Solvothermal-induced 3D macroscopic SnO2/nitrogen-doped graphene aerogels for high capacity and long-life lithium storage

Graphene-wrapped yolk-shell of silica-cobalt oxide as high-performing anode for lithium-ion batteries

Silica (SiO2) shows promise as anode material for lithium-ion batteries due to its low cost, comparable lithium storage discharge potential and high theoretical capacity (approximately 1961 mA h g-1). However, it is plagued by issues of low electrochemical activity, low conductivity and severe volume expansion. To address these challenges, we initially coat SiO2 with CoO, followed by introducing SiO2@CoO into graphene sheets to fabricate an anode composite material (SiO2@CoO/GS) with uniformly dispersed particles and a 3D graphene wrapped yolk-shell structure. The coating of CoO on SiO2 converted the negative surface charge of SiO2 to positive, enabling effective electrostatic interactions between SiO2@CoO and graphene oxide sheets, which provided essential prerequisites for synthesizing composite materials with uniformly dispersed particles and good coating effects. Furthermore, the Co-metal formed during the charge-discharge process can act as a catalyst and electron transfer medium, activating the lithium storage activity of SiO2 and enhancing the conductivity of the electrode, conclusively achieving a higher lithium storage capacity. Ultimately, due to the activation of SiO2 by Co-metal during cycling and the excellent synergistic effect between SiO2@CoO and graphene, SiO2@CoO/GS delivers a high reversible capacity of 738 mA h g-1 after 500 cycles at 200 mA g-1. The product also demonstrates excellent rate performance with a reversible capacity of 206 mA h g-1 at a high specific current of 12.8 A g-1. The outstanding rate performance of SiO2@CoO/GS may be ascribed to the pseudo-capacitive contribution at high specific current upon cycling.

The role of graphene aerogels in rechargeable batteries

Energy storage systems, particularly rechargeable batteries, play a crucial role in establishing a sustainable energy infrastructure. Today, researchers focus on improving battery energy density, cycling stability, and rate performance. This involves enhancing existing materials or creating new ones with advanced properties for cathodes and anodes to achieve peak battery performance. Graphene aerogels (GAs) possess extraordinary attributes, including a hierarchical porous and lightweight structure, high electrical conductivity, and robust mechanical stability. These qualities facilitate the uniform distribution of active sites within electrodes, mitigate volume changes during repeated cycling, and enhance overall conductivity. When integrated into batteries, GAs expedite electron/ion transport, offer exceptional structural stability, and deliver outstanding cycling performance. This review offers a comprehensive survey of the advancements in the preparation, functionalization, and modification of GAs in the context of battery research. It explores their application as electrodes and hosts for the dispersion of active material nanoparticles, resulting in the creation of hybrid electrodes for a wide range of rechargeable batteries including lithium-ion batteries (LIBs), Li-metal-air batteries, sodium-ion batteries (SIBs), zinc-ion batteries (AZIBs) and zinc-air batteries (ZABs), aluminum-ion batteries (AIBs) and aluminum-air batteries and other.

Hydrothermal-Freeze-Casting of Poly(amidoamine)-Modified Graphene Aerogels towards CO2 Adsorption

This article presents novel poly(amidoamine) (PAMAM) dendrimer-modified with partially-reduced graphene oxide (rGO) aerogels, obtained using the combined solvothermal synthesis-freeze-casting approach. The properties of modified aerogels are investigated with varying synthesis conditions, such as dendrimer generation (G), GO:PAMAM wt. ratio, solvothermal temperature, and freeze-casting rate. Scanning electron microscopy, Fourier Transform Infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy are employed to characterize the aerogels. The results indicate a strong correlation of the synthesis conditions with N content, N/C ratio, and nitrogen contributions in the modified aerogels. Our results show that the best CO₂ adsorption performance was exhibited by the aerogels modified with higher generation (G7) dendrimer at low GO:PAMAM ratio as 2:0.1 mg mL⁻¹ and obtained at higher solvothermal temperature and freeze-casting in liquid nitrogen. The enclosed results are indicative of a viable approach to modify graphene aerogels towards improving the CO₂ capture.

Au@SnO2-vertical graphene-based microneedle sensor for in-situ determination of abscisic acid in plants

For developing electrochemical plant sensors, in-situ detection of hormone levels in living plants is worth attempting. A microneedle array sensor based on Au@SnO₂-vertical graphene (VG)/Ta microelectrodes was constructed for analyzing abscisic acid (ABA) in plants. Graphene was vertically grown on Ta wires with a diameter of 0.6 mm by direct current arc plasma jet chemical vapor deposition with SnO₂ as the Au catalyst carrier. These VG nanosheets were embedded with core-shell Au@SnO₂ nanoparticles, and the formation mechanism of the sensing layer was investigated. Three Au@SnO₂-VG microelectrodes, one Ti wire, and one Pt wire were packed into a microneedle array sensor with a three-electrode system. ABA was then quantitatively detected by direct electrocatalytic oxidation, which involves the synergistic catalytic effects of the abundant catalytic active sites of the Au@SnO₂ nanoparticles and the excellent conductivity of the VG nanosheets. The microneedle array sensor responds to ABA in the pH range 4-7, the response concentration range was 0.012 (or 0.024)-495.2 μM, and the detection limit varied between 0.002 and 0.005 μM. The small size, wide pH range, low detection limit, and wide linear concentration range allow the microneedle array sensor to be inserted into plants for in-situ detection of ABA.

High Areal Capacity Porous Sn-Au Alloys with Long Cycle Life for Li-ion Microbatteries

Long-term stability is one of the most desired functionalities of energy storage microdevices for wearable electronics, wireless sensor networks and the upcoming Internet of Things. Although Li-ion microbatteries have become the dominant energy-storage technology for on-chip electronics, the extension of lifetime of these components remains a fundamental hurdle to overcome. Here, we develop an ultra-stable porous anode based on SnAu alloys able to withstand a high specific capacity exceeding 100 µAh cm^-2 at 3 C rate for more than 6000 cycles of charge/discharge. Also, this new anode material exhibits low potential (0.2 V versus lithium) and one of the highest specific capacity ever reported at low C-rates (7.3 mAh cm^-2 at 0.1 C). We show that the outstanding cyclability is the result of a combination of many factors, including limited volume expansion, as supported by density functional theory calculations. This finding opens new opportunities in design of long-lasting integrated energy storage for self-powered microsystems.

MOF-derived hollow SiOx nanoparticles wrapped in 3D porous nitrogen-doped graphene aerogel and their superior performance as the anode for lithium-ion batteries

A nanocomposite anode material consisting of metal-organic framework (MOF)-derived hollow SiOx nanoparticles wrapped in three dimensional (3D) nitrogen-doped graphene aerogel (N-GA) has been fabricated through a facile three-step approach, involving MOF-template inducting, self-assembly and nitrogen-doping, freeze-drying and thermal treatment process. The hollow SiOx nanoparticles with an average size of 100-160 nm are distributed on 3D N-GA. Such nanocomposites possess a 3D porous structure with a BET surface area as high as 426.3 m2 g-1. In this nanostructure, the N-GA's property of interconnected porous network enables it to provide pathways for rapid electron transfer and Li+ transport, while the MOF-derived hollow SiOx nanoparticles with void space can accommodate the volume change during a lithiation/delithiation process. As a result, high rate capability (675 mA h g-1 under 50 C) as well as long-life cycling stability (1233.2 mA h g-1 under 10 C, 86% capacity retention over 500 cycles) is achieved.

SnO2 Quantum Dots@Graphene Framework as a High-Performance Flexible Anode Electrode for Lithium-Ion Batteries

Three-dimensional (3D) layered tin oxide quantum dots/graphene framework (SnO₂ QDs@GF) were designed through anchoring SnO₂ QD on the graphene surface under the hydrothermal reaction. SnO₂ QDs@GF have a 3D skeleton with a large number of mesopores and ultrasmall SnO₂ QDs with a large surface area. The unique design of this structure improves the specific area and promotes ion transport. The mechanically strong SnO₂ QDs@GF can directly be used as the anode of lithium-ion batteries (LIBs); it displays a high reversible capacity (1300 mA h g^-1 at 100 mA g^-1), excellent rate performance (642 mA h g^-1 at 2000 mA g^-1), and superior cyclic stability (when the current density is 10 A g^-1, the capacity loss is less than 2% after 5000 cycles). This novel synthetic method can further be expanded for the production of other quantum dots/graphene composites with a 3D structure as high-performance electrodes for LIBs.

Porous materials of nitrogen doped graphene oxide@SnO2 electrode for capable supercapacitor application

The porous materials of SnO₂@NGO composite was synthesized by thermal reduction process at 550 °C in presence ammonia and urea as catalyst. In this process, the higher electrostatic attraction between the SnO₂@NGO nanoparticles were anchored via thermal reduction reaction. These synthesized SnO₂@ NGO composites were confirmed by Raman, XRD, XPS, HR-TEM, and EDX results. The SnO₂ nanoparticles were anchored in the NGO composite in the controlled nanometer scale proved by FE-TEM and BET analysis. The SnO₂@NGO composite was used to study the electrochemical properties of CV, GCD, and EIS analysis for supercapacitor application. The electrochemical properties of SnO₂@NGO exhibited the specific capacitance (~378 F/g at a current density of 4 A/g) and increasing the cycle stability up to 5000 cycles. Therefore, the electrochemical results of SnO₂@NGO composite could be promising for high-performance supercapacitor applications.

Porous multishelled NiO hollow microspheres encapsulated within three-dimensional graphene as flexible free-standing electrodes for high-performance supercapacitors

Exploration of electrode materials with well-defined nanostructures and good flexibility is an efficient approach for achieving high-performance and flexible energy storage systems. However, it is still challenging to well integrate active materials into flexible electrodes and simultaneously maintain satisfactory electrochemical performance. Herein, we successfully synthesize novel three-dimensional graphene (3DG)-encapsulated porous multishelled NiO hollow microsphere (3DG/pMS-NiO) composite aerogels via a modified self-templating method and a dopamine (DA)-assisted self-assembly route. The well-designed highly interconnected porous 3DG network and the close contact NiO-graphene structure of the 3DG/pMS-NiO composite aerogels offer multiple advantages such as high porosity and accessible area, improved conductivity, enhanced electrolyte diffusion and a simple electrode preparation process. Thus, the as-prepared flexible 3DG/pMS-NiO electrodes showed significantly improved specific capacitance of 710.4 F g-1 at 0.5 A g-1 and excellent rate capability with an ultrahigh capacitance retention of 92.5% at 10 A g-1. In addition, the fabricated asymmetric supercapacitors (3DG/pMS-NiO//AC) showed a high specific capacitance of 34.4 F g-1 at 1 A g-1 with a voltage window of 0-1.6 V, a large energy density of 12.3 W h kg-1 at a power density of 815.3 W kg-1, and a decent cycling stability. This work profoundly enlightens the material design and electrode preparation, and even opens up an avenue for the development of high-performance and flexible energy storage systems.

Manganese oxide doping carbon aerogels prepared with MnO2 coordinated by N, N - dimethylmethanamide for supercapacitors

Carbon aerogels with excellent conductive characteristics and high specific capacitance have attracted more and more interests for next-generation energy storage applications. Three-dimensional interconnected Mn₂O₃/carbon aerogel supercapacitor electrodes are prepared by a novel doping method using MnO₂ coordinated by N, N-dimethylmethanamide (DMF). The coordinative MnO₂ (DMF/MnO₂) plays a key role in the sol-gel process of resorcinol and formaldehyde. The doped carbon aerogels exhibits a high specific surface area of 859 m² g^-1 and a good pore-size distribution of 10-15 nm. All of the doped carbon aerogels exhibit higher specific capacitance than pure carbon aerogels, and the highest specific capacitance (170 F g^-1), at current density of 1.0 A g^-1, is obtained in Mn-CA-5% when 5 mol% DMF/MnO₂ is added to the precursor solution. The specific capacitance is as high as 100 F g^-1, at current density of 10.0 A g^-1, and 97% of initial capacitance is retained over 1000 cycles at a current density of 5.0 A g^-1. The doped carbon aerogels exhibits a high coulombic efficiency (up to 99.8%) and a good rate capability. The corresponding result is due to the novel doping method of DMF/MnO₂ addition.

Organometallic Precursor-Derived SnO2/Sn-Reduced Graphene Oxide Sandwiched Nanocomposite Anode with Superior Lithium Storage Capacity

Benefiting from the reversible conversion reaction upon delithiation, nanosized SnO₂, with its theoretical capacity of 1494 mA h g^-1, has gained special attention as a promising anode material. Here, we report a self-assembled SnO₂/Sn-reduced graphene oxide (rGO) sandwich nanocomposite developed by organometallic precursor coating and in situ transformation. Ultrafine SnO₂ nanoparticles with an average diameter of 5 nm are sandwiched within the rGO/carbonaceous network, which not only greatly alleviates the volume changes upon lithiation and aggregation of SnO₂ nanoparticles but also facilitates the charge transfer and reaction kinetics of SnO₂ upon lithiation/delithiation. As a result, the SnO₂/Sn-rGO nanocomposite exhibited a superior lithium storage capacity with a reversible capacity of 1307 mA h g^-1 at a current density of 80 mA g^-1 in the potential window of 0.01-2.5 V versus Li⁺/Li and showed a reversible capacity of 767 mA h g^-1 over 200 cycles at a current density of 400 mA g^-1. When cycling at a higher current density of 1600 mA g^-1, the SnO₂/Sn-rGO nanocomposite showed a highly stable capacity of 449 mA g^-1 without obvious decay after 400 cycles.

Self-Assembly of Transition Metal Oxide Nanostructures on MXene Nanosheets for Fast and Stable Lithium Storage

Recently, a new class of 2D materials, i.e., transition metal carbides, nitrides, and carbonitrides known as MXenes, is unveiled with more than 20 types reported one after another. Since they are flexible and conductive, MXenes are expected to compete with graphene and other 2D materials in many applications. Here, a general route is reported to simple self-assembly of transition metal oxide (TMO) nanostructures, including TiO₂ nanorods and SnO₂ nanowires, on MXene (Ti₃ C₂ ) nanosheets through van der Waals interactions. The MXene nanosheets, acting as the underlying substrate, not only enable reversible electron and ion transport at the interface but also prevent the TMO nanostructures from aggregation during lithiation/delithiation. The TMO nanostructures, in turn, serve as the spacer to prevent the MXene nanosheets from restacking, thus preserving the active areas from being lost. More importantly, they can contribute extraordinary electrochemical properties, offering short lithium diffusion pathways and additional active sites. The resulting TiO₂ /MXene and SnO₂ /MXene heterostructures exhibit superior high-rate performance, making them promising high-power and high-energy anode materials for lithium-ion batteries.

Enhancing the Lithium Storage Performance of Graphene/SnO2 Nanorods by a Carbon-Riveting Strategy

Graphene/metal oxide (MO) nanocomposites hold great promise for application as anodes in lithium-ion batteries (LIBs). However, the restacking of graphene during subsequent processing remains a challenge to overcome for enhanced lithium storage properties. Herein, the fabrication of sandwich-architecture carbon-riveted graphene/SnO₂ nanorods, in which the SnO₂ nanorods are confined in the nanospaces formed by the carbon layers on graphene, by a two-step hydrothermal process followed by thermal treatment, is reported. Electrochemical tests show that the carbon-riveted nanolayers significantly improve the lithium storage performance of graphene/SnO₂ . The nanocomposite displays a high reversible capacity of 815 mAh g^-1 after 150 cycles at 100 mA g^-1 and high cycling stability at 1000 mA g^-1 . This work provides an efficient way to manipulate graphene/MO-based nanocomposites for LIBs with improved performance.

Folding Graphene Film Yields High Areal Energy Storage in Lithium-Ion Batteries

We show that a high energy density can be achieved in a practical manner with freestanding electrodes without using conductive carbon, binders, and current collectors. We made and used a folded graphene composite electrode designed for a high areal capacity anode. The traditional thick graphene composite electrode, such as made by filtering graphene oxide to create a thin film and reducing it such as through chemical or thermal methods, has sluggish reaction kinetics. Instead, we have made and tested a thin composite film electrode that was folded several times using a water-assisted method; it provides a continuous electron transport path in the fold regions and introduces more channels between the folded layers, which significantly enhances the electron/ion transport kinetics. A fold electrode consisting of SnO₂/graphene with high areal loading of 5 mg cm^-2 has a high areal capacity of 4.15 mAh cm^-2, well above commercial graphite anodes (2.50-3.50 mAh cm^-2), while the thickness is maintained as low as ∼20 μm. The fold electrode shows stable cycling over 500 cycles at 1.70 mA cm^-2 and improved rate capability compared to thick electrodes with the same mass loading but without folds. A full cell of fold electrode coupled with LiCoO₂ cathode was assembled and delivered an areal capacity of 2.84 mAh cm^-2 after 300 cycles. This folding strategy can be extended to other electrode materials and rechargeable batteries.

A novel route to prepare N-graphene/SnO2 composite as a high-performance anode for lithium batteries

In this study, we report a simple method to prepare nitrogen-doped graphene, with which a nitrogen-doped graphene/SnO₂ composite was successfully fabricated and employed as a lithium battery anode.

Ultrafast, Highly Reversible, and Cycle-Stable Lithium Storage Boosted by Pseudocapacitance in Sn-Based Alloying Anodes

Boosting power density is one of the primary challenges that current lithium ion batteries face. Alloying anodes that possess suitable potential windows stand at the forefront in pursuing ultrafast and highly reversible lithium storage to achieve high power/energy lithium ion batteries. Herein, ultrafast lithium storage in Sn-based nanocomposite anodes is demonstrated, which is boosted by pseudocapacitance benefitting from a high fraction of highly interconnected interfaces of Fe/Sn/Li₂ O. By tailoring the voltage window in the range of 0.005-1.2 V for the alloying/dealloying reactions, such Sn-based nanocomposite anodes achieve simultaneous ultrahigh rate capability, superlong cycling performance, and close-to-100% Coulombic efficiency. The nanocomposite anode delivers a high reversible capacity (≈420 mAh g^-1 ) at 1 A g^-1 for more than 1200 cycles, corresponding to only 0.016% per cycle of capacity decay. A reversible capacity of 350 mAh g^-1 can be maintained at an ultrahigh current density of 80 A g^-1 , with 67.3% capacity retention relative to the capacity at 1 A g^-1 . This combination of pseudocapacitive lithium storage and spatially confined electrochemical reactions in Sn-based nanocomposite anode materials may pave the way for the development of high power/energy and long life lithium ion batteries.

Advances in Subcritical Hydro-/Solvothermal Processing of Graphene Materials

Many promising graphene-based materials are kept away from mainstream applications due to problems of scalability and environmental concerns in their processing. Hydro-/solvothermal techniques overwhelmingly satisfy both the aforementioned criteria, and have matured as alternatives to wet-chemical methods with advances made over the past few decades. The insolubility of graphene in many solvents poses considerable difficulties in their processing. In this context hydro-/solvothermal techniques present an ideal opportunity for processing of graphenic materials with their versatility in manipulating the physical and thermodynamic properties of the solvent. The flexibility in hydro-/solvothermal techniques for manipulation of solvent composition, temperature and pressure provides numerous handles to manipulate graphene-based materials during synthesis. This review provides a comprehensive look at the subcritical hydro-/solvothermal synthesis of graphene-based functional materials and their applications. Several key synthetic strategies governing the morphology and properties of the products such as temperature, pressure, and solvent effects are elaborated. Advances in the synthesis, doping, and functionalization of graphene in hydro-/solvothermal media are highlighted together with our perspectives in the field.

Porous Fe2O3 Nanoframeworks Encapsulated within Three-Dimensional Graphene as High-Performance Flexible Anode for Lithium-Ion Battery

Integrating nanoscale porous metal oxides into three-dimensional graphene (3DG) with encapsulated structure is a promising route but remains challenging to develop high-performance electrodes for lithium-ion battery. Herein, we design 3DG/metal organic framework composite by an excessive metal-ion-induced combination and spatially confined Ostwald ripening strategy, which can be transformed into 3DG/Fe₂O₃ aerogel with porous Fe₂O₃ nanoframeworks well encapsulated within graphene. The hierarchical structure offers highly interpenetrated porous conductive network and intimate contact between graphene and porous Fe₂O₃ as well as abundant stress buffer nanospace for effective charge transport and robust structural stability during electrochemical processes. The obtained free-standing 3DG/Fe₂O₃ aerogel was directly used as highly flexible anode upon mechanical pressing for lithium-ion battery and showed an ultrahigh capacity of 1129 mAh/g at 0.2 A/g after 130 cycles and outstanding cycling stability with a capacity retention of 98% after 1200 cycles at 5 A/g, which is the best results that have been reported so far. This study offers a promising route to greatly enhance the electrochemical properties of metal oxides and provides suggestive insights for developing high-performance electrode materials for electrochemical energy storage.

Flexible Paper-like Free-Standing Electrodes by Anchoring Ultrafine SnS2 Nanocrystals on Graphene Nanoribbons for High-Performance Sodium Ion Batteries

Ultrafine SnS₂ nanocrystals-reduced graphene oxide nanoribbon paper (SnS₂-RGONRP) has been created by a well-designed process including in situ reduction, evaporation-induced self-assembly, and sulfuration. The as-formed SnS₂ nanocrystals possess an average diameter of 2.3 nm and disperse on the surface of RGONRs uniformly. The strong capillary force formed during evaporation leads to a compact assembly of RGONRs to give a flexible paper structure with a high density of 0.94 g cm^-3. The as-prepared SnS₂-RGONRP composite could be directly used as free-standing electrode for sodium ion batteries. Due to the synergistic effects between the ultrafine SnS₂ nanocrystals and the conductive, tightly connected RGONR networks, the composite paper electrode exhibits excellent electrochemical performance. A high volumetric capacity of 508-244 mAh cm^-3 was obtained at current densities in the range of 0.1-10 A g^-1. Discharge capacities of 334 and 255 mAh cm^-3 were still kept, even after 1500 cycles tested at current densities of 1 and 5 A g^-1, respectively. This strategy provides insight into a new pathway for the creation of free-standing composite electrodes used in the energy storage and conversion.

Three-Dimensional Graphene/Single-Walled Carbon Nanotube Aerogel Anchored with SnO2 Nanoparticles for High Performance Lithium Storage

A unique 3D graphene-single walled carbon nanotube (G-SWNT) aerogel anchored with SnO₂ nanoparticles (SnO₂@G-SWCNT) is fabricated by the hydrothermal self-assembly process. The influences of mass ratio of SWCNT to graphene on structure and electrochemical properties of SnO₂@G-SWCNT are investigated systematically. The SnO₂@G-SWCNT composites show excellent electrochemical performance in Li-ion batteries; for instance, at a current density of 100 mA g^-1, a specific capacity of 758 mAh g^-1 was obtained for the SnO₂@G-SWCNT with 50% SWCNT in G-SWCNT and the Coulombic efficiency is close to 100% after 200 cycles; even at current density of 1 A g^-1, it can still maintain a stable specific capacity of 537 mAh g^-1 after 300 cycles. It is believed that the 3D G-SWNT architecture provides a flexible conductive matrix for loading the SnO₂, facilitating the electronic and ionic transportation and mitigating the volume variation of the SnO₂ during lithiation/delithiation. This work also provides a facile and reasonable strategy to solve the pulverization and agglomeration problem of other transition metal oxides as electrode materials.

Fe7Se8@C core–shell nanoparticles encapsulated within a three-dimensional graphene composite as a high-performance flexible anode for lithium-ion batteries

The composite Fe₇Se₈@C encapsulated within 3D-graphene serves as a high-performance flexible anode for LIBs with excellent rate performance.

Self-assembly of porous CuO nanospheres decorated on reduced graphene oxide with enhanced lithium storage performance

A Li full cell assembled by porous CuO-NSs/RGO anode and commercial LiFPO₄ cathode can light up an LED lamp.

An optimized 3D carbon matrix for high rate silicon anodes

A 3D porous carbon matrix with silicon particles embedded shows high rate performance in a lithium ion battery.

Three-dimensional nitrogen and boron codoped graphene for carbon dioxide and oils adsorption

Three-dimensional heteroatom-doped graphene macroporous structures possess superior features, such as the large pore volume, numerous surface active sites and the high specific surface area.

Electronic Coupling of Cobalt Nanoparticles to Nitrogen-Doped Graphene for Oxygen Reduction and Evolution Reactions

The rational design of nonprecious-metal electrocatalysts with activities comparable to or greater than that of platinum is extremely valuable to the development of high energy density metal-air batteries. Herein, the two-step preparation of a highly active oxygen electrocatalyst based on ultrasmall cobalt nanoparticles stabilized in a nitrogen-doped graphene matrix is reported. The catalyst performs as well as the commercial Pt/C catalyst in the oxygen reduction reaction, and better than the Pt/C catalyst in the oxygen evolution reaction. This particular electrocatalyst could significantly lower the overpotentials of oxygen electrochemical reactions in aqueous lithium-air batteries to attain a round-trip efficiency of about 79.0 % at a current density of 0.1 mA cm^-2 , thereby surpassing the performance of the commercial Pt/C catalyst. The good performance may be attributed to strong metal-support interactions, maximized by a high dispersion of ultrasmall cobalt nanocrystals in a nitrogen-doped graphene matrix, which yields electrocatalytic properties greater than the sum of its parts.