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.     

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.     

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.     

Hierarchical Li4Ti5O12 nanosheet arrays anchoring on carbon fiber cloth as ultra-stable free-standing anode of Li-ion battery

A flexible, free-standing composite anode with Li₄Ti₅O₁₂ nanosheet arrays anchoring on plain-weaved carbon fiber cloth (LTO@CC) is prepared by a hydrothermal and post-annealing process assisted by a TiO₂ seed layer. The LTO@CC anode free from polymeric binder and conducting agent exhibited much higher lithium storage capacity and cycling stability than the conventional slurry-processed electrode using the dandelion-like Li₄Ti₅O₁₂ microspheres prepared by the same hydrothermal process. A high specific capacity of 128.8 mA h g^?1 was obtained at a current rate of 30 C (1 C = 175 mA g^?1), and almost negligible capacity loses was observed when the cell was cycled at 10, 20 and 30 C each for 100 cycles. The carbon fiber matrix contributed to Li storage at low current rate, but the LTO nanosheet arrays have played the dominant role on the excellent rate capability. The improved electrochemical performance can be attributed to the synergetic effect between the hierarchical Li₄Ti₅O₁₂ nanosheet arrays and the carbon fiber matrix, which integrated short Li⁺ diffusion length, three-dimensional conductive architecture and well preserved structural integrity during the high rate and repeated charge-discharge measurements.     

LaF3 nanolayer surface modified spinel LiNi0.5Mn1.5O4 cathode material for advanced lithium-ion batteries

As an attractive high power-density cathode material for lithium-ion batteries, spinel-structured LiNi_0.5Mn_1.5O₄ (LNMO) so far still suffers fast capacity decay during repeated cycling due to transition metal (TM) dissolution and structure degradation. In this work, a thin nanolayer of LaF₃ is applied to modify the surface of LNMO. Electrochemical and thermal tests indicate that 4 wt% LaF₃ surface modification could greatly improve the electrode performances in terms of cycling stability and rate capability as well as thermal stability of LNMO compared with the pristine electrode, without influencing the crystallographic structure of bulk material. Further analysis for understanding the intrinsic mechanism reveals that the growth of solid electrolyte interface (SEI) film could be effectively suppressed by the surface LaF₃ nanolayer, which meanwhile stabilizes the bulk structure through retarding continuous TM dissolution from intensive chemical aging measurements at elevated temperature. This work, theoretically and technically, provides a promising alternative approach for enhancing electrochemical performances of high voltage LNMO cathode material.     

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.     

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.     

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.     

Liquid-phase synthesis of SrCo0.9Nb0.1O3-δ cathode material for proton-conducting solid oxide fuel cells

A novel liquid-phase synthesis strategy is demonstrated for the preparation of the Nb-containing ceramic oxide SrCo_0.9Nb_0.1O_3-δ (SCN). In comparison with the traditional solid-state reaction (SSR) method, the liquid-phase synthesis route offers a couple of advantages, including a lower phase formation temperature and a smaller particle size of the SCN materials that are beneficial for applications as proton-conducting fuel cell cathode. With BaCe_0.4Zr_0.4Y_0.2O_3-δ (BCZY442) as the electrolyte and the SCN synthesized in this work as the cathode, a proton-conducting solid oxide fuel cell (SOFC) shows a peak power density of 348 mW cm^?2 at 700 °C, significantly higher than that of a SOFC fabricated with SCN cathode prepared using the SSR method, which can only deliver 204 mW cm^?2 at the same temperature. Additionally, this new synthesis strategy allows impregnation of Sr²⁺, Co³⁺and Nb⁵⁺ on the solid backbone in aqueous solution, further improving cell performance to reach a peak power density of 488 mW cm^?2 at 700 °C.     

Studies on spinel cobaltites,MCo2O4 (M = Mn,Zn, Fe,Ni and Co) and their functional properties

Optimization of electrodes for charge storage with appropriate processing conditions places significant challenges in the developments for high performance charge storage devices. In this article, metal cobaltite spinels of formula MCo₂O₄ (where M = Mn, Zn, Fe, Ni and Co) are synthesized by oxalate decomposition method followed by calcination at three typical temperatures, viz. 350, 550, and 750 °C and examined their performance variation when used as anodes in lithium ion batteries. Phase and structure of the materials are studied by powder x-ray diffraction (XRD) technique. Single phase MnCo2O4,ZnCo2O4 and Co3O4 are obtained for all different temperatures 350 °C, 550 °C and 750 °C; whereas FeCo₂O₄ and NiCo₂O₄ contained their constituent binary phases even after repeated calcination. Morphologies of the materials are studied via scanning electron microscopy (SEM): needle-shaped particles of MnCo₂O₄ and ZnCo₂O₄, submicron sized particles of FeCo₂O₄ and agglomerated submicron particle of NiCo₂O₄ are observed. Galvanostatic cycling has been conducted in the voltage range 0.005–3.0 V vs. Li at a current density of 60 mA g^?1 up to 50 cycles to study their Li storage capabilities. Highest observed charge capacities are: MnCo₂O₄ – 365 mA h g^?1 (750 °C); ZnCo₂O₄ – 516 mA h g^?1 (550 °C); FeCo₂O₄ – 480 mA h g^?1 (550 °C); NiCo₂O₄ – 384 mA h g^?1 (750 °C); and Co₃O₄ – 675 mA h g^?1 (350 °C). The Co₃O₄ showed the highest reversible capacity of 675 mA h g^?1; the NiO present in NiCo₂O₄ acts as a buffer layer that results in improved cycling stability; the ZnCo₂O₄ with long needle-like shows good cycling stability.     

Enhanced electrochemical properties of LiFePO4–silicon composites as positive electrode materials fabricated using a solid-state method

LiFePO₄–silicon composites were fabricated by using a solid-state method for applying positive electrodes in lithium ion batteries. The LiFePO₄–silicon composites were characterized with X-ray diffraction and field emission scanning electron microscopy. Their electrochemical properties were investigated with cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge tests. The added silicon not only suppressed the surface corrosion caused by the decreasing H⁺ concentration in the electrolyte, but it also acted as a barrier between the LiFePO₄ particles and LiPF₆ electrolyte, thereby preventing the dissolution of Fe²⁺ in the electrode and enhancing the electrolyte/active material interactions. This resulted in improved lithium-ion transfer kinetics and excellent positive electrode performance, especially at high current densities and different operating temperatures (0, 25, and 50 °C). At 25 °C, the LiFePO₄ composite containing 2 wt% of silicon delivered the best electrochemical performance with a lithium-ion diffusion coefficient of 1.81×10⁻⁹ cm² s⁻¹, a specific discharge capacity of 143 mA h g⁻¹ for the initial cycle, and a capacity retention of 98% after 100 cycles. In contrast, the corresponding values for the pure LiFePO₄ were 1.19×10⁻¹¹ cm² s⁻¹, 115 mA h g⁻¹, and a capacity retention of 76% after 100 cycles, respectively.     

Improved cyclic performances of LiCoPO4/C cathode materials for high-cell-potential lithium-ion batteries with thiophene as an electrolyte additive

LiCoPO₄/C composites were synthesized through a sol–gel route, followed by thermal treatment. X-ray diffraction patterns demonstrate the phase formation of LiCoPO₄. Scanning electron microscopy and transmission electron microscopy show the network structure of LiCoPO₄/C composites with the grain size ranging from 240 to 350 nm. For the electrochemical measurements of LiCoPO₄/C composites in Li test cells, thiophene was added as an electrolyte additive. After 30 cycles, the discharge capacity of LiCoPO₄/C composites was 92.8 mAh g^?1 with 68% capacity retention; the improved cyclic performance was attributed to the combination of the network structure LiCoPO₄/C composites and the thiophene addition to the electrolyte.     

CeF3-modified LiNi1/3Co1/3Mn1/3O2 cathode material for high-voltage Li-ion batteries

A facile chemical deposition method has been adopted to prepare cerium fluoride (CeF₃) surface modified LiNi_1/3Co_1/3Mn_1/3O₂ as cathode material for lithium-ion batteries. Structure analyses reveal that the surface of LiNi_1/3Co_1/3Mn_1/3O₂ particles is uniformly coated by CeF₃. Electrochemical tests indicate that the optimal CeF₃ content is 1 wt%. The 1 wt% CeF₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ can deliver a discharge capacity of 107.1 mA h g⁻¹ even at 5 C rate, while the pristine does only 57.3 mA h g⁻¹. Compared to the pristine, the 1 wt% CeF₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ exhibits the greatly enhanced capacity and cycling stability in the voltage range of 3.0–4.5 V, which suggests that the CeF₃ coating has the positive effect on the high-voltage application of LiNi_1/3Co_1/3Mn_1/3O₂. According to the analyses from electrochemical impedance spectra, enhanced electrochemical performance is mainly because the stable CeF₃ coating layer can prevent the HF-containing electrolyte from continuously attacking the LiNi_1/3Co_1/3Mn_1/3O₂ cathode and retard the passivating layer growth on the cathode.     

Electrical behavior of the Ruddlesden–Popper phase, (Nd0.9La0.1)2 Ni0.75Cu0.25O4 (NLNC) and NLNC- x wt% Sm0.2Ce0.8O1.9 (SDC) (x = 10, 30 and 50), as intermediate‐temperature solid oxide fuel cells cathode

In the present work, a new Ruddlesden-Popper phase, (Nd_0.9La_0.1)₂ Ni_0.75Cu_0.25O₄ (NLNC) has been synthesized by solid state reaction for intermediate-temperature solid oxide fuel cells (IT-SOFCs) applications. The effect of sintering temperature on the microstructure and electrical properties of the NLNC cathode material is investigated. Likewise, composite cathode materials were also prepared by mixing the NLNC with 10, 30 and 50 wt% of Sm_0.2Ce_0.8O_1.9 (SDC) powders, and firing in the temperature range of 1000–1300 °C. The crystal structure and chemical compatibility of NLNC and SDC, and their microstructures were studied by XRD and SEM, respectively. Electrical conductivity and performance of monolithic and composite electrodes as a function of the electrode composition is investigated experimentally through four probe method and electrochemical impedance spectroscopy (EIS). The results proved that no reaction occur between NLNC and SDC compounds even at a temperature as high as 1300 °C. Maximum total electrical conductivity of 114.36 S cm^?1 at 500 °C is recorded for the pure NLNC material sintered at 1300 °C. The polarization resistance of pure NLNC cathode was 0.43 Ω cm² at 800 °C; the NLNC–SDC composite cathodes including 10, 30 and 50 wt% SDC displayed Rp value of 0.27 Ω cm², 0.11 Ω cm², and 0.19 Ω cm² at 800 °C, respectively.     

Surfactant-free microwave hydrothermal synthesis of SnO2 nanosheets as an anode material for lithium battery applications

SnO₂ nanosheets were synthesized using microwave hydrothermal method without using a surfactant and organic solvents. Formation of pure nanocrystalline rutile phase of SnO₂ sample was confirmed by X-ray diffraction (XRD) results and the average crystallite size of SnO₂ sample calculated using Scherrer's formula and XRD data is found to be 6 nm. HR-TEM, SAED and EDX results showed the formation of agglomerated nanosize sheets like morphology with high porous structured SnO₂ powder. Further, the formation of high porous structured SnO₂ powder was confirmed from BET surface area results (59.28 m² g^?1). The electrochemical performance of the lithium-ion battery made up of SnO₂ nanosheets, as an anode, was tested through the cyclic voltammetry and galvanostatic charge-discharge measurements. The galvanostatic charge-discharge results of the lithium-ion battery showed good discharge capacity of 257.8 mAh g^?1 after 50 cycles at a current density of 100 mA g^?1. The improved electrochemical properties may be due to the formation of a unique nanosize sheets type morphology with high porous structured SnO₂ powder. High porous structured nanosize sheets type morphology of SnO₂ can help to reduce the diffusion length and sustain the volume changes during the charging-discharging process.Hence, high porous structured nanosize sheets morphology of SnO₂ prepared using the microwave hydrothermal method without using a surfactant and organic solvents can be a better anode material for lithium ion battery applications.     

Efficient construction of a CoCO3/graphene composite anode material for lithium-ion batteries by stirring solvothermal reaction

Transition-metal carbonates have recently been investigated as anode materials for lithium-ion batteries because of their relatively high capacity compared with that of the corresponding transition-metal oxides. In this work, a facile stirring solvothermal reaction is used to prepare a CoCO₃/graphene composite without the use of an additional organic chelating agent. The as-prepared CoCO₃/graphene composite exhibits a smaller cubic particle size of 1–2 µm and a larger specific surface area than the composite obtained by a traditional solvothermal reaction. The composite prepared with stirring delivers a highly reversible capacity of 602 mAh g^?1 after 100 cycles. Even at a high current density of 2.0 A g^?1, the composite maintains charge–discharge capacities of 605/598 mAh g^?1. The composites contained the same amount of graphene, indicating that the improved electrochemical properties are attained independently of the amount of the graphene. In addition, the results of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS)experiments also reveal that the CoCO₃/graphene composite electrode materials synthesised via a stirring solvothermal reaction exhibit substantially enhanced kinetics. The stirring solvo/hydrothermal reaction develops in this work is considered a promising candidate for efficiently preparing carbonate/graphene composites with better electrochemical properties for practical applications, without the use of an extra chelating agent.     

Effect of Ni diffusion into BaZr0.1Ce0.7Y0.1Yb0.1O3−δ electrolyte during high temperature co-sintering in anode-supported solid oxide fuel cells

Diffusion behavior of Ni during high temperature co-sintering was quantitatively investigated for anode-supported solid oxide fuel cells (SOFCs) that had BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3?δ (BZCYYb) proton-conducting electrolyte and NiO-BZCYYb anode. Although diffused Ni in such SOFCs effectively acts as a sintering aid to densify the BZCYYb electrolyte layer, it often negatively affects the electrolyte conductivity. In the present study, field emission electron probe microanalysis (with wavelength dispersive X-ray spectroscopy) clearly revealed that Ni diffused into the BZCYYb electrolyte layer, and that the amount of diffused Ni increased with increasing co-sintering temperature. In particular, relatively high Ni concentration within the electrolyte layer was observed near the electrolyte/anode interface, e.g., approximately 1.5 and 2.8 wt% at co-sintering temperature of 1300 and 1400 °C, respectively. Electrochemical measurements showed that, compared with the lower co-sintering temperatures (1300–1350 °C), the highest co-sintering temperature (1400 °C) led to the highest ohmic resistance because of lower electrolyte conductivity. These results suggest that high co-sintering temperature causes excessive Ni diffusion into the BZCYYb electrolyte layer, thus degrading the intrinsic electrolyte conductivity and consequently degrading the SOFC performance.     

The effect of AlF3 modification on the physicochemical and electrochemical properties of Li-rich layered oxide

Lithium (Li)-rich layered oxides are considered promising cathode materials for Li-ion batteries because of their favorable properties. Here, we report our recent finding in the novel oxide, aluminum fluoride (AlF₃)-modified Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LMNCAF), which was synthesized via a facile, cost-effective and readily scalable solid-state reaction. LMNCAF possess an F and Al co-doped core structure with a LiF nano-coating on its surface which leads to considerably enhancement in the electrochemical performance of the oxide. The initial discharge capacity (at 0.05 C) increased from 212 mA h g⁻¹ for Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ to 291 mA h g⁻¹ for LMNCAF. A much higher discharge capacity of 211 mA h g⁻¹ was obtained for LMNCAF after 99 charge/discharge cycles at 0.2 C compared with that of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (160 mA h g⁻¹). Our preliminary results suggest that AlF₃ modification is an effective strategy to tailor the physicochemical and electrochemical properties of Li-rich layered oxides.     

Evaluation of supercapacitive and magnetic properties of Fe3O4 nano-particles electrochemically doped with dysprosium cations: Development of a novel iron-based electrode

In this research, a novel one-pot fabrication platform was developed for the preparation of Dy³⁺-doped iron oxide nanoparticles (Dy-IONPs). In the procedure, Dy-IONPs are electro-deposited from an additive-free aqueous mixed solution of iron(III) nitrate, iron(II) chloride and dysprosium chloride salts through applying a current density of 10 mA cm^–2 for 30 min. The analytical data obtained from X-ray diffraction (XRD), field emission electron microscopy (FE-SEM) and energy-dispersive X-ray (EDX) confirmed the deposited Dy-IONPs to be composed of magnetite nanoparticles (size≈20 nm) containing about 10 wt% of Dy³⁺ cations as the doping agent. The electrochemical data obtained through galvanostatic charge-discharge (GCD) tests showed that Dy-IONPs provide specific capacitances values of as high as 202 and 111 F g^?1at the discharge loads of 0.5 and 5 A g^?1, respectively, and reveal capacity retentions of 93.9% and 77.2% after 2000 GCD cycling. These could be held as proof that the electro-synthesized Dy³⁺-doped Fe₃O₄ NPs are suitable candidates for use in supercapacitors. Furthermore, the results of vibrating sample magnetometer (VSM) measurements indicated better superparamagnetic behavior of the Dy-IONPs (Mr = 0.34 emu g^–1 and H_Ci= 6.25 G) as opposed to pure IONPs (Mr = 0.95 emu g^–1 and H_Ci= 14.62 G), which originates from their lower Mr and Hci values. Based on the results, the proposed electro-synthesis method offers a facile procedure for the preparation of high- performance metal-ion-doped IONPs.     

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.