Graphene wrapping as a protective clamping layer anchored to carbon nanofibers encapsulating Si nanoparticles for a Li-ion battery anode

Reduced graphene oxide-encaged submicron-silicon anode interfacially stabilized by Al2O3 nanoparticles for efficient lithium-ion batteries

Silicon-carbon composites have been recognized as some of the most promising anode candidates for advancing new-generation lithium-ion batteries (LIBs). The development of high-efficiency silicon/graphene anodes through a simple and cost-effective preparation route is significant. Herein, by using micron silicon as raw material, we designed a mesoporous composite of silicon/alumina/reduced graphene oxide (Si/Al2O3/RGO) via a two-step ball milling combined annealing process. Commercial Al2O3 nanoparticles are introduced as an interlayer due to the toughening effect, while RGO nanosheets serve as a conductive and elastic coating to protect active submicron silicon particles during lithium alloying/dealloying reactions. Owing to the rational porous structure and dual protection strategy, the core/shell structured Si/Al2O3/RGO composite is efficient for Li+ storage and demonstrates improved electrical conductivity, accelerated charge transfer and electrolyte diffusion, and especially high structural stability upon charge/discharge cycling. As a consequence, Si/Al2O3/RGO yields a high discharge capacity of 852 mA h g-1 under a current density of 500 mA g-1 even after 200 cycles, exhibiting a high capacity retention of ∼85%. Besides, Si/Al2O3/RGO achieves excellent cycling reversibility and superb high-rate capability with a stable specific capacity of 405 mA h g-1 at 3000 mA g-1. Results demonstrate that the Al2O3 interlayer is synergistic with the indispensable RGO nanosheet shells, affording more buffer space for silicon cores to alleviate the mechanical expansion and thus stabilizing active silicon species during charge/discharge cycles. This work provides an alternative low-cost approach to achieving high-capacity silicon/carbon composites for high-performance LIBs.

Graphene Wrapping of Electrospun Nanofibers for Enhanced Electrochemical Sensing

This paper presents a scalable method of developing ultrasensitive electrochemical biosensors. This is achieved by maximizing sensor conductivity through graphene wrapping of carbonized electrospun nanofibers. The effectiveness of the graphene wrap was determined visually by scanning electron microscopy and chemically by Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray diffraction. The sensing performance of different electrode samples was electrochemically characterized using cyclic voltammetry and electrochemical impedance spectroscopy, with the graphene-wrapped carbonized nanofiber electrode showing significantly improved performance. The graphene-wrapped carbonized nanofibers exhibited a relative conductivity of ∼14 times and an electroactive surface area of ∼2 times greater compared to the bare screen-printed carbon electrode despite experiencing inhibitive effects from the carbon glue used to bind the samples to the electrode. The results indicate potential for a highly conductive, inert sensing platform.

Simultaneous Encapsulation of Nano-Si in Redox Assembled rGO Film as Binder-Free Anode for Flexible/Bendable Lithium-Ion Batteries

The emerging ubiquitous flexible/wearable electronics are in high demand for compatible flexible/high-energy rechargeable batteries, which set a collaborative goal to promote the electrochemical performance and the mechanical strength of the fundamental flexible electrodes involved. Herein, freestanding flexible electrode of Si/graphene films is proposed, which is fabricated through a scalable, zinc-driven redox layer-by-layer assembly process. In the hybrid films, silicon nanoparticles are intimately encapsulated and confined in multilayered reduced graphene oxide (rGO) nanosheet films. The designed monolithic rGO/Si film possesses several structural benefits such as high mechanical integrity and three-dimensional conductive framework for accessible charge transport and Li⁺ diffusion upon cycling. When adopted as binder-free electrode in half-cells, the optimized hybrid rGO/Si film delivers high gravimetric capacity (981 mA h g^-1 at 200 mA g^-1 with respect to the total weight of the electrode) and exceptional cycling stability (0.057% decay per cycle over 1000 cycles at 1000 mA g^-1). Besides, the binder-free rGO/Si film anode is further combined with a commercial LiCoO₂ foil cathode for completely flexible full cell/battery, which exhibits excellent cycling performance and a high capacity retention of over 95% after 30 cycles under continuous bending. This solution-processable, elaborately engineered, and robust Si/graphene films will further harness the potential of silicon-carbon composites for advanced flexible/wearable energy storage.

Improved Ionic Diffusion through the Mesoporous Carbon Skin on Silicon Nanoparticles Embedded in Carbon for Ultrafast Lithium Storage

Because of their combined effects of outstanding mechanical stability, high electrical conductivity, and high theoretical capacity, silicon (Si) nanoparticles embedded in carbon are a promising candidate as electrode material for practical utilization in Li-ion batteries (LIBs) to replace the conventional graphite. However, because of the poor ionic diffusion of electrode materials, the low-grade ultrafast cycling performance at high current densities remains a considerable challenge. In the present study, seeking to improve the ionic diffusion, we propose a novel design of mesoporous carbon skin on the Si nanoparticles embedded in carbon by hydrothermal reaction, poly(methyl methacrylate) coating process, and carbonization. The resultant electrode offers a high specific discharge capacity with excellent cycling stability (1140 mA h g^-1 at 100 mA g^-1 after 100 cycles), superb high-rate performance (969 mA h g^-1 at 2000 mA g^-1), and outstanding ultrafast cycling stability (532 mA h g^-1 at 2000 mA g^-1 after 500 cycles). The battery performances are surpassing the previously reported results for carbon and Si composite-based electrodes on LIBs. Therefore, this novel approach provides multiple benefits in terms of the effective accommodation of large volume expansions of the Si nanoparticles, a shorter Li-ion diffusion pathway, and stable electrochemical conditions from a faster ionic diffusion during cycling.

Reducing the barrier effect of graphene sheets on a Ag cocatalyst to further improve the photocatalytic performance of TiO2

By avoiding the possible barrier influence of graphene on other cocatalysts, the photocatalytic properties of the composites containing multi-cocatalysts could be further improved.

Carbon fibers as three-dimensional current collectors for silicon/reduced graphene oxide lithium ion battery anodes with improved rate performance and cycle life

Carbon fibers as 3D current collectors for Si/r-GO lithium ion battery anodes with improved rate performance were achieved.

Surface Decoration of Pt Nanoparticles via ALD with TiO2 Protective Layer on Polymeric Nanofibers as Flexible and Reusable Heterogeneous Nanocatalysts

Coupling the functional nanoheterostructures over the flexible polymeric nanofibrous membranes through electrospinning followed by the atomic layer deposition (ALD), here we presented a high surface area platform as flexible and reusable heterogeneous nanocatalysts. Here, we show the ALD of titanium dioxide (TiO₂) protective nanolayer onto the electrospun polyacrylonitrile (PAN) nanofibrous web and then platinum nanoparticles (Pt-NP) decoration was performed by ALD onto TiO₂ coated PAN nanofibers. The free-standing and flexible Pt-NP/TiO₂-PAN nanofibrous web showed the enhancive reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) within 45 seconds though the hydrogenation process with the degradation rate of 0.1102 s⁻¹. The TiO₂ protective layer on the PAN polymeric nanofibers was presented as an effective route to enhance the attachment of Pt-NP and to improve the structure stability of polymeric nanofibrous substrate. Commendable enhancement in the catalytic activity with the catalytic dosage and the durability after the reusing cycles were investigated over the reduction of 4-NP. Even after multiple usage, the Pt-NP/TiO₂-PAN nanofibrous webs were stable with the flexible nature with the presence of Pt and TiO₂ on its surface.

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

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

Novel Fe3O4@GNF@SiO2 nanocapsules fabricated through the combination of an in situ formation method and SiO2 coating process for magnetic resonance imaging

An in situ approach for the synthesis of Fe₃O₄ nanoparticles combined with a SiO₂ coating process was employed to prepare Fe₃O₄@GNF@SiO₂ nanocapsules.

Flexible hierarchical membranes of WS2 nanosheets grown on graphene-wrapped electrospun carbon nanofibers as advanced anodes for highly reversible lithium storage

It is still very challenging to achieve effective combination of carbon nanofibers and graphene sheets. In this study, a novel and facile method is developed to prepare flexible graphene/carbon nanofiber (GCNF) membranes with every carbon nanofiber wrapped by conductive graphene sheets, resulting in a remarkable improvement of their electrical conductivity. This method only entails a moderate process of soaking the pre-oxidized electrospun polyacrylonitrile (oPAN) nanofiber membranes in graphene oxide (GO) aqueous dispersion, and subsequent carbonization of the GO/oPAN hybrid membranes. By using the highly conductive GCNF membrane as a template, hierarchical WS₂/GCNF hybrid membranes with few-layer WS₂ nanosheets uniformly grown on GCNF nanofibers were fabricated as high-performance anodes for lithium ion batteries. Benefiting from the synergistic effects of GCNF nanofibers and WS₂ nanosheets, the resulting WS₂/GCNF hybrid membranes possessed a porous structure, large specific surface area, high electrical conductivity and good structural integrity, which are favorable for the rapid diffusion of lithium ions, fast transfer of electrons and overall electrochemical stability. As a result, the optimized WS₂/GCNF hybrid membrane exhibited a high initial charge capacity of 1128.2 mA h g^-1 at a current density of 0.1 A g^-1 and outstanding cycling stability with 95% capacity retention after 100 cycles.

Heterogeneous WSx/WO₃ Thorn-Bush Nanofiber Electrodes for Sodium-Ion Batteries

Heterogeneous electrode materials with hierarchical architectures promise to enable considerable improvement in future energy storage devices. In this study, we report on a tailored synthetic strategy used to create heterogeneous tungsten sulfide/oxide core-shell nanofiber materials with vertically and randomly aligned thorn-bush features, and we evaluate them as potential anode materials for high-performance Na-ion batteries. The WSx (2 ≤ x ≤ 3, amorphous WS3 and crystalline WS2) nanofiber is successfully prepared by electrospinning and subsequent calcination in a reducing atmosphere. To prevent capacity degradation of the WSx anodes originating from sulfur dissolution, a facile post-thermal treatment in air is applied to form an oxide passivation surface. Interestingly, WO3 thorn bundles are randomly grown on the nanofiber stem, resulting from the surface conversion. We elucidate the evolving morphological and structural features of the nanofibers during post-thermal treatment. The heterogeneous thorn-bush nanofiber electrodes deliver a high second discharge capacity of 791 mAh g(-1) and improved cycle performance for 100 cycles compared to the pristine WSx nanofiber. We show that this hierarchical design is effective in reducing sulfur dissolution, as shown by cycling analysis with counter Na electrodes.

Rational design of Sn-based multicomponent anodes for high performance lithium-ion batteries: SnO2@TiO2@reduced graphene oxide nanotubes

Reduced graphene oxide (rGO)-wrapped SnO₂@TiO₂ nanotubes (NTs) anodes exhibit superior rate capability and cycle retention due to stable solid electrolyte interphase (SEI) layer and enhanced electrical conductivity through TiO₂ and rGO-coated layer.

Graphene-Wrapped Anatase TiO2 Nanofibers as High-Rate and Long-Cycle-Life Anode Material for Sodium Ion Batteries

Anatase TiO₂ has been suggested as a potential sodium anode material, but the low electrical conductivity of TiO₂ often limits the rate capability, resulting in poor electrochemical properties. To address this limitation, we propose graphene-wrapped anatase TiO₂ nanofibers (rGO@TiO₂ NFs) through an effective wrapping of reduced graphene oxide (rGO) sheets on electrospun TiO₂ NFs. To provide strong electrostatic interaction between the graphene oxide (GO) sheets and the TiO₂ NFs, poly(allylamine hydrochloride) (PAH) was used to induce a positively charged TiO₂ surface by the immobilization of the -NH₃⁺ group and to promote bonding with the negatively charged carboxylic acid (-COO⁻) and hydroxyl (-O⁻) groups on the GO. A sodium anode electrode using rGO@TiO₂ NFs exhibited a significantly improved initial capacity of 217 mAh g⁻¹, high capacity retention (85% after 200 cycles at 0.2C), and a high average Coulombic efficiency (99.7% from the second cycle to the 200^th cycle), even at a 5C rate, compared to those of pristine TiO₂ NFs. The improved electrochemical performances stem from highly conductive properties of the reduced GO which is effectively anchored to the TiO₂ NFs.

Glassy Metal Alloy Nanofiber Anodes Employing Graphene Wrapping Layer: Toward Ultralong-Cycle-Life Lithium-Ion Batteries

Amorphous silicon (a-Si) has been intensively explored as one of the most attractive candidates for high-capacity and long-cycle-life anode in Li-ion batteries (LIBs) primarily because of its reduced volume expansion characteristic (∼280%) compared to crystalline Si anodes (∼400%) after full Li(+) insertion. Here, we report one-dimensional (1-D) electrospun Si-based metallic glass alloy nanofibers (NFs) with an optimized composition of Si60Sn12Ce18Fe5Al3Ti2. On the basis of careful compositional tailoring of Si alloy NFs, we found that Ce plays the most important role as a glass former in the formation of the metallic glass alloy. Moreover, Si-based metallic glass alloy NFs were wrapped by reduced graphene oxide sheets (specifically Si60Sn12Ce18Fe5Al3Ti2 NFs@rGO), which can prevent the direct exposure of a-Si alloy NFs to the liquid electrolyte and stabilize the solid-electrolyte interphase (SEI) layers on the surfaces of rGO sheets while facilitating electron transport. The metallic glass nanofibers exhibited superior electrochemical cell performance as an anode: (i) Si60Sn12Ce18Fe5Al3Ti2 NFs show a high specific capacity of 1017 mAh g(-1) up to 400 cycles at 0.05C with negligible capacity loss as well as superior cycling performance (nearly 99.9% capacity retention even after 2000 cycles at 0.5C); (ii) Si60Sn12Ce18Fe5Al3Ti2 NFs@rGO reveals outstanding rate behavior (569.77 mAh g(-1) after 2000 cycles at 0.5C and a reversible capacity of around 370 mAh g(-1) at 4C). We demonstrate the potential suitability of multicomponent a-Si alloy NFs as a long-cycling anode material.

Additive-free thick graphene film as an anode material for flexible lithium-ion batteries

This work demonstrates a simple route to develop mechanically flexible electrodes for Li-ion batteries (LIBs) that are usable as lightweight effective conducting networks for both cathodes and anodes. Removing electrochemically dead elements, such as binders, conducting agents and metallic current collectors, from the battery components will allow remarkable progress in this area. To investigate the feasibility of using thick, additive-free graphene films as anodes for flexible LIBs, we have synthesized and tested thick, additive-free, freestanding graphene films as anodes, first in a coin cell and further in a flexible full cell. As an anode material in a half cell, it showed a discharge capacity of about 350 mA h g(-1) and maintained nearly this capacity over 50 cycles at various current rates. This film was also tested as an anode material in a full cell with a LiCoO2 cathode and showed good electrochemical performance. Because the graphene-based flexible film showed good performance in half- and full coin cells, we used this film as a flexible anode for flexible LIBs. No conducting agent or binder was used in the anode side, which helped in realizing the flexible LIBs. Using this, we demonstrate a thin, lightweight and flexible lithium ion battery with good electrochemical performance in both its flat and bent states.

Conducting additive-free amorphous GeO2/C composite as a high capacity and long-term stability anode for lithium ion batteries

In this study, a novel method has been proposed for synthesizing amorphous GeO2/C composites. The amorphous GeO2/C composite without carbon black as an electrode for Li-ion batteries exhibited a high specific capacity of 914 mA h g(-1) at the rate of C/2 and enhanced rate capability. The amorphous GeO2/C electrode exhibited excellent electrochemical stability with a 95.3% charge capacity retention after 400 charge-discharge cycles, even at a high current charge-discharge of C/2. Furthermore, a full cell employing the GeO2/C anode and the LiCoO2 cathode displayed outstanding cycling performance. The superior performance of the GeO2/C electrode enables the amorphous GeO2/C to be a potential anode material for secondary Li-ion batteries.

Design and tailoring of three-dimensional graphene–Vulcan carbon–Bi2S3 ternary nanostructures for high-performance lithium-ion-battery anodes

Design of the structure and morphology of electrode materials is crucial for creating short transport pathways for lithium ions and electrons in high-performance lithium-ion battery systems.