PNNL

Abstract

Although Co-free cation disordered rocksalt (DRX) cathodes have high theoretical specific capacities (>300 mAh/g) and moderate operating voltages (~3.5 V vs. Li/Li+), DRX cathodes typically require high carbon content (=20 wt%) to fully utilize the active material which has a detrimental impact on cell-level energy density. To assess pathways to reduce the electrode’s carbon content, the present study investigates how the carbon’s microstructure and loading influence the performance of DRX cathodes with the nominal composition Li1.2Mn0.5Ti0.3O1.9F0.1. While electrodes prepared with conventional disordered carbon additives (C65 and ketjenblack) exhibit rapid capacity fade due to an unstable cathode/electrolyte interface, DRX cathodes containing 10 wt% graphite show superior cycling performance (e.g., ~260 mAh/g with 85% capacity retention after 50 cycles) and rate capability (~135 mAh/g at 1000 mA/g). Complementary measurements using a suite of characterization tools indicate the superior performance of the graphite-based cathodes is attributed to: (i) formation of a uniform graphitic coating on DRX particles which protects the surface from parasitic reactions at high states of charge and (ii) homogenous dispersion of active material and carbon which provides a robust electronically conductive network. Overall, this study provides key insights on how carbon microstructure influences the performance of DRX cathodes.