Capacity fade detection in lithium-ion batteries using non-linear frequency response analysis (NFRA) under multiple open-circuit voltages (OCVs)

Abstract

Determination of residual capacity, or ‘state of health’ (SOH), is important for the management of battery assets in service and when assessing batteries for re-use at the end of service. Nonlinear frequency response analysis (NFRA) has recently been demonstrated as a means to determine SOH, but the effects of temperature and state-of-charge (SOC) on battery NFRA measurements are not yet well understood. In this work, we investigate the effects of SOC on NFRA measurements performed on commercial 21700 cylindrical cells aged under different temperatures to various SOHs. Total harmonic distortion (THD%) is proposed as a capacity fade indicator. THD% in the range of 10 Hz–150 Hz are found to correlate well with SOH at all SOCs. For frequency < 1 Hz, the effect of aging on THD% is SOC dependent, with larger THDs for the new cell at low open-circuit voltages (OCVs) (2.75 V–3.2 V), and larger THDs for aged cells at higher OCVs (3.5 V–4.1 V). This work also demonstrates the feasibility of NFRA to distinguish between cells that have been aged differently based on temperature.