Elucidating the role of particle radius and active material diffusivity in metal-ion batteries

Abstract

The impact of particle size distribution and shape in metal-ion batteries has been widelyreported1. For the same active material properties (active material diffusivity, open circuitpotential etc.) the use of smaller or bigger particle sizes in the porous electrode matrixgreatly influences cell performance. From the design standpoint, a good balance of particleproperties is of great importance2. In the research community, Scanning ElectronMicroscopy (SEM), Dynamic Light Scattering (DLS) could be used to characterise the activematerial particles. Moreover, different techniques such as Galvanostatic or PotentiostaticIntermittent Tritiation Techniques (GITT/PITT) or Electrochemical Impedance Spectroscopy(EIS) could be conducted to calculate bulk solid diffusivities of those materials3,4. Theexperiments are usually performed at the electrode-level in half-cells, therefore, in orderto experimentally obtain bulk properties, the properties of the porous-electrode matrixneed to be known which requires heavy post-processing efforts.Physics-based models can aid in this research, analysing the electrodes at different scales5and fitting the diffusivity values4. The baseline of this research is the well-stablishedPseudo-two-Dimensional (P2D) model. This model assumes that particles are spherical,and monodispersed. This study will explore different model assumptions such as constantsolid diffusivity, stoichiometry dependent solid diffusivity (with ad-hoc analyticalfunctions), and Baker-Verbrugge diffusion model, among others. Moreover, the explicitconsideration of a particle size distribution is analyzed within the model. The aim is to geta compromise between the accuracy and speed of the model, as well as proposing amethod for post-processing and including higher fidelity considerations about particleradius and solid diffusion into P2D models.The focus of this research is to perform experimental and numerical analysis to discusshow to take into account the active material diffusivity and particle radius in continuumscalesimulations for metal-ion batteries. This work explores the benefits of differentassumptions (on particle size-distribution and solid diffusion) with the aim of applying thoseimprovements to a reduce order model that could potentially run in a real-timeenvironment to build advanced estimators with enhanced accuracy at high current rates.