Lithium-ion batteries self-discharge due to several reasons including internal chemical reactions, electrode impurities, and micro-leakage currents. These processes are often exacerbated by higher temperatures, which accelerate chemical degradation. Also, the physical and chemical condition of the battery, such as age, manufacturing defects, and the composition of the electrolyte, also influence the rate of charge loss. Even when not in use, these batteries gradually lose charge, impacting their efficiency and overall lifespan. This self-discharge is a natural outcome of the battery's internal dynamics and environmental interactions.

What is Self Discharge

Self-discharge is when a battery loses its charge over time, even when not in use. Lithium-ion batteries, like all rechargeable batteries, experience self-discharge, even when the battery is not connected to a device or under any load. This rate of self-discharge varies between different types of battery chemistries for example lithium ion batteries have a lower rate of self-discharge compared to disposable alkaline batteries. 

This phenomenon can affect the performance and lifespan of the battery. Here are the main reasons why lithium-ion batteries self-discharge:

Self Discharge Due to Internal Chemical Reactions

Lithium-ion batteries are made up of electrodes and an electrolyte that enables the flow of current. Over time, totally random, spontaneous chemical reactions can happen within the battery’s internal structure, even when the battery isn't being used. These reactions include the decomposition of the electrolyte and interactions between the electrodes and electrolyte, which generate internal currents that dissipate stored charge.

Electrode Impurities

Another issue is impurities within the electrodes can lead to unwanted chemical reactions that cause self-discharge. For instance, transition metal impurities in the cathode material can catalyze reactions with the electrolyte, leading to a slow but continuous degradation of the battery’s charge capacity.

Micro-Leakage Currents

Imperfect insulation and minute imperfections in the battery construction can allow small "leakage" currents to flow between the electrodes. These micro-leakage currents are essentially internal circuits that slowly drain the battery’s charge.

Temperature Effects

Temperature plays a significant role in the rate of self-discharge. Higher temperatures accelerate the chemical reactions within the battery, thus increasing the rate of self-discharge. This is why storing batteries in a cool place is recommended to slow down the loss of charge. You can also check our other articles for the best voltage to store lithium batteries for tips to reduce self-discharge. 

Parasitic Reactions at the Electrode Interfaces

Parasitic reactions, such as the formation of solid-electrolyte interphases (SEIs) on the electrodes, also contribute to self-discharge. The SEI layer is mostly beneficial as it stabilizes the electrode materials, but its formation and any ongoing reactions involving this layer can consume a part of the battery’s charge.

Age and Condition of the Battery

Older batteries tend to self-discharge faster than newer ones due to the degradation of the electrodes and the accumulation of internal structural defects over time. Wear and tear from regular use can exacerbate self-discharge rates.

Manufacturing Defects and Damage

Defects introduced during the manufacturing process (such as tiny metal particles that can cause internal short circuits) or physical damage to the battery (like punctures or tears in the separator between the electrodes) can significantly increase the rate of self-discharge.

State of Charge

The initial state of charge of a battery, when it begins storage, can influence self-discharge dynamics. A fully charged battery might experience faster self-discharge than one at a 50% state of charge, due to more intense activity at the electrodes.

Electrolyte Composition

Different formulations of the electrolyte can have varying resistance to chemical breakdown and may influence the rate of self-discharge. Electrolytes that are less stable chemically will likely contribute to higher self-discharge rates.

Self-discharge in lithium-ion batteries is influenced by a complex interplay of chemical, thermal, and physical factors. Understanding these can help in optimizing battery usage, maintenance, and storage conditions to minimize power loss over time and extend the battery's useful life. 

We hope this article answers all your questions regarding lithium ion self-discharge. Thanks for reading!