Nanocomposites that contain reinforcements with preferred orientation have attracted significant attention because of their promising applications in a wide range of multifunctional fields. Many efforts have recently been focused on developing facile methods for preparing aligned graphene sheets in solvents and polymers because of their fascinating properties including liquid crystallinity and highly anisotropic characteristics. Self-aligned in situ reduced graphene oxide (rGO)/polymer nanocomposites are prepared using an all aqueous casting method. A remarkably low percolation threshold of 0.12 vol% is achieved in the rGO/epoxy system owing to the uniformly dispersed, monolayer graphene sheets with extremely high aspect ratios (>30000). The self-alignment into a layered structure at above a critical filler content induces a unique anisotropy in electrical and mechanical properties due to the preferential formation of conductive and reinforcing networks along the alignment direction. Accompanied by the anisotropic electrical conductivities are exceptionally high dielectric constants of over 14000 with 3 wt% of rGO at 1 kHz due to the charge accumulation at the highly-aligned conductive filler/insulating polymer interface according to the Maxwell-Wagner-Sillars polarization principle. The highly dielectric rGO/epoxy nanocomposites with the engineered structure and properties present high performance electromagnetic interference shielding with a remarkable shilding efficiency of 38 dB.

cathodes, delivering comparable energy density with Li-ion batteries. Turning to the negative electrode for Na-ion batteries, carbons have emerged as one of the most promising classes of materials in the searching of anodes, [ 5 ] with therefore intensive parallel research on alloys and metal oxides. [6][7][8][9] Although widely used in Li-ion batteries, graphite cannot be blindly implemented to Na-ion ones in presence carbonate electrolyte. [ 10 ] It was recently shown that only solvated Na ions could be intercalated into graphite when appropriate electrolyte, such as ether-based electrolyte, [ 10,11 ] is used. Therefore, other forms of carbon, such as hard carbon [ 12 ] and graphene, [ 13 ] have been widely studied. A decent reversible capacity of ≈200 mAh g −1 could be obtained so that C-based Na-ion cells were assembled and tested. [ 14 ] Hard carbon materials that contain randomly oriented graphene layers are the most studied candidate anodes. They are usually prepared by pyrolysis of organic and polymer precursors, such as glucose, [ 12 ] sugar, [ 15 ] and polypyrrole, [ 16 ] at around 1000 °C. Due to the presence of large amount of sp 3 structure in the precursor, parallel growth of graphene layers is somewhat inhibited, giving rise to plenty of defects. Like Li ion storage in carbons, Na ions can equally be stored in carbons via (i) adsorption on the surface and defects, (ii) nanopore fi lling, and (iii) intercalation between the graphene layers of large d -spacing. Although a number of studies have been conducted on the hard carbon anode, there are numerous discrepancies concerning the Na ion storage mechanisms as a diversity of both voltage profi les and capacities are reported. The charge/discharge curves of hard carbon normally consist of two regions: (i) a slope between 1.0 and 0.1 V and (ii) one fl at plateau at ≈0.1 V. The fi rst one has been explained by either Na insertion into nearly parallel graphene layers [ 17 ] or binding of Na at vacancies. [ 18 ] Equally, there is no consensus regarding the assignment of the fl at plateau which is presented as due either to the Na intercalation between expanded graphene layers [ 19 ] or to nanopore fi lling/nanoplating. [ 12 , 17 ] Obviously, these different assignments come from the variation in the microstructure/texture which depends on both the carbon precursor and thermal annealing processes. Moreover, the high capacity at above 1 V is also assigned to heteroatom doping, [ 20 ] hence calling for a careful examination on the effect of functional Hard carbons are considered among the most promising anode materials for Na-ion batteries. Understanding their structure is of great importance for optimizing their Na storage capabilities and therefore achieving high performance. Herein, carbon nanofi bers (CNFs) are prepared by electrospinning and their microstructure, texture, and surface functionality are tailored through carbonization at various temperatures ranging from 650 to 2800 °C.Stepwise carbonization gradually removes the heteroatoms and increases...

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Potassium‐ion batteries (KIBs) are important alternatives to lithium‐ and sodium‐ion batteries. Herein, microsized a Bi electrode delivers exceptional potassium storage capacity, stability, and rate capability by the formation of an elastic and adhesive oligomer‐containing solid electrolyte interface with the assistance of diglyme electrolytes. The kinetics‐controlled K–Bi phase transitions are unraveled combining electrochemical profiles, in situ X‐ray diffraction and density functional theory calculations. Reversible, stepwise Bi–KBi2–K3Bi2–K3Bi transitions govern the electrochemical processes after the initial continuous surface potassiation. The Bi electrode outperforms the other anode counterparts considering both capacity and potential. This work provides critical insights into the rational design of high‐performance anode materials for KIBs.

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Sodium-ion batteries have been considered as potential candidates for stationary energy storage because of the low cost and wide availability of Na sources. However, their future commercialization depends critically on control over the solid electrolyte interface formation, as well as the degree of sodiation at the positive electrode. Here we report an easily scalable ball milling approach, which relies on the use of metallic sodium, to prepare a variety of sodium-based alloys, insertion layered oxides and polyanionic compounds having sodium in excess such as the Na4V2(PO4)2F3 phase. The practical benefits of preparing sodium-enriched positive electrodes as reservoirs to compensate for sodium loss during solid electrolyte interphase formation are demonstrated by assembling full C/P′2-Na1[Fe0.5Mn0.5]O2 and C/‘Na3+xV2(PO4)2F3' sodium-ion cells that show substantial increases (>10%) in energy storage density. Our findings may offer electrode design principles for accelerating the development of the sodium-ion technology.

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An optimized solid electrolyte interphase is the key to stabilization of microparticle anodes.