Non Equilibrium Phase Transition Kinetics in Manganese Substituted Lithium Iron Phosphate Screenings
Fast screening of manganese substituted LFP requires separating rate polarization from permanent capacity loss to prevent improper cell grading.
SEI Layer Growth
Meaning
Passivation films accrue on the anode surface as a result of the decomposition of electrolyte components during the initial battery cycles. While the first few layers protect the electrode from further degradation, excessive SEI layer growth increases internal impedance and consumes active lithium. This phenomenon is a primary driver of capacity fade over the life of a lithium-ion cell.
Formation Requirement
Chemical reactions occur primarily during the formation charge at the manufacturing plant. Controlled SEI layer growth requires precise voltage stepping and temperature management to create a stable and thin interface. A stable film allows lithium ions to pass through while preventing solvent molecules from reaching the carbon surface.
Degradation Path
Continuous cycling or high-temperature storage can cause the layer to thicken or fracture. When the interface breaks, new electrolyte is exposed to the anode and triggers further SEI layer growth which traps more lithium ions in the solid structure. This cycle leads to a gradual rise in resistance and a decrease in the available energy density of the pack.
Additive Influence
Electrolyte additives help regulate the chemistry of the interface to minimize capacity loss. Surface analysis confirms the presence of functional groups that promote the formation of a flexible and resilient film.