RESUMO
Lithium metal is regarded as the "holy grail" of lithium-ion battery anodes due to its exceptionally high theoretical capacity (3800 mAh g-1) and lowest possible electrochemical potential (-3.04 V vs Li/Li+); however, lithium suffers from the dendritic formation that leads to parasitic reactions and cell failure. In this work, we stabilize fast-charging lithium metal plating/stripping with dual-function alloying M-nitrate additives (M: Ag, Bi, Ga, In, and Zn). First, lithium metal reduces M, forming lithiophilic alloys for dense Li nucleation. Additionally, nitrates form ionically conductive and mechanically stable Li3N and LiNxOy, enhancing Li-ion diffusion through the passivation layer. Notably, Zn-protected cells demonstrate electrochemically stable Li||Li cycling for 750+ cycles (2.0 mA cm-2) and 140 cycles (10.0 mA cm-2). Moreover, Zn-protected Li||Lithium Iron Phosphate full-cells achieve 134 mAh g-1 (89.2% capacity retention) after 400 cycles (C/2). This work investigates a promising solution to stabilize lithium metal plating/stripping for fast-charging lithium metal batteries.
RESUMO
Sodium foil, promising for high-energy-density batteries, faces reversibility challenges due to its inherent reactivity and unstable solid electrolyte interphase (SEI) layer. In this study, a stable sodium metal battery (SMB) is achieved by tuning the electrolyte solvation structure through the addition of co-solvent 2-methyl tetrahydrofuran (MTHF) to diglyme (Dig). The introduction of cyclic ether-based MTHF results in increased anion incorporation in the solvation structure, even at lower salt concentrations. Specifically, the anion stabilization capabilities of the environmentally sustainable MTHF co-solvent lead to a contact-ion pair-based solvation structure. Time-of-flight mass spectroscopy analysis reveals that a shift toward an anion-dominated solvation structure promotes the formation of a thin and uniform SEI layer. Consequently, employing a NaPF6-based electrolyte with a Dig:MTHF ratio of 50% (v/v) binary solvent yields an average Coulombic efficiency of 99.72% for 300 cycles in Cu||Na cell cycling. Remarkably, at a C/2 cycling rate, Na||Na symmetric cell cycling demonstrates ultra-long-term stability exceeding 7000 h, and full cells with Na0.44MnO2 as a cathode retain 80% of their capacity after 500 cycles. This study systematically examines solvation structure, SEI layer composition, and electrochemical cycling, emphasizing the significance of MTHF-based binary solvent mixtures for high-performance SMBs.
RESUMO
The discovery of liquid battery electrolytes that facilitate the formation of stable solid electrolyte interphases (SEIs) to mitigate dendrite formation is imperative to enable lithium anodes in next-generation energy-dense batteries. Compared to traditional electrolyte solvents, tetrahydrofuran (THF)-based electrolyte systems have demonstrated great success in enabling high-stability lithium anodes by encouraging the decomposition of anions (instead of organic solvent) and thus generating inorganic-rich SEIs. Herein, by employing a variety of different lithium salts (i.e., LiPF6, LiTFSI, LiFSI, and LiDFOB), it is demonstrated that electrolyte anions modulate the inorganic composition and resulting properties of the SEI. Through novel analytical time-of-flight secondary-ion mass spectrometry methods, such as hierarchical clustering of depth profiles and compositional analysis using integrated yields, the chemical composition and morphology of the SEIs generated from each electrolyte system are examined. Notably, the LiDFOB electrolyte provides an exceptionally stable system to enable lithium anodes, delivering >1500 cycles at a current density of 0.5 mAh g-1 and a capacity of 0.5 mAh g-1 in symmetrical cells. Furthermore, Li//LFP cells using this electrolyte demonstrate high-rate, reversible lithium storage, supplying 139 mAh g(LFP) -1 at C/2 (≈0.991 mAh cm-2 , @ 0.61 mA cm-2 ) with 87.5% capacity retention over 300 cycles (average Coulombic efficiency >99.86%).