Lithium-ion batteries have revolutionized modern technology, powering everything from smartphones to electric vehicles. While they are highly efficient, their lifespan is limited by various factors that cause degradation over time. Understanding the causes of lithium-ion battery failure can help improve battery management and extend its lifespan. Below, we examine the critical reasons behind lithium-ion battery degradation.

1. Solid Electrolyte Interphase (SEI) Formation

One of the primary contributors to lithium-ion battery degradation is the formation of the Solid Electrolyte Interphase (SEI) layer. This layer forms naturally on the anode surface during the first few charge cycles as a result of electrolyte decomposition.

• Impact on Battery Performance: While the SEI is crucial for stabilizing the battery, it consumes lithium ions in the process, reducing the number of active ions available for energy transfer. Over time, the SEI layer continues to grow with each cycle, increasing internal resistance and reducing the battery’s overall capacity.
• Long-Term Effect: As the SEI thickens, it restricts the movement of lithium ions, further diminishing the battery’s ability to hold a charge. This is a key reason behind the gradual decline in battery performance with age.

2. Lithium Plating

Lithium plating occurs when lithium ions deposit as metallic lithium on the surface of the anode instead of being inserted into the anode material. This can occur under specific conditions, particularly during high-rate charging or when charging at low temperatures.

• Formation of Dendrites: Lithium plating can lead to the formation of dendrites, needle-like structures that grow on the anode surface. Dendrites can pierce through the separator between the anode and cathode, causing internal short circuits. This not only reduces the available lithium for cycling but also poses significant safety risks.
• Consequences: Lithium plating results in reduced capacity and efficiency, as some lithium becomes unavailable for charge storage. Over time, repeated plating and stripping can cause permanent damage to the battery.

3. Mechanical Stress

Lithium-ion batteries experience mechanical stress due to the physical expansion and contraction of materials during charging and discharging. This repeated cycling causes structural changes within the battery, particularly in the electrodes and electrolyte.

• Electrode Degradation: The electrodes can develop cracks or become disconnected from the conductive matrix, reducing the overall contact area for electron flow. This leads to reduced battery efficiency and capacity fade.
• Electrolyte Breakdown: Mechanical stress can also cause the electrolyte to break down, reducing its ability to transport lithium ions effectively. Over time, this impairs the battery’s overall performance and shortens its lifespan.

4. Temperature Effects

Temperature plays a significant role in lithium-ion battery degradation. Both high and low temperatures can have detrimental effects on battery health, with high temperatures being particularly damaging.

• High Temperatures: When a lithium-ion battery operates at elevated temperatures, it accelerates the thermal decomposition of the electrodes and electrolyte. High temperatures also promote SEI growth, increasing internal resistance and leading to faster capacity loss. Additionally, unwanted chemical reactions may occur, further degrading the active materials within the battery.
• Low Temperatures: Extremely low temperatures can hinder the mobility of lithium ions, making it more difficult for the battery to perform optimally. Charging at low temperatures increases the likelihood of lithium plating, which can permanently damage the battery.

5. Overcharging and Over-Discharging

Improper charging practices, such as overcharging and over-discharging, can significantly accelerate the degradation of lithium-ion batteries.

• Overcharging: When a battery is charged beyond its recommended voltage limit, it can cause excessive lithium plating and thermal stress. Over time, this depletes the battery’s capacity and increases the risk of safety failures.
• Over-Discharging: Discharging a battery below its safe voltage limit can cause irreversible damage to the electrodes, particularly the anode. This reduces the battery’s ability to recharge and retain energy, leading to premature failure.

6. Calendar Aging

Lithium-ion batteries degrade even when they are not actively in use, a phenomenon known as calendar aging. This degradation occurs due to ongoing chemical reactions between the electrolyte and electrodes, influenced by factors such as storage temperature and state of charge.

• Impact of Time: Calendar aging causes a gradual loss of capacity over time, regardless of the number of charge cycles. Batteries stored at high temperatures or at full charge tend to degrade faster, as these conditions accelerate unwanted chemical reactions within the battery.
• Storage Conditions: To minimize calendar aging, it is recommended to store lithium-ion batteries at cool temperatures and at partial charge (around 50%). Proper storage can slow down the degradation process and extend the battery’s usable life.

7. Electrolyte Decomposition

The electrolyte in a lithium-ion battery is responsible for conducting lithium ions between the anode and cathode. However, over time, the electrolyte can decompose, leading to the formation of gases and unwanted chemical compounds.

• Gas Formation: The decomposition of the electrolyte generates gases, which can cause swelling of the battery and increase internal pressure. This not only reduces the efficiency of ion movement but also poses a potential safety hazard, particularly in sealed battery packs.
• Capacity Loss: As the electrolyte degrades, it becomes less effective at conducting ions, resulting in higher internal resistance and reduced battery capacity. The gradual breakdown of the electrolyte is one of the key factors that contribute to the overall aging of lithium-ion batteries.

8. Manufacturing Variations

Not all lithium-ion batteries are created equal. Variability in manufacturing processes can lead to inconsistencies in battery performance and longevity.

• Material Impurities: Small impurities in the battery materials can accelerate degradation by introducing unwanted chemical reactions or increasing internal resistance. Even slight variations in the quality of materials can result in a significant difference in battery lifespan.
• Assembly Variations: Inconsistent manufacturing techniques can lead to poorly assembled cells, which may have weaker connections or suffer from premature capacity loss. Ensuring strict quality control during the production process is crucial for creating long-lasting lithium-ion batteries.

Conclusion

Lithium-ion batteries degrade due to a combination of chemical and physical processes that occur over time. Factors such as SEI formation, lithium plating, mechanical stress, temperature effects, and improper charging practices all contribute to their eventual failure. While some degree of degradation is inevitable, proper battery management, including avoiding extreme temperatures, preventing overcharging or over-discharging, and storing batteries in optimal conditions, can help extend their useful life. Understanding the causes of degradation is essential for maximizing battery performance and ensuring the longevity of lithium-ion-powered devices.