3D Simulation of Microstructure Effects in Alkaline Battery Cathodes

The objective of this work is to build an accurate 3D model to provide understanding of the effect of microstructure electrode performance, specifically on both electronic and ionic conductivity. The investigated system, the widely used primary alkaline battery, uses electrolytic manganese dioxide (EMD) active material in the cathode. An accurate and predictive 3D microstructure model of alkaline battery cathodes, which enables us to identify and quantify the processes that most affect performance, would be facilitate system optimization. The 3D model described here is part of ongoing work to investigate volumetrically efficient conductive carbon additives in primary alkaline battery cathodes [1,2].

The 3D simulation is based on the Monte Carlo method, in which a model generates a series of configurations that satisfy physical constraints in a statistically average way. The microstructure model is solved on a grid and is therefore called the stochastic grid (SG) model. The SG model is built by using the key statistics from microstructure analysis of FIB/SEM image of cathodes and includes short- and long-range order parameters. Toward this end, the work includes a full 3D reconstruction of a cathode using a sequence of 2D FIB/SEM images. This enables us to validate the SG model using measured microstructures. The SG model is additionally validated by electronic and ionic transport measurements.

Figure 1 shows preliminary 3D simulation results of particle distributions within the cathode. The model can describe the connectivity and distribution of carbon and porous domains throughout the cathode, which corresponds to the electron and ion pathways of interest. The model results suggest that carbon additives function more to make short-range connections, rather than long-range highways for electrons. The effective electronic conductivity calculated from the SG model is highly dependent on EMD intrinsic conductivity and contact resistances between particles, which suggests some possible electrode performance improvements may be possible through modified EMD particle arrangement.

The following will be presented and discussed: (1) a validated 3D model that effectively predicts microstructure and conductivity, which can be extended to multiple alkaline battery candidate systems; (2) Qualitative and quantitative model predictions of the performance effects of different carbon additives, pore volume fractions, and EMD distributions.

[1] Y Wen, Dean Wheeler.  3D Model and Experiments for Understanding Carbon Additive Behavior in Primary Alkaline Cells, ECS meeting, Canada, 2012, abstract number: 420

[2] Doug R. Never, Dean Wheeler. Effect of Carbon Additives On the Microstructure and Conductivity of Primary Alkaline Battery Cathodes, ECS meeting, San Francisco, 2012, Abstract Number: 285

Figure 1:  Preliminary 3D simulation results of particle distributions within a primary alkaline battery cathode. White represents large-size pores, gray represents EMD active material, and black represents graphite additive.