Nickel–Cobalt Layered Double Hydroxide Nanosheets for High‐performance Supercapacitor Electrode Materials

A facile and novel one‐step method of growing nickel‐cobalt layered double hydroxide (Ni‐Co LDH) hybrid films with ultrathin nanosheets and porous nanostructures on nickel foam is presented using cetyltrimethylammonium bromide as nanostructure growth assisting agent but without any adscititious alkali sources and oxidants. As pseudocapacitors, the as‐obtained Ni‐Co LDH hybrid film‐based electrodes display a significantly enhanced specific capacitance (2682 F g^?1 at 3 A g^?1, based on active materials) and energy density (77.3 Wh kg^?1 at 623 W kg^?1), compared to most previously reported electrodes based on nickel‐cobalt oxides/hydroxides. Moreover, the asymmetric supercapacitor, with the Ni‐Co LDH hybrid film as the positive electrode material and porous freeze‐dried reduced graphene oxide (RGO) as the negative electrode material, exhibits an ultrahigh energy density (188 Wh kg^?1) at an average power density of 1499 W kg^?1 based on the mass of active material, which greatly exceeds the energy densities of most previously reported nickel or cobalt oxide/hydroxide‐based asymmetric supercapacitors.     

Ultrathin Layered Double Hydroxide Nanosheets Enabling Composite Polymer Electrolyte for All-Solid-State Lithium Batteries at Room Temperature

Solid electrolytes are the most promising substitutes for liquid electrolytes to construct high-safety and high-energy-density energy storage devices. Nevertheless, the poor lithium ion mobility and ionic conductivity at room temperature (RT) have seriously hindered their practical usage. Herein, single-layer layered-double-hydroxide nanosheets (SLN) reinforced poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) composite polymer electrolyte is designed, which delivers an exceptionally high ionic conductivity of 2.2 × 10⁻⁴ S cm⁻¹ (25  ° C), superior Li⁺ transfer number ( ≈ 0.78) and wide electrochemical window ( ≈ 4.9 V) with a low SLN loading ( ≈ 1 wt%). The Li symmetric cells demonstrate ultra-long lifespan stable cycling over ≈ 900 h at 0.1 mA cm⁻², RT. Moreover, the all-solid-state Li|LiFePO₄ cells can run stably with a high capacity retention of 98.6% over 190 cycles at 0.1 C, RT. Moreover, using LiCoO₂/LiNi_0.8Co_0.1Mn_0.1O₂, the all-solid-state lithium metal batteries also demonstrate excellent cycling at RT. Density functional theory calculations are performed to elucidate the working mechanism of SLN in the polymer matrix. This is the first report of all-solid-state lithium batteries working at RT with PVDF-HFP based solid electrolyte, providing a novel strategy and significant step toward cost-effective and scalable solid electrolytes for practical usage at RT.     

High‐Yield Preparation,Versatile Structural Modification,and Properties of Layered Cobalt Hydroxide Nanocones

A low‐cost oil bath synthetic route is presented to produce uniform and highly crystalline layered cobalt hydroxide nanocones (NCs) intercalated with dodecyl sulfate anions (C₁₂H₂₅OSO₃^?, DS^?). A new exfoliating procedure, by gradually unravelling/unzipping these NCs through heat treatment in formamide‐water binary solution, is developed to prepare unilamellar nanosheets. Moreover, the NCs can be readily modified with various inorganic or organic anions via a conventional anion‐exchange process at ambient temperature. The exchanged product, for example, NO₃^?–intercalated NCs, can be more easily and rapidly transformed into cobalt oxides (e.g., Co₃O₄ and CoO) than the original DS^?–intercalated form while retaining a conical feature. Both the cobalt hydroxide NCs and exfoliated nanosheets are electrochemically redoxable, exhibiting a Faradaic pseudocapacitive behavior. The magnetic measurements further reveal both antiferromagnetic behaviors for transformed Co₃O₄ and CoO NCs. Their Néel temperature values are lower than those of bulk oxides due to finite size and geometric confinement effect. The peculiar conical feature of NCs with a hollow interior and tunable layer spacing, as well as exfoliated unilamellar nanosheets with all surface area exposed, may show promise for potential applications in electrochemical energy storage and magnetic devices.     

High‐Performing Monometallic Cobalt Layered Double Hydroxide Supercapacitor with Defined Local Structure

Through a topochemical oxidative reaction (TOR) under air, a β‐Co(OH)₂ brucite type structure is converted into a monometallic Co^IICo^III–CO₃ layered double hydroxide (LDH). The structural and morphological characterizations are performed using powder X‐ray diffraction, Fourier‐transformed IR spectroscopy, and scanning and transmission electron microscopy. The local structure is scrutinized using an extended X‐ray absorption fine structure, X‐ray absorption near‐edge structure, and pair distribution function analysis. The chemical composition of pristine material and its derivatives (electrochemically treated) are identified by thermogravimetry analysis for the bulk and X‐ray photoelectron spectroscopy for the surface. The electrochemical behavior is investigated on deposited thin films in aqueous electrolyte (KOH) by cyclic voltammetry and electrochemical impedance spectroscopy, and their capacitive properties are further investigated by Galvanostatic cycling with potential limitation. The charge capacity is found to be as high as 1490 F g^?1 for Co^IICo^III–CO₃ LDH at a current density of 0.5 A g^?1. The performances of these materials are described using Ragone plots, which finally allow us to propose them as promising supercapacitor materials. A surface‐to‐bulk comparison using the above characterization techniques gives insight into the cyclability and reversibility limits of this material.     

Hierarchical Ni–Co Hydroxide Petals on Mechanically Robust Graphene Petal Foam for High‐Energy Asymmetric Supercapacitors

A hierarchical structure consisting of Ni–Co hydroxide nanopetals (NCHPs) grown on a thin free‐standing graphene petal foam (GPF) has been designed and fabricated by a two‐step process for pseudocapacitive electrode applications. The mechanical behavior of GPFs has been, for the first time to our knowledge, quantitatively measured from in situ scanning electron microscope characterization of the petal foams during in‐plane compression and bending processes. The Young's modulus of a typical GPF is 3.42 GPa, indicating its outstanding mechanical robustness as a nanotemplate. The GPF/NCHP electrodes exhibit volumetric capacitances as high as 765 F cm^?3, equivalent to an areal capacitance of 15.3 F cm^?2 and high rate capability. To assess practical functionality, two‐terminal asymmetric solid‐state supercapacitors with 3D GPF/NCHPs as positive electrodes are fabricated and shown to exhibit outstanding energy and power densities, with maximum average energy density of ≈10 mWh cm^?3 and maximum power density of ≈3 W cm^?3, high rate capability (a capacitance retention of ≈60% at 100 mA cm^?2), and excellent long‐term cyclic stability (full capacitance retention over 15 000 cycles).     

A LiF Nanoparticle‐Modified Graphene Electrode for High‐Power and High‐Energy Lithium Ion Batteries

Surface modification of carbon materials plays an important role in tailoring carbon surface chemistry to specify their electrochemical performance. Here, a surface modification strategy for graphene is proposed to produce LiF‐nanoparticle‐modified graphene as a high‐rate, large‐capacity pre‐lithiated electrode for high‐power and high‐energy lithium ion batteries. The LiF nanoparticles covering the active sites of the graphene surface provide an extra Li source and act as an effective solid electrolyte interphase (SEI) inhibiter to suppress LiFP₆ electrolyte decomposition reactions, affect SEI components, and reduce their thickness. Consequently, the Li‐ion diffusion is greatly sped up and the thermodynamic stability of the electrode is significantly improved. This modified graphene electrode shows excellent rate capability and improved first‐cycle coulombic efficiency, cycling stability, and ultrahigh power and energy densities accessible during fast charge/discharge processes.     

Homogeneous CoO on Graphene for Binder‐Free and Ultralong‐Life Lithium Ion Batteries

Ultralong cycle life, high energy, and power density rechargeable lithium‐ion batteries are crucial to the ever‐increasing large‐scale electric energy storage for renewable energy and sustainable road transport. However, the commercial graphite anode cannot perform this challenging task due to its low theoretical capacity and poor rate‐capability performance. Metal oxides hold much higher capacity but still are plagued by low rate capability and serious capacity degradation. Here, a novel strategy is developed to prepare binder‐free and mechanically robust CoO/graphene electrodes, wherein homogenous and full coating of β‐Co(OH)₂ nanosheets on graphene, through a novel electrostatic induced spread growth method, plays a key role. The combined advantages of large 2D surface and moderate inflexibility of the as‐obtained β‐Co(OH)₂/graphene hybrid enables its easy coating on Cu foil by a simple layer‐by‐layer stacking process. Devices made with these electrodes exhibit high rate capability over a temperature range from 0 to 55 °C and, most importantly, maintain excellent cycle stability up to 5000 cycles even at a high current density.     

Lithium Ion Breathable Electrodes with 3D Hierarchical Architecture for Ultrastable and High‐Capacity Lithium Storage

Transition‐metal oxides show genuine potential in replacing state‐of‐the‐art carbonaceous anode materials in lithium‐ or sodium‐ion batteries because of their much higher theoretical capacity. However, they usually undergo massive volume change, which leads to numerous problems in both material and electrode levels, such as material pulverization, instable solid‐electrolyte interphase, and electrode failure. Here, it is demonstrated that lithium‐ion breathable hybrid electrodes with 3D architecture tackle all these problems, using a typical conversion‐type transition‐metal oxide, Fe₃O₄, of which nanoparticles are anchored onto 3D current collectors of Ni nanotube arrays (NTAs) and encapsulated by δ‐MnO₂ layers (Ni/Fe₃O₄@MnO₂). The δ‐MnO₂ layers reversibly switch lithium insertion/extraction of internal Fe₃O₄ nanoparticles and protect them against pulverizing and detaching from NTA current collectors, securing exceptional integrity retention and efficient ion/electron transport. The Ni/Fe₃O₄@MnO₂ electrodes exhibit superior cyclability and high‐capacity lithium storage (retaining ≈1450 mAh g^?1, ≈96% of initial value at 1 C rate after 1000 cycles).     

High‐Performance Polypyrrole/Graphene/SnCl2 Modified Polyester Textile Electrodes and Yarn Electrodes for Wearable Energy Storage

Flexible supercapacitors have potential for wearable energy storage due to their high energy/power densities and long operating lifetimes. High electrochemical performance with robust mechanical properties is highly desired for flexible supercapacitor electrodes. Usually, the mechanical properties are improved by choosing high flexible textile substrates but at the much expense of electrochemical performance due to the nonideal contact between conductive materials and textile substrates. Herein, the authors present an efficient, scalable, and general strategy for the simultaneous fabrication of high‐performance textile electrodes and yarn electrodes. It is interesting to find that the conformal reduced graphene oxide (RGO) layer is uniformly and successively painted on the surface of SnCl₂ modified polyester fibers (M‐PEF) via a repeated “dyeing and drying” strategy. The large‐area textile electrodes and ultralong yarn electrodes are fabricated by using RGO/M‐PEF as substrate with subsequent deposition of polypyrrole. This work provides new opportunities for developing high flexible textile electrodes and yarn electrodes with further increased electrochemical performance and scalable production.     

Tin Oxide with Controlled Morphology and Crystallinity by Atomic Layer Deposition onto Graphene Nanosheets for Enhanced Lithium Storage

As one of the most promising negative electrode materials in lithium‐ion batteries (LIBs), SnO₂ experiences intense investigation due to its high specific capacity and energy density, relative to conventional graphite anodes. In this study, for the first time, atomic layer deposition (ALD) is used to deposit SnO₂, containing both amorphous and crystalline phases, onto graphene nanosheets (GNS) as anodes for LIBs. The resultant SnO₂‐graphene nanocomposites exhibit a sandwich structure, and, when cycled against a lithium counter electrode, demonstrate a promising electrochemical performance. It is demonstrated that the introduction of GNS into the nanocomposites is beneficial for the anodes by increasing their electrical conductivity and releasing strain energy: thus, the nanocomposite electrode materials maintain a high electrical conductivity and flexibility. It is found that the amorphous SnO₂‐GNS is more effective than the crystalline SnO₂‐GNS in overcoming electrochemical and mechanical degradation; this observation is consistent with the intrinsically isotropic nature of the amorphous SnO₂, which can mitigate the large volume changes associated with charge/discharge processes. It is observed that after 150 charge/discharge cycles, 793 mA h g^?1 is achieved. Moreover, a higher coulombic efficiency is obtained for the amorphous SnO₂‐GNS composite anode. This study provides an approach to fabricate novel anode materials and clarifies the influence of SnO₂ phases on the electrochemical performance of LIBs.     

Nickel‐Catalyzed Synthesis of 3D Edge‐Curled Graphene for High‐Performance Lithium‐Ion Batteries

Effectively preventing graphene stacking and maintaining ultrathin layers remains a significant research effort for graphene preparation and applications. In this paper, a novel synthetic strategy based on catalyst migration on the surface of a salt template to control the growth of graphene is used to prepare 3D edge‐curled graphene (3D ECG). Under the synergistic effect of the steric hindrance and the migration of the Ni catalyst, 3D ECG forms a special structure in which the intermediate portion is flat and the edge is curled. The resultant unique structure not only effectively prevents the close stacking and aggregation of graphene, but also significantly improves its lithium storage performance. As an anode for lithium ion batteries, the reversible specific capacity can reach 907.5 and 347.8 mAh g^?1 at the current density of 0.05 and 5.0 A g^?1. Even after 1000 cycles, the specific capacity of 3D ECG can still be maintained at 605.2 mAh g^?1 at a current density of 0.5 A g^?1, demonstrating excellent rate performance and cycle performance. This new synthesis strategy and unique edge‐curled structure can be used to guide more design of 3D graphene materials for further functional applications.     

Layered Silicon‐Based Nanosheets as Electrode for 4 V High‐Performance Supercapacitor

Silicon‐based materials have shown great potential and been widely studied in various fields. Unlike its unparalleled theoretical capacity as anodes for batteries, few investigations have been reported on silicon‐based materials for applications in supercapacitors. Here, an electrode composed of layered silicon‐based nanosheets, obtained through oxidation and exfoliation, for a supercapacitor operated up to 4 V is reported. These silicon‐based nanosheets show an areal specific capacitance of 4.43 mF cm^?2 at 10 mV s^?1 while still retaining a specific capacitance of 834 µF cm^?2 even at an ultrahigh scan rate of 50 000 mV s^?1. The volumetric energy and power density of the supercapacitor are 7.65 mWh cm^?3 and 9312 mW cm^?3, respectively, and the electrode can operate for 12000 cycles in a potential window of 4 V at 2 A g^?1, while retaining 90.6% capacitance. These results indicate that the silicon‐based nanosheets can be a competitive candidate as the supercapacitor electrode material.     

High‐Performance Carbon‐LiMnPO4 Nanocomposite Cathode for Lithium Batteries

A cathode material of an electrically conducting carbon‐LiMnPO₄ nanocomposite is synthesized by ultrasonic spray pyrolysis followed by ball milling. The effect of the carbon content on the physicochemical and electrochemical properties of this material is extensively studied. A LiMnPO₄ electrode with 30 wt% acetylene black (AB) carbon exhibits an excellent rate capability and good cycle life in cell tests at 55 and 25 °C. This electrode delivers a discharge capacity of 158 mAh g^?1 at 1/20 C, 126 mAh g^?1 at 1 C, and 107 mAh g^?1 at 2 C rate, which are the highest capacities reported so far for this type of electrode. Transmission electron microscopy and Mn dissolution results confirm that the carbon particles surrounding the LiMnPO₄ protect the electrode from HF attack, and thus lead to a reduction of the Mn dissolution that usually occurs with this electrode. The improved electrochemical properties of the C‐LiMnPO₄ electrode are also verified by electrochemical impedance spectroscopy.     

CoFe–Cl Layered Double Hydroxide: A New Cathode Material for High‐Performance Chloride Ion Batteries

Chloride ion batteries (CIBs) are regarded as promising energy storage systems due to their large theoretical volumetric energy density, high abundance, and low cost of chloride resources. Herein, the synthesis of CoFe layered double hydroxide in the chloride form (CoFe–Cl LDH), for use as a new cathode material for CIBs, is demonstrated for the first time. The CoFe–Cl LDH exhibits a maximum capacity of 239.3 mAh g^?1 and a high reversible capacity of ≈160 mAh g^?1 over 100 cycles. The superb Cl^? ion storage of CoFe–Cl LDH is attributed to its unique topochemical transformation property during the charge/discharge process: a reversible intercalation/deintercalation of Cl^? ions in cathode with slight expansion/contraction of basal spacing, accompanied by chemical state changes in Co²⁺/Co³⁺ and Fe²⁺/Fe³⁺ couples. First‐principles calculations reveal that CoFe–Cl LDH is an excellent Cl^? ion conductor, with extremely low energy barriers (0.12?0.25 eV) for Cl^? diffusion. This work opens a new avenue for LDH materials as promising cathodes for anion‐type rechargeable batteries, which are regarded as formidable competitors to traditional metal ion‐shuttling batteries.     

Ultrathin Nickel–Cobalt Phosphate 2D Nanosheets for Electrochemical Energy Storage under Aqueous/Solid‐State Electrolyte

2D materials are ideal for constructing flexible electrochemical energy storage devices due to their great advantages of flexibility, thinness, and transparency. Here, a simple one‐step hydrothermal process is proposed for the synthesis of nickel–cobalt phosphate 2D nanosheets, and the structural influence on the pseudocapacitive performance of the obtained nickel–cobalt phosphate is investigated via electrochemical measurement. It is found that the ultrathin nickel–cobalt phosphate 2D nanosheets with an Ni/Co ratio of 4:5 show the best electrochemical performance for energy storage, and the maximum specific capacitance up to 1132.5 F g^?1. More importantly, an aqueous and solid‐state flexible electrochemical energy storage device has been assembled. The aqueous device shows a high energy density of 32.5 Wh kg^?1 at a power density of 0.6 kW kg^?1, and the solid‐state device shows a high energy density of 35.8 Wh kg^?1 at a power density of 0.7 kW kg^?1. These excellent performances confirm that the nickel–cobalt phosphate 2D nanosheets are promising materials for applications in electrochemical energy storage devices.     

Reconstruction of Conformal Nanoscale MnO on Graphene as a High‐Capacity and Long‐Life Anode Material for Lithium Ion Batteries

To tackle the issue of inferior cycle stability and rate capability for MnO anode materials in lithium ion batteries, a facile strategy is explored to prepare a hybrid material consisting of MnO nanocrystals grown on conductive graphene nanosheets. The prepared MnO/graphene hybrid anode exhibits a reversible capacity as high as 2014.1 mAh g^?1 after 150 discharge/charge cycles at 200 mA g^?1, excellent rate capability (625.8 mAh g^?1 at 3000 mA g^?1), and superior cyclability (843.3 mAh g^?1 even after 400 discharge/charge cycles at 2000 mA g^?1 with only 0.01% capacity loss per cycle). The results suggest that the reconstruction of the MnO/graphene electrodes is intrinsic due to conversion reactions. A long‐term stable nanoarchitecture of graphene‐supported ultrafine manganese oxide nanoparticles is formed upon cycling, which yields a long‐life anode material for lithium ion batteries. The lithiation and delithiation behavior suggests that the further oxidation of Mn(II ) to Mn(IV ) and the interfacial lithium storage upon cycling contribute to the enhanced specific capacity. The excellent rate capability benefits from the presence of conductive graphene and a short transportation length for both lithium ions and electrons. Moreover, the as‐formed hybrid nanostructure of MnO on graphene may help achieve faster kinetics of conversion reactions.     

Functionally Antagonistic Hybrid Electrode with Hollow Tubular Graphene Mesh and Nitrogen‐Doped Crumpled Graphene for High‐Performance Ionic Soft Actuators

Ionic soft actuators, which exhibit large mechanical deformations under low electrical stimuli, are attracting attention in recent years with the advent of soft and wearable electronics. However, a key challenge for making high‐performance ionic soft actuators with large bending deformation and fast actuation speed is to develop a stretchable and flexible electrode having high electrical conductivity and electrochemical capacitance. Here, a functionally antagonistic hybrid electrode with hollow tubular graphene meshes and nitrogen‐doped crumpled graphene is newly reported for superior ionic soft actuators. Three‐dimensional network of hollow tubular graphene mesh provides high electrical conductivity and mechanically resilient functionality on whole electrode domain. On the contrary, nitrogen‐doped wrinkled graphene supplies ultrahigh capacitance and stretchability, which are indispensably required for improving electrochemical activity in ionic soft actuators. Present results show that the functionally antagonistic hybrid electrode greatly enhances the actuation performances of ionic soft actuators, resulting in much larger bending deformation up to 620%, ten times faster rise time and much lower phase delay in a broad range of input frequencies. This outstanding enhancement mostly attributes to exceptional properties and synergistic effects between hollow tubular graphene mesh and nitrogen‐doped crumpled graphene, which have functionally antagonistic roles in charge transfer and charge injection, respectively.     

Smart Hybridization of TiO2 Nanorods and Fe3O4 Nanoparticles with Pristine Graphene Nanosheets: Hierarchically Nanoengineered Ternary Heterostructures for High‐Rate Lithium Storage

Today, the ever‐increasing demand for large‐size power tools has provoked worldwide competition in developing lithium‐ion batteries having higher energy and power densities. In this context, advanced anode materials are being extensively pursued, among which TiO₂ is particularly promising owing to its high safety, excellent cost and environmental performances, and high cycle stability. However, TiO₂ is faced with two detrimental deficiencies, that is, extremely low theoretical capacity and conductivity. Herein, a smart hybridization strategy is proposed for the hierarchical co‐assembly of TiO₂ nanorods and Fe₃O₄ nanoparticles on pristine graphene nanosheets, aiming to simultaneously address the capacity and conductivity deficiencies of TiO₂ by coupling it with high‐capacity (Fe₃O₄) and high‐conductivity (pristine graphene) components. The resulting novel, multifunctional ternary heterostructures effectively integrate the intriguing functionalities of the three building blocks: TiO₂ as the major active material can adequately retain such merits as high safety and cycle stability, Fe₃O₄ as the auxiliary active material can contribute extraordinarily high capacities, and pristine graphene as the conductive dopant can guarantee sufficient percolation pathways. Benefiting from a remarkable synergy, the ternary heterostructures deliver superior reversible capacities and rate capabilities, thus casting new light on developing next‐generation, high‐performance anode materials.     

Ultrathin MnO2/Graphene Oxide/Carbon Nanotube Interlayer as Efficient Polysulfide‐Trapping Shield for High‐Performance Li–S Batteries

Ultrathin MnO₂/graphene oxide/carbon nanotube (G/M@CNT) interlayers are developed as efficient polysulfide‐trapping shields for high‐performance Li–S batteries. A simple layer‐by‐layer procedure is used to construct a sandwiched vein–membrane interlayer of thickness 2 µm and areal density 0.104 mg cm^?2 by loading MnO₂ nanoparticles and graphene oxide (GO) sheets on superaligned carbon nanotube films. The G/M@CNT interlayer provides a physical shield against both polysulfide shuttling and chemical adsorption of polysulfides by MnO₂ nanoparticles and GO sheets. The synergetic effect of the G/M@CNT interlayer enables the production of Li–S cells with high sulfur loadings (60–80 wt%), a low capacity decay rate (?0.029% per cycle over 2500 cycles at 1 C), high rate performance (747 mA h g^?1 at a charge rate of 10 C), and a low self‐discharge rate with high capacity retention (93.0% after 20 d rest). Electrochemical impedance spectroscopy, cyclic voltammetry, and scanning electron microscopy observations of the Li anodes after cycling confirm the polysulfide‐trapping ability of the G/M@CNT interlayer and show its potential in developing high‐performance Li–S batteries.