Lithium polymer batteries (Li-Po). What are the features of lithium polymer batteries

Progress is moving forward, and replacing 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 cell, they have a larger capacitance compared to NiCd and NiMH, in addition, their cell voltage is three times higher - 3.6V/cell 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 rigid division here is very conditional, since both types differ mainly in the electrolyte used, and everything that will be said about lithium-polymer batteries applies almost fully to lithium-ion batteries (charge, discharge, operating features, safety precautions). ). From a practical point of view, we are only concerned with the fact that lithium-polymer batteries currently provide higher discharge currents. Therefore, in the model market, they are mainly offered as a source of energy for power plants.

Main characteristics

Lithium-polymer batteries with the same weight are 4-5 times more energy efficient than NiCd, NiMH 3-4 times. The number of operating cycles is 500-600, at discharge currents of 2C up to a capacity loss of 20% (for comparison, NiCd has 1000 cycles, NiMH has 500). Generally speaking, there is still very little data on the number of operating cycles, and their characteristics given in this case must be treated critically. In addition, the technology of their manufacture is improving, and it is possible that at the moment the numbers 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.

From the whole variety of commercially available power lithium-polymer batteries, two main groups can be distinguished - fast-discharge (Hi discharge) and conventional ones. They differ among themselves in the maximum discharge current - it is indicated either in amperes or in units of battery capacity, denoted by the beech "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 in the name they have the letters HD or HC after the capacity numbers, for example, the KKM1500 is a regular 1500 mAh battery, and the KKM1500HD is a fast-discharge battery. I would like to immediately make a small remark for fans of experiments. Fast-discharging batteries are not used in household appliances. Therefore, if you are visited by the idea of getting a cheap battery from a cell phone or camcorder, then it is difficult to count on a good result. Most likely, such a battery will die very quickly due to violation of the provided operating modes.

Applications and cost

The use of lithium-polymer batteries allows us to solve two important problems - to increase the operating time of the motor and reduce the weight of the battery.

When replacing the 8.4 V NiMH 650 mAh battery with two conventional, non-fast-discharging 2 Ah lithium batteries, we get a battery 3 times larger in capacity, 11 g lighter and with a slightly lower voltage (7.2 volts)! And if you use fast-discharging batteries, then large planes can fly, not inferior in terms of power to the internal combustion engine. In confirmation of this, the 7th place in the world championship in aerobatic models F3A was taken by an American on an electric plane. Moreover, it was not a small buzzer, but a normal two-meter aircraft, like the rest of the participants who had models with internal combustion engines!

Lithium-polymer batteries have proven themselves very well in small helicopters such as the Piccolo or Hummingbird - for example, even with a standard brushed motor, the flight time on two 1Ah cans 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 indispensable 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, the weight of a 45 mAh can is 1 g, 150 mAh - 3.2 d), which, with such a small weight, would give the necessary power - even for 1 minute!

The only area where so far lithium-polymer batteries are inferior to Ni-Cd is the area of \u200b\u200bsuperhigh (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 heard about fast-discharging 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
Kocam 1020	1020	61x33x5.5	20.5	3A, 3C
Kokam 1500HC	1500	76x40x6.5	35	12A, 8C
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. Thunder Power, I-Rate, E-Tec, and Tanic are also known (presumably this is the second name of Thunder Power or is it one of the sellers of Thunder Power under its own name). You can view Kokam types at www.fmadirect.com, batteries from different manufacturers are available at www.b-p-p.com and www.lightflightrc.com.

There is also Platinum Polymer available from 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 from 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 their electrodes is aluminum, and it is problematic to solder it. This makes them inconvenient when assembling the battery yourself.

E-Tec batteries are something in between, they are not claimed to be fast-discharging, but their discharge current is higher than that of conventional batteries - 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 (over 10 kg!). Obviously, this is due to the price and the presence in the range of powerful assemblies - up to 30 volts and 8Ah with a 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 flyers.

Charging Lithium Polymer Batteries

The batteries are charged according to a fairly simple algorithm - a 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 the 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 the voltage at the end of the charge - no worse than 0.01 V / bank.

Of the chargers on the market, we can distinguish the main types - simple, not "computer" chargers, in the price range of $ 10-40, intended only for lithium batteries, and universal - in the price range of $ 120-400, designed for various types of batteries, including for LiPo and Li-Ion.

The first, as a rule, have only an 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 show the end of the charge. They show only the moment of transition from the current stabilization mode to the voltage stabilization mode, which is approximately 70-80% of the capacity. To complete the charge, you still have to wait 30-40 minutes.

The second group of chargers has much wider possibilities, 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 the charger, the most important thing is to correctly set the required number of cans in the battery and the charge 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 “gentle” batteries in existence, that is, they require mandatory compliance with a few 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:

Charge up to a voltage greater than 4.20 volts/cell.
Short circuit of the battery.
Discharge with currents exceeding the load capacity or heating the battery above 60 ° C.
Discharge below 3.00 volts/cell.
Battery heating above 60°C.
Battery depressurization.
Storage in a discharged state.

Failure to comply with the first three points leads to a fire, all the rest - to a 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 charged cans on it. It is also necessary to use connectors that exclude the possibility of a short circuit of the battery (because of this, my friend burned the table on which the batteries were charged, 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, and if this is not possible, then special channels for cooling should be provided.

In cases where the current consumed by the motor is more than 2C, and the battery on the model is closed on all sides, after 5-6 minutes of running the motor, stop it, and then pull out and touch the battery - is it not 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 by it into heat, the battery literally spreads, setting fire to everything that can burn.

If you close an almost discharged battery, then there will be no fire, it will die quietly and peacefully due to overdischarge ... Hence the second important rule follows: watch the voltage at the end of the battery discharge and be sure to disconnect the battery after work!

Some speed controllers (Jeti is especially guilty of this) do not stop current consumption after turning off the standard switch. What made the Czechs make such a strange decision - I do not know. But the fact remains that almost all models of controllers for Jetti brushless motors (including the new "Advanced" series) that have a BEC, that is, a power supply stabilizer for the receiver and machines from the power supply, do not provide a 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, 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, it should be remembered that the engine controller must be able to work with lithium batteries, that is, it must 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 determines the number of connected cans.

Depressurization is another reason for the failure of lithium batteries, since air must not enter the cell. This can happen if the outer protective bag is damaged (the battery is sealed in a bag like a heat shrink tube), as a result of being hit or damaged by a sharp object, or if the battery terminal is overheated during soldering. Conclusion - do not drop from a great height and solder carefully.

Storage of batteries, judging by the recommendations of manufacturers, should be carried out in a 50-70% charged state, preferably in a cool place, at temperatures not higher than 20 ° C. Storage in a discharged state negatively affects the service life - like all batteries, lithium-polymer ones have a small self-discharge.

Battery assembly

To obtain batteries with high current output or high capacity, batteries are connected in parallel. If you buy a ready-made battery, then by marking you can find out how many cans are in it 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 of 3 pairs of batteries, and each pair is formed by 2 parallel connected batteries with a capacity of 1500mAh, that is, the battery capacity will be 3000mAh (when connected in parallel, the capacity increases), and the voltage - 3.7 * 3 \u003d 11.1V ..

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

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

Due to the drop in capacity as a result of operation, in no case should new banks be added sequentially to the old ones - the battery will be unbalanced in this case.

Of course, it is also impossible to 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 battery imbalance. When soldering, be careful not to overheat the leads - 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 PCB already soldered to the terminals for easy wiring. At the same time, extra weight is added - about 1 g per element, but it can take much longer to heat the places for soldering wires - fiberglass does not conduct heat well. Wires with connectors should be fixed on the battery case, at least with adhesive tape, so as not to accidentally tear off the terminal at the root.

Nuances of application

So, let's emphasize once again the most important points related to the use of lithium-polymer batteries.

Use a normal charger.
Use connectors that exclude the possibility of shorting the battery.
Do not exceed the allowable discharge currents.
Monitor the temperature of the battery in the absence of cooling.
Do not discharge the battery below 3V/cell (don't forget to disconnect the battery after the flight!).
Do not subject the battery to shock.

Here are some more useful examples that follow from what was said earlier, but are not obvious at first glance.

When using collector motors, it is necessary to avoid situations when the motor is stalled (for example, the model is on the ground), and the transmitter is at full throttle. The current is too high, and we risk blowing up the battery (if the motor or regulator does not burn out first). This issue has been discussed many 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 you to turn 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 the model on the transmitter belt and not notice it.

During the long operation of the battery, its elements become unbalanced due to the initial small scatter of capacities - some banks “age” earlier than others and lose their capacity faster. With more cans in the battery, the process goes faster.

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

It is not recommended to “zero out” the battery by driving the motor until it stops spinning at all. Such treatment will not harm a new battery, but for a slightly unbalanced one, this is an extra risk of discharging the “worst 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 fully charged without special measures!

For automatic balancing of battery cells during charging, so-called balancers (balancer) are used. This is a small board connected to each bank containing terminating resistors, a control circuit and an LED indicating that the voltage on this bank has reached a level of 4.17 - 4.19 volts. When the voltage on a separate element exceeds the threshold of 4.17 volts, the balancer closes part of the current “on itself”, preventing the voltage from exceeding the critical threshold. By the simultaneous ignition of the LEDs, you can see which banks have a lower capacity - on their balancer, the LED will light up first. One important additional requirement is imposed on the balancers - the current they consume from the battery in the "standby" mode must be small, usually it is 5-10 μA.

It should be added that the balancer does not save from overdischarging some cans 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 composed of 3 or more cells, for 2-cell batteries, balancers, as a rule, are not used.

There is an opinion that lithium-polymer batteries cannot be operated at low 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, it is possible to fly them at temperatures around -10 ... -15 ° С. The fact is that it is not necessary to freeze the battery before the flight - put it in your pocket, where it is warm. And in 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 output of the battery will be somewhat lower than at normal temperature.

Conclusion

Given the pace at which technological 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 the demand for batteries rises and production increases, the price will inevitably fall, and then lithium will finally become as common as NiMH. In the West, this time has already come for half a year, at least in America. The popularity of electric vehicles with lithium-polymer batteries is growing. Hopefully, brushless motors and controllers will also become cheaper, but in this area, the progress of price reduction is moving less rapidly. After all, just two years ago, the question was asked in the forum - “Does anyone really fly a brushless?”. And then there was no mention of lithium batteries at all ...

In general, wait and see.

Today, phones are more than just a means of communication.

With the help of smartphones, they go online, listen to music, watch movies, play games, take photos and shoot videos - such opportunities require a high-quality battery that will provide the device with long battery life. One of the most popular and modern are lithium polymer batteries. What are its features, advantages and disadvantages?

Features of lithium polymer (Li-pol) batteries

Lithium is the lightest of the metals and has the highest electrochemical potential, providing a high energy density. During operation, such a battery uses lithium metal electrodes.

Both polymer and ion batteries are significantly more efficient than their predecessors - nickel-cadmium and nickel-metal hydride batteries. In modern batteries, the capacity is much higher, more, there is no "memory effect", and they are more compact in size.

In terms of compactness, polymer batteries (Li-pol) occupy the first place. These batteries use a polymer - a thin and flexible plate impregnated with electrolytes. Due to its compactness, the battery has a thickness of only 1 mm. Such compact batteries allow designers to design smaller and lighter smartphones.

The main advantages of Li-pol batteries:

The flexible polymer will make it possible to achieve smaller batteries, respectively, compact devices are obtained. In this parameter, polymer batteries are preferable to ion ones, since the latter have reached the limit of thickness reduction.
Such a battery is considered the most advanced, therefore it provides a greater level of safety, reducing the risk of overcharging and electrolyte leakage.
Polymer batteries have a longer service life, slower aging process and self-discharge.

Flaws:

Polymer batteries have a higher cost of materials for manufacturing (compared to ion batteries). As a result, this affects the price of the phone.
High sensitivity to low temperatures.
They heat up more.

How to properly charge a lithium polymer battery?

Whatever battery is installed in a smartphone, without proper care, it will quickly begin to wear out and lose capacity. Protect your phone from overheating and hypothermia. High temperatures can cause fire. As for low temperatures, in the cold, the current output decreases in the battery due to the slowing down of the chemical reactions of electrolytes. That is why mobile devices are often such a kind of self-defense.

To prolong the life of a lithium polymer battery, charge it correctly and follow. Remember that many batteries are sensitive to temperature changes and.

Modern batteries have a special controller that protects the smartphone from overcharging and overdischarging. It does not allow you to continue to power the device after reaching 100% restored capacity, even if the charger cable is connected to the mains. When the phone is completely turned off due to battery depletion, there is always some power left in the battery, as the controller turns off the device in advance. However, the phone must then be charged as soon as possible.

Ideally, you should not allow the device to completely discharge. Some experts recommend not charging the gadget above 90% and not discharging below 10% - this can extend battery life. An exception is preventive calibration every six months. To do this, you must completely discharge the smartphone, and then charge the battery to 100%.

When buying a new smartphone, it is important to follow simple.

Results

Lithium-polymer batteries in the world of mobile devices are currently considered the most modern and relevant due to a number of positive qualities and compact size. Remember that the battery of the phone must be looked after - in this case, it will last much longer.

Portable chargers have become an integral part 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 construction - lithium-ion and lithium-polymer. For an ordinary consumer who is 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 will 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

Models of batteries produced by different technologies perform the same function of energy supply. The design features of each type affect the reported power, durability of operation, and the degree of protection against explosion. It cannot be stated unequivocally that more modern

the type of battery is better than the outdated one. Both technologies have practical advantages and disadvantages. Models Li-pol and Li-ion have similar schemes of work, 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. Compare the types of batteries and make a choice in the direction of one or another type should be based on the following indicators:

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

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

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 does not depend 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 an 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 drive chemical reactions, form bonds, and provide energy output. The principle of operation of a lithium-ion-based power supply resembles the operation of a full-size gel battery.

Lithium polymer batteries

Since lithium-ion models do not cope with many modern tasks, they gradually began to be 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, to make the batteries more efficient, the developers decided to change the electrolyte. Instead of impregnating a porous separator, polymer electrolytes were used in the battery design.

The lithium-polymer cell has a thickness of 1 mm, which allows you to make the size of the battery compact. Replacing liquid electrolytes with polymer films eliminated the high risk of battery ignition and made it safe. The comparison table below will help you visually 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
Size	small selection	high choice, independence from the standard cell format
	slightly heavier
		almost twice as high for the same size
Life time	about the same	about the same
Risk of explosion and fire	higher	built-in protection against leakage of electrolytes and overcharges
Charging time
	up to 0.1% monthly	less active

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

The introduction of polymer-lithium elements already assumed a solid-state basis. A characteristic difference from lithium-ion batteries is the process of contacting the active substance plate with lithium and preventing 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 intense aging. They provide about nine hundred full charge cycles, after which they become unusable. It does not matter how active the operation of the device was. If the battery has not been used at all for a long time, a reduction in life will still occur.

Already after a year, the capacities become significantly reduced in resource, and after two or three years it can be stated that the battery has completely failed. This is a common disadvantage of lithium batteries, and it is worth choosing a more durable model only depending on the manufacturer's reputation and reviews of specific models.

Additional protection

If we consider the question of what is the difference between Li-ion and Li-Pol batteries, you should pay attention to the built-in protective systems. Polymer-lithium based models require the use of 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 working areas.

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

Part of the design involves electrolytic components in a gel formation. Combination 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 inside 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 the requirements of operation, elements with a polymer component are used as backup.

Features of battery charging

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

It is necessary to connect the battery only to a stable working power supply, without voltage drops and interference. Use only appropriate chargers that match the characteristics stated in the description. An important point: during the charging process, all connectors must be connected correctly, opening must not be allowed. Li-Pol elements are extremely sensitive to all kinds of overloads, exceeded current rates, mechanical shocks and hypothermia. The tightness of solid elements should be monitored.

Li-ion cells are charged in much the same way as polymer ones, 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 "capricious" to the quality of the power supply point.

The better lithium-ion battery

Lithium-ion batteries are more familiar to the consumer, they have a number of operational advantages:

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

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.

An ordinary user does not feel a tangible difference, but, from the point of view of the rationality of the scope, this type of battery is convenient in chargers for the following equipment:

battery tools (screwdrivers, saws, grinders);
laptops;
Cell phones;
electric vehicles;
domestic 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.

Lithium-polymer batteries are rationally used 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 \u200b\u200buse:

quadrocopters;
airsoft guns;
toys;
CCTV Cameras.

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

Technological 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-polymer (Li-pol) batteries are trying to take the place of lithium-ion (Li-ion). What is the difference between Li-pol and Li-ion? What are the advantages of lithium polymer batteries 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, faced with the problem of a quick discharge of the gadget, do we begin to examine in more detail the “inside” of our device.

About lithium batteries became known in 1912, then the first experiments began, but they did not find wide application. And only in the 70s, six decades later, these charging cells took their places in almost all household devices. We emphasize that the conversation so far is only about batteries, not accumulators.

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 (the 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 threat. Because of these dangerous properties of lithium, scientists have turned all their efforts to non-metallic lithium batteries based on lithium ions. And after a while, a safer version of the charger was created, which was called lithium-ion (Li-ion).

Today, a lithium-ion battery is used 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 capacitance

Low self-discharge

Single cell high voltage. 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 maintenance (operating costs)

No memory effect requiring periodic discharge cycles to restore capacity.

Flaws:

The battery requires a built-in protection circuit (which adds to its cost) that limits the maximum voltage on each battery cell during charging and keeps the cell voltage from dropping too low when discharging.

The battery is subject to aging, even if not in use and just lying on the 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 a year, regardless of whether the battery was in operation or not. After two or three years, it often becomes unusable.

Higher cost compared to NiCd batteries.

Li-ion batteries constantly improving, technology is improving. And this battery would be good for everyone if it were not for the safety problems when using it 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 a 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

In general, 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 application 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 the original , but about how to understand with 100% certainty on the store's website that they will sell you a fake -

Battery production technologies do not stand still and gradually Ni-Cd (nickel-cadmium) and Ni-MH (nickel-metal hydride) batteries are being replaced on the market by batteries based on lithium technologies. Lithium-polymer (Li-Po) and lithium-ion (Li-ion) batteries are increasingly used in various electronic devices as a current source

Lithium- silver-white, soft and ductile metal, harder than sodium, but softer than lead. Lithium is the lightest metal in the world! Its density is 0.543 g/cm 3 . It can be processed by pressing and rolling. There are lithium deposits in Russia, Argentina, Mexico, Afghanistan, Chile, USA, Canada, Brazil, Spain, Sweden, China, Australia, Zimbabwe and Congo

Excursion into history

The first experiments on the creation of lithium batteries began in 1912, but only six decades later, in the early 70s, they were first introduced into household devices. And, I emphasize, it was just the batteries. Subsequent attempts to develop lithium batteries (rechargeable batteries) were unsuccessful due to problems associated with ensuring the safety of their operation. Lithium, the lightest of all metals, has the highest electrochemical potential and provides the highest energy density. Batteries using lithium metal electrodes are characterized by high voltage and excellent capacity. But as a result of numerous studies in the 80s, it was found that the 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 cell quickly approaches the melting point of lithium - and a violent reaction begins, igniting the gases released. For example, a large number of lithium batteries for mobile phones shipped to Japan in 1991 were recalled after several explosions.

Due to the inherent instability of lithium, researchers have turned their attention to non-metallic lithium batteries based on lithium ions. Having lost a little with energy density and taking some precautions when charging and discharging, they got safer so-called lithium-ion (Li-ion) batteries.

The energy density of Li-ion batteries is usually several times higher than that of standard NiCd and NiMH batteries. Thanks to the use of new active materials, this superiority is increasing every year. In addition to the large capacity, the Li-ion battery behaves similarly to nickel batteries when discharging (the shape of their discharge characteristics is similar and differs 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 in appearance. Therefore, we 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 (Li-Po) batteries.

Li-ion battery was good for everyone, but problems with ensuring the safety of its operation and the high cost led scientists to create a lithium-polymer battery (Li-pol or Li-po).

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 a plastic film and not conducting an electric current, but allowing the exchange of ions (electrically charged atoms or groups of atoms). The polymer electrolyte actually replaces the traditional porous separator impregnated with electrolyte, due to which they have a flexible plastic shell, have less weight, high current output and can be used as power batteries for devices with powerful electric motors.

This design simplifies the manufacturing process, is more secure, and allows the production of thin, free-form batteries. The minimum thickness of the element is about one millimeter, so that equipment designers are free to choose the shape, shape and size, up to incorporating it into clothing fragments.

Main advantages

Lithium-ion and lithium-polymer batteries with the same weight surpass nickel (NiCd and Ni-MH) batteries in energy intensity
Low self-discharge
High voltage of a single cell (3.6-3.7V versus 1.2V-1.4 for NiCd and NiMH), which simplifies the design - often the battery consists of only one cell. Many manufacturers use in various compact electronic devices (cell phones, communicators, navigators, etc.) just such a single-cell battery
Thickness of elements from 1 mm
Possibility to obtain very flexible forms

Flaws

The battery is subject to aging even if it is not used and just sits on a shelf. For obvious reasons, manufacturers are silent about this problem. The clock starts ticking from the moment the batteries are produced at the factory, and the decrease in capacity is the result of an increase in internal resistance, which in turn is generated by the oxidation of the electrolyte. As a result, the internal resistance will reach a level where the battery will no longer be able to deliver the stored energy, although there will be enough of it in the battery. After two or three years, it often becomes unusable.
Higher cost than NiCd and Ni-MH batteries
When using lithium-polymer batteries, there is always a risk of their ignition, which can happen due to contact closure, improper charging, or mechanical damage to the battery. Since the combustion temperature of lithium is very high (several thousand degrees), it can ignite nearby objects and cause a fire.

Main characteristics of Li-Po batteries

As mentioned above, lithium-polymer batteries with the same weight exceed NiCd and Ni-MH batteries by several times in terms of energy consumption. The service life of modern Li-Po batteries, as a rule, does not exceed 400-500 charge-discharge cycles. For comparison, the life of modern Ni-MH batteries with low self-discharge is 1000-1500 cycles.

Technologies for the production of lithium batteries do not stand still, and the above figures may lose their relevance at any time, because. battery manufacturers are increasing their characteristics every month through the introduction of new technological processes for their production.

Of the variety of commercially available lithium polymer batteries, two main groups can be distinguished - fast-discharge(Hi Discharge) and ordinary. They differ among themselves in the maximum discharge current - it is indicated either in amperes or in units of battery capacity, denoted by the letter "C".

Areas of application for Li-Po batteries

The use of Li-Po batteries allows you to solve two important problems - to increase the operating time of devices and reduce the weight of the battery

Ordinary Li-Po batteries are used as power sources in electronic devices with relatively low current consumption (mobile phones, communicators, laptops, etc.).

Fast Discharge Lithium polymer batteries are often referred to as " power"- such batteries are used to power devices with high current consumption. A striking example of the use of "power" Li-Po batteries are radio-controlled models with electric motors and modern hybrid cars. It is in this market segment that the main competitive struggle between various manufacturers of Li-Po batteries takes place.

The only area where so far lithium-polymer batteries are inferior to nickel ones is the area of \u200b\u200bsuperhigh (40-50C) discharge currents. In terms of price, in terms of capacity, lithium-polymer batteries cost about the same as NiMH. But competitors have already appeared in this market segment - (Li-Fe), the production technology of which is developing every day.

Charging Li-Po batteries

The charge of most Li-Po batteries is carried out according to a fairly simple algorithm - from a constant voltage source of 4.20V / cell with a current limit of 1C (some models of modern power Li-Po batteries allow charging them with a current of 5C). The charge is considered complete when the current drops to 0.1-0.2C. Before switching to voltage stabilization mode at a current of 1C, the battery gains approximately 70-80% of its capacity. It takes about 1-2 hours to fully charge. The charger is subject to rather stringent requirements for the accuracy of maintaining the voltage at the end of the charge - no worse than 0.01 V / bank.
Of the chargers on the market, two main types can be distinguished - simple, non-computer chargers in the $10-40 price range, designed only for lithium batteries, and universal chargers in the $80-400 price range, designed to serve various types of batteries. batteries.

The former, as a rule, have only an LED charge indication, the number of cans and the current in them are set by jumpers or by connecting the battery to various connectors on the charger. The advantage of such chargers is their low price. The main drawback is that some of these devices are not able to correctly determine the end of the charge. They determine only the moment of transition from the current stabilization mode to the voltage stabilization mode, which is approximately 70-80% of the capacity.

The second group of chargers has much wider possibilities, as a rule, they all show the voltage, current, and capacity in mAh that the battery “accepted” during the charge, which allows you to more accurately determine how charged the battery is. When using the charger, the most important thing is to correctly set the required number of cans in the battery and the charge current, which is usually 1C, on the charger.

Li-Po battery handling and precautions

It is safe to say that lithium-polymer batteries are the most “gentle” of the existing ones, i.e. require the observance of a few simple rules. We list them in descending order of danger:

Recharge battery - charge up to a voltage exceeding 4.20V per cell
Battery short circuit
Discharge with currents exceeding the load capacity or leading to heating of the Li-Po battery over 60 ° C
Discharge below 3V per cell
Battery heating above 60ºС
Battery depressurization
Storage in a discharged state

Failure to comply with the first three points leads to a fire, all the rest - to a 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 charged cans on it
It is also necessary to use connectors that exclude the possibility of a short circuit of the battery and control the current consumed by the device in which the Li-Po battery is installed.
You need to be sure that your electronic device in which the battery is installed does not overheat. At + 70ºС, a “chain reaction” begins in the battery, turning the energy stored by it into heat, the battery literally spreads, setting fire to everything that can burn
If you close an almost discharged battery, then there will be no fire, it will quietly and peacefully “die” due to overdischarge
Watch the voltage at the end of the battery discharge and be sure to turn it off after work
Depressurization is also the reason for the failure of lithium batteries. Air must not get inside the element. This can happen when the outer protective bag is damaged (the battery is sealed in a bag like a heat shrink tube) as a result of impact, or damage by a sharp object, or if the battery terminal is overheated during soldering. Conclusion - do not drop from a great height and solder carefully
According to the manufacturer's recommendations, batteries should be stored in a 50-70% charged state, preferably in a cool place, at a temperature not exceeding 30°C. Storage in a discharged state adversely affects the service life. Like all batteries, lithium polymer batteries have a small self-discharge.

Assembling Li-Po batteries

To obtain batteries with high current output or high capacity, batteries are connected in parallel. If you buy a ready-made battery, then by marking you can find out how many cans are in it 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" refers to a battery connected in series of three pairs of batteries, and each pair is formed by two 1500 mAh batteries connected in parallel, i.e. the battery capacity will be 3000 mAh (when connected in parallel, the capacity increases), and the voltage is 3.7V x 3 = 11.1V.

If you buy batteries separately, then before connecting them to a battery, you need to equalize their potentials, especially for the parallel connection option, since in this case one bank will start charging another and the charging current may exceed 1C. It is advisable to discharge all purchased banks before connecting to 3V with a current of about 0.1-0.2C. The voltage must be controlled with a digital voltmeter with an accuracy of at least 0.5%. This will ensure reliable battery performance in the future.

Due to the drop in capacity as a result of operation, in no case should new banks be added sequentially to the old ones - the battery will be unbalanced in this case.

When soldering, be careful not to overheat the leads - this can break the seal and permanently "kill" the battery that has not yet worked. Some Li-Po batteries come with pieces of a textolite printed circuit board already soldered to the terminals for easy wiring. At the same time, extra weight is added - about 1 g per element, but it is possible to heat places for soldering wires much longer - fiberglass does not conduct heat well. Wires with connectors should be fixed to the battery case, at least with adhesive tape, so as not to accidentally tear them off when repeatedly connected to the charger

The nuances of using Li-Po batteries

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

If a battery is found in the assembly, the capacity of which differs from other cells by more than 15-20%, it is recommended to refuse to use the entire assembly, or solder the battery with a smaller number of cells from the remaining batteries.

Modern chargers have built-in balancers (balancer), which allow you to charge all the elements in the battery separately under strict control. If the charger is not equipped with a balancer, then it must be purchased separately and it is advisable to charge the batteries using it.

An external balancer is a small board connected to each bank containing load resistors, a control circuit and an LED indicating that the voltage on this bank has reached 4.17-4.19V. When the voltage on a separate element exceeds the threshold of 4.17V, the balancer closes part of the current “on itself”, preventing the voltage from exceeding the critical threshold.

The above applies to batteries made up of three cells or more, for two-cell batteries, balancers, as a rule, are not used.

According to numerous reviews, the discharge of lithium batteries to a voltage of 2.7-2.8V has a more detrimental effect on capacity than, for example, overcharging to a voltage of 4.4V. It is especially harmful to store the battery in an over-discharged state.

There is an opinion that lithium-polymer batteries cannot be operated at low temperatures. Indeed, the technical specifications for the batteries indicate an operating range of 0-50 ° C (at 0 ° C, 80% of the battery capacity is preserved). But nevertheless, it is possible to use Li-Po batteries at negative temperatures, about -10 ... -15 ° С. The fact is that you do not need to freeze the battery before use - put it in your pocket, where it is warm. And in the process of use, the internal generation of heat in the battery turns out to be a useful property at the moment, preventing the battery from freezing. Of course, the output of the battery will be somewhat lower than at normal temperature.

Conclusion

Given the pace of technological progress in the field of electrochemistry, it can be assumed that the future belongs to lithium energy storage technologies if fuel cells do not catch up with them. Wait and see…

The article uses materials from articles by Sergei Potupchik and Vladimir Vasiliev