Constructive versus Destructive Heterogeneity in Porous Electrodes of Lithium-Ion Batteries

We introduce an efficient framework for investigating the heterogeneity in battery porous electrodes and its impacts on the performance and longevity of lithium-ion batteries. A phenomenological picture based on theory and experiment is presented to show how the spatial variations in the local porosity and thickness in a porous electrode result from a microscopically inhomogeneous slurry. A series of analogous bilayer LiNi0.6Mn0.2Co0.2O2 porous electrodes with different levels of heterogeneity, induced by a nonuniform distribution of carbon, is prepared as a model experimental system and established as a powerful tool in formalizing the concept of heterogeneity. We identify and distinguish between constructive and destructive heterogeneities as the two shades of nonuniformity in porous electrodes. Depending on the degree of heterogeneity, we observe up to 20% decline in the rate performance of the electrodes. The destructive and constructive heterogeneities in the analogous electrodes are manifested as 5-fold increase and 2-fold decrease, respectively, in the aging rate of Li4Ti5O12|LiNi0.6Mn0.2Co0.2O2 cells relative to that of a cell with a homogenous electrode after 200 cycles at 1 C.