Silver-coated LiVPO4F composite with improved electrochemical performance as cathode material for lithium-ion batteries

Nano-structured LiVPO₄F/Ag composite cathode material has been successfully synthesized via a sol–gel route. The structural and physical properties, as well as the electrochemical performance of the material are compared with those of the pristine LiVPO₄F. X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal that Ag particles are uniformly dispersed on the surface of LiVPO₄F without destroying the crystal structure of the bulk material. An analysis of the electrochemical measurements show that the Ag-modified LiVPO₄F material exhibits high discharge capacity, good cycle performance (108.5 mAh g⁻¹ after 50th cycles at 0.1 C, 93% of initial discharge capacity) and excellent rate behavior (81.8 mAh g⁻¹ for initial discharge capacity at 5 C). The electrochemical impedance spectroscopy (EIS) results reveal that the adding of Ag decreases the charge-transfer resistance (R_ct) of LiVPO₄F cathode. This study demonstrates that Ag-coating is a promising way to improve the electrochemical performance of the pristine LiVPO₄F for lithium-ion batteries cathode material.     

Sonochemically synthesized MnO2 nanoparticles as electrode material for supercapacitors

In this study, manganese oxide (MnO₂) nanoparticles were synthesized by sonochemical reduction of KMnO₄ using polyethylene glycol (PEG) as a reducing agent as well as structure directing agent under room temperature in short duration of time and characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM), Transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) analysis. A supercapacitor device constructed using the ultrasonically-synthesized MnO₂ nanoparticles showed maximum specific capacitance (SC) of 282 Fg⁻¹ in the presence of 1 M Ca(NO₃)₂ as an electrolyte at a current density of 0.5 mA cm⁻² in the potential range from 0.0 to 1.0 V and about 78% of specific capacitance was retained even after 1000 cycles indicating its high electrochemical stability.     

Sonochemical synthesis of LiNi0.5Mn1.5O4 and its electrochemical performance as a cathode material for 5 V Li-ion batteries

LiNi_0.5Mn_1.5O₄ was synthesized as a cathode material for Li-ion batteries by a sonochemical reaction followed by annealing, and was characterized by XRD, SEM, HRTEM and Raman spectroscopy in conjunction with electrochemical measurements. Two samples were prepared by a sonochemical process, one without using glucose (sample-S1) and another with glucose (sample-S2). An initial discharge specific capacity of 130 mA h g⁻¹ is obtained for LiNi_0.5Mn_1.5O₄ at a relatively slow rate of C/10 in galvanostatic charge–discharge cycling. The capacity retention upon 50 cycles at this rate was around 95.4% and 98.9% for sample-S1 and sample-S2, respectively, at 30 °C.     

Hexamethylenetetramine assisted hydrothermal synthesis of BiPO4 and its electrochemical properties for supercapacitors

The well defined microstructures of BiPO₄ were successfully synthesized by the facile hexamethylenetetramine (HMT) assisted hydrothermal method. The low temperature monoclinic BiPO₄ structure with space group P2₁/n, were obtained from X-ray diffraction (XRD) for the pristine and HMT-assisted BiPO₄ with 1, 3, 5 and 10 mmole concentration. A transformation from low temperature monazite-type phase to the high temperature SbPO₄-type phase of BiPO₄ was observed at the 10 mmole concentration. There was a variation in the morphology from polyhedron to octahedra-like and finally into cube shape upon an increase in concentration of HMT. The role of reaction time in the morphology of BiPO₄ particles was investigated. The selected area electron diffraction (SAED) pattern elucidated the ordered dot pattern and the calculated d-spacing revealed the formation of BiPO₄. An increased specific capacitance of HMT assisted materials (202 F/g) compared with pristine BiPO₄ (89 F/g) at 5 mA/cm² was observed upon morphological variation due to HMT addition.     

Potato starch-based activated carbon spheres as electrode material for electrochemical capacitor

Potato starch-based activated carbon spheres (PACS) were prepared from potato starch by stabilization, carbonization followed by activation with KOH. The obtained PACS are hollow and retain the original morphology of potato starch with decrease in size, as shown by scanning electron microscopy. Modification of textural properties of the PACS was achieved by varying the carbonization temperature and the ratio of KOH/PCS. The results of N₂ adsorption isotherms indicate that the samples prepared are mainly microporous. The electrochemical behaviors of the hollow PACS were studied by galvanostatic charge-discharge, cyclic voltammetry, and impedance spectroscopy. The results indicate that high specific capacitance of 335 F/g is obtained at current density 50 mA/g for PACS with specific surface area 2342 m²/g. Only a slight decrease in capacitance, to 314 F/g, was observed when the current density increases to 1000 mA/g, indicating a stable electrochemical property.     

Effects of additives and surface treatment on electrochemical performance for bafeo4 electrode

BaFeO₄ was prepared by using the raw material K₂FeO₄. The structure of the product was characterized by X-ray diffraction and infrared radiation. Particle size and morphology were analyzed by SEM. BaFeO₄, the mixture of BaFeO₄, and additives were used as cathode, zinc used as anode, with which discharge performance test was carried out in the KOH electrolyte with a concentration of 14 mol/L. The results show that the discharge performance of BaFeO₄ is obviously enhanced, the discharge platform is increased by 0.3 V, and the capacity reached up to 240 mAh/g, increased by 40 mAh/g after 5% of K₂S₂O₈ was added. In addition, the discharge capacity is increased by 65 mAh/g via treating the electrode surface with TiO₂ sol, reached up to 265 mAh/g, and electrochemical performance is obviously improved. The reason of improving property is discussed in the work too.     

Nickel, cobalt, and manganese oxide composite as an electrode material for electrochemical supercapacitors

A composite material, Ni_1/3Co_1/3Mn_1/3(OH)₂, is synthesized by chemical precipitation method for supercapacitors' electrode material. Physical characterizations using x-ray diffraction, energy-dispersive x-ray, and scanning electron microscopy show that Ni_1/3Co_1/3Mn_1/3(OH)₂ possesses an amorphous structure and higher specific surface area (268.5 m²?g^?1), which lead to a high initial specific capacitance of 1,403 F?g^?1 in the potential window of 0–1.5 V. It may be a potential electrode material for future supercapacitor when its cycling stability and rate performance are addressed.     

Investigation of polyaniline films doped with Co2+ as the electrode material for electrochemical supercapacitors

Ionics - H+ and Co2+ ions co-doped polyaniline were synthesized by cyclic voltammetry onto the stainless steel mesh with various concentrations of cobalt chloride (CoCl2 · 6H2O) in...     

Two-step process and fatigue in Li<Subscript><Emphasis Type="BoldItalic">x</Emphasis></Subscript>CrMnO<Subscript>4</Subscript> as positive electrode material for lithium ion batteries

The electrochemical behavior and structural changes of the positive electrode material LiCrMnO₄ are studied for different end-of-charge voltages. A potentiostatic intermittent titration technique (PITT) experiment performed up to 5.2 V shows three oxidative peaks. Cells charged to 4.88 V, which corresponds to the minimum between the second and the third oxidative peak, show 89% of capacity retention for the 60th cycle. Compared to that only 23% of capacity are preserved in the 60th cycle when the cell is charged to 5.2 V. The structural analysis by Rietveld refinement shows that for the former case, the amount of structural defects is low and their formation is reversible, while the defect amount is significantly higher for the latter case and the defect formation is only partially reversible. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007     

电化学制备钛网负载聚吡咯/石墨烯复合膜及其在超级电容器中的应用

通过电化学的方法在钛网上制备了聚吡咯与石墨烯的复合物薄膜,其过程是先在钛网上通过自组装干燥膜法附着上石墨烯氧化物膜,而后采用电化学还原的方法原位还原制备得到石墨烯膜,随后加入吡咯单体,再通过电化学聚合的方法在石墨烯的表面生长聚吡咯,得到的聚吡咯开始以颗粒的形式存在,而后随着聚合的进行得到了链状的聚吡咯.得到的复合膜有高的比表面积和导电性,可以作为电极活性材料用于超级电容器中提供赝电容,结果表明,复合膜作为电极材料的超级电容器拥有高的性能,比电容达400 F/g,并且电极的充放电稳定性高,5000次复合膜充放电循环后比电容还能保留82%,说明该材料适合于超级电容器.     

Silver-coated graphene electrode produced by electrolytic deposition for electrochemical behaviors

This study evaluates the excellent electrochemical performance of silver (Ag)-coated graphene electrode using an electrolytic deposition technique. Ag particles are introduced to the graphene surface as a function of the applied current. A half cell of the Ag-coated graphene electrode is fabricated to examine the electrochemical performance, such as the charge–discharge behaviors, cyclic voltammetry, and specific capacitance. As a result, the electrochemical performance of the Ag-coated graphene electrode is two times higher than that of the crude graphene electrode.     

Enhancement of the electrochemical properties of LiMn2O4 by glycolic acid-assisted sol-gel method

LiMn₂O₄ spinel cathode was synthesized by the sol–gel method by using glycolic acid as a chelating agent. The sample exhibited a pure cubic spinel structure without any impurities in the X-ray diffraction (XRD) patterns. The result of the electrochemical performances on the sample compared to those of electrodes based on LiMn₂O₄ spinel synthesized by solid state. LiMn₂O₄ synthesized by glycolic acid-assisted sol–gel method improves the cycling stability of electrode. The capacity retention of sol–gel-synthesized LiMn₂O₄ was about 90• after 100 cycles between 3.0 and 4.4 V at room temperature. The electrochemical performance of the LiMn₂O₄ (sol–gel) and LiMn₂O₄ (solid state) were investigated under 40• between 3.0 and 4.4 V. XRD results of the cathode material after 50 cycles at 40• revealed that LiMn₂O₄ (sol–gel) could effectively suppress the LiMn₂O₄ dissolving of into electrolyte and resulted in a better stability.     

Nanoscopic scale studies of LiFePO4 as cathode material in lithium-ion batteries for HEV application

We present a review of the structural properties of LiFePO₄. Depending on the mode of preparation, different impurities can poison this material. These impurities are identified and a quantitative estimate of their concentrations is deduced from the combination of X-ray diffraction analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, and magnetic measurements. An optimized preparation provides samples with carbon-coated particles free of any impurity phase, insuring structural stability and electrochemical performance that justify the use of this material as a cathode element a new generation of lithium secondary batteries.     

Highly amorphous PbO2 as an electrode in hybrid electrochemical capacitors

This paper presents a synthesis and characterizes highly amorphous lead dioxide and its use in hybrid electrochemical capacitor C/PbO₂. Highly amorphous lead dioxide with a small amount of β-PbO₂ was synthesized by galvanostatic deposition from acetate solution. The hybrid supercapacitor was constructed with PbO₂ as the positive electrode whereas activated carbon as the negative electrode. The morphology of materials was examined by scanning electron microscopy and their structure was characterized by means of an X-ray diffraction technique. The electrochemical performance of hybrid electrochemical capacitor with synthesized PbO₂ was studied by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. To indicate that the amorphous form of lead dioxide was predominant, results were compared to highly crystalline β-PbO₂. The hybrid electrochemical capacitor with synthesized material exhibits a much greater specific capacitance, higher specific energy and power than the highly crystalline one. The specific capacitance values obtained for the supercapacitor rose more than twice in favour of amorphous PbO₂. Also, long cycling did not influence any of the electrochemical properties of this hybrid electrochemical capacitor, which makes it an interesting energy storage device.     

Charge storage performance of lithiated iron phosphate/activated carbon composite as symmetrical electrode for electrochemical capacitor

In this study, a symmetric electrochemical capacitor was fabricated by adopting a lithium iron phosphate (LiFePO₄)-activated carbon (AC) composite as the core electrode material in 1.0 M Na₂SO₃ and 1.0 M Li₂SO₄ aqueous electrolyte solutions. The composite electrodes were prepared via a facile mechanical mixing process. The structural properties of the nanocomposite electrodes were characterised by scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) analysis. The electrochemical performances of the prepared composite electrode were studied using cyclic voltammetry (CV), galvanostatic charge–discharge (CD) and electrochemical impedance spectroscopy (EIS). The experimental results reveal that a maximum specific capacitance of 112.41 F/g was obtained a 40 wt% LiFePO₄ loading on an AC electrode compared with that of a pure AC electrode (76.24 F/g) in 1 M Na₂SO₃. The improvement in the capacitive performance of the 40 wt% LiFePO₄–AC composite electrode is believed to be attributed to the contribution of the synergistic effect of the electric double layer capacitance (EDLC) of the AC electrode and pseudocapacitance via the intercalation/extraction of H⁺, OH⁻, Na⁺ and SO₃²⁻ and Li⁺ ions in LiFePO₄ lattices. In contrast, it appears that the incorporation of LiFePO₄ into AC electrodes does not increase the charge storage capability when Li₂SO₄ is used as the electrolyte. This behaviour can be explained by the fact that the electrolyte system containing SO₄²⁻ only exhibits EDLC in the Fe-based electrodes. Additionally, Li⁺ ions that have lower conductivity and mobility may lead to poorer charge storage capability compared to Na⁺ ions. Overall, the results reveal that the AC composite electrodes with 40 wt% LiFePO₄ loading on a Na₂SO₃ neutral electrolyte exhibit high cycling stability and reversibility and thus display great potential for electrochemical capacitor applications.     

Ultrasonic-assisted preparation and characterization of hierarchical porous carbon derived from garlic peel for high-performance supercapacitors

Ultrasonic-assisted impregnation is used to synthesize physically modified garlic peel-based 3D hierarchical porous carbons (PCs), and the effect on PCs is investigated by changing ultrasonic time. The results show that ultrasonic waves can effectively peel off surface attachments of the carbonized product, so that activator has a better mass transfer process and create more active sites. The connectivity of 3D pore network is enhanced as well, so the structure and electrochemical properties of garlic peel-based porous carbon (GBPC) are improved. The ultrasonic disperser is used as an ultrasonic generator, specific conditions are as follows: ultrasonic frequency is 40 kHz, ultrasonic power is 500 W, and ultrasonic time is 0, 3, 6, and 9 min, respectively. With the increase of ultrasonic time, impurities again block the pore structure during dynamic movement, resulting in a decrease in electrochemical performance. Specifically, the performance of GBPC-6 is the most excellent, the specific surface area (SSA) increases from 2548 m² g⁻¹ to 3887 m² g⁻¹, the specific capacitance increases from 304 F g⁻¹ to 426 F g⁻¹ at a current density of 1 A g⁻¹ in a two-electrode test system. Energy density and cycle performance are also improved at the same time, which are attributed to rational structure. In addition, the effectiveness of the strategy of ultrasonic-assisted synthesis has been confirmed on another precursor material–scallion, meaning that this work proposes a new and simple modification method for improving the performance of biomass-based PCs.     

Nanophase ZnV2O4 as stable and high capacity Li insertion electrode for Li-ion battery

Spinel ZnV₂O₄ nanoparticles are synthesized by a hydrothermal method and its properties are characterized using XRD, SEM, TEM, and electrochemical test. The structural and morphological characterizations show that ZnV₂O₄ sample has high purity and well crystallization with crystal size less than 20 nm. The as prepared electrode shows stable capacity over 660 mAh g⁻¹ in the voltage range of 0.01–3.0 V at 50 mA g⁻¹. The reaction mechanism with lithium ion is also investigated through ex-XRD and -TEM. It shows that the pristine ZnV₂O₄ is transformed to isostructural spinel Li_xV₂O₄ (x close to 7.6) and metal Zn phase during the first lithiation process. Then the spinel Li_xV₂O₄ seems to perform a topotactic intercalation reaction mechanism and that the in-situ formed Li_xV₂O₄ can still keep its spinel matrix while allowing more than 5.7 lithium reversibly into/out over 50 cycles.     

Investigation on PVDF-HFP microporous membranes prepared by TIPS process and their application as polymer electrolytes for lithium ion batteries

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) microporous membranes were prepared via thermally induced phase separation (TIPS) process. Then they were immersed in a liquid electrolyte to form polymer electrolytes. The effects of polymer content in casting solution on the morphology, crystallinity, and porosity of the membranes were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and a mercury porosimeter, respectively. Ionic conductivity, lithium-ion transference number, and electrochemical stability window of corresponding polymer electrolytes were characterized by AC impedance spectroscopy, DC polarization/AC impedance combination method, and linear sweep voltammetry, respectively. The results showed that spherulites and “net-shaped” structure coexisted for the membranes. Polymer content had no effect on crystal structure of the membranes. The maximum transference number was 0.55. The temperature dependence of ionic conductivity followed the Vogel–Tammann–Fulcher (VTF) relation. The maximum ionic conductivity was 2.93 × 10⁻³ Scm⁻¹ at 20 °C. Electrochemical stability window was stable up to 4.7 V (vs. Li⁺/Li).     

Ultrasound-assisted fabrication of a new nanocomposite electrode of samaria and borazon for high performance supercapacitors

The fabrication of hetero structured materials with supercapacitor applications for industrial use remains a key challenge. This work reports a new supercapacitor material with high capacitance, comprising samaria and borazon (O₃Sm₂/BN) synthesized ultrasonically (40 ± 3 kHz, 200 W). The successful synthesis, probable interfaces between O₃Sm₂ and BN and thermal stability of the nanocomposite were studied by UV–Vis. and FT-IR spectroscopies, X-ray diffraction (XRD) and thermo gravimetric analyses (TGA). The morphology of nanocomposite was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Elemental mapping analysis and energy dispersive X-ray analysis (EDAX) confirmed the elements present in the material. This supercapacitor material shows a maximum discharge capacitance of 414 Fg⁻¹ at 0.25 Ag⁻¹ and an exceptional retention of specific capacitance (92.5%) in 5000 cycles. Such nanocomposite with better specific capacitance and charge/discharge rates makes it a right candidate as next generation supercapacitor, which certainly finds applications in various unconventional energy storage devices.     

Hydrogen bubble-assisted growth of Pt3Te4 for electrochemical catalysts

Novel materials and structures with abundant active sites have been in continuous demand for electrochemical catalytic applications. In this study, we synthesized platinum telluride (Pt₃Te₄) nanocrystals on two-dimensional metallic molybdenum ditelluride (MoTe₂) using a dynamic hydrogen bubble template method in the hydrogen evolution reaction (HER). The local crystal structure and chemical state of the Pt₃Te₄ nanocrystals were investigated using X-ray nano-diffraction and X-ray nano-absorption spectroscopy. In our electrochemical deposition method, the morphology, and HER performance of the Pt₃Te₄ nanocrystals could be manipulated through the hydrogen bubble generation rate. Thus, the nanorod-shaped Pt₃Te₄ nanocrystals, fabricated by a high rate of hydrogen bubble generation, exhibited outstanding HER performance, which is in contrast with the HER performance of hemisphere-shaped Pt₃Te₄. Our study provides a facile and systematic way of synthesizing high-performance electrochemical catalysts using the hydrogen bubble-assisted growth method.