Understand the cycle life and capacity of lithium battery, and the relationship between cycle times and battery

The life cycle times of lithium batteries are determined according to the battery quality and battery materials. The cycle times of lithium batteries are closely related to the service life of batteries. Lithium battery is a kind of battery commonly used in people‘s life. Now it has many applications in electric vehicles. After a period of use, the capacity of lithium battery will be reduced, which is a shortage of lithium battery. The battery capacity will be reduced a little after completing one cycle, and the service life of the battery will also be reduced.

Understand the cycle life and capacity of lithium battery

Cycle life refers to how many times the battery can withstand charging and discharging before the battery capacity decreases to a specified value under a certain charging and discharging system. The cycle life of a lithium battery represents the number of times that the battery can be recharged and discharged before its capacity drops to a certain level. In fact, if the capacity of the battery is only 60% to 80% of the rated capacity, it means that the cycle life of the battery has ended, but the actual situation depends on the charging/discharging situation.

The capacity of lithium battery mainly refers to the amount of electric energy stored in the battery. The larger the capacity of the battery, the longer the load working time of the lithium battery is, and it is an important indicator of battery performance. The capacity marked on the battery label is far greater than the results obtained from the above national standard tests. In short, the actual capacity of the lithium battery is far from the capacity value marked on the lithium battery. Such a scalar is called a virtual standard.

What is the relationship between the number of cycles and the battery?

The cycle times refer to the time and times when the battery is used. In other words, after the battery is fully charged, the battery is replaced, then fully charged, then discharged, and then recharged repeatedly. For power batteries, a complete charging and discharging process is a cycle. According to this, all batteries have cycles.

According to the service life of the ternary lithium battery, the service life of the battery is about 1500 to 2000 cycles, and the number of cycles will decrease as the battery is used. The number of cycles decreases means that the service life of the battery is also decreasing. During the use process, the number of cycles of the battery is decreasing, It means that irreversible electrochemical reaction will occur inside the lithium battery, which will lead to the decrease of capacity.

There are many factors affecting the cycle life of lithium batteries, but the underlying reason is that the number of lithium ions involved in energy transfer is decreasing. It should be noted that the total amount of lithium elements in the battery has not decreased, but the "activated" lithium ions are less. As long as we know where these lithium ions that should have participated in the redox reaction have gone, we can understand the mechanism of capacity decline, and we can also take targeted measures to slow down the capacity decline trend of lithium batteries and improve the cycle life of lithium batteries.

How to improve the cycle life of lithium battery?

1. Lithium metal has very active performance and strong reducibility. Its density during deposition is very important. This material can reduce some contact areas between lithium metal and electrolyte, and avoid some side effects, thus promoting the growth of cycle life.

3. Lithium battery has reasonable use conditions and range, such as cut-off voltage of charge and discharge, charge and discharge ratio, operating temperature range, storage temperature range, etc. However, in actual use, abuse beyond the allowable range is very common. Long term unreasonable use will lead to irreversible chemical reaction inside the battery, damage the battery mechanism, accelerate the aging of the battery, cause rapid decline in cycle life, and even cause safety accidents in serious cases.

2. In order to make the lithium battery have stronger stability and better cycle life growth, the composition ratio of substances in the electrolyte can be improved, and the proportion of substances with stronger stability can be increased, so as to improve the density and other performance of the battery. In a word, in order to improve the cycle life of lithium batteries, it is not only necessary to improve the high concentration of ether solvent in the electrolyte, but also to improve some deposition characteristics of lithium metal itself.

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