A Critical Size of Silicon Nano-Anodes for Lithium Rechargeable Batteries

A heart-coronary arteries structure of carbon nanofibers/graphene/silicon composite anode for high performance lithium ion batteries

In an animal body, coronary arteries cover around the whole heart and supply the necessary oxygen and nutrition so that the heart muscle can survive as well as can pump blood in and out very efficiently. Inspired by this, we have designed a novel heart-coronary arteries structured electrode by electrospinning carbon nanofibers to cover active anode graphene/silicon particles. Electrospun high conductive nanofibers serve as veins and arteries to enhance the electron transportation and improve the electrochemical properties of the active "heart" particles. This flexible binder free carbon nanofibers/graphene/silicon electrode consists of millions of heart-coronary arteries cells. Besides, in the graphene/silicon "hearts", graphene network improves the electrical conductivity of silicon nanopaticles, buffers the volume change of silicon, and prevents them from directly contacting with electrolyte. As expected, this novel composite electrode demonstrates excellent lithium storage performance with a 86.5% capacity retention after 200 cycles, along with a high rate performance with a 543 mAh g^-1 capacity at the rate of 1000 mA g^-1.

Tuning Porosity and Surface Area in Mesoporous Silicon for Application in Li-Ion Battery Electrodes

This work aims to improve the poor cycle lifetime of silicon-based anodes for Li-ion batteries by tuning microstructural parameters such as pore size, pore volume, and specific surface area in chemically synthesized mesoporous silicon. Here we have specifically produced two different mesoporous silicon samples from the magnesiothermic reduction of ordered mesoporous silica in either argon or forming gas. In situ X-ray diffraction studies indicate that samples made in Ar proceed through a Mg₂Si intermediate, and this results in samples with larger pores (diameter ≈ 90 nm), modest total porosity (34%), and modest specific surface area (50 m² g^-1). Reduction in forming gas, by contrast, results in direct conversion of silica to silicon, and this produces samples with smaller pores (diameter ≈ 40 nm), higher porosity (41%), and a larger specific surface area (70 m² g^-1). The material with smaller pores outperforms the one with larger pores, delivering a capacity of 1121 mAh g^-1 at 10 A g^-1 and retains 1292 mAh g^-1 at 5 A g^-1 after 500 cycles. For comparison, the sample with larger pores delivers a capacity of 731 mAh g^-1 at 10 A g^-1 and retains 845 mAh g^-1 at 5 A g^-1 after 500 cycles. The dependence of capacity retention and charge storage kinetics on the nanoscale architecture clearly suggests that these microstructural parameters significantly impact the performance of mesoporous alloy type anodes. Our work is therefore expected to contribute to the design and synthesis of optimal mesoporous architectures for advanced Li-ion battery anodes.

A Step toward High-Energy Silicon-Based Thin Film Lithium Ion Batteries

The next generation of lithium ion batteries (LIBs) with increased energy density for large-scale applications, such as electric mobility, and also for small electronic devices, such as microbatteries and on-chip batteries, requires advanced electrode active materials with enhanced specific and volumetric capacities. In this regard, silicon as anode material has attracted much attention due to its high specific capacity. However, the enormous volume changes during lithiation/delithiation are still a main obstacle avoiding the broad commercial use of Si-based electrodes. In this work, Si-based thin film electrodes, prepared by magnetron sputtering, are studied. Herein, we present a sophisticated surface design and electrode structure modification by amorphous carbon layers to increase the mechanical integrity and, thus, the electrochemical performance. Therefore, the influence of amorphous C thin film layers, either deposited on top (C/Si) or incorporated between the amorphous Si thin film layers (Si/C/Si), was characterized according to their physical and electrochemical properties. The thin film electrodes were thoroughly studied by means of electrochemical impedance spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. We can show that the silicon thin film electrodes with an amorphous C layer showed a remarkably improved electrochemical performance in terms of capacity retention and Coulombic efficiency. The C layer is able to mitigate the mechanical stress during lithiation of the Si thin film by buffering the volume changes and to reduce the loss of active lithium during solid electrolyte interphase formation and cycling.

Mesoporous Silicon Hollow Nanocubes Derived from Metal-Organic Framework Template for Advanced Lithium-Ion Battery Anode

Controlling the morphology of nanostructured silicon is critical to improving the structural stability and electrochemical performance in lithium-ion batteries. The use of removable or sacrificial templates is an effective and easy route to synthesize hollow materials. Herein, we demonstrate the synthesis of mesoporous silicon hollow nanocubes (m-Si HCs) derived from a metal-organic framework (MOF) as an anode material with outstanding electrochemical properties. The m-Si HC architecture with the mesoporous external shell (∼15 nm) and internal void (∼60 nm) can effectively accommodate volume variations and relieve diffusion-induced stress/strain during repeated cycling. In addition, this cube architecture provides a high electrolyte contact area because of the exposed active site, which can promote the transportation of Li ions. The well-designed m-Si HC with carbon coating delivers a high reversible capacity of 1728 mAhg^-1 with an initial Coulombic efficiency of 80.1% after the first cycle and an excellent rate capability of >1050 mAhg^-1 even at a 15 C-rate. In particular, the m-Si HC anode effectively suppresses electrode swelling to ∼47% after 100 cycles and exhibits outstanding cycle stability of 850 mAhg^-1 after 800 cycles at a 1 C-rate. Moreover, a full cell (2.9 mAhcm^-2) comprising a m-Si HC-graphite anode and LiCoO₂ cathode exhibits remarkable cycle retention of 72% after 100 cycles at a 0.2 C-rate.

Modeling of Stresses and Strains during (De)Lithiation of Ni3Sn2-Coated Nickel Inverse-Opal Anodes

Tin alloy-based anodes supported by inverse-opal nanoscaffolds undergo large volume changes from (de)lithiation during cyclic battery (dis)charging, affecting their mechanical stability. We perform continuum mechanics-based simulation to study the evolution of internal stresses and strains as a function of the geometry of the active layer(s): (i) thickness of Ni₃Sn₂ single layer (30 and 60 nm) and (ii) stacking sequence of Ni₃Sn₂ and amorphous Si in bilayers (60 nm thick). For single Ni₃Sn₂ active layers, a thinner layer displays higher strains and stresses, which are relevant to mechanical stability, but causes lower strains and stresses in the Ni scaffold. For Ni₃Sn₂-Si bilayers, the stacking sequence significantly affects the deformation of the active layers and thus its mechanical stability due to different lithiation behaviors and volume changes.

Electrochemically Induced Shape-Memory Behavior of Si Nanopillar-Patterned Electrode for Li Ion Batteries

A nanopillar-patterned Si substrate was fabricated by photolithography, and its potential as an anode material for Li ion secondary batteries was investigated. The Si nanopillar electrode showed a capacity of ∼3000 mAh g^-1 during 100 charging/discharging cycles, with 98.3% capacity retention, and it was revealed that the nanopillars underwent delithiation via a process similar to shape-memory behavior. Despite the tensile stress and structural fractures resulting from repeated lithiation, the nanoscale size and residual crystalline tip of the pillar (influenced by the bulk crystalline Si base) enabled recrystallization and transformation into a single-crystalline phase. To the best of our knowledge, this observation of shape memory recrystallization mechanism observation was not reported before for Si used as the active material in Li ion battery applications; these findings are expected to provide new insights into electrode materials for rechargeable batteries.

Nanospherical solid electrolyte interface layer formation in binder-free carbon nanotube aerogel/Si nanohybrids to provide lithium-ion battery anodes with a long-cycle life and high capacity

Silicon anodes for lithium ion batteries (LiBs) have been attracting considerable attention due to a theoretical capacity up to about 10 times higher than that of conventional graphite. However, huge volume expansion during the cycle causes cracks in the silicon, resulting in the degradation of cycling performance and eventual failure. Moreover, low electrical conductivity and an unstable solid electrolyte interface (SEI) layer resulting from repeated changes in volume still block the next step forward for the commercialization of the silicon material. Herein we demonstrate the carbon nanotube (CNT) aerogel/Si nanohybrid structure for anode materials of LiBs via freeze casting followed by an RF magnetron sputtering process, exhibiting improved capacity retention compared to Si only samples during 1000 electrochemical cycles. The CNT aerogels as 3D porous scaffold structures could provide buffer volume for the expansion/shrinkage of Si lattices upon cycling and increase electrical conductivity. In addition, the nanospherical and relatively thin SEI layers of the CNT aerogel/Si nanohybrid structure show better lithium ion diffusion characteristics during cycling. For this reason, the Si@CNT aerogel anode still yielded a high specific capacity of 1439 mA h g^-1 after 1000 charge/discharge cycles with low capacity fading. Our approach could be applied to other group IV LiB materials that undergo large volume changes, and also has promising potential for high performance energy applications.

Carbon-Coated Silicon Nanowires on Carbon Fabric as Self-Supported Electrodes for Flexible Lithium-Ion Batteries

A novel self-supported electrode with long cycling life and high mass loading was developed based on carbon-coated Si nanowires grown in situ on highly conductive and flexible carbon fabric substrates through a nickel-catalyzed one-pot atmospheric pressure chemical vapor deposition. The high-quality carbon coated Si nanowires resulted in high reversible specific capacity (∼3500 mA h g^-1 at 100 mA g^-1), while the three-dimensional electrode's unique architecture leads to a significantly improved robustness and a high degree of electrode stability. An exceptionally long cyclability with a capacity retention of ∼66% over 500 cycles at 1.0 A g^-1 was achieved. The controllable high mass loading enables an electrode with extremely high areal capacity of ∼5.0 mA h cm^-2. Such a scalable electrode fabrication technology and the high-performance electrodes hold great promise in future practical applications in high energy density lithium-ion batteries.

Cyclopentadithiophene-benzoic acid copolymers as conductive binders for silicon nanoparticles in anode electrodes of lithium ion batteries

Cyclopentadithiophene-benzoic acid copolymers have been synthesized by direct arylation followed by saponification for use as conductive binders for silicon nanoparticles in anode electrode of lithium ion batteries.

Foamed silicon particles as a high capacity anode material for lithium-ion batteries

The foamed Si particles prepared by a milling-assisted alkaline etching process showed excellent electrochemical performance as an anode for lithium-ion batteries.

Linking particle size to improved electrochemical performance of SiO anodes for Li-ion batteries

A first attempt to understand the relationship between the particle size and the electrochemical properties of SiO was conducted.

Novel core–shell structured Si/S-doped-carbon composite with buffering voids as high performance anode for Li-ion batteries

Novel core–shell structured Si/S-doped carbon composite with buffering voids prepared by hydrothermal method and followed by carbonization and removal of template layer, exhibiting a reversible capacity of 664 mA h g⁻¹ over 300 cycles.

A 3D pore-nest structured silicon–carbon composite as an anode material for high performance lithium-ion batteries

A novel silicon–carbon composite with a 3D pore-nest structure denoted as Si@SiO_x/CNTs@C was prepared and studied, and the capacity of a Si@SiO_x/CNTs@C composite anode can be maintained at above 1740 mA h g⁻¹ at a current density of 0.42 A g⁻¹ after 700 cycles.

Advances in electrode materials for Li-based rechargeable batteries

We summarize strategies to enhance the performance of electrode materials for Li-based batteries through nanoengineering and surface coating, and introduce new trends in developing alternative materials, battery concepts and cell configurations.

Room temperature solvent-free reduction of SiCl4 to nano-Si for high-performance Li-ion batteries

A highly efficient method to prepare Si nanoparticles for high-performance lithium ion batteries: direct reduction of SiCl₄ using Na metal by mechanical milling at room temperature without using any organic solvents.

Stabilized lithium-ion battery anode performance by calcium-bridging of two dimensional siloxene layers

A Ca-bridged siloxene exhibits stable charge/discharge capacity as a lithium-ion battery anode, suggesting the structural stability of Si-planes with Si₆H₆.

Dual Core-Shell Structured Si@SiOx@C Nanocomposite Synthesized via a One-Step Pyrolysis Method as a Highly Stable Anode Material for Lithium-Ion Batteries

Silicon (Si) has been regarded as a promising high-capacity anode material for developing advanced lithium-ion batteries (LIBs), but the practical application of Si anodes is still unsuccessful mainly due to the insufficient cyclability. To deal with this issue, we propose a new route to construct a dual core-shell structured Si@SiO_x@C nanocomposite by direct pyrolysis of poly(methyl methacrylate) (PMMA) polymer on the surface of Si nanoparticles. Since the PMMA polymers can be chemically bonded on the nano-Si surface through the interaction between ester group and Si surface group, and thermally decomposed in the subsequent pyrolysis process with their alkyl chains converted to carbon and the residue oxygen recombining with Si to form SiO_x, the dual core-shell structure can be conveniently formed in a one-step procedure. Benefiting from the strong buffering effect of the SiO_x interlayer and the efficient blocking action of dense outer carbon layer in preventing electrolyte permeation, the obtained nanocomposite demonstrates a high capacity of 1972 mA h g^-1, a stable cycling performance with a capacity retention of >1030 mA h g^-1 over 500 cycles, and particularly a superiorly high Coulombic efficiency of >99.5% upon extended cycling, exhibiting a great promise for practical uses. More importantly, the synthetic method proposed in this work is facile and low cost, making it more suitable for large-scale production of high capacity anode for advanced LIBs.

Silicon/Mesoporous Carbon/Crystalline TiO2 Nanoparticles for Highly Stable Lithium Storage

A core-shell-shell heterostructure of Si nanoparticles as the core with mesoporous carbon and crystalline TiO₂ as the double shells (Si@C@TiO₂) is utilized as an anode material for lithium-ion batteries, which could successfully tackle the vital setbacks of Si anode materials, in terms of intrinsic low conductivity, unstable solid-electrolyte interphase (SEI) films, and serious volume variations. Combined with the high theoretical capacity of the Si core (4200 mA h g^-1), the double shells can perfectly avoid direct contact of Si with electrolyte, leading to stable SEI films and enhanced Coulombic efficiency. On the other hand, the carbon inner shell is effective at improving the overall conductivity of the Si-based electrode; the TiO₂ outer shell is expected to serve as a rigid layer to achieve high structural stability and integrity of the core-shell-shell structure. As a result, the elaborate Si@C@TiO₂ core-shell-shell nanoparticles are proven to show excellent Li storage properties. It delivers high reversible capacity of 1726 mA h g^-1 over 100 cycles, with outstanding cyclability of 1010 mA h g^-1 even after 710 cycles.

A new strategy for developing superior electrode materials for advanced batteries: using a positive cycling trend to compensate the negative one to achieve ultralong cycling stability

In this communication, in order to develop superior electrode materials for advanced energy storage devices, a new strategy is proposed and then verified by the (Si@MnO)@C/RGO anode material for lithium ion batteries. The core idea of this strategy is the use of a positive cycling trend (gradually increasing Li-storage capacities of the MnO-based constituent during cycling) to compensate the negative one (gradually decreasing capacities of the Si anode) to achieve ultralong cycling stability. As demonstrated in both half and full cells, the as-prepared (Si@MnO)@C/RGO nanocomposite exhibits superior Li-storage properties in terms of ultralong cycling stability (no obvious increase or decrease of capacity when cycled at 3 A g^-1 after 1500 cycles) and excellent high-rate capabilities (delivering a capacity of ca. 540 mA h g^-1 at a high current density of 8 A g^-1) as well as a good full-cell performance. In addition, the structure of the electrodes is stable after 200 cycles. Such a strategy provides a new idea to develop superior electrode materials for next-generation energy storage devices with ultralong cycling stabilities.

5L-Scale Magnesio-Milling Reduction of Nanostructured SiO2 for High Capacity Silicon Anodes in Lithium-Ion Batteries

Nanostructured silicon (Si) is useful in many applications and has typically been synthesized by bottom-up colloid-based solution processes or top-down gas phase reactions at high temperatures. These methods, however, suffer from toxic precursors, low yields, and impractical processing conditions (i.e., high pressure). The magnesiothermic reduction of silicon oxide (SiO₂) has also been introduced as an alternative method. Here, we demonstrate the reduction of SiO₂ by a simple milling process using a lab-scale planetary-ball mill and industry-scale attrition-mill. Moreover, an ignition point where the reduction begins was consistently observed for the milling processes, which could be used to accurately monitor and control the reaction. The complete conversion of rice husk SiO₂ to high purity Si was demonstrated, taking advantage of the rice husk's uniform nanoporosity and global availability, using a 5L-scale attrition-mill. The resulting porous Si showed excellent performance as a Li-ion battery anode, retaining 82.8% of the initial capacity of 1466 mAh g^-1 after 200 cycles.

In situ Scanning Electron Microscopy of Silicon Anode Reactions in Lithium-Ion Batteries during Charge/Discharge Processes

A comprehensive understanding of the charge/discharge behaviour of high-capacity anode active materials, e.g., Si and Li, is essential for the design and development of next-generation high-performance Li-based batteries. Here, we demonstrate the in situ scanning electron microscopy (in situ SEM) of Si anodes in a configuration analogous to actual lithium-ion batteries (LIBs) with an ionic liquid (IL) that is expected to be a functional LIB electrolyte in the future. We discovered that variations in the morphology of Si active materials during charge/discharge processes is strongly dependent on their size and shape. Even the diffusion of atomic Li into Si materials can be visualized using a back-scattering electron imaging technique. The electrode reactions were successfully recorded as video clips. This in situ SEM technique can simultaneously provide useful data on, for example, morphological variations and elemental distributions, as well as electrochemical data.

Silica Wastes to High-Performance Lithium Storage Materials: A Rational Designed Al2 O3 Coating Assisted Magnesiothermic Process

Si/C yolk-shell structures have been developed to deal with the major issues associated with Si anodes: the huge volume changes and the low electrical conductivity. However, the fabrication process often involves expensive starting materials and/or simultaneously generates insulated SiC, which is harmful for Si anodes. Here, silica wastes from the optical fibers industry are used as starting materials to prepare high performance Si/C materials with Si@void@C yolk-shell structure via a rational designed Al₂ O₃ coating assisted magnesiothermic process. The obtained yolk-shell Si@void@C materials have a capacity of more than 1450 mA h g^-1 after 100 cycles at 0.4 A g^-1 . Thanks to the easily coated and removed Al₂ O₃ layer, the general formation of SiC can be avoided which is beneficial for improving the rate performances, and a capacity of ≈800 mA h g^-1 is still kept after 200 cycles at a high rate of 10 A g^-1 with a low capacity loss of 0.08% per cycle.

Rapid, in Situ Synthesis of High Capacity Battery Anodes through High Temperature Radiation-Based Thermal Shock

High capacity battery electrodes require nanosized components to avoid pulverization associated with volume changes during the charge-discharge process. Additionally, these nanosized electrodes need an electronically conductive matrix to facilitate electron transport. Here, for the first time, we report a rapid thermal shock process using high-temperature radiative heating to fabricate a conductive reduced graphene oxide (RGO) composite with silicon nanoparticles. Silicon (Si) particles on the order of a few micrometers are initially embedded in the RGO host and in situ transformed into 10-15 nm nanoparticles in less than a minute through radiative heating. The as-prepared composites of ultrafine Si nanoparticles embedded in a RGO matrix show great performance as a Li-ion battery (LIB) anode. The in situ nanoparticle synthesis method can also be adopted for other high capacity battery anode materials including tin (Sn) and aluminum (Al). This method for synthesizing high capacity anodes in a RGO matrix can be envisioned for roll-to-roll nanomanufacturing due to the ease and scalability of this high-temperature radiative heating process.

Lithiation of Crystalline Silicon As Analyzed by Operando Neutron Reflectivity

We present an operando neutron reflectometry study on the electrochemical incorporation of lithium into crystalline silicon for battery applications. Neutron reflectivity is measured from the ⟨100⟩ surface of a silicon single crystal which is used as a negative electrode in an electrochemical cell. The strong scattering contrast between Si and Li due to the negative scattering length of Li leads to a precise depth profile of Li within the Si anode as a function of time. The operando cell can be used to study the uptake and the release of Li over several cycles. Lithiation starts with the formation of a lithium enrichment zone during the first charge step. The uptake of Li can be divided into a highly lithiated zone at the surface (skin region) (x ∼ 2.5 in LixSi) and a much less lithiated zone deep into the crystal (growth region) (x ∼ 0.1 in LixSi). The total depth of penetration was less than 100 nm in all experiments. The thickness of the highly lithiated zone is the same for the first and second cycle, whereas the thickness of the less lithiated zone is larger for the second lithiation. A surface layer of lithium (x ∼ 1.1) remains in the silicon electrode after delithiation. Moreover, a solid electrolyte interface is formed and dissolved during the entire cycling. The operando analysis presented here demonstrates that neutron reflectivity allows the tracking of the kinetics of lithiation and delithiation of silicon with high spatial and temporal resolution.

Supercritical Carbon Dioxide-Assisted Process for Well-Dispersed Silicon/Graphene Composite as a Li ion Battery Anode

The silicon (Si)/graphene composite has been touted as one of the most promising anode materials for lithium ion batteries. However, the optimal fabrication method for this composite remains a challenge. Here, we developed a novel method using supercritical carbon dioxide (scCO2) to intercalate Si nanoparticles into graphene nanosheets. Silicon was modified with a thin layer of polyaniline, which assisted the dispersion of graphene sheets by introducing π-π interaction. Using scCO2, well-dispersed Si/graphene composite was successfully obtained in a short time under mild temperature. The composite showed high cycle performance (1,789 mAh/g after 250 cycles) and rate capability (1,690 mAh/g at a current density of 4,000 mA/g). This study provides a new approach for cost-effective and scalable preparation of a Si/graphene composite using scCO2 for a highly stable lithium battery anode material.

Mussel-inspired Polydopamine-treated Copper Foil as a Current Collector for High-performance Silicon Anodes

A new Cu current collector was prepared by introducing a mussel-inspired polydopamine coating onto a Cu foil surface to improve the electrochemical performance of a Si electrode. The polydopamine coating covalently bonded the polymeric binder (with hydroxyl functional groups) via a condensation reaction. The coating improved the adhesion strength between the Si composite electrode and the Cu current collector (245.5 N m(-1), 297.5 N m(-1), and 353.2 N m(-1) for the Si electrodes based on bare Cu, polydopamine-treated Cu without thermal treatment, and polydopamine-treated Cu with thermal treatment, respectively). We demonstrate that the detachment between the Si composite electrode and the current collector plays an important role in determining the electrochemical performance of the Si electrode. The cycle life and rate capability of the Si electrode improved when the polydopamine surface-treated Cu current collector was used (963.9 mAh g(-1), 1361.1 mAh g(-1), and 1590.0 mAh g(-1) for the Si electrodes based on bare Cu, polydopamine-treated Cu without thermal treatment, and polydopamine-treated Cu with thermal treatment, respectively, at C/2 after 500 cycles).

Enhanced Electrochemical Performance of Heterogeneous Si/MoSi2 Anodes Prepared by a Magnesiothermic Reduction

This work explores facile synthesis of heterogeneous Si/MoSi2 nanocomposites via a one-step magnesiothermic reduction. MoSi2 serves as a highly electrically conductive nanoparticle that has several advantages of electrochemical properties, which is formed through the absorption of local heat accumulation generated by magnesiothermic reduction. As a result, the Si/MoSi2 nanocomposites exhibit excellent electrochemical performance, showing initial charge capacity of 1933.9 mA h g(-1) at a rate of 0.2 C and retaining 85.2% after 150 cycles. This work using local heat accumulation generated by magnesiothermic reduction demonstrates a large-scale method for producing high-performance Si-based anode materials, which could provide referential significances for other materials.

Porous γ-Fe2O3 spheres coated with N-doped carbon from polydopamine as Li-ion battery anode materials

Nitrogen doping has been demonstrated to play a crucial role in controlling the electronic properties of carbon-based composites. In this paper, nitrogen-doped carbon coated γ-Fe2O3 (NC@γ-Fe2O3) composite was successfully fabricated through a facile and high-yield strategy, including a hydrothermal reaction process for porous γ-Fe2O3 and a subsequent coating of nitrogen-doped carbon by using dopamine as precursor. The resulting composite combines the superior properties of porous Fe2O3 and heteroatom-doped conductive carbon layer derived from polydopamine. When used as the anode material of the lithium-ion battery, the as-prepared NC@γ-Fe2O3 composite exhibits excellent lithium storage properties in terms of high capacity, stable cycling performance (869.6 mAh g(-1) at the current density of 0.5 A g(-1) after 150 cycles) and excellent rate capability.

Fabrication of Binder-Free Pencil-Trace Electrode for Lithium-Ion Battery: Simplicity and High Performance

A binder-free and solvent-free pencil-trace electrode with intercalated clay particles (mainly SiO2) is prepared via a simple pencil-drawing process on grinded Cu substrate with rough surface and evaluated as an anode material for lithium-ion battery. The pencil-trace electrode exhibits a high reversible capacity of 672 mA h g(-1) at 100 mA g(-1) after 100 cycles, which can be attributed to the unique multilayered graphene particles with lateral size of few micrometers and the formation of LixSi alloys generated by interaction between Li(+) and an active Si produced in the electrochemical reduction of nano-SiO2 in the clay particles between the multilayered graphene particles. The multilayered graphene obtained by this process consists of 1 up to 20 and occasionally up to 50 sheets and thus can not only help accommodating the volume change and alleviating the structural strain during Li ion insertion and extraction but also allow rapid access of Li ions during charge-discharge cycling. Drawing with a pencil on grinded Cu substrate is not only very simple but also cost-effective and highly scalable, easily establishing graphitic circuitry through a solvent-free and binder-free approach.

Sandwich electrode designed for high performance lithium-ion battery

We fabricated a sandwich structure Li-ion battery electrode by trapping micron-sized silicon between a copper current collector and a graphene coating. During dynamic electrochemical cycles, the volume change of the silicon can be buffered by the coating through the deformation of soft graphenes. This structure can effectively prevent the silicon particles from escaping from the current collector while keeping the buffered graphene coating integrated and unbroken during deformation. The electrodes could be maintained for 400 cycles at a constant charge capacity of 1000 mA h g(-1).

Graphene Folding in Si Rich Carbon Nanofibers for Highly Stable, High Capacity Li-Ion Battery Anodes

Silicon nanoparticles (Si NPs) wrapped by graphene in carbon nanofibers were obtained via electrospinning and subsequent thermal treatment. In this study, water-soluble poly(vinyl alcohol) (PVA) with low carbon yield is selected to make the process water-based and to achieve a high silicon yield in the composite. It was also found that increasing the amount of graphene helps keep the PVA fiber morphology after carbonization, while forming a graphene network. The fiber SEM and HRTEM images reveal that micrometer graphene is heavily folded into sub-micron scale fibers during electrospinning, while Si NPs are incorporated into the folds with nanospace in between. When applied to lithium-ion battery anodes, the Si/graphene/carbon nanofiber composites show a high reversible capacity of ∼2300 mAh g(-1) at a charging rate of 100 mA/g and a stable capacity of 1191 mAh g(-1) at 1 A/g after more than 200 cycles. The interconnected graphene network not only ensures the excellent conductivity but also serves as a buffering matrix for the mechanic stress caused by volume change; the nanospace between Si NPs and folded graphene provides the space needed for volume expansion.

Cellulose-Rich Nanofiber-Based Functional Nanoarchitectures

Surface self-assembly of functional molecules or nanoscale building blocks is an effective strategy for the syntheses of advanced materials. Natural cellulose-rich substances have unique macro-to-nano hierarchical structural features. The fabrication of nanoarchitectures, employing specific guest species on the surfaces of the fine structures of such substances, results in corresponding artificial nanomaterials that possess the chemical functionalities and physical properties of both sides. Metal oxide thin film coatings with nanometer precision on the nanofibers of bulk cellulose-rich substances not only yield replicas of nanostructured materials, but also make it possible for further assemblies of functional units on the surfaces. Hence, nanostructured metal oxides and further composites, as well as surface-functionalized cellulose-based composites are fabricated by employing cellulose-rich substances as templates or scaffolds. The three-dimensional cross-linked porous structures, with the high surface area of the resultant nanomaterials or composites, lead to superior performance when employed as photocatalysts, electrode materials, and sensing matrices, on which this report is focused.