Papers by Keyword: Electrochemical Performance

Abstract: LiCo_0.9X_0.1O₂ (where X=Mn and Fe) were synthesized using self-propagating combustion (SPC) method using citric acid as a combustion agent. The precursors of LiCo_0.9X_0.1O₂ were annealed at a temperature of 800 °C at 24 h. The phase and crystalinity of the materials were characterized using X-Ray Diffraction (XRD). All the materials were observed to be single and pure phase with no impurity peaks detected. The morphology and particle sizes of the materials were also analyzed using Field Emission Scanning Electron Microcopy (FESEM). Finally, the electrochemical performance of the materials was studied using charge-discharge cycling in the voltage range of 2.5 to 4.3 V. Based on the results from charge-discharge studies, Mn substituted cathode materials exhibit better specific discharge capacity compared with Fe substituted cathode materials.

Abstract: Spinel Li₄Ti₅O₁₂ (LTO) doped with Mg²⁺ was synthesized by solid-phase reaction method. The Mg²⁺ doping quantity was 3%, 6%, 9%, and 12%, respectively. The structure and electrochemical performance of the prepared LTO composites were investigated by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), and galvanostatic charge-discharge tests. It was found that the doped Mg ion did not change the structure of Li₄Ti₅O₁₂, and it was evenly distributed around Li₄Ti₅O₁₂. When Mg²⁺ doping quantity increased from 3% to 12%, the internal resistance and charge transfer resistance of the composite both decreased. The first discharge specific capacity of 6%-Mg²⁺ doped LTO composite was 168 mAh/g, which was close to the theoretical capacity of pure lithium titanate (175 mAh/g), and the capacity retention rate was 98% after 100 cycles.

Abstract: In this study, Si@C/Graphite composite anodes were synthesized through spray drying and pyrolysis using silica, artificial graphite, and two kinds of organics (phenolic resin or pitch). The Si@PR-C/Graphite exhibits enhanced electrochemical performance for lithium-ion batteries. The first charge-discharge specific capacity is 512.8mAh/g and 621.8mAh/g, respectively, the initial coulombic efficiency is 82.5% at 100mA/g, and its capacity retention rate reached as high as 85.4% with the capacity fade rate of less than 0.18% per cycle after 85 cycles. The Si@PI-C/Graphite also presents excellent discharge specific capacity of 702.8mAh/g with the capacity retention rate of 76.9% after 30 cycles. Mechanisms for high electrochemical performances of the Si@C/Graphite composite anode are discussed. It found that the enhanced electrochemical performance due to the formation of core/shell microstructure. These encouraging experimental results suggest that proper organic carbon source has great potential for improvement of electrochemical properties of pure silicon as anode. Key words:lithium-ion batteries; anode; Si@C/Graphite composite; electrochemical performance

Abstract: Using hydrated manganese sulfate and general type graphene (GR) as raw materials, Mn₃O₄/GR composite has been successfully prepared by the liquid phase chemical co-precipitation method at room temperature. X-ray diffraction (XRD) was used to investigate the phase structure of Mn₃O₄ powder and Mn₃O₄/GR composite; The electrochemical performances of the samples were elucidated by cyclic voltammetry and galvanostatic charge-discharge test in 0.5 mol/L Na₂SO₄ electrolyte. The results show that the Mn₃O₄/GR composite possesses graphene phase and good reversibility; the composite also displays a specific capacitance of 318.8 F/g at a current density of 1 A/g.

Abstract: As a kind of green, environment-friendly and sustainable carbon material, biomass carbon has simple processing technology and undoubtedly been the best candidate for industrialization. Different activation processes can be used to change the internal microstructure of carbons, and design pores that facilitate ions transport and electrons conduction, thereby achieving the ultimate goal of improving electrochemical performance. Herein, we select the same activator (KOH) and activation time (3 h) but change the activation temperature (300 °C, 600 °C, 800 °C) to obtain biomass-derived carbon with the different micromorphology, pores structure and heteroatoms content. Rather, We choose ether-based electrolyte, due to its highly reversible graphite co-intercalation reaction, the problem of extremely low electrochemical activity of graphite in ester electrolytes is avoided. Results indicate, the sample PCS-600 exhibites sheet structure with specific surface area of 38.3 m²/g and large average pore width of 2.77 nm, which providing sufficient conditions for ions transport. PCS-600 has 1.05 at% N and 5.75 at% O heteroatoms, which providing additional pseudocapacitance. In addition, the electrochemical performance of PCS-600 is optimal, at a current density of 0.1 A/g, its specific capacity is 198.6 mA h/g, maintain at ~95% after 100 cycles, with coulomb efficiency ~100%.

Abstract: Nickel-rich layered oxides (Ni ≥60%) are considered as the most promising cathode materials for lithium-ion batteries due to its high energy density and low cost. However, its cycling performance is seriously influenced by the synthesis condition, like the sintering temperature, time and atmosphere. Herein, we investigate different properties of LiNi_0.83Co_0.11Mn_0.06O₂ (LNCMO) sintered from 720 to780 °C, and the cathode calcined at 760 °C display the most perfect layered structure and the uniform distribution of primary particles size. Therefore, the LNCMO sintered at 760 °C exhibited the best rate capability of 118 mAh·g^-1 at 10 C and the highest capacity retention of 95.44 % after 100 cycles at 1 C. Our results indicate that the cycling performance and rate capability of LNCMO are heavily depended on the sintering temperature.

Abstract: The novel perovskite oxide series of Sm_1-xZr_xFe_1-yMg_yO₃ (x,y = 0.5, 0.7, 0.9) were synthesized by solid state reaction method. X-ray diffraction (XRD), Rietveld refinement, scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and conductivity analysis were carried out. XRD patterns of sintered materials revealed the shifted Bragg reflection to higher angle for the higher content of Zr and Mg. This is related to the ionic size of the dopant elements. Rietveld refinement showed that all compounds crystallized in cubic space group of Fm-3m. SEM images showed that the grains were well defined with highly dense surfaces makes it potential as an electrolyte material in solid oxide fuel cells (SOFCs) or gases sensors. Impedance spectroscopy at 550-800 °C shows that conductivity is higher at higher temperature. Sm_0.5Zr_0.5Fe_0.5Mg_0.5O₃ shows the highest conductivity of 5.451 × 10^-3 S cm^-1 at 800 °C. It was observed that 50% molar ratio of Mg and Zr doping performed highest conductivity.

Abstract: The development of high-performance cathodes is essential towards the operation of proton-conducting fuel cells (PCFCs) at intermediate temperatures. To that end, the performance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) cathodes is very attractive. In the present works, LSCF cathode powders were synthesized by a sol-gel method with the aid of ethylene glycol which served as the dispersing agent. The pristine and modified samples were each denoted as LSCF64 and LSCF-EG5. The phase formation and morphology of the cathode powders were examined by X-Ray diffractometer (XRD) and field emission scanning electron microscopy (FESEM), respectively. In order to evaluate the cathode performance, a symmetrical cell of electrolyte supported PCFCs were examined using an electrochemical impedance spectroscopy (EIS) at a 700 ^oC in atmosphere containing humidified air. The formation of LSCF single phase was attained at 700 °C for both prepared samples. The FESEM images confirms an improvement in the microstructure of the modified cathode. The impedance spectra obtained from the electrochemical impedance measurement were resolved by a fitting procedure using an equivalent circuit that consists of a combination of two parallel pairs of resistor-constant phase element (R-Q) in series. The area specific resistance (ASR) determined for LSCF64 and LSCF-EG5 is 1.55 and 0.23 Ωcm² , respectively. The better performance exhibited by LSCF-EG5 is attributed to its higher cathode reaction site due the improved microstucture. This study reveals that the application of ethylene glycol as dispersing agent is effective in producing a high quality cathode material for better PCFCs performance.

Abstract: In order to investigate the effect of lanthanum on the electrochemical properties of CoB amorphous alloy, Co-La_x-B alloys (x = 0, 0.1, 0.5, and 1) were prepared by chemical reduction method. As negative electrodes in alkaline rechargeable batteries, Co-La_x-B alloys exhibit superior electrochemical properties. For Co-La_0.1-B alloy, at the discharge current density of 100 mA/g, the initial discharge capacity is 830.6 mAh/g and the discharge capacity has remained around 317.3 mAh/g even after 100 cycles. Moreover, the high-rate discharge ability (HRD) of Co-La_0.1-B alloy electrode at the discharge current density of 300 mA/g, 600 mA/g, and 900 mA/g is 98.16%, 95.17%, and 91.86%, respectively. The anodic polarization (AP) and the electrochemical impedance spectra (EIS) measurements indicate that the kinetics of electrochemical performance of the alloys is remarkably improved with the addition of lanthanum.

Abstract: An attempt has been made to synthesize hexagonal LiMnBO₃ (h-LMB) through sol-gel technique. The synthesized h-LiMnBO₃ have been examined for their physical and electrochemical characteristics by X-ray diffraction analysis (XRD) and Thermal analysis (TG), Scanning electron microscopy (SEM), Raman spectroscopy as well as through charge –discharge cycling. XRD results revealed the existence of hexagonal polymorphs with P6 space group. Stability of h-LiMnBO₃ material is analyzed by thermal analysis. SEM image shows spherical shape nanoparticle with the average diameter 50 nm. Raman spectroscopy result indicates the presence of Mn-O vibration. An electrochemical study indicates the sol-gel derived hexagonal LiMnBO₃ delivers a first charging capacity of 97.5 mAh g^-1 and discharging capacity of 55. 85 mAh g^-1 within the potential window of 2V-4.5 V at C/10 rate and retaining a reversible discharge capacity of 42.71 mAh g^-1 at the 10^th cycle.