Analysis of factors affecting the service life of lithium battery

For energy-type lithium batteries, the service life is generally terminated when the available capacity of lithium batteries decays to 80% of the initial capacity. Its life includes cycle life and calendar life. The former refers to the number of cycles of lithium battery from a certain charging and discharging system to the end of its life, and the latter refers to the time required for lithium battery to be stored in a certain state until the end of its life.

1. Aging and decline of lithium battery materials

The materials inside the lithium battery mainly include: positive and negative active substances, adhesives, conductive agents, fluid collectors, separators and electrolyte. During the use of lithium batteries, these materials will be accompanied by a certain degree of deterioration and aging.

2. Charging and discharging system

A comprehensive comparison of several common charging methods is made, and it is found that the constant current charging causes gas evolution inside the lithium battery and damages the lithium battery due to excessive current in the later stage; However, the current of constant voltage charging is too large at the initial stage of charging, which directly damages the lithium battery; Constant current and constant voltage charging and step constant current charging overcome the shortcomings of constant current charging and constant voltage charging, and have the least damage to lithium batteries, which are currently the most widely used.

3. Temperature

Different types of lithium batteries have different environmental temperature requirements. Too high or too low temperature will directly or indirectly affect the service life of lithium batteries. Take the 18650 type lithium iron phosphate battery as an example, the capacity of lithium battery decays slowly at normal temperature, while at 55 ℃ or higher temperature, lithium battery will show some failure behavior.

4. Monomer consistency

Lithium battery modules generally connect several single lithium batteries in series or in parallel. According to the research, the life of lithium battery pack is always shorter than the life of the single lithium battery with the shortest life. The life of the single lithium battery with a life of 1000 times is less than 200 times after being grouped. Before the lithium battery is actually applied in groups, it will go through the screening and matching process to eliminate the single cells with large differences in performance parameters, so as to minimize the impact of the differences in the lithium battery manufacturing process on the use performance.

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