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Bryantsev V.S.,Liox Power Inc. | Blanco M.,Liox Power Inc.
Journal of Physical Chemistry Letters | Year: 2011

There is increasing experimental evidence that organic carbonate-based electrolytes are incompatible with the discharge products of the nonaqueous lithium-air (oxygen) battery. Theoretically, the lithium-air battery offers the highest gravimetric density for energy storage applications, promising to revolutionize electric vehicle transportation. Calculations suggest that propylene carbonate, ethylene carbonate, and dimethyl carbonate, commonly used electrolytes in Li-ion batteries, are easily decomposed by the superoxide ion via nucleophilic attack at the ethereal carbon atom. In the case of propylene carbonate, base-mediated proton abstraction from the methyl group has to be considered as an additional solvent decomposition pathway. The present study provides a mechanistic understanding of solvent instability to assist the design of stable electrolytes for Li-air energy storage systems. © 2011 American Chemical Society.

Bryantsev V.S.,Liox Power Inc. | Uddin J.,Liox Power Inc. | Giordani V.,Liox Power Inc. | Walker W.,Liox Power Inc. | And 2 more authors.
Journal of the American Chemical Society | Year: 2014

Electrolyte stability is an essential prerequisite for the successful development of a rechargeable organic electrolyte Li-O2 battery. Lithium nitrate (LiNO3) salt was employed in our previous work because it was capable of stabilizing a solid-electrolyte interphase on the Li anode. The byproduct of this process is lithium nitrite (LiNO2), the fate of which in a Li-O2 battery is unknown. In this work, we employ density functional theory and coupled-cluster calculations combined with an implicit solvation model for neutral molecules and a mixed cluster/continuum model for single ions to understand the chemical and electrochemical behavior of LiNO2 in acetonitrile (AN). The redox potentials of oxygenated nitrogen compounds predicted in this study are in excellent agreement with the experimental results (the average accuracy is 0.10 V). Theoretical calculations suggest that the reaction between the nitrite ion and its first oxidation product, nitrogen dioxide (NO2), in AN solution proceeds via the initial formation of a trans-ONO-NO2 dimer that is subject to autoionization and the subsequent reaction of produced nitrosyl ion (NO +) with NO2 -. Good agreement between experimental and simulated cyclic voltammograms for electrochemical oxidation of LiNO2 in AN provides support to the proposed mechanism of coupled electrochemical and chemical reactions. The results suggest a possible mechanism of regeneration of LiNO3 in electrolyte in the presence of oxygen, which is uniquely possible under charging conditions in a Li-O2 battery. © 2014 American Chemical Society.

Superoxide is a strong base that can induce base-catalyzed autoxidation of weakly acidic solvents. We report on the performance of several computational protocols for predicting pKa values for a wide range of aliphatic C-H acids in DMSO. Calculations at the MP2/CBS level with CCSD(T)/aug-cc-pVDZ corrections and solvent effects calculated using the SVPE model provide the best overall performance (rms deviation is 0.65 pKa). The B3LYP, M06, and M06-2X functionals can also achieve high accuracy (<1 pKa) by employing empirical corrections to fit the experimental data. Computational results provide a convenient means of screening for suitable solvents in Li-air batteries. © 2012 Elsevier B.V. All rights reserved.

Bryantsev V.S.,Liox Power Inc. | Uddin J.,Liox Power Inc. | Giordani V.,Liox Power Inc. | Walker W.,Liox Power Inc. | And 2 more authors.
Journal of the Electrochemical Society | Year: 2013

Solvent plays a major role in determining the nature of discharge products and the extent of rechargeability of the nonaqueous lithium-air (oxygen) battery. Here we investigate chemical stability for a number of aprotic solvents against superoxide, including N,N-dialkyl amides, aliphatic and aromatic nitriles, oxygenated phosphorus (V) compounds, substituted 2-oxazolidinones, and fluorinated ethers. The free energy barriers for nucleophilic attack by superoxide and the C-H acidity constants in dimethyl sulfoxide are reported, which provide a theoretical framework for computational screening of stable solvents for Li-air batteries. Theoretical results are complemented bycyclic voltammetryto study the electrochemical reversibilityof the O2/O 2- couple containing tetrabutylammonium salt and GCMS measurements to monitor solvent stability in the presence of KO2 and a Li salt. Excellent agreement among all quantum chemical, electrochemical, and chemical methods has been obtained in evaluating solvent stability against superoxide. The combined theoretical and experimental methodology provides a comprehensive testing ground to identify electrolyte solvents stable in the air cathode. Based upon this knowledge we report on the use of an amide-based electrolyte for rechargeable oxygen electrodes in Li-O2 secondary cells. © 2012 The Electrochemical Society.

Walker W.,Liox Power Inc. | Giordani V.,Liox Power Inc. | Uddin J.,Liox Power Inc. | Bryantsev V.S.,Liox Power Inc. | And 2 more authors.
Journal of the American Chemical Society | Year: 2013

A major challenge in the development of rechargeable Li-O2 batteries is the identification of electrolyte materials that are stable in the operating environment of the O2 electrode. Straight-chain alkyl amides are one of the few classes of polar, aprotic solvents that resist chemical degradation in the O2 electrode, but these solvents do not form a stable solid-electrolyte interphase (SEI) on the Li anode. The lack of a persistent SEI leads to rapid and sustained solvent decomposition in the presence of Li metal. In this work, we demonstrate for the first time successful cycling of a Li anode in the presence of the solvent, N,N-dimethylacetamide (DMA), by employing a salt, lithium nitrate (LiNO3), that stabilizes the SEI. A Li-O2 cell containing this electrolyte composition is shown to cycle for more than 2000 h (>80 cycles) at a current density of 0.1 mA/cm2 with a consistent charging profile, good capacity retention, and O2 detected as the primary gaseous product formed during charging. The discovery of an electrolyte system that is compatible with both electrodes in a Li-O2 cell may eliminate the need for protecting the anode with a ceramic membrane. © 2013 American Chemical Society.

Islam M.M.,Pennsylvania State University | Bryantsev V.S.,Liox Power Inc. | Van Duin A.C.T.,Pennsylvania State University
Journal of the Electrochemical Society | Year: 2014

Lithium-sulfur batteries are amongst the most appealing choices for the next generation large-scale energy storage applications. However, these batteries still suffer several formidable performance degradation issues that impede its commercialization. The lithium negative electrode yields high anodic capacity, but it causes dendrite formation and raises safety concerns. Furthermore, the high reactivity of lithium is accountable for electrolyte decomposition. To investigate these issues and possible countermeasures, we used ReaxFF reactive molecular dynamics simulations to elucidate anode-electrolyte interfacial chemistry and utilized an ex-situ anode surface treatment with Teflon coating. In this study, we employed Li/SWCNT (single-wall carbon nanotube) composite anode instead of lithium metal and tetra(ethylene glycol) dimethyl ether (TEGDME) as electrolyte.We find that at lithium rich environment at the anode-electrolyte interface, electrolyte dissociates and generates ethylene gas as a major reaction product, while utilization of Teflon layer suppresses the lithium reactivity and reduces electrolyte decomposition. Lithium discharge from the negative electrode is an exothermic event that creates local hot spots at the interfacial region and expedites electrolyte dissociation reaction kinetics. Usage of Teflon dampens initial heat flow and effectively reduces lithium reactivity with the electrolyte. © 2014 The Electrochemical Society.

Bryantsev V.S.,Liox Power Inc. | Faglioni F.,Liox Power Inc. | Faglioni F.,University of Modena and Reggio Emilia
Journal of Physical Chemistry A | Year: 2012

Finding suitable solvents remains one of the most elusive challenges in rechargeable, nonaqueous Li-air battery technology. Although ether and amides are identified as stable classes of aprotic solvents against nucleophilic attack by superoxide, many of them are prone to autoxidation under oxygen atmosphere. In this work, we use density functional theory calculations coupled with an implicit solvent model to investigate the autoxidative stability of ether- and N,N-dialkylamide-based solvents. The change in the activation free energy for the C-H bond cleavage by O2 is consistent with the extent of peroxide production for each class of solvent. Conversely, the thermodynamic stability alone is not sufficient to account for the observed variation in solvent reactivity toward O2. A detailed understanding of the factors influencing the autoxidative stability provides several strategies for designing molecules with enhanced air/O2 stability, comparable or superior to that of structurally related hydrocarbons. The mechanism of superoxide-mediated oxidation of hydroperoxides derived from ethers and amides is presented. The degradation mechanism accounts for the primary decomposition products (esters and carboxylates) observed in the Li-air battery with ether-based electrolytes. The identification of solvents having resistance to autoxidation is critical for the development of rechargeable Li-air batteries with long cycle life. © 2012 American Chemical Society.

Solvation effects play a major role in determining the cycling characteristics of the non-aqueous rechargeable Li-air battery. We use a mixed cluster/continuum solvent model with varying number of explicit solvent molecules (n = 4-10) to calculate the solvation free energies (ΔG solv *) of Li + and O 2 - ions and neutral LiO 2, Li 2O 2, LiO, and Li 2O species in acetonitrile solvent. Calculations for complexes with the full first solvation shell around Li + (n = 4) and O 2 - (n = 8) show excellent agreement with the solvation free energies obtained using the cluster pair approximation (the error is below 2.0 kcal/ mol). The use of the pure continuum model fitted to reproduce the experimental values of ΔG solv *(Li +) and ΔG solv *(O 2 -) gives the solvation free energies of various lithium-oxygen species (LixOy; x, y = 1, 2) that are in excellent agreement with the results obtained using mixed cluster/continuum models (n ≥ 8). This provides a theoretical framework for including solvent effects in the theoretical models of oxygen reduction and evolution reactions in the aprotic Li-air battery. © Springer-Verlag 2012.

High capacity alkali metal/oxygen batteries, e.g. Li/O_(2 )batteries, employing molten salt electrolytes comprising alkali metal cations and nitrate anions are disclosed. Batteries of the present invention operate at an intermediate temperature ranging from. 80 C. to 250 C. Molten alkali metal nitrate electrolytes employed in O_(2 )electrodes within this temperature range provide alkali metal/oxygen batteries having significantly improved efficiency and rechargeability compared to prior art systems.

High energy rechargeable batteries employing catalyzed molten nitrate positive electrodes and alkali metal negative electrodes are disclosed. Novel and advantageous aspects of the present invention are enabled by the provision catalytically active materials that support the reversible formation of NO_(3)^() from O^(2) and N0_(2)^( )during battery charging. Such catalytically active materials allow highly efficient cycling and selectively eliminate irreversible side reactions that occur when cycling without such catalysts.

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