(NH4)0.5V2O5 nanobelt with good cycling stability as cathode material for Li-ion battery

(NH₄)_0.5V₂O₅ nanobelt is synthesized by sodium dodecyl benzene sulfonate (SDBS) assisted hydrothermal reaction as a cathode material for Li-ion battery. The as-prepared (NH₄)_0.5V₂O₅ nanobelts are 50-200 nm in diameter and several micrometers in length. The reversible lithium intercalation behavior of the nanobelts has been evaluated by cyclic voltammetry, galvanostatic discharge-charge cycling, and electrochemical impedance spectroscopy. The (NH₄)_0.5V₂O₅ delivers an initial specific discharge capacity of 225.2 mAh g⁻¹ between 1.8 and 4.0 V at 15 mA g⁻¹, and still maintains a high discharge capacity of 197.5 mAh g⁻¹ after 11 cycles. It shows good rate capability with a discharge capacity of about 180 mAh g⁻¹ remaining after 40 cycles at various rates and excellent cycling stability with the capacity retention of 81.9% after 100 cycles at 150 mA g⁻¹. Interestingly, the excess 120 mAh g⁻¹ capacity in the first charge process is observed, most of which could be attributed to the extraction of NH₄⁺ group, verified by Fourier transform Infrared (FT-IR) and X-ray diffraction (XRD) results.     

Effect of O2 concentration on performance of solid oxide fuel cells with V2O5 or Cu added (LaSr)(CoFe)O3-(Ce,Gd)O2−x cathode with and without NO

A solid oxide fuel cell unit is constructed with Ni-(Ce,Gd)O_2−x (GDC) as the anode, yttria-stabilized zirconia as the electrolyte, and V₂O₅ or Cu added (LaSr)(CoFe)O₃-GDC as the cathode. The effect of the O₂ concentration on the open circuit voltage (OCV) is studied and a mass-transfer limited OCV is observed. The power density with Cu addition can be much higher than that with V₂O₅ addition but the effect of the O₂ concentration with Cu addition is larger than that with V₂O₅ addition. Without the presence of NO, both the power density and the OCV decrease with decreasing O₂ concentration. The OCV variation can be substantial with the variation of the flow rate, the O₂ concentration and the NO concentration. The presence of CO₂ can increase the OCV while that of NO can decrease the OCV; however, a synergistic effect can occur on the OCV when NO is present at a very low O₂ concentration which results in a sudden drop of the OCV.     

Performance improvement of LiMn2O4 as cathode material for lithium ion battery with bismuth modification

Spinel lithium manganese oxides (LiMn₂O₄) modified with and without bismuth by sol–gel method were investigated by theoretical calculation and experimental techniques, including galvanostatic charge/discharge test (GC), cyclic voltammetry (CV), chronopotentiometry (CP), electrochemical impedance spectroscopy (EIS), inductively coupled plasma (ICP), powder X-ray diffraction (XRD), BET measurement, and infrared spectroscopy (IR). It is found that the performance of LiMn₂O₄ can be improved by the bismuth modification. The modified and the unmodified samples have almost the same initial discharge capacity, 118 and 120 mAh g⁻¹, respectively. However, the modified sample has better cyclic stability than the unmodified sample. After 100 cycles, the capacity remains 100 and 89 mAh g⁻¹ for the modified and the unmodified samples, respectively. Moreover, the results from EIS show that the modified sample has a quicker kinetic process for Li ion intercalation/de-intercalation than the unmodified one; the charge-transfer resistance of the former is less than one-sixth of that of the latter. After immersion in electrolyte (DMC:EC:EMC = 1:1:1, 1 mol L⁻¹ LiPF₆) for 10 h at room temperature, the modified sample has less change in open circuit potential, crystal volume, and vibration absorption of Mn–O bond, and has less dissolution of manganese into solution than the unmodified sample.     

Effect of FePO4 coating on electrochemical and safety performance of LiCoO2 as cathode material for Li-ion batteries

LiCoO₂ was surface modified by a coprecipitation method followed by a high-temperature treatment in air. FePO₄-coated LiCoO₂ was characterized with various techniques such as X-ray diffraction (XRD), auger electron spectroscopy (AES), field emission scanning electron microscope (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), electrochemical impedance spectroscopy (EIS), 3 C overcharge and hot-box safety experiments. For the 14500R-type cell, under a high charge cutoff voltage of 4.3 and 4.4 V, 3 wt.% FePO₄-coated LiCoO₂ exhibits good electrochemical properties with initial discharge specific capacities of 146 and 155 mAh g⁻¹ and capacity retention ratios of 88.7 and 82.5% after 400 cycles, respectively. Moreover, the anti-overcharge and thermal safety performance of LiCoO₂ is greatly enhanced. These improvements are attributed to the FePO₄ coating layer that hinders interaction between LiCoO₂ and electrolyte and stabilizes the structure of LiCoO₂. The FePO₄-coated LiCoO₂ could be a high performance cathode material for lithium-ion battery.     

Preparation and performances of LiFePO4 cathode in aqueous solvent with polyacrylic acid as a binder

Here we report the preparation of LiFePO₄ cathode for lithium ion battery in the aqueous solvent with polyacrylic acid (PAA) as a binder. Its performances were studied by cyclic voltammetry (CV), charge–discharge cycle test, electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), and scanning electron microscopy (SEM), and compared with the cathode prepared in N-methyl-2-pyrrolidone (NMP) solvent by using polyvinylidene fluoride (PVDF) as a binder. It is found that the cathode prepared in the aqueous solvent shows better performances than that in NMP solvent, including the better reversibility, the smaller resistances of solid electrolyte interphase and charge exchange, the less polarization, higher capacity and cyclic stability for lithium ion intercalation in or de-intercalation from LiFePO₄. The aqueous solvent is also more environmental friendly and cheaper than NNP. In addition, PAA is less costly than PVDF. Consequently, the preparation of LiFePO₄ cathode in the aqueous solvent by using a PAA binder provides lithium ion battery with improved performances at a less cost and in a more environmental friendly way.     

Effect of protecting metal oxide (Co3O4) layer on electrochemical properties of spinel Li1.1Mn1.9O4 as a cathode material for lithium battery applications

Metal oxide (Co₃O₄) was coated on spinel Li_1.1Mn_1.9O₄ using glutamic acid. Powder X-ray diffraction pattern of Co₃O₄-coated spinel Li_1.1Mn_1.9O₄ showed that the Co₃O₄ coating medium was not incorporated in the spinel bulk structure. Morphology of the Co₃O₄-coated spinel Li_1.1Mn_1.9O₄ was observed by scanning electron microscopy and transmission electron microscopy. The cycling performance of the Co₃O₄-coated spinel Li_1.1Mn_1.9O₄ was obviously improved, compared to the pristine Li_1.1Mn_1.9O₄ at elevated temperature (55 °C). Improvement of rate capability was also achieved at high C-rates.     

Effect of lithium phosphate on the structural and electrochemical performance of nanocrystalline LiFePO4 cathode material with iron defects

The influence of excessive lithium on the crystal structure, morphology, and electrochemical properties of Fe-deficient Li_xFePO₄ (x = 1.00, 1.02, 1.04, 1.05) cathode material was investigated using co-precipitation and the carbon thermal method. The X-ray diffraction pattern and Rietveld refinement results show that excessive Li⁺ combines with the phosphate group to form Li₃PO₄ rather than occupying the Fe site to form antisite pairs. Benefitting from the intrinsic ion conductivity of lithium phosphate, the lithium diffusion coefficient of Li_xFePO₄ increases. However, the charge transfer impedance (Rct) also increases with increasing Li content due to the presence of Li₃PO₄, a nonconductive phase that can block the electric transfer channel. The biphasic Li_xFePO₄ (x = 1.02) compound shows the best performance. This work suggests an effective and easy way to improve the electrochemical performance by adding excessive Li, which leads to the formation of Li₃PO₄.     

A comparison of fluorine tin oxide and indium tin oxide as the transparent electrode for P3OT/TiO2 solar cells

Open circuit voltage (V_oc) and other photovoltaic parameters from fluorine tin oxide (FTO) P3OT/TiO₂ composite solar cells have been investigated in comparison with those from the indium tin oxide (ITO) devices with the same device structure and fabrication process. From the experimental results, the performance of FTO-based devices is better than that of ITO devices in terms of V_oc, short circuit current density (J_sc), and power conversion efficiency. The origin of V_oc and the higher V_oc of FTO can be explained and estimated by metal–insulator–metal model with a non-ohmic cathode contact.     

Structural,electrical, and electrochemical properties of cobalt-doped NiFe2O4 as a potential cathode material for solid oxide fuel cells

In this work, Co-doped NiFe₂O₄ spinels (NFCO-x) are successfully fabricated and characterized as possible cathode materials for the intermediate-temperature solid oxide fuel cells (SOFC). Results of the binding energy calculations using the density functional theory suggest that the reverse spinel structure is stable when Co³⁺ occupies the octahedral interstitial sites. Total and ionic-only conductivities indicate that NFCO-x are a kind of mixed electronic-ionic conductors. Ionic transferring numbers are approximately 0.049 and 0.006 for NFCO-0.1 and NFCO-0.5, respectively, measured at 700 °C in air. Co dopant in the NFCO-x improves the electronic conductivity at the expense of the ionic conductivity. For NFCO-0.5, electronic and ionic conductivities are approximately 0.24 and 9.6 × 10⁻⁴ S cm⁻¹, respectively, measured also at 700 °C in air. Unlike behaviour of the conductivities, the polarization resistance of symmetric cells with NFCO-x electrodes decreases when increasing the Co content (x) to a certain level, and then increases. The cell containing the NFCO-0.5 electrode exhibits the lowest polarization resistance (R_p), which is approximately 1.51 Ω cm² at 650 °C. For single cells, the maximum power density is 320 mW cm⁻² measured at 650 °C using a 38-μm-thick SDC electrolyte and an NFCO-0.5 cathode.     

Cycling and rate performance of Li-LiFePO4 cells in mixed FSI-TFSI room temperature ionic liquids

A study is conducted of the performance of lithium iron(II) phosphate, LiFePO₄, as a cathode material in a lithium secondary battery that features an ionic liquid electrolyte solution and a metallic lithium anode. The electrolyte solution comprises an ionic liquid of a N-methyl-N-alkyl-pyrrolidinium (alkyl = n-propyl or n-butyl) cation and either the bis(fluorosulfonyl)imide [(FSO₂)₂N⁻] or bis(trifluoromethanesulfonyl)imide [(F₃CSO₂)₂N⁻] anion, together with 0.5 mol kg⁻¹ of lithium bis(trifluoromethanesulfonyl)imide salt. For N-methyl-N-propyl-pyrrolidinium bis(fluorosulfonyl)imide, coin cells discharging at rates of C/10 and 4C yield specific capacities of 153 and 110 mAh g⁻¹, respectively, at an average coulombic efficiency of 99.8%. This performance is maintained for over 400 cycles at 50 °C and therefore indicates that these electrolyte solutions support long-term cycling of both LiFePO₄ and metallic lithium while, due to the negligible volatility of ionic liquids, surrounding the lithium in an inherently safe, non-flammable medium.     

Performance of double-proveskite YBa0.5Sr0.5Co2O5+δ as cathode material for intermediate-temperature solid oxide fuel cells

Double-proveskite YBa_0.5Sr_0.5Co₂O_5+δ (YBSC) was investigated as potential cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). YBSC material exhibited a good chemical compatibility with the La_0.9Sr_0.1Ga_0.8Mg_0.115Co_0.085O_2.85 (LSGMC) electrolyte up to 950 °C for 2 h. The substitution of Sr for Ba significantly enhanced the electrical conductivity of the YBSC sample compared to undoped YBaCo₂O_5+δ, and also slightly increased the thermal expansion coefficient. At 325 °C a semiconductor-metal transition was observed and the maximum electrical conductivity of YBSC was 668 S cm⁻¹. The maximum power densities of the electrolyte-supported single cell with YBSC cathode achieved 650 and 468 mW cm⁻² at 850 and 800 °C, respectively. Preliminary results suggested that YBSC could be considered as a candidate cathode material for application in IT-SOFCs.     

NiMn2O4 spinel as an alternative coating material for metallic interconnects of intermediate temperature solid oxide fuel cells

In an effort to improve the performance of SUS 430 alloy as a metallic interconnect material, a low cost and Cr-free spinel coating of NiMn₂O₄ is prepared on SUS 430 alloy substrate by the sol-gel method and evaluated in terms of the microstructure, oxidation resistance and electrical conductivity. A oxide scale of 3-4 μm thick is formed during cyclic oxidation at 750 °C in air for 1000 h, consisting of an inner layer of doped Cr₂O₃ and an outer layer of doped NiMn₂O₄ and Mn₂O₃; and the growth of Cr₂O₃ and formation of MnCr₂O₄ are depressed. The oxidation kinetics obeys the parabolic law with a rate constant as low as 4.59 × 10⁻¹⁵ g² cm⁻⁴ s⁻¹. The area specific resistance at temperatures between 600 and 800 °C is in the range of 6 and 17 mΩ cm². The above results indicate that NiMn₂O₄ is a promising coating material for metallic interconnects of the intermediate temperature solid oxide fuel cells.     

La(Ni,Fe)O3 as a cathode material with high tolerance to chromium poisoning for solid oxide fuel cells

A novel cathode material, La(Ni_0.4Fe_0.6)O₃ (LNF), is synthesized by a solid-state reaction for applications in solid oxide fuel cells (SOFCs). The electrochemical performance of the LNF cathode is investigated for the oxygen reduction reaction at 900 °C in the presence of a Fe–Cr alloy interconnect, and compared with (La,Sr)MnO₃ (LSM) cathodes. Under these conditions, the LNF electrode has a more stable electrochemical activity than that of the LSM electrode. There is no deposition of chromium species on the electrode surface or at the LNF electrode|yttria-stabilized zirconia (YSZ) electrolyte interface after passage of 200 mA cm⁻² for 20 h at 900 °C. By contrast, a significant amount of chromium species is preferentially deposited at the LSM|YSZ interface regions for the LSM electrode. The results demonstrate that the LNF electrode has high tolerance to chromium poisoning, and is, therefore, promising as a SOFC cathode when using chromia-forming alloy interconnects.     

Synthesis and performance of Sr1.5LaxMnO4 as cathode materials for intermediate temperature solid oxide fuel cell

A-site non-stoichiometric materials Sr_1.5La_xMnO₄ (x = 0.35, 0.40, 0.45) are prepared via solid state reaction. The structure of these materials is determined to be tetragonal. Both the lattice volume and the thermal expansion coefficient reduce with the decrease of lanthanum content. On the contrary, the conductivity increases and the maximum value of 13.9 S cm⁻¹ is found for Sr_1.5La_0.35MnO₄ at 750 °C in air. AC impedance spectroscopy and DC polarization measurements are used to study the electrode performance. The optimum composition of Sr_1.5La_0.35MnO₄ results in 0.25 Ω cm² area specific resistance (ASR) at 750 °C in air. The oxygen partial pressure measurement indicates that the charge transfer process is the rate-limiting step of the electrode reactions.     

Performance and stability characteristics of MEAs with carbon-supported Pt and Pt1Ni1 nanoparticles as cathode catalysts in PEM fuel cell

Polarization curves of membrane electrode assemblies (MEAs) containing carbon-supported platinum (Pt/C) and platinum-nickel alloy (Pt₁Ni₁/C) as cathode catalysts were obtained for durability test as a function of time over 1100 h at constant current. Charge transfer resistance was measured using electrochemical impedance spectroscopy and postmortem analysis such as X-ray diffraction and high-resolution transmission electron microscopy was conducted in order to elucidate the degradation factors of each MEA. Our results demonstrate that the reduced performance of MEAs containing Pt₁Ni₁/C as a cathode catalyst was due to decreased oxygen reduction reaction caused by the corrosion of Ni, whereas that of MEAs containing Pt/C was because of reduced electrochemical surface area induced by increased Pt particle size.     

Characterization of the 75% Gd0.8Sr0.2CoO3−δ/25% Ce0.9Gd0.1O2−δ composite cathode system for use in intermediate temperature solid oxide fuel cells

The composite cathode system is examined for suitability on a Ce_0.9Gd_0.1O_2−δ electrolyte based solid oxide fuel cell at intermediate temperatures (500–700 °C). The cathode is characterized for electronic conductivity and area specific charge transfer resistance. This cathode system is chosen for its excellent thermal expansion match to the electrolyte, its relatively high conductivity (115 S cm⁻¹ at 700 °C), and its low activation energy for oxygen reduction (99 kJ mol⁻¹). It is found that the decrease of sintering temperature of the composite cathode system produces a significant decrease in charge transfer resistances to as low as 0.25 Ω cm². The conductivity of the cathode systems is between 40 and 88 S cm⁻¹ for open porosities of 30–40%.