Hydrogen silsequioxane-derived Si/SiO(x) nanospheres for high-capacity lithium storage materials

Synergistic Protecting-Etching Synthesis of Carbon Nanoboxes@Silicon for High-Capacity Lithium-Ion Battery

Silicon (Si) is considered as the most likely choice for the high-capacity lithium-ion batteries owing to its ultrahigh theoretical capacity (4200 mA h g-1) being over 10 times than that of traditional graphite anode materials (372 mA h g-1). However, its widespread application is limited by problems such as a large volume expansion and low electrical conductivity. Herein, we design a hollow nitrogen-doped carbon-coated silicon (Si@Co-HNC) composite in a water-based system via a synergistic protecting-etching strategy of tannic acid. The prepared Si@Co-HNC composite can effectively mitigate the volume change of silicon and improve the electrical conductivity. Moreover, the abundant voids inside the carbon layer and the porous carbon layer accelerate the transport of electrons and lithium ions, resulting in excellent electrochemical performance. The reversible discharge capacity of 1205 mA h g-1 can be retained after 120 cycles at a current density of 0.5 A g-1. In particular, the discharge capacity can be maintained at 1066 mA h g-1 after 300 cycles at a high current density of 1 A g-1. This study provides a new strategy for the design of Si-based anode materials with excellent electrical conductivity and structural stability.

A Brief Overview of Silicon Nanoparticles as Anode Material: A Transition from Lithium-Ion to Sodium-Ion Batteries

The successful utilization of silicon nanoparticles (Si-NPs) to enhance the performance of Li-ion batteries (LIBs) has demonstrated their potential as high-capacity anode materials for next-generation LIBs. Additionally, the availability and relatively low cost of sodium resources have a significant influence on developing Na-ion batteries (SIBs). Despite the unique properties of Si-NPs as SIBs anode material, limited study has been conducted on their application in these batteries. However, the knowledge gained from using Si-NPs in LIBs can be applied to develop Si-based anodes in SIBs by employing similar strategies to overcome their drawbacks. In this review, a brief history of Si-NPs' usage in LIBs is provided and discuss the strategies employed to overcome the challenges, aiming to inspire and offer valuable insights to guide future research endeavors.

Endothermic Dehydrogenation-Driven Preventive Magnesiation of SiO for High-Performance Lithium Storage Materials

Silicon monoxide (SiO)-based materials have gained much attention as high-capacity lithium storage materials based on their high capacity and stable capacity retention. However, low initial Coulombic efficiency associated with the irreversible electrochemical reaction of the amorphous SiO₂ phase in SiO inhibits the wide usage of SiO-based anode materials for lithium-ion batteries. Magnesiation of SiO is one of the most promising solutions to improve the initial efficiency of SiO-based anode materials. Herein, we demonstrate that endothermic dehydrogenation-driven magnesiation of SiO employing MgH₂ enhanced the initial Coulombic efficiency of 89.5% with much improved long-term cycle performance over 300 cycles compared to the homologue prepared by magnesiation of SiO with Mg and pristine SiO. High-resolution transmission electron microscopy with thermogravimetry-differential scanning calorimetry revealed that the endothermic dehydrogenation of MgH₂ suppressed the sudden temperature rise during magnesiation of SiO, thereby inhibiting the coarsening of the active Si phase in the resulting Si/Mg₂SiO₄ nanocomposite.

Cross-Linked Sodium Alginate-Sodium Borate Hybrid Binders for High-Capacity Silicon Anodes in Lithium-Ion Batteries

Silicon is considered one of the most promising next-generation anode materials for lithium-ion batteries. It has the advantages of high theoretical specific capacity (4200 mAh·g^-1), which is 10 times larger than that of a commercial graphite anode (372 mAh·g^-1). However, there are some problems such as the pulverization of the electrode and an unstable solid electrolyte interphase (SEI) layer aroused by the huge bulk effect (>300%) of Si during the repeated lithiation/delithiation process. A binder plays a vital role in the conventional lithium-ion batteries that can effectively relieve the bulk expansion stress of a silicon anode. In this work, the inorganic cross-linker sodium borate (SB) and the commonly used binder sodium alginate (SA) were condensed through an esterification reaction and the reaction product was marked as SA-SB. It is found that the mechanical robustness and the peel strength of SA-SB are improved after cross-linking, which is conducive to maintaining the structural stability of the silicon anode in long cycle life. In consequence, the capacity retention of the silicon anode using the SA-SB binder (64.1%) is higher than that of SA (50.6%) after 100 cycles at 0.2 A·g^-1.

Fabrication of amorphous hollow mesoporous Si@SiOx nanoboxes as an anode material for enhanced lithium storage performance

Hollow mesoporous Si@SiOx nanoboxes are synthesized successfully by a simple sol–gel reaction of triethoxysilane using Fe2O3 nanocubes as the template, followed by a thermal reduction process and subsequent acid treatment process.

Swelling-Controlled Double-Layered SiOx/Mg2SiO4/SiOx Composite with Enhanced Initial Coulombic Efficiency for Lithium-Ion Battery

Si-based anode materials are considered as potential materials for high-energy lithium-ion batteries (LIBs) with the advantages of high specific capacities and low operating voltages. However, significant initial capacity loss and large volume variations during cycles are the primary restrictions for the practical application of Si-based anodes. Herein, we propose an affordable and scalable synthesis of double-layered SiO_x/Mg₂SiO₄/SiO_x composites through the magnesiothermic reduction of micro-sized SiO with Mg metal powder at 750 °C for 2 h. The distinctive morphology and microstructure of the double-layered SiO_x/Mg₂SiO₄/SiO_x composite are beneficial as they remarkably improve the reversibility in the first cycle and completely suppress the volume variations during cycling. In our material design, the outermost layer with a highly porous SiO_x structure provides abundant active sites by securing a pathway for efficient access to electrons and electrolytes. The inner layer of Mg₂SiO₄ can constrain the large volume expansion to increase the initial Coulombic efficiency (ICE). Owing to these promising structural features, the composite prepared with a 2:1 molar ratio of SiO to Mg exhibited initial charge and discharge capacities of 1826 and 1381 mA h g^-1, respectively, with an ICE of 75.6%. Moreover, it showed a stable cycle performance, maintaining high capacity retention of up to >86.0% even after 300 cycles. The proposed approach provides practical insight into the mass production of advanced anode materials for high-energy LIBs.

In Situ Construction of High-Performing Compact Si-SiOx-CNx Composites from Polyaminosiloxane for Li-Ion Batteries

Great efforts have been made to design high-performing Si/C composite anodes for Li-ion batteries to improve their energy density and cycling life. However, challenges remain in achieving fast electrical conductivity while accommodating significant electrode volumetric changes. Here, we report a unique Si/C-based anode architecture, a Si-SiO_x-CN_x composite, which is simultaneously constructed via the pyrolysis of a polyaminosiloxane precursor. The obtained structure features high-purity Si nanocrystals embedded in an amorphous silica matrix and then embraced by N-doped carbon layers. Notably, in this structure, all three components derived from the polyaminosiloxane precursor are linked by chemical bonding, forming a compact Si-SiO_x-CN_x triple heterostructure. Because of the improvement in the volumetric efficiency for accommodating Si active materials and electrical properties, this anode design enables promising electrochemical performance, including excellent cycle performance (830 mAh g^-1 after 100 cycles at 0.1 A g^-1) and outstanding rate performance (400 mAh g^-1 at 5 A g^-1). Moreover, this composite anode demonstrates great potential for high-energy Li-ion batteries, where a Si-SiO_x-CN_x//LiNi_0.9Co_0.1O₂ full-cell shows a high capacity of 180 mAh g^-1 as well as stable cycle performance (150 mAh g^-1 after 200 cycles at 0.19 A g^-1).

Titanium Monoxide-Stabilized Silicon Nanoparticles with a Litchi-like Structure as an Advanced Anode for Li-ion Batteries

Silicon (Si) has been considered as the most potential anode material for next-generation high-energy density lithium-ion batteries (LIBs) because of its extremely high theoretical capacity. However, the performance deterioration caused by volume change and low electrical conductivity of active Si particles greatly limit its commercial use. Here, we designed a nonstoichiometric TiO_x-coated Si anode with a litchi-like structure, in which Si-Ti and Si-O dual bonds are expected to form between the Si core and TiO_x shell. This unique structure plays a major role in preventing the volume expansion and improving the electrical conductivity of the Si anode. The as-prepared TiO_x-coated Si anode could exhibit excellent cycling stability after 1000 cycles at 1000 mA g^-1 with a relatively small capacity decay rate of ∼0.04% per cycle, which can be comparable to most of the modified Si anodes in references. This strategy of surface regulating on the Si anode could be extended to other electrodes with large volume expansion during cycling in LIBs for achieving competitive electrochemical properties.

Pomegranate-Like Structured Si@SiOx Composites With High-Capacity for Lithium-Ion Batteries

Silicon anodes with an extremely high theoretical specific capacity of 4,200 mAh g^-1 have been considered as one of the most promising anode materials for next-generation lithium-ion batteries. However, the large volume expansion during lithiation hinders its practical application. In this work, pomegranate-like Si@SiO_x composites were prepared using a simple spray drying process, during which silicon nanoparticles reacted with oxygen and generated SiO_x on the surface. The thickness of the SiO_x layer was tuned by adjusting the drying temperature. In the unique architecture, the SiO_x which serves as the protection layer and the void space in pomegranate-like structure could alleviate the volume expansion during repeated lithium insertion/extraction. As a lithium-ion battery anode, pomegranate-like Si@SiO_x composites dried at 180°C delivered a high specific capacity of 1746.5 mAh g^-1 after 300 cycles at 500 mA g^-1.

Modeling of Hydrogen Storage Utilizing Silsesquioxane Cages: Adsorption and Quasi-Dynamic Simulations of Encapsulation of H2 Molecule into Silsesquioxane Cages

Solid-state hydrogen storage may be the only promising way for mobile applications of hydrogen energy since it is safe, quickly reversible, cost-efficient, and has a high volumetric energy density under standard conditions. Silsesquioxane and its derivatives seem well suited for solid-state hydrogen storage and have attracted many experimental and theoretical researchers. In the present work, we have systematically studied four cages of T8, T10, and T12 (D_2d and D_6h) for hydrogen storage including adsorption and encapsulation of hydrogen molecules. We find that silsesquioxane cages have up to about 4150 m²/g specific surface area (SSA) and 7.81 wt % for hydrogen storage. These calculated values are comparable to the highest hydrogen storage values of metal-organic frameworks, porous polymer networks, and covalent organic frameworks. In addition, we use the quasi-dynamic method to study the encapsulation of hydrogen molecules into these cages because of the timescale limitation of ab initio molecular dynamics. Thermodynamic parameters such as enthalpy and Gibbs free energy at different temperatures are calculated during the insertion processes. We find that the insertion process of a hydrogen molecule into the T12 (D_6h) cage is almost energy-conserved and its energy barriers of enthalpy and free energy are moderate under standard conditions.

Chemically anchored two-dimensional-SiO x /zero-dimensional-MoO2 nanocomposites for high-capacity lithium storage materials

Silicon oxides are promising alternatives for graphite anodes in lithium-ion batteries. SiO x nanosheets exhibit favorable anodic performances, including outstanding capacity retention and dimensional stability, due to their unique two-dimensional (2D) microstructures, but suffer from low specific capacity and poor initial coulombic efficiency. Here we demonstrate that chemically anchoring of molybdenum dioxide (MoO2) nanoparticles on the surface of 2D-SiO x nanosheets via a Mo-O-Si bond boosts both the reversible capacity and initial coloumbic efficiency without sacrificing the useful properties of 2D-SiO x nanosheets. The enhancements can be attributed to the introduction of a zero-dimensional MoO2 nano-object, which offers abnormal storage sites for lithium. The proposed nano-architecturing shows how we can maximize the advantages of 2D nanomaterials for energy storage applications.

Magnetoelectric Plasma Preparation of Silicon-Carbon Nanocomposite as Anode Material for Lithium Ion Batteries

A high-performance silicon-carbon nanocomposite facilely prepared by one-step magnetoelectric plasma pyrolysis of the mixture of methane, silane, and hydrogen is proposed for lithium-ion batteries. The ratio of silane, methane, and hydrogen was studied to optimize the properties of the composite. When the ratio of hydrogen/silane/methane is 1:1:3, the composite is composed of spherical Si nanoparticles that uniformly attach to the surface of the tremelliform carbon nanosheets framework, in which the tremelliform carbon nanosheets can effectively resist the volumetric change of the Si nanoparticles during the cycles and serve as electronic channels. The silicon-carbon nanocomposite exhibits a high reversible capacity (1007 mAh g−1 after 50 cycles), a low charge transfer resistance, and an excellent rate performance. In addition, the proposed process for synthesizing silicon-carbon nanocomposite without expensive materials or toxic reagents is an environmentally friendly and cost-effective method for mass production.

Engineering Carbon Distribution in Silicon-Based Anodes at Multiple Scales

The successful commercialization of promising silicon-based anode materials has been hampered by their poor cycling stability caused by the huge volume change. Integration of the carbon matrix with silicon-based (C/Si-based) anode materials has been demonstrated to be a powerful solution to achieve satisfactory electrochemical performance. This minireview aims to outline recent developments on C/Si-based composites, with the emphasis on the importance of carbon distribution at multiple scales. In addition, the forms of the carbon framework (carbon sources and doping of heteroatoms) have been summarized. Particularly, a novel C/Si-based hybrid with carbon distributed at the atomic scale has been highlighted.

Everlasting Living and Breathing Gyroid 3D Network in Si@SiOx/C Nanoarchitecture for Lithium Ion Battery

Silicon-based materials are the most promising candidates to surpass the capacity limitation of conventional graphite anode for lithium ion batteries. Unfortunately, Si-based materials suffer from poor cycling performance and dimensional instability induced by the large volume changes during cycling. To resolve such problems, nanostructured silicon-based materials with delicately controlled microstructure and interfaces have been intensively investigated. Nevertheless, they still face problems related to their high synthetic cost and their limited electrochemical properties and thermal stability. To overcome these drawbacks, we demonstrate the strategic design and synthesis of a gyroid three-dimensional network in a Si@SiO_x/C nanoarchitecture (3D-Si@SiO_x/C) with synergetic interaction between the computational prediction and the synthetic optimization. This 3D-Si@SiO_x/C exhibits not only excellent electrochemical performance due to its structural stability and superior ion/electron transport but also enhanced thermal stability due to the presence of carbon, which was formed by a cost-effective one-pot synthetic route. We believe that our rationally designed 3D-Si@SiO_x/C will lead to the development of anode materials for the next-generation lithium ion batteries.

Metal-Organic Frameworks-Derived Mesoporous Si/SiOx @NC Nanospheres as a Long-Lifespan Anode Material for Lithium-Ion Batteries

Silicon (Si)-based anode materials with suitable engineered nanostructures generally have improved lithium storage capabilities, which provide great promise for the electrochemical performance in lithium-ion batteries (LIBs). Herein, a metal-organic framework (MOF)-derived unique core-shell Si/SiO_x @NC structure has been synthesized by a facile magnesio-thermic reduction, in which the Si and SiO_x matrix were encapsulated by nitrogen (N)-doped carbon. Importantly, the well-designed nanostructure has enough space to accommodate the volume change during the lithiation/delithiation process. The conductive porous N-doped carbon was optimized through direct carbonization and reduction of SiO₂ into Si/SiO_x simultaneously. Benefiting from the core-shell structure, the synthesized product exhibited enhanced electrochemical performance as an anode material in LIBs. Particularly, the Si/SiO_x @NC-650 anode showed the best reversible capacities up to 724 and 702 mAh g^-1 even after 100 cycles. The excellent cycling stability of Si/SiO_x @NC-650 may be attributed to the core-shell structure as well as the synergistic effect between the Si/SiO_x and MOF-derived N-doped carbon.

Nitrogen Plasma-Treated Core-Bishell Si@SiOx@TiO2-δ: Nanoparticles with Significantly Improved Lithium Storage Performance

Si-based anode materials have attracted considerable attention because of their ultrahigh reversible capacity. However, poor cycling stability caused by the large volume change during cycling prevented the commercial application of Si anodes for lithium-ion batteries (LIBs). To overcome these challenges, in the present study, we designed a nitrogen plasma-treated core-bishell nanostructure where the Si nanoparticle was encapsulated into a SiO_x shell and N-doped TiO_2-δ shell. Here, the SiO_x inside the shell and the TiO₂ outside the shell act as binary buffer matrices to accommodate the large volume change and also help to stabilize the solid electrolyte interphase films on the shell surface. More importantly, the plasma-induced N-doped TiO_2-δ shell with many Ti³⁺ species and oxygen vacancies plays a key role in improving the electrical conductivity of Si anodes. Owing to the synergistic effects of SiO_x and N-doped TiO_2-δ bishells, the cycling stability and rate performance of Si anodes are significantly enhanced. The as-obtained sample exhibits superior cycling stability with a capacity retention of 650 mA h g^-1 at 200 mA g^-1 after 300 cycles. This strategy is favorable for improving the electrochemical performances of Si-based anodes to employ in practical LIBs.

Anisotropic Compositional Expansion and Chemical Potential of Lithiated SiO2 Electrodes: Multiscale Mechanical Analysis

The use of high-capacity electrode materials (i.e., Si) in Li-ion batteries is hindered by their mechanical degradation. Thus, oxides (i.e., SiO₂) are commonly used to obtain high expected capacities and long-term cycle performances. Despite extensive studies of the electrochemical-mechanical behaviors of high-capacity energy storage materials, the mechanical behaviors of amorphous SiO₂ during electrochemical reaction remain largely unknown. Here, we systematically investigate the stress evolution, electronic structure, and mechanical deformation of lithiated SiO₂ through first-principles computation and the finite element method. The structural and thermodynamic role of O in the amorphous Li-O-Si system is reported and compared with that in Si. Strong Si-O bonds in SiO₂ show high mechanical strength and brittle behavior, but as Li is inserted, the Li-rich SiO₂ phases become mechanically softened. The relaxation kinetics of SiO₂, inducing deviatoric inelastic strains under mechanical constraints, is also compared with that of Si. The finite element model including the kinetic model for anisotropic expansion demonstrates that the long-term cycling stability of core-shell Si-SiO₂ nanoparticles mainly arises from the reaction kinetics and high mechanical strength of SiO₂. These results provide fundamental insights into the chemomechanical behavior of SiO₂ for practical use.

Silicon oxides: a promising family of anode materials for lithium-ion batteries

Silicon oxides have been recognized as a promising family of anode materials for high-energy lithium-ion batteries (LIBs) owing to their abundant reserve, low cost, environmental friendliness, easy synthesis, and high theoretical capacity. However, the extended application of silicon oxides is severely hampered by the intrinsically low conductivity, large volume change, and low initial coulombic efficiency. Significant efforts have been dedicated to tackling these challenges towards practical applications. This Review focuses on the recent advances in the synthesis and lithium storage properties of silicon oxide-based anode materials. To present the progress in a systematic manner, this review is categorized as follows: (i) SiO-based anode materials, (ii) SiO2-based anode materials, (iii) non-stoichiometric SiOx-based anode materials, and (iv) Si-O-C-based anode materials. Finally, future outlook and our personal perspectives on silicon oxide-based anode materials are presented.

Reaction-Ball-Milling-Driven Surface Coating Strategy to Suppress Pulverization of Microparticle Si Anodes

In this work, we report a novel reaction-ball-milling surface coating strategy to suppress the pulverization of microparticle Si anodes upon lithiation/delithiation. By energetically milling the partially prelithiated microparticle Si in a CO₂ atmosphere, a multicomponent amorphous layer composed of SiO _x, C, SiC, and Li₂SiO₃ is successfully coated on the surface of Si microparticles. The coating level strongly depends on the milling reaction duration, and the 12 h milled prelithiated Si microparticles (BM12h) under a pressure of 3 bar of CO₂ exhibit a good conformal coating with 1.006 g cm^-3 of tap density. The presence of SiC remarkably enhances the mechanical properties of the SiO _x/C coating matrix with an approximately 4-fold increase in the elastic modulus and the hardness values, which effectively alleviates the global volume expansion of the Si microparticles upon lithiation. Simultaneously, the existence of Li₂SiO₃ insures the Li-ion conductivity of the coating layer. Moreover, the SEI film formed on the electrode surface maintains relatively stable upon cycling due to the remarkably suppressed crack and pulverization of particles. These processes work together to allow the BM12h sample to offer much better cycling stability, as its reversible capacity remains at 1439 mAh g^-1 at 100 mA g^-1 after 100 cycles, which is nearly 4 times that of the pristine Si microparticles (381 mAh g^-1). This work opens up new opportunities for the practical applications of micrometer-scale Si anodes.

Multiscale Engineered Si/SiO x Nanocomposite Electrodes for Lithium-Ion Batteries Using Layer-by-Layer Spray Deposition

Si-based high-capacity materials have gained much attention as an alternative to graphite in Li-ion battery anodes. Although Si additions to graphite anodes are now commercialized, the fraction of Si that can be usefully exploited is restricted due to its poor cyclability arising from the large volume changes during charge/discharge. Si/SiO _x nanocomposites have also shown promising behavior, such as better capacity retention than Si alone because the amorphous SiO _x helps to accommodate the volume changes of the Si. Here, we demonstrate a new electrode architecture for further advancing the performance of Si/SiO _x nanocomposite anodes using a scalable layer-by-layer atomization spray deposition technique. We show that particulate C interlayers between the current collector and the Si/SiO _x layer and between the separator and the Si/SiO _x layer improved electrical contact and reduced irreversible pulverization of the Si/SiO _x significantly. Overall, the multiscale approach based on microstructuring at the electrode level combined with nanoengineering at the material level improved the capacity, rate capability, and cycling stability compared to that of an anode comprising a random mixture of the same materials.

Si Nanocrystal-Embedded SiO x nanofoils: Two-Dimensional Nanotechnology-Enabled High Performance Li Storage Materials

Silicon (Si) based materials are highly desirable to replace currently used graphite anode for lithium ion batteries. Nevertheless, its usage is still a big challenge due to poor battery performance and scale-up issue. In addition, two-dimensional (2D) architectures, which remain unresolved so far, would give them more interesting and unexpected properties. Herein, we report a facile, cost-effective, and scalable approach to synthesize Si nanocrystals embedded 2D SiO_x nanofoils for next-generation lithium ion batteries through a solution-evaporation-induced interfacial sol-gel reaction of hydrogen silsesquioxane (HSiO_1.5, HSQ). The unique nature of the thus-prepared centimeter scale 2D nanofoil with a large surface area enables ultrafast Li⁺ insertion and extraction, with a reversible capacity of more than 650 mAh g⁻¹, even at a high current density of 50 C (50 A g⁻¹). Moreover, the 2D nanostructured Si/SiO_x nanofoils show excellent cycling performance up to 200 cycles and maintain their initial dimensional stability. This superior performance stems from the peculiar nanoarchitecture of 2D Si/SiO_x nanofoils, which provides short diffusion paths for lithium ions and abundant free space to effectively accommodate the huge volume changes of Si during cycling.

Delicate Structural Control of Si-SiOx-C Composite via High-Speed Spray Pyrolysis for Li-Ion Battery Anodes

Despite the high theoretical capacity, silicon (Si) anodes in lithium-ion batteries have difficulty in meeting the commercial standards in various aspects. In particular, the huge volume change of Si makes it very challenging to simultaneously achieve high initial Coulombic efficiency (ICE) and long-term cycle life. Herein, we report spray pyrolysis to prepare Si-SiO_x composite using an aqueous precursor solution containing Si nanoparticles, citric acid, and sodium hydroxide (NaOH). In the precursor solution, Si nanoparticles are etched by NaOH with the production of [SiO₄]^4-. During the dynamic course of spray pyrolysis, [SiO₄]^4- transforms to SiO_x matrix and citric acid decomposes to carbon surface layer with the assistance of NaOH that serves as a decomposition catalyst. As a result, a Si-SiO_x composite, in which Si nanodomains are homogeneously embedded in the SiO_x matrix with carbon surface layer, is generated by a one-pot process with a residence time of only 3.5 s in a flow reactor. The optimal composite structure in terms of Si domain size and Si-to-O ratio exhibited excellent electrochemical performance, such as reversible capacity of 1561.9 mAh g^-1 at 0.06C rate and ICE of 80.2% and 87.9% capacity retention after 100 cycles at 1C rate.

Si/SiOx -Conductive Polymer Core-Shell Nanospheres with an Improved Conducting Path Preservation for Lithium-Ion Battery

Non-stoichiometric SiO_x based materials have gained much attention as high capacity lithium storage materials. However, their anode performance of these materials should be further improved for their commercial success. A conductive polymer, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS), is employed as a flexible electrical interconnector to improve the electrochemical performance of Si/SiO_x nanosphere anode materials for lithium ion batteries (LIBs). The resulting Si/SiO_x -PEDOT:PSS core-shell structured material with the small amount (1 wt %) of PEDOT:PSS shows the improved initial reversible capacity of 968.2 mA h g^-1 with excellent long-term cycle performance over 200 cycles. These promising properties can be attributed to the use of the electroconductive and flexible PEDOT:PSS shell layer, which protects the electrical conduction pathways in the electrode from the large volume changes of silicon during cycling.

Facile Synthesis of Carbon-Coated Silicon/Graphite Spherical Composites for High-Performance Lithium-Ion Batteries

A high-performance Si/carbon/graphite composite in which Si nanoparticles are attached onto the surface of natural graphite by carbonization of coal-tar pitch is proposed for use in lithium-ion batteries. This multicomponent structure is favorable for improving Li(+) storage capability because the amorphous carbon layer encapsulating Si nanoparticles offers sufficient electric conductivity and strong elasticity to facilitate relaxation of strain caused by electrochemical reaction of Si during cycles. The Si/carbon/graphite composite exhibits a specific capacity of 712 mAh g(-1) at a constant current density of 130 mA g(-1), and maintains more than 80% of its initial capacity after 100 cycles. Moreover, it shows a high capacity retention of approximately 88% even at a high current density of 5 C (3250 mA g(-1)). On the basis of electrochemical and structural analyses, we suggest that a rational design of the Si/carbon/graphite composite is mainly responsible for delivering a high reversible capacity and stable cycle performance. Furthermore, the proposed synthetic route for the Si/carbon/graphite composite is simple and cost-effective for mass production.

Carbon Nanofiber/3D Nanoporous Silicon Hybrids as High Capacity Lithium Storage Materials

Carbon nanofiber (CNF)/3D nanoporous (3DNP) Si hybrid materials were prepared by chemical etching of melt-spun Si/Al-Cu-Fe alloy nanocomposites, followed by carbonization using a pitch. CNFs were successfully grown on the surface of 3DNP Si particles using residual Fe impurities after acidic etching, which acted as a catalyst for the growth of CNFs. The resulting CNF/3DNP Si hybrid materials showed an enhanced cycle performance up to 100 cycles compared to that of the pristine Si/Al-Cu-Fe alloy nanocomposite as well as that of bare 3DNP Si particles. These results indicate that CNFs and the carbon coating layer have a beneficial effect on the capacity retention characteristics of 3DNP Si particles by providing continuous electron-conduction pathways in the electrode during cycling. The approach presented here provides another way to improve the electrochemical performances of porous Si-based high capacity anode materials for lithium-ion batteries.

High-Performance Si/SiOx Nanosphere Anode Material by Multipurpose Interfacial Engineering with Black TiO(2-x)

Silicon oxides (SiOx) have attracted recent attention for their great potential as promising anode materials for lithium ion batteries as a result of their high energy density and excellent cycle performance. Despite these advantages, the commercial use of these materials is still impeded by low initial Coulombic efficiency and high production cost associated with a complicated synthesis process. Here, we demonstrate that Si/SiOx nanosphere anode materials show much improved performance enabled by electroconductive black TiO(2-x) coating in terms of reversible capacity, Coulombic efficiency, and thermal reliability. The resulting anode material exhibits a high reversible capacity of 1200 mAh g(-1) with an excellent cycle performance of up to 100 cycles. The introduction of a TiO(2-x) layer induces further reduction of the Si species in the SiOx matrix phase, thereby increasing the reversible capacity and initial Coulombic efficiency. Besides the improved electrochemical performance, the TiO(2-x) coating layer plays a key role in improving the thermal reliability of the Si/SiOx nanosphere anode material at the same time. We believe that this multipurpose interfacial engineering approach provides another route toward high-performance Si-based anode materials on a commercial scale.

Oxidized starch as a superior binder for silicon anodes in lithium-ion batteries

Commercial oxidized starch (OS) containing oxidized amylose and oxidized amylopectin is proposed as a superior binder for silicon anodes.

A swelling-suppressed Si/SiOx nanosphere lithium storage material fabricated by graphene envelopment

A swelling-suppressed, Si nanocrystals-embedded SiO_x nanospheres lithium storage material was prepared by graphene envelopment.

SiOx and carbon double-layer coated Si nanorods as anode materials for lithium-ion batteries

SNs@SiO_x/C composite delivers a reversible capacity of 779 mA h g⁻¹ over 300 cycles at a current density of 400 mA g⁻¹.

Scalable Preparation of Ternary Hierarchical Silicon Oxide-Nickel-Graphite Composites for Lithium-Ion Batteries

Silicon monoxide is a promising anode candidate because of its high theoretical capacity and good cycle performance. To solve the problems associated with this material, including large volume changes during charge-discharge processes, we report a ternary hierarchical silicon oxide-nickel-graphite composite prepared by a facile two-step ball-milling method. The composite consists of nano-Si dispersed silicon oxides embedded in nano-Ni/graphite matrices (Si@SiOx /Ni/graphite). In the composite, crystalline nano-Si particles are generated by the mechanochemical reduction of SiO by ball milling with Ni. These nano-Si dispersed oxides have abundant electrochemical activity and can provide high Li-ion storage capacity. Furthermore, the milled nano-Ni/graphite matrices stick well to active materials and interconnect to form a crosslinked framework, which functions as an electrical highway and a mechanical backbone so that all silicon oxide particles become electrochemically active. Owing to these advanced structural and electrochemical characteristics, the composite enhances the utilization efficiency of SiO, accommodates its large volume expansion upon cycling, and has good ionic and electronic conductivity. The composite electrodes thus exhibit substantial improvements in electrochemical performance. This ternary hierarchical Si@SiOx /Ni/graphite composite is a promising candidate anode material for high-energy lithium-ion batteries. Additionally, the mechanochemical ball-milling method is low cost and easy to reproduce, indicating potential for the commercial production of the composite materials.

Mechanochemically Reduced SiO2 by Ti Incorporation as Lithium Storage Materials

This study presents a simple and effective method of reducing amorphous silica (a-SiO2 ) with Ti metal through high-energy mechanical milling for improving its reactivity when used as an anode material in lithium-ion batteries. Through thermodynamic calculations, it is determined that Ti metal can easily take oxygen atoms from a-SiO2 by forming a thermodynamically stable SiO2-x /TiOx composite, meaning that electrochemically inactive a-SiO2 is partially reduced by the addition of Ti metal powder during milling. This mechanically reduced SiO2-x /TiOx composite anode exhibits a greatly improved electrochemical reactivity, with a reversible capacity of more than 700 mAh g(-1) and excellent cycle performance over 100 cycles. Furthermore, an enhancement in the mechanical and thermal stability of the composite during cycling can be mainly attributed to the in situ formation of the SiO2-x /TiOx phase. These findings provide new insight into the rational design of robust, high-capacity, Si-based anode materials, as well as their reaction mechanism.

Dual-Size Silicon Nanocrystal-Embedded SiO(x) Nanocomposite as a High-Capacity Lithium Storage Material

SiOx-based materials attracted a great deal of attention as high-capacity Li(+) storage materials for lithium-ion batteries due to their high reversible capacity and good cycle performance. However, these materials still suffer from low initial Coulombic efficiency as well as high production cost, which are associated with the complicated synthesis process. Here, we propose a dual-size Si nanocrystal-embedded SiOx nanocomposite as a high-capacity Li(+) storage material prepared via cost-effective sol-gel reaction of triethoxysilane with commercially available Si nanoparticles. In the proposed nanocomposite, dual-size Si nanocrystals are incorporated into the amorphous SiOx matrix, providing a high capacity (1914 mAh g(-1)) with a notably improved initial efficiency (73.6%) and stable cycle performance over 100 cycles. The highly robust electrochemical and mechanical properties of the dual-size Si nanocrystal-embedded SiOx nanocomposite presented here are mainly attributed to its peculiar nanoarchitecture. This study represents one of the most promising routes for advancing SiOx-based Li(+) storage materials for practical use.

Encapsulating micro-nano Si/SiO(x) into conjugated nitrogen-doped carbon as binder-free monolithic anodes for advanced lithium ion batteries

Silicon monoxide, a promising silicon-based anode candidate for lithium-ion batteries, has recently attracted much attention for its high theoretical capacity, good cycle stability, low cost, and environmental benignity. Currently, the most critical challenge is to improve its low initial coulombic efficiency and significant volume changes during the charge-discharge processes. Herein, we report a binder-free monolithic electrode structure based on directly encapsulating micro-nano Si/SiOx particles into conjugated nitrogen-doped carbon frameworks to form monolithic, multi-core, cross-linking composite matrices. We utilize micro-nano Si/SiOx reduced by high-energy ball-milling SiO as active materials, and conjugated nitrogen-doped carbon formed by the pyrolysis of polyacrylonitrile both as binders and conductive agents. Owing to the high electrochemical activity of Si/SiOx and the good mechanical resiliency of conjugated nitrogen-doped carbon backbones, this specific composite structure enhances the utilization efficiency of SiO and accommodates its large volume expansion, as well as its good ionic and electronic conductivity. The annealed Si/SiOx/polyacrylonitrile composite electrode exhibits excellent electrochemical properties, including a high initial reversible capacity (2734 mA h g(-1) with 75% coulombic efficiency), stable cycle performance (988 mA h g(-1) after 100 cycles), and good rate capability (800 mA h g(-1) at 1 A g(-1) rate). Because the composite is naturally abundant and shows such excellent electrochemical performance, it is a promising anode candidate material for lithium-ion batteries. The binder-free monolithic architectural design also provides an effective way to prepare other monolithic electrode materials for advanced lithium-ion batteries.

Vesicular hydrogen silsesquioxane-mediated synthesis of nanocrystalline silicon dispersed in a mesoporous silica/suboxide matrix, with potential for electrochemical applications

Silicon nanoparticles embedded in a mesoporous SiO₂/SiO_x matrix have been prepared by pyrolysis of condensed hydrogen silsesquioxane vesicles.