Highly Dispersible Hexagonal Carbon-MoS2 -Carbon Nanoplates with Hollow Sandwich Structures for Supercapacitors.

MoS2 , a typical layered transition-metal dichalcogenide, is promising as an electrode material in supercapacitors. However, its low electrical conductivity could lead to limited capacitance if applied in electrochemical devices. Herein, a new nanostructure composed of hollow carbon-MoS2 -carbon was successfully synthesized through an l-cysteine-assisted hydrothermal method by using gibbsite as a template and polydopamine as a carbon precursor. After calcination and etching of the gibbsite template, uniform hollow platelets, which were made of a sandwich-like assembly of partial graphitic carbon and two-dimensional layered MoS2 flakes, were obtained. The platelets showed excellent dispersibility and stability in water, and good electrical conductivity due to carbon provided by the calcination of polydopamine coatings. The hollow nanoplate morphology of the material provided a high specific surface area of 543 m2 g-1 , a total pore volume of 0.677 cm3 g-1 , and fairly small mesopores (≈5.3 nm). The material was applied in a symmetric supercapacitor and exhibited a specific capacitance of 248 F g-1 (0.12 F cm-2 ) at a constant current density of 0.1 A g-1 ; thus suggesting that hollow carbon-MoS2 -carbon nanoplates are promising candidate materials for supercapacitors.

Nickel Oxide Decorated Halloysite Nanotubes as Sulfur Host Materials for Lithium-Sulfur Batteries.

Lithium-sulfur batteries with high energy density still confront many challenges, such as polysulfide dissolution, the large volume change of sulfur, and fast capacity fading in long-term cycling. Herein, a naturally abundant clay material, halloysite, is introduced as a sulfur host material in the cathode of Li-S batteries. Nickel oxide nanoparticles are embedded into the halloysite nanotubes (NiO@Halloysite) by hydrothermal and calcination treatment to improve the affinity of halloysite nanotubes to polysulfides. The NiO@Halloysite composite loaded with sulfur (S/NiO@Halloysite) is employed as the cathode of Li-S batteries, which combines the physical confinements of tubular halloysite particles and good chemical adsorption ability of NiO. The S/NiO@Halloysite electrode exhibits a high discharge capacity of 1205.47 mAh g-1 at 0.1 C. In addition, it demonstrates enhanced cycling stability, retaining ≈60% of initial capacity after 450 cycles at 0.5 C. The synthesized NiO@Halloysite can provide a promising prospect and valuable insight into applying natural clay materials in Li-S batteries.

Poly(ionic liquid) nanovesicles via polymerization induced self-assembly and their stabilization of Cu nanoparticles for tailored CO2 electroreduction.

Herein, we report a straightforward, scalable synthetic route towards poly(ionic liquid) (PIL) homopolymer nanovesicles (NVs) with a tunable particle size of 50 to 120 nm and a shell thickness of 15 to 60 nm via one-step free radical polymerization induced self-assembly. By increasing monomer concentration for polymerization, their nanoscopic morphology can evolve from hollow NVs to dense spheres, and finally to directional worms, in which a multilamellar packing of PIL chains occurred in all samples. The transformation mechanism of NVs' internal morphology is studied in detail by coarse-grained simulations, revealing a correlation between the PIL chain length and the shell thickness of NVs. To explore their potential applications, PIL NVs with varied shell thickness are in situ functionalized with ultra-small (1 âˆ¼ 3 nm in size) copper nanoparticles (CuNPs) and employed as electrocatalysts for CO2 electroreduction. The composite electrocatalysts exhibit a 2.5-fold enhancement in selectivity towards C1 products (e.g., CH4), compared to the pristine CuNPs. This enhancement is attributed to the strong electronic interactions between the CuNPs and the surface functionalities of PIL NVs. This study casts new aspects on using nanostructured PILs as new electrocatalyst supports in CO2 conversion to C1 products.

Poly(ionic liquid) Nanovesicle-Templated Carbon Nanocapsules Functionalized with Uniform Iron Nitride Nanoparticles as Catalytic Sulfur Host for Li-S Batteries.

Poly(ionic liquid)s (PIL) are common precursors for heteroatom-doped carbon materials. Despite a relatively higher carbonization yield, the PIL-to-carbon conversion process faces challenges in preserving morphological and structural motifs on the nanoscale. Assisted by a thin polydopamine coating route and ion exchange, imidazolium-based PIL nanovesicles were successfully applied in morphology-maintaining carbonization to prepare carbon composite nanocapsules. Extending this strategy further to their composites, we demonstrate the synthesis of carbon composite nanocapsules functionalized with iron nitride nanoparticles of an ultrafine, uniform size of 3-5 nm (termed "FexN@C"). Due to its unique nanostructure, the sulfur-loaded FexN@C electrode was tested to efficiently mitigate the notorious shuttle effect of lithium polysulfides (LiPSs) in Li-S batteries. The cavity of the carbon nanocapsules was spotted to better the loading content of sulfur. The well-dispersed iron nitride nanoparticles effectively catalyze the conversion of LiPSs to Li2S, owing to their high electronic conductivity and strong binding power to LiPSs. Benefiting from this well-crafted composite nanostructure, the constructed FexN@C/S cathode demonstrated a fairly high discharge capacity of 1085 mAh g-1 at 0.5 C initially, and a remaining value of 930 mAh g-1 after 200 cycles. In addition, it exhibits an excellent rate capability with a high initial discharge capacity of 889.8 mAh g-1 at 2 C. This facile PIL-to-nanocarbon synthetic approach is applicable for the exquisite design of complex hybrid carbon nanostructures with potential use in electrochemical energy storage and conversion.

Unveiling the Formation of Solid Electrolyte Interphase and its Temperature Dependence in "Water-in-Salt" Supercapacitors.

"Water-in-salt" (WIS) electrolytes have emerged as an excellent superconcentrated ionic medium for high-power energy storage systems such as supercapacitors due to their extended working potential compared to the conventional dilute aqueous electrolyte. In this work, we have investigated the performance of WIS supercapacitors using hollow carbon nanoplates as electrodes and compared it to that based on the conventional "salt-in-water" electrolytes. Moreover, the potentiostatic electrochemical impedance spectroscopy has been employed to provide an insightful look into the charge transport properties, which also, for the first time, reveals the formation of a solid-electrolyte interphase (SEI) and their temperature-dependent impedance for charge transfer and adsorption. Furthermore, the effect of temperature on the electrochemical performance of the WIS supercapacitors in the temperature range from 15 to 60 °C has been studied, which presents a gravimetric capacitance of 128 F g-1 and a volumetric capacitance of 197.12 F cm-3 at 55 °C compared to 87.5 F g-1 and 134.75 F cm-3 at 15 °C. The in-depth understanding about the formation of SEI layer and the electrochemical performance at different temperatures for WIS supercapacitors will assist the efforts toward designing better aqueous electrolytes for supercapacitors.

Efficient Sulfur Host Based on Yolk-Shell Iron Oxide/Sulfide-Carbon Nanospindles for Lithium-Sulfur Batteries.

Numerous nanostructured materials have been reported as efficient sulfur hosts to suppress the problematic "shuttling" of lithium polysulfides (LiPSs) in lithium-sulfur (Li-S) batteries. However, direct comparison of these materials in their efficiency of suppressing LiPSs shuttling is challenging, owing to the structural and morphological differences between individual materials. This study introduces a simple route to synthesize a series of sulfur host materials with the same yolk-shell nanospindle morphology but tunable compositions (Fe3 O4 , FeS, or FeS2 ), which allows for a systematic investigation into the specific effect of chemical composition on the electrochemical performances of Li-S batteries. Among them, the S/FeS2 -C electrode exhibits the best performance and delivers an initial capacity of 877.6 mAh g-1 at 0.5 C with a retention ratio of 86.7 % after 350 cycles. This approach can also be extended to the optimization of materials for other functionalities and applications.

The Nanostructure of Water-in-Salt Electrolytes Revisited: Effect of the Anion Size.

The increasing interest in developing safe and sustainable energy storage systems has led to the rapid rise in attention to superconcentrated electrolytes, commonly called water-in-salt (WiS). Several works indicate that the transport properties of these liquid electrolytes are related to the presence of nanodomains, but a detailed characterization of such structure is missing. Here, the structural nano-heterogeneity of lithium WiS electrolytes, comprising lithium trifluoromethanesulfonate (LiTf) and bis(trifluoromethanesulfonyl)imide (LiTFSI) solutions as a function of concentration and temperature, was assessed by resorting to the analysis of small-angle neutron scattering (SANS) patterns. Variations with the concentration of a correlation peak, rather temperature-independent, in a Q range around 3.5-5 nm-1 indicate that these electrolytes are composed of nanometric water-rich channels percolating a 3D dispersing anion-rich network, with differences between Tf and TFSI anions related to their distinct volumes and interactions. Furthermore, a common trend was found for both systems' morphology above a salt volume fraction of ∼0.5. These results imply that the determining factor in the formation of the nanostructure is the salt volume fraction (related to the anion size), rather than its molality. These findings may represent a paradigm shift for designing WiS electrolytes.

Peat-derived hard carbon electrodes with superior capacity for sodium-ion batteries.

Herein we demonstrate how peat, abundant and cheap biomass, can be successfully used as a precursor to synthesize peat-derived hard carbons (PDCs), applicable as electrode materials for sodium-ion batteries (SIB). The PDCs were obtained by pre-pyrolysing peat at 300-800 °C, removing impurities with base-acid solution treatment and thereafter post-pyrolysing the materials at temperatures (T) from 1000 to 1500 °C. By modification of pre- and post-pyrolysis temperatures we obtained hard carbons with low surface areas, optimal carbonization degree and high electrochemical Na+ storage capacity in SIB half-cells. The best results were obtained when pre-pyrolysing peat at 450 °C, washing out the impurities with KOH and HCl solutions and then post-pyrolysing the obtained carbon-rich material at 1400 °C. All hard carbons were electrochemically characterized in half-cells (vs. Na/Na+) and capacities as high as 350 mA h g-1 at 1.5 V and 250 mA h g-1 in the plateau region (E < 0.2 V) were achieved at charging current density of 25 mA g-1 with an initial coulombic efficiency of 80%.

Operando Analysis of a Lithium/Sulfur Battery by Small-Angle Neutron Scattering.

This study reports the use of operando small-angle neutron scattering to investigate processes in an operating Li/S battery. The combination with impedance spectroscopy yields valuable insights into the precipitation and dissolution of lithium sulfide during 10 cycles of galvanostatic cycling. The use of a deuterated electrolyte increases strongly the sensitivity to detect the sulfur and Li2S precipitates at the carbon host electrode and allows us to observe the time-dependent initial wetting of the system. No correlation of the scattering signal of the micropores with either lithium sulfide or sulfur is observable during the whole course of the experiment. Hence both reaction products do not precipitate inside the microporous structure but on the outer surface of the micrometer-sized carbon fibers used in this study. The excellent scattering contrast allows a detailed analysis of the formation and dissolution process of nanoscopic Li2S structures. While lithium sulfide particles grow homogeneously during the precipitation period, smaller Li2S particles dissolve first followed by a sudden dissolution of the larger Li2S particles.