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.     

A novel dendritic crystal Co3O4 as high-performance anode materials for lithium-ion batteries

The spinel-type Co₃O₄ with a dendritic nanostructure is prepared via homogeneous co-precipitation method in the presence of oxalic as complex agent. The special structure was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis, which show that the precursor can be transformed into dendritic crystal Co₃O₄ by calcining at 500 °C for 2 h with a diameter of 20–50 nm. Such a three-dimensional interconnected structure used as an anode material for lithium-ion batteries shows that the discharge specific capacity still remains at 951.7 mA h g^?1 after 100 cycles at a current density of 100 mA g^?1. Furthermore, this material also presents a good rate performance; when the current density increases to 1,000, 4,000, and 8,000 mA g^?1, the reversible capacity can render about 1,126.2, 932.3, and 344.2 mA h g^?1, respectively. The excellent electrochemical performance is mainly attributed to the dendritic nanostructure composed of interconnected Co₃O₄ nanoparticles.     

Porous Co3O4 nanorods as superior electrode material for supercapacitors and rechargeable Li-ion batteries

Porous aggregated nanorods of Co₃O₄ with a surface area of ~100 m² g^?1 synthesized without using any templates or surfactants give very high specific capacitance of ~780 F g^?1 when used as electrode in a faradaic supercapacitor, with a cycle life of more than 1,000 cycles. Further, in Li-ion batteries when used as an anode, the Co₃O₄ nanorods achieved a capacity of 1155 mA h g^?1 in the first cycle and upon further cycling it is stabilized at 820 mA h g^?1 for more than 25 cycles. Detailed characterization indicated the stability of the material and the improved performance is attributed to the shorter Li-insertion/desertion pathways offered by the highly porous nanostructures. The environmentally benign and easily scalable method of synthesis of the porous Co₃O₄ nanorods coupled with the superior electrode characteristics in supercapacitors and Li-ion batteries provide efficient energy storage capabilities with promising applications.     

Nanorod-like Fe2O3/graphene composite as a high-performance anode material for lithium ion batteries

In this study, a nanorod-like Fe₂O₃/graphene nanocomposite is synthesized by a facile template-free hydrothermal method and a following calcination in air at 300 °C for 2 h. The Fe₂O₃ nanorods with diameter of 15–30 nm and length of 120–300 nm are homogenous distributed on both sides of graphene. The morphologies of intermediates at different hydrothermal reaction times are investigated by transmission electron microscopy (TEM) characterization, and a possible growth mechanism of this one-dimensional structure is proposed. It is shown that the α-FeOOH rodlike precursors are formed through a rolling-broken-growth (RBG) model, then the α-FeOOH is transformed into α-Fe₂O₃ nanorods during calcinations, preserving the same rodlike morphology. Electrochemical characterizations demonstrate that the Fe₂O₃ nanorod/graphene composites exhibit a very large reversible capacity of 1063.2 mAh/g at the charge/discharge rate of 0.1 C.     

Lithium zirconate coated LiNi0.8Co0.15Al0.05O2 as a high-performance electrode material for advanced fuel cells

Surface modification of electrode materials could effectively enhance catalytic activity and stability for low temperature solid oxide fuel cells. In this paper, LiNi_0.8Co_0.15Al_0.05O₂ (NCAL), material with 1 wt % Li₂ZrO₃ (LZO) surface coating were successfully synthesized by a simple wet chemical method. The crystal structure, surface morphology and electrochemical properties of the modified NCAL materials were investigated by X-ray diffraction, scanning electron microscopy and photoelectron spectroscopy. The obtained results showed that the NCAL coated with LZO exhibited superior electrochemical performance. According to the EIS results, the polarization resistance of the 1 wt % LZO-modified NCAL based fuel cell at 550 °C was only 0.303 Ω cm², respectively, which were much lower than pure NCAL (1.33 Ω cm²). The results show that the LZO surfaced coated NCAL could be a promising anode material towards high-performance advanced fuel cells.Combined with XRD and XPS analysis, it can be inferred that: the surface modification of LZO did not affect the structure of the raw material, and during the test, LZO enabled the effective distribution of the oxygen vacancies on the surface of the material, which accelerated the catalytic activity of the electrode during the discharge process.     

溶胶凝胶法制备锂离子电池负极材料ZnMn_2O_4

采用溶胶凝胶法合成出锂离子电池用Zn Mn2O4负极材料,并用XRD,SEM和电化学性能测试对材料进行了表征。实验结果表明,随着焙烧温度与时间升高,晶体结晶更好。在焙烧温度达到800℃,焙烧时间为12 h时,能够形成单一四方相尖晶石结构的Zn Mn2O4粉体,结晶良好,当焙烧温度和时间继续升高,颗粒会出现较大的团聚体;将所制备的Zn Mn2O4粉体组装成扣式电池进行电化学测试的结果表明,800℃焙烧12 h的样品具有较好的电化学性能。首次充放电比容量分别为1096 m Ah·g-1和1310 m Ah·g-1,库伦效率为83.66%。有望成为锂离子电池石墨负极替代材料。     

Electrochemical preparation and properties of nanostructured Co3O4 as supercapacitor material

Nanostructured Co₃O₄ was prepared via a simple two-step process: cathodic electrodeposition of cobalt hydroxide from additive free nitrate bath and then heat treatment at 400 °C for 3 h. The prepared oxide product was characterized by powder X-ray diffraction, infrared spectroscopy, surface area measurement, scanning electron microscopy, and transmission electron microscopy. Morphological characterization showed that the oxide product was composed of porous nanoplates, and BET measurement displayed that the oxide plates have the average pore diameter and the surface area of 4.75 nm and 208.5 m² g⁻¹, respectively. The supercapacitive performance of the nanoplates was evaluated using cyclic voltammetry and charge–discharge tests. A specific capacitance as high as 393.6 F g⁻¹ at the constant current density of 1 A g⁻¹ and an excellent capacity retention (96.5% after 500 charge–discharge cycles) was obtained. These results indicate that Co₃O₄ nanoplates can be recognized as high-performance electrode materials.     

Facile synthesis of Ni0.5Mn0.5Co2O4 nanoflowers as high-performance electrode material for supercapacitors

The rational synthesis of mixed transition metal oxides (MTMOs) with three-dimensional hierarchical porous structure has been proved to be an effective strategy for improving electrochemical performances of binary metal oxides. Herein, the hierarchically Ni_1-xMn_xCo₂O₄ nanoflowers are synthesized by a facile hydrothermal method combined with subsequent heat-treatment. It is found that Ni/Mn atom ratio has a significant influence on the microstructures and electrochemical properties of Ni_1-xMn_xCo₂O₄. The Ni_0.5Mn_0.5Co₂O₄ sample with a Ni/Mn atom ratio of 1 exhibits the highest specific capacity of 366 F/g at a current density of 1 A/g as compared to the other Ni_1-xMn_xCo₂O₄ samples. In addition, Ni_0.5Mn_0.5Co₂O₄ displays high rate capability and cycling performance. The excellent electrochemical performances of Ni_0.5Mn_0.5Co₂O₄ could be ascribed to the large surface area and high mesoporosity, leading to the increased accessible surface for ion access and the rapid electrochemical reactions. The as-synthesized Ni_0.5Mn_0.5Co₂O₄ nanoflowers could be used as a potential electrode materials for Supercapacitors. Furthermore, this study provides a facile method to synthesize other MTMOs with three-dimensional hierarchical nanostructure. An asymmetric supercapacitor is assembled with Ni_0.5Mn_0.5Co₂O₄ as the positive electrode and activated carbon as the negative electrode. The supercapacitor shows an energy density of 20.2 Wh/kg at a power density of 700 W/kg. Cycling stability is achieved with 82% retention after 5000 charge-discharge cycles.     

Fabrication of CuFe2O4@g-C3N4@GNPs nanocomposites as anode material for supercapacitor applications

The aim of this study was to synthesize CuFe₂O₄ together with g-C₃N₄ and GNPs in various combinations on the surface of Ni foam for use as anode materials in supercapacitors. The fabricated electrodes were investigated by XRD, FTIR, XPS, BET, SEM and TEM for content and by CV, GCD and EIS analysis for electrochemistry. The characterization results showed that CuFe₂O₄ was successfully synthesized together with g-C₃N₄ and GNPs in a nanosponge-like geometry. The highest value of specific capacitance was found to be 989 mF/cm² at 2 mA measurement in the triple combination. Moreover, the stability of this electrode was measured to be 70% after 1500 cycles at 16 mA, while the energy and power densities were calculated to be 27.8 mWh/cm² and 300 mW/cm², respectively. The EIS results show that the carbon-based component increased the Cs value by decreasing the charge transfer and diffusion resistances of the electrodes. Compared to its counterparts in the literature, its Cs value is quite high, but its stability is low, so it can be used in low-cycle applications.     

Graphene nanosheet and carbon layer co-decorated Li4Ti5O12 as high-performance anode material for rechargeable lithium-ion batteries

In this study, we report a facile strategy for anchoring Li₄Ti₅O₁₂ (LTO) particles wrapped within carbon shells onto graphene nanosheet (GNS) using the freeze-drying assisted microwave irradiation method. In this designed structure, a conductive three-dimensional network can be formed by connecting the GNS and carbon layer which is benefit for the transport of electron and Li⁺-ion. When used as anode material for lithium-ion batteries, this hybrid composite exhibits an excellent high-rate performance with specific capacities of 171.5, 168.2, 160.1, 151.7 and 136.4 mAh g⁻¹ at various current rates of 1, 2, 5, 10 and 20 C, respectively. Furthermore, the specific capacity of the obtained anode still retains 99.6% of the initial value after 20 cycles at 20 C. The enhanced battery performance can be attributed to the improved electronic conductivity of each LTO grain via uniform carbon coating and GNS wrapping. As a consequence, this novel strategy developed in this study may open a new way to fabricate other electrodes for advanced renewable energy conversion and storage applications.     

Hydrazine hydrate-induced hydrothermal synthesis of MnFe2O4 nanoparticles dispersed on graphene as high-performance anode material for lithium ion batteries

Herein, a MnFe₂O₄/graphene (MnFe₂O₄/G) nanocomposite has been synthesized via a facile N₂H₄·H₂O-induced hydrothermal method. During the synthesis, N₂H₄·H₂O is employed to not only reduce graphene oxide to graphene, but also prevent the oxidation of Mn²⁺ in alkaline aqueous solution, thus ensuring the formation of MnFe₂O₄/G. Moreover, MnFe₂O₄ nanoparticles (5–20 nm) are uniformly anchored on graphene. MnFe₂O₄/G electrode delivers a large reversible capacity of 768 mA h g⁻¹ at 1 A g⁻¹ after 200 cycles and high rate capability of 517 mA h g⁻¹ at 5 A g⁻¹. MnFe₂O₄/G holds great promise as anode material in practical applications due to the outstanding electrochemical performance combined with the facile synthesis strategy.     

In-situ synthesis of reduced graphene oxide wrapped Mn3O4 nanocomposite as anode materials for high-performance lithium-ion batteries

We report a novel in-situ symbiosis method to prepare reduced graphene oxide wrapped Mn₃O₄ nanoparticles (rGO/Mn₃O₄) with uniform size about 50 nm as anodes for lithium-ion batteries (LIBs), which can simplify the preparation process and effectively reduce pollution. The rGO/Mn₃O₄ nanocomposite exhibited a reversible specific capacity of 795.5 mAh g^?1 at 100 mA g^?1 after 200 cycles (capacity retention: 87.4%), which benefits from the unique structural advantages and the synergistic effect of rGO and Mn₃O₄. The Mn₃O₄ nanoparticles encapsulated among the rGO nanosheets exhibited good electrochemical activity, and the multilayer wrinkled rGO sheets provided a stable 3D conduction channel for Li⁺/e^? transport. The rGO/Mn₃O₄ nanocomposite is a promising anode candidate for advanced LIBs with excellent cycling performance and rate performance. Furthermore, this new preparation method can be extended to green and economical synthesis of advanced graphene/manganese-based nanocomposites.     

Fe3O4 nanoparticles encapsulated in electrospun porous carbon fibers with a compact shell as high-performance anode for lithium ion batteries

Fe₃O₄ nanoparticles encapsulated in porous carbon fibers (Fe₃O₄@PCFs) as anode materials in lithium ion batteries are fabricated by a facile single-nozzle electrospinning technique followed by heat treatment. A mixed solution of polyacrylonitrile (PAN) and polystyrene (PS) containing Fe₃O₄ nanoparticles is utilized to prepare hybrid precursor fibers of Fe₃O₄@PS/PAN. The resulted porous Fe₃O₄/carbon hybrid fibers composed of compact carbon shell and Fe₃O₄-embeded honeycomb-like carbon core are formed due to the thermal decomposition of PS and PAN. The Fe₃O₄@PCF composite demonstrates an initial reversible capacity of 1015 mAh g⁻¹ with 84.4% capacity retention after 80 cycles at a current density of 0.2 A g⁻¹. This electrode also exhibits superior rate capability with current density increasing from 0.1 to 2.0 A g⁻¹, and capacity retention of 91% after 200 cycles at 2.0 A g⁻¹. The exceptionally high performances are attributed to the high electric conductivity and structural stability of the porous carbon fibers with unique structure, which not only buffers the volume change of Fe₃O₄ with the internal space, but also acts as high-efficient transport pathways for ions and electrons. Furthermore, the compact carbon shell can promote the formation of stable solid electrolyte interphase on the fiber surface.     

Structural and electrochemical characteristics of Li4/3Ti5/3O4 as an anode material for rechargeable lithium batteries

Li_4/3Ti_5/3O₄ is a good anode material for rechargeable lithium batteries. This material exhibits characteristic properties, including very flat discharge and charge curves and an infinitesimal structural change during discharge and charge. In this study the structural behaviour was confirmed by the Rietveld analysis of X-ray diffraction patterns: in situ UV–visible spectroscopy of Li_4/3Ti_5/3O₄ during discharge was also performed to observe the electronic structure change induced by lithium insertion. The Rietveld analysis clearly showed that no structural change could be detected during the lithium insertion and extraction processes. The UV–vis. spectroscopy revealed that the insertion of lithium into Li_4/3Ti_5/3O₄ results in the formation of a new phase with the same lattice constant. These results indicate that the insertion and extraction of lithium into and from Li_4/3Ti_5/3O₄ proceed via two-phase reactions, while the lattice parameter is the same as that of Li_4/3Ti_5/3O₄ with lithium insertion.     

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.     

Properties of Li4Ti5O12 as an anode material in non-flammable electrolytes

Two non-flammable electrolytes 1 M LiPF₆ in sulfolane (TMS) + 5 wt% VC and 0.7 M lithium bis(trifluoromethanesulphonyl)imide (LiNTf₂) in N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulphonyl)imide (MePrPyrNTf₂) + 10 wt% gamma-butyrolactone (GBL) were tested with Li₄Ti₅O₁₂ (LTO) as highly promising anode material for application in lithium-ion batteries. The results were compared for the titanium anode in the classic electrolyte: 1 M LiPF₆ in propylene carbonate + dimethyl carbonate (PC + DMC, 1:1). The performances of LTO/electrolyte/Li cell were tested using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge and scanning electron microscopy (SEM). SEM images of electrodes and those taken after electrochemical cycling showed changes which may be interpreted as a result of solid-state interface formation. Good charge/discharge capacities and low capacity loss at medium C rates preliminary cycling was obtained for the Li₄Ti₅O₁₂ anode. For LTO/1 M LiPF₆ in PC + DMC/Li system, the best capacity was obtained at C/10 and C/3 (145 and 154 mAh g^?1, respectively). In the case of a system working on the basis of a TMS solution (1 M LiPF₆ in TMS + 5 wt% VC) the best value was obtained at a C/5 current and an average of more than 150 mAh g^?1 (86 % of theoretical capacity). For the 0.7 M LiNTf₂ in MePrPyrNTf₂ + 10 wt% GBL electrolyte, the highest capacitance value (at C/20 current) of about 150 mAh g^?1 was observed. The 1 M LiPF₆ in TMS + 5 wt% VC and 0.7 M LiNTf₂ in MePrPyrNTf₂ + 10 wt% GBL electrolytes had a relatively broad thermal stability range and no decomposition peak was observed below 150 °C.     

Preparation of high-performance Ca3Co4O9 thermoelectric ceramics produced by a new two-step method

High-performance Ca₃Co₄O₉ thermoelectric ceramic has been prepared from a Ca_1?xCo_xO/Ca_yCo_1?yO divorced eutectic structure produced by a directional melt-grown using the laser floating zone technique. This material has been grown at very high solidification rate in order to produce a very fine microstructure to reduce the necessary annealing time to recover the Ca₃Co₄O₉ thermoelectric phase as the major one. As-grown and annealed samples were microstructurally characterized to determine the phases and estimate the extent of Ca₃Co₄O₉ formation with time and related with their thermoelectric performances. The optimum annealing time, 72 h, has been determined by the maximum power factor value (about 0.42 mW K^?2m^?1), which is around the best values reported in textured materials (～0.40 mW K^?2m^?1). This high power factor outcome from the high Ca₃Co₄O₉ phase content, apparent density and Co³⁺/Co⁴⁺ relationship determinations performed in the present work.     

Comparison between unsupported mesoporous Co3O4 and supported Co3O4 on mesoporous silica as catalysts for N2O decomposition

Mesoporous Co₃O₄ (meso-Co₃O₄) and Co₃O₄ nanoparticles supported on mesoporous silica SBA-15 (Co/SBA-15) were prepared by hydrothermal synthesis and an impregnation method, respectively. Although the as-prepared meso-Co₃O₄ had mesopores and a higher surface area comparable to that of Co/SBA-15, its catalytic activity for N₂O decomposition was much lower than that of Co₃O₄/SBA-15. The low catalytic activity of meso-Co₃O₄ mainly stems from the drastic decrease of the meso-Co₃O₄ surface area under the reaction condition used. On the other hand, Co/SBA-15 maintained its high surface area and mesopores with the aid of a robust silica support. This finding indicates that Co₃O₄ supported by a support is much more stable and efficient than meso-Co₃O₄ under N₂O decomposition reaction conditions.     

One-step synthesis of Li-doped NiO as high-performance anode material for lithium ion batteries

The poor electronic conductivity and huge volume expansion of NiO are the vital barriers when used as anode for lithium ion batteries. In order to solve above issues, Li-doped NiO are prepared by a facile one-step ultrasonic spray pyrolysis method. The effects of Li doping on the morphology, structure and chemical composition of the Li-doped NiO powders are extensively studied. When used as lithium ion batteries anode, it is demonstrated that the doping of Li has significant positive effect on improving the electrochemical performance. After 100 cycles at 400 mA g⁻¹, The Li-doped NiO samples deliver a discharge capacity of 907 mAh g⁻¹, much more than that of un-doped sample (736 mAh g⁻¹). The improved electrochemical performances can be ascribed to the improved p-type conductivity and lower impedance, which are confirmed by Rietveld refinement, X-ray photoelectron spectroscopy and electron impedance spectroscopy.     

Polydopamine-assisted formation of Co3O4-nanocube-anchored reduced graphene oxide composite for high-performance supercapacitors

Tailoring transition-metal oxide nanoparticles with two-dimensional carbon has become a favorite way to improve their electrochemical performance. In this study, a composite of reduced graphene oxide was anchored by Co₃O₄ nanocubes and easily prepared with the assistance of polydopamine (PDA), using a combination of hydrothermal reaction and pyrolysis (Co₃O₄@PDA-rGO). Polydopamine, which possesses abundant catechol and amine groups, could be easily grafted onto graphene oxide to reduce the aggregation of graphene particles. Furthermore, PDA provided active sites, i.e., catechol and amine groups, which coordinated with Co²⁺, enabling enrichment of metal ions on the surface of graphene. After the pyrolysis of Co²⁺-containing PDA-grafted graphene at 400 °C, the Co²⁺ ions were converted into Co₃O₄ nanocubes, while the PDA carbonized to form N-doped porous carbon on the surface of graphene. The resulting product, Co₃O₄@PDA-rGO, demonstrated extraordinary supercapacitive behavior with good cycling stability owing to its unique porous structure as well as the intimate contact between Co₃O₄ and the carbon matrix.