Non-aqueous Lithium-air Batteries Research Articles

Non-Aqueous Li-Air Flow Battery: Improving Capacity and Current Density through Cathode Optimization

Non-aqueous Lithium-air (Li-air) batteries are attractive energy storage systems due to their exceptionally high theoretical energy density. Despite its high energy density, issues such as cycle fading and low current density still need to be overcome. A major cause of these issues is the deposition of discharge products on the surface as well as inside the pores of the cathode. These deposits clog the pores and prevent continuous steady discharge. Recently we developed a Li-air battery configuration that has a flowing Li-ion free ionic liquid as the electrolyte, enabling the continuous removal of discharge products (Figure 1). This flow battery consists of two units, a flow battery for electrochemical reaction and a storage site for discharge products. In detail, a gas diffusion electrode (GDE) allows continuous supply of O2while fresh catholyte is continuously provided to transport discharge products away to the storage. Also, the Li metal anode is separated from the catholyte by a solid state Li-ion conducting separator. We successfully demonstrated separation of the electrochemical reaction on the cathode and storage of the discharge products by employing a flowing catholyte. This approach led to the flowing Li-air battery exhibiting a higher discharge capacity than a static Li-air battery (i.e. with a non-flowing electrolyte configuration). However, the discharge current density achieved with this Li-air flow battery was still low. To improve the discharge current density of the Li-air flow battery, we used COMSOL modelling to determine parameters that are key in optimizing battery performance modeling in COMSOL. We simulated a modified version of Li-air battery model, based on a model presented in prior work.1 This model identified optimal parameters for the cathode, including the porosity of electrode and the depth of immersion of the cathode with electrolyte. The maximum current density that can be achieved increases as the porosity of the cathode increases because a higher porosity improves O2 transport. However, a different trend was observed for the depth by which the electrolyte had penetrated the cathode. The maximum current density is observed at 30 and 50 µm for an initial concentration of O2 of 5 and 15 mol m3, respectively, suggesting that an optimum electrolyte immersion depth is key to achieve the highest current density. In parallel with these modeling efforts, the structure and surface of GDEs were modified and evaluated to increase discharge current density for Li-air flow battery. Specifically, we fabricated and evaluated hot-pressed GDEs, super-hydrophobic GDEs coated with PTFE, and GDEs on which additional material had been deposited. Especially the hot-pressed GDEs exhibited improved discharge current density, which we attribute to the hot-pressing decreasing the thickness of GDEs, thus enabling better O2transport. In summary, we established the concept of a Li-air battery with a flowing Li-ion free non-aqueous electrolyte. Also, we used modeling and experiments to analyze how different parameters, specifically the properties of the cathode, benefit the performance of the non-aqueous Li-air flow battery. We were able to optimize the gas diffusion electrode-based cathode for this Li-air flow battery, which lead to higher discharge current densities.

Phthalocyanines Based Two-Phase Catalysts for Lithium Oxygen Batteries

Li-air batteries, which are considered to offer much higher energy density than the current Li-ion batteries suffer from poor cycle life due to electrolyte decomposition and clogging of the air cathode by insoluble discharge products. Efficient bifunctional catalysts could improve the stability of Li-air batteries by lowering the overpotential and prolonging the battery cycle life. This study focuses on Iron phthalocyanines (FePc) as possible bifunctional electrocatalysts. Metal phthalocyanines were utilized mainly because of their structural analogy which could be fine- tuned by the metal being used, accessibility, and low cost. In this work, firstly, FePc supported on graphite nanofibres (GNF) was investigated as solid electrocatalyst in non-aqueous LiTFSI (TEGDME) electrolyte. Secondly, FePc was dissolved in the non-aqueous electrolyte and studied as liquid catalyst with GNF cathode. FePc/GNF (solid catalyst) delivered superior electrocatalytic performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) comparable to that of commercial Pt/C. FePc_electrolyte (liquid catalyst) exhibited a steady profile for chronoamperometry, and good diffusivity of lithium ions as measured from electrochemical impedance spectroscopy. The bifunctional catalysts when applied as electrocatalysts in non-aqueous lithium air batteries delivered better electrochemical performance mainly by reducing the large overpotential associated with ORR and OER. Both the cells with solid and soluble FePc exhibited better reversibility and cyclability. The performance of FePc catalyst as solid and liquid has been comparative analyzed in detail.

The Effects of Electrolyte Variations on the Oxygen Efficiency in Lithium Air Batteries

While the existing lithium-ion batteries have been extensively used in electric vehicles (EVs), their limited specific energy restricts the driving range. In this context, rechargeable lithium air (or Li-O2) batteries have attracted considerable interest in recent years as a potential power source for EVs, owing to their high theoretical specific energy. A typical non-aqueous lithium air battery consists of a porous air electrode, a lithium metal anode, and electrolyte containing lithium salt. The electrolyte is generally regarded as a critical component as it is directly related to the stability and the performance of a lithium air battery. While physicochemical properties of potential electrolytes are often discussed, the ability of electrolyte to utilize the oxygen during reversible charge/discharge cycle is rarely explored. In fact, previously reported gas analysis indicated low current efficiency for O2 evolution during charging (Li2O2 → 2Li+ + O2 + e-), accompanied the evolution of byproduct gases such as H2 and CO2.1-2 Furthermore, the O2 revolution (therefore, rechargeability) seemed highly dependable on the choice of electrolyte. In this work, we investigated the oxygen efficiency during discharge/charge cycle in lithium-air using differential electrochemical mass spectrometry (DEMS). We explored various electrolytes that have the potential to prompt reversible electrochemistry in Li-O2 battery. In addition to this, the effect of a catalyst and lithium salt variation on the O2 evolution was investigated. 1) B. D. McCloskey, D. S. Bethune, R. M. Shelby, G. Girishkumar, and A. C. Luntz, J. Phys. Chem. Lett., 2, 1161 (2011) 2) C. J. Barile and A. A. Gewirth, J. Electrochem. Soc., 160, A549 (2013)

Decomposition Mechanism of Discharged Product in Lithium Air Battery Optimized By Dandelion-like NiCo2O4 Hollow Sphere

Rechargeable non-aqueous lithium–air batteries have received worldwide attention over the past several years, because of their extremely high theoretical energy density which is 5–10 times higher than that of lithium-ion batteries.[1-2] However, there are many challenges to be overcome before it turning into practical devices, especially the high overpotentials and short cycling life. A lot of researchers have demonstrated the great influence of discharged products especially lithium peroxide (Li2O2) formation/decomposition on both discharge and charge process, which play a critical role in the LOB’s performance, like discharge capacity, overpotentials and cycling.[3-6] Understanding the formation/decomposition mechanism of the products can effectively reduce the overpotential through the origins of high overpotentials. Here, we show the film characteristic Li2O2 morphologies formed on the cathode surface, which can be smoothly decomposed at low potential using NiCo2O4 electro-catalyst of designed structure. The dandelion-like NiCo2O4 hollow sphere presents hybrid structure of macrospores and mesopores. The formation of oxygen vacancies on the metal oxide surface would also improve the adsorption of O2 and strengthen the reduction of O2. We also find that the designed NiCo­2O4 hollow sphere would enhance the OER kinetics and reduce the charge potential. The battery consisting of lithium metal anode, electrolyte comprising 1 mol·L-1 LiTFSI in DMSO and porous cathode, is discharged and charged in O2 atmosphere. The tested cathode is then removed, washed with CH3CN, and examined by X-ray diffraction, FTIR and 1H NMR spectroscopy. The existence of Li2O2 could be demonstrated from XRD pattern. As for the maybe discharge products like Li2CO3, HCO2Li, C2H4(OCO2Li)2 etc, it is difficult to identify all the specific species by FTIR alone. To analyze discharged products in details, the porous cathode is washed with D2O and the solution is subjected to 1H NMR spectroscopy. Besides that, the field emission scanning electron microscope is employed to observe the morphologies with different DODs (depth of discharge) and discharge/charge stages. Combined with SEM figures, the tested products can be observed directly and visually, which help us understand better how the products formation/decomposition influences the performance of LOBs.

Dandelion-like NiCo2O4 hollow microspheres as enhanced cathode catalyst for Li-oxygen batteries in ambient air

The high overpotentials of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in the air cathode are still big challenge to be overcome for the high performance non-aqueous lithium-air batteries (LABs), especially in ambient air. In this paper, dandelion-like NiCo2O4 hollow microspheres are prepared through a simple self-assembled hydrothermal process as cathode catalyst. The assembled LABs show relative high discharge potential in different oxygen partial pressure, and can deliver a reversible capacity of 8019mAh·g−1 at the current density of 300mA·g−1 with stable cycle performance for at least 40 times in ambient air. The excellent performance of NiCo2O4 cathode can be attributed to the dandelion hollow structure, together with the abundant oxygen vacancies, which would enhance the ORR and OER process. The study confirms the feasibility of dandelion-like NiCo2O4 hollow spheres as efficient cathode for the LABs in ambient air.

Carbon Based Phthalocyanines As Electrocatalysts for Li Air Batteries

Li-air batteries are appealing as they offer much higher energy density than the current Li-ion batteries. However, the non–aqueous Li-air batteries suffer from poor cycle life due to electrolyte decomposition and clogging of the air electrode by insoluble discharge products. Efficient bifunctional catalysts could lower the overpotential and improve the stability of Li-air batteries, thus prolonging its cycle life. This study focuses on Iron phthalocyanines (FePc) supported on carbon materials as a solid electrocatalyst for lithium air batteries. Metal phthalocyanines were utilized mainly because of their structural analogy which could be fine- tuned by the metal being used, accessibility, and low cost. The carbon supports such as reduced graphene oxide (rGO) and carbon nanotubes (CNT) were utilized which rendered desirable surface properties like high surface area and high electronic conductivity. FePc/carbons delivered superior electrocatalytic performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) comparable and better than that of commercial Pt/C. The bifunctional catalysts were then applied as electrocatalysts in non-aqueous lithium air batteries. The air cells delivered better electrochemical performance mainly by reducing the large overpotential associated with ORR and OER. The cells exhibited better reversibility and cyclability as well. The improved electrocatalytic activity was mainly because of the π–π interaction between carbons and iron phthalocyanines. In addition, the effects of ball milling by ball milling the FePc, and the effects of nitrogen (N2) doping by doping the carbon supports with N2 were investigated. Ball milling has significantly improved the electrocatalytic properties of FePc and N2 doping further enhanced the overall performance.

A Surface Enhanced Raman Spectroscopy (SERS)-Active Cathode for Lithium-Oxygen Battery Discharge Product Investigation

Nonaqueous Lithium-air (Li-O2) battery has attracted significant research interest in the past decade, because of its high theoretical specific energy far beyond conventional Li-ion battery. However, there are many challenges such as severe degradation during cycling that limits the practical utilization of Li-O2 battery. Hence, a powerful tool is necessary to be found to detect the intermediates and study side reactions in Li-O2 battery. In this work, we explored a method to fabricate larger-area regularly patterned gold nano-dots by using the mask of anodic aluminum oxide (AAO) membrane for surface enhanced Raman spectroscopy (SERS). The size effect of the small and large gold nano-dots on the enhancement of Raman signal was studied by Rhodamine 6G on Si. Small gold nano-dots on Au film and graphene were used as SERS-active cathodes in Li-O2 battery and showed great ability for detecting the component on planar electrode. After discharge, many peaks have been observed for the SERS-active gold electrode, which demonstrate the existence of Li2O2, LiOH and LiO2. On the other hand, when SERS-active graphene electrode was used as lithium oxygen battery cathode, Li2O2 and Li2CO3 were detected.

Molybdenum Disulfide Catalyst for Lithium-Oxygen Batteries

Molybdenum Disulfide Catalyst for Lithium–Oxygen Batteries Mohammad Asadi1, Cong Liu2, Patrick Phillips3, Peter Zapol2, Robert F. Klie 3, Larry A. Curtiss2, Amin Salehi-Khojin1 1Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL, 60607, USA 2Materials Science Division, Argonne National Laboratory, Argonne, IL, 60439, USA 3Department of Physics, University of Illinois at Chicago, Chicago, IL, 60607, USA Lithium–oxygen (Li-O2) batteries have been recognized as an emerging technology for energy storage systems owing to their high theoretical specific energy1 - 4. In this study, we discovered a system based on molybdenum disulfide (MoS2) nanoflakes and an ionic liquid (IL) that work together as an effective co-catalyst for discharge and charge in a Li-O2 battery. Cyclic voltammetry results show superior reaction rates for this co-catalyst at lower overpotentials for both oxygen reduction (15 mV) and evolution (20 mV) reactions compared to Au and Pt metal catalysts under identical experimental conditions. This MoS2/IL co-catalyst also performs remarkably well in the Li-O2battery system with 85% round-trip efficiency and reversibility up to 50 cycles. Deferential Electrochemical mass spectroscopy (DEMS), X-ray diffraction (XRD), Fourier transform spectroscopy (FT-IR) and Raman experiments were used to elucidate the cell performance. The results show the fully formation and decomposition of Li2O2 and demonstrate the cell cyclability and stability by the absence of any side products after 50 cycles charge and discharge. Atomic scale characterizations (STEM and EELS experiments) and DFT calculations were used to elucidate the mechanism by which the MoS2 nanoflakes and the ionic liquid electrolyte act together to promote the catalytic properties of the MoS2. The MoS2/IL co-catalyst discovered in this work provides new opportunities for exploiting the unique properties of ionic liquids such as their stability in Li-air batteries as well as activity of MoS2as a cathode material. Zu, C.-X. & Li, H. Thermodynamic analysis on energy densities of batteries. Energy Environ. Sci. 4, 2614 (2011).Rahman, M. A., Wang, X. & Wen, C. High Energy Density Metal-Air Batteries: A Review. J. Electrochem. Soc. 160, A1759–A1771 (2013).Zheng, J. P., Liang, R. Y., Hendrickson, M. & Plichta, E. J. Theoretical Energy Density of Li–Air Batteries. J. Electrochem. Soc. 155, A432 (2008).Shao, Y. et al. Electrocatalysts for Nonaqueous Lithium–Air Batteries: Status, Challenges, and Perspective. ACS Catal. 2, 844–857 (2012).

Improving the performance of a non-aqueous lithium-air battery by defective titanium dioxides with oxygen vacancies

In this work, we proposed using titanium dioxides (TiO2) with oxygen vacancies (H-TiO2) as cathode catalysts to improve the electrochemical performance of non-aqueous lithium-air batteries. Such H-TiO2 catalysts were attained by a facile heat treatment of rutile TiO2 and the existence of vacancies was confirmed by Raman spectra and X-ray photoelectron spectroscopy (XPS). It was demonstrated that due to the presence of defects which can facilitate the adsorption and dissociation of oxygen, the in-house lithium-air battery with H-TiO2 can be discharged at the current densities of 0.3 and 0.5mAcm−2 while maintaining the specific capacities of 3.2 and 2.8mAhcm−2, respectively, much higher than those of the batteries without catalysts or with pristine rutile TiO2. In addition, the cycling test showed that the battery with H-TiO2 can undergo 400 and 372 cycles, respectively, at the current densities of 0.3 and 0.5mAcm−2 with a fixed specific capacity of 0.1mAhcm−2 and a cutoff discharge voltage of 2.0V.

Porous Spinel Cobaltite with Core-Shell Architectures As High-Performance Catalysts for Rechargeable Lithium Air Batteries

Nowadays, the lithium-oxygen battery has captured world-wide attention recently because of its extremely high theoretical energy density. A typical nonaqueous Li-O2 battery consists of a lithium−metal anode, organic electrolyte, and a porous air cathode exposed to gaseous O2 during cell operation. The air electrode is crucial to improve the electrochemical performance for rechargeable nonaqueous lithium–air batteries. Among the components of the air electrode, the catalyst is important in that it can enhance the charge reaction by reducing the voltage required to dissociate the reaction products (such as Li2O2) into lithium metal and oxygen. The electrocatalyst is currently being investigated with special attention being paid to solve the sluggish kinetics related to the main electrochemical reactions, as well as the instability of the discharge products. Recently, a variety of electrocatalysts, including noble metals, transition metal oxides and carbon-based materials, have been explored in Li-O2 cells with a high reversible capacity and a lower charge potential for oxygen evolution reaction (OER) than bare carbon. A problem for the cathode lies in that the solid discharge products are insoluble and thus precipitate in the pores of cathode, which gradually block the catalytic sites as well as the diffusion pathways of electrolyte and oxygen, especially for the inner part next to the separator, and eventually degrade the performance of Li-O2 batteries. Considering this point, how to improve the pore utilization and promote the O2 transport in the electrode plays an important role in determining the battery performance. Therefore, it is challenging and highly desirable to develop optimum electrocatalysts to efficiently catalyze Li-O2 reactions while simultaneously facilitate rapid oxygen and electrolyte diffusion. In this work, we present a facile solvothermal synthesis of 3D hierarchical spinel core-shell microspheres with a porous structure and applied as efficient 3D electrocatalysts in nonaqueous Li-O2 batteries. Such unique structure can improve the availability of the catalytic sites and facilitate the diffusion of electrons and reactants. Due to the synergistic effect of high catalytic activity of the NiCo2O4 and unique porous core-shell, the 3D hiercarchical NiCo2O4 catalyst shows superior specific capacity, rate capability, and cycle stability in Li-O2 batteries. Furthermore, other spinel oxides (e.g. MnCo2O4 and ZnCo2O4) are also have been synthesized through similar procedures, suggesting the generality and feasibility of this facile strategy. The superior catalytic performance of NiCo2O4 was further examined in Li-O2 batteries. It is found that the Li–O2 battery with the NiCo2O4 electrode exhibits rather stable specific capacities above 7000 mAh g-1 carbon for five cycles and can keep specific capacities to be 6100 mAh g-1 carbon after 10 cycles at a current density of 100 mA g-1 carbon. Such performance can make NiCo2O4 core-shell microspheres as one of the best mixed metal oxides catalysts in Li-O2 batteries. Remarkably, it is found that our strategy could be extended to fabricate other spinel catalyst electrodes, such as MnCo2O4 and ZnCo2O4, suggesting the generality and feasibility of this facile strategy. In summary, we have demonstrated controlled synthesis of hierarchical spinel core-shell microspheres by a facile solvothermal method. The spinel microspheres constructed by porous nanoplates can act as high-performance catalysts in Li-O2 batteries. By taking advantage of the superior electrocatalytic activity and porous unique features, the as-prepared catalyst electrode exhibited low overpotentials, high rate capacity as well as excellent long-term cyclability. Significantly, this work offers exciting possibilities for the development of new functional materials in high-density storage devices Acknowledgements The authors are thankful for the support by funding from the Singapore National Research Foundation (NRF-CRP10-2012-06).

Fe2O3/Carbon Nanocomposite As Cathode Catalyst for Non-Aqueous Lithium-Air Batteries

Thanks to the highest capacity of lithium metal (3.86 × 103 mA h g-1) and inexhaustible oxygen in the atmosphere, lithium-air battery offers the promise of a remarkably high theoretical specific energy density up to ~11 kW h g-1, which is comparable to that of conventional fuels [1]. However, the development of lithium-air batteries is hindered by the high overpotential, low rate capacity, and poor cycling performance. The cathode has been shown to be the bottle-neck of rechargeable lithium-air batteries, wherein the sluggish oxygen reduction/evolution reaction (ORR/OER, especially OER) kinetics not only results in a large overpotential, but also causes the poor rechargeability. Thus, it is of great significance and urgency to enhance the electrochemical performances of the cathode. One effective way is to design high efficient catalysts to reduce the charge overpotential. Despite the precious Ru based catalysts have shown promising results as a catalyst for lithium-air batteries, its scarcity and high price will restrict the wide application. As a result, other non-noble transition metal/metal oxides (e.g., MnOx, CoOx) with activities for ORR and/or OER have drawn great interests for lithium-air batteries [2, 3]. Oxides of iron, which in the same group of Ru in the periodic table, however, is less investigated. Herein, we proposed a facile method to fabricate Fe2O3/carbon nanocomposite cathode materials in which Fe2O3 nanoparticles with a diameter of 4-6 nm are deposited onto the carbon surface, as shown in Figure 1. The electro-catalytic activities were investigated by linear sweeping voltammetry (LSV) and discharge-charge profiles. The results show a lower onset potential and a larger OER current density, suggesting that Fe2O3 is an effective OER catalyst. Moreover, a non-aqueous lithium-oxygen battery with this cathode demonstrates a remarkably 430 mV lower charge overpotential and a dramatically improved cycling life. More detailed experimental results will be presented in the meeting. And some possible mechanisms of the catalytic effect will also be discussed. Figure 1

Perovskite La0.6Sr0.4Co0.2Fe0.8O3 as an effective electrocatalyst for non-aqueous lithium air batteries

Non-aqueous lithium air batteries with high energy density have been regarded to be the most attractive contender in the future energy storage techniques. Herein, the perovskite La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) nanoparticles are studied as the cathode catalyst for non-aqueous lithium air batteries. The results confirm that nanostructured LSCF exhibits admirable electrochemical activity and can effectively reduce the overpotential. Batteries with LSCF catalyst can increase the discharge capacity from 9678mAhg−1 to 13979mAhg−1 and improve the cycle stability from 10 cycles to 20 cycles at 200mAg−1. The study reveals that the formation and decomposition processes of Li2O2 can be effectively promoted by the introduction of LSCF nanoparticles. The possible catalytic mechanism of LSCF in reducing overpotential is also proposed.

Recent Progress in Non-Aqueous Lithium-Air Batteries

Recent Progress in Non-Aqueous Lithium-Air Batteries

A nano-structured RuO2/NiO cathode enables the operation of non-aqueous lithium–air batteries in ambient air

A cathode composed of RuO2 nanoparticle-decorated NiO nanosheets not only catalyzes the oxygen reduction and evolution reactions, but also promotes the decomposition of the side products (LiOH and Li2CO3), enabling a non-aqueous lithium–air battery to be truly operated in ambient air.

Novel Flower-like Nickel Sulfide as an Efficient Electrocatalyst for Non-aqueous Lithium-Air Batteries.

In this paper, metal sulfide materials have been explored for the first time as a new choice of bifunctional cathode electrocatalyst materials for non-aqueous lithium-air batteries (LABs). Nickel sulfides with two different morphologies of flower-like (f-NiS) and rod-like (r-NiS) are successfully synthesized using a hydrothermal method with and without the assistance of cetyltrimethyl ammonium bromide. As LAB cathode catalysts, both f-NiS and r-NiS demonstrate excellent catalytic activities towards the formation and decomposition of Li2O2, resulting in improved specific capacity, reduced overpotentials and enhanced cycling performance when compared to those of pure Super P based electrode. Moreover, the morphology of NiS materials can greatly affect LAB performance. Particularly, the f-NiS is more favorable than r-NiS in terms of their application in LABs. When compared to both r-NiS and pure super P materials as LAB cathode materials, this f-NiS catalyst material can give the highest capacity of 6733 mA h g−1 and the lowest charge voltage of 4.24 V at the current density of 75 mA g−1 and also exhibit an quite stable cycling performance.

Performance Evaluation of Activated Carbon Nanofiber as Carbon Supports to Improve the Cyclability of Li-Air Batteries.

This study addresses the effects of the pore structures of carbon materials used as cathodes for non-aqueous lithium-air batteries on cycle life. Carbon Nanofibers (CNFs) were synthesized by electrospinning polyacrylonitrile (PAN) and carbonization. The synthesized CNF was then converted to activated carbon nanofibers (ACNFs) under flowing CO2. The specific surface areas CNFs were increased on activation. ACNFs were arranged randomly to form a web-like structure providing both oxygen pathways and a means of discharging products. To examine the electrochemical properties of ACNF, charge-discharge tests were conducted using a Swagelok-type cell at a constant current density of 0.2 mA/cm2; impedance tests were also conducted. ACNF sheet electrodes had cycle lives of up to 50 cycles, which was attributed to high surface area and porosity, although overpotentials for both charge and discharge were high. This cycling performance showed that the pore structure of sheet ACNF is more suitable for the transport of oxygen and for the storage of discharge products than carbon powders.

DISCHARGE OXIDE STORAGE CAPACITY AND VOLTAGE LOSS IN LI-AIR BATTERY

Air cathodes, where oxygen reacts with Li ions and electrons with discharge oxide stored in their pore structure, are often considered as the most challenging component in nonaqueous Lithium-air batteries. In non-aqueous electrolytes, discharge oxides are usually insoluble and hence precipitate at local reaction site, raising the oxygen transport resistance in the pore network. Due to their low electric conductivity, their presence causes electrode passivation. This study aims to investigate the air cathode’s performance through analytically obtaining oxygen profiles, modeling electrode passivation, evaluating the transport polarization raised by discharge oxide precipitate, and developing analytical formulas for insoluble Li oxides storage capacity. The variations of cathode quantities, including oxygen content and temperature, are evaluated and related to a single dimensionless parameter — the Damköhler Number (Da). An approximate model is developed to predict discharge voltage loss, along with validation against two sets of experimental data. Air cathode properties, including tortuosity, surface coverage factor and the Da number, and their effects on the cathode’s capacity of storing Li oxides are formulated and discussed.

A Comprehensive Model for Non-Aqueous Lithium Air Batteries Involving Different Reaction Mechanisms

There are various reaction mechanisms in the discharge process of a non-aqueous lithium air battery (LAB). Recently, it has been identified that low current rate and high donor number solvents can lead to solution phase reaction, but high current rate and low donor number solvents will cause thin film growth covering the active cathode surface. In this paper we extend our previous LAB multiscale model, which considers the thin film growth mode, to the general case where both surface thin film growth and solution phase reaction coexist. A detailed mechanism is proposed and simulation results are compared with experimental data.

Charting the known chemical space for non-aqueous lithium-air battery electrolyte solvents.

Li-air batteries are very promising candidates for powering future mobility, but finding a suitable electrolyte solvent for this technology turned out to be a major problem. We present a systematic computational investigation of the known chemical space for possible Li-air electrolyte solvents. It is shown that the problem of finding better Li-air electrolyte solvents is not only - as previously suggested - about maximizing Li(+) and O2(-) solubilities, but also about finding the optimal balance of these solubilities with the viscosity of the solvent. As our results also show that trial-and-error experiments on known chemicals are unlikely to succeed, full chemical sub-spaces for the most promising compound classes are investigated, and suggestions are made for further experiments. The proposed screening approach is transferable and robust and can readily be applied to optimize electrolytes for other electrochemical devices. It goes beyond the current state-of-the-art both in width (considering the number of compounds screened and the way they are selected), as well as depth (considering the number and complexity of properties included).

Review—Understanding and Mitigating Some of the Key Factors that Limit Non-Aqueous Lithium-Air Battery Performance

In this article, we have reviewed our work on understanding and mitigating some of the key factors that limit non-aqueous Li-air battery performance. Advances in Li-air battery technology require fundamental understanding of the discharge and charge processes. We first summarize an investigation of Li-air batteries based on a well-defined cathode surfaces having size-selected silver clusters. This work provided key insight into the nucleation and growth mechanism of the discharge product and its relationship to lowering charge potentials. We then describe the development of new cathode materials including ones based on Pd and Mo2C nanoparticles that give very low charge potentials. This work has shown that it is possible to achieve very good round-trip efficiencies as well as up to 100 cycles in a Li-air cell. Finally, we discuss investigations of likely sources of electrolyte decomposition at the cathode and anode, which need to be resolved in order to achieve the long cycle life that is necessary to enable Li-air batteries.