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Views: 0 Author: Site Editor Publish Time: 2026-01-13 Origin: Site
Lithium batteries are widely used in consumer electronics, electric vehicles, and energy storage systems due to their high energy density and long cycle life. However, their performance and safety are highly dependent on proper charging and discharging conditions. Among the most critical factors are overcharging and over-discharging, both of which can cause irreversible damage. This article explains what overcharge and over-discharge are, how they affect lithium batteries, and why proper control is essential.
Overcharging occurs when a lithium battery is charged beyond its designed upper voltage limit. For most lithium-ion batteries, this limit is around 4.2 V per cell, although it may vary slightly depending on the chemistry.
When a battery is overcharged, excess lithium ions can no longer be safely stored in the anode structure. This leads to side reactions inside the cell, including electrolyte decomposition and increased internal pressure. As a result, the battery experiences accelerated degradation and higher safety risk.
Capacity degradation
Overcharging damages the internal structure of both the cathode and anode, reducing the battery’s ability to store energy. Even a small number of overcharge events can cause permanent capacity loss.
Increased internal resistance
Chemical side reactions caused by overcharging increase internal resistance, leading to greater heat generation during normal operation and reduced efficiency.
Thermal runaway risk
Severe overcharging can trigger thermal runaway, a chain reaction that causes rapid temperature rise, gas generation, fire, or even explosion. This is one of the most serious safety hazards associated with lithium batteries.
Over-discharging occurs when a lithium battery is discharged below its lower voltage limit, typically around 2.5–3.0 V per cell, depending on the chemistry and manufacturer specifications.
At very low voltage, the battery can no longer maintain stable electrochemical reactions. This condition can cause copper dissolution from the current collector and damage to the anode structure.
Permanent capacity loss
Over-discharge leads to irreversible chemical changes that reduce usable capacity, even after the battery is recharged.
Internal short-circuit risk
When copper dissolves and redeposits inside the cell, it can form conductive paths that increase the risk of internal short circuits.
Reduced cycle life
Repeated over-discharge significantly shortens overall battery lifespan, causing early failure compared with properly managed batteries.
Both overcharging and over-discharging accelerate aging mechanisms within lithium batteries. They increase stress on electrode materials, degrade the electrolyte, and compromise structural stability. As a result, the battery shows reduced runtime, unstable voltage output, and shortened cycle life.
Even if a battery does not fail immediately, repeated exposure to improper voltage limits can dramatically reduce its long-term performance.
To prevent overcharging and over-discharging, most lithium battery packs are equipped with a Battery Management System (BMS). The BMS monitors cell voltage, current, and temperature, and disconnects the battery when safe limits are exceeded.
In single-cell applications, protection circuits serve a similar function. These systems are essential for ensuring safety, reliability, and long service life.
Overcharging and over-discharging have a significant and often irreversible impact on lithium batteries. They not only reduce capacity and lifespan but also increase safety risks. Proper charging equipment, correct usage habits, and effective protection systems are crucial for maintaining lithium battery performance and safety. By operating lithium batteries within their recommended voltage range, users can maximize both longevity and reliability.
