Lithium-ion batteries can degrade due to various operational stress factors. These factors include high temperatures, overcharging, over discharging, high current, mechanical stress, and more.
Temperature:
High temperatures accelerate chemical reactions in the battery, leading to increased rates of degradation (thermal aging). This can cause substantial capacity loss and increase internal resistance.
Overcharging/Over-discharging:
The structure of the active materials in the battery can change, resulting in capacity loss.
High Current:
Result in elevated temperatures and increased rates of parasitic reactions. This leads to faster degradation of the battery’s active material and an increase in its internal resistance.
Mechanical Stress:
Physical stresses, such as vibrations or shocks, can lead to mechanical failure within the cell structure, damaging the delicate electrode and separator layers, causing internal short circuits.
Aging Mechanisms:
Solid Electrolyte Interface (SEI) Layer Formation:
Overcharging, over-discharging, and high temperatures lead to unwanted side reactions, resulting in the formation of a solid electrolyte interface (SEI) layer on the electrode surface. This layer reduces the battery's capacity and increases internal resistance.
Lithium Plating:
High charging rates at low temperatures can result in lithium plating, a phenomenon where metallic lithium deposits on the anode, leading to reduced battery capacity and an increased risk of internal short circuits.
Electrode Material Degradation:
The structure of the active materials within the battery alters, leading to reduced capacity due to excessive charging/discharging/ high temperature.
Gas Generation:
The decomposition of the electrolyte caused by excessive charging, discharging, and high temperatures can result in the generation of gases, which can cause swelling and reduce the battery's lifespan.
Aging Mode: Two primary modes:
Cyclic Aging:
Degradation caused by charging and discharging cycles. High current and overcharging/over-discharging are operational stress factors that accelerate cyclic aging.
Calendar Aging:
Degradation occurring over time, regardless of usage. High temperatures are an operational stress factor that accelerates calendar aging.
Effect on Battery Aging:
Capacity Fade:
Decrease in the amount of charge a battery can hold.
Power Fade:
Reduction in the battery's ability to deliver power, often measured as an increase in internal resistance.