One-pot synthesis of core–shell-structured tin oxide–carbon composite powders by spray pyrolysis for use as anode materials in Li-ion batteries

Core–shell-structured tin oxide–carbon composite powders with mixed SnO₂ and SnO tetragonal crystals are prepared by one-pot spray pyrolysis from a spray solution with tin oxalate and polyvinylpyrrolidone (PVP). The aggregate, made up of SnO_x nanocrystals (several tens of nanometers), is uniformly coated with an amorphous carbon layer. The initial discharge capacities of the bare SnO₂ and SnO_x–carbon composite powders at a current density of 1 A g⁻¹ are 1473 and 1667 mA h g⁻¹, respectively; their discharge capacities after 500 cycles are 78 and 1033 mA h g⁻¹, respectively. The SnO_x–carbon composite powders maintain their spherical morphology even after 500 cycles. On the other hand, the bare SnO₂ powder breaks into several pieces after cycling. The structural stability of the SnO_x–carbon composite powders results in a low charge transfer resistance and high lithium ion diffusion rate even after 500 cycles at a high current density of 2 A g⁻¹. Therefore, the SnO_x–carbon composite powders have superior electrochemical properties compared with those of the bare SnO₂ powders with a fine size.     

Carbon-coated SiO/ZrO2 composites as anode materials for lithium-ion batteries

A combination of high-energy ball milling and constant pressure chemical vapor deposition was used to prepare carbon-coated SiO/ZrO₂ composites. It was found that the as-prepared composites were composed of amorphous carbon, amorphous SiO, and paracryslalline ZrO₂. The electrochemical analysis results revealed excellent electrochemical performances for the composites, including a high initial discharge capacity (1737 mA h g⁻¹), a remarkable cyclic stability (reversible capacity of 721 mA h g⁻¹ at 800 mA g⁻¹, after 100 cycles), and a good rate capability (870 mA h g⁻¹ at 800 mA g⁻¹). These features demonstrate that these composites are promising alternative candidates for high-efficiency electrode materials of Li-ion batteries.     

Sulfur-doped mesoporous carbon from surfactant-intercalated layered double hydroxide precursor as high-performance anode nanomaterials for both Li-ion and Na-ion batteries

We describe a preparation of sulfur-doped mesoporous amorphous carbon (SMAC) from a commercially available alkyl surfactant sulfonate anion-intercalated NiAl-layered double hydroxide precursor via thermal decomposition and subsequent acid leaching. The resultant amorphous carbon is endowed with the integrated advantage of featuring high reversible capacity and long cycling stability: intrinsic doping of sulfur, large specific area, and broad mesopore size distribution. Electrochemical evaluation shows that the SMAC electrode exhibits highly enhanced electrochemical performances, compared with the electrode of non-doped mesoporous and amorphous carbon prepared by using a different surfactant (sodium laurate). A high reversible capacity of 958 mA h g⁻¹ is achieved for the SMAC electrode after 110 cycles at 200 mA g⁻¹, and especially a superlong cycle life with a reversible capacity of 579 mA h g⁻¹ after 970 cycles at 500 mA g⁻¹. Moreover, the SMAC electrode can facilitate the reversible insertion/extraction of Na ion, owing to the proper specific area and mesopore size distribution, as well as the improved electronic conductivity resulted from doping of sulfur.     

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.     

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.     

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.     

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.     

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.     

Carbon-coated SnO2/graphene nanosheets as highly reversible anode materials for lithium ion batteries

A simple approach is reported to prepare carbon-coated SnO₂ nanoparticle–graphene nanosheets (Gr–SnO₂–C) as an anode material for lithium ion batteries. The material exhibits excellent electrochemical performance with high capacity and good cycling stability (757 mA h g^?1 after 150 cycles at 200 mA g^?1). The likely contributing factors to the outstanding charge/discharge performance of Gr–SnO₂–C could be related to the synergism between the excellent conductivity and large area of graphene, the nanosized particles of SnO₂, and the effects of the coating layer of carbon, which could alleviate the effects of volume changes, keep the structure stable, and increase the conductivity. This work suggests a strategy to prepare carbon-coated graphene–metal oxide which could be used to improve the electrochemical performance of lithium ion batteries.     

Self-standing flexible cathode of V2O5 nanobelts with high cycling stability for lithium-ion batteries

Self-standing V₂O₅ nanobelt electrode free of binders, conductive carbon or current collectors was successfully prepared via a simple one-step hydrothermal reaction. The length of V₂O₅ nanobelts was up to several hundreds micrometers and the thickness was around 40 nm. Ultralong nanobelts as building blocks and internal voids provide a robust mechanical flexibility and shortened ion/electron transport pathway. The self-standing electrode delivered an initial specific capacity of 127.4 mA h g⁻¹ at a current density of 60 mA g⁻¹ and exhibited excellent cycling stability with capacity retention up to 89.8% after 200 cycles. The outstanding cycling performance can be attributed to the excellent network stability, shortened Li-ion diffusion pathway and the high surface area between electrolyte/electrode interfaces.     

3D NiCo2S4 nanorod arrays as electrode materials for electrochemical energy storage application

It is essential to develop new electrode materials for electrochemical energy storage to meet the increasing energy demands, reduce environmental pollution and develop low-carbon economy. In this work, binder-free NiCo₂S₄ nanorod arrays (NCS NRAs) on nickel foam electrodes are prepared by an easy and low energy-consuming route. The electrodes exhibit superior electrochemical properties both for alkaline and Li-ion batteries. In 3 M KOH electrolyte, the NCS NRAs achieve a specific capacity of 240.5 mA h g⁻¹ at a current density of 0.2 A g⁻¹, and 105.7 mA h g⁻¹ after 1500 cycles at the current density of 5 A g⁻¹ with capacity retention of 87.3%. As the anode for LIBs, it shows a high initial capacity of 1760.7 mA h g⁻¹ at the current density of 100 mA g⁻¹, corresponding coulombic efficiency of 87.6%, and a rate capacity of 945 mA h g⁻¹ when the current density is improved 10 times. Hence, the NiCo₂S₄ nanorod arrays are promised as electrode materials with competitive performance.     

Ultrafine SnO2 nanoparticles as a high performance anode material for lithium ion battery

In this paper, the ultrafine tin oxides (SnO₂) nanoparticles are fabricated by a facile microwave hydrothermal method with the mean size of only 14 nm. Phase compositions and microstructures of the as-prepared nanoparticles have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the ultrafine SnO₂ nanoparticles are obtained to be the pure rutile-structural phase with the good dispersibility. Galvanostatic cycling and cyclic voltammetry results indicate that the first discharge capacity of the ultrafine SnO₂ electrode is 1196.63  mAh g⁻¹, and the reversible capacity could retain 272.63 mAh g⁻¹ at 100 mA g⁻¹ after 50 cycles for lithium ion batteries (LIBs). The excellent electrochemical performance of the SnO₂ anode for LIBs is attributed to its ultrafine nanostructure for providing active sites during lithium insertion/extraction processes. Pulverization and agglomeration of the active materials are effectively reduced by the microwave hydrothermal method.     

Fabrication of MnO@C-CNTs composite by CVD for enhanced performance of lithium ion batteries

A novel MnO@Amorphous C-Carbon nanotubes (MnO@C-CNTs) composite is prepared by chemical vapor deposition (CVD). When used as an anode material for Li-ion batteries, the MnO@C-CNTs composite exhibits an initial discharge capacity of 1164 mA h g⁻¹ at 100 mA g⁻¹ and the discharge capacity gradually increased from 571.7 mA h g⁻¹ to 654 mA h g⁻¹ after 100 cycles at 1 A g⁻¹, which shows an increase of the capacity rather than attenuation. Furthermore, the MnO@C-CNTs electrode can deliver a capacity of up to 228 mA h g⁻¹ at 5 A g⁻¹. These results indicate that the three-dimensional conductive network of the MnO@C-CNTs composite could prevent the aggregation of MnO particles, and its open structure allows electrolyte penetration, and reduces the diffusion path of the lithium ions, hence maximizes utilization of the electrochemically active MnO particles, while enhances the conductivity of electrode material and Li⁺ transport. This work offers a universal approach to design various metal oxides@C-CNTs composite.     

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.     

Electrochemical energy storage performance of heterostructured SnO2@MnO2 nanoflakes

In this work, we report synthesis of SnO₂@MnO₂ nanoflakes grown on nickel foam through a facile two-step hydrothermal route. The as-obtained products are characterized by series of techniques such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The as-obtained SnO₂@MnO₂ nanoflakes are directly used as supercapacitor electrode materials. The results show that the electrode possesses a high discharge areal capacitance of 1231.6 mF cm⁻² at 1 mA cm⁻² and benign cycling stability with 67.2% of initial areal capacitance retention when the current density is 10 mA cm⁻² after 6000 cycles. Moreover, the heterostructured electrode shows 41.1% retention of the initial capacitance when the current densities change from 1 to 10 mA cm⁻², which reveals good rate capability. SnO₂@MnO₂ nanoflakes products which possess excellent electrochemical properties might be used as potential electrode materials for supercapacitor applications.     

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.     

Pseudocapacitive Li+ intercalation in ZnO/ZnO@C composites enables high-rate lithium-ion storage and stable cyclability

Metallic oxide ZnO is considered to be a promising alternative anode material for lithium ion battery because of its high theoretical capacities (978 mA h g⁻¹). However, its inherent low electronic conductivity and undesirable large volume change result in inferior electrochemical performances and hinder its practical application. Herein, ZnO/ZnO@C composites are prepared by a simple carbonization process of ZnO/ZnO@ZIFs-8, which are constructed by using ZnO particles as both template and zinc sources for zeolitic imidazolate frameworks-8 (ZIF-8) preparation via a facile solution reaction. When evaluated as anode for lithium ion batteries, the as-prepared composites show an initial capacity of 878 mA h g⁻¹ at current density of 0.1 A g⁻¹ with high capacity retention of 95.6% after 50 cycles, and an initial capacity of 359 mA h g⁻¹ tested at 5.0 A g⁻¹ with a capacity retention of 85.3% after 500 cycles, exhibiting outstanding cycling stability and excellent rate capability. The ameliorated electrochemical performances are mainly attributed to the elevated conductivity and cushioning effects provided by carbon framework derived from ZIF-8, and the enhanced pseudocapacitance behavior originated from the decreased size of ZnO particles and high surface area of ZIFs-derived carbon.     

Aqueous slurry of S-doped carbon nanotubes as conductive additive for lithium ion batteries

S-doped carbon nanotubes (SCNTs) obtained by a post treatment approach are used as conductive additive for LiFePO₄ (LFP) cathodes in Lithium ion batteries (LIBs). The SCNTs exhibit higher specific surface area, higher conductivity and better hydrophily as compared to the pristine CNTs because of S doping. Thus the SCNTs can be stably dispersed in water, forming an aqueous conductive slurry. The LFP cathode using the aqueous SCNTs slurry as conductive additive exhibits excellent electrochemical performances in terms of capacity (143 mA h g⁻¹ at 2 C), rate capability and cycling stability (99.6% of initial capacity after 200 cycles) due to the uniform dispersibility of SCNTs in the bulk of electrodes forming a continuous conductive network. The full cell configuration with graphite as anode, affords a high reversible capability (150 mA h g⁻¹ at 0.2 C), good cycling stability (capacity retention of 87.6% at 2 C), ultrahigh energy density of 163.7 W h kg⁻¹ and power density of 296.8 W kg⁻¹. Our results provide an easy approach to prepare high performance LIB cathodes using water as solvent, thus leading to lower cost and more secure for the electrode production.     

Three-dimensional hierarchical ZnCo2O4 flower-like microspheres assembled from porous nanosheets: Hydrothermal synthesis and electrochemical properties

In this work, three-dimensional hierarchical ZnCo₂O₄ flower-like microspheres have been synthesized on a large scale via a facile and economical citrate-mediated hydrothermal method followed by an annealing process in air. The as-synthesized ZnCo₂O₄ flower-like microspheres are constructed by numerous interweaving porous nanosheets. According to the experimental results, a formation mechanism involving the assembly of the nanosheets from nanoparticles into flower-like microsphere is proposed. As a virtue of their beneficial structural features, the ZnCo₂O₄ flower-like microspheres exhibit a high lithium storage capacity and excellent cycling stability (1136 mA h g⁻¹ at 100 mA g⁻¹ after 50 cycles). This remarkable electrochemical performance can be ascribed to the hierarchical structure and porous structures in the nanosheets, which effectively increases the contact area between the active materials and the electrolyte, shortening the Li⁺ diffusion pathway and buffering the volume variation during cycling.     

Investigation on performances of Li1.2Co0.4Mn0.4O2 prepared by self-combustion reaction as stable cathode for lithium-ion batteries

Poor rate capability and cycling performance are the major barriers for Li-rich layered cathode materials to be applied as the next generation cathode materials for lithium-ion batteries. In our work, Li_1.2Co_0.4Mn_0.4O₂ has been successfully synthesized via a self-combustion reaction (SCR) and a calcination procedure. Compared with the material produced by the solid state method (SSM), the one by SCR exhibits both better rate capability and cycling performance. Its initial discharge capacity is 166.01 mA h g⁻¹ with the capacity retention of 85.98% after 50 cycles at a current density of 200 mA h g⁻¹. Its remarkable performance is attributed to a thin carbon coating layer, which not only slows down the transformation rate of layered to spinel structure, but provides a good electronic pathway to increase the Li⁺ diffusion coefficient.