Carbon inverse opal entrapped with electrode active nanoparticles as high-performance anode for lithium-ion batteries

Colloidal Templating in Catalyst Design for Thermocatalysis

Conventional catalyst preparative methods commonly entail the impregnation, precipitation, and/or immobilization of nanoparticles on their supports. While convenient, such methods do not readily afford the ability to control collective ensemble-like nanoparticle properties, such as nanoparticle proximity, placement, and compartmentalization. In this Perspective, we illustrate how incorporating colloidal templating into catalyst design for thermocatalysis confers synthetic advantages to facilitate new catalytic investigations and augment catalytic performance, focusing on three colloid-templated catalyst structures: 3D macroporous structures, hierarchical macro-mesoporous structures, and discrete hollow nanoreactors. We outline how colloidal templating decouples the nanoparticle and support formation steps to devise modular catalyst platforms that can be flexibly tuned at different length scales. Of particular interest is the raspberry colloid templating (RCT) method which confers high thermomechanical stability by partially embedding nanoparticles within its support, while retaining high levels of reactant accessibility. We illustrate how the high modularity of the RCT approach allows one to independently control collective nanoparticle properties, such as nanoparticle proximity and localization, without concomitant changes to other catalytic descriptors that would otherwise confound analyses of their catalytic performance. We next discuss how colloidal templating can be employed to achieve spatially disparate active site functionalization while directing reactant transport within the catalyst structure to enhance selectivity in multistep catalytic cascades. Throughout this Perspective, we highlight developments in advanced characterization that interrogate transport phenomena and/or derive new insights into these catalyst structures. Finally, we offer our outlook on the future roles, applications, and challenges of colloidal templating in catalyst design for thermocatalysis.

Underexcitation prevents crystallization of granular assemblies subjected to high-frequency vibration

Crystallization of dry particle assemblies via imposed vibrations is a scalable route to assemble micro/macro crystals. It is well understood that there exists an optimal frequency to maximize crystallization with broad acceptance that this optimal frequency emerges because high-frequency vibration results in overexcitation of the assembly. Using measurements that include interrupted X-ray computed tomography and high-speed photography combined with discrete-element simulations we show that, rather counterintuitively, high-frequency vibration underexcites the assembly. The large accelerations imposed by high-frequency vibrations create a fluidized boundary layer that prevents momentum transfer into the bulk of the granular assembly. This results in particle underexcitation which inhibits the rearrangements required for crystallization. This clear understanding of the mechanisms has allowed the development of a simple concept to inhibit fluidization which thereby allows crystallization under high-frequency vibrations.

Tailored engineering of Fe3O4 and reduced graphene oxide coupled architecture to realize the full potential as electrode materials for lithium-ion batteries

Developing advanced electrode materials with appropriate compositions and exquisite configurations is crucial in fabricating lithium-ion batteries (LIBs) with high energy density and fast charging capability plateau. Herein, a Fe₃O₄@reduced graphene oxide (Fe₃O₄@rGO) coupled architecture was rationally designed and in-situ synthesized. Monodispersed mesoporous Fe₃O₄ nanospheres were homogeneously formed and strongly bound on interconnected macroporous rGO frameworks to form well-defined three-dimensional (3D) hierarchical porous morphologies. This tailored Fe₃O₄@rGO coupled architecture fully exploited the advantages of Fe₃O₄ and rGO to overcome their inherent challenges, including spontaneous aggregating/excessive restacking tendency, sluggish ions diffusion/electrons transportation, and severe volume expansion/structural collapse. Benefitting from their synergistic effects, the optimized Fe₃O₄@rGO composite electrode exhibited an improved electrochemical reactivity, electrical conductivity, electrolyte accessibility, and structural stability. The optimized composite electrode displayed a high specific capacity of 1296.8 mA h g^-1 at 0.1 A g^-1 after 100 cycles, even retaining 555.1 mA h g^-1 at 2 A g^-1 after 2000 cycles. The electrochemical kinetics analysis revealed the predominantly pseudocapacitive behaviors of the Fe₃O₄@rGO heterogeneous interfaces, accounting for the excellent electrode performance. This study proposes a viable strategy for use in engineering hybrid composites with coupled architectures to optimize their potential as high-performance electrode materials for use in LIBs.

Compression-Responsive Photonic Crystals Based on Fluorine-Containing Polymers

Fluoropolymers represent a unique class of functional polymers due to their various interesting and important properties such as thermal stability, resistance toward chemicals, repellent behaviors, and their low refractive indices in comparison to other polymeric materials. Based on the latter optical property, fluoropolymers are particularly of interest for the preparation of photonic crystals for optical sensing application. Within the present study, photonic crystals were prepared based on core-interlayer-shell particles focusing on fluoropolymers. For particle assembly, the melt-shear organization technique was applied. The high order and refractive index contrast of the individual components of the colloidal crystal structure lead to remarkable reflection colors according to Bragg’s law of diffraction. Due to the special architecture of the particles, consisting of a soft core, a comparably hard interlayer, and again a soft shell, the resulting opal films were capable of changing their shape and domain sizes upon applied pressure, which was accompanied with a (reversible) change of the observed reflection colors as well. By the incorporation of adjustable amounts of UV cross-linking agents into the opal film and subsequent treatment with different UV irradiation times, stable and pressure-sensitive opal films were obtained. It is shown that the present strategy led to (i) pressure-sensitive opal films featuring reversibly switchable reflection colors and (ii) that opal films can be prepared, for which the written pattern—resulting from the compressed particles—could be fixed upon subsequent irradiation with UV light. The herein described novel fluoropolymer-containing photonic crystals, with their pressure-tunable reflection color, are promising candidates in the field of sensing devices and as potential candidates for anti-counterfeiting materials.

Fluoropolymer-Containing Opals and Inverse Opals by Melt-Shear Organization

The preparation of highly ordered colloidal architectures has attracted significant attention and is a rapidly growing field for various applications, e.g., sensors, absorbers, and membranes. A promising technique for the preparation of elastomeric inverse opal films relies on tailored core/shell particle architectures and application of the so-called melt-shear organization technique. Within the present work, a convenient route for the preparation of core/shell particles featuring highly fluorinated shell materials as building blocks is described. As particle core materials, both organic or inorganic (SiO₂) particles can be used as a template, followed by a semi-continuous stepwise emulsion polymerization for the synthesis of the soft fluoropolymer shell material. The use of functional monomers as shell-material offers the possibility to create opal and inverse opal films with striking optical properties according to Bragg’s law of diffraction. Due to the presence of fluorinated moieties, the chemical resistance of the final opals and inverse opals is increased. The herein developed fluorine-containing particle-based films feature a low surface energy for the matrix material leading to good hydrophobic properties. Moreover, the low refractive index of the fluoropolymer shell compared to the core (or voids) led to excellent optical properties based on structural colors. The herein described fluoropolymer opals and inverse opals are expected to pave the way toward novel functional materials for application in fields of coatings and optical sensors.

Assembly of large area crack free clay porous films

A method for making inverse opal-like porous clay films that are crack-free over a large area (on the scale of square centimeters).

One-pot synthesis of in-situ carbon-coated Fe3O4 as a long-life lithium-ion battery anode

Fe₃O₄ has been regarded as a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity, low cost, and environmental friendliness. In this work, we present a one-pot reducing-composite-hydroxide-mediated (R-CHM) method to synthesize in situ carbon-coated Fe₃O₄ (Fe₃O₄@C) at 280 °C using Fe(NO₃)₃ · 9H₂O and PEG800 as raw materials and NaOH/KOH as the medium. The as-prepared Fe₃O₄ octahedron has an average size of 100 nm in diameter, covered by a carbon layer with a thickness of 3 nm, as revealed by FESEM and HRTEM images. When used as anode materials in LIBs, Fe₃O₄@C exhibited an outstanding rate capability (1006, 918, 825, 737, 622, 455 and 317 mAh g^-1 at 0.1, 0.2, 0.5, 0.8, 1.0, 1.5 and 2.0 A g^-1). Moreover, it presented an excellent cycling stability, with a retained capacity of 261 mAh g^-1 after 800 cycles under an extremely high specific current density of 2.0 A g^-1. Such results indicate that Fe₃O₄@C can provide a new route into the development of long-life electrodes for future rechargeable LIBs. Importantly, the R-CHM developed in our work can be extended for the synthesis of other carbon-coated electrodes for LIBs and functional nanostructures for broader applications.

Carbon-Coated Honeycomb Ni-Mn-Co-O Inverse Opal: A High Capacity Ternary Transition Metal Oxide Anode for Li-ion Batteries

We present the formation of a carbon-coated honeycomb ternary Ni-Mn-Co-O inverse opal as a conversion mode anode material for Li-ion battery applications. In order to obtain high capacity via conversion mode reactions, a single phase crystalline honeycombed IO structure of Ni-Mn-Co-O material was first formed. This Ni-Mn-Co-O IO converts via reversible redox reactions and Li2O formation to a 3D structured matrix assembly of nanoparticles of three (MnO, CoO and NiO) oxides, that facilitates efficient reactions with Li. A carbon coating maintains the structure without clogging the open-worked IO pore morphology for electrolyte penetration and mass transport of products during cycling. The highly porous IO was compared in a Li-ion half-cell to nanoparticles of the same material and showed significant improvement in specific capacity and capacity retention. Further optimization of the system was investigated by incorporating a vinylene carbonate additive into the electrolyte solution which boosted performance, offering promising high-rate performance and good capacity retention over extended cycling. The analysis confirms the possibility of creating a ternary transition metal oxide material with binder free accessible open-worked structure to allow three conversion mode oxides to efficiently cycle as an anode material for Li-ion battery applications.

Ammonium Fluoride Mediated Synthesis of Anhydrous Metal Fluoride-Mesoporous Carbon Nanocomposites for High-Performance Lithium Ion Battery Cathodes

Metal fluorides (MF_x) are one of the most attractive cathode candidates for Li ion batteries (LIBs) due to their high conversion potentials with large capacities. However, only a limited number of synthetic methods, generally involving highly toxic or inaccessible reagents, currently exist, which has made it difficult to produce well-designed nanostructures suitable for cathodes; consequently, harnessing their potential cathodic properties has been a challenge. Herein, we report a new bottom-up synthetic method utilizing ammonium fluoride (NH₄F) for the preparation of anhydrous MF_x (CuF₂, FeF₃, and CoF₂)/mesoporous carbon (MSU-F-C) nanocomposites, whereby a series of metal precursor nanoparticles preconfined in mesoporous carbon were readily converted to anhydrous MF_x through simple heat treatment with NH₄F under solventless conditions. We demonstrate the versatility, lower toxicity, and efficiency of this synthetic method and, using XRD analysis, propose a mechanism for the reaction. All MF_x/MSU-F-C prepared in this study exhibited superior electrochemical performances, through conversion reactions, as the cathode for LIBs. In particular, FeF₃/MSU-F-C maintained a capacity of 650 mAh g^-1_FeF3 across 50 cycles, which is ∼90% of its initial capacity. We expect that this facile synthesis method will trigger further research into the development of various nanostructured MF_x for use in energy storage and other applications.

Conductive framework of inverse opal structure for sulfur cathode in lithium-sulfur batteries

As a promising cathode inheritor for lithium-ion batteries, the sulfur cathode exhibits very high theoretical volumetric capacity and energy density. In its practical applications, one has to solve the insulating properties of sulfur and the shuttle effect that deteriorates cycling stability. The state-of-the-art approaches are to confine sulfur in a conductive matrix. In this work, we utilize monodisperse polystyrene nanoparticles as sacrificial templates to build polypyrrole (PPy) framework of an inverse opal structure to accommodate (encapsulate) sulfur through a combined in situ polymerization and melting infiltration approach. In the design, the interconnected conductive PPy provides open channels for sulfur infiltration, improves electrical and ionic conductivity of the embedded sulfur, and reduces polysulfide dissolution in the electrolyte through physical and chemical adsorption. The flexibility of PPy and partial filling of the inverse opal structure endure possible expansion and deformation during long-term cycling. It is found that the long cycling stability of the cells using the prepared material as the cathode can be substantially improved. The result demonstrates the possibility of constructing a pure conductive polymer framework to accommodate insulate sulfur in ion battery applications.

Graphene Sandwiched Mesostructured Li-Ion Battery Electrodes

A deterministic graphene-sandwiched Li-ion battery electrode consisting of an integrated 3D mesostructure of electrochemically active materials and graphene is presented. As demonstrations, electrodes with active nanomaterials that coat (V2 O5 @graphene@V2 O5 cathode) or are coated by (graphene@Si@graphene anode) graphene are fabricated. These electrodes exhibit high capacities and ultralong cycle lives (the cathode can be cycled over 2000 times with minimal capacity fade).

High Volumetric Capacity Three-Dimensionally Sphere-Caged Secondary Battery Anodes

High volumetric energy density secondary batteries are important for many applications, which has led to considerable efforts to replace the low volumetric capacity graphite-based anode common to most Li-ion batteries with a higher energy density anode. Because most high capacity anode materials expand significantly during charging, such anodes must contain sufficient porosity in the discharged state to enable the expansion, yet not excess porosity, which lowers the overall energy density. Here, we present a high volumetric capacity anode consisting of a three-dimensional (3D) nanocomposite formed in only a few steps which includes both a 3D structured Sn scaffold and a hollow Sn sphere within each cavity where all the free Sn surfaces are coated with carbon. The anode exhibits a high volumetric capacity of ∼1700 mA h cm(-3) over 200 cycles at 0.5C, and a capacity greater than 1200 mA h cm(-3) at 10C. Importantly, the anode can even be formed into a commercially relevant ∼100 μm thick form. When assembled into a full cell the anode shows a good compatibility with a commercial LiMn2O4 cathode. In situ TEM observations confirm the electrode design accommodates the necessary volume expansion during lithiation.

Color-Coded Batteries - Electro-Photonic Inverse Opal Materials for Enhanced Electrochemical Energy Storage and Optically Encoded Diagnostics

For consumer electronic devices, long-life, stable, and reasonably fast charging Li-ion batteries with good stable capacities are a necessity. For exciting and important advances in the materials that drive innovations in electrochemical energy storage (EES), modular thin-film solar cells, and wearable, flexible technology of the future, real-time analysis and indication of battery performance and health is crucial. Here, developments in color-coded assessment of battery material performance and diagnostics are described, and a vision for using electro-photonic inverse opal materials and all-optical probes to assess, characterize, and monitor the processes non-destructively in real time are outlined. By structuring any cathode or anode material in the form of a photonic crystal or as a 3D macroporous inverse opal, color-coded "chameleon" battery-strip electrodes may provide an amenable way to distinguish the type of process, the voltage, material and chemical phase changes, remaining capacity, cycle health, and state of charge or discharge of either existing or new materials in Li-ion or emerging alternative battery types, simply by monitoring its color change.

Ge/GeO2-Ordered Mesoporous Carbon Nanocomposite for Rechargeable Lithium-Ion Batteries with a Long-Term Cycling Performance

Germanium-based nanostructures are receiving intense interest in lithium-ion batteries because they have ultrahigh lithium ion storage ability. However, the Germanium-based anodes undergo the considerably large volume change during the charge/discharge processes, leading to a fast capacity fade. In the present work, a Ge/GeO2-ordered mesoporous carbon (Ge/GeO2-OMC) nanocomposite was successfully fabricated via a facile nanocasting route by using mesoporous carbon as a nanoreactor, and was then used as an anode for lithium-ion batteries. Benefited from its unique three-dimensional "meso-nano" structure, the Ge/GeO2-OMC nanocomposite exhibited large reversible capacity, excellent long-time cycling stability and high rate performance. For instance, a large reversible capacity of 1018 mA h g(-1) was obtained after 100 cycles at a current density of 0.1 A g(-1), which might be attributed to the unique structure of the Ge/GeO2-OMC nanocomposite. In addition, a reversible capacity of 492 mA h g(-1) can be retained when cycled to 500 cycles at a current density of 1 A g(-1).

The formation and mechanism of nano-monocrystalline γ-Fe2O3 with graphene-shell for high-performance lithium ion batteries

We have synthesized nano-monocrystalline γ-Fe₂O₃ coated with graphene having high rate performance for lithium ion batteries.

A colloidoscope of colloid-based porous materials and their uses

Colloids assemble into a variety of bioinspired structures for applications including optics, wetting, sensing, catalysis, and electrodes.

Excellent lithium ion storage property of porous MnCo2O4 nanorods

The porous MnCo₂O₄ nanorods have been successfully prepared by a simple and economic method and exhibited a high electrochemical performance.

Perforated Metal Oxide-Carbon Nanotube Composite Microspheres with Enhanced Lithium-Ion Storage Properties

Metal oxide-carbon nanotube (CNT) composite microspheres with a novel structure were fabricated using a one-step spray pyrolysis process. Metal oxide-CNT composite microspheres with a uniform distribution of void nanospheres were prepared from a colloidal spray solution containing CNTs, metal salts, and polystyrene (PS) nanobeads. Perforated SnO2-CNT composite microspheres with a uniform distribution of void nanospheres showed excellent lithium storage properties as anode materials for lithium-ion batteries. Bare SnO2 microspheres and SnO2-CNT composite microspheres with perforated and filled structures had a discharge capacity of 450, 1108, and 590 mA h g(-1) for the 250th cycle at a current density of 1.5 A g(-1), and the corresponding capacity retention compared to the second cycle was 41, 98, and 55%, respectively. The synergetic combination of void nanospheres and flexible CNTs improved the electrochemical properties of SnO2. This effective and innovative strategy could be used for the preparation of perforated metal oxide-CNT composites with complex elemental compositions for many applications.

Polystyrene-Templated Aerosol Synthesis of MoS2 -Amorphous Carbon Composite with Open Macropores as Battery Electrode

MoS2 -amorphous carbon (MoS2 -AC) composite microspheres with macroporous structure were fabricated by one-pot spray pyrolysis. Single- or few-layered MoS2 were uniformly dispersed and oriented in random directions in the amorphous carbon microsphere with macropores sizes between 50 and 90 nm. The macroporous microspheres having a high contact area with liquid electrolyte exhibited overall superior Li- and Na-ion storage properties compared with those of the dense microspheres. After 250 charge/discharge cycles at a current density of 1.5 A g(-1) , the discharge capacities of the MoS2 -AC microspheres with dense and macroporous structures for Li-ion storage were 694 and 896 mAh g(-1) , respectively. In the case of Na-ion storage, discharge capacities of 336 and 425 mAh g(-1) were achieved for the dense and macroporous microspheres, respectively, after 100 cycles at 0.3 A g(-1) .

Beyond yolk-shell nanoparticles: Fe3O4@Fe3C core@shell nanoparticles as yolks and carbon nanospindles as shells for efficient lithium ion storage

To well address the problems of large volume change and dissolution of Fe3O4 nanomaterials during Li(+) intercalation/extraction, herein we demonstrate a one-step in situ nanospace-confined pyrolysis strategy for robust yolk-shell nanospindles with very sufficient internal void space (VSIVS) for high-rate and long-term lithium ion batteries (LIBs), in which an Fe3O4@Fe3C core@shell nanoparticle is well confined in the compartment of a hollow carbon nanospindle. This particular structure can not only introduce VSIVS to accommodate volume change of Fe3O4 but also afford a dual shell of Fe3C and carbon to restrict Fe3O4 dissolution, thus providing dual roles for greatly improving the capacity retention. As a consequence, Fe3O4@Fe3C-C yolk-shell nanospindles deliver a high reversible capacity of 1128.3 mAh g(-1) at even 500 mA g(-1), excellent high rate capacity (604.8 mAh g(-1) at 2000 mA g(-1)), and prolonged cycling life (maintaining 1120.2 mAh g(-1) at 500 mA g(-1) for 100 cycles) for LIBs, which are much better than those of Fe3O4@C core@shell nanospindles and Fe3O4 nanoparticles. The present Fe3O4@Fe3C-C yolk-shell nanospindles are the most efficient Fe3O4-based anode materials ever reported for LIBs.

One-pot synthesis of manganese oxide-carbon composite microspheres with three dimensional channels for Li-ion batteries

The fabrication of manganese oxide-carbon composite microspheres with open nanochannels and their electrochemical performance as anode materials for lithium ion batteries are investigated. Amorphous-like Mn₃O₄ nanoparticles embedded in a carbon matrix with three-dimensional channels are fabricated by one-pot spray pyrolysis. The electrochemical properties of the Mn₃O₄ nanopowders are also compared with those of the Mn₃O₄-C composite microspheres possessing macropores resembling ant-cave networks. The discharge capacity of the Mn₃O₄-C composite microspheres at a current density of 500 mA g⁻¹ is 622 mA h g⁻¹ after 700 cycles. However, the discharge capacity of the Mn₃O₄ nanopowders is as low as 219 mA h g⁻¹ after 100 cycles. The Mn₃O₄-C composite microspheres with structural advantages and high electrical conductivity have higher initial discharge and charge capacities and better cycling and rate performances compared to those of the Mn₃O₄ nanopowders.

Design and fabrication of new nanostructured SnO2-carbon composite microspheres for fast and stable lithium storage performance

One-pot method for metal oxide-carbon composite microsphere with three-dimensional ordered macroporous (3DOM) structure is first introduced. The 3DOM structured SnO2 -carbon microspheres prepared as the first target material show superior electrochemical properties as anode material for lithium ion batteries. The newly developed process can be applied to the preparation of 3DOM-structured metal oxide-carbon composite microspheres for wide applications.

A novel mesoporous carbon@silicon–silica nanostructure for high-performance Li-ion battery anodes

A novel hierarchical nanostructure with graphite-like carbon and small Si nanocrystals, respectively, encapsulated in the mesopores and embedded in a silica framework of mesoporous silica nanoparticles is constructed for high-performance Li-ion batteries.

Three-dimensional graphene foam supported Fe₃O₄ lithium battery anodes with long cycle life and high rate capability

Fe3O4 has long been regarded as a promising anode material for lithium ion battery due to its high theoretical capacity, earth abundance, low cost, and nontoxic properties. However, up to now no effective and scalable method has been realized to overcome the bottleneck of poor cyclability and low rate capability. In this article, we report a bottom-up strategy assisted by atomic layer deposition to graft bicontinuous mesoporous nanostructure Fe3O4 onto three-dimensional graphene foams and directly use the composite as the lithium ion battery anode. This electrode exhibits high reversible capacity and fast charging and discharging capability. A high capacity of 785 mAh/g is achieved at 1C rate and is maintained without decay up to 500 cycles. Moreover, the rate of up to 60C is also demonstrated, rendering a fast discharge potential. To our knowledge, this is the best reported rate performance for Fe3O4 in lithium ion battery to date.