Lithium batteries are rechargeable batteries that are widely used in digital products especially due to their many advantages, such as their high energy density. In this article, we will explore the various aspects to consider in order to prolong the life of lithium batteries.
Capacity loss of lithium batteries
Capacity loss can be understood under two categories: calendar aging, where the capacity of the battery decreases over time as it is left unused, and cycle aging, where the capacity decreases over time as it is used.
Calendar aging and cycle aging are completely independent of each other. Therefore, if a device can be directly powered by an external power source without the help of a lithium battery, then cycle aging can be eliminated, which is beneficial to the overall life of the lithium battery.
There are other additional circumstances that we are not able to control with capacity loss. One such example is the SEI (Solid Electrolyte interface), which is a thin film that forms when a battery is charged for the first time. In the process of the film-forming, a certain amount of lithium ions is consumed.
Some early rechargeable batteries, such as Nickel-Cadmium batteries, have a memory effect. If you charge such batteries without them running out of electricity, then the batteries can only discharge at the state you charged them, resulting in a reduction in battery capacity.
If the batteries start to discharge without overflowing, then the next charge is the same: It can no longer be charged, which also leads to a reduction in capacity. Therefore, the best way to use batteries with a memory effect is to recharge them when they run out and use them when they overflow.
Lithium batteries do not have this effect. On the contrary, a full charge and discharge of a lithium battery are extremely harmful to its capacity. Therefore, a lithium battery does not need to be fully charged and discharged.
State of Charge
The SOC (State of Charge) is also known as the amount of energy remaining in a battery, and it is represented by a percentage. The SOC of a battery can be different even when the DOD (Depth of Discharge) is the same. One such instance is if we were to cycle between 40-100% and 20-80% of the power. The depth of charge and discharge is the same in this case; however, the charging status is different, so the battery is impacted differently.
It is much better to keep the SOC low so that there can be a delay in calendar and cycle aging, as well as the life decay of a lithium battery. In other words, if you were to use an external power source to charge and discharge your device without the help of a lithium battery, it would be better to keep the power at 40% rather than 60%. The lower the power, the better. There are, of course, dangers if the power is too low, so it is better to maintain the battery by discharging it to about 5%.
If you were to use an external power source to charge and discharge your device with the help of a lithium battery, there are other circumstances to consider: If the power is too low, the internal resistance of the battery will increase.
To illustrate this, let’s say we have a 10Wh battery that is at 0%. Its internal resistance is very high at 0 to 10%, so you store 1Wh of electricity to charge it from 0% to 10%. You end up being able to use only 0.1Wh when you take it out. The other 0.9Wh is in the device. The hours of work are transformed into heat on the battery. However, if we charge the battery from 98% to 100%, less heat is generated during operation, and the cycle aging of the battery only requires 0.2Wh.
It’s not visible to the eye, but having the power level of a lithium battery below 20% can cause great harm to the life of the battery due to the increase in internal resistance
Depth of Discharge
The smaller the depth of charge and discharge, the better. Recharging your device a few more times a day is much better than running out of power almost every day and recharging at night.
Some people may believe that if we can use 500 cycles based on a 100% DOD, then we should, of course, expect to use double that (1000 cycles) based on a 50% depth. However, this is not the case: Each cycle is based on the cumulative charge and discharge volume reaching 100%.
Overcharge and over-discharge
When lithium batteries are overcharged or over-discharged, people run the risk of permanently damaging the capacity, and, in worse cases, causing an explosion or fire. That is why there are measures in some devices to automatically shop charging a battery or reduce the current to a minimum.
Before storing a battery in long-term storage, it is best to discharge the battery in storage mode to avoid damage. After a certain amount of time has passed, the battery should be checked upon and charged and discharged as necessary.
What temperature is the friendliest for lithium batteries? The data from different studies are not exactly the same, but there is a rough consensus that comfortable room temperature is best.
Outside of this, charging or using lithium batteries in high can permanently reduce their capacity. Charging lithium batteries in low temperatures (<0 ℃) can also pose a permanent hazard, and the performance of the batteries can decrease in cold climates.
If you’re looking for a low-temperature battery, Grepow can manufacture these for you so that you can operate your vehicle or device in environments that range between -50 ℃ to 50 ℃. Under our technology, the batteries can achieve a lower internal resistance and, thus, a high discharge rate. Compared to traditional Lithium Polymer batteries, Grepow’s batteries have broken through the discharge temperature limits of -20 ℃ to 60 ℃.
The life of a lithium battery is indeed related to the charging current. A lower charging rate is better. If the need is not urgent, it is recommended to reduce the uses of fast charging. A higher charging rate can negatively impact a lithium battery’s life.
The maximum charge rate of digital products, such as wearable devices and tablets, is about 2C. Therefore, the charging rate of these devices is a relatively small factor.
Time and Cycles
Obviously, the newer and the less used the battery, the less the capacity is damaged. It’s only natural that there is capacity loss over time and with the increase of cycles.
This article focuses on the “source” approach to batteries, but there are other, simpler ways to prolong the life of your lithium batteries. Some of them include using low-battery mode and closing unnecessary interface animations and effects to save on power usage, which ultimately protects the battery.