Rechargeable batteries eventually die due to several factors that contribute to their degradation over time. Understanding these factors can help users maximize battery lifespan and performance.
1. Chemical Reactions and Degradation Mechanisms
- Loss of Lithium Inventory (LLI): In lithium-ion batteries, some lithium ions become trapped in the battery’s structure through side reactions with the electrolyte, reducing the number of available ions for charging and discharging. This loss diminishes the battery’s capacity over time.
- Solid Electrolyte Interphase (SEI) Formation: The SEI layer forms on the anode during the first charge cycle, which is essential for battery function. However, as cycling continues, this layer can degrade, leading to increased internal resistance and reduced capacity.
2. Cycling and Calendar Aging
- Cycle Aging: Each charge and discharge cycle contributes to battery wear. Repeated cycling causes structural changes in the electrodes, leading to mechanical stress and degradation of materials.
- Calendar Aging: Even when not in use, batteries degrade over time due to chemical reactions occurring within them. Keeping a battery at a high state of charge (SOC) can accelerate this process.
3. Temperature Effects
- High Temperatures: Elevated temperatures can cause the electrolyte to break down and increase the rate of unwanted chemical reactions, significantly shortening battery life.
- Low Temperatures: At low temperatures, ion movement slows down, increasing internal resistance and reducing performance during discharge cycles.
4. Overcharging and Deep Discharging
- Overcharging: Attempting to charge a battery beyond its capacity can lead to overheating and potential failure. While modern batteries often have built-in protections against overcharging, prolonged exposure can still damage them.
- Deep Discharging: Allowing a battery to discharge too deeply can cause irreversible damage, particularly in lead-acid batteries. For lithium-ion batteries, deep discharges can lead to lithium plating on the anode, further reducing capacity.
5. Self-Discharge
All batteries experience self-discharge due to internal chemical reactions, even when not connected to a load. This phenomenon leads to gradual capacity loss over time.
Conclusion
Rechargeable batteries degrade due to a combination of chemical reactions, cycling effects, temperature influences, and improper charging practices. By understanding these factors, users can take steps to mitigate degradation—such as avoiding extreme temperatures, using appropriate chargers, and maintaining optimal charge levels—ultimately extending the lifespan of their rechargeable batteries.
