Facile synthesis and electrochemical properties of Co–S composites as negative materials for alkaline rechargeable batteries

A series of novel Co–S composites composed of metallic Co and Co₉S₈ were prepared via a facile hydrothermal method and investigated as negative electrodes for secondary alkaline batteries. Instrumental analyses reveal that the incorporation of Co₉S₈ nanoflakes leads to better dispersion of Co particles and increases the interspacing between Co particles, greatly increasing the Brunauer–Emmett–Teller (BET) surface area. Thus, the electrochemical performance of the Co electrode is significantly improved. The maximum discharge capacity of the Co–S electrode reaches 420 mAh g⁻¹ and remains at 410 mAh g⁻¹ after 200 cycles, which is much higher than the capacity of a pure Co electrode. The shift of the redox peaks in the CV curves and the negative movement of the discharge–potential plateau are attributed to the dissolution of sulfur in the composite, which also favors the capacity of Co. The measurements reveal that the reversible faradic reaction between highly dispersed Co and Co(OH)₂ is dominant for the Co–S composites.     

Hydrothermal synthesis and electrochemical properties of cobalt–carbon nanotubes nanocomposite

Cobalt–carbon nanotubes composite (Co–CNTs) is synthesized through a facile hydrothermal route. SEM and TEM characterizations reveal that the Co–CNTs composite contains abundance of carbon nanotubes connected by cobalt spheres and some of the CNTs are filled with metallic nanoparticles or nanorods. A series of electrochemical measurements show that the adding CNTs can remarkably enhance the electrochemical activity of the Co, leading to a notable improvement of the discharge capacity and the cycle performance. The practical maximum discharge capacity of the active Co is 495 mAh g⁻¹ after deducting the weight contribution of CNTs, which is about 280 mAh g⁻¹ higher than that of pure Co. The electrochemical reaction mechanism can be attributed to the dissolution–precipitation mechanism of Co in alkaline solution. And the functions of the CNTs are to improve dispersion of Co particles, increase contact area between Co and alkaline solution and promote the charge-transfer reaction.     

Lithium storage performance and interfacial processes of three dimensional porous Sn–Co alloy electrodes for lithium-ion batteries

Three-dimensional porous Cu film is prepared for the first time by electroless plating. Sn–Co alloy is electrodeposited on the porous Cu film to fabricate porous Sn–Co alloy electrode. SEM images evidence that porous Sn–Co alloy electrode presents a three-dimensional porous structure. XRD results show that the Sn–Co alloy electrode comprises pure Sn and CoSn₂ phases. Electrochemical discharge/charge results show that the three-dimensional porous Sn–Co alloy electrode exhibits much better cycleability than planar Sn–Co alloy electrode, with first discharge capacity and charge capacity of 636.3 and 528.7 mAh g⁻¹, respectively. After 70th cycling, capacity retention is 83.1% with 529.5 mAh g⁻¹. The lithiation and delithiation processes during first discharge and charge were investigated by electrochemical impedance spectroscopy (EIS). EIS results together with differential capacity curves describe the process of SEI formation, charge transfer and phase transformation in the alloy electrode in the first discharge, and phase transformation during charge at delithiation potential.     

Sulfur–carbon composite electrode for all-solid-state Li/S battery with Li2S–P2S5 solid electrolyte

All-solid-state Li/S batteries with Li₂S–P₂S₅ glass–ceramic electrolytes were fabricated and their electrochemical performance was examined. Sulfur–carbon composite electrodes were prepared by grinding with a mortar and milling with a planetary ball-mill apparatus. Milling of a mixture of sulfur, acetylene black and the Li₂S–P₂S₅ glass–ceramic electrolyte resulted in the amorphization of sulfur and a reduction in the particle size of the mixture. The charge–discharge properties of all-solid-state cells with the composite electrode were investigated at temperatures from −20 °C to 80 °C. The cells retained a reversible capacity higher than 850 mAh g⁻¹ for 200 cycles under 1.3 mA cm⁻² (333 mA g⁻¹) at 25 °C. The cell performance was influenced by the crystallinity of sulfur and the particle size of the electrode material, whereby improved contact among the electrode components achieved by milling contributed to enhancement of the capacity of an all-solid-state Li/S cell.     

Synthesis and electrochemical performance of bismuth–vanadium oxyfluoride

Bismuth–vanadium oxyfluoride (Bi₂VO₅F) has been synthesized using a simple, solid-state reaction process at different sintering temperatures. The structure and performance of the samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge experiments. The results show that bismuth–vanadium oxyfluoride belongs to a tetragonal crystal system with space group I4mm. The sample that was synthesized at 550 °C (P550) exhibits relatively good electrochemical properties. Sample P550 shows a high, initial discharge capacity of 222 mAh g⁻¹ at a rate of 100 mA g⁻¹ between 1.4 and 3.5 V. Sample P550 also shows acceptable electrochemical cycling properties. After the first cycle, the discharge specific capacity remains between 106 and 155 mAh g⁻¹, which plateaus between 2.1 and 1.9 V during the first 15 cycles.     

Carbon/PbO2 asymmetric electrochemical capacitor based on methanesulfonic acid electrolyte

A new hybrid electrochemical capacitor based on an activated carbon negative electrode, lead dioxide thin film and nanowire array positive electrode with an electrolyte made of a lead salt dissolved in methanesulfonic acid was investigated. It is shown that the maximum energy density and specific capacity of the C/PbO₂ nanowire system increase during the first 50 cycles before reaching their maximum values, which are 29 Wh kg⁻¹ and 34 F g⁻¹, respectively, at a current density of 10 mA cm⁻² and a depth of discharge (positive active electrode material) of 3.8%, that corresponds to a 22C rate. This is 7–8 times higher than the corresponding maximum values reached with a C/PbO₂ thin film cell operated in the same conditions. After an initial activation period, the performances of the C/PbO₂ nanowire system stay constant and do not show any sign of degradation during more than 5000 cycles. For comparison, the C/PbO₂ thin film system exhibits a 50% decrease of its performances in similar conditions.     

Facile preparation and good electrochemical hydrogen storage properties of chain-like and rod-like Co-B nanomaterials

Chain-like and rod-like Co-B nanomaterials are prepared by chemical reduction method in cetyltrimethylammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) aqueous solution, respectively. XRD patterns demonstrate that the two materials both have amorphous structures. SEM and TEM images show that the chain-like Co-B constructs of one-by-one tactic ball-like particles with nanoflakes on the surface, whereas the rod-like Co-B alloy possesses a porous nanostructure. The results of electrochemical measurements indicate that, as negative electrode materials of Ni-MH batteries, their electrochemical properties are both better than those of regular Co-B alloy. At the discharge current density 25 mA g⁻¹, the discharge capacities of the chain-like and the rod-like Co-B alloys are 314 mAh g⁻¹ and 292 mAh g⁻¹ after 50 cycles, respectively, which are both higher than that of regular Co-B alloy. XRD patterns of the electrodes on different charge-discharge states illustrate that the discharge capacity is attributed to hydrogenation of Co-B alloy.     

Investigation of electrochemical behavior of Mn–Co doped oxide electrodes for electrochemical capacitors

The electrochemical properties of nanocrystalline Co-doped Mn oxide electrodes were investigated to determine the relationship between physicochemical feature evolution and the corresponding electrochemical behavior of synthesized electrodes. Co-doped Mn oxide electrodes with a rod-like morphology and antifluorite-type structure were synthesized by anodic electrodeposition on Au coated Si substrates from a dilute solution of 0.01 M Mn acetate (Mn(CH₃COO)₂) and 0.001 M Co sulphate (CoSO₄).Electrochemical characterization of synthesized electrodes, with and without a conducting polymer (PEDOT) coating, was performed with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) at different scan rates. In addition, structural characterization of as-deposited and cycled electrodes was conducted using SEM, TEM and XPS.Capacitance values for all deposits increased with increasing scan rate to 100 mV s⁻¹, and then decreased after 100 mV s⁻¹. The Mn–Co oxide/PEDOT electrodes showed improved specific capacity and electrochemical cyclability relative to uncoated Mn–Co oxides. Mn–Co oxide/PEDOT electrodes with rod-like structures had high capacitances (up to 310 F g⁻¹) at a scan rate of 100 mV s⁻¹ and maintained their capacitance after 500 cycles in 0.5 M Na₂SO₄ (91% retention). Capacitance reduction for the deposits was mainly due to the loss of Mn ions by dissolution in the electrolyte solution.     

Electrochemically deposited hybrid nickel–cobalt hexacyanoferrate nanostructures for electrochemical supercapacitors

This study describes the use of electrodeposited nanostructured hybrid nickel–cobalt hexacyanoferrate in electrochemical supercapacitors. Herein, various compositions of nickel and cobalt hexacyanoferrates (Ni/CoHCNFe) nanostructures are electrodeposited on an inexpensive stainless steel substrate using cyclic voltammetric (CV) method. The morphology of the electrodeposited nanostructures is studied using scanning electron microscopy, while their electrochemical characterizations are investigated using CV, galvanostatic charge and discharge and electrochemical impedance spectroscopy. The results show that the nanostructures of hybrid metal cyanoferrate, shows a much higher capacitance (765 F g⁻¹) than those obtained with just nickel hexacyanoferrate (379 F g⁻¹) or cobalt hexacyanoferrate (277 F g⁻¹). Electrochemical impedance spectroscopy results confirm the favorable capacitive behavior of the electrodeposited materials. The columbic efficiency is approximately 95% based on the charge and discharge experiments. Long cycle-life and excellent stability of the nanostructured materials are also demonstrated during 1000 cycles.     

Tetraethylammonium difluoro(oxalato)borate as electrolyte salt for electrochemical double-layer capacitors

Difluoro(oxalato)borate (ODFB⁻) is a less symmetric borate anion, which makes it possible to increase the solubility of tetraethylammonium (TEA⁺) salt in propylene carbonate (PC) and improve the capacitance of electrochemical double-layer capacitors (EDLCs). The use of TEAODFB with PC solvent in EDLCs was investigated in the paper. The results show that TEAODFB has good solubility in PC, and the conductivity is comparable to TEABF₄/PC electrolyte. When the molar concentration of TEAODFB reaches to 1.6 M, the TEAODFB/PC electrolyte has superior conductivity of 14.46 mS cm⁻¹ and good capacitor characteristics. Despite the less accessible to the electrode and low energy density was achieved, the specific capacitance of 1.6 M TEAODFB/PC electrolyte is 21.4 F g⁻¹ at 1 A g⁻¹, and the energy density and power density were comparable to 1 M TEABF₄/PC electrolyte at 1–5 A g⁻¹. Temperature characteristic was also tested by 3.3 F circular capacitors from −40 to 60 °C, the result demonstrates that capacitors using 1.6 M TEAODFB/PC electrolyte show much higher capacitance and energy density at the investigated temperatures, and the discharge capacitance of capacitors using 1.6 M TEAODFB/PC electrolyte varies with the temperature less than that of 1 M TEABF₄/PC electrolyte.     

Electrochemical and interfacial behavior of a FeSi2.7 thin film electrode in an ionic liquid electrolyte

A FeSi_2.7 thin film is deposited on a copper substrate by RF magnetron sputtering of a Fe–Si alloy target. The electrochemical behavior of the FeSi_2.7 electrode in ionic liquid electrolyte based on 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide is investigated and compared with that of a FeSi_2.7 electrode in conventional liquid electrolyte. The FeSi_2.7 electrode in the ionic liquid electrolyte delivers an initial discharge capacity of 756 mAh g⁻¹ at room temperature, and its discharge capacity is maintained to be 92% of the initial discharge capacity after the 100th cycle. AC impedance and FTIR analysis reveal that the formation of a stable solid electrolyte interphase (SEI) layer on the FeSi_2.7 electrode in the ionic liquid electrolyte leads to a good capacity retention. This study demonstrates that the FeSi_2.7 electrode exhibits stable cycling behavior and good interfacial characteristics in the ionic liquid electrolyte without any solvents and additives.     

Effect of carbon coating on low temperature electrochemical performance of LiFePO4/C by using polystyrene sphere as carbon source

Carbon perfectly coated LiFePO₄ cathode materials are synthesized by carbon-thermal reduction method using polystyrene (PS) spheres as carbon source. The PS spheres with diameters of 150–300 nm used for the pyrolysis reaction not only inhibit the particle growth but also lead to uniform distribution of carbon coating on the surface of LiFePO₄ particles. Rate capability and cycling stability of LiFePO₄/C with the carbon contents ranging from 1.4 wt% to 3.7 wt% are investigated at −20 °C. The LiFePO₄/C with 3.0 wt% C exhibits excellent electrochemical capability at low temperature, which delivers 147 mAh g⁻¹ at 0.1 C. After 100 cycles at a charge–discharge rate of 1 C, there is still 100% of initial capacity retained for the LiFePO₄/C electrode at −20 °C. According to the transmission electron microscope analysis and cyclic voltammetry measurement, this can be attributed to the good carbon coating morphology and optimal carbon coating thickness.     

A novel micro-spherical CoSn2/Sn alloy composite as high capacity anode materials for Li-ion rechargeable batteries

Micro-scaled spherical CoSn₂/Sn alloy powders synthesized from oxides of Sn and Co via carbothermal reduction at 800 °C were examined for use as anode materials in Li-ion battery. The phase composition and particle morphology of the CoSn₂/Sn alloy composite powders were investigated by XRD, SEM and TEM. The prepared CoSn₂/Sn alloy composite electrode exhibits a low initial irreversible capacity of ca. 140 mAh g⁻¹, a high specific capacity of ca. 600 mAh g⁻¹ at constant current density of 50 mA g⁻¹, and a good rate capability. The stable discharge capacities of 500-515 mAh g⁻¹ and the columbic efficiencies of 95.8-98.1% were obtained at current density of 500 mA g⁻¹. The relatively large particle size of CoSn₂/Sn alloy composite powder is apparently favorable for the lowering of initial capacity loss of electrode, while the loose particle structural characteristic and the Co addition in Sn matrix should be responsible for the improvement of cycling stability of CoSn₂/Sn electrode.     

Electrochemical properties of bare and Ta-substituted Nb2O5 nanostructures

In this work, bare and Ta-substituted Nb₂O₅ nanofibers are prepared by electrospinning followed by sintering at temperatures in the 800–1100 °C range for 1 h in air. Obtained bare and Ta-substituted Nb₂O₅ polymorphs are characterized by X-ray diffraction, scanning electron microscopy, density measurement, and Brunauer, Emmett and Teller surface area. Electrochemical properties are evaluated by cyclic voltammetry and galvanostatic techniques. Cycling performance of Nb₂O₅ structures prepared at temperature 800 °C, 900 °C, and 1100 °C shows following discharge capacity at the end of 10th cycle: 123, 140, and 164 (±3) mAh g⁻¹, respectively, in the voltage range 1.2–3.0 V and at current rate of 150 mA g⁻¹ (1.5 C rate). Heat treated composite electrode based on M-Nb₂O₅ (1100 °C) in argon atmosphere at 220 °C, shows an improved discharge capacity of 192 (±3) mAh g⁻¹ at the end of 10th cycle. The discharge capacity of Ta-substituted Nb₂O₅ prepared at 900 °C and 1100 °C showed a reversible capacity of 150, 202 (±3) mAh g⁻¹, respectively, in the voltage range 1.2–3.0 V and at current rate of 150 mA g⁻¹. Anodic electrochemical properties of M-Nb₂O₅ deliver a reversible capacity of 382 (±5) mAh g⁻¹ at the end of 25th cycle and Ta-substituted Nb₂O₅ prepared at 900 °C, 1000 °C and 1100 °C shows a reversible capacity of 205, 130 and 200 (±3) mAh g⁻¹ (at 25th cycle) in the range, 0.005–2.6 V, at current rate of 100 mA g⁻¹.     

Hollow CuFe2O4 spheres encapsulated in carbon shells as an anode material for rechargeable lithium-ion batteries

We report here a polymer-templated hydrothermal growth method and subsequent calcination to achieve carbon coated hollow CuFe₂O₄ spheres (H–CuFe₂O₄@C). This material, when used as anode for Li-ion battery, retains a high specific capacity of 550 mAh g⁻¹ even after the 70th cycle, which is much higher than those of both CuFe₂O₄@C (∼300 mAh g⁻¹) and H–CuFe₂O₄ (∼120 mAh g⁻¹). And galvanostatic cycling at different current densities reveals that a capacity of 480 mAh g⁻¹, 91% recovery of the specific capacity cycling at 100 mA g⁻¹, can be obtained even after 50 cycles running from 100 to 1600 mA g⁻¹. The significantly enhanced electrochemical performances of H–CuFe₂O₄@C with regard to Li-ion storage are ascribed to the following factors: (1) the hollow void, which could mitigate the pulverization of electrode and facilitate the lithium-ion, electron and electrolyte transport; (2) the conductive carbon coating, which could enhance the conductivity, alleviate the agglomeration problem, prevent the formation of an overly thick SEI film and buffer the electrode. Such a structural motif of H–CuFe₂O₄@C is promising, for electrode materials of LIBs, and points out a general strategy for creating other hollow-shell electrode materials with improved electrochemical performances.     

Preparation and characterization of core–shell structure Fe3O4/C nanoparticles with unique stability and high electrochemical performance for lithium-ion battery anode material

Core–shell structure carbon coating Fe₃O₄ nanoparticles are prepared by a two-step method. The crystalline structure and the electrochemical performance of the prepared samples are investigated. The results indicate that a uniform and continuous carbon layer is formed on the surface of Fe₃O₄ nanoparticles. The core–shell structure Fe₃O₄/C nanoparticles show a high initial discharge capacity of 1546 mAh g⁻¹ and a specific stable discharge capacity of about 800 mAh g⁻¹ at 0.5 C with no noticeable capacity fading up to 100 cycles.     

Preparation and electrochemistry of NiO/SiNW nanocomposite electrodes for electrochemical capacitors

This paper studies nickel oxide/silicon nanowires (NiO/SiNWs) as composite thin films in electrodes for electrochemical capacitors. The SiNWs as backbones were first prepared by chemical etching, and then the Ni/SiNW composite structure was obtained by electroless plating of nickel onto the surface of the SiNWs. Next, the NiO/SiNW nanocomposites were fabricated by annealing Ni/SiNW composites at different temperatures in an oxygen atmosphere. Once the electrodes were constructed, the electrochemical behavior of these electrodes was investigated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In 2 M KOH solution, the electrode material was found to have novel capacitive characteristics. Finally, when the NiO/SiNW composites were annealed at 400 °C, the maximum specific capacitance value was found to be as high as 681 F g⁻¹ (or 183 F cm⁻³), and the probing of the cycling life indicated that only about 3% of the capacity was lost after 1000 charge/discharge cycles. This study demonstrated that NiO/SiNW composites were the optimal electrode choice for electrochemical capacitors.     

The characteristics of Ni–Co–Mn–O precursor and Li(Ni1/3Co1/3Mn1/3)O2 cathode powders prepared by spray pyrolysis

Ni–Co–Mn–O precursor powders with spherical shape and dense structure were prepared by spray pyrolysis from a spray solution containing a drying control chemical additive (DCCA) and polymeric precursors. In contrast, the Ni–Co–Mn–O precursor powders obtained from a spray solution without additives had a hollow and porous morphology. Ni–Co–Mn–O precursor powders with a spherical shape and dense structure yielded Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode powders with a spherical shape and fine size by means of a solid-state reaction with lithium hydroxide. The mean size of the spherical cathode powder was 1.1 μm. The discharge capacity of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders with spherical shape and filled morphology was 195 mA h g⁻¹ at a current density of 0.1 C. The discharge capacities of the cathode powders with spherical shape and filled morphology at 55 °C decreased from 183 to 154 mA h g⁻¹ by the 30th cycle at a current density of 0.5 C.     

Electrodeposition and lithium storage performance of three-dimensional porous reticular Sn-Ni alloy electrodes

Three-dimensional (3D) porous materials of Sn-Ni alloy with reticular structure were prepared by electroplating using copper foam as current collector. The structure and electrochemical performance of the electroplated 3D porous Sn-Ni alloys were investigated in detail. Experimental results illustrated that the 3D porous Sn-Ni alloy consists of mainly Ni₃Sn₄ phase with a hexagonal structure. Galvonostatic charging/discharging of annealed 3D porous Sn-Ni alloy confirmed its excellent performances: at 50th charge-discharge cycle, the discharge specific capacity is 505 mAh g⁻¹ and the corresponding charge (delithiation) specific capacity is 501 mAh g⁻¹, yielding columbic efficiency as high as 99%. It has revealed that the porous structure of the alloy can restrain the pulverization of electrode in charge/discharge cycles, and accommodate partly the volume expansion and phase transition, resulting in a significant improvement of cycle life of the Sn-Ni electrode.     

Electroplating synthesis and electrochemical properties of macroporous Sn-Cu alloy electrode for lithium-ion batteries

Macroporous material of Sn-Cu alloy of different pore sizes designated as anode in lithium-ion batteries were fabricated through colloidal crystal template method. The structure and electrochemical properties of the macroporous Sn-Cu alloy electrodes were examined by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and galvanostatic cycling. The results demonstrated that the electrodes of macroporous Sn-Cu alloy with pore size respectively of 180 and 500 nm can deliver reversible capacity of 350 and 270 mAh g⁻¹ up to 70th cycles of charge/discharge. The cycle performance of the macroporous Sn-Cu alloy of 180 nm in pore size is better than that of the macroporous Sn-Cu alloy with 500-nm-diameter pores. It has revealed that the porous structure of the macroporous Sn-Cu alloy material is of importance to strengthen mechanically the electrode and to reduce significantly the effect of volume expansion during cycling.