Investigate Thermodynamic and Kinetic Degradation of Lithium-Ion Batteries through a Combined Experimental and Modeling Approach

Abstract

With the significant cost reduction of Li-ion battery (LIB) (85% in the past 10 years), 50-fold growth in market penetration of the technology has been projected through to 2030 for modern transportation and renewable energy integration [1]. LIB is a high energy density, high round-trip efficiency, high reliability energy storage device [2]. Different from Internal Combustion Engine, as a power generator, LIB pack is sealed in a certain container and its status need to be estimated by additional diagnostic instruments with specific electrochemical performance data. The traditional methods to estimate State of Charge (SOC) and State of Health (SOH) include current integration method and open circuit voltage method, which are time-consuming (over 1 day) and rely on historical information of the system [3]. Impedance spectroscopy technique can capture both thermodynamic and kinetic information of the LIB in a relatively short time, however, it is difficult and sometimes unreliable to interpret the data by using a simplified equivalent circuit method (ECM). In our recent publication [4], we also find that nonideality effect caused by interaction among high concentration Li ions could lead to nonlinear transport and kinetic parameters as a function of SOC. In this research work, we would like to use the perturbation form of a physics-based LIB model considering the nonideality feature of the cell to deconvolute the electrochemical impedance spectroscopy (shown in Fig.1) of a LIB coin cell operating under different SOCs and different number of cycles. After proper status evaluation of beginning of life (BOL) of the cell, parasitic side reactions, the solid electrolyte interface (SEI) formation in anode and cathode, are included as the indicators of degradation. A nonlinear optimization procedure will be used to identify the parameters associated with the cell capacity loss in each electrode, solid/liquid interface reaction, Li-ion diffusion, ohmic resistance, etc. The results will map out the cell capacity loss caused by thermodynamic degradation and deteriorated reaction kinetics and diffusivity caused by the growth of the SEI layers during cycling. It will provide important guidance in designing fast and accurate LIB real-time diagnostic devices.