Modeling 3D-microbatteries based on carbon foams

Abstract

Porous electrodes are considered attractive for potential use as 3D current collectors in Li-ion microbatteries. Carbon foams, in particular, can be coated with a variety of active materials to prepare electrodes which can maximize energy and power density simultaneously. Modeling such electrodes will aid the selection of microstructural parameters (e.g. porosity) required to optimize their electrochemical performance. Here, experimentally-validated Finite Element Methodology (FEM) is used to simulate a 3D Li-ion microbattery featuring a carbon foam electrode coated by layers of LiFePO4 nanoparticles. The electrodes are cycled against Li-metal at various current densities, and the electrochemical data obtained are used to benchmark and parametrize the simulations. By systematic variation of the LiFePO4 coating thickness and homogeneity and the foam substrate, it is revealed that LiFePO4 exhibits a uniform delithiation process and that the electrochemical reactions favor particles closer to the carbon structure, which is due to the poor electrical conductivity of LiFePO4. Therefore, the cell capacity (mAh cm−2) per footprint area can be increased by using lower charging currents, smaller carbon macropore sizes and thicker LiFePO4 coatings. The porous carbon structure provides an excellent template for loadings of LiFePO4 material, which in turn allows using thicker coatings with improved cell performance.