Quantitative Analyses of the Interfacial Properties of Current Collectors at the Mesoscopic Level in Lithium Ion Batteries by Using Hierarchical Graphene.

At the mesoscopic level of commercial lithium ion battery (LIB), it is widely believed that the poor contacts between current collector (CC) and electrode materials (EM) lead to weak adhesions and large interfacial electric resistances. However, systematic quantitative analyses of the influence of the interfacial properties of CC are still scarce. Here, we built a model interface between CC and electrode materials by directly growing hierarchical graphene films on commercial Al foil CC, and we performed systematic quantitative studies of the interfacial properties therein. Our results show that the interfacial electric resistance dominates, i.e. ∼2 orders of magnitude higher than that of electrode materials. The interfacial resistance could be eliminated by hierarchical graphene interlayer. Cathode on CC with eliminated interfacial resistance could deliver much improved power density outputs. Our work quantifies the mesoscopic factors influencing the battery performance and offers practical guidelines of boosting the performance of LIBs and beyond.

PVDF-supported graphene foam as a robust current collector for lithium metal anodes.

Lithium metal batteries have drawn much attention due to their ultrahigh energy density. However, the safety hazards and limited lifetime caused by severe lithium dendrite growth during cycling hinder their real application. To address this issue and improve the electrochemical performance of current lithium batteries, a current collector beyond the traditional copper foil for lithium anodes is highly needed. We proposed and prepared a PVDF-supported graphene foam (PSGF) structure as an effective current collector for lithium metal anodes. Because of its structural stability, large surface area, and lithiophilic surface chemistry, the corresponding lithium metal anode (PSGF@Li) shows an extended cycling life (∼1000 h), a decreased voltage hysteresis (∼80 mV) and an improved coulombic efficiency (∼99%). Furthermore, the practical application of the PSGF@Li anode in a full cell system was also demonstrated.

Scalable chemical-vapour-deposition growth of three-dimensional graphene materials towards energy-related applications.

Three-dimensional (3D) graphene materials, which are integrated using graphene structural units, show great promise for energy-related applications because of the high specific surface area, fast electron transport, and low density. Beyond solution-phase assembly of graphene sheets, chemical vapour deposition (CVD) has been recently introduced as a scalable, high-yield, and facile strategy for preparing 3D graphene materials with relatively high crystallinity and controllable layer numbers. Such 3D graphene structures have served as ideal platforms for constructing next-generation energy storage and conversion devices such as supercapacitors, batteries, and fuel cells. In this tutorial review, we focus on recent progress in the scalable CVD growth of 3D graphene materials (e.g., foams, shells, and hierarchical structures) as well as their applications in energy-related fields. First, we emphasize the role of substrate shape and composition (metal or non-metal) in the CVD growth of diverse 3D graphene materials. The related growth mechanisms of these 3D graphene materials are also analysed and discussed. Second, we demonstrate the applications of the CVD-derived 3D graphene materials in various energy-related devices. Finally, we conclude this review with our insights into the challenges and future opportunities for CVD synthesis as well as the application of such intriguing 3D graphene materials.

Graphene-Armored Aluminum Foil with Enhanced Anticorrosion Performance as Current Collectors for Lithium-Ion Battery.

Aluminum (Al) foil, as the most accepted cathode current collector for lithium-ion batteries (LIBs), is susceptible to local anodic corrosions during long-term operations. Such corrosions could lead to the deterioration or even premature failure of the batteries and are generally believed to be a bottleneck for next-generation 5 V LIBs. Here, it is demonstrated that Al foil armored by conformal graphene coating exhibits significantly reinforced anodic corrosion resistance in both LiPF6 and lithium bis(trifluoromethanesulphonyl) imide (LiTFSI) based electrolytes. Moreover, LiMn2 O4 cells using graphene-armored Al foil as current collectors (LMO/GA) demonstrate enhanced electrochemical performance in comparison with those using pristine Al foil (LMO/PA). The long-term discharge capacity retention of LMO/GA cell after ≈950 h straight operations at low rate (0.5 C) reaches up to 91%, remarkably superior to LMO/PA cell (75%). The self-discharge propensity of LMO/GA is clearly relieved and the rate/power performance is also improved with graphene mediations. This work not only contributes to the long-term stable operations of LIBs but also might catalyze the deployment of 5 V LIBs in the future.

Vertical Graphene Growth on SiO Microparticles for Stable Lithium Ion Battery Anodes.

Silicon-based materials are considered as strong candidates to next-generation lithium ion battery anodes because of their ultrahigh specific capacities. However, the pulverization and delamination of electrochemical active materials originated from the huge volume expansion (>300%) of silicon during the lithiation process results in rapid capacity fade, especially in high mass loading electrodes. Here we demonstrate that direct chemical vapor deposition (CVD) growth of vertical graphene nanosheets on commercial SiO microparticles can provide a stable conducting network via interconnected vertical graphene encapsulation during lithiation, thus remarkably improving the cycling stability in high mass loading SiO anodes. The vertical graphene encapsulated SiO (d-SiO@vG) anode exhibits a high capacity of 1600 mA h/g and a retention up to 93% after 100 cycles at a high areal mass loading of 1.5 mg/cm2. Furthermore, 5 wt % d-SiO@vG as additives increased the energy density of traditional graphite/NCA 18650 cell by ∼15%. We believe that the results strongly imply the important role of CVD-grown vertical graphene encapsulation in promoting the commercial application of silicon-based anodes.

Growing three-dimensional biomorphic graphene powders using naturally abundant diatomite templates towards high solution processability.

Mass production of high-quality graphene with low cost is the footstone for its widespread practical applications. We present herein a self-limited growth approach for producing graphene powders by a small-methane-flow chemical vapour deposition process on naturally abundant and industrially widely used diatomite (biosilica) substrates. Distinct from the chemically exfoliated graphene, thus-produced biomorphic graphene is highly crystallized with atomic layer-thickness controllability, structural designability and less noncarbon impurities. In particular, the individual graphene microarchitectures preserve a three-dimensional naturally curved surface morphology of original diatom frustules, effectively overcoming the interlayer stacking and hence giving excellent dispersion performance in fabricating solution-processible electrodes. The graphene films derived from as-made graphene powders, compatible with either rod-coating, or inkjet and roll-to-roll printing techniques, exhibit much higher electrical conductivity (∼110,700 S m-1 at 80% transmittance) than previously reported solution-based counterparts. This work thus puts forward a practical route for low-cost mass production of various powdery two-dimensional materials.

Scalable Seashell-Based Chemical Vapor Deposition Growth of Three-Dimensional Graphene Foams for Oil-Water Separation.

A seashell-based CVD technique for preparing three-dimensional (3D) graphene foams is reported. The graphene sheets in thus-obtained foams are seamlessly interconnected into a 3D flexible network, forming highly porous materials with negligible non-carbon impurities, ultralow density, and outstanding mechanical flexibility and electrical conductivity. These 3D graphene foams demonstrate a fast adsorption performance toward various oils and organic solvents, with adsorption capacity up to 250-fold weight gain. The present approach offers a practical route for scalable construction of 3D graphene foams for versatile applications such as energy storage and water remediation.

Catalyst-Free Growth of Three-Dimensional Graphene Flakes and Graphene/g-C3N4 Composite for Hydrocarbon Oxidation.

Mass production of high-quality graphene flakes is important for commercial applications. Graphene microsheets have been produced on an industrial scale by chemical and liquid-phase exfoliation of graphite. However, strong-interaction-induced interlayer aggregation usually leads to the degradation of their intrinsic properties. Moreover, the crystallinity or layer-thickness controllability is not so perfect to fulfill the requirement for advanced technologies. Herein, we report a quartz-powder-derived chemical vapor deposition growth of three-dimensional (3D) high-quality graphene flakes and demonstrate the fabrication and application of graphene/g-C3N4 composites. The graphene flakes obtained after the removal of growth substrates exhibit the 3D curved microstructure, controllable layer thickness, good crystallinity, as well as weak interlayer interactions suitable for preventing the interlayer stacking. Benefiting from this, we achieved the direct synthesis of g-C3N4 on purified graphene flakes to form the uniform graphene/g-C3N4 composite, which provides efficient electron transfer interfaces to boost its catalytic oxidation activity of cycloalkane with relatively high yield, good selectivity, and reliable stability.

Microscopic Dimensions Engineering: Stepwise Manipulation of the Surface Wettability on 3D Substrates for Oil/Water Separation.

Microscopic dimensions engineering is proposed to devise a series of 3D superhydrophobic substrates with microstructures of different dimensions. Combined theoretical modeling and experiments give the relationship of surface roughness and superhydrophobic properties, important for guiding the design of superior superwettable materials for water remediation and other uses.

Direct Synthesis of Few-Layer Graphene on NaCl Crystals.

Chemical vapor deposition is used to synthesize few-layer graphene on micro crystalline sodium chloride (NaCl) powder. The water-soluble nature of NaCl makes it convenient to produce free standing graphene layers via a facile and low-cost approach. Unlike traditional metal-catalyzed or oxygen-aided growth, the micron-size NaCl crystal planes play an important role in the nucleation and growth of few-layer graphene. Moreover, the possibility of synthesizing cuboidal graphene is also demonstrated in the present approach for the first time. Raman spectroscopy, optical microscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy are used to evaluate the quality and structure of the few-layer graphene along with cuboidal graphene obtained in this process. The few-layer graphene synthesized using the present method has an adsorption ability for anionic and cationic dye molecules in water. The present synthesis method may pave a facile way for manufacturing few-layer graphene on a large scale.