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    Electrochemical performance comparison of MWCNTs Ni (OH)2 composite materials by two preparation routes
    (Springer, 2017) Ortiz, Mariela; Castro, Élida Beatriz; Real, Silvia
    Carbon materials are used to improve the nickel hydroxide electrode capacity in rechargeable alkaline batteries. Herein, we present the preparation of multiwall carbon nanotubes/nickel hydroxide composites (MWCNTs/Ni (OH)2) by two different routes. The first method consists of the direct incorporation of MWCNTs in the active material, and the second is based on the hydrothermal synthesis of β-nickel hydroxide, where MWCNTs are added to the precursor solutions. The electrochemical properties of the prepared positive electrodes containing MWCNTs/Ni (OH)2 composites are studied. Electrochemical results indicate that the active material with MWCNTs incorporated before the hydrothermal synthesis is capable of delivering a higher discharge capacity and exhibits a better reversibility than those composites prepared with MWCNTs after the hydrothermal route.
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    Electrochemical characterization of nickel hydroxide nanomaterials as electrodes for NiMH batteries
    (Springer, 2016-08-23) Real, Silvia; Ortiz, Mariela; Castro, Élida Beatriz
    β-Nickel hydroxide was successfully synthesized by a hydrothermal method. Nano-nickel hydroxide material was characterized by X-ray diffraction, infrared absorption spectroscopy, and transmission electron microscopy. They were employed as additives to the positive electrode of Ni-MH batteries. Working electrodes, with mixtures of commercial nickel hydroxide and nano-nickel hydroxide (0–10 wt.%) as active material, were prepared. Cyclic voltammetry, charge discharge profiles, and electrochemical impedance spectroscopy studies were carried out to evaluate the electrochemical performance of the nickel electrode, in 7 M KOH electrolyte, at 25 °C. The presence of nano-nickel hydroxide improves the electrochemical behavior of the active material. The electrochemical impedance spectroscopy (EIS) results were analyzed employing a modified version of previously developed physicochemical model that takes into account the main structural and physicochemical parameters that control these systems.
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    Electrochemical characterization of MWCNT Ni(OH)2 composites as cathode materials
    (Springer, 2015-09-04) Ortiz, Mariela; Real, Silvia; Castro, Élida Beatriz
    The hydrothermal method was used to synthesize multi-walled carbon nanotube/nickel hydroxide composites (MWCNT/Ni(OH)2). The structure and morphology of the prepared materials were characterized by X-ray diffraction and transmission electron microscopy. The electrochemical performance of cathodes prepared with multi-walled carbon nanotubes (MWCNT) loaded into the β-nickel hydroxide materials was investigated employing cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopic measurements. It is shown that the cathode active material utilization increases for MWCNT/ Ni(OH)2 obtained after 24 h of hydrothermal synthesis. These composites exhibit a fairly good electrochemical performance as cathode materials. Based on the results, this fact could be associated with the formation of a continuous conductive network structure in the hydroxide matrix. The analyses of impedance data, according to a physicochemical model, allow the improvement of a better understanding of the main structural and physicochemical parameters that control the electrochemical performance of these systems.
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    Characterization of anodes for lithium ion batteries
    (Springer, 2015-08-14) Humana, Rita; Ortiz, Mariela; Thomas, Jorge; Real, Silvia; Sedlarikova, Marie; Vondrak, Jiri; Visintin, Arnaldo
    The lithium-ion batteries are energy storage systems of high performance and low cost. They are employed in multiple portable devices, and these require the use of increasingly smaller and lighter batteries with high energy and power density, fast charging, and long service life. Moreover, these systems are promising for use in electric or hybrid vehicles. However, the lithium-ion battery still requires the improvement of the electrode material properties, such as cost, energy density, cycle life, safety, and environmental compatibility. These batteries use carbon as anode material, usually synthetic graphite, because of its high coulombic efficiency and acceptable specific capacity for the formation of intercalation compounds (LiC6). In this paper, the methodology used to prepare and characterize the reversible and irreversible capacity and cyclic stability of graphite materials as anodes in lithium-ion batteries of commercial carbon and shungite carbon is presented. The results obtained using electrochemical techniques are discussed. These electrodes exhibited good activation process and high-rate dischargeability performance. For carbon and shungite electrodes, the maximum discharge capacity values were 259 and 170 mA h g−1, respectively.
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    Effect of cobalt electroless deposition on nickel hydroxide electrodes
    (Elsevier, 2014-02-21) Ortiz, Mariela; Castro, Élida Beatriz; Real, Silvia
    The effects of cobalt additive on the positive electrode surface of nickel alkaline batteries are investigated. Electrode surface modifications by electroless cobalt deposits were made at different immersion times. The performance of nickel hydroxide electrodes was studied by optical techniques, such as scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and electrochemical methods as cyclic voltammetry, charge discharge curves and electrochemical impedance spectroscopy (EIS). According to these results, electroless cobalt deposits obtained with 5 min of immersion time in the electroless-bath exhibit a better electrode performance.
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    Preparation and characterization of positive electrode of NiMH batteries with cobalt additives
    (Elsevier, 2014-02-18) Ortiz, Mariela; Real, Silvia; Castro, Élida Beatriz
    The present paper shows the preparation and characterization of alkaline batteries cathodes formed by nickel hydroxide with the addition of cobalt. This additive was incorporated by two methods: on the electrode surface, using the electroless technique and by direct incorporation of cobalt powder in the active material. The electrochemical behavior of both nickel hydroxide electrodes was investigated and compared. The results indicate that active materials containing cobalt additive by the electroless technique exhibit an improvement on the electrochemical performance.
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    Preparation and characterization of graphite anodes for lithium ion batteries
    (The Electrochemical Society, 2014) Humana, Rita; Ortiz, Mariela; Thomas, Jorge; Real, Silvia; Sedlarikova, Marie; Vondrak, Jiri; Visintin, Arnaldo
    The lithium-ion batteries are energy storage systems of high performance and low cost. They are employed in multiple portable devices and these require the use of increasingly smaller and lighter batteries with high energy and power density, fast charging and long service life. Moreover, these systems are promising for use in electric or hybrid vehicles. However, the lithium-ion battery still requires to improve the electrode materials properties, such as cost, energy density, cycle life, safety, and environmental compatibility. These batteries use carbon as anode material, usually synthetic graphite, because of its high coulombic efficiency and acceptable specific capacity for the formation of intercalation compounds (LiC6). In this paper the methodology used to prepare and characterize the reversible and irreversible capacity and, cyclic stability of graphite materials as anodes in lithium-ion batteries of commercial carbon and Sungite carbon, is presented. The results obtained using electrochemical techniques, are discussed.
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    Synthesis and electrochemical properties of Nickel oxide as anode for Lithium ion batteries
    (Topical Meeting of the International Society of Electrochemistry, 2017-03-19) Ortiz, Mariela; Visintin, Arnaldo; Real, Silvia
    Transition-metal oxides (MO, where M is Fe, Ni, Co and Cu) have been studied since these materials were proposed by Tarascon and co-workers [1-6]. These oxides can offer higher capacities (600-1000 mAh g-1) that graphite material (372 mAh g-1); in particular, NiO has high theoretical capacity values (718 mA h g-1 for 2Li+per NiO) also present many advantages such as natural abundance, low cost and environmental friendless In this contribution we would like to present the preparation and characterization of nickel oxide as anodes materials in lithium-ion batteries. Two processes are involved in the synthetic procedure; in the first step the nickel hydroxide was obtained by hydrothermal synthesis (4h, 180°C) and then the precipitated was washed with distilled water to remove the residual species. The second step consists of the material calcinations in air at 300ºC, for 4 (NiO-4h) and 24(NiO-24h) hours. The structural characteristics and electrochemical properties of the obtained nickel oxides are subsequently investigated by optical and electrochemical techniques such as: FTIR, SEM, chargedischarge cycles, galvanostatic discharge at different currents, cyclic voltammetry and electrochemical impedance spectroscopy.
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    Study of the electrochemical behavior of different carbon materials as anode material for lithium ion batteries
    (Topical Meeting of the International Society of Electrochemistry, 2017-03-19) Ortiz, Mariela; Visintin, Arnaldo; Real, Silvia
    Since the lithium ion battery was first commercialized by the Sony Corporation in 1991, the development for improvement it is critical for advancements in a variety of applications ranging from hybrid electric vehicles to consumer electronic [1]. Most lithium ion commercial battery use LiCoO2, LiNiO2 or LiFePO4 as cathode material, organic solvent as the electrolyte and carbon composites as anode material [1-2]. The electrochemical reactions involve Li transfer and exchange of electron. A number of studies have so far been performed for providing a high performance carbonaceous material for the anode of Li-ion batteries [3]. In this study, out of the many available carbonaceous materials we have selected some of them to prepared anodes material and study their electrochemical behavior and correlation to their physical, chemical and physic-chemical parameters.
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    Electrochemical performance of Carbon Sulfur as Lithium Sulfur battery cathodes
    (Topical Meeting of the International Society of Electrochemistry, 2017-03-19) Ortiz, Mariela; Visintin, Arnaldo; Real, Silvia
    Nowadays, rechargeable batteries with higher energy density are required for our society due to the needs of cleaner and more efficient energy systems and with the objective of supplying the increasing technological demands. Commercial lithium batteries are systems based on intercalation compounds able to delivering specific energies about 150-200 WhKg-1, one-third of their theoretical energy ( ≈ 600 Wh kg-1). It is difficult for the reversible capacity of these intercalation compounds to be increased, thus the need to explore new cathodes formed by lighter materials and involving electrochemical reactions of more than one electron. An element satisfying these conditions is sulfur (with a theoretical capacity of 1675 mAhg-1 and a specific energy of 2600 WhKg-1). The lithium-sulfur battery has been investigated by different groups in past decades; however, there are serious drawbacks, which have not been overcome yet, so it limits the practical development of this system [3]. Moreover, sulfur is much more abundant, inexpensive, and non-toxic compared to the transition-metal oxide cathodes. We present here the preparation of composites with carbon and sulfur materials in a single fabrication process: using S2C as the solvent. The characterization of the prepared material was performed using optical techniques (X-ray diffraction, scanning electron microscopy and transmission) and its electrochemical performance in lithium-sulfur batteries was studied using electrochemical techniques such as: charge-discharge cycles, galvanostatic discharges to different currents and cyclic voltammetry. The prepared composite materials delivered higher capacities in the first cycles (≈800 mAhg-1) and then it were stabilized at values around 60% of the initial capacity. Also, carbon electrochemical response was not observed, so its main function is to act effectively as an electron-conducting and support matrix.