High Donor Number Research Articles

Achieving three-dimensional lithium sulfide growth in lithium-sulfur batteries using high-donor-number anions

Uncontrolled growth of insulating lithium sulfide leads to passivation of sulfur cathodes, which limits high sulfur utilization in lithium-sulfur batteries. Sulfur utilization can be augmented in electrolytes based on solvents with high Gutmann Donor Number; however, violent lithium metal corrosion is a drawback. Here we report that particulate lithium sulfide growth can be achieved using a salt anion with a high donor number, such as bromide or triflate. The use of bromide leads to ~95 % sulfur utilization by suppressing electrode passivation. More importantly, the electrolytes with high-donor-number salt anions are notably compatible with lithium metal electrodes. The approach enables a high sulfur-loaded cell with areal capacity higher than 4 mA h cm−2 and high sulfur utilization ( > 90 %). This work offers a simple but practical strategy to modulate lithium sulfide growth, while conserving stability for high-performance lithium-sulfur batteries.

Correlating Ionic Conductivity, Oxygen Transport and ORR with Structure of Dialkylacetamide-Based Electrolytes for Lithium-Air Batteries

Chemical structures of lithium and tetrabutylammonium (TBA) salt solutions in N,N-dimethylacetamide (DMAc) and N,N-diethylacetamide (DEAc), two high Donor Number organic solvents, have been studied. In LiX salt solutions (where X = PF6−, CF3SO3−, ClO4− and NO3−), solvation occurs when the Li+ bonds with the solvent's carbonyl group forming Li+[O=C(CH3)N(CH3)2]nX− ion pairs. Infrared and 13C-NMR spectra are consistent with the ion pair being solvent-separated when the anion is PF6−, ClO4− or NO3−, and a contact ion pair in the case of CF3SO3−. Chemical interactions between TBA+ and the solvents to form conducting solutions appeared to be dipolar in nature. Ionic conductivities of TBA+ and Li+ electrolytes were measured and correlated with their viscosities. In 0.1M TBAPF6/DMAc, the O2 solubility and diffusion coefficient (3.09 × 10−6 mol/cm−3 and 5.09 × 10−5 cm2s−1, respectively) measured using microelectrode technique are typical of values measured in several TBA+ solutions. Microelectrode voltammetry revealed steady-state limiting current behavior for oxygen reduction reactions (ORR) in TBAX/DMAc electrolytes indicating a reversible ORR process. Conversely, microelectrode current-voltage data for ORR in LiX/DMAc electrolytes revealed irreversible behavior mainly ascribed to the blockage of the electrode surface by insoluble ORR products. The ORR in DMAc correlated with its high Donor Number and the overall process conformed to the Hard-Soft Acid-Base theory.

Seroepidemiology of transfusion-transmitted infections among blood donors at a tertiary care center in Navi Mumbai, Maharashtra

Background: Blood is precious as well as scarce lifesaving medication. Proper screening of transfusion-transmitted infections (TTIs) such as human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), syphilis, and malarial parasite (MP) with appropriate methods is needed to ensure that the donated blood is made innocuous for transfusion. Objective: The aim of the study was to estimate the prevalence of TTI and their epidemiological aspects in blood donors in a hospital-based blood bank in Nerul, Navi Mumbai. Materials and Methods: A retrospective study of the total of 4708 donors was carried out from January 2015 to December 2018 year. Screening of HIV was done using the fourth-generation enzyme-linked immunosorbent assay (ELISA) and for hepatitis B surface antigen (HbsAg) and HCV by the third-generation ELISA kit. Testing for syphilis was done with rapid plasma reagin and MP was tested with rapid card test. Results: Voluntary donors were 4702 (99.9%) while replacement constituted for 6 (0.12%) number of cases. Among 4708 donors, 4079 (96%) were male and 629 (4%) were female. Among 66 (1.4%) transfusion transmitted diseases (TTD)-positive donors, the highest number of donors 28 (42%) belongs to 18–27 years of age group while the lowest 5 (2%) belonged to 48–57 years. Overall prevalence of HIV, HbsAg, HCV, syphilis, and MP was 0.08%, 1.1%, 0.2%, 0.04%, and 0.02%, respectively. Conclusion: The prevalence of TTD was more in males, in 18–27 age groups, and in voluntary donors. The most common TTI was HBV, followed by HCV, HIV, syphilis, and MP, respectively.

Highly Solvating Electrolytes for Lithium-Sulfur Batteries.

There is a critical need to evaluate lithium-sulfur (Li-S) batteries with practically relevant high sulfur loadings and minimal electrolyte. Under such conditions, the concentration of soluble polysulfide intermediates in the electrolyte drastically increases, which can alter the fundamental nature of the solution-mediated discharge and thereby the total sulfur utilization. In this work, we present an investigation into various high donor number (DN) electrolytes that allow for increased polysulfide dissolution, and demonstrate how this property may in fact be necessary for increasing sulfur utilization at low electrolyte and high loading conditions. The solvents dimethylacetamide, dimethyl sulfoxide, and 1-methylimidazole are holistically evaluated against dimethoxyethane as electrolyte co-solvents in Li-S cells, and they are used to investigate chemical and electrochemical properties of polysulfide species at both dilute and practically relevant conditions. The nature of speciation exhibited by lithium polysulfides is found to vary significantly between these concentrations, particularly in regards to the S3 •- species. Furthermore, the extent of the instability in conventional electrolyte solvents and high DN solvents with both lithium metal and polysulfides is thoroughly investigated. These studies establish a basis for future efforts into rationally designing an optimal electrolyte for a lean electrolyte, high energy density Li-S battery.

Ink-jet printing films of molybdates of alkaline earth metals with scheelite structure applied in the photocatalytic CO2 reduction

The photocatalytic CO2 reduction is a clean and sustainable process to generate value-added products by using water, sunlight, and photocatalysts materials. In this work, it is proposed the use of thin films based on molybdates of alkaline earth metals of general formula AMoO4 (A = Ca, Sr, and Ba) with scheelite-structure as photocatalysts for the conversion of CO2. The films were deposited by ink-jet printing, which is a technique that offers high speed and low cost of fabrication, and provide the possibility to print over different substrates. The AMoO4 films were characterized by razing incidence X-ray diffraction (GZXD), Fourier-transform Infrared Spectroscopy (FTIR), Scanning Electronic Microscopy (SEM), Diffuse Reflectance Spectroscopy (DRS), profilometry, spectroscopic ellipsometry (SE), Electrochemical Impedance Spectroscopy (EIS), and zeta potential measurements. According to the characterization, it was confirmed the crystallization of the scheelite structure in the CaMoO4, SrMoO4, and BaMoO4 films. The effect of the type and size of the A cation affected several physical properties such as crystallite size, thickness, potential of the conduction band, zeta potential, and the affinity for CO2 adsorption, which it was reflected in the photocatalytic activity of each film. The main product of the photocatalytic CO2 reduction was CH3OH, although it was detected the formation of H2 as by-product of the reaction. The photocatalytic activity for methanol production increased as follows: CaMoO4>SrMoO4>BaMoO4, which it was related to a higher affinity for CO2 molecule, low crystallite size, low thickness, adequate potential of conduction band and a higher donor number. The highest solar fuel yield obtained was 18 μmol cm−2 h−1, which it was higher than previous reports using films of other semiconductor materials.

Continuous synthesis of high quality metal–organic framework HKUST-1 crystals and composites via aerosol-assisted synthesis

Highly crystalline metal–organic framework (MOF) crystals are desirable for their practical applications and synthesized predominantly using batch processes that are less scalable. More scalable continuous processes for MOF synthesis such as spray-drying and aerosol-assisted synthesis have been recently developed. However, these techniques often resulted in poorly crystalline nanoparticles and their assemblies primarily due to extremely short (sub-second) crystallization time and fast solvent evaporation. Here we report facile continuous aerosol-assisted production of highly crystalline HKUST-1 crystals with relatively narrow size distributions as well as their composites with both inorganic and organic materials exhibiting unique microstructures. Solvents with high donor numbers and low vapor pressures were found desirable to increase both crystallization and solvent evaporation times. Dimethyl sulfoxide (DMSO) was used as a co-solvent with DMF to form phase-pure high quality HKUST-1 crystals revealed by SEM, XRD, and N2 adsorption. Furthermore, alumina nanoparticles and polyethersulfone (PES) polymer were incorporated to create unique microstructures.

The Rechargeable Aprotic Lithium-oxygen Battery

Interest in the rechargeable Li-O2 battery is driven by its high theoretical specific energy (3500 Whkg-1).1-2 However, a number of challenges face the realization of practical devices.3-10 Overcoming these challenges requires an understanding of the reactions and processes in the cell, especially at the electrodes. Our focus has been on the reaction at the positive electrode: O2 + 2e- + 2Li+ = Li2O2 This simple reaction belies the complexity of the problems during charge and discharge. Li2O2, is an insulating solid, if it grows on the electrode surface it can only do so to a thickness of approx. 6 to 7 nm. The resulting passivation leads to low rates and low capacities.11 If Li2O2 grows from solution, passivation is avoided, leading to high rates and capacities.12 The solvent donor number is an important factor in controlling which pathway, surface film or solution growth, occurs. Low donor number ethers promote surface films while high donor numbers result in solution growth. Unfortunately, high donor number solvents are more susceptible to decomposition by the reactive O2 - nucleophile (the intermediate in the O2/Li2O2 reaction is LiO2).13 We show that using redox mediator molecules to shuttle electrons between the electrode surface and solution, Li2O2 can be formed and decomposed in solution even in low donor number solvent like ethers.14 As a result, rates and capacities of several mA and mAh cm-2 respectively are observed. The impact of the mediators on solvent and electrode stability will be discussed in the context of the mechanism of Li2O2 formation and decomposition. Ultimately, the Li-O2 cell must operate in air. The effect of H2O in the gas stream and hence in the electrolyte solution on the mechanism of O2/Li2O2 and the effect on cell performance are important. The influence of H2O on the O2 reduction mechanism will be considered. REFERENCES [1] D. Aurbach; B.D. McCloskey; L.F. Nazar; P.G. Bruce, Nature Energy 2016, 1, 16128. [2] J.W. Choi; D. Aurbach, Nature Reviews Materials 2016, 1, 16013. [3] N. Mahne; B. Schafzahl; C. Leypold; M. Leypold, et al., Nature Energy 2017, 2, 17036. [4] K.U. Schwenke; M. Metzger; T. Restle; M. Piana, et al., Journal of The Electrochemical Society 2015, 162 (4), A573-A584. [5] D. Grübl; B. Bergner; D. Schröder; J. Janek, et al., The Journal of Physical Chemistry C 2016, 120 (43), 24623-24636. [6] H.-D. Lim; B. Lee; Y. Zheng; J. Hong, et al., Nature Energy 2016, 1 (6), 16066. [7] B.D. McCloskey; D. Addison, ACS Catalysis 2017, 7 (1), 772-778. [8] S. Ganapathy; J.R. Heringa; M.S. Anastasaki; B.D. Adams, et al., The Journal of Physical Chemistry Letters 2016. [9] A.I. Belova; D.G. Kwabi; L.V. Yashina; Y. Shao-Horn, et al., The Journal of Physical Chemistry C 2017, 121 (3), 1569-1577. [10] D. Krishnamurthy; H.A. Hansen; V. Viswanathan, ACS Energy Letters 2016, 1 (1), 162-168. [11] V. Viswanathan; K.S. Thygesen; J.S. Hummelshoj; J.K. Norskov, et al., Journal of Chemical Physics 2011, 135 (21), 214704. [12] L. Johnson; C. Li; Z. Liu; Y. Chen, et al., Nature Chemistry 2014, 6 (12), 1091-1099. [13] A. Khetan; A. Luntz; V. Viswanathan, The Journal of Physical Chemistry Letters 2015, 6 (7), 1254-1259. [14] X. Gao; Y. Chen; L.R. Johnson; Z.P. Jovanov, et al., Nature Energy 2017, 2, 17118.

Control of Interfacial Properties between Polymer Gel Electrolytes and Counter Electrodes for Efficient Quasi-Solid Photoelectrochemical Solar Cells

There has been much attention towards dye-sensitized solar cells (DSSCs) for the past decades due to their attractive features such as reasonable energy conversion efficiency and low energy production cost. Recently, cobalt complexes have been suggested as one of the most promising candidates for replacing conventional iodine redox shuttles owing to their high voltage characteristics. Although high energy efficiency exceeding 12% was reported by employing liquid electrolyte that consists of cobalt complex redox mediator and volatile solvent, the use of volatile liquid solvent cannot ensure the long-term stability of DSSCs. In this work, therefore, novel polymer gel electrolytes (PGEs) including cobalt complexes as redox couples have been developed for efficient and long-term stable DSSCs. The physicochemical properties of PGEs were adjusted by selecting proper solvent and functional additives (for improving cobalt complex solubility and cation transference number etc.). Polyethers with polar groups (e.g. PEO and PMO) and polymers without polar groups (e.g. PVdF-HFP) were used as the polymer additives for the gelation of the liquid electrolytes with various blending ratios. Especially, various organic solvents with relatively high boiling points were tested to prepare long-term stable polymer gel electrolytes containing cobalt complex redox shuttles. Solvents with high donor number induced significant dissolution of dyes attached on TiO2 and therefore the low volatile solvents with moderate donor number and dielectric constant were utilized in this work. DSSCs employing PGEs with cobalt redox couples also showed better long-term stability compared with those of DSSCs filled with liquid electrolytes at 50 oC for 700 h. In addition, several types of conjugated polymer based counter electrodes have been prepared and used for the fabrication of DSSCs to decrease the high charge transport resistance occurred between the PGE and counter electrode. The photovoltaic and electrochemical performances of the DSSCs have been systematically analyzed via the J-V curve measurement and various electrochemical characterizations such as EIS and CV analyses. Acknowledgments: This work was supported by a grant (No.2017000140002/ RE201702218) from the Environmental Industry Advancement Technology Development Project of Korea Environmental Industry & Technology (KEITI) funded by Korea Ministry of Environment (MOE).

Elucidating the Structure and Electrochemical Properties of Dimethylacetamide-Based Electrolytes for Lithium-Air Batteries

Improving the performance and rechargeability of Lithium-air batteries, which offer up to ten times more energy density than Li-ion batteries, has been the focus of much research in the last decade.1, 2 One of the ways to improve these batteries is to gain a deeper understanding of the oxygen reduction reactions (ORR) in non-aqueous electrolytes in order to find an optimum combination of Li salt and solvent that provides chemical stability and rechargeability. In this paper, we report the results of a study of the physical and electrochemical properties of N,N-dimethylacetamide (DMAc)-based electrolytes containing either lithium or tetrabutylammonium (TBA) salts (LiX and TBAX, where X= PF6 -, CF3SO3 -, ClO4 - and NO3 -). The chemical structures of the salt solutions were determined from NMR and FTIR spectroscopic data. The spectra revealed that DMAc (CH3CON(CH3)2) solvates the lithium salts via bonding between its carbonyl (C=O) group and Li+ to form ion pairs. In the case of Li salts with the anions PF6 -, ClO4 - or NO3, the ion pairs are solvent separated while in the case of CF3SO3 -, it is a contact ion pair. On the other hand, the nature of the interactions between DMAc and the TBA+ ions appeared to be dipolar in agreement with its soft Lewis acidity.3 The conductivities of these electrolytes were measured as a function of temperature from -20 to 40 oC and correlated with their concentrations and viscosities. The conductivities plotted versus temperature showed a linear fit for Vogel-Tamman-Fulcher (VTF) relationship indicating a solvent-assisted ion conduction mechanism. Diffusion coefficient and solubility of O2 in the various electrolytes measured using a microelectrode technique are reported in Table 1. Cyclic voltammograms (CV) for ORR on microelectrode in TBA/DMAc electrolytes (Figure 1A) showed steady-state limiting current behavior indicating that the ORR process is electrochemically reversible. In all Li/DMAc electrolytes the CVs (Figure 1B) on microelectrodes showed an electrochemical irreversible behavior. The irreversibility of the ORR process in Li/DMAc electrolytes is primarily caused by the deposition of insoluble reduction products on the electrode surface. The results obtained in this study correlates with the high donor number of DMAc (27.8) and comply with the Hard Soft acid base (HSAB) theory.3, 4

On PEO-Based MWCNT and Graphene Composite Electrolyte Structure

Novel and highly effective polyethylene oxide (PEO) based composite electrolytes were prepared by combining the graphene nanoplatelets (GR) and multiwall carbon nanotubes (MWCNT) for the application as solid polymer electrolyte. MWCNT and GR were used as reinforcing filler and as electrical conductivity enhancement agent. Dispersions in N,N-dimethylformamide (DMF) of MWCNT and GR within the PEO matrix were prepared. DMF are featured by high electron-pair donor number and low hydrogen-bonding parameters, therefore DMF is considered a standard for liquid-phase exfoliation of MWCNT and GR. In our study, the MWCNT and GR solutions were tip sonicated using an ultrasonic processor, operated at 80% amplitude. A pulse-mode (cycle of 0.5 s) sonication was used because of the system relaxation role for the off phase, allowing a higher cavitation intensity and lower heat generation to be reached. Subsequent heat pressing was applied to obtain thin solid PEO composite electrolytes. Analyses of the experimental and theoretical density of prepared solid PEO composite electrolytes are calculated and discussed. GR and MWCNT functionalization effect on void content of polymer composites is evaluated. FTIR analysis was carried out to further investigate the effect of fillers content. The SEM results showed that surface of electrolyte film became rougher after the addition of MWCNT and GR. It is concluded, that the higher is filler fraction, the lower is void content and greater is composite density.

Effect of high donor number solvent and cathode morphology on interfacial processes in Li-air batteries

The work is focused on the investigation of the effect of solvent and carbon cathode morphology on the performance of Li-air batteries. Molecular dynamics simulation was used to explore the interfacial behavior of the main reactants (O2 and Li+) of the oxygen reduction reaction in high donor number solvent dimethyl sulfoxide (DMSO) at the following carbon surfaces: graphene plane, graphene edge, nanotube. It was shown that the adsorption barrier of O2 molecules decreases in the order graphene plane > nanotube > graphene edge, leading to the fastest adsorption kinetics on graphene edges. Strong solvation of Li+ in DMSO prevents ions adsorption on defect-free graphene planes and nanotubes, which is qualitatively different from low donor number solvents, such as acetonitrile. It can be concluded from these results, that nucleation and growth of discharge products in DMSO is shifted from the surface towards the solvent bulk that, in turn, leads to capacity increase of Li-air batteries.

In Situ Surface-Enhanced Infrared Spectroscopy to Identify Oxygen Reduction Products in Nonaqueous Metal–Oxygen Batteries

We report on the detection of metastable, solvated, and surface adsorbed alkali metal–oxygen (M–O2) discharge species using in situ attenuated total reflectance surface enhanced infrared absorption spectroscopy (ATR-SEIRAS). Oxygen–oxygen stretching bands (νO–O) of superoxide species formed during M–O2 battery discharge have been challenging to observe by conventional infrared (IR) techniques, and because of this, there has been limited use of IR techniques for in situ monitoring of the discharge products at the cathode in metal–O2 batteries. We explore SEIRAS technique to investigate lithium–oxygen and sodium–oxygen electrochemistry in acetonitrile (MeCN; a low Gutmann donor number solvent) as well as dimethyl sulfoxide (DMSO; a high Gutmann donor number solvent) in order to demonstrate the feasibility of our approach in the ongoing efforts toward the realization of M–O2 battery technology. In situ IR spectroscopy studies, together with a coupled-cluster method including perturbative triple excitations [...

Electrode/Electrolyte Interface in the Li–O2 Battery: Insight from Molecular Dynamics Study

In this paper, for the first time, we report the results of molecular dynamics simulation of the electrode/electrolyte interface of a Li–O2 cathode under potentials close to experimental values in 1 M dimethyl sulfoxide (DMSO) solution of LiPF6 salt. Electric potential profiles, solvent structuring near the electrode surface, and salt ion distributions are presented and discussed here as well as potentials of mean force (PMFs) of oxygen and its reduction products. The latter would be of a great use for future theoretical studies of reaction kinetics as PMF is essentially the work term required for reaction rate constant estimations. At the electrode/electrolyte interface under realistic potentials, oxygen anions are effectively pushed out of the reaction layer, making the second reduction of superoxide anion hardly probable. This indicates that the main cause of the electrode surface passivation should be lithium superoxide presence near the electrode surface. The way to suppress the passivation is to shift the equilibrium Ȯ2– + Li+ ⇌ LiO2 to the side of separately solvated ions, for example, by using solvents resulting in lower free energy of the ions. This conclusion is in agreement with the hypothesis stating that high donor number solvents lead to dominant solution Li2O2 growth and significantly higher cell discharge capacities.

The impact of solvent properties on the performance of oxygen reduction and evolution in mixed tetraglyme-dimethyl sulfoxide electrolytes for Li-O2 batteries: Mechanism and stability

The instability of the electrolyte and the sluggish kinetics of the reactions hinder the application of Li-O2 batteries. In this study, we aim to better understand the behavior of oxygen reduction (ORR) and evolution (OER) reactions in dimethyl sulfoxide (DMSO), Tetraglyme (G4) and their blend DMSO-G4, with emphasis on the role of solvent nature in the mechanism and reaction route, using rotating ring-disc electrode (RRDE) and differential electrochemical mass spectrometry (DEMS). Interestingly, RRDE results showed that the stability and the ratio of the formed O2−·: Li2O2 increase with addition of DMSO to G4. A proposed mechanism for ORR is discussed. Depending on the solvation ability of the solvent, which primarily determines the lifetime and solubility of the superoxide intermediate in solution, a solution or a surface-based pathway is followed: in highly solvating solvents (e.g. those with high donor or acceptor number) such as DMSO, superoxide is stabilized in solution; while in low solvating solvent, it is further reduced to Li2O2, blocking the surface. The results of the scan rate variation under defined mass transport in DMSO suggest a sequential formation of monolayers of Li2O2 during reduction. In G4-solutions, despite of the reversible formation of Li2O2, deactivation of the electrode takes place, as evidenced by DEMS. This could arise from a reduction products-induced decomposition of the electrolyte, forming a deactivating film on the surface during ORR, which is only partially removed at higher potentials evolving CO2. Also, we found that DMSO is more active towards OER than G4. The electrode material as well influences the kinetics, in particular of OER. These findings could have implications for the development of Li-air battery.

Lithium-Oxygen Battery with a Phosphorene-Derived Protective Layer on a Lithium Anode

Although Li-ion batteries have been considered as promising power sources of electric vehicles, their energy and power densities should be improved to satisfy the demanded electrochemical performance of the electric vehicles1, 2. In this regard, lithium-oxygen batteries with high energy densities have attracted a great deal of attention as an alternative to replace conventional Li-ion batteries. However, there are several challenging issues for the development of Li-O2 batteries. First, the large polarization of an oxygen electrode observed during charging should be improved by developing appropriate catalysts. Second, Li dendrite growth leads to poor cycle performance and safety. Third, stable electrolytes against both superoxide radicals and Li metal should be introduced. Many electrolytes are easily decomposed by nucleophilic attack of superoxide radicals, forming lithium alkyl carbonates such as Li2CO3 3-5. In this respect, high donor number solvents such as N,N-dimethylacetamide (DMA) are appropriate for Li-O2 batteries because they are chemically and electrochemically stable against superoxide radicals. However, most high donor number solvents cannot be used as electrolytes because they are known to be decomposed with Li metal6-8. Therefore, Li metal protection should be demanded to use high donor number solvents for Li-O2batteries. Many efforts have been made to protect Li metal, leading to improved electrochemical performance. However, many problems still remain unsolved. There are at least three requirements for Li metal protection in Li-O2 batteries, as follows: i) The electrolyte should be rarely decomposed on a protective layer, ii) Li dendrite growth on a protective layer should be thermodynamically unfavorable, and iii) the mechanical strength of a protective layer should be sufficiently high to suppress Li dendrite growth (> 3.4 GPa)9. In this study, as a promising protective layer satisfying these requirements, we introduce a two-dimensional phosphorene-derived Li3P protective layer for the first time. An electrochemically active phosphorene-derived Li3P protective layer thermodynamically suppresses electrolyte decomposition because the redox potential of Li3P is higher than the lowest unoccupied molecular orbital level (LUMO) of electrolyte solvents. In addition to the suppressed electrolyte decomposition, the phosphorene-derived Li3P protective layer thermodynamically inhibits Li dendrite growth because Li plating is thermodynamically unfavorable on Li3P surfaces compared to Li metal surfaces. This is supported by density functional theory (DFT) calculations that compared Li addition and removal energies on Li metal and Li3P surfaces. Because of these properties, the phosphorene-coated Li metal anode shows excellent electrochemical performance including stable cycle performance of Li symmetric cells over 500 cycles with a variety of electrolytes and no capacity fading of Li-O2 batteries over 50 cycles even with 1 MLiTFSI in DMA.

Designer interphases for the lithium-oxygen electrochemical cell.

An electrochemical cell based on the reversible oxygen reduction reaction: 2Li+ + 2e - + O2↔ Li2O2, provides among the most energy dense platforms for portable electrical energy storage. Such Lithium-Oxygen (Li-O2) cells offer specific energies competitive with fossil fuels and are considered promising for electrified transportation. Multiple, fundamental challenges with the cathode, anode, and electrolyte have limited practical interest in Li-O2 cells because these problems lead to as many practical shortcomings, including poor rechargeability, high overpotentials, and specific energies well below theoretical expectations. We create and study in-situ formation of solid-electrolyte interphases (SEIs) based on bromide ionomers tethered to a Li anode that take advantage of three powerful processes for overcoming the most stubborn of these challenges. The ionomer SEIs are shown to protect the Li anode against parasitic reactions and also stabilize Li electrodeposition during cell recharge. Bromine species liberated during the anchoring reaction also function as redox mediators at the cathode, reducing the charge overpotential. Finally, the ionomer SEI forms a stable interphase with Li, which protects the metal in high Gutmann donor number liquid electrolytes. Such electrolytes have been reported to exhibit rare stability against nucleophilic attack by Li2O2 and other cathode reaction intermediates, but also react spontaneously with Li metal anodes. We conclude that rationally designed SEIs able to regulate transport of matter and ions at the electrolyte/anode interface provide a promising platform for addressing three major technical barriers to practical Li-O2 cells.

A 1-hydroxy-2,3,1-benzodiazaborine-containing π-conjugated system: Synthesis, optical properties and solvent-dependent response toward anions

Our interest in the functionalization of OH-substituted azaborines prompted us to synthesize a 1-hydroxy-2,3,1-benzodiazaborine conjugated with 1,8-naphthalimide 1. Its fluorescence was dramatically affected by the nature of the solvent. In particular, the use of DMSO, which has a relatively high donor number (DN = 29.8), led to a remarkable decrease in the fluorescence intensity (ΦF = 0.0014), possibly due to intermolecular hydrogen-bonding interactions (Me2SO⋯HOB). The presence of the hydroxyl group on boron led to a solvent-driven colorimetric response towards anions; high selectivity for F− over other anions in DMSO, and responded to AcO− and F− in THF, as shown by UV/vis titrations, NMR, and mass spectroscopic analysis. The nucleus-independent chemical shift (NICS) indices suggested that hydrogen bonding interactions between Me2SO and HOB reduced the aromaticity of the benzodiazaborine macrocycle, causing an increase in the negative character of the boron. The increase in the polarity of the BN bond may prevent acetate-binding of 1 in DMSO.

Potassium Ions Promote Solution-Route Li2O2 Formation in the Positive Electrode Reaction of Li–O2 Batteries

Lithium-oxygen system has attracted much attention as a battery with high energy density that could satisfy the demands for electric vehicles. However, because lithium peroxide (Li2O2) is formed as an insoluble and insulative discharge product at the positive electrode, Li-O2 batteries have poor energy capacities. Although Li2O2 deposition on the positive electrode can be avoided by inducing solution-route pathway using electrolytes composed of high donor number (DN) solvents, such systems generally have poor stability. Herein we report that potassium ions promote the solution-route formation of Li2O2. The present findings suggest that potassium or other monovalent ions have the potential to increase the volumetric energy density and life cycles of Li-O2 batteries.

Electrolyte-controlled discharge product distribution of Na-O2 batteries: a combined computational and experimental study.

Tuning the composition of discharge products is an important strategy to reduce charge potential, suppress side reactions, and improve the reversibility of metal-oxygen batteries. In the present study, first-principles calculations and experimental confirmation were performed to unravel the influence of O2 pressure, particle size, and electrolyte on the composition of charge products in Na-O2 batteries. The electrolytes with medium and high donor numbers (>12.5) are favorable for the formation of sole NaO2, while those with low donor numbers (<12.5) may permit the formation of Na2O2 by disproportionation reactions. Our comparative experiments under different electrolytes confirmed the calculation prediction. Our calculations indicated that O2 pressure and particle size hardly affect discharge products. On the electrode, only one-electron-transfer electrochemical reaction to form NaO2 takes place, whereas two-electron-transfer electrochemical and chemical reactions to form Na2O2 and Na3O4 are prevented in thermodynamics. The present study explains why metastable NaO2 was identified as a sole discharge product in many experiments, while thermodynamically more stable Na2O2 was not observed. Therefore, to achieve low overpotential, a high-donor-number electrolyte should be applied in the discharge processes of Na-O2 batteries.

Solid Phase FePC Catalysts for Increased Stability of Oxygen Reduction Reaction Intermediates at the Cathode/Electrolyte Interface in Lithium Air Batteries

Solid-phase catalysts prepared by pyrolysis of Iron(II) phthalocyanine (FePC) embedded in high-surface carbons were evaluated for the catalysis of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in Li+-conducting non-aqueous electrolytes. The ORR mechanism in high donor number (DN) dimethyl sulfoxide (DMSO)-based electrolytes is markedly different from that occurs in low DN acetonitrile(MeCN)-based electrolytes. The ORR is catalyzed by the reduced Fe(I) state of Fe(II)PC. Consequently, the Fe(II)PC/Fe(I)PC redox potential relative to O2 reduction potential in each electrolyte is important for ORR catalysis. In MeCN-based electrolytes, the Fe(I)PC catalyst is formed at a higher potential than the ORR potential. Hence the catalyzed ORR occurs at the inner-Helmholtz plane of the electrode, stabilizing the superoxide ion (O2−) formed by one-electron reduction of O2, as Fe(I)PC–O2−. Indeed, LiO2 was identified in the Raman spectra of cathodes from discharged Li-O2 battery cells. In DMSO-based electrolytes, the Fe(I)PC formation potential occurs below the ORR potential and accordingly LiO2 is more stable in its solvated state in the electrolyte solution as the Li(DMSO)n–O2− ion pair. This drives the ORR at the outer-Helmholtz plane of both catalyzed and uncatalyzed electrodes in DMSO-based electrolytes. The FePC embedded carbon electrode doubled the cycle life of Li-O2 cells utilizing low DN electrolytes.