Interplay of electrolyte transport, electrode balancing, and cathode loading in rate-dependent behavior of...

The rate-dependent behavior of lithium-ion batteries is governed by the coupled interplay of transport processes, electrochemical kinetics, and electrode architecture. Here, we employ multiphase porous electrode theory (MPET) to elucidate the mechanistic effects of cathode loading and electrode balancing (N/P ratio) on the performance of graphite‖NMC532 full cells. By systematically exploring a multidimensional parameter space spanning electrode design and discharge rate, we identify a transition from near-equilibrium operation at low rates to strongly transport-limited dynamics at high rates. This transition is characterized by pronounced electrolyte concentration gradients, increased polarization, and reduced utilization of active material, leading to a significant loss in accessible capacity. Increasing cathode loading enhances the stored charge under near-equilibrium conditions but intensifies transport limitations at higher rates, promoting electrolyte depletion and spatially localized reaction fronts. In contrast, variations in N/P ratio exert a secondary influence under the near-room-temperature discharge conditions considered here, indicating that cathode-side transport dominates the overall response within this operating regime. Analysis of internal fields reveals the coupling between ionic transport, reaction kinetics, and heterogeneous utilization as the primary origin of performance degradation at high rates. These results establish a physics-based framework linking electrode structure to rate-dependent electrochemical behavior and provide generalizable insight into the design of porous electrodes. From a practical perspective, the findings provide design guidelines for graphite‖NMC cells by highlighting the need to optimize cathode loading and electrolyte transport pathways to balance energy density, power capability, and active-material utilization under high-rate discharge operation.