Carbon-coated Si Research Articles

Synergetic effect of double-layer coating on silicon nanoparticles for high-performance lithium-ion battery anodes

Silicon has emerged as a potential candidate for next-generation lithium-ion battery (LIB) anodes owing to its exceptionally high theoretical capacity (3580 mAh g−1) and environmental abundance. However, the practical application of Si anodes is severely hindered by low electrical conductivity and a substantial volume expansion rate of over 300 % during the lithiation–delithiation process, leading to rapid capacity degradation. To address these challenges, a double-layer coating strategy was developed and successfully applied to simultaneously enhance the electrical conductivity and mechanical integrity of Si nanoparticles (Si). The double coating layer was designed with an inside conductive pathway and outside robust coverage, which was achieved by encapsulating silicon with a conductive amorphous carbon layer on the silicon surface and coating it with a TiO2 layer (Si@C@TiO₂). These features improved the interfacial and structural stability of the electrodes during repeated cycling. Compared with its respective uncoated and single-coated analogous anodes, the Si, carbon-coated Si (Si@C), and TiO2-coated Si (Si@TiO2) anodes, the Si@C@TiO₂ anode demonstrates exceptional cycling stability and power capability. We believe that this study offers a breakthrough in the design of high-performance Si-based anodes for LIBs.

One-pot synthesis of interconnected carbon-coated silicon nanosheets from clay minerals for high-performance lithium-ion battery anodes

The silicon nanosheet/carbon composite emerges as a promising anode material for the next-generation commercial lithium-ion batteries. However, complex, costly, and energy-intensive synthesis procedures impede its practical application. Herein, the carbon-coated silicon nanosheets (Si/C) have been successfully synthesized via a one-pot strategy, involving a modified magnesiothermic reduction of talc followed by a reaction with CO2. The distinct chemical composition and layered nanostructure of talc enable the retention of Si nanosheets during exothermic reactions without additional templates or heat absorbents. The method shows significant potential for the scalable production of Si/C owing to the abundant silicon source, sustainable carbon source, and straightforward protocol. The resulting Si/C displays a hierarchical porous structure, with both macropores and mesopores, and an interconnected network of carbon-coated Si nanosheets. These structural characteristics facilitate rapid Li+ diffusion and enable the material to accommodate the lithiation-induced mechanical strains. As a result, the Si/C electrode exhibits outstanding electrochemical performance, including a remarkable rate capability (with a specific capacity of 1220 mAh g−1 at 10.0 A g−1) and a high initial Coulombic efficiency of 88%. The work opens a new avenue for the development of Si/C composites from natural clay minerals through an economical and scalable strategy, which would contribute to the practical application of advanced Si-based anodes in lithium-ion batteries.

Double Nitrogenation Layer Formed Using Nitric Oxide for Enhancing Li+ Storage Performance, Cycling Stability, and Safety of Si Electrodes.

To enhance Li storage properties, nitrogenation methods are developed for Si anodes. First, melamine, urea, and nitric oxide (NO) precursors are used to nitrogenize carbon-coated Si particles. The properties of the obtained particles are compared. It is found that the NO process can maximize the graphitic nitrogen (N) content and electronic conductivity of a sample. In addition, optimized N functional groups and O─C species on the electrode surface increase electrolyte wettability. However, with a carbon barrier layer, NO hardly nitrogenizes the Si cores. Therefore, bare Si particles are reacted with NO. Core-shell Si@amorphous SiNx particles are produced using a facile and scalable NO treatment route. The effects of the NO reaction time on the physicochemical properties and charge-discharge performance of the obtained materials are systematically examined. Finally, the Si@SiNx particles are coated with N-doped carbon. Superior capacities of 2435 and 1280 mAh g-1 are achieved at 0.2 and 5Ag-1, respectively. After 300 cycles, 90% of the initial capacity is retained. In addition, differential scanning calorimetry data indicate that the multiple nitrogenation layers formed by NO significantly suppress electrode exothermic reactions during thermal runaway.

Realization of high-capacity coulombic efficiency in sodium alginate/carbon nanotube double network coated Si-anode for lithium-ion batteries

Silicon (Si) is considered as one of the most promising anodes for the next-generation lithium-ion batteries (LIBs) owing to its ultra-high specific capacity, low redox potential and the second abundance of elements in the earth's crust. However, drastic volume change will directly cause electrode pulverization, thus leading to low initial coulombic efficiency (ICE) and terrible cycling stability. In this work, a sodium alginate (SA)‑carbon nanotube (CNT) derived double carbon-coated Si composite (SA-CNT@Si) was prepared through freeze-drying technique followed by high-temperature carbonization, where SA was utilized to encase Si nanospheres, with CNT serving as the conductive framework that interconnects Si spheres. These composites exhibit improved electrical conductivity and stability throughout the charge and discharge cycles when employed as the anodes in LIBs, demonstrating superior electrochemical properties. The SA-CNT@Si electrode with a mass ratio of Si: SA: CNT = 5: 1: 0.75, achieved a first discharge specific capacity of 2200.8 mAh g−1 at a current density of 500 mA g−1 (with the initial three cycles at 100 mA g−1), along with an ICE of 86.2%. Even after 500 cycles, it maintained a capacity of 607 mAh g−1. This study presents a novel approach to designing Si-based anode materials characterized by both high electrical conductivity and structural stability.

Carbon-Coated Si Nanosheets as Anode Materials for High-Performance Lithium-Ion Batteries

Carbon-Coated Si Nanosheets as Anode Materials for High-Performance Lithium-Ion Batteries

Correlation between surface/bulk properties and electrochemical cycling performance of pure silicon anode materials

State-of-the-art lithium-ion batteries (LIBs) employ silicon (Si)-graphite composite anode with just a few percentages of Si active material, whose cycle-life relies on a stable solid electrolyte interphase (SEI) layer. As a number of various types of industrial Si active materials are currently available, an informative guideline based on the material properties and resultant cycling performance of different pure Si (i.e., without graphite) anode materials is strongly needed for material selection. The present study provides for the first time the correlation among material's surface and bulk properties, the SEI formation behavior, and cycling behavior of highly loaded pure Si anodes (2.3 mAh cm−2) prepared from four different industrial active materials, which are SiOx, carbon-coated Si, and bare Si with submicron and micron sizes. Commercial electrolyte with 10 wt% fluoroethylene carbonate additive is used for electrochemical performance evaluation. Based on solid-state NMR, XPS, and electrochemical analysis results, SiOx is determined to be relatively beneficial for practical applications beyond Si materials, in the aspects of high structural and particle morphology stability, cycling stability and suppressed interfacial resistance. This is mainly because of more effective accommodation of volume change of Si and oxygen-enriched surface (SEI) stability. The data give insight into the rational design of well-working Si-dominant or pure Si anodes for high energy density LIBs.

Tailoring chemical composition of solid electrolyte interphase by selective dissolution for long-life micron-sized silicon anode

Micron-sized Si anode promises a much higher theoretical capacity than the traditional graphite anode and more attractive application prospect compared to its nanoscale counterpart. However, its severe volume expansion during lithiation requires solid electrolyte interphase (SEI) with reinforced mechanical stability. Here, we propose a solvent-induced selective dissolution strategy to in situ regulate the mechanical properties of SEI. By introducing a high-donor-number solvent, gamma-butyrolactone, into conventional electrolytes, low-modulus components of the SEI, such as Li alkyl carbonates, can be selectively dissolved upon cycling, leaving a robust SEI mainly consisting of lithium fluoride and polycarbonates. With this strategy, raw micron-sized Si anode retains 87.5% capacity after 100 cycles at 0.5 C (1500 mA g−1, 25°C), which can be improved to >300 cycles with carbon-coated micron-sized Si anode. Furthermore, the Si||LiNi0.8Co0.1Mn0.1O2 battery using the raw micron-sized Si anode with the selectively dissolved SEI retains 83.7% capacity after 150 cycles at 0.5 C (90 mA g−1). The selective dissolution effect for tailoring the SEI, as well as the corresponding cycling life of the Si anodes, is positively related to the donor number of the solvents, which highlights designing high-donor-number electrolytes as a guideline to tailor the SEI for stabilizing volume-changing alloying-type anodes in high-energy rechargeable batteries.

ZIF-90 derived carbon-coated kerf-loss silicon for enhanced lithium storage

The utilization of kerf-loss silicon (KL-Si) waste as anode materials in lithium-ion batteries (LIBs) faces limitations of the rapid structural degradation during repeated charging/discharging. To overcome this limitation, 3D carbon-coated Si is constructed to buffer the Si volume expansion caused by the lithiation, while simultaneously forming a robust conductive network. Meanwhile, the well-dispersed porous carbon (C) shell, doped with suitable heteroatoms, plays a pivotal role in facilitating rapid ion transfer rates. In addition, a cobalt (Co) and nitrogen (N)-doped C shell is employed to encapsulate KL-Si, aimed at enhancing its lithium (Li) storage performances. The electrochemical performance of KL-Si@C-ZIF/N/Co composites, synthesized through the encapsulation of KL-Si with a metal-organic framework (MOF) structure (ZIF-90) followed by heat treatment. The resulting composites exhibit an outstanding reversible capacity of 981 mAh g−1 and an impressive capacity retention of 81.9% at 2 A g−1 even after 350 cycles. This paper presents a promising method for maximizing the value-added utilization of KL-Si and reveals the advantages of MOF-derived porous C shell in accommodating the inherent volume expansion of Si-based anodes.

Electrical bridging effects of dual-carbon microsphere frameworks in Si-based composite anodes for high-performance Li-ion batteries

Herein, the successful fabrication of a high-performance Si-based composite Li-ion battery (LIB) anode, comprising a dual-carbon framework of reduced graphene oxide (r-GO) and oxidized single-walled carbon nanohorns (o-NHs), was demonstrated using a simple and scalable spray-drying process followed by heat treatment (h-s-GO/Si/NH). The r-GO nanosheets in the h-s-GO/Si/NH anode acted as a robust spherical framework that facilitated the mechanical and electrical connection between the carbon-coated Si (c-Si) nanoparticles, homogeneous dispersion of c-Si and o-NH nanoparticles, and suppression of the volume expansion and pulverization that occur during lithiation/delithiation. Additionally, the o-NH nanoparticles incorporated in the h-s-GO/Si/NH composite served as electrical bridges between the r-GO nanosheets, resulting in enhanced electrical conductivity and effortless Li-ion shuttling. The h-s-GO/Si/NH composite anode exhibited high electrochemical performance with a very high initial gravimetric charge capacity (2961 mAh g−1 at 0.1 A g−1), stable initial Coulombic efficiency (80.6% at 0.2 A g−1), and high cycling stability (983 mAh g−1 at 0.2 A g−1 after 50 cycles). This study highlights the importance of the effective design of electrically conductive three-dimensional frameworks in Si-based composite anodes, which may contribute to the development of high-performance LIB anode materials.

Advancing silicon-based Li-ion batteries: enhanced stability and performance through carbon-coated Si and rGO linkage

Advancing silicon-based Li-ion batteries: enhanced stability and performance through carbon-coated Si and rGO linkage

Investigating Mechanisms Leading to Enhanced Performance of Carbon-Coated Si Anodes By Chemical Vapor Deposition Method

Prior research on carbon-coated silicon (Si@C) for Si-based lithium-ion batteries have shown improved electrochemical performance upon coating. However, the underlying mechanisms responsible for the enhancement in performance have not been fully explored and are typically attributed to the protective influence of the carbon coating around the Si particles as well as the improved electronic conductivity of the electrode. In this work, we investigate the contribution of coating on the processing of the electrodes as well as on the formed solid electrolyte interphase (SEI). Si@C particles were prepared by chemical vapor deposition (CVD) technique to achieve a homogeneous carbon layer on the Si surface. The influence of coating time as well as processing temperature was investigated. X-ray photoelectron spectroscopy (XPS), neutron reflectivity (NR) measurements, and transmission electron microscopy (TEM) reveal the coating characteristics such as its extremely thin nature, ~2.5 nm, allowing us to rule out the protective function of carbon coating to prevent Si volume expansion as the governing mechanism for the improved electrochemical behavior. Instead, Raman mapping of the electrodes reveal a uniform distribution of Si and carbon conductive additive, indicating that the coating on the Si particles can facilitate slurry processing which yields to more homogeneous electrodes. Consequently, this leads to the commonly reported improved electronic connections within the electrodes as supported by electrochemical impedance spectroscopy (EIS) data. Furthermore, SEI studies using XPS reveal similar SEI characteristics of the Si electrodes after cycling in half and full cell format. In summary, we assign the improved performance of Si@C on the beneficial effect of carbon coating on the processing of Si electrodes, but not on the electrochemical passivation.

Carbon Nanotube-Reinforced Dual Carbon Stress-Buffering for Highly Stable Silicon Anode Material in Lithium-Ion Battery.

Silicon (Si) anode suffers from huge volume expansion which causes poor structural stability in terms of electrode material, solid electrolyte interface, and electrode, limiting its practical application in high-energy-density lithium-ion batteries. Rationally designing architectures to optimize the stress distribution of Si/carbon (Si/C) composites has been proven to be effective in enhancing their structural stability and cycling stability, but this remains a big challenge. Here, metal-organic frameworks (ZIF-67)-derived carbon nanotube-reinforced carbon framework is employed as an outer protective layer to encapsulate the inner carbon-coated Si nanoparticles (Si@C@CNTs), which features dual carbon stress-buffering to enhance the structural stability of Si/C composite and prolong their cycling lifetime. Finite element simulation proves the structural advantage of dual carbon stress-buffering through significantly relieving stress concentration when Si lithiation. The outer carbon framework also accelerates the charge transfer efficiency during charging/discharging by the improvement of lithium-ion diffusion and electron transport. As a result, the Si@C@CNTs electrode exhibits excellent long-term lifetime and good rate capability, showing a specific capacity of 680 mAh g-1 even at a high rate of 1 A g-1 after 1000 cycles. This work provides insight into the design of robust architectures for Si/C composites by stress optimization.

Toward the Improvement of Silicon-Based Composite Electrodes via an In-Situ Si@C-Graphene Composite Synthesis for Li-Ion Battery Applications

Using Si as anode materials for Li-ion batteries remain challenging due to its morphological evolution and SEI modification upon cycling. The present work aims at developing a composite consisting of carbon-coated Si nanoparticles (Si@C NPs) intimately embedded in a three-dimensional (3D) graphene hydrogel (GHG) architecture to stabilize Si inside LiB electrodes. Instead of simply mixing both components, the novelty of the synthesis procedure lies in the in situ hydrothermal process, which was shown to successfully yield graphene oxide reduction, 3D graphene assembly production, and homogeneous distribution of Si@C NPs in the GHG matrix. Electrochemical characterizations in half-cells, on electrodes not containing additional conductive additive, revealed the importance of the protective C shell to achieve high specific capacity (up to 2200 mAh.g-1), along with good stability (200 cycles with an average Ceff > 99%). These performances are far superior to that of electrodes made with non-C-coated Si NPs or prepared by mixing both components. These observations highlight the synergetic effects of C shell on Si NPs, and of the single-step in situ preparation that enables the yield of a Si@C-GHG hybrid composite with physicochemical, structural, and morphological properties promoting sample conductivity and Li-ion diffusion pathways.

Carbon-Coated Si Nanoparticles Anchored on Three-Dimensional Carbon Nanotube Matrix for High-Energy Stable Lithium-Ion Batteries

An easy and scalable synthetic route was proposed for synthesis of a high-energy stable anode material composed of carbon-coated Si nanoparticles (NPs, 80 nm) confined in a three-dimensional (3D) network-structured conductive carbon nanotube (CNT) matrix (Si/CNT@C). The Si/CNT@C composite was fabricated via in situ polymerization of resorcinol formaldehyde (RF) resin in the co-existence of Si NPs and CNTs, followed by carbonization at 700 °C. The RF resin-derived carbon shell (~10 nm) was wrapped on the Si NPs and CNTs surface, welding the Si NPs to the sidewall of the interconnected CNTs matrix to avoid Si NP agglomeration. The unique 3D architecture provides a highway for Li+ ion diffusion and electron transportation to allow the fast lithiation/delithiation of the Si NPs; buffers the volume fluctuation of Si NPs; and stabilizes solid–electrolyte interphase film. As expected, the obtained Si/CNT@C hybrid exhibited excellent lithium storage performances. An initial discharge capacity of 1925 mAh g−1 was achieved at 0.1 A g−1 and retained as 1106 mAh g−1 after 200 cycles at 0.1 A g−1. The reversible capacity was retained at 827 mAh g−1 when the current density was increased to 1 A g−1. The Si/CNT@C possessed a high Si content of 62.8 wt%, facilitating its commercial application. Accordingly, this work provides a promising exploration of Si-based anode materials for high-energy stable lithium-ion batteries.

Electrochemical and X-ray Photoelectron Spectroscopic Study of Early SEI Formation and Evolution on Si and Si@C Nanoparticle-Based Electrodes.

Carbon coatings can help to stabilize the electrochemical performance of high-energy anodes using silicon nanoparticles as the active material. In this work, the comparison of the behavior and chemical composition of the Solid Electrolyte Interphase (SEI) was carried out between Si nanoparticles and carbon-coated Si nanoparticles (Si@C). A combination of two complementary analytical techniques, Electrochemical Impedance Spectroscopy and X-ray Photoelectron Spectroscopy (XPS), was used to determine the intrinsic characteristics of the SEI. It was demonstrated that the SEI on Si particles is more resistive than the SEI on the Si@C particles. XPS demonstrated that the interface on the Si particles contains more oxygen when not covered with carbon, which shows that a protective layer of carbon helps to reduce the number of inorganic components, leading to more resistive SEI. The combination of those two analytical techniques is implemented to highlight the features and evolution of interfaces in different battery technologies.

Scalable synthesized high-performance TiO2-Si-C hybrid anode for lithium batteries

At present, developing a simple strategy to effectively solve the shackles of volume expansion, poor conductivity and interface compatibility faced by Si-C anode in lithium batteries (LIBs) is the key to its commercialization. Here, low-cost nano-Si powders were prepared from Si-waste of solar-cells by sanding treatment, which can effectively reduce the commercialization cost for Si-C anode. Furthermore, micro-nano structured Gr@Si/C/TiO2 anode materials with graphite (Gr) as the inner core, TiO2-doped and carbon-coated Si as the outer coating-layer, were synthesized at kilogram-scale per milling batch. Comprehensive characterization results indicate that TiO2-doped carbon layer can improve the interface compatibility with the electrolyte, further promote the reduction of electrode polarization, and finally enhance the battery performance for the Gr@Si/C/TiO2 anodes. Accordingly, Gr@Si/C/TiO2 composites can output excellent LIB performance, especially with high initial coulombic efficiency (ICE) of 82.51% and large average reversible capacity of ∼ 810 mA h g−1 at 0.8 A g−1 after 1000 cycles. Moreover, Gr@Si/C/TiO2||NCM811 pouch full cells deliver impressive performance especially with high energy density of ∼ 489.3 W h kg−1 based on the total weight of active materials, suggesting its promising application in the high performance LIBs.

Study on nano-graphitic carbon coating on Si mold insert for precision glass molding

Precision glass molding is an efficient and promising technique for large-volume micro-optical manufacturing. Even though significant progress in precision glass molding has been achieved on the anti-adhesive coating, technical challenges and barriers still exist towards tailoring the coating layer to ensure durability and long-term processing consistency in numerous molding cycles. This manuscript presents a novel molding technique utilizing micro-patterned Si mold inserts coated with a newly developed nano-graphitic carbon coating as an isolation layer in high-precision glass molding. The coating is prepared by atmospheric pressure chemical vapor deposition (APCVD), in which the liquid benzene and silicone rubber are used as the carbon source and silicon oxycarbide (SiOC) source, respectively. The nano-morphologies of the nano-graphitic carbon coating with different conditions are characterized and analyzed, illustrating notable differences in surface features with the addition of silicone rubber and various growth durations. In the demonstration, the nano-graphitic carbon-coated Si mold inserts exhibit unique properties, including anti-adhesive and hydrophobic at elevated temperatures. Two kinds of micro-patterned Si mold inserts, a micro-pillar matrix and a micro-lens array, generated by UV lithography and diamond turning, are utilized to demonstrate the feasibility of the anti-adhesive coating in precision glass molding. The obtained results indicate that the micro-optical features on the coated Si mold inserts are successfully transferred to glass substrates with high replication fidelity without notable signs of adhesion or contamination in repetitive molding cycles. This emerging technology makes Si an alternative mold material with low surface adhesion, enhances micro-optical machining efficiency, and replicates high-precision, low-cost micro-optics on large scales that were previously unavailable.

Multi-buffer engineering of nitrogen-doped carbon nanosheets/carbon nanotubes network encapsulated and carbon coated silicon anode for high performance lithium-ion batteries

The commercial application of silicon (Si) anode is still hindered by unfavorable phenomena such as huge volume expansion, low intrinsic conductivity and unstable solid electrolyte interface film of Si during cycling. Developing a simple and scalable synthesis for multi-buffer engineering with different carbon structures is significant and challenging for the commercial prospects of Si anode. Herein, we propose a multi-buffer engineering strategy with nitrogen-doped carbon nanosheets/carbon nanotubes network encapsulated and carbon-coated Si hybrid structure (Si@C@N-CNs/CNTs) via an efficient and convenient resin coating followed by in-situ catalytic pyrolysis of melamine and paraffin oil. The designed Si@C@N-CNs/CNTs delivers high discharge capacity (2950.6 mAh g−1 at 0.4 A g−1), good cyclability (1017.4 mAh g−1 after 350 cycles), and outstanding rate performance (1068.5 mAh g−1 at 8 A g−1). The electrochemical kinetics and structural stability test results demonstrate such superior performance is originated from the multi-buffer engineering by the 3D conductive N-CNs/CNTs networks, carbon coated layer and fine dispersed CoSi2 nanoparticles, which can provide fast electron and ion transfer, effective volume buffer effect and excellent structural stability. Direct comparison with other two Si anodes reveals the significance of the multi-buffering synergistic effect and its great potential in application of high-performance anode for lithium-ion batteries.

Performance enhancement of carbon-coated Si nanoparticles for lithium-ion batteries through the generation of lithophilic sites by a simple oxidation process

Silicon nanoparticles (Si NPs) are potential anode materials for next-generation lithium-ion batteries due to their natural abundance, low discharge potential, and high theoretical capacity. Carbon coating improves the capacity of the Si NPs, protects them from disintegration during the lithiation/delithiation process, and provides an additional conductive matrix. Surface modification as a tool leading to capacity enhancement in carbon-coated Si NPs has rarely been explored. It is a straightforward process that involves the surface functionalization of carbon-coated Si NPs (Si-C) with the oxidizing acidic mixture. The surface-treated Si-C functionalized with carboxyl and hydroxyl groups in excess on the carbon surface of Si-C NPs. As a result of surface modification, the acid-treated Si-C (Si-C-AT) displayed a higher reversible capacity of 1575 mA h g−1 after 200 cycles compared to the Si-C (1261 mA h g−1) and bare Si (961 mA h g−1). This high capacity of Si-C-AT is a cumulative outcome of the functional groups and the disordered structure of the carbon shell. The functional groups act as lithophilic sites, and the disordered carbon shell facilitates the insertion-desertion of lithium ions. The simple surface modification strategy proposed in the present study significantly enhances the cyclability of the Si-C-AT NPs and has great potential for application in carbon-coated materials for lithium-ion batteries.

Designed Formation of Yolk–Shell-Like N-Doped Carbon-Coated Si Nanoparticles by a Facile Method for Lithium-Ion Battery Anodes

Designed Formation of Yolk–Shell-Like N-Doped Carbon-Coated Si Nanoparticles by a Facile Method for Lithium-Ion Battery Anodes