How to restore a lithium-ion battery after a deep discharge

Article updated: 12/07/2020 There are 2 common situations in which the question arises about the possibility or impossibility of restoring an 18650 battery. In the first case, it quickly discharges under load, because. has exhausted its resource, and a natural loss of capacity has occurred. In the 2nd case, the battery does not accept a charge because it is in a critically discharged state.

The chemical structure of lithium-based batteries undergoes irreversible changes over time. Therefore, it will not be possible to return the original capacity of a Li-ion battery that has honestly exhausted its service life (about 1000 cycles). Moreover, the capacity of lithium cells gradually decreases not only during their charge-discharge process, but even during storage - by approximately 4-5% annually.

A decrease in battery capacity can occur even before the working resource is exhausted. This problem is often observed due to improper use, overcharging or over-discharging the cells. In order for Li-ion batteries to last longer, you need to use chargers compatible with them with the correct limitation of the charge level, avoid critical discharge and storage in a dead state.

How to restore a Li-ion battery

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

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

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

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

We swing the battery as carefully as possible. The charging program is set to Li-Po, the charging mode is selected depending on the type of battery: for Li-ion - 3.6 V, or 3.7 V for Li-pol

Important: during the recovery process, set the Auto parameter - without it, the start will not start due to the low battery charge. The current value is selected using the “+” and “–” buttons

1 A is the safest and optimal current for boosting.

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

Restoring 18650 Battery Capacity

The capacity of a battery depends on the ability of the internal components to accept a charge through an electrochemical reaction. But during the use of the element, undercharging and overdischarging occurs, the reaction occurs at high or low temperatures. The complex composition of elements participating in the reaction loses its equilibrium. At the same time, parasitic reactions occur in parallel. They bind the active substance, removing it from the electrochemical process. The concentration of active particles decreases, the battery takes less charge. This leads to a decrease in capacity.

Lithium batteries are very active; during the non-working period, self-discharge with parasitic reactions continues, the battery loses capacity. Therefore, during storage, monitoring the battery condition and recharging it are mandatory.

The lost capacity of any lithium batteries, including the 18650 form factor, cannot be restored. Decomposed lithium salts cannot be revived.

Model range, selection of suitable products

Products in this category are produced in a standard design to match the dimensions and electrical parameters of standard “A” and “AA” disposable batteries. Such batteries are installed in flashlights, radios, alarm clocks, and toys.

Something to remember! The charge of a lithium battery decreases during storage. The storage capacity is gradually decreasing, so you cannot count on many years of operation without deterioration in the initial consumer parameters.

Modern smartphones and tablets are often created in a non-separable version using adhesive joints. This helps reduce production costs, but makes repairs much more difficult. The equipment is equipped with unique built-in charging (protection) devices. Work cycles are controlled by specially tuned software. Sometimes it is simply impossible to find a suitable alternative rechargeable battery.

Must be emphasized! Do-it-yourself repair work using products from another brand will void your rights to official warranties.

Standard battery sizes

It is worth paying attention to the “18650” model. These numbers encode the dimensions (length x diameter, 65 x 18 mm, respectively)

Such batteries are gradually becoming the most popular. They are connected into blocks, creating power sources of the required capacity for automobile transport, ATVs, aircraft models, and other equipment.

As is clear from the above description, some products can be purchased legally only in the official retail chain of certain manufacturers. High-quality universal batteries in different formats are created by Japanese and Korean enterprises. The products of responsible Chinese manufacturers are not inferior in technical parameters. However, we should not forget about the large number of fakes that do not differ in appearance from the originals.

Example of a fake

Through testing or destructive disassembly, deficiencies can be identified. However, some correct conclusions can be drawn after carefully studying the photographs. Thus, the real capacity of “branded” products of the “18650” format does not exceed 3,400 mA/hours. In advertising materials there are products with fantastic parameters - 10-15 thousand mAh or more.

Safety precautions

Before pushing your phone battery, always remember safety precautions and responsibility for your actions. Before blindly trusting unverified data posted on websites, consult with knowledgeable people.

Remember these simple but important rules:

• If the battery is swollen, do not get rid of the gases, but throw it away immediately. Reviving the battery by releasing gases is simply impossible! Moreover, do not try to charge or heat it - it may explode!
• Do not leave a problem or repaired device without proper supervision.
• When carrying out repair work, monitor its temperature. Use a thermocouple or a special thermometer for this. Stop work immediately if the surface becomes very hot.
• When charging, do not use currents higher than 50 mA. Determine the current strength by connecting a multimeter or milliammeter in series in the circuit.

Finally, a video about how not to restore a battery.

Now you know how to charge a completely discharged phone battery and you can do it yourself. But don't overdo your self-esteem. Once again, consult with professionals.

Operating principle

The first devices in this category were created in the 70s of the last century. But only 20 years later the first lithium-ion batteries with characteristics acceptable to ordinary consumers were produced. Today, technology continues to be improved in order to improve operational parameters.

Functional components, operating cycles

Due to the high chemical activity of pure lithium, the developers decided to use less dangerous ions. According to the standard scheme, during the charging process they are built into a holding region with a positive electric potential, which is formed from a graphite crystal lattice. When a consumer is connected to a removable aluminum terminal, the current in the circuit provokes the movement of ions to the negative copper electrode. Inside the battery, the discharge is moved by a conductive fluid. Its mixing is blocked by a semi-permeable partition made of porous polymer.

For your information. Crystallization of the water-based electrolyte explains the deterioration of technical characteristics at low temperature conditions.

The battery is dead, how to charge without charging

If the energy of a dead battery after a long period of inactivity is not enough to set the car in motion, charging from external sources will be required. This could be recharging from the battery of another car or using an external energy source in the form of a battery or booster. You may have to use a pusher. How to apply the first pulse charge, in the future the generator will add energy, but after an emergency drop in charge, it is necessary to take measurements and charge the dead battery with a network station.

A battery that has reached zero is charged with a current of 2-3 A. If the voltage at the terminals does not increase within several hours, the battery needs to be replaced.

What to do if the battery does not charge

If the above methods did not help, then we recommend that you familiarize yourself with the following methods on how to revive a 18650 battery.

Using a special charger

This action is carried out using a Chinese copy of the “IMAX B6” charger and a multimeter. This charger is widely available, and it perfectly restores the battery at home. First, you need to check the battery itself by connecting a multimeter to it and setting the device to voltage measurement mode. If the battery is deeply discharged, the multimeter will show low U readings in millivolts.

The essence of the method is that the controller “interferes” with the measurement of the real amount of U in the battery. There are two pins, plus and minus, that go directly from the battery to the controller. The voltage at the terminals is most often 2.6 V, which is a fairly small value.

The tension will rise little by little. This means that the restoration of the li ion battery is successful. After some time, the U value will reach 3.2 volts, and the battery will begin to “sway”. Later it can be charged from the “native” charger.

Using a resistor and a “native” memory

This method is even easier to implement than the previous one. Here it is necessary to bring the “minus” of recharging to the “minus” of the battery. And bring the “plus” through a resistor to the “plus” of the battery. After this, power should be applied and the voltage will increase. It can be raised to 3B; to achieve this indicator, you need to carry out the procedure within fifteen minutes. Once the method is completed, the battery can be tested for functionality.

With a fan

To implement this method, we need a power supply with an output voltage of at least 12V. The “minus” of the fan should be connected to the “minus” connector of the power supply, and its “positive” connector to the plus, and be sure to manually fix it on the battery. When we turn on the device, the fan will start working. This means that current is already flowing in the battery. The procedure should not be continued for long; after about 30 seconds you need to turn off the network. After such restoration, the voltage usually increases to 3V.

Recovering 18650 batteries by charging from another battery

There is a way to revive a lithium-ion battery using another car battery. To do this we need any other 9 V battery, adhesive tape, and also a thin wire. The method is carried out in the following steps:

• The wiring needs to be connected to the contacts of the battery that we want to revive. There must be a separate wire for each contact.
• You cannot connect the plus and minus contacts with just one wire. Because of this, a short circuit may occur, and it will be impossible to revive the battery.
• The connections must be secured with tape, on which you must first make a mark with a marker, which wire will be connected to which contact.
• The wire from the “plus” of the nine-volt battery should be connected to the “plus” of the battery being restored.
• The negative contacts must be connected using the same method.
• We secure all contacts with electrical tape so that the wires do not come loose.
• We wait a certain time and monitor the condition of the battery, it should heat up minimally.
• When the battery becomes warm, immediately disconnect the batteries from the battery.
• We are recharging.
• We check the work.

Through the use of training cycles

This method is carried out to prevent sulfation and also to determine the battery capacity. Such cycles must be carried out at least once a year and the procedure is performed in the following steps:

• The lithium-ion battery should be charged at normal current until it is fully charged.
• We keep it for four hours after the power has stopped.
• We adjust the density of the electrolyte.
• We turn on the charge for 25-35 minutes so that the electrolyte is mixed.
• It is necessary to carry out a control discharge with a constant normal current of ten-hour mode and monitor the time of complete discharge before the voltage drops to 1.7 V per jar
• Battery capacity can be defined as the level of discharge current multiplied by the discharge time.
• After the test discharge has been completed, you must immediately completely discharge the battery. If it turns out that the capacity is not charging, the 18650 battery most likely cannot be fixed.

The main disadvantages of this method:

• Service life is reduced.
• Long recovery time for lithium-ion batteries.
• Huge energy costs.
• Low efficiency of the method.

Closing the battery contacts to restore charge

This method can only be used if other methods do not help. You can see many reviews on the Internet that it can revive a 18650 lithium-ion battery. This method is very risky for preserving battery capacity.

To close the contacts, you need special tools, to disassemble the battery, in addition, you need a wire to short-circuit the battery terminals.

The battery control board is usually located in a plastic frame. The minus and plus contacts are connected to it. They are exactly what we need. They should be short-circuited for a minimum period of time.

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We revive the battery using cold

Using a refrigerator to recondition a lithium battery is useless. Alkaline nickel-cadmium batteries can “add” a little capacity, but this type of element is not installed on any modern smartphone.

Storing the battery in the refrigerator will lead to its complete discharge, but will certainly not help start the charging process. If you remove an element from your phone, store it at room temperature on a dry surface.

Important! Overcooling of Li-ion cells will lead to their failure and loss of the manufacturer's warranty.

Design, main parameters

A detailed study of chemical and physical processes is redundant for the average user. An inquisitive person can easily find the necessary additional data on the Internet on intercalation and experiments with different materials. Below is information that will be useful in practice. They are typical for typical models of lithium-ion batteries on the market today:

• Load current – ​​from 1 to 50 C in different modes;
• Rated voltage – from 3 to 4.35V;
• Resistance (internal) – 5-15 mOhm;
• Energy capacity per 1 kg of product – 112-246 Wh;
• Maintaining normal performance – up to 550-650 cycles;
• Charging time to 80% of the nominal capacity – 60 minutes;
• The permissible temperature range is from -30°C to +60°C.

Lithium-ion battery design
The figure shows typical components of a “flat” model. Similar products are installed in smartphones and other mobile equipment. After filling the electrolyte, the inlet hole is sealed. The durable housing provides good protection against mechanical stress. The built-in valve is activated when a large amount of gases forms, preventing an explosion. The current fuse breaks the circuit, which prevents a short circuit and excessive temperature rise.

One of the first power sources for cars created on the principles of lithium ion charging

The diagram shows:

• mounting brackets (1), which simultaneously serve as cooling elements;
• typical lithium-ion batteries (2);
• electronic unit that controls the charging process;
• valve (4), through which the refrigerant is replenished;
• connector (5) for connecting to the on-board network;
• protective and regulating device (6).

Why does the controller block the operation of lithium batteries?

The reasons for blocking a lithium battery are the following factors:

1. Short circuit. Occurs when the permissible charge level is exceeded. The controller breaks the electrical circuit. It is restored only after the short circuit is eliminated. To unlock, the battery is connected to the charger.
2. Deep discharge. The protection system prevents further consumption of battery energy. You can save the battery by starting charging the phone with the original charger.
3. The course of dangerous processes. During a critical discharge, a rapid flow of chemical reactions begins. Lithium crystals form inside the case. Interacting with the electrodes, they cause an explosion. A dangerous situation occurs when voltage is applied. The flow of current is blocked by the controller.

The charge controller for Li-Ion batteries protects the battery from short circuits and overcharging.

Avoid deep discharge

There are different options for using battery life. If you discharge the battery quickly and completely each time, this will regularly be accompanied by the release of a large amount of heat, because considerable discharge currents will flow through the battery, and this is a destructive load on the battery.

If small discharge cycles are short, even if the battery is then recharged and then discharged again in several portions, the battery life will last longer.

Modern lithium batteries can withstand partial discharge and recharging normally, not like the very first lithium batteries!

And if we consider the influence of discharge-charge cycles on the overall lifespan of the battery, then in fact three cycles of discharge to 66% and recharge to 100% are fundamentally equivalent in terms of wear and tear to a pair of cycles of discharge to 50% and then recharge to 100%.

Avoid deep discharge

Many short discharge-charge cycles are no more harmful than several longer cycles. An intense discharge is harmful - it causes heating and leads to irreversible processes if it is deep (up to 20% and below).

Heating and high current load definitely reduce the overall lifespan of the battery. Each deep discharge slowly but surely leads to irreversible damage, so try to avoid deep discharge altogether. If the smartphone turns itself off - this is a sign of a deep discharge - you should not let it get to this point. 20% is enough to recharge the device or insert a backup battery.

Restoring lithium LiIon LiPo tablet batteries using Imax B6.

By recovery we mean a “push” of the battery. All tablet batteries are equipped with power controllers designed to protect the battery from overcharging or “deep discharge”. If, however, the battery was discharged below the minimum, the controller goes into protection and applying current to its terminals will lead to nothing. To start the battery, we need to apply directly to the battery a minimum current of 0.1A in the nickel battery charging mode, thus bringing the voltage to just over 3V and then start charging as usual in the LiIon or LiPo mode.

Device

Lithium-ion battery. Scheme of work

A lithium-ion battery consists of electrodes (cathode material on aluminum foil and anode material on copper foil) separated by a porous separator impregnated with electrolyte. The electrode package is placed in a sealed housing, the cathodes and anodes are connected to current collector terminals. The housing is sometimes equipped with a safety valve that relieves internal pressure in emergency situations or violations of operating conditions. Lithium-ion batteries vary in the type of cathode material used. The charge carrier in a lithium-ion battery is a positively charged lithium ion, which has the ability to penetrate (intercalate) into the crystal lattice of other materials (for example, into graphite, metal oxides and salts) to form a chemical bond, for example: into graphite with the formation of LiC6, oxides (LiMnO2) and salts (LiMnRON) of metals.

Initially, lithium metal was used as negative plates, then coal coke. Later, graphite began to be used. The use of cobalt oxides allows batteries to operate at significantly lower temperatures and increases the number of discharge/charge cycles of one battery. The proliferation of lithium iron phosphate batteries is due to their relatively low cost. Lithium-ion batteries are used in conjunction with a monitoring and control system - SKU or BMS (battery management system) - and a special charge/discharge device.

There are currently three classes of cathode materials used in the mass production of lithium-ion batteries:

• lithium cobaltate LiCoO2 and solid solutions based on its isostructural lithium nickelate
• lithium manganese spinel LiMn2O4
• lithium ferrophosphate LiFePO4.

Electrochemical circuits of lithium-ion batteries:

• lithium-cobalt LiCoO2 + 6C → Li1-xCoO2 + LiC6
• lithium ferrophosphate LiFePO4 + 6C → Li1-xFePO4 + LiC6

Due to low self-discharge and a large number of charge/discharge cycles, Li-ion batteries are most preferable for use in alternative energy. At the same time, in addition to the I&C system, they are equipped with inverters (voltage converters).

How long to charge a dead car battery?

The energy spent on starting the car, servicing the alarm system and other on-board systems is replenished by the generator. The voltage in the relay network is regulated by a regulator, which is designed for 13.9 - 14.3 V. The battery is not fully charged and periodically requires recharging. After being idle, the remaining battery charge may not be enough to start the engine. How to determine how long to charge a dead battery?

To charge a dead car battery, you will need to determine the degree of discharge of the battery by the voltage in the open circuit. In a serviced or hybrid battery, the residual charge can be determined by the actual density of the electrolyte.

The charging time is set by dividing the charging capacity by the charging current, which should be less than 10% of the charging capacity. The efficiency of the electrochemical reaction is assumed to be 50%. This means that the calculated time should be doubled.

Before charging, a dead car battery should be prepared for recharging - cleaned of dirt and acid deposits on the terminals. The plugs of low-maintenance batteries need to be unscrewed, the density and level of electrolyte in the banks must be checked.

How to charge a battery, rules

Lithium-ion batteries are similar to people in that they do not behave the same and work best at temperatures that are neither too hot nor too cold.

These batteries perform better at high temperatures than at low temperatures because the heat reduces internal resistance and speeds up the chemical reaction inside the battery. A side effect of this process is that it puts a strain on the battery, which can lead to shortened life in hot conditions for extended periods.

On the other hand, low temperatures increase internal resistance, which increases the load on the battery and reduces its capacity. Batteries that provide 100% capacity at 27°C are typically reduced by 50% at -18°C and so on.

How to charge Li ion batteries correctly?

Do not discharge completely

Failure to follow these tips and instructions may damage the battery to the point that it becomes unusable. You may also endanger your safety and the safety of others if the battery is not used properly. When combined with a mismatched charger, overheating or overcharging may occur and there is a risk of fire.

Complete discharge is carried out no more than once every 3 months

How to properly charge lithium ion batteries?

Charging lithium ion batteries is very different from charging nickel-cadmium or nickel-metal hydride batteries.

The differences are that lithium-ion batteries have a higher voltage per cell. They also require much tighter voltage tolerances when detecting a full charge, and once fully charged they do not allow or require recharging

It is especially important to be able to accurately determine the state of full charge since lithium-ion batteries cannot be overcharged

Low charge storage

Most consumer-oriented lithium-ion batteries charge to 4.2V per cell, and this allows for a deviation of about ±50mV per cell. Charging beyond this stresses the cell and leads to oxidation, which reduces life and performance. This may also cause security problems.

Charge only with original charger

Charging lithium-ion batteries can be divided into two main stages:

• Constant current charging: In the first stage of charging a lithium-ion battery or cell, the charging current is controlled. Typically, this is between 0.5 and 1.0 C. (Note: For a 2000 mAh battery, the charging rate will be 2000 mA for the C charging rate). For LCO consumer cells and batteries, a charging rate of no more than 0.8 °C is recommended. At this point, the voltage across the lithium ion cell is increased for constant current charging. Charging time can be around an hour for this stage.
• Charge Saturation: After some time, the voltage peaks at 4.2V for the LCO cell. At this point, the cell or battery should enter the second stage of charging, known as saturation charge. A constant voltage of 4.2V is maintained and the current will drop continuously. The end of the charging cycle is reached when the current drops to approximately 10% of the rated current. Charging time can be around two hours for this stage depending on cell type and manufacturer, etc.

Charge efficiency, that is, the amount of charge held by a battery or cell relative to the amount of charge entering the cell, is high. Charging efficiency is between 95 and 99%. This reflects relatively low levels of cell temperature rise.

Do not overheat the battery when charging

There are times when you cannot use the battery for an extended period of time. Here are tips for maintaining maximum battery capacity for long-term storage.

Revive the battery using cold

The fact is that low temperatures are better tolerated by the battery than heat. Many experts give advice on preventing the device using freezing. The first step is to remove the battery from the device and put it in a tight bag. It is necessary for protection and water penetration inside. After this, the battery must be placed in the freezer compartment of the refrigerator. The battery must be kept in the freezer for 12 hours. After 12 hours, the device is taken out and dried with paper towels. After this process, you should place the 18650 Li-ion battery into the device and charge it.

Once the device is charged, its capacity should increase by about 20% due to supercooling.

Installing a lithium-ion battery in an LED flashlight

Before starting work, you need to check the functionality of the controller and battery.

The controller can be supplied with voltage without load. In this case, the output voltage is set to 4.2 V and the blue LED on the board lights up. Next, you need to check the battery by connecting it to the controller output and charging it completely. The red LED will light up while charging, and the blue LED will light up when the battery is charging.

After charging, it is advisable to run test the battery, connect it instead of an acid one and see how long the flashlight illuminates. It worked for me for 10 hours and continued to shine. I didn’t wait any longer, since this time was quite enough for my tasks.

New electrical circuit of LED flashlight

At the next step, a new electrical circuit diagram of the flashlight is developed. The negative wire is common to all components and the battery. In the left position of switch SA1, its common contact connects the battery to the positive terminal of the controller. By connecting the middle pin to pin 3, voltage is applied to the narrow beam board, and with pin 4 to the diffuse light LED strip.

The SA2 toggle switch is used to select the battery from which the LEDs will operate. Since there were two batteries available, I decided to install both in the flashlight. There is no clear answer to the question about the admissibility of parallel connection of lithium-ion batteries without a special controller. Therefore, I decided to go the proven route and provided the ability to connect the batteries separately.

Separate connection of each battery made it possible not only to ensure their operation and charging in optimal conditions, but also to know during the operation of the flashlight how long it will last. Knowing how much time was enough to operate from one battery, you will know how much more the flashlight can illuminate.

In addition, if one of the batteries fails, this will not lead to loss of performance of the flashlight. Two separate LED units and two batteries ensure you're never left in the dark.

Assembling a flashlight with a lithium-ion battery

Now everything is prepared and you can start upgrading the flashlight - reworking its circuit to work with a lithium-ion battery.

First, all wires are unsoldered from the switch and the old charger board is removed.

The body of the modernized flashlight had a compartment designed for a short power cord, which was closed with a folding bar with diffused light LEDs. The SA2 toggle switch for battery selection was inserted into it.

Double-sided tape in the form of two strips was used to secure the batteries. You can also secure the batteries using silicone.

Before attaching the batteries and the controller board, wires of the required length were first soldered to them with a soldering iron. Due to the fact that two batteries were not conveniently placed in one half of the flashlight body, I installed them one in each half of the body. The controller board was secured to the case using two screws with M2 nuts.

When soldering wires to the terminals of the battery, care must be taken so that the free ends of the wires do not accidentally touch and short-circuit its terminals

The photo shows the lantern after installation. All that remains is to check the operation of its components and assemble it.

It is impossible to measure the charging current by connecting an ammeter to the open circuit after the controller, since the internal resistance of the device is large and the measurement results will be incorrect. I have a USB tester with which you can find out the voltage supplied from the charger, the current charge current, the charge time and the energy capacity that the battery has received. The tester showed that the controller charges the battery with a current of 0.42 A. Therefore, the controller charges the battery normally.

After assembling the flashlight, it turned out that its red body does not transmit blue light and it is impossible to know when charging is complete.

I had to disassemble the flashlight and make a slot hole in the area where the indicator LEDs are located.

Now that the battery is charged, the blue LED glow is clearly visible.

Deep overdischarge of Li-ion using the example of Sony-Murata US18650VTC6

There is an opinion that over-discharging lithium-ion batteries is not only not useful, but even harmful. So let’s check how much this affects the “health” of some of the best batteries of the 18650 form factor. It turned out to be long, but it’s 3 months of experiments, processing their results and searching for information. 1. What-where-how much

Test subjects – Sony (now Murata) US18650VTC6 were purchased from a well-known Indian on ru.nkon.nl.

The order was made together. Check:

Since 30 pieces of VTC6 weigh about 1.5 kg, and 9.90 € is for any parcel weighing up to 2 kg, several blisters with small Enelupes were added to the parcel.

Even if we do not take this addition into account, the price of sending 1 can of VTC6 is 9.90/30=0.33 €. Which at the time of writing is 23 Russian rubles and is equal to the fare for a Voronezh minibus. It turns out that 1 can from Aunt Sonya’s assembly line cost 80.40/30+0.33=2.68+0.33=3.01 € or ~210 re at the current exchange rate. In my opinion, this is quite a good purchase, because... VTC6 are considered one of the best batteries in the 18650 form factor. VTC6 seems to have come from the wrong place, at least the QR codes on different copies never match.

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Holders (type 1) – HERE. I have two slot ones. Very rigid contact lamellas with a golden-colored coating. There are plus and minus markings inside the slots. There are small holes on the outer pads. There are 2 holes in the plastic between the slots for mechanical fastening to the board or device body.

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Holders (type 2) – HERE. Single-slot. Very hard contact lamellas without coating (or nickel-plated?). There are plus and minus markings inside the slots. External contacts are made in the form of thin and narrow flexible slats.

2. About overdischarges, battery storage, cycling, etc.

Attention, this section is very long, tedious and sometimes difficult to understand. The author doesn’t even know how to present this in a way that would be interesting and understandable to everyone. But for those interested it may contain something useful. At the very least, food for thought...

2.1. About Ni-MH (regarding the previous review)

The previous review was also devoted to the overdischarge of single cells. But not lithium-ion, but Ni-MH. Deep and long (up to 14 days) overcharges of Ni-MH from 4 vendors did not affect their capacity in any way (according to GOST). The obscure parameter IR(@1kHz), which housewives associate with “correctly measured internal resistance,” has only slightly increased. It's funny, but the result noticeably surprised only me. At least that's what I thought. I was even more surprised that many commentators treated Ni-MH overdischarges below 0.5V as something quite common, allowed and taken for granted. And there was something to be surprised about. At one time, more than a dozen stories for HIT users were posted on cadex.ru, translated into the great and mighty. Here is one of them - TYTS. It should be remembered that this was written quite a long time ago - at the very beginning of the 2000s. Below the spoiler is an excerpt from there, regarding the Ni-Cd discharge to zero.

Excerpt from the book Batteries in a Portable World by Isidor Buchmann. Translation by Vladimir Vasiliev. Notes INN36.

FROM THE TRANSLATOR I asked a question to Mr. Isidor Buchmann, head of the Canadian company Cadex Electronics Inc., manufacturer of battery analyzers, author of the project and book “Batteries in a Portable World. A handbook on rechargeable batteries for non-engineers":

I have one more question about your book “Batteries in the World of Portable Devices.
A Non-Engineer's Guide to Batteries,” Chapter 15, “Caring for Batteries from Purchase to Failure.” You write that for best results NiCd batteries should be fully charged and then discharged to 0 volts. My question is: why does a NiCd battery need to be discharged to 0 volts? I have not seen such information and such requirements in the recommendations of NiCd battery manufacturers. To which I received the following answer:
Good question, Vladimir.
I attended a one week training seminar in the US on aircraft battery maintenance. Mostly aviation batteries are flooded NiCd
*.
As part of the maintenance procedure, the battery is first discharged to 1 volt per cell, then each cell is discharged to 0 volts. After this, all cells are short-circuited for 24 hours, then the battery is charged and tested. This procedure cannot be performed on portable batteries
**.
Tests conducted by the US Army have shown that a NiCd cell must be discharged to at least 0.6V to effectively destroy more resistant crystalline formations. Discharging from 1.0V down must be done at a significantly reduced current to avoid damaging the battery. The Cadex Battery Analyzer discharges the battery to 0.4V using the primary and secondary discharge method. I am not aware of any studies that show the benefits of discharge lower than 0.4V per cell
. When I asked the instructor (teacher) at this seminar regarding the benefits of discharging to 0V and shorting the cells for 24 hours, he did not give a clear and precise answer. He said they always did it this way.

Translator's conclusion: therefore, do not try to discharge your NiCd or NiMH*** battery to 0. At home, a discharge of up to 1 volt per cell should be considered acceptable

.
=== Notes INN36.
* We are talking about serviceable (non-sealed) batteries. Those that allow you to perform various manipulations with the electrolyte (pour out, fill in, change the composition of the solution). ** Not “portable”, but “sealed”. Those. – unattended. *** Which way is Ni-MH going? We were talking exclusively about the Ni-Cd system. It has never been recommended to discharge Ni-MH below 0.9-1.0V. And even more so to discharge “to zero”. Firstly, this makes no sense, because even if Ni-MH has the so-called. “memory effect”, then it has a different nature. In Ni-Cd, the “memory effect” is associated with the enlargement of Cd(OH)2 grains if not completely discharged batteries are constantly charged. In the Ni-MH electrochemical system, the "cadmium" electrode is replaced by a "metal hydride" MH, consisting of nickel (alligated with Co, Mn and Al) and mischmetal enriched with lanthanum (50–60% La + 30–40% Ce + 10–15% Nd + 1–2% Pr). There is no cadmium or cadmium hydroxide. And the MN electrode works in a completely different way: there is no enlargement of solid phase crystals during charging or discharging as a class. Quite the opposite is true - during charge-discharge cycles, the metal hydride anode slowly but inevitably becomes more and more finely dispersed. At the beginning of the life cycle of a Ni-MH cell this is even good, but at the end it is very bad. Secondly, when Ni-MH (and Ni-Cd) are overdischarged, a side process becomes noticeable: the release of hydrogen from water. In theory, excess hydrogen should be destroyed using the so-called. "hydrogen cycle":

But the conversion of hydrogen back into water at the MH electrode H2+2OH(–)=2H2O+2e(–) usually occurs quite hard (significant overvoltage), which can be fraught.
By the way, to reduce the overvoltage of hydrogen gas, alloying additives are introduced into nickel (the one that forms the basis of the MH electrode) (see above). So Ni-MH discharges below the “correct” 0.9-1.0V are not only meaningless, but can also be harmful. 2.2.
About Li-ion: how to store and how to use it happily ever after? Have you ever tried to figure out why advanced users of Li-ion/Li-pol batteries are suddenly confident that the optimal charge level for “lithium” during storage is SoC (State of Charge) = 50%? As a result, in the most “serious” charge-discharge devices (CDDs) there is sometimes a special mode for transferring a Li-ion can or battery to the “storage” state, i.e. reduction to SoC ~50%. Because the client’s desire is the law for the hairdresser ©. But no matter how much you ask modellers, flashlight workers, electric transport workers, etc. “technical bloggers” of all stripes, where did this magical 50% come from - they are silent like fish on ice. Or they say: “this is common knowledge.” Or something like “my ZRU has this, which means it’s good and correct.” I have the only version regarding the origin of the belief “SoC 50% = rules”. Somewhat strange, but at the moment I don’t see any other options. 50% appeared like a “golden mean” between diametrically opposed points of view from two well-known and respected companies: Sony and Kadex.

2.2.1. Cadex's opinion

Here is another excerpt from the book “Batteries in a Portable World” by Isidor Buchmann (at that time - CEO of Cadex) with a sentence-by-sentence analysis [my comments in square brackets].

Like SLA (lead acid), Li-ion and Li-pol batteries must be stored in a charged state.
If a Li-ion battery is left in storage at a voltage below 2.5V for three months or more, a permanent loss of capacity occurs. [Where did this come from? Did Kadex conduct special research? If yes, then when, how, on what specific commercial samples. Where are the official results? Capacity loss: complete or partial? If partial, is it a few percent or tens of percent?]

In addition, corrosion of elements may occur.

[What is “corrosion”?
Or a crooked translation?]. Some Li-ion batteries do not allow recharging if the voltage at the cell terminals drops below a critical level.
[Which ones? Which ones are protected?]

This requirement is made for safety reasons, because the chemical structure of a deeply discharged cell changes and recharging can be dangerous.

[It’s possible that they were confused with overcharging: growth of lithium dendrides, damage to the separator, internal short circuit... No?]

The best results will be obtained when storing Li-ion batteries charged to their capacity from 70 to 90%.

[Drumroll. Kadex for “storage” recommends SoC ~70-90%. And 90% is an almost fully charged cell, because for any HIT the concepts of “fully charged” and “fully discharged” are very arbitrary.]

Some manufacturers may recommend lower storage capacities.

[If I understand correctly, “some” primarily means the Sony company.;)]

2.2.2.
Sony's opinion Let's talk about recommendations from Aunt Sonya. At the very beginning of the 2000s, Sony released a brochure that was widely distributed on the Internet: “Lithium Ion Rechargeable Batteries. Technical Handbook". It may also be called “Sony Lithium Ion Battery MSDS”. Here it is - TYTS. Among other things, it also addresses issues of charge loss (self-discharge) during storage of both single Li-ion cans and batteries made from them. It states that “ during long-term storage of batteries in a charged state for a long time, their degradation is possible to the point that the battery ceases to hold a charge after recharging

"
The probability of this is greater: - the higher the temperature; — the larger the SoC was before storage. It follows that: - temperature d.b.
as low as possible (within reason); — element d.b. in the most discharged state. The last point is reflected in three pictures, located in three different subsections:

Why are there similar pictures in 3 subsections?
The fact is that the brochure provides data on cells of three types, differing either in the anode material (+) or in the form factor. 1.US18650. Cylindrical 18650. The anode is made of so-called. "hard carbon" in Sony's terminology. In human translation, “hard carbon” is nothing more than coke obtained by coking coal. It was with “hard carbon” anodes that Sony introduced Li-ion batteries to the market in 1991. Then it turned out that it was more correct to use TC as the anode material (see below). The complete replacement of “hard carbon” with TU occurred somewhere in the early 2000s. 2.US18650GR. Cylindrical 18650. The anode is made of so-called. "graphite" in Sony's terminology. I think this is not a very good name, because... The main component of “hard carbon” is also graphite (>90%), although there are also some impurities (inorganic salts and some organics). And “graphite” is almost pure graphite, which with a 99.9% probability is nothing more than carbon black (carbon black). ru.wikipedia.org/wiki/Technical_carbon Essentially, technical carbon is soot, but not quite ordinary. Obtained artificially and under strictly controlled conditions. 3. UP383562 (Polumer). In terms of electrochemistry, they are identical to the US18650GR. The only difference is in the form factor: To begin with, in order to avoid misunderstandings: why do “fully discharged” cells (0%) instead of 2.7V or 3.0V (end-of-discharge voltage according to the methods outlined in the brochure) have an NRC of 3.2-3.3V? A common occurrence is depolarization after removal of the load. The phenomenon of depolarization was discussed in detail in the previous review. Now the main thing: the three graphs presented above illustrate the main thesis from Sony: for “better preservation” the element must be
in the most discharged state. Compare with the statement
from Kadex: the best results will be when storing Li-ion batteries charged to their capacity from 70 to 90%.
Who to believe?

&&&&&&&&&&&&&&&&&&&&&&& And a couple more funny quotes from Sony Lithium Ion Battery MSDS 1) The sixth section of Sony Lithium Ion Battery MSDS talks about batteries (assemblies) of lithium batteries. For those who don’t speak English very well, the point is as follows. If the batteries will not be used for a long period of time, they should be - discharged - removed from the equipment - stored in a dry, cool place. But, when stored for 1 year or more, they must be recharged at least once a year to avoid overdischarge (“overdischarge”), because The control board consumes electricity. 2) What do Sony engineers consider overdischarge? Let's go back to the page and read in plain English:

Overdischarge from Sonya’s point of view is 1 volt or lower, Karl! Not 2.5 volts and not one and a half!

&&&&&&&&&&&&&&&&&&&&&&&&

Now let's turn to more modern research.

2.2.3. What does modern science say?

Well, it’s a stretch to call it science. Rather, more or less systematic research with a practical orientation. At the same time, they are scientific in the technique of setting up full-scale experiments and in general approaches to solving problems. From what I have come across over the past few years, the publication of Germans from the University of Aachen seemed quite interesting: J. Schmalstieg, S. Kabitz, M. Ecker, DU Sauer From Accelerated Aging Tests to a Lifetime Prediction Model: Analyzing Lithium-Ion Batteries. Conference report: EVS27 International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium (Barcelona, ​​Spain, November 17 - 20, 2013).

Below is a summary, in the form of a digest. As far as I translated and understood all this correctly, I could be wrong.

WHAT AND HOW THE GERMANS DID 1) The influence of various factors on the intensity of Li-ion capacity loss during cycling was studied. 2) Storage and all operations with the cells were carried out at 50 degrees C, since artificial aging technology was used. A small number of measurements were made at 35 and 40 degrees Celsius, solely for the purpose of determining the constants in the Arrhenius equation (exponential dependence on temperature). 3) More than 60 Sanyo UR18650E “cans” were involved in the tests. The anode is standard (graphite), the cathode is not uncommon - Li(NiMnCo)O2 (NMC). If anything, the US18650GR and UP383562 mentioned above have the same anode, and the cathode is made of “classical” LiCoO2 (LCO). 4) At the same time, measurements were taken of the so-called. “internal resistance”, measured in one of the most unfortunate ways. Essence: I have already given a link to an article that compares various methods for estimating the mass of a spherical horse in a vacuum (electricians call this quantity “internal resistance of a chemical current source” and think that it is something of a certain value) in previous reviews - (lies in the cloud under No. 19): HG. Schweiger et al. Comparison of Several Methods for Determining the Internal Resistance of Lithium Ion Cells // Sensors, 2010. No. 10, pp. 5604-5625.

WHAT WAS RECEIVED BY THE GERMANS 5) Conclusion No. 1. About capacity loss during storage: the lower the cell’s charge level, the less the loss. Aunt Sonya turned out to be right.

Please note that with SoC (State of Charge) = 0% and a storage time of 500 days, the loss of capacity (the ability to accumulate electrical charge) is only 5-6%. And no one cares about the horrors of a possible overdischarge. Since the banks are “bare”, without any protection boards. During the same time, cells with SoC = 50% degrade 5 times faster:

Or, the same thing, in the most compact form (the smaller α, the lower the rate of degradation during storage): 6) Conclusion No. 2. The greater the cycling depth, the greater the relative loss of capacity (normalized to a depth of 100%). Although, this has been known for a long time. But the dependence of capacity losses on cycling depth can be linear or nonlinear. In this work, a linear relationship was recorded. 7) Conclusion No. 3. The funniest one. About SoC = 50%.;) But we are not talking about battery storage. But just the opposite: about the modes of their use. It is optimal for this to happen with maximally shallow discharges and everything spins around SoC = 50% (red curve): Moreover, shallow cycling at charge levels below 50% (20-30%, green curve) is preferable than the other way around (70-80 %, turquoise curve). The rest of the lies show that: - you shouldn’t get carried away with constantly recharging almost charged cells to 100%, those that are “at the beginning of the discharge curve” (SoC > 80%); — working with constantly heavily discharged batteries (SoC < 15-20%) is also not good.

3. Statement of the problem and preliminary research plan

An interesting point was made in the discussion of the previous review. For effective degradation of an electrochemical cell, it is not only (and not so much?) the depth of overdischarge that is important, but the total duration of the CIT’s stay in this state. The maximum duration of stay in the overdischarge state that was obtained for Ni-MH using MS3000 was 14 days. Perhaps this is not enough and it takes several months to detect the effect of interest. How much is unknown, but Kadex seems to subtly hint that about three: “If a Li-ion battery is left in storage at a voltage below 2.5V for a period of three months or more, an irrecoverable loss of its capacity occurs” (see above). It was decided to approach these 3 months. First slowly - 0.5 and 2 days in a state of deep overdischarge. Then in broad steps: 1, 2 and 3 months. Total: 5 cans. This is half of the 10 copies that I received when distributing this order. And this is the maximum that at that time I could afford to ditch to satisfy my own curiosity, because... the remaining batteries were used for practical purposes. Now it is clear that such a division into time intervals turned out to be not very successful. But I was guided by the issue from Kadex about 3 months of lying in a discharged state (see above). And in general, as they say in Odessa; “Oh, if only I were as smart BEFORE as my mother AFTER...”

4. What and how + preliminary tests (12-hour discharge)

The idea is simple - closing the HIT contacts for a fairly long period. Through a known resistance - a resistor of optimal value and power. The resistors were soldered to two-slot type 1 holders (see the beginning of the review): After which the total resistance of the slots was measured:

Before carrying out the main tests, it was decided to see what the discharge curves I = f (time) and U = f (time) look like. Fluke 287 acted as a recording recorder. And at the same time, check the calculations for the maximum current and whether the resistors can withstand such heat generation. Looking ahead, I’ll note that the resistor of the tested slot No. 3 was terribly hot for the first few hours. If they touched it with a finger, it burned. But after the end of the tests, its resistance did not change one iota. To begin with, the additional resistance provided by the alligator wires and the multimeter shunt was measured: An open circuit was made, Fluke was switched to current recording mode at 1-minute intervals. The total recording time is 12 hours exactly. Result:

The Sony-Murata US18650VTC6 used here received serial number 0 (due to preliminary tests). After 24 hours of rest of the battery in an over-discharged state: IR(@1kHz) = 13.6 mOhm, and the NRC increased 0.20V -> 2.38V (due to depolarization). Cycling was carried out with capacity measurement (GOST) according to the algorithm outlined in the next paragraph. Table 1: Nothing interesting yet. Let's move on.

5. Multi-day discharges

For multi-day discharges, new, never used Sony-Murata US18650VTC6 were used as test subjects. Before short-circuiting, their capacity was assessed by carrying out 3 charge-discharge cycles according to the scheme (GOST IEC 61960-2007): Charge according to the CC/CV algorithm: current 0.2C (600 mA) / 4.20V, cut-off - 100 mA Pause 1 hour Discharge with current 0.2C (600 mA) to 2.50V - capacitance measurement Pause 1 hour After the 3rd cycle - charge all the way to 0.2C, long pause and IR measurement (@1kHz). Table 2.

Then I stuffed all this beauty into short-circuited slots and time went by...

5.1. Sample No. 1 (2 days)

Sample No. 1 was removed after 2 days (48 hours). At the time of extraction, the NRC was 0.0158V.

After 24 hours of rest - 0.973V (depolarization) and IR(@1kHz) = 14.0 mOhm. It was necessary to put it on cycling to determine the capacitance characteristics, but a small (but completely solvable) problem arose: at such low NRC values, the battery is not defined as “lithium” » in all home chargers (SkyRC MC3000, Lii-500, Lii-100). Because foolproof protection works. For semi-automatic devices like Liitokal-Opus, everything that has an NRC less than 2V is Ni-MH/Ni-Cd and the maximum they charge to is 1.6V. When trying to force the battery type, the MC3000 gives a message like “voltage is incorrect.” In principle, a situation with a fairly strong overdischarge of HIT occurs regularly in real life. Theoretically savvy users know what to do in such cases: long and tedious multi-hour recharging with low currents. And preferably in impulses. I usually act simpler and more crudely: on the LBP in CV mode I set it to 4.2V (or a little less), the upper current limit is 0.1-0.2C and cling to the battery down conductors for 5-10-15 seconds. After this, check with your fingers for warming up and measure the NRC. If NRC > 2V, then this operation can not be repeated, but immediately put on charging. Familiar repairmen call this procedure “push the battery.” But this time the LBP was located somewhere under piles of stupid rubbish (everything acquired through back-breaking labor), because the apartment had been undergoing permanent cosmetic renovations for several months now. Therefore, armed with a soldering iron, in a couple of minutes I whipped up a simple uncontrollable “pusher” from two type 2 holders (see above).

A donor (normally charged battery) is inserted on one side, and an over-discharged acceptor* is inserted on the other. *Note. Ideally, it would be nice to add 2 or 3 more elements to the circuit: a switch, a potentiometer and sockets for ammeter probes. For obvious reasons, a switch is not required.

Experienced people put all this in a zinc bucket with sand and cover with a lid. I put my fingertips on the acceptor body. After 20-30 seconds I felt that the case became noticeably warm. Took it out of the slot. A quick measurement with a multimeter showed NRC ~ 3.5V. After half an hour, the battery cooled down to room temperature and went for cycling.

In addition to the initial ones, 4 more groups (pools) of cycling were carried out, 3 cycles per group. The “comparison standards” were two previously never used batteries, labeled “Z” and “ZZ”. It should be noted that in terms of capacitive characteristics, cells Z and ZZ turned out to be twin cells. Table 3: What we have as a result:

The straight lines in the pictures are trend lines (linear approximation). It can be seen that for Z and ZZ these lines practically coincide (twin cells ;)). The equations corresponding to the trend lines are also shown in the pictures. The coefficients in front of the “x” variable have practical meaning. They characterize the degree of cell instability to cycling. So, 7x in the first picture means that the average capacity loss is 7 mAh/cycle. And 20x is already 20 mAh/cycle. It follows that at a cycling depth of 100%, sample No. 1 (after a short circuit of 2 days) loses capacity 20/7 = 3 times faster than the “reference” Z and ZZ. The same thing happens with energy losses: 0.068/0.022=3 times. According to GOST IEC 61960-2007, a “lithium” battery must withstand at least 400 cycles according to the algorithm outlined above until the capacity is lost by 40% of the nominal. If these dependencies remained unchanged (which is unlikely for decent manufacturers and quite likely for the Chinese no-name type Liitokal), then the critical value (60% of the residual capacity relative to the nominal) would be reached: in the case of Z and ZZ after 257 cycles (including those that already were). And for sample No. 1 - already after 60. As will be shown below, the relatively rapid loss of capacity in the first 1-2 dozen cycles will then slow down significantly. Which is normal and expected for decent batteries. 5.2. Sample No. 2 (30 days)

Sample No. 2 was brought out of the short-circuit state after exactly 30 days (720 hours). At the time of extraction, the NRC was 0.61 mV.

Out of curiosity, I decided to observe how the process of cell depolarization proceeds. Due to the lack of automatic recording on the YR1035, this task is quite dreary and lengthy: a lot of manual work. It is clear that no one except me is mentally prepared to perform such feats “out of love for art.” The interesting thing about this event is getting the final result. And if the time dependence of the NRC is quite well predictable (the curve for the relaxation process with slight distortions), then how the formal parameter IR(@1kHz) behaves during the depolarization process is completely unpredictable. During the first hour: During the first day:

The uniqueness of this case is that IR(@1kHz) practically does not change. I am inclined to attribute fluctuations in the range of 15.9...16.2 mOhm to the instability of the YR1035 readings, rather than trying to explain them by the sluggish occurrence of some mysterious physical and chemical processes. At least there is no smell of relaxation here, unlike U=f(τ). For comparison, how does the IR(@1kHz) parameter for Ni-MH behave in a similar situation (from the previous review) after 6.5 days of discharge by pulses in the MS3000: Depolarization graphs IR(@1kHz)=f(τ) for overdischarged Ni-MH – relaxation type curves (under load - higher value, in equilibrium - lower). And this despite the fact that the discharge depths and (as a consequence) the deviation from equilibrium in the previous review are a couple of orders of magnitude less than in the case of a short circuit for 30 days.

And this is done like this: 1) with the camera turned on, after removing the load, the HIT is connected to the measuring system as quickly as possible and the stopwatch is turned on: 2) a video is shot for the first hour 3) then photos are taken at intervals of 1-2 hours 4) parameter values ​​from the photo and video are transferred into Excel tables 5) graphical dependencies are built and exported to a graph. editor

After recording the depolarization curves, 4 pools of cycling were performed, 3 cycles per group. Result:

After 30 days of short circuit, sharp and irreparable losses of cell capacity and energy reserve are observed.

Their magnitude can be estimated by comparing the free terms B in the equations y=Ax+B for the green and purple trend lines.
It is easy to calculate that these differences are ~330-340 mAh and 1.4 Wh.
Which is more than 10% of the nominal values. After each pool, there was a pause of 13-15 hours and the IR parameter (@1kHz) was measured, the value of which remained practically unchanged and amounted to 13.9-14.0 mOhm.

5.3. Sample No. 3 (57 days)

Initially, it was planned to end the torment of sample No. 3 on the 60th day and record daily depolarization graphs again. But on the 60th day it was Tuesday, and on weekdays I was at work from morning to night. In general, everything happened on Saturday, at the end of 57 days in the state of short circuit. The potential difference between the electrodes before removing the load was a record low of 0.31 mV

: Depolarization sample No. 3, first 60 minutes: Depolarization, first 24 hours:

Cell depolarization is the process of transition of DES (double electrical layers) on electrodes from a nonequilibrium (polarized) state to an equilibrium (non-polarized) state*. In the case of Li-ion, the IR(@1kHz) parameter does not actually change after disconnecting the load. Those. is insensitive to the depolarization process of heavily discharged batteries. *Note. As you know, achieving equilibrium is a process that extends infinitely over time.

And, for comparison: daily depolarization curves of samples No. 2 and No. 3 (after 30 and 57 days of short circuit): &&&&&&&&& Naturally, the sample had to be “pushed” to the NRC ~3 V. Moreover, this was only possible the second time. The first 20-second “revival”, despite the noticeable release of heat, gave only 2.5 V, which within 7-10 seconds. “went” below 2.0 V due to rapidly occurring depolarization. I had to repeat it. Then 12 charge-discharge cycles were made (according to GOST).

6. Additional long cycling

In conclusion, to complete the picture, it was decided to make a fairly long cycling of cells No. Z (standard) and No. 1, 2, 3 according to GOST. What samples 1-3 are is shown in the table. Table 4:

Let me also remind you that Nos. Z, 1, 2, 3 have already gone through 15 full charge-discharge cycles according to GOST and this is taken into account in the graphs below. This is what happened. Dynamics of capacity loss during cycling

The same thing, larger. Dynamics of energy loss during cycling. The same thing, larger. What are the dotted lines shown in the pictures? 60% - in accordance with GOST IEC 61960-2007 (I mentioned this in paragraph 5.1) 80% - decent, those included in the “Big Five” often consider a loss of capacity of no more than 20% of the nominal to be acceptable.

6. Bottom line

1. Deep overdischarges lasting 2-30 days of Sony-Murata US18650VTC6 batteries reduce their capacity. 2. A longer overdischarge (more than 30 days) no longer has a significant effect on the degradation of cans. Moreover, the value is 30 days. defined very conditionally, because in the interval 2...30 there are no experimental data. It is possible that the limit value is 20 days. or even 5 days. The study was exploratory in nature under conditions of complete uncertainty and was limited to 5 prototypes. So I'm sorry. 3. In the worst case (30 days or more), a one-time loss by new Sony-Murata US18650VTC6 cells is: - capacity ~ 500 mAh - energy reserve ~ 1.7 Wh 4. When writing reviews on Chinese-made products such as Liitokal, etc. . noname it is highly recommended to cycle the cans (at least 50 cycles to begin with, then depending on the circumstances) in order to determine the dynamics of capacity loss by the cells. In order not to lead the respected public into the temptation of buying Chinese ones, “the same capacity as branded ones” (at the first 1-2 measurements), “but 2 times cheaper.” If during cycling these Kals lose capacity N times faster, then the purchase is unlikely to be justified. Where N > 2.

Good luck.

Li-Polymer batteries

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

Remanufacturing Li-ion LiIon 18650 batteries using IMax B6.

To bring this type of battery back to life, we connect it to Imax and select the charging mode for 1 element, type LiIon, charge current 0.5A.

• If you receive a “Connection Error” message, the gas safety valve in the top cap of the element has most likely tripped. The reason for this is a violation of the charging-discharging mode, resulting in overheating and valve activation. To return it to its working position, you need to remove the paper (plastic) ring around the positive electrode of the 18650 battery and press it with a thin awl or a clock screwdriver through the technological holes on all sides. After that, move on to the next step.
• If the Imax B6 displays the message “Low power voltage”, you need to “push” the battery, to do this we switch to the nickel battery charging mode, and begin charging with a current of 0.1A until the voltage supplied to the battery rises to the minimum 3-3.1V. Then we again switch to the lithium-ion (LiIon) battery charging mode and charge as usual. Also, if the supplied voltage has increased to approximately 1.5V and is charging further in the range of approximately 1.3-1.6V and does not want to increase further, try starting the charging cycle in nickel mode one more time. Attention!!! If, when charging in NiMH mode, your 18650 starts to get very hot or has not reached more than 3 Volts for more than 30 minutes, immediately disconnect this battery and throw it in the trash.

How to replace a rechargeable 18650 battery

Another 18650 battery option.

Instead of one lithium battery, you can use 3 AA batteries. True, the quality of food will suffer somewhat, because... the voltage will not be maintained exactly. The voltage of disposable AA batteries is 1.5 V, while for rechargeable batteries it is 3.2-3.6 V.

Decoding the inscriptions on the battery

The photo below shows a standard 18650 battery.

The markings on the body mean the following:

1. The first letter I means that these are ion batteries.
2. The second letter of the designation is the type of battery (cobalt is shown in the photo - C).
3. The Latin letter “R” following it means that this is a battery.
4. The numbers 18 and 65 indicate the diameter and length of the battery in mm.
5. The last number “0” means the shape, in this case cylindrical.

The word "power", which sometimes appears in symbols, means power.

How to make a battery from 18650 batteries

To do this, connect the poles of the batteries. With the series connection method, each positive pole is connected to a negative one. With a parallel connection, it’s the other way around—the plus is connected to the minus.

Both methods are used depending on the goals and objectives pursued when creating the battery. In the first case, the connection is used when it is necessary for the entire assembly to be turned on at the right moment. In the second case, you can turn on the required number of batteries when required.

18650 battery specifications

Voltage

Depending on the different types and manufacturer, the nominal voltage of 18650 rechargeable batteries ranges from 3.6 to 4.3 V. For a finger-type battery, this figure is 1.5 V. Therefore, in order to replace the disposable batteries we ourselves use with rechargeable batteries 18650, you need to remember this.

How many amps are in a 18650 battery?

The current strength, measured in amperes (A), depends on the internal resistance of the connected device. The permissible current values ​​are indicated in the battery specifications.

These values ​​are 0.5-1 A, and they cannot be exceeded for accelerated charging, as they may overheat and even explode. Although these are high current devices, to be on the safe side, it is best to use them only where they were originally installed by the equipment manufacturer.

Battery capacity

This parameter is indicated on the battery case and is about 3200-3600 mAh. The capacity of a battery determines how long it will last until it is completely discharged.

Dimensions

The batteries are slightly larger than AA size disposable batteries. Their diameter is 18 mm. The length depends on the type of design (protected or unprotected). If there is a protection board, the length increases by 2-3 millimeters.

Color

These batteries come in different colors. The color of the case does not determine either its capacity or the manufacturer. You can buy batteries of any color.

Main advantages

The significant advantages of rechargeable batteries are saving money and long operation without recharging, small size and weight.

Application of 18650 batteries

18650 batteries are a common power source because they have many advantages over other power devices. They are used where it is necessary to maintain a charge for a long time at a small size. These are flashlights, players, laptops, electric scooters and other household appliances.

Battery braid

The battery housing is braided. This is shrink film. After using for a long time, chips, cracks, roughness appear on it and it becomes unusable. You can replace the braid yourself by purchasing special heat shrink. You must first carefully remove the battery from the old coating, insert it into a new film and seal it using a hairdryer or any other heat source.

How much do batteries cost?

High-quality batteries are not cheap, but this is exactly the case when it is better not to save. The cost of these devices will be recouped through repeated use.

The difference between 18650 and AA batteries

The main factors are capacity and reusability. The minimum voltage of 18650 batteries is 2 times that of AA batteries. Therefore, in case of replacement with 18650 AA batteries, you should calculate the resulting total value of this parameter and compare it with that indicated in the technical characteristics of the battery. After this, evaluate the possibility of exceeding or decreasing the voltage of the device in which batteries are used, paying attention to the permissible deviation values.

What does protected battery mean?

This means protection against too high a charge and, as a result, overheating or overdischarge, which leads to the unusability of the device. The presence of protection is indicated in the description of the device and using the corresponding inscription on the case. However, protected batteries are 2-3 mm longer, which should be taken into account when choosing.

18650 specifications table

The parameters of some types of batteries are shown in the table below.