Performance Of Li-O2 Batteries Research Articles

Nanocrystalline Metal–Organic Frameworks/Carbon Nanotubes Composites As Catalytic Cathode Materials for Lithium–Oxygen Batteries with Long Cycle Life

To meet the needs of emerging technologies such as all-electric vehicles with a long drive range, there are now strong motivations for the development of rechargeable batteries with high specific energy, so called “beyond Li-ion batteries.” Among these beyond Li-ion batteries, lithium–air (Li–O2) batteries have received much attention owing to their five times higher theoretic energy density (ca. 3500 W h/kg) than that of lithium-ion batteries. However, Li–O2 batteries still suffer from several challenges that hinder their practical applications, including low energy efficiency, short cycle life, and poor rate capability. These problems are mainly caused by the sluggish oxygen reduction/evolution reaction (ORR/OER), low stability of electrolyte against O2 −•, and the poor conductivity of discharge product (Li2O2).1 To improve the performance of Li–O2 batteries, much effort has been devoted to searching for new catalytic cathode materials to promote ORR/OER kinetics, which is crucial to lowering overpotential and improving the reversibility.2 Metal–organic frameworks (MOFs), a novel type of crystalline porous materials, are built with metal nodes or clusters (secondary building units) and organic linkers. For the last two decades, MOFs have received considerable attentions for gas storage, catalysis, and energy storage, due to their high surface area and chemically unsaturated metal sites.3 It has been also demonstrated that bulk MOFs could be good electrocatalysts for Li–O2 batteries.4 However, most of MOFs have poor electrical conductivity, which limits their applications in electrocatalysis. Herein, we report nanocrystalline MOFs/CNTs composites as catalytic cathode materials for Li–O2 batteries to further enhance the catalytic performance of MOFs. The direct growth of MOFs on CNTs (MOFs@CNTs) can not only enhance the electronic conductivity but also mitigate the agglomeration issues of MOFs nanoparticles, making them suitable in the applications of electrocatalysis. The as-prepared MOF-74@CNTs hybrid cathodes showed the improved cycling performance of Li-O2 batteries. We have also investigated the effects of chemically unsaturated and various redox-active metal sites on the catalytic performance in Li–O2 batteries. The fundamental mechanism of how MOFs enhance the performance of Li-O2 batteries will also be discussed. Reference 1 Aurbach, D., McCloskey, B. D., Nazar, L. F. & Bruce, P. G. Advances in understanding mechanisms underpinning lithium–air batteries. Nature Energy 1, 16128, doi:10.1038/nenergy.2016.128 (2016). 2 Ma, Z. et al. A review of cathode materials and structures for rechargeable lithium–air batteries. Energy & Environmental Science 8, 2144-2198 (2015). 3 Furukawa, H., Cordova, K. E., O’Keeffe, M. & Yaghi, O. M. The chemistry and applications of metal-organic frameworks. Science 341, 1230444 (2013). 4 Wu, D. et al. Metal–organic frameworks as cathode materials for Li–O2 batteries. Adv Mater 26, 3258-3262, doi:10.1002/adma.201305492 (2014).

Preparation of Polymer-Derived Nitrogen-Doped Hollow Carbon Nanofiber As a Free Standing Oxygen Electrode for Li-O2 Battery

Li-O2 battery has got much attention as a beyond Li-ion battery (LIB), due to its higher energy density and exceeding specific capacity than those of commercial LIB. Though it has a promising potential for large-scale energy storage device, Li-O2 battery still has several problems to be overcome in aspects of poor rate capability and limited stability. Especially, the oxygen electrode is one of the most closely related component to the performance of Li-O2 battery since it is the actual site for formation and decomposition of discharge products. Thus, in order to achieve the Li-O2 battery with improved performance, the oxygen electrode should provide favorable structure for not only discharge product storage, but also facile transfer of reactants such as Li ion and O2. Moreover, bicatalytic activity for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is also significant on oxygen electrode by determining the morphology of discharge product. Furthermore, the oxygen electrode has to be chemically and electrochemically stable as well for extended durability of Li-O2 battery. In this regards, we develop a binder free oxygen electrode composed of nitrogen-doped hollow carbon nanofiber, which is derived from nitrogen-containing polymer. Each carbon nanofiber has an empty space inside the fiber even after the heat treatment at high temperature of 900 °C, and it can facilitate the mass transfer of reactants. Due to this unique structure and high nitrogen content of 4.5 at. %, nitrogen-doped hollow carbon nanofiber indicates the lower ORR overpotential and larger discharge capacity than commercial carbon material, Super P, as shown in Fig. 1. Interestingly, it shows the reduced ORR/OER overpotential which is lower than 1 V with the curtaining capacity of 500 mAh g-1 carbon. The notably reduced overpotential might be attributable to the synergetic effect of nitrogen doping, unique structure of hollow carbon nanofiber and absence of binder by promoting the catalytic activity, facilitating the mass transfer and suppressing the side reactions, respectively. The effects of heat treatment temperature and metal incorporation are also investigated and optimized. As for the result, it can be demonstrated that the binder-free nitrogen-doped hollow carbon nanofiber is an enhanced oxygen electrode of Li-O2 battery. Figure 1

High Concentration of LiBr in Electrolyte and Graphene-Polydopamine Composite Layer on Li Metal for High Efficient and Long Term Cycling Li-O2 Batteries

For advanced applications such as electric vehicles (EV), Li-O2 batteries are considered as a prospective candidate for next-generation to replace conventional Li-ion batteries. However, the catalytic effect of the redox mediator for oxygen evolution gradually deteriorates during repeated cycling owing to its decomposition at the surfaces of both the oxygen electrode (cathode) and the Li metal electrode (anode).1,2 Here, we designed optimized Li-O2 batteries with a continuously effective redox mediator and a stable protective layer for the Li metal electrode by optimizing the LiBr concentration and introducing a graphene–polydopamine composite layer, respectively.3 These synergistic modifications lead to a reduction of the charge potential to below 3.4 V and significantly improved the stability and cycle life of Li–O2 batteries. Consequently, a high energy efficiency of above 80% was maintained over 150 cycles. Herein, we confirmed that the relationships between all the battery materials should be understood in order to improve the performance of Li-O2 batteries. References W.-J. Kwak, D. Hirshberg, D. Sharon, H.-J. Shin, M. Arfi, J.-B. Park, A. Garsuch, F. F. Chesneau, A. A. Frimer, D. Aurbach, Y.-K. Sun, Mater. Chem. A 2015, 3, 8855. W.-J. Kwak, D. Hirshberg, D. Sharon, M. Arfi, A. A. Frimer, H.-G. Jung, D. Aurbach, Y.-K. Sun, Energy Environ. Sci. 2016, 9, 2334. W.-J. Kwak, S.-J. Park, H.-G. Jung, and Y.-K. Sun, Adv. Energy Mater. 2017, 7, 1702258

Lithiation/Delithiation Synthesis of Few Layer Silicene Nanosheets for Rechargeable Li-O2 Batteries.

Silicene has recently received increasing interest due to its unique properties. However, the synthesis of silicene remains challenging, which limits its wide applications. In this work, a top-down lithiation and delithiation process is developed to prepare few layer silicene-like nanosheets from ball-milled silicon nanopowders. It is found that delithiation solvent plays a critical role in the structure evolution of the final products. The use of isopropyl alcohol renders 2D silicene-like products 30-100 nm in length and ≈2.4 nm in thickness. The electrochemical characterization analysis suggests that the product shows high performance for rechargeable Li-O2 batteries with 73% energy efficiency and high stability. The top-down synthesis strategy proposed in this work not only provides a new solution to the challenging preparation issue of few layer silicene but also demonstrates the feasibility of producing 2D materials from nonlayered starting structures.

Porous Co3O4 nanorods anchored on graphene nanosheets as an effective electrocatalysts for aprotic Li-O2 batteries

The large over-potential during the battery operation is a great obstacle for the application of Li-O2 batteries. The porous structure and electrical conductivity of the electrocatalysts are significant for the electrocatalytic performance of Li-O2 batteries. In this work, a porous Co3O4/GN nanocomposite (Co3O4 nanorods anchored on graphene nanosheets) is prepared via a facile hydrothermal method assisted with heat treatment. The unique structure of Co3O4/GN endows efficient electrocatalystic activity for Li-O2 batteries. In comparison to the Co3O4, the Co3O4/GN demonstrates a better cycle performance showing more than 40 cycles with a 1500 mAh g−1 capacity limit strategy at a current density of 300 mA g−1, and a reduced over-potential of 110 mV at high current density (1200 mA g−1). The Co3O4/GN also displays a high initial specific capacity (7600 mAh g−1) and a good reversibility in full cycle with a coulombic efficiency of 99.8% in the first cycle. The impressed cyclability, specific capacity, rate performance, and low over-potentials indicate that the as-prepared Co3O4/GN nanocomposite is a promising catalyst candidate for reversible Li-O2 batteries.

Cation-Assisted Formation of Porous TiO2–x Nanoboxes with High Grain Boundary Density as Efficient Electrocatalysts for Lithium–Oxygen Batteries

Despite the ultrahigh energy density of rechargeable lithium–oxygen (Li-O2) batteries, their practical use is still hindered by the poor performance of electrocatalysts. Recently, porous and hollow nanostructured catalysts have been found to be promising electrocatalysts toward the ORR/OER to improve the performance of Li-O2 batteries. However, the catalytic activities of the catalysts are still insufficient and the nanopores are easily clogged by the insoluble discharge products. Herein, highly porous and hollow TiO2–x nanoboxes (TiO2–x NBs) with large surface areas, increased oxygen vacancies, and high grain boundary density have been developed as an electrocatalyst for Li-O2 batteries via a cation-assisted synthetic approach. The Li-O2 batteries with TiO2–x NBs as the electrocatalyst exhibit a high specific capacity of 8569 mA h g–1, excellent rate capability, and long cycle life up to 200 cycles when the capacity is limited to 1000 mA h g–1. Moreover, this cation-assisted approach for fine-tuning the ...

Performance-improved Li-O2 batteries by tailoring the phases of MoxC porous nanorods as an efficient cathode.

Novel nitrogen-doped porous molybdenum carbide (α-MoC1-x and β-Mo2C) architectures were prepared using Mo-based metal-organic frameworks (MOFs) as the precursor. The synthesized molybdenum carbides consist of numerous nanocrystals organized into micro-sized rods with interpenetrating mesoporous-channels and macroporous-tunnels along the axial direction. When employed as the cathode catalyst for Li-O2 batteries, this dual pore configuration offers abundant active sites for the electrochemical reaction and many nucleation sites for the discharge product of Li2O2; hence, decent performances were obtained. Among the two synthesized molybdenum carbides, the α-MoC1-x electrode stands out as being better due to its lower charge transfer resistance (395.8 Ω compared to 627.9 Ω) and better O2 adsorption (binding energy of -1.87 eV of α-(111)-Mo compared to -0.72 eV of β-(101)-Mo). It delivered a high full discharge of 20 212 mA h g-1 with a discharge voltage of 2.62 V at 200 mA g-1. A good cycling stability was also obtained: i.e. 100 stable cycles with a fixed capacity of 1000 mA h g-1 (at a current density of 200 mA g-1) with a charging voltage of 4.24 V and maintaining a respectable round-trip efficiency of ∼70%.

Role of flower-like ultrathin Co3O4 nanosheets in water splitting and non-aqueous Li–O2 batteries

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are both fundamental and essential processes for various energy conversion and storage systems. The kinetics of ORR and OER play a critical role in their energy efficiency and practicality. Here, flower-like ultrathin Co3O4 nanosheets synthesized through a facile solvothermal technique were studied as a bifunctional catalyst for both water splitting and non-aqueous Li-O2 batteries. Due to the novel structure and highly active {110} and {100} exposed facets, which can effectively facilitate mass transfer and enhance catalytic capability, Co3O4 nanosheets exhibit better stability and higher ORR/OER activity than Co3O4 nanoparticles, Co3O4 bulks, Pt/C, and RuO2 in alkaline solution. More importantly, Li-O2 batteries with ultrathin Co3O4 nanosheets catalyst can enhance the initial discharge capacity from 6400 to 8600 mA h g-1 and improve the cyclability up to 160 cycles at 500 mA g-1. Unexpectedly, XRD and UV/Vis techniques suggest that the main product in Co3O4 nanosheets based cathodes is LiOH, with resulting LiOH also demonstrating reversible formation/decomposition behavior, rather than Li2O2 in pure Super P based cathodes. Further investigation confirms that Co3O4 can also catalyze the electrolyte decomposition responsible for the formation of LiOH, and a reaction mechanism was illustrated. This work highlights that the traditional high-efficiency bifunctional catalyst in aqueous media may not be suitable for non-aqueous Li-O2 batteries, and the effect of catalyst on electrolyte besides the discharge product should also be carefully considered for the design of more stable and practical Li-O2 systems.

Bimetallic Metal-Organic Frameworks as Efficient Cathode Catalysts for Li-O2 Batteries.

Metal-organic frameworks (MOFs) have the potential to improve the electrochemical performance of Li-O2 batteries with high O2 accessibility and catalytic activity of the open metal sites. Here, we explored bimetallic MnCo-MOF-74 as a cathode catalyst in Li-O2 batteries. MnCo-MOF-74 was synthesized with the Mn to Co ratio of 1:4 by a simple hydrothermal reaction. Compared to monometallic Mn-MOF-74 and Co-MOF-74 with only single catalytic activity for LiOH formation or oxygen evolution reactions, bimetallic MnCo-MOF-74 demonstrated a capability to facilitate improved reversibility and efficiency during both discharge and charge cycles. Benefitting from the porous structure of the MOF as well as the complementary contribution from both Mn- and Co-metal clusters, MnCo-MOF-74 outperformed Mn-MOF-74 and Co-MOF-74. A high full discharge capacity of 11 150 mAh g-1 at 200 mA g-1 was achieved in MnCo-MOF-74. During the cycling test, MnCo-MOF-74 stably delivered a limited discharge capacity of 1000 mAh g-1 for 44 cycles at 200 mA g-1, which is remarkably longer than those of carbon black, Mn-MOF-74, and Co-MOF-74 with cycle lives of 8, 22, and 18 cycles, respectively.

Positive role of oxygen vacancy in electrochemical performance of CoMn2O4 cathodes for Li-O2 batteries

The thermally induced oxygen vacancies present across the intra/inter-crystalline sites and surface of ultrafine CoMn2O4 (CMO) electrodes ameliorate electrochemical performance of Li-O2 batteries (LOBs). Oxygen deficient CMOs are synthesized via a two-step process: in situ reduction to achieve a large surface area of 151.3 m2 g−1 and thermal treatment at 400 °C in pure Ar. The oxygen deficient CMO electrode presents a higher initial capacity, lower overpotential, better cyclic stability, higher Coulombic efficiencies and higher rate capabilities than the as-prepared CMO electrode without heat treatment. While the CMO electrode presents an excellent catalytic behavior in oxygen reduction reaction (ORR), the oxygen vacancies mitigate the migration of Li+ ions and electrons and act as active sites for O2 in the oxygen evolution reaction (OER). The ex situ characterization also proves a lower kinetic charge transfer resistance and higher catalytic activities of the oxygen deficient CMO electrodes in the decomposition of discharge products during the discharge/charge cycles.

Influence of the Oxygen Electrode Open Ratio and Electrolyte Evaporation on the Performance of Li-O2 Batteries.

This study experimentally investigates and numerically simulates the influence of the cathode electrode open ratio (ratio of oxygen-opening area to the total electrode surface area) on the performance of Li-O2 batteries at various discharge current densities. At the current density of 0.1 mA/cm2, the maximum discharge capacity is achieved at 25% open ratio among the tested open ratios (0-100%). As the open ratio increases from 25% to 100%, the specific discharge capacity decreases from 995 to 397 mA h/gcarbon. A similar trend is observed at 0.3 mA/cm2, while the maximum discharge capacity is obtained at 3% open ratio among the tested open ratios. The model that assumes the electrode is always fully saturated by the electrolyte does not obtain similar trends with experimental results, while the model that considers electrolyte loss by evaporation and the volume change of the solid obtains the same trend with experimental observations. The open ratio governs not only availability of oxygen but also the evaporation of the electrolyte and the contact resistance. The faster evaporation of the electrolyte at a higher open ratio can be the main reason for the decrease of the discharge capacity, especially when the open ratio is relatively high (above 25%). Meanwhile, the contact resistance of the battery, measured by the electrochemical impedance spectroscopy (EIS), increases from 3.97 to 7.02 Ω when the open ratio increased from 3% to 95%. The increase of the Ohmic overpotential, however, is negligible (on the order of millivolts) because of the low discharge and charge current rates (on the order of 0.1 mA).

The Effect of Li Ion Dissociation Level in Gel Polymer Electrolytes on Electrochemical Performance of Li-O2 Batteries

Li-O2 batteries have been recently considered as next generation of energy storage systems for electric vehicle application due to their high specific energy densities, which are comparable to gasoline [1]. Li-O2 batteries however suffer poor cycling and reachability due to a sever electrolyte decomposition [2]. It has been shown that the electrolyte decomposition by-products such as lithium carbonate species gradually cover the surface of cathodes and shuts down the batteries quickly [3]. Although many attempts have been made to overcome the detrimental formation of these carbonate species on the surface of cathode, their formation and electrolyte instability still remains a very big challenge in this filed [4]. Recently, it has been reported that tailoring the coordination of Li ion and solvent molecules in Li-O2 battery electrolytes is a promising method to improve the electrolyte stabilities [5,6]. In this study, we report that the inclusion of inorganic fillers in gel polymer electrolytes using different salt concentration can reduce the electrolyte decomposition by-products such as lithium carbonate species during the Li-O2 battery cycling. The improved electrochemical performance of Li-O2 batteries can be attributed to the interaction of filler with Li salt which in turn can tailor the interaction of Li ion and solvent molecules. To asses our hypothesis different electrochemical tests including in-depth electrochemical impedance spectroscopy, lithium transference number measurements along with other characterization methods such as Raman spectroscopy has been used. [1] G. Girishkumar, B. McCloskey, A.C. Luntz, S. Swanson, W. Wilcke, Lithium-air battery: Promise and challenges, J. Phys. Chem. Lett. 2010,1, 2193–2203. [2] B. D. McCloskey, C. M. Burke, J. E. Nichols and S. E. Renfrew, Chem. Commun., 2015, 51, 12701–12715 [3] S. A. Freunberger, Y. Chen, N. E. Drewett, L. J. Hardwick, F. Bardé and P. G. Bruce, Angew. Chemie - Int. Ed., 2011, 50, 8609–8613 [4] R. Younesi, G.M. Veith, P. Johansson, K. Edstrom, T. Vegge, Lithium salts for advanced lithium batteries: Li-metal, Li-O2, and Li-S, Energy Environ. Sci.,2015, 8, 1905–1922. [5] F. Li, T. Zhang, Y. Yamada, A. Yamada and H. Zhou, Adv. Energy Mater., 2013, 3, 532–538. [6] B. Liu, W. Xu, P. Yan, X. Sun, M. E. Bowden, J. Read, J. Qian, D. Mei, C. M. Wang and J. G. Zhang, Adv. Funct. Mater., 2016, 26, 605–613.

Investigation of Electrochemical Performance of Li-O2 Batteries Using Catalyst Containing Carbon Nanotube Cathodes

Batteries with high specific energy densities have attracted a lot of attention due to their demand in electric vehicles (EVs). Due to the increase in demand for energy storage devices for applications such as load-levelling of electrical energy supply and demand propulsion for electric vehicles and microelectro-mechanical devices, the research for new classes of electrode materials that provide high energy, high power and cycle life longer than lithium-ion batteries is being motivated. Lithium air batteries have high specific energy density and they can achieve four times higher energy density than the current lithium ion batteries. The search for high energy density batteries has motivated the research in lithium-air batteries. Catalysts have been shown to improve both the battery capacity and the recyclability of these batteries when used in cathodes. Several catalysts have been discovered for lithium air batteries. Debart et al. used several catalysts for lithium oxygen batteries with non-aqueous electrolyte. The electro-catalysts used by them included Pt, La0.8Sr0.2MnO3, Fe2O3, NiO, CuO, CoFe2O4. Co3O4 exhibited highest discharge capacity and best cycling performance. Later Debart et al. examined manganese oxides as catalysts for lithium oxygen batteries. Mn3O4, bulk Mn2O3, bulk α, β, λ, γ-MnO2, α-MnO2 nanowires and β-MnO2 nanowires were used as catalysts. The air cathode with α-MnO2 as the catalyst showed the highest capacity of about 3000 mAh/g (carbon) Lu et al. reported ORR studies on polycrystalline metal catalysts of palladium, platinum, ruthenium, gold and glassy carbon surfaces in non-aqueous electrolyte. In our study, we investigate various modes of loading palladium-based catalysts and their effect on the capacity and round-trip efficiency of lithium-air batteries. Our aim is to increase the first discharge capacity, improve the recyclability, increase capacity retention and improve the recyclability of the battery. The loading and morphology the catalyst-CNT cathode is studied using transmission electron microscopy. Electrochemical testing using electrochemical impedance spectroscopy and charge-discharge cycling is also investigated. Voltammetry, Raman spectroscopy, FTIR, XRD, UV/Vis spectroscopy and visual inspection of the discharge products using scanning electron microscopy confirms the increased stability of the electrolyte due to this encapsulation and suggest that this approach could lead the increasing Li-O2 battery capacity and cyclability performance.

Mesoporous Pd/Co3O4 nanosheets nanoarrays as an efficient binder/carbon free cathode for rechargeable Li-O2 batteries

In this work, two shapes of mesoporous Co3O4 nanoarrays (i.e., nanosheets, nanowires) were synthesized through a facile hydrothermal method on nickel foam (Ni foam) substrates and tested as the Li-O2 cathodes. The comparison of these two shapes of Co3O4 nanoarrays revealed that the single crystalline feature of Co3O4 nanosheets with a predominant high reactivity {112} exposed crystal plane, favorable nanostructure and high specific area displayed better catalytic performance. Furthermore, a new binder/carbon-free Pd nanoparticles (PdNPs) decorated Co3O4 nanosheets cathode was also fabricated through the chemical reduction method. The presence of PdNPs effectively promotes the uniform growth of a fluffy, porous discharge product Li2O2 layer on the surface of Pd/Co3O4 electrode. The Pd/Co3O4 electrode catalyzed Li-O2 battery exhibited a higher specific capacity (1551mAhg−1 at 50mAg−1), lower over-potential and longer cycle life over 72 cycles at 100mAg−1 with the capacity limited at 300mAhg−1. The superior catalytic performance for Li-O2 batteries is ascribed to the unique design in both component and architecture of Pd/Co3O4 electrode.

Hierarchical ordered macroporous/ultrathin mesoporous carbon architecture: A promising cathode scaffold with excellent rate performance for rechargeable Li-O2 batteries

In spite of the ultrahigh theoretical energy density, non-aqueous Li-O2 batteries are still constrained by their inefficient cathodes. Here, we report the synthesis of a distinctive hierarchical carbon architecture (HOM-AMUW) for Li-O2 batteries, which consists of highly ordered macropores (250 nm) with abundant mesopores on their ultrathin walls (4–5 nm). This carbon architecture exhibits unprecedented discharge capacity of 37523 mAh g−1 and 12686 mAh g−1 at the current density of 500 mA g−1 and even 2000 mA g−1, respectively. After further functionalization by low crystalline Ru nanoclusters, the resulted Ru-HOM-AMUW architecture presents a much low charge polarization and outstanding cycling stability. The significant performance enhancement is mainly attributed to the unique hierarchical porous structure, wherein the ordered macropores and ultrathin mesoporous walls remarkably enhance the access capability of O2 or Li+ to the numerous active sites, and the large pore volume easily accommodates the discharge products. Moreover, the hierarchical porous structure modulates the morphology of discharge products to three-dimensional porous structure with high charge transport, which also contributes to the striking rate capability. This HOM-AMUW architecture is a promising scaffold to design the gas electrodes with ultrahigh rate performance not only for Li-O2 batteries but also for other metal-air batteries.

Three-dimensionally branched carbon nanowebs as air-cathode for redox-mediated Li-O2 batteries

The optimal design of air-electrodes is one of the important keys to achieve the high rechargeability of Li-O2 batteries, however, remains as a challenging issue to date. Herein, we propose an air-electrode architecture based on three-dimensionally open macroporous carbon nanowebs (3-DOM-CNWs), which can be easily scaled-up maintaining its hierarchical structure of nano/micrometer-scale pores. It is demonstrated that the open macroporous nanoweb electrode is particularly advantageous for Li-O2 batteries utilizing the redox mediators in the electrolyte by facilitating the efficient transport of them. The 3-DOM-CNWs electrode could deliver higher specific capacity (∼14,000 mAh g−1) and longer cyclic stability with a better energy efficiency than the conventionally used Ketjen black (KB)-based electrode for redox-mediated Li-O2 batteries, while the specific surface area of 3-DOM-CNWs is only one fourteenth of that of the KB-based air-electrode. This result clearly demonstrates that the electrode architecture based on the hierarchical pore structures significantly enhances the electrochemical performance of Li-O2 batteries by aiding in the transport not only of lithium and oxygen but also the redox mediators.

Enhanced Electrochemical Performance of Non-Aqueous Li-O2 Batteries with Triethylene Glycol Dimethyl Ether-Based Electrolyte

Triethylene glycol dimethyl ether (G3) is evaluated as an electrolyte solvent for non-aqueous lithium-oxygen (Li-O2) batteries. A liquid electrolyte of 1 M LiTFSI in G3 shows lower viscosity, higher oxygen solubility and diffusion, higher ionic conductivity and lithium ionic transference number compared to the conventional liquid electrolyte of 1 M LiTFSI in tetraethylene glycol dimethyl ether (G4). Then the Li-O2 battery using the G3-based electrolyte shows better cycling stability and higher rate capability compared to the battery using the G4-based electrolyte. At a higher current density of 2.5 A gcarbon−1, the discharge capacity of the battery using the G3-based electrolyte is about 1472 mAh gcarbon−1, which is about four times higher than that of the battery using the G4-based electrolyte. At current density of 1 A gcarbon−1 with a fixed capacity of 1000 mAh gcarbon−1, the battery using the G3-based electrolyte can be operated stably for 80 cycles, while only 20 cycles are achieved by using the G4-based electrolyte. Therefore, we think the G3-based electrolyte could be a proper alternative electrolyte to the conventional G4-based electrolyte for the development of Li-O2 batteries.

Polydopamine-Derived Nitrogen-Doped Graphitic Carbon for a Bifunctional Oxygen Electrode in a Non-Aqueous Li-O2 Battery

Nitrogen-doped graphitic carbon was developed through a simple, facile and controllable method in the pursuit of advanced oxygen electrode materials for use in non-aqueous Li-O2 batteries. These materials were synthesized by directly coating a thin layer of polydopamine (PDA) on the cage-like structure of graphitic carbon followed by subsequent carbonization without the aid of metal catalysts. By virtue of the versatile coating ability associated with the high nitrogen content, dopamine was demonstrated to be an effective precursor for the preparation of nitrogen-doped graphitic carbon. Various experimental results indicated that dopamine-derived nitrogen-doped graphitic carbon improved the performance of Li-O2 batteries in terms of capacity, rate capability and cycle life. The enhanced performance was attributed to the formation of active nitrogen functional groups, which benefit the fast electrochemical kinetics of the oxygen reduction and oxygen evolution reactions in the oxygen electrode of Li-O2 batteries.

Palladium-Filled Carbon Nanotubes Cathode for Improved Electrolyte Stability and Cyclability Performance of Li-O2 Batteries

Li–oxygen (Li-O2) cathodes using palladium-coated and palladium-filled carbon nanotubes (CNTs) were investigated for their battery performance. The full discharge of batteries in the 2–4.5 V range showed 6-fold increase in the first discharge cycle of the Pd-filled over the pristine CNTs and 35% increase over their Pd-coated counterparts. The Pd-filled also exhibited improved cyclability with 58 full cycles of 500 mAh·g−1 at current density of 250 mA·g−1 versus 35 and 43 cycles for pristine and Pd-coated CNTs, respectively. In this work, the effect of encapsulating the Pd catalysts inside the CNTs proved to increase the stability of the electrolyte during both discharging and charging. Voltammetry, Raman spectroscopy, FTIR, XRD, UV/Vis spectroscopy and visual inspection of the discharge products using scanning electron microscopy confirmed the improved stability of the electrolyte due to this encapsulation and suggest that this approach could lead increasing the Li-O2 battery capacity and cyclability performance.

Hierarchically porous Pd/NiO nanomembranes as cathode catalysts in Li-O2 batteries

Exploring highly efficient electrocatalysts is crucial for aprotic Li-O2 batteries. Pd/NiO nanomembranes with hierarchical pores are fabricated and employed as cathode catalysts in Li-O2 batteries. By means of standard photolithography, ordered macropores were prepared in the nanomembranes. Moreover, we developed a facile template-free method to create nanopores with sizes ranging from 50 to 200nm in the composite. The diverse pores of micro- and nanometer sizes and the resulting loose structure supply fast channels for the transportation of reactants, thus efficiently promoting the performance of Li-O2 batteries by lowering the overvoltages and enhancing the rate capability and stability.