Enhancing Hydrophilicity of Thick Electrodes for High Energy Density Aqueous Batteries.

Thick electrodes can substantially enhance the overall energy density of batteries. However, insufficient wettability of aqueous electrolytes toward electrodes with conventional hydrophobic binders severely limits utilization of active materials with increasing the thickness of electrodes for aqueous batteries, resulting in battery performance deterioration with a reduced capacity. Here, we demonstrate that controlling the hydrophilicity of the thicker electrodes is critical to enhancing the overall energy density of batteries. Hydrophilic binders are synthesized via a simple sulfonation process of conventional polyvinylidene fluoride binders, considering physicochemical properties such as mechanical properties and adhesion. The introduction of abundant sulfonate groups of binders (i) allows fast and sufficient electrolyte wetting, and (ii) improves ionic conduction in thick electrodes, enabling a significant increase in reversible capacities under various current densities. Further, the sulfonated binder effectively inhibits the dissolution of cathode materials in reactive aqueous electrolytes. Overall, our findings significantly enhance the energy density and contribute to the development of practical zinc-ion batteries.

Synergistic Interactions of Different Electroactive Components for Superior Lithium Storage Performance.

The fusion of different electroactive components of lithium-ion batteries (LIBs) sometimes brings exceptional electrochemical properties. We herein report the reduced graphene-oxide (rGO)-coated Zn2SnO4z@NiO nanofibers (ZSO@NiO@G NFs) formed by the synergistic fusion of three different electroactive components including ZnO, SnO2, and NiO that exhibit exceptional electrochemical properties as negative electrodes for LIBs. The simple synthetic route comprised of electrospinning and calcination processes enables to form porous one-dimensional (1D) structured ZSO, which is the atomic combination between ZnO and SnO2, exhibiting effective strain relaxation during battery operation. Furthermore, the catalytic effect of Ni converted from the surface-functional NiO nanolayer on ZSO significantly contributes to improved reversible capacity. Finally, rGO sheets formed on the surface of ZSO@NiO NFs enable to construct electrically conductive path as well as a stable SEI layer, resulting in excellent electrochemical performances. Especially, exceptional cycle lifespan of more than 1600 cycles with a high capacity (1060 mAh g-1) at a high current density (1000 mA g-1), which is the best result among mixed transition metal oxide (stannates, molybdates, cobaltates, ferrites, and manganates) negative electrodes for LIBs, is demonstrated.

Colorimetric Dye-Loaded Nanofiber Yarn: Eye-Readable and Weavable Gas Sensing Platform.

The colorimetric gas sensor offers an opportunity for the simple and rapid detection of toxic gaseous substances based on visually discernible changes in the color of the sensing material. In particular, the accurate detection of trace amounts of certain biomarkers in a patient's breath provides substantial clues regarding specific diseases, for example, hydrogen sulfide (H2S) for halitosis and ammonia (NH3) for kidney disorder. However, conventional colorimetric sensors often lack the sensitivity, selectivity, detection limit, and mass-productivity, impeding their commercialization. Herein, we report an inexpensive route for the meter-scale synthesis of a colorimetric sensor based on a composite nanofiber yarn that is chemically functionalized with an ionic liquid as an effective H2S adsorbent and lead acetate as a colorimetric dye. As an eye-readable and weavable sensing platform, the single-strand yarn exhibits enhanced sensitivity supported by its high surface area and well-developed porosity to detect the breath biomarker (1 ppm of H2S). Alternatively, the yarn loaded with lead iodide dyes could reversibly detect NH3 gas molecules in the ppm-level, demonstrating the facile extensibility. Finally, we demonstrated that the freestanding yarns could be sewn into patterned textiles for the fabrication of a wearable toxic gas alarm system with a visual output.

Gallium Nitride Nanoparticles Embedded in a Carbon Nanofiber Anode for Ultralong-Cycle-Life Lithium-Ion Batteries.

Recently, gallium (Ga), one of the liquid metals (LMs), has been explored with special attention because of its liquid phase nature as a self-healing agent and Li storage characteristics. The current challenge that restricts the practical use of Ga is handling Ga easily without loss and understanding its reaction behavior in Li-ion batteries. One solution that helps to address the problem associated with liquid phases is to make solid phases such as gallium oxides and nitrides as starting materials for a stable conversion reaction. Here, we have successfully incorporated GaN nanoparticles into carbon confiners [1D carbon nanofibers (CNFs) with the outermost carbon coating layer] as an anode for the Li-ion battery. By preserving liquid Ga derived from GaN after the conversion reaction in conductive walls, long-term cycling performance (over 5000 cycles) is achievable. This work provides an insight into the LM-relevant materials/carbon composite in the area of the rechargeable battery.

Atomic-scale combination of germanium-zinc nanofibers for structural and electrochemical evolution.

Alloys are recently receiving considerable attention in the community of rechargeable batteries as possible alternatives to carbonaceous negative electrodes; however, challenges remain for the practical utilization of these materials. Herein, we report the synthesis of germanium-zinc alloy nanofibers through electrospinning and a subsequent calcination step. Evidenced by in situ transmission electron microscopy and electrochemical impedance spectroscopy characterizations, this one-dimensional design possesses unique structures. Both germanium and zinc atoms are homogenously distributed allowing for outstanding electronic conductivity and high available capacity for lithium storage. The as-prepared materials present high rate capability (capacity of ~ 50% at 20 C compared to that at 0.2 C-rate) and cycle retention (73% at 3.0 C-rate) with a retaining capacity of 546 mAh g-1 even after 1000 cycles. When assembled in a full cell, high energy density can be maintained during 400 cycles, which indicates that the current material has the potential to be used in a large-scale energy storage system.

High-Power Aqueous Zinc-Ion Batteries for Customized Electronic Devices.

Wireless electronic devices require small, rechargeable batteries that can be rapidly designed and fabricated in customized form factors for shape conformable integration. Here, we demonstrate an integrated design and manufacturing method for aqueous zinc-ion batteries composed of polyaniline (PANI)-coated carbon fiber (PANI/CF) cathodes, laser micromachined zinc (Zn) anodes, and porous separators that are packaged within three-dimensional printed geometries, including rectangular, cylindrical, H-, and ring-shapes. The PANI/CF cathode possesses high surface area and conductivity giving rise to high rate (∼600 C) performance. Due to outstanding stability of Zn-PANI batteries against oxygen and moisture, they exhibit long cycling stability in an aqueous electrolyte solution. As exemplar, we demonstrated rechargeable battery packs with tunable voltage and capacity using stacked electrodes that are integrated with electronic components in customized wearable devices.

Ultrastable Graphene-Encapsulated 3 nm Nanoparticles by In Situ Chemical Vapor Deposition.

Nanoscale materials offer enormous opportunities for catalysis, sensing, energy storage, and so on, along with their superior surface activity and extremely large surface area. Unfortunately, their strong reactivity causes severe degradation and oxidation even under ambient conditions and thereby deteriorates long-term usability. Here superlative stable graphene-encapsulated nanoparticles with a narrow diameter distribution prepared via in situ chemical vapor deposition (CVD) are presented. The judiciously designed CVD protocol generates 3 nm size metal and ceramic nanoparticles intimately encapsulated by few-layer graphene shells. Significantly, graphene-encapsulated Co3 O4 nanoparticles exhibit outstanding structural and functional integrity over 2000 cycles of lithiation/delithiation for Li-ion battery anode application, accompanied by 200% reversible volume change of the inner core particles. The insight obtained from this approach offers guidance for utilizing high-capacity electrode materials for Li-ion batteries. Furthermore, this in situ CVD synthesis is compatible with many different metal precursors and postsynthetic treatments, including oxidation, phosphidation, and sulfidation, and thus offers a versatile platform for reliable high-performance catalysis and energy storage/conversion with nanomaterials.

Stress-Tolerant Nanoporous Germanium Nanofibers for Long Cycle Life Lithium Storage with High Structural Stability.

Nanowires (NWs) synthesized via chemical vapor deposition (CVD) have demonstrated significant improvement in lithium storage performance along with their outstanding accommodation of large volume changes during the charge/discharge process. Nevertheless, NW electrodes have been confined to the research level due to the lack of scalability and severe side reactions by their high surface area. Here, we present nanoporous Ge nanofibers (NPGeNFs) having moderate nanoporosity via a combination of simple electrospinning and a low-energetic zincothermic reduction reaction. In contrast with the CVD-assisted NW growth, our method provides high tunability of macro/microscopic morphologies such as a porosity, length, and diameter of the nanoscale 1D structures. Significantly, the customized NPGeNFs showed a highly suppressed volume expansion of less than 15% (for electrodes) after full lithation and excellent durability with high lithium storage performance over 500 cycles. Our approach offers effective 1D nanostructuring with highly customized geometries and can be extended to other applications including optoelectronics, catalysis, and energy conversion.

Feasible Defect Engineering by Employing Metal Organic Framework Templates into One-Dimensional Metal Oxides for Battery Applications.

Facile synthesis of rationally designed nanostructured electrode materials with high reversible capacity is highly critical to meet ever-increasing demands for lithium-ion batteries. In this work, we employed defect engineering by incorporating metal organic framework (MOF) templates into one-dimensional nanostructures by simple electrospinning and subsequent calcination. The introduction of Co-based zeolite imidazole frameworks (ZIF-67) resulted in abundant oxygen vacancies, which induce not only more active sites for Li storage but also enhanced electrical conductivity. Moreover, abundant mesoporous sites are formed by the decomposition of ZIF-67, which are present both inside and outside the resultant SnO2-Co3O4 nanofibers (NFs). Attributed to the creation of vacancy sites along with the synergistic effects of SnO2 and Co3O4, SnO2-Co3O4 NFs exhibit an excellent reversible capacity for 300 cycles (1287 mA h g-1 at a current density of 500 mA g-1) along with superior rate capabilities and improved initial Coulombic efficiency compared with pristine SnO2 NFs. This is an early report on utilizing MOF structures as the defect formation platform into one-dimensional nanostructures, which is expected to result in superior electrochemical performances required for advanced electrodes.

Metal nanotrough embedded colorless polyimide films: transparent conducting electrodes with exceptional flexibility and high conductivity.

Reliable performances with a long lifetime are the most important factors of transparent conducting electrodes (TCEs). Here, we report a new synthesis strategy for high-performance TCEs based on the fusion of a polyimide (PI) substrate and silver layer-coated PI nanofibers. Due to the successful fusion of the substrate into the core without immiscibility, the as-synthesized TCEs showed excellent performances (a sheet resistance of 1.33 Ω sq-1 and a total optical transmittance of 88%) even after 100 000 bending cycles at a bending radius of 1.75 mm.

Brush-Like Cobalt Nitride Anchored Carbon Nanofiber Membrane: Current Collector-Catalyst Integrated Cathode for Long Cycle Li-O2 Batteries.

To achieve a high reversibility and long cycle life for lithium-oxygen (Li-O2) batteries, the irreversible formation of Li2O2, inevitable side reactions, and poor charge transport at the cathode interfaces should be overcome. Here, we report a rational design of air cathode using a cobalt nitride (Co4N) functionalized carbon nanofiber (CNF) membrane as current collector-catalyst integrated air cathode. Brush-like Co4N nanorods are uniformly anchored on conductive electrospun CNF papers via hydrothermal growth of Co(OH)F nanorods followed by nitridation step. Co4N-decorated CNF (Co4N/CNF) cathode exhibited excellent electrochemical performance with outstanding stability for over 177 cycles in Li-O2 cells. During cycling, metallic Co4N nanorods provide sufficient accessible reaction sites as well as facile electron transport pathway throughout the continuously networked CNF. Furthermore, thin oxide layer (<10 nm) formed on the surface of Co4N nanorods promote reversible formation/decomposition of film-type Li2O2, leading to significant reduction in overpotential gap (∼1.23 V at 700 mAh g-1). Moreover, pouch-type Li-air cells using Co4N/CNF cathode stably operated in real air atmosphere even under 180° bending. The results demonstrate that the favorable formation/decomposition of reaction products and mediation of side reactions are hugely governed by the suitable surface chemistry and tailored structure of cathode materials, which are essential for real Li-air battery applications.

In Situ High-Resolution Transmission Electron Microscopy (TEM) Observation of Sn Nanoparticles on SnO2 Nanotubes Under Lithiation.

We trace Sn nanoparticles (NPs) produced from SnO2 nanotubes (NTs) during lithiation initialized by high energy e-beam irradiation. The growth dynamics of Sn NPs is visualized in liquid electrolytes by graphene liquid cell transmission electron microscopy. The observation reveals that Sn NPs grow on the surface of SnO2 NTs via coalescence and the final shape of agglomerated NPs is governed by surface energy of the Sn NPs and the interfacial energy between Sn NPs and SnO2 NTs. Our result will likely benefit more rational material design of the ideal interface for facile ion insertion.

Cu Microbelt Network Embedded in Colorless Polyimide Substrate: Flexible Heater Platform with High Optical Transparency and Superior Mechanical Stability.

Metal nanowires have been considered as essential components for flexible transparent conducting electrodes (TCEs) with high transparency and low sheet resistance. However, large surface roughness and high interwire junction resistance limit the practical use of metal wires as TCEs. Here, we report Cu microbelt network (Cu MBN) with coalescence junction and low surface roughness for next-generation flexible TCEs. In particular, the unique embedded structure of Cu MBN in colorless polyimide (cPI) film was achieved to reduce the surface roughness as well as enhance mechanical stability. The TCEs using junction-free Cu MBN embedded in cPI exhibited excellent mechanical stability up to 100 000 bending cycles, high transparency of 95.18%, and a low sheet resistance of 6.25 Ω sq-1. Highly robust Cu MBN-embedded cPI-based TCE showed outstanding flexible heater performance, i.e., high saturation temperature (120 °C) at very low voltage (2.3 V), owing to the high thermal stability of cPI and excellent thermal conductivity of the Cu MBN.

Rational Design of 1-D Co3O4 Nanofibers@Low content Graphene Composite Anode for High Performance Li-Ion Batteries.

Cobalt oxide that has high energy density, is the next-generation candidate as the anode material for LIBs. However, the practical use of Co3O4 as anode material has been hindered by limitations, especially, low electrical conductivity and pulverization from large volume change upon cycling. These features lead to hindrance to its electrochemical properties for lithium-ion batteries. To improve electrochemical properties, we synthesized one-dimensional (1-D) Co3O4 nanofibers (NFs) overed with reduced graphene oxide (rGO) sheets by electrostatic self-assembly (Co3O4 NFs@rGO). The flexible graphene oxide sheets not only prevent volume changes of active materials upon cycling as a clamping layer but also provide efficient electrical pathways by three-dimensional (3-D) network architecture. When applied as an anode for LIBs, the Co3O4 NFs@rGO exhibits superior electrochemical performance: (i) high reversible capacity (615 mAh g-1 and 92% capacity retention after 400 cycles at 4.0 A g-1) and (ii) excellent rate capability. Herein, we highlighted that the enhanced conversion reaction of the Co3O4 NFs@rGO is attributed to effective combination of 1-D nanostructure and low content of rGO (~3.5 wt%) in hybrid composite.

Formation of a Surficial Bifunctional Nanolayer on Nb2 O5 for Ultrastable Electrodes for Lithium-Ion Battery.

Safe and long cycle life electrode materials for lithium-ion batteries are significantly important to meet the increasing demands of rechargeable batteries. Niobium pentoxide (Nb2 O5 ) is one of the highly promising candidates for stable electrodes due to its safety and minimal volume expansion. Nevertheless, pulverization and low conductivity of Nb2 O5 have remained as inherent challenges for its practical use as viable electrodes. A highly facile method is proposed to improve the overall cycle retention of Nb2 O5 microparticles by ammonia (NH3 ) gas-driven nitridation. After nitridation, an ultrathin surficial layer (2 nm) is formed on the Nb2 O5 , acting as a bifunctional nanolayer that allows facile lithium (Li)-ion transport (10-100 times higher Li diffusivity compared with pristine Nb2 O5 microparticles) and further prevents the pulverization of Nb2 O5 . With the subsequent decoration of silver (Ag) nanoparticles (NPs), the low electric conductivity of nitridated Nb2 O5 is also significantly improved. Cycle retention is greatly improved for nitridated Nb2 O5 (96.7%) compared with Nb2 O5 (64.7%) for 500 cycles. Ag-decorated, nitridated Nb2 O5 microparticles and nitridated Nb2 O5 microparticles exhibit ultrastable cycling for 3000 cycles at high current density (3000 mA g-1 ), which highlights the importance of the surficial nanolayer in improving overall electrochemical performances, in addition to conductive NPs.

Direct Realization of Complete Conversion and Agglomeration Dynamics of SnO2 Nanoparticles in Liquid Electrolyte.

The conversion reaction is important in lithium-ion batteries because it governs the overall battery performance, such as initial Coulombic efficiency, capacity retention, and rate capability. Here, we have demonstrated in situ observation of the complete conversion reaction and agglomeration of nanoparticles (NPs) upon lithiation by using graphene liquid cell transmission electron microscopy. The observation reveals that the Sn NPs are nucleated from the surface of SnO2, followed by merging with each other. We demonstrate that the agglomeration has a stepwise process, including rotation of a NP, formation of necks, and subsequent merging of individual NPs.

A High-Capacity and Long-Cycle-Life Lithium-Ion Battery Anode Architecture: Silver Nanoparticle-Decorated SnO2/NiO Nanotubes.

The combination of high-capacity and long-term cyclability has always been regarded as the first priority for next generation anode materials in lithium-ion batteries (LIBs). To meet these requirements, the Ag nanoparticle decorated mesoporous SnO2/NiO nanotube (m-SNT) anodes were synthesized via an electrospinning process, followed by fast ramping rate calcination and subsequent chemical reduction in this work. The one-dimensional porous hollow structure effectively alleviates a large volume expansion during cycling as well as provides a short lithium-ion duffusion length. Furthermore, metallic nickel (Ni) nanoparticles converted from the NiO nanograins during the lithiation process reversibly decompose Li2O during delithiation process, which significantly improves the reversible capacity of the m-SNT anodes. In addition, Ag nanoparticles uniformly decorated on the m-SNT via a simple chemical reduction process significantly improve rate capability and also contribute to long-term cyclability. The m-SNT@Ag anodes exhibited excellent cycling stability without obvious capacity fading after 500 cycles with a high capacity of 826 mAh g-1 at a high current density of 1000 mA g-1. Furthermore, even at a very high current density of 5000 mA g-1, the charge-specific capacity remained as high as 721 mAh g-1, corresponding to 60% of its initial capacity at a current density of 100 mA g-1.

Dimensional Effects of MoS2 Nanoplates Embedded in Carbon Nanofibers for Bifunctional Li and Na Insertion and Conversion Reactions.

Controlling structural and morphological features of molybdenum disulfide (MoS2) nanoplates determines anode reaction performance for Li-ion and Na-ion batteries. In this work, we investigate dimensional effects of MoS2 nanoplates randomly embedded in twisted mesoporous carbon nanofibers (MoS2@MCNFs) on Li and Na storage properties. Considering dimensions of the MoS2 nanoplates (e.g., interlayer, lateral distance, and slabs of stacking in number), we controlled thermolysis temperature to synthesize the MoS2 nanoplates with different geometry and optimize them in the hybrid anode for delivering high performance. The MoS2@MCNFs electrode exhibits reversible Li and Na capacities greater than 1000 cycles even at high current density of 1.0 A g-1 (1221.94 mAh g-1 with capacity retention of 95.6% for Li-ion batteries and 447.29 mAh g-1 with capacity retention of 87.11% for Na-ion batteries). We elucidated the insertion, conversion, and interfacial reaction characteristics of the thermosensitive MoS2 nanoplates in the MCNFs, especially associated with a reversible capacity. Our study will hint at rational design of the nanostructured MoS2 electrodes and focus on significance of their dimensional effects on anode performance.

A facile route for growth of CNTs on Si@hard carbon for conductive agent incorporating anodes for lithium-ion batteries.

Conductive agent incorporating Si anodes consisting of directly grown carbon nanotubes on hard carbon encapsulating Si nanoparticles were prepared by a one-pot chemical vapour deposition process. Owing to this fabulous structure, Si-based anodes exhibit excellent cycle retention and rate capability with a high-mass-loading of 3.5 mg cm(-2).

Multifunctional molecular design as an efficient polymeric binder for silicon anodes in lithium-ion batteries.

This work demonstrates the design, synthesis, characterization, and study of the electrochemical performance of a novel binder for silicon (Si) anodes in lithium-ion batteries (LIBs). Polymeric binders with three different functional groups, namely, carboxylic acid (COOH), carboxylate (COO(-)), and hydroxyl (OH), in a single polymer backbone have been synthesized and characterized via (1)H NMR and FTIR spectroscopies. A systematic study that involved varying the ratio of the functional groups indicated that a material with an acid-to-alcohol molar ratio of 60:40 showed promise as an efficient binder with an initial columbic efficiency of 89%. This exceptional performance is attributed to the strong adhesion of the binder to the silicon surface and to cross-linking between carboxyl and hydroxyl functional groups, which minimize the disintegration of the Si anode structure during the large volume expansion of the lithiated Si nanoparticle. Polymers with multiple functional groups can serve as practical alternative binders for the Si anodes of LIBs, resulting in higher capacities with less capacity fade.