The lithium polymer battery is an improved version of the traditional lithium-ion battery. Its main difference is the use of a special polymer material, in which gel-like lithium-conducting inclusions are used as filling. This type of battery is used in many models of mobile devices, phones, digital devices, radio-controlled cars, and so on.

A traditional lithium polymer battery for household use cannot supply too much current. However, today there are special power varieties of such devices that can deliver a current that is many times greater than its capacity in ampere-hours.

Lithium polymer battery design

The difference between lithium polymer and lithium ion energy storage is the type of electrolyte used. Polymer batteries use a special polymer with a lithium-containing solution, while ion batteries use a regular gel electrolyte. The power systems of most modern models use a lithium polymer battery. This is due to the fact that it provides more powerful discharge currents. However, there is no too strict division between these types of batteries, since they differ only in the nature of the electrolyte. This applies to charging and discharging features, operating rules and safety precautions.

Main characteristics

A modern lithium-polymer battery with the same mass is significantly more energy-intensive than nickel-cadmium (NiCd) and nickel-metal hydride (NiMH) batteries. They have a number of operating cycles of approximately 500-600. Let us recall that for NiCd it is 1000 cycles, and for NiMH it is about 500. Like lithium-ion, polymer carriers also age over time. Therefore, after 2 years, such a battery will lose up to 20% of its capacity.

Types of power lithium polymer batteries

Today there are two main types of such batteries - standard and fast-discharge. They differ in the level of maximum discharge current. This indicator is indicated either in units of battery capacity or in amperes. In most cases, the maximum level of discharge current does not exceed 3C. However, some models can produce a current of 5C. In fast-discharge devices, a discharge current of up to 8-10C is allowed. However, fast-discharge models are not used for household appliances.

Features of application

The use of a lithium-polymer battery can significantly increase the operating time of the electric motor while reducing the weight of the battery itself. Therefore, if you replace a regular NiMH 650 mAh battery with two regular lithium-polymer batteries, you can get 3 times more energy-capacious energy. Moreover, such a battery will be more than 10 g lighter. If you take fast-discharging batteries, then you can achieve even higher performance. Such a system will be an excellent option not only for small models of airplanes or helicopters, but also for impressive radio-controlled devices.

Lithium polymer batteries, unlike lithium-ion batteries, have performed well in small helicopters such as the Hummingbird and Piccolo. Similar models with conventional commutator motors can fly on two polymer batteries for half an hour. When using a brushless motor, this time increases to 50 minutes. This type of battery is considered an ideal option for light-weight indoor aircraft. Their efficiency in this case is determined by their much lighter weight compared to NiCd batteries.

The only area in which a lithium-polymer battery is inferior to NiCd is its use in devices with ultra-high discharge currents of up to 50 C. However, it is quite possible that in a few years more powerful batteries of this type will appear. At the same time, prices for lithium-polymer, lithium-ion and NiCd batteries are approximately the same for the same mass of devices.

Features of operation

The operating rules for lithium-polymer and lithium-ion batteries are largely similar. When using a polymer battery, you must avoid certain dangerous situations that can cause irreparable harm to it:

• charging the device with a voltage of 4.2 volts per jar;
• discharge with currents with a load capacity exceeding the proper one;
• discharge with a voltage below 3 volts per cell;
• battery depressurization;
• heating the device above 60 degrees;
• long-term storage in a completely discharged state.

Lithium polymer and lithium ion batteries have a fire hazard when overheated and overdischarged. To combat this phenomenon, all modern batteries are equipped with a built-in electronic system that prevents overdischarge or overheating. This is why a lithium polymer battery requires special charging algorithms.

Charger

The process of charging lithium-polymer batteries is practically no different from charging lithium-ion batteries. Charging of most lithium-polymer batteries with a starting charging current of 1C is achieved in approximately 3 hours. To achieve a full charge, it is necessary to have the battery voltage corresponding to the upper threshold. In addition, a necessary condition is to reduce the charge current to 3% of the nominal value. Moreover, during such charging, such a battery always remains cold. If you want to keep the battery constantly charged, then it is advisable to recharge approximately once every 500 hours, which corresponds to 20 days. As a rule, charging is usually carried out when the voltage at the battery terminals drops to 4.05V. Charging is stopped after the voltage at the terminals reaches 4.2V.

Charge temperature

Most lithium-polymer batteries can be charged at a temperature of 5-45 degrees at a current of 1C. If the temperature is in the range from 0 to 5 degrees, then it is recommended to switch to a current of 0.1C. Charging at sub-zero temperatures is completely prohibited in this case. Traditionally, it is believed that the most favorable conditions for charging are 15-25 degrees. Since all charging processes in lithium-polymer and lithium-ion batteries are almost identical, the same chargers can be used for them.

Discharge conditions

Traditionally, this type of battery discharges at a voltage of 3.0V per battery. However, some types of devices must be discharged at a minimum threshold of 2.5V. Manufacturers of mobile devices provide a switch-off threshold of 3.0V, which will be suitable for any type of battery. That is, as the battery discharges while the mobile device is turned on, the voltage gradually drops and, when it reaches 3.0V, the device automatically warns you and turns off. However, the device still continues to consume some energy from the battery. This is required to detect when the power button is pressed or for other similar functions. Also, the energy here can be used for its own protection and control circuit. Moreover, a low level of self-discharge still remains characteristic of lithium-polymer carriers. Therefore, if you leave such batteries for a long time, the voltage in them may drop below 2.5V, which is very harmful. All internal protection and control systems may be disabled. As a result, such batteries can no longer be charged with conventional chargers. In addition, complete discharge is very harmful to the internal structure of the battery. Therefore, a completely discharged battery must be charged at the first stage with a minimum current of 0.1C.

Temperature during discharge

The lithium polymer battery performs best at room temperature. If you use your device in hotter environments, battery life may be significantly reduced. As for the lithium-ion battery, this battery works best at high temperatures. Initially, it prevents the internal resistance of the battery from increasing, which is considered a result of aging. However, subsequently the energy output is reduced and an increase in temperature accelerates the aging process due to an increase in internal resistance.

The lithium polymer battery has slightly different operating conditions, since it has a dry and solid electrolyte. The ideal temperature for its operation is 60-100 degrees. Therefore, such an energy carrier has become an ideal option for backup power sources in regions with hot climates. They are specially placed in a heat-insulating housing with built-in heating elements powered from an external network.

• The lithium polymer battery has superior capacity and durability to the lithium-ion battery.
• Ease of use in field conditions when there is no way to control the temperature.
• High energy density per unit weight and volume.
• Low self-discharge.
• Thin elements no more than 1 mm.
• Flexibility of form.
• No memory effect.
• Wide operating temperature range from −20 to +40 °C.
• Insignificant voltage drop during discharge.

Disadvantages of lithium polymer batteries:

• Low efficiency at temperatures of -20 degrees and below.
• High price.

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, which are based on lithium metal electrodes, have a 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, a safer version of the charger was created, which was called lithium-ion (Li-ion).

Today, the lithium-ion battery is 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 of a 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 further increases its cost) that limits the maximum voltage across each battery cell during charging and prevents the cell voltage from dropping too low when discharging

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 were not for the safety problems associated with its use and the 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 the possible versions expressed by experts is that investors who have invested large sums in the development and mass introduction of 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 technology, 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 is not to run into scammers (we wrote more about how to distinguish a fake from an original , but about how to understand with 100% certainty from a store’s website 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 currently provide higher discharge currents. Therefore, on the model market they are mainly offered as a source of energy for power plants.

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 their characteristics given in this case must be taken 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 is a regular battery with a capacity of 1500 mAh, and KKM1500HD is a fast-discharge battery. 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 get the idea of ​​getting a battery from a cell phone or video camera on the cheap, it’s difficult to count on a good result. 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 it comes to indoor aircraft weighing 4-20 g. In this area, NiCd cannot compare with them - there are simply no such batteries (for example, a 45 mAh can weighs 1 g, 150 mAh - 3.2 d), which with such a small weight would provide the necessary 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 of Kokam LiPo batteries:

Name	Capacity, mAh	Dimensions, mm	Weight, g	Maximum current
Kokam 145	145	27.5x20.4x4.3	3.5	0.7A, 5C
Kokam 340SHC	340	52x33x2.8	9	7A, 20C
Kokam 1020	1020	61x33x5.5	20.5	3A, 3C
Kokam 1500HC	1500	76x40x6.5	35	12A, 8C
Kokam 1575	1575	74x41x5.5	32	7A, 5C

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

Manufacturers

Currently, there are several manufacturers of 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 capacities, parallel connection of batteries is used.

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 inconvenient to assemble the battery yourself.

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 on the market, we can distinguish the main types - simple, non-“computer” chargers, in the price category of $10-40, intended only for lithium batteries, and universal ones - in the price category of $120-400, intended for various types of batteries, including for 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 their 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 correctly set the required number of cans in the battery and the charging current on the charger. 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 voltage 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 eliminate the possibility of short-circuiting the battery (because of this, my friend had a table on which batteries were charged and a curtain burned) and to 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 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 package is damaged (the battery is sealed in a package like heat-shrink tubing), as a result of impact or damage with a sharp object, or if the battery terminal is overheated during 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 high capacity, parallel connection of batteries is used. 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 the charging current may exceed 1C. It is advisable to discharge all purchased cans to 3 volts with a current of 0.1C - 0.2C before connecting. The voltage must be monitored with a 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 related to 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 us give a few more useful examples that follow from what was said earlier, but are 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, this is an extra risk of discharging the “badest bank” below 3 volts, due to which it will 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 is a small board connected to each bank, containing load resistors, a control circuit and an LED indicating that the voltage on that 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 cannot be used at subzero 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 turns out to be a useful property at the moment, 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.

Portable chargers have become an integral element of modern everyday life. The quality of batteries is the main condition for their performance, efficiency and safety. Manufacturers of chargers use two types of batteries in their designs - lithium-ion and lithium-polymer. For the average consumer, unfamiliar with the features of different types, it often becomes a problem to choose one or another type of battery.

What is the difference between these varieties, which one would be more correct to choose - all these questions require detailed knowledge about each type. In this article we will reveal the features of lithium-ion and lithium-polymer batteries, introduce them to their technical properties, charging methods, and service life.

Differences between lithium-ion and lithium-polymer batteries

Battery models produced using different technologies perform the same energy supply function. The design features of each type affect the reported power, service life, and degree of explosion protection. It cannot be stated unequivocally that the more modern

The battery type is better than the outdated one. There are practical advantages and disadvantages to both technologies. The Li-pol and Li-ion models have similar operating schemes, but differ in configuration and technical parameters.

To understand which is better - Li-polymer or Li-ion, let's take a closer look at each type separately. You should compare battery types and make a choice in favor of one type or another based on the following indicators:

• price;
• weight to capacity ratio;
• safety;
• intended use in a device for a specific purpose;
• temperature operating conditions.

When choosing one of the two types, consider the scope of application and financial capabilities.

Lithium-ion batteries: features and specifications

Initially, lithium-based models were produced using manganese and cobalt as the main element (active electrolyte). Modern lithium-ion batteries have undergone design changes. Their productivity depends not on the substance used, but on the order in which the elements are placed in the block. The components of a modern Li-Ion battery are electrodes and a separator. Materials – aluminum and copper (copper anodes and aluminum foil as a cathode base).

Special current collector terminals provide internal connection between the anode and cathode, and the electrolyte impregnation of the separator mass creates a favorable environment for charge maintenance. The positive charges of lithium ions trigger chemical reactions, form bonds, and provide energy output. The principle of operation of a lithium-ion based power supply is reminiscent of the operation of a full-size gel battery.

Lithium polymer batteries

Since lithium-ion models cannot cope with many modern tasks, they are gradually being replaced by polymer elements. Li-ion batteries did not have a high level of safety and were quite expensive. To eliminate these shortcomings and operational problems, and make the batteries more efficient, the developers decided to change the electrolyte. Instead of impregnating the porous separator, polymer electrolytes were used in the battery design.

The lithium polymer cell has a thickness of 1 mm, which allows the battery to be compact in size. Replacing liquid electrolytes with polymer films eliminated the high risk of battery ignition and made it safe. The comparison table below will help you clearly determine how Li-ion differs from Li-Pol.

Specifications	Li-ion	Li-Pol
Energy intensity		low, the number of charge and discharge cycles is less
Standard size	small selection	high choice, independence from standard cell format
	slightly heavier
		almost twice as high for the same size
Life time	approximately the same	approximately the same
Risk of explosion and fire	taller	built-in protection against electrolyte leakage and overcharging
Charging time
	up to 0.1% monthly	less active

The design of polymer lithium battery devices completely eliminates the presence of electrolyte in the form of liquid or gel. You can clearly imagine the difference in technology when considering the operating principle of modern automotive power supply devices. Safety concerns have led to the exclusion of liquid electrolytes from everyday practice. But until recently, impregnated porous structures were used in car batteries.

The introduction of polymer-lithium elements presupposed a solid-state basis. A characteristic difference from lithium-ion batteries is the process of contact action of the active substance plate with lithium and the prevention of the formation of dendrites during cycling. It is this feature that protects the battery cells from fire or explosion.

Life time

Both lithium-ion and lithium-polymer batteries are subject to intensive aging. They provide about nine hundred full charge cycles before they become unusable. It does not matter how active the device was used. If the battery has not been used at all for a long time, a reduction in service life will nevertheless occur.

After just a year, the capacity becomes significantly reduced in service life, and after two or three years it can be stated that the battery has completely failed. This is a common drawback of lithium batteries, and you should choose a more durable model only depending on the reputation of the manufacturer and reviews of specific models.

Additional protection

If we consider the question of what is the difference between Li-ion and Li-Pol batteries, it is worth paying attention to the built-in protective systems. Lithium polymer models require additional internal protection features. They are characterized by cases of burnout due to overheating of the elements. Such consequences are caused by the internal stress of various work areas.

In order to protect the device from unauthorized overcharging, overheating of parts and burnout, the design uses a special stabilizing system and a current limiting mechanism. This increases the safety of lithium-polymer models, but significantly increases the cost of the battery due to the use of protective elements.

Part of the design involves electrolytic components in the gel formation. Composite batteries are used in many portable devices. They are extremely sensitive to temperature changes and require strict adherence to operating rules. The polymer-based battery can be used in devices with heating in the range of 60-100 degrees.

Manufacturers enclose the internal part in a housing with heat-insulating properties - it is convenient to use such batteries in hot climates. In conditions where the temperature regime does not meet operating requirements, elements with a polymer component are used as backup.

Features of battery charging

The lithium polymer battery will require at least three hours of charging to recharge. In this case, the block does not heat up. There are two stages of filling. The first occurs until peak mode is established, which is maintained until charging reaches 70%. Under normal voltage conditions, a residual charge of 30% is accumulated. Recharging must be performed according to a strict schedule, waiting for complete discharge and carrying out the procedure every 500 hours of use of the device. This mode maintains a constant filling volume.

The battery must only be connected to a stable power supply, without voltage surges or interference. Only use appropriate chargers that match the characteristics stated in the description. An important point: during the charging process, all connectors must be connected correctly; disconnection must not be allowed. Li-Pol elements are extremely sensitive to all kinds of overloads, excessive current levels, mechanical shock and hypothermia. The tightness of solid elements should be ensured.

Li-ion cells charge using much the same principles as polymer cells, but are more sensitive and less reliable in terms of safety. The charging time for both types is approximately the same, but the polymer element is more capricious in terms of the quality of the power supply point.

The better lithium-ion battery

Lithium-ion batteries are more familiar to consumers; they have a number of operational advantages:

• the price is lower than a lithium polymer battery;
• standardized standard sizes allow you not to make mistakes when choosing a model;
• widespread scope of application.

Powerful lithium batteries are effectively used for devices that require short-term high current consumption. The temperature regime, as with polymer-based devices, is of key importance during operation.

The average user does not feel a noticeable difference, but, from the point of view of the rationality of the scope of application, this type of battery is convenient in chargers for the following equipment:

• cordless tools (screwdrivers, saws, grinders);
• laptops;
• Cell phones;
• electric cars;
• home robots;
• wheelchairs.

Before choosing the optimal type of charging, you need to know exactly what device it will be used for. This is especially important if you plan to universally use and service several portable devices at once.

It is rational to use lithium polymer batteries where weight and temperature are important factors. They are “afraid” of frost and are not very convenient for portable tools and gadgets. Therefore the main area of ​​use:

• quadcopters;
• airsoft guns;
• toys;
• CCTV Cameras.

When choosing the appropriate type of charger, pay attention to the scope of use, cost and level of safety. Read user reviews about products from different manufacturers and make a choice.

Lithium-ion and lithium-polymer batteries

Engineering thought is constantly evolving: it is stimulated by constantly emerging problems that require the development of new technologies to be solved. At one time, nickel-cadmium (NiCd) batteries were replaced by nickel-metal hydride (NiMH), and now lithium-ion (Li-ion) batteries are trying to take the place of lithium-ion (Li-ion) batteries. NiMH batteries have to some extent supplanted NiCd, but due to such undeniable advantages of the latter as the ability to deliver high current, low cost and long service life, they could not provide their full replacement. But what about lithium batteries? What are their features and how do Li-pol batteries differ from Li-ion? Let's try to understand this issue.

As a rule, when buying a mobile phone or laptop computer, we all don’t think about what kind of battery is inside and how these devices differ in general. And only then, having encountered in practice the consumer qualities of certain batteries, do we begin to analyze and choose. For those who are in a hurry and want to immediately get an answer to the question of which battery is optimal for a cell phone, I will answer briefly - Li-ion. The following information is intended for the curious.

First, a short excursion into history.

The first experiments on creating lithium batteries began in 1912, but it was only six decades later, in the early 70s, that they were first introduced into household devices. Moreover, let me emphasize, these were just batteries. Subsequent attempts to develop lithium batteries (rechargeable batteries) failed due to safety concerns. Lithium, the lightest of all metals, has the greatest electrochemical potential and provides the greatest energy density. Batteries using lithium metal electrodes offer both high voltage and excellent capacity. But as a result of numerous studies in the 80s, it was found that cyclic operation (charge - discharge) of lithium batteries leads to changes in the lithium electrode, as a result of which thermal stability decreases and there is a threat of the thermal state getting out of control. When this happens, the temperature of the element quickly approaches the melting point of lithium - and a violent reaction begins, igniting the gases released. For example, a large number of lithium mobile phone batteries shipped to Japan in 1991 were recalled after several fire incidents.

Because of lithium's inherent instability, researchers have turned their attention to non-metallic lithium batteries based on lithium ions. Having lost a little in energy density and taking some precautions when charging and discharging, they received safer so-called Li-ion batteries.

The energy density of Li-ion batteries is usually twice that of standard NiCd, and in the future, thanks to the use of new active materials, it is expected to increase it even further and achieve three times superiority over NiCd. In addition to the large capacity, Li-ion batteries behave similarly to NiCds when discharged (their discharge characteristics are similar in shape and differ only in voltage).

Today there are many varieties of Li-ion batteries, and you can talk for a long time about the advantages and disadvantages of one type or another, but it is impossible to distinguish them by appearance. Therefore, we will note only those advantages and disadvantages that are characteristic of all types of these devices, and consider the reasons that led to the birth of lithium-polymer batteries.

Main advantages.

• High energy density and, as a result, large capacity with the same dimensions compared to nickel-based batteries.
• Low self-discharge.
• High voltage per cell (3.6 V versus 1.2 V for NiCd and NiMH), which simplifies the design - often the battery consists of only one cell. Many manufacturers today use just such a single-cell battery in cell phones (remember Nokia). However, to provide the same power, a higher current must be supplied. And this requires ensuring low internal resistance of the element.
• Low maintenance (operating) costs result from the absence of memory effect, requiring periodic discharge cycles to restore capacity.

Flaws.

Li-ion battery manufacturing technology is constantly improving. It is updated approximately every six months, and it is difficult to understand how new batteries “behave” after long-term storage.

In a word, a Li-ion battery would be good for everyone if it were not for the problems with ensuring the safety of its operation and the high cost. Attempts to solve these problems led to the emergence of lithium-polymer (Li-pol or Li-polymer) batteries.

Their main difference from Li-ion is reflected in the name and lies in the type of electrolyte used. Initially, in the 70s, a dry solid polymer electrolyte was used, similar to plastic film and not conducting electricity, but allowing the exchange of ions (electrically charged atoms or groups of atoms). The polymer electrolyte effectively replaces the traditional porous separator impregnated with electrolyte.

This design simplifies the production process, is safer, and allows the production of thin, free-form batteries. In addition, the absence of liquid or gel electrolyte eliminates the possibility of ignition. The thickness of the element is about one millimeter, so equipment developers are free to choose the shape, shape and size, even including its implementation in fragments of clothing.

But so far, unfortunately, dry Li-polymer batteries have insufficient electrical conductivity at room temperature. Their internal resistance is too high and cannot provide the amount of current required for modern communications and power supply to the hard drives of laptop computers. At the same time, when heated to 60 °C or more, the electrical conductivity of Li-polymer increases to an acceptable level, but this is not suitable for mass use.

Researchers are continuing to develop Li-polymer batteries with a dry solid electrolyte that operates at room temperature. Such batteries are expected to become commercially available by 2005. They will be stable, allow 1000 full charge-discharge cycles and have a higher energy density than today's Li-ion batteries

Meanwhile, some types of Li-polymer batteries are now used as backup power supplies in hot climates. For example, some manufacturers specifically install heating elements that maintain a favorable temperature for the battery.

You may ask: how can this be? Li-polymer batteries are widely sold on the market, manufacturers equip phones and computers with them, but here we are saying that they are not yet ready for commercial use. Everything is very simple. In this case, we are talking about batteries not with dry solid electrolyte. In order to increase the electrical conductivity of small Li-polymer batteries, a certain amount of gel-like electrolyte is added to them. And most Li-polymer batteries used for cell phones today are actually hybrids because they contain a gel-like electrolyte. It would be more correct to call them lithium-ion polymer. But most manufacturers simply label them as Li-polymer for advertising purposes. Let us dwell in more detail on this type of lithium-polymer batteries, since at the moment they are of the greatest interest.

So, what is the difference between a Li-ion and a Li-polymer battery with gel electrolyte added? Although the characteristics and efficiency of both systems are largely similar, the uniqueness of the Li-ion polymer (you can call it that) battery is that it still uses a solid electrolyte, replacing a porous separator. Gel electrolyte is added only to increase ionic conductivity.

Technical difficulties and delays in ramping up production have delayed the introduction of Li-ion polymer batteries. This is caused, according to some experts, by the desire of investors who have invested a lot of money in the development and mass production of Li-ion batteries to get their investments back. Therefore, they are in no hurry to switch to new technologies, although with mass production of Li-ion polymer batteries will be cheaper than lithium-ion ones.

And now about the features of operating Li-ion and Li-polymer batteries.

Their main characteristics are very similar. The charging of Li-ion batteries is described in sufficient detail in the article. In addition, I will only give a graph (Fig. 1) from, illustrating the stages of charge, and small explanations to it.

The charging time for all Li-ion batteries with an initial charging current of 1C (numerically equal to the nominal value of the battery capacity) averages 3 hours. Full charge is achieved when the battery voltage is equal to the upper threshold and when the charging current is reduced to a level approximately equal to 3% of the initial value. The battery remains cold during charging. As can be seen from the graph, the charging process consists of two stages. In the first (a little over an hour), the voltage increases at an almost constant initial charge current of 1C until the upper voltage threshold is first reached. At this point, the battery is charged to approximately 70% of its capacity. At the beginning of the second stage, the voltage remains almost constant and the current decreases until it reaches the above 3%. After this, the charge stops completely.

If you need to keep the battery charged all the time, it is recommended to recharge after 500 hours, or 20 days. Usually it is carried out when the voltage at the battery terminals decreases to 4.05 V and stops when it reaches 4.2 V

A few words about the temperature range during charging. Most types of Li-ion batteries can be charged with a current of 1C at temperatures from 5 to 45 °C. At temperatures from 0 to 5 °C, it is recommended to charge with a current of 0.1 C. Charging at sub-zero temperatures is prohibited. The optimal temperature for charging is 15 to 25 °C.

The charging processes in Li-polymer batteries are almost identical to those described above, so the consumer has absolutely no need to know which of the two types of batteries he has in his hands. And all those chargers that he used for Li-ion batteries are suitable for Li-polymer.

And now about the discharge conditions. Typically, Li-ion batteries discharge to a value of 3.0 V per cell, although for some varieties the lower threshold is 2.5 V. Manufacturers of battery-powered equipment typically design devices with a shutdown threshold of 3.0 V (for all occasions). What does this mean? The voltage on the battery gradually decreases when the phone is turned on, and as soon as it reaches 3.0 V, the device will warn you and turn off. However, this does not mean that it has stopped consuming energy from the battery. Energy, albeit small, is required to detect when the phone's power key is pressed and some other functions. In addition, energy is consumed by its own internal control and protection circuit, and self-discharge, although small, is still typical even for lithium-based batteries. As a result, if lithium batteries are left for a long period of time without recharging, the voltage on them will drop below 2.5 V, which is very bad. In this case, the internal control and protection circuit may be disabled, and not all chargers will be able to charge such batteries. In addition, deep discharge negatively affects the internal structure of the battery itself. A completely discharged battery must be charged at the first stage with a current of only 0.1C. In short, batteries like to be in a charged state rather than in a discharged state.

A few words about temperature conditions during discharge (read during operation).

In general, Li-ion batteries perform best at room temperature. Operating in warmer conditions will seriously reduce their lifespan. Although, for example, a lead-acid battery has the highest capacity at temperatures above 30 °C, long-term operation in such conditions shortens the life of the battery. Likewise, Li-ion performs better at high temperatures, which initially counteracts the increase in battery internal resistance that results from aging. But the increased energy output is short-lived, since increasing temperature, in turn, promotes accelerated aging, accompanied by a further increase in internal resistance.

The only exceptions at the moment are lithium-polymer batteries with dry solid polymer electrolyte. They require a vital temperature of 60 °C to 100 °C. And such batteries have found their niche in the market for backup sources in hot climates. They are placed in a thermally insulated housing with built-in heating elements powered from an external network. Li-ion polymer batteries as a backup are considered to be superior in capacity and durability to VRLA batteries, especially in field conditions where temperature control is not possible. But their high price remains a limiting factor.

At low temperatures, the efficiency of batteries of all electrochemical systems drops sharply. While NiMH, SLA and Li-ion batteries stop functioning at -20°C, NiCd batteries continue to function down to -40°C. Let me just note that again we are talking only about batteries of wide use.

It is important to remember that although a battery can operate in low temperatures, this does not mean that it can also be charged in these conditions. The charge responsiveness of most batteries at very low temperatures is extremely limited, and the charge current in these cases should be reduced to 0.1C.

In conclusion, I would like to note that you can ask questions and discuss problems related to Li-ion, Li-polymer, as well as other types of batteries, on the forum in the accessories subforum.

When writing this article, materials were used [—Batteries for mobile devices and laptop computers. Battery analyzers.