similar to a conventional capacitor, but these devices differ in the materials used. Porous materials are used as linings in such elements - activated carbon, which is a good conductor, or foamed metals. This makes it possible to increase their area many times over and, since the capacitance of the capacitor is directly proportional to the area of the electrodes, it increases to the same extent. In addition, an electrolyte is used as a dielectric, as in electrolytic capacitors, which reduces the distance between the plates and increases the capacitance. The most common parameters are several farads at a voltage of 5-10V.
Types of ionistors
There are several types of such devices:
- With perfectly polarizable activated carbon electrodes. Electrochemical reactions do not occur in such elements. Aqueous solutions of sodium hydroxide (30% KOH), sulfuric acid (38% H2SO4) or organic electrolytes are used as an electrolyte;
- A perfectly polarizable activated carbon electrode is used as one plate. The second electrode is weakly or non-polarizable (anode or cathode, depending on the design);
- Pseudocapacitors. In these devices, reversible electrochemical reactions occur on the surface of the plates. They have a large capacity.
Advantages and disadvantages of ionistors
Such devices are used instead of batteries or accumulators. Compared to them, such elements have advantages and disadvantages.
Disadvantages of supercapacitors:
- low discharge current in common elements, and designs without this drawback are highly expensive;
- the voltage at the device output drops during discharge;
- in the event of a short circuit in high-capacity elements with low internal resistance, the contacts burn out;
- reduced permissible voltage and discharge rate compared to conventional capacitors;
- higher self-discharge current than in batteries.
Advantages of ultracapacitors:
- higher speed, charge and discharge current than in batteries;
- durability - when tested after 100,000 charge/discharge cycles, no deterioration in parameters was noted;
- high internal resistance in most designs, preventing self-discharge and failure during a short circuit;
- long service life;
- less volume and weight;
- bipolarity - the manufacturer marks “+” and “-“, but this is the polarity of the charge applied during production tests;
- wide range of operating temperatures and resistance to mechanical overloads.
Energy Density
The ability to store energy in supercapacitors is 8 times less than that of lead batteries, and 25 times less than that of lithium batteries. The energy density depends on the internal resistance: the lower it is, the higher the specific energy capacity of the device. Recent developments by scientists make it possible to create elements whose ability to store energy is comparable to lead batteries.
In 2008, an ionistor was created in India, in which the plates were made of graphene. The energy intensity of this element is 32 (Wh)/kg. For comparison, the energy capacity of car batteries is 30-40 (Wh)/kg. The accelerated charging of these devices allows them to be used in electric vehicles.
In 2011, Korean designers created a device in which, in addition to graphene, nitrogen was used. This element provided double the specific energy intensity.
Reference. Graphene is a layer of carbon, 1 atom thick.
Application of ionistors
The electrical properties of supercapacitors are used in various fields of technology.
Public transport
Electric buses, which use ionistors instead of batteries, are produced by Hyundai Motor, Trolza, Belkommunmash and some others.
These buses are structurally similar to trolleybuses without bars and do not require a contact network. They are recharged at stops while passengers are disembarking and boarding, or at the end points of the route in 5-10 minutes.
Trolleybuses equipped with ionistors are able to bypass broken contact lines and traffic jams and do not require wires in depots and parking lots at the end points of the route.
Electric cars
The main problem with electric vehicles is long charging times. An ultracapacitor with a high charging current and short charging time allows recharging during short stops.
In Russia, an Yo-mobile has been developed that uses a specially created ionistor as a battery.
In addition, installing a supercapacitor in parallel with the battery allows you to increase the current consumed by the electric motor during startup and acceleration. This system is used in KERS, in Formula 1 cars.
Consumer electronics
These devices are used in flashes and other devices in which the ability to quickly charge and discharge is more important than the size and weight of the device. For example, the cancer detector charges in 2.5 minutes and operates for 1 minute. This is enough to conduct research and prevent situations in which the device is inoperable due to discharged batteries.
In car stores you can purchase ionistors with a capacity of 1 farad for use in parallel with the car radio. They smooth out voltage fluctuations during engine starting.
DIY ionistor
If you wish, you can make a supercapacitor with your own hands. Such a device will have worse parameters and will not last long (until the electrolyte dries out), but will give an idea of the operation of such devices in general.
In order to make an ionistor with your own hands, you need:
- copper or aluminum foil;
- salt;
- activated carbon from a pharmacy;
- cotton wool;
- flexible wires for leads;
- plastic box for the case.
The manufacturing procedure for an ultracapacitor is as follows:
- cut two pieces of foil so large that they fit on the bottom of the box;
- solder the wires to the foil;
- moisten the coal with water, grind into powder and dry;
- prepare a 25% salt solution;
- mix coal powder with saline solution to a paste;
- moisten cotton wool with salt solution;
- apply the paste in a thin, even layer on the foil;
- make a “sandwich”: foil with charcoal up, a thin layer of cotton wool, foil with charcoal down;
- place the structure in the box.
The permissible voltage of such a device is 0.5 V. When it is exceeded, the electrolysis process begins, and the ionistor turns into a gas battery.
Interesting. If you assemble several such structures, the operating voltage will increase, but the capacity will drop.
Ionistors are promising electrical devices that, thanks to their high charge and discharge rates, can replace conventional batteries.
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