The development of lithium batteries is becoming more and more rapid, because lithium batteries have good battery life and high safety, and their advantages have become more and more prominent in the new energy vehicle market. But lithium batteries are electricity after all, and under certain circumstances, they are still harmful. So in order to avoid some problems about lithium batteries, today I will introduce you to the harm of lithium battery inconsistency and how to deal with it.
The inconsistency of battery core performance is formed during the production process and deepened during use. The batteries in the same battery pack are always weak for the weak, and become weaker at an accelerated rate. The degree of dispersion of the parameters between the single cells increases as the degree of aging deepens.
Why are most lithium batteries small
Lithium batteries, cylindrical batteries, soft-pack batteries, and square batteries we see are generally beautiful in appearance. We can’t find a big man like traditional lead-acid batteries. Why? Because of the high energy density, lithium batteries are often afraid to design large capacity. First of all, it is very dangerous that the lithium battery that can only be used for excessively high doses encounters an accident and causes thermal runaway. The internal battery reacts sharply. In a short time, too much energy is nowhere to be released, which is very dangerous. Especially when the development of safety technology and management and control capabilities is not sufficient, the capacity of each battery should be restrained. Secondly, once an accident occurs, the energy wrapped in the lithium battery shell will be inaccessible and powerless by firefighters and extinguishing agents. They can only isolate the scene in the event of an accident and allow the accident battery to react by itself until the energy is exhausted.
Lithium battery consistency problem
Lithium batteries can’t be made into a large battery, so many small batteries have to be organized. Everyone can work hard and cooperate with each other to fly with electric cars. At this time, you need to face a problem, consistency. Our daily experience is that if the positive and negative poles of two dry batteries are connected, the flashlight can emit light. Who cares about the same and inconsistent things. The large-scale application of lithium batteries is not so simple. The inconsistency of lithium battery parameters mainly refers to the inconsistency of capacity, internal resistance, and open circuit voltage. If inconsistent batteries are used in series, the following problems will occur.
Capacity loss
The battery cells are composed of single cells, and the capacity is in accordance with the “barrel principle”. The capacity of the worst cell determines the capacity of the entire battery pack.
Life loss
Similarly, the life of the battery pack is determined by the cell with the shortest life. It is very likely that the cell with the shortest life span is the cell with a small capacity. Small-capacity batteries are fully charged and discharged every time, and the output is too strong, which is likely to reach the focus of life first. The life of the battery cell has ended, and a group of battery cells welded together will die.
Increased internal resistance
Different internal resistances flow the same current, and batteries with large internal resistances will generate more heat. The battery temperature is too high, causing the deterioration rate to accelerate, and the internal resistance will further increase. Internal resistance and temperature rise form a pair of negative feedback, which accelerates the deterioration of high internal resistance cells. The above three parameters are not completely independent. The internal resistance of the battery with a deep aging degree is larger, and the capacity attenuation is also more. Separate explanations, just to express clearly their respective directions of influence.
How to deal with inconsistencies
The inconsistency of battery core performance is formed during the production process and deepened during use. The batteries in the same battery pack are always weak for the weak, and become weaker at an accelerated rate. The degree of dispersion of the parameters between the single cells increases as the degree of aging deepens. Currently, engineers mainly consider three aspects to deal with the inconsistency of single cells. Single battery sorting, thermal management after grouping, the battery management system provides equalization function when a small amount of inconsistency occurs.
https://www.hrl-battery.com/lithium-battery-pack/
Post time: Dec-16-2020
