Technical knowledge of lithium battery use and maintenance

How to maintain the lithium battery of our love machine is correct? This problem has been plagued by many mobile phone loyal users, including me. After consulting some information, I had the opportunity to consult a Ph.D. in electrochemistry and a deputy director of a well-known battery research institute in China. I will write some relevant knowledge and experience recently obtained to readers.

The positive electrode material of a lithium ion battery usually consists of an active compound of lithium, and the negative electrode is a carbon of a special molecular structure. The main component of the common positive electrode material is LiCoO2. When charging, the potential applied to the two poles of the battery forces the compound of the positive electrode to release lithium ions, and is embedded in the carbon in which the negative electrode molecules are arranged in a sheet structure. At the time of discharge, lithium ions are precipitated from the carbon of the sheet structure and recombined with the compound of the positive electrode. The movement of lithium ions produces a current.

Although the principle of chemical reaction is very simple, in actual industrial production, there are many practical problems to be considered: the material of the positive electrode needs additives to maintain the activity of multiple charge and discharge, and the material of the negative electrode needs to be designed at the molecular structure level. It contains more lithium ions; the electrolyte filled between the positive and negative electrodes needs to have good conductivity and reduce the internal resistance of the battery, in addition to being stable.

Although lithium-ion batteries have little memory effect of nickel-cadmium batteries, the principle of memory effect is crystallization, and this reaction is hardly produced in lithium batteries. However, lithium-ion batteries still have a reduced capacity after multiple charge and discharge cycles, which are complicated and diverse. Mainly the change of the positive and negative materials themselves. From the molecular point of view, the hole structure containing lithium ions on the positive and negative electrodes will gradually collapse and block. From the chemical point of view, positive and negative materials are passivated and side reactions occur to produce stable other compounds. Physically, will gradually peel off the positive electrode material, and in the end, the number of lithium ions in the battery that can freely move during charge and discharge is finally reduced.

Overcharging and over-discharging will cause permanent damage to the positive and negative electrodes of lithium-ion batteries. From a molecular perspective, it can be intuitively understood that excessive discharge will cause the anode carbon to release lithium ions excessively, causing the sheet structure to collapse. Overcharging will hardly plug too much lithium into the negative carbon structure, and some of the lithium ions will no longer be released. This is why lithium-ion batteries are usually equipped with a charge and discharge control circuit.

Unsuitable temperatures will cause other chemical reactions inside the lithium-ion battery to form compounds that we do not want to see, so there are protective temperature-controlled separators or electrolyte additives between the positive and negative electrodes of many lithium-ion batteries. When the temperature of the battery is raised to a certain extent, the pores of the composite membrane are closed or the electrolyte is denatured, and the internal resistance of the battery is increased until the circuit is broken, and the battery is no longer heated to ensure that the charging temperature of the battery is normal.

And deep charge and discharge can improve the actual capacity of lithium-ion batteries? Experts clearly told me that this is meaningless. They even said that the so-called "activation" of the first three full charge and discharge, in the knowledge of their two doctors, can not figure out what is necessary. However, why do many people change the capacity indicated in BatteryInformation after deep charging? It will be mentioned later.

Lithium-ion batteries generally have management chips and charging control chips. Among them, there are a series of registers in the management chip, which contain values such as capacity, temperature, ID, charging state, and number of discharges. These values will gradually change during use. In my personal opinion, the main function of using the "use should be fully charged once a month or so" approach in the instructions should be to correct the improper values in these registers so that the battery charge control and nominal capacity match the actual situation of the battery.

The charging control chip mainly controls the charging process of the battery. The charging process of lithium-ion battery is divided into two stages, the constant current fast charging phase (when the battery indicator is yellow) and the constant voltage current decreasing phase (the battery indicator light flashes green. During the constant current fast charging phase, the battery voltage is gradually increased. The standard voltage to the battery is then transferred to the constant voltage stage under the control chip, the voltage is no longer raised to ensure that it will not overcharge, and the current gradually decreases to zero as the battery power rises, and the charging is finally completed.

The electricity statistics chip can calculate the battery power by recording the discharge curve (voltage, current, time), which is the wh value we read in BatteryInformation. After the lithium-ion battery is used for many times, the discharge curve will change. If the chip has no chance to read the complete discharge curve again, the calculated power is not accurate, so we need deep charge to calibrate. Battery chip.

1. Understanding memory effect Battery memory effect refers to the reversible failure of the battery, that is, the performance that can be restored after the battery fails. The memory effect is that the battery automatically maintains this particular tendency after it has been subjected to a specific duty cycle for a long time. This was first defined in nickel-cadmium batteries, nickel-cadmium bag batteries have no memory effect, and sintered batteries have a memory effect. Today's nickel metal hydride (commonly known as nickel hydride) batteries are not subject to the definition of this memory effect. Because of the improvement of the modern nickel-cadmium battery process, the above memory effect has been greatly reduced, and another phenomenon replaces this definition, which is the "lattice" of nickel-based batteries. Generally, nickel-cadmium batteries are subject to these two types. The combined effect of the effect, while the nickel-hydrogen battery is only affected by the "lattice" memory effect, and the impact is smaller than that of the nickel-cadmium battery. In practical applications, methods for eliminating memory effects have strict specifications and an operational procedure. Improper operation can be counterproductive.

For nickel-cadmium batteries, the normal maintenance is regular deep discharge: a deep discharge is performed every one month (or 30 cycles) (discharge to 1.0 v / section, foreigners call it movement), usually used as much as possible Or use the shutdown method to ease the formation of memory effect, but this is not exercise, because the instrument (such as mobile phone) will not use 1.0 v / each section to shut down, you must have a special equipment or line to complete the work. Fortunately, many NiMH battery chargers have this feature. For nickel-cadmium batteries that have not been exercised for a long time, the memory capacity cannot be recovered due to the accumulation of memory effects. In this case, a deeper discharge (foreigner called repair) is required, which is a battery with a small current for a long time. A process that discharges to 0.4 v per section requires professional equipment. For NiMH batteries, the frequency of exercise can be effectively relieved every three months. Because the cycle life of nickel-metal hydride batteries is much lower than that of nickel-cadmium batteries, it is almost impossible to repair this method.

2. Does the battery need to be activated?

The answer is that the battery needs to be activated, but this is not what the user has to do. I have visited the production plant of lithium-ion batteries. The lithium-ion battery has to undergo the following process before leaving the factory: the lithium-ion battery case is filled with electrolyte---sealing--forming, which is constant-voltage charging, then discharging, so several cycles are performed. The electrode is fully immersed in the electrolyte, fully activated, and the capacity is up to the requirement. This is the activation process. - - - Distillation, which is to test the capacity of the battery, select the battery with different performance capacity (quantity), classify the battery, and classify the battery. Capacity matching, etc. The lithium-ion battery thus come out has been activated to the user. The nickel-cadmium batteries and nickel-hydrogen batteries that we all use are also activated after they are activated. Some of these batteries require the battery to be in an open state. After activation, the battery is sealed. This process can only be completed by the battery manufacturer. There is a problem here, that is, the battery from the battery factory to the user's hand, this time is sometimes very long, short one month, long half year, this time, because the battery electrode material will be passivated, so the manufacturer recommends the first use the battery is preferably subjected to 3 to 5 times to  full charge and discharge processes to eliminate passivation of the electrode material to achieve maximum capacity. Three of the nickel hydrogens were issued in 2001. In the national standard of nickel-cadmium and lithium-ion batteries, the initial capacity detection is clearly defined, and the battery can be deep-filled for 5 times. When one time meets the requirements, the test can be stopped. This is a good explanation of the phenomenon I am talking about.So it can call it "second activation", and the "new" battery that the user uses for the first time should try to perform several deep charge and discharge cycles.However, according to my test (for lithium-ion batteries), the lithium-ion battery with a storage period of 1 to 3 months is subjected to deep-filling and deep-discharging, and the capacity increase phenomenon is almost non-existent. (I have a test report on battery activation in the panel discussion area).

3. Do you have to charge 12 hours in the first three times?

This problem is closely related to the battery activation problem above, let the factory battery to the user's hand has electrode passivation phenomenon, in order to activate the battery for deep charge deep discharge cycle 3 times. In fact, whether this problem is translated into deep charge is whether it is to charge for 12 hours. Then my other article "On the charging time of mobile phone batteries" has already answered this question.

The answer is that you don't need to charge for 12 hours. Early mobile phone NiMH batteries, because of the need for replenishment and trickle charging, to achieve the most perfect state of fullness, may take about 5 hours, but it does not need 12 hours. The constant current and constant voltage charging characteristics of the lithium ion battery determine that its deep charging time does not require 12 hours. For lithium-ion batteries, some people will ask, since the current of the lithium-ion battery in the constant-voltage phase is gradually reduced, is it true when the current is small to infinity? I once plotted the curve of current reduction in time during constant voltage, and performed multiple curve fittings on it. It was found that this curve can be approximated to zero current with a 1/x function. Actually, the lithium ion battery itself exists. Self-discharge, this zero current is never reached. Take the 600 mah battery as an example, set the cutoff current to 0.01 degrees (6 ma), its 1 c charging time does not exceed 150 minutes, then set the off current to 0.001 degrees (0.6 ma), its charging time may be 10 hours - this is impossible to obtain accurately due to the accuracy of the instrument, but the capacity obtained from 0.01 degrees Celsius to 0.001 degrees Celsius is calculated to be only 1.7 mah, and more than 7 hours of multi-use is exchanged for this only three thousandths. The capacity to arrive does not have any practical significance. Moreover, there are other charging methods, such as the pulse charging method to make the lithium-ion battery reach the 4.2 v limit voltage, it does not cut off the minimum current judgment stage, and generally it is 100% full after 150 minutes. Many mobile phones use pulse charging. Some people used to display the fullness of the mobile phone, and then use the charger to charge to confirm the fullness of the phone. This test method is not rigorous. First of all, the green light is not a basis for detecting whether it is fully charged or not.

The only final way to detect the saturation of a lithium-ion battery is to test the voltage of the lithium-ion battery in the uncharged (and non-discharged) state. The so-called constant voltage phase current reduction is the real purpose of gradually reducing the additional voltage generated by the charging current in the internal resistance of the battery. When the current is as small as 0.01 degrees Celsius, such as 6ma, this current is multiplied by the internal resistance of the battery (generally 200 mΩ within) is only 1 mv, and it can be considered that the voltage at this time is the battery voltage without current. Secondly, the reference voltage of the mobile phone is not necessarily equal to the reference voltage of the charger. The mobile phone thinks that the fully charged battery has reached the charger, but the charger does not think that it is full, but continues to charge.

4. Is the rechargeable battery optimal?

There is a saying that if the rechargeable battery is used properly, it will have the best state in a certain cycle range, that is, the maximum capacity. In this case, sealed NiMH batteries and nickel-cadmium batteries, if used properly (such as regular maintenance to prevent the generation and accumulation of memory effects), generally reach their maximum capacity at 100 ~ 200 cycles, such as After 120 cycles of a nickel-hydrogen battery with a factory capacity of 1000 mah, its capacity may reach 1100 mah. I can see this description on the graphs describing the cycle characteristics of nickel-based batteries in the technical specifications of almost all Japanese NiMH battery manufacturers.

Nickel-based batteries have the best condition, generally reach their maximum capacity between 100 and 200 cycles. For liquid lithium-ion batteries, there is no such hump phenomenon of circulating capacity, from the factory of lithium-ion batteries to the end of battery scrapping. The performance of its capacity is to use it once less. I have never seen signs of capacity recovery when I am doing cycle performance on lithium-ion batteries.

Lithium-ion batteries are not optimal. It is worth mentioning that lithium-ion batteries are more susceptible to different performances due to changes in ambient temperature. They exhibit the best performance at ambient temperatures of 25 to 40 degrees, and their performance is greatly compromised at low or high temperatures. In order for your lithium-ion battery to fully display its capacity, it is necessary to pay close attention to the use environment to prevent high and low temperature phenomena. For example, the mobile phone is placed in the front of the car, and the direct sun at noon can easily make it exceed 60 degrees. The user's battery standby time, under the same network conditions, there is no long-term user in the South.

5. Is it really the charging current, the faster the charging?

This issue has already been addressed in the article "On the charging time of mobile phone batteries". For nickel-based batteries with constant current charging, this can be said, and for lithium-ion batteries, this is not completely correct.

For the charging of lithium-ion batteries, in a certain current range (1.5 ~ 0.5 c), increasing the constant current value of the constant current and constant voltage charging mode does not shorten the time for charging the lithium ion battery.

6. Is the output current of the direct charge equal to the charge current?

This is to discuss the charging method of the mobile phone. For the charging management in the mobile phone, set the output of the same direct charge (actually called the power adapter) such as: 5.3 v600maa. The charging management is the switching mode (high-frequency pulse width adjustment pwm mode). This charging mode does not fully utilize the direct charging output capability of the mobile phone. The direct charging works in the constant voltage section and outputs 5.3 v. At this time, the real charging current is from the mobile phone. The charge management is adjusted and must be less than 600 ma, typically between 300 and 400 ma. At this time, the direct charge output current that everyone sees is not the charging current of the mobile phone. For example, many of Motorola's direct charge output is 5.0 v1a. If the battery is actually charged, it will be used for 500 feet, because the battery capacity of the mobile phone. Also 580 mah.

At this time, the output current of the direct charge superscript is not equal to the actual charging current.

7. When should I start charging during normal use?

Since the number of charge and discharge cycles is limited, the power of the lithium battery should be recharged as much as possible. But I found an experimental table on the charge and discharge cycle of lithium-ion batteries. The data on cycle life are listed below: Cycle life (10% DOD): > 1000 cycles (100% DOD): > 200 times where the Ministry of Defense is The abbreviation of the depth of discharge. The number of chargeables is related to the depth of discharge. The cycle life at 10% DOD is much longer than that of 100% DOD. Of course, if you convert the relative total capacity to the actual charge: 10% * 1000 = 100100% * 200 = 200, the latter's full charge and discharge is still better, but the previous netizen's statement has to be corrected: under normal circumstances You should reserve the charge according to the principle that the remaining battery power is used up and recharge, but if your battery is not likely to hold the whole day during the second day, you should start charging in time. Of course, if you are willing to carry it back It’s a different matter to get the charger to the office. And you need to charge to cope with the expected important events that will cause the communication to be busy, even if the battery still has a lot of power, then you only charge in advance, because you have not really lost "1" charge cycle life. That is, "0. times", and often this x will be small.

In conclusion:

1. Overcharge and overdischarge will cause permanent damage to the positive and negative terminals of lithium ion batteries. Therefore, no matter whether it is used for the first time or daily charging, it does not need to be overcharged and discharged, and it can be charged according to the time indicated in the manual.

2. Under normal circumstances, you should have the reserve to charge according to the principle that the remaining battery power is used up, but if your battery is not likely to hold the whole day on the 2nd day, you should start charging in time. .

3. For a period of time, you can do a deep charge and discharge under the control of the protection circuit to correct the battery's power statistics, but this will not increase the actual capacity of your battery.

4. Long-term unused batteries should be placed in a cool place to reduce the speed of their internal passivation reaction, and should be charged with a certain amount of electricity to prevent over-discharge damage caused by excessive self-discharge of the battery during storage.

5. In fact, there is not much use in the battery to pay attention to, in other words, it is not too much to consider. How many times a battery can be used, perhaps more different from the individual differences in the manufacture of the battery itself, rather than the method of use. Choosing a mobile phone brand with good reputation is undoubtedly one of the guarantees for the long life of battery use.

6. The only way to extend the life of a lithium battery is to extend the charging cycle, that is, to save power as much as possible while ensuring normal use.

The page contains the contents of the machine translation.