Fabrication and Model-Guided Design of Thick-Format Lithium Ion Electrodes

Abstract

To enable the use of renewable energy in place of fossil fuels for grid-scale electricity generation, low-cost, long-duration (3 hr charge, 12 hr discharge) energy storage systems must be developed to bridge the intermittency of these resources. This present work explores the adoption of thick-format lithium-ion electrodes to minimize inactive material cost and achieve <$100/kWh of storage. Thick lithium iron phosphate (LFP) pellets were fabricated using a dry pressing process, and the effects of composition, thickness/porosity balance, and electrolyte choice on the performance of the LFP half cells were explored. LFP electrodes with thicknesses up to 1 mm and capacities up to ~15 mAh/cm2 exhibited good rate performance (~90% utilization at a C/10 rate) and stable cycling over 100 cycles. A physics-based model was used to study transport within these thick electrodes. As thickness increases, large concentration gradients form across the electrode, with salt depletion at the current collector and salt accumulation at the separator exceeding the solubility limit of conventional electrolytes. Unlike fast-charging thin electrodes where kinetic overpotentials dominate inefficiencies, thick electrode performance is diffusion-limited, suggesting that methods for minimizing tortuosity and increasing ionic conductivity will be key in enabling low-cost thick electrodes. Figure 1