(533b) Predicting Transport, Mechanical, and Microstructural Properties of Porous Li-Ion Battery Electrodes By a Particle-Based Simulation
AIChE Annual Meeting
2015
2015 AIChE Annual Meeting Proceedings
Engineering Sciences and Fundamentals
Fundamentals of Electrochemical Processes II
Wednesday, November 11, 2015 - 12:55pm to 1:20pm
Predicting Transport, Mechanical, and
Microstructural Properties of Porous Li-Ion Battery Electrodes by a Particle-Based
Simulation
Transport properties and
performance of porous electrodes in Li-ion batteries are highly affected by
microstructure, and in turn, the microstructure is influenced by the fabrication
process. Therefore, a detailed knowledge of the relationships between transport
properties, microstructure, and fabrication process variables is essential for
battery researchers and manufacturers in order to model and design optimized
batteries.
Factors that influence
electrode microstructure include high-level variables such as composition and
porosity, as well as detailed fabrication conditions. The fabrication process for
Li-ion electrode films includes mixing a slurry of carbon, binder, solvent, and
active material; coating the slurry onto a metallic current collector; drying
the film; and calendering to the desired porosity. The resulting microstructure
of commercially made battery electrodes is not necessarily optimal, and
improvements could be made with a detailed physical understanding of each step.
In this work experiments and
computer simulations are performed in order to elucidate fabrication-microstructure-performance
relationships. A slurry made with a representative composition, namely with
spherical active material particles (Toda NCM 523), carbon
black, polymeric binder, and NMP solvent, was made in our laboratory. Slurry
viscosity measurements at different shear rates, shrinkage ratio during the
drying process, and dried electrode film elasticity (Young Modulus) were
measured and used to parameterize the model.
LAMMPS, a molecular simulation code, was
adapted for the mesoscale particle simulations. Shifted force Lennard-Jones and
granular Hertzian potential were used to represent the interaction between
particles. Relatively soft particles were used to represent implicit solvent,
carbon, and binder aggregates. Relatively hard particles were used to represent
active material. Equations of motion coupled to inter-particle forces are
solved to simulate particle motion and subsequent immobilization during drying
steps.
The
microstructure of the dried film was validated by comparing to experimental
results, namely FIB/SEM sequential cross-sections of real composite electrodes.
Image processing algorithms were used to segment the images into three phases
also used in the model: active material, carbon/binder domains, and macroscopic
pores. In addition, effective electronic and ionic conductivities of the model
structures were compared to experimental values.
This
work is supported by the U.S. Department of Energy through the BMR program.
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