Facile Thermal Annealing Research Articles

Surface modification, counter-ion exchange effect on thermally annealed sulfonated poly (ether ether ketone) membranes for vanadium redox flow battery

In this work, we report new approaches to sulfonated poly ether ether ketone (SPEEK) membranes to improve its inhibition to vanadium ions along with polymer reinforcement. First approach includes facile thermal annealing of SPEEK membrane (SPEEK-T) which could reinforce the polymer matrix. Second approach was to exchange the labile proton of SPEEK with benzimidazole to protect the hydrolytic decomposition of sulfonic acid followed by thermal annealing (SPEEK-Benz), and third approach focused on creating barrier layer for vanadium ions by coating polyethyleneimine on SPEEK membrane followed by thermal treatment (SPEEK-PEI). The chemical stability study of the membranes revealed acceptable dimension change and VO2+ electrolyte sorption for all the membranes with least dimension change and weight gain of 5 % and 12 %, respectively, for SPEEK-PEI. Amongst four prepared membranes, SPEEK-PEI membrane displayed least diffusion coefficient of 8.04 × 10−7, 8.94 × 10−7, 4.20 × 10−7 cm2 min−1 for V3+, VO2+, and VO2+ ions respectively. VRFB assembled with SPEEK-PEI resulted highest Coulombic efficiency (CE) of 97 % and energy efficiency (EE) of 66 % over 50 charge/discharge cycles at 100 mA cm−2. Peak power density of 255, 248, 240 and 235 mW cm−2 at current density of 300 mA cm−2 was observed for SPEEK-PEI, SPEEK-Benz, SPEEK-T, and SPEEK-48, respectively; these values were higher than 225 mW cm−2 for Nafion®117 in identical experimental conditions. The excellent VRFB performance suggest that the developed new approaches have pronounced effect on the membrane properties and can be further improved to obtain an ideal VRFB separator. Furthermore, the surface modification approaches adopted in this work is facile, reproducible and scalable and can be further designed to develop high performance ion exchange membranes for separation/purification and energy.

CdS/Bi12O17Cl2 Heterostructure Promotes Visible-Light-Driven Photocatalytic CH4 Generation and Phenol Conversion

We report a heterojunction photocatalyst by coupling CdS with Bi12O17Cl2 via a facile thermal annealing process. Such heterostructure can promote the charge separation between CdS and Bi12O17Cl2, thereby leading to a considerable improvement on the performance for CO2 reduction into valuable CH4 and phenol conversion under visible light exposure. The CdS/Bi12O17Cl2 heterojunction with mass ratio of 1 : 1 (50% CdS/Bi12O17Cl2) shows the highest CH4 production rate (1.28 μmol·h-1·g-1), which is as 9.8 and 5.8 times as the CH4 generation rate of pure Bi12O17Cl2 and CdS (0.13 and 0.22 μmol·h-1·g-1), respectively. Also, the 50% CdS/Bi12O17Cl2 sample shows the highest activity of phenol conversion with a conversion ratio of 92%, which is as 2.2 times and 1.9 times as the conversion ratio of pristine Bi12O17Cl2 (41%) and CdS (48%), respectively. The present study demonstrates the great potential of the CdS/Bi12O17Cl2 heterojunction for efficient charge separation towards increased photocatalytic CH4 production and phenol conversion.

Stable interphase chemistry of textured Zn anode for rechargeable aqueous batteries

Despite the advances of aqueous zinc (Zn) batteries as sustainable energy storage systems, their practical application remains challenging due to the issues of spontaneous corrosion and dendritic deposits at the Zn metal anode. In this work, conformal growth of zinc hydroxide sulfate (ZHS) with dominating (001) facet was realized on (002) plane-dominated Zn metal foil fabricated through a facile thermal annealing process. The ZHS possessed high Zn2+ conductivity (16.9 mS cm−1) and low electronic conductivity (1.28 × 104 Ω cm), and acted as a heterogeneous and robust solid electrolyte interface (SEI) layer on metallic Zn electrode, which regulated the electrochemical Zn plating behavior and suppressed side reactions simultaneously. Moreover, low self-diffusion barrier along the (002) plane promoted the 2D diffusion and horizontal electrochemical plating of metallic Zn for (002)-textured Zn electrode. Consequently, the as-achieved Zn electrode exhibited remarkable cycling stability over 7000 cycles at 2 mA cm−2 and 0.5 mAh cm−2 with a low overpotential of 25 mV in symmetric cells. Pairing with a MnO2 cathode, the as-achieved Zn electrode achieved stable cell cycling with 92.7% capacity retention after 1000 cycles at 10 C with a remarkable average Coulombic efficiency of 99.9%.

Increased crystallinity of RuSe2/carbon nanotubes for enhanced electrochemical hydrogen generation performance.

Ru-Based catalysts are significant in the green hydrogen generation via the electrochemical water-splitting reaction. Herein, it is found that the increased crystallinity of cubic RuSe2 nanoparticles anchored over carbon nanotubes (RuSe2/CNTs) could largely increase the hydrogen generation performance both in acidic and alkaline electrolytes. The freshly prepared RuSe2/CNTs with low crystallinity had a very low catalytic performance for the HER, while the catalytic ability could be largely boosted by facile thermal annealing at 650 °C in an N2 atmosphere, resulting from the increased crystallinity and electronic effect. The crystal structure enhancement of the RuSe2 nanoparticles was well supported by the X-ray diffraction technique and the lattice fringes in the high-resolution transmission electron microscopy images. As a result, the catalyst exhibited largely improved catalytic performance compared to the freshly prepared RuSe2/CNTs; specifically, the overpotentials of 48 and 64 mV were required to drive 10 mA cm-2 in alkaline and acidic media when loaded on a glassy carbon electrode, much less than those of 109 and 120 mV for the freshly prepared RuSe2/CNTs; the catalytic performance in the alkaline electrolyte was even close to that of the commercial Pt/C catalyst. Correspondingly, the improved catalytic stability, catalytic kinetics, charge transfer ability and catalytic efficiency of the active sites were also observed. The current work shows an effective approach and important understanding for catalytic performance enhancement via increased crystallinity by facile thermal annealing.

Perfluorocyclobutyl-containing multiblock copolymers to induce enhanced hydrophilic/hydrophobic phase separation and high proton conductivity at low humidity

A multiblock copolymer containing a highly sulfonated poly(phenylene sulfide sulfone) (sPPSS) hydrophilic oligomer and a partially fluorinated perfluorocyclobutyl (PFCB)-containing hydrophobic oligomer was synthesized. The sharp contrast between the hydrophilic and hydrophobic moieties induced a well-developed phase separation, which was observed in the transmission electron microscopy (TEM) images within the polymer electrolyte membrane (PEM). The increased chain mobility from the flexible ether and PFCB groups afforded facile thermal annealing of the membrane. Thermal annealing induced polymer chain packing of the hydrophobic moieties, enhancing the hydrophilic/hydrophobic phase separation. The fabricated membranes exhibited higher proton conductivity compared with those of conventional hydrocarbon PEM possessing a random copolymer architecture, while their dimensional swelling was suppressed. Additionally, under low humidification (a relative humidity (RH) of 50%), the sulfonated–fluorinated membrane achieved a high proton conductivity of up to 41.9 mScm−1. A high adhesion strength of 32.7 mNcm−1 was also observed, indicating strong interfacial compatibility in the membrane electrode assembly (MEA) due to its structural affinity for the contacting perfluorosulfonated binder. The enhanced hydrophilic/hydrophobic phase separations facilitated fuel cell performances of 1.13 and 0.61 Acm−2 at 0.6 V and 65 °C under 100% and 50% RH conditions, respectively, in addition to achieving stable chemical and physical durabilities.

Conjugated polymer with dynamic and thermoreversible hydrogen bonding on the backbone

Two conjugated polymers containing isoindigo (IIDG) or 3,3-(ethane-1,2-diylidene)bis(indolin-2-one) (EBI) with latent hydrogen bonding were synthesized and characterized. The tert-butyloxycarbonyl (t-Boc) side unit could be removed by facile thermal annealing treatment, generating the actual hydrogen-bonded, fully conjugated polymers. Despite the similar structure of IIDG and EBI, the hydrogen bonds formed in two polymers are different. The polymer based on IIDG possesses a “fixed” hydrogen bonding, which won't be dissociated before thermal degradation. On the contrary, the polymer based on EBI exhibits dynamic and thermoreversible hydrogen bonds upon heating and cooling cycles. The dynamic hydrogen bonding enables the investigation of these special conjugated polymers under the decoupling conditions of hydrogen bonding and other intermolecular interactions. Kinetic FTIR was applied to study the association/dissociation process of hydrogen bonds in the polymer. It is demonstrated that the ratio of hydrogen-bonded donor-acceptor units in the polymer thin film could be determined and its impact on optical properties and charge transport was investigated. The results also suggested that the hydrogen bonding driven molecular aggregation in the polymer thin film enhanced the charge transport mobility in the thin film transistor devices.

Non-enzymatic multispecies sensing of key wine attributes with nickel nanoparticles on N-doped graphene composite

A non-enzymatic sensor was developed for simultaneous detection of glucose, ethanol, and glycerol concentrations in wine using nickel nanoparticles on nitrogen-doped graphene, Ni-NGr. The sensor was fabricated from nickel nitrate, graphene oxide, and uric acid via facile thermal annealing process. The Ni-NGr sensor exhibited superior electrocatalytic activity compared with glassy carbon, NGr, and Ni-Gr electrodes. The anodic outputs from cyclic voltammetry for the target analyte sensing were confirmed with square wave voltammetry measurements. The Ni-NGr composite presented outstanding limit of detection (LOD = 1 μM, S/N = 3) and sensitivity for glucose with comparable performance for ethanol and glycerol. The sensor was tested for simultaneous multispecies analysis of commercial wine samples with excellent results in terms of accuracy, stability, and recovery.

Significantly enhanced thermoelectric performance in SWCNT films via carrier tuning for high power generation

Carbon nanotubes (CNTs) are promising flexible thermoelectric materials in the field of large-scale low-grade thermal energy utilization. However, the relatively poor thermoelectric performance of CNTs near ambient temperature is a big issue for their application as flexible power generator. Here, we improved the thermoelectric properties of SWCNT films in a wide temperature range from room temperature (RT) to 200 °C via facile thermal annealing process. The effects of heat treatment at different temperatures and atmospheres on the thermoelectric properties of SWCNT films were studied. A maximum power factor (PF) of 113.7 μW/m∙K2 at RT is obtained with average PF 111.7 μW/m∙K2 in the RT to 200 °C range, which is more than threefold the value of as-prepared SWCNT film. Flexible and compact power generator based on annealed p-type SWCNT films and n-type polyethylenimine-doped SWCNT films with 8 couples of p-n legs was assembled. An outstanding output power of 1.16 μW with power density of 0.48 W/m2 at temperature difference 49.5 K was achieved. The device showed good air stability within one month and excellent mechanical flexibility. This study thus provides a feasible and low-cost strategy for high power energy generation.

Facile synthesis of CeO2/g-C3N4 nanocomposites with significantly improved visible-light photocatalytic activity for hydrogen evolution

Ceria dioxide supported on graphitic carbon nitride (CeO2/g-C3N4) composites were facilely synthesized to be application for photocatalytic hydrogen (H2) generation in this present work. The physical and chemical properties of CeO2/g-C3N4 nanocomposites were determined via a series of characterizations. The CeO2/g-C3N4 composites prepared by facile thermal annealing and rotation-evaporation method exhibit excellent photocatalytic H2 evolution with visible-light illumination. The best hydrogen generation rate of CeO2/g-C3N4 composite with 1.5 wt% Pt is 0.83 mmol h−1 g−1, which is almost same as that of composite with 3 wt% Pt prepared by simple physical mixing method. The significantly developed photocatalytic activity of CeO2/g-C3N4 composite is majorly ascribed to the stronger interfacial effects with the more visible-light absorbance and faster electron transfer. This work reveals that construction of the CeO2/g-C3N4 composite with high disperse and close knit by the facile thermal annealing and rotation-evaporation method could be an effective method to achieve excellent photocatalytic hydrogen evolution performance.

Magnetic graphene enabled tunable microwave absorber via thermal control

By synthesizing nitrogen-doped graphene (NG) via a facile thermal annealing method, a fine control of the amount and location of doped nitrogen as well as the oxygen-containing functional groups is achieved with varying annealing temperature. The favorable magnetic properties have been achieved for N-doped rGO samples obtained at two temperatures of all NG samples, i.e., 500 °C and 900 °C with saturation magnetization of 0.63 emu g−1 and 0.67 emu g−1 at 2 K, respectively. This is attributed to the optimized competition of the N-doping and reduction process at 500 °C and the dominated reduction process at 900 °C. NG obtained at 300 °C affords the best overall absorbing performance: when the absorber thickness is 3.0 mm, the maximum absorption was −24.6 dB at 8.51 GHz, and the absorption bandwidth was 4.89 GHz (7.55–12.44 GHz) below −10 dB. It owes its large absorbing intensity to the good impedance match and significant dielectric loss. The broad absorption bandwidth benefits from local fluctuations of dielectric responses contributed by competing mechanisms. Despite the significant contribution from materials loss to the absorption, the one quarter-wavelength model is found to be responsible for the reflection loss peak positions. Of particular significance is that an appropriate set of electromagnetic parameters associated with reasonable reduction is readily accessible by convenient control of annealing temperature to modulate the microwave absorbing features of graphene. Thus, NG prepared by thermal annealing promises to be a highly efficient microwave absorbent.

Thermal annealing assisted synthesis of Sb@C yolk-shell microspheres for sodium-ion batteries.

Sb@C yolk–shell spheres with tunable interior space have been obtained via a facile thermal annealing strategy and used as anodes for sodium-ion batteries. The proportion of interior space in the yolk–shell structure has a significant influence on the electrochemical performance of the electrode material.

Graphene Composites with Cobalt Sulfide: Efficient Trifunctional Electrocatalysts for Oxygen Reversible Catalysis and Hydrogen Production in the Same Electrolyte.

Nitrogen and sulfur-codoped graphene composites with Co9 S8 (NS/rGO-Co) are synthesized by facile thermal annealing of graphene oxides with cobalt nitrate and thiourea in an ammonium atmosphere. Significantly, in 0.1 m KOH aqueous solution the best sample exhibits an oxygen evolution reaction (OER) activity that is superior to that of benchmark RuO2 catalysts, an oxygen reduction reaction (ORR) activity that is comparable to that of commercial Pt/C, and an overpotential of only -0.193 V to reach 10 mA cm-2 for hydrogen evolution reaction (HER). With this single catalyst for oxygen reversible electrocatalysis, a potential difference of only 0.700 V is observed in 0.1 m KOH solution between the half-wave potential in ORR and the potential to reach 10 mA cm-2 in OER; in addition, an overpotential of only 450 mV is needed to reach 10 mA cm-2 for full water splitting in the same electrolyte. The present trifunctional catalytic activities are markedly better than leading results reported in recent literature, where the remarkable trifunctional activity is attributed to the synergetic effects between N,S-codoped rGO, and Co9 S8 nanoparticles. These results highlight the significance of deliberate structural engineering in the preparation of multifunctional electrocatalysts for versatile electrochemical reactions.

Polymers Based on Benzodipyrrolidone and Naphthodipyrrolidone with Latent Hydrogen‐Bonding on the Main Chain

A series of soluble π‐conjugated small molecules and polymers containing benzodipyrrolidone (BDP) or naphthodipyrrolidone (NDP) units with latent hydrogen‐bonding on the main chain is synthesized and characterized. Spectroscopic study confirms that the tert‐butyloxycarbonyl (t‐Boc) side unit can be removed by facile thermal annealing treatment, generating the actual hydrogen‐bonded compounds. The resulting hydrogen‐bonded compounds exhibit distinctly different properties, for instance poorer solubility and smaller bandgap, as compared with their precursors with latent hydrogen‐bonding. The single crystal X‐ray structure analysis of t‐Boc group substituted BDP and NDP indicates that the NDP compounds exhibit better coplanarity and a stronger π–π interaction. The density functional theory computation results of the polymer backbone segments show that the coplanarity of aromatic units is slightly improved. Such a hydrogen‐bonding‐mediated enhancement of π–π stacking exhibits potential for improving the performance of solution processable organic electronic materials. Hydrogen‐bonded polymer P‐NDP‐FL‐2 is an air stable n‐type semiconductor with electron mobility 40 times larger than its precursor polymer P‐NDP‐FL‐1 with latent hydrogen‐bonding. image

Nanostructured ultrathin catalyst layer based on open-walled PtCo bimetallic nanotube arrays for proton exchange membrane fuel cells

Nanostructured ultrathin catalyst layer based on open-walled PtCo bimetallic nanotube arrays has been designed and constructed through a hydrothermal and physical vapor deposition method for proton exchange membrane fuel cells (PEMFCs). The open-walled PtCo bimetallic NTAs with a diameter ca. 100nm were directly aligned with proton exchange membrane, forming an ultrathin catalyst layer with a thickness ca. 300nm. The incorporation of Co in Pt is realized by a facile thermal annealing method, endowing the catalyst layer with improved activity. During the purification of catalyst-coated-membrane (CCM) electrode, the sealed off PtCo nanotubes cracked into open-walled nanotubes, making both the interior and exterior surfaces exposed to the surroundings. The catalyst layer is binder-free and beneficial for exposing catalytic active sites, enhancing mass transport during the operation of PEMFCs. Serving as cathode, a maximum power density of 14.38kWgPt−1 was achieved with a cathodic Pt loading of 52.7μgcm−2, which is 1.7 fold higher than the conventional CCM. Accelerated degradation test (ADT) manifests that the prepared nanostrucutred ultrathin catalyst layer is more stable than the conventional CCM. The proposed catalyst layer structure and also its preparation method hold great potential for PEMFCs and other applications.

NiFe Layered‐Double‐Hydroxide‐Derived NiO‐NiFe2O4/Reduced Graphene Oxide Architectures for Enhanced Electrocatalysis of Alkaline Water Splitting

AbstractElectrochemical water splitting is an environmentally friendly technology to store renewable but intermittent energy into hydrogen fuels. Nowadays, exploiting low‐costing, high‐performance, and robust catalysts for the electrochemical oxygen evolution reaction (OER) is essential to improve the overall efficiency of water splitting. Herein, the synthesis, structural characterization, and electrocatalytic OER performance of NiO‐NiFe2O4 nanoparticles anchored on reduced graphite oxide frameworks (NiO‐NiFe2O4/rGO) were investigated. Facile thermal annealing of the NiFe layered double hydroxide (NiFe‐LDH) precursor led to the formation of highly dispersible NiO‐NiFe2O4 nanoparticles (20–30 nm in size) across the rGO substrate with a NiO/NiFe2O4 molar ratio up to 4.42. In contrast to the nanostructured NiFe‐LDH/rGO catalyst, the NiO‐NiFe2O4/rGO nanohybrid exhibits a lower OER onset potential (Eonset=1.436 V vs. RHE), affords a smaller overpotential of 296 mV, and achieves a current density of 10 mA cm−2 with a Tafel slope of about 43 mV dec−1; these values are comparable to those of the benchmark IrO2 catalyst. The synergy between the abundant catalytically active sites through good dispersion of NiO‐NiFe2O4 across the rGO substrate and fluent electron transport arising from the rGO and NiFe2O4 components results in the outstanding electrocatalytic activity. The extremely high catalytic activity, facile synthesis, and low‐cost of the NiO‐NiFe2O4/rGO nanohybrid make it a very promising catalyst for the OER.

Strongly coupled hybrid ZnCo2O4 quantum dots/reduced graphene oxide with high-performance lithium storage capability

Mesoporous binary metal oxides/reduced graphene oxide (rGO) two-dimensional nanostructures can provide open large surface areas for lithium ion access and storage, holding a great promise as high-performance electrode materials for next-generation energy storage. In this work, we develop an effective strategy involving a simple polyol process and a facile thermal annealing treatment, to synthesize ZnCo2O4 Quantum Dots (QDs)/rGO hybrid. Due to the large specific surface area, strongly coupled interaction and synergic effect between ZnCo2O4 QDs and rGO, the hybrid shows excellent lithium storage ability, with high reversible specific capacity, and superior rate performance, as well as ultralong cycle life. After 100 cycles, the ZnCo2O4 QDs/rGO2 delivers a capacity of 1062mAhg−1 at a current density of 500mAg−1. Even cycling at 2000mAg−1 up to 1000 cycles, the reversible capacity still preserves 682.5mAhg−1. These electrochemical results indicate the ZnCo2O4 QDs/rGO2 hybrid could be a promising candidate material as a high-performance anode material for lithium-ion batteries.

Synthesis and Electrocatalytic Activity of Nitrogen and Phosphorus Co-Doped Graphene for Oxygen Reduction

The oxygen reduction reaction (ORR) at the cathode plays an important role in the performance of fuel cells and metal-air batteries. Due to the high cost and scarcity of Pt-based electrocatalysts, intensive efforts have been focused on reducing or replacing Pt catalyst in fuel cells and metal-air batteries. [1-4] Graphene, single-atom-thick layer of sp2-hybridized carbon atoms packed into two-dimension hexagonal lattice, has been rapidly developed in recent years. Recently, both theoretical and experimental studies show that the electrical and physicochemical properties of graphene can be significantly modified by incorporation foreign atoms into graphene. [5-8] Especially for catalytic applications, doping pristine graphene with heteroatoms, such as N, B, S, I and P, is an effcient approch to alter the electron-donor property and consequently increase the electrocatalytic performance for ORR. [9-12] Particularly, co-doping multiple heteroatoms endows graphene much imrpoved ORR activity than doping with single atom. Such multiple-doped graphene can create a unique electronic structure with a synergistic effect in these heteroatoms, efficiently enhancing the ORR activity. In this work, for the first time, we have successfully synthesized P and N binary-doped graphene (PNG) through a facile thermal annealing method by using urea and tetraphenylphosphonium bromide (C24H20BrP) as N and P precursors, respectively. The as-prepared PNG catalysts with a large specific surface area up to 1207.03 m2 g-1 act as efficient metal-free electrocatalysts for ORR, showing remarkable electrocatalytic activity and excellent long-term stability as well as high tolerance to methanol in alkaline solution. The content of N and P has a significant impact on the activity of the PNG as shown in Figure 1.The outstanding electrocatalytic activity and long-term durability of PNG toward ORR are primarily attributed to the synergetic effect arising from co-doping graphene with both P and N. This work may provide an efficient approach for the synthesis of heteroatom multiple-doped graphene. Acknowledgements This work is supported by National Natural Science Foundation of China (Nos.51272167, 21206101 and 51572181 ).

Facile thermal annealing of graphite oxide in air for graphene with a higher C/O ratio

The C/O ratio of reduced graphene oxide can be improved to 25.9 by simple two-step thermal annealing in air.

Hybrid CuO/SnO2 nanocomposites: Towards cost-effective and high performance binder free lithium ion batteries anode materials

Hybrid CuO/SnO2 nanocomposites are synthesized by a facile thermal annealing method on Cu foils. Compared to pristine CuO and SnO2 nanostructures, hybrid CuO/SnO2 nanocomposites exhibit the enhanced electrochemical performances as the anode material of lithium ion batteries (LIBs) with high specific capacity and excellent rate capability. The binder free CuO/SnO2 nanocomposites deliver a specific capacity of 718 mA h g−1 at a current density of 500 mA g−1 even after 200 cycles. The enhanced electrochemical performances are attributed to the synergistic effect between SnO2 nanoparticles and CuO nanoarchitectures. Such hybrid CuO/SnO2 nanocomposites could open up a new route for the development of next-generation high-performance and cost-effective binder free anode material of LIBs for mass production.

Micro-Sized Silicon-Carbon Composite Composed of Carbon-Coated Sub-10 Nm Si Primary Particles As High-Performance Anode Materials for Lithium-Ion Batteries

Recently, silicon has attracted considerable interest as a high-capacity anode material owing to its highest known capacity of 3580 mAh/g at room temperature, which is about 10 times larger than that of commercial graphite anodes (~370mAh/g). Despite promising advantages, practical application of silicon anodes in high performance Li-ion batteries is seriously hindered by its rapid capacity fading as a result of dramatic volume changes (>400 %) during lithium insertion and extraction processes. The huge volume changes of Si cause pulverization and loss of electrical contact between Si particles and conductive additives, as well as an unstable solid electrolyte interphase (SEI) layer, which in effect results in severe capacity fading. Constructing nanostructured silicon is a promising strategy and has been demonstrated to improve battery performance.1,2 However, there are some challenges involved in introducing these nanomaterials into electrode fabrication for practical application. One is the lower tap density of the nanoparticles, in contrast to commercially used micro-sized electrode materials, resulting in a lower volumetric energy density; the other is the difficulty with handling the chemicals, such as inhalation and explosion risks, arising from these nanoparticles in fabrication of electrodes.Thus, Control of primary particle sizes of Si below critical diameter (around 10 nm) in the micro-sized composite is more important in achieving good cycling stability as micro-sized aggregated structures of Si can expedite the capacity fading.3,4 Herein, we report a synthesis of micro-sized Si-C composites composed of carbon-coated sub-10 nm Si primary particles interconnected into secondary micro-sized particles, and its use as high-performance Li-ion anodes. This synthesis process involves facile thermal annealing of silsesquioxane with size-controlled formation of Si primary particles and subsequent carbon coating steps. The as-prepared Si-C composites anode material shows stabilized capacity of ~1600 mAh/g with excellent capacity retention (90% after 150 cycles). Moreover, the volumetric capacity can reach 1088 mAh/cm3 attributed to a high tap density (0.68 g/cm3) of micro-sized Si-C composites. Taking the facile synthesis and excellent performance of Si-C composites into account, it would be of significant interest for scalable fabrication for rechargeable lithium batteries. Furthermore, the silicon nanoparticles with controllable size are also easily used in other applications, such as light-emitting diodes, and high efficiency photovoltaic devices. Acknowledgements This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, Subcontract NO. 6951378 under the Batteries for Advanced Transportation Technologies (BATT) Program