What Factors Affect the Lifespan Degradation of Power Batteries?

During long-term cyclic use, the capacity of electric vehicle power batteries inevitably degrades, affecting the driving range and lifespan of the electric vehicle. The mechanism of battery degradation is very complex, involving multiple aspects such as electrochemistry, thermodynamics, mechanics, and environment. This article will conduct an in-depth analysis of the degradation mechanism of electric vehicle power batteries, providing a foundation for the establishment of battery life prediction models.

1. Electrochemical Reactions are one of the main mechanisms of battery degradation.

During charging and discharging, a series of complex electrochemical reactions occur inside the battery. These reactions include:

(1) Charge-discharge reaction of active materials: The active materials at the positive and negative electrodes of the battery undergo reversible redox reactions during charging and discharging, generating or consuming electrical energy.

(2) Electrolyte decomposition reaction: The electrolyte decomposes under high voltage or high temperature, producing gases, acids, or other byproducts. These byproducts corrode battery materials, leading to a decline in battery performance.

(3) Lithium and Hydrogen Evolution Reactions: Under overcharge or over-discharge conditions, lithium or hydrogen evolution reactions may occur on the battery electrodes, producing metallic lithium or hydrogen gas. These reactions damage the electrode structure, leading to battery capacity decay and safety hazards.

2. Thermodynamic Effects

The charging and discharging process of a battery generates heat, affecting the internal temperature distribution of the battery. High temperatures accelerate electrochemical reactions and material degradation, leading to battery degradation. Specifically:

(1) High temperatures accelerate the dissolution and migration of active materials, resulting in decreased electrode material activity and capacity decay.

(2) High temperatures promote electrolyte decomposition, producing corrosive substances that damage battery materials.

(3) High temperatures also soften the battery separator, reducing its puncture resistance and increasing the risk of short circuits.

3. Mechanical Stress

During charging and discharging, the battery undergoes volume expansion and contraction, generating mechanical stress. These stresses damage battery materials and accelerate battery degradation. Specifically:

(1) Electrode materials undergo volume changes during charging and discharging, leading to electrode structure deformation, cracks, or peeling.

(2) The battery separator has limited mechanical strength and may rupture during repeated charging and discharging, causing a short circuit.

(3) The battery casing deforms under external forces, affecting the stability of the battery's internal structure.

4. Other Factors

Besides the main mechanisms mentioned above, other factors also affect battery degradation, including:

(1) Battery Type: Different types of batteries have different degradation characteristics. For example, lithium-ion batteries degrade more slowly than lead-acid batteries.

(2) Manufacturing Process: The battery manufacturing process has a significant impact on battery life.

(3) Battery Management System (BMS): The BMS can extend battery life by controlling the charging and discharging process.

(4) Usage Habits: Battery usage habits, such as depth of charge/discharge, charge/discharge rate, and charging voltage, also affect battery degradation.

In summary, the degradation mechanism of electric vehicle power batteries is very complex, involving multiple aspects such as electrochemical reactions, thermodynamic effects, mechanical stress, and environmental factors. A deep understanding of the battery degradation mechanism is the foundation for establishing accurate battery life prediction models.