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.     

High capacity Li storage in sulfur and nitrogen dual-doped graphene networks

Three-dimensional (3D) networks composing of S and N dual-doped graphene (SNG) were synthesized by a chemical vapor deposition approach using MgSO₄-containing whiskers as templates and S source and NH₃ as N source. Energy dispersive spectrometer mapping and X-ray photoelectron spectroscopy coupled with Raman analysis have revealed that S and N atoms with concentrations of 5.2 and 1.8 atom%, respectively, have been substitutionally incorporated into the graphene networks via covalent bonds. The SNG, as an anode material for lithium ion batteries (LIBs), exhibits extremely high capacity (3525 mAh/g at the current density of 50 mA/g) and superior rate capability (870 mAh/g at 1000 mA/g) with excellent cycling stability (remaining a reversible capacity of 400 mAh/g at 10 A/g after 2500 cycles). The enhanced conductivity, the 3D porous network with many disorders and the intrinsically high Li storage capacity of S and N-doped carbon segments have led to the excellent electrode performance of the SNG networks. The effects of binder content and calendaring pressure on the electrode performance have been investigated. The full LIB with SNG as anode and LiCoO₂ as cathode can afford a high reversible capability (164 mAh/g at 0.2 C) and good cycling stability.     

Improving electrochemical properties of LiCoO2 by enhancing thermal decomposition of Cobalt and Lithium carbonates to synthesize ultrafine powders

Ultrafine LiCoO₂ powders were directly synthesized by enhancing thermal decomposition of Cobalt and Lithium carbonates through a mechanochemical activation treatment to intensify the solid state diffusion reaction. Effects of activation treatment time on particle size and structure of the LiCoO₂ compound were investigated. In the present study, the optimum mechano-chemical activation time was found to be 10 h. In this study, the ultrafine LiCoO₂ powders (particle size in the range from 200 nm to 400 nm) show good structural stability and higher structural integrity. X-ray photoelectron spectroscopy (XPS) results indicate that most of Co cations exist as Co³⁺, which contributes to the improvement of the electrochemical performance. Cyclic voltammetry (CV) curves of different cycles display almost a complete overlap, which can be regarded as another evidence of the excellent cycle performance. The LiCoO₂ powders exhibit a high initial discharge specific capacity of 175.2 mAh/g at 0.1 C (274 mA/g at 1 C) and a remarkable cycle stability from 167.5 mAh/g to 146.2 mAh/g at 0.5 C and from 147.5 mAh/g to 115.2 mAh/g at 3 C after 100 cycles in the range of 3.3–4.3 V. The apparent activation energy and the frequency factor of the decomposition of CoCO₃ are 69.83 kJ/mol and 1.369×10⁶, respectively, indicating that the ultrafine in-process product of Co₃O₄ can be quickly prepared at a low temperature.     

Unique porous yolk-shell structured Co3O4 anode for high performance lithium ion batteries

This paper introduces a unique porous yolk-shell structured Co₃O₄ microball, which is synthesized by spray pyrolysis from precursor solution with polyvinylpyrrolidone (PVP) additive. PVP acts as an organic template in the pyrolytic reaction facilitating the formation of yolk-shell structure. The electrochemical properties of porous yolk-shell Co₃O₄ microballs evaluated as anode materials for lithium ion batteries exhibit high initial columbic efficiency of 77.9% and high reversible capacity of 1025 mAh g⁻¹ with capacity retention of 98.8% after 150 cycles at 1 A g⁻¹. In contrast, the hollow microballs obtained without PVP addition show obvious capacity decay from 1033 to 748 mAh g⁻¹ after 150 cycles with the capacity retention of 72.3%. In addition, the microballs with porous yolk-shell structure exhibit better rate performance. The superior electrochemical performance is mainly attributed to the unique porous yolk-shell structure which provides large voids to buffer volume expansion and enlarge the contact area with the electrolyte, shortening the diffusion path of the lithium ions.     

Preparation of graphene supported porous Si@C ternary composites and their electrochemical performance as high capacity anode materials for Li-ion batteries

Graphene supported porous Si@C ternary composites had been synthesized by various routes and their structural, morphological and electrochemical properties were investigated. Porous Si spheres coated with carbon layer and supported by graphene have been designed to form a 3D carbon conductive network. Used as anode materials for lithium ion batteries, graphene supported porous Si@C ternary composites demonstrate excellent electrochemical performance and cycling stability. The first discharge capacity is 2184.7 mA h/g at a high current density of 300 mA/g. After 50 cycles, the reversible capacity is 652.4 mA h/g at a current density of 300 mA/g and the coulomb efficiency reaches at 98.7%. Due to their excellent electrochemical properties, graphene supported porous Si@C ternary composites can be a kind of promising anode materials for lithium ion batteries.     

Electrochemical performance of cobalt-substituted lithium nickel oxides synthesized from lithium and nickel carbonates and cobalt oxide

LiNi_1?yCo_yO₂ (y=0.1, 0.3 and 0.5) cathode materials were synthesized by a solid-state reaction method at different temperatures using Li₂CO₃ as a Li source, NiCO₃ as a Ni source, and Co₃O₄ as a Co source. The electrochemical properties of the synthesized samples were then investigated. Structures of the synthesized LiNi_1?yCo_yO₂ (y=0.1, 0.3 and 0.5) samples were analyzed, and microstructures of the samples were observed. Voltage vs. x in Li_xNi_1?yCo_yO₂ curves for the first and second charge–discharge cycles and intercalated and deintercalated Li quantity Δx were studied. LiNi_0.9Co_0.1O₂ synthesized at 800 °C had the largest first discharge capacity (152 mAh/g) and quite good cycling performance, with a discharge capacity of 146 mAh/g at n=5. It had a discharge capacity fading rate of 1.4 mAh/g/cycle.     

Synthesis of lithium LiNi1−yCoyO2 from lithium carbonate,nickel oxide and cobalt carbonate and their electrochemical properties

LiNi_1?yCo_yO₂ (y = 0.1, 0.3 and 0.5) were synthesized by solid state reaction method at 800 °C and 850 °C from Li₂CO₃, NiO and CoCO₃ as starting materials. The electrochemical properties of the synthesized LiNi_1?yCo_yO₂ were investigated. As the content of Co decreases, particle size decreases rapidly and particle size gets more homogeneous. When the particle size is compared at the same composition, the particles synthesized at 850 °C are larger than those synthesized at 800 °C. Among LiNi_1?yCo_yO₂ (y = 0.1, 0.3 and 0.5) synthesized at 850 °C, LiNi_0.7Co_0.3O₂ has the largest intercalated and deintercalated Li quantity Δx at the first charge–discharge cycle, followed in order by LiNi_0.9Co_0.1O₂ and LiNi_0.5Co_0.5O₂. LiNi_0.7Co_0.3O₂ synthesized at 850 °C has the largest first discharge capacity (142 mAh/g), followed in order by LiNi_0.9Co_0.1O₂ synthesized at 850 °C (113 mAh/g), and LiNi_0.5Co_0.5O₂ synthesized at 800 °C (109 mAh/g).     

Design and self-assembly of metal-organic framework-derived porous Co3O4 hierarchical structures for lithium-ion batteries

Porous metal oxides hierarchical structures with controlled morphologies have received great attention because of their promising applications in catalysis, energy storage, gas sensing, etc. Porous Co₃O₄ hierarchical structures with controlled morphologies were synthesized on the basis of a pyrolytic conversion of Co-based metal-organic frameworks (Co-MOFs), which were initially grown in solutions containing Co(NO₃)₂·6H₂O, 1,3,5-Benzentricarboxylic acid and pyrazine as solute and N,N-dimethylformamide (DMF) as solvent under a solvothermal condition. Porous Co₃O₄ with twin hemispherical and flower-like structures were obtained with the assistance of PVP by adjusting the amount of pyrazine. The results of nitrogen adsorption–desorption indicate the BET surface area (22.6 m² g⁻¹) of twin hemispherical Co₃O₄ structures is lower than that (33.3 m² g⁻¹) of flower-like Co₃O₄ structures. However, the pore size of twin hemispherical Co₃O₄ structures is smaller, which is centered at about 2.5, 4.0 and 20.0 nm. The Co₃O₄ with twin hemispherical structures exhibit more excellent electrochemical performance as anode materials for lithium ion batteries than that of flower-like Co₃O₄ structures, which may be attributed to the smaller particle size and compact porous structures with suitable pore size.     

Facile synthesis and electrochemical performance of nitrogen-doped porous hollow coaxial carbon fiber/Co3O4 composite

Economy and efficiency are two important indexes of lithium-ion batteries (LIBs) materials. In this work, nitrogen doped hollow porous coaxial carbon fiber/Co₃O₄ composite (N-PHCCF/Co₃O₄) is fabricated using the fibers of waste bamboo leaves as the template and carbon resource by soaking and thermal treatment, respectively. The N-PHCCF/Co₃O₄ exhibits an outstanding electrochemical performance as anode material for lithium ion batteries, due to the nitrogen doping, coaxial configuration and porous structure. Specifically, it delivers a high discharge reversible specific capacity of 887 mA h g^?1 after 100 cycles at the current density of 100 mA g^?1. Furthermore a high capability of 415 mA h g^?1 even at 1 A g^?1 is exhibited. Most impressively, the whole process is facile and scalable，exhibiting recycling of resource and turning waste into treasure in an eco-friendly way.     

Synthesis and electrochemical properties of LiV3O8 via an improved sol–gel process

LiV₃O₈ cathode material was synthesized via a hydrothermal improved sol–gel process using LiOH, NH₄VO₃ and oxalic acid as raw materials. The thermal decomposition process of the as-prepared LiV₃O₈ precursor was investigated by thermogravimetric (TG) and differential scanning calorimetry (DSC). The structure, morphology and electrochemical performance of the as-synthesized LiV₃O₈ samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM) and the galvanostatic charge–discharge test. The effects of synthesis conditions on phases, structure and electrochemical performance of the LiV₃O₈ samples were particularly discussed. Result shows that pure LiV₃O₈ sample can be obtained at 300 °C, which is much lower than that of normal citric assisted sol–gel method. The sample synthesized at 350 °C exhibits the best electrochemical performance, which can present an initial discharge capacity of 301.1 mAh/g at a current density of 50 mA/g and maintain 271.6 mA/g (about 90.2% of its initial value) after 10 cycles.     

Electrochemical characteristics of LiNi0.5Co0.5O2 synthesized at 800 °C from the different combinations of carbonates,oxides, and hydroxides

LiNi_0.5Co_0.5O₂ cathode materials were synthesized by a solid-state reaction method at 800 °C using Li₂CO₃, LiOH·H₂O; NiO, NiCO₃; CoCO₃, or Co₃O₄ as the sources of Li, Ni, and Co, respectively. The electrochemical properties of the synthesized samples were then investigated. The structure of the synthesized LiNi_0.5Co_0.5O₂ was analyzed, and the microstructures of the samples were observed. The curves of voltage vs. x in Li_xNi_0.5Co_0.5O₂ for first charge–discharge and intercalated and deintercalated Li quantity Δx were studied. Destruction of unstable 3b sites and phase transitions were discussed from the first and second charge–discharge curves of voltage vs. x in Li_xNi_0.5Co_0.5O₂. The LiNi_0.5Co_0.5O₂ sample synthesized from Li₂CO₃, NiCO₃ and Co₃O₄ has the largest first discharge capacity (142 mAh/g). The LiNi_0.5Co_0.5O₂ sample synthesized from Li₂CO₃, NiO and Co₃O₄ has a relatively large first discharge capacity (141 mAh/g) and the smallest capacity deterioration rate (4.6 mAh/g/cycle).     

Electrochemical characteristics of LiNi0.9Co0.1O2 synthesized at 800 °C from the different combinations of carbonates and oxides

Cathode active materials with a composition of LiNi_0.9Co_0.1O₂ were synthesized by a solid-state reaction method at 800 °C using Li₂CO₃, NiO or NiCO₃, and CoCO₃ or Co₃O₄ as the sources of Li, Ni, and Co, respectively. The electrochemical properties of the synthesized samples were then investigated. The structure of the synthesized LiNi_0.9Co_0.1O₂ was analyzed, and the microstructures of the samples were observed. The curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂ for the first charge–discharge and the intercalated and deintercalated Li quantity Δx were studied. The LiNi_0.9Co_0.1O₂ sample synthesized from Li₂CO₃, NiCO₃, and Co₃O₄ had the largest first discharge capacity (152 mAh/g), with a discharge capacity deterioration rate of 1.4 mAh/g/cycle.     

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.     

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.     

Fabrication of carbon encapsulated Co3O4 nanoparticles embedded in porous graphitic carbon nanosheets for microwave absorber

Carbon-encapsulated Co₃O₄ nanoparticles homogeneously embedded 2D (two-dimensional) porous graphitic carbon (PGC) nanosheets were prepared by a facile and scalable synthesis method. With assistance of sodium chloride, the Co₃O₄ nanoparticles (10–20 nm) with magnetic loss were well encapsulated by onion-like carbon shells homogeneously embedded porous graphitic carbon nanosheets (thickness of less than 50 nm) with dielectric loss. In the architecture, the well impedance matching for microwave absorption can be obtained by the synergetic effect between Co₃O₄ nanoparticles and encapsulated porous carbon nanosheets. The minimum reflection loss value of −32.3 dB was observed at 11.4 GHz with a matching thickness of 2.3 mm for 2D Co₃O₄@C@PGC nanosheets. The 2D Co₃O₄@C@PGC nanosheets can be used as a kind of candidate for microwave absorbing materials.     

Preparation and characterization of LiNi0.8Co0.15Al0.05O2 with high cycling stability by using AlO2- as Al source

We report the preparation of a series of LiNi_0.8Co_0.15Al_0.05O₂ materials with different reaction time (10, 20, 30 and 40 h) of precursor and their electrochemical properties as cathode material for lithium-ion batteries (LIBs). The preparation of LiNi_0.8Co_0.15Al_0.05O₂ was divided into two steps: a co-precipitation process to obtain Ni_0.8Co_0.15Al_0.05(OH)₂ precursor and a calcination step with LiOH. During the co-precipitation process, AlO₂^- was employed as Al source so as to guarantee Ni²⁺, Co²⁺ and Al³⁺ co-precipitation. The impacts of different synthesis time of the precursor on crystal structure, morphology and electrochemical performance of LiNi_0.8Co_0.15Al_0.05O₂ were systematically investigated. The samples with various synthesis time of precursor possessed spherical morphology and a layered α-NaFeO₂ structure with R-3m space group. Especially, when the reaction time of precursor was 30 h, the LiNi_0.8Co_0.15Al_0.05O₂ had the weakest degree of Li⁺/Ni²⁺ ions mixing and the best uniformity and integrity. When used as cathode materials for LIBs, the LiNi_0.8Co_0.15Al_0.05O₂ with 30 h exhibited high discharge capacity, good cycling performance and remarkable rate capability. The maximum discharge capacity was 202.3 mAh g⁻¹ at 0.1 C and the capacity retention approached 99.4% after 100 cycles at 1 C. At 10 C, the discharge capacity exceeded 140 mAh g⁻¹, suggesting a possible application in the high rate LIBs. The excellent electrochemical performance might be attributed to the uniform co-precipitation of Ni²⁺, Co²⁺ and Al³⁺ and well layered structure with less Li⁺/Ni²⁺ mixing.     

Towards high purity graphene/single-walled carbon nanotube hybrids with improved electrochemical capacitive performance

CoMgAl layered double hydroxides were prepared as catalysts for the in situ synchronous growth of graphene and single-walled carbon nanotubes (SWCNTs) from methane by chemical vapor deposition. The as-calcined CoMgAl layered double oxide (LDO) flakes served as the template for the deposition of graphene, and Co nanoparticles (NPs) embedded on the LDOs catalyzed the growth of SWCNTs. After the removal of CoMgAl LDO flakes, graphene (G)/SWCNT/Co₃O₄ hybrids with SWCNTs directly grown on the surface of graphene and 27.3 wt.% Co₃O₄ NPs encapsulated in graphene layers were available. Further removal of the Co₃O₄ NPs by a CO₂-oxidation assistant purification method induced the formation of G/SWCNT hybrids with a high carbon purity of 98.4 wt.% and a high specific surface area of 807.0 m²/g. The G/SWCNT/Co₃O₄ hybrids exhibited good electrochemical performance for pseudo-capacitors due to their high Co₃O₄ concentration and the high electrical conductivity of SWCNTs and graphene. In another aspect, the G/SWCNT hybrids can be used as excellent electrode materials for double-layer capacitors. A high capacity of 98.5 F/g_electrode was obtained at a scan rate of 10 mV/s, 78.2% of which was retained even when the scan rate increased to 500 mV/s.     

Charge–discharge curves and discharge capacities of LiNi1−yCoyO2 synthesized from lithium carbonate and nickel and cobalt oxides

LiNi_1?yCo_yO₂ (y=0.1, 0.3, and 0.5) were synthesized by a solid-state reaction method at 800 °C and 850 °C using Li₂CO₃, NiO, and Co₃O₄ as the starting materials. The electrochemical properties of the synthesized LiNi_1?yCo_yO₂ were then investigated. For samples with the same composition, the particles synthesized at 850 °C were larger than those synthesized at 800 °C. The particles of all the samples synthesized at 850 °C were larger than those synthesized at 800 °C. LiNi_0.5Co_0.5O₂ synthesized at 850 °C had the largest first discharge capacity (159 mA h/g), followed in order by LiNi_0.7Co_0.3O₂ synthesized at 800 °C (158 mA h/g) and LiNi_0.9Co_0.1O₂ synthesized at 850 °C (151 mA h/g). LiNi_0.9Co_0.1O₂ synthesized at 850 °C had the best cycling performance with discharge capacities of 151 mA h/g at n=1 and 156 mA h/g at n=5.     

Cobalt oxide nanocubes as electrode material for the performance evaluation of electrochemical supercapacitor

Porous cobalt oxide (Co₃O₄) nanocubes (NCs) were synthesized by a simple and cost-effective hydrothermal technique for the potential application of electrochemical supercapacitors. The hydrothermally synthesized materials exhibited the small cube like morphology with the average size of ~ 50 to 60 nm. The surface analysis revealed a good surface area, and high pore volume of the synthesized porous Co₃O₄ NCs. The capacitive properties of porous Co₃O₄ NCs electrode were investigated by cyclic voltammetry (CV) in 6 M KOH electrolyte and a high specific capacitance of ~ 430.6 F/g at a scan rate of ~ 10 mV s^?1 was observed. The capacity retention of up to ~ 85% after 1000 cycles was shown by the fabricated porous Co₃O₄ NCs electrode. The porous Co₃O₄ NCs showed excellent structural stability through cycling with promising capacity retention which suggested a good quality of porous Co₃O₄ NCs as electrochemical supercapacitor electrode.     

One-step microwave-assisted synthesis of Sb2O3/reduced graphene oxide composites as advanced anode materials for sodium-ion batteries

Sb₂O₃/reduced graphene oxide (RGO) composites were prepared through a facile microwave-assisted reduction of graphite oxide in SbCl₃ precursor solution, and investigated as anode material for sodium-ion batteries (SIBs). The experimental results show that a maximum specific capacity of 503 mA h g⁻¹ is achieved after 50 galvanostatic charge/discharge cycles at a current density of 100 mA g⁻¹ by optimizing the RGO content in the composites and an excellent rate performance is also obtained due to the synergistic effect between Sb₂O₃ and RGO. The high capacity, superior rate capability and excellent cycling performance of Sb₂O₃/RGO composites demonstrate their excellent sodium-ion storage ability and show their great potential as electrode materials for SIBs.