The "lifetime" of the battery usually refers to the amount of battery used before the battery capacity decays to 80%-for example, the battery capacity drops to 80% after the accumulative charge and discharge of 1000Ah, which is of course lower than that after the accumulative charge and discharge of 500Ah. 80% is better.
1. Some well-known basic knowledge Lithium-ion batteries, as rechargeable batteries, have many advantages such as high energy density, and are now widely used in digital products.
(1) Some early rechargeable batteries, such as nickel-cadmium batteries, have a memory effect. If the battery is not used up and start charging, then the next time it is discharged and placed in this place, it can no longer be placed, resulting in a decrease in battery capacity; if the battery is not fully charged, it will start to discharge, then the next time it will be charged and then recharged to this place , It can’t be charged, which also leads to a decrease in capacity. Therefore, for nickel-cadmium batteries and other batteries that have a memory effect, the best way to use them is to recharge them when they are used up and use them when they are full. Lithium batteries do not have this effect. On the contrary, fully charging and discharging the lithium battery will greatly damage the capacity of the lithium battery. Therefore, the lithium battery does not need to be fully charged.
(2) Lithium batteries are extremely harmful whether they are overcharged or overdischarged. If it is overcharged, it will permanently damage the capacity of the lithium battery; if it is overcharged, there will be risks such as explosion. However, there is no danger of overcharging if the lithium battery device is plugged in overnight, because of course these devices will stop charging or reduce the current to a very low level when they are fully charged (only to make up for a small amount of power consumption overnight). In fact, the ten-dollar 18650 lithium battery that I usually use in DIY has a built-in protection board, so it is sure to have it on mobile phones and so on. If it is over-discharged, the lithium battery will no longer be charged and cannot be used directly. It needs to be disassembled for special activation; if it is over-discharged, it will be completely "starved" and completely unusable. Therefore, because the lithium battery itself has a certain degree of self-discharge, it is necessary to ensure that the device has a certain amount of power before storing the lithium battery device for a long time to prevent the battery from starvation; after a certain period of time, check whether it needs to be recharged.
(3) The life of a lithium battery is indeed related to the charging current (or charging rate). Therefore, it can be said that the life of a lithium battery is related to the power supply. Generally speaking, the service life of lithium batteries will be lower if fast charging is used. However, as long as the current does not exceed the amount of full charge in 1 hour, the impact of the charging rate on the life is not significant. The only "problem" when using power banks, computer USB ports, etc., is that the power supply current is relatively small and the charging is very slow; for the battery life, this is not harmful. Except for extremely inferior chargers, today's devices basically don't pick up the charging power source, unlike in the early days, each mobile phone battery must be equipped with a special charger. On the contrary, the slower charging current is more protective of the battery.
(4) Lithium batteries are best operated at room temperature. Using lithium batteries at high temperatures, charging them, or storing them for long periods of time will permanently reduce the capacity. Charging the lithium battery at low temperature (<0°C) will cause permanent damage, but only using it at low temperature will basically only temporarily experience a decrease in capacity, and it will recover when it returns to normal temperature. It is not a big problem to store lithium batteries at lower temperatures, but they cannot be stored at too low temperatures for too long.
2. More detailed knowledge The capacity loss of lithium batteries is an extremely complex process involving many factors. There is no space here to explain the specific mechanism through which each factor has an impact, but a brief list of these factors. The capacity loss of lithium batteries can be mainly divided into two parts: the capacity loss over time (calendar aging) (the lithium battery is left unused, the capacity will decrease after a long time) and the capacity loss caused by use (cycle aging). Regarding the former, the main factors involved are: State of Charge. This refers to the place where the power is in the total capacity. For example, it is 40% or 60%; temperature (Temperature); storage time (time). Regarding the latter, the main factors involved are: Depth of Discharge each time. For example, each time you charge from 0% to 100%, and then charge to 0%, or start charging when the battery is 20%, and unplug it when it reaches 80%. This is not the same; State of Charge (State of Charge), which is commonly referred to as electricity. For the same DoD, the average SoC can be different. For example, if the battery is kept between 40% and 100%, and kept between 20% and 80%, although the charging and discharging depth is the same, the impact on the battery is different due to the different charging state; (Rate of Charge). If the charging current can fully charge the battery in 1 hour, we say that the charging rate is 1C on average; if the charging current can fully charge the battery in 2 hours, we say that the charging rate is 0.5C on average; etc.; Temperature (Temperature ); Number of cycles. Obviously, a cycle of two hundred cycles is more lossy than a hundred cycles... In addition, there are some factors that are almost beyond our control. For example, a lithium battery in the initial stage of use will undergo a process of forming a solid electrolyte phase interface film (SEI film). This process consumes a certain amount of lithium ions. As long as the battery needs to be used, this process cannot be bypassed, so we don't have to think about it too much. Calendar aging and cycle aging are basically independent. Therefore, if the device can directly use an external power source without charging and discharging the lithium battery, then cycle aging can be avoided, which is beneficial to the life of the lithium battery. However, what SoC should we stay in? This is what will be discussed below: the qualitative law about the influence of various factors on the life loss of lithium batteries.
(1) State of Charge Research shows that when the SoC is lower, both calendar aging and cycle aging will be delayed. Therefore, if we want to minimize the life decay of lithium batteries, we should keep its power low. For example, if you want the device to directly use an external power source without charging and discharging the lithium battery, it is better to keep the battery level at 40% than at 60%. So, as long as the use requires permission, is the lower the battery, the better? Long-term low power consumption will accelerate the growth of the negative SEI layer, resulting in an irreversible increase in the internal resistance of the battery. Also, when the battery voltage is lower than 3.6V (about 30% power), the volume of the negative electrode will expand significantly. The physical expansion and contraction will damage the negative electrode microstructure and increase the internal resistance, so keep the power of about 30% as the lower limit. That's it.
(2) Temperature (Temperature) What temperature is most friendly to lithium batteries? The data obtained from different studies are not exactly the same, but it is roughly similar to the comfortable temperature of the human body. So, keep the temperature at a room temperature that makes you comfortable. At higher temperatures (almost higher than a person's normal oral temperature), the aging process is much faster anyway. At a lower temperature (almost 0°C), storage is basically no problem, but if it is charged, it will cause more damage than usual. At extremely low temperatures (almost <20°C), even storage is not suitable. (Insert: The research on humidity seems to be rarely seen, but according to common sense, don’t think it’s too damp...)
(3) Depth of Discharge (Depth of Discharge) The shallower the depth of discharge, the better. It is much better to charge for a short period of time a few more times a day than to charge the battery almost completely every day and then charge it again at night. You may have a question: If the charge is shallow, wouldn't the number of cycles naturally increase? For example, if we can use 500 cycles according to 100% of the charge and discharge depth, don't we of course expect to use 1000 cycles according to the 50% depth? In fact, this is not the case. The researchers say that each cycle is based on the cumulative amount of charge and discharge reached 100%. Under this definition, we still get the conclusion that the shallower the charge and discharge, the better, which means that, for example, at a depth of 50%, you can count on 2000 charge and discharge times.
(4) Charge rate (rate of Charge) Lower charge rate is better. If you are not in a hurry, it is recommended to reduce the use of fast charging. However, the fast charge rate of digital products such as mobile phones and tablets is at most about 2C, which is far less than the 5C or even 15C that researchers found to be more harmful during the study. Therefore, the charging rate of these devices is a relatively small factor.
(5) Time and Number of cycles This is obvious. The newer the battery and the less used it is, the less the capacity loss will of course be. However, if there is a new device, putting it for less use means that more lifespan will be taken away by time, instead of turning it into use time to accompany us. This seems to be more than just a technical problem. The benevolent see benevolence, and the wise see wisdom.
To sum up: Try to use lithium batteries and charge them at room temperature; choose a relatively low power level, keep the actual power above and below it, and avoid always being fully charged; shallow charge and shallow discharge, eat less and more meals; use less quickly Charge. This article mainly introduces the method of "open source" at the battery. However, this is not the only advisable measure: "throttling" at power-consuming devices has the same help. Turning on the flight mode when not in use at night, reducing meaningless operations (such as boring fingers on the screen), using low battery mode, turning off some interface animations and effects, etc., can save power usage and also protect the battery. It is more like reducing the brightness of the screen appropriately, reducing the use of equipment, etc., in addition to saving power, it is also beneficial to your health.
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