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Electrode materials with high conductivity, strong chemisorption, and catalysis toward polysulfides are recognized as key factors for metal-sulfur batteries. Nevertheless, the construction of such functional material is a challenge for room-temperature sodium-sulfur (RT-Na/S) batteries. Herein, a multiregion Janus-featured CoP-Co structure obtained via sequential carbonization-oxidation-phosphidation of heteroseed zeolitic imidazolate frameworks is introduced. The structural virtues include a heterostructure existing in a CoP-Co structure and a conductive network of N-doped porous carbon nanotube hollow cages (NCNHCs), endowing it with superior conductivity in both the short- and long-range and strong polarity toward polysulfides. Thus, the S@CoP-Co/NCNHC cathode exhibits superior electrochemical performance (448 mAh g-1 remained for 700 times cycling under 1 A g-1) and an optimized redox mechanism in polysulfides conversion. Density functional theory calculations present that the CoP-Co structure optimizes bond structure and bandwidth, whereas the pure CoP is lower than the corresponding Fermi level, which could essentially benefit the adsorptive capability and charge transfer from the CoP-Co surface to Na2Sx and therefore improve its affinity to polysulfides.

2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Applications of room-temperature-sodium sulfur (RT-Na/S) batteries are currently impeded by the insulating nature of sulfur, the slow redox kinetics of sulfur with sodium, and the dissolution and migration of sodium polysulfides. Herein, a novel micrometer-sized hierarchical S cathode supported by FeS2 electrocatalyst, which is grown in situ in well-confined carbon nanocage assemblies, is presented. The hierarchical carbon matrix can provide multiple physical entrapment to polysulfides, and the FeS2 nanograins exhibit a low Na-ion diffusion barrier, strong binding energy, and high affinity for sodium polysulfides. Their combination makes it an ideal sulfur host to immobilize the polysulfides and achieve reversible conversion of polysulfides toward Na2S. Importantly, the hierarchical S cathode is suitable for large-scale production via the inexpensive and green spray-drying method. The porous hierarchical S cathode offers a high sulfur content of 65.5 wt%, and can deliver high reversible capacity (524 mAh g−1 over 300 cycles at 0.1 A g−1) and outstanding rate capability (395 mAh g−1 at 1 A g−1 for 850 cycles), holding great promise for both scientific research and real application.

Since the development of various forms of renewable energy such as solar, wind and tidal energy, burning scarce fossil fuel is no longer the only option for electricity. Manufacturing inexpensive and efficient energy storage systems on a massive scale is fundamentally important for our society due to the intermittency of the renewable energy. Recently, sodium-ion batteries (SIBs) have been considered as a promising alternative to their lithium-ion battery counterparts for next-generation energy storage because of the abundant and cost-effective nature of sodium resources. Based on the success of commercial layered oxide cathodes in LIBs, NaxTMO2 (with TM representing Ni, Co, Mn, and other transition metals) has been regarded as one of the most promising cathodes for commercial SIBs. Nevertheless, the introduction of expensive transition metals (Ni and Co) in layered oxide cathode, and their inevitably complicated phase transitions, and weak kinetics during the charge/discharge process have greatly limited the practical application of SIBs. The cost of raw materials and the electrochemical reversibility of the cathode are key factors in the SIB systems. Low-cost layered oxides free of Ni and Co with reversible mechanisms are considered to be the most promising cathode materials for future SIBs. Thus, we propose using inexpensive Cu and Zn to replace Ni and Co, and have obtained biphasic Na0.78Cu0.27Zn0.06Mn0.67O2 with superficial atomic-scale P3 intergrowth with P2 phase, which represents a promising cathode for SIBs.

Room-temperature sodium-sulfur (RT-Na/S) batteries hold great promise for sustainable and cost-effective applications. Nevertheless, it remains a great challenge to achieve high capacity and cycling stability due to the low activity of sulfur and the sluggish conversion kinetics between polysulfide intermediates and sodium sulfide. Herein, an electrocatalyzing S cathode is fabricated, which consists of porous core-shell structure and multisulfiphilic sites. The flexible carbon structure effectively buffers volume changes during cycling and provides enclosed spaces to store S8 with exceptional conductivity. Significantly, the multisulfiphilic sites (ZnS and CoS2) enhance catalysis toward multistep S conversion, which effectively suppresses long-chain polysulfides dissolution and improves the kinetics of short-chain polysulfides. Thus, the obtained S cathodes achieve an enhanced cycling performance (570 mAh g-1 at 0.2 A g-1 over 1000 cycles), decent rate capability (250 mAh g-1 at 1.0 A g-1 over 2000 cycles), and high energy density of 384 Wh kg-1 toward practical applications.

Two-dimensional (2D) superlattices offer promising technological opportunities in tuning the intercalation chemistry of metal ions. Now, well-ordered 2D superlattices of monolayer titania and carbon with tunable interlayer-spacing are synthesized by a molecularly mediated thermally induced approach. The 2D superlattices are vertically encapsulated in hollow carbon nanospheres, which are embedded with TiO2 quantum dots, forming a 0D-2D-3D multi-dimensional architecture. The multi-dimensional architecture with the 2D superlattices encapsulated inside exhibits a near zero-strain characteristic and enriched electrochemical reactivity, achieving a highly efficient Na+ storage performance with exceptional rate capability and superior long-term cyclability.

Low‐cost layered oxides free of Ni and Co are considered to be the most promising cathode materials for future sodium‐ion batteries. Biphasic Na0.78Cu0.27Zn0.06Mn0.67O2 obtained via superficial atomic‐scale P3 intergrowth with P2 phase induced by Zn doping, consisting of inexpensive transition metals, is a promising cathode for sodium‐ion batteries. The P3 phase as a covering layer in this composite shows not only in excellent electrochemical performance but also its tolerance to moisture. The results indicate that partial Zn substitutes can effectively control biphase formation for improving the structural/electrochemical stability as well as the ionic diffusion coefficient. Based on in situ synchrotron X‐ray diffraction coupled with electron‐energy‐loss spectroscopy, a possible Cu2+/3+ redox reaction mechanism has now been revealed.