Here is a 18650 lithium battery produced by a famous lithium battery manufacturer in China. The purpose is only to let beginners understand the charging and discharging characteristics of lithium batteries.
0.2c, 0.5c, and 1c mean 0.2 times, 0.5 times, 1 times the battery capacity (0.2c, 0.5c, 1c of a 1000mAh battery are 200mA, 500mA, 1000mA respectively)
1.2 Charging method
The meaning of cc/cv is constant current first, then constant voltage. The current of constant current is determined by the following parameters. Then there is constant voltage. The voltage of constant voltage is 4.2v plus or minus 0.05v for lithium batteries. There are two kinds of judgments for the end of charging,
(1) When the current is small to a certain level, for example, 10 mA.
(2) When the charging time reaches a certain time, for example, 2 hours after switching to a constant voltage charging state.
This may be the most interesting content for beginners, and this probability is also the most confusing. According to industry standards, for lithium batteries, the general nominal capacity is the minimum capacity. This capacity is a batch of batteries, at a room temperature of 25 degrees, first fully charged with cc/cv0.5c, and left 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 quickly does not have much 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. Please pay attention to several key parameters here, one is the temperature, the second is the charging method, and the most critical is the discharge current. These factors will affect the final measured capacity. Why is this concept confusing? It is because objectively, many factors have a great influence on this parameter; subjectively, there are many lithium battery manufacturers trying their best on this parameter, and the standard value is the highest. It’s worth it, and it’s just blatant, anyway. The market places great importance on this parameter. Anyway, not all consumers and merchants have conditions to test, and of course there is room for fraud.
1.4 Internal resistance
This is also a troublesome concept. For beginners, as long as you know that the definition refers to the resistance that the current flows through the battery when the battery is working. The internal resistance of the battery is divided into AC internal resistance and DC internal resistance, as well as charging internal resistance and discharging internal resistance. Because the internal resistance of the rechargeable battery is very small, it is impossible to measure the true value due to the polarization of the electrode capacity when measuring the DC internal resistance, and the AC internal resistance can be measured to avoid the influence of the polarization internal resistance. The true inner value. The AC internal resistance test method is: using the battery’s characteristic that it is equivalent to an active resistor, giving the battery a constant current of 1000HZ, 50mA, sampling its voltage, rectifying, and filtering a series of processes to accurately measure its resistance. Therefore, the general manufacturer gives the AC internal resistance charging and the internal resistance increases as the charging is completed, because the electrolysis of the electrolyzable electrolyte is completed, and the electrolysis is complete, and then some things that should not be electrolyzed are electrolyzed, and a large amount of gas is generated. With a good design, it may explode. The internal resistance of discharge decreases with the increase of the remaining capacity of the battery, that is, the more the remaining capacity, the smaller the internal resistance of the battery, the less the remaining capacity, and the higher the internal resistance of discharge, because the electrolyte gradually changes from a high-energy state to a low-energy state. Electrolyzable substances. At this time, as the discharge continues, the electrolyzable electrolyte gradually increases, and the internal resistance of charging decreases. At the same time, the battery voltage is also reduced.
2 Advantages and disadvantages of Li-ion
According to the IEC61960 standard, the identification of the secondary lithium battery is as follows:
A. The battery logo consists of 3 letters followed by 5 numbers, cylindrical or 6 square numbers
B. The first letter indicates the negative electrode material of the battery. I indicates the lithium ion with a built-in battery. L indicates the lithium metal electrode or lithium alloy electrode.
C. The second letter indicates the cathode material of the battery C Cobalt-based electrode N Nickel-based electrode M Manganese-based electrode V Vanadium-based electrode
D. The third letter represents the shape of the battery R represents a cylindrical battery L represents a square battery
E. The 5 numbers of the digital cylindrical battery respectively indicate the diameter and height of the battery. The unit of diameter is millimeters. The unit of height is one-tenth of a millimeter. If any dimension of diameter or height is greater than or equal to 100mm, an oblique line should be added between the two dimensions. The 6 numbers of the linear square battery respectively indicate the thickness, width and height of the battery in millimeters. When any one of the three dimensions is greater than or equal to 100mm, a diagonal line should be added between the dimensions. If any of the three dimensions is less than 1mm, it is before this size Add the letter t and the unit of this size is one-tenth of a millimeter. For example: ICR18650 indicates that a cylindrical secondary lithium ion battery cathode material is cobalt with a diameter of about 18mm and a height of about 65mm.
ICR20/1050ICP083448 indicates that a rectangular secondary lithium-ion battery cathode material is cobalt with a thickness of about 8mm, a width of about 34mm, and a height of about 48mm. ICP08/34/150 indicates that a rectangular secondary lithium-ion battery cathode material is cobalt with a thickness of about 8mm, a width of about 34mm, and a height of about 150mm.
ICPt73448 indicates that a rectangular secondary lithium-ion battery cathode material is cobalt with a thickness of about 0.7mm, a width of about 34mm, and a height of about 48mm.
2.1 Advantages of Li-ion battery
1) The working voltage of the single battery is as high as 3.6-3.8V;
2) Greater than energy. At present, the actual specific energy that HYB steel shell battery can achieve is 100-135W.h/Kg and 280-353W.h/L (2 times Ni-Cd, 1.5 times Ni-MH). With the development of technology, the specific energy It can be as high as 150W.h/Kg and 400W.h/L.
3) Long cycle life. Generally, it can reach more than 500 times, or even 1000 times.
4) Good safety performance, no pollution, no memory effect. As the predecessor of Li-ion, the lithium battery has a short circuit due to the formation of dendritic lithium due to metal lithium, which shortens its application field; Li-ion does not contain cadmium, lead, mercury and other elements that pollute the environment; some processes (such as winding A major drawback of Ni-Cd batteries (resultant type) is the “memory effect”, which severely restricts the use of batteries, but Li-ion does not have this problem.
5) The self-discharge is small. The self-discharge rate of fully charged Li-ion stored at room temperature for 1 month is about 10%, which is much lower than 25-30% of Ni-Cd and 30-35% of Ni-MH.
2.2 Disadvantages of Li-ion
1) The battery cost is relatively high. It is mainly manifested in the high price of LiCoO2 (the resource of Co is less) and the difficulty in purification of the electrolyte system.
2) Cannot discharge with high current. Due to the organic electrolyte system and other reasons, the internal resistance of the battery is larger than that of other types of batteries, so a smaller current density is required. Generally, the discharge current is below 0.5C, which is only suitable for small and medium current electrical appliances.
3) Need to protect the circuit control.
The cathode material of lithium ion batteries is lithium cobalt oxide, and the anode is carbon. 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, when 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 lithium-ion batteries, lithium ions are in a state of movement from positive electrode to negative electrode to 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 both ends of the rocking chair. Therefore, the experts gave the lithium-ion battery a lovely name, rocking chair battery.
When charging a lithium battery, if the starting voltage is low, it cannot be charged according to the standard current. It should be charged with a small current first, and then turn to normal when the voltage reaches a certain value. In this way, adding the subsequent CC/CV, there are a total of three curves. In addition, when the constant current (CC) charging is over, some do not use constant voltage (CV), but use pulsed mode. Lithium batteries are fragile and dangerous. The most important thing is that charging cannot be over-current or over-voltage, otherwise it will generate heat or even explode. Discharge cannot be overcurrent or undervoltage, otherwise it will cause permanent damage. Therefore, lithium batteries generally have a protection circuit, and the protection circuit cannot be removed for reasons such as convenience or performance and price.
The battery is an energy conversion device, and it has no electricity inside, nor does it store electricity. Who can say that the generator also has electricity? The battery is actually a generator with a certain amount of fuel.