Perspective on State-of-Health Determination in Lithium-Ion Batteries

Abstract

State-of-health (SOH) is an essential parameter for the proper functioning of large battery packs. A wide array of methodologies has been proposed in the literature to track state of health, but they often lack the proper validation that needed to be universally adaptable to large deployed systems. This is likely induced by the lack of knowledge bridge between scientists, who understand batteries, and engineers, who understand controls. In this work, we will attempt to bridge this gap by providing definitions, concepts, and tools to apply necessary material science knowledge to advanced battery management systems (BMS). We will address SOH determination and prediction, as well as BMS implementation and validation using the mechanistic framework developed around electrochemical voltage spectroscopies. Particular focus will be set on the onset and the prediction of the second stage of accelerating capacity loss that is commonly observed in commercial lithium-ion batteries.

Perspective on Commercial Li-ion Battery Testing, Best Practices for Simple and Effective Protocols

“…SOH is gauged from the quantification of the degradation modes, the loss of active material, loss of reactant, and kinetic degradation. A discussion on SOH is out of the scope of this paper and can be found in [10]. The RPT needs to provide as much information as possible on SOH without being intrusive [37].…”

“…However, in that case, only trends can be used to compare the mechanistic simulations to the experimental data. For analysis, the FOI selection must only be made after an exhaustive sensibility analysis [10,53]. It is highly recommended to first simulate a degradation map with the voltage changes and capacity loss associated with all the individual modes to gain an understanding of which FOI is more sensible to a degradation mode.…”

“…The definition of the duty cycle test is the most important part of any degradation or validation study. Battery degradation is path dependent [10,74,[76][77][78][79][80] meaning that different conditions are degrading battery differently, not just increasing or decreasing the rate. Therefore, to be representative of a given application, the duty cycle to be applied needs to be as close as possible to the real use, which is most likely stochastic [74,[76][77][78][79][80].…”

“…This is meant to provide newcomers and non-battery specialists some details, definitions, and explanations on how to perform simple and effective battery testing in order to improve validation studies. This publication does not aim to compare different approaches to testing protocols nor discuss the complex question of battery SOH, such discussions can be found in [9,10], respectively, but is intended to describe the Hawaii Natural Energy Institute (HNEI) methodology. In the past decade and a half, HNEI has been in the forefront of the development of methodologies to improve non-intrusive characterization of commercial lithium ion cells to extract maximum relevant information from minimum amount of testing and instrumentation.…”

“…Electronics 2020, 9, x FOR PEER REVIEW 2 of 17 The purpose of this publication is to complement [9,10] and describe, in more detail than typical publications, a testing strategy to address all these issues together. This is meant to provide newcomers and non-battery specialists some details, definitions, and explanations on how to perform simple and effective battery testing in order to improve validation studies.…”