Hierarchically Hollow and Porous NiO/NiCo2O4 Nanoprisms Encapsulated in Graphene Oxide for Lithium Storage

Porous Co3O4/NiO@C Chains Assembled from Nanosheets with Excellent Lithium Storage Performance

Carbon layers-coated porous Co3O4/NiO (denoted as PCNO@C) chains are synthesized by the facile solvothermal method and subsequently annealing treatment under an Ar atmosphere, which are assembled from numerous Co3O4/NiO nanosheets. Benefiting from the unique porous chain structure, the volume change of the electrode is greatly relieved during the long-term cycling processes, and then an excellent cycling stability is obtained (the reversible specific capacity of the 1000th cycle can reach 637.3 mA h g-1 at 5000 mA g-1). Besides, a continuous conductive network is constructed by the coated carbon layers and long chains, the movement rate of electrons is effectively accelerated, and the high rate capability is obtained (the high reversible specific capacity of 480.6 mA h g-1 is retained at 10,000 mA g-1). This work contributes a new idea to construct porous chain structure anode materials.

Bimetallic Cobalt-Nickel Selenide Nanocubes Embedded in a Nitrogen-Doped Carbon Matrix as an Excellent Li-Ion Battery Anode

Lithium-ion batteries (LIBs) have been widely used for portable electronics and electric vehicles; however, the low capacity in the graphite anode limits the improvement of energy density. Transition-metal selenides are promising anode material candidates due to their high theoretical capacity and controllable structure. In this study, we successfully synthesize a bimetallic transition-metal selenide nanocube composite, which is well embedded in a nitrogen-doped carbon matrix (denoted as CoNiSe₂/NC). This material shows a high capacity and excellent cycling for Li-ion storage. Specifically, the reversible capacity approaches ∼1245 mA h g^-1 at 0.1 A g^-1. When cycled at 1 A g^-1, the capacity still remains at 642.9 mA h g^-1 even after 1000 cycles. In-operando XRD tests have been carried out to investigate the lithium storage mechanism. We discover that the outstanding performance is due to the unique CoNiSe₂/NC nanocomposite characteristics, such as the synergistic effect of bimetallic selenide on lithium storage, the small particle size, and the stable and conductive carbon structure. Therefore, this morphology structure not only reduces the volume change of metal selenides but also produces more lithium storage active sites and shortens lithium diffusion paths, which results in high capacity, good rate, and long cycling.

Hematite: A Good Catalyst for the Thermal Decomposition of Energetic Materials and the Application in Nano-Thermite

Metal oxides (MOs) are of great importance in catalysts, sensor, capacitor and water treatment. Nano-sized MOs have attracted much more attention because of the unique properties, such as surface effect, small size effect and quantum size effect, etc. Hematite, an especially important additive as combustion catalysts, can greatly speed up the thermal decomposition process of energetic materials (EMs) and enhance the combustion performance of propellants. This review concludes the catalytic effect of hematite with different morphology on some EMs such as ammonium perchlorate (AP), cyclotrimethylenetrinitramine (RDX), cyclotetramethylenete-tranitramine (HMX), etc. The method for enhancing the catalytic effect on EMs using hematite-based materials such as perovskite and spinel ferrite materials, making composites with different carbon materials and assembling super-thermite is concluded and their catalytic effects on EMs is also discussed. Therefore, the provided information is helpful for the design, preparation and application of catalysts for EMs.

Layered Assembly of Graphene Oxide Paper for Mechanical Structures

Graphene oxide (GO) paper is an attractive material because of high stiffness and strength, light weight, and multiple functionalities. While these properties are now widely exploited in nanoinclusions or flat sheets, three-dimensional (3D) structures from GO paper are not widely studied because of a lack of suitable processing methods. In this study, we report a layered assembly method to make stiff and strong 3D GO structures with the aid of a sodium tetraborate (borax) solution. By comparing mechanical properties of assembled GO paper using water or borax solution, we found that the borax-assembled layers had the highest stiffness. To demonstrate the versatility of our assembly protocol, we then fabricated a variety of 3D structures including I-beams, cylindrical tubes, and bridge-like structures from GO paper. These GO structures were stiff and light weight, and the stiffness to mass ratio was around 2-4 times higher than other polymer samples including cellulose, fluorinated ethylene propylene, and poly(vinyl alcohol). The versatile processing method to make stiff and strong GO structures will enable new engineering applications where nonplanar GO structures are required.

CuCo2O4 Hollow Microspheres with Graphene Composite Targeting Superior Lithium-Ion Storage

CuCo₂O₄, a type of promising lithium-ion storage material, exhibits high electrochemical properties in lithium-ion batteries and enormous economic benefits. However, its practical application is limited by problems such as structural collapse and electrochemical stability during the charging and discharging process. In this work, the reduced graphene oxide (rGO)-coated CuCo₂O₄ (CuCo₂O₄/rGO) hollow microspheres were successfully prepared by electrostatic self-assembly. The CuCo₂O₄/rGO electrode shows an outstanding capability for lithium-ion storage and a remarkable rate capacity, e.g., 445 mA h g^-1 at 5 A g^-1. After 150 cycles at 0.1 A g^-1, the reversible capacity of the CuCo₂O₄/rGO electrode is as high as 1080 mA h g^-1, and it can still retain about 530 mA h g^-1 in the 400th cycle at 1 A g^-1. The hollow microspheres with mesoporous shells can cause electrolyte penetration into the spherical shell to effectively shorten the transfer distance of lithium ions, and the encapsulation of graphene improves the conductivity and stability of CuCo₂O₄, which endows CuCo₂O₄/rGO with a wonderful Li⁺ storage performance. It is proved that this is an efficient method to improve the electrochemical performance of metal compounds for better applications in energy storage.

Graphene Oxide/Fe2O3 Nanocomposite as an Efficient Catalyst for Thermal Decomposition of Ammonium Perchlorate via the Vacuum-Freeze-Drying Method

The combination of graphene oxide (GO) and iron oxide (Fe₂O₃) may induce property enforcement and application extension. Herein, GO/Fe₂O₃ nanocomposites were synthesized via the vacuum-freeze-drying method and used for the thermal decomposition of ammonium perchlorate (AP). A series of characterization techniques were applied to elucidate the as-obtained nanomaterial's physicochemical properties. These results show that the treated GO is consistent with the pristine GO after the freeze-drying treatment. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses show that iron oxide nanoparticles are anchored on and between the GO sheets. The catalytical effect investigation on AP with different Fe₂O₃: GO ratios indicates that the high-temperature decomposition temperature of AP could be decreased by a temperature as high as 77 °C compared to pure AP accompanied by 3 wt % GO/Fe₂O₃ nanocomposite which proves the high catalytic performance of the nanocomposites. The first-principles calculation was employed to elaborate the synergistic effect, and the findings demonstrate that the presence of graphene in the catalyst can enhance the catalytic effect via reducing the activation energy barrier by ∼17% in the reaction of AP thermal decomposition.

Nb2CTx MXene as High-Performance Energy Storage Material with Na, K, and Liquid K-Na Alloy Anodes

Two-dimensional MXenes perform well as hosts in batteries, which are promising for next-generation energy storage materials. With low price and high performance, sodium (Na) and potassium (K) own the potential to replace lithium in energy storage devices, but the larger radii and dendrite growth restrict their commercialization. Herein, we successfully synthesized an accordion-like Nb₂CT_x MXene, whose crystal structure integrity and lamellar separation have been confirmed by characterization methods like high-resolution transmission electron microscopy (HR-TEM). Combined with solid Na and K and liquid K-Na alloy as anodes, the Nb₂CT_x MXene shows excellent electrochemical performance, such as high capacity retention after large current shock in tests of rate performance and long time stability for more than 500 cycles, etc. Also, the Nb₂CT_x MXene coupled with liquid K-Na anode performs better than that coupled with solid K for the dendrite-controlling character of the liquid electrode. The Nb₂CT_x MXene would boost the exploitation of more suitable host materials for Na/K-ion batteries and promote an in-depth understanding of MXenes.

Selective Phosphorization Boosting High-Performance NiO/Ni2Co4P3 Microspheres as Anode Materials for Lithium Ion Batteries

Phosphorization of metal oxides/hydoxides to promote electronic conductivity as a promising strategy has attracted enormous attention for improving the electrochemical properties of anode material in lithium ion batteries. For this article, selective phosphorization from NiCo₂O₄ to NiO/Ni₂Co₄P₃ microspheres was realized as an efficient route to enhance the electrochemical lithium storage properties of bimetal Ni-Co based anode materials. The results show that varying phosphorizaed reagent amount can significantly affect the transformation of crystalline structure from NiCo₂O₄ to intermediate NiO, hybrid NiO/Ni₂Co₄P₃, and, finally, to Ni₂Co₄P₃, during which alterated sphere morphology, shifted surface valance, and enhanced lithium-ion storage behavior are detected. The optimized phosphorization with 1:3 reagent mass ratio can maintain the spherical architecture, hold hybrid crystal structure, and improve the reversibly electrochemical lithium-ion storage properties. A specific capacity of 415 mAh g⁻¹ is achieved at 100 mA g⁻¹ specific current and maintains at 106 mAh g⁻¹ when the specific current increases to 5000 mA g⁻¹. Even after 200 cycles at 500 mA g⁻¹, the optimized electrode still delivers 224 mAh g⁻¹ of specific capacity, exhibiting desirable cycling stability. We believe that understanding of such selective phosphorization can further evoke a particular research enthusiasm for anode materials in lithium ion battery with high performances.