Correct charging of lithium polymer batteries. Difference between lithium polymer and lithium ion battery

Lithium polymer batteries (Li-po) differ from lithium-ion batteries in that they do not have separators and liquid electrolyte. Lithium polymers use a homogeneous electrolyte with lithium salts in the form of a gel, or a composite polymer with lithium salts in a dry state (often the base is polyethylene oxide). Lithium polymer batteries can also consist of a non-aqueous solution of lithium salts. Read more about the differences.

Advantages of lithium polymer batteries.

The main advantages of lithium polymers over batteries is that they have a fairly low self-discharge and have 4 and a half times more energy capacity than Ni-CD batteries of the same mass.

Lithium polymers usually have a service life of 300 - 600 charge/discharge cycles, but are sometimes found with 1000 recharge cycles.

Very common lithium polymer batteries are shaped like a button and only 1 mm thick. (tablet). Also, these batteries have the smallest weight relative to lithium-ion, nickel-cadmium batteries and non-rechargeable batteries, provided they have the same capacity.

Application

Small-sized button-shaped lithium-polymer batteries with a thickness of only 1 mm are widespread. In addition, these batteries have the least weight compared to the batteries and non-rechargeable batteries discussed above with the same energy capacity. This factor determined further niches for the use of lithium-polymer batteries:

Cell phones
DVRs and navigators
radio controlled models
various gadgets and devices.

Disadvantages of lithium polymer batteries:

■ Energy density is lower than that of ;

■ The high internal resistance of lithium polymers cannot provide high discharge currents. Therefore, lithium polymers cannot be used in screwdrivers and other highly powerful equipment.

■ Rapid degradation, so lithium polymer batteries lose most of their capacity after a couple of years, even during storage.

These batteries are very sensitive to the temperature conditions under which they operate. So Lithium polymers cannot work normally at negative ambient temperatures. Surely you have often noticed how quickly your mobile phone discharges in the cold. Lithium polymers can explode at temperatures above 70°C and cause a fire.

Lithium polymer batteries can deteriorate over time, even if not used. Therefore, you should not buy lithium polymers in reserve. Lithium polymers, like lithium-ion batteries, do not possess, but it is still recommended to adhere to some rules regarding these batteries:

Fully charge the first time you use it
Go through several full recharge cycles using a voltage stabilizer.
It is recommended to store lithium-polymer batteries in a cool place, but not at sub-zero temperatures.
Avoid full discharge
Frequent short-term recharging should be avoided.
The most optimal temperatures for the battery are from +10°C to plus 25°C.

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 the battery can operate in low temperatures, this does not mean that it can also be charged in these conditions. The charge susceptibility 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.

A polymer battery is a modernized version of lithium power sources. A special gel with certain characteristics is used as a filler for a lithium polymer battery.

In order to decide whether it is worth using li pol advanced batteries, you need to study certain information and take into account the advantages and disadvantages.

The performance of equipment, a portable device or installation largely depends on how correctly the power source is selected. Thus, a lithium ion or lithium ion polymer battery is used to complete portable chargers. In order to make the right choice, you need to know what the difference is. It is mandatory to take into account the pros and cons of power sources.

Interesting video about lithium-polymer batteries.

Lithium-ion batteries

The demonstration of the first ion batteries occurred in the last century. Then the developers presented models in which the electrodes were prepared from lithium metal. They were characterized by a low level of safety and short operation. Therefore, lithium metal was replaced with li ions.

The upgraded lithium-ion battery has the following advantages:

Increased capacity, electrolyte density.
Possibility of operation at higher voltage.
Easy to maintain due to lack of memory effect.
Minimum self-discharge.

The service life of an ion battery also depends on whether the disadvantages are taken into account:

Constant monitoring of voltage, current and temperature levels is required. This requires a special controller. This is exactly what distinguishes ionic batteries from polymer ones.
Gradual reduction in capacity.
The composition must include a proven protective circuit, a controller with the necessary components. Such work requires certain materials and tools. The procedure for manufacturing a protective circuit takes some time. All this leads to an increase in the cost of li ion po batteries by 1.5–2 times.

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Lithium polymer batteries

The development of a high-quality lithium polymer battery began due to the fact that the safety level of ion power sources was low. As a result, manufacturers received batteries that have special advantages in contrast to li.

Instead of the standard electrolytic composition, a dry polymer electrolyte is used, presented in the form of a film. It does not conduct current and does not interfere with the exchange of charged particles. Unlike an ion power source, a porous separator is not included in the polymer battery device.

Due to the fact that this design is used, the level of safety of li pol household batteries is higher. After all, the likelihood of ignition is reduced to zero.

Polymer electrolyte is easy to process. Therefore, manufacturers can easily create a li ion polymer battery of the required shape and optimal configuration. Therefore, such power supplies are used in phones, laptops, portable equipment, and video cameras.

Unfortunately, lithium ion polymer batteries have low electrical conductivity. Its level increases only when heated. But such an effect is not always acceptable. For example, heating the battery is not allowed if there is no cooling system.

The resistance level of li ion polymer batteries is high, so it is quite difficult to obtain the required current value. Because of this, modern devices cannot be equipped with such power sources.

But the above problems are inherent only in those li ion poly power sources in which the electrolyte is presented in dry form.

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Upgraded lithium polymer batteries

The problem associated with the lack of electrical conductivity was solved by introducing certain components into the electrolyte. Now they produce polymer batteries, the electrolyte in which is presented in the form of a gel. These power sources are called lithium ion polymer batteries. They are equipped with the best mobile phones, chargers and portable devices.

Rechargeable polymer batteries are found everywhere, no matter what kind of technology is presented.

Fundamental differences

What to choose: li ion or li polymer battery? Both designs have similar characteristics and parameters. The difference lies in the presence of solid electrolyte in li ion pol batteries.

The upgraded li-ion polymer battery does not come with a porous separator. It stands out for its increased capacity, long service life, and increased electrical conductivity.

When deciding which battery is best for a phone, manufacturers take into account design features, as well as the difference between pol and li types. Moreover, most often they use ion li polymer batteries, which have all the advantages.

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Features of using lithium batteries

The use of li ion and li ion pol follows a similar principle. To prevent problems you need:

Maintain a voltage of 4.2–2.7 V throughout the entire period of operation. These indicators correspond to the maximum and minimum charge.
Taking into account voltage restrictions introduced by manufacturers. For careful control, the use of proven schemes is allowed.
The service life of batteries charged up to 45–46% pol or li is the longest.
The introduction of controllers into ion polymer batteries helps maintain an acceptable voltage level.

Rules for charging lithium polymer batteries

To increase the operating time of the battery without additional recharging, you need to take into account the charging operating rules.

Full discharge is not acceptable. Polymer batteries do not have a memory effect. Therefore, the use of the charger is acceptable even with a small discharge. To extend the life of the li ion po battery, you need to charge it more often. In this case, you need to use a “native” charger.
Constantly using a battery that is fully charged is harmful. Therefore, the power source must be discharged to zero at certain intervals. Caused by charging instability and the use of different circuits and devices. With periodic discharge, the likelihood of the formation of lower and upper thresholds is eliminated.
Unused li ion po power supplies are stored at a temperature of 15–20 degrees. The charge level should be 40%. A fully charged power source should not be stored. After all, this is fraught with loss of capacity and deterioration of performance.
Original chargers are used to charge lithium-ion polymer batteries. Some mobile phones have built-in chargers. An external adapter is supplied separately to help stabilize the voltage. Some equipment is not equipped with such devices. Therefore, the battery is removed for charging.
Polymer batteries must not be overheated. Even an excess of 1–2 degrees has a detrimental effect on the condition of the power source. Low temperatures also have a negative impact. Therefore, you need to use the battery only in an acceptable mode.
It is prohibited to operate power sources in close proximity to heaters. The battery should not be exposed to direct sunlight. After all, all this helps to reduce the period of use.
It is unsafe to use chargers that have not been certified. So how do you charge a battery? The best solution is to use tested and certified chargers recommended by manufacturers.
All connectors used must be the same size. This is the only way to eliminate the possibility of shorting the battery.
The temperature of the power supply must be constantly monitored. This is especially important if there is no cooling system.
Mechanical loads are prohibited. This can cause the formation of microcracks and other damage.

Video about the restoration of lithium-polymer batteries.

Before using the universal charger you must:

Compare technical parameters.
Check capacity indicators. If you use limited chargers, it will be difficult to charge the power source.
Make sure the charger is working properly. After all, Chinese products may have defects.

If necessary, you can check how the old battery will charge.

Storage and disposal of polymer batteries

The service life of ion polymer batteries depends on compliance with storage rules.

Primary power sources do not require special storage conditions. It is enough to follow the manufacturers' recommendations.
The battery removed from the device is placed on a dry surface. In this case, it is necessary to minimize the likelihood of sunlight hitting the surface of the power source.
The likelihood of freezing increases if the battery is discharged. Therefore, premises with the required conditions are selected for storage.
Polymer batteries should be stored with a small charge (40–50%).
It is not worth using and storing lithium polymer batteries, whose voltage constantly decreases. Such devices must be recycled.
After long-term storage, the energy source must be inspected. Damaged or swollen batteries should be replaced.

The electrochemical system of polymer batteries is harmless. After all, during the preparation, environmental standards and requirements were taken into account. But the disposal of failed devices is mandatory. Such actions help preserve the environment. Failed sources are transferred to the appropriate organizations in the prescribed manner.

Modernized lithium polymer batteries are gradually replacing traditional power sources. And this is due to considerable capabilities, technical characteristics and an increased level of safety.

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.

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 technology. Lithium polymer (Li-Po) and lithium-ion (Li-ion) batteries are increasingly used as a power source in various electronic devices

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/cm3. It can be processed by pressing and rolling. Lithium deposits are found in Russia, Argentina, Mexico, Afghanistan, Chile, USA, Canada, Brazil, Spain, Sweden, China, Australia, Zimbabwe and Congo

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 are characterized by 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. By playing around a little with energy density and taking some precautions when charging and discharging, they came up with 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 its large capacity, Li-ion batteries behave similarly to nickel batteries when discharged (their discharge characteristics are similar and differ only in voltage).

The Li-ion battery was good for everyone, but problems with ensuring the safety of its operation and 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 plastic film and not conducting electricity, but allowing the exchange of ions (electrically charged atoms or groups of atoms). The polymer electrolyte essentially replaces the traditional porous separator impregnated with electrolyte, so they have a flexible plastic shell, are lighter, have higher current output and can be used as power batteries for devices with powerful electric motors.

This design simplifies the production process, is characterized by higher safety and allows the production of thin batteries of any shape. The minimum 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 clothing fragments.

Main advantages

Lithium-ion and lithium-polymer batteries with the same weight are superior in energy intensity to nickel (NiCd and Ni-MH) batteries
Low self-discharge
High voltage per 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 just such a single-cell battery in various compact electronic devices (cell phones, communicators, navigators, etc.)
Element thickness from 1 mm
Possibility of obtaining very flexible forms

Flaws

The battery is subject to aging, even if it is not used and just sitting 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 oxidation of the electrolyte. Eventually, the internal resistance will reach a level where the battery can no longer supply the stored energy, even though there is enough energy in the battery. After two or three years, it often becomes unusable.
Higher cost compared to NiCd and Ni-MH batteries
When using lithium polymer batteries, there is always a risk of ignition, which can occur due to shorted contacts, 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 are several times higher in energy intensity than NiCd and Ni-MH batteries. The service life of modern Li-Po batteries, as a rule, does not exceed 400-500 charge-discharge cycles. For comparison, the service 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 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 lithium-polymer batteries available for sale, two main groups can be distinguished: fast-discharge(Hi Discharge) and ordinary. 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”.

Application areas of Li-Po batteries

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

Regular 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 called " by force"- 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 competition between various manufacturers of Li-Po batteries takes place.

The only area where lithium-polymer batteries are still inferior to nickel ones is the area of super-high (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

Most Li-Po batteries are charged using 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 them to be charged 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 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, two main types can be distinguished - simple, non-“computer” chargers in the price category of $10-40, designed only for lithium batteries, and universal chargers in the price category of $80-400, designed to serve various types batteries.

The first ones, as a rule, have only an LED charge indication; the number of cans and the current in them are set using 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 cannot correctly detect 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 capabilities; as a rule, they all show the voltage, current, and capacity in 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 charge current on the charger, which is usually 1C.

Li-Po Battery Operation and Precautions

It’s safe to say that lithium polymer batteries are the most “delicate” that exist, i.e. require mandatory compliance with several simple rules. We list them in descending order of danger:

Battery recharge - charge 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 above 60°C
Discharge below 3V voltage per jar
Battery heating above 60ºС
Battery depressurization
Storing in a discharged state

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

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

To avoid a fire, you must have a normal charger and correctly set the number of cans to be charged on it.
It is also necessary to use connectors that exclude the possibility of short-circuiting 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 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 quietly and peacefully “die” due to overdischarge
Monitor the voltage at the end of the battery discharge and be sure to turn it off after use
Depressurization is also the reason for failure of lithium batteries. No air should get inside the element. This can happen if the outer protective package (the battery is sealed in a package like heat-shrink tubing) is damaged due to an impact, or damage with a sharp object, or if the battery terminal is severely 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 a temperature not exceeding 30°C. Storing in a discharged state has a negative impact on service life. Like all batteries, lithium polymer batteries have a slight self-discharge.

Li-Po 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 with three pairs of batteries, and each pair is formed by two batteries connected in parallel with a capacity of 1500 mAh, i.e. The battery capacity will be 3000 mAh (when connected in parallel, the capacity increases), and the voltage will be 3.7V x 3 = 11.1V.

If you buy batteries separately, then before connecting them into a battery you need to equalize their potentials, especially 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 banks to 3V with a current of about 0.1-0.2C 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 should be careful; you should not allow the terminals to overheat - this can break the seal and permanently “kill” a battery that has not yet been used. Some Li-Po batteries come with pieces of a textolite printed circuit board already soldered to the terminals for easy wiring. This adds extra weight - about 1 g per element, but it takes much longer to heat the places for soldering wires - fiberglass does not conduct heat well. Wires with connectors should be secured to the battery case, at least with tape, so as not to accidentally tear them off when connecting to the charger multiple times

The nuances of using Li-Po batteries

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

Over the long life of a battery, 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: it is necessary to monitor the capacity of each battery element.

If a battery is found in an assembly whose capacity differs from other elements by more than 15-20%, it is recommended to refuse to use the entire assembly, or to solder a battery with fewer elements from the remaining batteries.

Modern chargers have built-in balancers, which allow you to charge all 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 a given bank has reached the level of 4.17-4.19V. When the voltage on a separate element exceeds the threshold of 4.17V, the balancer closes part of the current “to itself,” preventing the voltage from exceeding the critical threshold.

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 elements during charging and as a means of identifying “bad” elements in the battery.

The above applies to batteries composed of three or more elements; for two-can batteries, balancers, as a rule, are not used

According to numerous reviews, discharging lithium batteries to a voltage of 2.7-2.8V has a more detrimental effect on capacity than, for example, recharging 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 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 battery capacity is retained). But nevertheless, it is possible to use Li-Po batteries at subzero temperatures, about -10...-15°C. The point is that you don’t need to freeze the battery before use - put it in your pocket where it’s warm. And during use, 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 lies with 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