Localized Tortuosity Determination of Li-Ion Battery Electrode Using SECM and SICM

Abstract

Li-ion batteries’ limited power represents a barrier to their application in the domain of renewable energy. To examine the origin of this limitation, the effect of microstructural parameters such as porosity and tortuosity on ionic transport, especially through the electrolyte within the electrode pores needs to be studied. In this work, we tried to determine the local tortuosity in Li4Ti5O12 (LTO) electrodes with various porosities using two scanning probe microscopic techniques: Scanning Ion Conductance Microscopy (SICM) and Scanning Electrochemical Microscopy (SECM). SICM measures the effective ionic conductivity of Li+ ions whereas SECM probes the diffusion of electroactive species like anthracene.1,2 We observed that in both cases, the normalized current increases with porosity as more ions reach the tip through the pores of the electrode. The MacMullin number calculated from SICM and SECM measurements for the LTO electrodes having porosities from 50% to 63% shows that these techniques are complementary. Improved transport through these porous electrodes is indicated by the lower tortuosity values obtained compared to those anticipated by the mass transport models like the Bruggeman relationship. Hence, the tortuosity values determined from these microscopic techniques can be used as a strong tool to improve the modeling of electrolyte transport within electrodes. In turn, this should be highly valuable in the design of batteries with high power density.