Electrode-Specific State of Health Diagnostics for Lithium Ion Batteries Using Cell Voltage and Expansion

Authors: Suhak Leea, Peyman Mohtata, Jason B Siegela and Anna G Stefanopoulou – University of Michigan

Abstract

Li-ion batteries degrade over time. Traditionally, capacity and resistance of the cell have been used as the state of health (SOH) indicators. However, these parameters cannot provide detail information about the degradation mechanisms. Thus, recently, there have been many efforts on developing diagnostics algorithm that can identify the degradation mechanisms. There exist many degradation mechanisms for Li-ion batteries such as SEI layer growth or lithium plating consuming lithium, structure disordering and metal ion dissolution making active material unavailable for insertion and extraction of lithium. Identifying these mechanisms is challenging due to complex inter-correlations between them. Instead, it is possible to categorize these mechanisms into two degradation modes: loss of lithium inventory (LLI) and loss of active material (LAM) at each electrode. On the electrode level, capacity and utilization window of the individual electrode are proposed as electrode-specific SOH parameters that can be related to the degradation modes. The differential voltage analysis (DVA) is one of the common approaches for estimating these electrode parameters. In this method, the phase transition of the electrode material is used as a fingerprint of each electrode in the cell’s differential voltage (dV/dQ) curve using a low C-rate constant current pseudo-OCV data [1,2]. Another interesting type of battery response is the mechanical response measured as a cell expansion. Batteries expand during charge and contract while discharge in repeatable patterns. Hence, similar to the voltage analysis, the expansion of a cell can be used for identifying the electrode parameters [3].

Download document