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 widely reported1. For the same active material properties (active material diffusivity, open circuit potential etc.) the use of smaller or bigger particle sizes in the porous electrode matrix greatly influences cell performance. From the design standpoint, a good balance of particle properties is of great importance2. In the research community, Scanning Electron Microscopy (SEM), Dynamic Light Scattering (DLS) could be used to characterise the active material particles. Moreover, different techniques such as Galvanostatic or Potentiostatic Intermittent Tritiation Techniques (GITT/PITT) or Electrochemical Impedance Spectroscopy (EIS) could be conducted to calculate bulk solid diffusivities of those materials3,4. The experiments are usually performed at the electrode-level in half-cells, therefore, in order to experimentally obtain bulk properties, the properties of the porous-electrode matrix need to be known which requires heavy post-processing efforts. Physics-based models can aid in this research, analysing the electrodes at different scales5 and fitting the diffusivity values4. The baseline of this research is the well-stablished Pseudo-two-Dimensional (P2D) model. This model assumes that particles are spherical, and monodispersed. This study will explore different model assumptions such as constant solid diffusivity, stoichiometry dependent solid diffusivity (with ad-hoc analytical functions), and Baker-Verbrugge diffusion model, among others. Moreover, the explicit consideration of a particle size distribution is analyzed within the model. The aim is to get a compromise between the accuracy and speed of the model, as well as proposing a method for post-processing and including higher fidelity considerations about particle radius and solid diffusion into P2D models. The focus of this research is to perform experimental and numerical analysis to discuss how to take into account the active material diffusivity and particle radius in continuumscale simulations for metal-ion batteries. This work explores the benefits of different assumptions (on particle size-distribution and solid diffusion) with the aim of applying those improvements to a reduce order model that could potentially run in a real-time environment to build advanced estimators with enhanced accuracy at high current rates.