Characteristics and electrochemical performances of silicon/carbon nanofiber/graphene composite films as anode materials for binder-free lithium-ion batteries

Innovative Solutions for High-Performance Silicon Anodes in Lithium-Ion Batteries: Overcoming Challenges and Real-World Applications

Silicon (Si) has emerged as a potent anode material for lithium-ion batteries (LIBs), but faces challenges like low electrical conductivity and significant volume changes during lithiation/delithiation, leading to material pulverization and capacity degradation. Recent research on nanostructured Si aims to mitigate volume expansion and enhance electrochemical performance, yet still grapples with issues like pulverization, unstable solid electrolyte interface (SEI) growth, and interparticle resistance. This review delves into innovative strategies for optimizing Si anodes' electrochemical performance via structural engineering, focusing on the synthesis of Si/C composites, engineering multidimensional nanostructures, and applying non-carbonaceous coatings. Forming a stable SEI is vital to prevent electrolyte decomposition and enhance Li+ transport, thereby stabilizing the Si anode interface and boosting cycling Coulombic efficiency. We also examine groundbreaking advancements such as self-healing polymers and advanced prelithiation methods to improve initial Coulombic efficiency and combat capacity loss. Our review uniquely provides a detailed examination of these strategies in real-world applications, moving beyond theoretical discussions. It offers a critical analysis of these approaches in terms of performance enhancement, scalability, and commercial feasibility. In conclusion, this review presents a comprehensive view and a forward-looking perspective on designing robust, high-performance Si-based anodes the next generation of LIBs.

Unlocking High-Current Performance in Silicon Anode: Synergistic Phosphorus Doping and Nitrogen-Doped Carbon Encapsulation to Enhance Lithium Diffusivity

The silicon (Si) offers enormous theoretical capacity as a lithium-ion battery (LIB) anode. However, the low charge mobility in Si particles hinders its application for high current loading. In this study, ball-milled phosphorus-doped Si nanoparticles encapsulated with nitrogen-doped carbon (P-Si@N-C) are employed as an anode for LIBs. P-doped Si nanoparticles are first obtained via ball-milling and calcination of Si with phosphoric acid. N-doped carbon encapsulation is then introduced via carbonization of the surfactant-assisted polymerization of pyrrole monomer on P-doped Si. While P dopant is required to support the stability at high current density, the encapsulation of Si particles with N-doped carbon is influential in enhancing the overall Li+ diffusivity of the Si anode. The combined approaches improve the anode's Li+ diffusivity up to tenfold compared to the untreated anode. It leads to exceptional anode stability at a high current, retaining 87 % of its initial capacity under a large current rate of 4000 mA g-1. The full-cell comprising P-Si@N-C anode and LiFePO4 cathode demonstrates 94 % capacity retention of its initial capacity after 100 cycles at 1 C. This study explores the effective strategies to improve Li+ diffusivity for high-rate Si-based anode.

Predicting of tunneling resistivity between adjacent nanosheets in graphene-polymer systems

In this work, the tunneling resistivity between neighboring nanosheets in grapheme-polymer nanocomposites is expressed by a simple equation as a function of the characteristics of graphene and tunnels. This expression is obtained by connecting two advanced models for the conductivity of graphene-filled materials reflecting tunneling role and interphase area. The predictions of the applied models are linked to the tested data of several samples. The impressions of all factors on the tunneling resistivity are evaluated and interpreted using the suggested equation. The calculations of tunneling resistivity for the studied examples by the model and suggested equation demonstrate the same levels, which confirm the presented methodology. The results indicate that the tunneling resistivity decreases by super-conductive graphene, small tunneling width, numerous contacts among nanosheets and short tunneling length.

Carbon Nanofiber-Sodium Alginate Composite Aerogels Loaded with Vitamin D: The Cytotoxic and Apoptotic Effects on Colon Cancer Cells

Colorectal cancer (CRC) is the fourth most commonly diagnosed cancer and the third leading cause of cancer-related deaths worldwide. A substantial body of literature supports the crucial role of vitamin D (VD) in the etiology, progression, prognosis, and treatment of cancer. Recent clinical studies have found an inverse correlation between CRC incidence and serum VD levels. However, the low water solubility of VD and its anticarcinogenic activity at supraphysiological plasma levels, which causes hypercalcemia, required carrier systems. Carbon-based nanomaterials are excellent eco-friendly candidates, with exceptional chemical resistance, efficient mechanical properties, and negligible weight. Furthermore, composite aerogels manufactured from these nanomaterials have gained interest due to their extensive surface areas and porous structures, which make them suitable for delivering drugs. Our research aimed to study the development of composite aerogels loaded with VD by utilizing carbon nanofibers (CNFs) in an aerogel matrix provided to colon cancer cells. For this purpose, Aero1 as a drug delivery system was first prepared and characterized using XRD, FTIR, and SEM methods. Biochemical methods were employed to evaluate the antiproliferative, apoptotic, and anti-migratory effects on colon cancer cells. FTIR and XRD measurements confirmed the production of aerogels. SEM analysis revealed that aerogels have a non-uniform surface. The findings showed that aerogels can effectively deliver VD to the colon cancer cells, while also inhibiting cancer cell proliferation and migration. This research suggests that the Aero1 drug delivery system could be a valuable tool in the fight against colon cancer and other health issues.

Effect of contact number among graphene nanosheets on the conductivities of tunnels and polymer composites

Simple equations are expressed for tunnel conductivity, tunnel resistance and conductivity of a graphene-filled composite by the number of contacts and interphase part. More specially, the active filler amount is suggested by interphase depth, which changes the contact number. The conductivity of nanocomposite is presented by filler content, filler dimensions, tunneling length and interphase depth. The innovative model is surveyed by the experimented conductivity of real examples. Too, the impacts of numerous issues on the tunnel resistance, tunnel conductivity and conductivity of nanocomposite are discussed to validate the novel equations. The estimates agree with the experimented data and the impacts of several terms on the tunnel resistance, tunnel conductivity and conductivity of system are sensible. Thin and big nanosheets positively affect the nanocomposite's conductivity, but thick nanosheets improve the tunnel conductivity. High conductivity is found at short tunnels, while the nanocomposite's conductivity directly depends on the tunneling length. The dissimilar effects of these features on the tunneling properties and conductivity are described.

Silicon nanoparticles encapsulated in Si3N4/carbon sheaths as an anode material for lithium-ion batteries

Novel composite materials comprising of silicon nanoparticles (SiNPs) encapsulated with thin layers of silicon nitride and reduced graphene oxide shells (Si@Si₃N₄@rGO) are prepared using a simple and scalable method. The composite exhibits significantly improved cycling stability and rate capability compared to bare SiNPs. The presence of inactiveαandβphases of Si₃N₄increases the mechanical endurance of SiNPs. Amorphous SiN_x, which is possibly present with Si₃N₄, also contributes to high capacity and Li-ion migration. The rGO sheath enhances the electronic conduction and improves the rate capability. 15-Si@Si₃N₄@rGO, which is prepared by sintering SiNPs for 15 min at 1300 °C, spontaneous-coating GO on Si@Si₃N₄, and reducing GO to rGO, delivers the highest specific capacity of 1396 mAh g^-1after 100 cycles at a current density of 0.5 A g^-1. The improved electrochemical performance of 15-Si@Si₃N₄@rGO is attributed to the unique combination of positive effects by Si₃N₄and rGO shells, in which Si₃N₄mitigates the issue of large volume changes of Si during charge/discharge, and rGO provides efficient electron conduction pathways. Si@Si₃N₄@rGO composites are likely to have great potential for a high-performance anode in lithium-ion batteries.

Nanofiber-based sorbents: Current status and applications in extraction methods

Advanced sorbents gradually become a research hotspot on account of the increasing attention paid to environmental problems. Due to the prominent physicochemical features of nanofibers (NFs), such as high porosity, large surface area, favorable interconnectivity, high adsorption capacity, wettability, and the possibility of surface modification using functional groups, these nanostructures are regarded as excellent candidates for extraction applications. Therefore, the research in the field of NFs and their nanocomposites has been increasing in recent years. In the present review, we summarize the most recent studies on NFs-based sorbents focusing on strategies for preparation, characterization, and their unique capabilities as porous sorbents in various sorbent-based extraction methods. Moreover, we further described the performance and selectivity of sorbents to achieve improved extraction efficiency. Finally, some perspectives on the challenges and outlook are provided to aid future investigations related to this topic.

Development of Kovacs model for electrical conductivity of carbon nanofiber-polymer systems

This study develops a model for electrical conductivity of polymer carbon nanofiber (CNF) nanocomposites (PCNFs), which includes two steps. In the first step, Kovacs model is developed to consider the CNF, interphase and tunneling regions as dissimilar zones in the system. In the second step, simple equations are expressed to estimate the resistances of interphase and tunnels, the volume fraction of CNF and percolation onset. Although some earlier models were proposed to predict the electrical conductivity of PCNFs, developing of Kovacs model causes a better understanding of the effects of main factors on the nanocomposite conductivity. The developed model is supported by logical influences of all factors on the conductivity and by experimented conductivity of several samples. The calculations show good accordance to the experimented data and all factors rationally manage the conductivity of PCNFs. The highest conductivity of PCNF is gained as 0.019 S/m at the lowest ranges of polymer tunnel resistivity (ρ = 500 Ω m) and tunneling distance (d = 2 nm), whereas the highest levels of these factors (ρ > 3000 Ω m and d > 6 nm) cannot cause a conductive sample. Also, high CNF volume fraction, poor waviness, long and thin CNF, low "k", thick interphase, high CNF conduction, high percentage of percolated CNFs, low percolation onset and high interphase conductivity cause an outstanding conductivity in PCNF.

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.

Catalyst Composites of Palladium and N-Doped Carbon Quantum Dots-Decorated Silica and Reduced Graphene Oxide for Enhancement of Direct Formic Acid Fuel Cells

Pd-based catalysts consisting of Pd nanoparticles on nitrogen-doped carbon quantum dots (N-CQDs) modified silica (SiO₂) and reduced graphene oxide have been synthesized through reduction for use as catalysts for improved formic acid oxidation. The structure, morphology, chemical composition, functional groups, and porosity of the synthesized catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and Brunauer-Emmett-Teller (BET) spectroscopy, respectively. Their electrocatalytic activities were also evaluated by electrochemical measurements. The differences in the average particle sizes found for Pd/N-CQDs-SiO₂-rGO, Pd/N-CQDs-rGO, and Pd/rGO were 4.81, 5.56, and 6.31 nm, respectively. It was also found that the Pd/xN-CQDs-SiO₂-yrGO composite catalysts (where x and y is 1 to 4) can significantly improve the activity and stability toward formic acid electrooxidation compared with Pd/rGO and commercial Pt/C. The mass activities of Pd/N-CQDs-SiO₂-rGO, Pd/N-CQDs-rGO, and Pd/rGO were 951.4, 607.8, and 157.6 mA g^-1, respectively, which was ca. 6-7 times compared with Pd/rGO and approximately 3-4 times compared with commercial Pt/C. With low potential for CO oxidation and high current intensity, the composites of rGO, SiO₂, and N-CQDs into Pd-based catalysts improved the catalytic activity of the prepared catalyst for the oxidation of formic acid in acidic media. The value of the Tafel slope designated that the chief path of the prepared catalysts is the dehydrogenation process. These prepared catalysts exhibit promise toward the development of high-performance Pd-based electrocatalysts for formic acid oxidation.

Spheres of Graphene and Carbon Nanotubes Embedding Silicon as Mechanically Resilient Anodes for Lithium-Ion Batteries

Novel anode materials for lithium-ion batteries were synthesized by in situ growth of spheres of graphene and carbon nanotubes (CNTs) around silicon particles. These composites possess high electrical conductivity and mechanical resiliency, which can sustain the high-pressure calendering process in industrial electrode fabrication, as well as the stress induced during charging and discharging of the electrodes. The resultant electrodes exhibit outstanding cycling durability (∼90% capacity retention at 2 A g^-1 after 700 cycles or a capacity fading rate of 0.014% per cycle), calendering compatibility (sustain pressure over 100 MPa), and adequate volumetric capacity (1006 mAh cm^-3), providing a novel design strategy toward better silicon anode materials.

Plasma-assisted three-dimensional lightscribe graphene as high-performance supercapacitors

Graphene-based supercapacitors demonstrate extraordinary energy storage capacity due to their layered structure, large effective surface area, high electrical conductivity and acceptable chemical stability. Herein, reduced graphene oxide (rGO)-based supercapacitors were introduced in a simple, and fast method with considerable performance. For this purpose, graphene oxide (GO) was synthesized by the modified Hummers' method and then easily reduced to desired patterns of rGO using a commercial LightScribe DVD drive. In order to increase the effective surface area, as well as the electrical conductivity of rGO layers, oxygen/sulfur hexafluoride plasma was applied to the rGO followed by laser irradiation. By performing such sequential processes, an rGO-based supercapacitor was introduced with a capacitance of about 10.2 F/cm3, which had high stability for more than 1000 consecutive charge-discharge cycles. The fabrication steps of the electrodes were investigated by different analyses such as SEM, TEM, Raman, surface resistance, BET, and XPS measurements. Results showed that these rGO-based electrodes fabricated by sequential processes are very interesting for practical applications of energy storage.

Industrial Silicon-Wafer-Wastage-Derived Carbon-Enfolded Si/Si-C/C Nanocomposite Anode Material through Plasma-Assisted Discharge Process for Rechargeable Li-Ion Storage

Silicon is a promising anode material for high-performance Li-ion batteries as a result of its high theoretical specific capacity and elemental abundance. Currently, the commercial application of the Si-based anode is still restricted by its large volume changes during the lithiation cycles and low electrical conductivity. To address these issues, we demonstrate a facile plasma-assisted discharge process to anchor nano-sized Si particles into methanol with quick quenching. After the subsequent sintering process, we obtained a Si/SiC/C composite (M-Si). The unique structure not only allowed for the electrolyte infiltration to enhance lithium ion diffusion during charge and discharge process, but also buffered the volume expansion of silicon particles to enhance the rate capability and cycle stability. The M-Si cell electrochemical results exposed good Li-ion storage performance compared to that of the bare Si used cell (B-Si). The electrode cell consisting of M-Si exhibited remarkable enhanced cyclic stability and sustained the reversible specific capacity of 563 mAhg-1 after 100 cycles, with a coulombic efficiency of 99% at a current density of 0.1C, which is higher than that of the B-Si electrode cell that was used. Hence, the as-prepared Si/SiC/C composite is an efficient anode material for Li-ion battery applications. Moreover, these results indicate that the novel plasma-assisted discharge technique will bring a potential durable methodology to produce novel high-performance electrode materials for future advanced large-scale energy-storage applications.

Highly sensitive and selective detection of glutathione using ultrasonic aided synthesis of graphene quantum dots embedded over amine-functionalized silica nanoparticles

Glutathione (GSH) is the most abundant antioxidant in the majority of cells and tissues; and its use as a biomarker has been known for decades. In this study, a facile electrochemical method was developed for glutathione sensing using voltammetry and amperometry analyses. In this study, a novel glassy carbon electrode composed of graphene quantum dots (GQDs) embedded on amine-functionalized silica nanoparticles (SiNPs) was synthesized. GQDs embedded on amine-functionalized SiNPs were physical-chemically characterized by different techniques that included high resolution-transmission electron microscopy (HR-TEM), X-ray diffraction spectroscopy (XRD), UV-visible spectroscopy, Fourier-transform infrared spectroscopy(FTIR), and Raman spectroscopy. The newly developed electrode exhibits a good response to glutathione with a wide linear range (0.5-7 µM) and a low detection limit (0.5 µM) with high sensitivity(2.64 µA µM-1). The fabricated GQDs-SiNPs/GC electrode shows highly attractive electrocatalytic activity towards glutathione detection in the neutral media at low potential due to a synergistic surface effect caused by the incorporation of GQDs over SiNPs. It leads to higher surface area and conductivity, improving electron transfer and promoting redox reactions. Besides, it provides outstanding selectivity, reproducibility, long-term stability, and can be used in the presence of interferences typically found in real sample analysis.

A Comparative Study of the Effect of Graphene Oxide, Graphitic Carbon Nitride, and Their Composite on the Photocatalytic Activity of Cu3SnS4

Photocatalysis has shown high potential in dealing with the ever-broadening problem of wastewater treatment, escalated by the increasing level of recalcitrant chemicals often referred to as emerging contaminants. In this study, the effect of support material on the photocatalytic activity of copper tin sulfide (Cu3SnS4) nanoparticles for the degradation of tetracycline as an emerging contaminant is presented. Graphene oxide, protonated graphitic carbon nitride, and a composite of graphitic carbon nitride and graphene oxide were explored as support materials for Cu3SnS4 nanoparticles. The nanoparticles were incorporated with the different carbonaceous substrates to afford graphene-supported Cu3SnS4 (GO-CTS), protonated graphitic carbon nitride-supported Cu3SnS4 (PCN-CTS), and graphene oxide/protonated graphitic carbon nitride-supported Cu3SnS4 (GO/PCN-CTS). Physicochemical, structural, and optical properties of the prepared nanocomposites were characterized using techniques such as Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis near infrared, and fluorescence spectrophotometry. The compositing of the Cu3SnS4 nanoparticles on the support materials was confirmed by the characterization techniques, and the optical properties of the composites were found to be influenced by the nature of the support material. The incorporation of CTS into the support materials resulted in a reduction in band gap energy with evaluated band gaps of 1.65, 1.46, 1.43 eV, and 1.16 eV. The reduction in band gap energy suggests the potential of the composites for enhanced photocatalytic activity. From the photocatalytic study, the degradation efficiency of tetracycline by CTS, PCN-CTS, GO-CTS, and PC/GO-CTS was 74.1, 85.2, 90.9, and 96.5%, respectively. All the composites showed enhanced activity compared to pristine CTS, and the existence of a synergy between GO and PCN when both were employed as support materials was observed. Based on the charge carrier recombination characteristics and the band edge potential calculations from the composites, a possible mechanism of action of each composite was proposed. This study therefore confirms the possibility of modulating the mechanism of action and subsequently the efficiency of semiconductor materials by altering the nature of the support material.

Synthesis and Electrochemical Performance of Electrostatic Self-Assembled Nano-Silicon@N-Doped Reduced Graphene Oxide/Carbon Nanofibers Composite as Anode Material for Lithium-Ion Batteries

Silicon-carbon nanocomposite materials are widely adopted in the anode of lithium-ion batteries (LIB). However, the lithium ion (Li⁺) transportation is hampered due to the significant accumulation of silicon nanoparticles (Si) and the change in their volume, which leads to decreased battery performance. In an attempt to optimize the electrode structure, we report on a self-assembly synthesis of silicon nanoparticles@nitrogen-doped reduced graphene oxide/carbon nanofiber (Si@N-doped rGO/CNF) composites as potential high-performance anodes for LIB through electrostatic attraction. A large number of vacancies or defects on the graphite plane are generated by N atoms, thus providing transmission channels for Li⁺ and improving the conductivity of the electrode. CNF can maintain the stability of the electrode structure and prevent Si from falling off the electrode. The three-dimensional composite structure of Si, N-doped rGO, and CNF can effectively buffer the volume changes of Si, form a stable solid electrolyte interface (SEI), and shorten the transmission distance of Li⁺ and the electrons, while also providing high conductivity and mechanical stability to the electrode. The Si@N-doped rGO/CNF electrode outperforms the Si@N-doped rGO and Si/rGO/CNF electrodes in cycle performance and rate capability, with a reversible specific capacity reaching 1276.8 mAh/g after 100 cycles and a Coulomb efficiency of 99%.