Quantifying the Effect of Separator Thickness on Rate Performance in Lithium-Ion Batteries

Abstract

In addition to improving parameters such as energy density and stability, it is important to maximise rate performance in lithium ion batteries. While much work has focused on rate-limiting factors associated with the electrodes, much less attention has been paid to the effect of the separator on rate-performance. Here we perform a quantitative study on the effect of separator thickness on the rate-performance of a model system of NMC-based half cells. By fitting experimental capacity vs rate curves, we measured the characteristic time associated with charge/discharge as a function of separator thickness, finding a roughly linear increase for separator thicknesses below ∼65 μm. This behaviour is consistent with a simple physical model which shows the separator thickness dependence to be dominated by electrolyte resistance effects. The predictions of the model match the data extremely well with no adjustable parameters