Precision and Accuracy in Coulombic Efficiency Measurements (High Precision Coulometry HPC) Battery – Application Note 53

Abstract

Coulombic efficiency is one of the main factors determining the useful life of a Li-ion cell and battery. Therefore the accurate determination of any capacity loss and/or inefficiency in subsequent charge-discharge cycles may allow making predictions with respect to the useful battery life. However, this requires reliable and precise data, with as little noise as possible, so that the only factor contributing to the measured capacities is the cell itself, and not inaccuracies of the instrumentation, and/or temperature changes. Being able to predict what the battery will be after 2000 cycles, after running on 20 or 30 streamlines and accelerating battery testing, makes it also a lot cheaper. Very precise Coulometry also allows for fast and efficient prescreening of different electrode and electrolyte formulations.

AN#53 discusses instrument accuracy according to prof. Jeff Dahn’s definition, the idea that no stochastic phenomena takes place inside the battery cell. This most likely is not the case, given that different accuracies are measured for the same instrument, but different battery chemistries. It is likely that Bio-Logic potentiostats, galvanostats and battery cyclers are so precise that they do not introduce any significant artifacts to measured Coulombic efficiencies.

Introduction

In the last years, several types of research were focused on the Coulombic Efficiency (CE) as a a tool to study the battery lifetime [1–8]. Quantifying the influence on the battery lifetime by changes in the electrodes or electrolytes, under classical testing conditions (simply charge-discharge conditions), requires extremely long times. Contrarily tosimple cycle cell measurements (until the cells reach the end of life), CE measurements can be improved in a short amount of time (3-4 weeks) and also provide a tool to evaluate and compare the stability of different cells.

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