Although "Cell reversal" is less common in lithium-ion batteries compared to nickel-based batteries, it is still essential to understand its causes, consequences, and prevention methods.
Cell reversal, or polarity reversal, occurs when the voltage of an individual cell within a battery pack drops below zero volts during discharge. While lithium-ion batteries are less prone to cell reversal, it can still happen under certain circumstances, such as when cells are connected in series and become unbalanced.
Causes of Cell Reversal in Lithium-ion Batteries:
a) Unbalanced cells: Cell reversal can be caused by the presence of weaker or unbalanced cells within a lithium-ion battery pack. When a weak cell reaches its discharged state before the others, it continues to discharge, causing its voltage to drop below zero. The stronger cells in the series force the weak cell to reverse its polarity.
b) Over-discharge: Over-discharging a lithium-ion battery can lead to cell reversal. When a battery is discharged beyond its recommended limits, its voltage drops significantly, potentially causing cell reversal in the weakest cells.
c) Manufacturing defects: In some cases, manufacturing defects or poor quality control can lead to imbalanced cells within a lithium-ion battery pack. This may result in cell reversal when the battery is subjected to heavy loads or deep discharges.
d) Prolonged storage: When lithium-ion batteries are stored for extended periods without use or proper maintenance, self-discharge can cause some cells to become weaker than others. These imbalanced cells are then more susceptible to cell reversal during discharge.
Consequences of Cell Reversal in Lithium-ion Batteries:
a) Reduced battery life: When cell reversal occurs, the affected cell's capacity is permanently reduced. This weakens the overall battery pack and limits its ability to hold a charge, ultimately shortening its useful life.
b) Damage to the battery: Cell reversal can cause physical damage to the affected cell, such as a build-up of heat, internal short-circuiting, or even rupture. This damage can compromise the safety and functionality of the entire battery pack.
c) Damage to the device: In some cases, cell reversal can cause damage to the device the lithium-ion battery powers, especially if the battery's voltage drops below the minimum operating voltage required by the device.
Preventing Cell Reversal in Lithium-ion Batteries:
a) Use balanced cells
b) Proper battery management
c) Avoid over-discharging
d) Regular maintenance and inspection
e) Proper storage of batteries