State of Health Estimation Methods for Lithium-Ion Batteries

Abstract

Contemporary lithium-ion batteries (LIBs) are one of the main components of energy storage systems that need effective management to extend service life and increase reliability and safety. Their characteristics depend highly on internal and external conditions (ageing, temperature, and chemistry). Currently, the state of batteries is determined using two parameters: the state of charge (SOC) and the state of health (SOH). Applying these two parameters makes it possible to calculate the expected battery life and a battery’s performance. There are many methods for estimating the SOH of batteries, including experimental, model-based, and machine learning methods. By comparing model-based estimations with experimental techniques, it can be concluded that the use of experimental methods is not applicable for commercial cases. The electrochemical model-based SOH estimation method clearly explains processes in the battery with the help of multidifferential equations. The machine learning method is based on creating a program trained to predict the battery’s state of health with the help of past ageing data. In this review paper, we analyze the research available in the literature in this direction. It is found that all methods used to assess the SOH of an LIB play an essential role, and each method has its pros and cons.

Artificial Intelligence Opportunities to Diagnose Degradation Modes for Safety Operation in Lithium Batteries

“…Estimating the battery's state of health (SOH) and state of charge (SOC) enables the study, diagnosis, and prediction of DMs [47,48]. Various methodologies exist, including experimental testing, physical modeling, data-driven approaches, and hybrid methods, each of which have strengths and challenges [49][50][51]. Experimental methods require time and scientific knowledge for data interpretation, whereas physical models rely on extensive experimental databases [52].…”

“…One of the methodologies that plays a significant role is internal resistance measurement, which provides substantial information about the end of life of a battery [12,50,69]. It consists of the resistance of a substance when an electric current passes through.…”

“…Furthermore, polarization resistance (PR) and ohmic resistance (OR) are the two main contributions of internal resistance. In addition, OR contributes to the contact resistance of the separator, electrolyte, and electrode material cell components [50,72]. However, PR consists of the conversion state between the electrodes and the electrolyte during the correspondent electrochemical reactions.…”

“…Therefore, it could be said that the increase in internal capacity is directly related to battery capacity and discharge time. It is important to remark that even if it is a time-consuming and non-suitable technique for online assessment, it is reliable, noninvasive, direct, and widely used as an indicator for charge evaluation [50,68,73,74]. One of the most common methods is the current pulse method, based on Ohm's law.…”

Online Lifetime Prediction for Lithium-Ion Batteries with Cycle-by-Cycle Updates, Variance Reduction, and Model Ensembling

“…This is because LIBs are deployed into various applications, including energy storage systems and electric vehicles (EVs), and thus efficient, reliable, and accurate methods for monitoring their degradation are needed. One of the large problems here-and not the focus of this work-is the 'state of health' estimation, and approaches for it have been reviewed in [2][3][4]. The counterpart problem-and the focus of this paper-is the long-time prediction of life.…”