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Journal of Electrochemistry ›› 2021, Vol. 27 ›› Issue (6): 646-657.  doi: 10.13208/j.electrochem.210210

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Cyclic Voltammetric Simulations on Batteries with Porous Electrodes

Xue-Fan Cai, Sheng Sun*()   

  1. Materials Genome Institute, Shanghai University, Shanghai 200444, China
  • Received:2021-02-10 Revised:2021-04-07 Online:2021-12-28 Published:2021-04-14
  • Contact: Sheng Sun E-mail:mgissh@t.shu.edu.cn

Abstract:

Lithium-ion batteries (LIBs) are among the most widely used energy storage devices. Whole-cell modeling and simulations of LIBs can optimize the design of batteries with lower costs and higher speeds. The Pseudo-Two-Dimensional (P2D) electrochemical model is among the most famous whole-cell models and widely applied in LIB simulations. P2D model consists of a series of kinetic equations to model Li+/Li diffusion in working/counter electrodes and electrolytes, which are filled in the porous electrodes and separator, and reactions at the interface of electrolyte and active particles. The traditional applications of P2D model, however, are limited to the cases where the current is the control variable and the voltage is the dependent variable. The present work tries to apply boundary conditions with the electrode potential as the control variable to simulate cyclic voltammetric (CV) experiments on the whole battery, based on a detailed analysis on different potentials, including Galvani potential, Volta potential, electrode potential and battery terminal voltage, as well as their relationships. In many CV experiments, only two electrodes, the working and the counter electrodes, are used. The experimental results are usually explained by using theoretical results directly taken from textbooks. The theories of CV are, however, based on three-electrode systems with a reference electrode to provide a reference voltage. The differences of CV curves between the two- and the three-electrode systems have never been studied by using P2D models. The present work performs numerical simulations of CV on both two- and three-electrode systems by using finite element methods, brought with the software of COMSOL Multiphysics, to study the influences of scanning rate, effective radius of active particles, lithium ion diffusivity and stoichiometric maximum concentration in electrode on CV curves. The three-electrode system is simulated by applying a potential detector at the separator region of a battery. The applied potentials are changed in time based on the magnitude of the detected potential. Results show that, for CV curves on both two- and three-electrodes systems, the peak current determined by the complex electrode dynamics process increases with the increases of scanning rate, lithium ion diffusivity in electrode and stoichiometric maximum lithium ion concentration, but with the decrease of the radius of electrode active particles. The peak currents obtained from CV curves are larger in three-electrode systems than in two-electrode systems under the same applied parameters. CV curves of three-electrode systems are more symmetric for the anodic and cathodic currents than those in two-electrode systems.

Key words: lithium ion battery, cyclic voltammetry, P2D model, two/three electrode system, finite element simulation