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.     

Syntheses of nano-sized Co-based powders by carbothermal reduction for anode materials of lithium ion batteries

Co oxide powders were synthesized by spray drying, calcining, and then ball milling. Nano-sized Co-based powders were then prepared by carbothermal reduction at 873 K, 1073 K, and 1173 K of the synthesized Co oxide powders. Then, the electrochemical properties of the electrodes made with the Co-based powders were examined to evaluate their suitability as anode materials for Li-ion batteries. It was reported that among Co, CoO, and Co₃O₄, Co₃O₄ had the best cycling performance. However, in this work, Co showed the best cycling performance. This means that the mechanisms of the cycling performance of CoO and Co which were synthesized by different heat treatment methods are different from each other. The initial discharge capacities of three electrodes made with the powders reduction-treated at 873 K, 1073 K, and 1173 K were similar and about 1100 mA h/g, respectively. However, the electrodes made with the powders reduction-treated at 873 K and 1073 K had the discharge capacities at the second cycle which were less than 50% of the discharge capacity of the electrode made with the powder reduction-treated at 1173 K. The electrode made with the powder reduction-treated at 1173 K had a discharge capacity of 750 mA h/g at the 20th cycle, demonstrating that this electrode had good cycling performance.     

Optimal synthesis and new understanding of P2-type Na2/3Mn1/2Fe1/4Co1/4O2 as an advanced cathode material in sodium-ion batteries with improved cycle stability

A sol-gel method with ethylene diamine tetraacetic acid and citric acid as co-chelates is employed for the synthesis of P2-type Na_2/3Mn_1/2Fe_1/4Co_1/4O₂ as cathode material for sodium-ion batteries. Among the various calcination temperatures, the Na_2/3Mn_1/2Fe_1/4Co_1/4O₂ with a pure P2-type phase calcined at 900 °C demonstrates the best cycle capacity, with a first discharge capacity of 157 mA h g^?1 and a capacity retention of 91 mA h g^?1 after 100 cycles. For comparison, the classic P2-type Na_2/3Mn_1/2Fe_1/2O₂ cathode prepared under the same conditions shows a comparable first discharge capacity of 150 mA h g^?1 but poorer cycling stability, with a capacity retention of only 42 mA h g^?1 after 100 cycles. Based on X-ray photoelectron spectroscopy, the introduction of cobalt together with sol-gel synthesis solves the severe capacity decay problem of P2-type Na_2/3Mn_1/2Fe_1/2O₂ by reducing the content of Mn and slowing down the loss of Mn on the surface of the Na_2/3Mn_1/2Fe_1/4Co_1/4O₂, as well as by improving the activity of Fe³⁺ and the stability of Fe⁴⁺ in the electrode. This research is the first to demonstrate the origin of the excellent cycle stability of Na_2/3Mn_1/2Fe_1/4Co_1/4O₂, which may provide a new strategy for the development of electrode materials for use in sodium-ion batteries.     

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.     

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.     

Performance of LiNi1/3Co1/3Mn1/3O2 prepared from spent lithium-ion batteries by a carbonate co-precipitation method

Spherical LiNi_1/3Co_1/3Mn_1/3O₂ cathode particles were resynthesized by a carbonate co-precipitation method using spent lithium-ion batteries (LIBs) as a raw material. The physical characteristics of the Ni_1/3Co_1/3Mn_1/3CO₃ precursor, the (Ni_1/3Co_1/3Mn_1/3)₃O₄ intermediate, and the regenerated LiNi_1/3Co_1/3Mn_1/3O₂ cathode material were investigated by laser particle-size analysis, scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS), thermogravimetry–differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), inductively coupled plasma–atomic emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS). The electrochemical performance of the regenerated LiNi_1/3Co_1/3Mn_1/3O₂ was studied by continuous charge–discharge cycling and cyclic voltammetry. The results indicate that the regenerated Ni_1/3Co_1/3Mn_1/3CO₃ precursor comprises uniform spherical particles with a narrow particle-size distribution. The regenerated LiNi_1/3Co_1/3Mn_1/3O₂ comprises spherical particles similar to those of the Ni_1/3Co_1/3Mn_1/3CO₃ precursor, but with a narrower particle-size distribution. Moreover, it has a well-ordered layered structure and a low degree of cation mixing. The regenerated LiNi_1/3Co_1/3Mn_1/3O₂ shows an initial discharge capacity of 163.5 mA h g^?1 at 0.1 C, between 2.7 and 4.3 V; the discharge capacity at 1 C is 135.1 mA h g^?1, and the capacity retention ratio is 94.1% after 50 cycles. Even at the high rate of 5 C, LiNi_1/3Co_1/3Mn_1/3O₂ delivers the high capacity of 112.6 mA h g^?1. These results demonstrate that the electrochemical performance of the regenerated LiNi_1/3Co_1/3Mn_1/3O₂ is comparable to that of a cathode synthesized from fresh materials by carbonate co-precipitation.     

One-pot dual product synthesis of hierarchical Co3O4@N-rGO for supercapacitors,N-GDs for label-free detection of metal ion and bio-imaging applications

Cobalt oxide nanoparticles@nitrogen-doped reduced graphene oxide (Co₃O₄@N-rGO) composite and nitrogen-doped graphene dots (N-GDs) were synthesized by a one-pot simple hydrothermal method. The average sizes of the synthesized bare cobalt oxide nanoparticles (Co₃O₄ NPs) and Co₃O₄ NPs in the Co₃O₄@N-rGO composite were around 22 and 24 nm, respectively with an interlayer distance of 0.21 nm, as calculated using the XRD patterns. The Co₃O₄@N-rGO electrode exhibits superior capacitive performance with a high capability of about 450 F g^?1 at a current density of 1 A g^?1 and has excellent cyclic stability, even after 1000 cycles of GCD at a current density of 4 A g^?1. The obtained N-GDs exhibited high sensitivity and selectivity towards Fe²⁺ and Fe³⁺, the limit of detection was as low as 1.1 and 1.0 μM, respectively, representing high sensitivity to Fe²⁺ and Fe³⁺. Besides, the N-GDs was applied for bio-imaging. We found that N-GDs were suitable candidates for differential staining applications in yeast cells with good cell permeability and localization with negligible cytotoxicity. Hence, N-GDs may find dual utility as probes for the detection of cellular pools of metal ions (Fe³⁺/Fe²⁺) and also for early detection of opportunistic yeast infections in biological samples.     

Hydrothermal synthesis of reduced graphene oxide-Mn3O4 nanocomposite as an efficient electrode materials for supercapacitors

Mn₃O₄ nanoparticles (NPs) are decorated with reduced graphene oxide nanosheets (rGO-Mn₃O₄) through a facile and eco-friendly hydrothermal method. The as-synthesized composite was characterized by XRD, SEM, TEM and Raman spectroscopy. The electrochemical properties of (rGO-Mn₃O₄) nanocomposite were studied as electrode materials for supercapacitors. The rGO-Mn₃O₄ nanocomposite exhibit high specific capacitance of 457 Fg^?1 at 1.0 A/g in 1 M Na₂SO₄ aqueous electrolyte. The rGO-Mn₃O₄ exhibits good capacitance retention by achieving 91.6% of its initial capacitance after 5000 cycles. The excellent electrochemical performance is attributed to the increased electrode conductivity in the presence of graphene network.     

Porous rod-shaped Co3O4 derived from Co-MOF-74 as high-performance anode materials for lithium ion batteries

Porous rod-shaped Co₃O₄ has been successfully synthesized by one-step thermal annealing of the as-prepared Co-MOF-74 precursor and tested as anode materials for lithium ion batteries. The porous rod-shaped Co₃O₄ is found to be very attractive for lithium-ion batteries. It demonstrates a reversible capacity of 683 mAh/g after 80 cycles at 100 mA/g and an excellent rate performance with high average discharge specific capacities of 1231, 1026, 733 and 502 mAh/g at 50, 100, 200 and 400 mA/g, respectively. The excellent electrochemical performance should be due to the porous structural and composition characteristics.     

AlF3-modified LiCoPO4 for an advanced cathode towards high energy lithium-ion battery

Surface-interface reaction between the electrode and electrolyte plays a key role in lithium-ion storage properties, especially for high voltage cathode such as LiCoPO₄ and Ni-riched cathode. Generally, surface modification is an effective method to improve the electrochemical performance of electrode materials. Herein, in order to revise the LiCoPO₄ cathode with desirable properties, uniform AlF₃-modified LiCoPO₄ (LiCoPO₄@AlF₃) cathode materials in nano-sized distribution are synthesized. XRD result indicates that there is no structural transformation observed after AlF₃ coating. TEM characterization and XPS analysis reveal that the surface of LiCoPO₄ particle is coated by a nano-sized uniform AlF₃ layer. Further, the electrochemical results indicate that AlF₃ layer significantly improves the cycling and rate performances of LiCoPO₄ cathode within the voltage range of 3.0–5.0 V. After a series of optimization, 4 mol% AlF₃-coated LiCoPO₄ material exhibits the best properties including an initial discharge capacity of 159 mA h g^?1 at 0.1 C with 91% capacity retention after 50 cycles, especially a discharge capacity of 90 mA h g^?1 can be obtained at 1 C rate. CV curves indicate that the polarization of cathode is reduced by AlF₃ layer and EIS curves reveal that AlF₃ layer relieves the increase of resistance to facilitate Li-ion transfer at the interface between electrode and electrolyte during the cycling process. The enhanced electrochemical performances are attributed to that the AlF₃ layer can stabilize the interface between the cathode and electrolyte, form steady SEI film and suppress the electrolyte continuous decomposition at 5 V high voltages. This feasible strategy and novel characteristics of LiCoPO₄@AlF₃ could promise the prospective applications in the stat-art of special lithium-ion battery with high energy and/or power density.     

Nano-sized over-lithiated oxide by a mechano-chemical activation-assisted microwave technique as cathode material for lithium ion batteries and its electrochemical performance

Over-lithiated oxide has been attracting enormous attention due to its high work voltage and high specific capacity. However, the bottlenecks of low initial coulombic efficiency and voltage decay block its industrial application. In this paper, nano-sized Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ was successfully synthesized by a mechano-chemical activation-assisted microwave technique, in which Mn-Co-Ni-based micro spherical precursor by conventional co-precipitation method was ball milled with Li₂CO₃ as lithium source and alcohol as dispersant into nano size and then sintered by microwave to obtain the final product. The as-prepared sample sintered for 30 min exhibited a superior electrochemical performance: almost no capacity fading after 100 cycles at 0.1 C. The rate performance was also improved significantly and the one sintered for 30 min delivered a discharge capacity of 239, 228, 215, 193 mA h g^?1 at 0.1 C, 0.2 C, 0.5 C and 1 C respectively. The distinctive electrochemical performance benefits from the uniform nano-sized particle distribution and good electrode kinetics. It is concluded that such mechano-chemical activation-assisted microwave technique featuring high time and energy efficiency can be considered as one of the dominant routes to realize the industrialization of over-lithiated oxide.     

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.     

Comparison of lithium nickel cobalt oxides synthesized from NiO,Co3O4, and LiOH·H2O or Li2CO3 by solid-state reaction method

LiNi_1?yCo_yO₂ (y = 0.1, 0.3 and 0.5) cathode materials were synthesized by the solid-state reaction method at different temperatures from LiOH·H₂O, NiO and Co₃O₄ and from Li₂CO₃, NiO and Co₃O₄ as the starting materials. The physical and electrochemical properties of the synthesized samples were then compared. Among LiNi_1?yCo_yO₂ (y = 0.1, 0.3 and 0.5) synthesized for 40 h from LiOH·H₂O, NiO and Co₃O₄, and from Li₂CO₃, NiO and Co₃O₄, LiNi_0.5Co_0.5O₂ synthesized from Li₂CO₃, NiO and Co₃O₄ at 800 °C has relatively large first discharge capacity and relatively good cycling performance. This sample is considered the best one with relatively good electrochemical properties.     

Synthesis of LiNi1/3Mn1/3Co1/3O2@graphene for lithium-ion batteries via self-assembled polyelectrolyte layers

LiNi_1/3Co_1/3Mn_1/3O₂ cathode coated with a thin layer of graphene (~8 nm) is successfully synthesized by self-assembly and pyrolysis of polyelectrolyte layers on the surface of NMC particles. The graphene coated NMCs still possess a layered structure with good crystallinity and demonstrate a superior electrochemical performance (e.g., rate capability and cycling stability). The best graphene coated NMC cathode is prepared at a calcination temperature of 800 °C, exhibiting a capacity retention of ~90% vs. 78% for pristine NMC @ cycle 100 and 1 C rate. The improvement in cycling performance is further enlarged after 500 cycles (74% vs. 51%). This can be attributed to the dual functions of graphene coating in enhancing electronic conductivity and protecting NMC surface from the contact with electrolyte during the electrochemical reaction.     

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.     

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.     

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.     

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).     

Nano-structured birnessite prepared by electrochemical activation of manganese(III)-based oxides for aqueous supercapacitors

Powdery Mn₃O₄ and Mn₂O₃ electrodes with carbon and binding polymer were electrochemically stimulated and activated by successive potential cycles in a mild aqueous electrolyte containing alkali sulfate. The activation of the manganese oxides is affected by the electrode material, milling treatment, potential region, and electrolyte solution. It is found that the ball-milled Mn₃O₄ electrode demonstrated the highest specific capacitance, 190 F g^?1, in 1 mol dm^?3 Na₂SO₄ aqueous solution due to the phase transition from Mn₃O₄ to electrochemically active birnessite, Na_yMnO₂·nH₂O. The increase in capacitance originated from the formation of birnessite possessing highly porous morphology. The nano-structured birnessite demonstrated long cycle life of about 2000 cycles with acceptable capacitance retention of 190–160 F g^?1. The birnessite was applied as positive electrode of the asymmetric electrochemical capacitor with activated carbon negative electrode in the mild aqueous solution.     

Honeycomb-like NiCo2O4@Ni(OH)2 supported on 3D N−doped graphene/carbon nanotubes sponge as an high performance electrode for Supercapacitor

In order to increase the energy density of supercapacitor, a new kind electrode material with excellent structure and outstanding electrochemical performance is highly desired. In this article, a new type of three-dimensional (3D) nitrogen-doped single-wall carbon nanotubes (SWNTs)/graphene elastic sponge (TRGN?CNTs?S) with low density of 0.8 mg cm^?3 has been successfully prepared by pyrolyzing SWNTs and GO coated commercial polyurethane (PU) sponge. In addition, high performance electrode of the honeycomb-like NiCo₂O₄@Ni(OH)₂/TRGN-CNTs-S with core-shell structure has been successfully fabricated through hydrothermal method and then by annealing treatment and electrochemical deposition method, respectively. Benefited from 3D structural feature, the compressed NiCo₂O₄@Ni(OH)₂/TRGN-CNTs-S electrode exhibits high gravimetric and volumetric capacitance of 1810 F g^?1, 847.7 F cm^?3 at 1 A g^?1. The high rate performance and long-term stability was also obtained. Furthermore, an asymmetric supercapacitor using NiCo₂O₄@Ni(OH)₂/TRGN-CNTs-S cathode and NGN/CNTs anode delivered high gravimetric and volumetric energy density of 54 W h kg^?1 at 799.9 W kg^?1 and 37 W h L^?1 at 561.5 W L^?1. In summary, an excellent electrochemical electrode with new elastic 3D SWNTs/graphene supports and binder free pseudocapacitive materials was introduced.