Which battery is better, lithium ion or lithium polymer? Lithium polymer batteries. Types and device. Advantages and disadvantages

Growing consumer interest in mobile gadgets and technologically advanced portable equipment in general, it forces manufacturers to improve their products in a variety of directions. At the same time, there is whole line general parameters, work on which is carried out in the same direction. These include the method of energy supply. Just a few years ago active participants market could observe the process of displacement by more advanced elements of nickel-metal hydride origin NiMH. Today, new generations of batteries are competing with each other. The widespread use of lithium-ion technology in some segments is being successfully replaced by the lithium-polymer battery. The difference from the ionic one in the new unit is not so noticeable for the average user, but in some aspects it is significant. At the same time, as in the case of competition between NiCd and NiMH elements, the replacement technology is far from flawless and in some respects is inferior to its analogue.

Li-ion battery device

The first models of serial lithium-based batteries began to appear in the early 1990s. However, cobalt and manganese were then used as the active electrolyte. In modern ones, it is not so much the substance that is important, but the configuration of its placement in the block. Such batteries consist of electrodes that are separated by a separator with pores. The mass of the separator, in turn, is impregnated with electrolyte. As for the electrodes, they are represented by a cathode base on aluminum foil and a copper anode. Inside the block they are connected to each other by current collector terminals. Charge maintenance is performed by the positive charge of the lithium ion. This material is advantageous in that it has the ability to easily penetrate the crystal lattices of other substances, forming chemical bonds. However, positive qualities Such batteries are increasingly proving to be insufficient for modern tasks, which led to the emergence of Li-pol cells, which have many features. In general, it is worth noting the similarity of lithium-ion power supplies with gel full-size batteries for cars. In both cases, the batteries are designed to be physically practical to use. In part, this direction of development was continued by polymer elements.

Lithium polymer battery design

The impetus for improving lithium batteries was the need to combat two shortcomings of existing Li-ion batteries. Firstly, they are unsafe to use, and secondly, they are quite expensive. Technologists decided to get rid of these disadvantages by changing the electrolyte. As a result, the impregnated porous separator was replaced by a polymer electrolyte. It should be noted that the polymer has previously been used for electrical needs as a plastic film that conducts current. In a modern battery, the thickness of the Li-pol element reaches 1 mm, which also removes restrictions on the use of various shapes and sizes from developers. But the main thing is that there is no liquid electrolyte, which eliminates the risk of ignition. Now it’s worth taking a closer look at the differences from lithium-ion cells.

What is the main difference from an ion battery?

The fundamental difference is the abandonment of helium and liquid electrolytes. For a more complete understanding of this difference, it is worth turning to modern models car batteries. The need to replace the liquid electrolyte was, again, due to safety interests. But if in the case of car batteries progress stopped at the same porous electrolytes with impregnation, then lithium models received a full-fledged solid base. What is so good about a solid-state lithium polymer battery? The difference from the ionic one is that the active substance in the form of a plate in the contact zone with lithium prevents the formation of dendrites during cycling. It is this factor that eliminates the possibility of explosions and fires of such batteries. This is only about the advantages, but there are also weak spots with new batteries.

Lithium polymer battery life

On average, such batteries can withstand about 800-900 charging cycles. This indicator is modest compared to modern analogues, but not even this factor can be considered as determining the resource of the element. The fact is that such batteries are subject to intensive aging, regardless of the nature of use. That is, even if the battery is not used at all, its life will be reduced. It does not matter whether it is a lithium-ion battery or a lithium-polymer cell. All lithium based power supplies are characterized by this process. A significant loss in volume can be noticed within a year after acquisition. After 2-3 years, some batteries completely fail. But a lot depends on the manufacturer, since within the segment there are also differences in the quality of the battery. Similar problems occur with NiMH cells, which are subject to aging due to sudden temperature fluctuations.

Flaws

In addition to problems with rapid obsolescence, such batteries need additional system protection. This is due to the fact that internal tension in different areas can lead to burnout. Therefore, a special stabilization circuit is used to prevent overheating and overcharging. This same system also entails other disadvantages. The main one is current limitation. But, on the other hand, additional protective circuits make the lithium polymer battery safer. There is also a difference from ionic in terms of cost. Polymer batteries are cheaper, but not by much. Their price tag also increases due to the introduction of electronic protection circuits.

Operational features of gel-like modifications

In order to increase electrical conductivity, technologists still add a gel-like electrolyte to polymer elements. There is no talk of a complete transition to such substances, since this contradicts the concept of this technology. But in portable technology, hybrid batteries are often used. Their peculiarity is sensitivity to temperature. Manufacturers recommend using these battery models in conditions ranging from 60 °C to 100 °C. This requirement also determined a special niche of application. Gel-type models can only be used in places with a hot climate, not to mention the need to be immersed in a heat-insulated case. Nevertheless, the question of which battery to choose - Li-pol or Li-ion - is not so pressing in enterprises. Where temperature has a particular influence, combined solutions are often used. In such cases, polymer elements are usually used as reserve elements.

Optimal charging method

The usual recharge time for lithium batteries is on average 3 hours. Moreover, during the charging process the unit remains cold. Filling occurs in two stages. At the first, the voltage reaches peak values, and this mode is maintained until it reaches 70%. The remaining 30% is gained under normal stress conditions. Another interesting question is how to charge a lithium-polymer battery, if necessary. constant mode maintain its full volume? In this case, you should follow the recharging schedule. It is recommended to carry out this procedure approximately every 500 hours of operation with a full discharge.

Precautionary measures

During operation, you should only use a charger that meets the characteristics, connecting it to a network with stable voltage. It is also necessary to check the condition of the connectors so that the battery does not open. It is important to consider that, despite the high degree of safety, this is still an overload-sensitive type of battery. The lithium-polymer element does not tolerate excessive current or excessive cooling external environment and mechanical shocks. However, according to all these indicators, polymer blocks are still more reliable than lithium-ion ones. Still, the main aspect of safety lies in the harmlessness of solid-state power supplies - of course, provided that they are kept sealed.

Which battery is better - Li-pol or Li-ion?

This issue is largely determined by operating conditions and target object energy supply. The main benefits of polymer devices are more likely to be felt by manufacturers themselves, who can more freely use new technologies. For the user, the difference will be barely noticeable. For example, in the question of how to charge a lithium polymer battery, the owner will have to pay more attention to the quality of the power supply. In terms of charging time, these are identical elements. As for durability, the situation in this parameter is also ambiguous. The aging effect characterizes polymer elements to a greater extent, but practice shows different examples. For example, there are reviews about lithium-ion cells that become unusable after just a year of use. And polymer ones in some devices are used for 6-7 years.

Conclusion

There are still many myths and false opinions around batteries that relate to various nuances of operation. On the contrary, some battery features are hushed up by manufacturers. As for the myths, one of them is refuted by the lithium polymer battery. The difference from the ionic analogue is that polymer models experience less internal stress. For this reason, charging sessions for batteries that have not yet run out have no effect harmful effects on the characteristics of the electrodes. If we talk about the facts hidden by manufacturers, then one of them concerns durability. As already mentioned, battery life is characterized not only by a modest rate of charging cycles, but also by the inevitable loss of the useful volume of the battery.

The most common types of batteries are lithium polymer and lithium ion. What are their features?

Facts about lithium polymer batteries

IN lithium polymer batteries a solid polymer electrolyte is used. In the very first samples of batteries of this type, created in the 70s, it was present mainly in a dry modification. This electrolyte did not actually conduct electric current, but it could exchange ions formed by lithium compounds. IN modern devices- laptops, mobile phones, gadgets - batteries are used that also contain a certain amount of electrolyte in the form of a gel.

Lithium polymer batteries are capable of providing high level electricity density based on its size and weight. They are characterized by a fairly low self-discharge, do not have the so-called memory effect - when a charged battery during use is sometimes discharged only to a level that corresponds to the moment the battery is charged (that is, not necessarily to zero), and can also operate over a wide range of temperatures.

However, lithium polymer batteries are not always safe - especially if they overheat or become too hot. long charging. Batteries of the type under consideration have about 800-900 operating cycles, at which the level of capacity loss does not exceed 20%. The battery loses the same 20% of performance after 2 years of operation, even if it is not used but is in storage.

Lithium-polymer batteries are often very small in size - it is theoretically possible to produce batteries with a thickness of about a millimeter. Application metal case not necessary in their design.

Facts about lithium-ion batteries

Design lithium ion battery consists of electrodes and separators, usually impregnated with liquid electrolyte. The first are represented by aluminum cathodes and copper anodes. Electric charge in batteries of this type is carried by a positively charged lithium ion, which has the ability to integrate into the crystal lattices of other substances and thus form new compounds. The cathodes in modern lithium-ion batteries are usually represented by compounds of lithium with cobalt, nickel, manganese, and iron phosphate.

Batteries of this type are characterized, like lithium-polymer products, by low self-discharge, but slightly exceed them in energy intensity. Lithium-ion batteries do not need to be charged and discharged periodically to maintain functionality.

Older models of lithium-ion batteries are considered unsafe to use, but those that include elements made from a lithium iron phosphate compound are considered quite reliable. Like lithium polymer devices, batteries of the type in question lose capacity over time - even if not used.

Comparison

The main difference between a lithium-polymer battery and a lithium-ion battery is the use of a predominantly dry electrolyte (with a small percentage of gel) in the structure of the former, while the latter, as a rule, uses a liquid electrolyte. This predetermines the possibility, first of all, not to use a metal shell in the design of lithium-polymer batteries and to produce a battery of small size and thickness. In lithium-ion batteries, in turn, it is necessary - otherwise the electrolyte will leak out. The importance of using a metal shell can make it difficult for manufacturers to reduce the size of their batteries.

Having determined what the difference is between lithium polymer and lithium-ion battery, we will reflect the conclusions in a small table.

Table

Lithium polymer batteries represent an improved design of the world famous lithium ion batteries. It is planned that these devices will soon completely displace nickel-metal hydride and nickel-cadmium devices from the market. batteries. Lithium polymer cells are increasingly used in a variety of electronic devices ah in the form of a power source. With the same weight, their energy capacity is several times higher than nickel-metal hydride and nickel-cadmium structures.

Potentially, lithium polymer cells will cost less than lithium-ion batteries. However, at the moment they are still quite expensive. At the moment, only a few large companies are engaged in their production. By design they are similar to lithium-ion cells, but they use a gel electrolyte. As a result, they are distinguished by a low discharge current, significant energy density and a significant number of charge and discharge cycles. Their shape can be very different, and they themselves stand out for their light weight and compactness.

Kinds

Currently, lithium-polymer batteries can be of several types, which differ in the structure of the electrolyte:

• Items having gel-like homogeneous electrolyte , which is created by introducing lithium salts into the composition of polymers.
• Items having dry polymer electrolyte . This type is produced on the basis of polyethylene oxide using a variety of lithium salts.
• Having polymer matrix electrolyte , having a microporous structure. It contains non-aqueous components of lithium salts.

Due to the fact that a liquid electrolyte is used in the polymer element, their operational safety is an order of magnitude higher. In addition, they can be manufactured in various shapes and configurations.

Some lithium polymer cells are made from a metallic polymer. However, at low temperatures, the parameters of such batteries are significantly reduced due to polymer crystallization.

There are developments of polymer batteries that use a metal anode. Some companies have managed to significantly expand the operating temperature range and current density. These types of batteries can be used in different household appliances and electronics.

At the same time, different manufacturers use different electrode materials, electrolyte structure and assembly technology. As a result, manufactured batteries may have completely different parameters. But all companies producing similar batteries, note that the stability of the functioning of lithium-polymer batteries is ensured by the homogeneity of the polymer electrolyte. This in turn depends on the number of components, as well as the polymerization temperature.

Battery options are already being produced with a thickness of only 1 millimeter. Thanks to this, manufacturers can produce very compact mobile devices.

Also, commercially available lithium polymer batteries are divided into:

• Regular.
• Fast-discharge.

Device

Lithium polymer batteries work on the principle of moving a number of polymer elements into semiconductor substances, provided that electrolyte ions are included in them. As a result, a significant increase in conductivity occurs. According to the design, these batteries are distinguished by their electrolytic composition.

The essence of polymer technology is that an electrolyte is applied to a plastic film. It does not allow the conduction of electricity, but allows the exchange of ions. In other words, the polymer electrolyte replaces the standard porous separator impregnated with liquid electrolyte. Thanks to the dry polymer design, it is possible to ensure a minimum cell thickness of about 1 mm, safety of use and ease of production. Thanks to this design, developers have the opportunity to implement such batteries in shoes, clothing, miniature equipment and other devices.

But a dry polymer battery has disadvantages in the form of reduced conductivity and internal resistance of polymers, which is unacceptable for a number of powerful mobile devices. To make a small polymer battery more advanced, a certain percentage of gel cells is added to the electrolyte. Most commercial batteries currently used in cell phones are polymer-gel hybrids. Hybrid batteries are currently the most popular.

Operating principle

Lithium polymer batteries operate on a principle similar to lithium-ion cells, meaning they operate on a reversible chemical reaction. Here, the anode is a carbon material into which lithium ions are introduced. Vanadium, manganese or cobalt oxides are used in the cathode. The operation of such a battery is based on the ability of polymers to transform into a semiconductor state due to the inclusion of electrolytic ions in them.

Lithium salts are still used as the chemical basis of the electrolyte. However, they are located in a corresponding polymer spacer, which is located between the cathode and anode. Thanks to this, lithium polymer batteries can be made in any free form. They can be placed in a variety of inaccessible locations, opening up new possibilities for electronics manufacturers.

Application

Lithium polymer batteries are increasingly used. Such batteries can significantly increase the operating time of the device with a reduced battery weight. Thanks to this, it is possible to obtain an energy carrier that will have several times greater capacity. Using fast-discharging batteries will provide even greater performance. Therefore, such batteries become an excellent option for radio-controlled models of airplanes and helicopters, including other radio-controlled devices.

Application Li-Pol batteries makes it possible to reduce the weight of the battery and increase the operating period of devices. Lithium polymer batteries have demonstrated excellent performance in helicopters. small size, for example, Piccolo. Such devices are capable of flying on such batteries for 30 minutes or more. The specified items are good option for small flying structures.

Typical lithium polymer batteries are used as power sources, which are required for electronic devices that consume relatively little current. These could be laptops, smartphones, and so on. Fast-discharging batteries are used in devices where high current consumption is required. Similar batteries are used in modern, portable electric tools and radio-controlled devices.

Limitations of use

These batteries will be widely used in the automotive industry in the future. Today they are used to create new technologies and test electric vehicles. At the same time, there are certain restrictions, which prevent the use of these batteries everywhere.

• Lithium polymer batteries require special regime charging. In principle, this is not difficult, but the usual cannot be used for this. This is due to the fact that they are a fire hazard during the period of overdischarge. To combat this phenomenon, all such batteries have an electronic system that prevents overdischarge and overheating.
• If the lithium polymer battery is not used correctly, it may cause a fire.
• The lithium polymer battery should not be used immediately after charging. First, it should be cooled to ambient temperature. Otherwise, the battery may be damaged.
• Short circuit is not allowed.
• Depressurization of the battery is not allowed.
• Battery discharge is below 3 volts.
• Do not heat above 60 degrees.
• Batteries should not be exposed to microwaves or pressure. This can lead to smoke, fire and more serious consequences.
• It is necessary to protect the battery from damage and shock. Strong mechanical stress can lead to damage to the internal structure.

However, these disadvantages do not prevent them from being used in a wide variety of areas. In the future, all these shortcomings will be leveled out by the introduction of new technologies and developments.

Benefits of Lithium Polymer Batteries

• Quite high energy density.
• Small self-discharge parameter.
• There is no memory effect.
• Lithium polymer batteries are slightly superior to their lithium counterparts in terms of battery capacity and duration of use.
• Manufacturing batteries only one millimeter thick.
• Applications in a fairly wide temperature range: from minus 20 to plus 40 degrees Celsius.
• Possibility of giving the battery different shapes.
• Slight voltage drop during discharge.

Technical progress is a machine that rolls without stopping! The fuel for this machine is more and more new problems of our modern world. Remember, not so long ago nickel-cadmium (NiCd) batteries were in use, they were replaced by nickel-metal hydride (NiMH). But today, lithium-ion (Li-ion) batteries are trying to take the place of lithium-ion (Li-pol) batteries. What is the difference between Li-pol and Li-ion? What are the advantages of lithium polymer over lithium ion batteries? Let's try to figure it out.

When we buy a phone or tablet, few people ask themselves the question - what kind of battery is inside? Only later, when faced with the problem of quickly discharging the gadget, do we begin to take a more detailed look at the “inside” of our device.

Lithium batteries became known in 1912, when the first experiments began, but they were not widely used. And only in the 70s, six decades later, these charging elements took their place in almost all household devices. Let us emphasize that for now we are talking only about batteries, not rechargeable batteries.

Lithium is the lightest metal, it also provides the highest energy density and has significant electrochemical potential. Batteries that are based on lithium metal electrodes have large capacity and high voltage. In the 80s, as a result of numerous studies, it turned out that the cyclic operation of lithium batteries (charge/discharge process) leads to the ignition of chargers, and after them, the gadgets themselves. So, in 1991, several thousand phones were recalled in Japan due to a fire hazard. Because of these dangerous properties of lithium, scientists have turned all their efforts to non-metallic lithium batteries based on lithium ions. And after some time more was created safe option charger, which was named lithium-ion (Li-ion).

Today, lithium-ion batteries are found in almost all mobile devices, it has a large number of varieties, has a lot of positive qualities, but also disadvantages, which we will talk about in more detail.

Advantages of lithium-ion batteries:

High energy density and, as a result, high capacity

Low self-discharge

High voltage single element. This simplifies the design - often the battery consists of only one element. Many manufacturers today use just such a single-cell battery in cell phones (remember Nokia)

Low cost of maintenance (operating costs)

No memory effect requiring periodic discharge cycles to restore capacity.

Flaws:

The battery requires a built-in protection circuit (which leads to additional increase its cost), which limits maximum voltage on each battery cell during charging and prevents the cell voltage from dropping too low during discharge

The battery is subject to aging, even if not used and just sitting on a shelf. The aging process is typical for most Li-ion batteries. For obvious reasons, manufacturers are silent about this problem. A slight decrease in capacity becomes noticeable after just a year, regardless of whether the battery has been in use or not. After two or three years it often becomes unusable

Higher cost compared to NiCd batteries.

Lithium-ion batteries are constantly being improved, technology is improving. And this battery would be good for everyone if it weren’t for the safety problems when using it and high price. All these reasons became the basis for the creation lithium polymer batteries (Li-pol or Li-polymer). The most obvious and most basic difference between Li-pol and Li-ion is the type of electrolyte used. The use of solid polymer electrolyte significantly reduces the cost of creating a battery and makes it safer, and also allows you to create thinner chargers. Why hasn't the lithium-polymer battery completely replaced its predecessor? One of possible versions, which is expressed by experts - investors who have invested large sums in the development and mass implementation Li-ion batteries are trying to return the investment.

Let's summarize. Generally speaking, a lithium polymer battery is a more advanced version of a lithium-ion battery. Judge for yourself:

Advantages of Li-pol and Li-ion batteries

To summarize, we can say that, thanks to modern technologies, we have two types of reliable external batteries. With the development of mobile technologies, with the advent of smartphones, tablets and many other digital gadgets, with the creation of energy-intensive applications, users are faced with the problem of a “dead battery”. Of course, both Li-ion and Li-Pol batteries immediately found their use in external chargers.

This is an excellent solution for modern life. The most important thing when choosing a powerbank- this is not to run into scammers (we wrote more about how to distinguish a fake from an original , but about how to use a store’s website to understand with 100% certainty that they will sell you a fake -

Progress is moving forward, and to replace the traditionally used NiCd (nickel-cadmium) and NiMh (nickel-metal hydride) we have the opportunity to use lithium batteries. With a comparable weight of one element, they have a higher capacity compared to NiCd and NiMH, in addition, their element voltage is three times higher - 3.6V/element instead of 1.2V. So for most models, a battery of two or three cells is sufficient.

Among lithium batteries, there are two main types - lithium-ion (Li-Ion) and lithium polymer (LiPo, Li-Po or Li-Pol). The difference between them is the type of electrolyte used. In the case of LiIon, this is a gel electrolyte; in the case of LiPo, it is a special polymer saturated with a lithium-containing solution. But for use in power plants of models, lithium-polymer batteries are most widely used, so in the future we will talk about them. However, the strict division here is very arbitrary, since both types differ mainly in the electrolyte used, and everything that will be said about lithium-polymer batteries almost fully applies to lithium-ion batteries (charge, discharge, operating features, safety precautions ). From a practical point of view, our only concern is that lithium polymer batteries are currently provide higher discharge currents. Therefore, in the model market as an energy source for power plants These are basically what they offer.

Main characteristics

Lithium-polymer batteries with the same weight exceed the energy intensity of NiCd by 4-5 times, NiMH by 3-4 times. The number of operating cycles is 500-600, with discharge currents of 2C until a loss of capacity of 20% (for comparison - for NiCd - 1000 cycles, for NiMH - 500). Generally speaking, there is still very little data on the number of operating cycles and to those given in in this case their characteristics must be viewed critically. In addition, their manufacturing technology is improving, and it is possible that at the moment the figures for this type of battery are already different. Just like all batteries, lithium batteries are subject to aging. After 2 years, the battery loses about 20% of its capacity.

Of the variety of power lithium-polymer batteries available for sale, two main groups can be distinguished - high-discharge (Hi discharge) and conventional. They differ from each other in the maximum discharge current - it is indicated either in amperes or in units of battery capacity, designated by the letter “C”. For example, if the discharge current is 3C and the battery capacity is 1 Ah, then the current will be 3 A.

The maximum discharge current of conventional batteries, as a rule, does not exceed 3C; some manufacturers indicate 5C. Fast-discharge batteries allow a discharge current of up to 8-10C. Such batteries are somewhat heavier than their low-current counterparts (by about 20%), and their names contain the letters HD or HC after the capacity numbers, for example KKM1500 - regular battery with a capacity of 1500 mAh, and the KKM1500HD is fast-discharging. I would like to immediately make a small note for those who like to experiment. Fast-discharge batteries are not used in household appliances. Therefore, if you are struck by the idea of ​​getting a battery on the cheap from cell phone or video cameras, then on good result It's hard to calculate here. Most likely, such a battery will die very quickly due to violation of the intended operating modes.

Applications and cost

The use of lithium-polymer batteries allows solving two important problems - increasing the operating time of the motor and reducing the weight of the battery.

When replacing an 8.4 V NiMH 650 mAh battery with two regular, non-fast-discharging lithium batteries with a capacity of 2 Ah, we get a battery with 3 times the capacity, 11 g lighter and with a slightly lower voltage (7.2 volts)! And if you use fast-discharging batteries, then large aircraft can fly without being inferior in power to an internal combustion engine. To confirm this, the 7th place in the F3A World Aerobatic Championship was taken by an American in an electric aircraft. Moreover, it was not a small buzzer, but a normal two-meter plane, like the other participants who had models with internal combustion engines!

Lithium polymer batteries have proven themselves very well in small helicopters such as Piccolo or Hummingbird - for example, even when using a standard brushed motor, the flight time on two 1 Ah banks is more than 25 minutes! And when replacing the motor with a brushless one - more than 45 minutes!

And, of course, lithium batteries are simply irreplaceable when we're talking about about indoor aircraft weighing 4-20 g. In this area, NiCd cannot compare with them - there are simply no batteries (for example, the weight of a 45 mAh can is 1 g, 150 mAh is 3.2 g) that would give required power- even for 1 minute!

The only area where lithium-polymer batteries are still inferior to Ni-Cd is the area of ​​super-high (40-50C) discharge currents. But progress is moving forward, and maybe in a couple of years we will hear about new successes in this area - after all, 2 years ago no one had heard of fast-discharge lithium batteries either...

Here, for example, are the main characteristics LiPo batteries Kokam:

In terms of price, in terms of capacity, lithium polymer batteries cost about the same as NiMH.

Manufacturers

Currently there are several manufacturing companies lithium polymer batteries. The leader in the number of batteries produced and one of the first in quality is Kokam. Also known are Thunder Power, I-Rate, E-Tec, and Tanic (presumably this is a second name for Thunder Power or is one of the Thunder Power sellers under its own name). You can view Kokam types on the website www.fmadirect.com, batteries from different manufacturers are offered on the website www.b-p-p.com and www.lightflightrc.com.

There is also Platinum Polymer, offered on the website www.batteriesamerica.com, presumably another name for I-Rate.

The range of battery capacities is very wide – from 50 to 3000 mAh. To obtain large containers use parallel connection batteries.

All batteries are flat in shape. As a rule, their thickness is more than 3 times less than the shortest side, and the conclusions are made on the short side in the form of flat plates.

I-Rate, as far as I know, does not yet make fast-discharge batteries, and their batteries have one feature: one of the electrodes is aluminum, and soldering it is problematic. This makes them uncomfortable when self-assembly batteries.

E-Tec batteries are something in between, they are not declared as fast-discharging, but their discharge current is higher than that of conventional ones - 5-7C.

The leaders in popularity are Kokam and Thunder Power, with Kokam mainly used in light and medium models, and Thunder Power in medium, large and giant (more than 10 kg!). Obviously, this is due to the price and the availability of powerful assemblies in the range - up to 30 volts and 8Ah capacity. Next come Tanic and E-tec, but there is little mention of I-rate. For some reason, Platinum Polymer is popular only in America, and it is used almost exclusively on slow slow flyers.

Charging Lithium Polymer Batteries

The batteries are charged according to a fairly simple algorithm - charge from a constant voltage source of 4.20 volts/cell with a current limit of 1C. The charge is considered complete when the current drops to 0.1-0.2C. After switching to voltage stabilization mode at a current of 1C, the battery gains approximately 70-80% of its capacity. It takes about 2 hours to fully charge. The charger is subject to fairly stringent requirements for the accuracy of maintaining voltage at the end of the charge - no worse than 0.01 V/cell.

Of the chargers presented on the market, the main types can be distinguished - simple, not “computer” chargers, in price category$10-40, intended only for lithium batteries, and universal ones - in the price category of $120-400, intended for various types of batteries, including LiPo and Li-Ion.

The first ones, as a rule, have only LED charge indication; the number of cans and the current in them are set by jumpers. The advantage of such chargers is low price. The main drawback is that some of them do not know how to correctly indicate the end of the charge. They show only the moment of transition from current stabilization mode to voltage stabilization mode, which is approximately 70-80% of the capacity. To complete the charge, you need to wait another 30-40 minutes.

The second group of chargers has much wider capabilities; as a rule, they all show the voltage, current and capacity (mAh) that the battery “accepted” during the charging process, which allows you to more accurately determine how charged the battery is.

When using a charger, the most important thing is to set it correctly on the charger required quantity cans in the battery and charging current. The charge current is usually 1C.

Operation and Precautions

It is safe to say that lithium-polymer batteries are the most “delicate” batteries in existence, that is, they require mandatory compliance with several simple, but mandatory rules, due to non-compliance with which, either a fire occurs or the battery “dies”.

We list them in descending order of danger:

1. Charge to a voltage greater than 4.20 volts/cell.
2. Battery short circuit.
3. Discharge with currents exceeding the load capacity or heating the battery above 60°C.
4. Discharge below 3.00 volts/cell.
5. Battery heating above 60°C.
6. Battery depressurization.
7. Storage in a discharged state.

Failure to comply with the first three points leads to a fire, all others - to complete or partial loss of capacity.

From all that has been said, the following conclusions can be drawn:

To avoid a fire, you must have a normal charger and correctly set the number of cans to be charged on it. It is also necessary to use connectors that exclude the possibility short circuit batteries (because of this, my friend burned the table on which the batteries were charging, and the curtain) and control the current consumed by the motor at “full throttle”. In addition, it is not recommended to cover the batteries on all sides from the air flow on the model, and if this is not possible, then special channels for cooling should be provided.

In cases where the current consumed by the engine is more than 2C, and the battery on the model is closed on all sides, after 5-6 minutes of running the motor, you should stop it, and then pull it out and touch the battery to see if it is too hot. The fact is that after heating above a certain temperature (about 70 degrees), a “chain reaction” begins to occur in the battery, turning the energy stored in it into heat, the battery literally spreads, setting fire to everything that can burn.

If you short-circuit an almost discharged battery, there will be no fire; it will die quietly and peacefully due to overdischarge... This leads to the second important rule: monitor the voltage at the end of the battery discharge and be sure to disconnect the battery after use!

Some speed controllers (Jeti is especially guilty of this) do not stop consuming current after turning off the standard switch. I don’t know what made the Czechs make such a strange decision. But the fact remains that almost all models of controllers for Jetti brushless motors (including the new “Advanced” series), which have a BEC, that is, a power supply stabilizer for the receiver and machines from the power supply, do not provide complete de-energization of the circuit with a standard switch. Only the receiver and servos are turned off, and the controller continues to consume a current of about 20 mA. This is especially dangerous, since you can’t see that the power is on, the cars are standing still, the motor is silent... And if you forget about the connected battery for a day or two, it turns out that you can say goodbye to it - it doesn’t like deep-discharge lithium.

Of course, you should remember that the engine controller must be able to work with lithium batteries, that is, have an adjustable engine shutdown voltage. And we must not forget to program the controller for the required number of cans. However, now a new generation of controllers has appeared that automatically determine the number of connected cans.

Depressurization is another reason for lithium batteries to fail, since air should not get inside the cell. This can happen if the outer protective pouch (the battery is sealed in a pouch like heat shrink tubing) is damaged, due to impact or damage from a sharp object, or severe overheating battery output when soldering. Conclusion - do not drop from a great height and solder carefully.

Based on the manufacturers' recommendations, batteries should be stored in a 50-70% charged state, preferably in a cool place, at temperatures no higher than 20°C. Storing in a discharged state negatively affects service life - like all batteries, lithium-polymer batteries have a small self-discharge.

Battery assembly

To obtain batteries with high current output or large capacity use parallel connection of batteries. If you buy a ready-made battery, then by the marking you can find out how many cans it contains and how they are connected. The letter P (parallel) after the number indicates the number of cans connected in parallel, and S (serial) - in series. For example, "Kokam 1500 3S2P" means a battery connected in series from 3 pairs of batteries, and each pair is formed by 2 batteries connected in parallel with a capacity of 1500 mAh, that is, the battery capacity will be 3000 mAh (when connected in parallel, the capacity increases), and the voltage – 3.7*3 = 11.1V..

If you buy batteries separately, then before connecting them into a battery you need to equalize their potentials. This is especially true for the parallel connection option, since in this case one bank will begin to charge the other, and charging current may exceed the value of 1C. It is advisable to discharge all purchased cans to 3 volts with a current of 0.1C - 0.2C before connecting. Voltage needs to be controlled digital voltmeter with an accuracy of at least 0.5%. This will ensure reliable battery performance in the future.

It is also advisable to perform potential equalization (balancing) even on already assembled branded batteries before their first charge, since many companies that assemble cells into a battery do not balance them before assembly.

Due to the decrease in capacity as a result of operation, in no case should you add new banks in series with the old ones - the battery will be unbalanced.

Of course, you also cannot combine batteries of different, even similar capacities into a battery - for example, 1800 and 2000 mAh, and also use batteries from different manufacturers in one battery, since different internal resistance will lead to unbalance of the battery. When soldering, you must be careful; you must not allow the terminals to overheat, as this can break the seal and permanently kill the battery that has not yet had time to fly. Some types of Kokam batteries come with pieces of the circuit board already soldered to the terminals for easy wiring. This adds extra weight - about 1g per element, but it takes much longer to heat the places for soldering wires - fiberglass does not conduct heat well. The wires with connectors should be secured to the battery case, at least with tape, so as not to accidentally tear off the terminal at the root.

Application nuances

So, let us emphasize once again the most important points associated with the use of lithium polymer batteries.

• Use a normal charger.
• Use connectors that prevent short-circuiting the battery.
• Do not exceed permissible discharge currents.
• Monitor the battery temperature when there is no cooling.
• Do not discharge the battery below a voltage of 3 V/cell (remember to disconnect the battery after the flight!).
• Do not subject the battery to shock.

Let's give a few more useful examples, arising from what was said earlier, but not obvious at first glance.

When using commutator motors, it is necessary to avoid situations where the motor is stopped (for example, the model is lying on the ground) and the transmitter is given full throttle. The current is too high, and we risk exploding the battery (if the motor or regulator does not burn out first). This issue has been discussed numerous times in the RC Groups forums. Most regulators for brushed motors turn off the motor when the signal from the transmitter is lost, and if your regulator can do this, I would advise turning off the transmitter if the model fell, for example, into the grass far from you - there is less risk of touching the dangling throttle when searching for a model on the transmitter belt and not notice it.

Over the course of a long battery life, its elements, due to the initial small dispersion of capacities, become unbalanced - some banks “age” earlier than others and lose their capacity faster. With a larger number of cans in the battery, the process goes faster.

This leads to the following rule - sometimes it is necessary to control the capacity of each battery element separately. To do this, you can measure its voltage at the end of the charge. How often? It is still difficult to establish exactly this - too little operating experience has been accumulated. As a rule, it is recommended that approximately 40-50 cycles after the start of operation, every 10-20 cycles, check the voltage of the battery cells during charging to identify “bad cells”.

It is not recommended to “zero” the battery by driving the motor until it stops rotating altogether. Such treatment will not harm a new battery, but for a slightly unbalanced one it will unnecessary risk discharge the “badest bank” below 3 volts, which will cause it to lose capacity even more.

When the capacities differ by more than 20%, such a battery cannot be charged entirely without special measures!

To automatically balance battery cells when charging, so-called balancers are used. This small fee, connected to each bank, containing load resistors, a control circuit and an LED indicating that the voltage on this bank has reached the level of 4.17 - 4.19 volts. When the voltage on an individual element exceeds the threshold of 4.17 volts, the balancer closes part of the current “to itself,” preventing the voltage from exceeding the critical threshold. By the simultaneous lighting of the LEDs, you can see which banks have a lower capacity - the LED on their balancer will light up first. Balancers have one important additional requirement: the current they consume from the battery in “standby” mode must be small, usually 5-10 µA.

It should be added that the balancer does not prevent the overdischarge of some cells in an unbalanced battery; it only serves to protect against damage to the cells during charging and as a means of indicating “bad” cells in the battery. The above applies to batteries made up of 3 or more elements; balancers, as a rule, are not used for 2-can batteries.

There is an opinion that lithium polymer batteries should not be used at negative temperatures. Indeed, the technical specifications for the batteries indicate an operating range of 0-50 °C (at 0 °C 80% of the capacity is retained). But nevertheless, you can fly them at temperatures around –10...-15 °C. The point is that you don’t need to freeze the battery before the flight - put it in your pocket where it’s warm. And during flight, the internal heat generation in the battery is at the moment useful property, preventing the battery from freezing. Of course, the battery performance will be slightly lower than at normal temperatures.

Conclusion

Considering the pace at which technical progress in the field of electrochemistry is moving, it can be assumed that the future belongs to lithium-polymer batteries - if fuel cells do not catch up with them. As demand for batteries increases and production volume increases, the price will inevitably fall, and then lithium will finally become as common as NiMH. In the West, this time has already arrived for six months, at least in America. The popularity of electric aircraft with lithium-polymer batteries is growing. I would like to hope that brushless motors and controllers for them will also become cheaper, but in this area the progress of price reductions is moving less rapidly. After all, just two years ago the question was asked on the forum: “Does anyone really fly a brushless?” And there was no mention of lithium batteries at all then...

In general, we'll wait and see.