Experts tell you the correct way to use lithium batteries

　　I recently found an article about batteries, so I picked it up and shared it with my friends. Although the article mainly talks about mobile phone batteries, most digital cameras now use lithium-ion batteries, which have the same principle as mobile phone batteries. Therefore, it is still of great practical significance to read this article.

　　This article is divided into 11 questions and corresponding answers.

　　1. Understand the memory effect

　　2.Does the battery need to be activated?

　　3. Do I need to charge for 12 hours for the first three times?

　　4. Is there an optimal state for rechargeable batteries?

　　5. Is it true that the greater the charging current, the faster the charging?

　　6. Is the output current of the direct charging label equal to the charging current?

　　7. Does one cycle of charge and discharge mean a reduction in lifespan?

　　8. Is a higher battery capacity better?

　　9. Is it okay to store fully charged batteries?

　　10. Is it useful to charge for an extra hour after the green light on the charger is on?

　　11. Is charging via a charger more effective than charging directly?

　　1. Understanding the memory effect (mainly talking about NiCd and NiMH batteries, if you are not interested, you can skip and go directly to Part 2)

　　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 refers to the tendency of the battery to automatically maintain this specific tendency after a long period of time under a specific working cycle. This was first defined in nickel-cadmium batteries. Nickel-cadmium pouch batteries do not have a memory effect, but sintered batteries do. The current nickel metal hydride (commonly known as nickel-hydrogen) battery is not subject to this definition of memory effect.

　　Due to the improvement of modern nickel-cadmium battery technology, the above-mentioned memory effect has been greatly reduced, and another phenomenon has replaced this definition, that is, the "crystallization" of nickel-based batteries. Usually, nickel-cadmium batteries are affected by the combined effect of these two effects, while nickel-metal hydride batteries are only affected by the "crystallization" memory effect, and the impact is smaller than that of nickel-cadmium batteries.

　　In practical applications, the method of eliminating memory effect has strict specifications and an operation process. Improper operation will be counterproductive.

　　For nickel-cadmium batteries, normal maintenance is regular deep discharge: on average, perform a deep discharge (discharge to 1.0V/cell, foreigners call it exercise) every month (or 30 cycles) of use. In normal use, try to use the battery as much as possible or shut down the battery to alleviate the formation of memory effect, but this is not exercise, because instruments (such as mobile phones) will not use 1.0V/cell before shutting down. Special equipment or circuits must be used to complete this task. Fortunately, many nickel-metal hydride battery chargers have this function.

　　For nickel-cadmium batteries that have not been exercised for a long time, the capacity cannot be restored by exercise due to the accumulation of memory effect. At this time, a deeper discharge (foreigners call it reconditioning) is required. This is a process of discharging the battery to 0.4V per cell for a long time with a very small current, which requires professional equipment.

　　For NiMH batteries, exercising once every three months can effectively alleviate the memory effect. Because the cycle life of NiMH batteries is much lower than that of NiCd batteries, reconditioning is rarely used.

　　▲Suggestion 1: Discharging the battery before each charge is unnecessary and harmful because the battery life is needlessly shortened.

　　▲Suggestion 2: It is not advisable to use a resistor to connect the positive and negative poles of the battery for discharge. The current cannot be controlled and it is easy to over-discharge to 0V, or even cause the polarity of the batteries in the series battery pack to reverse.

　　2.Does the battery need to be activated?

　　The answer is that the battery needs to be activated, but this is not something the user has to do. I have visited a lithium-ion battery production plant, and lithium-ion batteries go through the following process before leaving the factory:

　　The lithium-ion battery shell is infused with electrolyte, sealed, and then formed, which is constant voltage charging, and then discharged. This is repeated for several cycles to fully infiltrate the electrodes with electrolyte and fully activate them until the capacity reaches the required level. This is the activation process. Capacity division is to test the capacity of the battery, select batteries with different performance (capacity) for classification, divide the battery level, and perform capacity matching. The lithium-ion batteries produced in this way are already activated when they reach the user. The nickel-cadmium batteries and nickel-metal hydride batteries that we all commonly use are also formed and activated before leaving the factory. The activation process of some batteries requires the batteries to be in an open state, and then sealed after activation. This process can only be completed by battery cell manufacturers.

　　There is a problem here. It takes a long time for the battery to leave the factory and reach the user, sometimes as short as one month or as long as half a year. During this time, because the battery electrode material will be passivated, the manufacturer recommends that the battery be fully charged and discharged 3 to 5 times before being used for the first time in order to eliminate the passivation of the electrode material and achieve maximum capacity.

　　In the three national standards for nickel-metal hydride, nickel-cadmium and lithium-ion batteries issued in 2001, the initial capacity test is clearly stipulated, and the battery can be deeply charged and discharged five times. If one of them meets the requirements, the test can be stopped. This explains the phenomenon I mentioned very well.

　　★Then it can be called "second activation". The user should try to perform several deep charge and discharge cycles on the "new" battery when using it for the first time.

　　●However, according to my test (for lithium-ion batteries), for lithium-ion batteries with a storage period of 1 to 3 months, the capacity increase phenomenon is almost non-existent if they are subjected to deep charge and deep discharge cycles. (I have a test report on battery activation in the special discussion area)

　　3.Do I need to charge for 12 hours for the first three times?

　　This question is closely related to the battery activation question mentioned above. Let's assume that the battery has electrode passivation when it leaves the factory and the user has to perform deep charge and deep discharge cycles three times to activate the battery. In fact, this question turns into the question of whether deep charging means charging for 12 hours. Then my other article "On the Charging Time of Mobile Phone Batteries" has already answered this question.

　　★★★The answer is no need to charge for 12 hours.

　　Early mobile phone NiMH batteries needed to be replenished and trickle charged, so it might take about 5 hours to reach the perfect full charge state, but it did not take 12 hours. The constant current and constant voltage charging characteristics of lithium-ion batteries determine that its deep charge time does not need 12 hours.

　　Some people may ask about lithium-ion batteries, since the current of lithium-ion batteries gradually decreases during the constant voltage stage, is it true deep charging when the current is infinitesimal? I once drew a curve of the current decrease versus time during the constant voltage stage, and performed curve fitting on it many times, and found that this curve can be close to zero current in the form of a 1/x function. In actual testing, due to the self-discharge phenomenon of lithium-ion batteries themselves, this zero current can never be reached.

　　Taking a 600mAh battery as an example, if the cut-off current is set to 0.01C (i.e. 6mA), its 1C charging time will not exceed 150 minutes. If the cut-off current is set to 0.001C (i.e. 0.6mA), its charging time may be 10 hours. This value cannot be accurately obtained due to the accuracy of the instrument. However, the capacity gained from 0.01C to 0.001C is only 1.7mAh after calculation. There is no practical significance in exchanging more than 7 hours of use for less than 0.3% of the capacity.

　　Moreover, there are other charging methods, such as pulse charging, which allows lithium-ion batteries to reach the 4.2V limit voltage. It does not have a minimum current judgment stage at all. Generally, it is 100% charged after 150 minutes. Many mobile phones use pulse charging.

　　Some people have used a charger to confirm the charge level of their mobile phone after the mobile phone shows that it is fully charged. This testing method is not rigorous.

　　First of all, the green light displayed on the charger is not a basis for detecting whether it is fully charged or not.

　　★★The only final way to detect whether a lithium-ion battery is fully charged or not is to test the voltage of the lithium-ion battery when it is not charging (nor discharging).

　　The real purpose of the so-called constant voltage stage current reduction is to gradually reduce the additional voltage generated by the charging current on the battery's internal resistance. When the current is as small as 0.01C, such as 6mA, this current multiplied by the battery's internal resistance (generally within 200 milliohms) is only 1mV. It can be considered that the voltage at this time is the battery voltage in the no-current state.

　　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 battery is fully charged when it is put on the charger, but the charger does not think it is fully charged and continues to charge.

　　4.Is there an optimal state for rechargeable batteries?

　　There is a saying that if a rechargeable battery is used properly, it will reach the best state in a certain cycle range, that is, the capacity is the largest. This depends on the situation. If sealed NiMH batteries and NiCd batteries are used properly (such as regular maintenance to prevent the generation and accumulation of memory effect), they will generally reach their maximum capacity at 100 to 200 cycles. For example, after 120 cycles, the capacity of a NiMH battery with a factory capacity of 1000mAh may reach 1100mAh. I can see such descriptions in 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 an optimal state, generally reaching their maximum capacity between 100 and 200 cycles

　　For liquid lithium-ion batteries, there is no such hump phenomenon in cycle capacity. From the time a lithium-ion battery leaves the factory to the time it is scrapped, its capacity decreases with each use. When I was testing the cycle performance of lithium-ion batteries, I never saw any sign of capacity recovery.

　　★Lithium-ion batteries do not have an optimal state.

　　It is worth mentioning that lithium-ion batteries are more susceptible to changes in ambient temperature and show different performance. They will show their best performance in an ambient temperature of 25 to 40 degrees, while their performance will be greatly reduced in low or high temperature conditions. To make your lithium-ion battery fully display its capacity, you must pay careful attention to the use environment and prevent high and low temperature phenomena. For example, if a mobile phone is placed on the front table of a car, the direct sunlight at noon can easily make it exceed 60 degrees. The battery standby time of users in the north is not as long as that of users in the south under the same network conditions.

　　5.Is it true that the greater the charging current, the faster the charging?

　　This issue has been discussed in the article "On the Charging Time of Mobile Phone Batteries". This can be said for nickel-based batteries with constant current charging, but this is not entirely correct for lithium-ion batteries.

　　★★For charging lithium-ion batteries, within a certain current range (1.5C~0.5C), increasing the constant current value of the constant current and constant voltage charging method does not shorten the time to fully charge the lithium-ion battery.

　　6.Is the output current of the direct charging label equal to the charging current?

　　This is to discuss the charging method of the mobile phone. For the charging management in the mobile phone, set the same direct charger (actually should be called a power adapter) output such as: 5.3V 600mA

　　A. Charging management is a switch mode (high-frequency pulse width adjustment PWM mode). In this charging mode, the mobile phone does not fully utilize the output capacity of the direct charger. The direct charger works in the constant voltage stage and outputs 5.3V. At this time, the actual charging current is adjusted by the charging management of the mobile phone, and it must be less than 600mA, generally 300~400mA. At this time, the output current of the direct charger you see is not the charging current of the mobile phone. For example, many direct chargers of Motorola have an output of 5.0V 1A, and the actual battery charging only uses 500mA, because the battery capacity of the mobile phone is only 580mAh.

　　★At this time, the output current marked on the direct charge is not equal to the actual charging current

　　B. The charging management is in pulse mode. In this charging mode, the mobile phone fully utilizes the current limiting current of direct charging, that is, 600mA is used on the battery. At this time, the output current of direct charging is the charging current.

　　Of course, the above all refers to the constant current stage of lithium-ion batteries or the charging of nickel-metal hydride batteries.

　　If the mobile phone does not have charging management, and the charging management is moved to direct charging, such as many CDMA mobile phones, there is nothing to say about this. Its output is clearly written, such as output: 4.2V 500mA, which is the constant current and constant voltage data of the lithium-ion battery.

　　7. Does every charge and discharge cycle mean a reduction in lifespan?

　　Cycle means use. We are using batteries and we care about the time of use. In order to measure the performance of how long a rechargeable battery can be used, the definition of cycle number is stipulated. Actual user use varies greatly, and tests under different conditions are not comparable. To make comparisons, the definition of cycle life must be standardized.

　　The national standard stipulates the test conditions and requirements for the cycle life of lithium-ion batteries as follows: charging for 150 minutes at a constant current and constant voltage of 1C at room temperature of 25 degrees, and discharging to 2.75V at a constant current and 1C discharge system as one cycle. The test ends when one discharge time is less than 36 minutes, and the number of cycles must be greater than 300 times.

　　explain:

　　A. This definition stipulates that the cycle life test is carried out in a deep charge and deep discharge mode.

　　B. It is stipulated that the cycle life must be more than 300 times according to this mode, and the capacity is still more than 60% after that.

　　In fact, the number of cycles obtained by different cycling systems is quite different. For example, if the other conditions above remain unchanged and only the constant voltage of 4.2V is changed to 4.1V to conduct cycle life test on the same type of battery, then the battery is no longer in deep charging mode. Finally, the test shows that the cycle life can be increased by nearly 60%. Then, if the cut-off voltage is increased to 3.9V for testing, the number of cycles should be able to increase several times.

　　Many friends have discussed the idea that each cycle reduces the life span. I am just adding a comment. When talking about the number of cycles, we must not ignore the conditions of the cycle.

　　●It is meaningless to talk about the number of cycles without considering the rules, because the number of cycles is a means to detect the battery life, not an end!

　　▲Misconception: Many people like to use the lithium-ion battery of their mobile phone until it shuts down automatically before charging it. This is totally unnecessary.

　　In fact, it is impossible for users to use the battery according to the national standard test mode. No mobile phone will shut down at 2.75V, and its discharge mode is not a large current constant current discharge, but a mixture of GSM pulse discharge and normal small current discharge.

　　There is another way to measure cycle life, which is time. Some experts have proposed that the life of general civilian lithium-ion batteries is 2 to 3 years. Combined with actual conditions, such as 60% capacity as the end of life, plus the aging effect of lithium-ion batteries (see point 9), I think it is more reasonable to use time to express cycle life.

　　The charging mechanism of lead-acid batteries is similar to that of lithium-ion batteries, which is a current-limiting and voltage-limiting method. The method of use is shallow charging and shallow discharging. Its life span is expressed in time, not number of times, such as 10 years.

　　★★★Therefore, for lithium-ion batteries, there is no need to shut down the phone before charging. Lithium-ion batteries are suitable for use in a charging mode at any time. This is also one of its biggest advantages over nickel-metal hydride batteries. Please make good use of this feature.

　　8.Is a higher battery capacity better?

　　For batteries of different models (especially different sizes), the higher the capacity, the longer the battery life. Regardless of the size and weight, the higher the capacity, the better.

　　However, for batteries of the same model and nominal capacity (e.g. 600mAh), the actual measured initial capacity may be different: for example, one is 660mAh and the other is 605mAh, so is the 660mAh better than the 605mAh?

　　The actual situation may be that the high capacity is because the electrode material has more things that increase the initial capacity, while the things that stabilize the electrode are reduced. As a result, after dozens of cycles, the high-capacity battery quickly loses capacity, while the low-capacity battery remains strong. Many domestic battery cell manufacturers often use this method to obtain high-capacity batteries. However, after using it for half a year, the standby time is terrible.

　　The AA nickel-metal hydride batteries (also known as No. 5 batteries) for civilian use are generally 1400mAh, but there are also those with ultra-high capacity (1600mAh), and the principle is the same.

　　★The price of increasing capacity is sacrificing cycle life. If manufacturers do not work on modifying battery materials, it is impossible to truly "increase" battery capacity.

　　9.Is it okay to store fully charged batteries?

　　Lithium-ion batteries have a very bad characteristic, which is the aging of lithium-ion batteries (or aging, which is called aging in foreigners). After a lithium-ion battery is stored for a period of time, even if it is not recycled, part of its capacity will be permanently lost. This is because the positive and negative electrode materials of lithium-ion batteries have already begun their exhaustion process since they left the factory. Different temperatures and battery fullness have different aging consequences. The following data is excerpted from reference [1] and listed in the form of percentage of capacity:

　　Storage temperature--40% state of charge-------100% state of charge

　　0 degrees ------- 98% (one year later) ------ 94% (one year later)

　　25 degrees -------96% (one year later) ------80% (one year later)

　　40 degrees ------85% (one year later) ------65% (one year later)

　　60 degrees -------75% (after one year) ------60% (after three months)

　　It can be seen that the higher the storage temperature and the more fully the battery is charged, the greater the capacity loss. Therefore, it is not recommended to store lithium-ion batteries for a long time. On the contrary, manufacturers should recycle them like rotten food. Users should pay close attention to the production date of the battery.

　　If users have idle batteries, experts recommend storage conditions of 40% charge level and 15 degrees or lower storage temperature.

　　However, nickel-metal hydride batteries and nickel-cadmium batteries are almost not affected by this aging effect. Nickel-based batteries that have been stored for a long time can restore their original capacity after several deep charges and discharges.

　　10. Is it useful to charge for one more hour after the green light on the charger is on?

　　The green light is just an indication. Whether the battery is fully charged or not depends on the charger's control and judgment of the charging process. Let's take a 4.2V lithium-ion battery as an example to discuss this issue.

　　The first is control. The output of the battery is controlled by constant current first and constant voltage later (the current gradually decreases).

　　Then it is judged that when the current is less than a certain current value, the green light is displayed. Because the accuracy of analog-to-digital conversion and the voltage accuracy itself are limited, the charger usually sets this current value to 50mA. At this time, the green light is displayed, and the battery is indeed less than 10% away from being fully charged (according to my measurement, if the current lithium-ion battery is charged at 50mA, its capacity can reach 95%, and the charging acceptance capacity is greatly improved. The current question is what the charger is doing next:

　　A. If the charger completely shuts off the charging circuit and does not continue constant voltage charging, then leaving it on the charger for another 10 hours will not help. Many charger designs are like this, such as TI's BQ2057 series charging chips and Linear's LT1800 series.

　　B. The charger continues to charge at a constant voltage and strictly controls the voltage not to exceed 4.2V. There is no doubt that charging for another hour can increase the battery capacity.

　　C. The charger continues to charge, but its current control is very poor, and the battery accidentally exceeds 4.2V, and continues to go up. Because lithium-ion batteries cannot absorb any overcharge. Continuously applying current to the battery will cause this result, and then overcharge occurs. This is of course a poorly designed charger, such as the common "egg charger" that costs more than ten yuan and can charge both lithium-ion batteries and nickel-metal hydride batteries.

　　D. There is also a charging management chip, such as maxim's 1679 chip. Like many mobile phone charging management, it uses pulse charging. When it displays a green light, it means the lithium-ion battery is 100% charged. Of course, it will not be overcharged if left for another hour, and it is obviously doing useless work.

　　Users actually don't know what the charger is doing after the green light comes on. It could be A, B or D. The charger manual doesn't mention these things. Excluding unqualified chargers, we should actually trust qualified and original chargers. If the green light is on, why not take it off and use it? This doesn't actually have much impact on users. Not fully charging does not affect the cycle life (as mentioned in point 7 above), and 95% capacity is acceptable. Unless there are enthusiasts who can deeply analyze how their chargers are charging, otherwise we might as well------★Take it off and use it after the green light comes on.

　　11.Is charging via a charger more effective than charging directly?

　　After reading the previous mother-in-law's words, this question is the easiest to answer. The essence of the question is the difference in charging methods.

　　★There is no saying that a charger will definitely charge more fully than a direct charger, and there is no saying that a direct charger will definitely charge more fully than a charger. What is important is whether their charging methods can charge the battery as quickly and fully as possible.