Characteristics of lithium-ion batteries. Lithium battery: overview, description, types, manufacturers and reviews

Testing features

The main difficulty in the experiments is the discrepancy between the declared capacity and the real one. All batteries have a capacity higher than stated, from 0.1% to 5%, which introduces an additional element of unpredictability.

The most commonly used batteries were NCA and NMC, but lithium cobalt and lithium phosphate batteries were also tested.

Few terms:
DoD - Depth of Discharge - depth of discharge.
SoC - State of Charge - charge level.

Battery use

The number of cycles

This curve is called the Wöhler curve. The basic idea came from mechanics about the dependence of the number of stretches of a spring on the degree of stretching. The initial value of 3000 cycles at 100% battery discharge is a weighted average of 0.1C discharge. Some batteries show better results, some worse. At a current of 1C, the number of full cycles at 100% discharge drops from 3000 to 1000-1500, depending on the manufacturer.

In general, this ratio, presented in the graphs, was confirmed by the results of experiments, because it is advisable to charge the battery whenever possible.

Cycle superposition calculation

According to the results of the experiments, the combined cycle showed results, both from the addition of full equivalent cycles of two independent cycles. Those. the relative capacity of the battery in the combined cycle fell according to the sum of discharges in the small and large cycles (linearized graph is presented below).


The effect of long discharge cycles is more significant, which means that the battery is better charged at every opportunity.

memory effect

Battery storage

Storage temperatures

Charge level

Main problems of experimental results

Results of experiments

Sources

Operation, charging, pros and cons of lithium batteries

Many people today use electronic devices in their daily lives. Cell phones, tablets, laptops… Everyone knows what it is. But few people know that the key element of these devices is the lithium battery. Almost every mobile device is equipped with this type of rechargeable batteries. Today we will talk about lithium batteries. These batteries and their production technology are constantly evolving. A significant update of technology occurs every 1-2 years. We will consider the general principle of operation of lithium batteries, and separate materials will be devoted to varieties. The history of the emergence, operation, storage, advantages and disadvantages of lithium batteries will be discussed below.

Research in this direction was carried out at the beginning of the 20th century. The "first signs" in the family of lithium batteries appeared in the early seventies of the last century. The anode of these batteries was made of lithium. They quickly became in demand due to the fact that they had a high specific energy. Due to the presence of lithium, a very active reducing agent, the developers managed to greatly increase the nominal voltage and specific energy of the element. The development, subsequent testing and refinement of the technology "to the mind" took about two decades.

Materials for the positive electrode were developed quite quickly. The main requirement for them was that they undergo reversible processes.

We are talking about anodic extraction and cathodic insertion. These processes are also called anodic deintercalation and cathodic intercalation. The researchers tested various materials as the cathode.

The requirement was that there should be no cycling changes. In particular, materials such as:

• TiS2 (titanium disulphide);
• Nb(Se)n (niobium selenide);
• sulfides and diselenides of vanadium;
• copper and iron sulfides.

All of these materials have a layered structure. Studies were also carried out with materials of more complex compositions. For this, additives of some metals were used in small quantities. These were elements with cations of a larger radius than Li.

High specific characteristics of the cathode were obtained on metal oxides. Various oxides were tested for reversible work, which depends on the degree of distortion of the crystal lattice of the oxide material when lithium cations are introduced there. The electronic conductivity of the cathode was also taken into account. The task was to ensure that the cathode volume changes by no more than 20 percent. According to studies, the best results were shown by oxides of vanadium and molybdenum.

With the anode, the main difficulties arose in the creation of lithium batteries. More precisely, during the charging process, when cathodic deposition of Li occurs. This forms a surface with a very high activity. Lithium is deposited on the cathode surface in the form of dendrites and as a result a passive film is formed.

It turns out that this film envelops the lithium particles and prevents their contact with the base. This process is called encapsulation and leads to the fact that after the battery is charged, a certain part of the lithium is excluded from the electrochemical processes.

As a result, after a certain number of cycles, the electrodes wore out and the temperature stability of the processes inside the lithium battery was disturbed.

At some point, the element was heated to the melting point of Li and the reaction passed into an uncontrolled phase. So, in the early 90s, a lot of lithium batteries were returned to the enterprises of the companies involved in their production. These were one of the first batteries to be used in mobile phones. At the time of the conversation (the current reaches its maximum value) on the phone, a flame was emitted from these batteries. There have been many cases where the user's face was burned. The formation of dendrites during the deposition of lithium, in addition to the risk of fire and explosion, can lead to a short circuit.

Therefore, researchers have spent a lot of time and effort on the development of a method for treating the surface of the cathode. Methods have been developed for introducing additives into the electrolyte that prevent the formation of dendrites. Scientists have made progress in this direction, but the problem has not been completely solved so far. These problems with the use of metallic lithium were also tried to be solved by another method.

So, the negative electrode began to be made from lithium alloys, and not from pure Li. The most successful was an alloy of lithium and aluminum. When the discharge process is in progress, lithium is etched in the electrode from such an alloy, and vice versa when charging. That is, during the charge-discharge cycle, the concentration of Li in the alloy changes. Of course, there was some loss of lithium activity in the alloy compared to Li metal.

The potential of the alloy electrode decreased by about 0.2-0.4 volts. The operating voltage of the lithium battery decreased, and at the same time, the interaction between the electrolyte and the alloy decreased. This was a positive factor, since the self-discharge decreased. But the alloy of lithium and aluminum is not widely used. The problem here was that cycling greatly changed the specific volume of this alloy. When a deep discharge occurred, the electrode became brittle and crumbled. Due to the decrease in the specific characteristics of the alloy, research in this direction was discontinued. Other alloys have also been studied.

Studies have shown that Li alloy with heavy metals is best suited. An example is Wood's alloy. They showed themselves well in terms of maintaining the specific volume, but the specific characteristics were insufficient for use in lithium batteries.

As a result, due to the fact that lithium metal is unstable, research began to go in a different direction. It was decided to exclude pure lithium from the battery components, and use its ions. This is how lithium-ion (Li-Ion) batteries appeared.

The energy density of lithium-ion batteries is less than that of lithium. But their safety and ease of use are much higher. You can read more about the given link.

Operation and service life

Exploitation

The operating rules will be considered using the example of common lithium batteries that are used in mobile devices (phones, tablets, laptops). In most cases, such batteries are protected from the "fool" by the built-in controller. But it is useful for the user to know basic things about the device, parameters and operation of lithium batteries.

To begin with, you should remember that a lithium battery must have a voltage of 2.7 to 4.2 volts. The lower value here indicates the minimum charge level, the upper one indicates the maximum. In modern Li batteries, the electrodes are made of graphite and in their case the lower voltage limit is 3 volts (2.7 is the value for coke electrodes). The electrical energy that a battery gives off when the voltage drops from the upper to the lower limit is called its capacity.

To extend the life of lithium batteries, manufacturers narrow the voltage range somewhat. Often it is 3.3-4.1 volts. As practice shows, the maximum service life of lithium batteries is achieved at a charge level of 45 percent. If the battery is overcharged or over-discharged, its life will be shortened. It is generally recommended to charge a lithium battery at 15-20% charge. And you need to stop charging immediately after reaching 100% capacity.

But, as already mentioned, the controller saves the battery from overcharging and deep discharge. This IC control board is found on almost all lithium batteries. In various consumer electronics (tablets, smartphones, laptops), the operation of the controller integrated into the battery is complemented by a microcircuit that is soldered on the board of the device itself.

In general, the correct operation of lithium batteries is ensured by their controller. The user is mainly required not to get involved in this process and not to engage in amateur activities.

Life time

The service life of lithium batteries is about 500 charge-discharge cycles. This value is valid for most modern lithium-ion and lithium-polymer batteries. The service life may vary. It depends on how much you use your mobile device. With constant use, load with resource-intensive applications (video, games), the battery can exhaust its limit in a year. But the average life of lithium batteries is 3-4 years.

Charging process

It should be noted right away that for normal operation of the battery, you need to use a standard charger that comes with the gadget. In most cases, this is a 5 volt DC source. Regular chargers for a phone or tablet usually give off a current of about 0.5─1 * C (C is the nominal capacity of the battery).
The standard mode for charging a lithium battery is as follows. This mode is used in controllers from Sony and provides maximum completeness of charging. The figure below shows this process graphically.

The process consists of three stages:

• The duration of the first stage is about one hour. In this case, the charging current is kept at a constant level until the battery voltage reaches 4.2 volts. At the end, the degree of charge is 70%;
• The second stage also takes about an hour. At this time, the controller maintains a constant voltage of 4.2 volts, while the charging current decreases. When the current drops to about 0.2*C, the final stage starts. At the end, the degree of charge is 90%;
• in the third stage, the current constantly decreases at a voltage of 4.2 volts. In principle, this stage repeats the second stage, but has a strict time limit of 1 hour. The controller then disconnects the battery from the charger. At the end, the degree of charge is 100%.

Controllers that are able to provide such staging are quite expensive. This is reflected in the cost of the battery. In order to reduce the cost, many manufacturers install controllers with a simplified charging system in batteries. Often this is just the first step. Charging is interrupted when the voltage reaches 4.2 volts. But in this case, the lithium battery is charged only 70% of its capacity. If your device's lithium battery takes 3 hours or less to charge, it most likely has a simplified controller.

It is worth noting a number of other points. Periodically (every 2-3 months) do a full discharge of the battery (so that the phone turns off). Then a full charge to 100% is carried out. After that, remove the battery for 1-2 minutes, insert and turn on the phone. The charge level will be less than 100%. Charge fully and do this several times until a full charge is displayed when the battery is inserted.

Remember that through the USB connector of a laptop, desktop, cigarette lighter adapter in a car, charging is much slower than from a regular charger. This is due to the current limitation of the USB interface at 500 mA.

Also remember that in the cold and at low atmospheric pressure, lithium batteries lose some of their capacity. At negative temperatures, this type of battery becomes inoperable.

The consumer market for lithium-ion (Li-ion) batteries is huge, around $10 billion, and is fairly resilient, growing at only 2% per year. But what about electric cars, you ask? Indeed, in the coming years, due to the development of electric vehicles, the annual growth rate of lithium-ion batteries is predicted to be 10%. Surprisingly, the biggest growth area for the Li-ion battery market is still "everything else," from mobile phones to forklifts.

The "other" applications for lithium-ion batteries tend to have one thing in common - they are devices that are powered by sealed lead acid (SLA) batteries. Lead-acid batteries have dominated the electronics market for nearly 200 years, but have been pushed out of the market by lithium-ion batteries for several years now. Since in many cases lithium-ion batteries have begun to replace lead-acid batteries (accumulators), it is worth comparing these two types of energy storage devices, emphasizing the main technical features and economic feasibility of using Li-ion instead of traditional SLA devices.

History of battery applications

The lead acid battery was the first rechargeable battery developed for commercial use in the 1850s. Despite a fairly decent age of more than 150 years, they are still actively used in modern devices. Moreover, they are actively used in applications where, it would seem, it is quite possible to get by with modern technologies. Some common devices make heavy use of SSCs, such as uninterruptible power supplies (UPS), golf carts, or forklifts. Surprisingly, the market for lead acid batteries is still growing for certain niches and projects.

The first significant innovation in lead-acid technology came in the 1970s with the invention of sealed SBCs or maintenance-free SBCs. This modernization consisted in the appearance of special valves for bleeding gases when charging / discharging batteries. In addition, the use of a humidified separator made it possible to operate the battery in an inclined position without electrolyte leakage.

SKB, or English. SLAs are often classified by type or application. Currently, two types are most common: gel, also known as valve-regulated lead acid (VRLA) and absorbent glass mat (AGM). AGM batteries are used for small UPSs, emergency lights and wheelchairs, while VRLA is for larger applications such as back-up power for cell towers, Internet centers and forklifts. Lead-acid batteries can also be classified according to the following criteria: automotive (starter or SLI - starting, lighting, ignition); traction (traction or deep cycle); stationary (uninterruptible power supplies). The main disadvantage of SLAs in all these applications is the life cycle - if they are repeatedly discharged, they are severely damaged.

Surprisingly, lead-acid batteries were the undisputed leaders in the battery market for many decades, until the advent of lithium-ion batteries in the 1980s. A lithium-ion battery is a rechargeable cell in which lithium ions move from the negative to the positive electrode during discharge and vice versa during charging. Lithium-ion batteries use intercalated lithium compounds but do not contain lithium metal, which is used in disposable batteries.

The lithium-ion battery was first invented in the 1970s. In the 1980s, the first commercial version of a battery with a cobalt oxide cathode was released to the market. This type of device had significantly greater weight and capacity capabilities compared to nickel-based systems. New lithium-ion batteries have contributed to the huge growth of the mobile phone and laptop market. Initially, due to safety concerns, safer options were introduced that included nickel-based and manganese-based additions to the cobalt oxide cathode material, in addition to cell building innovations.

The first lithium-ion cells on the market were in rigid aluminum or steel cans, and typically came in only a few cylindrical or prismatic (brick-shaped) form factors. However, with the expansion of the range of applications of lithium-ion technology, their overall dimensions also began to change.

For example, less expensive versions of older technology are used in laptops and cell phones. Modern thin lithium polymer cells are used in smartphones, tablets and wearable devices. Currently, lithium-ion batteries are used in power tools, electric bicycles and other devices. This variation portends the complete replacement of lead-acid devices in more and more new applications aimed at improving overall and power performance.

Chemical Features

The fundamentals of cell chemistry give lead-acid and lithium-ion devices certain properties and varying degrees of functionality. Below are some of the advantages of lead-acid batteries that have made it the mainstay for decades and the disadvantages that now lead to its replacement, as well as similar aspects for lithium-ion devices.

Lead acid battery

• SKB is simple, reliable and inexpensive. It can be used over a wide temperature range.
• Batteries must be stored in a permanently charged state (SoC) and are not fast-chargeable.
• SKB have a lot of weight. Their gravimetric energy density is very low.
• The life cycle is usually 200 to 300 discharges/charges, which is very short.
• The charge/discharge curve allows you to measure SOC with simple voltage control.

Li-ion battery

• They have the highest energy density in terms of size and weight.
• The life cycle is usually between 300 and 500, but can be measured in the thousands for lithium phosphate cells;
• Very small operating temperature range;
• Various cell sizes, shapes and other possibilities are available;
• No need for maintenance. The self-discharge level is very low.
• Implementation of safety schemes is required. Sophisticated charging algorithm.
• SoC measurements require difficult decisions due to the non-linearity of the voltage curve.

Electronics

It is important to understand the difference between a battery pack and a rechargeable battery. The cell is the main constituent element of the package. In addition, the package also includes electronics, connectors and a case. The figure above shows examples of these devices. A lithium-ion battery must have, at a minimum, implemented cell protection and control circuits, and the charger and voltage measurement system is much more complex than in lead-acid devices.

When using lithium-ion and lead-acid batteries, the main differences in electronics will be as follows:

Charger

Charging a lead-acid battery is quite simple, as long as certain voltage thresholds are met. Lithium-ion batteries use a more complex algorithm, with the exception of iron phosphate packages. The standard charging method for such devices is the constant current/constant voltage (CC/CV) method. It includes a two-stage charging process. At the first stage, a constant current charge occurs. This lasts until the cell voltage reaches a certain threshold, after which the voltage remains constant, and the current decreases exponentially until it reaches the cutoff value.

Charge Counting and Communication

As mentioned earlier, the charge of the SCB can be measured by simple means of measuring voltage. When using lithium-ion batteries, it is necessary to control the charge level of the cells, which requires the implementation of complex algorithms and learning cycles.

I 2 C is the most common and economical communication protocol used in Li-ion batteries, but it has limitations in terms of noise immunity, signal integrity over distance, and total bandwidth. SMBus (System Management Bus), a derivative of I2C, is very common in smaller batteries, but does not currently have any effective support for powerful or larger packages. CAN is great for high noise environments or where long runs are required, such as in many SKB applications, but it comes at a cost.

Direct replacements

It should be emphasized that there are now several standard formats for lead-acid batteries. An example is U1, a standard form factor used in medical backup power applications. The lithium-iron-phosphate battery proved to be quite a worthy replacement for lead-acid. Iron phosphate has an excellent life cycle, good charge conductivity, improved safety and low impedance. Lithium iron phosphate battery voltages also match well with lead acid voltages (12V and 24V), allowing the same chargers to be used. Battery maintenance and monitoring software packages include smart features such as charge tracking, charge/discharge cycle counter, and more.

Lithium iron phosphate batteries retain 100% capacity in storage, unlike SKB batteries which lose capacity over several months of storage. The figure above compares the two products and the types of advances made in the transition from SKB to Li-ion.

conclusions

Very few batteries exist that can store as much energy as lead acid, making this type of battery economical for many high power applications. Lithium-ion technology is constantly declining in price, and the constant improvement of their chemical structures and safety systems makes them a worthy competitor to lead-acid technology. Devices for their use can be very different, ranging from uninterruptible power supplies to electric vehicles and drones.

Today, lithium-ion batteries are most often used in various fields. They are especially widely used in mobile electronics (PDAs, mobile phones, laptops, and more), electric vehicles, and so on. This is due to their advantages over the previously widely used nickel-cadmium (Ni-Cd) and nickel-metal hydride (Ni-MH) batteries. And if the latter have come close to their theoretical limit, then lithium-ion battery technologies are at the beginning of the journey.

Device

In lithium-ion batteries, aluminum acts as the negative electrode (cathode), and copper acts as the positive electrode (anode). The electrodes can be made in different shapes, however, as a rule, this is a foil in the form of an oblong package or a cylinder.

• The anode material on the copper foil and the cathode material on the aluminum foil are separated by a porous separator which is impregnated with an electrolyte.
• The electrode package is installed in a sealed housing, and the anodes and cathodes are connected to the current collector terminals
• There may be special devices under the battery cover. One device responds by increasing resistance to the PTC. The second device breaks the electrical connection between the positive terminal and the cathode when the gas pressure in the battery rises above the allowable limit. In some cases, the body is equipped with a safety valve that relieves internal pressure in case of violations of operating conditions or emergency situations.
• To improve the safety of operation in a number of batteries, external electronic protection is also used. It prevents the possibility of excessive heating, short circuit and overcharging of the battery.
• Structurally, batteries are produced in prismatic and cylindrical versions. A rolled package of separator and electrodes in cylindrical batteries is placed in an aluminum or steel case, to which the negative electrode is connected. The positive pole of the battery is led through the insulator to the cover. Prismatic batteries are created by stacking rectangular plates on top of each other.

Such lithium-ion batteries allow for denser packing, but it is more difficult to maintain compressive forces on the electrodes in them than in cylindrical ones. A number of prismatic batteries use a roll assembly of a package of electrodes twisted into an elliptical spiral.

Most of the batteries are produced in prismatic versions, since their main purpose is to ensure the operation of laptops and mobile phones. The design of Li-ion batteries is completely sealed. This requirement is dictated by the inadmissibility of leakage of liquid electrolyte. If water vapor or oxygen gets inside, then a reaction occurs with the electrolyte and electrode materials, which leads to a complete failure of the battery.

Operating principle

• Lithium-ion batteries have two electrodes, an anode and a cathode, with an electrolyte in between. At the anode, when the battery is connected to a closed circuit, a chemical reaction is formed, which leads to the formation of free electrons.
• These electrons tend to get to the cathode, where their concentration is lower. However, the electrolyte between the electrodes keeps them from a direct path to the cathode from the anode. The only way left is through the circuit where the battery closes. In this case, the electrons, moving along the indicated circuit, feed the device with energy.
• The positively charged lithium ions that were left behind by the runaway electrons are at the same time directed through the electrolyte towards the cathode in order to satisfy the need for electrons on the cathode side.
• After moving all the electrons to the cathode, the "death" of the battery occurs. But the lithium-ion battery is rechargeable, meaning the process can be reversed.

With the help of a charger, energy can be introduced into the circuit, thereby starting the flow reaction in the opposite direction. As a result, an accumulation of electrons at the anode will be obtained. After the battery is recharged, it will mostly remain so until it is activated. However, over time, the battery will lose some of its charge even in standby mode.

• Battery capacity refers to the amount of lithium ions that can be embedded in craters and tiny pores in the anode or cathode. Over time, after numerous recharges, the cathode and anode degrade. As a result, the number of ions they can hold decreases. In this case, the battery can no longer hold the previous amount of charge. In the end, he completely loses his functions.

Lithium-ion batteries are designed in such a way that their charging must be constantly monitored. For this purpose, a special board is installed in the case, it is called a charge controller. The chip on the board controls the battery charging process.

A typical battery charge looks like this:

• The controller at the beginning of the charging process supplies a current of 10% of the nominal. At the moment, the voltage rises to 2.8 V.
• Then the charge current rises to the nominal. During this period, the voltage at direct current rises to 4.2 V.
• At the end of the charging process, the current drops at a constant voltage of 4.2 V until the battery is 100% charged.

The staging may differ due to the use of different controllers, which leads to different charging speeds and, accordingly, the total cost of the battery. Lithium-ion batteries can be unprotected, that is, the controller is in the charger, or with built-in protection, that is, the controller is located inside the battery. There may be devices where the protection board is built directly into the battery.

Varieties and applications

There are two form factors for lithium-ion batteries:

1. Cylindrical lithium-ion batteries.
2. Tablet lithium-ion batteries.

Different subspecies of the electrochemical lithium-ion system are named according to the type of active substance used. What all these lithium-ion batteries have in common is that they are all sealed, maintenance-free batteries.

There are 6 most common types of lithium-ion batteries:

1. Lithium cobalt battery . It is a popular solution for digital cameras, laptops and mobile phones due to its high energy density. The battery consists of a cobalt oxide cathode and a graphite anode. Disadvantages of lithium-cobalt batteries: limited load capacity, low thermal stability and relatively short service life.

Areas of use ; mobile electronics.

1. Lithium manganese battery . The crystalline lithium-manganese spinel cathode is distinguished by a three-dimensional framework structure. Spinel provides low resistance, but has a more moderate energy density than cobalt.

Areas of use; electrical power units, medical equipment, power tools.

1. Lithium Nickel Manganese Cobalt Oxide Battery . The cathode of the battery combines cobalt, manganese and nickel. Nickel is famous for its high energy density, but low stability. Manganese provides low internal resistance but results in low energy density. The combination of metals allows you to compensate for their disadvantages and use their strengths.

Areas of use; for private and industrial use (, security systems, solar power plants, emergency lighting, telecommunications, electric vehicles, electric bicycles, and so on).

1. Lithium iron phosphate battery . Its main advantages are: long service life, high current strength, resistance to misuse, increased safety and good thermal stability. However, this battery has a small capacity.

Applications; stationary and portable specialized devices where endurance and high load currents are needed.

1. Lithium Nickel Cobalt Aluminum Oxide Battery . Its main advantages: high energy density and energy intensity, durability. However, safety performance and high cost limit its use.

Areas of use; electrical power units, industry and medical equipment.

1. Lithium titanate battery . Its main advantages are fast charging, long service life, wide temperature range, excellent performance and safety. This is the safest lithium-ion battery.

However, it has a high cost and low specific energy intensity. At the moment, developments are underway to reduce the cost of production and increase the specific energy intensity.

Areas of use; street, electric power units of cars (Honda Fit-EV, Mitsubishi i-MiEV), UPS.

Typical characteristics

In general, lithium-ion batteries have the following typical characteristics:

• The minimum voltage is not lower than 2.2-2.5V.
• The maximum voltage is not higher than 4.25-4.35V.
• Charging time: 2-4 hours.
• Self-discharge at room temperature is about 7% per year.
• Operating temperature range from -20 °C to +60 °C.
• The number of charge / discharge cycles before reaching the loss of 20% of the capacity is 500-1000.

Advantages and disadvantages

The benefits include:

• High energy density compared to nickel-based alkaline batteries.
• Sufficiently high voltage of one battery cell.
• No "memory effect" for easy operation.
• A significant number of charge-discharge cycles.
• Long service life.
• Wide temperature range for consistent performance.
• Relative ecological safety.

Among the disadvantages are:

• Moderate discharge current.
• Relatively fast aging.
• Relatively high cost.
• Impossibility of work without the built-in controller.
• Possibility of spontaneous combustion at high loads and at too deep a discharge.
• The design requires significant improvements, because it is not brought to perfection.

The growing consumer interest in mobile gadgets and high-tech portable technology in general is forcing manufacturers to improve their products in a variety of ways. At the same time, there are a number of common parameters that are being worked on in the same direction. These include the method of energy supply. Just a few years ago, active market participants could observe the process of being replaced by more advanced elements of NiMH origin. Today, new generations of batteries are competing with each other. The widespread lithium-ion technology in some segments is successfully replacing the lithium-polymer battery. The difference from the ionic in the new block is not so noticeable to the average user, but in some aspects it is significant. At the same time, as in the case of competition between NiCd and NiMH elements, the replacement technology is far from flawless and is inferior to its analog in some respects.

Li-ion battery device

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

Lithium polymer battery device

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

What is the main difference from the ion battery?

The fundamental difference lies in the rejection of helium and liquid electrolytes. For a more complete understanding of this difference, it is worth referring to modern models of car batteries. The need to replace the liquid electrolyte was driven, again, by safety concerns. But if in the case of automotive batteries, progress has stopped on the same impregnated porous electrolytes, then lithium models have received a full-fledged solid base. Why is a solid-state lithium polymer battery so good? The difference from the ionic one is that the active substance in the form of a plate in the zone of contact with lithium prevents the formation of dendrites during cycling. Just this factor excludes the possibility of explosions and fires of such batteries. This is only what concerns the advantages, but there are also weaknesses in the new batteries.

Lithium polymer battery life

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

Flaws

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

Operational features of gel-like modifications

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

Optimal charging method

The usual recharge time for lithium batteries is an average of 3 hours. Moreover, the unit remains cold during charging. Filling takes place in two stages. At the first, the voltage reaches peak values, and this mode is maintained until a set of 70%. The remaining 30% are already recruited under normal voltage conditions. Another question is also interesting - how to charge a lithium-polymer battery if you need to constantly maintain its full volume? In this case, you should follow the schedule of recharging. This procedure is recommended to be carried out approximately every 500 hours of operation with a full discharge.

Precautionary measures

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

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

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

Conclusion

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