18650 Li-ion batteries have become more and more popular lately. According to their technical characteristics, they are ahead of the well-known finger-type batteries. The concepts of “finger” and “little finger”, used for the well-known sizes of batteries, are incorrect from the point of view of correct terminology. All batteries, regardless of size, have their own codes indicating their size. So, 18650 is also a code. That's the whole secret.
Battery size 18650
This five-digit code expresses the width and length of the battery, where the first two digits are the width (diameter) in mm, and the last three are the length in mm with tenths. There is an erroneous opinion that the zero at the end of this code indicates the cylindrical shape of the battery (there are batteries of different shapes). Such an exact designation of the length of the battery is not necessary. When specifying its size, it is often limited to the first four digits (1865). By the way, finger and little finger batteries also have their own code - 14500 and 10440. In addition to the digital code,size can also be indicated by letters. For example, the above two battery sizes have alternative letter codes - AA (finger) and AAA (little finger). There are many alphabetic and numerical codes indicating the size of various batteries: CR123 (16340), A (17500), Fat A (18500), 4/3 A (17670), etc.
For 18650 batteries, this size designation is inaccurate. Other parameters must also be taken into account. The size of an 18650 battery can be affected, for example, by the presence of a built-in special board (charge controller). Some batteries may have a slightly longer length in this case. It is not uncommon for a battery to simply not fit into the compartment of the device where they want to use it, despite the fact that this device (for example, an electronic cigarette battery pack) is designed to work with this type of battery.
Li-ion 18650 battery life
The amount of time a given battery can last depends on the concept of "milliamps per hour" (mAh). For large batteries, such as automobiles, the term "amps per hour" is used. For a 18650 mAh battery, this is a derived value. One ampere is equal to 1000 milliamps. A milliamp per hour is the current that a battery can produce during a conventional hour of use. In other words, if you divide this value by a certain number of hours, you can find out the battery life. For example, the battery has a capacity of 3000 mAh. This means that for two hourswork, it will give out 1500 milliamps. Four - 750. The battery from the above example will be completely discharged after 10 hours of operation, when its capacity reaches 300 milliamps (deep discharge limit).
These calculations give only a rough idea of the battery life. Its real operating time depends on what load it has to deal with, that is, on the device that it must provide power.
Current, voltage and power
Before dwelling on the general description of the technical characteristics of 18650 lithium-ion batteries and precautions in working with them, we will briefly define the above concepts. The current (maximum discharge current, current output) is expressed in amperes and is marked on the battery with the letter "A". Voltage is expressed in volts and is denoted by the letter "V". On many batteries you can find such designations. For a lithium-ion battery, the voltage is always 3.7 volts, and the current can be different. Battery power as the dominant parameter of its strength is expressed as the product of voltage and current (volts must be multiplied by amperes).
Description of the pros and cons of a lithium-ion battery
The main disadvantage of 18650 Li-Ion batteries is that they have a small operating temperature range. Normal operation of a lithium-ion battery is possible only in the range from -20 to +20 degrees Celsius. If it is used or charged at temperatures below or abovemarked, it spoils it. For comparison, nickel-cadmium and nickel-metal hydride batteries have a wider temperature range - from -40 to +40. But, unlike the latter, lithium-ion batteries have a higher nominal voltage - 3.7 volts versus 1.2 volts for nickel batteries.
Also, lithium-ion batteries are practically not affected by self-discharge and memory effects common among many types of batteries. Self-discharge is the loss of charged energy when idle. The memory effect occurs in some types of batteries as a result of systematic charging after incomplete discharge. That is, it develops on batteries that are not completely discharged.
With the memory effect, the battery “remembers” the degree of discharge after which it is started to be charged, and is discharged, having reached this limit in the next cycle. Its true capacity at that time is actually greater. If there is a board that displays the battery level, then it will also show the discharge. This effect does not develop immediately, but gradually. It can also develop in conditions where the battery is constantly working from the mains, that is, it is continuously charging.
Self-discharge and memory effect are extremely low in lithium-ion batteries.
There is one more thing to pay attention to: such batteries cannot be stored in a discharged state, otherwise they will quickly fail.
Li-ion battery precautions
Many types of batteries are flammable andexplosions. It depends on the chemical composition of the internal structure of the battery. For 18650 lithium-ion batteries, this problem is quite acute. It is not uncommon for e-cigarette users to suffer serious burns on their hands and face, or even more serious injuries. Since lithium-ion batteries are found in laptops, tablets and cell phones, it is not uncommon for them to ignite.
In the first place among the causes of such incidents is, of course, low-quality (cheap) battery assembly. However, in the case of electronic cigarettes, it is easy to provoke a lithium-ion battery explosion on your own, even if the battery is not cheap. To do this, you need to understand a little about what electrical resistance is.
If we explain this concept in the simplest language, then this is a parameter that determines the requirements of the conductor to the battery. The lower the resistance of the conductor, the more current (amperes) the battery must give. If the resistance is very low, then the battery will work with such a conductor to a large load. The resistance can be so low that it will provoke an exorbitant load on the battery and its subsequent explosion or ignition. In other words, it will be a short circuit. Since electronic cigarettes work on the principle of evaporation, which requires a heating element (filament coil), inept users may mistakenly force the battery to work with a heating element withextremely low resistance. Knowing the current output of a particular battery and the resistance of the conductor, using simple calculations using the Ohm's law formula, you can determine whether this battery can handle a particular conductor.
These hazards do not always occur in all cases. Battery protection technologies are constantly evolving. Many batteries have a special charge controller inside that can de-energize the battery in time when a short circuit occurs. These are protected batteries.
Li-ion battery device
The 18650 battery is based on an electrolyte, a special liquid in which chemical reactions take place.
These chemical reactions are reversible. This is the principle of operation of any battery. In simple terms, the formula for such reactions can proceed both from left to right (discharge) and from right to left (charge). Such reactions occur between the cathode and anode of the cell. The cathode is the negative electrode (minus), the anode is the positive electrode (plus) of the power source. During the reaction, an electric current is formed between them. The chemical reactions of discharge and charge between cathode and anode are oxidation and reduction processes, but that's another story. We will not delve into the process of electrolysis. The current is formed at the moment when the cathode and anode begin to interact, that is, something is connected to the plus and minus of the battery. The cathode and anode must be electrically conductive.
During breach of conditionsDuring operation, molecules of chemical elements appear in the electrolyte, which close the cathode and anode, which leads to internal short circuits. As a result of this, the temperature of the battery increases and more molecules appear, closing the plus and minus. This whole process, like a snowball, acquires speed exponentially. Without the possibility of taking the electrolyte out (the battery case is sealed), thermal expansion occurs, which increases the internal pressure. What happens next can be understood without comment.
Charging the lithium-ion battery
As a charger for a 18650 battery, any device designed for batteries of this format is suitable. The main thing is not to change the correct polarity when charging. Place the batteries in the charger slots exactly according to the plus and minus signs. It's a good idea to read the other precautions for using the 18650 battery charger, which are always listed on the battery case.
The best option for charging lithium-ion batteries is to use more expensive chargers with fine-tuned charging process. Many of them have the function of charging batteries using the CC / CV method, which stands for constant current, constant voltage. This method is good because it can charge the battery more than conventional chargers. This is due to such a concept as overcharging.
During charging or discharging the battery, its voltageis changing. Increases when charging, decreases when discharging. Rated 3.7 volts is an average value.
There are two effects that detrimentally affect the battery - overcharging and overdischarging. There are thresholds for charging and discharging the battery. If the battery voltage goes beyond these limits, then the battery gets overcharged or overdischarged, depending on whether it is charging or discharging. In the normal charging mode for 18650 Li-ion, the charger and charge controller inside the battery itself (if any) read the voltage of the battery and cut off the charge when it reaches the threshold to avoid overcharging. In this case, the battery is not actually fully charged. Its capacity may allow it to charge more, but the threshold prevents it from doing so.
The principle of charging by the CC / CV method is designed so that the current supplied to the charge is not cut off, but is sharply reduced, preventing the internal voltage of the battery from going beyond the threshold value. Thus, the battery is fully charged without being recharged.
Types of lithium-ion batteries
Types of 18650 Li-ion batteries:
- lithium iron phosphate (LFP);
- lithium-manganese (IMR);
- lithium-cob alt (ICR);
- lithium polymer (LiPo).
All types except the last one are cylindrical and can be made in 18650 format. Lithium polymer batteries differ in that they do not have a specific shape. This is due to the fact that they have a solidelectrolyte (polymer). It is due to this unusual property of the electrolyte that these batteries are often used in tablets and cell phones.
Application of lithium-ion batteries
As already mentioned, 18650 size Li-ion batteries are widely used in electronic cigarettes. They can be built into the battery pack or removable, i.e. installed separately in it. There may also be several, connected in parallel or in series.
Lithium-ion batteries have long been used in the construction of various batteries, such as laptop batteries. Such batteries are a chain of several interconnected 18650 batteries inside a single case. Such batteries can also be found as capacious power banks - portable chargers.
The scope of the batteries themselves is very wide: from the named chargers to the constituent elements of modern large mechanisms (automobile or aviation). At the same time, the number of 18650 lithium-ion batteries that make up a single battery can vary from a few to hundreds. It is worth mentioning the lithium-polymer batteries. Although they are not available in 18650 Li-ion format, they are the most common, as they are used in tablets and cell phones.
