What is Self-Discharge? Self-Discharge Definition & Impact for Lithium Batteries

One-Sentence Definition

Self-discharge is the natural loss of stored charge in a battery over time—when it is not connected to a device—caused by internal chemical or physical processes.

Detailed Explanation: Mechanisms in Lithium Batteries

Every rechargeable battery gradually loses its stored energy even while not in use, but lithium-ion (Li-ion) and lithium-polymer batteries have significantly lower self-discharge rates than other chemistries. In these lithium-based batteries, self-discharge results primarily from:

• Irreversible chemical reactions: Residual activity between electrodes and the electrolyte continues even at rest.
• SEI (Solid Electrolyte Interphase) layer defects or aging: If this critical film covering the anode is imperfect or degrades, unwanted reactions persist, consuming stored energy.
• Electrochemical impurities: Tiny amounts of metal (like iron) or assembly materials can accelerate self-discharge by causing micro-shorts or shuttle reactions.
• Temperature and cell aging: Higher temperature and prolonged storage amplify these reactions, increasing energy loss (source).

Typical lithium battery self-discharge rate: About 1–3% per month at room temperature, much less than NiMH (up to 30%) or lead-acid (4–6%) batteries.

Key Influencing Factors

• State of Charge (SOC): Full charge accelerates self-discharge; moderate SOC is best for storage.
• Cell purity and assembly quality: High-purity materials and precise manufacturing reduce internal loss.
• Environmental conditions: Elevated temperatures or humidity worsen internal reactions.
• Battery age or manufacturing defects: Both can escalate self-discharge unpredictably.

Practical Applications & Impact

Why is self-discharge important?

• Shelf life and readiness: Batteries stored as backup or for shipping (e.g., in industrial UPS, medical devices, solar power packs, or consumer electronics) must retain most of their charge without frequent recharging.
• Predictable reliability: Excessive self-discharge leads to shorter usable life and unpredictable device failure.
• Best practices: Store lithium batteries in cool, dry areas at 30–50% charge, use high-quality batteries, and rely on battery management systems (BMS) to monitor and balance cells (detailed guide).

Comparative Chart: Self-Discharge Rates by Battery Type

Li-ion’s lower rate is a key factor in its adoption for high-reliability electronics and industrial storage applications.

Related Terms & Concepts

• Capacity Retention: The ability of a battery to preserve its original charge and performance over time, directly impacted by self-discharge.
• BMS (Battery Management System): Electronics that monitor cell health, SOC, and can help detect abnormal self-discharge to prevent premature battery wear.
• Calendar Aging: The gradual decline in battery performance due to chemical changes over time, whether or not cycles are performed. Different from self-discharge, though both reduce available energy over time.
• Internal Resistance: An increase can signal aging or defects that also contribute to higher self-discharge.

For more on lithium battery performance and best practices, see Battery University: Self-Discharge.