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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]

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]