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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]

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]

This work relates to the preparation of CNT-MnO 2 hybrid electrode by a simple solvent-assisted synthesis. This one-step method is also cost-effective, scalable, and addition of surfactant or other additives for carrying out the synthesis is not necessary.The effect of selected solvents (DMF vs. ethanol) on the properties and performance of the prepared materials is depicted during this work using XRD, Raman, TEM, SEM and porosity estimation by nitrogen adsorption-desorption isotherm at 77 K. The electrochemical behavior was studied using cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy in a K 2 SO 4 aqueous electrolyte. The superior electrochemical performance of the CNT-MnO2 hybrid obtained by DMF assisted synthesis were explicated by its favorable texture and morphology. Furthermore, an asymmetric 2 V aqueous supercapacitor was assembled and tested using hybrid CNT-MnO 2 and reduced graphene oxide (rGO) as positive and negative electrodes respectively. The supercapacitor showed an excellent stability under cycling (6000 cycles) with a specific energy of 14 Wh/kg at a power density of 3000 W kg −1 . [ABSTRACT FROM AUTHOR]

Herein, synthesis and characterization of amorphous MnO 2 and application in asymmetric aqueous ultracapacitors are reported. Different amorphous manganese oxide (MnO 2 ) materials were synthesized from the reduction of KMnO 4 in different media such as ethanol (EtOH) or dimethylformamide (DMF). The electrochemical behavior of amorphous MnO 2 , labeled MnO 2 -Et and MnO 2 -DMF, were studied by using cyclic voltammetry, impedance spectroscopy, and galvanostatic cycling in aqueous electrolyte. XRD, BET, TEM, and SEM characterizations highlighted the amorphous nature and the nanostructuration of these MnO 2 materials. BET measurement established that these amorphous MnO 2 are mesoporous. In addition, MnO 2 -Et exhibits a larger specific surface area (168 m 2 g −1 ), a narrower pore diameters distribution with lower diameters compared to MnO 2 -DMF. These results are in agreement with the electrochemical results. Indeed, MnO 2 -Et shows a higher specific capacitance and lower impedance in aqueous K 2 SO 4 electrolyte. Furthermore, aqueous asymmetric ultracapacitors were assembled and studied using amorphous MnO 2 as positive electrode and reduced graphene oxide (rGO) as negative electrode. These asymmetric systems exhibit an electrochemical stability for more than 20,000 galvanostatic cycles at current density of 1 A g −1 with an operating voltage of 2 V. [ABSTRACT FROM AUTHOR]

Dielectric materials have been used for decades for energy applications where their insulation and polarizability properties are critical. In the energy storage field, most material scientists envision high-k dielectric layers in contact with an active material only as an insulating passivation layer. In microelectronics, this concept has been modified with the study of dielectrics at nanoscale level revealing interesting properties scarcely known by other fields. We propose to reconsider the vision of high-k dielectric materials for energy at nanoscale specifically. Based on microelectronic measurement techniques and nanometric control of dielectric thickness by Atomic Layer Deposition (ALD), an ultra-thin pinhole-free alumina (Al 2 O 3) layer on a silicon nanowire (SiNW) is shown to display thickness dependent tunneling electrical conduction. This result brings a new light on this material class in the energy field and allows original approaches toward achieving scientific leaps. As an illustrative application, a silicon based micro-supercapacitor (MSC) protected by 3 nm of alumina dielectric layer exhibits Electrical Double Layer Capacitance (EDLC) by means of tunneling current in aqueous electrolyte, an unprecedented result for this material, with outstanding lifetime capacity retaining 99% of its initial capacitance after 2 million cycles. Extended to multiple energy materials, such method could lead to notable progress. [Display omitted] [ABSTRACT FROM AUTHOR]