Encapsulating Si Nanoparticles Research Articles

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.

A honeycomb-cobweb inspired hierarchical core–shell structure design for electrospun silicon/carbon fibers as lithium-ion battery anodes

The silicon/carbon (Si/C) hybrid fibers with a hierarchical core–shell structure are prepared by encapsulating Si nanoparticles in the interconnected hollow carbon fibers (Si@IHCFs) based on a dual coaxial electrospinning technique. For the hierarchical structure, Si nanoparticles are embedded in the honeycomb-like carbon framework in the fiber core, which is further wrapped by the interlocked cobweb-like carbon shell network. As lithium-ion battery anode, the well-defined Si@IHCFs demonstrates a reversible capacity of 903 mAh g−1 and a capacity retention of 89% after 100 cycles with a current density of 0.2 A g−1. With the current density gradually increasing to 2.0 A g−1, the electrode shows a specific capacity of 743 mAh g−1, exhibiting superior rate capability compared to the Si/C fibers with a core–shell but unconnected structure. The excellent electrochemical properties are attributed to the hierarchical core–shell structure and cross-linked network for the Si/C composite fibers. The carbon framework in the core region accommodates the volume expansion of Si by the honeycomb-like pores. And the interconnected carbon shell can not only prevent electrolyte from permeating into the core section, but also improve the electronic conductivity by the connections in the fiber network.

Three‐Dimensional Interconnected Network of Graphene‐Wrapped Silicon/Carbon Nanofiber Hybrids for Binder‐Free Anodes in Lithium‐Ion Batteries

AbstractA three‐dimensional (3D) silicon/carbon nanofiber–graphene (Si/CNF‐G) nanostructure is constructed by encapsulating Si nanoparticles in carbon nanofibers, followed by wrapping with graphene nanosheets. The graphene‐wrapped silicon/carbon nanofibers hybrids have the advantages of good dispersion of Si nanoparticles inside the 3D carbon network. Meanwhile, the 3D carbon network can also act as a current collector to promote charge transfer and maintain stable electrical contact of the Si nanoparticles. The resulting Si/CNF‐G composites can be used directly as binder‐free electrodes. The composite exhibits a stable capacity retention and a reversible capacity of 878 mAh g−1 for up to 100 cycles, along with a high rate capacity (514 mAh g−1 at 5.0 A g−1). These results provide a promising research platform for fabricating stable electrodes with improved electrochemical performance.

Direct amination of Si nanoparticles for the preparation of Si@ultrathin SiOx@graphene nanosheets as high performance lithium-ion battery anodes

Graphene nanosheet encapsulated Si nanoparticles with an ultrathin silica shell have been fabricated by an environmentally friendly and effective amination method.

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

Carbon nanofibers encapsulating Si nanoparticles (CNFs/SiNPs) were prepared via an electrospinning method and chemically functionalized with 3-aminopropyltriethoxysilane (APS) to be grafted onto graphene oxide (GO). As a result, the thin and flexible GO, which exhibits a negative charge in aqueous solution, fully wrapped around the APS-functionalized CNFs with a positive surface charge via electrostatic self-assembly. After the formation of chemical bonds between the epoxy groups on GO and the amine groups in APS via an epoxy ring opening reaction, the GO was chemically reduced to a reduced graphene oxide (rGO). Electrochemical and morphological characterizations showed that capacity loss by structural degradation and electrolyte decomposition on Si surface were significantly suppressed in the rGO-wrapped CNFs/SiNPs (CNFs/SiNPs@rGO). Superior capacities were consequently maintained for up to 200 cycles at a high current density (1048 mA h g(-1) at 890 mA g(-1)) compared to CNFs/SiNPs without the rGO wrapping (304 mA h g(-1) at 890 mA g(-1)). Moreover, the resistance of the SEI layer and charge transfer resistance were also considerably reduced by 24% and 88%, respectively. The described graphene wrapping offers a versatile way to enhance the mechanical integrity and electrochemical stability of Si composite anode materials.

Enhanced cycling stability of silicon anode by in situ polymerization of poly(aniline-co-pyrrole)

Poly(aniline-co-pyrrole)-encapsulated Si nanoparticles composite anode material were prepared by an in situ chemical oxidation polymerization method.

Graphene‐Bonded and ‐Encapsulated Si Nanoparticles for Lithium Ion Battery Anodes

Silicon (Si) has been considered a very promising anode material for lithium ion batteries due to its high theoretical capacity. However, high-capacity Si nanoparticles usually suffer from low electronic conductivity, large volume change, and severe aggregation problems during lithiation and delithiation. In this paper, a unique nanostructured anode with Si nanoparticles bonded and wrapped by graphene is synthesized by a one-step aerosol spraying of surface-modified Si nanoparticles and graphene oxide suspension. The functional groups on the surface of Si nanoparticles (50-100 nm) not only react with graphene oxide and bind Si nanoparticles to the graphene oxide shell, but also prevent Si nanoparticles from aggregation, thus contributing to a uniform Si suspension. A homogeneous graphene-encapsulated Si nanoparticle morphology forms during the aerosol spraying process. The open-ended graphene shell with defects allows fast electrochemical lithiation/delithiation, and the void space inside the graphene shell accompanied by its strong mechanical strength can effectively accommodate the volume expansion of Si upon lithiation. The graphene shell provides good electronic conductivity for Si nanoparticles and prevents them from aggregating during charge/discharge cycles. The functionalized Si encapsulated by graphene sample exhibits a capacity of 2250 mAh g⁻¹ (based on the total mass of graphene and Si) at 0.1C and 1000 mAh g⁻¹ at 10C, and retains 85% of its initial capacity even after 120 charge/discharge cycles. The exceptional performance of graphene-encapsulated Si anodes combined with the scalable and one-step aerosol synthesis technique makes this material very promising for lithium ion batteries.

Effects of surrounding confinements of Si nanoparticles on Si-based anode performance for lithium ion batteries

We report herein the effects of various surrounding confinements of Si nanoparticles on the electrochemical performance of Si nanoparticles based anode for lithium ion batteries (LIBs). Three different types of surrounding confinements are incorporated onto or around the surface of Si nanoparticles: Si nanoparticles-embedded carbon nanofibers (Si@CNF) via electrospinning, carbon nitride encapsulated Si nanoparticles with core/shell structure (Si@CND), and binder enriched Si nanoparticles-based anode (Si@RBD). Morphology and microstructure of the samples are characterized using X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, and the results were discussed in relation to the electrochemical performances. It is found that Si@CNF which has conducting hard surrounding confinements and Si@RBD exhibited high reversible specific capacity of 620 mA hg −1 and 1200 mA hg −1, up to 30th cycle, respectively. Meanwhile, Si@CND that has mechanically hard but poor electrical conductivity exhibits low specific capacity compared with the other two samples.