Carbon nanotubes (CNTs) are of great interest for many potential applications because of their extraordinary electronic, mechanical and structural properties. However, issues of chaotic staking, high cost and high energy dissipation in the synthesis of CNTs remain to be resolved. Here we develop a facile, general and high-yield strategy for the oriented formation of CNTs from metal-organic frameworks (MOFs) through a low-temperature (as low as 430 °C) pyrolysis process. The selected MOF crystals act as a single precursor for both nanocatalysts and carbon sources. The key to the formation of CNTs is obtaining small nanocatalysts with high activity during the pyrolysis process. This method is successfully extended to obtain various oriented CNT-assembled architectures by modulating the corresponding MOFs, which further homogeneously incorporate heteroatoms into the CNTs. Specifically, nitrogen-doped CNT-assembled hollow structures exhibit excellent performances in both energy conversion and storage. On the basis of experimental analyses and density functional theory simulations, these superior performances are attributed to synergistic effects between ideal components and multilevel structures. Additionally, the appropriate graphitic N doping and the confined metal nanoparticles in CNTs both increase the densities of states near the Fermi level and reduce the work function, hence efficiently enhancing its oxygen reduction activity. The viable synthetic strategy and proposed mechanism will stimulate the rapid development of CNTs in frontier fields.

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K-ion battery (KIB) is a new-type energy storage device that possesses potential advantages of low-cost and abundant resource of K precursor materials. However, the main challenge lies on the lack of stable materials to accommodate the intercalation of large-size K-ions. Here we designed and constructed a novel earth abundant Fe/Mn-based layered oxide interconnected nanowires as a cathode in KIBs for the first time, which exhibits both high capacity and good cycling stability. On the basis of advanced in situ X-ray diffraction analysis and electrochemical characterization, we confirm that interconnected KFeMnO nanowires can provide stable framework structure, fast K-ion diffusion channels, and three-dimensional electron transport network during the depotassiation/potassiation processes. As a result, a considerable initial discharge capacity of 178 mAh g is achieved when measured for KIBs. Besides, K-ion full batteries based on interconnected KFeMnO nanowires/soft carbon are assembled, manifesting over 250 cycles with a capacity retention of ∼76%. This work may open up the investigation of high-performance K-ion intercalated earth abundant layered cathodes and will push the development of energy storage systems.

Nanowires and nanotubes have been the focus of considerable efforts in energy storage and solar energy conversion because of their unique properties. However, owing to the limitations of synthetic methods, most inorganic nanotubes, especially for multi-element oxides and binary-metal oxides, have been rarely fabricated. Here we design a gradient electrospinning and controlled pyrolysis method to synthesize various controllable 1D nanostructures, including mesoporous nanotubes, pea-like nanotubes and continuous nanowires. The key point of this method is the gradient distribution of low-/middle-/high-molecular-weight poly(vinyl alcohol) during the electrospinning process. This simple technique is extended to various inorganic multi-element oxides, binary-metal oxides and single-metal oxides. Among them, Li3V2(PO4)3, Na0.7Fe0.7Mn0.3O2 and Co3O4 mesoporous nanotubes exhibit ultrastable electrochemical performance when used in lithium-ion batteries, sodium-ion batteries and supercapacitors, respectively. We believe that a wide range of new materials available from our composition gradient electrospinning and pyrolysis methodology may lead to further developments in research on 1D systems.

Development of three-dimensional nanostructures with high surface area and excellent structural stability is an important approach for realizing high-rate and long-life battery electrodes. Here, we report VO2 hollow microspheres showing empty spherical core with radially protruding nanowires, synthesized through a facile and controllable ion-modulating approach. In addition, by controlling the self-assembly of negatively charged C12H25SO4(-) spherical micelles and positively charged VO(2+) ions, six-armed microspindles and random nanowires are also prepared. Compared with them, VO2 hollow microspheres show better electrochemical performance. At high current density of 2 A/g, VO2 hollow microspheres exhibit 3 times higher capacity than that of random nanowires, and 80% of the original capacity is retained after 1000 cycles. The superior performance of VO2 hollow microspheres is because they exhibit high surface area about twice higher than that of random nanowires and also provide an efficient self-expansion and self-shrinkage buffering during lithiation/delithiation, which effectively inhibits the self-aggregation of nanowires. This research indicates that VO2 hollow microspheres have great potential for high-rate and long-life lithium batteries.

Rechargeable aqueous Zn-based batteries, benefiting from their good reliability, low cost, high energy/power densities, and ecofriendliness, show great potential in energy storage systems. However, the poor cycling performance due to the formation of Zn dendrites greatly hinders their practical applications. In this work, a trilayer 3D CC-ZnO@C-Zn anode is obtained by in situ growing ZIFs (zeolitic-imidazolate frameworks) derived ZnO@C coreshell nanorods on carbon cloth followed by Zn deposition, which exhibits excellent antidendrite performance. Using CC-ZnO@C-Zn as the anode and a branch-like Co(CO 3 ) 0.5 (OH) x ·0.11H 2 O@CoMoO 4 (CC-CCH@CMO) as the cathode, a Zn-Co battery is rationally designed, displaying excellent energy/power densities (235 Wh kg −1 , 12.6 kW kg −1 ) and remarkable cycling performance (71.1% after 5000 cycles). Impressively, when using a gel electrolyte, a highly customizable, fiber-shaped flexible all-solid-state Zn-Co battery is assembled for the first time, which presents a high energy density of 4.6 mWh cm −3 , peak power density of 0.42 W cm −3 , and long durability (82% capacity retention after 1600 cycles) as well as excellent flexibility. The unique 3D electrode design in this study provides a novel approach to achieve high-performance Zn-based batteries, showing promising applications in flexible and portable energy-storage systems.

The emerging electrochemical energy storage systems beyond Li‐ion batteries, including Na/K/Mg/Ca/Zn/Al‐ion batteries, attract extensive interest as the development of Li‐ion batteries is seriously hindered by the scarce lithium resources. During the past years, large amounts of studies have focused on the investigation of various electrode materials toward emerging metal‐ion batteries to realize high energy density, high power density, and a long cycle life. In particular, vanadium‐based nanomaterials have received great attention. Vanadium‐based compounds have a big family with different structures, chemical compositions, and electrochemical properties, which provide huge possibilities for the development of emerging electrochemical energy storage. In this review, a comprehensive overview of the recent progresses of promising vanadium‐based nanomaterials for emerging metal‐ion batteries is presented. The vanadium‐based materials are classified into four groups: vanadium oxides, vanadates, vanadium phosphates, and oxygen‐free vanadium‐based compounds. The structures, electrochemical properties, and modification strategies are discussed. The structure–performance relationships and charge storage mechanisms are focused on. Finally, the perspectives about future directions of vanadium‐based nanomaterials for emerging energy storage devices are proposed. This review will provide comprehensive knowledge of vanadium‐based nanomaterials and shed light on their potential applications in emerging energy storage.

Benefiting from the loose assembly conditions, high safety and environmental-friendly characteristics, rechargeable aqueous Zn-ion batteries (AZIBs) are attracting intensive attention. In fact, either the water in electrolyte or electrode materials...