State-of-Charge Monitoring and Battery Diagnosis of NiCd Cells Using Impedance Spectroscopy

Peter Kurzweil,Wolfgang Scheuerpflug

doi:10.3390/batteries6010004

Peter Kurzweil, Wolfgang Scheuerpflug

Open Access

https://doi.org/10.3390/batteries6010004

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Abstract

With respect to aeronautical applications, the state-of-charge (SOC) and state-of-health (SOH) of rechargeable nickel–cadmium batteries was investigated with the help of the frequency-dependent reactance Im Z(ω) and the pseudo-capacitance C(ω) in the frequency range between 1 kHz and 0.1 Hz. The method of SOC monitoring using impedance spectroscopy is evaluated with the example of 1.5-year long-term measurements of commercial devices. A linear correlation between voltage and capacitance is observed as long as overcharge and deep discharge are avoided. Pseudo-charge Q(ω) = C(ω)⋅U at 1 Hz with respect to the rated capacity is proposed as a reliable SOH indicator for rapid measurements. The benefit of different evaluation methods and diagram types for impedance data is outlined.

Highlights

Emergency power supplies in aircrafts require high reliability
Based on preliminary work on SOC determination by impedance spectroscopy [1,2,3,4,5,6,7], we studied new and aged batteries
Since the frequency response depends on the cell chemistry, we focused on nickel–cadmium batteries [8,9,10] in this work

Summary

Introduction

Emergency power supplies in aircrafts require high reliability. After parking for a longer period of time without electric supply, the state-of-charge (SOC) of airplane batteries drops by self-discharge.Scheduled take-offs may be delayed by this. Emergency power supplies in aircrafts require high reliability. After parking for a longer period of time without electric supply, the state-of-charge (SOC) of airplane batteries drops by self-discharge. Scheduled take-offs may be delayed by this. According to the state-of-the-art, the complete procedure of capacity determination lasts several hours. Freshly charged batteries must be held in stock. With respect to more extended maintenance intervals, a reliable method for fast battery diagnosis is required, which reflects at least the upper SOC range

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Conclusion