CuO Quantum Dots Embedded in Carbon Nanofibers as Binder‐Free Anode for Sodium Ion Batteries with Enhanced Properties

The design of sodium ion batteries is proposed based on the use of flexible membrane composed of ultrasmall transition metal oxides. In this paper, the preparation of CuO quantum dots (≈2 nm) delicately embedded in carbon nanofibers (denoted as 2‐CuO@C) with a thin film via a feasible electrospinning method is reported. The CuO content can be controlled by altering the synthetic conditions and is optimized to 54 wt%. As binder‐free anode for sodium ion batteries, 2‐CuO@C delivers an initial reversible capacity of 528 mA h g^?1 at the current density of 100 mA g^?1, an exceptional rate capability of 250 mA h g^?1 at 5000 mA g^?1, and an ultra‐stable capacity of 401 mA h g^?1 after 500 cycles at 500 mA g^?1. The enhancement of electrochemical performance is attributed to the unique structure of 2‐CuO@C, which offers a variety of advantages: highly conductive carbon matrix suppressing agglomeration of CuO grains, interconnected nanofibers ensuring short transport length for electrons, well‐dispersed CuO quantum dots leading to highly utilization rate, and good mechanical properties resulting in strong electrode integrity.     

In Situ Growth of CoP3/Carbon Polyhedron/CoO/NF Nanoarrays as Binder‐Free Anode for Lithium‐Ion Batteries with Enhanced Specific Capacity

Advanced functional materials enable lithium‐ion batteries to reach high specific capacity. To achieve this goal, nickel foam (NF), as current collector, is chosen to in situ form aligned nanoarrays composed of CoP₃/carbon polyhedron (CP)/CoO. The CoO nanowire acts as bridge to link NF and CoP₃/CP which not only reinforces the adhesion between active material and NF but also enhances the capacity of whole electrode. Besides, CoP₃ is evenly coupled with CP, which can effectively buffer the volume expansion of CoP₃ during the charge/discharge process. Moreover, the novel architecture of CoP₃/CP/CoO/NF is beneficial to improve the electronic conductivity. As a result, the CoP₃/CP/CoO/NF anode delivers an ultrahigh specific capacity of 1715 mAh g^?1 at 0.5 A g^?1 which can remain at 1150 mAh g^?1 after 80 cycles, demonstrating the good durability. Thus, this work develops a facile strategy to design self‐supporting electrodes for an enhanced energy storage device.     

An Advanced MoS2/Carbon Anode for High‐Performance Sodium‐Ion Batteries

Molybdenum disulfide (MoS₂) is a promising anode for high performance sodium‐ion batteries due to high specific capacity, abundance, and low cost. However, poor cycling stability, low rate capability and unclear electrochemical reaction mechanism are the main challenges for MoS₂ anode in Na‐ion batteries. In this study, molybdenum disulfide/carbon (MoS₂/C) nanospheres are fabricated and used for Na‐ion battery anodes. MoS₂/C nanospheres deliver a reversible capacity of 520 mAh g^?1 at 0.1 C and maintain at 400 mAh g^?1 for 300 cycles at a high current density of 1 C, demonstrating the best cycling performance of MoS₂ for Na‐ion batteries to date. The high capacity is attributed to the short ion and electron diffusion pathway, which enables fast charge transfer and low concentration polarization. The stable cycling performance and high coulombic efficiency (～100%) of MoS₂/C nanospheres are ascribed to (1) highly reversible conversion reaction of MoS₂ during sodiation/desodiation as evidenced by ex‐situ X‐ray diffraction (XRD) and (2) the formation of a stable solid electrolyte interface (SEI) layer in fluoroethylene carbonate (FEC) based electrolyte as demonstrated by fourier transform infrared spectroscopy (FTIR) measurements.     

Room‐Temperature Liquid Metal Confined in MXene Paper as a Flexible,Freestanding, and Binder‐Free Anode for Next‐Generation Lithium‐Ion Batteries

Exploring flexible lithium‐ion batteries is required with the ever‐increasing demand for wearable and portable electronic devices. Selecting a flexible conductive substrate accompanying with closely coupled active materials is the key point. Here, a lightweight, flexible, and freestanding MXene/liquid metal paper is fabricated by confining 3 °C GaInSnZn liquid metal in the matrix of MXene paper without any binder or conductive additive. When used as anode for lithium‐ion cells, it can deliver a high discharge capacity of 638.79 mAh g^?1 at 20 mA g^?1. It also exhibits satisfactory rate capacities, with discharge capacities of 507.42, 483.33, 480.22, 452.30, and 404.47 mAh g^?1 at 50, 100, 200, 500, and 1000 mA g^?1, respectively. The cycling performance is obviously improved by slightly reducing the charge–discharge voltage range. The composite paper also has better electrochemical performance than liquid metal coated Cu foil. This study proposes a novel flexible anode by a clever combination of MXene paper and low‐melting point liquid metal, paving the way for next‐generation lithium‐ion batteries.     

FeP@C Nanotube Arrays Grown on Carbon Fabric as a Low Potential and Freestanding Anode for High‐Performance Li‐Ion Batteries

An anode of self‐supported FeP@C nanotube arrays on carbon fabric (CF) is successfully fabricated via a facile template‐based deposition and phosphorization route: first, well‐aligned FeOOH nanotube arrays are simply obtained via a solution deposition and in situ etching route with hydrothermally crystallized (Co,Ni)(CO₃)_0.5OH nanowire arrays as the template; subsequently, these uniform FeOOH nanotube arrays are transformed into robust carbon‐coated Fe₃O₄ (Fe₃O₄@C) nanotube arrays via glucose adsorption and annealing treatments; and finally FeP@C nanotube arrays on CF are achieved through the facile phosphorization of the oxide‐based arrays. As an anode for lithium‐ion batteries (LIBs), these FeP@C nanotube arrays exhibit superior rate capability (reversible capacities of 945, 871, 815, 762, 717, and 657 mA h g⁻¹ at 0.1, 0.2, 0.4, 0.8, 1.3, and 2.2 A g⁻¹, respectively, corresponding to area specific capacities of 1.73, 1.59, 1.49, 1.39, 1.31, 1.20 mA h cm⁻² at 0.18, 0.37, 0.732, 1.46, 2.38, and 4.03 mA cm⁻², respectively) and a stable long‐cycling performance (a high specific capacity of 718 mA h g⁻¹ after 670 cycles at 0.5 A g⁻¹, corresponding to an area capacity of 1.31 mA h cm⁻² at 0.92 mA cm⁻²).     

Penne‐Like MoS2/Carbon Nanocomposite as Anode for Sodium‐Ion‐Based Dual‐Ion Battery

The dual‐ion battery (DIB) system has attracted great attention owing to its merits of low cost, high energy, and environmental friendliness. However, the DIBs based on sodium‐ion electrolytes are seldom reported due to the lack of appropriate anode materials for reversible Na⁺ insertion/extraction. Herein, a new sodium‐ion based DIB named as MoS₂/C‐G DIB using penne‐like MoS₂/C nanotube as anode and expanded graphite as cathode is constructed and optimized for the first time. The hierarchical MoS₂/C nanotube provides expanded (002) interlayer spacing of 2H‐MoS₂, which facilitates fast Na⁺ insertion/extraction reaction kinetics, thus contributing to improved DIB performance. The MoS₂/C‐G DIB delivers a reversible capacity of 65 mA h g^?1 at 2 C in the voltage window of 1.0–4.0 V, with good cycling performance for 200 cycles and 85% capacity retention, indicating the feasibility of potential applications for sodium‐ion based DIBs.     

N‐Doped Carbon Nanofibers with Interweaved Nanochannels for High‐Performance Sodium‐Ion Storage

Although graphite materials have been applied as commercial anodes in lithium‐ion batteries (LIBs), there still remain abundant spaces in the development of carbon‐based anode materials for sodium‐ion batteries (SIBs). Herein, an electrospinning route is reported to fabricate nitrogen‐doped carbon nanofibers with interweaved nanochannels (NCNFs‐IWNC) that contain robust interconnected 1D porous channels, produced by removal of a Te nanowire template that is coelectrospun within carbon nanofibers during the electrospinning process. The NCNFs‐IWNC features favorable properties, including a conductive 1D interconnected porous structure, a large specific surface area, expanded interlayer graphite‐like spacing, enriched N‐doped defects and active sites, toward rapid access and transport of electrolyte and electron/sodium ions. Systematic electrochemical studies indicate that the NCNFs‐IWNC exhibits an impressively high rate capability, delivering a capacity of 148 mA h g^?1 at current density of as high as 10 A g^?1, and has an attractively stable performance over 5000 cycles. The practical application of the as‐designed NCNFs‐IWNC for a full SIBs cell is further verified by coupling the NCNFs‐IWNC anode with a FeFe(CN)₆ cathode, which displays a desirable cycle performance, maintaining acapacity of 97 mA h g^?1 over 100 cycles.     

CuO Nanoplates for High‐Performance Potassium‐Ion Batteries

Potassium‐ion batteries (KIBs) are promising alternatives to lithium‐ion batteries because of the abundance and low cost of K. However, an important challenge faced by KIBs is the search for high‐capacity materials that can hold large‐diameter K ions. Herein, copper oxide (CuO) nanoplates are synthesized as high‐performance anode materials for KIBs. CuO nanoplates with a thickness of ≈20 nm afford a large electrode–electrolyte contact interface and short K⁺ ion diffusion distance. As a consequence, a reversible capacity of 342.5 mAh g^?1 is delivered by the as‐prepared CuO nanoplate electrode at 0.2 A g^?1. Even after 100 cycles at a high current density of 1.0 A g^?1, the capacity of the electrode remains over 206 mAh g^?1, which is among the best values for KIB anodes reported in the literature. Moreover, a conversion reaction occurs at the CuO anode. Cu nanoparticles form during the first potassiation process and reoxidize to Cu₂O during the depotassiation process. Thereafter, the conversion reaction proceeds between the as‐formed Cu₂O and Cu, yielding a reversible theoretical capacity of 374 mAh g^?1. Considering their low cost, easy preparation, and environmental benignity, CuO nanoplates are promising KIB anode materials.     

High‐Performance Sodium‐Ion Battery Anode via Rapid Microwave Carbonization of Natural Cellulose Nanofibers with Graphene Initiator

Cellulose is a promising natural bio‐macromolecule due to its abundance, renewability and low cost. Here, a new method is developed to prepare pre‐sodiated carbonaceous anodes for sodium‐ion batteries (SIBs) from cellulose nanofibers (CNFs) under microwave irradiation for potential ultrafast and large‐scale manufacturing. While direct carbonization of CNFs through microwave treatment is usually impossible due to the weak microwave absorption of CNFs, it is found that a small amount of reduced graphene oxide (rGO) can act as an effective initiator. Microwaving rGO releases extremely high energy, giving rise to local ultrahigh temperature as well as ultrahigh heating rate, which then induces the fast carbonization of CNFs and the production of pre‐sodiated carbonaceous materials within seconds. The sodium in the carbonaceous materials, introduced from the carbonization of CNFs containing sodium‐ion carboxyl, offer favorable spaces for sodiation/desodiation, which improves the electrochemical performance of the sodium‐inserted carbonaceous anode. When the microwaved rGO‐CNF (MrGO‐CNF) is used as an anode for SIBs, a high initial capacity of 558 mAh g^?1 is delivered and the capacity of 340 mAh g^?1 remains after 200 cycles. The excellent reversible capacity and cycling stability indicate MrGO‐CNF a promising anode for sodium‐ion batteries.     

Flexible and Binder‐Free Electrodes of Sb/rGO and Na3V2(PO4)3/rGO Nanocomposites for Sodium‐Ion Batteries

Flexible power sources have shown great promise in next‐generation bendable, implantable, and wearable electronic systems. Here, flexible and binder‐free electrodes of Na₃V₂(PO₄)₃/reduced graphene oxide (NVP/rGO) and Sb/rGO nanocomposites for sodium‐ion batteries are reported. The Sb/rGO and NVP/rGO paper electrodes with high flexibility and tailorability can be easily fabricated. Sb and NVP nanoparticles are embedded homogenously in the interconnected framework of rGO nanosheets, which provides structurally stable hosts for Na‐ion intercalation and deintercalation. The NVP/rGO paper‐like cathode delivers a reversible capacity of 113 mAh g^?1 at 100 mA g^?1 and high capacity retention of ≈96.6% after 120 cycles. The Sb/rGO paper‐like anode gives a highly reversible capacity of 612 mAh g^?1 at 100 mA g^?1, an excellent rate capacity up to 30 C, and a good cycle performance. Moreover, the sodium‐ion full cell of NVP/rGO//Sb/rGO has been fabricated, delivering a highly reversible capacity of ≈400 mAh g^?1 at a current density of 100 mA g^?1 after 100 charge/discharge cycles. This work may provide promising electrode candidates for developing next‐generation energy‐storage devices with high capacity and long cycle life.