18650 lithium ion battery classification
18650 lithium-ion battery processing must have a protection circuit to prevent the battery from being overcharged and over-discharged. Of course, this is a must for lithium-ion batteries. This is also a common drawback of lithium-ion batteries, because the materials used in lithium-ion batteries are basically lithium cobalt oxide materials, and lithium-ion batteries made of lithium cobalt oxide materials cannot provide high current. Discharge has poor safety. From the perspective of classification, the classification of 18650 lithium-ion batteries can be classified in the following way.
1. Classified according to the practical performance of the battery
Power battery and energy battery. Energy batteries are characterized by high energy density and are mainly used for high energy output; power batteries are characterized by high power density and are mainly used for batteries with instantaneous high power output and output. The power energy lithium-ion battery is accompanied by the emergence of plug-in hybrid vehicles. It requires the battery to store high energy, which can support pure electric driving for a certain distance, but also has good power characteristics, and enters the hybrid mode when the battery is low.
Simply understand, the energy type is similar to a marathon runner. To have endurance, it requires high capacity, and does not require high current discharge performance; then the power type is a sprinter, fighting for explosive power, but endurance is also necessary, otherwise the capacity is too large. You can't run far when you are young.
2. According to electrolyte material
Lithium ion batteries are divided into liquid lithium ion batteries (LIb) and polymer lithium ion batteries (PLb).
Liquid lithium-ion batteries use liquid electrolytes (currently power batteries are mostly of this type). Polymer lithium-ion batteries are replaced by solid polymer electrolytes, which can be dry or colloidal, and most of them currently use polymer gel electrolytes. Regarding solid-state batteries, in a strict sense it means that the electrodes and electrolyte are both solid.
3. Classified by product appearance
Divided into: cylinder, soft bag, square.
Cylindrical and square outer packagings are mostly steel shells or aluminum shells. The outer packaging of the soft pack is aluminum-plastic film. In fact, the soft pack is also a square shape. In the market, it is customary to call the aluminum-plastic film package as a soft pack, and some people call the soft pack battery a polymer battery.
Regarding cylindrical lithium-ion batteries, the model is generally 5 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 millimeters. For example, the 18650 lithium ion battery has a diameter of 18 mm and a height of 65 mm.
4. Classification by pole piece material
Cathode material: lithium iron phosphate battery (LFP), lithium cobalt oxide battery (LCO), lithium manganate battery (LMO), (binary battery: lithium nickel manganate/lithium nickel cobalt oxide), (ternary: Nickel cobalt manganate lithium ion battery (NCM), nickel cobalt aluminate lithium ion battery (NCA)).
Anode material: Lithium titanate battery (LTO), graphene battery, nano-carbon fiber battery.
Regarding the concept of graphene on the market, it mainly refers to graphene-based batteries, that is, graphene slurry is added to the pole piece, or a graphene coating is added to the diaphragm. Lithium nickelate and magnesium-based batteries basically do not exist in the market.
5. Charging and discharging of 18650 lithium ion battery
According to industry standards, the nominal capacity of lithium-ion batteries is generally the minimum capacity. This capacity is a batch of batteries, at a room temperature of 25 degrees, overflowing with cc/cv0.5c, and standing for a period of time. (Usually 12 hours). Discharge at a constant current of 0.2c to 3.0v (there is also a standard of 2.75V, but the effect is not big, and the drop from 3v to 2.75v will quickly reduce the capacity). The discharged capacity value, because a batch of batteries must have individual The difference is the capacity value of the battery with the lowest actual discharge capacity. In other words, the actual capacity of any battery in this batch should be greater than or equal to the nominal capacity.
1. The charging process of 18650 lithium ion battery
Some chargers are implemented using cheap methods, and the control accuracy is not good enough, which can easily cause abnormal battery charging and even damage the battery. When choosing a charger, try to choose a big brand of 18650 lithium-ion battery charger, quality and after-sales are guaranteed, and the service life of the battery is prolonged. The brand-guaranteed 18650 lithium-ion battery charger has four protections: short-circuit protection, over-current protection, over-voltage protection, battery reverse connection protection, etc. Overcharge protection: When the charger overcharges the lithium-ion battery, it is necessary to terminate the charging state in order to guard against the increase in internal pressure caused by the rise in temperature.
For this reason, the protection device needs to monitor the battery voltage, and when it reaches the battery overcharge voltage, it activates the overcharge protection function and stops charging. Over-discharge protection: In order to guard against the over-discharge status of the lithium-ion battery, when the voltage of the lithium-ion battery is lower than its over-discharge voltage test point, the over-discharge protection is activated, the discharge is stopped, and the battery is kept in a low quiescent current standby mode. Over-current and short-circuit protection: When the discharge current of the lithium-ion battery is too large or a short-circuit condition occurs, the protection device will activate the over-current protection function.
Li-ion 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 with a constant current. The second stage is the constant voltage charging stage. When the battery voltage reaches 4.2V, due to the characteristics of lithium-ion batteries, if the voltage is higher, it will be damaged. The charger will fix the voltage at 4.2V and the charging current will gradually decrease. When the current decreases to a certain value (generally 1/10 of the set current), the charging circuit is cut off, the charging completion indicator light is on, and the charging is completed.
Excessive charging and discharging of lithium-ion batteries can cause permanent damage to the positive and negative electrodes. Excessive discharge causes the negative carbon sheet structure to collapse, and the collapse will cause lithium ions to be unable to be inserted during the charging process; overcharging causes too much lithium ions to be inserted into the negative carbon structure, causing some of the lithium ions to be unable to be released anymore.
2. Charging principle of 18650 lithium ion battery
The working principle of a lithium-ion battery refers to its charging and discharging principle. When the battery is charged, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move to the negative electrode through the electrolyte. The carbon as the negative electrode has a layered structure. 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 are inserted, the higher the charging capacity.
In the same way, when the battery is discharged (that is, the process we use the battery), the lithium ions embedded in the carbon layer of the negative electrode are released and move back to the positive electrode. The more lithium ions returned to the positive electrode, the higher the discharge capacity. What we usually call 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, the lithium ion is in a state of movement from the positive electrode & rarr; negative electrode & rarr; positive electrode. If we compare the lithium ion battery to a rocking chair, the two ends of the rocking chair are the two poles of the battery, and the lithium ion is like an excellent athlete running back and forth on the two ends of the rocking chair. Therefore, the experts gave the lithium-ion battery a lovely name, rocking chair battery.
