Is there any scientific proof that passive cell balancing can improve the life of a battery pack?

Question

Passive balancing usually works only in the charging end area, i.e. when the cells of a battery pack are almost fully charged. In the case of those cells that have already reached the end-of-charge voltage, a resistor is connected in parallel by the balancer and the voltage is thus limited to the end-of-charge voltage. In this procedure the average cell voltages in the pack would rather decline.

As far as I understand passive cell balancing in a battery pack, it can maintain the state of symmetry within the pack so that all cells maintain or regain the same state of charge. This can certainly be one reason why a well-balanced battery pack will perform better and maybe even longer than an unbalanced battery pack. In addition, since each of the cells within the pack has its own slightly different self-discharge ratio, if this is not balanced, the pack will gradually lose usable capacity, which is an important aging factor.

In the case of the BMS I actually have in mind balancing is allowed/started after rest phases (as the state of charge (SOC) can be estimated or set by open-circuit-voltage (OCV) recalibration) based on certain:

• temperature (min, max values),
• SOC (min and max values),
• and voltage conditions (min, max and delta voltage values).

For example balancing could start at 20% SOC till 90% SOC, when the spreading between the minimum und maximum cell voltage is above 15mV within a given temperature range.

My question is as follows: Can passive balancing in general or balancing as applied in this BMS improve the lifespan of a lithium-ion battery pack? (I've done some research and still do to find relevant studies but so far failed, I only found typical articles saying balancing is good for both performance and a longer age, as if the topic was self-explanatory: some studies on the topic might be much appreciated)

Or could you at least confirm or correct the above logic as I understand it?

Answer 1

Here is a step-by-step proof.

A) The lifespan of a battery is defined as the time between when it is first put in use to the moment it is no longer usable by a given application.

B) When the effective capacity of a battery is lower than required by a given application, it is no longer usable

C) The effective capacity of a battery that uses cells in series is limited by the most charged cell at the fully charged end, and by the most discharged cell at the fully discharged end

D) Due to variations in self discharge rates and Coulombic Efficiency in the various cells, the State of Charge (SoC) of each cell in a series string drifts over time, resulting in one cell being the most charged and another cell being the most discharged

E) Top balancing restores the SoC of all the cells to 100 % when the battery is fully charged, making the cell with the lowest capacity be the limiting one for both charging and discharging, and therefore raising the battery's effective capacity to be equal to the capacity of that cell.

F) Therefore, the effective capacity of a battery with series cells without balancing is less than the effective capacity of a battery with series cells with balancing

G) And, therefore, the lifetime of a battery with series cells without balancing is less than the lifetime of a battery with series cells with balancing