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Preparation of a material with excellent rate performance and high capacity contribution is significant for sodium-ion hybrid capacitors (SIHCs). TiO2 has been extensively studied due to its outstanding chemical stability, but the low specific capacity greatly hinders its practical application. Herein, TiO2 with a foveolate-shape is prepared via a precisely controlled Ostwald maturation procedure. Benefiting from the unique structure, foveolate TiO2 possesses satisfactory electrochemical performance. When used as the anode for SIHCs, a high reversible specific capacity of 290 mA h g−1 is obtained with an ultrahigh initial coulombic efficiency of 96% at 100 mA g−1. Even if the current density increases to 1000 mA g−1, the specific discharge capacity can still be maintained at 158 mA h g−1 after 1500 cycles. To further improve its capacity, the TiO2@MoSe2 composite electrode is synthesized by using foveolate TiO2 as the skeleton for the successful growth of MoSe2 nanosheets. A higher reversible specific capacity of 551 mA h g−1 is achieved at 100 mA g−1. Moreover, a reversible specific capacity of 164 mA h g−1 is maintained after 500 cycles at 5000 mA g−1. The foveolate TiO2 preparation method developed in this work provides new ideas for the development of both substrate materials and active materials in the field of energy storage. [ABSTRACT FROM AUTHOR]

Polyanion-type compounds, used as promising cathode materials for sodium-ion batteries (SIBs), have attracted great attention because of their suitable operating voltage, stable framework and good thermal stability. However, they suffer from inherent low conductivity, poor high-rate capability and unsatisfactory cycle stability. Herein, in order to overcome these deficiencies, a feasible strategy, which integrates high conductivity reduced graphene oxide (rGO) with the representative vanadium-based fluorophosphates to form a 3D carbon network constructed in NaVPO4F, is proposed and investigated. Based on microstructural and morphological characterization, the NaVPO4F nanoparticles are successfully synthesized and uniformly embedded in a robust rGO carbon network. Ascribed to the multifunctional structure design, the reaction kinetics of NaVPO4F were significantly improved, as demonstrated by the electrochemical impedance spectroscopy, cyclic voltammetry at varied scan rates and galvanostatic intermittent titration technique. Moreover, the hard carbon (HC) and the NaVPO4F@rGO composite are employed as the anode and the cathode, respectively, to fabricate a sodium-ion full battery, which exhibits an excellent high-rate capability (75.1 mA h g−1 at 15C) and an outstanding cycling stability (0.0115% capacity decay per cycle over 1500 cycles at 5C rate). This study provides a feasible and effective method to develop high-performance polyanion-type electrode materials for SIBs. [ABSTRACT FROM AUTHOR]

In this study, the double transition metal selenide Ni1.5CoSe5 with cube-like nanoaggregate morphology was successfully embedded into a three-dimensional (3D) dual N-doped carbon network, developing an advanced anode material for sodium-ion batteries (SIBs). In the prepared composite, Ni1.5CoSe5 nanoparticles were first coated by N-doped carbon (NC), which further aggregated to form nanocubes, and finally embedded into interconnected N-doped reduced graphene oxide (rGO) nanosheets; hence, the material was abbreviated as Ni1.5CoSe5@NC@rGO. It delivered a reversible Na-storage capacity of 582.5 mA h g−1 at a low current density of 0.05 A g−1 and exhibited ultra-fast rate properties (e.g., with the specific capacities of 180.8 and 96.3 mA h g−1 at high current densities of 30 and 50 A g−1, respectively). The much enhanced Na-storage properties were ascribed to the highly conductive 3D network constructed by dual N-doped carbonaceous materials, which acted not only as a highway for ultrafast charge transfer but also as an effective protector for the active Ni1.5CoSe5 material and cube-like nanoaggregates with nanometer-sized primary particles. More significantly, the Ni1.5CoSe5@NC@rGO electrode also exhibited superior energy storage performance in sodium-ion full cells when coupled with a high-voltage Na3V2(PO4)2O2F cathode, making it a promising anode material for practical SIBs. [ABSTRACT FROM AUTHOR]

Coaxial nanotubes are a significant class of nanoscale building blocks for advanced electrodes of secondary batteries. Herein, one-dimensional (1D) coaxial double nanotubes (DNTs) consisting of α-MnSe inner tubes and N-doped carbon (N–C) outer tubes (abbreviated as α-MnSe@N–C DNTs) are successfully prepared and are demonstrated to be promising anode material for Li-ion and Na-ion batteries (LIBs/NIBs). When used in LIBs, it was revealed by ex situ XRD/HRTEM studies and electrode kinetics that a new electrochemical α→β phase transition plays a crucial role in improving the cycling stability. As a result, the α-MnSe@N–C DNTs electrode delivers a high Li-storage capacity (800 mA h g−1 at 50 mA g−1), excellent rate capability (405 mA h g−1 at 14 A g−1) and ultra-long cycling stability (a high capacity retention of 87.2% even after 9000 cycles at 2 A g−1) with retained 1D morphology. In addition, the outer N–C nanotube can effectively protect the active α-MnSe inner nanotube to realize such outstanding electrochemical properties owing to the high electrical conductivity and particular 1D coaxial nanoarchitecture of the inner nanotube. Moreover, α-MnSe@N–C DNTs also exhibit excellent Li/Na-storage properties and full-cell performances when coupled with commercial LiFePO4 and LiNi0.6Co0.2Mn0.2O2 cathodes in LIBs as well as with the Na3V2(PO4)2O2F cathode in NIBs. [ABSTRACT FROM AUTHOR]

In recent years, metal-organic compounds have been considered as ideal sacrificial templates to obtain transition metal oxides for electrochemical applications due to their diverse structures and tunable properties. In this work, a new kind of cobalt-based metal organic compound with a layered structure was designed and prepared, which was then transformed into ultrafine cobalt oxide (Co3O4) nanocrystallites via a facile annealing treatment. The obtained Co3O4 nanocrystallites further assembled into a hierarchical shale-like structure, donating extremely short ion diffusion pathway and rich porosity to the materials. The special structure largely alleviated the problems of Co3O4 such as inferior intrinsic electrical conductivity, poor ion transport kinetics and large volume changes during the redox reactions. When evaluated as anode materials for lithium-ion batteries, the shale-like Co3O4 (S-Co3O4) exhibited superior lithium storage properties with a high capacity of 1045.3 mA h g−1 after 100 cycles at 200 mA g−1 and good rate capabilities up to 10 A g−1. Moreover, the S-Co3O4 showed decent electrochemical performance in sodium-ion batteries due to the above-mentioned comprehensive merits (380 and 153.8 mA h g−1 at 50 and 5000 mA g−1, respectively). [ABSTRACT FROM AUTHOR]

A dissolution–recrystallization method was developed to prepare flexible paper electrodes constructed of Zn2GeO4 nanofibers anchored with amorphous carbon (ZGO/C-P) for high energy and power Li-ion batteries. The ZGO/C-P exhibits superior long-term cycle stability (up to 2000 cycles at 1 A g−1) and excellent rate capability. [ABSTRACT FROM AUTHOR]

Nanostructured transition metal oxides are attractive pseudocapacitive materials with high theoretical specific capacitance, scale-up potential and environmental benignity. However, realizing high capacitance and excellent rate capability remains a critical challenge. Herein, a three-dimensional carbon support of cellulose-fiber covered with graphene (CFG) to induce the growth of a hierarchical nanostructured Ni(OH)2 (Ni(OH)2–CFG) is fabricated through a one-pot hydrothermal reaction without using any surfactants or hard templates. The resulting Ni(OH)2–CFG composite exhibits a special vertical and cross-linked network structure with a large surface area (425.9 m2 g−1, higher than that of unsupported Ni(OH)2, 366.9 m2 g−1) and appropriate pore size distribution of micro–mesopores, which offer fast electrolyte ion-transport and short ion-diffusion pathways. Electrochemical characterization demonstrates that the Ni(OH)2–CFG composite as a binder-free electrode reveals high mass capacitance (2276 F g−1, at 1 A g−1), good rate capability and excellent cycling stability (no capacitance decay after 1000 cycles at a high current density of 5 A g−1). In addition, an asymmetric Ni(OH)2–CFG//activated carbon supercapacitor exhibits a high cell-voltage of 1.6 V and a maximum specific capacitance of 191.3 F g−1 with an energy density up to 15.0 W h kg−1. The excellent performances of the Ni(OH)2–CFG composite demonstrate its promising potential for future capacitor based energy storage and conversion. [ABSTRACT FROM AUTHOR]