Quantifying the Dependence of Battery Rate Performance on Common Physical Parameters

Simultaneous optimisation of capacity and rate-performance in battery electrodes would be much simplified by access to a simple equation relating rate-performance to electrode thickness. While a number of equations have been proposed, data on the effect of electrode thickness on rate-performance is not extensive enough to identify the most appropriate model for thickness-dependence. Here, using LiNi_0.815Co_0.15Al_0.035O₂ (NCA) as a model system, we use chronoamperometry as a procedure to rapidly generate capacity-rate curves for &gt”;”50 different electrode thicknesses. Using a semi-empirical fitting equation, we extract the characteristic time (t) associated with charge/discharge for each thickness (L_E). We find the resultant t-L_E curve to be inconsistent with minimal models based on liquid- or solid-phase-diffusion alone, but to be in excellent agreement with a relatively simple rate model which includes liquid- and solid-phase-diffusion effects as well as electrical and electrochemical limitations. Thickness-dependent impedance measurements show that the magnitudes of the electrochemical and solid-state diffusion contributions are perfectly in line with the outputs of the rate model.