Session: 09-16-03: Energy-Related Multidisciplinary III

Paper Number: 165955

State of Health Evaluation for Large Lithium-Ion Batteries Using Pseudo-EIS 

Pseudo-Electrochemical Impedance Spectroscopy (pseudo-EIS) is a promising technique used for estimating the state of health (SOH) and performance evaluation of lithium-ion batteries (LIBs). Unlike conventional EIS, pseudo-EIS can be implemented in Battery Management Systems for real-time battery health diagnostics and in conventional battery cyclers for lab characterization. The analysis relies on the identification of the transition impedance (ZTR), a concept defined as the impedance threshold between charge transfer and diffusion phenomena. T The advantage of transition impedance over internal resistance is that it can detect traces of lithium plating as the cell ages. This SOH technique had previously been applied to new or minimally degraded batteries as a proof of concept. The present study seeks to extend the analysis to long-term aged batteries under two aging conditions: cycling and storage, and to corroborate any indication of lithium plating.

In this paper, pseudo-EIS was applied to large pouch-type LIBs (> 70 Ah) aged through long-term cycling and storage. Calendar aging was conducted over 40 weeks at three storage temperatures (25 °C, 45 °C, 55 °C) and three different states of charge (SOC) (30%, 50%, 80%). Cycle aging was performed for twenty weeks at the same ambient temperatures and three SOC ranges (30%, 60%, 90%). Cycling was carried out using constant power charge and discharge with different power levels tailored to the electrochemical characteristics (capacity, power, and internal resistance at different SOCs) of each cell type. State of health was periodically checked via Reference Performance Tests (RPTs). RPTs included static capacity (SC) measurement, hybrid pulse power characterization test (HPPC), and pseudo-EIS test. SC and HPPC provided the conventional Coulomb counting and internal resistance variation as cells aged, whereas pseudo-EIS provided the transition impedance. Pseudo-EIS consisted of a charge pulse followed by a three-second rest and a three-second discharge pulse. One hundred charge-rest-discharge pulse profiles were applied until the cell reached Vmax. The charge profile was repeated twice using low (C/5) and high (1C) current pulses. High-current pulses were aimed at setting the cell under a limited diffusion condition capable of inducing lithium deposition on the anode active material surface. The results correlated transition impedance, capacity, and resistance changes with the fingerprints of well-known phenomena such as SEI thickening, electrolyte decomposition, and lithium plating. By analyzing the evolution of the transition impedance with aging, we seek to illustrate the potential detection of lithium plating and its utility for accurate SOH assessment in real-world applications.

Presenting Author: Daniel Juarez Robles Southwest Research Institute

Presenting Author Biography: Dr. Daniel Juarez-Robles currently serves as a Research Engineer within the Powertrain Engineering Division at Southwest Research Institute (SwRI®). His expertise lies in advanced battery safety and performance research, with a particular focus on Energy Storage Systems, including lithium-ion batteries.

Dr. Juarez Robles holds a Ph.D. in Mechanical Engineering from Purdue University. Leveraging his expertise, he has established and conducts experiments and tests on lithium-ion battery cells, modules, and packs at SwRI®. These experiments evaluate the safety, reliability, lifecycle, and performance of batteries under nominal and off-nominal conditions.

Authors:

Daniel Juarez Robles Southwest Research Institute
Swapnil S. Salvi Southwest Research Institute
Andre Swarts Southwest Research Institute
Jayant Sarlashkar Southwest Research Institute