Meaning
Quantitative measurement of accessible discharge capacity remaining in a secondary battery relative to its nominal or initial discharge capacity after undergoing repeated charge-discharge cycling or extended storage. Expressing retention capacity as a percentage allows engineers and procurement specialists to evaluate active material degradation and battery service life. Commercial warranties mandate minimum capacity thresholds, frequently eighty percent of initial capacity, over a specified cycle count or calendar duration.
Factors influencing capacity loss include solid electrolyte interphase growth, active lithium consumption, transition metal dissolution and electrode mechanical cracking.
Cycle Evaluation
Standardized cycle life testing records discharge capacity at periodic intervals under controlled current and temperature settings. Rapid drops in capacity indicate accelerated active material degradation within cell structures.
Degradation Mechanism
Cumulative side reactions between liquid electrolyte and electrode surfaces continuously consume cyclable lithium ions during operation. Structural phase transitions within cathode microstructures induce mechanical micro-cracking, severing electrical pathways and reducing accessible active mass. Higher operating temperatures and elevated upper cut-off voltages accelerate these degradation mechanisms, causing steep retention capacity loss over shorter operational windows.
Commercial Specification
Purchase contracts for battery energy storage systems tie financial guarantees and warranty claims directly to validated capacity metrics. Cell suppliers must provide verified cycle decay curves demonstrating that retention capacity remains above contractual thresholds under target duty cycles. Operating outside specified temperature or voltage limits voids supplier warranty obligations.
