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

Abstract

Cobalt-free cation-disordered rocksalt (DRX) cathodes are a promising class of materials for next-generation Li-ion batteries. Although they have high theoretical specific capacities (>300 mA h/g) and moderate operating voltages (∼3.5 V vs Li/Li + ), DRX cathodes typically require a high carbon content (up to 30 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 (10−20 wt %) influence the performance of DRX cathodes with the nominal composition Li 1.2 Mn 0.5 Ti 0.3 O 1.9 F 0.1 . 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., reversible capacities ∼260 mA h/g with 85% capacity retention after 50 cycles) and rate capability (∼135 mA h/g at 1000 mA/g). A suite of characterization tools was employed to evaluate the performance differences among these composite electrodes. Overall, these results indicate that the superior performance of the graphite-based cathodes is largely attributed to the: (i) formation of a uniform graphitic coating on DRX particles which protects the surface from parasitic reactions at high states of charge and (ii) homogeneous dispersion of the active material and carbon throughout the composite cathode which provides a robust electronically conductive network that can withstand repeated charge−discharge cycles. Overall, this study provides key scientific insights on how the carbon microstructure and electrode processing influence the performance of DRX cathodes. Based on these results, exploration of alternative routes to apply graphitic coatings is recommended to further optimize the material performance.

Elucidating the Role of Carbon Conductive Additive in the Processing and Electrochemical Behavior of Surface-Modified Si Anodes

“…Moreover, Han et al observed that carbon black additives facilitated an open electrode structure in lithium–sulfur batteries, whereas graphene nanosheets resulted in a closed structure, emphasizing the significance of carbon additives not only in the electronic properties but also in influencing the electrode structure. Likewise, the impact of carbon conductive additives on electrode structure was reported in disordered rocksalt (DRX) cathodes, noting that graphite additive yields a homogeneous distribution of the active material and conductive carbon throughout the electrode …”

“…Likewise, the impact of carbon conductive additives on electrode structure was reported in disordered rocksalt (DRX) cathodes, noting that graphite additive yields a homogeneous distribution of the active material and conductive carbon throughout the electrode. 9 Although carbon plays a significant role in the performance of lithium-ion batteries, its surface reactivity has been revealed in recent years and has been recognized as a major contributor to the decomposition of electrolyte at the electrode/electrolyte interface. 10 This is due to the high surface area of common carbonaceous materials used as conducting agents like carbon black, e.g., 67 m 2 g −1 for Super C45 and 87 m 2 g −1 for Super C65, 11 plus the various functional groups attached to their surface, such as carbonyl, carboxyl, and aromatic groups, that react readily upon contact with the electrolyte and during electrochemical cycling.…”