Aprotic and aqueous Li-O₂ batteries

High-Performance Li-O2 Batteries with Trilayered Pd/MnO x /Pd Nanomembranes

Trilayered Pd/MnO _x /Pd nanomembranes are fabricated as the cathode catalysts for Li-O₂ batteries. The combination of Pd and MnO _x facilitates the transport of electrons, lithium ions, and oxygen-containing intermediates, thus effectively decomposing the discharge product Li₂O₂ and significantly lowering the charge overpotential and enhancing the power efficiency. This is promising for future environmentally friendly applications.

Simple synthesis of highly catalytic carbon-free MnCo2O4@Ni as an oxygen electrode for rechargeable Li-O2 batteries with long-term stability

An effective integrated design with a free standing and carbon-free architecture of spinel MnCo₂O₄ oxide prepared using facile and cost effective hydrothermal method as the oxygen electrode for the Li–O₂ battery, is introduced to avoid the parasitic reactions of carbon and binder with discharge products and reaction intermediates, respectively. The highly porous structure of the electrode allows the electrolyte and oxygen to diffuse effectively into the catalytically active sites and hence improve the cell performance. The amorphous Li₂O₂ will then precipitate and decompose on the surface of free-standing catalyst nanorods. Electrochemical examination demonstrates that the free-standing electrode without carbon support gives the highest specific capacity and the minimum capacity fading among the rechargeable Li–O₂ batteries tested. The Li-O₂ cell has demonstrated a cyclability of 119 cycles while maintaining a moderate specific capacity of 1000 mAh g⁻¹. Furthermore, the synergistic effect of the fast kinetics of electron transport provided by the free-standing structure and the high electro-catalytic activity of the spinel oxide enables excellent performance of the oxygen electrode for Li-O₂ cells.

A Polymer Lithium-Oxygen Battery

Herein we report the characteristics of a lithium-oxygen battery using a solid polymer membrane as the electrolyte separator. The polymer electrolyte, fully characterized in terms of electrochemical properties, shows suitable conductivity at room temperature allowing the reversible cycling of the Li-O2 battery with a specific capacity as high as 25,000 mAh gC(-1) reflected in a surface capacity of 12.5 mAh cm(-2). The electrochemical formation and dissolution of the lithium peroxide during Li-O2 polymer cell operation is investigated by electrochemical techniques combined with X-ray diffraction study, demonstrating the process reversibility. The excellent cell performances in terms of delivered capacity, in addition to its solid configuration allowing the safe use of lithium metal as high capacity anode, demonstrate the suitability of the polymer lithium-oxygen as high-energy storage system.

The water catalysis at oxygen cathodes of lithium-oxygen cells

Lithium–oxygen cells have attracted extensive interests due to their high theoretical energy densities. The main challenges are the low round-trip efficiency and cycling instability over long time. However, even in the state-of-the-art lithium–oxygen cells the charge potentials are as high as 3.5 V that are higher by 0.70 V than the discharge potentials. Here we report a reaction mechanism at an oxygen cathode, ruthenium and manganese dioxide nanoparticles supported on carbon black Super P by applying a trace amount of water in electrolytes to catalyse the cathode reactions of lithium–oxygen cells during discharge and charge. This can significantly reduce the charge overpotential to 0.21 V, and results in a small discharge/charge potential gap of 0.32 V and superior cycling stability of 200 cycles. The overall reaction scheme will alleviate side reactions involving carbon and electrolytes, and shed light on the construction of practical, rechargeable lithium–oxygen cells.

The main challenges in lithium-oxygen batteries are the low round-trip efficiency and decaying cycle life. Here, the authors present that a trace amount of water in electrolytes facilitates oxygen cathode reactions, enabling the batteries to be operated with small overpotential and good cycling stability.

Carbon-Based Materials for Lithium-Ion Batteries, Electrochemical Capacitors, and Their Hybrid Devices

A rapidly developing market for portable electronic devices and hybrid electrical vehicles requires an urgent supply of mature energy-storage systems. As a result, lithium-ion batteries and electrochemical capacitors have lately attracted broad attention. Nevertheless, it is well known that both devices have their own drawbacks. With the fast development of nanoscience and nanotechnology, various structures and materials have been proposed to overcome the deficiencies of both devices to improve their electrochemical performance further. In this Review, electrochemical storage mechanisms based on carbon materials for both lithium-ion batteries and electrochemical capacitors are introduced. Non-faradic processes (electric double-layer capacitance) and faradic reactions (pseudocapacitance and intercalation) are generally explained. Electrochemical performance based on different types of electrolytes is briefly reviewed. Furthermore, impedance behavior based on Nyquist plots is discussed. We demonstrate the influence of cell conductivity, electrode/electrolyte interface, and ion diffusion on impedance performance. We illustrate that relaxation time, which is closely related to ion diffusion, can be extracted from Nyquist plots and compared between lithium-ion batteries and electrochemical capacitors. Finally, recent progress in the design of anodes for lithium-ion batteries, electrochemical capacitors, and their hybrid devices based on carbonaceous materials are reviewed. Challenges and future perspectives are further discussed.

Direct fabrication of nanoporous graphene from graphene oxide by adding a gasification agent to a magnesiothermic reaction

CaCO3 acts as a gasification agent during magnesiothermic reduction of graphene oxide, thus preventing the newly formed graphene from restacking. The surface area of the obtained graphene increases from 66 m(2) g(-1) to 603 m(2) g(-1) by adding CaCO3 with a high yield of ∼70% based on the carbon content in graphene oxide.

Pd nanoparticles on ZnO-passivated porous carbon by atomic layer deposition: an effective electrochemical catalyst for Li-O2 battery

Uniformly dispersed Pd nanoparticles on ZnO-passivated porous carbon were synthesized via an atomic layer deposition (ALD) technique, which was tested as a cathode material in a rechargeable Li-O2 battery, showing a highly active catalytic effect toward the electrochemical reactions-in particular, the oxygen evolution reaction. Transmission electron microscopy (TEM) showed discrete crystalline nanoparticles decorating the surface of the ZnO-passivated porous carbon support in which the size could be controlled in the range of 3-6 nm, depending on the number of Pd ALD cycles performed. X-ray absorption spectroscopy (XAS) at the Pd K-edge revealed that the carbon-supported Pd existed in a mixed phase of metallic palladium and palladium oxide. The ZnO-passivated layer effectively blocks the defect sites on the carbon surface, minimizing the electrolyte decomposition. Our results suggest that ALD is a promising technique for tailoring the surface composition and structure of nanoporous supports for Li-O2 batteries.

Compatible interface design of CoO-based Li-O2 battery cathodes with long-cycling stability

Lithium-oxygen batteries with high theoretical energy densities have great potential. Recent studies have focused on different cathode architecture design to address poor cycling performance, while the impact of interface stability on cathode side has been barely reported. In this study, we introduce CoO mesoporous spheres into cathode, where the growth of crystalline discharge products (Li2O2) is directly observed on the CoO surface from aberration-corrected STEM. This CoO based cathode demonstrates more than 300 discharge/charge cycles with excessive lithium anode. Under deep discharge/charge, CoO cathode exhibited superior cycle performance than that of Co3O4 with similar nanostructure. This improved cycle performance can be ascribed to a more favorable adsorption configuration of Li2O2 intermediates (LiO2) on CoO surface, which is demonstrated through DFT calculation. The favorable adsorption of LiO2 plays an important role in the enhanced cycle performance, which reduced the contact of LiO2 to carbon materials and further alleviated the side reactions during charge process. This compatible interface design may provide an effective approach in protecting carbon-based cathodes in metal-oxygen batteries.

Recycling application of Li-MnO₂ batteries as rechargeable lithium-air batteries

The ever-increasing consumption of a huge quantity of lithium batteries, for example, Li-MnO2 cells, raises critical concern about their recycling. We demonstrate herein that decayed Li-MnO2 cells can be further utilized as rechargeable lithium-air cells with admitted oxygen. We further investigated the effects of lithiated manganese dioxide on the electrocatalytic properties of oxygen-reduction and oxygen-evolution reactions (ORR/OER). The catalytic activity was found to be correlated with the composition of Li(x)MnO2 electrodes (0<x<1) generated in situ in aprotic Li-MnO2 cells owing to tuning of the Mn valence and electronic structure. In particular, modestly lithiated Li(0.50)MnO2 exhibited superior performance with enhanced round-trip efficiency (ca. 76%), high cycling ability (190 cycles), and high discharge capacity (10,823 mA h g(carbon)(-1)). The results indicate that the use of depleted Li-MnO2 batteries can be prolonged by their application as rechargeable lithium-air batteries.

The lithium/air battery: still an emerging system or a practical reality?

Lithium/air is a fascinating energy storage system. The effective exploitation of air as a battery electrode has been the long-time dream of the battery community. Air is, in principle, a no-cost material characterized by a very high specific capacity value. In the particular case of the lithium/air system, energy levels approaching that of gasoline have been postulated. It is then not surprising that, in the course of the last decade, great attention has been devoted to this battery by various top academic and industrial laboratories worldwide. This intense investigation, however, has soon highlighted a series of issues that prevent a rapid development of the Li/air electrochemical system. Although several breakthroughs have been achieved recently, the question on whether this battery will have an effective economic and societal impact remains. In this review, a critical evaluation of the progress achieved so far is made, together with an attempt to propose future R&D trends. A forecast on whether Li/air may have a role in the next years' battery technology is also postulated.

Enabling catalytic oxidation of Li2O2 at the liquid-solid interface: the evolution of an aprotic Li-O2 battery

We show that by using a suitable soluble redox mediator, the charging overpotential can be reduced and the round-trip efficiency can be improved in an aprotic Li-O2 battery. Not only do we explore a new redox couple, 10-methyl-10H-phenothiazine, as a soluble catalyst that improves the electrochemical performance, but we also propose possible challenges that need to be overcome for the future improvement of aprotic Li-O2 batteries.

A mesoporous catalytic membrane architecture for lithium-oxygen battery systems

Controlling the mesoscale geometric configuration of catalysts on the oxygen electrode is an effective strategy to achieve high reversibility and efficiency in Li-O2 batteries. Here we introduce a new Li-O2 cell architecture that employs a catalytic polymer-based membrane between the oxygen electrode and the separator. The catalytic membrane was prepared by immobilization of Pd nanoparticles on a polyacrylonitrile (PAN) nanofiber membrane and is adjacent to a carbon nanotube electrode loaded with Ru nanoparticles. During oxide product formation, the insulating PAN polymer scaffold restricts direct electron transfer to the Pd catalyst particles and prevents the direct blockage of Pd catalytic sites. The modified Li-O2 battery with a catalytic membrane showed a stable cyclability for 60 cycles with a capacity of 1000 mAh/g and a reduced degree of polarization (∼ 0.3 V) compared to cells without a catalytic membrane. We demonstrate the effects of a catalytic membrane on the reaction characteristics associated with morphological and structural features of the discharge products via detailed ex situ characterization.

Direct growth of flower-like 3D MnO2 ultrathin nanosheets on carbon paper as efficient cathode catalyst for rechargeable Li–O2 batteries

Structure and working mechanism of the MnO₂/CP air electrode.

Palladium nanoparticle functionalized graphene nanosheets for Li–O2batteries: enhanced performance by tailoring the morphology of the discharge product

The Li–O₂battery with palladium functionalized graphene nanosheets cathode exhibits enhanced discharge capacity and improved ORR/OER performance through tailoring the morphology of discharge product.

A lithium-ion oxygen battery using a polyethylene glyme electrolyte mixed with an ionic liquid

An efficient, safe lithium-ion oxygen battery is formed by combining an oxygen cathode and a lithium-alloy anode in a glyme-based ionic liquid-containing electrolyte.

Lithium–oxygen batteries with ester-functionalized ionic liquid-based electrolytes

An ester-functionalized ionic liquid-based solution was successfully employed as a promising electrolyte for lithium–oxygen batteries.

A high performance O2selective membrane based on CAU-1-NH2@polydopamine and the PMMA polymer for Li–air batteries

A novel oxygen selective membrane was prepared and assembled in Li-air batteries operating under real air conditions with 30% RH. Due to its high O₂permeability, remarkable CO₂capture ability and excellent hydrophobic behavior, extremely stable cycling performance was achieved.

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.

Investigating dendrites and side reactions in sodium–oxygen batteries for improved cycle lives

Sodium dendrites and side reactions were investigated in the sodium–oxygen batteries, the cyclability of which was greatly improved by a sodium ion selective polymer membrane.

Mechanistic insights for the development of Li–O2battery materials: addressing Li2O2conductivity limitations and electrolyte and cathode instabilities

This featured article provides a perspective on challenges facing Li–air battery cathode development, including Li₂O₂conductivity limitations and instabilities of electrolyte and high surface area carbon.

Porous nanoarchitectures of spinel-type transition metal oxides for electrochemical energy storage systems

Transition metal oxides possessing two kinds of metals (denoted as A_xB_3−xO₄, which is generally defined as a spinel structure; A, B = Co, Ni, Zn, Mn, Fe,etc.), with stoichiometric or even non-stoichiometric compositions, have recently attracted great interest in electrochemical energy storage systems (ESSs).

The importance of nanometric passivating films on cathodes for Li-air batteries

Recently, there has been a transition from fully carbonaceous positive electrodes for the aprotic lithium oxygen battery to alternative materials and the use of redox mediator additives, in an attempt to lower the large electrochemical overpotentials associated with the charge reaction. However, the stabilizing or catalytic effect of these materials can become complicated due to the presence of major side-reactions observed during dis(charge). Here, we isolate the charge reaction from the discharge by utilizing electrodes prefilled with commercial lithium peroxide with a crystallite size of about 200-800 nm. Using a combination of S/TEM, online mass spectrometry, XPS, and electrochemical methods to probe the nature of surface films on carbon and conductive Ti-based nanoparticles, we show that oxygen evolution from lithium peroxide is strongly dependent on their surface properties. Insulating TiO2 surface layers on TiC and TiN - even as thin as 3 nm-can completely inhibit the charge reaction under these conditions. On the other hand, TiC, which lacks this oxide film, readily facilitates oxidation of the bulk Li2O2 crystallites, at a much lower overpotential relative to carbon. Since oxidation of lithium oxygen battery cathodes is inevitable in these systems, precise control of the surface chemistry at the nanoscale becomes of upmost importance.

Carbon-, binder-, and precious metal-free cathodes for non-aqueous lithium-oxygen batteries: nanoflake-decorated nanoneedle oxide arrays

Rechargeable lithium-oxygen (Li-O2) batteries have higher theoretical energy densities than today's lithium-ion batteries and are consequently considered to be an attractive energy storage technology to enable long-range electric vehicles. The main constituents comprising a cathode of a lithium-oxygen (Li-O2) battery, such as carbon and binders, suffer from irreversible decomposition, leading to significant performance degradation. Here, carbon- and binder-free cathodes based on nonprecious metal oxides are designed and fabricated for Li-O2 batteries. A novel structure of the oxide-only cathode having a high porosity and a large surface area is proposed that consists of numerous one-dimensional nanoneedle arrays decorated with thin nanoflakes. These oxide-only cathodes with the tailored architecture show high specific capacities and remarkably reduced charge potentials (in comparison with a carbon-only cathode) as well as excellent cyclability (250 cycles).

Integrating a redox-coupled dye-sensitized photoelectrode into a lithium-oxygen battery for photoassisted charging

With a high theoretical specific energy, the non-aqueous rechargeable lithium-oxygen battery is a promising next-generation energy storage technique. However, the large charging overpotential remains a challenge due to the difficulty in electrochemically oxidizing the insulating lithium peroxide. Recently, a redox shuttle has been introduced into the electrolyte to chemically oxidize lithium peroxide. Here, we report the use of a triiodide/iodide redox shuttle to couple a built-in dye-sensitized titanium dioxide photoelectrode with the oxygen electrode for the photoassisted charging of a lithium-oxygen battery. On charging under illumination, triiodide ions are generated on the photoelectrode, and subsequently oxidize lithium peroxide. Due to the contribution of the photovoltage, the charging overpotential is greatly reduced. The use of a redox shuttle to couple a photoelectrode and an oxygen electrode offers a unique strategy to address the overpotential issue of non-aqueous lithium-oxygen batteries and also a distinct approach for integrating solar cells and batteries.

A PtRu catalyzed rechargeable oxygen electrode for Li-O2 batteries: performance improvement through Li2O2 morphology control

Albeit ultrahigh in energy density, the Li-O2 battery technology still suffers from the high overpotential of Li2O2 oxidation upon charging and the low cyclability. In the present work, we use Pt2Ru/C as the oxygen-electrode catalyst and study how it improves the cell performance and changes the reaction mechanism, as compared with a carbon electrode. Multiple methods, including X-ray diffraction, transmission/scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry, have been employed for material characterization and reaction monitoring. The Li-O2 cell with a Pt2Ru/C catalyst shows lower charge voltage, higher specific capacity, and enhanced cyclability than does a carbon catalyst. The key for this improvement is ascribed to the morphology change of Li2O2. Whereas the Li2O2 formed in the carbon electrode is rod-shaped, the Li2O2 in the Pt2Ru/C electrode is mud shaped and closely attached to the electrode substrate, thus benefiting the subsequent Li2O2 oxidation. This study indicates that the charging performance of the Li-O2 battery can be improved not only by using proper catalysts, but also by controlling the Li2O2 morphology during discharge.

Molecular-level insights into the reactivity of siloxane-based electrolytes at a lithium-metal anode

A molecular-level understanding of the reactions that occur at the lithium-metal anode/electrolyte interphase is essential to improve the performance of Li-O(2) batteries. Experimental and computational techniques are applied to explore the reactivity of tri(ethylene glycol)-substituted trimethylsilane (1NM3), a siloxane-based ether electrolyte, at the lithium-metal anode. In situ/ex situ X-ray diffraction and Fourier-transform infrared spectroscopy studies provide evidence of the formation of lithium hydroxide and lithium carbonates at the anode upon gradual degradation of the metallic lithium anode and the solvent molecules in the presence of oxygen. Density functional calculations performed to obtain a mechanistic understanding of the reductive decomposition of 1NM3 indicate that the decomposition does not require any apparent barrier to produce lithium hydroxide and lithium carbonates when the reduced 1NM3 solvent molecules interact with the oxygen crossing over from the cathode. This study indicates that degradation may be more significant in the case of the 1NM3 solvent, compared to linear ethers such as tetraglyme or dioxalone, because of its relatively high electron affinity. Also, both protection of the lithium metal and prevention of oxygen crossover to the anode are essential for minimizing electrolyte and anode decomposition.