Low-Temperature, Universal Synthetic Route for Mesoporous Metal Oxides by Exploiting Synergistic Effect of Thermal Activation and Plasma.

Mesoporous metal oxides exhibit excellent physicochemical properties and are widely used in various fields, including energy storage/conversion, catalysis, and sensors. Although several soft-template approaches are reported, high-temperature calcination for both metal oxide formation and template removal is necessary, which limits direct synthesis on a plastic substrate for flexible devices. Here, a universal synthetic approach that combines thermal activation and oxygen plasma to synthesize diverse mesoporous metal oxides (V2O5, V6O13, TiO2, Nb2O5, WO3, and MoO3) at low temperatures (150-200 °C), which can be applicable to a flexible polymeric substrate is introduced. As a demonstration, a flexible micro-supercapacitor is fabricated by directly synthesizing mesoporous V2O5 on an indium-tin oxide-coated colorless polyimide film. The energy storage performance is well maintained under severe bending conditions.

Hierarchically Superstructured Anisotropic Carbon Particles by Multiscale Assembly Driven by Spinodal Decomposition.

Hierarchical superstructures have novel shape-dependent properties, but well-defined anisotropic carbon superstructures with controllable size, shape, and building block dimensionality have rarely been accomplished thus far. Here, a hierarchical assembly technique is presented that uses spinodal decomposition (SD) to synthesize anisotropic oblate particles of mesoporous carbon superstructure (o-MCS) with nanorod arrays by integrating block-copolymer (BCP) self-assembly and polymer-polymer interface behaviors in binary blends. The interaction of major and minor phases in binary polymer blends leads to the formation of an anisotropic oblate particle, and the BCP-rich phase enables ordered packing and unidirectional alignment of carbon nanorods. Consequently, this approach enables precise control over particles' size, shape, and over the dimensionality of their components. Exploiting this functional superstructure, o-MCS are used as an anode material in potassium-ion batteries, and achieve a notable specific capacity of 156 mA h g-1 at a current density of 2 A g-1, and long-term stability for 3000 cycles. This work presents a significant advancement in the field of hierarchical superstructures, providing a promising strategy for the design and synthesis of anisotropic carbon materials with controlled properties, offering promising applications in energy storage and beyond.

Block Copolymer-Directed Facile Synthesis of N-Doped Mesoporous Graphitic Carbon for Reliable, High-Performance Zn Ion Hybrid Supercapacitor.

Ordered mesoporous carbons (OMCs) are promising materials for cathode materials of a Zn ion hybrid capacitor (Zn HC) due to their high surface area and interconnected porous structure. Graphitization of the framework and nitrogen doping have been used to improve the energy storage performance of the OMCs by enhancing electrical conductivity, pseudocapacitive reaction sites, and surface affinity toward aqueous electrolytes. Thus, when both methods are simultaneously implemented to the OMCs, the Zn HC would have improved energy storage performance. Herein, we introduce a facile synthetic method for N-doped mesoporous graphitic carbon (N-mgc) by utilizing polystyrene-block-poly(2-vinlypyridine) copolymer (PS-b-P2VP) as both soft-template and carbon/nitrogen sources. Co-assembly of PS-b-P2VP with Ni precursors for graphitization formed a mesostructured composite, which was converted to N-doped graphitic carbon through catalytic pyrolysis. After selective removal of Ni, N-mgc was prepared. The obtained N-mgc exhibited interconnected mesoporous structure with high nitrogen content and high surface area. When N-mgc was employed as a cathode material in Zn ion HC, excellent energy storage performance was achieved: a high specific capacitance (43 F/g at 0.2 A/g), a high energy density of 19.4 Wh/kg at a power density of 180 W/kg, and reliable cycle stability (>3000 cycles).

Spinodal Decomposition Method for Structuring Germanium-Carbon Li-Ion Battery Anodes.

To increase the energy density of lithium-ion batteries (LIBs), high-capacity anodes which alloy with Li ions at a low voltage against Li/Li+ have been actively pursued. So far, Si has been studied the most extensively because of its high specific capacity and cost efficiency; however, Ge is an interesting alternative. While the theoretical specific capacity of Ge (1600 mAh g-1) is only half that of Si, its density is more than twice as high (Ge, 5.3 g cm-3; Si, 2.33 g cm-3), and therefore the charge stored per volume is better than that of Si. In addition, Ge has a 400 times higher ionic diffusivity and 4 orders of magnitude higher electronic conductivity compared to Si. However, similarly to Si, Ge needs to be structured in order to manage stresses induced during lithiation and many reports have achieved sufficient areal loadings to be commercially viable. In this work, spinodal decomposition is used to make secondary particles of about 2 µm in diameter that consist of a mixture of ∼30 nm Ge nanoparticles embedded in a carbon matrix. The secondary structure of these germanium-carbon particles allows for specific capacities of over 1100 mAh g-1 and a capacity retention of 91.8% after 100 cycles. Finally, high packing densities of ∼1.67 g cm-3 are achieved in blended electrodes by creating a bimodal size distribution with natural graphite.

A Versatile Strategy for Achieving Fast-Charging Batteries via Interfacial Engineering: Pseudocapacitive Potassium Storage without Nanostructuring.

The rapid transport of alkali ions in electrodes is a long-time dream for fast-charging batteries. Though electrode nanostructuring has increased the rate-capability, its practical use is limited because of the low tap density and severe irreversible reactions. Therefore, development of a strategy to design fast-charging micron-sized electrodes without nanostructuring is of significant importance. Herein, a simple and versatile strategy to accelerate the alkali ion diffusion behavior in micron-sized electrode is reported. It is demonstrated that the diffusion rate of K+ ions is significantly improved at the hetero-interface between orthorhombic Nb2 O5 (001) and monoclinic MoO2 (110) planes. Lattice distortion at the hetero-interface generates an inner space large enough for the facile transport of K+ ions, and electron localization near oxygen-vacant sites further enhances the ion diffusion behavior. As a result, the interfacial-engineered micron-sized anode material achieves an outstanding rate capability in potassium-ion batteries (KIBs), even higher than nanostructured orthorhombic Nb2 O5  which is famous for fast-charging electrodes. This is the first study to develop an intercalation pseudocapacitive micron-sized anode without nanostructuring for fast-charging and high volumetric energy density KIBs. More interestingly, this strategy is not limited to K+ ion, but also applicable to Li+ ion, implying the versatility of interfacial engineering for alkali ion batteries.

Synthesis of Sodium Cobalt Fluoride/Reduced Graphene Oxide (NaCoF3/rGO) Nanocomposites and Investigation of Their Electrochemical Properties as Cathodes for Li-Ion Batteries.

In this study, sodium cobalt fluoride (NaCoF3)/reduced graphene oxide (NCF/rGO) nanocomposites were fabricated through a simple one-pot solvothermal process and their electrochemical performance as cathodes for Li-ion batteries (LIBs) was investigated. The NCF nanoclusters (NCs) on the composites (300-500 nm in size) were formed by the assembly of primary nanoparticles (~20 nm), which were then incorporated on the surface of rGO. This morphology provided NCF NCs with a large surface area for efficient ion diffusion and also allowed for close contact with the conductive matrix to promote rapid electron transfer. As a cathode for LIBs, the NCF/rGO electrode achieved a high reversible capacity of 465 mAh·g-1 at 20 mA·g-1 via the conversion reaction, and this enhancement represented more than five times the reversible capacity of the bare NCF electrode. Additionally, the NCF/rGO electrode exhibited both better specific capacity and cyclability within the current density testing range (from 20 to 200 mA·g-1), compared with those of the bare NCF electrode.

A Review of Functional Separators for Lithium Metal Battery Applications.

Lithium metal batteries are considered "rough diamonds" in electrochemical energy storage systems. Li-metal anodes have the versatile advantages of high theoretical capacity, low density, and low reaction potential, making them feasible candidates for next-generation battery applications. However, unsolved problems, such as dendritic growths, high reactivity of Li-metal, low Coulombic efficiency, and safety hazards, still exist and hamper the improvement of cell performance and reliability. The use of functional separators is one of the technologies that can contribute to solving these problems. Recently, functional separators have been actively studied and developed. In this paper, we summarize trends in the research on separators and predict future prospects.

Bicontinuous phase separation of lithium-ion battery electrodes for ultrahigh areal loading.

Ultrathick battery electrodes are appealing as they reduce the fraction of inactive battery parts such as current collectors and separators. However, thick electrodes are difficult to dry and tend to crack or flake during production. Moreover, the electrochemical performance of thick electrodes is constrained by ion and electron transport as well as fast capacity degradation. Here, we report a thermally induced phase separation (TIPS) process for fabricating thick Li-ion battery electrodes, which incorporates the electrolyte directly in the electrode and alleviates the need to dry the electrode. The proposed TIPS process creates a bicontinuous electrolyte and electrode network with excellent ion and electron transport, respectively, and consequently achieves better rate performance. Using this process, electrodes with areal capacities of more than 30 mAh/cm2 are demonstrated. Capacity retentions of 87% are attained over 500 cycles in full cells with 1-mm-thick anodes and cathodes. Finally, we verified the scalability of the TIPS process by coating thick electrodes continuously on a pilot-scale roll-to-roll coating tool.

Photo-Rechargeable Zinc-Ion Capacitor Using 2D Graphitic Carbon Nitride.

Off-grid energy storage devices are becoming increasingly important to power distributed applications, such as the Internet of things, and smart city ubiquitous sensor systems. To date, this has been achieved by combining an energy storage device, e.g., a battery or capacitor with an energy harvester, e.g., a solar cell. However, this approach inherently increases the device footprint and the output voltages of energy harvesters often do not match those required by energy storage device. Here we propose the first photo-rechargeable zinc-ion capacitors, where graphitic carbon nitride acts simultaneously as the capacitor electrode and light harvesting material. This approach allows light to be used to recharge the capacitor directly and they can be operated in a continuous light powered mode. These capacitors show a photo-rechargeable specific capacitance of ∼11377 mF g-1, a photo-charging voltage response of ∼850 mV, and a cyclability with ∼90% capacitance retention over 1000 cycles.

Mesoporous carbon host material for stable lithium metal anode.

Lithium (Li) metal is a promising anode material for next-generation batteries because of its low standard reduction potential (-3.04 V vs. SHE) and high specific capacity (3860 mA h g-1). However, it is still challenging to directly use Li metal as anode material in commercial batteries because of unstable Li dendrite formation and accumulated solid-electrolyte interphase. Possible methods that can suppress the unwanted formation of Li dendrites are (i) by increasing the electrode surface area and (ii) formation of porosity for confining Li. Here, we tested microporous (<2 nm) carbon and mesoporous (2-50 nm) carbon as host materials for the Li metal anode to avoid their degradation during cycling of lithium metal batteries (LMBs). Mesoporous carbon was more effective than microporous carbon as a host material to confine the Li metal and the lifetime of mesoporous carbon was more than twice as long as those of the Cu foil and microporous carbon. After confirmed better anode performance of mesoporous carbon host material, we applied Li-plated mesoporous carbon as an anode in a lithium-sulfur battery (Li-S) full cell. This research work suggests that mesopores, in spite of their low specific surface area, are better than micropores in stabilizing the Li metal and that a mesoporous host material can be applied to Li metal anodes for use in next-generation battery applications.

Morphological Control of Nanostructured V2O5 by Deep Eutectic Solvents.

Herein, we show a facile surfactant-free synthetic platform for the synthesis of nanostructured vanadium pentoxide (V2O5) using reline as a green and eco-friendly deep eutectic solvent. This new approach overcomes the dependence of the current synthetic methods on shape directing agents such as surfactants with potential detrimental effects on the final applications. Excellent morphological control is achieved by simply varying the water ratio in the reaction leading to the selective formation of V2O5 3D microbeads, 2D nanosheets, and 1D randomly arranged nanofleece. Using electrospray ionization mass spectroscopy (ESI-MS), we demonstrate that alkyl amine based ionic species are formed during the reline/water solvothermal treatment and that these play a key role in the resulting material morphology with templating and exfoliating properties. This work enables fundamental understanding of the activity-morphology relationship of vanadium oxide materials in catalysis, sensing applications, energy conversion, and energy storage as we prove the effect of surfactant-free V2O5 structuring on battery performance as cathode materials. Nanostructured V2O5 cathodes showed a faster charge-discharge response than the counterpart bulk-V2O5 electrode with V2O5 2D nanosheet presenting the highest improvement of the rate performance in galvanostatic charge-discharge tests.

Plasma production of nanomaterials for energy storage: continuous gas-phase synthesis of metal oxide CNT materials via a microwave plasma.

In this work we show for the first time that a continuous plasma process can synthesize materials from bulk industrial powders to produce hierarchical structures for energy storage applications. The plasma production process's unique advantages are that it is fast, inexpensive, and scalable due to its high energy density that enables low-cost precursors. The synthesized hierarchical material is comprised of iron oxide and aluminum oxide aggregate particles and carbon nanotubes grown in situ from the iron particles. New aerosol-based methods were used for the first time on a battery material to characterize aggregate and primary particle morphologies, while showing good agreement with observations from TEM measurements. As an anode for lithium ion batteries, a reversible capacity of 870 mA h g-1 based on metal oxide mass was observed and the material showed good recovery from high rate cycling. The high rate of material synthesis (∼10 s residence time) enables this plasma hierarchical material synthesis platform to be optimized as a means for energetic material production for the global energy storage material supply chain.

Continuous-Flow Synthesis of Carbon-Coated Silicon/Iron Silicide Secondary Particles for Li-Ion Batteries.

The development of better Li-ion battery (LIB) electrodes requires an orchestrated effort to improve the active materials as well as the electron and ion transport in the electrode. In this paper, iron silicide is studied as an anode material for LIBs because of its higher conductivity and lower volume expansion compared to pure Si particles. In addition, carbon nanotubes (CNTs) can be synthesized from the surface of iron-silicides using a continuous flow coating process where precursors are first spray dried into micrometer-scale secondary particles and are then flown through a chemical vapor deposition (CVD) reactor. Some CNTs are formed inside the secondary particles, which are important for short-range electrical transport and good utilization of the active material. Surface-bound CNTs on the secondary particles may help establish a long-range conductivity. We also observed that these spherical secondary particles allow for better electrode coating quality, cyclability, and rate performance than unstructured materials with the same composition. The developed electrodes retain a gravimetric capacity of 1150 mAh/g over 300 cycles at 1A/g as well as a 43% capacity retention at a rate of 5 C. Further, blended electrodes with graphite delivered a 539 mAh/g with high electrode density (∼1.6 g/cm3) and areal capacity (∼3.5 mAh/cm2) with stable cycling performance.

A Comprehensive Review of Materials with Catalytic Effects in Li-S Batteries: Enhanced Redox Kinetics.

Lithium-sulfur batteries (LSBs) are cost-effective and high-energy-density batteries. However, the insulating nature of active materials, the shuttle effect, and slow redox kinetics lead to severe capacity decay and low rate capabilities. Numerous multimodal approaches have been attempted to tackle these issues and have pushed the cycle stability and energy density to higher levels. Recently, accelerating the redox kinetics using catalytic materials has been considered as a means to realize high-performance LSBs. In this Minireview, we provide an insightful overview of the advances in the design of LSB catalytic materials and mechanistic descriptions of their catalytic activities.

Amorphous Tin Oxide Nanohelix Structure Based Electrode for Highly Reversible Na-Ion Batteries.

An array of amorphous tin oxide (a-SnOx) nanohelixes (NHs) was fabricated on copper foil as an electrode for Na-ion batteries via the oblique angle deposition method, a solution- and surfactant-free process. The combination of the amorphous phase SnOx with a low oxidation number and its vertically aligned NH geometry with a large surface area and high porosity, which facilitate Na-ion dynamics and accommodate the volume changes, enabled a reversible capacity of up to 915 mA h g-1 after 50 cycles, fast rate capability with 48.1% retention at 2 A g-1, and high stability, which are superior to those of crystalline nanoparticle-based electrodes.

Self-Assembly of Hybrid Nanorods for Enhanced Volumetric Performance of Nanoparticles in Li-Ion Batteries.

The benefits of nanosize active particles in Li-ion batteries are currently ambiguous. They are acclaimed for enhancing the cyclability of certain electrode materials and for improving rate performance. However, at the same time, nanoparticles are criticized for causing side reactions as well as for their low packing density and, therefore, poor volumetric battery performance. This paper demonstrates for the first time that self-assembly can be used to pack nanoparticles into dense battery electrodes with up to 4-fold higher volumetric capacities. Furthermore, despite the dense packing of the self-assembled electrodes, they retain a higher volumetric capacity than randomly dispersed nanoparticles up to rates of 5 C. Finally, we did not observe substential degradation in capacity after 1000 cycles, and post-mortem analysis indicates that the self-assembled structures are maintained during cycling. Therefore, the proposed self-assembled electrodes profit from the advantages of nanostructured battery materials without compromising the volumetric performance.

Approaching Ultrastable High-Rate Li-S Batteries through Hierarchically Porous Titanium Nitride Synthesized by Multiscale Phase Separation.

Porous architectures are important in determining the performance of lithium-sulfur batteries (LSBs). Among them, multiscale porous architecutures are highly desired to tackle the limitations of single-sized porous architectures, and to combine the advantages of different pore scales. Although a few carbonaceous materials with multiscale porosity are employed in LSBs, their nonpolar surface properties cause the severe dissolution of lithium polysulfides (LiPSs). In this context, multiscale porous structure design of noncarbonaceous materials is highly required, but has not been exploited in LSBs yet because of the absence of a facile method to control the multiscale porous inorganic materials. Here, a hierarchically porous titanium nitride (h-TiN) is reported as a multifunctional sulfur host, integrating the advantages of multiscale porous architectures with intrinsic surface properties of TiN to achieve high-rate and long-life LSBs. The macropores accommodate the high amount of sulfur, facilitate the electrolyte penetration and transportation of Li+ ions, while the mesopores effectively prevent the LiPS dissolution. TiN strongly adsorbs LiPS, mitigates the shuttle effect, and promotes the redox kinetics. Therefore, h-TiN/S shows a reversible capacity of 557 mA h g-1 even after 1000 cycles at 5 C rate with only 0.016% of capacity decay per cycle.

Synergistic Effect of Molecular-Type Electrocatalysts with Ultrahigh Pore Volume Carbon Microspheres for Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are regarded as potential high-energy storage devices due to their outstanding energy density. However, the low electrical conductivity of sulfur, dissolution of the active material, and sluggish reaction kinetics cause poor cycle stability and rate performance. A variety of approaches have been attempted to resolve the above issues and achieve enhanced electrochemical performance. However, inexpensive multifunctional host materials which can accommodate large quantities of sulfur and exhibit high electrode density are not widely available, which hinders the commercialization of Li-S batteries. Herein, mesoporous carbon microspheres with ultrahigh pore volume are synthesized, followed by the incorporation of Fe-N-C molecular catalysts into the mesopores, which can act as sulfur hosts. The ultrahigh pore volume of the prepared host material can accommodate up to ∼87 wt % sulfur, while the uniformly controlled spherical morphology and particle size of the carbon microspheres enable high areal/volumetric capacity with high electrode density. Furthermore, the uniform distribution of Fe-N-C (only 0.33 wt %) enhances the redox kinetics of the conversion reaction of sulfur and efficiently captures the soluble intermediates. The resulting electrode with 5.2 mg sulfur per cm2 shows excellent cycle stability and 84% retention of the initial capacity even after 500 cycles at a 3 C rate.

Programmed Nanoparticle-Loaded Nanoparticles for Deep-Penetrating 3D Cancer Therapy.

Tumors are 3D, composed of cellular agglomerations and blood vessels. Therapies involving nanoparticles utilize specific accumulations due to the leaky vascular structures. However, systemically injected nanoparticles are mostly uptaken by cells located on the surfaces of cancer tissues, lacking deep penetration into the core cancer regions. Herein, an unprecedented strategy, described as injecting "nanoparticle-loaded nanoparticles" to address the long-lasting problem is reported for effective surface-to-core drug delivery in entire 3D tumors. The "nanoparticle-loaded nanoparticle" is a silica nanoparticle (≈150 nm) with well-developed, interconnected channels (diameter of ≈30 nm), in which small gold nanoparticles (AuNPs) (≈15 nm) with programmable DNA are located. The nanoparticle (AuNPs)-loaded nanoparticles (silica): (1) can accumulate in tumors through leaky vascular structures by protecting the inner therapeutic AuNPs during blood circulation, and then (2) allow diffusion of the AuNPs for penetration into the entire surface-to-core tumor tissues, and finally (3) release a drug triggered by cancer-characteristic pH gradients. The hierarchical "nanoparticle-loaded nanoparticle" can be a rational design for cancer therapies because the outer large nanoparticles are effective in blood circulation and in protection of the therapeutic nanoparticles inside, allowing the loaded small nanoparticles to penetrate deeply into 3D tumors with anticancer drugs.

Multiscale Phase Separations for Hierarchically Ordered Macro/Mesostructured Metal Oxides.

Porous architectures play an important role in various applications of inorganic materials. Several attempts to develop mesoporous materials with controlled macrostructures have been reported, but they usually require complicated multiple-step procedures, which limits their versatility and suitability for mass production. Here, a simple approach for controlling the macrostructures of mesoporous materials, without templates for the macropores, is reported. The controlled solvent evaporation induces both macrophase separation via spinodal decomposition and mesophase separation via block copolymer self-assembly, leading to the formation of hierarchically porous metal oxides with periodic macro/mesostructures. In addition, using this method, macrostructures of mesoporous metal oxides are controlled into spheres and mesoporous powders containing isolated macropores. Nanocomputed tomography, focused ion beam milling, and electron microscopy confirm well-defined macrostructures containing mesopores. Among the various porous structures, hierarchically macro/mesoporous metal oxide is employed as an anode material in lithium-ion batteries. The present approach could provide a broad and easily accessible platform for the manufacturing of mesoporous inorganic materials with different macrostructures.