Knowledge of 18650 lithium battery was widely spread

In more than three hundred years ago, Benjamin Franklin began to catch lightning, opens the people understanding of lightning, also opens the people understanding of electricity, since that time, there are a lot of people also think about how to capture the electricity in storage, so such thing as a battery is produced gradually, indeed, as a very important in the history of the invention, the battery really solved a lot of problems, greatly improve the efficiency of various kinds of life, and the emergence of lithium batteries more makes people understanding of electricity is becoming more and deeper, 18650 lithium-ion battery is to use the longest time, and now there is still a kind of lithium battery, In many places to be able to see the shadow of 18650 lithium batteries, because the battery compared to other battery, advantage is very obvious, and the safety was relatively well, too, even has been used in the large equipment, this article is to introduce the knowledge of 18650 batteries, introduce why there will be a blast.

18650 lithium batteries

I. advantages of 18650 lithium battery

Generally, the no-load voltage of lithium battery is considered to be used up when it is below 3.0v (the specific value depends on the threshold value of the battery protection board, such as low as 2.8v or 3.2v). Most lithium batteries cannot discharge the no-load voltage below 3.2v, or excessive discharge will damage the battery (generally, lithium batteries in the market are basically used with a protective plate, so excessive discharge will lead to the protection plate cannot detect the battery, thus unable to charge the battery).

4.2 V is the highest limit of the battery voltage, it is generally believed to the no-load voltage of lithium-ion batteries charged to 4.2 V is considered the electricity, the battery charging process, the battery voltage rises gradually in 3.7 V to 4.2 V, lithium batteries cannot be no-load voltage to over 4.2 V, otherwise will damage the battery, this is the place where special lithium-ion batteries, generally speaking, 18650 lithium-ion battery has the following advantages.

1. Wide range of use

Notebook computer, walkie-talkie, portable DVD, instruments and meters, audio equipment, model aircraft, toys, cameras, digital cameras, and other electronic equipment.

2, series

The 18650 lithium battery pack can be combined in series or in parallel.

3. Low internal resistance

The internal resistance of the polymer batteries is less than liquid batteries, domestic the internal resistance of the polymer batteries can even do below 35 m Ω, greatly reduced the battery power consumption, extend the standby time of the mobile phone, can reach with the international level. This kind of polymer lithium battery which supports large discharge current is the ideal choice of remote control model and becomes the most promising alternative to NiMH battery.

4. No memory effect

It is not necessary to empty the remaining power before charging, which is convenient to use.

5. High voltage

The voltage of 18650 lithium battery is generally 3.6v, 3.8v and 4.2v, which is much higher than the 1.2v voltage of NiCd and NiMH batteries.

6. High safety performance

High safety performance, no explosion, no combustion; Non-toxic, pollution-free, RoHS trademark certification; Various safety performance in one go, cycle times more than 500 times; High-temperature performance, 65 degrees under the conditions of the discharge efficiency of 100%. To prevent short circuit, the positive and negative electrodes of the 18650 lithium battery are separated. So the possibility of a short circuit has been minimized. Protective plates can be added to avoid over-charging and over-discharge of the battery, which can also extend the service life of the battery.

7. Long service life

The service life of 18650 lithium battery is very long, the cycle life of normal use can reach more than 500 times, which is more than twice the ordinary battery.

8. Large capacity

The capacity of 18650 lithium battery is generally between 1200mah~3600mah, while the general battery capacity is only about 800. If you combine 18650 lithium battery into 18650 lithium battery pack, then 18650 lithium battery pack can easily break through 5000mah.

Ii. Comparison between 18650 lithium battery and polymer battery

The so-called polymer lithium battery refers to the use of polymer as an electrolyte lithium ion battery, specifically divided into "semi-polymer" and "full polymer" two kinds. "Semi-polymer" refers to a layer of polymer (usually PVDF) on the barrier film to make the cell more cohesive, the battery can be made harder, and the electrolyte remains a liquid electrolyte. The term "whole polymer" refers to the use of polymers to form a network of gels inside the cell and then to inject an electrolyte to form an electrolyte. Although "all-polymer" batteries still use liquid electrolytes, they use far less of them, which greatly improves the safety of lithium-ion batteries. As far as I know, only SONY produces "all-polymer" lithium-ion batteries in mass production.

On the other hand, polymer battery refers to the use of aluminum plastic packaging film as the outer package of the lithium-ion battery, also known as the soft pack battery. The packaging film consists of three layers, namely the PP layer, Al layer, and nylon layer. Since PP and nylon are polymers, this kind of cell is called a polymer battery.

1. Lower price

The international price of 18650 is about 1USD/ PCS, which is about 3RMB/Ah in terms of 2Ah. And the price of polymer lithium battery, low-end copycat factory in 4RMB/Ah, 5~7RMB/Ah in the middle, in the high end of more than 7RMB/Ah. Like ATL and Lishen, they can generally be sold at about 10RMB/Ah, and you are too small to accept.

2. Can not be customized

SONY has always wanted to make lithium-ion batteries like alkaline batteries, with certain industrial standards, like no. 5 batteries, no. 7 batteries, basically the same all over the world. However, one of the advantages of lithium-ion battery is that it can be designed according to the needs of customers, so there is no uniform standard. So far, there is only one standard model of 18650 in the lithium-ion battery industry, and the rest are designed according to the needs of customers.

3. Poor security

We know that lithium-ion batteries in extreme circumstances (such as overcharge, high temperature, etc.), the internal will occur violent chemical reaction, produce a lot of gas. The 18650 battery USES a metal shell with a certain strength. When the internal pressure reaches a certain level, the steel shell will burst and explode, causing a terrible safety accident.

That's why rooms that test 18650 batteries generally have to be protected with layers of protection, and no one should ever enter the room during the test. Polymer batteries do not have this problem, even in the same extreme case, because the packaging film strength is low, as long as the pressure is slightly higher will be broken, will not produce an explosion, the worst case is combustion. So polymer batteries are better than 18650 batteries in terms of safety.

4. Low energy density

In general, the capacity of 18650 battery can be about 2200mAh, so the energy density is about 500Wh/L, while the mass production of polymer battery can be close to 600Wh/L.

But polymer batteries have their drawbacks. The main reason is that the cost is relatively high. Since we can design according to customers' requirements, the research and development cost should be included. And the appearance is changeful, variety is various, bring about in manufacturing process all sorts of jig are not standard part, also increased cost accordingly. Polymer battery itself is poor in versatility, which is also brought by the flexible design, often in order to be so, 1mm difference needs to be redesigned for the customer.

Iii. Application of 18650 lithium battery

The application of lithium secondary battery in the energy battery industry benefits from its superior performance. With the development of lithium secondary battery technology, it has been widely used in our daily life. Rechargeable batteries that have been used many times are increasingly popular with consumers. Pay attention to the energy battery industry, fully understand the battery so that we can do "for our own use", the current 18650 lithium battery in the following areas have some applications.

1. Energy storage

It is mainly used in base station power supply, clean energy storage, power grid power storage, household light storage system, etc.

2. Power class

Mainly refers to electric vehicles, electric bicycles, new energy vehicles.

3. Digital

Mobile phone, tablet, laptop, electric toy, MP3/MP4, earphone, charger, model airplane, mobile power supply, etc.

Iv. Classification of 18650 lithium batteries

The production of 18650 lithium battery requires a protective circuit to prevent the battery from being over-charged and over-discharged. , of course, this is a must for lithium battery, this also is the a general disadvantages of lithium battery, because the materials used are basic cobalt acid lithium batteries, lithium materials, and cobalt acid lithium materials of lithium battery can't large current discharge, poor security, from the classification, the classification of 18650 lithium batteries can be classified in the following ways.

1. Classification according to the practical performance of the battery

Power type battery and energy type battery. Energy type batteries are characterized by high energy density and are mainly used for high energy output. Power type batteries are characterized by high power density and are mainly used for instantaneous high power output and output batteries. And power and energy lithium batteries came with the advent of plug-in hybrids. It requires the battery to store a high amount of energy, be capable of driving pure electric for a certain distance, and have good power characteristics to enter hybrid mode when the power is low.

Simply understand, energy type is similar to marathon runners, to have endurance, is the requirement of high capacity, high current discharge performance requirements are not high; So power type is a sprinter, spell is to break out force, but endurance also should have, otherwise the capacity is too small to run not far.

2, according to the electrolyte material points

Lithium-ion batteries are divided into liquid lithium ion batteries (LIB) and polymer lithium-ion batteries (PLB).

Liquid lithium-ion batteries use liquid electrolytes (most of the current power batteries). Polymer lithium-ion batteries are replaced by solid polymer electrolytes, which can be "dry" or "colloidal," and most currently use polymer gel electrolytes. In the case of solid-state batteries, strictly speaking, the electrodes and electrolytes are both solid.

3. Classification by-product appearance

Divided into: cylinder, soft package, square.

Cylindrical and square outer packing for steel or aluminum shell. Soft packaging for aluminum plastic film, in fact, soft packaging is also a kind of square, the habit of the market will be aluminum plastic film packaging called soft packaging, also some people will be called soft packaging battery polymer battery.

For cylindrical lithium-ion batteries, the figure is typically five digits. The first two digits are the diameter of the battery, and the middle two digits are the height of the battery. The unit is millimeter. For example, the 18650 lithium battery has a diameter of 18 mm and a height of 65 mm.

4. Classification by pole material

Anode materials: lithium iron phosphate battery (LFP), lithium cobalt oxide battery (LCO), lithium manganese acid battery (LMO), (binary battery: lithium nickel manganese acid/lithium nickel cobalt acid), (ternary: lithium nickel cobalt manganese acid battery (NCM), lithium nickel cobalt aluminate battery (NCA)).

Anode materials: lithium titanate battery (LTO), graphene battery, carbon nanofiber battery.

The concept of graphene on the market mainly refers to graphene-based batteries, in which graphene slurry is added to the pole sheet or graphene coating is added to the diaphragm. Lithium nickelate, magnesium-based battery market is basically non-existent.

V. charge and discharge of 18650 lithium battery

According to industrial standards, the nominal capacity of lithium battery is the minimum capacity. This capacity is the capacity of a batch of batteries, which is filled with cc/cv0.5c at room temperature of 25 degrees Celsius and left for a period of time (usually 12 hours). Discharge from 0.2c constant-current current to 3.0v (there is also a standard of 2.75v, but the effect is not big, 3v to 2.75v drop very fast without much capacity), the released capacity value, because a batch of batteries must have individual differences, the actual output capacity value of the lowest battery. In other words, the actual capacity of any battery in this batch should be greater than or equal to the nominal capacity.

1. Charging process of 18650 lithium battery

Some chargers use cheap solutions to achieve, in the control accuracy is not good enough, easy to cause abnormal battery charging, or even damage the battery. When choosing a charger, try to choose a big brand of 18650 lithium ion battery charger, the quality, and after-sales guarantee, to extend the service life of the battery. The 18650 lithium-ion battery charger guaranteed by the brand has four protection functions: short circuit protection, over current protection, over voltage protection and battery reverse connection protection. Overcharge protection: when the charger overcharges the lithium-ion battery, the charging state shall be terminated to prevent the rise of internal pressure caused by temperature rise.

To this end, the protection device needs to monitor the battery voltage, and when it reaches the battery overcharge voltage, it will activate the overcharge protection function and stop charging. Over discharge protection: in order to prevent the over-discharge state of lithium ion battery, when the voltage of lithium-ion battery is lower than the detection point of its over-discharge voltage, the over discharge protection will be activated and the discharge will be stopped, and the battery will be kept in the standby mode of low static current. Over current and short circuit protection: when the discharge current of the lithium-ion battery is too large or short circuit occurs, the protective device will activate the overcurrent protection function.

The lithium battery charging control is divided into two stages. The first stage is constant current charging. When the battery voltage is lower than 4.2v, the charger will charge at a constant current. The second stage is the constant voltage charging stage, when the battery voltage is 4.2 V, due to the lithium battery characteristics, if the voltage is high, will damage, the charger voltage will be fixed in 4.2 V, the charging current will be reduced gradually, when the current decreases to a certain value (usually 1/10 set current), to cut off the charging circuit, a complete charging indicator, charging is complete.

Excessive charge and discharge of lithium-ion battery will cause permanent damage to the positive and negative electrodes. The excessive discharge will lead to the collapse of the structure of the negative carbon sheet layer, which will cause the lithium ions cannot be inserted in the charging process. Overcharging causes too many lithium ions to embed themselves in the negative carbon structure, so that some of them can no longer be released.

2. Charging principle of 18650 lithium battery

The working principle of lithium ion battery is its charge and discharge principle. When the battery is charged, lithium ions are formed on the positive electrode of the battery, and the lithium ions generated move to the negative electrode through the electrolyte. As the carbon of the negative electrode is layered, it has many micropores. The lithium ions that reach the negative electrode are embedded in the micropores of the carbon layer. The more lithium ions embedded, the higher the charging capacity.

Similarly, when a battery is discharged (the process by which we use the battery), lithium ions embedded in the negative carbon layer escape and move back to the positive electrode. The more lithium ions that return to the positive electrode, the higher the discharge capacity. We usually say the battery capacity refers to the discharge capacity.

It is not difficult to see that during the charging and discharging process of the lithium-ion battery, lithium ion is in the motion state from the positive pole to the negative pole to positive pole. If we think of the lithium-ion battery as a rocking chair, the two ends of the rocking chair are the two poles of the battery, and the lithium ion is like a good athlete, running back and forth between the two ends of the rocking chair. So, the experts gave the lithium-ion battery a cute name: the rocking chair battery.

6. Why did 18650 lithium battery have an explosion history

The majority of 18650 batteries are encapsulated in a steel shell. The battery with poor quality has no protective function. Under the condition of overcharge (overcharge), the internal pressure will increase sharply, and it will explode when the bearing value is exceeded. Short circuit, high temperature or the battery is squeezed deformation and even puncture problems can cause the battery explosion.

After 30 years of development, the preparation process of the 18650 battery has become very mature. In addition to greatly improving its performance, its safety is also very perfect. To avoid an explosion in a sealed metal case, the 18650 battery is now topped with a safety valve, the standard accessory for each 18650 battery and the most important barrier.

When the internal pressure of the battery is too high, the top safety valve will open the exhaust pressure relief to avoid explosion. However, when the safety valve is opened, chemicals leaked from inside the battery can react with oxygen in the air at high temperatures and still cause a fire. In addition, now part of the 18650 battery also comes with a protective plate, with over charge and discharge and short circuit protection and other functions, safety performance is very high.

The previous explosion of mobile power supply was all caused by the unqualified and inferior 18650 batteries used by unscrupulous manufacturers to save costs, or even the second-hand waste electricity. At present, the 18650 battery produced by major battery manufacturers such as Panasonic, SONY, Samsung and so on is actually very safe, and the 18650 battery usage rate is very high, we can do the correct use in daily use and avoid short circuit, damage or high temperature of the battery, do not have to worry about the battery will explode. We cannot knock over a boatload of people with one bamboo pole and judge the safety of 18650 by some inferior products.

Summary: in fact for lithium battery, will be caused the explosion is understandable, after all in the past, for the understanding of this kind of stability will be less severe, but 18650 as a comparative performance very high lithium battery, its application will certainly be more and more widely, so far, after all this indispensable to battery, 18650 lithium-ion battery is one of the best choice.

The page contains the contents of the machine translation.