Hollow core–shell ZnMn2O4 microspheres as a high-performance anode material for lithium-ion batteries

The hollow core–shell ZnMn₂O₄ microspheres are successfully prepared by a solvothermal carbon templating method and then a annealing process. The crystal phase and particle morphology of resultant ZnMn₂O₄ microspheres are characterized by XRD and TEM. The electrochemical properties of the ZnMn₂O₄ microspheres as an anode material are investigated for lithium ion batteries. The results show that the ZnMn₂O₄ microspheres exhibit a reversible capacity of 855.8 mA h g⁻¹ at a current density of 200 mA g⁻¹ after 50 cycles. Even at 1000 mA g⁻¹, the reversible capacity of the ZnMn₂O₄ microspheres is still kept at 724.4 mA h g⁻¹ after 60 cycles. The enhanced electrochemical performance suggests the promising potential of the hollow core–shell ZnMn₂O₄ microspheres in lithium-ion batteries.     

Synthesis and characterization of MnCo2O4 microspheres based air electrode for rechargeable sodium-air batteries

In this work, the nanosized porous MnCo₂O₄ microspheres were synthesized by a hydrothermal method and their electrochemical behaviors were investigated based on a carbon supported composite air electrode for rechargeable sodium-air batteries. Under dry air test condition, the MnCo₂O₄/C air electrode demonstrated a stable working voltage of around 2.1 V vs. Na⁺/Na and a high initial discharge capacity of 7709.4 mA h g⁻¹, based on the active material mass, at a current density of 0.1 mA cm⁻². By a limit on the depth of discharge, the cell exhibited a specific capacity of 1000 mA h g⁻¹ with a high cycling stability up to 130 cycles. The considerable electrocatalytic activity suggests that the as-proposed MnCo₂O₄ is a highly efficient catalyst as air electrode for rechargeable sodium-air batteries.     

Facile synthesis of three dimensional flower-like Co3O4@MnO2 core-shell microspheres as high-performance electrode materials for supercapacitors

In this work, we reported the synthesis of three dimensional flower-like Co₃O₄@MnO₂ core-shell microspheres by a controllable two-step reaction. Flower-like Co₃O₄ microspheres cores were firstly built from the self-assembly of Co₃O₄ nanosheets, on which MnO₂ nanosheets shells were subsequently grown through the hydrothermal decomposition of KMnO₄. The MnO₂ nanosheets shells were found to increase the electrochemical active sites and allow faster redox reaction kinetics. Based on these advantages, when used as an electrode for supercapacitors, the prepared flower-like Co₃O₄@MnO₂ core-shell composite electrode demonstrated a significantly enhanced specific capacitance (671 F g⁻¹ at 1 A g⁻¹) as well as improved rate capability (84% retention at 10 A g⁻¹) compared with the pristine flower-like Co₃O₄ electrode. Moreover, the optimized asymmetric supercapacitor device based on the flower-like Co₃O₄@MnO₂//active carbon exhibited a high energy density of 34.1 W h kg⁻¹ at a power density of 750 W kg⁻¹, meaning its great potential application for energy storage devices.     

A nest-like hierarchical porous V2O5 as a high-performance cathode material for Li-ion batteries

In this article, V₂O₅ with a novel nest-like hierarchical porous structure has been synthesized by a facile solvothermal method and investigated as cathode material for lithium-ion batteries. The nest-like V₂O₅ with a diameter of about 1.5 µm, was composed of interconnected nanosheets with a highly porous structure. Without other modification, the as-prepared V₂O₅ electrode exhibited superior capacity. An initial discharge capacity of 330 mAh g⁻¹ (at a current density of 100 mA g⁻¹) could be delivered and a stable discharge capacity of 240 mAh g⁻¹ after 50 cycles is maintained. The excellent performance was attributed to the hierarchical porous structure that could buffer against the local volume change and shorten the lithium-ions diffusion distance.     

Microemulsion-mediated hydrothermal growth of pagoda-like Fe3O4 microstructures and their application in a lithium–air battery

This paper reported the growth of novel pagoda-like Fe₃O₄ particles via a facile microemulsion-mediated hydrothermal procedure. The chemical compositions and morphologies of the as-grown Fe₃O₄ particles were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and field emission scanning electron microscopy (FE-SEM). The morphologies of the as-prepared sample evolved from pagoda-like to pinwheel-like to flower-like shapes with increasing reaction time. In addition, the NaOH concentration and polyethylene glycol (PEG)-2000 had key effects on the formation of the final product. The electrocatalytic properties of the prepared pagoda-like micro-Fe₃O₄, as catalytic materials for a lithium–air battery, were further evaluated by galvanostatic charge/discharge cycling and electrochemical impedance spectrometry (EIS). Results showed that the cell displayed an initial discharge capacity of 1429 mA h g⁻¹ at a voltage of 1.5–4.5 V at 100 mA g⁻¹.     

Nb2O5 nanospheres/surface-modified graphene composites as superior anode materials in lithium ion batteries

Uniform Nb₂O₅ nanospheres/surface-modified graphene (SMG) composites for anode materials in lithium ion batteries were synthesized by hydrothermal method. The microstructure and morphology of composites were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscope techniques. The experimental results showed that Nb₂O₅ nanospheres were tightly and uniformly grown on the surface of SMG nanosheets. Nb₂O₅ nanospheres/SMG composites exhibited an impressive reversible capacity of 404.6 mA h g⁻¹ at the current density of 40 mA g⁻¹ after 100 cycles, and an excellent rate capacity of 345.5 mA h g⁻¹ at the current density of 400 mA g⁻¹.     

Facile synthesis of porous hollow Co3O4 microfibers derived-from metal-organic frameworks as an advanced anode for lithium ion batteries

Co₃O₄, as a promising anode material for the next generation lithium ion batteries to replace graphite, displays high theoretical capacity (890 mAh g⁻¹) and excellent electrochemical properties. However, the drawbacks of its poor cycle performance caused by large volume changes during charge-discharge process and low initial coulombic efficiency due to large irreversible reaction impede its practical application. Herein, we have developed a porous hollow Co₃O₄ microfiber with 500 nm diameter and 60 nm wall thickness synthesized via a facile chemical precipitation method with subsequent thermal decomposition. As an advanced anode for lithium ion batteries, the porous hollow Co₃O₄ microfibers deliver an obviously enhanced electrochemical property in terms of lithium storage capacity (1177.4 mA h g⁻¹ at 100 mA g⁻¹), initial coulombic efficiency (82.9%) and cycle performance (76.6% capacity retention at 200th cycle). This enhancement could be attributed to the well-designed microstructure of porous hollow Co₃O₄ microfibers, which could increase the contact surface area between electrolyte and active materials and accommodate the volume variations via additional void space during cycling.     

Effect of graphene nanosheets on electrochemical performance of Li4Ti5O12 in lithium-ion capacitors

In order to improve the electrochemical performance of lithium titanium oxide, Li₄Ti₅O₁₂ (LTO), for the use in the lithium-ion capacitors (LICs) application, LTO/graphene composites were synthesized through a solid state reaction. The composite exhibited an interwoven structure with LTO particles dispersed into graphene nanosheets network rather than an agglomerated state pristine LTO particles. It was found that there is an optimum percentage of graphene additives for the formation of pure LTO phase during the solid state synthesis of LTO/graphene composite. The effect of graphene nanosheets addition on electrochemical performance of LTO was investigated by a systemic characterization of galvanostatic cycling in lithium and lithium-ion cell configuration. The optimized composite exhibited a decreased polarization upon cycling and delivered a specific capacity of 173 mA h g⁻¹ at 0.1 C and a well maintained capacity of 65 mA h g⁻¹ even at 20 C. The energy density of 14 Wh kg⁻¹ at a power density of 2700 W kg⁻¹ was exhibited by a LIC full cell with a balanced mass ratio of anode to cathode along with a superior capacitance retention of 97% after 3000 cycles at a current density of 0.4 A g⁻¹. This boost in reversible capacity, rate capability and cycling performance was attributed to a synergistic effect of graphene nanosheets, which provided a short lithium ion diffusion path as well as facile electron conduction channels.     

Porous carbon spheres as anode materials for sodium-ion batteries with high capacity and long cycling life

Porous carbon spheres (PCSs) with high surface area were fabricated by the reaction of D-Glucose monohydrate precursor with sodium molybdate dihydrate (Na₂MoO₄·2H₂O) via a facile hydrothermal method followed by carbonization and aqueous ammonia solution (NH₃·H₂O) treatment. The as-prepared PCSs exhibit a highly developed porous structure with a large specific surface area and show an excellent electrochemical performance as anode material of sodium-ion batteries (SIBs). A reversible capacity of 249.9 mA h g⁻¹ after 50 cycles at a current density of 50 mA g⁻¹ and a long cycling life at a high current density of 500 mA g⁻¹ are achieved. The excellent cycling performance and high capacity make the PCSs a promising candidate for long cycling SIBs.     

Carbon coated porous tin peroxide/carbon composite electrode for lithium-ion batteries with excellent electrochemical properties

A porous tin peroxide/carbon (SnO₂/C) composite electrode coated with an amorphous carbon layer is prepared using a facile method. In this electrode, spherical graphite particles act as supporter of electrode framework, and the interspace among particles is filled with porous amorphous carbon derived from decomposition of polyvinylidene fluoride and polyacrylonitrile. SnO₂ nanoparticles are uniformly embedded in the porous amorphous carbon matrix. The pores in amorphous carbon matrix are able to buffer the huge volume expansion of SnO₂ during charge/discharge cycling, and the carbon framework can prevent the SnO₂ particles from pulverization and re-aggregation. The carbon coating layer on the outermost surface of electrode can further prevent porous SnO₂/C electrode from contacting with electrolyte directly. As a result, the repeated formation of solid electrolyte interface is avoided and the cycling stability of electrode is improved. The obtained SnO₂/C electrode presents an initial coulombic efficiency of 77.3% and a reversible capacity of 742 mA h g⁻¹ after 130 cycles at a current density of 100 mA g⁻¹. Furthermore, a reversible capacity of 679 mA h g⁻¹ is obtained at 1 A g⁻¹.     

Bitter gourd-shaped Ni3V2O8 anode developed by a one-pot metal-organic framework-combustion technique for advanced Li-ion batteries

The present study reports on the one-pot synthesis of Ni₃V₂O₈ (NVO) electrodes by a simple metal organic framework-combustion (MOF-C) technique for anode applications in Li-ion batteries (LIBs). The particle morphology of the prepared NVO is observed to vary as irregular rods, porous bitter gourd and hybrid micro/nano particles depending on the concentration of the framework linker used during synthesis. In specific, the orthorhombic phase and the unique bitter gourd-type secondary structure comprised of agglomerated nanoparticles and porous morphologies is confirmed using powder X-ray diffraction, electron microscopies, X-ray photoelectron spectroscopy and N₂ adsorption–desorption measurements. When tested for lithium batteries as anode, the bitter gourd-type NVO electrode shows an initial discharge capacity of 1362 mA h g⁻¹ and a reversible capacity of 822 mA h g⁻¹ are sustained at a rate of 200 mA g⁻¹ after 100 cycles. Moreover, at 2000 mA g⁻¹, a reversible capacity of 724 mA h g⁻¹ is retained after 500 cycles. Interestingly, the porous bitter gourd-shaped NVO electrode registered significantly high rate performance and reversible specific capacities of 764, 531 and 313 mA h g⁻¹ at high rates of 1, 5 and 10 A g⁻¹, respectively.     

NiCo2O4 nanosheets and nanocones as additive-free anodes for high-performance Li-ion batteries

Development of novel electrode materials with high energy and power densities for lithium-ion batteries (LIBs) is the key to meet the demands of electric vehicles. Transition metal oxides that can react with large amounts of Li⁺ for electrochemical energy storage are considered promising anode materials for LIBs. In this work, NiCo₂O₄ nanosheets and nanocones on Ni foam have been synthesized via general hydrothermal growth and low-temperature annealing treatment. They exhibit high rate capacities and good cyclic performance as LIB anodes owing to their architecture design, which reduces ion and electron transport distance, expands the electrode–electrolyte contact, increases the structural stability, and buffers volume change during cycles. Notably, NiCo₂O₄ nanosheets deliver an initial capacity of 2239 mAh g⁻¹ and a rate capacity of 964 mAh g⁻¹ at current densities of 100 and 5000 mA g⁻¹, respectively. The corresponding values of nanocones are 1912 and 714 mAh g⁻¹. Hence, the as-synthesized NiCo₂O₄ nanosheets and nanocones, which are carbon-free and binder-free with higher energy densities and stronger connections between active materials and current collectors for better stability, are promising for use in advanced anodes for high-performance LIBs.     

Evaluation of reduced graphene oxide-supported NiSb2O6 nanocomposites for reversible lithium storage

NiSb₂O₆ and reduced graphene oxide (NiSb₂O₆/rGO) nanocomposites are successfully fabricated by a solid-state method combined with a subsequent solvothermal treatment and further used as anode material of lithium-ion battery. The NiSb₂O₆/rGO nanocomposites exhibit a higher reversible capacity (of ca. 1240.5 mA h g⁻¹ at a current density of 50 mA g⁻¹), along with a good rate capability (395.2 mA h g⁻¹ at a current density of 1200 mA g⁻¹) and excellent capacity retention (684.5 mA h g⁻¹ after 150 cycles). These good performances could be attributed to the incorporated reduced grapheme oxide, which significantly improves the electronic conductivity of the NiSb₂O₆.     

Porous nitrogen-doped carbon vegetable-sponges with enhanced lithium storage performance

Porous nitrogen-doped carbon vegetable-sponges (N-DCSs) have been fabricated by chemical treatment of the Cu@C precursors using HNO₃ for the first time. The obtained N-DCSs are porous three-dimensional (3D)-structure and similar to numerous agglomerated fluffy micro-vegetable-sponges. When the precursors are treated by H₂SO₄, carbon vegetable-sponges (CSs) without nitrogen doping are prepared. As anode materials in lithium ion batteries, the as-prepared N-DCSs show improved Li-storage capacity and cycling stability as compared with the pure CSs. They offer 870 mA h g⁻¹ at 0.5 A g⁻¹ after 300 cycles and high reversible capacity with 910 mA h g⁻¹ at 0.2 A g⁻¹ after cycled at different current densities, which are much higher than those of CSs. It is envisaged that the large surface area, unique 3D porous nanostructure and appropriate nitrogen doping are favorable for the superior electrochemical properties of N-DCSs.     

Hierarchical Co3O4@ZnWO4 core/shell nanostructures on nickel foam: Synthesis and electrochemical performance for supercapacitors

To improve the electrochemical properties of Co₃O₄ for supercapacitors application, a hierarchical Co₃O₄@ZnWO₄ core/shell nanowire arrays (NWAs) material is designed and synthesized successfully via a facile two-step hydrothermal method followed by the heat treatment. Co₃O₄@ZnWO₄ NWAs exhibits excellent electrochemical performances with areal capacitance of 4.1 F cm⁻² (1020.1 F g⁻¹) at a current density of 2 mA cm⁻² and extremely good cycling stability (99.7% of the initial capacitance remained even after 3000 cycles). Compared with pure Co₃O₄ electrodes, the results prove that this unique hierarchical hybrid nanostructure and reasonable assembling of two electrochemical pseudocapacitor materials are more advantageous to enhance the electrochemical performance. Considering these remarkable capacitive behaviors, the hierarchical Co₃O₄@ZnWO₄ core/shell NWAs nanostructure electrode can be revealed promising for high-performance supercapacitors.     

Ag enhanced electrochemical performance for Na2Li2Ti6O14 anode in rechargeable lithium-ion batteries

Due to the characteristics of an electronic insulator, Na₂Li₂Ti₆O₁₄ always suffers from low electronic conductivity as anode material for lithium storage. Via Ag coating, Na₂Li₂Ti₆O₁₄@Ag is fabricated, which has higher electronic conductivity than bare Na₂Li₂Ti₆O₁₄. Enhancing the Ag coating content from 0.0 to 10.0 wt%, the surface of Na₂Li₂Ti₆O₁₄ is gradually deposited by Ag nanoparticles. At 6.0 wt%, a continuous Ag conductive layer is formed on Na₂Li₂Ti₆O₁₄. While, particle growth and aggregation take place when the Ag coating content reaches 10.0 wt%. As a result, Na₂Li₂Ti₆O₁₄@6.0 wt% Ag displays better cycle and rate properties than other samples. It can deliver a lithium storage capacity of 131.4 mAh g⁻¹ at 100 mA g⁻¹, 124.9 mAh g⁻¹ at 150 mA g⁻¹, 119.1 mAh g⁻¹ at 200 mA g⁻¹, 115.8 mAh g⁻¹ at 250 mA g⁻¹, 111.9 mAh g⁻¹ at 300 mA g⁻¹ and 109.4 mAh g⁻¹ at 350 mA g⁻¹, respectively.     

Electrochemical presodiation promoting lithium storage performance of Mo-based anode materials

Stabilizing the layer structures of Mo-based anode materials is still a challenge for Li ion batteries. Herein, we proposed an electrochemical presodiation strategy for MoS₂ and MoO₃ to improve their cycling stability. It is interesting to note that the cycling stability of as-treated MoS₂ and MoO₃ was significantly improved. Although the reversible discharge capacity was slightly decreased, the capacity of the pretreated MoS₂ at 300 mA g⁻¹ was retained at 345 mA h g⁻¹ after 100 cycles while that of the pristine one decreased to 151 mA h g⁻¹. The capacity of the pretreated MoO₃ after 60 cycles was also improved from 275 mA h g⁻¹ (the pristine one) to 460 mA h g⁻¹. The stabilizing effect was further verified by scanning electron microscope (SEM) analysis. Electrochemical presodiation here could be a promising modification strategy for Mo-based anode materials.     

Amorphous CoS nanoparticle/reduced graphene oxide composite as high-performance anode material for sodium-ion batteries

Transition metal sulfides have been proved as promising candidates of anode materials for sodium-ion batteries (SIBs) due to their high sodium storage capacity, low cost and enhanced safety. In this study, the amorphous CoS nanoparticle/reduced graphene oxide (CoS/rGO) composite has been fabricated by a facile one-step electron beam radiation route to in situ decorate amorphous CoS nanoparticle on the rGO nanosheets. Benefiting from the small particle size (~2 nm), amorphous structure, and electronic conductive rGO nanosheets, the CoS/rGO nanocomposite exhibits high sodium storage capacity (440 mAh g⁻¹ at 100 mA g⁻¹), excellent cycling stability (277 mAh g⁻¹ after 100 cycles at 200 mA g⁻¹, 79.6% capacity retention) and high rate capability (149.5 mAh g⁻¹ at 2 A g⁻¹). The results provide a facile approach to fabricate promising amorphous and ultrafine metal sulfides for energy storage.     

Polymer microsphere-assisted synthesis of lithium-rich cathode with improved electrochemical performance

The Li-rich layered cathode material Li_1.165Mn_0.501Ni_0.167Co_0.167O₂ with porous structure has been successfully synthesized through a facile co-precipitation approach followed with a high-temperature calcination treatment, adopting polymer microsphere (PSA) as a template and conductive agent. The PSA-assisted Li_1.165Mn_0.501Ni_0.167Co_0.167O₂ composite exhibits remarkably improved cycling stability and rate capability compared with the bare composite. It delivers a high initial discharge capacity of 267.0 mA h g⁻¹ at 0.1 C (1 C=250 mA g⁻¹) between 2.0 V and 4.65 V. A discharge capacity of 214.9 mA h g ⁻¹ is still obtained after 100 cycles. Furthermore, the diffusion coefficients of Li⁺ investigated by the cyclic voltammetry technique are approximately 10⁻¹⁵–10⁻¹⁴ cm² s⁻¹. Such outstanding performance is mainly ascribed to: on one hand, the carbon residue of PSA after being calcined at high temperature contributes to enhance the electronic conductivity of the electrode and alleviates the volume changes during the Li⁺-insertion/extraction, leading to an improved rate capability; on the other hand, the unique porous structure and small particle size are conductive to increase the exposed electrochemical active surface, shorten Li⁺ diffusion distance and thus enhance the lithium storage capacity.     

Synthesis of Mn3O4/N-doped graphene hybrid and its improved electrochemical performance for lithium-ion batteries

Mn₃O₄/N-doped graphene (Mn₃O₄/NG) hybrids were synthesized by a simple one-pot hydrothermal process. The scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray powder diffraction (XRD), Thermogravimetric analysis (TG), Raman Spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the microstructure, crystallinity and compositions. It is demonstrated that Mn₃O₄ nanoparticles are high-dispersely anchored onto the individual graphene nanosheets, and also found that, in contrast with pure Mn₃O₄ obtained without graphene added, the introduction of graphene effectively restricts the growth of Mn₃O₄ nanoparticles. Simultaneously, the anchored well-dispersed Mn₃O₄ nanoparticles also play a role as spacers in preventing the restacking of graphene sheets and producing abundant nanoscale porous channels. Hence, it is well anticipated that the accessibility and reactivity of electrolyte molecules with Mn₃O₄/NG electrode are highly improved during the electrochemical process. As the anode material for lithium ion batteries, the Mn₃O₄/NG hybrid electrode displays an outstanding reversible capacity of 1208.4 mAh g⁻¹ after 150 cycles at a current density of 88 mA g⁻¹, even still retained 284 mAh g⁻¹ at a high current density of 4400 mA g⁻¹ after 10 cycles, indicating the superior capacity retention, which is better than those of bare Mn₃O₄, and most other Mn₃O₄/C hybrids in reported literatures. Finally, the superior performance can be ascribed to the uniformly distribution of ultrafine Mn₃O₄ nanoparticles, successful nitrogen doping of graphene and favorable structures of the composites.