18650 lithium-ion batteries have recently become increasingly popular. According to their technical characteristics, they are ahead of the well-known finger batteries. The concepts “finger-type” and “little finger” used for 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
In this five-digit code, the width and length of the battery are expressed, 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 (batteries of various shapes exist). Such an accurate indication 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 pinky batteries also have their own code - 14500 and 10440. In addition to the digital code, the size can also be indicated by letters. For example, the two above-mentioned battery sizes have alternative letter codes - AA (finger-type) and AAA (pinky). There are many alphanumeric codes that indicate the sizes 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 need to be considered. The size of the 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. There are often cases when the battery simply does not fit in the compartment of the device where they want to use it, despite the fact that this device (for example, the battery pack of an electronic cigarette) is focused on working with batteries of this type.
Duration of use of 18650 lithium-ion battery
The time that this battery can work depends on a concept such as milliamps per hour (mAh). For large batteries, such as automobiles, the term "amperes per hour" is used. For a 18650 mAh battery, this is a derivative. One ampere is 1000 milliamps. Milliampere per hour is the current that the battery can produce during a conditional hour of use. In other words, if you divide this value by a certain number of hours, you can find out the operating time of the battery. For example, a battery has a capacity of 3000 mAh. This means that for two hours of operation, it will give out 1,500 milliamps. For four - 750. The battery from the above example will be completely discharged after 10 hours of operation, when its capacity reaches 300 milliamps (the limit of deep discharge).
Such calculations give only an approximate idea of the battery life. His real time of work depends on what kind of load he has to deal with, that is, on the device that he needs to provide power.
Current, voltage and power
Before dwelling on a general description of the technical characteristics of 18650 lithium-ion batteries and the precautions for working with them, we briefly define the above concepts. The current (maximum discharge current, current output) is expressed in amperes and marked on the battery with the letter “A”. Voltage is expressed in volts and is indicated 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 the 18650 size lithium-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 lower or higher than indicated, 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 rated voltage - 3.7 volts versus 1.2 volts for nickel batteries.
Also, lithium-ion batteries are practically not affected by the effects of self-discharge and memory, 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 fully landed.
With the memory effect, the battery “remembers” that degree of discharge, after which it begins to charge, and discharges, reaching this limit in the next cycle. Its true capacity at that time is actually more. If there is a board that displays the battery level, then it will also show a discharge. This effect does not develop immediately, but gradually. It can also develop in conditions when the battery is constantly working on the electric network, that is, it is continuously charging.
Self-discharge and the memory effect are manifested very little in lithium-ion batteries.
There is another point to which you should pay attention: such batteries can not be stored in a discharged state, otherwise they quickly fail.
Li-ion Battery Precautions
Many types of batteries are subject to fire and explosion. It depends on the chemical component of the internal device of the battery. For lithium-ion batteries size 18650, this problem is quite acute. There are frequent cases where users of electronic cigarettes receive serious burns on their hands and face, and even more serious injuries. Since lithium-ion batteries are present in laptops, tablets and cell phones, cases of ignition are not uncommon.
In the first place among the causes of such incidents is, of course, poor-quality (cheap) battery assembly. However, in the case of electronic cigarettes, a lithium-ion battery explosion can easily be provoked independently, even if the battery is not cheap. To do this, a little understanding of what electrical resistance is.
If we explain this concept in the most simple 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 under heavy 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 can not do without a heating element (incandescent spiral), inept users can mistakenly make the battery work with a heating element with an extremely low resistance. Knowing the current output of a specific battery and the resistance of a conductor, using simple calculations using the formula of Ohm's law, you can determine whether a given battery can cope with a specific conductor.
These dangerous phenomena do not always occur and not in all cases. Battery protection technology is constantly being improved. Many batteries have a special charge controller inside, which can de-energize the battery in time when a short circuit occurs. These are protected batteries.
Lithium ion battery device
The 18650 battery is based on an electrolyte, a special fluid in which chemical reactions occur.
These chemical reactions are reversible. The principle of operation of any battery is based on this. In simple terms, the formula for such reactions can proceed from left to right (discharge), and from right to left (charge). Such reactions occur between the cathode and the anode of the element. The cathode is the negative electrode (minus), the anode is the positive electrode (plus) of the power source. Between them at the moment of reaction an electric current is formed. The chemical reactions of discharge and charge between the cathode and anode are processes of oxidation and reduction, but this is a completely different story. We will not go deep into the electrolysis process. Current is generated 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 the violation of operating conditions, 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. The whole process, like a snowball, acquires speed exponentially. Without the possibility of electrolyte out (the battery case is sealed), thermal expansion occurs , increasing internal pressure. What happens next can be understood without comment.
Charging a Li-ion Battery
As a charge for the 18650 battery, any device designed for batteries of this format is suitable. The main thing is not to change the correct polarity when charging. The batteries must be located in the slots of the charger in accordance with the plus and minus signs. It will not be superfluous to familiarize yourself with other precautions when using charging for the 18650 battery, which are always indicated on its case.
The best option for charging lithium-ion batteries is to use more expensive chargers with fine-tuning the charging process. Many of them have the function of charging the batteries according to the CC / CV method, which stands for direct current, constant voltage. This method is good in that it can charge the battery more than conventional chargers do. This is due to such understandable as recharge.
When charging or discharging a battery, its voltage changes. When charging increases, when discharging decreases. Nominal 3.7 volts is an average value.
There are two effects that adversely affect the battery - overcharge and overdischarge. There are thresholds for charging and discharging the battery. If the voltage of the battery 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 the 18650 Li-ion, the charger and the charge controller inside the battery (if any) read the battery voltage and cut off the charge when the threshold is reached to avoid overcharging. However, the battery does not actually fully charge. Its capacity may allow it to charge more, but the threshold value does not allow it to be done.
The CC / CV charging principle is designed so that the current supplied to the charge does not cut off, but decreases sharply, preventing the internal voltage of the battery from exceeding the threshold value. Thus, the battery is fully charged without getting a recharge.
Types of Li-ion batteries
Types of 18650 Li-ion batteries:
- lithium iron phosphate (LFP);
- lithium manganese (IMR);
- lithium cobalt (ICR);
- lithium polymer (LiPo).
All types, except the last, are cylindrical in shape and can be made in the 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 solid electrolyte (polymer). It is due to this unusual property of electrolyte that these batteries are often used in tablets and cell phones.
The use of lithium-ion batteries
As already mentioned, lithium-ion batteries size 18650 are widely used in electronic cigarettes. They can be built-in to the battery pack or removable, i.e. installed separately. They can also be several, connected in parallel or in series.
Lithium-ion batteries have long been used in the design of various batteries, such as laptop batteries. Such batteries are a chain of several interconnected 18650 batteries inside a single housing. 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). Moreover, the number of 18650 lithium-ion batteries that make up a single battery can vary from a few to hundreds. It is worth mentioning about 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.