Fluoride in the SEI Stabilizes the Li Metal Interface in Li-S Batteries with Solvate Electrolytes.

Lithium-sulfur (Li-S) batteries offer high theoretical gravimetric capacities at low cost relative to commercial lithium-ion batteries. However, the solubility of intermediate polysulfides in conventional electrolytes leads to irreversible capacity fade via the polysulfide shuttle effect. Highly concentrated solvate electrolytes reduce polysulfide solubility and improve the reductive stability of the electrolyte against Li metal anodes, but reactivity at the Li/solvate electrolyte interface has not been studied in detail. Here, reactivity between the Li metal anode and a solvate electrolyte (4.2 M LiTFSI in acetonitrile) is investigated as a function of temperature. Though reactivity at the Li/electrolyte interface is minimal at room temperature, we show that reactions between Li and the solvate electrolyte significantly impact the solid electrolyte interphase (SEI) impedance, cyclability, and capacity retention in Li-S cells at elevated temperatures. Addition of a fluoroether cosolvent to the solvate electrolyte results in more fluoride in the SEI which minimizes electrolyte decomposition, reduces SEI impedance, and improves cyclability. A 6 nm AlF3 surface coating is employed at the Li anode to further improve interfacial stability at elevated temperatures. The coating enables moderate cyclability in Li-S cells at elevated temperatures but does not protect against capacity fade over time.

Multielectron, Cation and Anion Redox in Lithium-Rich Iron Sulfide Cathodes.

Conventional Li-ion cathodes store charge by reversible intercalation of Li coupled to metal cation redox. There has been increasing interest in new materials capable of accommodating more than one Li per transition-metal center, thereby yielding higher charge storage capacities. We demonstrate here that the lithium-rich layered iron sulfide Li2FeS2 as well as a new structural analogue, LiNaFeS2, reversibly store ≥1.5 electrons per formula unit and support extended cycling. Ex situ and operando structural and spectroscopic data indicate that delithiation results in reversible oxidation of Fe2+ concurrent with an increase in the covalency of the Fe-S interactions, followed by reversible anion redox: 2 S2-/(S2)2-. S K-edge spectroscopy unequivocally proves the contribution of the anions to the redox processes. The structural response to the oxidation processes is found to be different in Li2FeS2 in contrast to that in LiNaFeS2, which we suggest is the cause for capacity fade in the early cycles of LiNaFeS2. The materials presented here have the added benefit of avoiding resource-sensitive transition metals such as Co and Ni. In contrast to Li-rich oxide materials that have been the subject of so much recent study and that suffer capacity fade and electrolyte degradation issues, the materials presented here operate within the stable potential window of the electrolyte, permitting a clearer understanding of the underlying processes.

Importance of time-to-reperfusion in patients with acute myocardial infarction with and without cardiogenic shock treated with primary percutaneous coronary intervention.

BACKGROUND: Time-to-treatment is important for survival in patients with acute myocardial infarction (AMI) treated with fibrinolytic therapy, but the importance of time-to-treatment with primary percutaneous coronary intervention (PCI) is controversial. Previous studies evaluating the importance of time-to-treatment with primary PCI have not analyzed patients with cardiogenic shock separately. METHODS: Consecutive patients with AMI (n = 1843) treated with primary PCI were prospectively enrolled in the LeBauer Cardiovascular Research Foundation Registry. Late clinical follow-up was obtained in 98% of patients, at a mean time of 6.1 years. RESULTS: Reperfusion times were longer in women and patients with diabetes mellitus and shorter in patients with prior myocardial infarction. In patients with shock (n = 138), the inhospital mortality rate increased progressively with increasing time-to-reperfusion (<3 hours, 31%; 3-<6 hours, 50%; > or =6 hours, 62%; P =.01), whereas in patients without shock (n = 1705), inhospital and late mortality rates were similar across 3 categories of time to reperfusion (<3 hours, 5.8%; 3-<6 hours, 4.6%; > or =6 hours, 4.8%; P =.46). After adjusting for differences in baseline variables, reperfusion time was a significant independent predictor of inhospital mortality in patients with shock, but not in patients without shock. CONCLUSIONS: Reperfusion time with primary PCI is important for survival in patients with shock, but appears to be less important in patients without shock. These data emphasize the importance of achieving early reperfusion in patients with shock and have implications on the triage of patients without shock for mechanical reperfusion and the mechanism of benefit of reperfusion therapy with primary PCI.

Effect of treatment delay on outcomes in patients with acute myocardial infarction transferred from community hospitals for primary percutaneous coronary intervention.

Outcomes were evaluated in 1,841 consecutive patients with acute myocardial infarction treated with primary percutaneous coronary intervention from 1984 to 2000 comparing patients transferred from community hospitals (n = 680) with patients presenting locally (n = 1,161). Baseline variables were similar except transferred patients had fewer prior infarctions (13% vs 21%, p <0.001) and underwent less prior bypass surgery (2.8% vs 6.0%, p = 0.002). Median times from symptom onset to emergency department arrival were similar, but door-to-balloon times and reperfusion times were approximately 1 hour longer in transferred patients (2.8 vs 1.9 hours [p <0.001] and 4.5 vs 3.5 hours [p <0.001], respectively). Despite longer treatment times, there were no significant differences between transferred and nontransferred patients in 30-day mortality (7.6% vs 8.1%, p = 0.73), reinfarction, urgent target vessel revascularization, stroke, and late mortality. After adjusting for differences in baseline variables, mortality remained similar between transferred and nontransferred patients (odds ratio 0.90, 95% confidence interval 0.59 to 1.36). Peak cardiac enzyme values were higher in transferred patients, but there were no differences in 6-month ejection fractions between groups. In conclusion, patients transferred from community hospitals for primary percutaneous coronary intervention have almost 1-hour additional treatment delay, but this does not appear to have a major adverse effect on clinical outcomes. These data should encourage further randomized trials to evaluate the role of transfer for mechanical reperfusion in patients presenting to community hospitals with acute myocardial infarction.