Mesh-like vertical structures enable both high areal capacity and excellent rate capability

In order to balance electrochemical kinetics with loading level for achieving efficient energy storage with high areal capacity and good rate capability simultaneously for wearable electronics,herein,2 D meshlike vertical structures(NiCo_2 S_4@Ni(OH)_2) with a high mass loading of 2.17 mg cm^(-2) and combined merits of both 1 D nanowires and 2 D nanosheets are designed for fabricating flexible hybrid supercapacitors.Particularly,the seamlessly interconnected NiCo_2 S_4 core not only provides high capacity of 287.5 μAh cm^(-2) but also functions as conductive skeleton for fast electron transport;Ni(OH)_2 sheath occupying the voids in NiCo_2 S_4 meshes contributes extra capacity of 248.4 μAh cm^(-2);the holey features guarantee rapid ion diffusion along and across NiCO_2 S_4@Ni(OH)_2 meshes.The resultant flexible electrode exhibits a high areal capacity of 535.9 μAh cm^(-2)(246.9 mAh g^(-1)) at 3 mA cm^(-2) and outstanding rate performance with 84.7% retention at 30 mA cm^(-2),suggesting efficient utilization of both NiCo_2 S_4 and Ni(OH)_2 with specific capacities approaching to their theoretical values.The flexible solid-state hybrid device based on NiCo_2 S_4@Ni(OH)_2 cathode and Fe_2 O_3 anode delivers a high energy density of 315 μWh cm^(-2) at the power density of 2.14 mW cm^(-2) with excellent electrochemical cycling stability.

Recent Advances in Molybdenum-Based Materials for Lithium-Sulfur Batteries

Lithium-sulfur(Li-S)batteries as power supply systems possessing a theoretical energy density of as high as 2600 Wh kg−1 are considered promising alternatives toward the currently used lithium-ion batteries(LIBs).However,the insulation characteristic and huge volume change of sulfur,the generation of dissolvable lithium polysulfides(LiPSs)during charge/discharge,and the uncontrollable dendrite formation of Li metal anodes render Li-S batteries serious cycling issues with rapid capacity decay.To address these challenges,extensive efforts are devoted to designing cathode/anode hosts and/or modifying separators by incorporating functional materials with the features of improved conductivity,lithiophilic,physical/chemical capture ability toward LiPSs,and/or efficient catalytic conversion of LiPSs.Among all candidates,molybdenum-based(Mo-based)materials are highly preferred for their tunable crystal structure,adjustable composition,variable valence of Mo centers,and strong interactions with soluble LiPSs.Herein,the latest advances in design and application of Mo-based materials for Li-S batteries are comprehensively reviewed,covering molybdenum oxides,molybdenum dichalcogenides,molybdenum nitrides,molybdenum carbides,molybdenum phosphides,and molybdenum metal.In the end,the existing challenges in this research field are elaborately discussed.