An efficient and robust electrocatalyst of a Co/CoO hybrid containing oxygen vacancies rooted on carbon cloth with anion pre-intercalation.

Na3V2(PO4)3 has attracted great attention due to its high energy density and stable structure. However, in order to boost its application, the discharge potential of 3.3–3.4 V (vs Na+/Na) still needs to be improved and substitution of vanadium with other lower cost and earth‐abundant active redox elements is imperative. Therefore, the Na superionic conductor (NASICON)‐structured Na4MnV(PO4)3 seems to be more attractive due to its lower toxicity and higher voltage platform resulting from the partial substitution of V with Mn. However, Na4MnV(PO4)3 still suffers from poor electronic conductivity, leading to unsatisfactory capacity delivering and poor high‐rate capability. In this work, a graphene aerogel–supported in situ carbon–coated Na4MnV(PO4)3 material is synthesized through a feasible solution‐route method. The elaborately designed Na4MnV(PO4)3 can reach ≈380 Wh kg−1 at 0.5 C (1 C = 110 mAh g−1) and realize superior high‐rate capability evenat 50 C (60.1 mAh g−1) with a long cycle‐life of 4000 cycles at 20 C. This impressive progress should be ascribed to the multifunctional 3D carbon framework and the distinctive structure of trigonal Na4MnV(PO4)3, which are deeply investigated by both experiments and calculations.

Nonaqueous Li-O-2 batteries are of great interest because of their high theoretical energy density, and a stable porous cathode plays a vital role in electrochemical performance of Li-O-2 batteries. Herein, catalyst nanoarchitecturing via functionally implanted cobalt nanoparticles in N-doped carbon host is fabricated by an ultrasonic method combined with controlled calcination process and served as an effective electrocatalyst for Li-O-2 batteries. The synthesized catalyst holds a three-dimensional porous network structure, which could offer numerous active sites and provide the channels for mass transfer. When employed as an oxygen electrode, the Li-O-2 battery shows improved discharge capacity of 3862 mA h g(-1) at a current density of 0.1 mA cm(-2) and superior cycling stability up to 40 cycles with a limited capacity of 500 mA h g(-1), owing to the porous carbon substrate with highly graphitic and better catalytic activity of implanted Co nanoparticles. The N-doped carbon with a high degree of graphitization is obtained by a catalytic pyrolysis method and Co as main catalyst also give a good reference for future design of efficient catalysts for electrochemical application.

Na2MnP2O7 has been considered as a promising cathode candidate for advanced sodium-ion batteries due to its high potential, low cost and non-toxicity. However, the low initial Coulombic efficiency, poor high-rate and unsatisfactory cycling ability originated from the intrinsic inferior electronic conductivity and manganese dissolution severely hinder its practical application. Herein, we report an approach based on a feasible high energy vibrating activation process to fabricate a robust graphene layers (GL) modified Na2MnP2O7 material (noted as NMP@GL) for the first time. The as-prepared NMP@GL could exhibit an ultrahigh initial Coulombic efficiency of 90%, and a high energy density over 300 Wh kg(-1). In addition, rate performance and cycling stability were also improved, with high capacity retention of 83% after 600 cycles at 2 C. These impressive progresses should be ascribed to the enhanced electron transportation with distinctive framework through graphene layer modifying, and structural stability of triclinic Na2MnP2O7 with spacious 3D ion migration channels. Ex-situ XRD and GITT demonstrate a consecutive multi-phase reaction mechanism with facile sodium diffusion. Our design makes Na2MnP2O7@GL to achieve its potential for practical application.

Na2FeP2O7, which is considered as a promising cathode for sodium ion batteries (SIBs) on account of its economical efficiency and outstanding thermal stability, has been widely studied for the purpose of enhancing its electronic conductivity and interface ion transportation. In this paper, a double-carbon synergistically modified strategy was firstly introduced to facilitate the electrochemical performance of Na2FeP2O7. Na2FeP2O7 particles are enwrapped in situ by a carbon layer and further anchored in reduced graphene oxide (RGO) framework through a facile urea-nitrate combustion method. Consequently, the excellent rate performance and durable cycle stability of this compound are identified, which exhibits a reversible sodium storage capacity of 65 mAh g(-1) at a current density of 10 C and no obvious decay in capacity after circling for 300 cycles at 1 C. What's more, no drastic degradation in capacity is observed when the cycling current density is brought back to high rates after cycling for more than 360 cycles at various rates. (C) 2017 Elsevier B.V. All rights reserved.

3D porous carbons have shown great potential in electrochemical energy storage. However, traditional template assisted methods suffer from complicated synthesis processes as well as the difficulty of removing template. In this paper, 3D neat porous carbon aerogels have been designed and synthesized by a green and novel way via self-assembly of hydrogel with NaCl as the template and the flux during in-situ polymerization and carbonization. NaCl can be easily recovered with simple recrystallization in the end of synthesis. The as-synthesized 3D porous carbon aerogels display excellent structural stability, large specific surface area (1665.5 m(2) g(-1)), porous structure centered at microporous (0.71 nm and 1.24 nm) and macropores for ionic diffusion and electrolyte transport, as well as large interlayer spacings (0.386 nm) for sodium storage. When employed as anode materials for sodium-ions batteries, the electrodes exhibit high reversible specific capacity of 287 mAh g(-1) at 50 mA g(-1) after 100 cycles, superior cycling stability of 154 mAh g(-1) at 500 mA g(-1) after 1000 cycles as well as excellent rate capability of 139 mAh g(-1) at 1000 mA g(-1). This work inspires a new strategy in the fabrication of advanced carbon structures for sodium-ion batteries and other applications. (C) 2017 Elsevier B.V. All rights reserved.