Why do lithium-ion batteries die so early? Lithium-ion batteries

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, ranging from 0.1% to 5%, which introduces an additional element of unpredictability.

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

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

Using batteries

Number of cycles

This curve is called the Wöhler curve. The main 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 at 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 relationship, presented in the graphs, was confirmed by the results of experiments, because It is advisable to charge the battery whenever possible.

Calculation of superposition of cycles

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


The effect of large discharge cycles is more significant, which means that it is better to charge the battery at every opportunity.

Memory effect

Battery storage

Storage temperatures

Charge level

Main problems of the experimental results

Results of the experiments

Sources

Lithium batteries

Lithium or lithium-ion (Li-ion) batteries are mainly found in cell phones, laptops, and video cameras. The products are expensive, and so are the batteries, so you need to handle them even more competently than any other batteries. So what is the power of Li-Ion? There are probably even more rumors and myths here. Firstly, it begins to appear by itself, if only because sellers of equipment with Li-ion batteries do not give any special instructions, saying that the battery is “smart” and will do everything as it should. But not herself. After all, there are so many cases when owners of new laptops rendered the battery unusable within a month and then paid good money for a new battery. Of course, lithium batteries are expensive because they are packed with electronics, but, unfortunately, they do not save you from being a fool.

Overdischarge

As with nickel batteries, lithium batteries are also very susceptible to overcharging and overdischarging. But, since these batteries are used in smart devices and come with their own chargers, their electronics do not allow overcharging - i.e. you don't have to be afraid of him. But overdischarge is more difficult to control, which is why it is the most common cause of premature battery failure. Of course, in expensive and complex devices, such as laptops, shutdown occurs before the voltage drops to a critical value. But precedents indicate that this emergency shutdown is best viewed as an emergency measure, which, if possible, is best avoided. The most important rule is to avoid complete discharge, since low voltage can trip the emergency protection circuit. It happens that people “kill” their batteries when they get carried away by training. Training is a good thing, but for lithium batteries 2-3 full cycles are enough.

There is no memory effect for lithium batteries, so they can be charged whenever you want, so it is better not to completely discharge the batteries after training. The recommended lower threshold is 5-10%. The critical lower threshold is 3%.

Many incomplete cycles or one complete

Lithium batteries have a service life of approximately 300 cycles. A full cycle is considered to be a cycle of full charge and complete (i.e. up to approximately 3% capacity) discharge, or vice versa. If you discharge the battery to 50% and then charge it, it will be 1/2 cycle, if to 75% and charge it will be 1/4 cycle, etc. So, for phones and laptops, the difference in benefits between full and incomplete cycles is different. It is persistently stated on the Internet that a lot of people charged their phones when they were not fully discharged (i.e., they recharged the phone every day) and eventually ruined them. At the same time, for laptops it is reliably known that full cycles wear out the battery faster than incomplete ones. The situation becomes clearer with a detailed examination of the structure of Li-ion batteries (see additional materials). It turns out that a lot depends on the controller. It is he who controls the charge current, monitors the condition of the battery, etc. So, in laptops the controller is located in the battery itself and is adjusted by system utilities, such as calibration. In cell phones, the controller is located in the phone itself and cannot be easily adjusted. Although there is no memory effect in lithium batteries, there is a so-called “digital memory” effect. The fact is that the charge-discharge control electronics located in the battery itself operate independently of the device using the battery. Internal electronics monitor the voltage level of the element, interrupt the charge when the set maximum value is reached (taking into account the change in voltage due to the charging current and battery temperature), interrupt the discharge when a critical value is reached and report this “upstream” (for these purposes, a large range of specialized microcircuits). The battery monitoring system “at the top” calculates the charge level based on information about the moments of switching off the charge and discharge from the battery and the readings of the current measurement system. But if operating conditions are such that complete discharging does not occur before hardware shutdown or full charging occurs, these calculations after several cycles may not be entirely correct - the battery capacity drops over time, and the current meter readings may not always correspond to reality. Typically, deviations do not exceed one percent for each cycle, unless serious changes occur during operation, associated, for example, with the failure of one of the battery cells. The monitoring system has the ability to “learn”, that is, recalculate the value of the full capacity of the battery, but for this it is necessary to perform at least one full charge-discharge cycle before the hardware circuits of the battery itself are triggered. So it turns out that with very frequent cycles, the controller gets confused, and, therefore, incorrectly calculates the battery charge and carries out incorrect charging, as a result of which the battery deteriorates. Unlike a laptop, a phone cannot be recalibrated. All that remains in this case is to do a couple of full cycles to get the controller in order. I recommend, ideally, combining full and incomplete cycles, adhering to the “golden mean” principle. Personally, I did this with my cell phone - as a result, after 2 years of operation, the drop in capacity was no more than 40%, which is the norm. In part, time is also not kind to lithium batteries - they wear out over time, regardless of use; Their lifespan is short and it is reasonable to change batteries every 2-3 years.

Storage

When the battery is not in use, it is recommended to store it at 40% capacity in a cool place. The lower temperature limit for storage and operation is 00 C. In general, lithium batteries like to be charged, i.e. They are better to store and keep in a charged state, unlike nickel ones. But during long-term storage, the maximum charge still wears out the battery more, so the optimal state is considered to be 40% charge.

Battery resuscitation

In general, if the battery is dead, it is better to buy a new one; this is the most logical option, although it is expensive. I have not seen any reliable recipes for resuscitating batteries. There are real legends here, especially about laptops, that people have revived their ruined laptop battery and everything is fine with them. One of them sounds like this: “You need to completely discharge the battery, leave the laptop for a week; then fully charge the battery and also leave it for a week; in two months the capacity should be restored.”

For cell phones: combine full and incomplete cycles (in the “XZ” proportion).
For laptops: as few complete cycles as possible (after training).
For everyone: it is recommended to do 80% cycles; do not allow complete discharge (below 3%).

Greetings, my dear friends and admirers, readers of this blog. Instead of another lesson, it would be more correct to say articles in photo school piggy bank, I decided to write an article about a topic that is sore and important to everyone.

I think many, including you, my dear readers, will find it both interesting and useful to know what such fundamental things are lithium ion batteries, what are their limiting characteristics, how should they be used, what can be obtained with proper use, and of course, what should be the care for long battery life. So go ahead.

Why? - you ask me, I actually started writing on this topic. Well, a battery and a battery and what about it. So? But no. Li-ion battery, this is essentially a fuel tank for many of our favorite devices, or devices in common parlance. So what? - you tell me, - what difference does it make to us? And the difference is big and important for you. The idea to write this article came about after my photography school students and I attended. The weather conditions are quite ordinary, about -7 -10 Celsius, sunny, light breeze, clear. Generally pleasant weather for the inquisitive eye of an amateur photographer. However, many students became worried: Isn’t this dangerous for the camera? Won't she freeze? What happens if it freezes? (I will write a separate note about the temperature conditions of the camera) What will happen to the camera battery? We heard that the camera battery is very sensitive to the cold and can fail, is this true? True, but not all and not entirely. Let's figure it out.

Our cameras contain lithium-ion batteries. What would that mean? Here's what. Li-ion batteries have significantly better usage parameters compared to other types of batteries. I won’t go into details, but nowadays, most manufacturers of consumer electronics are trying to equip their products with Li-ion batteries, since they are simpler and cheaper to produce and are less harmful to the environment.

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 less energy density than lithium batteries, Li-ion batteries are safe when properly charged and discharged.

If further, someone is interested in the part about what chemical processes were and are in lithium-ion batteries, and how these same processes were tamed, then go to Google. I’m not strong enough in chemistry and physics to write an article that would make me fall asleep reading it.

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 just a few years ago, manufacturing developers considered the maximum achievable capacity of Li-ion batteries to be no more than several ampere-hours (remember the school physics course), now most of the reasons limiting the increase in capacity have been overcome and many manufacturers began to produce batteries with a capacity of hundreds of amperes -hours, or even thousands.

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 (Ni-Cd) batteries, both at 20 °C and at 40 °C. Resource of lithium-ion batteries: 500-1000 charge-discharge cycles.

And here many will say: -Ahhh. This is why you can shoot with your camera in moderately cold temperatures. Yes, I will answer you. Plus, when the battery works, releasing energy, chemical reactions occur in it, the side effect of which is the release of thermal energy, which allows the battery to maintain its operating temperature range longer. In addition, when we take the camera out of the case on the street, it (the camera, the camera) also has a positive temperature, that is, we further increase the time resource during which we can shoot on the street at -7 ..-15 °C. Add to this the thermal heating of the camera processor during shooting, the heating of the matrix, even the warmth of the hands with which we hold the camera and transfer it to it, extends the thermal and time life of the camera at moderately low temperatures.

This concerns the use of batteries in work. Now let's look a little at the charge and storage side. Lithium-ion batteries do not require any special care. The basic rules for their operation can be found in the instructions for the phone/laptop/camera, and everything else is taken care of by the BMS circuit and the charge controller in the powered device. However, when buying, you can often hear the following statements from a salesperson or a fellow “guru”:

“...first charge - 12–15 hours...” or, alternatively, “...just leave the device connected all night...”;

“...you need to do 3-5 full cycles for the battery to gain capacity...”;

“...it is advisable to charge and discharge the battery completely...”;

“... so what if the battery is already a year old, it hasn’t been used; its service life depends solely on the number of charge-discharge cycles...".

Let's see how true the above is.

The first statement is simply meaningless - the control electronics will not allow the battery to be charged more than it should be.

Tip #2 is also untenable. After the first charge, lithium-ion batteries work with full efficiency, and at first they discharge faster simply because the owner of the device sets up and studies it, shows it to friends and acquaintances, etc. After a week or two, the gadget enters normal mode, which is natural , has a positive effect on autonomy. But one full charge before use is still advisable. This is not necessary for the battery, but so that the device can determine its real capacity and subsequently correctly display the remaining charge.

Recommendation No. 3 has “legs growing” even from the rules for operating nickel-cadmium batteries, which had to be completely discharged first, otherwise part of the capacity would be irreversibly lost. Their lithium-ion counterparts do not have a similar “memory effect”; moreover, deep discharge is contraindicated for them. With frequent use, this is not relevant, since the BMS system does not allow the battery to discharge completely, but if it remains in a discharged state for a month or more, the remaining charge will “leak away”, the protection circuit will block the charging process and turn off, after which charging will no longer be possible. Overcharging is also harmful, but most devices have already taken this into account and do not charge the battery to 100%.

There is also advice like “charge as you wish, but at least once a week (month) carry out a complete cycle.” This operating scheme is optimal for nickel-metal hydride batteries - they also have a memory effect, but much less than Ni-Cd, and restore capacity after 1-2 full cycles. For lithium-ion batteries this is only partially true; for example, it is recommended to do this after long-term storage.

From statement number 4, a seemingly logical conclusion follows: since the battery life is measured by the number of cycles, it means that it is better to use it to the maximum. This is a mistake. Full charge and discharge wear it out faster, while incomplete cycles, on the contrary, prolong life. In addition, lithium-ion batteries lose capacity even without use. Already after a year “on the shelf” their resource decreases by 5–10%, after 2 years – by 20–30%. Therefore, when purchasing a new portable device, pay attention to the release date of the power supply. It is also obvious that buying a battery for future use, even if it is difficult to find on sale, is useless.

It is very important to observe the operating temperature conditions of lithium-ion batteries. In frost below -20 °C they simply stop delivering current, and in heat above +45 °C although they function, such climatic conditions activate the aging process, significantly reducing the life of the battery. But you can charge it only at positive (Celsius) temperatures, otherwise there is a high risk of device failure. In general, the optimal operating temperature of lithium-ion batteries is +20 °C.

Lithium-ion batteries are constantly being improved, and manufacturers are actively experimenting with electrode and electrolyte materials. In 1994, batteries with lithium-manganese cathodes appeared, and in 1996 - with lithium-iron-phosphate cathodes. They are much more stable and can easily withstand high discharge currents, so they are used in power tools and electric vehicles. Since 2003, batteries have been produced that use a complex cathode composition (LiNiMnCoO2) and have the best combination of characteristics among all listed. But no one has yet been able to surpass lithium-cobalt specimens in terms of specific capacity and price, and the advantages of the new types are not in demand in mobile phones and laptops that consume relatively little current.

If you have temporarily put your device aside, but want to keep its battery in working condition, know that lithium-ion batteries are best stored at a temperature of about +5 ° C. The higher it is and the closer the charge level is to 100%, the faster the battery ages and loses capacity. It is best to charge it to 40–50%, remove it from the device, pack it in a sealed plastic bag, put it in the refrigerator (but not in the freezer!) and recharge it periodically.

That's all I wanted to say about batteries, our friends, electronic pets. Be it a phone, a player or a camera.

This article was prepared based on materials found on the Internet and collected here in a pile for convenience and understanding of the essence of the process.

Any questions? Write in the comments and I will definitely answer.

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Among the most modern batteries, lithium ones occupy a special place. In chemistry, lithium is the most active metal.

It has a huge energy storage resource. 1 kg of lithium can store 3860 ampere hours. The well-known zinc lags far behind. His figure is 820 ampere-hours.

Lithium-based cells can produce voltages up to 3.7V. But laboratory samples are capable of producing a voltage of about 4.5V.

Modern lithium batteries do not use pure lithium.

There are currently 3 common types of lithium batteries:

Lithium-ion ( Li-ion). Rated voltage (U nom.) - 3.6V;

Lithium polymer ( Li-Po, Li-polymer or "lipo"). U nom. - 3.7V;

Lithium iron phosphate ( Li-Fe or LFP ). U nom. - 3.3V.

All these types of lithium batteries differ in the cathode or electrolyte material. Li-ion uses a lithium cobaltate cathode LiCoO2, Li-Po uses a gel polymer electrolyte, and Li-Fe uses a lithium ferrophosphate cathode LiFePO 4.

Any lithium battery (or the device in which it operates) is equipped with a small electronic circuit - a charge/discharge controller. Since lithium-based batteries are very sensitive to overcharging and deep discharge, this is necessary. If you “pick apart” any lithium battery from a cell phone, you can find a small electronic circuit in it - this is the protective controller ( Protection IC ).

If there is no built-in controller (or charge supervisor) in a lithium battery, then such a battery is called unprotected. In this case, the controller is built into the device, which is powered by such a battery, and charging is possible only from the device or from a special charger.

The photo shows an unprotected Li-Po battery Turnigy 2200 mAh 3C 25C Lipo Pack. This battery consists of 3 cells connected in series (3C - 3 cell) of 3.7V each and therefore has a balancing connector. The continuous discharge current can reach 25C, i.e. 25 * 2200 mA = 55000 mA = 55 A! And the short-term discharge current (10 sec.) is 35C!

Lithium batteries, which consist of several cells connected in series, require a complex charger equipped with a balancer. This functionality is implemented, for example, in such universal chargers as Turnigy Accucell 6 and IMAX B6.

A balancer is needed to equalize the voltage across individual cells during charging of a composite lithium battery. Due to differences between cells, some may charge faster and others slower. Therefore, a special circuit for shunting the charging current is used.

This is the wiring for the balancing and power cables of an 11.1V LiPo battery.

As is known, overcharging a lithium battery cell (especially Li-Polymer) above 4.2V can lead to an explosion or spontaneous combustion. Therefore, during charging it is necessary to control the voltage on each cell compound battery battery!

Correct charging of lithium batteries.

Lithium batteries (Li-ion, Li-Po, Li-Fe) are charged according to the CC/CV method (“constant current/constant voltage”). The method is that first, when the voltage on the element is low, it is charged with a constant current of a certain value. When the voltage across the cell reaches (for example, up to 4.2V - depends on the type of battery), the charge controller maintains a constant voltage across it.

First stage lithium battery charge - CC- implemented through feedback. The controller selects the voltage on the element so that the charge current is strictly constant.

During the first charging stage, the lithium battery accumulates most of the power (60 - 80%).

Second stage charge - CV- begins when the voltage on the element reaches a certain threshold level (for example, 4.2V). After this, the controller simply maintains a constant voltage on the element and gives it the current it needs. Towards the end of the charge, the current decreases to 30 - 10 mA. At this current, the element is considered charged.

During the second stage, the battery accumulates the remaining 40 - 20% of the power.

It is worth noting that exceeding the threshold voltage on a lithium battery can cause it to overheat and even explode!

When charging lithium batteries, it is recommended to place them in a fireproof bag. This is especially true for batteries that do not have a special box. For example, those that are used in radio-controlled models (car, aircraft modeling).

Disadvantages of lithium-ion batteries.

The main and most frightening disadvantage of lithium-based batteries is their fire hazard if the operating voltage is exceeded, overheating, improper charging and illiterate operation. There are especially many complaints regarding lithium-polymer (Li-Polymer) batteries. However, lithium iron phosphate (Li-Fe) batteries do not have such a negative feature - they are fireproof.

Also, lithium batteries are very afraid of the cold - they quickly lose their capacity and stop charging. This applies to Li-ion and Li-Po batteries. Lithium iron phosphate (Li-Fe) batteries are more resistant to frost. Actually, this is one of the positive qualities of Li-Fe batteries.

The disadvantage of lithium batteries is that they require a special charge controller - an electronic circuit. And in the case of a composite battery and balancer.

When deeply discharged, lithium batteries lose their original properties. Li-ion and Li-Po batteries are especially susceptible to deep discharge. Even after restoration, such a battery will have a lower capacity.

If a lithium battery does not “work” for a long time, then first the voltage on it will drop to a threshold level (usually 3.2-3.3V). The electronic circuit will completely turn off the battery cell, and then a deep discharge will begin. If the voltage on the cell drops to 2.5V, this may lead to its failure.

Therefore, it is worth recharging the batteries of laptops, cell phones, and mp3 players from time to time during long periods of inactivity.

Typically, the service life of an ordinary lithium battery is 3 - 5 years. After 3 years, the battery capacity begins to decrease quite noticeably.

Lithium-ion batteries are not as finicky as their nickel-metal hydride counterparts, but they still require some care. Sticking to five simple rules, you can not only extend the life cycle of lithium-ion batteries, but also increase the operating time of mobile devices without recharging.

Do not allow complete discharge. Lithium-ion batteries do not have the so-called memory effect, so they can and, moreover, need to be charged without waiting for them to discharge to zero. Many manufacturers calculate the life of a lithium-ion battery by the number of full discharge cycles (up to 0%). For quality batteries this 400-600 cycles. To extend the life of your lithium-ion battery, charge your phone more often. Optimally, as soon as the battery charge drops below 10-20 percent, you can put the phone on charge. This will increase the number of discharge cycles to 1000-1100 .
Experts describe this process with such an indicator as Depth Of Discharge. If your phone is discharged to 20%, then the Depth of Discharge is 80%. The table below shows the dependence of the number of discharge cycles of a lithium-ion battery on the Depth of Discharge:

Discharge once every 3 months. Fully charging for a long time is just as harmful to lithium-ion batteries as constantly discharging to zero.
Due to the extremely unstable charging process (we often charge the phone as needed, and wherever possible, from USB, from a socket, from an external battery, etc.), experts recommend completely discharging the battery once every 3 months and then charging it to 100% and holding it on charge 8-12 hours. This helps reset the so-called high and low battery flags. You can read more about this.

Store partially charged. The optimal condition for long-term storage of a lithium-ion battery is between 30 and 50 percent charge at 15°C. If you leave the battery fully charged, its capacity will decrease significantly over time. But the battery, which has been collecting dust on a shelf for a long time, discharged to zero, is most likely no longer alive - it’s time to send it for recycling.
The table below shows how much capacity remains in a lithium-ion battery depending on storage temperature and charge level when stored for 1 year.

Use the original charger. Few people know that in most cases the charger is built directly into mobile devices, and the external network adapter only lowers the voltage and rectifies the current of the household electrical network, that is, it does not directly affect the battery. Some gadgets, such as digital cameras, do not have a built-in charger, and therefore their lithium-ion batteries are inserted into an external “charger”. This is where using an external charger of questionable quality instead of the original one can negatively affect the performance of the battery.

Avoid overheating. Well, the worst enemy of lithium-ion batteries is high temperature - they cannot tolerate overheating at all. Therefore, do not expose your mobile devices to direct sunlight or place them near heat sources such as electric heaters. Maximum permissible temperatures at which lithium-ion batteries can be used: from –40°C to +50°C

Also, you can look