Tailoring interfacial stability with lithium salt additives for long-cycling Ni-rich cathodes in lithium metal batteries

The development of next-generation battery systems with high energy density is crucial for the advancement of electric vehicles (EVs). The combination of a high-nickel cathode with a lithium-metal anode is a particularly promising candidate for this application, as both materials demonstrate individually high theoretical specific capacities. However, each electrode presents intrinsic challenges that must be individually understood and synergistically mitigated to unlock their full potential. In this study, the effectiveness of various lithium salts as electrolyte additives for stabilizing LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathodes is investigated. A systematic comparison of lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluoro(oxalate)borate (LiDFOB), lithium nonafluoro-1-butanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, and lithium trimethylsilanolate (LiTMS) is conducted in a LiPF₆-based electrolyte to evaluate their impact on interfacial chemistry and long-term cycling performance. Among the additives tested, LiDFOB demonstrates the most promising results, retaining approximately 70 % of its initial capacity after 400 cycles at 25 °C and 87.7 % at 50 °C. In contrast, while LiTMS initially appears effective in forming a protective cathode electrolyte interphase (CEI), it ultimately leads to significant impedance growth and capacity degradation over extended cycling. Comprehensive electrochemical evaluations and ex situ characterizations reveal that the interfacial reactivity and integrity of the resulting CEI play a more critical role in determining long-term stability than the mechanical degradation traditionally attributed to particle cracking. These findings challenge the conventional emphasis on structural failure as the primary mode of degradation in high-Ni cathodes and underscore the significance of rational CEI design through electrolyte additive engineering.