Direct Observation of Reversible Heat Absorption in Li-ion Battery Enabled by Ultra-Sensitive Thermometry

TL;DR

This study introduces an ultra-sensitive thermometry technique enabling direct measurement of reversible heat in lithium-ion batteries, revealing entropy changes and potential for heat management during charging.

Contribution

The paper presents a novel ultra-sensitive thermometry method that allows direct observation of reversible heat in LIBs, advancing understanding of entropy effects and thermal behavior.

Findings

Reversible heat absorption observed during charging with negligible irreversible heat.

Large reversible entropy change can cancel irreversible entropy generation.

Potential for zero-heat-dissipation LIBs during charging.

Abstract

The reversible heat in lithium-ion batteries (LIBs) due to entropy change is fundamentally important for understanding the chemical reactions in LIBs and developing proper thermal management strategies. However, the direct measurements of reversible heat are challenging due to the limited temperature resolution of applied thermometry. In this work, by developing an ultra-sensitive thermometry with a differential AC bridge using two thermistors, the noise-equivalent temperature resolution we achieve (10 uK) is several orders of magnitude higher than previous thermometry applied on LIBs. We directly observe reversible heat absorption of a LIR2032 coin cell during charging with negligible irreversible heat generation and a linear relation between heat generations and discharging currents. The cell entropy changes determined from the reversible heat agree excellently with those measured from temperature dependent open circuit voltage. Moreover, it is found that the large reversible entropy change can cancel out the irreversible entropy generation at a charging rate as large as C/3.7 and produce a zero-heat-dissipation LIB during charging. Our work significantly contributes to fundamental understanding of the entropy changes and heat generations of the chemical reactions in LIBs, and reveals that reversible heat absorption can be an effective way to cool LIBs during charging.