Li-ion batteries, which restrict their wide applications, especially for environments that require mechanical stability and extreme conditions. [8][9][10][11] Alternatively, fl exible supercapacitors, especially quasi-solid state ones, have received considerate attention recently. [12][13][14][15] Although some of the fl exible supercapacitors so far reported can provide high power density and long-term stability, the energy density is relatively low. [16][17][18][19] Thus great challenges still remain in developing the overall high-performance solid/quasi-solid-state fl exible electrochemical energy storage devices with both high energy density and high power density. [20][21][22][23][24] As a typical type of traditional aqueous rechargeable batteries, Ni/Fe battery has been studied for a long period of time, because of its relatively high safety, lowcost, and high energy density. [ 25,26 ] In general, it can provide better safety and lower cost as compared with Li-ion battery; its energy density is higher in contrast to that of common supercapacitors. However, the low power density and poor cycling ability have limited the wide application of Ni/Fe battery. [ 27 ] On the other hand, recent development of nanomaterials and nanotechnology has enabled advanced electrode materials that can greatly enhance the performance of Ni/Fe battery. For example, by proper synergizing of nanostructured active materials (FeO x , NiO, or Ni(OH) 2 ) with carbonaceous materials (such as graphene, carbon nanofi bers, and carbon nanotubes (CNTs)), the power density of Ni/Fe battery can be greatly enhanced. [ 28,29 ] In some of these previous studies, the active materials are controlled in powder forms, such that carbon black and polymer additives have been employed in electrodes, where heavy metal foils or foams are used as the current collectors. The gravimetric/volumetric capacity of the full cell is therefore limited and the cell can be hardly fl exible. Some other works have focused on fl exible electrode materials for Ni/Fe batteries, where the device is assembled using liquid electrolytes. [ 30,31 ] In addition to the overall electrochemical performance, it would be a plus to eliminate liquid electrolytes, such that the safety issue in connection with the potential leakage problem can be solved. In order to promote the application of Ni/Fe batteries as a class of energy storage components for fl exible electronics Aqueous Ni/Fe batteries have great potential as fl exible energy storage devices, owing to their low cost, low toxicity, high safety, and high energy density. However, the poor cycling stability has limited the widely expected application of Ni/Fe batteries, while the use of heavy metal substrates cannot meet the basic requirement for fl exible devices. In this work, a fl exible type of solid-state Ni/Fe batteries with high energy and power densities is rationally developed using needle-like Fe 3 O 4 and fl ake-like NiO directly grown on carbon cloth/carbon nanofi ber (CC-CF) matrix as the anode and cathode, respecti...

Na-ion batteries are emerging as one of the most promising energy storage technologies, particularly for grid-level applications. Among anode candidate materials, hard carbon is very attractive due to its high capacity and low cost. However, hard carbon anodes often suffer a low first-cycle Coulombic efficiency and fast capacity fading. In this study, we discover that doping graphene oxide into sucrose, the precursor for hard carbon, can effectively reduce the specific surface area of hard carbon to as low as 5.4 m(2)/g. We further reveal that such doping can effectively prevent foaming during caramelization of sucrose and extend the pyrolysis burnoff of sucrose caramel over a wider temperature range. The obtained low-surface-area hard carbon greatly improves the first-cycle Coulombic efficiency from 74% to 83% and delivers a very stable cyclic life with 95% of capacity retention after 200 cycles.

Phosphorus compounds, such as metal phosphides and phosphates have shown excellent performances and great potential in electrochemical energy storage, which are demonstrated by research works published in recent years. Some of these metal phosphides and phosphates and their hybrids compare favorably with transition metal oxides/hydroxides, which have been studied extensively as a class of electrode materials for supercapacitor applications, where they have limitations in terms of electrical and ion conductivity and device stability. To be specific, metal phosphides have both metalloid characteristics and good electric conductivity. For metal phosphates, the open-framework structures with large channels and cavities endow them with good ion conductivity and charge storage capacity. In this review, we present the recent progress on metal phosphides and phosphates, by focusing on their advantages/disadvantages and potential applications as a new class of electrode materials in supercapacitors. The synthesis methods to prepare these metal phosphides/phosphates are looked into, together with the scientific insights involved, as they strongly affect the electrochemical energy storage performance. Particular attentions are paid to those hybrid-type materials, where strong synergistic effects exist. In the summary, the future perspectives and challenges for the metal phosphides, phosphates and hybrid-types are proposed and discussed.

Removal of contaminants in wastewater, such as heavy metals, has become a severe problem in the world. Numerous technologies have been developed to deal with this problem. As an emerging technology, nanotechnology has been gaining increasing interest and many nanomaterials have been developed to remove heavy metals from polluted water, due to their excellent features resulting from the nanometer effect. In this work, novel nanomaterials, including carbon-based nanomaterials, zero-valent metal, metal-oxide based nanomaterials, and nanocomposites, and their applications for the removal of heavy metal ions from wastewater were systematically reviewed. Their efficiency, limitations, and advantages were compared and discussed. Furthermore, the promising perspective of nanomaterials in environmental applications was also discussed and potential directions for future work were suggested.

To address the worldwide energy challenges, advanced energy storage and conversion systems with high comprehensive performances, as the promising technologies, are inevitably required on a timely basis. The performance of these energy systems is intimately dependent on the properties of their electrodes. In addition to the electrode materials selection and their compositional optimization, materials fabrication with the designed nanostructure also provides significant benefits for their performances. In the past decade, considerable efforts have been made to promote the search for multidimensional nanostructures containing both onedimensional (1D) and two-dimensional (2D) nanostructures in synergy, namely, 1D-2D synergized nanostructures. By developing the freestanding electrodes with such unique nanoarchitectures, the structural features and electroactivities of each component can be manifested, where the synergistic properties among them can be simultaneously obtained for further enhanced properties, such as the increased number of active sites, fast electronic/ionic transport, and so forth. This review overviews the state-of-the-art on the 1D-2D synergized nanostructures, which can be broadly divided into three groups, namely, core/shell, cactus-like, and sandwich-like nanostructures. For each category, we introduce them from the aspects of structural features, fabrication methodologies to their successful applications in different types of energy storage/conversion devices, including rechargeable batteries, supercapacitors, water splitting, and so forth. Finally, the main challenges faced by and perspectives on the 1D-2D synergized nanostructures are discussed. K E Y W O R D S1D-2D synergized nanostructure, cactus-like nanostructure, core/shell nanostructure, energy storage/conversion, sandwich-like nanostructure

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A high‐power P2‐Na2/3(Mn1/2Fe1/4Co1/4)O2 (P2‐MFC) cathode material is synthesized and investigated for Na‐ion batteries. P2 type stacking is observed for a wide range of Na content (0.34 < x < 0.95). Even at 30 C rate a discharge capacity of 130 mAh g−1 is maintained, which is currently the highest rate performance among Na ion intercalation compounds.