Each Lipo cell has an internal resistance that determines how easily current flows through it. Variations in internal resistance can cause some cells to heat up more or discharge unevenly, contributing to imbalance.
Ohmic Resistance arises from the conductive materials in the cell, such as electrodes, electrolyte, and connectors. It determines the immediate voltage drop when current flows. Reaction Resistance is related to the electrochemical processes inside the cell, such as ion transport and charge transfer at the electrodes. Together, these resistances influence how efficiently a cell can deliver and accept current.
Cells with higher internal resistance generate more heat. This localized heating can cause faster aging or degradation of the affected cells. There will also be increased thermal stress on adjacent cells, potentially creating a cascade effect.
During discharge, cells with higher resistance experience a larger voltage drop. This means that these cells may reach their cutoff voltage earlier, effectively limiting the usable capacity of the entire battery pack. Also, cells with lower resistance continue to discharge, increasing the risk of over-discharge in weaker cells. During charging, cells with higher resistance may charge more slowly, while those with lower resistance accept current more readily. Over time cells with lower resistance may overcharge, leading to overheating and possible degradation. In contrast, cells with higher resistance may undercharge, reducing the overall state of charge consistency across the pack.