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

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

We report a comparative study of two silica-based ionogel electrolytes for electrochemical cycling applications. The ionogels considered represent two classes of gel networks, a covalently formed network generated by the polymerization of tetramethoxysilane catalyzed by formic acid, and a network formed by weak intermolecular forces obtained by mixing fumed silica nanopowder with ionic liquid. In both cases, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide is utilized as the ion conductor in the gel network. With increasing temperature it is shown that the electrochemical stability window is reduced, the conductivity of the electrolyte is increased, and the double layer capacitance is increased for both types of ionogels. Long-term stability of the two ionogels is excellent, with 90% capacitance retained after 10,000 repetitive CV cycles at 100 °C. Our results indicate that both of these ionogel electrolytes are promising for application in solid-state electrochemical systems at high temperature. [ABSTRACT FROM AUTHOR]

Abstract Herein we report the successful use of a polyisoindigo derivative (P(iso)) as a new conductive binder inside electrode formulations containing silicon nanoparticles covered with a carbon shell (Si@C) for Li-ion batteries. The expected role of the carbon shell is to stabilize the Solid Electrolyte Interphase layer (SEI) to prevent it from cracking under nanoparticle volume variations during lithiation processes. The P(iso) conducting polymer is used to act both as mechanical binder and n-type conductive component in replacement of usual carbonaceous additive materials. Ultimately, the cumulative contributions of both materials inside a two-electrode component formulation (Si@C P(iso)) aim to address the stability drawbacks commonly faced by silicon electrodes. Physico-chemical characterizations revealed that the Si@C nanoparticles are uniformly embedded inside the polymeric matrix. Electrochemical measurements in half-cells clearly show the formation of Li Si alloys during cycling. Moreover specific capacities up to 1400 mAh/g with a remarkable stability until 500 cycles have been achieved, proving this conductive polymer to be a valid alternative to classical polymeric binders mixed with carbonaceous additives. These very promising results highlight the use of this polyisoindigo family as new conductive binders inside Si@C electrode formulations for Li-ion battery applications. Highlights • Synthesis of a polyisoindigo derivative (P(iso)) by Yamamoto cross-coupling. • Characterization of the (P(iso)) as a new conductive binder with Si@C nanoparticles. • High stability of the Si@C P(iso) electrode (1400 mAh/g) over 500 cycles. • Higher capacity retention for Si@C P(iso) electrode than Si@C/CMC/CB electrode. [ABSTRACT FROM AUTHOR]

Core-shell silicon-carbon nanoparticles are attractive candidates as active material to increase the capacity of Li-ion batteries while mitigating the detrimental effects of volume expansion upon lithiation. However crystalline silicon suffers from amorphization upon the first charge/discharge cycle and improved stability is expected in starting with amorphous silicon. Here we report the synthesis, in a single-step process, of amorphous silicon nanoparticles coated with a carbon shell (a-Si@C), via a two-stage laser pyrolysis where decomposition of silane and ethylene are conducted in two successive reaction zones. Control of experimental conditions mitigates silicon core crystallization as well as formation of silicon carbide. Auger electron spectroscopy and scanning transmission electron microscopy show a carbon shell about 1 nm in thickness, which prevents detrimental oxidation of the a-Si cores. Cyclic voltammetry demonstrates that the core-shell composite reaches its maximal lithiation during the first sweep, thanks to its amorphous core. After 500 charge/discharge cycles, it retains a capacity of 1250 mAh.g −1 at a C/5 rate and 800 mAh.g −1 at 2C, with an outstanding coulombic efficiency of 99.95%. Moreover, post-mortem observations show an electrode volume expansion of less than 20% and preservation of the nanostructuration. [ABSTRACT FROM AUTHOR]

Silicon is a promising material for high-energy anode materials for the next generation of lithium-ion batteries. The gain in specific capacity depends highly on the quality of the Si dispersion and on the size and shape of the nano-silicon. The aim of this study is to investigate the impact of the size/shape of Si on the electrochemical performance of conventional Li-ion batteries. The scalable synthesis processes of both nanoparticles and nanowires in the 10–100 nm size range are discussed. In cycling lithium batteries, the initial specific capacity is significantly higher for nanoparticles than for nanowires. We demonstrate a linear correlation of the first Coulombic efficiency with the specific area of the Si materials. In long-term cycling tests, the electrochemical performance of the nanoparticles fades faster due to an increased internal resistance, whereas the smallest nanowires show an impressive cycling stability. Finally, the reversibility of the electrochemical processes is found to be highly dependent on the size/shape of the Si particles and its impact on lithiation depth, formation of crystalline Li15Si4 in cycling, and Li transport pathways. [ABSTRACT FROM AUTHOR]