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Estimate Transport & Kinetic Parameters of NMC Electrodes Through Experimental & Modeling Approach
Xiting Duan , PhD candidate, Department of Mechanical Engineering at University of Massachusetts Lowell Abstract: With the significant cost reduction of Li-ion Battery (LIB) (85% in the past 10 years), a 50-fold growth in market penetration of the technology has been projected through to 2030 for modern transportation and renewable energy integration. LIB is a high energy density, high round-trip efficiency, high-reliability energy storage device. Different from Internal Combustion Engine, as a power generator, the LIB pack is sealed in a certain container and its status needs 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 the current integration method and open-circuit voltage method, which are time-consuming (over 1 day) and rely on historical information of the system. 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, we also find that the nonideality effect caused by interaction among high concentration Li-ions could lead to nonlinear transport and kinetic parameters as a function of SOC. In recent 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 a different number of cycles. A nonlinear optimization procedure will be used to identify the parameters associated with the transport and kinetic in each electrode, solid/liquid interface reaction, Li-ion diffusion, ohmic resistance, etc. In addition, we will measure the chemical Diffusion coefficient of Lithium-ions (DLi) in spherical Li[Ni0.5Mn0.3Co0.2]O2 by Galvanostatic Intermittent Titration Technique (GITT) technique as a comparison with Electrochemical Impedance Spectroscopy (EIS) method. The result shows the kinetic parameters of exchange current density, electronic conductivity and diffusion coefficients of solid Li[Ni0.5Mn0.3Co0.2]O2 are greatly dependent on the lithium content and cell potential. The results will provide important guidance in designing fast and accurate LIB real-time diagnostic devices. Biography: Xiting Duan is a Ph.D. candidate in the Department of Mechanical Engineering at the University of Massachusetts Lowell. He received his B.S degree and M.S degree in Material Science and Engineering from the Xiangtan University. His current research interest is on multi-physics modeling of lithium-ion batteries, investigate thermodynamic and kinetic degradation of lithium-ion batteries through a combined experimental and modeling approach.
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