Hollow Mesoporous Carbon Nanocubes: Rigid‐Interface‐Induced Outward Contraction of Metal‐Organic Frameworks

Novel carbon materials derived from metal‐organic frameworks (MOFs) have attracted much attention, but the commonly inevitable inward contraction during the carbonization process has restricted their structural variety and applications. In this work, a novel rigid‐interface induced outward contraction approach is reported for synthesizing hollow mesoporous carbon nanocubes (HMCNCs) by using ZIF‐8 nanocubes as precursors. HMCNCs exhibit a cubic morphology with the particle sizes slightly larger than ZIF‐8 nanocubes. Due to the unique outward contraction process, uniform carbon nanocubes with a hollow cavity, an outer microporous shell, and an inner mesoporous wall are simultaneously formed with a large pore size (25 nm), high surface area (1085.7 m² g^?1), high porosity (3.77 cm³ g^?1), and high nitrogen content (12.2%). When used as a cathode material for Li–SeS₂ batteries, the HMCNCs deliver a stable capacity of 812.6 mA h g^?1 at 0.2 A g^?1 after 100 cycles and an outstanding rate capability (455.1 mA h g^?1 at 5.0 A g^?1). The findings may pave the way for the construction of distinctive MOF‐derived carbon materials for various applications.     

Carbon Nanotubes Rooted in Porous Ternary Metal Sulfide@N/S‐Doped Carbon Dodecahedron: Bimetal‐Organic‐Frameworks Derivation and Electrochemical Application for High‐Capacity and Long‐Life Lithium‐Ion Batteries

Lithium ion battery is the predominant power source for portable electronic devices, electrical vehicles, and back‐up electricity storage units for clean and renewable energies. High‐capacity and long‐life electrode materials are essential for the next‐generation Li‐ion battery with high energy density. Here bimetal‐organic‐frameworks synthesis of Co_0.4Zn_0.19S@N and S codoped carbon dodecahedron is shown with rooted carbon nanotubes (Co‐Zn‐S@N‐S‐C‐CNT) for high‐performance Li‐ion battery application. Benefiting from the synergetic effect of two metal sulfide species for Li‐storage at different voltages, mesoporous dodecahedron structure, N and S codoped carbon overlayer and deep‐rooted CNTs network, the product exhibits a larger‐than‐theoretical reversible Li‐storage capacity of 941 mAh g^?1 after 250 cycles at 100 mA g^?1 and excellent high‐rate capability (734, 591, 505 mAh g^?1 after 500 cycles at large current densities of 1, 2, and 5 A g^?1 , respectively).     

Ultrafine Amorphous SnOx Embedded in Carbon Nanofiber/Carbon Nanotube Composites for Li‐Ion and Na‐Ion Batteries

Core–shell‐structured, ultrafine SnO_x/carbon nanofiber (CNF)/carbon nanotube composite films are in situ synthesized by electrospinning through a dual nozzle. The carbon shell layer functions as a buffer to prevent the separation of SnO_x particles from the CNF core, allowing full utilization of high‐capacity SnO_x in both Li‐ion and Na‐ion batteries. The composite electrodes reveal an anomalous Li‐ and Na‐ion storage mechanism where all the intermediate phases, like Li_xSn and Na_xSn alloys, maintain amorphous states during the entire charge/discharge process. The uniform dispersion on an atomic scale and the amorphous state of the SnO_x particles remain intact in the carbon matrix without growth or crystallization even after 300 cycles, which is responsible for sustaining excellent capacity retention of the electrodes. These discoveries not only shed new insights into fundamental understanding of the electrochemical behavior of SnO_x electrodes but also offer a potential strategy to improve the cyclic stability of other types of alloy anodes that suffer from rapid capacity decays due to large volume changes.     

Copper‐Stabilized Sulfur‐Microporous Carbon Cathodes for Li–S Batteries

A copper‐stabilized sulfur‐microporous carbon ( MC‐Cu‐S) composite is synthesized by uniformly dispersing 10% highly electronically conductive Cu nanoparticles into microporous carbon (MC), followed by wet‐impregnating S. In the MC‐Cu‐S composite, the MC host that physically confines S/polysulfides provides free space to accommodate volumetric expansion of S during lithiation, while the Cu nanoparticles that are anchored in the MC further chemically interact with S/polysulfides through bonding between Cu and S/polysulfides. The Cu loading allows the S content to increase from 30 to 50% in the carbon‐S cathode material without scarifying the electrochemical performance in a low‐cost carbonate electrolyte. At a current density of 100 mA g^‐1, the MC‐Cu‐S cathode shows that Coulumbic efficiency is close to 100% and capacity maintains more than 600 mAh g^‐1 with progressive cycling up to more than 500 cycles. In addition, the Cu nano‐inclusins also enhance the electronic conductivity of the MC‐Cu‐S composite, remarkably increasing the rate capabilities. Even the current density increases 10.0 A g^‐1, the MC‐Cu‐S cathode can still deliver a capacity of 200 mAh g^‐1. This strategy of stabilization of S with small amount of metal nanoparticles anchored in MC provides an effective approach to improve the cycling stability, Coulumbic efficiency, and S loading for Li–S batteries.     

Accommodation of Silicon in an Interconnected Copper Network for Robust Li‐Ion Storage

Silicon (Si)‐based materials are one of the most promising anodes to be applied in rechargeable lithium ion batteries. However, the active Si/electrolyte interface causes continuous side reactions and poor conductivity, which significantly decreases the cycling stability. Cu is the only metallic current collector that has been known to promote electron conduction and lithium‐ion transfer without alloying reaction occurrence. However, to the best current knowledge, scalable interface engineering incorporating Cu has not been reported. Herein, this conductive Cu interface (CCI) is constructed through a self‐assembly carbothermic reduction method to achieve efficient protection of Si/electrolyte interfaces while allowing for fast Li⁺ diffusion. The energy barrier of lithium‐ion diffusion through Cu is calculated to be 0.1965 eV, which is much lower than that through Au, Fe, and Ni films. Benefiting from the enhanced interfacial protection and kinetics of Si with CCI, a fading rate of only 0.068% is maintained for 1000 cycles and an aerial capacity of 4.78 mAh cm^?2 is achieved after 280 cycles, which is comparable to the industry standards required for practical application.     

Fast and Reversible Li Ion Insertion in Carbon‐Encapsulated Li3VO4 as Anode for Lithium‐Ion Battery

Carbon‐encapsulated Li₃VO₄ is synthesized by a facile environmentally benign solid‐state method with organic metallic precursor VO(C₅H₇O₂)₂ being chosen as both V and carbon sources yielding a core–shell nanostructure with lithium introduced in the subsequent annealing process. The Li₃VO₄ encapsulated with carbon presents exceeding rate capability (a reversible capability of 450, 340, 169, and 106 mAh g^?1 at 0.1 C, 10 C, 50 C, and 80 C, respectively) and long cyclic performance (80% capacity retention after 2000 cycles at 10 C) as an anode in lithium‐ion batteries. The superior performance is derived from the structural features of the carbon‐encapsulated Li₃VO₄ composite with oxygen vacancies in Li₃VO₄, which increase surface energy and could possibly serve as a nucleation center, thus facilitating phase transitions. The in situ generated carbon shell not only facilitates electron transport, but also suppresses Li₃VO₄ particle growth during the calcination process. The encouraging results demonstrate the significant potential of carbon encapsulated Li₃VO₄ for high power batteries. In addition, the simple generic synthesis method is applicable to the fabrication of a variety of electrode materials for batteries and supercapacitors with unique core–shell structure with mesoporous carbon shell.     

B‐doped Carbon Coating Improves the Electrochemical Performance of Electrode Materials for Li‐ion Batteries

An evolutionary modification approach, boron doped carbon coating, is initially used to improve the electrochemical properties of electrode materials of lithium‐ion batteries, such as Li₃V₂(PO₄)₃, and demonstrates apparent and significant modification effects. Based on the precise analysis of X‐ray photoemission spectroscopy results, Raman spectra, and electrochemical impedance spectroscopy results for various B‐doped carbon coated Li₃V₂(PO₄)₃ samples, it is found that, among various B‐doping types (B₄C, BC₃, BC₂O and BCO₂), the graphite‐like BC₃ dopant species plays a huge role on improving the electronic conductivity and electrochemical activity of the carbon coated layer on Li₃V₂(PO₄)₃ surface. As a result, when compared with the bare carbon coated Li₃V₂(PO₄)₃, the electrochemical performances of the B‐doped carbon coated Li₃V₂(PO₄)₃ electrode with a moderate doping amount are greatly improved. For example, when cycled under 1 C and 20 C in the potential range of 3.0–4.3 V, this sample shows an initial capacity of 122.5 and 118.4 mAh g^?1, respectively; after 200 cycles, nearly 100% of the initial capacity is retained. Moreover, the modification effects of B‐doped carbon coating approach are further validated on Li₄Ti₅O₁₂ anode material.     

In Situ Reversible Ionic Control for Nonvolatile Magnetic Phases in a Donor/Acceptor Metal‐Organic Framework

Reversible magnetic control by electrical means, which is highly desired from the viewpoint of fundamentals and technological applications such as data storage devices, has been a challenging topic. In this study, the authors demonstrate in situ magnetic phase switching between the ferrimagnetic and paramagnetic states of an electron‐donor/‐acceptor metal‐organic framework (D/A‐MOF) using band‐filling control mediated by the Li⁺‐ion migration that accompanies redox reactions, i.e., “magneto‐ionic control”. By taking advantage of the rechargeability of lithium‐ion battery systems, in which Li⁺‐ions and electrons are simultaneously inserted into/extracted from a cathode material, the reversible control of nonvolatile magnetic phases in a D/A‐MOF has been achieved. This result demonstrates that the combination of a redox‐active MOF with porous flexibility and ion‐migration capability enables the creation of new pathways toward magneto‐electric coupling devices in the field of ionics.     

Uniformly Confined Germanium Quantum Dots in 3D Ordered Porous Carbon Framework for High‐Performance Li‐ion Battery

Although abundant germanium (Ge)‐based anode materials have been explored to obtain high specific capacity, high rate performance, and long charge/discharge lifespans for lithium‐ion batteries (LIBs), their performances are still far from satisfactory due to the intrinsic defects of Ge and the relatively intricate anode structure. To work out these issues, a 3D ordered porous N‐doped carbon framework with Ge quantum dots uniformly embedded (3DOP Ge@N? C) as a binder‐free anode for LIBs via a facile polystyrene colloidal nanospheres template‐confined strategy is proposed. This unique structure not only facilitates Li‐ion diffusion and electron transport that can guarantee rapid de/alloying reaction, but also alleviates the huge volume changes during reactions and improves cycling stability. Notably, the resulting anode delivers a high specific reversible capacity (≈1160 mA h g^?1 at 1 A g^?1), superior rate properties (exceeding 500 mA h g^?1 at 40 A g^?1), and excellent cycling stability (over 90% capacity retention after 1200 cycles even at 5 A g^?1). Furthermore, both the 3DOP Ge@N? C anode with high areal mass loading (up to 8 mg cm^?2) and the full cell coupled with LiFePO₄ cathode display high capacity and cycling stability, further indicative of the favorable real‐life application prospects for high‐energy LIBs.     

High Voltage,Transition Metal Complex Enables Efficient Electrochemical Energy Storage in a Li‐Ion Battery Full Cell

Efficient energy storage systems impact profoundly the renewable energy future. The performance of current electrical energy storage technologies falls well short of requirements for using electrical energy efficiently in transportation, commercial, and residential applications. This paper explores the possibility by using transition‐metal‐based complexes as active materials in a Li‐ion battery full cell that synergizes the concept of both lithium‐ion batteries and redox flow batteries. A cathode made from transition metal complex, [Fe(bpy)₃](BF₄)₂, exhibits high discharge voltage approaching 4 V (vs Li/Li⁺). When coupled with a Li₄Ti₅O₁₂ anode, the Li‐ion full battery exhibits a cell voltage exceeding 2.2 V and decent cycling efficiencies with Coulombic efficiency and energy/voltage efficiencies above 99% and 92%/93%, respectively. Such a Li‐ion battery full cell offers distinct features such as low cost and flexibility in molecular structure design. The result reveals a generic design route toward iron‐based complexes as cathode materials with good electrochemical performances.     

A General Metal‐Organic Framework (MOF)‐Derived Selenidation Strategy for In Situ Carbon‐Encapsulated Metal Selenides as High‐Rate Anodes for Na‐Ion Batteries

On account of increasing demand for energy storage devices, sodium‐ion batteries (SIBs) with abundant reserve, low cost, and similar electrochemical properties have the potential to partly replace the commercial lithium‐ion batteries. In this study, a facile metal‐organic framework (MOF)‐derived selenidation strategy to synthesize in situ carbon‐encapsulated selenides as superior anode for SIBs is rationally designed. These selenides with particular micro‐ and nanostructured features deliver ultrastable cycling performance at high charge–discharge rate and demonstrate ultraexcellent rate capability. For example, the uniform peapod‐like Fe₇Se₈@C nanorods represent a high specific capacity of 218 mAh g^?1 after 500 cycles at 3 A g^?1 and the porous NiSe@C spheres display a high specific capacity of 160 mAh g^?1 after 2000 cycles at 3 A g^?1. The current simple MOF‐derived method could be a promising strategy for boosting the development of new functional inorganic materials for energy storage, catalysis, and sensors.     

Rapid Room‐Temperature Synthesis of Metal–Organic Framework HKUST‐1 Crystals in Bulk and as Oriented and Patterned Thin Films

Whereas the preparation of defined metal–organic framework (MOF) materials via hydrothermal or diffusion methods typically requires hours to days, our simple precipitation route opens the access to the well‐known HKUST‐1 frameworks within minutes. Crucial for the formation of a well‐defined, crystalline material is the choice of suitable precipitating solvents, with methanol and ethanol being the most favorable ones. This approach could be extended to the formation of dense, surface‐mounted MOF films (so‐called SURMOFs), in particular if the surfaces are decorated with suitable binding groups by formation of self‐assembled monolayers (SAMs). By combination with micro‐contact printing (μCP), patterned SURMOFs became accessible, in which the precipitating solvent is decisive on the formation of either spatially restricted films or single particles.     

Metal–Organic Framework (MOF) Derived Electrodes with Robust and Fast Lithium Storage for Li‐Ion Hybrid Capacitors

Hybrid metal–organic frameworks (MOFs) demonstrate great promise as ideal electrode materials for energy‐related applications. Herein, a well‐organized interleaved composite of graphene‐like nanosheets embedded with MnO₂ nanoparticles (MnO₂@C‐NS) using a manganese‐based MOF and employed as a promising anode material for Li‐ion hybrid capacitor (LIHC) is engineered. This unique hybrid architecture shows intriguing electrochemical properties including high reversible specific capacity 1054 mAh g^?1 (close to the theoretical capacity of MnO₂, 1232 mAh g^?1) at 0.1 A g^?1 with remarkable rate capability and cyclic stability (90% over 1000 cycles). Such a remarkable performance may be assigned to the hierarchical porous ultrathin carbon nanosheets and tightly attached MnO₂ nanoparticles, which provide structural stability and low contact resistance during repetitive lithiation/delithiation processes. Moreover, a novel LIHC is assembled using a MnO₂@C‐NS anode and MOF derived ultrathin nanoporous carbon nanosheets (derived from other potassium‐based MOFs) cathode materials. The LIHC full‐cell delivers an ultrahigh specific energy of 166 Wh kg^?1 at 550 W kg^?1 and maintained to 49.2 Wh kg^?1 even at high specific power of 3.5 kW kg^?1 as well as long cycling stability (91% over 5000 cycles). This work opens new opportunities for designing advanced MOF derived electrodes for next‐generation energy storage devices.     

Layered Double Hydroxide Nano‐ and Microstructures Grown Directly on Metal Substrates and Their Calcined Products for Application as Li‐Ion Battery Electrodes

Layered double hydroxide (LDH) nano‐ and microstructures with controllable size and morphology have been fabricated on “bivalent metal” substrates such as zinc and copper by a one‐step, room‐temperature process, in which metal substrates act as both reactants and supports. By manipulating the concentration of NH₃ · H₂O, the thickness and lateral size of the LDH materials can be tuned from several tens of nanometers to several hundreds of nanometers and from several hundreds of nanometers to several micrometers, respectively. This method is general and may be readily extended to any other alkali‐resisted substrate coated with Zn and Cu. As an example, Zn‐covered stainless steel foil has been shown to be effective for the growth of a Zn? Al LDH film. After calcinating the as‐grown LDH at high temperature (650 °C) in argon gas, a ZnO/ZnAl₂O₄ porous nanosheet film is obtained, which is then directly used for the first time as the anode material for Li‐ion batteries with the operating voltage window of 0.05–2.5 V (vs. Li). The result demonstrates that ZnO/ZnAl₂O₄ has higher discharge and charge capacities and considerably better cycling stability compared to pure ZnO (Li insertion/extraction rate: 200 or 500 mA g^?1). The improved electrochemical performance can be ascribed to the buffering effect of the inactive matrix ZnAl₂O₄ by relieving the stress caused by the volume change during charge–discharge cycling. This work represents a successful example for the development of promising ZnO‐based anode materials for Li‐ion batteries.     

Cubic Perovskite Fluoride as Open Framework Cathode for Na‐Ion Batteries

Exploring novel structure prototype and mineral phase, especially open framework material, is crucial to developing high‐performance Na‐ion battery cathodes in view of potentially faster intrinsic diffusion of Na⁺ in lattices. Perovskite phases have been widely applied in solar cells, fuel cells, and electrocatalysis; however, they are rarely attempted as energy storage electrode materials. This study proposes pre‐expanding perovskite iron fluoride (KFeF₃) framework by stuffing large‐sized K⁺ as a channel filler, which is advantageous over Na⁺, NH₄⁺, and H₂O molecule filler in terms of structure robustness, symmetry, and connectivity. K⁺ stuffing leads to the preservation of a more “regular” cubic phase with fast isotropic 3D diffusion as a consequence of no distortion of FeF₆ octahedra during K‐Na electrochemical exchange and following Na‐insertion cycling. High‐rate Na‐storage is achievable with a reversible capacity of 110, 70, and 40 mAh g^?1 at 0.1, 2, and 10 C, respectively, for this open framework fluoride cathode, benefiting from solid solution electrochemical behavior and high intrinsic diffusion coefficient. It is thought that this rate performance is currently the best among Na‐storage fluoride materials.     

Binary Li4Ti5O12‐Li2Ti3O7 Nanocomposite as an Anode Material for Li‐Ion Batteries

Li₄Ti₅O₁₂ typically shows a flat charge/discharge curve, which usually leads to difficulty in the voltage‐based state of charge (SOC) estimation. In this study, a facile quench‐assisted solid‐state method is used to prepare a highly crystalline binary Li₄Ti₅O₁₂‐Li₂Ti₃O₇ nanocomposite. While Li₄Ti₅O₁₂ exhibits a sudden voltage rise/drop near the end of its charge/discharge curve, this binary nanocomposite has a tunable sloped voltage profile. The nanocomposite exhibits a unique lamellar morphology consisting of interconnected nanograins of ≈20 nm size with a hierarchical nanoporous structure, contributing to an enhanced rate capability with a capacity of 128 mA h g^?1 at a high C‐rate of 10 C, and excellent cycling stability.     

Iron Oxide Nanoparticle‐Encapsulated CNT Branches Grown on 3D Ozonated CNT Internetworks for Lithium‐Ion Battery Anodes

Multidimensional hierarchical architecturing is a promising chemical approach to provide unique characteristics synergistically integrated from individual nanostructured materials for energy storage applications. Herein, hierarchical complex hybrid architectures of CNT‐on‐OCNT‐Fe are reported, where iron oxide nanoparticles are encapsulated inside carbon nanotube (CNT) branches grown onto the ozone‐treated surface of 3D CNT internetworked porous structures. The activated surface of the 3D ozonated CNT (OCNT) interacts with the iron oxide nanoparticles, resulting in different chemical environments of inner and outer tubes and large surface area. The mixed phases of iron oxide nanoparticles are confined by full encapsulation inside the conductive nanotubes and act as catalysts to vertically grow the CNT branches. This unique hierarchical architecture allows CNT‐on‐OCNT‐Fe to achieve a reasonable capacity of >798 mA h g^?1 at 50 mA g^?1, with outstanding rate capability (≈72% capacity retention at rates from 50 to 1000 mA g^?1) and cyclic stability (>98.3% capacity retention up to 200 cycles at 100 mA g^?1 with a coulombic efficiency of >97%). The improved rate and cyclic capabilities are attributed to the hierarchical porosity of 3D OCNT internetworks, the shielding of CNT walls for encapsulated iron oxide nanoparticles, and a proximate electronic pathway for the isolated nanoparticles.     

Prussian Blue@C Composite as an Ultrahigh‐Rate and Long‐Life Sodium‐Ion Battery Cathode

Rechargeable sodium ion batteries (SIBs) are surfacing as promising candidates for applications in large‐scale energy‐storage systems. Prussian blue (PB) and its analogues (PBAs) have been considered as potential cathodes because of their rigid open framework and low‐cost synthesis. Nevertheless, PBAs suffer from inferior rate capability and poor cycling stability resulting from the low electronic conductivity and deficiencies in the PBAs framework. Herein, to understand the vacancy‐impacted sodium storage and Na‐insertion reaction kinetics, we report on an in‐situ synthesized PB@C composite as a high‐performance SIB cathode. Perfectly shaped, nanosized PB cubes were grown directly on carbon chains, assuring fast charge transfer and Na‐ion diffusion. The existence of [Fe(CN)₆] vacancies in the PB crystal is found to greatly degrade the electrochemical activity of the Fe^LS(C) redox couple via first‐principles computation. Superior reaction kinetics are demonstrated for the redox reactions of the Fe^HS(N) couple, which rely on the partial insertion of Na ions to enhance the electron conduction. The synergistic effects of the structure and morphology results in the PB@C composite achieving an unprecedented rate capability and outstanding cycling stability (77.5 mAh g^?1 at 90 C, 90 mAh g?¹ after 2000 cycles at 20 C with 90% capacity retention).     

Nanoporous Nitrogen‐Doped Graphene Oxide/Nickel Sulfide Composite Sheets Derived from a Metal‐Organic Framework as an Efficient Electrocatalyst for Hydrogen and Oxygen Evolution

Engineering of controlled hybrid nanocomposites creates one of the most exciting applications in the fields of energy materials and environmental science. The rational design and in situ synthesis of hierarchical porous nanocomposite sheets of nitrogen‐doped graphene oxide (NGO) and nickel sulfide (Ni₇S₆) derived from a hybrid of a well‐known nickel‐based metal‐organic framework (NiMOF‐74) using thiourea as a sulfur source are reported here. The nanoporous NGO/MOF composite is prepared through a solvothermal process in which Ni(II) metal centers of the MOF structure are chelated with nitrogen and oxygen functional groups of NGO. NGO/Ni₇S₆ exhibits bifunctional activity, capable of catalyzing both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) with excellent stability in alkaline electrolytes, due to its high surface area, high pore volume, and tailored reaction interface enabling the availability of active nickel sites, mass transport, and gas release. Depending on the nitrogen doping level, the properties of graphene oxide can be tuned toward, e.g., enhanced stability of the composite compared to commonly used RuO₂ under OER conditions. Hence, this work opens the door for the development of effective OER/HER electrocatalysts based on hierarchical porous graphene oxide composites with metal chalcogenides, which may replace expensive commercial catalysts such as RuO₂ and IrO₂.