A Bilayer Cathode Design Procedure for Li Ion Batteries Using the Multilayer Doyle-Fuller-Newman Model (M-DFN)

Abstract

Heterogeneities in lithium ion batteries can be significant factors in electrode under utilisation and degradation while charging. Bilayer electrodes have been proposed as a convenient and scalable way to homogenise the electrode response. In this paper, the design of a bilayer cathode for Li-ion batteries composed of separate layers of lithium nickel manganese cobalt oxide Li[Ni 0.6 Mn 0.2 Co 0.2 ]O 2 (NMC622) and lithium iron phosphate LiFePO 4 (LFP) is optimised using the multilayer Doyle-Fuller-Newman (M-DFN) model. Changes to the carbon binder domain, electrolyte volume fraction, and tortuosity provided the greatest control for improving Li-ion charge mobility. The optimised bilayer design was able to charge at 3C between 0-90% SOC in 18.6 minutes, achieving 4.4 mAh cm −2 . Comparing the optimal bilayer to the existing bilayer benchmark, an 8% increase in 3C charging capacity was achieved, along with 41% higher capacity compared to the LFP-only electrode. Through mechanistic physics-based modelling, it was shown that the 3C charging improvement of the optimised bilayer was achieved by enabling a more homogeneous current density distribution through the thickness of the electrode and electrolyte depletion prevention. The findings were confirmed on a high-fidelity X-ray computed tomography (CT) based microstructural model. The results illustrate how modelling can be used to rapidly search novel electrode designs and accelerate the deployment of fast-charging thick electrodes by adapting existing manufacturing processes.