It is installed in all laptops, tablets, mobile phones and other equipment. The rated voltage of such a battery is 3.7-3.8 V, the maximum is up to 4.4 V, and the minimum is from 2.5 to 3.0 V.

From the history of creation

Li-ion batteries first appeared in the early 90s. Their leading manufacturer was initially Sony. This battery contains two electrodes. The cathode is placed on an aluminum foil, and the anode is placed on a copper foil. Separators containing liquid or gel electrolyte are placed between the electrodes. Lithium ions with a “+” charge are current carriers, ions that can penetrate other chemical elements, thereby giving rise to an electrochemical reaction that provides power to a particular device.

Lithium batteries of the previous generation were “famous” for their increased explosion hazard due to the use of a lithium metal anode in them and the occurrence of gaseous chemical compounds inside the battery. With multiple charge-discharge cycles, a short circuit could occur, and then an explosion of the lithium battery. Explosions also occurred because lithium ions reacted dangerously with other substances in the batteries.

When the anode chemical was finally changed to graphite, this was completely corrected. By the way, all modern charging devices, through which batteries receive power, protect them from overheating and “excessive” current. In lithium ferrum phosphate batteries, this serious drawback is completely eliminated. However, it took about 20 years to develop safe battery devices.

To avoid spontaneous combustion of a lithium battery when charging it, manufacturers began to build a battery charge controller into the case. The controller regulates the temperature inside the battery, the depth of discharge and the amount of current consumed. But not all lithium batteries are equipped with a controller. Often the manufacturer does not install it - in order to save money and increase capacity. It is for this reason that some batteries still explode.

However, unlike their predecessors in the form of batteries, ion batteries have much better characteristics. The low level of self-discharge in such batteries ensures their longer shelf life, and the high capacity allows them to work much longer. In addition, not a single lithium cell requires additional maintenance, and if it finally fails, it is better not to restore it, but to replace it.

How to properly use and store a lithium-ion battery

It is important to ensure that the battery always has at least a minimum amount of charge. Any ion battery cannot be allowed to fully discharge. If it is not in use and is completely discharged, it will result in a short battery. The temperature factor greatly affects the safety of the battery.Do not charge or storelithium batteriesat excessively high and low temperatures, as their capacity indicator will quickly begin to fall.

Li-ion is sensitive to voltage changes. If U in the charger is increased even slightly (for example, by only 4%), the battery will lose capacity with each charge-discharge cycle.

The best storage conditions for Li-ion: the charge should be at least 40% of the capacity of the ionic cell, and the temperature should be from 0 to +10°C.

Despite all the positive characteristics, it makes no sense to purchase Li-ion for future use: the battery loses about 4% of its capacity in 2 years. When purchasing, be sure to pay attention to the date of manufacture. If more time has passed since production, it is not recommended to buy such a battery.

The usual one is 2 years, but now manufacturing companies have invented a method that allows them to be stored for a longer time. A special preservative is added to the battery, allowing it to be stored for more than two years. If there is a preservative in the electrolyte, before using it for the first time, the battery should be completely discharged by giving it a kind of training in the form of two or three charge-discharge cycles. With this reactivation, the electrolyte in the battery gradually disintegrates, and the battery returns to its normal capacity level.

If this is not done with lithium cells, the battery will acquire a “memory effect”, and then, since the preservative is still inside, when a charge is applied and the battery current increases, it will begin to quickly disintegrate, and the battery may swell.

If ion batteries are handled carefully and carefully, observing all storage conditions, with proper use they will last a long time, and the capacity level in such batteries will remain at a high level for a long time.

Lithium polymer battery as an alternative to Li-ion

Polymer batteries are an improved version of lithium-ion batteries. Technical progress does not stand still, and now they are already being considered as a serious alternative to previous lithium-based batteries. The purpose of creating batteries based on polymer materials was, first of all, to possibly eliminate the disadvantages of Li-ion in the form of high cost and increased risk of spontaneous combustion.

The main difference between a polymer battery and Li-ion is that not liquid or gel, but solid polymers are used as the electrolyte in its manufacture. Changing the electrolyte is a big achievement because these batteries are safer and you can now worry much less about potential explosions when using them.

Solid materials have played a major role in current conduction before - for example, using a film of plastic, and their use inside a Li-pol battery, instead of a porous liquid-impregnated separator between its two poles, was a significant step forward.

Li-pol batteries also have improved characteristics in terms of convenient shape, since polymers make it possible to obtain different sizes and types of such batteries. The minimum thickness of polymer batteries can be only 1 mm.

Along with the differences, there are also similarities between Li-ion and Li-pol. For the most part, this means that not all shortcomings have been eliminated, and the possibilities for further work by manufacturers have not yet been fully exhausted. For example, there is not much difference between them in terms of service life and the problem of “aging” if they are not used.

Polymer batteries, like Li-ion, are used in cell phones, radio-controlled equipment, and portable electric tools, such as electric drills and screwdrivers.

Some manufacturers of polymer batteries claim that they do not have a memory effect, and they can allegedly operate in a wider temperature range: from -20 to +40-60°C, which makes it possible to use them in hot tropical climates. Since the danger of spontaneous combustion has not yet been completely eliminated, polymer batteries are usually equipped with a built-in electrical circuit that prevents overcharging and overheating.

How to restore a Li-ion battery

Despite the fact that the service life of many modern batteries is quite long, there comes a time when the charge of any chemical current source is depleted. The capacity drops, and the battery can no longer work for a long time and properly. Especially if the discharged power source has been stored for a long time without recharging. There are several common ways to bring it back to life. The reconditioned battery will not last long, but this will buy you time before it needs to be replaced.

The most unexpected and sometimes completely illogical methods are described on the Internet. For example, there are articles that you can effectively stretch a battery if you charge and discharge it several times in a row. Of course, this is a myth, and this “method” should not be used. Also on one of the popular forums, a real-life example is described of how one person rocked a battery by putting it in the refrigerator. It swelled to enormous sizes and burst after it was removed from the freezer - naturally, due to the temperature change.

To the serious question of how to really recharge a cell phone battery, you can give a simple and clear answer: take any battery charger with a voltage of 5-12 V and a resistor with a resistance of 330 Ohms to 1 kiloOhm. The connection diagram is extremely simple: the “minus” of the power source is connected to the “minus” of the battery, and the “plus” to the “plus”, through a resistor. Now you need to plug in the charger and regularly check the voltage increase using a multimeter for 10-15 minutes. The voltage gradually increases, and when it reaches approximately 3.31 V, the phone “finds” the battery and accepts it.

Swinging up Li-ion, turned off by the controller, with quickly bringing the battery into working condition is also possible . In this case, when measuring the current voltage, its value will be about 2.5 V. The battery is “alive” and can still work for some time, although, at first glance, it looks almost discharged. We restore it like this: for this you will need a “people’s charger” Imax B6 and a multimeter. The protective circuit of the battery is unsoldered and connected to Imax. And how to check the voltage is already clear: it is always monitored with a multimeter.

We rock the battery as carefully as possible. The charging program is set to Li-Po, the charging mode is selected depending on the type of battery: for Li-ion - 3.6 V, or 3.7 V for Li-pol. Important: during the recovery process, set the Auto parameter - without it, the start will not start due to the low battery charge. The current value is selected using the “+” and “–” buttons. 1 A is the safest and optimal current for boosting.

When the voltage reaches 3.2-3.3 V, the battery will begin its full operation.

Is it possible to fix a swollen battery?

There are a large number of popular articles on this topic on the Internet and even videos like “I restore swollen batteries in a simple way.” What follows is a description or filming of the process of disassembling the battery, piercing it with a needle or awl in order to “release gases”, and then inserting the battery back into the phone.

Unfortunately, the unlucky authors of such videos and publications do not explain to people why the battery is swollen, but boldly proceed to very dubious actions that may be unsafe both for the person and for the device in which such a battery is placed.

“Training the intellect” and engaging in such restoration is strongly discouraged. It should be understood that any lithium-ion battery is, first of all, a source of chemical reactions that can be both toxic and explosive.

Battery swelling can occur either as a result of a disruption in the chemical processes inside it due to a manufacturing defect, or due to the fault of the gadget owner if the operation was incorrect.

If, for example, a cheap battery is swollen due to a defect in its manufacture, you should think about whether the manufacturer was trusted, and next time it is better to purchase a battery at a higher price, but with a guarantee of quality.

Batteries also swell when moisture gets inside, which most often occurs due to the negligence of the owner of the phone or tablet. If you use the wrong device when charging your phone, the battery will sooner or later swell due to a high current level, which disrupts the speed of chemical processes inside it. If the phone is designed for a current of 1A, charging with a current of 2A can no longer be used. As an alternative, you can take a device with a lower, but not higher current rating - in case the “original” charger is lost or fails.

Using the battery in hot climates can also cause it to swell. You should not leave a fully charged phone in the heat, and if the battery is swollen for some reason, it should not be disassembled and pierced, but replaced with a new one.

It's been a long time since Ni-Cd and Ni-Mh batteries reigned supreme in mobile devices, but since the beginning of the era of Li-ion and Li-pol, there has been ongoing debate about whether these batteries need to be "trained" immediately after purchase.
It’s getting ridiculous, in the ZP100 discussion thread on china-iphone, all newbies were recommended in an orderly tone to go through 10 charge-discharge cycles, and only then come with questions about batteries.

Let's try to figure out whether such a recommendation has the right to life, or whether these are reflexes of the spinal cord (in the absence of the brain, probably) of some individuals who have them left over from the times of nickel batteries.

The text can and most likely contains spelling, punctuation, grammatical and other types of errors, including semantic ones. The author will be grateful for information about them (of course, in private, and even better with the help of this wonderful extension), but does not guarantee their elimination.

About terminology

About reading datasheets

A datasheet for the battery was found on Google, consisting of one page:


I'll decipher what is written there.
I think what is it Nominal capacity And Minimum capacity Everyone understands - the usual capacity, and the minimum capacity. The designation 0.2 C means that it reaches such a capacity only if it is discharged with a current of 0.2 of its capacity - 720 * 0.2 = 144 mA.
Charding voltage And Nominal Voltage- Charging voltage and operating voltage are also simple and clear.
But the next point is more difficult - Charging.
Method: CC/CV- Means that the first half of the charging process must be maintained at a constant current (it is indicated below, 0.5C is standard - i.e. 350mA, and 1C is maximum - 700mA). And after the voltage on the battery reaches 4.2V, you need to set a constant voltage, the same 4.2V.
Point below - Standard Discharge, Discharge. They suggest discharging with current from 0.5C - 350mA and up to 2C - 1400mA up to a voltage of 3V. Manufacturers are lying - at such currents the capacity will be lower than declared.
The maximum discharge current is precisely determined by the internal resistance. But it is necessary to distinguish between the maximum discharge current and the maximum permissible. If the first can be 5A, or even more, then the second is strictly specified - no more than 1.4A. This is due to the fact that at such high discharge currents the battery begins to irreversibly deteriorate.
Next comes information about weight and operating temperature: charging from 0 to 45 degrees, discharging from -20 to 60. Storage temperature: from -20 to 45 degrees, usually with a charge of 40% -50%.
The lifetime is promised to be at least 300 cycles (full discharge-charge with a current of 1C) at a temperature of 23 degrees. This does not mean that after 300 cycles the battery will turn off and will not turn on again, no. The manufacturer simply guarantees that the battery capacity will not decrease after 300 cycles. And then - how lucky you are, depends on the currents, temperature, operating conditions, batch, position of the moon, and so on.

About charging

The standard method by which all lithium batteries are charged (li-pol, li-ion, lifepo, only the currents and voltages are different) is CC-CV, mentioned above.
At the very beginning of the charge, we maintain a constant current. This is usually done with a feedback circuit in the charger - the voltage is automatically selected so that the current passing through the battery is equal to the required one.
As soon as this voltage becomes equal to 4.2 volts (for the described battery), this current cannot be maintained any longer - the voltage on the battery will increase too much (we remember that the operating voltage of lithium batteries cannot be exceeded), and it can heat up and even explode.
But now the battery is not fully charged - usually 60% -80%, and to charge the remaining 40% -20% without explosions, the current must be reduced.
The easiest way to do this is to maintain a constant voltage on the battery, and it will take the current it needs. When this current decreases to 30-10 mA, the battery is considered charged.
To illustrate all of the above, I colored in Photoshop and prepared a charge graph taken from an experimental battery:


On the left side of the graph, highlighted in blue, we see a constant current of 0.7A while the voltage gradually rises from 3.8V to 4.2V. It can also be seen that during the first half of the charge the battery reaches 70% of its capacity, while during the remaining time it reaches only 30%

About testing technology

The following battery was chosen as a test battery:


An Imax B6 was connected to it (I wrote about it here):


Which downloaded information about charge and discharge to the computer. The graphs were created in LogView.
Then I just came up every few hours and alternately switched on the charge and discharge.

About the results

As a result of painstaking work (you yourself try to charge for 2 weeks) two graphs were obtained:


As its name implies, it shows the change in battery capacity over the first 10 cycles. It floats a little, but the fluctuations are about 5% and have no trend. In general, the battery capacity does not change. All points were taken with a discharge current of 1C (0.7A), which corresponds to the active operation of the smartphone.
Two of the three points at the end of the graph show how the capacity changes at low battery temperatures. The last one is how the capacitance changes when discharged with a high current. The following graph describes this:

Shows that the greater the discharge current, the less energy can be obtained from the battery. Although, here's a joke, even at the smallest current of 100 mA, the battery capacity does not correspond to the datasheet. Everyone lies.

Although no, a battery test from Mugen Power at 1900mAh for Zopo ZP100 showed quite honest almost-two-amps:

But the Chinese 5000mAh battery only scored 3000:

About the conclusions

1. Training single cell lithium batteries is pointless. Not harmful, but wastes battery life cycles. In mobile devices, training cannot even be justified by the operation of the controller - the battery parameters are the same and do not change depending on the model and time. The only thing that an insufficient discharge can affect is the accuracy of the charge indicator readings (but not the operating time), but for this, one complete discharge every six months is enough.
   Again. If you have a player, phone, walkie-talkie, PDA, tablet, dosimeter, multimeter, watch or any other mobile device that uses a Li-Ion or Li-Pol battery (if it is removable, it will be written on it, if it is not removable, then 99 % is lithium) - “training” longer than one cycle is useless. One cycle is also most likely useless.
   If you have a battery for controlled models, then the first few cycles must be discharged with low currents (small, hehe. For them, small is 3-5C. This is actually one and a half amperes at 11 volts. And the operating currents there are up to 20C). Well, anyone who uses these batteries knows. But for everyone else, this will not be useful, except for general development.
2. In some cases, when using batteries with multiple banks, a full discharge-charge can increase capacity. In laptop batteries, if the manufacturer has skimped on a smart battery controller that doesn't balance the banks in series with each charge, a full cycle can increase capacity for the next couple of cycles. This happens by equalizing the voltage on all banks, which leads to their full charge. Several years ago I came across laptops with such controllers. Now I do not know.
3. Don't trust what's on the labels. Especially Chinese. In the last topic I provided a link in which a huge test of Chinese batteries did not reveal a single one whose capacity corresponded to the inscription. NONE! They always overestimate. And if they don’t overestimate it, they guarantee the capacity only in greenhouse conditions and when discharging with low current.
4. Keep the battery warm. A smart phone in a jeans pocket will work a little longer than in an outer jacket pocket. The difference can be 30%, and even more in winter.
5. Follow me. You can do this in my profile (the “subscribe” button).

You can charge lithium-ion (li-ion) batteries using chargers or yourself. We will not consider the design of li-ion and polymer (li-pol) batteries, but will immediately move on to practice. Both types of batteries charge the same way, so further we will talk about li-ion.

Rules for charging a Li-Ion battery:

• The battery can only be charged at temperatures from 0 to +45 degrees. Until the battery warms up, it will not take a charge normally;
• The minimum voltage for a Li-Ion battery is 2.5 or 3 volts, depending on the chemical composition. It is better to focus on 3B;
• Nominal voltage 3.7 V;
• The maximum charge voltage is 4.2V or 4.3V, depending on the chemical composition. It is better to focus on 4.2V;
• The capacity is indicated on the battery or device, let's call it C. Next it will be clear why you need to know it for charging;
• Normal charging mode: current is limited to 0.5*C (i.e., a value equal to half the battery capacity), voltage is limited to 4.2V;
• If the battery is discharged to 3V and below: the current should be limited to 0.1*C until the voltage exceeds 3V;
• The battery is charged until the current stops decreasing or there is no current at all, if you have limited the voltage to 4.2V. If you do not limit the voltage, until the voltage rises to 4.2V;
• Never raise the voltage above 4.2 or 4.3 volts. When the voltage is consistently exceeded, deposits occur on the electrodes. In the best case, the battery will lose capacity forever. If the process lasts for a long time, the deposit causes a short circuit. It may heat up, destroy the electrodes and catch fire.

Additionally

To charge yourself, you need to limit the voltage and current. Ideal for this laboratory power supply.

In lithium-ion batteries with voltages above 3.7 V, the batteries are connected in parallel. Dividing the battery voltage by 3.7 gives the number of batteries connected in series. Multiplying the number of batteries by 3 will give you the minimum voltage for your battery. Multiplying by 4.2 we get the maximum voltage.

Li-Ion batteries are practically devoid of “memory effect” and therefore do not require training. Try not to completely discharge the battery or keep it constantly charged.

The optimal charge for the battery is 50-80%. However, it is pointless to suffer and maintain such values ​​when using a laptop, smartphone or even a flashlight. Usually they charge when convenient and when necessary, and discharge until necessary. This is what Li-Ion was created for, there is no point in limiting yourself.

Following the above methods of charging batteries with high voltages or “jump” currents are harmful to the battery. It is better to leave the battery at low current for several hours or a couple of days. This is a more economical way to revive the battery. This will allow the controller to work as expected and allow charging at normal currents.

I guess that's all, happy exercises.

The charging and discharging processes of any battery occur in the form of a chemical reaction. However, charging lithium-ion batteries is an exception to the rule. Scientific research shows the energy of such batteries as the chaotic movement of ions. The statements of pundits deserve attention. If the science is to charge lithium-ion batteries correctly, then these devices should last forever.

Scientists see evidence of loss of useful battery capacity, confirmed by practice, in ions blocked by so-called traps.

Therefore, as is the case with other similar systems, lithium-ion devices are not immune to defects during their use in practice.

Chargers for Li-ion designs have some similarities to devices designed for lead-acid systems.

But the main differences between such chargers are seen in the supply of increased voltages to the cells. In addition, there are tighter current tolerances, plus the elimination of intermittent or floating charging when the battery is fully charged.

A relatively powerful power device that can be used as an energy storage device for alternative energy source designs
Cobalt-blended lithium-ion batteries are equipped with internal protective circuits, but this rarely prevents the battery from exploding when overcharged.

There are also developments of lithium-ion batteries, where the percentage of lithium has been increased. For them, the charge voltage can reach 4.30V/I and higher.

Well, increasing the voltage increases the capacity, but if the voltage goes beyond the specification, it can lead to destruction of the battery structure.

Therefore, for the most part, lithium-ion batteries are equipped with protective circuits, the purpose of which is to maintain the established standard.

Full or partial charge

However, practice shows: most powerful lithium-ion batteries can accept a higher voltage level, provided that it is supplied for a short time.

With this option, the charging efficiency is about 99%, and the cell remains cool during the entire charging time. True, some lithium-ion batteries still heat up by 4-5C when they reach a full charge.

This may be due to protection or due to high internal resistance. For such batteries, the charge should be stopped when the temperature rises above 10ºC at a moderate charge rate.

Lithium-ion batteries in the charger are being charged. The indicator shows the batteries are fully charged. Further process threatens to damage the batteries

Full charging of cobalt-blended systems occurs at a threshold voltage. In this case, the current drops by up to 3-5% of the nominal value.

The battery will show a full charge even when it reaches a certain capacity level that remains unchanged for a long time. The reason for this may be increased self-discharge of the battery.

Increasing charge current and charge saturation

It should be noted that increasing the charge current does not speed up the achievement of a full charge state. Lithium will reach peak voltage faster, but charging until the capacity is completely saturated takes longer. However, charging the battery at high current quickly increases the battery capacity to approximately 70%.

Lithium-ion batteries do not require a full charge, as is the case with lead-acid devices. Moreover, this charging option is undesirable for Li-ion. In fact, it is better to not fully charge the battery, because high voltage “stresses” the battery.

Selecting a lower voltage threshold or completely removing the saturation charge helps extend the life of the lithium-ion battery. True, this approach is accompanied by a decrease in the battery energy release time.

It should be noted here: household chargers, as a rule, operate at maximum power and do not support adjustment of the charging current (voltage).

Manufacturers of consumer lithium-ion battery chargers consider long battery life to be less important than the cost of circuit complexity.

Li-ion battery chargers

Some cheap household chargers often work using a simplified method. Charge a lithium-ion battery in one hour or less, without going to saturation charge.

The ready indicator on such devices lights up when the battery reaches the voltage threshold in the first stage. The state of charge is about 85%, which often satisfies many users.

This domestically produced charger is offered to work with different batteries, including lithium-ion batteries. The device has a voltage and current regulation system, which is already good

Professional chargers (expensive) are distinguished by the fact that they set the charging voltage threshold lower, thereby extending the life of the lithium-ion battery.

The table shows the calculated power when charging with such devices at different voltage thresholds, with and without saturation charge:

Charge voltage, V/per cell	Capacity at high voltage cut-off, %	Charging time, min	Capacity at full saturation, %
3.80	60	120	65
3.90	70	135	75
4.00	75	150	80
4.10	80	165	90
4.20	85	180	100

As soon as the lithium-ion battery begins to charge, there is a rapid increase in voltage. This behavior is comparable to lifting a load with a rubber band when there is a lag effect.

Capacity will eventually be gained when the battery is fully charged. This charge characteristic is typical for all batteries.

The higher the charging current, the brighter the rubber band effect. Low temperature or the presence of a cell with high internal resistance only enhances the effect.

The structure of a lithium-ion battery in its simplest form: 1- negative busbar made of copper; 2 — positive tire made of aluminum; 3 - cobalt oxide anode; 4- graphite cathode; 5 - electrolyte

Assessing the state of charge by reading the voltage of a charged battery is impractical. Measuring the open circuit (idle) voltage after the battery has been sitting for several hours is the best evaluation indicator.

As with other batteries, temperature affects idle speed in the same way it affects the active material of a lithium-ion battery. , laptops and other devices is estimated by counting coulombs.

Lithium-ion battery: saturation threshold

A lithium-ion battery cannot absorb excess charge. Therefore, when the battery is completely saturated, the charging current must be removed immediately.

A constant current charge can lead to metallization of lithium elements, which violates the principle of ensuring the safe operation of such batteries.

To minimize the formation of defects, you should disconnect the lithium-ion battery as quickly as possible when it reaches peak charge.

This battery will no longer take exactly as much charge as it should. Due to improper charging, it lost its main properties as an energy storage device.

As soon as the charge stops, the voltage of the lithium-ion battery begins to drop. The effect of reducing physical stress appears.

For some time, the open circuit voltage will be distributed between unevenly charged cells with a voltage of 3.70 V and 3.90 V.

Here, the process also attracts attention when a lithium-ion battery, which has received a fully saturated charge, begins to charge the neighboring one (if one is included in the circuit), which has not received a saturation charge.

When lithium-ion batteries need to be constantly kept on the charger in order to ensure their readiness, you should rely on chargers that have a short-term compensation charge function.

The flash charger turns on when the open circuit voltage drops to 4.05 V/I and turns off when the voltage reaches 4.20 V/I.

Chargers designed for hot-ready or standby operation often allow the battery voltage to drop to 4.00V/I and will only charge Li-Ion batteries to 4.05V/I rather than reaching the full 4.20V/I level.

This technique reduces physical voltage, which is inherently associated with technical voltage, and helps extend battery life.

Charging cobalt-free batteries

Traditional batteries have a nominal cell voltage of 3.60 volts. However, for devices that do not contain cobalt, the rating is different.

Thus, lithium phosphate batteries have a nominal value of 3.20 volts (charging voltage 3.65V). And new lithium titanate batteries (made in Russia) have a nominal cell voltage of 2.40V (charger voltage 2.85).

Lithium phosphate batteries are energy storage devices that do not contain cobalt in their structure. This fact somewhat changes the charging conditions for such batteries.

Traditional chargers are not suitable for such batteries, as they overload the battery with the risk of explosion. Conversely, a charging system for cobalt-free batteries will not provide sufficient charge to a traditional 3.60V lithium-ion battery.

Exceeded charge of lithium-ion battery

The lithium-ion battery operates safely within specified operating voltages. However, battery performance becomes unstable if it is charged above operating limits.

Long-term charging of a lithium-ion battery with a voltage above 4.30V, designed for an operating rating of 4.20V, is fraught with lithium metalization of the anode.

The cathode material, in turn, acquires the properties of an oxidizing agent, loses its stability, and releases carbon dioxide.

The pressure of the battery cell increases and if charging continues, the internal protection device will operate at a pressure between 1000 kPa and 3180 kPa.

If the pressure rise continues after this, the protective membrane opens at a pressure level of 3.450 kPa. In this state, the lithium-ion battery cell is on the verge of exploding and eventually does just that.

Structure: 1 - top cover; 2 - upper insulator; 3 - steel can; 4 - lower insulator; 5 — anode tab; 6 - cathode; 7 - separator; 8 - anode; 9 — cathode tab; 10 - vent; 11 - PTC; 12 — gasket

Triggering of the protection inside a lithium-ion battery is associated with an increase in the temperature of the internal contents. A fully charged battery has a higher internal temperature than a partially charged battery.

Therefore, lithium-ion batteries appear to be safer when charged at a low level. That is why the authorities of some countries require the use of Li-ion batteries in aircraft that are saturated with energy no more than 30% of their full capacity.

The internal battery temperature threshold at full load is:

• 130-150°C (for lithium-cobalt);
• 170-180°C (for nickel-manganese-cobalt);
• 230-250°C (for lithium manganese).

It should be noted: lithium phosphate batteries have better temperature stability than lithium manganese batteries. Lithium-ion batteries are not the only ones that pose a danger in energy overload conditions.

For example, lead-nickel batteries are also prone to melting with subsequent fire if energy saturation is carried out in violation of the passport regime.

Therefore, using chargers that are perfectly matched to the battery is of paramount importance for all lithium-ion batteries.

Some conclusions from the analysis

Charging lithium-ion batteries has a simplified procedure compared to nickel systems. The charging circuit is straightforward, with voltage and current limits.

This circuit is much simpler than a circuit that analyzes complex voltage signatures that change as the battery is used.

The energy saturation process of lithium-ion batteries allows for interruptions; these batteries do not need to be fully saturated, as is the case with lead-acid batteries.

Controller circuit for low-power lithium-ion batteries. A simple solution and a minimum of details. But the circuit does not provide cycle conditions that maintain a long service life

The properties of lithium-ion batteries promise advantages in the operation of renewable energy sources (solar panels and wind turbines). As a rule, a wind generator rarely provides a full battery charge.

For lithium-ion, the lack of steady-state charging requirements simplifies the charge controller design. A lithium-ion battery does not require a controller to equalize voltage and current, as is required by lead-acid batteries.

All household and most industrial lithium-ion chargers fully charge the battery. However, existing lithium-ion battery charging devices generally do not provide voltage regulation at the end of the cycle.

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 switches 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.