Cycle life

Cycle count alone has no complete meaning; rate, temperature, SOC window, rest, cutoffs, and retention definition are required. If protocol changes, reported life may not be directly comparable even when the cell is unchanged.

Capacity loss and impedance rise can arise from side reactions, active-material change, contact loss, sodium-inventory imbalance, manufacturing defect, or thermal stress. Diagnosis should combine electrochemistry, teardown, controls, and production traceability rather than infer one root cause from one symptom.

Storage dispatch, start-stop pulses, and telecom backup differ in temperature, depth of discharge, rest, and power requirements. Application-life assessment should use representative duty cycles and include maintenance, BMS control, and system thermal conditions.