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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]

Silicon nanowires are appealing structures to enhance the capacity of anodes in lithium-ion batteries. However, to attain industrial relevance, their synthesis requires a reduced cost. An important part of the cost is devoted to the silicon growth catalyst, usually gold. Here, we replace gold with tin, introduced as low-cost tin oxide nanoparticles, to produce a graphite–silicon nanowire composite as a long-standing anode active material. It is equally important to control the silicon size, as this determines the rate of decay of the anode performance. In this work, we demonstrate how to control the silicon nanowire diameter from 10 to 40 nm by optimizing growth parameters such as the tin loading and the atmosphere in the growth reactor. The best composites, with a rich content of Si close to 30% wt., show a remarkably high initial Coulombic efficiency of 82% for SiNWs 37 nm in diameter. [ABSTRACT FROM AUTHOR]

Considering its specific capacity, silicon is one of the most promising materials to replace graphite in lithium ion batteries anodes. However, its rapid capacity fading prevents its use in current batteries. Understanding lithiation and degradation mechanisms of silicon is important for improving its cyclability. In this work a novel approach is developed by using a focused ion beam implemented in the analysis chamber of a state-of-the-art time of flight secondary ion mass spectrometer. Detailed mapping of elements distribution, including lithium, inside a silicon particle or in the entire depth of the electrode, can thus be performed. During the first lithiation, a core-shell mechanism is observed and its evolution upon electrochemical cycling was examined. This mechanism is observed for all particles in the electrode, independently of their position. Cross analysis with Auger spectroscopy allowed Li concentration in the entire shell to be quantified. Fast lithiation paths getting through the pure silicon core have been evidenced by complementary scanning electron microscopy and transmission electron microscopy (TEM) analyses. Defects observed by TEM are supposed to contribute significantly in the Li diffusion inside the particle. This approach also provided evidence of lithium progressively trapped in Si particles after aging, in close relationship with capacity loss found for silicon anodes along cycling. [ABSTRACT FROM AUTHOR]

Bringing solid-state lithium batteries to market is a challenge; in part because their fabrication requires a technically difficult step of solid-electrolyte separator assembly, and because thus far, solid-state cells have only cycled under high pressure. Here, we address both these bottlenecks by assembling lithium-ion batteries based on the argyrodite Li 6 PS 5 Cl as the electrolyte using standard coating processes. Moreover, we upscaled to 10 cm2 pouch cells in a dry room by a double casting technique, thanks to the use of fluorine-free polyisobutene as the binder and nanosilicon and LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) respectively as the anode and cathode active materials. Electrode casting is shown to significantly improve the cycling stability when compared to the conventional pelletizing process. The all-coated pouch cells, cycled at a pressure as low as 1 MPa over 160 cycles, show a better capacity retention than the pelletized cells cycling under >100 MPa. The higher performance of the sheet-type cell is thought to originate in the better densification and homogeneity of the cell, attested by its low resistance. [Display omitted] • Si-NMC pouch cells with Li 6 PS 5 Cl solid electrolyte. • Both electrodes and separator casted via conventional ink coating process. • Cell scaled up from 0.4 cm2 (pelletized cell) to 10 cm2 (all-coated pouch cell). • The coating process improved long-term stability. • Pouch cells cycled under 1 MPa perform better than pelletized cells at 127 MPa. [ABSTRACT FROM AUTHOR]

Thanks to their high ionic conductivity and appropriate mechanical properties, sulfide-based solid electrolytes (SSE) are increasingly studied for a use in all-solid-state batteries (ASSBs). Silicon is abundant, non toxic and has a high theoretical capacity, and therefore is a promising active material in ASSBs. We first study the compatibility between two different solid electrolytes with similar ionic conductivity, Li 10 SnP 2 S 12 (LSnPS) and Li 6 PS 5 Cl (LPSCl), and micron-sized silicon based anode. LPSCl appears to be less reactive than LSnPS and it is then used to determine the most appropriate silicon size and shape for efficient cycling. Two silicon materials are compared, micron-sized silicon particles (μSi) and silicon nanowires (SiNWs). Energy Dispersive X-ray spectroscopy (EDX) mapping of the composite powders shows a better dispersion of the SiNWs in the LPSCl matrix. Galvanostatic cycling and Electrochemical Impedance Spectroscopy (EIS) measurements highlight the greater compatibility of SiNWs compared to μSi in ASSBs with a high specific delithiation capacity of 2600 mAh/g Si at the first cycle, while limiting the polarization and maintaining a relatively stable lithiation mechanism during cycling. [Display omitted] • Comparing solid electrolytes Li 10 SnP 2 S 12 and Li 6 PS 5 Cl for reactivity to Si. • Thinner SEI formed on Si nanowires. • Si nanowires more suitable for ASSB cycling than micron-sized Si. [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]