Among the "beyond Li-ion" battery chemistries, nonaqueous Li-O 2 batteries have the highest theoretical specific energy and, as a result, have attracted significant research attention over the past decade. A critical scientific challenge facing nonaqueous Li-O 2 batteries is the electronically insulating nature of the primary discharge product, lithium peroxide, which passivates the battery cathode as it is formed, leading to low ultimate cell capacities. Recently, strategies to enhance solubility to circumvent this issue have been reported, but rely upon electrolyte formulations that further decrease the overall electrochemical stability of the system, thereby deleteriously affecting battery rechargeability. In this study, we report that a significant enhancement (greater than fourfold) in Li-O 2 cell capacity is possible by appropriately selecting the salt anion in the electrolyte solution. Using 7 Li NMR and modeling, we confirm that this improvement is a result of enhanced Li + stability in solution, which, in turn, induces solubility of the intermediate to Li 2 O 2 formation. Using this strategy, the challenging task of identifying an electrolyte solvent that possesses the anticorrelated properties of high intermediate solubility and solvent stability is alleviated, potentially providing a pathway to develop an electrolyte that affords both high capacity and rechargeability. We believe the model and strategy presented here will be generally useful to enhance Coulombic efficiency in many electrochemical systems (e.g., Li-S batteries) where improving intermediate stability in solution could induce desired mechanisms of product formation.donor number | solubility | lithium nitrate | NMR | Li-air battery T he lithium-oxygen (Li-O 2 ) battery has garnered significant research interest in the past 10 y due to its high theoretical specific energy compared with current state-of-the-art lithiumion (Li-ion) batteries (1, 2). Consisting of a lithium anode and an oxygen cathode, the nonaqueous Li-O 2 battery operates via the electrochemical formation and decomposition of lithium peroxide (Li 2 O 2 ). The ideal overall reversible cell reaction is thereforeOne challenge preventing the realization of a modest fraction of the Li-O 2 battery's high theoretical specific energy is that the discharge product, Li 2 O 2 , which is generally insoluble in aprotic organic electrolytes, is an insulator (3-5). As Li 2 O 2 is conformally deposited on the cathode's carbon support during discharge, it electronically passivates the cathode, resulting in practical capacities much smaller than theoretically attainable (6). Recently, two reports described the engineering of electrolytes to circumvent this passivation and improve Li-O 2 battery discharge capacity. Aetukuri et al. suggested that adding ppm quantities of water to a 1,2-dimethoxyethane (DME)-based electrolyte increases the solubility of intermediates during Li 2 O 2 formation (7). This increased solubility allows a reduced oxygen species shuttling mechanism that promotes deposi...

Lithium metal cells are key towards achieving high specific energy and energy density for electrification of transportation and aviation. Anode-free cells are the limiting case of lithium metal cells involving no excess lithium and the highest possible specific energy. In addition, anode-free cells are easier, cheaper and safer as they avoid handling and manufacturing of lithium metal foils. Issues related to dendrite growth and arXiv:1909.02404v1 [cond-mat.mtrl-sci]

Solvent-free single-ion polymer electrolytes with high conductivity have historically been prepared in the form of block copolymer or polymer blends. In this work, single-ion homopolymer electrolytes consisting of poly­(poly­(ethylene oxide) methacrylate lithium sulfonyl­(tri­fluoro­methyl­sulfonyl)­imide), poly­(PEOMA-TFSI–Li+), were prepared for the first time by photoinduced metal-free atom-transfer radical polymerization. The PEO-based macromonomer PEOMA-TFSI–Li+ was synthesized via click chemistry, copper-catalyzed alkyne–azide cycloaddition. Because of the conductive, amorphous PEO phase in which the lithium ions are located, these polymers showed improved ionic conductivity (10–5–10–4 S/cm at 90 °C) and high transference number (0.97–0.99). A continued lithium plating–stripping experiment was performed at current density ≥0.1 mA/cm2 over 300 cycles at 90 °C. The potential dendrite-suppressing capability of the polymer with such high transference number was also estimated by employing a kinetic model using the measured transport and transference properties to study the current density at the dendrite tip. The analysis indicates that the synthesized polymers could have a high propensity to suppress dendrite growth.

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The path toward Li-ion batteries with higher energy densities will likely involve use of thin lithium (Li)-metal anode (<50 µm thickness), whose cyclability today remains limited by dendrite formation and low coulombic efficiency (CE). Previous studies have shown that the solid–electrolyte interface (SEI) of the Li metal plays a crucial role in Li-electrodeposition and -stripping behavior. However, design rules for optimal SEIs are not well established. Here, using integrated experimental and modeling studies on a series of structurally similar SEI-modifying model compounds, we reveal the relationship between SEI compositions, Li deposition morphology, and CE and identify two key descriptors for the fraction of ionic compounds and compactness, leading to high-performance SEIs. We further demonstrate one of the longest cycle lives to date (350 cycles for 80% capacity retention) for a high specific-energy Li||LiCoO2 full cell (projected >350 watt hours [Wh]/kg) at practical current densities. Our results provide guidance for rational design of the SEI to further improve Li-metal anodes.

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Density Functional Theory (DFT) calculations have been widely used to predict the activity of catalysts based on the free energies of reaction intermediates. The incorporation of the state of the catalyst surface under the electrochemical operating conditions while constructing the free energy diagram is crucial, without which even trends in activity predictions could be imprecisely captured. Surface Pourbaix diagrams indicate the surface state as a function of the pH and the potential. In this work, we utilize error-estimation capabilities within the BEEF-vdW exchange correlation functional as an ensemble approach to propagate the uncertainty associated with the adsorption energetics in the construction of Pourbaix diagrams. Within this approach, surfacetransition phase boundaries are no longer sharp and are therefore associated with a finite width. We determine the surface phase diagram for several transition metals under reaction conditions and electrode potentials relevant for the Oxygen Reduction Reaction (ORR). We observe that our surface phase predictions for most predominant species are in good agreement with cyclic voltammetry experiments and prior DFT studies. We use the OH * intermediate for comparing adsorption characteristics on Pt(111), Pt(100), Pd(111), Ir(111), Rh(111), and Ru(0001) since it has been shown to have a higher prediction efficiency relative to O * , and find the trend Ru>Rh>Ir>Pt>Pd for (111) metal facets, where Ru binds OH * the strongest. We robustly predict the likely surface phase as a function of reaction conditions by associating c-values to quantifying the confidence in predictions within the Pourbaix diagram. We define a confidence quantifying metric using which certain experimentally observed surface phases and peak assignments can be better rationalized. The probabilistic approach enables a more accurate determination of the surface structure, and can readily be incorporated in computational studies for better understanding the catalyst surface under operating conditions. arXiv:1710.08407v2 [cond-mat.mtrl-sci]

Singlet oxygen has emerged as a real mystery puzzling battery science, having been observed in Li−O 2 and Na−O 2 batteries, in conventional Li-ion batteries with NMC cathodes, and during the oxidation of Li 2 CO 3 . The formation of singlet oxygen has been directly linked to the degradation and catastrophic fade seen in these battery chemistries. While there are several proposed hypothesis for its origin, the exact mechanism for the formation of singlet oxygen remains unclear. In this Letter, we attempt to unify these findings by proposing a mechanism of singlet oxygen production in metal−air and Li-ion batteries. We show that a potential dependence of surface termination explains the onset potentials of singlet oxygen release, and in all considered cases the mechanism of singlet oxygen generation is through the chemical disproportionation of the uncoordinated superoxide anion in solution; therefore, the singlet oxygen yield is determined by the concentration of free superoxide versus alkali superoxide ion pairs in solution.