Li‐ion hybrid capacitors (LIHCs), consisting of an energy‐type redox anode and a power‐type double‐layer cathode, are attracting significant attention due to the good combination with the advantages of conventional Li‐ion batteries and supercapacitors. However, most anodes are battery‐like materials with the sluggish kinetics of Li‐ion storage, which seriously restrict the energy storage of LIHCs at the high charge/discharge rates. Herein, vanadium nitride (VN) nanowire is demonstated to have obvious pseudocapacitive characteristic of Li‐ion storage and can get further gains in energy storage through a 3D porous architecture with the assistance of conductive reduced graphene oxide (RGO). The as‐prepared 3D VN–RGO composite exhibits the large Li‐ion storage capacity and fast charge/discharge rate within a wide working widow from 0.01–3 V (vs Li/Li+), which could potentially boost the operating potential and the energy and power densities of LIHCs. By employing such 3D VN–RGO composite and porous carbon nanorods with a high surface area of 3343 m2 g−1 as the anode and cathode, respectively, a novel LIHCs is fabricated with an ultrahigh energy density of 162 Wh kg−1 at 200 W kg−1, which also remains 64 Wh kg−1 even at a high power density of 10 kW kg−1.

The novel PDDA-NPCNs/Ti3C2 hybrids via an electrostatic attraction self-assembly approach effectively accelerate reaction kinetics and improve electrochemical performance as PIBs anodes.

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A new hybrid supercapacitor with excellent electrochemical performance is fabricated by using the flower-like Co(OH)2 and urchin-like VN.

Carbon based materials as one promising cathode to accommodate the insoluble and insulating discharge products (Li2O2) for lithium oxygen (Li‐O2) batteries have attracted great attention due to their large energy density store ability compared with the other carbon‐free cathodes. However, the side reaction occurring at carbon/Li2O2 interfaces hinders their large‐scale application in Li‐O2 batteries. Herein, a simple and cost‐effective strategy is developed for the growth of core‐shell‐like Co/CoO nanoparticles on 3D graphene‐wrapped carbon foam using 3D melamine foam as the initial backbone. This unique 3D hierarchical carbonized melamine foam‐graphene‐Co/CoO hybrid (CMF‐G‐Co/CoO) with a continuous conductive network and elastic properties is used as binder‐free oxygen electrode for Li‐O2 batteries. Electrochemical and structural measurements show that a synergistic effect is observed between Co/CoO and graphene, where Li2O2 grows on the Co/CoO surfaces instead of the carbon surfaces at the initial discharge state (500 mAh ), indicating the reduced carbon/Li2O2 interfaces and alleviative side reactions during the electrochemical process. Importantly, the CMF‐G‐Co/CoO electrode can achieve greatly improved cycle life over the electrode without aid of the Co/CoO. Furthermore, it delivers a large capacity of ≈7800 mAh and outstanding rate capability, exhibiting the great potential for the application in Li‐O2 batteries.

Two-dimensional (2D) layered materials have shown great promise for electrochemical energy storage applications. However, they are usually limited by the sluggish kinetics and poor cycling stability. Interface modification on 2D layered materials provides an effective way for increasing the active sites, improving the electronic conductivity, and enhancing the structure stability so that it can potentially solve the major issues on fabricating energy storage devices with high performance. Herein, we synthesize a novel MoS-carbon (MoS-C) monolayer interoverlapped superstructure via a facile interface-modification route. This interlayer overlapped structure is demonstrated to have a wide sodium-ion intercalation/deintercalation voltage range of 0.4-3.0 V and the typical pseudocapacitive characteristics in fast kinetics, high reversibility, and robust structural stability, thus displaying a large reversible capacity, a high rate capability, and an improved cyclability. A full cell of sodium-ion hybrid supercapacitor based on this MoS-C hybrid architecture can operate up to 3.8 V and deliver a high energy density of 111.4 Wh kg and a high power density exceeding 12 000 W kg. Furthermore, a long cycle life of 10 000 cycles with over 77.3% of capacitance retention can be achieved.

Graphene coupled Ti3C2MXenes-derived TiO2mesostructure with robust Na-ion charge storage properties enables the fabrication of high-performance Na-ion capacitors.

Nanosizing is the fashionable method to obtain a desirable electrode material for energy storage applications, and thus, a question arises: do smaller electrode materials exhibit better electrochemical performance? In this context, theoretical analyses on the particle size, band gap and conductivity of nano-electrode materials were performed; it was determined that a critical size exist between particle size and electrochemical performance. To verify this determination, for the first time, a scalable formation and disassociation of nickel-citrate complex approach was performed to synthesize ultra-small Ni(OH) 2 nanoparticles with different average sizes (3.3, 3.7, 4.4, 6.0, 6.3, 7.9, 9.4, 10.0 and 12.2 nm). The best electrochemical performance was observed with a specific capacity of 406 C g − 1 , an excellent rate capability was achieved at a critical size of 7.9 nm and a rapid decrease in the specific capacity was observed when the particle size was o7.9 nm. This result is because of the quantum confinement effect, which decreased the electrical conductivity and the sluggish charge and proton transfer. The results presented here provide a new insight into the nanosize effect on the electrochemical performance to help design advanced energy storage devices. INTRODUCTIONRecently, electrochemical energy storage devices, such as batteries and supercapacitors, have attracted great attention because of their many advantages compared with other power-source technologies. However, these devices could realize further gains in energy and power densities if the electrochemical performance of electrode materials is largely improved. 1,2 Reducing the dimensions of electrode materials down to the nanoscale level is an effective strategy to promote their electrochemical performance, which primarily benefits from the nanosize effect, that is, achieving a higher surface area and a shorter ion diffusion length. 3,4 In this context, various nanosize electrode materials with greatly improved electrochemical performance have been synthesized. 5-9 Thereupon a fundamental question arises: do smaller electrode materials exhibit better electrochemical performance?According to the relationship between the band gap (E g ) and the size (a) of a nanoparticle (for semiconductor) defined by [Equation (1)] 10-12