Formation Of Li2O2 Research Articles

Operando X-ray photoelectron spectroscopy of solid electrolyte interphase formation and evolution in Li2S-P2S5 solid-state electrolytes

Solid-state electrolytes such as Li2S-P2S5 compounds are promising materials that could enable Li metal anodes. However, many solid-state electrolytes are unstable against metallic lithium, and little is known about the chemical evolution of these interfaces during cycling, hindering the rational design of these materials. In this work, operando X-ray photoelectron spectroscopy and real-time in situ Auger electron spectroscopy mapping are developed to probe the formation and evolution of the Li/Li2S-P2S5 solid-electrolyte interphase during electrochemical cycling, and to measure individual overpotentials associated with specific interphase constituents. Results for the Li/Li2S-P2S5 system reveal that electrochemically driving Li+ to the surface leads to phase decomposition into Li2S and Li3P. Additionally, oxygen contamination within the Li2S-P2S5 leads initially to Li3PO4 phase segregation, and subsequently to Li2O formation. The spatially non-uniform distribution of these phases, coupled with differences in their ionic conductivities, have important implications for the overall properties and performance of the solid-electrolyte interphase.

A novel ZnO-based inorganic/organic bilayer with low resistance for Li metal protection

Although Li metal has a great potential for application as anode of the next generation batteries, the existing problems of the lithium dendrite growth and volume expansion need to be solved to pave the way for the real application of Li metal anode. Here, a double-layer structure consisting of poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP)/ZnO composite membrane and ZnO buffer layer was fabricated by solid-state method and spin coating to protect the Li metal. Compared to the bare Li electrode, the protected Li electrode displays the advantages of stable voltage profiles and long lifespan. Interestingly, the ZnO buffer layer between Li metal and PVDF-HFP/ZnO composite membrane can significantly reduce the battery resistance because of the formation of Li2O on the ZnO nanorod surface, which can guide Li+ flux to deposit uniformly onto Li metal. Results show that the double-layer structure on the Li metal surface can inhibit dendrite growth and volume expansion. The analyses in this paper may contribute to a better understanding of the reaction mechanism between ZnO and Li+.

PEEK‐WC/Nanosponge Membranes for Lithium‐Anode Protection in Rechargeable Li−O2 Batteries

AbstractDextrin‐based nanosponges (NSs) are hyper‐crosslinked polymers characterized by the ability to encapsulate a great variety of substances in liquid phase. More importantly, dextrin‐based NSs are nanostructured within a three‐dimensional network. Here, an amorphous modified polyetheretherketone (PWC) and NS‐derived from crosslinking dextrin and β‐ciclodextrins are used to prepare flat‐sheet membranes. The presence of NSs in the membrane changes the features of PWC. The PWC/NS membrane displays very low oxygen permeability, good ionic conductivity, and assure a suitable interfacial stability with Li metal. For such properties, the membrane is suitable to protect the highly reactive Li‐metal anode from oxygen crossover, dendrite formation, and from side reactions due to the oxygenated dimethyl sulfoxide (DMSO)‐based electrolyte. Li−O2 lab‐scale cells are assembled with the membrane sandwiched between Li and the separator soaked by electrolyte, with continuous oxygen flow of 3 mL/min at the cathode side. XRD analysis demonstrates that the membrane does not interfere with the formation and decomposition of Li2O2. Membranes assure long cell‐cycle life at reversible capacity and better capacity retention during cycling in full discharge/charge conditions.

High Volumetric Energy Density Li-Air Battery; Cell Scale Design, Modeling and Simulation

Ever been higher demands for energy storage systems that can exceed the energy density of current Li-ion battery encourage researchers to investigate new battery chemistries that are beyond the limitation of the current intercalation mechanism based battery chemistry.1–3 Among many candidates for the beyond-intercalation batteries, Li-air battery, also known as Li-O2 battery, got enormous research attention owing to their ultra-high theoretical gravimetric energy density of 3,458 Wh/kg. Althogh high volumetric energy density is desired for transportation applications due to the space limitation in a vehicle, its volumetric energy density (Wh/L) with actual cell scale evaluation has been rarely discussed.4 It may be due to the theoretical maximum value, 2,040 Wh/L of Li-O2 battery with lithium anode, is not much superior than Li-ion battery with LiCoO2 cathode with carbon anode, 1,940 Wh/L.5 Here, we demonstrate the Li-O2 battery cells perfuming 700 Wh/kg and 610 Wh/L of complete cell level gravimetric and volumetric energy density, respectively, by seamless integration of all the best performing components. To understand transport phenomena inside of the cell and predict maximum performances, specifically designed modeling and simulation was conducted by combining physics of oxygen gas flow into the GDL, dissolution of O2 into the electrolyte, electrochemistry across the whole cell components, and dynamically changing carbon surfaces and porosity by Li2O2 formation.

Mechanistic Insights into Oxygen Reduction Reactions in Non-Aqueous Metal-Air Batteries

Non-aqueous metal-air batteries have generated strong research interest because they possess much greater theoretical gravimetric energy storage density than today’s rechargeable battery technologies.1-4 This has re-kindled research into the fundamentals of oxygen reduction reaction (ORR) in non-aqueous electrolytes because they are the central electrochemical processes at metal-air cathodes. Understanding the reaction mechanisms is critical to improving cycling efficiency and making rechargeable metal-air batteries a reality. ORR in these metal air batteries typically lead to discharge products that are either metal superoxides or metal peroxides. The discharge products can grow either through a surface mediated mechanism5 that produces the discharge product directly on the electrode or a solution mediated mechanism6-7 which leads to the precipitation of nanoparticles. In this talk, we will present the results of extensive DFT-based theoretical studies of ORR by different cations (M, where M=H, Li, Na, and K) on Au surfaces. The computational electrode approach allows us to shed light on the mechanism of surface-mediated ORR, which in a stable organic solvent such as DMSO always involves the superoxide anion (O2 -) as the first reduction product within one volt of the relevant open cell potential. This is followed by the direct reduction of O2 by cation/electron transfer to form MO2 and M2O2 species at lower potentials. We will show that in modeling the electrochemical stability of the adsorbed molecular superoxide species, the effects of the interfacial electric field and solvent molecules need to be included to avoid errors on the order of a few tenths of a volt. The field effect can be readily approximated by the first-order Stark effect. At the same time, the formation and solvation of O2 - open up pathways to thermochemical ORR in the solution phase, which leads preferentially to the formation of solid Li2O2 vs. solid NaO2 and KO2 at small overpotentials. We propose, based on additional theoretical calculations, the reaction pathways for the formation of alkali superoxide and peroxide in several solvents that explain the observed product selectivity. References Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J. M., Li-O-2 and Li-S batteries with high energy storage. Nature Materials 2012, 11 (1), 19-29.Lu, J.; Li, L.; Park, J.-B.; Sun, Y.-K.; Wu, F.; Amine, K., Aprotic and aqueous Li–O2 batteries. Chem. Rev. 2014, 114 (11), 5611-5640.Luntz, A. C.; McCloskey, B. D., Nonaqueous Li–air batteries: a status report. Chem. Rev. 2014, 114 (23), 11721-11750.Black, R.; Adams, B.; Nazar, L., Non‐Aqueous and Hybrid Li‐O2 Batteries. Advanced Energy Materials 2012, 2 (7), 801-815.Xu, Y.; Shelton, W. A., O2 reduction by lithium on Au(111) and Pt(111). J. Chem. Phys. 2010, 133 (2), 024703.Aetukuri, N. B.; McCloskey, B. D.; García, J. M.; Krupp, L. E.; Viswanathan, V.; Luntz, A. C., Solvating additives drive solution-mediated electrochemistry and enhance toroid growth in non-aqueous Li–O2 batteries. Nat. Chem. 2015, 7 (1), 50-56.Lutz, L.; Alves Dalla Corte, D.; Tang, M.; Salager, E.; Deschamps, M.; Grimaud, A.; Johnson, L.; Bruce, P. G.; Tarascon, J.-M., Role of Electrolyte Anions in the Na–O2 Battery: Implications for NaO2 Solvation and the Stability of the Sodium Solid Electrolyte Interphase in Glyme Ethers. Chem. Mater. 2017, 29 (14), 6066-6075.

Design and Preparation of Cathode Catalysts for High-Performance Lithium-Oxygen Batteries

The lithium-oxygen batteries have received considerable attention recently due to their high theoretical energy densities, which is highly desirable for long-range electric vehicles. However, their poor electrochemical performance, particularly the large overpotential, makes the practical application of Li-O2 battery full of challenge. In a typical prototype, non-aqueous Li-O2 battery is composed of a catalytic cathode, a lithium anode, and an organic Li+ conducting electrolyte. During the discharge process, oxygen molecules are reduced and reacted with the Li+ ions from the electrolyte (oxygen reduction reactions, ORRs), leading to the formation of dissoluble Li2O2 attached to the porous cathode. These Li2O2 species would reversibly decompose into Li+ ions and oxygen (oxygen evolution reactions, OERs) in the following charging process. Thus, the design of cathode catalysts with high ORR and OER reactivity, and porous structures with appropriate pore size for the permeation of O2 is of particular importance. In addition, polymer binders would react with superoxide Li2O2, consequently leading to the instability of Li-O2 batteries. It is also highly desired to develop novel binder-free cathode materials. Herein, strategies have been proposed for the preparation of free-standing porous structures promote the ORR and OER activities for high-performance Li-O2 batteries.

Enhanced Stability of Coated Carbon Electrode for Li–O2 Batteries and Its Limitations

The increasing demands for electric vehicles have spurred a worldwide search for next-generation rechargeable batteries with higher energy density. Among various battery systems, the lithium–oxygen (Li–O2) chemistry offers one of the highest theoretical energy densities, which can reach 3500 Wh kg−1 based on the reaction 2Li+ + O2 + 2e− = Li2O2 (E0 = 2.96 V vs. Li/Li+). The most widely used air electrodes are carbon-based materials because of their large surface areas per weight and high electrical conductivity, which are suitable for promoting the electrochemical formation of Li2O2 on the electrode, providing a high gravimetric energy density. For these reasons, carbon-based air electrodes have been intensely researched in recent years, and various types of carbon materials such as porous carbon, carbon nanotubes (CNTs), and graphene have been reported as air electrodes. Recent studies, however, have shown that parasitic reactions involving carbon-based air electrodes could be one of the factors resulting in the deterioration of the electrochemical cycling of Li–O2 batteries.[1-3] Upon cycling, carbon can react with Li2O2, a discharge product deposited on the carbon electrode, to form insulating Li2CO3, which degrades the efficiency and cycle stability. Moreover, carbon itself can be corroded under high oxidizing potential in Li–O2 batteries and can thus be passivated with carbon-containing byproducts. The damaged carbon surface aggravates the electrolyte decomposition, resulting in the formation of additional byproducts. These byproducts from the electrolyte and carbon electrode can be partially decomposed during charge and typically lead to the evolution of CO2 gas instead of O2. As the cycle continues, insulating byproducts are gradually accumulated, which generally results in a high overpotential, low round-trip efficiency, and short cycle life. Therefore, the design of a strategy to reduce side reactions in the carbon electrode is imperative to achieve high electrochemical stability of Li–O2 batteries. Our previous work demonstrated that defect sites on carbon materials are more susceptible to reaction with discharge products and are prone to decompose more easily, serving as seeds for side reactions.[3] Thus, a carbon air electrode with higher crystallinity could exhibit more stable cycle properties. However, the preparation of highly crystalline carbon generally requires high-temperature treatment above 2000°C and substantially reduces the surface area, leading to a relatively small discharge capacity. Moreover, the complete removal of the defects in the production of large-surface carbon materials is not trivial. Instead, appropriate passivation of defect sites for a given carbon material may be a suitable approach to fabricate stable carbon-based air electrodes. Selective growth of materials specifically on the defect sites with the minimal amount of coating would be ideal to prohibit the side reactions without excessively increasing the weight of the air electrode. It was previously reported that Al2O3 and Pd could be coated on carbon using atomic layer deposition (ALD) to protect the air electrode and reduce the overpotential, resulting in enhanced cycle stability.[4] Nevertheless, the insulating nature of Al2O3 caused a large overpotential during cycling, and the high price of the noble metal remains an issue. Moreover, it is not clearly understood how and to what extent these coating materials can aid in the reduction of the side reactions and whether its effect is maintained with extended cycling. Herein, we demonstrate that the effect of coating is not limited to the protection of the carbon electrode but also remarkably suppresses the decomposition of the electrolyte. These results were analyzed using in situ differential electrochemical mass spectroscopy (DEMS) with labeled isotopic 13C air electrode in the electrolyte composed of 12C for the Li–O2 cell. In contrast to the pristine carbon electrode, the coating provided effective protection, which reduced the evolution of undesirable gases from both the electrolyte (12CO2) and carbon electrode (13CO2), with high efficiency of O2 evolution, resulting in enhanced cycle stability (>100 cycles). Nevertheless, the coating materials were gradually detached from the surface of the carbon materials because of the formation of a discharge product at the interface between the carbon and coating materials during cycling, leading to exposure of the bare carbon electrode and degradation of the Li–O2 cell. This study suggests that a method to prevent the detachment of the coating material as well as further understanding of the growth mechanism of discharge products, which affects the delamination of the coating, should be sought after in the future.

Fe2O3 Nanoparticle Seed Catalysts Enhance Cyclability on Deep (Dis)charge in Aprotic LiO2 Batteries

AbstractAlthough the high energy density of LiO2 chemistry is promising for vehicle electrification, the poor stability and parasitic reactions associated with carbon‐based cathodes and the insulating nature of discharge products limit their rechargeability and energy density. In this study, a cathode material consisting of α‐Fe2O3 nanoseeds and carbon nanotubes (CNT) is presented, which achieves excellent cycling stability on deep (dis)charge with high capacity. The initial capacity of Fe2O3/CNT electrode reaches 805 mA h g−1 (0.7 mA h cm−2) at 0.2 mA cm−2, while maintaining a capacity of 1098 mA h g−1 (0.95 mA h cm−2) after 50 cycles. The operando structural, spectroscopic, and morphological analysis on the evolution of Li2O2 indicates preferential Li2O2 growth on the Fe2O3. The similar d‐spacing of the (100) Li2O2 and (104) Fe2O3 planes suggest that the latter epitaxially induces Li2O2 nucleation. This results in larger Li2O2 primary crystallites and smaller secondary particles compared to that deposited on CNT, which enhances the reversibility of the Li2O2 formation and leads to more stable interfaces within the electrode. The mechanistic insights into dual‐functional materials that act both as stable host substrates and promote redox reactions in LiO2 batteries represent new opportunities for optimizing the discharge product morphology, leading to high cycling stability and coulombic efficiency.

Operando observations of RuO2 catalyzed Li2O2 formation and decomposition in a Li-O2 micro-battery

RuO2 displays excellent bifunctional catalysis towards the oxygen reduction and evolution reactions of Li-O2 battery. Nevertheless, how the solid catalyst successively catalyzes solid Li2O2 formation and decomposition, confronting passivation and loss of RuO2/Li2O2 contact, during discharging and charging remains a mystery. Here we report operando observations of RuO2 catalyzed oxygen reduction and evolution reactions of Li2O2 by utilizing a liquid cell scanning transmission electron microscope. Upon discharging, RuO2 obviously accelerates formation of soluble LiO2 intermediates and acts as preferential sites of Li2O2 precipitation. During charging, the catalytic activation of RuO2 takes place at electrolyte-RuO2-Li2O2 triple-phase interfaces. Importantly, RuO2 not only catalyzes the decomposition of directly contacted Li2O2, but also promotes oxidation of soluble LiO2 for rapid dissolution of isolated Li2O2 nanoparticles by a chemical comproportionation reaction. The observation unveils how RuO2 catalyzes the formation and decomposition of Li2O2 during discharging and charging and provides nanoscale insights into cathodic reactions of Li-O2 batteries with solid catalysts.

Improved electrochemical performance of ordered mesoporous carbon by incorporating macropores for Li‒O2 battery cathode

Optimized porous structure is a prerequisite for high performance Li‒O2 battery cathode. Macroporous-mesoporous carbon (MMC) is fabricated via a nano-replication method using mesoporous SiO2 (KIT-6) containing NiO as the template. By varying the amount of NiO in the KIT-6/NiO composite template, the amount of macropores inside MMC is easily controlled. The as-prepared MMC exhibits a highly porous structure with abundant ordered mesopores along with macropores that are larger than 200 nm in size. When the MMC is applied as the cathode material in a Li‒O2 battery, the cell exhibits greatly improved electrochemical performance in comparison to a cell using conventional ordered mesoporous carbon (OMC) without macropores. Systematic studies indicate that while mesopores in the OMC are clogged with Li2O2 formed during the early stage of discharge, the MMC sufficiently accommodates a large amount of Li2O2 in the pores. In addition, Li2O2 with poor crystallinity forms on the cathode containing MMC during subsequent discharge processes, which can be due to the accumulated side product and the limited size of pores. The formation of amorphous Li2O2 and the expedited mass transport through the interconnected meso- and macropores of MMC can attribute to the improved electrochemical performance of the MMC cathode material.

3D Foam-Like Composites of Mo2C Nanorods Coated by N-Doped Carbon: A Novel Self-Standing and Binder-Free O2 Electrode for Li-O2 Batteries.

The development of self-standing and binder-free O2 electrodes is significant for enhancing the total specific energy density and suppressing parasitic reactions for Li-O2 batteries, which is still a formidable challenge thus far. Here, a three-dimensional foam-like composite composed of Mo2C nanorods decorated by different amounts of N-doped carbon (Mo2C-NR@xNC (x = 5, 11, and 16 wt %)) was directly employed as the O2 electrode without applications of any binders and current collectors. Mo2C-NR@xNC presents a network microstructure with interconnected macropore and mesoporous channels, which is beneficial to achieving fast Li+ migration and O2 diffusion, facilitating the electrolyte impregnation, and providing enough space for Li2O2 storage. Additionally, the coated N-doped carbon layer can largely improve the electrochemical stability and conductivity of Mo2C. The cell with Mo2C-NR@11NC shows a considerable cyclability of 200 cycles with an overpotential of 0.28 V in the first cycle at a constant current density of 100 mA g-1, a superior reversibility associated with the formation and decomposition of Li2O2 as desired, and a high electrochemical stability. On the basis of the experimental results, the electrochemical mechanism for the cell using Mo2C-NR@11NC is proposed. These results represent a promising process in the development of a self-standing and binder-free foam-based electrode for Li-O2 batteries.

Three-Dimensional Nanofibrous Air Electrode Assembled With Carbon Nanotubes-Bridged Hollow Fe2O3 Nanoparticles for High-Performance Lithium-Oxygen Batteries.

Lithium-oxygen batteries have been considered as one of the most viable energy source options for electric vehicles due to their high energy density. However, they are still faced with technical challenges, such as low round-trip efficiency and short cycle life, which mainly originate from the cathode part of the battery. In this work, we designed a three-dimensional nanofibrous air electrode consisted of hierarchically structured carbon nanotube-bridged hollow Fe2O3 nanoparticles (H-Fe2O3/CNT NFs). Composite nanofibers consisted of hollow Fe2O3 NPs anchored by multiple CNTs offered enhanced catalytic sites (interconnected hollow Fe2O3 NPs) and fast charge-transport highway (bridged CNTs) for facile formation and decomposition of Li2O2, leading to outstanding cell performance: (1) Swagelok cell exhibited highly reversible cycling characteristics for 250 cycles with a fixed capacity of 1000 mAh g-1 at a current density of 500 mA g-1. (2) A module composed of two pouch-type cells stably powered an light-emitting diode lamp operated at 5.0 V.

Nitrogen-Doped Perovskite as a Bifunctional Cathode Catalyst for Rechargeable Lithium-Oxygen Batteries.

In this work, nitrogen-doped LaNiO3 perovskite was prepared and studied, for the first time, as a bifunctional electrocatalyst for oxygen cathode in a rechargeable lithium-oxygen battery. N doping was found to significantly increase the Ni3+ contents and oxygen vacancies on the bulk surface of the perovskite, which helped to promote the oxygen reduction reaction and oxygen evolution reaction of the cathode and, therefore, enabled reversible Li2O2 formation and decomposition on the cathode surface. As a result, the oxygen cathodes loaded with N-doped LaNiO3 catalyst showed an improved electrochemical performance in terms of discharge capacity and cycling stability to promise practical Li-O2 batteries.

Cobalt Nanoparticles Chemically Bonded to Porous Carbon Nanosheets: A Stable High-Capacity Anode for Fast-Charging Lithium-Ion Batteries.

A two-dimensional electrode architecture of ∼25 nm sized Co nanoparticles chemically bonded to ∼100 nm thick amorphous porous carbon nanosheets (Co@PCNS) through interfacial Co-C bonds is reported for the first time. This unique 2D hybrid architecture incorporating multiple Li-ion storage mechanisms exhibited outstanding specific capacity, rate performance, and cycling stabilities compared to nanostructured Co3O4 electrodes and Co-based composites reported earlier. A high discharge capacity of 900 mAh/g is achieved at a charge-discharge rate of 0.1C (50 mA/g). Even at high rates of 8C (4 A/g) and 16C (8 A/g), Co@PCNS demonstrated specific capacities of 620 and 510 mAh/g, respectively. Integrity of interfacial Co-C bonds, Co nanoparticles, and 90% of the initial capacity are preserved after 1000 charge-discharge cycles. Implementation of Co nanoparticles instead of Co3O4 restricted Li2O formation during the charge-discharge process. In situ formed Co-C bonds during the pyrolysis steps improve interfacial charge transfer, and eliminate particle agglomeration, identified as the key factors responsible for the exceptional electrochemical performance of Co@PCNS. Moreover, the nanoporous microstructure and 2D morphology of carbon nanosheets facilitate superior contact with the electrolyte solution and improved strain relaxation. This study summarizes design principles for fabricating high-performance transition-metal-based Li-ion battery hybrid anodes.

Clean Electrocatalysis in a Li2O2 Redox-Based Li–O2 Battery Built with a Hydrate-Melt Electrolyte

The electrocatalysis of the oxygen reduction reaction and oxygen evolution reaction in nonaqueous Li–O2 batteries suffers from severe side reactions and high charge potential. Herein, we design an unreported hydrate-melt Li–O2 battery without use of an unstable organic solvent. Its redox reaction depends on the formation of Li2O2 in high yield (96%) and its full decomposition. The designed battery shows an ultralow charge potential of ∼3.16 V, a high discharge capacity of 38 mAh cm–2, and stable cycling ability. After careful comparison of the discharge and charge products by XRD, SEM, Raman, FTIR, NMR, and quantitative titration, the great improvement in performance is attributed to the efficient avoidance of side reactions related to organic solvent degradation, which may be the primary cause of the high charge potential in a nonaqueous Li–O2 battery. These results should initiate a deep understanding of Li–O2 batteries and indicate another strategy toward practical Li–air batteries with moisture-proof ...

Operando structural study of non-aqueous Li–air batteries using synchrotron-based X-ray diffraction

Non-aqueous lithium–air batteries (LABs) attract attention as a candidate technology for next-generation energy storage devices. It is crucial to understand how the discharge product Li2O2 is formed and decomposed by the electrochemical reactions to improve the cycle performance and decrease the charge voltage, which are the most important subjects for LAB development. Here, operando X-ray diffraction with high-brilliant X-rays in a transmission mode was used to observe the intensity and structural changes of crystalline Li2O2 in an operating non-aqueous LAB in real time, and the Li–O2 electrochemical reaction involving Li2O2 formation and decomposition was clearly demonstrated. The electrochemically formed Li2O2, which had an anisotropic domain size of 10 nm in the c-direction and 40–70 nm in the ab-plane, grew due to the increase of the number of domains during the discharge process. No other reaction products with a crystalline phase such as LiOH were found in either the cathode or anode of the LAB, whereas the accelerated decomposition rate of the domains was accompanied with the change of the domain shape and lattice constant of the c-axis in the latter half of the charge process with voltage higher than 4 V.

Controlling to Expand Reversibly Li2O2-formation/decomposition by Modifying Electrolyte in Lithium-oxygen Batteries

Aprotic lithium-oxygen (Li-O2) battery has attracted worldwide attention because of its ultrahigh theoretical energy density. However, its practical application is critically hindered by cathode passivation, large polarization and severe parasitic reactions. Here, we demonstrated a newly designed ruthenium (II) polypyridyl complex (RuPC) by which an expanded reversibly Li2O2-formation/decomposition could be achieved in lithiumoxygen batteries. Experimental and theoretical results revealed that the RuPC can not only expand the formation of Li2O2 in electrolyte, but also suppress the reactivity of LiO2 intermediate during discharge, thus alleviating the cathode passivation and parasitic reactions significantly. In addition, an initial delithiation pathway can be achieved when charging in turn, thus the Li2O2 products can be decomposed reversibly with a low overpotential. As a result, the RuPC-catalyzed Li-O2 batteries exhibited a high discharge capacity (~9281 mAh g-1), a low charge overpotential (0.54 V) and a ultralong cycle life (371 cycles). This work provides an alternative way of designing the soluble organic catalysts for metal-oxygen batteries.

Comparative Study of Special Features of the Oxygen Reaction (Molecular Oxygen Ionization and Evolution) in Aqueous and Nonaqueous Electrolyte Solutions (a Review)

Studies of the oxygen reaction, including the oxygen ionization and evolution processes occurring at typical electrode materials in aqueous and nonaqueous electrolytes, are analyzed. A connection between the problematics of the oxygen electrode reaction in nonaqueous media and the developing of novel batteries, in the first place, Li–O2 batteries, is emphasized. Unlike aqueous solutions, the oxygen reduction in aprotic electrolytes was shown to occur without breaking of the O–O bond; it is accompanied by formation of poorly soluble product of two-electron reaction (Li2O2) in the pores of positive electrode. The effect of the solvent donor number and the anion composition on the oxygen reduction mechanism and the lithium peroxide deposit structure is described. A marked reduction of the Li2O2 oxidation overvoltage when passing from carbonaceous materials to platinum-containing catalysts in the positive electrode is elucidated; in the latter case, the effect of electrocatalyst type upon the Li2O2 formation reaction is somewhat reduced. The elucidation of the contribution of processes occurring at the free and lithium-peroxide-covered electrode surface during the oxygen reaction for wide variety of active materials is formulated as the main basic problem of the future research.

A high-performance tin dioxide@carbon anode with a super high initial coulombic efficiency via a primary cell prelithiation process

Recently, many exciting achievements have been made in improving the cycling performance of SnO2-based electrode. However, the low initial Coulombic efficiency of SnO2-based electrode caused by the formation of solid electrolyte interphase and some of the irreversible formation of Li2O in SnO2 structure still remains unresolved. Here this work reports a primary-cell process to prelithiate the SnO2-based composites to compensate the irreversible loss during the first cycle. The primary-cell-prelithiated SnO2@C composites performs a high initial Coulombic efficiency from 92.7% to >100% with the prelithiation time extends. Even after 600 cycles, the prelithiated (24 h) SnO2@C composites show a high capacity retention of 95% (848 mAh g−1) at a current density of 0.5 A g−1.

High-Capacity and High-Rate Discharging of a Coenzyme Q10 -Catalyzed Li-O2 Battery.

Discharging of the aprotic Li-O2 battery relies on O2 reduction to insulating solid Li2 O2 , which can either deposit as thin films on the cathode surface or precipitate as large particles in the electrolyte solution. Toward realizing Li-O2 batteries with high capacity and high rate capability, it is crucially important to discharge Li2 O2 in the electrolyte solution rather than on the cathode surface. Here, a soluble electrocatalyst of coenzyme Q10 (CoQ10 ) that can efficaciously drive solution phase formation of Li2 O2 in current benchmark ether-based Li-O2 batteries is reported, which would otherwise lead to Li2 O2 surface-film growth and premature cell death. In the range of current densities of 0.1-0.5 mA cm-2areal , the CoQ10 -catalyzed Li-O2 battery can deliver a discharge capacity that is ≈40-100 times what the pristine Li-O2 battery could achieve. The drastically enhanced electrochemical performance is attributed to the CoQ10 that not only efficiently mediates the electron transfer from the cathode to dissolve O2 but also strongly interacts with the newly formed Li2 O2 in solution retarding its precipitation on the cathode surface. The mediated oxygen reduction reaction and the bonding mechanism between CoQ10 and Li2 O2 are understood with density functional theory calculations.