Galvanostatic Charge-discharge Curves Research Articles

Electrochemical behavior of Bi4B2O9 towards lithium-reversible conversion reactions without nanosizing.

Conversion type materials, in particular metal fluorides, have emerged as attractive candidates for positive electrodes in next generation Li-ion batteries (LIBs). However, their practical use is being hindered by issues related to reversibility and large polarization. To minimize these issues, a few approaches enlisting the anionic network have been considered. We herein report the electrochemical properties of bismuth oxyborate Bi4B2O9 and show that this compound reacts with lithium via a conversion reaction leading to a sustained capacity of 140 mA h g-1 when cycled between 1.7 and 3.5 V vs. Li+/Li0 while having a surprisingly small polarization (∼300 mV) in the presence of solely 5% in weight of a carbon additive. These observations are rationalized in terms of charge transfer kinetics via complementary XRD, HRTEM and NMR measurements. This finding demonstrates that borate based conversion type materials display rapid charge transfer with limited carbon additives, hence offering a new strategy to improve their overall cycling efficiency.

Surfactant-Free One-Pot Hydrothermal Growth of Micro-Flower-Like Copper Tin Sulfide Electrode Material for Pseudocapacitor Applications

Ternary Cu2SnS3 (CTS) metal chalcogenide is an important potential electrode material in the field of energy storage systems due to the tunnels in its crystal structure and good electrochemical properties. Herein, the CTS micro-flowers were successfully synthesized by a facile strategy of one-step hydrothermal method without the addition of any other surfactants or templates. The phase form, functional groups, and existence of the valence states in the prepared CTS powder sample were characterized by X-ray diffraction pattern, Fourier transform infrared spectroscopy, and the X-ray photoelectric spectroscopy, respectively. The CTS sample revealed flower-like morphology which was confirmed by field-emission scanning electron microscopy. In alkaline 1 M KOH electrolyte media, the cyclic voltammetry and galvanostatic charge-discharge curves of the micro-flower CTS electrode material were measured using a traditional three-electrode system. The electrochemical data exhibited a specific capacitance value of 183 F/g at 1 A/g of current density, and it maintained 56.2% specific capacitance retention (103 F/g) at higher current density (9 A/g), which is a good sign for rate capability of the electrode. Additionally, the micro-flower CTS electrode composite revealed 88.5% capacitance retention after performing 2000 cycles at 1 A/g of current density, indicating its good cycling stability.

Nickel-cobalt layered double hydroxide ultrathin nanosheets coated on reduced graphene oxide nonosheets/nickel foam for high performance asymmetric supercapacitors

Here in, for the first time, we report a new and simple procedure for preparing reduced graphene oxide/nickel-cobalt double layered hydroxide composite on the nickel foam (Ni-Co LDH/rGO/NF) via a fast and simple two-step electrochemical method including potentiostatic routes in the presence of CTAB as a cationic surfactant. Graphene oxide coated nickel foam prepared by simple immersion method. After that, the prepared electrode reduced electrochemically to obtain rGO/NF electrode. Finally, the rGO/NF electrode was used as cathode for electrodeposition of Ni-Co LDH in the presence of CTAB as cationic surfactant. The prepared electrodes were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDS), Brunauer, Emmett and Teller (BET) and electrochemical techniques such as voltammetry (CV), galvanostatic charge-discharge curves (GCD) and electrochemical impedance spectroscopy (EIS). The resulting electrode which prepared in the presence of CTAB afforded extremely high specific capacitance of 2133.3 F g−1 at a current density of 4 A g−1. FE-SEM, TEM and EDS mapping results showed that Ni-Co LDH nanosheets uniformly covered the surface of rGO/NF in the presence of CTAB, and is closely packed and thinner in thickness compared with the sample prepared in similar way without using surfactant. Such new thin and dense morphology facilitates electrolyte ions diffusion through the prepared electrode. A good cycling stability was obtained for the electrode in alkaline media. EIS measurements showed low values of internal resistance (Rs) and charge transfer resistance (Rct), indicating that the prepared nanocomposite is a promising candidate for supercapacitor applications. The asymmetric supercapacitor (ASC) based on the Ni-Co LDH/CTAB/rGO/NF as a positive electrode and rGO/NF as a negative electrode was assembled and it exhibited a Cs of 71.4 F g−1 at a current density of 2 A/g and correspondingly energy density of as high as 68 Wh kg−1.

HMTA-assisted uniform cobalt ions activated copper oxide microspheres with enhanced electrochemical performance for pseudocapacitors

Supercapacitors are being considered to be one of important electrochemical energy storage devices due to their high power density as compared with batteries and have remarkable applications. The large surface area transition metal oxides or hydroxides are excellent conductive materials and have been extensively used for supercapacitors. Herein, uniform copper oxide (CuO) and cobalt (Co) activated CuO (CuO:Co) microspheres were synthesized by a hexamethylenetetramine (HMTA)-assisted hydrothermal method. The HMTA was used as an additive surfactant to acquire the uniform microsphere morphology, which was confirmed by high-resolution field-emission scanning electron microscope and field-emission transmission electron microscope images. The phase form of the pristine CuO and CuO:Co powder samples was examined by X-ray diffraction patterns. For the application of pseudocapacitors, electrochemical studies were performed for the CuO and CuO:Co electrode materials in a three-electrode electrochemical cell system. The cyclic voltammetry and galvanostatic charge-discharge curves were measured at different scan rates and current densities, respectively, in 1 M KOH electrolyte solution. The calculated specific capacitance values of the CuO and CuO:Co electrodes were 77 and 284 F/g at a current density of 1 A/g, respectively. Interestingly, by incorporating small concentration of Co into CuO, the specific capacitance was enhanced approximately 4 times when compared with the pristine CuO electrode. The electrochemical impedance spectroscopy spectrum was analyzed for the pseudocapacitive behavior of CuO:Co electrode material. Furthermore, the CuO:Co electrode showed a capacitance retention (75.6%) after 1000 cycles at a current density of 3 A/g. Therefore, the obtained remarkable electrochemical results suggest that the low-cost CuO:Co electrode materials with improved electrochemical performance have promising applications in the field of pseudocapacitors.

Improving the symmetry of asymmetric supercapacitors using battery-type positive electrodes and activated carbon negative electrodes by mass and charge balance

Asymmetric supercapacitors (ASCs) are routinely fabricated using battery-type electrode materials as a positive electrode and electrochemical double layer materials as a negative electrode; the mass-loading in the electrodes is determined by assuming both to be capacitive charge storage materials. This protocol is erroneous as the cyclic voltammograms and galvanostatic charge-discharge curves of the resulting devices showed dissimilarity in the stored charges of the two electrodes and battery-type behaviors, respectively. Herein, we show by employing two choices of battery-type electrodes as positive electrodes and commercial activated carbon as negative electrode in 3M LiOH electrolyte that equal mass loading in both electrodes leads to supercapacitive charge storage. The positive electrode to negative electrode mass ratio is varied from 0.75 to 1.5 in a mass interval of 0.25 which includes a mass ratio of the conventional method. The electrochemical studies of the fabricated ASCs show that the charge storage capabilities depend on the electrode mass. Electrochemical impedance spectroscopy studies show that the equal mass ratio has low series and charge transfer resistances and wider frequency dispersion of capacitance.

Electrochemical co‐deposition and characterization of polyaniline and manganese oxide nanofibrous composites for energy storage properties

AbstractIon diffusion rate and contact surface area of conducting polymers increased by composite formation with nanometric‐size materials make them promising materials in the fabrication of energy storage devices. In this work, electronically conducting polyaniline and manganese oxide (PANI/MnO2) nanofibrous composites were electrochemically co‐deposited on stainless steel from binder‐free electrolyte solution. Structural characterization and morphological characterization of the materials were performed with Fourier‐transformed infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). SEM images show fibrous micro/nano‐architecture of the composites with cluster networking structure having 200–500 nm length and 100–200 nm diameter. Electrochemical and energy storage properties of the as‐synthesized materials were investigated with cyclic voltammetry (CV), galvanostatic charge discharge curves(GCDC), and potentiostatic electrochemical impedance spectroscopy (PEIS) without any binders. Electrochemical measurements as well as galvanostatic charge discharge curves at 1 mA constant current have shown maximum specific capacitance of 149 F/g for the composite prepared with 0.15 M MnSO4 in the co‐deposition bath. The composites retain 67% specific capacitance even after 400 cycles, indicating the stability of synthesized composite. PEIS confirms the pseudocapacitive nature of the synthesized composites.

Enhanced Electrochemical Performance of Li2Mn0.25Co0.75SiO4/C Cathode Materials for Li-Ion Batteries through Reduced Graphene Oxide Addition

Lithium transition metal orthosilicates (Li2MSiO4, where M=Fe, Mn, Co, or Ni)1 are promising cathode materials for Li-ion batteries with their high capacity (>300 mAh g−1) and high safety. Particularly, Li2MnSiO4 is expected to have a higher discharge capacity than Li2FeSiO4 and Li2CoSiO4, owing to the extraction of two lithium ions at lower voltage (4.1 and 4.5V) relative to them.1 However, practical energy density of Li2MnSiO4 is much less than the theoretical one due to its lower average discharge voltage (~3 V).2 One strategy to improve discharge voltage of Li2MnSiO4 is to substitute Co into Mn. Because Li2CoSiO4 practically exhibits a well-defined plateau near 4.25 V,3 and this is higher than that of Li2MnSiO4. On the other hand, recently, many researchers have focused their work on reduced graphene oxide (RGO) addition for cathode materials to improve their electrochemical performance.4 In this work, various content of RGO addition for Li2Mn0.25Co0.75SiO4/C (LMCS/RGO/C) were investigated to improve its electrochemical performance. LMCS/RGO/C was synthesized by hydrothermal method followed by carbon coating. In addition, Li2Mn0.25Co0.75SiO4/C (LMCS/C) was also synthesized for comparison. Furthermore, crystallographical and morphological data by x-ray diffraction and transmission electron microscope as well as galvanostatic cycling and rate performance were also collected. Fig. 1 shows the first galvanostatic charge-discharge curves for LMCS/RGO/C and LMCS/C at a current rate of 330 mA g−1 in a voltage range of 1.5–4.5 V at 30 °C. The first discharge capacities of LMCS/RGO/C and LMCS/C were 160 and 143 mAh g−1, respectively, and the corresponding coulombic efficiencies were 78.2 and 71.9 %. This indicates that RGO addition for LMCS/C enhances the electrochemical performance. Detailed data of our investigation will be presented in the meeting.

Interfacial characterization and supercapacitive properties of polyaniline—Gum arabic nanocomposite/graphene oxide LbL modified electrodes

In this manuscript, we describe the synthesis and electrochemical characterization of polyaniline—gum arabic nanocomposites and graphene oxide (PANI-GA/GO) modified electrodes with a detailed study concerning their supercapacitive properties. The electrode modification was carried out by using the Layer-by-Layer technique (LbL), where the PANI-GA nanocomposite dispersion was used as polycation and the GO colloidal dispersion as polyanion. The bilayer growth was followed by both UV–vis spectroscopy and cyclic voltammetry, and an increase in the characteristic PANI absorption and in the electrochemical signal was verified, confirming the electrode build up. Galvanostatic charge-discharge curves (GCDC) were performed to evaluate the supercapacitive properties of the modified electrodes, these results showed the dependence of the specific capacitance with the number of bilayers, where values of CS around 15mFcm−2 (i=0.1mAcm−2) were found. Electrochemical impedance spectroscopy confirmed the pseudocapacitive properties of the modified electrodes, showing an increase in the low-frequency capacitance with the number of bilayers. Hereby the (PANI-GA/GO)-LbL electrodes were shown to be good candidates for active materials in supercapacitors.

Study on the specific capacitance of an activated carbon cloth modified with reduced graphene oxide and polyaniline by cyclic voltammetry

This work describes a two-step process for the electrochemical coating of reduced graphene oxide (RGO) and polyaniline (PANI) onto an activated carbon cloth (ACC) by cyclic voltammetry (CV). The fact that the two syntheses are carried out independently of each other, makes it possible to select the experimental conditions for each one and to study the electrochemical response of RGO, PANI, and PANI onto RGO (RGOPANI), separately. Thus, by modifying the potential limits of the aniline-polymerization reaction, it was possible to observe the influence of RGO and the maximum amount of PANI that the carbon cloth can receive in terms of proper electrochemical response. Electrochemical properties were characterized by CV, galvanostatic charge-discharge curves (using three or two-electrodes symmetric cell configurations) and electrochemical impedance spectroscopy (EIS). A maximum improvement of 25%, 56% and 61% over the initial specific capacitance of ACC (about 129Fg−1) were obtained for RGO, PANI and RGOPANI coatings, respectively. Good cycling stability retaining 83% of the initial capacitance, after 1000 cycles stability test, was obtained for RGOPANI sample. Promising results of energy and power densities were also achieved. In the analyses by Fourier transform infrared spectroscopy (FTIR), the PANI-bands could be clearly identified which is indicative of a significant presence of PANI. Field emission scanning electron microscopy (FESEM) showed the morphology of RGO, PANI and RGOPANI onto the ACC fibers. These analyses helped to explain the electrochemical results.

Facile hydrothermal synthesis and characterization of Co2GeO4/r-GO@C ternary nanocomposite as negative electrode for Li-ion batteries.

Ternary nanocomposite of Co2GeO4/r-GO@C is synthesized by single step hydrothermal method followed by calcination. The XRD analysis reveals the formation of cubic structured Co2GeO4 and their corresponding functional groups identified through Raman analysis. The TEM analysis assures that uniform distribution of Co2GeO4 nanoparticles on the r-GO layers. The Galvanostatic charge-discharge (GCD) curve demonstrates that the initial discharge capacity of pristine Co2GeO4, Co2GeO4/r-GO and Co2GeO4/r-GO@C composite is 1400, 1284 and 1594mAhg-1 at 50mAg-1, respectively. The cycling stability curve shows the specific capacity of 609, 970 and 1180mAhg-1 for pristine, Co2GeO4/r-GO and Co2GeO4/r-GO@C composite, respectively over 15 cycles. The ternary composite of Co2GeO4/r-GO@C delivers the discharge capacity of 323mAhg-1 at high current density of 1Ag-1 over 500 cycles with capacity retention of 71%. The rate capability curve indicates that Co2GeO4/r-GO@C composite shows the better rate capability.

Pyridine-containing metal-organic frameworks as precursor for nitrogen-doped porous carbons with high-performance capacitive behavior

A novel pyridine-containing metal-organic framework (MOF, [Zn(bpdc)DMA]·DMF, bpdc = 2,2′-bipyridine-5,5′-dicarboxylate) was directly carbonized at different temperature to produce nitrogen-doped porous carbons (NPCs). The as-prepared porous carbons, NPC800 (obtained at 800 °C) and NPC1000 (obtained at 1000 °C), were characterized by scanning electron microscopy, X-ray powder diffraction, N2 sorption isotherms, and X-ray photoelectron spectroscopy (XPS). The results from elemental analysis and XPS confirmed that the pyridine groups in MOF served as nitrogen sources to produce NPCs, and NPC800 possessed the higher nitrogen content than NPC1000. N2 sorption data demonstrated that NPC800 exhibited the larger specific surface area and pore volume than NPC1000. The capacitive properties of NPC800 and NPC1000 were investigated in KOH aqueous electrolyte by cyclic voltammetry and galvanostatic charge–discharge curves. NPC800 showed the higher specific capacitance (226.6 F g−1 at 1 A g−1) than NPC1000 and retained 178.0 F g−1 even at a high current density up to 10 A g−1. It was found that the donation of N species to capacitance was more than the role of porosity in view of their synergetic effect.

Electrochemical impedance spectroscopy characterization of LiFePO4 cathode material with carboxymethylcellulose and poly-3,4-ethylendioxythiophene/polystyrene sulfonate

Novel cathode material compositions based on lithium iron phosphate (LFP) were prepared using conducting polymer dispersion poly-3,4-ethylenedioxythiopene/polystyrene sulfonate (PEDOT:PSS) and water-based carboxymethylcellulose (СМС) as a binder solely and in mixture PEDOT:PSS/СМС. The electrochemical properties of materials in lithium-ion batteries were investigated by galvanostatic charge-discharge curves and by electrochemical impedance spectroscopy and the results were compared with conventional PVDF-bound material. Our best materials consisting of 92wt% of C-LiFePO4, 4wt% of carbon black and 4wt% of conducting polymer binder exhibited excellent rate capability with discharge capacity 148mAhg−1 (at 0.2C, normalized by the electrode mass), 143mAhg−1 at 1C and 128mAhg−1 at 5C as well as good cycling stability at 1C (less than 1% decay after 100 cycles).Impedance spectra of batteries with different compositions were measured and analyzed. Comparison of kinetic parameters obtained for different electrodes revealed main factors responsible for significant improvement of electrochemical performance of LFP-based cathode materials modified with conducting polymer in comparison with conventional electrode. The transition from conventional PVDF-bound LFP-based cathode composition to modified by conducting polymer PEDOT:PSS/CMC was found very effective. The electrode with optimal composition showed substantial decrease of interfacial charge transfer resistance for 30 times, and decrease of Warburg diffusion resistance.The mechanism of positive influence of conducting binder on electrochemical properties of cathode material is discussed.

Porous cellulose/graphene oxide nanocomposite as flexible and renewable electrode material for supercapacitor

The increasing demand for portable, wearable, miniaturized and flexible consumer electronic devices requests the development of flexible and renewable energy storage devices. This paper reports a flexible and renewable electrode material for supercapacitor. The electrode material is made by preparing a porous structured cellulose/graphene oxide (GO) nanocomposite. The morphology of the nanocomposite is shown to be porous structure with a pore size about 10μm. The Fourier transform infrared spectroscopy of the nanocomposites exhibits that the cellulose and GOs are successfully grafted by a grafting agent, which results in uniform dispersion of GOs in the cellulose matrix. The electrical performance of the nanocomposite is evaluated by measuring cyclic voltammograms and galvanostatic charge-discharge curves. Low cost and sustainability of the cellulose and graphene oxide nanocomposite encourage its possible use for electrode material of flexible energy storage devices.

Nickel hydroxide obtained by high-temperature two-step synthesis as an effective material for supercapacitor applications

Hybrid supercapacitors with nickel hydroxide electrode are widely used as modern power sources for electrovehicles, ignition of different electric engines, etc. Nickel hydroxide for supercapacitor use must satisfy special features which are quite different from those requested for battery application. The aim of this work is to improve the promising two-stage high-temperature method by altering hydrolysis condition (hot and cold) in order to obtain Ni(OH)2 with improved electrochemical activity. Ni(OH)2 samples have been investigated by PXRD, TG, DSC, SEM, TEM, cyclic voltammogramm, and galvanostatic charge-discharge cycling. It has been established from PXRD, TG, and DSC analyses that material obtained by hydrolysis at high temperature is a highly crystalline β-Ni(OH)2 characterized by high thermal stability. Materials prepared by cold hydrolysis are a highly defective βbc-Ni(OH)2, with 6.3 % water content and a lower thermal stability. It has been shown that samples prepared by hot hydrolysis have a high redox reversibility and electrochemical cycling stability, but a lower electrochemical capacity. This suggests that the electrochemical processes are localized in the thin layer at the particle surface. Cyclic voltammograms of samples prepared by cold hydrolysis exhibit gradual activation of the active material, anyhow resulting in higher capacity. By means of the galvanostatic charge-discharge curves at different current densities, the specific capacities of the samples have been calculated. The sample prepared by cold hydrolysis has higher specific capacities than the sample prepared by hot hydrolysis.

Preparation of porous carbon nanofibers derived from PBI/PLLA for supercapacitor electrodes

Porous carbon nanofibers were prepared by electrospinning blend solutions of polybenzimidazole/poly-L-lactic acid (PBI/PLLA) and carbonization. During thermal treatment, PLLA was decomposed, resulting in the creation of pores in the carbon nanofibers. From SEM images, it is shown that carbon nanofibers had diameters in the range of 100–200 nm. The conversion of PBI to carbon was confirmed by Raman spectroscopy, and the surface area and pore volume of carbon nanofibers were determined using nitrogen adsorption/desorption analyses. To investigate electrochemical performances, coin-type cells were assembled using free-standing carbon nanofiber electrodes and ionic liquid electrolyte. cyclic voltammetry studies show that the PBI/PLLA-derived porous carbon nanofiber electrodes have higher capacitance due to lower electrochemical impedance compared to carbon nanofiber electrode from PBI only. These porous carbon nanofibers were activated using ammonia for further porosity improvement and annealed to remove the surface functional groups to better match the polarity of electrode and electrolyte. Ragone plots, correlating energy density with power density calculated from galvanostatic charge–discharge curves, reveal that activation/annealing further improves energy and power densities.

Facile one-step synthesis of nanocomposite based on carbon nanotubes and Nickel-Aluminum layered double hydroxides with high cycling stability for supercapacitors

Nickel-Aluminum Layered Double Hydroxide (NiAl-LDH) and nanocomposite of Carbon Nanotubes (CNTs) and NiAl-LDH (CNTs/NiAl-LDH) were prepared by using a facile one-step homogeneous precipitation approach. The morphology, structure and electrochemical properties of the as-prepared CNTs/NiAl-LDH nanocomposite were then systematically studied. According to the galvanostatic charge-discharge curves, the CNTs/NiAl-LDH nanocomposite exhibited a high specific capacitance of 694Fg−1 at the 1Ag−1. Furthermore, the specific capacitance of the CNTs/NiAl-LDH nanocomposite still retained 87% when the current density was increased from 1 to 10Ag−1. These results indicated that the CNTs/NiAl-LDH nanocomposite displayed a higher specific capacitance and rate capability than pure NiAl-LDH. And the participation of CNTs in the NiAl-LDH composite improved the electrochemical properties. Additionally, the capacitance of the CNTs/NiAl-LDH nanocomposite kept at least 92% after 3000cycles at 20Ag−1, suggesting that the nanocomposite exhibited excellent cycling durability. This strategy provided a facile and effective approach for the synthesis of nanocomposite based on CNTs and NiAl-LDH with enhanced supercapacitor behaviors, which can be potentially applied in energy storage conversion devices.

Lithium-Rich Layered Oxide Li1.18 Ni0.15 Co0.15 Mn0.52 O2 as the Cathode Material for Hybrid Sodium-Ion Batteries.

Li-rich layered oxide Li1.18 Ni0.15 Co0.15 Mn0.52 O2 (LNCM) is, for the first time, examined as the positive electrode for hybrid sodium-ion battery and its Na(+) storage properties are comprehensively studied in terms of galvanostatic charge-discharge curves, cyclic voltammetry and rate capability. LNCM in the proposed sodium-ion battery demonstrates good rate capability whose discharge capacity reaches about 90 mA h g(-1) at 10 C rate and excellent cycle stability with specific capacity of about 105 mA h g(-1) for 200 cycles at 5 C rate. Moreover, ex situ ICP-OES suggests interesting mixed-ions migration processes: In the initial two cycles, only Li(+) can intercalate into the LNCM cathode, whereas both Li(+) and Na(+) work together as the electrochemical cycles increase. Also the structural evolution of LNCM is examined in terms of ex situ XRD pattern at the end of various charge-discharge scans. The strong insight obtained from this study could be beneficial to the design of new layered cathode materials for future rechargeable sodium-ion batteries.

Investigation on Electrochemical Properties of TiNb6O17 As the New Anode Materials for High Power Lithium Ion Batteries

Among the commercial anode materials, graphite isn`t suitable for high-power applications such as electric vehicles and large-scale energy storage due to formation of the solid-electrolyte interphase (SEI) leading to lithium irreversibly at about 0.8V and inactive high rate performance. Although, Li4Ti5O12 (LTO) are being pursued as alternatives to graphite electrodes due to high lithium storage voltages (1.0~2.0V) which are higher than the formation of SEI voltage and high rate capability, it has low theoretical capacity (~175mAhg-1). Recently titanium-niobium oxides (TNO) such as TiNb2O7, Ti2Nb10O29 with high redox potential range have been considered as interesting candidates for anode material of LIB. Because they have higher theoretical capacity of 380~396mAhg-1 due to multiple redox couples such as Ti4+/Ti3+, Nb5+/Nb4+, Nb4+/Nb3+ by compared with LTO having only Ti4+/Ti3+ redox couple. In addition, they have good stability, high rate capability. However, they are show limited reversible capacities (240~270mAhg-1) owing to low electronic conductivity and lithium diffusion coefficient. Chunfu Lin et al. presented that TiNb6O17 showed higher capacity, lithium diffusion coefficient and high rate performance than Ti2Nb10O29. Because it is consist of larger amount of Nb5+ ions with larger size (0.64A) than that of Ti4+ ions (0.605A). As a result, it has more open lithium insertion structure and lithium diffusion coefficient than Ti2Nb10O29. But this study not exactly proposed chemical properties such as oxidation state, lithium insertion behavior of TiNb6O17. Based on above study, we have compared physical properties and electrochemical performance of new compound TiNb6O17 and TiNb2O7 which were fabricated using a solid-state reaction method. In a typical synthesis, TiO2 and Nb2O5 in the molar ratio (1:2, 1:6) were mixed with ethanol in a ball mill at 300rpm for 4h. After drying, calcination treatment is carried at 1100°C for 10h in air atmosphere. The crystal structures were determined by X-ray diffraction (XRD), rietveld refinement in order to compare lattice parameters and unit cell volume. X-ray absorption spectroscopy (XAS) was measured to confirm variation of oxidation state and lithium insertion/extraction behavior after charge and discharge. The morphologies were observed by scanning electron microscope (SEM). Finally, we investigated electrochemical performance by measuring cyclic voltammetry, galvanostatic charge-discharge curve and C-rate. Also, electrochemical impedance spectroscopy (EIS) and slow scan rate cyclic voltammetry (SSCV) were measured to compare lithium diffusion coefficients of TiNb2O7 and TiNb6O17. As the result of, TiNb6O17 exhibited better electrochemical performance with lithium diffusion coefficient, charge-discharge capacities and high rate performance than TiNb2O7.

Hydrothermal Synthesis and Characterization of Co2GeO4/Rgo@C Ternary Composite As Negative Electrodes for Li-Ion Batteries

In this present work, pristine Co2GeO4, binary Co2GeO4/reduced graphene oxide (rGO) composite and ternary composite of Co2GeO4/rGO@C is prepared by single step hydrothermal process followed by calcination. The amount of carbon content and rGO is identified through thermogravimetric analysis (TGA). XRD analysis reveals the compound formation of single phase Co2GeO4. TEM and HRTEM images clearly elucidate the presence of ternary phases of Co2GeO4, r-GO and C in the ternary composite. The Galvanostatic charge-discharge (GCD) curve demonstrates that the initial discharge capacity of pristine Co2GeO4, Co2GeO4/rGO and Co2GeO4/rGO@C composite is 1400, 1284 and 1594 mAh g-1 at 50 mAh g-1, respectively. The observed discharge capacity is higher than the theoretical capacity of Co2GeO4 which is due to reduction of organic electrolyte and the formation of solid electrolyte interphase film (SEI). The cycling stability curve shows the specific capacity of 609, 970 and 1180 mAh g-1 for pristine, Co2GeO4/rGO and Co2GeO4/rGO@C composite respectively over 15 cycles which confirms that Co2GeO4/rGO@C composite exhibits the stable and high specific capacity. The rate capability curve and EIS spectrum is carried out for the prepared samples which indicates that Co2GeO4/rGO@C composite shows the better rate capability and good electronic conductivity.

The application of catalyst-recovered SnO2 as an anode material for lithium secondary batteries.

We studied the electrochemical characteristics of tin dioxide (SnO2) recovered from waste catalyst material which had been previously used in a polymer synthesis reaction. In order to improve the electrochemical performance of the SnO2 anode electrode, we synthesized a nanocomposite of recovered SnO2 and commercial iron oxide (Fe2O3) (weight ratio 95:5) using a solid state method. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analyses revealed an additional iron oxide phase within a porous nanocomposite architecture. The electrochemical characterizations were based on galvanostatic charge-discharge (CD) curves, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). In the first discharge, the capacity of the SnO2-Fe2O3 nanocomposite was 1700mAhg(-1), but was reduced to about 1200mAhg(-1) in the second discharge. Thereafter, a discharge capacity of about 1000mAhg(-1)was maintained up to the 20th cycle. The SnO2-Fe2O3 nanocomposite showed better reversible capacities and rate capabilities than either the recovered SnO2 or commercial Fe2O3 nanoparticle samples.