Internal resistance is a measure of how much a battery resists the flow of electric current within it. There are several contributing factors: the ionic resistance of the electrolyte, the electronic resistance of the electrodes and current collectors (electrons moving through solids), contact resistances at interfaces (between active material particles, current collectors, etc.), and the charge transfer resistance at the electrode-electrolyte interfaces. A battery with lower internal resistance can deliver higher current (more power) with less voltage drop and heating. Conversely, higher internal resistance means more energy is wasted as heat, and the battery’s voltage will drop more under load. Internal resistance typically increases as a battery ages, due to factors like the buildup of insulating layers or the loss of conductive pathways.
NOVONIX measures internal resistance using both direct methods (like DCIR, applying a pulse of current and measuring the instantaneous voltage drop) and AC methods (like impedance spectroscopy at 1 kHz as a quick indicator, or full EIS across frequencies for a detailed picture). By performing internal resistance tests on new and aged cells, NOVONIX tracks how different designs degrade. With the insight gained, NOVONIX helps in developing strategies to keep resistance low, such as better conductive additives in electrodes, optimized electrolyte formulations to improve ionic conductivity and more stable, low-resistance SEI. Keeping internal resistance minimal is crucial for applications requiring high power.
