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 it is not typical, in fact, they have it too, 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 are 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 different types 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

The 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 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. Construction of a voltage converter to connect the load and charger are 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. In case you are working with regular battery with a voltage of 12 V, then the control electronics must 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 difficulty in building a converter and stabilizer that can explain the fact that supercapacitors, serial production which was started back in the 70s of the 20th century, have only now begun to be widely used in a variety of fields.

Schematic diagram source 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 you accept it output voltage independent of the degree of discharge and equal to 3.6 V, then the amount of energy 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 source can be integrated directly into LED lamp T8. 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 use so far 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 power 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.

A supercapacitor or ionistor is a device for storing energy masses; charge accumulation occurs at the boundary between the electrode and the electrolyte. The useful energy volume is stored as a static type charge. The cumulative process comes down to interaction with constant voltage, when the ionistor receives a potential difference across its plates. Technological implementation, as well as the very idea of ​​​​creating such devices, appeared relatively recently, but they managed to receive experimental use to solve a certain number of problems. The part can replace current sources of chemical origin, being a backup or the main means of power supply in watches, calculators, and various microcircuits.

The elementary design of a capacitor consists of a plate, the material for which is foil, delimited by a dry separating substance. The ionistor consists of a number of capacitors with an electrochemical type charger. Special electrolytes are used for its production. Coverings can be of several varieties. Activated carbon is used for the manufacture of large-scale linings. Metal oxides and polymer materials with high conductivity can also be used. To achieve the required capacitive density, it is recommended to use highly porous carbon materials. In addition, this approach allows you to make an ionistor at an impressively low cost. Such parts belong to the category of DLC capacitors, which accumulate charge in a double compartment formed on the plate.

The design solution, when the ionistor is combined with a water electrolyte base, is characterized by low resistance of the internal elements, while the charge voltage is limited to 1 V. The use of organic conductors guarantees voltage levels of about 2...3 V and increased resistance.

Electronic circuits operate with higher energy demands. The solution to this problem is to increase the number of power points used. The ionistor is installed not just one, but in an amount of 3-4 pieces, giving the required amount of charge.

Compared to a nickel-metal hydride battery, the ionistor is capable of containing a tenth of the energy reserve, while its voltage drops linearly, excluding zones of planar discharge. These factors affect the ability to fully retain charge in the ionistor. The charge level directly depends on the technological purpose of the element.

Quite often, an ionistor is used to power memory chips and is included in filter circuits and smoothing filters. They can also be combined with batteries of various types to combat the consequences of sudden surges in current: when a low current is supplied, the ionistor is recharged, otherwise it releases part of the energy, thereby reducing the overall load.

The hype surrounding Elon Musk's construction of a "Battery Gigafactory" for production lithium ion batteries had not yet subsided 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. Note main advantages of graphene supercapacitorsV.

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. Huge territories and capital investments, masses of workers, toxic and dangerous substances used in technological process lithium-ion batteries are in stark contrast to 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. The disc is then inserted into a regular DVD drive and burned with a laser 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 new technology, this does not mean that she will come to us in a year or two. The world of capital cannot avoid financial shocks, but it has been quite successful in avoiding technological ones. IN similar cases Behind-the-scenes agreements between large investors and political players begin to work. 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 solve complex design problems with their help. different 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 allowed us to achieve more high density 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 It 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 charge. batteries.

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 capacitors large capacity, 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 density electric current equal to 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, crystal cell which has a monatomic thickness, among other things, was 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 were able to achieve is comparable to 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 in factory workshops and even on outdoors"says James Tur.

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.

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

The 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 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 power 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 electrical capacity of the globe, as is known from physics courses, is approximately 700 μF. An ordinary capacitor of this capacity can be compared in weight and volume to a brick. But there are also capacitors with the electrical capacity of the globe, equal in size to a grain of sand - supercapacitors.

Such devices appeared relatively recently, about twenty years ago. They are called differently: ionistors, ionixes or simply supercapacitors.

Don't think that they are only available to some high-flying aerospace firms. Today you can buy in a store an ionistor the size of a coin and a capacity of one farad, which is 1500 times more than the capacity of the globe and close to the capacity of the largest planet in the solar system - Jupiter.

Any capacitor stores energy. To understand how large or small the energy stored in the supercapacitor is, it is important to compare it with something. Here is a somewhat unusual, but clear way.

The energy of an ordinary capacitor is enough for it to jump about a meter and a half. A tiny supercapacitor of type 58-9V, having a mass of 0.5 g, charged with a voltage of 1 V, could jump to a height of 293 m!

Sometimes they think that ionistors can replace any battery. Journalists depicted a future world with silent electric vehicles powered by supercapacitors. But this is still a long way off. An ionistor weighing one kg is capable of accumulating 3000 J of energy, and the worst lead-acid battery is 86,400 J - 28 times more. However, when delivering high power in a short time, the battery quickly deteriorates and is only discharged by half. The ionistor repeatedly and without any harm to itself delivers any power, as long as the connecting wires can withstand it. In addition, the supercapacitor can be charged in a matter of seconds, while the battery usually needs hours to do this.

This determines the scope of application of the ionistor. It is good as a power source for devices that consume a lot of power for a short time, but quite often: electronic equipment, flashlights, car starters, electric jackhammers. The ionistor can also have military applications as a power source for electromagnetic weapons. And in combination with a small power station, an ionistor makes it possible to create cars with electric wheel drive and fuel consumption of 1-2 liters per 100 km.

Ionistors for a wide range of capacities and operating voltages are available for sale, but they are quite expensive. So if you have time and interest, you can try to make an ionistor yourself. But before giving specific advice, a little theory.

It is known from electrochemistry: when a metal is immersed in water, a so-called double electrical layer is formed on its surface, consisting of opposite electric charges- ions and electrons. Mutual attractive forces act between them, but the charges cannot approach each other. This is hampered by the attractive forces of water and metal molecules. At its core, an electrical double layer is nothing more than a capacitor. The charges concentrated on its surface act as plates. The distance between them is very small. And, as you know, the capacitance of a capacitor increases as the distance between its plates decreases. Therefore, for example, the capacity of an ordinary steel spoke immersed in water reaches several mF.

Essentially, an ionistor consists of two electrodes with a very large area immersed in an electrolyte, on the surface of which a double electrical layer is formed under the influence of an applied voltage. True, using ordinary flat plates, it would be possible to obtain a capacitance of only a few tens of mF. To obtain the large capacitances characteristic of ionistors, they use electrodes made of porous materials that have a large pore surface with small external dimensions.

Sponge metals from titanium to platinum were once tried for this role. However, the incomparably better one was... ordinary activated carbon. This is charcoal, which after special treatment becomes porous. The surface area of ​​the pores of 1 cm3 of such coal reaches a thousand square meters, and the capacity of the double electrical layer on them is ten farads!

Homemade ionistor Figure 1 shows the design of an ionistor. It consists of two metal plates pressed tightly against a “filling” of activated carbon. Coal is laid in two layers, between which there is a thin separating layer of a substance that does not conduct electrons. All this is impregnated with electrolyte.

When charging the ionistor, a double electric layer with electrons on the surface is formed in one half of the carbon pores, and in the other half with positive ions. After charging, ions and electrons begin to flow towards each other. When they meet, neutral metal atoms are formed, and the accumulated charge decreases and over time may disappear altogether.

To prevent this, a separating layer is introduced between the layers of activated carbon. It can consist of various thin plastic films, paper and even cotton wool.
In amateur ionistors, the electrolyte is a 25% solution of table salt or a 27% solution of KOH. (At lower concentrations, a layer of negative ions will not form on the positive electrode.)

Copper plates with wires pre-soldered to them are used as electrodes. Their working surfaces should be cleaned of oxides. In this case, it is advisable to use coarse sandpaper that leaves scratches. These scratches will improve the adhesion of the coal to the copper. For good adhesion, the plates must be degreased. Degreasing of the plates is carried out in two stages. First, they are washed with soap, and then rubbed with tooth powder and washed off with a stream of water. After this, you should not touch them with your fingers.

Activated carbon, purchased at a pharmacy, is ground in a mortar and mixed with electrolyte to obtain a thick paste, which is spread on thoroughly degreased plates.

During the first test, the plates with a paper gasket are placed one on top of the other, after which we will try to charge it. But there is a subtlety here. When the voltage is more than 1 V, the release of gases H2 and O2 begins. They destroy carbon electrodes and do not allow our device to operate in capacitor-ionistor mode.

Therefore, we must charge it from a source with a voltage no higher than 1 V. (This is the voltage for each pair of plates that is recommended for the operation of industrial ionistors.)

Details for the curious

At a voltage of more than 1.2 V, the ionistor turns into a gas battery. This is an interesting device, also consisting of activated carbon and two electrodes. But structurally it is designed differently (see Fig. 2). Typically, take two carbon rods from an old galvanic cell and tie gauze bags of activated carbon around them. KOH solution is used as an electrolyte. (A solution of table salt should not be used, since its decomposition releases chlorine.)

The energy intensity of a gas battery reaches 36,000 J/kg, or 10 Wh/kg. This is 10 times more than an ionistor, but 2.5 times less than a conventional lead battery. However, a gas battery is not just a battery, but a very unique fuel cell. When charging it, gases are released on the electrodes - oxygen and hydrogen. They “settle” on the surface of the activated carbon. When a load current appears, they are connected to form water and electric current. This process, however, goes very slowly without a catalyst. And, as it turned out, only platinum can be a catalyst... Therefore, unlike an ionistor, a gas battery cannot produce high currents.

However, Moscow inventor A.G. Presnyakov (http://chemfiles.narod.r u/hit/gas_akk.htm) successfully used a gas battery to start a truck engine. His considerable weight - almost three times more than usual - in this case turned out to be tolerable. But the low cost and the absence of harmful materials such as acid and lead seemed extremely attractive.

A gas battery of the simplest design turned out to be prone to complete self-discharge in 4-6 hours. This put an end to the experiments. Who needs a car that cannot be started after being parked overnight?

And yet, “big technology” has not forgotten about gas batteries. Powerful, lightweight and reliable, they are found on some satellites. The process in them takes place under a pressure of about 100 atm, and sponge nickel is used as a gas absorber, which under such conditions acts as a catalyst. The entire device is housed in an ultra-light carbon fiber cylinder. The resulting batteries have an energy capacity almost 4 times higher than that of lead batteries. An electric car could travel about 600 km on them. But, unfortunately, they are still very expensive.