Meaning
Decomposition or disruption of the protective passivation film on the anode surface of a lithium-ion cell constitutes a primary driver of capacity loss and resistance growth. Researchers and battery material scientists analyze sei layer degradation to understand how the protective interface of the anode fails under continuous cycling and high temperatures. When the passivation layer breaks down, the graphite anode is exposed to the liquid electrolyte, initiating further reactions that consume active lithium.
This degradation cycle is a major factor in the lifetime limits of lithium-ion batteries.
Chemical Decomposition
Operating conditions such as high charge rates and elevated temperatures accelerate the breakdown of the protective film. Sourcing engineers seek electrolyte additives that can stabilize the anode interface and mitigate sei layer degradation. Additives such as vinylene carbonate or fluoroethylene carbonate help form a more robust passivation layer that resists chemical decomposition.
This optimization is critical for cells intended for fast-charging applications.
Capacity Loss
Continuous repair of a broken passivation layer requires the consumption of active lithium ions from the cathode material. This consumption permanently reduces the quantity of cyclable lithium available within the cell, leading to a steady decrease in the capacity of the cell. Tracking sei layer degradation reveals the rate at which this active lithium is lost over thousands of cycles.
This analysis helps engineers refine their lifetime prediction models for energy storage systems. Additionally, the formation of decomposition byproducts can block the pores of the separator, which limits ion transport and further reduces the high-rate capacity of the cell under cold-temperature conditions.
Impedance Growth
Growth of the passivation layer over time increases the resistance that lithium ions encounter as they migrate to the anode. This resistance rise causes a larger voltage drop during discharge and accelerates the onset of lithium plating during charging. By analyzing the resistance growth associated with sei layer degradation, designers can select anodes with surface coatings that prevent the growth from becoming excessive.
This design choice maintains high power delivery throughout the lifetime of the cell.
