There is an ever-growing desire to use and store energy from sustainable resources. Pillared graphene materials offer high capacitive performances in supercapacitors, presumably through enhanced electrolytic ion sorption in their chemically engineered inter-layer graphene galleries. Herein, a judicious combination of the removal of excess electrolytes, isotopic enrichment of the pillar molecules, and the use of low temperatures (100 K) enables solid-state nuclear magnetic resonance spectroscopy to efficiently probe nuclear spin polarization exchange between the electrolyte and the electrode. This provides the direct detection of electrolyte ions in proximity to the gallery pillars, evidencing the adsorption of ions in such two-dimensional galleries. However, when the ions are larger than the gallery d-spacing, they are not observed to enter the galleries, and the total storage capacity is accordingly reduced. This methodology provides a means to locate electrolyte ions upon charging or discharging devices and thus will be invaluable in the quest for the design of materials with vastly improved power densities.
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.
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