The performance of current Li–air batteries is greatly limited by critical obstacles such as electrolyte decomposition, high charging overpotentials, and limited cycle life. Thus, much effort is devoted to fundamental studies to understand the mechanisms of discharge/charge processes and overcome the above-mentioned obstacles. In particular, the search for new stable electrolytes is vital for long-lasting and highly cyclable batteries. The highly reactive lithium superoxide intermediate (LiO2) produced during discharge process can react with the electrolyte and produce a variety of byproducts that will shorten battery life span. To study this degradation mechanism, we investigated oxygen reduction reaction (ORR) in highly concentrated electrolyte solutions of lithium bis­(trifluoromethanesulfonyl)­amide (Li­[TFSA])/dimethyl sulfoxide (DMSO). On the basis of rotating ring disk electrode measurements, we showed that LiO2 dissolution can be limited by increasing lithium salt concentration over 2.3 mol dm–3. Our Raman results suggested that this phenomenon can be related to lack of free DMSO molecules and increasing DMSO–Li+ interactions with higher Li+ concentration. X-ray diffraction measurements for the products of ORR suggested that the side reaction of DMSO with Li2O2 and/or LiO2 could be suppressed by decreasing the solubility of LiO2 in highly concentrated electrolytes.

A solvate ionic liquid (SIL) was compared with a conventional organic solvent for the electrolyte of the Li-O battery. An equimolar mixture of triglyme (G3) and lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]), and a G3/Li[TFSA] mixture containing excess glyme were chosen as the SIL and the conventional electrolyte, respectively. Charge behavior and accompanying gas evolution of the two electrolytes was investigated by electrochemical mass spectrometry (ECMS). From the linear sweep voltammetry performed on an as-prepared cell, we demonstrate that the SIL has a higher oxidative stability than the conventional electrolyte and, furthermore, offers the advantage of lower volatility, which would benefit an open-type lithium-O cell design. Moreover, CO evolution during galvanostatic charge was less in the SIL, which implies less side reaction. However, O evolution during charge did not reach the theoretical value in either of the two electrolytes. Several mass spectral fragments were generated during the charge process, which provided evidence for side reactions of glyme-based electrolytes. We further relate the difference in observed discharge product morphology for these electrolytes to the solubility of the superoxide intermediate, determined by rotating ring disk electrode (RRDE) measurements.

The use of LiI as redox mediator for the charge reaction in nonaqueous Li/O 2 cells has been widely studied recently, as a possible means to fulfill the great promise of the Li/O 2 system as a high energy density "beyond Li-ion" battery. In this work, we highlight the importance of considering the redox potential for both the I − /I 3 − and I 3 − /I 2 redox couples and how the electrolyte solvent (here tetraglyme (G4) and dimethyl sulfoxide (DMSO)) and concentration (here 1.0 and 2.8 M) have a profound influence on these potentials. Through a combination of galvanostatic cycling, electrochemical mass spectrometry, and cyclic voltammetry, we thus consider the influence of solvent and electrolyte concentration on both the redox mediation and redox shuttle processes and suggest that this important aspect must be considered for further studies with mediators in Li/O 2 and related systems. We demonstrate that, in our system, 100 mM LiI in 1.0 M Li[TFSA]/DMSO provides the most effective redox mediation among the electrolytes we have studied but conversely exhibits the highest degree of redox shuttling (in the absence of O 2 ). The balance between effective limitation of redox shuttle and ease of mediator diffusion to discharge products is of great importance and should be considered in any future cell design utilizing a mediator.

This study reports a reversible oxygen reduction–oxygen evolution reaction (ORR–OER) that uses a solvate ionic liquid, [Li(triglyme)1][NTf2], as an electrolyte for a rechargeable Li–air (O2) battery. Significantly, it was found that the reversibility and capacity retention for ORR–OER in the solvate ionic liquid was greatly improved with a decrease in the ORR discharge depth; the discharge to 2.2 V vs. Li/Li+ gave much better reversibility than that to 2.0 V vs. Li/Li+.

Three-dimensionally macroporous nitrogen-doped carbon materials are fabricated via carbonization of an ionic-liquid-based small molecule precursor, 1-ethyl-3-methylimidazolium dicyanamide, using opal silica colloidal crystals as ah ard template. As compared to traditional polymerizable monomer-based precursors such as furfuryl alcohol, the entire process involving ionic liquid does not require any acid catalyst and prepolymerization step. More importantly,n itrogen heteroatomsc an be incorporated into the carbon skeleton in situ. The obtained inverse opal carbonsp ossess large surface areas and pore volumes, and high nitrogen content. When acting as metal-free electrocatalysts, the inverse opal carbonse xhibit high catalytic activity and selectivityt owards the oxygen reduction reaction in alkaline electrolyte, much better than that of the furfuryl-alcohol-derived inverse opal carbon and close to that of commercial Pt/C catalysts.The oxygen reduction reaction( ORR) is ak ey process in fuel cells and metal-air batteries. Platinumn anoparticless upported on high-surface-area carbon materials (Pt/C) are the most widely used electrocatalysts for ORR to date. However,h igh cost, the sluggish kinetics of the ORR process, and an intolerance to fuel crossover have limitedt he scalingu po fc orresponding renewable energy technologiesu sing Pt/C catalysts.[1] Consequently, there have been tremendous efforts on finding replacements for Pt-based catalysts. Amongt hese candidates, N-doped carbon materials as alternative metal-free catalysts are of particular interest.[2] Conjugation between the lone pair of the nitrogen heteroatom and p system of the carbon lattices results in structural irregularities in hexagonal carbon rings, imparting new catalytic sites and ah igh catalytic activity.[3] Despite the high performance of N-doped carbons, their catalytic activities are still far from satisfactory.T his is partly because of their relatively low nitrogen content as well as al ow surface utilization, resulting from randomly formed inaccessible narrow,s mall mesopores. Thus, aw ell-defineda nd continuousp orous structure with ar elativelyl arge surface area, large pore volume, regularp ores, and high nitrogen content is more preferable for high electrocatalytic activity.In this respect, inverse opal carbons (IOCs), which possess cage-like, orderedm acropores and three-dimensionally interconnected windows, could meet these requirements.[4] The large surface area and uniform pore size may facilitate the access of reactants to the active sites and allow ag ood reactant flux, resulting in high catalytic activity.I OC is technologically important for variousa pplicationss uch as photonic crystals, catalysis,s ensing, and separation techniques. For example, it has been previously reported that graphitic carbon nitride supported on three-dimensional interconnected macroporous carbon showed catalytic activity towards ORR comparable to that of commercial Pt/C.[5] Additionally,t he graphitic nature of the macroporous carbon could improve...

This study demonstrates that the amount of discharge product (Li 2 O 2 ) precipitated on the separator in a lithium oxygen cell using glyme-based electrolytes depends on the anion. The stability of the discharge intermediate (LiO 2 ) in the electrolyte has been shown to depend on the anionic species, which is related to Li 2 O 2 precipitation on the separator. The implications for producing an efficient and long-life Li-O 2 cell are elaborated. Keywords: Li-O 2 battery | Lithium superoxide | AnionThe Li-O 2 battery has been attracting a great deal of attention due to its high theoretical energy density.1 The solubility of the) is a critical parameter, because its solubility is believed to directly affect the morphology of the final discharge product, Li 2 O 2 .2 This morphology determines the rate of cathode clogging, thus also the maximum discharge capacity.2,3 The morphology has also been shown to affect the charging potential, 4 and thus directly influences the energy efficiency. However, a little-considered aspect is the extent to which the solubility of the O 2•¹ may allow the transport of reduced O 2 species away from the electrode. Nazar et al. reported SEM observation of discharge product deposition on glass fiber (separator) for a cell using 1 M lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA])/tetraethylene glycol dimethyl ether (G4) electrolyte. 5 The implications, in terms of cell cyclability, of precipitation of discharge product on an electronically nonconductive component of the cell are self-evident. Moreover, Liu et al. have demonstrated the presence of large amounts of predominantly amorphous precipitates in the separator of a Li-O 2 battery using a 1 M lithium trifluoromethanesulfonate (Li[OTf])/ G4 electrolyte, and commented on their detrimental effects on cell overpotential and cyclability. 6 In their later work, they also reported X-ray diffraction-based evidence for crystalline Li 2 O 2 in the separator.7 A means to tune the degree of discharge product loss to the separator (and elsewhere in the cell) by variation of the electrolyte properties is thus desirable. The effect of variation of electrolyte, and in particular the anion, on this phenomenon has not yet been reported, to the best of our knowledge.In this study, we present an analysis of the variation of O 2•¹ solubility, and its subsequent effect on Li 2 O 2 distribution in the cell, for a series of glyme-based electrolyte solutions. In our previous study, 8 we applied a 1:1 mixture of Li salt and glyme for oxygen reduction/evolution. We have also recently shown that variation of the anion in such 1:1 solutions results in large differences in the amount of free glyme depending on the choice of Li salt. 9 Thus, to fully characterize the direct effect of the anion on the intermediate solubility and stability, we have chosen to explore more dilute solutions in this study, in which the effects may be more easily observed. The molar ratio of lithium salt to triethylene glycol dimethyl ether (G3) was kept constant (1:4), and the vario...

revealed that solvate ILs are suitable candidates for Li-S battery electrolytes because they greatly suppress the dissolution of lithium polysulfides [10] due to the formation of the complexes which can weaken the donor ability of the ethers. We have also studied solvate ILs as electrolytes for the Li-air battery. [11] Regarding the design of a future energy storage device based on the nonaqueous lithium-air system, a closed system using pure oxygen within a pressure vessel was proposed. However, an open system is more desirable with respect to high energy density if ambient air can be used as the cathode active material. [12] In this study we focus on overcoming one of the main limitations of this "open" design, namely, the possibility for moisture, as well as CO 2 , from ambient air to react with lithium metal at the anode and also to deteriorate the cathode reaction. [13][14][15][16][17] Most existing reports concern battery experiments under dry conditions, which would incur large energy losses upon removal of moisture to obtain dry gas. [18] Hence a lithium conducting glass-ceramic is known to be a desirable material to protect the lithium metal from moisture. [19,20] However, the cathode reaction would still be deteriorated when employing anode protection. Also hydrophobic membranes that block moisture but permeate O 2 , [21] for example, a commodity polymer [22] such as polytetrafluoroethylene or immobilized liquid membranes [23,24] and other hydrophobic layers [25] have been studied for application with ambient air instead of dry air (O 2 ) as the cathode active material. These strategies can delay the ingress of water vapor, but water absorbed to the electrolyte (i.e., the equilibrium moisture content upon prolonged exposure of the device to humid air) cannot be eliminated in the long term. [26] Hydrophobic ionic liquids offer another potential solution. In order to limit the inherent equilibrium moisture content of the battery, careful consideration of the molecular design of the electrolyte is needed. Considering ionic liquids, both anion and cation can affect the sorption of moisture as previously reported. [27] [TFSA] is known to be a relatively hydrophobic anion, [28] but when applied in the previously reported solvate ILs, such as [Li (G4)] [TFSA], the resulting electrolyte absorbs a considerable amount of water. The equilibrium moisture content in [Li(G4)][TFSA] is more than 25 wt% at 30 °C and 90% RH, corresponding to a molar ratio of H 2 O to Li[TFSA] ([H 2 O]/[Li]) of about 9.9. So it is unlikely that [Li(G4)][TFSA] can be applied as the electrolyte forIn this study, the effect of water on the oxygen reduction reaction is initially investigated in aprotic ionic liquids by cyclic voltammetry, revealing that the presence of water significantly deteriorates the reversibility of the oxygen reduction reaction and oxygen evolution reaction, which will be detrimental to performance of a practical lithium-air battery. In order to prevent moisture intrusion from ambient air, a hydrophobic electrolyte is...