Effective Mass Transport Properties in Lithium Battery Electrodes

Lithium ion battery performance becomes increasingly limited by ionic transport as the current demand increases. Especially detrimental is the transport within the liquid electrolyte that fills the porous electrode, yet reliable measurement of practical lithium diffusivity within this complex structure has been a longstanding challenge. In this work, we have developed a "single sided" analytical technique to determine the diffusivity in porous networks using scanning electrochemical microscopy (SECM) and a molecular redox marker: SECM surface mapping of porous films shows measurement consistency, and diffusion limited currents through a test structure with well-defined geometry matches the results of numerical modeling within 10%. Diffusivity measurement shows significant deviation from the Bruggeman model for porosities below 60%. The developed technique is applicable to all porous structures independent of their electronic conductivity. Importantly, for lithium-ion batteries the technique does not require freestanding electrodes and therefore is applicable to industrially relevant high power electrodes as a tool for optimization as well as for quality control.