Estimate your Lithium Battery Life Span
Compared with other kinds of chemical batteries, lithium ion cell has longer life. Of course, it still has limited calender life and cycle life. In other words, lithium ion cell also will be aging like people and any other objects. Cycle life can symbolizes lithium ion battery life. Where can we get the information of battery life cycle?
When we tend to buy a battery, we may browse product description like battery capacity and cycle life and so on.
DNK 18650 2600mah battery cell
You may be confused about them. Today let us break them down one by one.
So what does 1000 life cycles mean? What does 1000 mean?
One complete charge cycle is the process of charging a rechargeable battery from empty to full and then discharging current from full to zero. Typically, this term is used to specify a battery’s expected life. The number of charge cycles represent the expected charging-and-discharging times. And it is usually given by manufactures.
In ideal condition, 1000 life cycles means that this DNK 18650 battery can undergo 1000 times complete charging and discharging process with nominal capacity. When life cycles has been over 1000 times, battery capacity will decrease which will affect battery performance. Then you will find that your battery is not durable and you will charge your battery frequently. When battery capacity decrease to limit level, its capacity will drop to its limited 75%. If its capacity drops, low capacity will effect battery performance.
Generally, in ideal condition, after 1000 times charge cycle, this DNK 18650 battery will lose its performance, the life task of this battery is almost finished.
However, this battery still can be used with relatively poor performance. The best advice for you is that you need to buy another battery before it dies.
Does this battery become useless after reaching the number of life cycles?
Nope.
The number of life cycles in this standard does not mean that the battery can no longer be used, but that after many cycles, the storage capacity of the battery decreases to a certain extent.
No less than 75% of nominal capacity after 1000 cycles”
That is, after 1000 cycles, the maximum charge of the battery is only 70 percent of the new battery, and the performance drops to a certain point. We can also use this battery with lower performance. When its effective capacity has fallen to its unique limit, 60%,for example, the battery stop working.
If battery life cycle number will lose one time as well as we charge the battery?
Nope. A charge cycle refers to the process in which all the charge of a lithium battery goes from full to empty and then back to full. For example, if we discharge 25% energy and then we charge 25% energy again, this process is just a quarter of a life cycle. In other words, you have to repeat the same steps four time to equal one complete cycle.
How to estimate life span of a battery?
As consumers, we care about how long the battery we can use. We name it as battery calender life.
Combined battery cycle life,we can make reasonable guesses about how long it will last.
Determine how often your battery will get a complete charging-and-discharging cycle
Multiple by numbers of cycle life
For example, there is a battery gives a clear definition of 500 life cycles. And we do a complete charging-and-discharging cycle takes an average of 5 days.
5 days*500=2500days
2500÷365=6.849years
Convert into years, we may totally use this battery for 6 to 7 years in ideal condition. But this is just an estimate, actual battery life span depends on how you use it.
Influencing factors of lithium battery capacity attenuation
The performance of the battery will deteriorate with the deepening of the degree of battery use, which is mainly reflected in the attenuation of the battery capacity. And lithium battery capacity is directly related to the battery cycle life.
The capacity attenuation is related to the following factors to varying degrees:
(1) the deposition of lithium ions;
(2) the decomposition of the electrolyte;
(3) the dissolution of the active substance;
(4) the phase transition of the electrode material;
(5) the continuous growth of the solid electrolyte interface membrane (SEI).
Among them, the metamorphosis of the cathode material is the main cause of the attenuation of the battery capacity.The thickening of the negative electrode surface film makes it difficult for lithium-ion diffusion and accelerates the capacity attenuation of lithium batteries.
In addition, unreasonable use will also exacerbate the attenuation of lithium battery capacity. Overcharging and over-discharging of the battery may cause electrolyte decomposition. Furthermore, negative lithium deposition, blockage of lithium ion migration channels, changes in electrode material structure, thermal runaway and other undesirable consequences will influence lithium battery life span as well.Too high or too low temperature may affect the lithium ion diffusion coefficient, electrolyte decomposition, reactivity, electrochemical impedance and other factors.
No matter if the battery is in charging cycle state or not, its capacity is gradually decreasing. All of us have mobile phones, no one knows this fact better than us.
Look at this “capacity-cycle times” curve chart, we can discover that the capacity of a cell decreases linearly with the increasing number of charging and discharging cycles, and the rate is related to the discharge current of a single battery.
The following is a chart describing the relation between internal resistance and cycle times of lithium ion cell. We can easily gain that: for several times of cycle, the internal resistance decreases slightly while after hundreds of cycle times, the internal resistance is on the rise with quiet fast speed.
Under a certain discharge system, before the capacity of the secondary battery drops to a specified value, the number of cycles that the battery can withstand is called the cycle life or service cycle of the battery. Cycle life is an important parameter to evaluate the practical technology economy of battery.Cycle life is affected by the maximum discharge depth of the battery, so the expression of cycle life should also indicate the discharge depth. For example, the battery cycle life is 400 cycles /100% DOD or 1000 cycles /50%DOD.
| Depth of Discharge | Discharge cycles | |
|---|---|---|
| NMC | LiPO4 | |
| 100% DoD | 300 | ~600 |
| 80% DoD | ~400 | ~900 |
| 60% DoD | ~600 | ~1,500 |
| 40% DoD | ~1,000 | ~3,000 |
| 20% DoD | ~2,000 | ~9,000 |
| 10% DoD | ~6,000 | ~15,000 |
All kinds of secondary battery cycle life are different, even the same series, the same specification of products, cycle life may also be very different. Currently commonly used battery, lithium ion battery life is the longest, cycle life can reach more than 1,000 times.
With the increase of charge and discharge cycles, the secondary battery capacity attenuation is an inevitable process.
This is because during the charging and discharging process, some irreversible processes will occur in the battery, causing the attenuation of the battery discharge capacity. These irreversible factors are mainly as follows:
- The active surface area of the electrode decreased during the charge-discharge cycle, resulting in the increase of the working current density and the increase of polarization.
- Shedding or transfer of active material on the electrode.
- Some electrode materials corrode during battery operation.
- Dendrites are generated on the electrode during the cycle, resulting in micro short circuit inside the battery.
- Diaphragm aging
- In the process of charging and discharging, the crystal shape of the active substance changes irreversibly, thus reducing its activity.
Here are some tips to prolong your battery life.
Don’t put your device in extreme temperature. Both too hot or too cold temperatures affect batteries
The high temperature increases the internal pressure of the battery, resulting in water loss of the battery, which will reduce the battery activity and accelerate the softening of the plate. And then shorten the battery life.
If the temperature is too low, the discharge capacity of lithium ion power battery will decrease. Because the ionic conductivity of the electrolyte decreases will cause a rapid increase in the internal resistance of the battery and then result in poor output performance.For lithium Ion battery, the rang from 0 to 40 ℃ is optimum.
Don’t charge your battery when energy level is very low
For lithium battery, the most healthy state is 20-80% electric quantity. Take the analogy of eating, that is, it is better for people to eat less for every meal and increase times. Keep stomach not empty and not full is the most healthy way.
Don’t leave the battery idle for a long time
In the process of storage, batteries will naturally discharge and excessively discharge finally. So long periods of use can lead to a permanent decline in battery capacity. We need to charge the battery for a period of time while it is idle. It will protect the battery efficiently.
Prevent the battery pack from bumping and deep water
Although there will be explosion-proof and water-proof tests before the battery leaves the factory, it is also necessary to avoid damage to the battery by external factors as far as possible.
That’s all about how to estimate your lithium battery life span. Now, are you clear about how to cycle life? If you are interested in batteries, you can leave a message about your doubts.
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Thank you very much for the article, very explanatory and interesting.
One question, how can I estimate the battery life of a UPS? considering that it is connected to the load most of the time and only activates when there is a power outage.