Lithium battery voltage consistency: Why has it become the "fatal shortcoming" of power batteries?

With the booming development of new energy vehicles and energy storage power stations, the performance of lithium batteries directly affects the reliability of the entire system. The voltage consistency hidden behind it is the core factor that determines the life and safety of lithium battery packs.



1. Voltage inconsistency: the "barrel effect" of lithium batteries
A group of lithium batteries is like a football team. If the players are in uneven condition, even if the star player is strong, it is difficult for the team to win the championship. ​The manifestations of poor voltage consistency include:
​Capacity waste: The highest voltage cell triggers protection in advance, resulting in the actual capacity of the entire group of lithium batteries being only 60%-70% of the lowest cell;
Life loss: Batteries with a difference of more than 5% age three times faster within half a year;
​Thermal runaway risk: When a battery voltage is abnormal, it may trigger a chain reaction. This is the cause of a fire accident in a certain brand of electric vehicles in 2021.
Data show that for every 10% increase in the consistency of a lithium battery pack, its cycle life can be extended by more than 200 times.

2. Three major culprits: Who is destroying voltage consistency?
​Congenital defects:
The capacity error of the same batch of lithium batteries may be as high as ±5%, and the internal resistance fluctuation exceeds 10mΩ;
Uneven coating of the pole piece leads to differences in the distribution of active materials. CATL has recalled millions of defective batteries for this reason.
Bad habits of use:
Under high temperature environment (>45℃), the aging speed of lithium batteries increases by 3 times;
Frequent fast charging increases the voltage fluctuation by 5 times, accelerating the accumulation of monomer differences.
Management loopholes:
The traditional BMS system can only monitor 5% of abnormal parameters. Huawei's latest Fusion Battery system has improved the detection accuracy to 0.1mV level;
Due to defects in the BMS algorithm, the consistency of the lithium battery pack of a certain brand of electric vehicles has deteriorated by 40% in three years.

3. How to improve voltage consistency?
Optimize the process: strictly control the quality of raw materials, optimize the production process parameters, improve the level of production automation, and reduce the differences between single cells from the source.
Strict screening: Before assembling the battery pack, strictly screen and match the single cells, and select batteries with similar parameters such as voltage, internal resistance, and capacity, just like selecting players with similar abilities when forming a team.
Optimize the design: adopt a reasonable battery pack structure and connection method, optimize the heat dissipation design, and reduce the differences between single cells, just like formulating a reasonable training plan and tactics for the team.
Intelligent management: Use the battery management system (BMS) to monitor and manage the battery pack in real time, and actively adjust the voltage of the single cell through technical means such as balanced control, just like the coach adjusts the training intensity and tactics according to the status of the players.