3D nitrogen-doped graphene foam with encapsulated germanium/nitrogen-doped graphene yolk-shell nanoarchitecture for high-performance flexible Li-ion battery

Three-Dimensional Self-Supported Ge Anode for Advanced Lithium-Ion Batteries

Three-dimensional (3D) self-supported Ge anode is one of the promising candidates to replace the traditional graphite anode material for high-performance binder-free lithium-ion batteries (LIBs). The enlarged surface area and the shortened ions/electrons transporting distance of the 3D electrode would greatly facilitate the rapid transfer of abundant lithium ions during cycling, thus achieve enhanced energy and power density during cycling. Cycle stability of the 3D self-supported Ge electrode would be improved due to the obtained enough space could effectively accommodate the large volume expansion of the Ge anode. In this review, we first describe the electrochemical properties and Li ions storage mechanism of Ge anode. Moreover, the recent advances in the 3D self-supported Ge anode architectures design are majorly illustrated and discussed. Challenges and prospects of the 3D self-supported Ge electrode are finally provided, which shed light on ways to design more reliable 3D Ge-based electrodes in energy storage systems.

Multiscale Structural Design of 2D Nanomaterials-based Flexible Electrodes for Wearable Energy Storage Applications

2D nanomaterials play a critical role in realizing high-performance flexible electrodes for wearable energy storge devices, owing to their merits of large surface area, high conductivity and high strength. The electrode is a complex system and the performance is determined by multiple and interrelated factors including the intrinsic properties of materials and the structures at different scales from macroscale to atomic scale. Multiscale design strategies have been developed to engineer the structures to exploit full potential and mitigate drawbacks of 2D materials. Analyzing the design strategies and understanding the working mechanisms are essential to facilitate the integration and harvest the synergistic effects. This review summarizes the multiscale design strategies from macroscale down to micro/nano-scale structures and atomic-scale structures for developing 2D nanomaterials-based flexible electrodes. It starts with brief introduction of 2D nanomaterials, followed by analysis of structural design strategies at different scales focusing on the elucidation of structure-property relationship, and ends with the presentation of challenges and future prospects. This review highlights the importance of integrating multiscale design strategies. Finding from this review may deepen the understanding of electrode performance and provide valuable guidelines for designing 2D nanomaterials-based flexible electrodes.

Engineering contact curved interface with high-electronic-state active sites for high-performance potassium-ion batteries

Potassium-ion batteries (PIBs) have attracted ever-increasing interest due to the abundant potassium resources and low cost, which are considered a sustainable energy storage technology. However, the graphite anodes employed in PIBs suffer from low capacity and sluggish reaction kinetics caused by the large radius of potassium ions. Herein, we report nitrogen-doped, defect-rich hollow carbon nanospheres with contact curved interfaces (CCIs) on carbon nanotubes (CNTs), namely CCI-CNS/CNT, to boost both electron transfer and potassium-ion adsorption. Density functional theory calculations validate that engineering CCIs significantly augments the electronic state near the Fermi level, thus promoting electron transfer. In addition, the CCIs exhibit a pronounced affinity for potassium ions, promoting their adsorption and subsequently benefiting potassium storage. As a result, the rationally designed CCI-CNS/CNT anode shows remarkable cyclic stability and rate capability. This work provides a strategy for enhancing the potassium storage performance of carbonaceous materials through CCI engineering, which can be further extended to other battery systems.

Macroscopic assembly of 2D materials for energy storage and seawater desalination

Since the discovery of graphene in 2004, two-dimensional (2D) materials have attracted widespread attention due to their excellent physical and chemical properties in the fields of energy, environment, catalysis, and optoelectronics. However, there are still many key problems in the process of practical application. To further promote the potential of 2D materials for practical applications, macroscopic assembly of 2D materials is crucial for the continued development of 2D materials, especially in the fields of energy storage and seawater desalination. Therefore, this review focuses on the latest progress and current status related to the macroscopic assembly of 2D materials, including 1D fibers, 2D films, and 3D architectures. In addition, the application of macroscopic bodies assembled based on 2D materials in the fields of energy storage and seawater desalination is also introduced. Finally, future directions for the macroscopic assembly of 2D materials and their applications are prospected.

Lithium Azides Induced SnS Quantum Dots for Ultra-Fast and Long-Term Sodium Storage

Tin sulfide (SnS) is an attractive anode for sodium ion batteries (NIBs) because of its high theoretical capacity, while it seriously suffers from the inherently poor conductivity and huge volume variation during the cycling process, leading to inferior lifespan. To intrinsically maximize the sodium storage of SnS, herein, lithium azides (LiN3 )-induced SnS quantum dots (QDs) are first reported using a simple electrospinning strategy, where SnS QDs are uniformly distributed in the carbon fibers. Taking the advantage of LiN3 , which can effectively prevent the growth of crystal nuclei during the thermal treatment, the well-dispersed SnS QDs performs superior Na+ transfer kinetics and pseudocapacitive when used as an anode material for NIBs. The 3D SnS quantum dots embedded uniformly in N-doped nanofibers (SnS QDs@NCF) electrodes display superior long cycling life-span (484.6 mAh g-1 after 5800 cycles at 2 A g-1 and 430.9 mAh g-1 after 7880 cycles at 10 A g-1 ), as well as excellent rate capability (422.3 mAh g-1 at 20 A g-1 ). This fabrication of transition metal sulfides QDs composites provide a feasible strategy to develop NIBs with long life-span and superior rate capability to pave its practical implementation.

3D Printing-Enabled Design and Manufacturing Strategies for Batteries: A Review

Lithium-ion batteries (LIBs) have significantly impacted the daily lives, finding broad applications in various industries such as consumer electronics, electric vehicles, medical devices, aerospace, and power tools. However, they still face issues (i.e., safety due to dendrite propagation, manufacturing cost, random porosities, and basic & planar geometries) that hinder their widespread applications as the demand for LIBs rapidly increases in all sectors due to their high energy and power density values compared to other batteries. Additive manufacturing (AM) is a promising technique for creating precise and programmable structures in energy storage devices. This review first summarizes light, filament, powder, and jetting-based 3D printing methods with the status on current trends and limitations for each AM technology. The paper also delves into 3D printing-enabled electrodes (both anodes and cathodes) and solid-state electrolytes for LIBs, emphasizing the current state-of-the-art materials, manufacturing methods, and properties/performance. Additionally, the current challenges in the AM for electrochemical energy storage (EES) applications, including limited materials, low processing precision, codesign/comanufacturing concepts for complete battery printing, machine learning (ML)/artificial intelligence (AI) for processing optimization and data analysis, environmental risks, and the potential of 4D printing in advanced battery applications, are also presented.

Microporous 3D-Structured Hierarchically Entangled Graphene-Supported Pt3Co Alloy Catalyst for PEMFC Application with Process-Friendly Features

To improve the oxygen reduction reaction (ORR) performance in a proton-exchange membrane fuel cell (PEMFC) cathode with respect to mass activity and durability, a suitable electrocatalyst design strategy is essentially needed. Here, we have prepared a sub-three nm-sized platinum (Pt)-cobalt (Co) alloy (Pt₃Co)-supported N-doped microporous 3D graphene (Pt₃Co/pNEGF) by using the polyol synthesis method. A microwave-assisted synthesis method was employed to prepare the catalyst based on the 3D porous carbon support with a large pore volume and dense micro-/mesoporous surfaces. The ORR performance of Pt₃Co/pNEGF closely matches with the state-of-the-art commercial Pt/C catalyst in 0.1 M HClO₄, with a small overpotential of 10 mV. The 3D microporous structure of the N-doped graphene significantly improves the mass transport of the reactant and thus the overall ORR performance. As a result of the lower loading of Pt in Pt₃Co/pNEGF as compared to that in Pt/C, the alloy catalyst achieved 1.5 times higher mass activity than Pt/C. After 10,000 cycles, the difference in the electrochemically active surface area (ECSA) and half-wave potential (E_1/2) of Pt₃Co/pNEGF is found to be 5 m² g_Pt^-1 (ΔECSA) and 24 mV (ΔE_1/2), whereas, for Pt/C, these values are 9 m² g_Pt^-1 and 32 mV, respectively. Finally, in a realistic perspective, single-cell testing of a membrane electrode assembly (MEA) was made by sandwiching the Pt₃Co/pNEGF-coated gas diffusion layers as the cathode displayed a maximum power density of 800 mW cm^-2 under H₂-O₂ feed conditions with a clear indication of helping the system in the mass-transfer region (i.e., the high current dragging condition). The nature of the I-V polarization shows a progressively lower slope in this region of the polarization plot compared to a similar system made from its Pt/C counterpart and a significantly improved performance throughout the polarization region in the case of the system made from the Pt₃Co/NEGF catalyst (without the microwave treatment) counterpart. These results validate the better process friendliness of Pt₃Co/pNEGF as a PEMFC electrode-specific catalyst owing to its unique texture with 3D architecture and well-defined porosity with better structural endurance.

Recent Advances in Carbon-Based Electrodes for Energy Storage and Conversion

Carbon-based nanomaterials, including graphene, fullerenes, and carbon nanotubes, are attracting significant attention as promising materials for next-generation energy storage and conversion applications. They possess unique physicochemical properties, such as structural stability and flexibility, high porosity, and tunable physicochemical features, which render them well suited in these hot research fields. Technological advances at atomic and electronic levels are crucial for developing more efficient and durable devices. This comprehensive review provides a state-of-the-art overview of these advanced carbon-based nanomaterials for various energy storage and conversion applications, focusing on supercapacitors, lithium as well as sodium-ion batteries, and hydrogen evolution reactions. Particular emphasis is placed on the strategies employed to enhance performance through nonmetallic elemental doping of N, B, S, and P in either individual doping or codoping, as well as structural modifications such as the creation of defect sites, edge functionalization, and inter-layer distance manipulation, aiming to provide the general guidelines for designing these devices by the above approaches to achieve optimal performance. Furthermore, this review delves into the challenges and future prospects for the advancement of carbon-based electrodes in energy storage and conversion.

2D TaSe2 as a zero-strain and high-performance anode material for Li+ storage

The zero-strain property of anode materials plays a determining role in their safety and cycling performance. However, the zero-strain anode materials currently developed are very limited and show significant performance trade-offs. Herein, novel highly conductive two-dimensional (2D) TaSe₂ is first explored as an anode material. Due to the reaction mechanism of Li⁺ solid-solution, the 2D TaSe₂ anode shows the zero-strain feature (0.042%) at full lithiation, resulting in excellent cycling stability. Owing to the dual active sites (Ta and Se atoms) and the double-sided Li⁺ storage mechanism, the 2D TaSe₂ anode exhibits the highest specific capacity of zero-strain anode materials, and it is the only zero-strain anode material that exceeds the graphite anode in energy density. Additionally, because of its remarkable Li⁺/electronic conductivity and high mass density, the anode is insensitive to the loading mass (3.78-12.66 mg cm^-2), resulting in high areal (9.94 mA h cm^-2), volumetric (∼5 times greater than the graphite anode), and gravimetric specific capacities (the only zero-strain anode higher than the graphite anode). When matched with the high-loading LiFePO₄ cathode (11.4 mg cm^-2), the full cell also presents overall good performance. Experiment results combined with density functional theory (DFT) calculations are adopted together to reveal the mechanisms of Li⁺ storage and transfer. This work provides a good paradigm to design zero-strain and high-performance alkali-metal-ion anode materials.

Achieving ultrastability and efficient lithium storage capacity with high-energy iron(II) oxalate anode materials by compositing Ge nano-conductive sites

Transition metal oxalates (TMOxs, represented by iron oxalate) have attracted considerable interest in anode materials due to their excellent lithium storage properties and consistent cyclic performance. Although investigations into their electrochemical capabilities and lithium storage mechanisms are gradually deepening, the complex and varied electrochemical reactions in the initial cycle, poor inherent conductivity, and high irreversible capacity constrain their further development. Herein, to solve the above-mentioned problems, we controlled the hydrothermal synthesis conditions of iron oxalate with the assistance of organic solvents, which induced the growth of iron oxalate crystals with nano Ge metal as the core. The metal Ge space sites compounded to the stacked iron oxalate particles act as conductive nodes and metal frames, which enhances both the strength of iron oxalate samples and electronic conductivity and lithium-ion diffusion inside the electrode materials. This special structure enhances the electrochemical activity of iron oxalates and improves their lithium storage capability. The iron oxalate @ nano Ge metal composite (FCO@Ge-1) exhibits an excellent cycling performance and an appreciable reversible specific capacity (1090 mA h g^-1 after 200 cycles at 1 A g^-1). The obvious polarization and variation of the electrochemical reaction in the initial cycle of iron oxalate are reduced by compositing nano Ge metal. It is demonstrated that nano Ge metal can promote reversible capacity retention from 67.72% to 80.69% in the early cycles. The distinctive structure of iron oxalate @ nano Ge metal composite provides a fresh pathway to enhance oxalate electrochemical reversible lithium storage activity and develop high-energy electrode material by constructing composite space conductive sites.

Enabling Durable Ultralow-k Capacitors with Enhanced Breakdown Strength in Density-Variant Nanolattices

Ultralow-k materials used in high voltage devices require mechanical resilience and electrical and dielectric stability even when subjected to mechanical loads. Existing devices with organic polymers suffer from low thermal and mechanical stability while those with inorganic porous structures struggle with poor mechanical integrity. Recently, 3D hollow-beam nanolattices have emerged as promising candidates that satisfy these requirements. However, their properties are maintained for only five stress cycles at strains below 25%. Here, we demonstrate that alumina nanolattices with different relative density distributions across their height elicit a deterministic mechanical response concomitant with a 1.5-3.3 times higher electrical breakdown strength than nanolattices with uniform density. These density-variant nanolattices exhibit an ultralow-k of ≈1.2, accompanied by complete electric and dielectric stability and mechanical recoverability over 100 cyclic compressions to 62.5% strain. We explain the enhanced insulation and long-term cyclical stability by the bi-phase deformation where the lower-density region protects the higher-density region as it is compressed before the higher-density region, allowing to simultaneously possess high strength and ductility like composites. This study highlights the superior electrical performance of the bi-phase nanolattice with a single interface in providing stable conduction and maximum breakdown strength.

Electrospun Nanofiber Electrodes for Lithium-Ion Batteries

Electrospun nanofiber materials have the advantages of good continuity, large specific surface areas, and high structural tunability, which provide many desirable characteristics for lithium-ion battery electrodes. Here, the principles and advantages of electrospinning technology are first elaborated, then the previous studies on high-performance nanofibrous electrode materials prepared by electrospinning technology are comprehensively summarized, and the correlation between 1D nanostructured materials and electrode performances is discussed. Finally, the remaining challenges of nanofibrous electrodes are proposed and some future study directions of this particular area are pointed out. This review provides new enlightenment for the design of nanofibrous electrodes toward high-performance lithium-ion batteries.

Thickness Dependency of Battery Anode Properties in Multilayer Graphene

With the development of practical thin-film batteries, multilayer graphene (MLG) is being actively investigated as an anode material. Therefore, research on determining a technique to fabricate thick MLG on arbitrary substrates at low temperatures is essential. In this study, we formed an MLG with controlled thickness at low temperatures using a layer exchange (LE) technique and evaluated its anode properties. The LE technique enabled the formation of a uniform MLG with a wide range of thicknesses (25-500 nm) on Ta foil. The charge/discharge characterization using coin-type cells revealed that the total capacity, which corresponded to Li intercalation into the MLG interlayer, increased with increasing MLG thickness. In contrast, cross-sectional transmission electron microscopy showed a metal oxide formed at the MLG/Ta interface during annealing, which had small Li capacity. MLG with sufficient thickness (500 nm) exhibited an excellent Coulombic efficiency and capacity retention compared to bulk graphite formed at high temperatures. These results have led to the development of inexpensive and reliable rechargeable thin-film batteries.

Three-dimensional network of nitrogen-doped carbon matrix-encapsulated Si nanoparticles/carbon nanofibers hybrids for lithium-ion battery anodes with excellent capability

Three-dimensionally structured silicon (Si)–carbon (C) nanocomposites have great potential as anodes in lithium-ion batteries (LIBs). Here, we report a Nitrogen-doped graphene/carbon-encapsulated Si nanoparticle/carbon nanofiber composite (NG/C@Si/CNF) prepared by methods of surface modification, electrostatic self-assembly, cross-linking with heat treatment, and further carbonization as a potential high-performance anode for LIBs. The N-doped C matrix wrapped around Si nanoparticles improved the electrical conductivity of the composites and buffered the volume change of Si nanoparticles during lithiation/delithiation. Uniformly dispersed CNF in composites acted as conductive networks for the fast transport of ions and electrons. The entire tightly connected organic material of NG/C@Si and CNF prevented the crushing and shedding of particles and maintained the integrity of the electrode structure. The NG/C@Si/CNF composite exhibited better rate capability and cycling performance compared with the other electrode materials. After 100 cycles, the electrode maintained a high reversible specific capacity of 1371.4 mAh/g.

Study on High Temperature Pyrolysis Light Cycle Oil to Acetylene and Carbon Black

The reaction performance of producing acetylene by light cycle oil (LCO) high temperature pyrolysis was investigated with a self-made electromagnetic induction heating device. The results showed that the reaction temperature and residence time were the main factors restricting the production of acetylene during LCO high temperature cracking. When the reaction temperature was 1800 °C and the residence time was 8.24 ms, the yield of acetylene reached 7.90%. At the same time, the comparative study of different raw materials shows that Yangzhou heavy cycle oil (YZHCO) with a higher content of chain alkanes, cycloalkanes, and tetrahydro-naphthalene aromatics was beneficial to the formation of acetylene, and the highest yield of acetylene reached to 12.7%. The preliminary characterization of byproduct carbon black showed it had a good structure and could be used for lithium electron conductive agent.

Recent Progress on Graphene-Based Nanocomposites for Electrochemical Sodium-Ion Storage

In advancing battery technologies, primary attention is paid to developing and optimizing low-cost electrode materials capable of fast reversible ion insertion and extraction with good cycling ability. Sodium-ion batteries stand out due to their inexpensive price and comparable operating principle to lithium-ion batteries. To achieve this target, various graphene-based nanocomposites fabricate strategies have been proposed to help realize the nanostructured electrode for high electrochemical performance sodium-ion batteries. In this review, the graphene-based nanocomposites were introduced according to the following main categories: graphene surface modification and doping, three-dimensional structured graphene, graphene coated on the surface of active materials, and the intercalation layer stacked graphene. Through one or more of the above strategies, graphene is compounded with active substances to prepare the nanocomposite electrode, which is applied as the anode or cathode to sodium-ion batteries. The recent research progress of graphene-based nanocomposites for SIBs is also summarized in this study based on the above categories, especially for nanocomposite fabricate methods, the structural characteristics of electrodes as well as the influence of graphene on the performance of the SIBs. In addition, the relevant mechanism is also within the scope of this discussion, such as synergistic effect of graphene with active substances, the insertion/deintercalation process of sodium ions in different kinds of nanocomposites, and electrochemical reaction mechanism in the energy storage. At the end of this study, a series of strategies are summarized to address the challenges of graphene-based nanocomposites and several critical research prospects of SIBs that provide insights for future investigations.

Recent Progress in Metal Nanowires for Flexible Energy Storage Devices

With the rapid evolution of wearable electronics, the demand for flexible energy storage devices is gradually increasing. At present, the commonly used energy storage devices in life are based on rigid frames, which may lead to failure or explosion when mechanical deformation occurs. The main reason for this phenomenon is the insufficient elastic limit of the metal foil current collector with a simple plane structure inside the electrodes. Obviously, the design and introduction of innovative structural materials in current collectors is the key point to solving this problem. Several recent studies have shown that metal nanowires can be used as novel current collector materials to fabricate flexible energy storage devices. Herein, we review the applications of metal nanowires in the field of flexible energy storage devices by selecting the three most representative metals (Au, Ag, and Cu). By the analysis of the various typical literature, the advantages and disadvantages of these three metal nanowires (Au, Ag, and Cu) are discussed respectively. Finally, we look forward to the development direction of one-dimensional (1D) metal nanowires in flexible energy storage devices and show the personal opinions with a reference value, hoping to provide the experience and ideas for related research in the future.

Functional Nanomaterial-Based Flexible Electronics

With the rapid development of society, the growing interest in flexible electronics has led to remarkable progress in recent advances in the manufacture of flexible electronics [...]

Nitrogen-doped graphene supported Ni as an efficient and stable catalyst for levulinic acid hydrogenation

Transforming levulinic acid (LA) toγ-valerolactone (GVL) is a significant route for converting biomass into valuable chemicals. The development of an efficient and robust heterogeneous catalyst for this reaction has aroused great interest. In this work, nitrogen-doped graphene (NG) supported nickel (Ni) based heterogeneous catalyst with excellent activities was successfully synthesized. The Ni/NG catalyst shows outstanding performance for hydrogenation of LA to GVL at a relatively low temperature of 140 °C, which is superior to most of reported heterogeneous catalysts. Further investigations indicate Ni nanoparticles are the active sites and the NG also plays an indispensable role. The catalytic performance is highly depended on the crystallinity, particles sizes and electronic structure of Ni in Ni/NG catalyst, which can be optimized by nitrogen doping. This work affords a new route for designing robust and excellent heterogeneous catalysts by doping method to optimize the support.

3D Continuously Porous Graphene for Energy Applications

Constructing bulk graphene materials with well-reserved 2D properties is essential for device and engineering applications of atomically thick graphene. In this article, the recent progress in the fabrications and applications of sterically continuous porous graphene with designable microstructures, chemistries, and properties for energy storage and conversion are reviewed. Both template-based and template-free methods have been developed to synthesize the 3D continuously porous graphene, which typically has the microstructure reminiscent of pseudo-periodic minimal surfaces. The 3D graphene can well preserve the properties of 2D graphene of being highly conductive, surface abundant, and mechanically robust, together with unique 2D electronic behaviors. Additionally, the bicontinuous porosity and large curvature offer new functionalities, such as rapid mass transport, ample open space, mechanical flexibility, and tunable electric/thermal conductivity. Particularly, the 3D curvature provides a new degree of freedom for tailoring the catalysis and transport properties of graphene. The 3D graphene with those extraordinary properties has shown great promises for a wide range of applications, especially for energy conversion and storage. This article overviews the recent advances made in addressing the challenges of developing 3D continuously porous graphene, the benefits and opportunities of the new materials for energy-related applications, and the remaining challenges that warrant future study.

NiO-Based Electronic Flexible Devices

Personal, portable, and wearable electronics have become items of extensive use in daily life. Their fabrication requires flexible electronic components with high storage capability or with continuous power supplies (such as solar cells). In addition, formerly rigid tools such as electrochromic windows find new utilizations if they are fabricated with flexible characteristics. Flexibility and performances are determined by the material composition and fabrication procedures. In this regard, low-cost, easy-to-handle materials and processes are an asset in the overall production processes and items fruition. In the present mini-review, the most recent approaches are described in the production of flexible electronic devices based on NiO as low-cost material enhancing the overall performances. In particular, flexible NiO-based all-solid-state supercapacitors, electrodes electrochromic devices, temperature devices, and ReRAM are discussed, thus showing the potential of NiO as material for future developments in opto-electronic devices.

Highly Stable Germanium Microparticle Anodes with a Hybrid Conductive Shell for High Volumetric and Fast Lithium Storage

The ability to realize a highly capacitive/conductive electrode is an essential factor in large-scale devices, requiring a high-power/energy density system. Germanium is a feasible candidate as an anode material of lithium-ion batteries to meet the demands. However, the application is constrained due to low charge conductivity and large volume change on cycles. Here, we design a hybrid conductive shell of multi-component titanium oxide on a germanium microstructure. The shell enables facile hybrid ionic/electronic conductivity for swift charge mobility in the germanium anode, revealed through computational calculation and consecutive measurement of electrochemical impedance spectroscopy. Furthermore, a well-constructed electrode features a high initial Coulombic efficiency (90.6%) and stable cycle life for 800 cycles (capacity retention of 90.4%) for a fast-charging system. The stress-resilient properties of dense microparticle facilitate to alleviate structural failure toward high volumetric (up to 1737 W h L^-1) and power density (767 W h L^-1 at 7280 W L^-1) of full cells, paired with highly loaded NCM811 in practical application.

Three-dimensional porous structured germanium anode materials for High-Performance Lithium-Ion Full-cell

Germanium (Ge) has a high specific capacity when used as an alloying anode in lithium ion batteries. Despite this, the large volume of expansion that occurs during charging and discharging...

Reductively disilylated N-heterocycles as versatile organosilicon reagents

The reductively disilylated N-heterocyclic systems 1,4-bis(trimethylsilyl)-1-aza-2,5-cyclohexadiene (1Si), 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (2Si) and its methyl derivatives (3Si and 4Si), and 1,1'-bis(trimethylsilyl)-4,4'-bipyridinylidene (5Si) are proficient organosilicon reagents owing to their low first vertical ionization potentials and the heterophilicity of the polarized N-Si bonds. These have prompted their reactivity as two-electron reductants or reductive silylations. These reactions benefit from the concomitant rearomatization of the N-heterocycles and liberation of trimethylsilyl halides or (Me₃Si)₂O, which are mostly volatile or easily removable byproducts. In this perspective, we have discussed the utilization of these reductively disilylated N-heterocyclic systems as versatile reagents in the salt-free reduction of transition metals (A) and main-group halides (B), in organic transformations (C) and in materials syntheses (D).

Graphene-Based Nanomaterials for Flexible and Stretchable Batteries

Recently, as flexible and wearable electronic devices have become widely popular, research on light weight and large-capacity batteries suitable for powering such devices has been actively conducted. In particular, graphene has attracted considerable attention from researchers in the battery field owing to its good mechanical properties and its applicability in various processes to fabricate electrodes for batteries. Graphene is classified into two types: flake-type, fabricated from graphite, and film-type, synthesized using chemical vapor deposition. The unique processes involved in these two types enable the fabrication of flexible and stretchable batteries with various shapes and functions. In this article, the recent progress in the development of flexible and stretchable batteries based on graphene, as well as its important technical issues are reviewed.

Atomically Thin Materials for Next-Generation Rechargeable Batteries

Atomically thin materials (ATMs) with thicknesses in the atomic scale (typically <5 nm) offer inherent advantages of large specific surface areas, proper crystal lattice distortion, abundant surface dangling bonds, and strong in-plane chemical bonds, making them ideal 2D platforms to construct high-performance electrode materials for rechargeable metal-ion batteries, metal-sulfur batteries, and metal-air batteries. This work reviews the synthesis and electronic property tuning of state-of-the-art ATMs, including graphene and graphene derivatives (GE/GO/rGO), graphitic carbon nitride (g-C₃N₄), phosphorene, covalent organic frameworks (COFs), layered transition metal dichalcogenides (TMDs), transition metal carbides, carbonitrides, and nitrides (MXenes), transition metal oxides (TMOs), and metal-organic frameworks (MOFs) for constructing next-generation high-energy-density and high-power-density rechargeable batteries to meet the needs of the rapid developments in portable electronics, electric vehicles, and smart electricity grids. We also present our viewpoints on future challenges and opportunities of constructing efficient ATMs for next-generation rechargeable batteries.

Commercialization-Driven Electrodes Design for Lithium Batteries: Basic Guidance, Opportunities, and Perspectives

Current lithium-ion battery technology is approaching the theoretical energy density limitation, which is challenged by the increasing requirements of ever-growing energy storage market of electric vehicles, hybrid electric vehicles, and portable electronic devices. Although great progresses are made on tailoring the electrode materials from methodology to mechanism to meet the practical demands, sluggish mass transport, and charge transfer dynamics are the main bottlenecks when increasing the areal/volumetric loading multiple times to commercial level. Thus, this review presents the state-of-the-art developments on rational design of the commercialization-driven electrodes for lithium batteries. First, the basic guidance and challenges (such as electrode mechanical instability, sluggish charge diffusion, deteriorated performance, and safety concerns) on constructing the industry-required high mass loading electrodes toward commercialization are discussed. Second, the corresponding design strategies on cathode/anode electrode materials with high mass loading are proposed to overcome these challenges without compromising energy density and cycling durability, including electrode architecture, integrated configuration, interface engineering, mechanical compression, and Li metal protection. Finally, the future trends and perspectives on commercialization-driven electrodes are offered. These design principles and potential strategies are also promising to be applied in other energy storage and conversion systems, such as supercapacitors, and other metal-ion batteries.

Bidirectional Planar Flexible Snake-Origami Batteries

With the rapid development of commercial flexible/wearable devices, flexible batteries have attracted great attention as optimal power sources. However, a combination of high energy density and excellent arbitrary deformation ability is still a critical challenge to satisfy practical applications. Inspired by rigid and soft features of chemical molecular structures, novel bidirectional flexible snake-origami lithium-ion batteries (LIBs) with both high energy density and favorable flexibility are designed and fabricated. The flexible snake-origami battery consists of rigid and soft segments, where the former is designed as the energy unit and the latter served as the deformation unit. With the unique features from such design, the as-fabricated battery with calculating all the components exhibits a record-setting energy density of 357 Wh L-1 (133 Wh kg-1 ), compared with the cell-scale flexible LIBs achieved from both academic and industry. Additionally, a design principle is established to verify the validity of utilizing rigid-soft-coupled structure for enduring various deformations, and the intrinsic relationship between battery structure, energy density, and flexibility can be confirmed. The results suggest that the design principle and performance of bidirectional flexible snake-origami batteries will provide a new reliable strategy for achieving high energy flexible batteries for wearable devices.

Conductive Polymer Nanocomposites for Stretchable Electronics: Material Selection, Design, and Applications

Stretchable electronics that can elongate elastically as well as flex are crucial to a wide range of emerging technologies, such as wearable medical devices, electronic skin, and soft robotics. Critical to stretchable electronics is their ability to withstand large mechanical strain without failure while retaining their electrical conduction properties, a feat significantly beyond traditional metals and silicon-based semiconductors. Herein, we present a review of the recent advances in stretchable conductive polymer nanocomposites with exceptional stretchability and electrical properties, which have the potential to transform a wide range of applications, including wearable sensors for biophysical signals, stretchable conductors and electrodes, and deformable energy-harvesting and -storage devices. Critical to achieving these stretching properties are the judicious selection and hybridization of nanomaterials, novel microstructure designs, and facile fabrication processes, which are the focus of this Review. To highlight the potentials of conductive nanocomposites, a summary of some recent important applications is presented, including COVID-19 remote monitoring, connected health, electronic skin for augmented intelligence, and soft robotics. Finally, perspectives on future challenges and new research opportunities are also presented and discussed.

Progress in Iron Oxides Based Nanostructures for Applications in Energy Storage

The demand for green and efficient energy storage devices in daily life is constantly rising, which is caused by the global environment and energy problems. Lithium-ion batteries (LIBs), an important kind of energy storage devices, are attracting much attention. Graphite is used as LIBs anode, however, its theoretical capacity is low, so it is necessary to develop LIBs anode with higher capacity. Application strategies and research progresses of novel iron oxides and their composites as LIBs anode in recent years are summarized in this review. Herein we enumerate several typical synthesis methods to obtain a variety of iron oxides based nanostructures, such as gas phase deposition, co-precipitation, electrochemical method, etc. For characterization of the iron oxides based nanostructures, especially the in-situ X-ray diffraction and ⁵⁷Fe Mössbauer spectroscopy are elaborated. Furthermore, the electrochemical applications of iron oxides based nanostructures and their composites are discussed and summarized.

Graphic Abstract

Black phosphorene/blue phosphorene van der Waals heterostructure: a potential anode material for lithium-ion batteries

Van der Waals (vdW) heterostructure-based electrodes have invoked tremendous research interest due to their intriguing properties and their capability to break the limitations of the restricted properties of single-material systems. Herein, based on first-principles approaches, we propose that the black phosphorene/blue phosphorene (BLK-P/BLE-P) vdW heterostructure can be a capable anode material for power-driving lithium-ion batteries (LIBs), as it exhibits a large theoretical capacity, together with a relatively strong binding strength compared with the individual BLK-P and BLE-P monolayers. Our calculation results show that the Li adatom prefers to intercalate into the interlayer of the BLK-P/BLE-P vdW heterostructure due to the synergistic interfacial effect, resulting in a high binding strength and a diffusivity comparable to the BLK-P and BLE-P monolayers. Subsequently, the theoretical specific capacity is found to be as high as 552.8 mA h g^-1, which can be attributed to the much higher storage capacity of Li adatoms in the BLK-P/BLE-P vdW heterostructure. Furthermore, electronic structure calculations reveal that a large amount of charge transfer assists in semiconductor to metallic transition upon lithiation, which would ensure good electrical conductivity. These simulations prove that the BLK-P/BLE-P heterostructure has great potential in LIBs and is essential for future battery design.

Controlling Void Space in Crumpled Graphene-Encapsulated Silicon Anodes using Sacrificial Polystyrene Nanoparticles

Silicon anodes have a theoretical capacity of 3590 mAh g^-1 (for Li₁₅ Si₄ , at room temperature), which is tenfold higher than the graphite anodes used in current Li-ion batteries. This, and silicon's natural abundance, makes it one of the most promising materials for next-generation batteries. Encapsulating silicon nanoparticles (Si NPs) in a crumpled graphene shell by spray drying or spray pyrolysis are promising and scalable methods to produce core-shell structures, which buffer the extreme volume change (>300 vol %) caused by (de)lithiaton of silicon. However, capillary forces cause the graphene-based materials to tightly wrap around Si NP clusters, and there is little control over the void space required to further improve cycle life. Herein, a simple strategy is developed to engineer void-space within the core by incorporating varying amounts of similarly sized polystyrene (PS) nanospheres in the spray drier feed mixture. The PS completely decomposes during thermal reduction of the graphene oxide shell and results in Si cores of varying porosity. The best performance is achieved at a 1 : 1 ratio (PS/Si), leading to high capacities of 1638, 1468, and 1179 mAh g^-1 _Si+rGO at 0.1, 1, and 4 A g^-1 , respectively. Moreover, at 1 A g^-1 , the capacity retention is 80.6 % after 200 cycles. At a practical active material loading of 2.4 mg cm^-2 , the electrodes achieve an areal capacity of 2.26 mAh cm^-2 at 1 A g^-1 .

Encapsulate α-MnO2 nanofiber within graphene layer to tune surface electronic structure for efficient ozone decomposition

Major challenges encountered when developing manganese-based materials for ozone decomposition are related to the low stability and water inactivation. To solve these problems, a hierarchical structure consisted of graphene encapsulating α-MnO₂ nanofiber was developed. The optimized catalyst exhibited a stable ozone conversion efficiency of 80% and excellent stability over 100 h under a relative humidity (RH) of 20%. Even though the RH increased to 50%, the ozone conversion also reached 70%, well beyond the performance of α-MnO₂ nanofiber. Here, surface graphite carbon was activated by capturing the electron from inner unsaturated Mn atoms. The excellent stability originated from the moderate local work function, which compromised the reaction barriers in the adsorption of ozone molecule and the desorption of the intermediate oxygen species. The hydrophobic graphene shells hindered the chemisorption of water vapour, consequently enhanced its water resistance. This work offered insights for catalyst design and would promote the practical application of manganese-based catalysts in ozone decomposition.

Ozone is a major air pollutant, but its elimination is challenging. Here the authors encapsulate defective α-MnO₂ nanofiber within ultrathin graphene shells to construct a hierarchical MnO₂@graphene catalyst for ozone decomposition that possesses high activity and stability under humid conditions.

Surface and Interface Engineering of Nanoarrays toward Advanced Electrodes and Electrochemical Energy Storage Devices

The overall performance of electrochemical energy storage devices (EESDs) is intrinsically correlated with surfaces and interfaces. As a promising electrode architecture, 3D nanoarrays (3D-NAs) possess relatively ordered, continuous, and fully exposed active surfaces of individual nanostructures, facilitating mass and electron transport within the electrode and charge transfer across interfaces and providing an ideal platform for engineering. Herein, a critical overview of the surface and interface engineering of 3D-NAs, from electrode and interface designs to device integration, is presented. The general merits of 3D-NAs and surface/interface engineering principles of 3D-NA hybrid electrodes are highlighted. The focus is on the use of 3D-NAs as a superior platform to regulate the interface nature and unveiling new mechanism/materials without the interference of binders. The engineering and utilization of the surface of 3D-NAs to develop flexible/solid-state EESDs with 3D integrated electrode/electrolyte interfaces, or 3D triphase interfaces involving other active species, which are characteristic of (quasi-)solid-state electrolyte infiltration into the entire device, are also considered. Finally, the challenges and future directions of surface/interface engineering of 3D-NAs are outlined. In particular, potential strategies to obtain electrode charge balance, optimize the multiphase solid-state interface, and attain 3D solid electrolyte infiltration are proposed.

A Self-Healing Flexible Quasi-Solid Zinc-Ion Battery Using All-In-One Electrodes

Self-healing and flexibility are significant for many emerging applications of secondary batteries, which have attracted broad attention. Herein, a self-healing flexible quasi-solid Zn-ion battery composing of flexible all-in-one cathode (VS2 nanosheets growing on carbon cloth) and anode (electrochemically deposited Zn nanowires), and a self-healing hydrogel electrolyte, is presented. The free-standing all-in-one electrodes enable a high capacity and robust structure during flexible transformation of the battery, and the hydrogel electrolyte possesses a good self-healing performance. The presented battery remains as a high retention potential even after healing from being cut into six pieces. When bending at 60°, 90°, and 180°, the battery capacities remain 124, 125, and 114 mAh g-1, respectively, cycling at a current density of 50 mA g-1. Moreover, after cutting and healing twice, the battery still delivers a stable capacity, indicating a potential use of self-healing and wearable electronics.

A Stretchable, Self-Healable Triboelectric Nanogenerator as Electronic Skin for Energy Harvesting and Tactile Sensing

Electronic skin that is deformable, self-healable, and self-powered has high competitiveness for next-generation energy/sense/robotic applications. Herein, we fabricated a stretchable, self-healable triboelectric nanogenerator (SH-TENG) as electronic skin for energy harvesting and tactile sensing. The elongation of SH-TENG can achieve 800% (uniaxial strain) and the SH-TENG can self-heal within 2.5 min. The SH-TENG is based on the single-electrode mode, which is constructed from ion hydrogels with an area of 2 cm × 3 cm, the output of short-circuit transferred charge (Qsc), open-circuit voltage (Voc), and short-circuit current (Isc) reaches ~6 nC, ~22 V, and ~400 nA, and the corresponding output power density is ~2.9 μW × cm⁻² when the matching resistance was ~140 MΩ. As a biomechanical energy harvesting device, the SH-TENG also can drive red light-emitting diodes (LEDs) bulbs. Meanwhile, SH-TENG has shown good sensitivity to low-frequency human touch and can be used as an artificial electronic skin for touch/pressure sensing. This work provides a suitable candidate for the material selection of the hydrogel-based self-powered electronic skin.

All carbon hybrid N-doped carbon dots/carbon nanotube structures as an efficient catalyst for the oxygen reduction reaction

This paper reports the facile and scalable synthesis of hybrid N-doped carbon quantum dots/multi-walled carbon nanotube (CD/CNT) composites, which are efficient alternative catalysts for the oxygen reduction reaction (ORR) in fuel cells. The N-doped CDs for large-scale production were obtained within 5 minutes via a one-step polyol process using ethylenediamine (ED) in the presence of hydrogen peroxide as an oxidizing agent. For comparison, different CDs were also prepared using ethylene glycol (EG) and ethanolamine (EA) in the same manner. Physicochemical characterization suggested the successful formation of a CD(ED)/CNT hybrid without individual CD(ED)s and CNTs. The N-doped CD(ED)/CNT catalyst exhibited excellent electrocatalytic activity in an alkaline solution compared to other composites (CD(EG)/CNT and CD(EA)/CNT). The Tafel slope (−60.9 mV dec⁻¹) and durability (∼9.1% decay over 10 h) for CD(ED)/CNT were superior to high-performance Pt/C catalysts. The electrochemical double-layer capacitance on the CD(ED)/CNT hybrid showed apparent improvement of the active surface area because of N-doping and highly decorated CDs on the CNT wall. These results provide an innovative approach for the potential application of all carbon hybrid structures in electrocatalysis.

The ORR measurements showed that the CD(ED)/CNT catalyst was superior to CD(EG)/CNT and CD(EA)/CNT. They even surpassed the activity of commercial Pt/C in terms of durability, Tafel slope, and MeOH tolerance.

Stable Li-ion storage in Ge/N-doped carbon microsphere anodes

The development of environmentally benign, low-cost and high-performance Ge-based materials for lithium-ion batteries (LIBs) has remained a great challenge. Herein, the synthesis of Ge/N-doped carbon microspheres (Ge/NC) is firstly performed using N-(2hydroxyethyl)ethylenediamine (AEEA) and ethanediamine (EDA) as solvents, ligands and carbon sources. The three-dimensional Ge/NC microspheres prepared with AEEA (Ge/NC-A) are constructed from nanosheets with a thickness of about 20 nm. Such a hierarchically structured material not only allowed sufficient contact between the nanosheets and electrolyte, but also provided sufficient void space and uniform conductive sites. At the same time, N-doped carbon in the Ge/NC-A microspheres can greatly improve the electrical conductivity and the structural stability. This material exhibited a superior rate performance (633.1 mA h g-1 at 20 A g-1), favorable reversible capacity (1113.2 mA h g-1 at 0.2 A g-1) and good cycling stability (a high reversible capacity of 965.0 mA h g-1 after 1000 cycles) when examined as an anode for LIBs. A full cell was fabricated using Ge/NC-A as an anode and LiFePO4 as a cathode and delivered a capacity of 100.7 mA h g-1 after 100 cycles. Furthermore, the lithiation/delithiation mechanisms in the Ge/NC-A microspheres were revealed by in situ Raman and in situ XRD measurements, indicating that the crystalline Ge was firstly converted into amorphous Li-Ge phases and transformed into amorphous Ge during the discharge/charge process. Therefore, the repeated transition between the amorphous and crystalline phases can be avoided, thus improving the cycling stability.

Coaxial spinning fabricated high nitrogen-doped porous carbon walnut anchored on carbon fibers as anodic material with boosted lithium storage performance

Commercial graphite with low theoretical capacity cannot meet the ever-increasing requirement demands of lithium-ion batteries (LIBs) caused by the rapid development of electric devices. Rationally designed carbon-based nanomaterials can provide a wide range of possibilities to meet the growing requirements of energy storage. Hence, the porous walnut anchored on carbon fibers with reasonable pore structure, N-self doping (10.2 at%) and novel structure and morphology is designed via interaction of inner layer polyethylene oxide and outer layer polyacrylonitrile and polyvinylpyrrolidone during pyrolysis of the obtained precursor, which is fabricated by coaxial electrospinning. As an electrode material, the as-made sample shows a high discharge capacity of 965.3 mA h g^-1 at 0.2 A g^-1 in the first cycle, retains a capacity of 819.7 mA h g^-1 after 500 cycles, and displays excellent cycling stability (475.2 mA h g^-1 at 1 A g^-1 after 1000 cycles). Moreover, the capacity of the electrode material still keeps 260.5 mA h g^-1 at 5 A g^-1 after 1000 cycles. Therefore, the obtained sample has a bright application prospect as a high performance anode material for LIBs. Besides, this design idea paves the way for situ N-enriched carbon material with novel structure and morphology by coaxial electrospinning.

Advanced Boiling-A Scalable Strategy for Self-Assembled Three-Dimensional Graphene

Currently, researchers are paying much attention to the development of effective 3D graphene for applications in energy storage and environmental purification. Before commercialization, however, it is necessary to develop a method that allows for the large-scale production of such materials and enables good control over their structural and chemical properties. With this objective, we herein developed a simple method for the formation of large-scale (4 in. wafer) 3D graphene networks via the self-assembly of graphene sheets at a superheated liquid-vapor interface. The structural morphology of this porous network could be modified by controlling the vaporization rate, surface temperature of the target substrate, and amount of discharged colloids. The key mechanism behind this intriguing result was investigated by high-speed visualization of microdroplet behavior and extensive thermal analysis. This self-assembled 3D graphene had excellent electrical and mechanical properties. Our approach can be directly used for the mass production of graphene-based materials.

Review on carbonaceous materials and metal composites in deformable electrodes for flexible lithium-ion batteries

With the rapid propagation of flexible electronic devices, flexible lithium-ion batteries (FLIBs) are emerging as the most promising energy supplier among all of the energy storage devices owing to their high energy and power densities with good cycling stability. As a key component of FLIBs, to date, researchers have tried to develop newly designed high-performance electrochemically and mechanically stable pliable electrodes. To synthesize better quality flexible electrodes, based on high conductivity and mechanical strength of carbonaceous materials and metals, several research studies have been conducted. Despite both materials-based electrodes demonstrating excellent electrochemical and mechanical performances in the laboratory experimental process, they cannot meet the expected demands of stable flexible electrodes with high energy density. After all, various significant issues associated with them need to be overcome, for instance, poor electrochemical performance, the rapid decay of the electrode architecture during deformation, and complicated as well as costly production processes thus limiting their expansive applications. Herein, the recent progression in the exploration of carbonaceous materials and metals based flexible electrode materials are summarized and discussed, with special focus on determining their relative electrochemical performance and structural stability based on recent advancement. Major factors for the future advancement of FLIBs in this field are also discussed.

Fast conversion of lithium (poly)sulfides in lithium–sulfur batteries using three-dimensional porous carbon

A three-dimensional porous carbon was prepared as a sulfur host. It effectively restrains dissolution of polysulfides by improving the conversion kinetics between polysulfides, thereby enhancing the electrochemical cycling stability.

Engineering flexible carbon nanofiber concatenated MOF-derived hollow octahedral CoFe2O4 as an anode material for enhanced lithium storage

We constructed a necklace-like structure consisting of hollow CoFe₂O₄ octahedral nanoparticles encapsulated in N-doped carbon nanofibers (CoFe₂O₄@CNFs), which deliver an excellent electrochemical performance as free-standing anodes for LIBs.