Lithium ion li ion batteries. Lithium-ion battery. Chemical processes of Li-ion batteries

Today, special batteries are used for mobile, household appliances, and tools. They differ in performance characteristics. In order for the battery to work for a long time, without failures, you need to take into account the requirements of the manufacturers of the presented products.

One of the most popular types today are Li-Ion batteries. How to properly charge this type of battery, as well as the features of its operation, should be considered in detail before operating the device.

general characteristics

One of the most common types of batteries today is the Li-Ion type. Such devices are relatively low in cost. At the same time, they are undemanding to operating conditions. In this case, the user rarely has a question about how to properly charge a cylindrical Li-Ion 18650 battery or another type.

Most often, the presented batteries are installed in smartphones, laptops, tablets and other similar devices. The presented batteries are characterized by durability and reliability. They are not afraid of complete discharge.

One of the main features of the presented products is the absence of a “memory effect”. These batteries can be charged at almost any convenient time. The “memory effect” occurs when the battery is not completely discharged. If there is a small amount of charge left in it, the battery's capacity will begin to decrease over time. This will lead to insufficient power supply for the equipment. In lithium-ion batteries, the “memory effect” is minimized.

Design

The design of a lithium-ion battery depends on the type of device for which it is intended. A mobile phone uses a battery called a “jar”. It has a rectangular shape and includes one structural element. Its nominal voltage is 3.7 V.

The presented type of battery for a laptop has a completely different design. There may be several individual battery cells in it (2-12 pieces). Each of them has a cylindrical shape. These are Li-Ion 18650 batteries. The manufacturer of the equipment indicates in detail how to charge them correctly. This design includes a special controller. It looks like a microcircuit. The controller controls the charging procedure and does not allow the battery's rated capacity to be exceeded.

Modern batteries for tablets and smartphones also provide a charge control function. This significantly extends the battery life. It is protected from various adverse factors.

Charging Features

When considering how to properly charge Li-Ion batteries of a phone, laptop and other equipment, you need to pay attention to the operating features of the presented device. It should be said that lithium-ion batteries do not tolerate deep discharge and overcharging. This is controlled by a special device that is added to the design (controller).

It is ideal to maintain the charge of the presented type of battery at a level of 20 to 80% of full capacity. The controller monitors this. However, experts do not recommend leaving the device connected to charging all the time. This significantly reduces battery life. In this case, the controller is subject to a constant load. Over time, its functionality may decrease because of this.

At the same time, the controller will also not allow deep discharge. It will simply turn off the battery at a certain moment. This protective function is extremely necessary. Otherwise, the user could accidentally overcharge or over-discharge the battery. Modern batteries also provide high-quality protection against overheating.

Battery operating principle

To understand how to properly charge a Li-Ion battery (new or used), you need to consider the principle of its operation. This will allow you to assess the need to monitor the level of discharge and charge of the device.

Lithium ions in a battery of this type move from one electrode to another. In this case, an electric current appears. Electrodes can be made of different materials. This indicator has a lesser impact on the performance characteristics of the device.

Lithium ions grow on the crystal lattice of the electrodes. The latter, in turn, change their volume and composition. When the battery is charged or discharged, there are more ions on one of the electrodes. The higher the load on metal structural elements that lithium places, the shorter the service life of the device will be. Therefore, it is better not to allow a high percentage of ions to settle on one or the other electrode.

Charging options

Before using the battery, you need to consider how to properly charge the Li-Ion battery of a smartphone, tablet and other equipment. There are several ways to do this.

One of the most correct solutions would be to use a charger. It is supplied complete with electronic equipment by every manufacturer.

The second option is to charge the battery from a desktop computer connected to a household network. A USB cable is used for this. In this case, the charging procedure will take longer than when using the first method.

You can perform this procedure using the cigarette lighter in your car. Another less popular method is to charge a lithium-ion battery using a universal device. It is also called "frog". Most often, such devices are used to recharge smartphone batteries. The contacts of this device can be adjusted in width.

Charging a new battery

The new battery must be put into operation correctly. To do this, your phone, tablet or other equipment must be completely discharged. Only when the device turns off can it be connected to the network. The controller will prevent the battery from draining too much. It is he who turns off the device when the battery loses capacity to a predetermined level.

Next, you need to connect the electrical equipment to the network using a standard charger. The procedure is performed until the indicator lights up green. You can leave the device online for a few more hours. This procedure is carried out several times. There is no need to specifically discharge your phone, tablet or laptop.

Normal charging

Knowing how to properly charge Li-Ion batteries can significantly extend the life of the battery. Experts recommend following the correct procedure for this process for a new battery. After this, it is not advisable to completely discharge the battery. When the indicator shows that the battery capacity is only 14-15% charged, it needs to be connected to the network.

At the same time, it is also not recommended to use devices other than the standard one to fill the battery capacity. It has the maximum acceptable current ratings allowed for a specific battery model. Other options should only be used if absolutely necessary.

Calibration

There is one more nuance that you need to know when studying the question of how to properly charge Li-Ion batteries. Experts recommend periodically calibrating this device. It is held once every three months.

First, in normal mode, you need to discharge the electrical equipment before turning it off. Next it is connected to the network. Charging continues until the indicator turns green (battery is 100% charged). This procedure must be followed for the controller to operate correctly.

When carrying out such a procedure, the battery circuit board determines the charging and discharging limits. This is necessary to ensure normal operation of the controller and avoid failures. In this case, a standard charger is used, which is supplied by the manufacturer with the phone, tablet or laptop.

Storage

In order for the battery to work as long and efficiently as possible, you also need to consider the question of how to properly charge a Li-Ion battery for storage. In some cases, a situation may arise when the device for powering equipment is temporarily not in use. In this case, it must be properly prepared for storage.

The battery is charged to 50%. In this state it can be stored for quite a long time. However, the ambient temperature should be around 15 ºC. If it increases, the rate at which the battery loses its capacity will increase.

If the battery needs to be stored for a sufficiently long time, it must be completely discharged and charged once a month. The battery reaches 100% of its specified capacity. Then the device is discharged again and charged to 50%. If this procedure is carried out regularly, the battery can be stored for a very long time. After this, it will be fully usable.

By considering how to properly charge Li-Ion batteries, you can significantly extend the life of this type of battery.

I’m sharing my idea of ​​the easiest way to measure battery capacity without buying expensive measuring instruments. The test sample was a 18650 lithium-ion battery, but my method of measuring capacity will work for other batteries as well.
The first part of the article describes the budget option.
In the second - (without a multimeter and USB tester).
At the end of the article there is a small one.

Li-Ion batteries.

Modern electronic devices widely use lithium-ion (Li-Ion) batteries of various shapes and sizes.
Regardless of the standard size, they all have similar characteristics and, by and large, differ only in capacity.
As a rule, there are batteries with a nominal voltage of 3.7 Volts (although there are also 3.8 Volts).
3.7 V Li-Ion batteries cannot be charged above a voltage of 4.23 V and cannot be discharged below 2.5 V, otherwise an irreversible process will occur and the cell will only have to be thrown away. The battery can be discharged and charged to any value (it does not have a memory effect), as long as the voltage is in the range from 2.5 to 4.23 V. However, a completely discharged battery should be charged as soon as possible so that it does not lose its capacity prematurely.
Also, lithium-ion batteries differ from each other in the presence of protection. The battery may have no electronic protection (just a galvanic cell), or it may have a built-in circuit that protects the cell from over-discharge, overcharging and overheating.
But no matter how you protect and monitor the condition of the battery, its capacity will steadily decrease over time. The higher the operating temperature and the more charge-discharge cycles are performed, the faster the battery ages.

18650 Li-ion battery.

18650 batteries from a laptop battery

18650 is the designation of the most common Li-Ion battery, the dimensions of which are slightly larger than a regular AA battery (18x65 mm). Everything that applies to the 18650 battery also applies to other lithium-ion batteries!
The 18650 battery size is often used in high-power flashlights, lasers, and various electronics. Batteries for laptops, some screwdrivers, and even electric vehicles are assembled from 18650 cells.
If you buy a branded battery, it most likely has built-in electronic protection. Cheap Chinese batteries, ordered for example from Aliexpress, do not have protection. In addition, their capacity is usually several times lower than declared.

Measuring the capacity of a 18650 battery.

The capacity of lithium-ion batteries is usually expressed in milliamp-hours (mAh). If your 18650 cell has an inscription like “1800” or “2200” on it, this is its declared capacity. It is more correct to measure capacity in Watt hours, but when marking elements, only milliamp hours are indicated.
To measure battery capacity, charging and other research, there are many special devices in a wide price range. The most famous of them, IMAX, costs about 2,000 rubles. Such a purchase will be justified only if you charge different types of batteries every day.

A budget option for measuring the capacity of a lithium-ion battery.

What was it all about? My laptop battery began to drain very quickly. Typically, a battery consists of 6 18650 cells. If even one cell fails, it affects the performance of the battery as a whole. Therefore, I decided to find out which of the elements had decreased in capacity in order to replace it with a new one. Cells from a laptop battery, as well as most budget 18650 batteries, do not have individual protection, so when working with them, they should not be over-discharged or overcharged.

Operating procedure

1. Before measuring capacitance, the 18650 element under test should be disconnected from other circuit elements and fully charged (up to 4.23 V). I looked at inexpensive chargers from the Chinese and, based on reviews, realized that due to their poor quality, many people had already ruined their batteries. For my own purposes, I bought the cheapest Powerbank. This is a box with an electronic converter for 1 or several 18650 batteries, which, in addition to its intended purpose, allows you to charge the battery to a voltage of 4.23 V and discharge to 2.5 V.
   To charge, just put the battery inside the Powerbank and connect it to a regular mobile phone charger.
2. When the battery is fully charged, disconnect the Powerbank from the telephone charger.
   The battery is ready for capacity measurement. What we now need are those purchased on the same Aliexpress USB tester(220 rubles) and load resistor(50 rubles).
   Just connect the USB tester at one end to the Powerbank, and the other to the load resistor. Be careful when purchasing, there are different types of USB testers. Some USB testers only show current and voltage, but we need one that, in addition to them, also measures capacity!

A few photos and a short review of the USB tester at the end of the article

Measuring battery capacity without measuring instruments.

Circuit diagram of a homemade USB tester, measuring the capacity of a Li-ion 18650 battery

I intended to find out the battery capacity using the method described above, but the USB tester that arrived from China 2 months later turned out to be faulty, so I decided to measure the capacity without measuring instruments.
Luckily I already had a Powerbank. Its design is such that, on the one hand, it prevents the battery from being discharged below the permissible voltage, and on the other, it maintains a constant 5 Volts at its output. If we connect a 5 Ohm resistor to the 5 Volt output, we get a discharge current of 1 ampere. And this value should theoretically be maintained throughout the entire discharge time. The current (1 A) and voltage (5 V) are known, all that remains is to note the time. In order not to sit for an hour with a timer in your hand, you should connect a regular household electromechanical alarm clock (clock) to the Powerbank output in parallel with a five-ohm resistor. But the clock requires 1.5 volts (the voltage of a AA battery), and we have as many as 5. Therefore, we connect the clock through a voltage divider consisting of two resistors - 470 and 1070 Ohms. If you have a multimeter, you can use a 470 Ohm - 1.5 kOhm variable resistor instead of these resistors, setting the clock input to 1.5-1.8 Volts.
So, I set the hands to 12:00 and connect the ballast with the clock to the Powerbank. After some time, the battery will discharge to 2.5 Volts. The power bank turns off, the clock stops and the hands record the time. In my case, the discharge time was 50 minutes (50 min/60= 0.83 hours).

Now let's calculate the battery capacity.
If we wanted to calculate the capacity of the Powerbank as an independent device, we would simply multiply the current and time: 1A*0.83h=0.83 Ah or 830 milliamp-hours.
But we need to know battery capacity 18650, so you should multiply the result by the ratio of the Powerbank voltage (U.pwb) to the rated voltage of the 18650 cell (U.b). In addition, for a more accurate result, we divide everything by the efficiency of the Powerbank converter, which is approximately 0.95.
In view of the above, the final formula for calculating battery capacity will take the form:

I * t * U.pwb / U.battery / efficiency = 1A * 0.83h * 5V / 3.7V / 0.95 = 1.18 Ah (1180 milliamp-hour)

Observations and corrections.

The experiment revealed the occurrence of pulsations that interfere with the operation of the clock. Therefore, a capacitor had to be soldered parallel to their input (in place of the battery). The capacitance at which the circuit operates stably is 100 microfarads (more is possible), the capacitor voltage is any, but not less than 5 volts.
During the discharge, the 5 Ohm ballast resistor heats up above 100 degrees, so do not grab it. Solder the circuit so that this resistor does not touch the Powerbank body or capacitor, otherwise they will melt.
If you want the discharge to go faster, use 2 5 Ohm resistors soldered in parallel, in this case the current will double and the discharge time will be halved. The video demonstrates in accelerated mode the operation of a watch with a stepper motor, which also turned out to be Chinese and periodically jammed when lying down. For further experiments, I connected a Soviet clock with a pendulum mechanism, which works absolutely stably.
For convenience, you can calculate the price of dividing the dial in accordance with your scheme and mark the scale in American hours and/or in Watt hours. In this case, the clock will always have a ready result and additional calculations will never be needed.

A short review of the USB tester

So, a brief review of the USB tester purchased in China through the Aliexpress website - everything that we managed to film before it failed.

After receiving and unpacking, I decided to check the performance of the tester. To do this, I connected it between the charger and the smartphone. You can see that the device shows voltage, current, current power consumption, operating time and energy consumed (Watt-hour). To measure the battery capacity, just connect the USB tester between the battery and the load resistor; after the battery is completely discharged, the USB tester will turn off and the measured capacity will be stored in its memory. However, the matter did not go further than theory, because the tester turned out to be defective. When connecting a load of 5 Ohms, which corresponds to 1 ampere, the device stopped displaying current and other parameters to be measured, although the declared permissible load current is 3 Amps. At the end of the video, the operation of a mouse connected to a laptop via a USB tester is demonstrated. Here the tester is already in a faulty state. Previously, the mouse current he measured was from 10 to 30 milliamps for the resting and active states, respectively, but now the current is not displayed.

USB tester disassembled:

When they talk about lithium batteries or accumulators, most often they don’t even realize that almost a dozen of them have appeared in the last couple of years, each of which is lithium with various additives of other chemical elements, which ultimately differ significantly from each other.

Let's look at their types and start with the classics:

Lithium-ion batteries are classic rechargeable batteries in which lithium ions move from the negative electrode to the positive electrode during discharge and back again when charging. Lithium-ion batteries are widely used in consumer electronics. They are one of the most popular types of rechargeable batteries for portable electronics, with one of the best energy densities, no memory effect and slow loss of charge when not in use (low self-discharge).

This series covers cylindrical and prismatic battery sizes. Li-ion has the highest power density of any old type battery. Very light weight and long life cycle makes it an ideal product for many solutions.

Lithium titanate (lithium titanate) is a relatively new class of lithium-ion batteries - (more details). It is characterized by a very long life cycle, measured in thousands of cycles. Lithium lead titanate is also very safe and comparable in this regard to iron phosphate. The energy density is lower than other lithium-ion power sources and its rated voltage is 2.4V.

This technology features very fast charging, low internal resistance, very high life cycle and excellent endurance (also safety). LTO has found its application mainly in electric vehicles and wristwatches. Recently, it has begun to find application in mobile medical devices due to its high security. One of the features of the technology is that it uses nanocrystals on the anode instead of carbon, which provides a much more efficient surface area. Unfortunately, this battery has lower voltages than other types of lithium batteries.

Peculiarities:

• Specific energy: about 30-110Wh/kg
• Energy density: 177 W * h/l
• Specific power: 3,000-5,100 W/kg
• Discharge efficiency: approximately 85%; charging efficiency more than 95%
• Energy-price: 0.5 W/dollar
• Shelf life: >10 years
• Self-discharge: 2-5%/month
• Durability: 6000 cycles to 90% capacity
• Nominal voltage: 1.9 to 2.4 V
• Temperature: -40 to +55°C
• Charging method: Uses stable constant current, then constant voltage until it reaches the threshold.

Chemical formula: Li4Ti5O12 + 6LiCoO2< >Li7Ti5O12 + 6Li0.5CoO2(E=2.1 V)

Lithium polymer has a higher energy density in terms of weight than lithium-ion batteries. In very thin cells (up to 5 mm), lithium polymer provides high volumetric energy density. Excellent stability in overvoltage and high temperatures.

This series of batteries can be produced in the range from 30 to 23000 mAh, prismatic and cylindrical housing types. Lithium polymer batteries offer a number of advantages: greater energy density by volume, flexibility in cell sizes, and a wider margin of safety, with excellent voltage stability even at high temperatures. Main areas of application: portable players, Bluetooth, wireless devices, PDAs and digital cameras, electric bicycles, GPS navigators, laptops, e-readers.

Peculiarities:

• Rated voltage: 3.7V
• Charging voltage: 4.2±0.05V
• Charge current, speed: 0.2-10C
• Discharge voltage limit: 2.5 V
• Discharge speed: up to 50C
• Cycle endurance: 400 cycles

Lithium iron phosphate has good safety characteristics, long service life (up to 2000 cycles), and low production cost. LiFePO4 batteries are well suited for high discharge current applications such as military equipment, power tools, electric bicycles, mobile computers, UPS and solar power systems.

As a new anode material for lithium-ion batteries, lifepo4 was first introduced in 1997 and has been continuously improved to date. It has attracted the attention of experts due to its reliable safety, durability, low environmental impact during disposal, and convenient charging and discharging characteristics. Many experts claim that lifepo4 batteries are by far the best option for autonomously powering electronics.

Lithium sulfur dioxide (Li and SO2 battery) - these batteries have high energy density and good resistance to high power discharge. Such elements are used mainly in military science, meteorology and astronautics.

Lithium sulfur dioxide batteries with a lithium metal anode (the lightest of all metals) and a liquid cathode containing a porous carbon current collector filled with sulfur dioxide (SO2) produce a voltage of 2.9 V and are cylindrical in shape.

Peculiarities:

• High operating voltage, stable throughout most of the discharge
• Extremely low self-discharge
• Performance in extreme conditions
• Wide operating temperature range (-55°C to +65°C)

Lithium-manganese dioxide (Li-MnO2 battery) - these batteries have a lightweight lithium metal anode and a solid manganese dioxide cathode, immersed in a non-corrosive, non-toxic organic electrolyte. This type of battery is EU RoHS compliant and is characterized by large capacity, high discharge capacity and long service life.

Li-MnO2 is widely used in backup power supplies, emergency beacons, fire alarms, electronic access control systems, digital cameras, medical equipment.

Peculiarities:

• High energy density
• Very stable discharge voltage
• More than 10 year shelf life
• Operating temperature: -40 to +60°C

Lithium thionyl chloride (lithium-SOCl2) batteries feature a lightweight lithium metal anode and a liquid cathode containing a porous carbon current collector filled with thionyl chloride (SOCl2). Li-SOCL2 batteries are ideal for automotive devices, medical devices, and military and aerospace applications. They have the widest operating temperature range from -60 to + 150°C.

Peculiarities:

• High energy density
• Long shelf life
• Wide temperature range
• Good sealing
• Stable discharge voltage

Li-FeS2 batteries

Li-FeS2 batteries and batteries stand for lithium iron disulfide. Information about them will be added later.

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.

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 materials. 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 power subsystems that take 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.