Lithium battery related knowledge

Battery life
I believe that most consumers have heard that the life of lithium batteries is "500 times". If the battery is charged and discharged 500 times, it will "die". In order to extend the life of the battery, many friends only charge it when the battery is completely exhausted. However, this does not extend the life of the lithium battery. The life of a lithium battery is "500 times", which does not refer to the number of charges, but a charge and discharge cycle.
A charging cycle means the process of using up all the power of the battery from full to empty, and then charging from empty to full, which is not equivalent to charging once. For example, a lithium battery only uses half of its power on the first day, and then fully charges it. If it is the same on the second day, that is, charging half of it, a total of two charges, this can only be counted as one charging cycle, not two. Therefore, it may usually take several charges to complete a cycle. After each charging cycle, the battery capacity will decrease a little. However, this reduction in power is very small. After multiple cycles of charging, high-quality batteries will still retain 80% of their original capacity. Many lithium-powered products are still in normal use after two or three years. Of course, lithium batteries still need to be replaced at the end of their life.
The so-called 500 times means that the manufacturer has achieved about 625 rechargeable times at a constant discharge depth (such as 80%), reaching 500 charging cycles.
(80%*625=500) (ignore factors such as the reduction in lithium battery capacity)
Due to various influences in real life, especially the fact that the discharge depth during charging is not constant, "500 charging cycles" can only be used as a reference battery life.
Influencing factors
Lithium batteries can generally be charged and discharged 300-500 times. It is best to partially discharge lithium batteries rather than fully discharge them, and try to avoid frequent full discharges. Once the battery is off the production line, the clock starts moving. Whether it is used or not, the service life of lithium batteries is only in the first few years. The reduction in battery capacity is due to the increase in internal resistance caused by oxidation (this is the main reason for the reduction in battery capacity). Finally, the electrolytic cell resistance will reach a certain point, and although the battery is fully charged at this time, the battery cannot release the stored power.
The aging rate of lithium batteries is determined by temperature and charging state. The following table illustrates the reduction in battery capacity under two parameters.
Effect of temperature and initial charge on lithium battery storage
Temperature
Charge 40%
Charge 100%
0°C
Capacity after one year 98%
Capacity after one year 94%
25°C
Capacity after one year 96%
Capacity after one year 80%
40°C
Capacity after one year 85%
Capacity after one year 65%
60°C
Capacity after one year 75%
Capacity after three months 60%
High state of charge and increased temperature accelerate the reduction in battery capacity.
If possible, charge the battery to 40% and place it in a cool place. This allows the battery's own protection circuit to operate during the long storage period. If the battery is placed in high temperature after being fully charged, it will cause great damage to the battery. (Therefore, when using a fixed power supply, the battery is fully charged at this time, and the temperature is generally between 25-30°C, which will damage the battery and cause its capacity to decrease).
Influencing factor 1: Depth of discharge and number of recharges
From the experimental data in Figure 1, it can be seen that the number of recharges is related to the depth of discharge. The deeper the battery discharge depth, the fewer recharges it can be.
The number of recharges * depth of discharge = the total number of completed charging cycles. The higher the total number of completed charging cycles, the longer the battery life, that is, the number of recharges * depth of discharge = actual battery life (ignoring other factors)
Influencing factor 2: Overcharge, over-discharge, and large charging and discharging currents
Avoid overcharging the battery. Any form of overcharging of lithium-ion batteries will cause serious damage to battery performance or even explosion.
Avoid deep discharge below 2V or 2.5V, as this will quickly and permanently damage lithium-ion batteries. Internal metal plating may occur, which will cause a short circuit and make the battery unusable or unsafe.
Most lithium-ion batteries have electronic circuits inside the battery pack that disconnect the battery if the battery voltage is below 2.5V, exceeds 4.3V, or if the battery current exceeds a predetermined threshold value during charging or discharging.
Avoid large charging and discharging currents, as large currents put too much pressure on the battery.
Influencing factor 3: Overheated or overcooled environment
Temperature also has a great impact on the life of lithium batteries. An environment below freezing may cause lithium batteries to burn out the moment the electronic product is turned on, while an overheated environment will reduce the battery capacity. Therefore, if the laptop uses an external power supply for a long time without removing the battery, the battery will be in the high heat discharged by the laptop for a long time and will soon be scrapped.
Influencing factor 4: Fully charged or no power for a long time
Excessively high and low power states have an adverse effect on the life of lithium batteries. Most of the rechargeable times marked on the electrical appliances or batteries sold are based on 80% discharge as the benchmark test. Experiments show that for some laptop lithium batteries, if the battery voltage is often allowed to exceed the standard voltage by 0.1 volt, that is, from 4.1 volts to 4.2 volts, the battery life will be halved, and if it is increased by 0.1 volt, the life will be reduced to 1/3 of the original; the more fully the battery is charged, the greater the battery loss will be. Long-term low power or no power state will make the resistance to the movement of electrons inside the battery greater and greater, thus causing the battery capacity to decrease. Lithium batteries are best kept in an intermediate state of charge, as this will give them the longest battery life.