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Voltage of a charged lithium-ion battery. How to properly charge Li-ion batteries: tips. How to properly charge lithium-ion batteries

In modern society, you can often hear opposing opinions about features. This situation has arisen due to the fact that the development of innovations in the field of portable electronics and technology is very impulsive and society does not always have time to quickly respond to improvements.

It is because of this that numerous stereotypes arise, which do not always correspond to the reality of our time.

City's legends

Previously, almost all types of electronic devices used nickel-cadmium or nickel-metal hydride batteries. When used, these galvanic cells had to be completely discharged, which made it possible to extend their service life and prevent a drop in energy capacity. Now these batteries have not lost their position, but the scope of their application has shifted, and now they cannot be found in mobile phones, laptops or tablets. But the catchphrase of sellers “first discharge, then charge, repeat three times” still occurs. After all, such useful advice was remembered in society, and it is now passed on from mouth to mouth. However, progress took its course, and Ni-Cd, Ni-MH energy cells began to be replaced by a Li-ion battery, and a little later by a lithium-polymer battery. Nickel-cadmium or nickel-metal hydride began to be found in less productive electronics - calculators, navigators, amateur cameras, and so on. While their more innovative counterparts have found their niche in laptops, mobile phones, smartphones, tablets and much more.

Principles of use

The design by which it was created requires a specific attitude towards it. It does not tolerate deep discharge and may even fail if this situation is repeated. Therefore, all devices that use them are not sold dead - this significantly extends the service life of their energy cells. However, the ossified thinking of the masses is doing its dirty work - voices are still heard passing from mouth to mouth how it is necessary to charge a Li-ion battery, focusing on the common rules for Ni-Cd, Ni-MH galvanic cells or without even focusing on their type . After all, even the storage of these energy cells must be carried out in different ways. It is important to completely discharge nickel-cadmium or metal hydride batteries, while lithium-ion and lithium-polymer batteries, on the contrary, need to leave an energy reserve of 60-80 percent.

Complaints and liability

Very often you can hear from people that the purchased Li-ion battery does not serve them for long and they have to change it again. For example, after some time the phone discharges very quickly. Although after purchase it could work for a very long time and made its owner happy. If you look at it, the blame for such a mess lies not with the manufacturers, but with the conditions under which the Li-ion batteries were charged and used. After all, all the harmful models of human behavior with them have already been described above, and the owner only strictly follows them.

Features of application

Thus, when modern energy cells operate in harsh environmental conditions (in frost or cold), the battery spends much more resources than in a warm room, which causes increased wear. In such cases, it is most rational to use electronics not too intensively (do not run GPRS Internet, navigation, games and other resource-intensive applications), then there will be much more. A logical question also arises: how to charge a Li-ion battery under such conditions? The device must be connected to power sources in a warm room, when it is not completely dead. Thus, the battery is operated in the most favorable conditions for which it was designed.

"Preservation" of galvanic cells

• charge it to 40-50 percent;
• remove from the device;
• seal hermetically in polyethylene, if possible, create a vacuum in this bag;
• stack each battery separately from the others;
• move the galvanic cells to the refrigerator (but not to the freezer);
• once every few months, remove from there and, after warming up at room temperature, restore to the above capacity;
• Fully charge before intensive use.

These measures will help keep your battery from losing its efficiency. Since they are intended for constant use only in conditions where you yourself would feel comfortable - at room temperature or close to it.

Using quality equipment

In addition, any type of battery - Li-ion, Ni-Cd, Ni-MH - must be charged with the original device, which is recommended by its manufacturer, since cheaper analogues are very different from the original equipment in their parameters. After all, even a slight excess can reduce it by almost half. In the opposite scenario, i.e., a decrease of only 0.1 volts, battery life is reduced by more than 10 percent and the battery is never fully charged. With regular use in this mode, it loses its capacity and no longer corresponds to the manufacturer’s declared values.

For a long time, the acid battery was the only device capable of providing electric current to autonomous objects and mechanisms. Despite the high maximum current and minimal internal resistance, such batteries had a number of disadvantages that limited their use in devices that consume large amounts of electricity or in enclosed spaces. In this regard, lithium-ion batteries lack many of the negative qualities of their predecessors, although they do have disadvantages.

Contents

What is a lithium ion battery

The first lithium batteries appeared 50 years ago. Such products were a regular battery, in which a lithium anode was installed to increase the level of electricity output. Such products had very high performance characteristics, but one of the most serious drawbacks was the high probability of lithium ignition when the cathode overheated. Given this feature, scientists eventually replaced the pure element with metal ions, as a result of which safety increased significantly.

Modern li-ion batteries are very reliable and can withstand a large number of charge and discharge cycles. They have minimal memory effect and relatively light weight. Due to these properties, lithium batteries are widely used in many devices. The product can be used as a battery, in the form of batteries for household appliances, and also as a highly efficient traction source of electricity.

Today, such devices have several disadvantages:

• high cost;
• do not like deep discharges;
• may die at low temperatures;
• lose capacity when overheated.

How is li-ion battery production carried out?

Lithium-ion batteries are produced in several stages:

1. Manufacturing of electrodes.
2. Combining electrodes into a battery.
3. Installing the protection board.
4. Installing the battery into the case.
5. Filling with electrolyte.
6. Testing and charging.

At all stages of production, technology and safety measures must be observed, which ultimately allows us to obtain a high-quality product.

Lithium-ion batteries use foil as a cathode with a lithium-containing substance deposited on its surface.

Depending on the purpose of the battery, the following lithium compounds can be used:

• LiCoO2;
• LiNiO2;
• LiMn2O4.

When producing cylindrical power sources of size AA and AAA, the main electrode is rolled into a roll, which is separated from the anode by a separator. With a large cathode area, the film of which has a minimum thickness, it is possible to achieve high energy intensity of the product.

Operating principle and design of a li-ion battery

A lithium ion battery works as follows:

1. When direct electric current is applied to the battery contacts, lithium cations move into the anode material.
2. During the discharge process, lithium ions leave the anode and penetrate into the dielectric to a depth of 50 nm.

In the “life” of a lithium-ion battery, there can be up to 3,000 such cycles, while the battery can deliver almost all the electric current accumulated during the charging process. A deep discharge does not lead to oxidation of the plates, which makes such products stand out compared to acid batteries.

Not all li-ion batteries tolerate deep discharges well. If such a battery is installed in a phone or camera (AAA type), then if it is deeply discharged, the controller board blocks the ability to charge the battery for safety reasons, so it will not be possible to charge it without a special charger. If this is a traction lithium battery for a boat motor, then it will not be at all afraid of a deep discharge.

Unlike AA batteries, complex batteries consist of several separate sources of electricity connected in parallel or in series. The connection method depends on what electricity indicator needs to be increased.

Sizes and types of li-ion batteries

Lithium-ion batteries have become widespread. Such sources of electric current are used in various household devices, gadgets and even cars. In addition, industrial lithium-ion batteries with large capacity and high voltage are manufactured. The most popular types of lithium batteries are:

Name	Diameter, mm	Length, mm	Capacity, mAh
10180	10	18	90
10280	10	28	180
10440 (AAA)	10	44	250
14250 (AA/2)	14	25	250
14500	14	50	700
15270 (CR2)	15	27	750-850
16340 (CR123A)	17	34.5	750-1500
17500 (A)	17	50	1100
17670	17	67	1800
18500	18	50	1400
18650 (168A)	18	65	2200-3400
22650	22	65	2500-4000
25500 (type C)	25	50	2500-5000
26650	26	50	2300-5000
32600 (type D)	34	61	3000-6000

The first two digits of such designations indicate the diameter of the product, the second pair - the length. The last “0” is placed if the batteries are cylindrical in shape.

In addition to cylindrical batteries, the industry produces batteries of the "" type with a voltage of 9v and powerful industrial batteries with a voltage of 12v, 24v, 36v and 48v.

Battery for stacker

Depending on the elements that are added to the product, the battery case may have the following markings:

• ICR – containing cobalt;
• IMR - - - - manganese;
• INR - - - - nickel and manganese;
• NCR - - - - nickel and cobalt.

Lithium batteries differ not only in size and chemical additives, but primarily in capacity and voltage. These two parameters determine the possibility of their use in certain types of electrical devices.

Where are li-ion batteries used?

Lithium-ion batteries have no alternative where a battery is needed that can deliver almost all of the electricity and perform a large number of charge/discharge cycles without reducing capacity. The advantage of such devices is their relatively low weight, because there is no need to use lead gratings in such devices.

Given their high performance characteristics, such products can be used:

1. As starter batteries. Lithium batteries for cars are becoming cheaper every year, thanks to new developments that reduce production costs. Unfortunately, the price of such batteries can be very high, so many car owners cannot afford such a battery. The disadvantages of lithium-ion batteries include a significant drop in power at temperatures below minus 20 degrees, so in northern regions the operation of such products will be impractical.
2. As traction devices. Due to the fact that lithium-ion batteries can easily withstand deep discharge, they are often used as traction batteries for electric boat motors. If the engine power is not too high, then one charge is enough for 5 - 6 hours of continuous operation, which is quite enough for fishing or taking a boat trip. Traction lithium-ion batteries are also installed on various loading equipment (electric stackers, electric forklifts) operating in enclosed spaces.
3. In household appliances. Lithium-ion batteries are used in various household devices instead of standard batteries. Such products have a voltage of 3.6v - 3.7v, but there are models that can replace a regular salt or alkaline battery with 1.5 Volts. You can also find 3v batteries (15270, ), which can be installed instead of 2 standard batteries.

Such products are used mainly in powerful devices in which conventional salt batteries discharge very quickly.

Traction battery

Rules for using li ion batteries

The service life of a lithium battery is influenced by many factors, knowledge of which will significantly increase the resource. When using this type of battery you must:

1. Try not to let the battery drain completely. Despite the high resistance of the battery to such influences, it is advisable not to squeeze all the “juices” out of it. Particular care should be taken when operating these batteries with UPS and high power electric motors. If the battery is completely discharged, it is necessary to immediately revive it, that is, connect it to a special charger. You can boost the battery even after a long stay in a state of deep discharge, for which you need to perform a high-quality charge for 12 hours, then discharge the battery.
2. Avoid overcharging. Overcharging negatively affects the performance of the product. The built-in controller is not always able to turn off the battery in time, especially when charging is carried out in a cold room.

In addition to overcharging and excessive discharge, the battery should be protected from excessive mechanical stress, which can cause depressurization of the case and fire of the internal components of the battery. For this reason, it is prohibited to send by mail batteries containing more than 1 g of pure lithium.

Used as a battery for screwdrivers, laptops and phones

How to store lithium ion batteries

If there is a need for long-term storage of lithium-ion batteries, then to minimize the negative impact on the products, you must adhere to the following recommendations:

1. Store the product only in a dry, cool place.
2. The battery must be removed from the electrical device.
3. The battery must be charged before storage. The minimum voltage at which internal corrosion processes will not form is 2.5 Volts per 1 element.

Considering the low self-discharge of such batteries, the battery can be stored in this way for several years, but during this period the cell’s capacity will inevitably decrease.

Recycling lithium-ion batteries

Lithium-ion batteries contain substances that are hazardous to health and should never be disassembled at home. After the battery has exhausted its service life, it must be returned for further recycling. At specialized collection points you can receive monetary compensation for an old lithium battery, because such products contain expensive elements that can be reused.

Since any battery (battery) is a source of constant electric current, sooner or later its charge will inevitably be depleted. With each recharge, its capacity will become less and less. These are the laws of physics.

You can only extend its work for a short time. Let's look at how to recondition a lithium-ion battery to gain the time needed to replace the battery.

IMPORTANT. If you are new to technology, then, in general, there is nothing worth reading further - just go get a new battery or invite a competent friend. (No need to call godfather!).

In addition, you will learn about the causes of fire, explosion hazards, and aging of LIBs. This information will help determine what exactly happened to the battery, and will also make it possible to avoid operational errors.

So, lithium-ion batteries (LIB) are used in a wide range of various modern technologies as a source of electricity. energy from mobile phones to storage devices in energy systems.

Their main performance indicators may vary within the following limits (this depends on their chemical composition):

• Voltage (nominal) - 3.7 V or 3.8 V;
• Maximum voltage - 4.23 V or 4.4 V;
• Minimum voltage - 2.5–2.75 V or 3.0 V;
• The number of charge-discharges is 600 (with a loss of 20% of capacity);
• Internal resistance 5–15 mOhm/Ah;
• Under normal conditions, the self-discharge value is 3% per month;
• The operating temperature range is from minus 20°C to plus 60°C, the optimal temperature is plus 20°C.
• If the voltage is exceeded when charging the LIB, it may catch fire. To protect against this, a controller is inserted into the housing. Its function is to disable the LIA. (Also controlling current, overheating and depth of discharge).
• To reduce costs, not every lithium battery is equipped with a controller (or does not provide protection for all parameters).

INTERESTING: The first manufacturer of lithium batteries was Sony Corporation in 1991.

Design and advantages of LIB

A LIB consists of a cathode (on aluminum foil) and an anode (on copper foil), separated by an electrolytic separator and placed in a sealed “can.”

The cathode and anode are connected to the current collecting terminals.

The housing is sometimes equipped with a valve to relieve pressure in case of emergency operation.

In a lithium-ion battery (LIB), the charge is carried by a lithium ion. Its characteristic ability is the ability to penetrate into the crystal lattice of other materials (in our case, graphite, oxides or salts of metals), thereby forming chemical bonds.

Currently, three types of cathode materials are used:

• Lithium cobaltates (thanks to cobalt, the number of charge-discharge cycles increases, and it also becomes possible to operate at low temperatures);
• Lithium manganese;
• Lithium ferrophosphate (low cost).
• The advantages of LIBs are low self-discharge and a large number of cycles.

Disadvantages of LIA

The explosion hazard of Li-ion batteries in the first generation was justified by the occurrence of gaseous formations that led to a short circuit between the electrodes. This has now been eliminated by changing the anode material from lithium metal to graphite.

Explosion hazards also arose in cobalt oxide LIBs due to operational failures.

LIBs based on lithium ferrophosphate are completely free of this disadvantage.

IMPORTANT. Discharging LIBs at low temperatures (especially repeated discharge) leads to a reduction in recoil energy of up to tens of percent. In addition, LIBs “sharply” react to temperature when charging: the optimal temperature is +20 °C, and +5 °C is no longer recommended.

Memory effect

Research has confirmed the existence of a memory effect in LIB. But the point is its fundamental presence, and not its influence on the work as a whole.

The explanation for this process is as follows: the battery operates by periodically releasing and capturing lithium ions, and this process, when not fully charged, deteriorates due to disruption of the microstructure of the electrode.

IMPORTANT. Experts have identified two rules for extending the service life of LIBs:

• Preventing complete discharge;
• Do not charge near heat sources.

Aging

LIBs age even when not in use. Twenty percent of capacity is lost after just two years. You should not buy them “for the table”. When purchasing, look at the production date.

Low temperatures and power

Up to fifty percent of battery power is lost at operating temperatures below 0 °C.

Spontaneous combustion

LIBs are prone to spontaneous combustion. During thermal acceleration of a faulty (damaged) battery, substances are released that accelerate its self-heating (oxygen plus flammable gases). Therefore, it is capable of burning even in the absence of air.

To extinguish in such cases, provide for a lower temperature and prevent the spread of fire.

Let's start restoration

Once you already know from the above the “physics” and “chemistry” of the operation of the LIB and its filling, you can independently choose one of the methods for treating your battery, and also evaluate the “reasonableness” of the methods below.

Getting rid of gases

We already know that if used incorrectly, gaseous substances can form inside the “can.”

The essence of this method is that you need to get rid of them. To do this, first remove the upper block (controller), then pierce the discovered cap, and then press it against a hard surface with some kind of press to release gases.

After this, seal the hole with epoxy resin and return the controller to its place.

But before you revive your phone battery in this way, remember the expected dangers of this method:

• Damage to the device due to excessive impact;
• Damage to the electronics under the cap;
• Possibility of explosion (spontaneous combustion) when the cathode is short-circuited with the anode.

Short-term “return” of capacity

You can briefly revive the battery if you “revive” it using a 5–12 Volt power supply, a resistor from 330 to 1000 Ohms and a power of at least 500 mW.

To do this, the contacts of the power supply are connected to the contacts of the LIB: minus to minus, and plus to plus through a resistor, the polarity of which is checked with a multimeter. Consumption time is no more than two to three minutes.

Please note that the parameters of the supplied current must correspond to the required ones, and use a voltmeter or tester to control the voltage.

We use the refrigerator

Following this simple method, battery restoration is carried out as follows:

The battery removed from the smartphone must be placed in the refrigerator for a period of twenty to thirty minutes, after placing it in a plastic bag. Then connect it to the charger for one minute, and then wait until it warms up to room temperature.

Allegedly, after these manipulations it can be used as usual.

Charge-discharge method

This method should be called a method of resuscitating a battery for a fifth-grade student.

According to the popularizers of this “joke,” the phone’s battery can be “brought to life” by charging it “several times” (the number of times is not specified) to 100% and then completely discharging the battery. To discharge, it is advised to use some resource-intensive game or AnTuTu utility, each time removing and inserting it back into the mobile phone.

It remains unclear how the battery will be charged several times to 100 percent if it is already inoperative?

"Wild" recovery method

This “maneuver” consists in the fact that after removing the protective controller, you need to short-circuit the output current collector terminals with some metal object. After this, the controller returns to its place.

At the same time, another significant point is added - at the beginning of the procedure, for some reason, you need to peel off the sticker with the technical characteristics of the LIB. This is truly “dancing with a tambourine”!

Rocking the LIB disabled by the controller

To prevent deep discharge, lithium-ion batteries are equipped with a controller that puts them into a “shutdown” state. In this case, when measuring the voltage at its terminals in front of the controller, you can detect a value of about 2.5 volts. This means the battery is still alive!

To do this, the protection circuit is first turned off (unsoldered).

The “can” is connected to a universal charge-discharge device (for example, Turnigy Accucell 6). In this case, the device itself monitors the process and the restoration takes place under its control.

The “TYPE” button selects the “Li-Po” charging program, because our LIB is 3.7V.

By short pressing “START” the charging parameters are selected. For Li-ion - the value is 3.6 V, for Li-pol - 3.7 V.

You need to select “AUTO” for the parameter, since in our case the charging will not start due to the low battery charge.

The charge current must be set at ten percent of the battery capacity (in our case, 150 mA). The value is set using the “+” and “-” buttons.

When the battery charge reaches 4.2 V, the device will be switched to voltage stabilization mode, and upon completion of the process, a sound signal will sound and the message “FULL” will appear on the display.

And finally, a video about how you don’t need to recharge batteries

Safety Notes

Before reconditioning a lithium-ion battery, you should remember the following rules:

• You should not leave a problematic LIB unattended during repairs. Spontaneous combustion is not a threat, but a real fact.
• It is necessary to periodically monitor the temperature of the phone battery with a remote thermocouple, an electronic thermometer, or at least with your hand. If the surface appears hot rather than warm, repairs must be stopped immediately.
• Do not use high currents for charging. The possible permissible maximum is 50 mA. This parameter is calculated by dividing the power supply voltage by the resistor capacitance. For example, at 12 V and 500 ohms it will be 24 mA.
• Instead of a resistor, it is permissible to use a standard 80 mm computer fan.

Remember that the above methods do not give a 100% result, and in any case the responsibility lies with you. This is especially true for humanists.

Don't overestimate your knowledge and capabilities. It’s better to consult with knowledgeable people once again.

Share your experience with friends and write in the comments.

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

Li-ion battery device

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

Lithium polymer battery design

The impetus for improving lithium batteries was the need to combat two shortcomings of existing Li-ion batteries. Firstly, they are unsafe to use, and secondly, they are quite expensive. Technologists decided to get rid of these disadvantages by changing the electrolyte. As a result, the impregnated porous separator was replaced by a polymer electrolyte. It should be noted that the polymer has previously been used for electrical needs as a plastic film that conducts current. In a modern battery, the thickness of the Li-pol element reaches 1 mm, which also removes restrictions on the use of various shapes and sizes from developers. But the main thing is the absence of liquid electrolyte, which eliminates the risk of ignition. Now it’s worth taking a closer look at the differences from lithium-ion cells.

What is the main difference from an ion battery?

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

Lithium polymer battery life

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

Flaws

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

Operational features of gel-like modifications

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

Optimal charging method

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

Precautionary measures

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

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

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

Conclusion

There are still many myths and false opinions around batteries that relate to various nuances of operation. On the contrary, some battery features are hushed up by manufacturers. As for the myths, one of them is refuted by the lithium polymer battery. The difference from the ionic analogue is that polymer models experience less internal stress. For this reason, charging sessions for batteries that have not yet run out do not have a harmful effect on the characteristics of the electrodes. If we talk about the facts hidden by manufacturers, then one of them concerns durability. As already mentioned, battery life is characterized not only by a modest rate of charging cycles, but also by the inevitable loss of the useful volume of the battery.

Lithium-ion (Li-ion) batteries are most often used in mobile devices (laptops, mobile phones, PDAs and others). This is due to their advantages over the previously widely used nickel-metal hydride (Ni-MH) and nickel-cadmium (Ni-Cd) batteries.

Li-ion batteries have significantly better parameters.
Primary cells (“batteries”) with a lithium anode appeared in the early 70s of the 20th century and quickly found application due to their high specific energy and other advantages. Thus, a long-standing desire was realized to create a chemical current source with the most active reducing agent - an alkali metal, which made it possible to sharply increase both the operating voltage of the battery and its specific energy. While the development of primary cells with a lithium anode was crowned with relatively quick success and such elements firmly took their place as power sources for portable equipment, the creation of lithium batteries encountered fundamental difficulties, which took more than 20 years to overcome.

After many tests during the 1980s, it turned out that the problem with lithium batteries revolved around the lithium electrodes. More precisely, around the activity of lithium: the processes that occurred during operation ultimately led to a violent reaction, called “ventilation with flame emission.” In 1991, a large number of lithium batteries, which were first used as a power source for mobile phones, were recalled by manufacturers. The reason was that during a conversation, when the current consumption was at its maximum, a flame erupted from the battery, burning the face of the mobile phone user.

Due to the inherent instability of lithium metal, especially during charging, research has moved towards creating a battery without the use of Li, but using its ions. Although lithium-ion batteries provide slightly lower energy density than lithium batteries, Li-ion batteries are safe when properly charged and discharged.

Chemical processes of Li-ion batteries.

The development of rechargeable lithium batteries has been revolutionized by the announcement that Japan has developed batteries with a negative electrode made from carbon materials. Carbon turned out to be a very convenient matrix for lithium intercalation.
In order for the battery voltage to be high enough, Japanese researchers used cobalt oxides as the active material of the positive electrode. Litered cobalt oxide has a potential of about 4 V relative to the lithium electrode, so the operating voltage of a Li-ion battery has a characteristic value of 3 V and higher.

When a Li-ion battery discharges, lithium is deintercalated from the carbon material (at the negative electrode) and lithium is intercalated into the oxide (at the positive electrode). When charging the battery, the processes go in the opposite direction. Consequently, there is no metallic (zero-valent) lithium in the entire system, and the processes of discharge and charge are reduced to the transfer of lithium ions from one electrode to another. Therefore, these batteries are called "lithium-ion" or rocking chair batteries.

Processes on the negative electrode of a Li-ion battery.

In all Li-ion batteries brought to commercialization, the negative electrode is made of carbon materials. Intercalation of lithium into carbon materials is a complex process, the mechanism and kinetics of which largely depend on the nature of the carbon material and the nature of the electrolyte.

The carbon matrix used as an anode can have an ordered layered structure, like natural or synthetic graphite, disordered amorphous, or partially ordered (coke, pyrolysis or mesophase carbon, soot, etc.). When introduced, lithium ions push the layers of the carbon matrix apart and are located between them, forming intercalates of various structures. The specific volume of carbon materials in the process of intercalation-deintercalation of lithium ions changes slightly.
In addition to carbon materials, structures based on tin, silver and their alloys, tin sulfides, cobalt phosphorides, and carbon composites with silicon nanoparticles are being studied as a negative electrode matrix.

Processes on the positive electrode of a Li-ion battery.

While primary lithium cells use a variety of active materials for the positive electrode, lithium batteries have a limited choice of positive electrode material. The positive electrodes of lithium-ion batteries are created exclusively from lithiated cobalt or nickel oxides and lithium manganese spinels.

Currently, materials based on mixed oxides or phosphates are increasingly used as cathode materials. It has been shown that the best battery performance is achieved with mixed oxide cathodes. Technologies for coating cathode surfaces with finely dispersed oxides are also being mastered.

Li-ion battery design

Structurally, Li-ion batteries, like alkaline batteries (Ni-Cd, Ni-MH), are produced in cylindrical and prismatic versions. In cylindrical batteries, a rolled-up package of electrodes and a separator is placed in a steel or aluminum case, to which the negative electrode is connected. The positive pole of the battery is brought out through the insulator to the cover (Fig. 1). Prismatic batteries are made by stacking rectangular plates on top of each other. Prismatic batteries provide tighter packing within the battery, but are more difficult to maintain compressive forces on the electrodes than cylindrical batteries. Some prismatic batteries use a roll assembly of a package of electrodes, which is twisted into an elliptical spiral (Fig. 2). This allows you to combine the advantages of the two design modifications described above.

Fig.1 Design of a cylindrical Li-Ion battery.

Fig.2. The device of a prismatic lithium-ion (Li-ion) battery with rolled electrodes.

Some design measures are usually taken to prevent rapid heating and ensure safe operation of Li-ion batteries. Under the battery cover there is a device that responds to the positive temperature coefficient by increasing resistance, and another that breaks the electrical connection between the cathode and the positive terminal when the gas pressure inside the battery increases above the permissible limit.

To increase the safety of operation of Li-ion batteries, external electronic protection is also required as part of the battery, the purpose of which is to prevent the possibility of overcharging and overdischarging each battery, short circuit and excessive heating.
Most Li-ion batteries are manufactured in prismatic versions, since the main purpose of Li-ion batteries is to power cell phones and laptops. As a rule, the designs of prismatic batteries are not unified and most manufacturers of cell phones, laptops, etc. do not allow the use of third-party batteries in devices.

Characteristics of Li-ion batteries.

Modern Li-ion batteries have high specific characteristics: 100-180 Wh/kg and 250-400 Wh/l. Operating voltage - 3.5-3.7 V.
If a few years ago developers considered the achievable capacity of Li-ion batteries to be no higher than several ampere-hours, now most of the reasons limiting the increase in capacity have been overcome and many manufacturers have begun to produce batteries with a capacity of hundreds of ampere-hours.
Modern small-sized batteries are operational at discharge currents of up to 2 C, powerful ones - up to 10-20 C. Operating temperature range: from -20 to +60 °C. However, many manufacturers have already developed batteries that operate at -40 °C. It is possible to expand the temperature range to higher temperatures.
The self-discharge of Li-ion batteries is 4-6% in the first month, then it is significantly less: in 12 months the batteries lose 10-20% of their stored capacity. The capacity loss of Li-ion batteries is several times less than that of nickel-cadmium batteries, both at 20 °C and at 40 °C. Resource: 500-1000 cycles.

Charge Li-ion batteries.

Li-ion batteries are charged in a combined mode: first at constant current (in the range from 0.2 C to 1 C) to a voltage of 4.1-4.2 V (depending on the manufacturer’s recommendations), then at constant voltage. The first charging stage can last about 40 minutes, the second stage longer. Faster charging can be achieved with pulse mode.
In the initial period, when Li-ion batteries using the graphite system first appeared, a charge voltage limit of 4.1 V per cell was required. Although the use of higher voltages allows for higher energy density, the oxidation reactions that occurred in these types of cells at voltages exceeding the 4.1 V threshold led to a reduction in their service life. Over time, this drawback was eliminated through the use of chemical additives, and currently Li-ion cells can be charged up to a voltage of 4.20 V. The voltage tolerance is only about ±0.05 V per cell.
Li-ion batteries for industrial and military use must have a longer service life than batteries for commercial use. Therefore, for them, the threshold end-of-charge voltage is 3.90 V per cell. Although the energy density (kWh/kg) of such batteries is lower, the increased service life with small size, low weight and higher energy density compared to other types of batteries make Li-ion batteries unrivaled.
When charging Li-ion batteries with a current of 1C, the charging time is 2-3 hours. The Li-ion battery reaches a state of full charge when the voltage across it becomes equal to the cut-off voltage, and the current decreases significantly and is approximately 3% of the initial charge current (Fig. 3).

Fig.3. Dependence of voltage and current on time when charging a lithium-ion (Li-ion) battery

If Fig. 3 shows a typical charge graph for one of the types of Li-ion batteries, then Fig. 4 shows the charging process more clearly. When the charging current of a Li-ion battery increases, the charging time does not decrease significantly. Although the battery voltage rises faster at higher charging currents, the recharging phase after the first stage of the charge cycle is completed takes longer.
Some types of chargers require 1 hour or less to charge a lithium-ion battery. In such chargers, stage 2 is eliminated, and the battery goes into a ready state immediately after the end of stage 1. At this point, the Li-ion battery will be approximately 70% charged, and additional recharging is possible after that.

Fig.4. Dependence of voltage and current on time when charging a Li-ion battery.

• STAGE 1 - The maximum permissible charging current flows through the battery until the voltage across it reaches a threshold value.
• STAGE 2 - The maximum battery voltage has been reached, the charging current is gradually reduced until it is fully charged. The moment of completion of the charge occurs when the value of the charge current decreases to a value of 3% of the initial value.
• STAGE 3 - Periodic compensating charge carried out during battery storage, approximately every 500 hours of storage.

The trickle charging stage is not applicable for Li-ion batteries due to the fact that they cannot absorb energy when recharged. Moreover, trickle charging can cause lithium metallization, which makes the battery unstable. On the contrary, short charging with direct current can compensate for the small self-discharge of the Li-ion battery and compensate for the energy losses caused by the operation of its protection device. Depending on the type of charger and the degree of self-discharge of the Li-ion battery, such recharging can be performed every 500 hours or 20 days. Typically, this should be done when the open circuit voltage drops to 4.05 V/cell and stops when it reaches 4.20 V/cell.
So, Li-ion batteries have low overcharge resistance. On the negative electrode on the surface of the carbon matrix, with a significant recharge, it becomes possible for the deposition of metallic lithium (in the form of a finely crushed mossy sediment), which has a high reactivity to the electrolyte, and the active evolution of oxygen begins at the cathode. There is a threat of thermal runaway, increased pressure and depressurization. Therefore, Li-ion batteries can only be charged up to the voltage recommended by the manufacturer. With increased charging voltage, battery life decreases.
The safe operation of Li-ion batteries must be given serious attention. Commercial Li-ion batteries have special protection devices that prevent the charging voltage from exceeding a certain threshold value. An additional protection element ensures that the charge is completed if the battery temperature reaches 90 °C. The most advanced batteries in design have another element of protection - a mechanical switch, which is triggered when the internal pressure of the battery increases. The built-in voltage control system is configured for two cut-off voltages - upper and lower.
There are exceptions - Li-ion batteries, in which there are no protection devices at all. These are rechargeable batteries that contain manganese. Thanks to its presence, during recharging, the reactions of metallization of the anode and the release of oxygen at the cathode occur so slowly that it has become possible to abandon the use of protection devices.

Safety of Li-ion batteries.

All lithium batteries are characterized by fairly good preservation. Capacity loss due to self-discharge is 5-10% per year.
The given figures should be considered as some nominal guidelines. For each specific battery, for example, the discharge voltage depends on the discharge current, discharge level, temperature; the resource depends on the modes (currents) of discharge and charge, temperature, and depth of discharge; the range of operating temperatures depends on the level of service life, permissible operating voltages, etc.
The disadvantages of Li-ion batteries include sensitivity to overcharging and overdischarging, which is why they must have charge and discharge limiters.
A typical type of discharge characteristics of Li-ion batteries is shown in Fig. 5 and 6. From the figures it is clear that with increasing discharge current, the discharge capacity of the battery decreases slightly, but the operating voltage decreases. The same effect appears when discharged at a temperature below 10 °C. In addition, at low temperatures an initial voltage drop occurs.

Fig.5. Discharge characteristics of a Li-ion battery at various currents.

Fig.6. Discharge characteristics of a Li-ion battery at different temperatures.

As for the operation of Li-ion batteries in general, taking into account all the structural and chemical methods of protecting batteries from overheating and the already established idea of ​​the need for external electronic protection of batteries from overcharging and overdischarging, the problem of the safety of operating Li-ion batteries can be considered solved. And new cathode materials often provide even greater thermal stability for Li-ion batteries.

Safety of Li-ion batteries.

When developing lithium and lithium-ion batteries, as well as during the development of primary lithium cells, special attention was paid to the safety of storage and use. All batteries are protected against internal short circuits (and in some cases, also against external short circuits). An effective way of such protection is to use a two-layer separator, one of the layers of which is made not of polypropylene, but of a material similar to polyethylene. In cases of a short circuit (for example, due to the growth of lithium dendrites to the positive electrode), due to local heating, this separator layer melts and becomes impenetrable, thus preventing further dendritic growth.

Li-ion battery protection devices.

Commercial Li-ion batteries have the most advanced protection of any battery type. As a rule, the Li-ion battery protection circuit uses a field-effect transistor switch, which opens when the battery cell voltage reaches 4.30 V and thereby interrupts the charging process. In addition, the existing thermal fuse, when the battery heats up to 90 ° C, disconnects its load circuit, thus providing its thermal protection. But that's not all. Some batteries have a switch that is activated when a threshold pressure level inside the housing is reached, equal to 1034 kPa (10.5 kg/m2), and breaks the load circuit. There is also a deep discharge protection circuit that monitors the battery voltage and breaks the load circuit if the voltage drops to 2.5 V per cell.
The internal resistance of the mobile phone battery protection circuit when turned on is 0.05-0.1 Ohm. Structurally, it consists of two keys connected in series. One of them is triggered when the upper and the other reaches the lower voltage threshold on the battery. The total resistance of these keys effectively doubles its internal resistance, especially if the battery consists of just one cell. Mobile phone batteries must provide high load currents, which is possible with the battery's internal resistance as low as possible. Thus, the protection circuit represents an obstacle that limits the operating current of the Li-ion battery.
In some types of Li-ion batteries that use manganese in their chemical composition and consist of 1-2 elements, the protection circuit is not used. Instead, they only have one fuse. And such batteries are safe due to their small size and small capacity. In addition, manganese is quite tolerant of violations of the rules of operation of Li-ion batteries. The lack of a protection circuit reduces the cost of the Li-ion battery, but introduces new problems.
In particular, mobile phone users may use non-standard chargers to recharge their batteries. When using inexpensive chargers designed for charging from the mains or from the vehicle's on-board network, you can be sure that if the battery has a protection circuit, it will turn it off when the end of charge voltage is reached. If there is no protection circuit, the battery will be overcharged and, as a result, it will fail irreversibly. This process is usually accompanied by increased heating and swelling of the battery case.

Mechanisms leading to a decrease in the capacity of Li-ion batteries

When cycling Li-ion batteries, among the possible mechanisms for reducing capacity, the following are most often considered:
- destruction of the crystal structure of the cathode material (especially LiMn2O4);
- graphite delamination;
- build-up of a passivating film on both electrodes, which leads to a decrease in the active surface of the electrodes and blocking of small pores;
- deposition of metallic lithium;
- mechanical changes in the structure of the electrode as a result of volumetric vibrations of the active material during cycling.
Researchers disagree about which electrode undergoes the most changes during cycling. This depends both on the nature of the selected electrode materials and on their purity. Therefore, for Li-ion batteries it is possible to describe only the qualitative change in their electrical and operational parameters during operation.
Typically, the service life of commercial Li-ion batteries before the discharge capacity is reduced by 20% is 500-1000 cycles, but it significantly depends on the value of the maximum charging voltage (Fig. 7). As the cycling depth decreases, the service life increases. The observed increase in service life is associated with a decrease in mechanical stresses caused by changes in the volume of the implantation electrodes, which depend on the degree of their charge.

Fig.7. Changing the capacity of a Li-ion battery at different maximum charge voltages

Increasing the operating temperature (within the operating range) can increase the rate of side processes affecting the electrode-electrolyte interface and slightly increase the rate of decrease in discharge capacity with cycles.

Conclusion.

As a result of the search for the best material for the cathode, modern Li-ion batteries are turning into a whole family of chemical current sources that differ markedly from each other in both energy capacity and charge/discharge mode parameters. This, in turn, requires a significant increase in the intelligence of control circuits, which have now become an integral part of batteries and powered devices - otherwise damage (including irreversible damage) to both batteries and devices is possible. The task is further complicated by the fact that developers are trying to make maximum use of battery energy, achieving increased battery life while minimizing the volume and weight occupied by the power source. This allows you to achieve significant competitive advantages. According to D. Hickok, vice president of mobile power components at Texas Instruments, when using cathodes made from new materials, battery developers do not immediately achieve the same design and performance characteristics as in the case of more traditional cathodes. As a result, new batteries often have significant operating conditions limitations. Moreover, recently, in addition to the traditional manufacturers of rechargeable cells and batteries - Sanyo, Panasonic and Sony - new manufacturers, mostly from China, are very actively making their way into the market. Unlike traditional manufacturers, they supply products with a significantly larger range of parameters within one technology or even one batch. This is due to their desire to compete primarily through low product prices, which often results in savings on process compliance.
So, at present, the importance of the information provided by the so-called. "smart batteries": battery identification, battery temperature, residual charge and permissible overvoltage. According to Hickok, if off-the-shelf device developers design a power subsystem that takes into account both operating conditions and cell parameters, this will eliminate differences in battery parameters and increase the degree of freedom for end users, which will give them the opportunity to choose not only the devices recommended by the manufacturer, but also and batteries from other companies.