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Lithium metal batteries promise higher energy densities than current lithium-ion batteries but require novel electrolytes to extend their cycle life. Fluorinated solvents help stabilize the solid electrolyte interphase (SEI) with lithium metal, but are believed to have weaker solvation ability compared to their nonfluorinated counterparts and are deemed 'poorer electrolytes'. In this work, we synthesize tris(2-fluoroethyl) borate (TFEB) as a new fluorinated borate ester solvent and show that TFEB unexpectedly has higher lithium salt solubility than its nonfluorinated counterpart (triethyl borate). Through experiments and simulations, we show that the partially fluorinated –CH2F group acts as the primary coordination site that promotes lithium salt dissolution. TFEB electrolyte has a higher lithium transference number and better rate capability compared to methoxy polyethyleneglycol borate esters reported in the literature. In addition, TFEB supports compact lithium deposition morphology, high lithium metal Coulombic efficiency, and stable cycling of lithium metal/LiFePO4 cells. This work ushers in a new electrolyte design paradigm where partially fluorinated moieties enable salt dissolution and can serve as primary ion coordination sites for next-generation electrolytes. [ABSTRACT FROM AUTHOR]

Amorphous Li3PS4 (LPS) solid-state electrolytes are promising for energy-dense lithium metal batteries. LPS glass, synthesized from a 3 : 1 mol ratio of Li2S and P2S5, has high ionic conductivity and can be synthesized by ball milling or solution processing. Ball milling has been attractive because it provides the easiest route to access amorphous LPS with a conductivity of 3.5 × 10−4 S cm−1 (20 °C). However, achieving the complete reaction of precursors via ball milling can be difficult, and most literature reports use X-ray diffraction (XRD) or Raman spectroscopy to confirm sample purity, both of which have limitations. Furthermore, the effect of residual precursors on ionic conductivity and lithium metal cycling is unknown. In this work, we illustrate the importance of multimodal characterization to determine LPS phase and chemical purity. To determine the residual Li2S content in LPS, we show that (1) XRD and 31P solid state nuclear magnetic resonance (ssNMR) are insufficient and (2) Raman loses sensitivity at concentrations below 12 mol% Li2S. Most importantly, we show that 7Li ssNMR is highly sensitive. Using 7Li ssNMR, we investigate the effect of ball milling parameters and develop a robust and highly reproducible procedure for pure LPS synthesis. We find that as the residual Li2S precursor content increases, LPS conductivity decreases and lithium metal batteries exhibit higher overpotentials and poor cycle life. Our work reveals the importance of multimodal characterization techniques for amorphous solid-state electrolyte characterization and will enable better synthetic strategies for highly conductive electrolytes for efficient energy-dense solid-state lithium metal batteries. [ABSTRACT FROM AUTHOR]

Development of better energy storage media is vital in the adoption of renewable energy technologies, and lithium-air (O2) batteries have spurred great interest. However, current Li-O2 batteries are plagued by unwanted side reactions, flammable electrolytes, and slow kinetics attributed to the 2 mol e-/mol O2 peroxide chemistry. In this work, we show that a gel polymer electrolyte consisting of a polymer, ionic liquid, and salt can control the oxygen reduction chemistry in a Li-O2 cell (switching from a 2 e- to a 1 e- superoxide chemistry), support the formation of ionic liquid-superoxide complexes, and reduce the number of reactive species present in the cell. A one electron process could allow for newer energy-dense Li-O2 batteries with faster kinetics and higher energy efficiencies typical of superoxide-dominant Na-O2 and K-O2 batteries. [ABSTRACT FROM AUTHOR]

Charging kinetics and reversibility of Na–O2 batteries can be influenced greatly by the particle size of NaO2 formed upon discharge, and exposure time (reactivity) of NaO2 to the electrolyte. Micrometer-sized NaO2 cubes formed at high discharge rates were charged at smaller overpotentials compared to nanometer-sized counterparts formed at low rates. [ABSTRACT FROM AUTHOR]

Recent studies have shown that manyaprotic electrolytes used inlithium–air batteries are not stable against superoxide andperoxide species formed upon discharge and charge. However, the stabilityof polymers often used as binders and as electrolytes is poorly understood.In this work, we select a number of polymers heavily used in the Li–air/Li-ionbattery literature, and examine their stability, and the changes inmolecular structure in the presence of commercial Li2O2. Of the polymers studied, poly(acrylonitrile) (PAN), poly(vinylchloride) (PVC), poly(vinylidene fluoride) (PVDF), poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP), andpoly(vinylpyrrolidone) (PVP) are reactive and unstable in the presenceof Li2O2. The presence of the electrophilicnitrile group in PAN allows for nucleophilic attack by Li2O2at the nitrile carbon, before further degradation ofthe polymer backbone. For the halogenated polymers, the presence ofthe electron-withdrawing halogens and adjacent α and βhydrogen atoms that become electron-deficient due to hyperconjugationmakes PVC, PVDF, and PVDF-HFP undergo dehydrohalogenation reactionswith Li2O2. PVP is also reactive, but with muchslower kinetics. On the other hand, the polymers poly(tetrafluoroethylene)(PTFE), Nafion, and poly(methyl methacrylate) (PMMA) appear stableagainst nucleophilic Li2O2attack. The lackof labile hydrogen atoms and the poor leaving nature of the fluoridegroup allow for the stability of PTFE and Nafion, while the methyland methoxy functionalities in PMMA reduce the number of potentialreaction pathways for Li2O2attack in PMMA.Poly(ethylene oxide) (PEO) appears relatively stable, but may undergosome cross-linking in the presence of Li2O2.Knowledge gained from this work will be essential in selecting anddeveloping new polymers as stable binders and solid or gel electrolytesfor lithium–air batteries. [ABSTRACT FROM AUTHOR]

Reducing the energy loss associated with Li2O2 electrochemical oxidation is paramount to the development of efficient rechargeable lithium–oxygen (Li–O2) batteries for practical use. The influence of a series of perovskites with different eg filling on the kinetics of Li2O2 oxidation was examined using Li2O2-prefilled electrodes. While LaCrO3 is inactive for oxygen evolution upon water oxidation in alkaline solution, it was found to provide the highest specific current towards Li2O2 oxidation among all the perovskites examined. Further exploration of Cr-based catalysts showed that Cr nanoparticles (Cr NP) with an average particle size of 40 nm, having oxidized surfaces, had comparable surface area activities to LaCrO3 but much greater mass activities. Unlike Pt/C and Ru/C that promote electrolyte oxidation in addition to Li2O2 oxidation, no evidence of enhanced electrolyte oxidation was found for Cr NP relative to Vulcan carbon. X-ray absorption spectroscopy at the O K and Cr L edge revealed a redox process of Cr3+↑ Cr6+ on the surface of Cr NP upon Li2O2 oxidation, which might be responsible for the enhanced oxidation kinetics of Li2O2 and the reduced charging voltages of Li–O2 batteries. [ABSTRACT FROM AUTHOR]

Correction for ‘Revealing instability and irreversibility in nonaqueous sodium–O2 battery chemistry’ by Sayed Youssef Sayed et al., Chem. Commun., 2016, 52, 9691–9694. [ABSTRACT FROM AUTHOR]

CO 2 electrochemical reduction (CO 2 R) in aprotic media is a promising alternative to aqueous electrocatalysis, as it minimizes the competing hydrogen evolution reaction while enhancing CO 2 solubility. To date, state-of-the-art alkali salts used as electrolytes for selective aqueous CO 2 R are inaccessible in aprotic systems due to the inactivation of the electrode surface from carbonate deposition. In this work, we demonstrate that an acidic nonaqueous environment enables sustained CO 2 electrochemical reduction with common alkali salts in dimethyl sulfoxide. Electrochemical and spectroscopic techniques show that at low pH carbonate buildup can be prevented, allowing CO 2 R to proceed. Product distribution with a copper electrode revealed up to 80% Faradaic efficiency for CO 2 R products, including carbon monoxide, formic acid, and methane. By understanding the mechanism for electrode inactivation in an aprotic medium and addressing that challenge with dilute acid addition, we pave the way toward the development of more efficient and selective electrolytes for CO 2 R.

Successful transformation of carbon dioxide (CO 2 ) into value-added products is of great interest, as it contributes in part to the circular carbon economy. Understanding chemical interactions that stabilize crucial reaction intermediates of CO 2 is important, and in this contribution, we employ atom centered density matrix propagation (ADMP) molecular dynamics simulations to investigate interactions between CO 2 - anion radicals with surrounding solvent molecules and electrolyte cations in both aqueous and nonaqueous environments. We show how different cations and solvents affect the stability of the CO 2 - anion radical by examining its angle and distance to a coordinating cation in molecular dynamics simulations. We identify that the strength of CO 2 - interactions can be tailored through choosing an appropriate cation and solvent combination. We anticipate that this fundamental understanding of cation/solvent interactions can facilitate the optimization of a chemical pathway that results from selective stabilization of a crucial reaction intermediate., Competing Interests: The authors declare no competing financial interest., (© 2022 Chicago Argonne, LLC, Operator of Argonne National Laboratory. Published by American Chemical Society.)

Correction for 'Revealing instability and irreversibility in nonaqueous sodium-O 2 battery chemistry' by Sayed Youssef Sayed et al., Chem. Commun., 2016, 52, 9691-9694.