Dual-protection of cathode from HF corrossion enabling high-performance lithium metal batteries

Abstract

Lithium metal batteries (LMBs) encounter substantial challenges related to hydrogen fluoride (HF)-induced degradation of electrode materials and interfacial instability. The predominant sources of HF are attributed to the hydrolysis of lithium hexafluorophosphate (LiPF₆) in the electrolyte and the decomposition of fluorine-containing solvents, which result in transition metal dissolution, rapid capacity fading, and overall battery performance deterioration. To mitigate these issues, we introduce a dual-protection strategy via the synergistic incorporation of pentafluorophenyl trifluoroacetate (PFTFA) and lithium difluoro(oxalato)borate (LiDFOB) additives, achieving both chemical HF capture and physical HF defense. The optimized electrolyte system not only promotes the formation of a robust cathode-electrolyte interphase layer enriched with LiF and LiB_xO_y compounds but also effectively scavenges HF through PFTFA coordination, thereby ensuring enhanced cathode stability. Consequently, the Li||LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cells demonstrate remarkable cyclic stability with 80% capacity retention over 420 cycles at the cutoff voltage of 4.4 V under 1 C rate, whereas conventional carbonate-based electrolytes only retain 54.8% capacity after 150 cycles under identical conditions. Even under high voltage conditions (4.8 V, 0.5 C), the developed electrolyte maintains 77.8% capacity retention over 200 cycles. This work provides valuable insights into the rational design of multifunctional electrolyte additives for high-performance LMBs.