Solvated Graphene Frameworks as High-Performance Anodes for Lithium-Ion Batteries

Covalent Organic Frameworks: Their Composites and Derivatives for Rechargeable Metal-Ion Batteries

Covalent organic frameworks (COFs) have attracted considerable interest in the field of rechargeable batteries owing to their three-dimensional (3D) varied pore sizes, inerratic porous structures, abundant redox-active sites, and customizable structure-adjustable frameworks. In the context of metal-ion batteries, these materials play a vital role in electrode materials, effectively addressing critical issues such as low ionic conductivity, limited specific capacity, and unstable structural integrity. However, the electrochemical characteristics of the developed COFs still fall short of practical battery requirements due to inherent issues such as low electronic conductivity, the tradeoff between capacity and redox potential, and unfavorable micromorphology. This review provides a comprehensive overview of the recent advancements in the application of COFs, COF-based composites, and their derivatives in rechargeable metal-ion batteries, including lithium-ion, lithium-sulfur, sodium-ion, sodium-sulfur, potassium-ion, zinc-ion, and other multivalent metal-ion batteries. The operational mechanisms of COFs, COF-based composites, and their derivatives in rechargeable batteries are elucidated, along with the strategies implemented to enhance the electrochemical properties and broaden the range of their applications.

NbO2 a Highly Stable, Ultrafast Anode Material for Li- and Na-Ion Batteries

Anode materials with fast charging capabilities and stability are critical for realizing next-generation Li-ion batteries (LIBs) and Na-ion batteries (SIBs). The present work employs a simple synthetic strategy to obtain NbO2 and studies its applications as an anode for LIB and SIB. In the case of the LIB, it exhibited a specific capacity of 344 mAh g-1 at 100 mA g-1. It also demonstrated remarkable stability over 1000 cycles, with 92% capacity retention. Additionally, it showed a unique fast charging capability, which takes 30 s to reach a specific capacity of 83 mAh g-1. For the SIB, NbO2 exhibited a specific capacity of 244 mAh g-1 at 50 mA g-1 and showed 70% capacity retention after 500 cycles. Furthermore, detailed density functional theory reveals that various factors like bulk and surface charging processes, lower ion diffusion energy barriers, and superior electronic conductivity of NbO2 are responsible for the observed battery performances.

Amorphous Vanadium Oxide Nanosheets with Alterable Polyhedron Configuration for Fast-Charging Lithium-Ion Batteries

Transition metal oxides with high theoretical capacities are promising anode materials for lithium-ion batteries (LIBs). However, the sluggish reaction kinetics remain a bottleneck for fast-charging applications due to its slow Li+ migration rate. Herein, a strategy is reported of significantly reducing the Li+ diffusion barrier of amorphous vanadium oxide by constructing a specific ratio of the VO local polyhedron configuration in amorphous nanosheets. The optimized amorphous vanadium oxide nanosheets with a ratio ≈1:4 for octahedron sites (Oh ) to pyramidal sites (C4v ) revealed by Raman spectroscopy and X-ray absorption spectroscopy (XAS) demonstrate the highest rate capability (356.7 mA h g-1 at 10.0 A g-1 ) and long-term cycling life (455.6 mA h g-1 at 2.0 A g-1 over 1200 cycles). Density functional theory (DFT)calculations further verify that the local structure (Oh :C4v = 1:4) intrinsically changes the degree of orbital hybridization between V and O atoms and contributes to a higher intensity of electron occupied states near the Fermi level, thus resulting in a low Li+ diffusion barrier for favorable Li+ transport kinetics. Moreover, the amorphous vanadium oxide nanosheets possess a reversible VO vibration mode and volume expansion rate close to 0.3%, as determined through in situ Raman and in situ transmission electron microscopy.

Realizing Highly-Ordered Laser-Reduced Graphene for High-Performance Flexible Microsupercapacitor

Laser reduction of graphene oxide (GO) with direct-write technology is promising to develop miniaturized energy storage devices because of highly flexible, mask-free, and chemical-free merits. However, laser reduction of GO is often accompanied with deflagration (spectacular and violent deoxygenating reaction), leading reduced graphene oxide (rGO) films into brittle and irregular internal structure which is harmful to the applications. Here, a pre-reduction strategy is demonstrated to avoid this deflagration and realize a uniform laser-reduced GO (LrGO) matrix for the application of flexible micro-supercapacitors (MSCs).The pre-reduction process with ascorbic acid decreases the content of oxygen-containing functional groups on GO in advance, and thus relieves gases emission and avoids unconstrained expansion during the laser reduction process. In addition, a self-assembled skeleton with pre-reduced GO (PGO) nanosheets could be constructed which is a more appropriate aforehand framework for laser reduction to establish controllable rGO films with the homogenous porosity. The quasi-solid-state MSCs assembled with laser-reduced PGO exhibit the maximum areal capacitance of 88.32 mF cm-2 , good cycling performance (capacitance retention of 82% after 2000 cycles), and outstanding flexibility (no capacitance degradation after bending for 5000 times). This finding provides opportunities to enhance quality of LrGO which is promising for micro-power devices and beyond.

On the Road to the Frontiers of Lithium-Ion Batteries: A Review and Outlook of Graphene Anodes

Graphene has long been recognized as a potential anode for next-generation lithium-ion batteries (LIBs). The past decade has witnessed the rapid advancement of graphene anodes, and considerable breakthroughs are achieved so far. In this review, the aim is to provide a research roadmap of graphene anodes toward practical LIBs. The Li storage mechanism of graphene is started with and then the approaches to improve its electrochemical performance are comprehensively summarized. First, morphologically engineered graphene anodes with porous, spheric, ribboned, defective and holey structures display improved capacity and rate performance owing to their highly accessible surface area, interconnected diffusion channels, and sufficient active sites. Surface-modified graphene anodes with less aggregation, fast electrons/ions transportation, and optimal solid electrolyte interphase are discussed, demonstrating the close connection between the surface structure and electrochemical activity of graphene. Second, graphene derivatives anodes prepared by heteroatom doping and covalent functionalization are outlined, which show great advantages in boosting the Li storage performances because of the additionally introduced defect/active sites for further Li accommodation. Furthermore, binder-free and free-standing graphene electrodes are presented, exhibiting great prospects for high-energy-density and flexible LIBs. Finally, the remaining challenges and future opportunities of practically available graphene anodes for advanced LIBs are highlighted.

Recent advances in epitaxial heterostructures for electrochemical applications

Construction of epitaxial heterostructures is crucial for boosting the electrochemical properties of various materials, however a review dedicated to this attractive topic is still lacking. In this Minireview, a timely summary on the achievements of epitaxial heterostructure design for electrochemical applications is provided. We first introduce the synthesis strategies to provide fundamental understanding on how to create epitaxial interfaces between different components. Secondly, the superiorities of epitaxial heterostructures in electrocatalysis, supercapacitors and batteries are highlighted with the underlying structure-property relationship elucidated. Finally, a discussion on the challenges and future prospects of this field is presented.

Synthesis and Electrochemical Performance of KVO/GO Composites as Anodes for Aqueous Rechargeable Lithium-Ion Batteries

K_0.25V₂O₅ (KVO) and K_0.25V₂O₅/graphene oxide (KVO/GO) have been successfully synthesized by a chemical coprecipitation method and a subsequent calcination process. The structure and morphology of KVO and KVO/GO were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The as-obtained vanadate and vanadate modified by GO materials were used as anodes with LiMn₂O₄ as a cathode and saturated LiNO₃ as an electrolyte to assemble an aqueous rechargeable lithium-ion battery (ARLB). The cyclic voltammogram curves of both KVO and KVO/GO electrodes exhibited three pairs of redox peaks corresponding to charge/discharge platforms. We found that a small amount of graphene oxide added improved the electrochemical performance more significantly than excess graphene oxide. The as-prepared KVO/GO//LiMn₂O₄ could not only improve the initial discharge capacity but could also reduce the attenuation at a high current density. Furthermore, the ARLB with a KVO/GO anode exhibited an excellent rate performance and super long cycle life. These good electrochemical properties of this new ARLB system actually provided feasibility for application in large-scale power sources and energy storage devices.

Multifunctional Cr Substitution Modulates Electrochemical Activity of Mn1-xCrxO for High-Performance Lithium-Ion Battery Anodes

Metal oxides are a promising candidate for lithium-ion battery (LIB) anodes due to their high theoretical capacity and long cycle life but also face inherent poor conductivity and volume variation, making them difficult to promote the application. The cation substitution strategy is an important means to facilitate improved rate and cycling performance. However, the effect of cation substitution on electrochemical activity is multivariate and complex, and a comprehensive and systematic analysis is essential for understanding the relationship between components and properties. Herein, the aliovalent heterogeneous Cr-substituted MnO was used as a model to systematically investigate the effects of Cr substitution on the crystal structure, electron distribution, defect construction, and electrochemical reaction processes. Theoretical calculations and experimental results reveal that Cr substitution can effectively modulate the electronic structure, build a built-in electric field, generate cationic defects, and catalyze the electrochemical reaction process, thereby improving the electrode kinetics and electrochemical activity of active materials. When the optimized Mn_0.94Cr_0.06O was used as the anode for LIBs, a reversible capacity of 1547.3 mAh g^-1 was obtained after 450 cycles at a current density of 1 C (1 C = 756 mA g^-1 for half-cells), and a reversible capacity of up to 1126.2 mAh g^-1 could be maintained even after 700 cycles at a current density of 2 C. The assembled Mn_0.94Cr_0.06O//LiCoO₂ full cell further confirms the scalability of the heterogeneous atom substitution strategy.

Reduced graphene oxide (rGO) supported and p yrolytic carbon (PC) coated γ-Fe2O3/PC-rGO composite anode material with enhanced Li-storage performance

As a high-capacity anode material for lithium ion batteries, γ-Fe 2 O 3 is a promising alternative to conventional graphite among multifarious transition metal oxides owing to its high theoretical specific capacity (1007 mAh g -1 ), abundant reserves, good safety and low cost. However, improving the electrical conductivity and overcoming the morphological damage caused by the severe volume expansion during cycling are still the tricky problems to be solved. Herein, a three-dimensional heterostructure composite (γ-Fe 2 O 3 /PC-rGO 60 ) was prepared by a facile solvothermal reaction followed by heat treatment in inert atmosphere. This composite material exhibits a reversible charge specific capacity of 1035 mAh g -1 at the current density of 0.1 A g -1 . After 100 cycles at 0.2 A g -1 , the capacity is increased from 966.2 to 1091.1 mAhg -1 . Even cycled for 200 cycles at 1 A g -1 , the capacity is only decreased from 751.4 to 670.6 mAh g -1 , giving capacity retention of 89.3%. The rGO network supported flexible composite architecture is beneficial for accommodating the volume expansion of the γ-Fe 2 O 3 active material during the lithiation/delithiation process. Besides, the conductive rGO network and the in-situ formed pyrolytic carbon (PC) can provide a smooth electron transmission path and a favorable lithium ion transport channel.

Interfacial Hydrothermal Assembly of Three-Dimensional Lamellar Reduced Graphene Oxide Aerogel Membranes for Water Self-Purification

Energy-saving membrane separation for water purification is increasingly desired, which requires appropriate nanofiltration membranes enabling to reject undesired solutes efficiently and allows high permeation of water. Herein, we report the fabrication of three-dimensional lamellar reduced graphene oxide (rGO) hydrogel membranes with a one-step, environment-friendly and water/vapor interfacial hydrothermal assembly process and the corresponding aerogel membranes by the freeze-drying method. The structures of the aerogel membranes can be tuned from lamellar to porously interconnected morphologies by controlling the volume of GO suspensions during the hydrothermal process. The rGO aerogel membrane was extremely flexible, which can be bent in liquid nitrogen and boiling water without any deformation, and highly stable in various solvents for at least 2 months. When used as nanofiltration membranes, the rGO aerogel membranes showed ∼100% rejection of organic dyes and a moderate water flux (up to 53 L m^-2 h^-1) only under the gravity of organic dye aqueous solutions of a 30 cm height. This water self-purification property of our flexible and stable aerogel membranes without extra energy consumption provides a possibility to make cheap, portable water purification devices for utilization in emergency and home-used water purification systems in the areas with electricity unavailable or inconvenient.

Smart fibers for energy conversion and storage

Fibers have played a critical role in the long history of human development. They are the basic building blocks of textiles. Synthetic fibers not only make clothes stronger and more durable, but are also customizable and cheaper. The growth of miniature and wearable electronics has promoted the development of smart and multifunctional fibers. Particularly, the incorporation of functional semiconductors and electroactive materials in fibers has opened up the field of fiber electronics. The energy supply system is the key branch for fiber electronics. Herein, after a brief introduction on the history of smart and functional fibers, we review the current state of advanced functional fibers for their application in energy conversion and storage, focusing on nanogenerators, solar cells, supercapacitors and batteries. Subsequently, the importance of the integration of fiber-shaped energy conversion and storage devices via smart structure design is discussed. Finally, the challenges and future direction in this field are highlighted. Through this review, we hope to inspire scientists with different research backgrounds to enter this multi-disciplinary field to promote its prosperity and development and usher in a truly new era of smart fibers.

Phosphorus-doping-induced kinetics modulation for nitrogen-doped carbon mesoporous nanotubes as superior alkali metal anode beyond lithium for high-energy potassium-ion hybrid capacitors

Alkali metal ion beyond lithium based energy storage systems have recently attracted increasing attention due to their unique advantages of high natural abundance and low cost. Herein, we report the fabrication of P,N-codoped carbon mesoporous nanotubes (denoted as PNC-MeNTs) through a facile two-step strategy with MnO₂ nanowires as a dual-function sacrificing template, where the in situ oxidative polymerization formation of pyrrole-aniline-phytic acid composite nanotubes and a subsequent carbonization treatment are involved. The PNC-MeNTs exhibit outstanding electrochemical performance for both Na⁺ and K⁺ storage, respectively, where high specific capacities of 287.2 mA h g^-1 and 219.6 mA h g^-1 at 0.1 A g^-1 and remarkable cycling stability over 10 000 cycles at 10 A g^-1 and 3000 cycles at 1 A g^-1 can be achieved. More importantly, potassium-ion hybrid capacitors with a PNC-MeNT anode and an activated carbon cathode can deliver remarkable energy/power density of 175.1 W h kg^-1/160.6 W kg^-1, as well as a long cycling life. The possible origins and storage mechanisms are investigated with combined characterization methods including in situ Raman spectroscopy and a galvanostatic intermittent titration technique. This study may introduce a new avenue for designing carbonaceous electrode candidates for future high-performance energy storage devices.

Graphene Matrix Sheathed Metal Vanadate Porous Nanospheres for Enhanced Longevity and High-Rate Energy Storage Devices

Rational design of anode materials comprising rich benefits of high capacity, superior rate capability, and exalted lifetime is of considerable significance in the progress of high-performance Li-ion batteries (LIBs) and supercapatteries. Herein, highly porous cobalt vanadate (Co₂VO₄) nanospheres encapsulated with reduced graphene oxide (rGO) nanosheets (rGO@CoV PNSs) were prepared by a facile hydrothermal method and employed as a hybrid composite-based anode material for energy storage devices. The nanocavities and porous features of CoV nanospheres, and the laminated rGO nanosheets over CoV PNSs can significantly surpass the volume changes and enhance the surface electrokinetics, respectively. With benefits of rich redox activity and constructive traits, the rGO@CoV PNSs as an electrode material in LIBs exhibited superior reversible capacity of 780.6 mAh/g after 100 cycles with remarkable rate performance. Moreover, the hybrid composite displayed an excellent reversible capacity of 531.8 mAh/g even after 1000 cycles performed at 1000 mA/g. Utilizing the synergistic features, the rGO@CoV PNSs composite was also explored as a battery-type electrode for supercapatteries. The fabricated supercapattery device with rGO@CoV PNSs and rGO demonstrated good rate performance including superior areal energy (0.048 mWh/cm²) and power (9.96 mW/cm²) densities. Therefore, the graphene sheathed metal vanadates would be an ultrahigh rate electrode candidates for energy storage devices.

Insights into Lithium and Sodium Storage in Porous Carbon

The lithium and sodium storage behavior of porous carbon remains controversial, though it shows excellent cycling stability and rate performances. This Letter discloses the insertion, adsorption, and filling properties of porous carbon. ⁷Li nuclear magnetic resonance (NMR) spectroscopy recognized inserted and adsorbed lithium in this porous carbon but did not observe any other forms of lithium above 0.0 V vs. Li⁺/Li. In addition, although lithium insertion mainly takes place at low potentials, adsorption was found to be the main form of lithium storage throughout the investigated potential range. Such a storage feature is responsible for the excellent rate performance and high specific capacity of porous carbon. Raman spectroscopy further demonstrated the structural reversibility of the carbon in different potential ranges, verifying the necessity to optimize the potential range for a better cycling performance. These findings provide insights for the design and application of porous carbon.

2 D Materials for Electrochemical Energy Storage: Design, Preparation, and Application

Electrochemical energy storage is a promising route to relieve the increasing energy and environment crises, owing to its high efficiency and environmentally friendly nature. However, it is still challenging to realize its widespread application because of unsatisfactory electrode materials, with either high cost or poor activity and new electrode materials are urgently needed. Two-dimensional (2 D) materials are possible candidates, owing to their unique geometry and physicochemical properties. This Review summarizes the latest advances in the development of 2 D materials for electrochemical energy storage. Computational investigation and design of 2 D materials are first introduced, and then preparation methods are presented in detail. Next, the application of such materials in supercapacitors, alkali metal-ion batteries, and metal-air batteries are summarized comprehensively. Finally, the challenges and perspectives are discussed to offer a guideline for future exploration of high-efficiency 2 D materials for electrochemical energy storage.

Tin-graphene tubes as anodes for lithium-ion batteries with high volumetric and gravimetric energy densities

Limited by the size of microelectronics, as well as the space of electrical vehicles, there are tremendous demands for lithium-ion batteries with high volumetric energy densities. Current lithium-ion batteries, however, adopt graphite-based anodes with low tap density and gravimetric capacity, resulting in poor volumetric performance metric. Here, by encapsulating nanoparticles of metallic tin in mechanically robust graphene tubes, we show tin anodes with high volumetric and gravimetric capacities, high rate performance, and long cycling life. Pairing with a commercial cathode material LiNi_0.6Mn_0.2Co_0.2O₂, full cells exhibit a gravimetric and volumetric energy density of 590 W h Kg⁻¹ and 1,252 W h L⁻¹, respectively, the latter of which doubles that of the cell based on graphite anodes. This work provides an effective route towards lithium-ion batteries with high energy density for a broad range of applications.

Here the authors report a tin anode design by encapsulating tin nanoparticles in graphene tubes. The design exhibits high capacity, good rate performance and cycling stability. Pairing with NMC, the full cell delivers a volumetric energy density twice as high as that for the commercial cell.

Scalable Synthesis of One-Dimensional Mesoporous ZnMnO3 Nanorods with Ultra-Stable and High Rate Capability for Efficient Lithium Storage

The cost-efficient ZnMnO₃ has attracted increasing attention as a prospective anode candidate for advanced lithium-ion batteries (LIBs) owing to its resourceful abundance, large lithium storage capacity and low operating voltage. However, its practical application is still seriously limited by the modest cycling and rate performances. Herein, a facile design to scalable synthesize unique one-dimensional (1D) mesoporous ZnMnO₃ nanorods (ZMO-NRs) composed of nanoscale particles (≈11 nm) is reported. The 1D mesoporous structure and nanoscale building blocks of the ZMO-NRs effectively promote the transport of ions/electrons, accommodate severe volume changes, and expose more active sites for lithium storage. Benefiting from these appealing structural merits, the obtained ZMO-NRs anode exhibits excellent rate behavior (≈454 mAh g^-1 at 2 A g^-1 ) and ultra-long term cyclic performance (≈949.7 mAh g^-1 even over 500 cycles at 0.5 A g^-1 ) for efficient lithium storage. Additionally, the LiNi_0.8 Co_0.1 Mn_0.1 O₂ //ZMO-NRs full cell presents a practical energy density (≈192.2 Wh kg^-1 ) and impressive cyclability with approximately 91 % capacity retention over 110 cycles. This highlights that the ZMO-NRs product is a highly promising high-rate and stable electrode candidate towards advanced LIBs in electronic devices and sustainable energy storage applications.

Bio-derived Carbon Nanofibres from Lignin as High-Performance Li-Ion Anode Materials

Development of cost-effective and increasingly efficient sustainable materials for energy-storage devices, such Li-ion batteries, is of crucial future importance. Herein, the preparation of carbon nanofibres from biopolymer blends of lignin (byproduct from the paper and pulp industry) and polylactic acid (PLA) or a thermoplastic elastomeric polyurethane (TPU) is described. SEM analysis shows the evolving microstructural morphology after each processing step (electrospinning, stabilisation and carbonisation). Importantly, it is possible to tailor the nanofibre porosity by utilising miscibility/immiscibility rules between lignin and the polymer additive (PLA/TPU). PLA blends (immiscible) generate porous structures whereas miscible lignin/TPU blends are solid when carbonised. Electrodes produced from 50 % PLA blends have capacity values of 611 mAh g^-1 after 500 charge/discharge cycles, the highest reported to date for sustainable electrodes for Li-ion batteries. Thus, this work will promote the development of lignocellulose waste materials as high-performance energy-storage materials.

Which is the most effective pristine graphene electrode for energy storage devices: aerogel or xerogel?

The morphological design of graphene materials is definitely important since their electrochemical properties as an electrode in energy storage devices are mainly dominated by their charge accessibility and active area. In this work, we present a systematic investigation on the prospects of a pristine graphene aerogel and a pristine graphene xerogel as electrode materials for both supercapacitors and lithium-ion batteries. We confirm that the graphene aerogel has a significantly higher surface area, needed for effective charge storage, than the xerogel, which offers a clear advantage for supercapacitors. In terms of battery performance, the quality of the pristine graphene raw materials is a more critical factor than their shape owing to the lithium intercalation mechanism. As a result, the graphene aerogel supercapacitors exhibited a specific capacitance of about 700 F g-1 at 10 mV s-1 in 1 M LiPF6 electrolyte, which is 3.6 times higher than the values for the xerogel devices. On the other hand, the electrochemical battery performances of the graphene aerogel and xerogel show no significant difference considering their high specific capacity of about 380 mA h g-1 at 1C. Further, the surface control kinetics of the graphene aerogel are much more dominant in the supercapacitor and battery applications than those of the xerogel. This study provides more practical approaches in order to design electrodes using lightweight, high-performance, and low-cost materials for the effective use of energy storage systems.

Comment on "Hierarchically porous, ultra-strong reduced graphene oxide-cellulose nanocrystal sponges for exceptional adsorption of water contaminants" by N. Yousefi, K. K. W. Wong, Z. Hosseinidoust, H. O. Sørensen, S. Bruns, Y. Zheng and N. Tufenkji, Nanoscale, 2018, 10, 7171

The MB-spot test is extensively applied to specific surface area measurement due to its simplicity compared to the classical BET test. However, the MB-spot test is vulnerable to multiple factors, preventing this newly-prevalent technique from accurately characterising the specific surface area. The inaccuracy of the MB-spot test is discussed here at length, which is urgently needed to avoid mistakes and inconsistencies regarding specific surface area characterization for carbon-based materials.

High-quality mesoporous graphene particles as high-energy and fast-charging anodes for lithium-ion batteries

The application of graphene for electrochemical energy storage has received tremendous attention; however, challenges remain in synthesis and other aspects. Here we report the synthesis of high-quality, nitrogen-doped, mesoporous graphene particles through chemical vapor deposition with magnesium-oxide particles as the catalyst and template. Such particles possess excellent structural and electrochemical stability, electronic and ionic conductivity, enabling their use as high-performance anodes with high reversible capacity, outstanding rate performance (e.g., 1,138 mA h g-1 at 0.2 C or 440 mA h g-1 at 60 C with a mass loading of 1 mg cm-2), and excellent cycling stability (e.g., >99% capacity retention for 500 cycles at 2 C with a mass loading of 1 mg cm-2). Interestingly, thick electrodes could be fabricated with high areal capacity and current density (e.g., 6.1 mA h cm-2 at 0.9 mA cm-2), providing an intriguing class of materials for lithium-ion batteries with high energy and power performance.

Mechanochemical Synthesis of γ-Graphyne with Enhanced Lithium Storage Performance

γ-Graphyne is a new nanostructured carbon material with large theoretical Li⁺ storage due to its unique large conjugate rings, which makes it a potential anode for high-capacity lithium-ion batteries (LIBs). In this work, γ-graphyne-based high-capacity LIBs are demonstrated experimentally. γ-Graphyne is synthesized through mechanochemical and calcination processes by using CaC₂ and C₆ Br₆ . Brunauer-Emmett-Teller, atomic force microscopy, X-ray photoelectron spectroscopy, solid-state ¹³ C NMR and Raman spectra are conducted to confirm its morphology and chemical structure. The sample presents 2D mesoporous structure and is exactly composed of sp and sp² -hybridized carbon atoms as the γ-graphyne structure. The electrode shows high Li⁺ storage (1104.5 mAh g^-1 at 100 mA g^-1 ) and rate capability (435.1 mAh g^-1 at 5 A g^-1 ). The capacity retention can be up to 948.6 (200 mA g^-1 for 350 cycles) and 730.4 mAh g^-1 (1 A g^-1 for 600 cycles), respectively. These excellent electrochemical performances are ascribed to the mesoporous architecture, large conjugate rings, enlarged interplanar distance, and high structural integrity for fast Li⁺ diffusion and improved cycling stability in γ-graphyne. This work provides an environmentally benign and cost-effective mechanochemical method to synthesize γ-graphyne and demonstrates its superior Li⁺ storage experimentally.

Ultrathin Nitrogen-Doped Carbon Layer Uniformly Supported on Graphene Frameworks as Ultrahigh-Capacity Anode for Lithium-Ion Full Battery

The designable structure with 3D structure, ultrathin 2D nanosheets, and heteroatom doping are considered as highly promising routes to improve the electrochemical performance of carbon materials as anodes for lithium-ion batteries. However, it remains a significant challenge to efficiently integrate 3D interconnected porous frameworks with 2D tunable heteroatom-doped ultrathin carbon layers to further boost the performance. Herein, a novel nanostructure consisting of a uniform ultrathin N-doped carbon layer in situ coated on a 3D graphene framework (NC@GF) through solvothermal self-assembly/polymerization and pyrolysis is reported. The NC@GF with the nanosheets thickness of 4.0 nm and N content of 4.13 at% exhibits an ultrahigh reversible capacity of 2018 mA h g^-1 at 0.5 A g^-1 and an ultrafast charge-discharge feature with a remarkable capacity of 340 mA h g^-1 at an ultrahigh current density of 40 A g^-1 and a superlong cycle life with a capacity retention of 93% after 10 000 cycles at 40 A g^-1 . More importantly, when coupled with LiFePO₄ cathode, the fabricated lithium-ion full cells also exhibit high capacity and excellent rate and cycling performances, highlighting the practicability of this NC@GF.

Reduced graphene oxide doped predominantly with CF2 groups as a superior anode material for long-life lithium-ion batteries

A fluorine-doped reduced graphene oxide (F-rGO), doped predominantly with CF₂ groups, was synthesized through a solvothermal process, and applied as the anode material in a lithium-ion battery.

Ultralight Interconnected Graphene-Amorphous Carbon Hierarchical Foam with Mechanical Resiliency for High Sensitivity and Durable Strain Sensors

Ultralight graphene-amorphous carbon (AC) hierarchical foam (G-ACHF) was synthesized by chemical vapor deposition at 1065 °C, close to the melting point of copper. The high temperature leads to the hierarchical structure with an inner layer of graphene and an outer layer of AC. The inner graphene layer with high conductivity and integrity provides high sensitivity. The outer AC layer helps to enhance its durability and mechanical resiliency. The hierarchical structure recovers without damaging the structural integrity after a large strain of 90%. The electrical resistance of G-ACHF remains stable after 200 cycles of compression to a strain level of 50%. The fluctuation of the resistance value remains within ±3%, showing its stability in sensing performance. The pressure sensitivity of G-ACHF reaches as high as ∼11.47 Pa^-1. Finite element simulation reveals that the stress borne by the key position of G-ACHF is 47% lower than that of graphene foam without the AC layer, proving that the AC layer can disperse the stress effectively. With a very low density of 1.17 × 10^-3 g cm^-1, the reversibly compressible G-ACHF strain sensor material exhibits its promising application potential in lightweight and wearable devices.

Porous and Low-Crystalline Manganese Silicate Hollow Spheres Wired by Graphene Oxide for High-Performance Lithium and Sodium Storage

Herein, a graphene oxide (GO)-wired manganese silicate (MS) hollow sphere (MS/GO) composite is successfully synthesized. Such an architecture possesses multiple advantages in lithium and sodium storage. The hollow MS structure provides a sufficient free space for volume variation accommodation; the porous and low-crystalline features facilitate the diffusion of lithium ions; meanwhile, the flexible GO sheets enhance the electronic conductivity of the composite to a certain degree. When applied as the anode material for lithium-ion batteries (LIBs), the as-obtained MS/GO composite exhibits a high reversible capacity, ultrastable cyclability, and good rate performance. Particularly, the MS/GO composite delivers a high capacity of 699 mA h g^-1 even after 1000 cycles at 1 A g^-1. The sodium-storage performance of MS/GO has been studied for the first time, and it delivers a stable capacity of 268 mA h g^-1 after 300 cycles at 0.2 A g^-1. This study suggests that the rational design of metal silicates would render them promising anode materials for LIBs and SIBs.

Critical Insight into the Relentless Progression Toward Graphene and Graphene-Containing Materials for Lithium-Ion Battery Anodes

Used as a bare active material or component in hybrids, graphene has been the subject of numerous studies in recent years. Indeed, from the first report that appeared in late July 2008, almost 1600 papers were published as of the end 2015 that investigated the properties of graphene as an anode material for lithium-ion batteries. Although an impressive amount of data has been collected, a real advance in the field still seems to be missing. In this framework, attention is focused on the most prominent research efforts in this field with the aim of identifying the causes of such relentless progression through an insightful and critical evaluation of the lithium-ion storage performances (i.e., 1^st cycle irreversible capacity, specific gravimetric and volumetric capacities, average delithiation voltage profile, rate capability and stability upon cycling). The "graphene fever" has certainly provided a number of fundamental studies unveiling the electrochemical properties of this "wonder" material. However, analysis of the published literature also highlights a loss of focus from the final application. Hype-driven claims, not fully appropriate metrics, and negligence of key parameters are probably some of the factors still hindering the application of graphene in commercial batteries.

Flexible Micro-Supercapacitor Based on Graphene with 3D Structure

Flexible micro-supercapacitors (MSCs) are constructed by 3D graphene from chemical vapor deposition. Without using any binder or metal current collector, the as-prepared 3D graphene MSC exhibits good flexibility, excellent cyclic life, and high areal capacitance of 1.5 mF cm^-2 at a scan rate of 10 V s^-1 . The electrochemical performance is further improved by oxygen plasma functionalization.