Battery pack self-discharge standard

What is self-discharge? Battery self-discharge is caused by the internal reactions in a battery that reduce the energy stored without any connection with an external circuit. In other words, the battery loses the energy stored in it by itself due to its internal behaviour even when the connected application is not demanding any energy.

So far, the self-discharge in LIBs is comparatively the most studied device up to the pouch cell level. However, in contrast, the self-discharge studies in other rechargeable batteries are in an immature state, and more investigations are required.

For instance, rechargeable batteries take a long time to self-discharging (weeks or months, e.g., self-discharge in Li-ion battery is < 2–5 % per month), whereas the electrochemical capacitors (ECs), which store energy physically, can hold charge only for few minutes to days (0.9 % per hour).

Lithium-ion batteries, despite their high energy density, exhibit a gradual loss of charge even when not in use. This phenomenon, known as self-discharge, significantly impacts battery lifespan and performance. Understanding the underlying mechanisms of self-discharge is crucial for optimizing battery design and maximizing operational life.

Generally, high-power energy storage devices show comparatively higher self-discharge than high-energy rechargeable batteries, mainly depending upon their mode of energy storage.

The main factors that cause the self-discharge in rechargeable batteries include internal electron leakage due to electrolyte partial electronic conductivity, external electron leakage from poor battery sealing, electrolyte leakage, electrode mechanical isolation from the current collector, etc.