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Abstract: The charging process of Li2O2-based air electrodes in Li–O2 batteries with organic carbonate electrolytes was investigated using in situ gas chromatography/mass spectroscopy (GC/MS) to analyze gas evolution. A mixture of Li2O2/Fe3O4/Super P carbon/polyvinylidene fluoride (PVDF) was used as the starting air electrode material, and 1-M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) in carbonate-based solvents was used as the electrolyte. We found that Li2O2 was actively reactive to 1-methyl-2-pyrrolidinone and PVDF that were used to prepare the electrode. During the first charging (up to 4.6V), O2 was the main component in the gases released. The amount of O2 measured by GC/MS was consistent with the amount of Li2O2 that decomposed during the electrochemical process as measured by the charge capacity, which is indicative of the good chargeability of Li2O2. However, after the cell was discharged to 2.0V in an O2 atmosphere and then recharged to ∼4.6V, CO2 was dominant in the released gases. Further analysis of the discharged air electrodes by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy indicated that lithium-containing carbonate species (lithium alkyl carbonates and/or Li2CO3) were the main discharge products. Therefore, compatible electrolytes and electrodes, as well as the electrode-preparation procedures, need to be developed for rechargeable Li-air batteries for long term operation. [Copyright &y& Elsevier]

Abstract: In this work, Li/air batteries based on nonaqueous electrolytes were investigated in ambient conditions (with an oxygen partial pressure of 0.21atm and relative humidity of ∼20%). A heat-sealable polymer membrane was used as both an oxygen-diffusion membrane and as a moisture barrier for Li/air batteries. The membrane also can minimize the evaporation of the electrolyte from the batteries. Li/air batteries with this membrane can operate in ambient conditions for more than one month with a specific energy of 362Whkg−1, based on the total weight of the battery including its packaging. Among various carbon sources used in this work, Li/air batteries using Ketjenblack (KB) carbon-based air electrodes exhibited the highest specific energy. However, KB-based air electrodes expanded significantly and absorbed much more electrolyte than electrodes made from other carbon sources. The weight distribution of a typical Li/air battery using the KB-based air electrode was dominated by the electrolyte (∼70%). Lithium metal anodes and KB-carbon account for only 5.12% and 5.78% of the battery weight, respectively. We also found that only ∼20% of the mesopore volume of the air electrode was occupied by reaction products after discharge. To further improve the specific energy of the Li/air batteries, the microstructure of the carbon electrode needs to be further improved to absorb much less electrolyte while still holding significant amounts of reaction products. [Copyright &y& Elsevier]

Abstract Irreversible parasitic reactions and the resulting accumulation of insulating side products are main barriers for practical application of rechargeable lithium–oxygen (Li O 2) batteries. Therefore, it is critical to develop multifunctional oxygen electrodes suitable for oxygen reduction reaction, oxygen evolution reaction, and decomposition of side reaction products. Here we report the application of ultrafine ruthenium on boron carbide (Ru/B 4 C) with highly efficient multifunctional activities as carbon-free oxygen electrodes for Li O 2 batteries. Li 2 CO 3 and LiOH can be completely decomposed by Ru/B 4 C at 4.0 V and 4.1 V, respectively, within the stability window of the electrolyte. A Li O 2 battery using the Ru/B 4 C oxygen electrode achieves low overpotentials for Li O 2 reactions, and excellent cycling performance under the capacities of 300 and 500 mAh g−1 Ru/B4C. In-situ gas chromatography analysis reveals that O 2 is the major gas product during charging. Only a negligible amount of CO 2 is observed in the first charging process. Therefore, Ru/B 4 C can be a very promising oxygen-electrode material for Li O 2 batteries and Li–air batteries operated in ambient air. Graphical abstract Image 1 Highlights • Non-carbon-based Ru/B 4 C oxygen electrode shows good activity for both ORR and OER. • Ru/B 4 C can completely decompose Li 2 CO 3 and LiOH below 4.1 V. • Ru/B 4 C is very stable against superoxide radical anion and Li 2 O 2. • Li O 2 batteries using Ru/B 4 C oxygen electrodes exhibit long cycling stability. • Side reaction during charge accounts for degradation of Ru/B 4 C oxygen electrode. [ABSTRACT FROM AUTHOR]

Highlights • X-ray photoelectron spectroscopy can provide atomistic and microscopic view of chemical speciation and distribution at complexelectrode-electrolyte interfaces. • Identifying the reactant and products of decomposition reaction can help evaluate the longevity of electrolyte and subsequent life cycle of battery. • Novelin situ XPS can provide real time view of electrode-electrolyte interphase formation and help us correlate the battery failure mechanisms. Abstract Technological development requires reliable power sources where energy storage devices are emerging as a critical component. Wide range of energy storage devices, Redox-flow batteries (RFB), Lithium ion based batteries (LIB), and Lithium-sulfur (LSB) batteries are being developed for various applications ranging from grid-scale level storage to mobile electronics. Material complexities associated with these energy storage devices with unique electrochemistry are formidable challenge which needs to be address for transformative progress in this field. X-ray photoelectron spectroscopy (XPS) - a powerful surface analysis tool - has been widely used to study these energy storage materials because of its ability to identify, quantify and image the chemical distribution of redox active species. However, accessing the deeply buried solid-electrolyte interfaces (which dictates the performance of energy storage devices) has been a challenge in XPS usage. Herein we report our recent efforts to utilize the XPS to gain deep insight about these interfaces under realistic conditions with varying electrochemistry involving RFB, LIB and LSB. [ABSTRACT FROM AUTHOR]

Abstract: To understand the limited cycle life performance and poor energy efficiency associated with rechargeable lithium–oxygen (Li–O2) batteries, the discharge products of primary Li–O2 cells at different depths of discharge (DOD) were systematically analyzed using XRD, FTIR and Ultra-high field MAS NMR. When discharged to 2.0V, the reaction products of Li–O2 cells include a small amount of Li2O2 along with Li2CO3 and RO–(C;OLi in the alkyl carbonate-based electrolyte. However, regardless of the DOD, there is no Li2O detected in the discharge products in the alkyl-carbonate electrolyte. For the first time it was revealed that in an oxygen atmosphere the high surface area carbon significantly reduces the electrochemical operation window of the electrolyte, and leads to plating of insoluble Li salts on the electrode at the end of the charging process. Therefore, the impedance of the Li–O2 cell continues to increase after each discharge and recharge process. After only a few cycles, the carbon air electrode is completely insulated by the accumulated Li salt terminating the cycling. [Copyright &y& Elsevier]

Abstract: The entropy changes (ΔS) in various cathode and anode materials, as well as in complete Li-ion batteries, were measured using an electrochemical thermodynamic measurement system (ETMS). LiCoO2 has a much larger entropy change than electrodes based on LiNi x Co y Mn z O2 and LiFePO4, while lithium titanate based anodes have lower entropy change compared to graphite anodes. The reversible heat generation rate was found to be a significant portion of the total heat generation rate. The appropriate combinations of cathode and anode were investigated to minimize reversible heat generation rate across the 0–100% state of charge (SOC) range. In addition to screening for battery electrode materials with low reversible heat, the techniques described in this paper can be a useful engineering tool for battery thermal management in stationary and transportation applications. [Copyright &y& Elsevier]