Enhanced Electrochemical Performance of Disordered Rocksalt Cathodes Enabled by a Graphite Conductive Additive

Cobalt-freecation-disordered rocksalt (DRX) cathodesare a promisingclass of materials for next-generation Li-ion batteries. Althoughthey have high theoretical specific capacities (>300 mA h/g) andmoderateoperating voltages (& SIM;3.5 V vs Li/Li+), DRX cathodestypically require a high carbon content (up to 30 wt %) to fully utilizethe active material which has a detrimental impact on cell-level energydensity. To assess pathways to reduce the electrode's carboncontent, the present study investigates how the carbon's microstructureand loading (10-20 wt %) influence the performance of DRX cathodeswith the nominal composition Li1.2Mn0.5Ti0.3O1.9F0.1. While electrodes preparedwith conventional disordered carbon additives (C65 and ketjenblack)exhibit rapid capacity fade due to an unstable cathode/electrolyteinterface, DRX cathodes containing 10 wt % graphite show superiorcycling performance (e.g., reversible capacities & SIM;260 mA h/gwith 85% capacity retention after 50 cycles) and rate capability (& SIM;135mA h/g at 1000 mA/g). A suite of characterization tools was employedto evaluate the performance differences among these composite electrodes.Overall, these results indicate that the superior performance of thegraphite-based cathodes is largely attributed to the: (i) formationof a uniform graphitic coating on DRX particles which protects thesurface from parasitic reactions at high states of charge and (ii)homogeneous dispersion of the active material and carbon throughoutthe composite cathode which provides a robust electronically conductivenetwork that can withstand repeated charge-discharge cycles.Overall, this study provides key scientific insights on how the carbonmicrostructure and electrode processing influence the performanceof DRX cathodes. Based on these results, exploration of alternativeroutes to apply graphitic coatings is recommended to further optimizethe material performance.