Meaning
Capacity loss describes the permanent reduction in the energy storage capability of a battery during its operational life. Engineers quantify energy density degradation as the decrease in watt-hours per kilogram or watt-hours per liter over thousands of cycles. This process determines the useful life of a battery in mobile applications.
Capacity Fade
Loss of mobile lithium ions through side reactions at the electrode surface reduces the total charge available. Such energy density degradation occurs when the electrolyte decomposes to form a passivation layer on the anode. This layer consumes active material and increases internal resistance.
Structural Change
Mechanical stress from repeated expansion and contraction of the electrode lattice leads to particle cracking. Persistent energy density degradation results from these cracks which isolate portions of the active material from the electrical circuit. These isolated regions can no longer contribute to the capacity of the cell.
Physical separation of the active material from the current collector further reduces the available energy.
Commercial Life
Vehicle range decreases as the battery storage capacity moves toward its end of life threshold. Monitoring energy density degradation allows fleet operators to predict when a battery will no longer meet the minimum distance requirements. Most industrial standards set this threshold at eighty percent of the original capacity.
