A lithium–oxygen battery based on lithium superoxide

Electrolyte-controlled discharge product distribution of Na–O2 batteries: a combined computational and experimental study

Tuning the composition of discharge products is an important strategy to reduce charge potential, suppress side reactions, and improve the reversibility of metal–oxygen batteries.

Reaction chemistry in rechargeable Li–O2batteries

This progress report reviews the most recent discoveries regarding Li–O₂chemistry during each discharge and charge process.

Air electrode based on poly(3,4-ethylenedioxythiophene) microflower/graphene composite for superior Li–O2batteries with excellent cycle performance

A PEDOT microflower/graphene composite was introduced as a potential electrode material for Li–O₂batteries with enhanced electrochemical performance.

Mechanistic origin of low polarization in aprotic Na–O2 batteries

The mechanistic difference between Li–O₂ and Na–O₂ batteries has been revealed by in situ spectroscopy coupled with theory calculations.

Fast iterative reconstruction of data in full interior tomography

This paper introduces two novel strategies for iterative reconstruction of full interior tomography (FINT) data, i.e. when the field of view is entirely inside the object support and knowledge of the object support itself or the attenuation coefficients inside specific regions of interest are not available. The first approach is based on data edge-padding. The second technique creates an intermediate virtual sinogram, which is, then, reconstructed by a standard iterative algorithm. Both strategies are validated in the framework of the alternate direction method of multipliers plug-and-play with gridding projectors that provide a speed-up of three orders of magnitude with respect to standard operators implemented in real space. The proposed methods are benchmarked on synchrotron-based X-ray tomographic microscopy datasets of mouse lung alveoli. Compared with analytical techniques, the proposed methods substantially improve the reconstruction quality for FINT underconstrained datasets, facilitating subsequent post-processing steps.

Energy and fuels from electrochemical interfaces

Advances in electrocatalysis at solid-liquid interfaces are vital for driving the technological innovations that are needed to deliver reliable, affordable and environmentally friendly energy. Here, we highlight the key achievements in the development of new materials for efficient hydrogen and oxygen production in electrolysers and, in reverse, their use in fuel cells. A key issue addressed here is the degree to which the fundamental understanding of the synergy between covalent and non-covalent interactions can form the basis for any predictive ability in tailor-making real-world catalysts. Common descriptors such as the substrate-hydroxide binding energy and the interactions in the double layer between hydroxide-oxides and H---OH are found to control individual parts of the hydrogen and oxygen electrochemistry that govern the efficiency of water-based energy conversion and storage systems. Links between aqueous- and organic-based environments are also established, encouraging the 'fuel cell' and 'battery' communities to move forward together.

Sustainability and in situ monitoring in battery development

The development of improved rechargeable batteries represents a major technological challenge for this new century, as batteries constitute the limiting components in the shift from petrol (gasoline) powered to electric vehicles, while also enabling the use of more renewable energy on the grid. To minimize the ecological implications associated with their wider use, we must integrate sustainability of battery materials into our research endeavours, choosing chemistries that have a minimum footprint in nature and that are more readily recycled or integrated into a full circular economy. Sustainability and cost concerns require that we greatly increase the battery lifetime and consider second lives for batteries. As part of this, we must monitor the state of health of batteries continuously during operation to minimize their degradation. It is thus important to push the frontiers of operando techniques to monitor increasingly complex processes. In this Review, we will describe key advances in both more sustainable chemistries and operando techniques, along with some of the remaining challenges and possible solutions, as we personally perceive them.

The role of nanotechnology in the development of battery materials for electric vehicles

A significant amount of battery research and development is underway, both in academia and industry, to meet the demand for electric vehicle applications. When it comes to designing and fabricating electrode materials, nanotechnology-based approaches have demonstrated numerous benefits for improved energy and power density, cyclability and safety. In this Review, we offer an overview of nanostructured materials that are either already commercialized or close to commercialization for hybrid electric vehicle applications, as well as those under development with the potential to meet the requirements for long-range electric vehicles.

Mechanistic Insights into the Challenges of Cycling a Nonaqueous Na-O2 Battery

Superoxide-based nonaqueous metal-oxygen batteries have received considerable research attention as they exhibit high energy densities and round-trip efficiencies. The cycling performance, however, is still poor. Here we study the cycling characteristic of a Na-O₂ battery using solid-state nuclear magnetic resonance, Raman spectroscopy, and scanning electron microscopy. We find that the poor cycling performance is primarily caused by the considerable side reactions stemming from the chemical aggressiveness of NaO₂ as both a solid-phase and dissolved species in the electrolyte. The side reaction products cover electrode surfaces and hinder electron transfer across the electrode-electrolyte interface, being a major reason for cell failure. In addition, the available electrode surface and porosity change considerably during cell discharging and charging, affecting the diffusion of soluble species (superoxide and water) and resulting in inhomogeneous reactions across the electrode. This study provides insights into the challenges associated with achieving long-lived superoxide-based metal-O₂ batteries.

Cathode Surface-Induced, Solvation-Mediated, Micrometer-Sized Li2 O2 Cycling for Li-O2 Batteries

The "nonsticky" surface of a highly stable RuO₂ /carbon nanotube cathode enhances the formation and decomposition of cathode surface-induced, solvation-mediated, micrometer-sized discharge products Li₂ O₂ in Li-O₂ batteries and thus significantly improves the specific capacity, overpotentials, and cycle life. These findings contribute to a new understanding how the cathode surface controls Li-O₂ electrochemistry.

Ultrafine Mn3O4 Nanowires/Three-Dimensional Graphene/Single-Walled Carbon Nanotube Composites: Superior Electrocatalysts for Oxygen Reduction and Enhanced Mg/Air Batteries

The exploration of highly efficient catalysts for the oxygen reduction reaction to improve sluggish kinetics still remains a great challenge for advanced energy conversion and storage in metal/air batteries. In this work, ultrafine Mn₃O₄ nanowires/three-dimensional graphene/single-walled carbon nanotube catalysts with an electron transfer number of 3.95 (at 0.60 V vs Ag/AgCl) and kinetic current density of 21.7-28.8 mA cm^-2 were developed via a microwave-irradiation-assisted hexadecyl trimethylammonium bromide (CTAB) surfactant procedure to greatly enhance the overall catalytic performance in Mg/air batteries. To match the electrochemical activity of the cathode catalysts, a large-scale Mg anode prepared with micropersimmon-like particles via a mechanical disintegrator and Mg(NO₃)₂-NaNO₂-based electrolyte containing 1.0 wt % trihexyl(tetradecyl)phosphonium chloride ionic liquid were applied. Combining the ultrafine Mn₃O₄ nanowires/three-dimensional graphene/single-walled carbon nanotube as an efficient electrocatalyst for the oxygen reduction reaction and an Mg micro-/nanoscale anode in the novel electrolyte, the advanced Mg/air batteries demonstrated a high cell open circuit voltage (1.49 V), a high plateau voltage (1.34 V), and a long discharge time (4177 min) at 0.2 mA cm^-1, showing a high energy density. Therefore, it is believed that this device configuration has great potential for application in new energy storage technologies.

Heme biomolecule as redox mediator and oxygen shuttle for efficient charging of lithium-oxygen batteries

One of the greatest challenges with lithium-oxygen batteries involves identifying catalysts that facilitate the growth and evolution of cathode species on an oxygen electrode. Heterogeneous solid catalysts cannot adequately address the problematic overpotentials when the surfaces become passivated. However, there exists a class of biomolecules which have been designed by nature to guide complex solution-based oxygen chemistries. Here, we show that the heme molecule, a common porphyrin cofactor in blood, can function as a soluble redox catalyst and oxygen shuttle for efficient oxygen evolution in non-aqueous Li-O2 batteries. The heme's oxygen binding capability facilitates battery recharge by accepting and releasing dissociated oxygen species while benefiting charge transfer with the cathode. We reveal the chemical change of heme redox molecules where synergy exists with the electrolyte species. This study brings focus to the rational design of solution-based catalysts and suggests a sustainable cross-link between biomolecules and advanced energy storage.

Vertically Aligned Two-Dimensional Graphene-Metal Hydroxide Hybrid Arrays for Li-O2 Batteries

Lithium oxygen batteries (LOBs) are a very promising upcoming technology which, however, still suffers from low lifespan and dramatic capacities fading. Solid discharge products increase the contact resistance and block the electrochemically active electrodes. The resulting high oxidative potentials and formation of Li₂CO₃ due to electrolyte and carbon electrode decomposition at the positive electrode lead to irreversible deactivation of oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) sites. Here we demonstrate a facile strategy for the scalable production of a new electrode structure constituted of vertically aligned carbon nanosheets and metal hydroxide (M(OH)_x@CNS) hybrid arrays, integrating both favorable ORR and OER active materials to construct bifunctional catalysts for LOBs. Excellent lithium-oxygen battery properties with high specific capacity of 5403 mAh g^-1 and 12123 mAh g^-1 referenced to the carbon and M(OH)_x weight, respectively, long cyclability, and low charge potentials are achieved in the resulting M(OH)_x@CNS cathode architecture. The properties are explained by improved O₂/ion transport properties and spatially limited precipitation of Li₂O₂ nanoparticles inside interstitial cavities resulting in high reversibility. The strategy of creating ORR and OER bifunctional catalysts in a single conductive hybrid component may pave the way to new cathode architectures for metal air batteries.

Nanostructured transition metal dichalcogenide electrocatalysts for CO2 reduction in ionic liquid

Conversion of carbon dioxide (CO2) into fuels is an attractive solution to many energy and environmental challenges. However, the chemical inertness of CO2 renders many electrochemical and photochemical conversion processes inefficient. We report a transition metal dichalcogenide nanoarchitecture for catalytic electrochemical CO2 conversion to carbon monoxide (CO) in an ionic liquid. We found that tungsten diselenide nanoflakes show a current density of 18.95 milliamperes per square centimeter, CO faradaic efficiency of 24%, and CO formation turnover frequency of 0.28 per second at a low overpotential of 54 millivolts. We also applied this catalyst in a light-harvesting artificial leaf platform that concurrently oxidized water in the absence of any external potential.

Hierarchical nanoporosity enhanced reversible capacity of bicontinuous nanoporous metal based Li-O2 battery

High-energy-density rechargeable Li-O2 batteries are one of few candidates that can meet the demands of electric drive vehicles and other high-energy applications because of the ultra-high theoretical specific energy. However, the practical realization of the high rechargeable capacity is usually limited by the conflicted requirements for porous cathodes in high porosity to store the solid reaction products Li2O2 and large accessible surface area for easy formation and decomposition of Li2O2. Here we designed a hierarchical and bicontinuous nanoporous structure by introducing secondary nanopores into the ligaments of coarsened nanoporous gold by two-step dealloying. The hierarchical and bicontinuous nanoporous gold cathode provides high porosity, large accessible surface area and sufficient mass transport path for high capacity and long cycling lifetime of Li-O2 batteries.

Rapid, in Situ Synthesis of High Capacity Battery Anodes through High Temperature Radiation-Based Thermal Shock

High capacity battery electrodes require nanosized components to avoid pulverization associated with volume changes during the charge-discharge process. Additionally, these nanosized electrodes need an electronically conductive matrix to facilitate electron transport. Here, for the first time, we report a rapid thermal shock process using high-temperature radiative heating to fabricate a conductive reduced graphene oxide (RGO) composite with silicon nanoparticles. Silicon (Si) particles on the order of a few micrometers are initially embedded in the RGO host and in situ transformed into 10-15 nm nanoparticles in less than a minute through radiative heating. The as-prepared composites of ultrafine Si nanoparticles embedded in a RGO matrix show great performance as a Li-ion battery (LIB) anode. The in situ nanoparticle synthesis method can also be adopted for other high capacity battery anode materials including tin (Sn) and aluminum (Al). This method for synthesizing high capacity anodes in a RGO matrix can be envisioned for roll-to-roll nanomanufacturing due to the ease and scalability of this high-temperature radiative heating process.

Facile Synthesis of Boron-Doped rGO as Cathode Material for High Energy Li-O2 Batteries

To improve the electrochemical performance of the high energy Li-O2 batteries, it is important to design and construct a suitable and effective oxygen-breathing cathode. Herein, a three-dimensional (3D) porous boron-doped reduction graphite oxide (B-rGO) material with a hierarchical structure has been prepared by a facile freeze-drying method. In this design, boric acid as the boron source helps to form the 3D porous structure, owing to its cross-linking and pore-forming function. This architecture facilitates the rapid oxygen diffusion and electrolyte penetration in the electrode. Meanwhile, the boron-oxygen functional groups linking to the carbon surface or edge serve as additional reaction sites to activate the ORR process. It is vital that boron atoms have been doped into the carbon lattices to greatly activate the electrons in the carbon π system, which is beneficial for fast charge under large current densities. Density functional theory calculation demonstrates that B-rGO exhibits much stronger interactions with Li5O6 clusters, so that B-rGO more effectively activates Li-O bonds to decompose Li2O2 during charge than rGO does. With B-rGO as a catalytic substrate, the Li-O2 battery achieves a high discharge capacity and excellent rate capability. Moreover, catalysts could be added into the B-rGO substrate to further lower the overpotential and enhance the cycling performance in future.

Why Do Lithium-Oxygen Batteries Fail: Parasitic Chemical Reactions and Their Synergistic Effect

As an electrochemical energy-storage technology with the highest theoretical capacity, lithium-oxygen batteries face critical challenges in terms of poor stabilities and low charge/discharge round-trip efficiencies. It is generally recognized that these issues are connected to the parasitic chemical reactions at the anode, electrolyte, and cathode. While the detailed mechanisms of these reactions have been studied separately, the possible synergistic effects between these reactions remain poorly understood. To fill in the knowledge gap, this Minireview examines literature reports on the parasitic chemical reactions and finds the reactive oxygen species a key chemical mediator that participates in or facilitates nearly all parasitic chemical reactions. Given the ubiquitous presence of oxygen in all test cells, this finding is important. It offers new insights into how to stabilize various components of lithium-oxygen batteries for high-performance operations and how to eventually materialize the full potentials of this promising technology.

A Unique Hybrid Quasi-Solid-State Electrolyte for Li-O2 Batteries with Improved Cycle Life and Safety

In the context of the development of electric vehicle to solve the contemporary energy and environmental issues, the possibility of pushing future application of Li-O2 batteries as a power source for electric vehicles is particularly attractive. However, safety concerns, mainly derived from the use of flammable organic liquid electrolytes, become a major bottleneck for the strategically crucial applications of Li-O2 batteries. To overcome this issue, rechargeable solid-state Li-O2 batteries with enhanced safety is regarded as an appealing candidate. In this study, a hybrid quasi-solid-state electrolyte combing a polymer electrolyte with a ceramic electrolyte is first designed and explored for Li-O2 batteries. The proposed rechargeable solid-state Li-O2 battery delivers improved cycle life (>100 cycles) and safety. The feasibility study demonstrates that the hybrid quasi-solid-state electrolytes could be employed as a promising alternative strategy for the development of rechargeable Li-O2 batteries, hence encouraging more efforts devoted to explore other hybrid solid-state electrolytes for Li-O2 batteries upon future application.

Direct Evidence of Solution-Mediated Superoxide Transport and Organic Radical Formation in Sodium-Oxygen Batteries

Advanced large-scale electrochemical energy storage requires cost-effective battery systems with high energy densities. Aprotic sodium-oxygen (Na-O2) batteries offer advantages, being comprised of low-cost elements and possessing much lower charge overpotential and higher reversibility compared to their lithium-oxygen battery cousins. Although such differences have been explained by solution-mediated superoxide transport, the underlying nature of this mechanism is not fully understood. Water has been suggested to solubilize superoxide via formation of hydroperoxyl (HO2), but direct evidence of these HO2 radical species in cells has proven elusive. Here, we use ESR spectroscopy at 210 K to identify and quantify soluble HO2 radicals in the electrolyte-cold-trapped in situ to prolong their lifetime-in a Na-O2 cell. These investigations are coupled to parallel SEM studies that image crystalline sodium superoxide (NaO2) on the carbon cathode. The superoxide radicals were spin-trapped via reaction with 5,5-dimethyl-pyrroline N-oxide at different electrochemical stages, allowing monitoring of their production and consumption during cycling. Our results conclusively demonstrate that transport of superoxide from cathode to electrolyte leads to the nucleation and growth of NaO2, which follows classical mechanisms based on the variation of superoxide content in the electrolyte and its correlation with the crystallization of cubic NaO2. The changes in superoxide content upon charge show that charge proceeds through the reverse solution process. Furthermore, we identify the carbon-centered/oxygen-centered alkyl radicals arising from attack of these solubilized HO2 species on the diglyme solvent. This is the first direct evidence of such species, which are likely responsible for electrolyte degradation.

Tailored Combination of Low Dimensional Catalysts for Efficient Oxygen Reduction and Evolution in Li-O2 Batteries

The development of efficient bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is a key issue pertaining high performance Li-O2 batteries. Here, we propose a heterogeneous electrocatalyst consisting of LaMnO3 nanofibers (NFs) functionalized with RuO2 nanoparticles (NPs) and non-oxidized graphene nanoflakes (GNFs). The Li-O2 cell employing the tailored catalysts delivers an excellent electrochemical performance, affording significantly reduced discharge/charge voltage gaps (1.0 V at 400 mA g(-1) ), and superior cyclability for over 320 cycles. The outstanding performance arises from (1) the networked LaMnO3 NFs providing ORR/OER sites without severe aggregation, (2) the synergistic coupling of RuO2 NPs for further improving the OER activity and the electrical conductivity on the surface of the LaMnO3 NFs, and (3) the use of GNFs providing a fast electronic pathway as well as improved ORR kinetics.

A New Design Strategy for Observing Lithium Oxide Growth-Evolution Interactions Using Geometric Catalyst Positioning

Understanding the catalyzed formation and evolution of lithium-oxide products in Li-O2 batteries is central to the development of next-generation energy storage technology. Catalytic sites, while effective in lowering reaction barriers, often become deactivated when placed on the surface of an oxygen electrode due to passivation by solid products. Here we investigate a mechanism for alleviating catalyst deactivation by dispersing Pd catalytic sites away from the oxygen electrode surface in a well-structured anodic aluminum oxide (AAO) porous membrane interlayer. We observe the cross-sectional product growth and evolution in Li-O2 cells by characterizing products that grow from the electrode surface. Morphological and structural details of the products in both catalyzed and uncatalyzed cells are investigated independently from the influence of the oxygen electrode. We find that the geometric decoration of catalysts far from the conductive electrode surface significantly improves the reaction reversibility by chemically facilitating the oxidation reaction through local coordination with PdO surfaces. The influence of the catalyst position on product composition is further verified by ex situ X-ray photoelectron spectroscopy and Raman spectroscopy in addition to morphological studies.

Solvent-Mediated Control of the Electrochemical Discharge Products of Non-Aqueous Sodium-Oxygen Electrochemistry

The reduction of dioxygen in the presence of sodium cations can be tuned to give either sodium superoxide or sodium peroxide discharge products at the electrode surface. Control of the mechanistic direction of these processes may enhance the ability to tailor the energy density of sodium-oxygen batteries (NaO2 : 1071 Wh kg(-1) and Na2 O2 : 1505 Wh kg(-1) ). Through spectroelectrochemical analysis of a range of non-aqueous solvents, we describe the dependence of these processes on the electrolyte solvent and subsequent interactions formed between Na(+) and O2 (-) . The solvents ability to form and remove [Na(+) -O2 (-) ]ads based on Gutmann donor number influences the final discharge product and mechanism of the cell. Utilizing surface-enhanced Raman spectroscopy and electrochemical techniques, we demonstrate an analysis of the response of Na-O2 cell chemistry with sulfoxide, amide, ether, and nitrile electrolyte solvents.

The Sodium-Oxygen/Carbon Dioxide Electrochemical Cell

Electrochemical cells that utilize metals in the anode and an ambient gas as the active material in the cathode blur the lines between fuel cells and batteries. Such cells are under active consideration worldwide because they are considered among the most promising energy storage platforms for electrified transportation. Li-air batteries are among the most actively investigated cells in this class, but long-term challenges, such as CO2 contamination of the cathode gas and electrolyte decomposition, are associated with loss of rechargeability owing to metal carbonate formation in the cathode. Remediation of the first of these problems adds significant infrastructure burdens to the Li-air cell that bring into question its commercial viability. Several recent studies offer contradictory evidence, namely, that the presence of substantial fractions of CO2 in the cathode gas stream can have significant benefits, including increasing the already high specific energy of a Li-O2 cell by as much as 200 %. In this report, we consider electrochemical processes in model Na-O2 /CO2 cells and find that, provided the electrode/electrolyte interfaces are electrochemically stable, such cells are able to deliver both exceptional energy storage capacity and stable long-term charge-discharge cycling behaviors at room temperature.

Robust NaO2 Electrochemistry in Aprotic Na-O2 Batteries Employing Ethereal Electrolytes with a Protic Additive

Aprotic metal-oxygen batteries, such as Li-O2 and Na-O2 batteries, are of topical research interest as high specific energy alternatives to state-of-the-art Li-ion batteries. In particular, Na-O2 batteries with NaO2 as the discharge product offer higher practical specific energy with better rechargeability and round-trip energy efficiency when compared to Li-O2 batteries. In this work, we show that the electrochemical deposition and dissolution of NaO2 in Na-O2 batteries is unperturbed by trace water impurities in Na-O2 battery electrolytes, which is desirable for practical battery applications. We find no evidence for the formation of other discharge products such as Na2O2·H2O. Furthermore, the electrochemical efficiency during charge remains near ideal in the presence of trace water in electrolytes. Although sodium anodes react with trace water leading to the formation of a high-impedance solid electrolyte interphase, the increase in discharge overpotential is only ∼100 mV when compared to cells employing nominally anhydrous electrolytes.

Utilizing in Situ Electrochemical SHINERS for Oxygen Reduction Reaction Studies in Aprotic Electrolytes

Spectroscopic detection of reaction intermediates upon a variety of electrode surfaces is of major interest within physical chemistry. A notable technique in the study of the electrochemical interface has been surface-enhanced Raman spectroscopy (SERS). The drawback of SERS is that it is limited to roughened gold and silver substrates. Herein we report that shell-isolated nanoparticles for enhanced Raman spectroscopy (SHINERS) can overcome the limitations of SERS and has followed the oxygen reduction reaction (ORR), within a nonaqueous electrolyte, on glassy carbon, gold, palladium, and platinum disk electrodes. The work presented demonstrates SHINERS for spectroelectrochemical studies for applied and fundamental electrochemistry in aprotic electrolytes, especially for the understanding and development of future metal-oxygen battery applications. In particular, we highlight that with the addition of Li(+), both the electrode surface and solvent influence the ORR mechanism, which opens up the possibility of tailoring surfaces to produce desired reaction pathways.

A SnO2-Based Cathode Catalyst for Lithium-Air Batteries

SnO2 and SnO2@C have been successfully synthesized with a simple hydrothermal procedure combined with heat treatment, and their performance as cathode catalysts of Li-air batteries has been comparatively evaluated and discussed. The results show that both SnO2 and SnO2@C are capable of catalyzing oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) at the cathode of Li-air batteries, but the battery with SnO2@C displays better performance due to its unique higher conductivity, larger surface area, complex pore distribution, and huge internal space.

Lithium-Air Batteries with Hybrid Electrolytes

During the past decade, Li-air batteries with hybrid electrolytes have attracted a great deal of attention because of their exceptionally high capacity. Introducing aqueous solutions and ceramic lithium superionic conductors to Li-air batteries can circumvent some of the drawbacks of conventional Li-O2 batteries such as decomposition of organic electrolytes, corrosion of Li metal from humidity, and insoluble discharge product blocking the air electrode. The performance of this smart design battery depends essentially on the property and structure of the cell components (i.e., hybrid electrolyte, Li anode, and air cathode). In recent years, extensive efforts toward aqueous electrolyte-based Li-air batteries have been dedicated to developing the high catalytic activity of the cathode as well as enhancing the conductivity and stability of the hybrid electrolyte. Herein, the progress of all aspects of Li-air batteries with hybrid electrolytes is reviewed. Moreover, some suggestions and concepts for tailored design that are expected to promote research in this field are provided.

Controlling Solution-Mediated Reaction Mechanisms of Oxygen Reduction Using Potential and Solvent for Aprotic Lithium-Oxygen Batteries

Fundamental understanding of growth mechanisms of Li2O2 in Li-O2 cells is critical for implementing batteries with high gravimetric energies. Li2O2 growth can occur first by 1e(-) transfer to O2, forming Li(+)-O2(-) and then either chemical disproportionation of Li(+)-O2(-), or a second electron transfer to Li(+)-O2(-). We demonstrate that Li2O2 growth is governed primarily by disproportionation of Li(+)-O2(-) at low overpotential, and surface-mediated electron transfer at high overpotential. We obtain evidence supporting this trend using the rotating ring disk electrode (RRDE) technique, which shows that the fraction of oxygen reduction reaction charge attributable to soluble Li(+)-O2(-)-based intermediates increases as the discharge overpotential reduces. Electrochemical quartz crystal microbalance (EQCM) measurements of oxygen reduction support this picture, and show that the dependence of the reaction mechanism on the applied potential explains the difference in Li2O2 morphologies observed at different discharge overpotentials: formation of large (∼250 nm-1 μm) toroids, and conformal coatings (<50 nm) at higher overpotentials. These results highlight that RRDE and EQCM can be used as complementary tools to gain new insights into the role of soluble and solid reaction intermediates in the growth of reaction products in metal-O2 batteries.

CoS2nanoparticles–graphene hybrid as a cathode catalyst for aprotic Li–O2batteries

A CoS₂nanoparticles–graphene hybrid was first used as a cathode catalyst for aprotic Li–O₂batteries, exhibiting low discharge/charge overpotentials and a high rate capability.

Facile synthesis of flower-like hierarchical NiCo2O4 microspheres as high-performance cathode materials for Li–O2 batteries

The Li–O₂ battery with flower-like hierarchical NiCo₂O₄ microspheres cathode exhibits a low discharge/charge voltage gap of 0.86 V, much lower than previously reported results for NiCo₂O₄.