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Carbon spheres are widely used in energy storage due to their adjustable particle size, controllable shape, and variable surface physical and chemical properties. However, there are still problems such as low specific surface area and unsatisfactory ion transport kinetics in K+ storage. Although increasing the specific surface area of the active material can increase the K+ storage sites, the contact area between the active material and the electrolyte also increases, aggravating the occurrence of side reactions and the consumption of the active materials. We developed an N-doped mesoporous hollow carbon sphere with a novel morphology-a smooth exterior and wrinkled interior structure with a carbon-supported pseudo-bilayer carbon structure (IW-MHCS). Its smooth outer structure sufficiently reduces the contact area with the electrolyte, and the wrinkled inner structure effectively increases the specific surface area. The obtained IW-MHCS exhibits superior rate performance (120.6 mAh g−1 at 5 A g−1) and sufficient capacity (202.7 mAh g−1 after 800 cycles at 1 A g−1) for K+ storage. This study provides a new insight into the structural design and morphological control of high-energy-storage carbon-based materials. [Display omitted] • A novel mesoporous hollow carbon spheres (HCSs) with pseudo-bilayer structure were synthesized. • The HCSs possess a smooth exterior surface and a wrinkled interior morphology. • The optimized sample exhibited excellent potassium storage performance. • The good electrochemical performance is ascribed to the unique microstructure of HCSs. [ABSTRACT FROM AUTHOR]

The phase-transition engineering has shown great potential in designing high-performance energy storage and catalytic materials. Herein, we report the phase transition and selenium vacancy induced by the trace boron doping into CoSe 2 , realizing an enhancement of the performance of supercapacitor. The trace amounts of boron doping (∼ 0.07 wt%) induce the phase-transition from cubic to orthorhombic structures and trigger selenium vacancies in orthorhombic cobalt diselenide (o-CoSe 2). The doped defective cobalt diselenide (o-CoSe 2−x /B) exhibits a high specific capacity of 376.3 mA h g−1 at a current density of 1 A g−1, which is much larger than that of the undoped cubic cobalt diselenide (211.3 mA h g−1) and annealed cubic cobalt diselenide (208.3 mA h g−1). A hybrid supercapacitor assembled using o-CoSe 2−x /B and activated carbon delivers a high energy density of 102.5 W h kg−1 at a power density of 850.4 W kg−1 and maintains an energy density of 34.0 W h kg−1 at 16,767.1 W kg−1. In addition, the device possesses an excellent cycling stability that remains 83.5 % of the initial capacitance after 25,000 cycles at a current density of 10 A g−1. These results demonstrate that the boron is a new efficient dopant that can dramatically improve the supercapacitor performance of CoSe 2 through the structural phase transition and defect engineering. [Display omitted] • Trace amounts of boron induces phase-transition from c-CoSe 2 to o-CoSe 2. • Se vacancies defects arise with the help of boron doping engineering. • The o-CoSe 2−x /B shows the enhanced performance as electrode for supercapacitor. • Providing an efficient dopant for design of CoSe 2 based energy storage materials. [ABSTRACT FROM AUTHOR]

• Zn-substituted Co 3 O 4 microspheres with a rough surface are synthesized. • Zn substitution modifies the lithium storage mechanism of Co 3 O 4 anodes. • The optimized sample exhibits good performance within half and full cells. Substituting Co 3 O 4 submicron spheres with Zn ions modifies the lithium storage mechanism, leading to an enhanced electrochemical performance. [Display omitted] Carbonaceous materials are used as the anode for rechargeable lithium-ion batteries (LIBs), however, lithium dendrites are easily formed during cycling due to the low lithium insertion potential (~0.1 V versus Li+/Li). As alternative anodes, transition metal oxides based on conversion mechanism have attached much attention. But the high lithiation potential (>1.0 V vs. Li+/Li) usually leads to a low output voltage and energy density when used in a full cell configuration. Herein, Zn-substituted Co 3 O 4 submicron spheres are successfully synthesized by a facile solvothermal reaction and subsequent calcination method. When used as the anode for LIB, the optimized sample shows a specific capacity of 686 mAh g−1 at 0.8 A g−1 after 500 cycles, and a specific capacity of 692.9 mAh g−1 at a higher current density of 3.2 A g−1 in a half-cell. Thanks to the controlled Zn substitution, the discharge voltage plateau is 0.16 V lower than that of the pure Co 3 O 4 anode at a current density of 0.4 A g−1. Further investigation of the 0.5Zn-Co 3 O 4 //LiCoO 2 full cells also displays a high capacity (400.7 mAh g−1 after 200 cycles at 0.4 A g−1) and an excellent rate capability (658.1 mAh g−1 at 1.6 A g−1) compared with the Co 3 O 4 //LiCoO 2 full cells. This work confirms that substituting suitable metal elements into sub-micron conversion based anodes can reduce the voltage plateau, which is of great significance for the practical applications in high performance energy storage devices. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the MnO 2 /three-dimensional carbon nanotubes-graphene nanocomposite was synthesized on Cu foil substrate by chemical vapor deposition and subsequent thermal decomposition of manganese acetyllacetonate precursors. The nanocomposite material was directly used as a binder-free electrode to investigate the supercapacitive performance. The results indicate that the appropriate defects and MnO 2 nanoparticles are introduced simultaneously into the carbon nanotubes-graphene architecture in one-step. The specific capacitance of MnO 2 /three-dimensional carbon nanotubes-graphene/Cu electrode is up to 365 F g−1 at a current density of 1 A g−1 in 1.0 M Na 2 SO 4 solution, which is 9 times higher than that of electrode without MnO 2 modification. After 1000 cycles at 1 A g−1, the capacity retention is still maintained at 97.0%, suggesting potential applications in high-performance energy storage devices. The excellent electrochemical performances of nanocomposite electrode can be attributed to the significantly synergistic effects between the lasting electronic conductivity of three-dimensional carbon nanotubes-graphene/Cu with the appropriate defects and the pseudocapacitance of the MnO 2 nanoparticles. Graphical abstract Image 1 Highlights • MnO 2 /3D CNTs-G/Cu was fabricated as a binder-free electrode using a facile method. •Defects and α-MnO 2 was introduced simultaneously into the 3D CNTs-G/Cu in one-step. •The specific capacitance of MnO 2 /3D CNTs-G/Cu reached 365 F g−1 at 1 A g−1 current. •Synergistic effects of 3D CNTs-G/Cu lasting conductivity and MnO 2 pseudocapacitance. [ABSTRACT FROM AUTHOR]

• Utilizing the well-designed Ni 2 CoS 4 @ZIF-67 precursor as self-sacrificing templates. • Constructing the porous α-Ni(Co)S@NiCoO 2 composites with core–shell like structure. • Novel combination of Ni-Co-S and Ni-Co-O shows outstanding capacitive performance. As inspired by the surging demand for high performance energy storage systems, researchers have been designing and exploring advanced electrode materials exhibiting higher energy and power densities. In this study, a novel combination of nickel-cobalt sulfide and oxide was reported for high performance supercapacitors. The porous α-Ni(Co)S@NiCoO 2 composites with core–shell structure were derived from the well-designed precursor with Ni 2 CoS 4 and ZIF-67 serving as the self-sacrificing templates through a two-step calcination process at elevated temperatures. Such a heterostructure exhibited an ultra-high specific capacity of 502.4 mA h g–1 at a current density of 1 A g–1, which was attributed to the unique porous core–shell structure and the ingenious combination of bimetallic sulfide and oxide. Furthermore, a hybrid supercapacitor based on the α-Ni(Co)S@NiCoO 2 composite and commercial activated carbon achieved a high energy density of 82.4 Wh kg–1 at a power density of 847.5 W kg–1. The prominent electrochemical performance exhibited by the α-Ni(Co)S@NiCoO 2 heterostructure in this study was demonstrated to be promising to practically serve as advanced electrode materials in supercapacitors. [ABSTRACT FROM AUTHOR]

Transition metal oxide (TMO) anodes show promising applications in energy storage due to the unique physical and chemical properties and high theoretical capacity to storage ions. Their practical usages are restricted by low intrinsic electronic conductivity, sluggish ionic diffusion, and large volume change during continuous cycling. In this work, we propose a strategy of selective solution-phase reduction on specific crystalline planes to generate the defect chemistry and thus improve the intrinsic electronic conductivity. Taking Co 3 O 4 electrode as a typical example, we prepared the structures with different exposed planes, which were then subjected to solution-phase reduction at room temperature. When used as the electrodes for lithium ion batteries, the optimized material possesses a high reversible capacity of 873.5 mAh g−1 at a current of 0.1 A g−1, even at a large current density of 5 A g−1, a remarkable discharge capacity of 569.1 mA h g−1 can still be achieved. The improved performance is attributed to the synergistic effects of the optimized amount of Co2+ species and oxygen vacancies. The current strategy can be extended to other TMO electrodes, paving an alternative way to optimize the electrochemical performance for different applications. Selective solution-phase reduction on specific exposed crystalline planes generates defect structures and thus improves the lithium storage properties in a given material. Image 1 • Exposed crystalline planes are selective reduced in solution. • Defect structures can be generated. • The optimized sample exhibits enhanced lithium storage properties. [ABSTRACT FROM AUTHOR]

• The CNTs/NiCo 2 S 4 hybrids with three kinds of interfaces were designed and prepared. • Supercapacitive properties of CNTs/NiCo 2 S 4 were improved by interface regulation. • An aqueous asymmetric supercapacitor was successfully assembled and evaluated. • An CNT:Ni@NiCo 2 S 4 //AC device showed excellent electrochemical energy storage. Integrating metal sulfides with carbon materials is considered as one of effective approaches to meet the demand of high-performance electrochemical energy storage materials. In this paper, we emphasize the critical role of interface between NiCo 2 S 4 and CNTs for supercapacitive performance of the hybrid structures. The CNTs/NiCo 2 S 4 nanocomposites with three kinds of interfaces are prepared using a one-step hydrothermal method by adding the pristine CNTs, surface-oxidized CNTs and nickel-coated CNTs, respectively. Benefiting from the unique nickel interface structure that adequately realizes the effective utilization of the conductive CNTs owing to the homogeneous dispersion of CNTs throughout the matrix as well as the strong interface adhesion by a bridging role, the CNTs:Ni@NiCo 2 S 4 nanocomposite exhibits a high specific capacity of 224.0 mAh g−1 at a current density of 1 A g−1. An asymmetric supercapacitor assembled by the CNTs:Ni@NiCo 2 S 4 nanocomposite and activated carbon as positive electrode and negative electrode, respectively, exhibits a high energy density of 60.7 Wh kg−1 at a power density of 800 W kg−1 and an excellent cycling stability of 88% capacitance retention after 10,000 cycles at 10 A g−1. This work described herein provides a new strategy for development of high-performance energy storage materials. [ABSTRACT FROM AUTHOR]