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

TL;DR

This paper demonstrates how ambient temperature data can be reanalyzed to reveal detailed cycling behavior of energy-storage devices during testing, uncovering previously unknown operational details without additional measurements.

Contribution

It introduces a novel method to extract charge/discharge cycle information from ambient temperature variations, providing new insights into device behavior during standard tests.

Findings

Revealed the number of cycles and cycle period from temperature data

Identified charge/discharge asymmetry in the device behavior

Confirmed the device completed 338 cycles without thermal degradation

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temperature signal alone -- together with some quite mild and reasonable assumptions -- allow to extract previously unpublished information on the simultaneously run test on the other cells: 1) the number of charge/discharge cycles 2) the cycle period, 3) the charge/discharge half-cycle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.