Meaning
Energy storage systems undergo progressive capacity loss and resistance rise due to parasitic chemical reactions and mechanical stresses within the electrodes. The phenomenon of lithium ion cell degradation occurs as active material is isolated and lithium inventory is consumed during cycling. This process presents as a gradual decline in the usable energy of the battery pack and a reduction in power capability.
Understanding these degradation pathways is critical for predicting the operational life of the energy storage system. Sourcing decisions rely on these metrics to select cell chemistries that withstand specific operational profiles.
Physical Mechanism
Solid electrolyte interphase growth occurs continuously on the anode surface, trapping active lithium ions and consuming electrolyte solvent. At the same time, mechanical strain from repeated volume changes causes micro-cracking of the electrode particles. These cracks expose fresh graphite to the electrolyte, accelerating the consumption of lithium.
Over time, these combined processes lead to lithium plating and rapid cell failure.
Measurement Technique
Electrochemical impedance spectroscopy tracks the evolution of internal resistance by measuring the cell response across a range of frequencies. Incremental capacity analysis monitors the peaks in the differential capacity curve to identify specific degradation modes, such as the loss of active material or the depletion of the lithium inventory.
Commercial Impact
Warranty planning utilizes these degradation rates to estimate the lifetime cost of energy storage installations. Cells with lower degradation rates command higher prices because they reduce the frequency of system replacements.
