Polysulfide dissolution and slow electrochemical kinetics of conversion reactions lead to low utilization of sulfur cathodes that inhibits further development of room-temperature sodium-sulfur batteries. Here we report a multifunctional sulfur host, NiS2 nanocrystals implanted in nitrogen-doped porous carbon nanotubes, which is rationally designed to achieve high polysulfide immobilization and conversion. Attributable to the synergetic effect of physical confinement and chemical bonding, the high electronic conductivity of the matrix, closed porous structure, and polarized additives of the multifunctional sulfur host effectively immobilize polysulfides. Significantly, the electrocatalytic behaviors of the Lewis base matrix and the NiS2 component are clearly evidenced by operando synchrotron X-ray diffraction and density functional theory with strong adsorption of polysulfides and high conversion of soluble polysulfides into insoluble Na2S2/Na2S. Thus, the as-obtained sulfur cathodes exhibit excellent performance in room-temperature Na/S batteries.

in reversible oxidation/reduction reaction to achieve a high energy density. (ii) Fast charge transport and high exchanging current density of materials dramatically reduce the polarization and further provide a high power density. (iii) Uniform micro/nanostructures are associated with increased specific surfaces areas and decreased ionic diffusion over distance and time, resulting in a long lifetime and a good cycling stability.Among various energy sources in history, rechargeable cells are lead (Pb)-acid, nickel-chromium (Ni-Cr), nickel-metal hydride (Ni-MH), redox flow, lithiumion, fuel cells and metal-air batteries. [2] In particular, rechargeable metal-air batteries have received great interest due to a huge theoretical specific energy density, deriving from a unique cell structure. In this system, only the metal (Li, Na, Mg, Al, Zn, Si, Fe, Sn, etc.) anode is assembled in the cell, while the active cathode material is oxygen (O 2 ), directly obtained from the atmosphere. [12][13][14][15][16][17] Figure 1a presents a summary of basic theoretical properties and electrochemical reactions in typical metal-air batteries. For instance, rechargeable Li-air batteries can provide a theoretical cell voltage of 2.96 V and a theoretical specific energy density of 3.4 kW h kg −1 . In this particular battery, the decomposition of lithium peroxide (Li 2 O 2 ), despite being an explosive and poisonous compound, plays a vital role in the improved charge transport because it demonstrates a highly reversible reaction between the discharge and charge process. [18,19] The maximum specific capacity of secondary Li-air batteries reaches an initial discharge capacity of 14000 mA h g −1 at a current density of 140 mA g −1 , using Co 3 O 4 /reduced graphene oxide nanocomposites as electrocatalysts. [20] Unfortunately, although they are the focus of numerous investigations, lithium-air batteries are still accompanied by the major drawbacks of the high price of metallic lithium (The USD $160000-180000/ton as of May 2017) and safety issues in an organic electrolyte.Magnesium provides a number of improvements compared to metallic Li, including its abundance in the earth's crust (2.08% for Mg vs 0.0065% for Li) and environmental friendliness. Moreover, rechargeable Mg-O 2 battery allows a theoretical volumetric density and a specific energy density of 14 kW h L −1 and 3.9 kW h kg −1 , respectively, assuming MgO is formed as the discharge product. [21,22] These values are much larger than those of Li-O 2 cells on the basis of Li 2 O 2 (8.0 kW h L −1 and 3.4 kW h kg −1 ). Though a great number of efforts have focused on the widespread studies of Li-air Rechargeable Mg-air batteries are a promising alternative to Li-air cells owing to the safety, low price originating from the abundant resource on the earth, and high theoretical volumetric density (3832 A h L −1 for Mg anode vs 2062 A h L −1 for Li). Only a few works are related to the highly reversible Mg-air batteries. The fundamental scientific difficulties hindering the rapid developmen...

Transition Metal Oxides (Na x MO 2 , x ≤ 1, M = Transition Metal)Transition metal oxides Na x MO 2 , (x ≤ 1, M = transition metal, Co, Mn, Fe, Ni, etc.) have recently received increased attention due to their high energy density, above 400 W h kg −1 . [69,75,76] Moreover, its lithium counterpart-Li x MO 2 has been successfully applied in commercial LIBs. Generally speaking, Na x MO 2 can Sodium ion batteries (SIBs) have recently attracted considerable attention and are considered as an alternative to lithium ion batteries (LIBs), owing to the cheap price and abundance of sodium resources. However, the commercialization of SIBs has so far been impeded by the low energy density and unstable cycle life of electrodes, especially as cathodes. Although some cathode candidates with a stable cycle life and high energy density have been developed using nanotechnologies, the commercial feasibility is seldom taken into account. This research news article provides an insight into the commercial prospects of existing cathode materials for SIBs in terms of environmental friendliness, manufacturing cost, synthesis methods and electrochemical performance. Sodium Ion Batteries IntroductionRecently, owing to the ever-increasing consumption of lithium resources, the price of lithium ion batteries (LIBs) has increased rapidly. As researchers strive to seek an alternative to LIBs for energy storage, sodium ion batteries (SIBs) have been attracting more attention due to their similar electrochemical properties to LIBs and low cost. The major challenge for SIB commercialization is the low energy density and unstable cycle life of electrode materials. The energy density is related to the capacity and potential plateau.A wide variety of materials have been investigated as electrode materials for SIBs. Anode candidates, include carbonaceous materials, [26][27][28][29][30][31][32][33][34][35][36] alloy-forming elements (Sn, Sb, Ge and P), and alloy compound (SnSb, phosphide, et al). [59,60,[63][64][65] Moreover, the current anode candidates can deliver more than 200 mA h g −1 capacity, and most of them can show stable cycle life more than 200 cycles through various strategies of structural modification and nanotechnology. Reported cathode materials candidates can be divided into four classes: transition metal (M) oxides (Na x MO 2+y ), [8][9][10][11] Adv. Energy

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Phosphorus-based heterocycles provide access to materials with properties that are inaccessible from all-carbon architectures. The unique hybridization of phosphorus gives rise to electron-accepting capacities, a large variety of coordination reactions, and the possibility of controlling the electronic properties through phosphorus postfunctionalization. Herein, we describe a new noncatalyzed synthetic protocol to prepare fused six-membered phosphorus heterocycles. In particular, we report the synthesis of novel phosphaphenalenes. These fused systems exhibit the benefits of both five- and six-membered phosphorus heterocycles and enable a series of versatile postfunctionalization reactions. This work thus opens up new horizons in the field of conjugated materials.