Indirect monitoring of fast-charge cycling behavior of an energy-storage device-analysis of ambient temperature variations

Abstract

I present a reanalysis of temperature data from a publicly available certified laboratory report that documented the self-discharging behavior of an energy-storage device during 10 days. Graphs of temperature variations of both the tested device itself and the test chamber (fume hood) were given mainly for monitoring without further analysis, and variations in the ambient temperature signal were attributed to "other cells being cycled simultaneously in the same fume hood". I show that the ambient temperature signal alone -- together with some quite mild and reasonable assumptions -- allow to extract previously unpublished information on the simultaneously run test on the other cells: 1) the number of charge/discharge cycles 2) the cycle period, 3) the charge/discharge half-cycle asymmetry, and -- most significantly -- evidence that 4) the mentioned "other device" completed 338 full charge/discharge cycles at 3C rate at room temperature without any detectable thermal degradation signature.

Figures (8)

• Figure 1: Zoomed windows ZE (top) and ZL (bottom): raw fume-hood temperature (blue) and cubic-spline drift baseline (orange dashed).
• Figure 2: Full 254h record. Top: fume-hood temperature (blue) and contact sensor on the self-discharge cell (red); shaded bands are analysis segments OE, OI, OL; hatched regions are gap windows. Bottom: blue signal with scaled reference (red dashed) and fitted drift baselines (coloured lines) per segment.
• Figure 3: Detrended $\Delta T$ (left) and DFT amplitude spectra (right) for ZE (top) and ZL (bottom). Dashed lines mark the harmonic series $f_n = nf_1$.
• Figure 4: As Fig. \ref{['fig:fftA']} for OE (top), OI (middle), OL (bottom).
• Figure 5: Peak-to-peak interval sequence (left) and per-cycle charge / discharge durations (right) for ZE and ZL.