Showing papers in "Electrochemical and Solid State Letters in 2004"
TL;DR: In this article, the structural changes in silicon electrochemically lithiated and delithiated at room temperature were studied by X-ray powder diffraction, and it was shown that highly lithiated amorphous silicon suddenly crystallizes at 50 mV to form a new lithium-silicon phase, identified as This phase is the fully lithiated phase for silicon at room-temperature, not as is widely believed.
Abstract: The structural changes in silicon electrochemically lithiated and delithiated at room temperature were studied by X-ray powder diffraction. Crystalline silicon becomes amorphous during lithium insertion, confirming previous studies. Highly lithiated amorphous silicon suddenly crystallizes at 50 mV to form a new lithium-silicon phase, identified as This phase is the fully lithiated phase for silicon at room temperature, not as is widely believed. Delithiation of the phase results in the formation of amorphous silicon. Cycling silicon anodes above 50 mV avoids the formation of crystallized phases completely and results in better cycling performance. © 2004 The Electrochemical Society. All rights reserved.
1,686 citations
TL;DR: In this article, activation barriers to Li ion motion are calculated and an estimate for Li diffusion constants, in the absence of electrical conductivity constraints, is made using first-principles methods.
Abstract: Materials with the olivine structure form an important class of rechargeable battery cathodes. Using first-principles methods, activation barriers to Li ion motion are calculated and an estimate for Li diffusion constants, in the absence of electrical conductivity constraints, is made. Materials with Fe, Co, Ni are considered. Li diffuses through one-dimensional channels with high energy barriers to cross between the channels. Without electrical conductivity limitations the intrinsic Li diffusivity is high. © 2003 The Electrochemical Society. All rights reserved.
1,005 citations
TL;DR: Si composite negative electrodes for lithium secondary batteries degrade in the dealloying period with an abrupt increase in internal resistance that is caused by a breakdown of conductive network made between Si and carbon particles as discussed by the authors.
Abstract: Si composite negative electrodes for lithium secondary batteries degrade in the dealloying period with an abrupt increase in internal resistance that is caused by a breakdown of conductive network made between Si and carbon particles. This results from a volume contraction of Si particles after expansion in the previous alloying process. Due to the large internal resistance, the dealloying reaction is not completed while Si remains as a lithiated state. The anodic performance is greatly improved either by applying a pressure on the cells or loading a larger amount of conductive carbon in the composite electrodes.
603 citations
TL;DR: In this paper, the influence of platinum on the corrosion of carbon catalyst supports has been characterized by on-line mass spectroscopy during cyclic voltammetry, with varying Pt mass fraction, catalyst type, and temperature.
Abstract: The influence of platinum on the corrosion of carbon catalyst supports has been characterized by on-line mass spectroscopy during cyclic voltammetry, with varying Pt mass fraction, catalyst type, and temperature. The generation rates increased with higher Pt mass fraction (0, 10, and 39% balanced by Vulcan XC-72). A peak observed at approximately for Pt/C was lowered to for PtRu/C. An Arrenhius plot indicated higher apparent activation energy for production at the positive potential limit of the cyclic voltammogram on 0% Pt (carbon-only) electrode than on 39% Pt/C electrode. It was concluded that platinum accelerated the corrosion rate of the carbon catalyst support. © 2003 The Electrochemical Society. All rights reserved.
599 citations
TL;DR: In this paper, a room-temperature ionic liquid (RTIL) solvent, N-methyl, Nalkyl pyrrolidinium bis(trifluoromethanesulfonyl)amide (P 1 X (Tf) 2 N), has been investigated for use in a lithium metal battery.
Abstract: A room-temperature ionic liquid (RTIL) solvent, N-methyl, N-alkyl pyrrolidinium bis(trifluoromethanesulfonyl)amide (P 1 X (Tf) 2 N), has been investigated for use in a lithium metal battery. An average cycling efficiency of>99% is achieved at 1.0 mA cm - 2 (I d e p = I d i s s ) on platinum. At deposition rates up to 1.75 mA cm - 2 optical micrographs indicate that the deposit is uniform and nondendritic. Above 1.75 mA cm - 2 , the deposit becomes dendritic and efficiency decays. High cycling efficiency (>99%) can also be obtained on copper, but at relatively low current density (0.1 mA cm - 2 ). The deposition/cycling history also influences the cycling behavior of the deposit.
451 citations
TL;DR: Using an optical /air polymer electrolyte fuel cell (PEFC), the mechanics of liquid water transport, starting from droplet emergence on the gas diffusion layer (GDL) surface, droplet growth and departure, to the two-phase flow in gas channels, was characterized under automotive conditions of 0.82 A/cm2, 70°C, and 2 atm as discussed by the authors.
Abstract: Using an optical /air polymer electrolyte fuel cell (PEFC), the mechanics of liquid water transport, starting from droplet emergence on the gas diffusion layer (GDL) surface, droplet growth and departure, to the two-phase flow in gas channels, is characterized under automotive conditions of 0.82 A/cm2, 70°C, and 2 atm. It is observed that water droplets emerge from the GDL surface under oversaturation of water vapor in the gas phase, appear only at preferential locations, and can grow to a size comparable to the channel dimension under the influence of surface adhesion. Liquid film formation on more hydrophilic channel walls and channel clogging are also revealed and analyzed. © 2004 The Electrochemical Society. All rights reserved.
387 citations
TL;DR: In this paper, the degradation of the membrane electrode assembly (MEA) for proton exchange membrane fuel cells (PEMFCs) under low humidity conditions was investigated, and the degradation was observed during low humidity open-circuit voltage tests.
Abstract: The degradation study of the membrane electrode assembly (MEA) for proton exchange membrane fuel cells (PEMFCs) under low humidity conditions was conducted. The MEA degradation was observed during low humidity open-circuit voltage tests. To investigate the degradation mechanism, we conducted electron spin resonance studies of the degenerated MEA, and confirmed the formation of radicals in the catalyst layers. The MEA degradation mechanism that includes the radical formation reaction was verified. © 2004 The Electrochemical Society. All rights reserved.
288 citations
TL;DR: In this article, the surface structure, surface species, and ionic oxidation state of fresh and stored LiNiO 2 materials were investigated by investigating surface structure and surface species of Li NiO 2.
Abstract: Lithium nickel oxide, a potential candidate for cathode material for lithium-ion batteries, showed a distinct deterioration after storage in air for a time. The origin of this deterioration was explored by investigating surface structure, surface species, and ionic oxidation state of fresh and stored LiNiO 2 materials. Rietveld analysis of X-ray diffraction patterns showed not only the formation of Li 2 CO 3 on the surface, but also a weakening of ordered layered structure for the stored materials. X-ray photoelectron spectroscopy revealed that Ni 3 + transforms to Ni 2 + and active oxygen species exist on the surface of stored materials. Temperature programmed desorption-mass spectroscopy measurements gave evidence that active oxygen species (O-, O - 2) occur on the surface of LiNiO 2 after storage. A surface reaction mechanism based on the transformation of Ni 3 + /Ni 2 + and the evolution of active oxygen species is proposed.
238 citations
TL;DR: In this article, the sulfur tolerance of the various perovskite-based anodes was examined at 1273 K in a H 2 /H 2 O fuel and showed no degradation when the fuel was switched back to hydrogen.
Abstract: Solid oxide fuel cells (SOFCs) using yttria-stabilized zirconia (YSZ) electrolytes, lanthanum strontium manganate cathodes, and La 1 - x Sr x BO 3 /YSZ anodes (where B = Mn, Cr, and Ti) were fabricated. The sulfur tolerance of the various perovskite-based anodes was examined at 1273 K in a H 2 /H 2 O fuel. The Sr 0 . 6 La 0 . 4 TiO 3 /YSZ (50/50 wt %) anode showed no degradation in the presence of up to 5000 ppm of H 2 S in a hydrogen fuel. This anode was also able to operate for 8 h with 1% H 2 S as a fuel and showed no degradation when the fuel was switched back to hydrogen.
213 citations
TL;DR: In this paper, the effect of agglomeration on hydrogen peroxide formation in oxygen reduction was investigated by the rotating ring-disk electrode technique, which revealed that series two-electron reduction pathway, which is negligible on clean bulk Pt surface, does exist on Pt particles supported on carbon.
Abstract: Various amounts of 20 wt % Pt/C catalysts (56.7-5.7 μg c a r b o n cm - 2 ) were loaded on glassy carbon (GC) disk electrode, and the effect of agglomeration on hydrogen peroxide formation in oxygen reduction was investigated by the rotating ring-disk electrode technique. The formation of H 2 O 2 was enhanced with a decrease in agglomeration of Pt/C. Even in the operating potential range of polymer electrolyte fuel cell cathodes (0.6-0.8 V), 10% hydrogen peroxide was formed at 5.7 μg c a r b o n cm - 2 Pt/C loaded on GC. These results revealed that series two-electron reduction pathway, which is negligible on clean bulk Pt surface, does exist on Pt particles supported on carbon.
210 citations
TL;DR: In this paper, a patterned photoresist is pyrolyzed in inert environment at high temperature, which constitutes a powerful approach to building 3D carbon microelectrode arrays for 3D microbattery applications.
Abstract: We have demonstrated that carbon-microelectromechanical systems (C-MEMS), in which patterned photoresist is pyrolyzed in inert environment at high temperature, constitutes a powerful approach to building 3D carbon microelectrode arrays for 3D microbattery applications. High aspect ratio carbon posts (>10:1) are achieved by pyrolyzing SU-8 negative photoresist in a simple one step process. Lithium can be reversibly charged and discharged into these C-MEMS electrodes. Because of the additional volume of the posts, higher capacities are achieved with the 3D array electrodes as compared to unpatterned carbon films with the same projected electrode area. These novel electrode arrays represent one of the critical components for 3D batteries, which may be interconnected with C-MEMS leads to enable smart power management schemes.
TL;DR: In this paper, short-range ordering in Li[Ni x Mn ( 2 - x ) / 3 Li ( 1 - 2 x )/3 ]O 2 was investigated with 6 Li NMR and first principles structure computations.
Abstract: Short-range ordering in Li[Ni x Mn ( 2 - x ) / 3 Li ( 1 - 2 x ) / 3 ]O 2 was investigated with 6 Li NMR and first principles structure computations. NMR indicates that the tendency for Ni 2 + to replace Li + in the Li + layers decreases with decreasing nickel content. Li in the Ni/Mn layers preferentially occupies sites near Mn 4 + and avoids the Ni 2 + ions, leading to nonrandom configurations. Calculations indicate that the ground state of Li(Ni 0 . 5 Mn 0 . 5 )O 2 contains zigzag rows of Ni 2 + and Mn 4 + ions. Although a disordering temperature of approximately 1000 K is calculated, ordered fragments persist above the phase transition and these materials contain significant short-range order, even when quenched from high temperature.
TL;DR: In this article, the spatial distribution of the water content within a polymer electrolyte membrane (PEM) under fuel cell operation was measured using Magnetic Resonance Imaging (MRI) to measure the water concentration gradient in the PEM and the overall water content decreased with an increase of the cell current.
Abstract: Magnetic resonance imaging (MRI) to measure the spatial distribution of the water content within a polymer electrolyte membrane (PEM) under fuel cell operation is described. By designing and building a fuel cell that can operate in an MRI system and making measurements during the cell operation, the water concentration gradient in the PEM and the overall water content decreased with an increase of the cell current. Furthermore, the water content in the anode side of the PEM decreased significantly within 200 s of the cell start-up, and this caused a similarly rapid decrease of the cell voltage.
TL;DR: In this article, the self-ordering behavior of porous anodic alumina induced by the burning phenomenon on the specimen where extremely high and local current concentrations occurred was studied and the domains of highly self-ordered cell arrangement were found at the locally thickened film formed by burning.
Abstract: The self-ordering behavior of porous anodic alumina induced by the burning phenomenon on the specimen where extremely high and local current concentrations occurred was studied. The domains of highly self-ordered cell arrangement were found at the locally thickened film formed by burning. At the center of the burnt area, the regularity of cell arrangement was higher and the barrier layer thickness as well as the cell size was remarkably lower. These results clearly suggest that the condition inducing film growth under high current density, i.e., high electric field is the key factor determining the self-ordering.
TL;DR: In this article, secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM) were used for diffusion studies on physical vapor deposited Cu/Ru(∼20 nm)/Si samples.
Abstract: Diffusion studies were carried out on physical vapor deposited Cu/Ru(∼20 nm)/Si samples using secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM). Back side SIMS depth profiling revealed well-defined interfaces and showed that Cu interdiffusion was impeded by Ru thin film up to 450°C vacuum annealing. TEM showed a 20-22 nm Ru barrier layer with a columnar microstructure oriented vertically with respect to Si substrate. TEM results corroborate with SIMS data to indicate stability of the Ru film barrier for annealing temperatures up to 450°C. Direct Cu electroplating on ultrathin Ru barrier layers (<20 nm) was investigated in sulfuric acid. The electroplated Cu film is shiny, smooth, and without agglomeration under scanning electron microscopy. Excellent adhesion between interfacial layers was confirmed by the scribe-peel test. The interfacial characterization results indicate that Ru thin film is a promising candidate as a directly plateable Cu diffusion barrier.
TL;DR: In this paper, an autocatalytic mechanism initiated by trace impurities of water or alcohol is used to prevent the thermal decomposition of lithium metal oxides in the presence of Lewis basic additives.
Abstract: Liquid electrolytes typically used in commercial lithium-ion batteries are comprised of lithium hexafluorophosphate in carbonate solvents. This electrolyte undergoes thermal decomposition at moderately elevated temperatures (80-100°C), encountered in the normal operation of these rechargeable power sources, to quantitatively generate highly toxic alkylfluorophosphates. The decomposition occurs via an autocatalytic mechanism initiated by trace impurities of water or alcohol. The thermal decomposition is inhibited in the presence of lithium metal oxides frequently used as the cathode of lithium-ion batteries or Lewis basic additives.
TL;DR: The morphology and bond strength of copper-bonded wafer pairs prepared under different bonding/annealing temperatures and durations are presented in this article, where the interfacial morphology was examined by transmission electron microscopy while the bond strength was examined from a diesaw test.
Abstract: The morphology and bond strength of copper-bonded wafer pairs prepared under different bonding/annealing temperatures and durations are presented. The interfacial morphology was examined by transmission electron microscopy while the bond strength was examined from a diesaw test. Physical mechanisms explaining the different roles of postbonding anneals at temperatures above and below 300°C are discussed. A map summarizing these results provides a useful reference on process conditions suitable for actual microelectronics fabrication and three-dimensional integrated circuits based on Cu wafer bonding. © 2003 The Electrochemical Society. All rights reserved.
TL;DR: In this article, the detrimental surface species can be subsequently reformed on heat-treated materials by exposure of LiCoO 2 to water, suggesting prolonged air exposure is responsible for their formation on commercial samples.
Abstract: Impedance growth of LiCoO 2 electrodes cycled with an upper cutoff potential of 4.5 V is caused by side reactions involving species on the surface of LiCoO 2 and LiPF 6 -based electrolyte. These detrimental chemical speciescan apparently be removed by a heat-treatment to 550°C because electrodes made with heat-treated materials show excellent capacity retention even when cycled to 4.5 V. The detrimental surface species can be subsequently reformed on heat-treated materials by exposure of LiCoO 2 to water, suggesting prolonged air exposure is responsible for their formation on commercial samples.
TL;DR: In this article, double-layer capacitance and electronic conductance of an activated carbon electrode in an aprotic electrolyte solution, 1 mol/L in acetonitrile, were measured.
Abstract: We have measured double-layer capacitance and electronic conductance of an activated carbon electrode in an aprotic electrolyte solution, 1 mol/L in acetonitrile. Both quantities show a similar dependence on the electrode potential with distinct minima near the potential of zero charge. This correlation suggests that the capacitance like the conductance is governed substantially by the electronic properties of the solid, rather than by the properties of the solution side of the double layer. These findings can be explained by treating activated carbon as a metal with a finite density of electronic states at the Fermi level, and with hopping conduction between these states. © 2003The Electrochemical Society. All rights reserved.
TL;DR: In this paper, the electronic structure of LiFePO 4 in the ordered olivine structure was calculated by a first-principles method to determine (i) the effective mass of carriers and (ii) the nature of the band structure.
Abstract: The electronic structure of LiFePO 4 underpins transport properties important to its use as a lithium storage electrode. Here we have calculated the electronic structure of LiFePO 4 in the ordered olivine structure by a first-principles method to determine (i) the effective mass of carriers and (ii) the nature of the band structure. The electrical conductivity in high purity undoped LiFePO 4 has also been measured experimentally. Spin-polarized calculations show a large electron effective mass and a much smaller but highly anisotropic hole effective mass, suggesting that hole-doped compositions should have the greater electronic conductivity. More surprisingly, the calculations show that this polyanion compound is a half-metal with spin-sensitive band structure, like some other oxides being studied for spintronics applications. This previously unappreciated aspect of the LiFePO 4 electronic structure may play a role in determining transport properties including those relevant to electrochemical applications.
TL;DR: A combination of first principles calculations and lithium NMR spectroscopy was used to examine the effect of electrochemical cycling on lithium ions located in the transition metal layers in layered lithium nickel manganates.
Abstract: A combination of first principles calculations and lithium NMR spectroscopy was used to examine the effect of electrochemical cycling on lithium ions located in the transition metal layers in layered lithium nickel manganates. These lithium ions participate in the electrochemical process with NMR results showing that they are removed from the octahedral sites on charging, but return on discharging. Calculations indicate that the lithium ions become increasingly unstable, as the concentration of vacancies in the lithium layers increases. A lithium ion nearby three vacancies in the lithium layers drops immediately, with no activation barrier, into the adjacent tetrahedral site in the lithium layers; charging to higher potentials is then required to remove this lithium ion.
TL;DR: In this paper, a reaction model has been proposed to explain the reaction mechanisms of lithium insertion and extraction in the Si-MCMB electrode, which demonstrated a reversible capacity of 1066 mAh/g with good cyclability.
Abstract: Nanocrystalline Si-mesocarbon microbeads (MCMB) composite anode materials were prepared by ballmilling. Scanning electron microscopic observation showed that the spherical shape of MCMB particles can be retained via moderate ballmilling. Ballmilling conditions have an impact on the capacity and cyclability of nanocrystalline Si-MCMB composites. The optimized Si-MCMB composite anode demonstrated a reversible capacity of 1066 mAh/g with good cyclability. A reaction model has been proposed to explain the reaction mechanisms of lithium insertion and extraction in the Si-MCMB electrode.
TL;DR: In this paper, the formation of the SEI layer on graphite anodes cycled in propylene carbonate (PC) lithium bis(oxolato)borate (LiBOB) electrolyte was studied by ex-situ Fourier Transform Infrared Spectroscopy (FTIR) analysis in the attenuated total reflection (ATR) mode.
Abstract: Formation of the SEI layer on graphite anodes cycled in propylene carbonate (PC) lithium bis(oxolato)borate (LiBOB) electrolyte was studied by ex-situ Fourier Transform Infrared Spectroscopy (FTIR) analysis in the attenuated total reflection (ATR) mode. The results provide a more refined description of the composition than earlier analyses with x-ray photoelectron spectroscopy (XPS). The vibrational spectra clearly show that electrochemical reduction of the BOB anion is a part of the SEI formation chemistry. Carboxylate and/or oxalate functional groups derived from the BOB anion were the components assigned as the ''semicarbonate'' species in the C 1s XPS spectra of the SEI layer formed in LiBOB electrolyte. Reduction of the BOB anion changes the oxygen coordination around the B atom from tetrahedral BO4 to trigonal BO3, e.g., meta- or orthoborate. Based on the combination of electrochemical and FTIR data, we propose that the preferential reduction of the BOB anion versus the PC solvent molecule is responsible for the cyclability of graphite anodes in purely PC-based electrolyte.
TL;DR: In this article, the surface composition ratio between LiNi 0. 8 Co 0. 1 5 Al 0. 0 5 O 2 and carbon in the composite cathode increases upon cell aging and cycling.
Abstract: High-power Li-ion cells tested at elevated temperatures showed a significant impedance rise, which was associated primarily with the LiNi 0 . 8 Co 0 . 1 5 Al 0 . 0 5 O 2 cathode. Raman microscopy mapping provided evidence that the surface composition ratio between LiNi 0 . 8 Co 0 . 1 5 Al 0 . 0 5 O 2 and carbon in the composite cathode increases upon cell aging and cycling. Current-sensing atomic force microscopy imaging of single grains of pristine LiNi 0 . 8 Co 0 . 1 5 Al 0 . 0 5 O 2 powder revealed poor residual electronic contact between submicrometer primary particles within LiNi 0 . 8 Co 0 . 1 5 Al 0 . 0 5 O 2 agglomerates. Carbon retreat or rearrangement that occurs during cell testing allows residual interparticle resistance to dominate cathode interfacial charge-transfer impedance and accounts for the observed cell power and capacity loss.
TL;DR: In this article, a nonaqueous sol-gel method for the synthesis of carbon-coated LiFePO 4 as high-performance cathode is reported, which consists of two simple steps: (i) dissolve lithium acetate, iron(II) acetate and phosphoric acid in ethylene glycol to form a molecularly homogeneous, monolithic organo-gel and (ii) directly heat the gel in nitrogen atmosphere to form carboncoated, phase-pure LiFe PO 4.
Abstract: A simple, versatile nonaqueous sol-gel method for the synthesis of carbon-coated LiFePO 4 as high-performance cathode is reported. The method consists of two simple steps: (i) dissolve lithium acetate, iron(II) acetate and phosphoric acid in ethylene glycol to form a molecularly homogeneous, monolithic organo-gel and (ii) directly heat the gel in nitrogen atmosphere to form carbon-coated, phase-pure LiFePO 4 . The LiFePO 4 formed consists of 200-300 nm particles with rather uniform size distribution and with 1-4 wt % surface carbon coating formed in situ. The favorable physical characteristics of the synthesized LiFePO 4 give rise to excellent rate performance.
TL;DR: In this article, a superstructure for this material with space group P3 1 12, and a √3a h e x. × √ 3a h er e x, ordering in the transition metal layers is proposed, indicating the presence of long-range interactions between different transition-metal layers.
Abstract: A combination of experimental techniques that probe different relevant length scales is necessary to truly understand the structure of complex solids. In LiNi 0 . 5 Mn 0 . 5 O 2 electron diffraction reveals the presence of long-range ordering, previously undetected with X-ray diffraction and neutron diffraction. We propose a superstructure for this material with space group P3 1 12, and a √3a h e x . × √3a h e x . ordering in the transition metal layers. Surprisingly, these ordered layers are stacked in abcabc sequence along the c axis, indicating the presence of long-range interactions between different transition-metal layers. Electron diffraction evidence indicates that Li, Ni, and Mn ions are not distributed randomly in the transition-metal layers, but order and form two sublattices with significantly different occupation. We further demonstrate that this ordering would be extremely difficult to detect experimentally, if not impossible, with powder diffraction by X-rays and neutrons.
TL;DR: In this article, the authors evaluated the ability of three pigments (Benzotriazolate, ethyl xanthate, and oxalate anion-exchanged hydrotalcite (HT) pigments) with respect to their ability to inhibit filiform corrosion (FFC) on organic coated AA2024-T3 aluminum alloy.
Abstract: Benzotriazolate, ethyl xanthate, and oxalate anion-exchanged hydrotalcite (HT) pigments are evaluated with respect to their ability to inhibit filiform corrosion (FFC) on organic coated AA2024-T3 aluminum alloy. FollowingFFC initiation by application of aqueous HCl to a penetrative coating defect, the time-dependent extent of coating delamination was determined both optically and by repeated in situ measurements performed using a scanning Kelvin probe (SKP). Inhibitor efficiency is shown to increase in the order ethyl xanthate « oxalate < benzotriazolate. Benzotriazolate is also shown to interact specifically with the alloy surface, depressing Volta potential values by up to 0.4 V.
TL;DR: In this paper, a silicon/carbon composite was synthesized by two polyvinyl chloride (PVC) pyrolysis reactions, combined with an intervening high-energy mechanical milling (HEMM) step.
Abstract: A silicon/carbon composite has been synthesized by two poly(vinyl chloride) (PVC) pyrolysis reactions, combined with an intervening high-energy mechanical milling (HEMM) step. As lithium storage host, the composite demonstrates high initial coulombic efficiency of 82% and a large capacity at ca. 900 mAh g - 1 over 40 cycles. Controlling Li-insertion level at 600 mAh g - 1 can greatly extend the cycles to over 100. Another composite prepared by ballmilling a mixture of graphite and silicon and followed by a PVC pyrolysis process also shows both good capacity and capacity retention.
TL;DR: In this article, the structural change of LiNi 0. 5 Mn 1. 5 O 4 with two different crystallographic structures of Fd3m and P4 3 32 was studied during Li extraction.
Abstract: Structural change of LiNi 0 . 5 Mn 1 . 5 O 4 with two different crystallographic structures of Fd3m and P4 3 32 was studied during Li extraction. Ex situ X-ray diffraction and transmission electron microscopy studies on partially delithiated Li 1 - δ Ni 0 . 5 Mn 1 . 5 O 4 revealed that LiNi 0 . 5 Mn 1 . 5 O 4 (Fd3m) structure lost its characteristic diagonal glide symmetry, suggesting a structural transition arising from the possible migration of cations during oxidation from Ni 2 + to Ni 4 + . For the Li 1 - δ Ni 0 . 5 Mn 1 . 5 O 4 (P4 3 32), ordering of cations was destroyed by random migration of cations during Li extraction, resulting in the formation of intermediate phase with the Fd3m structure. The phase transitions were reversible, meaning that migration of cations is highly reversible during lithiation/delithiation.
TL;DR: In this article, the same strontium-doped LaMnO 3 and yttria doped zirconia (LSM-YSZ) composite electrodes were characterized in three separate cell configurations, in air at 973 K using impedance spectroscopy.
Abstract: Identical strontium-doped LaMnO 3 and yttria-doped zirconia (LSM-YSZ) composite electrodes were characterized in three separate cell configurations, in air at 973 K using impedance spectroscopy. These configurations included a single-cell solid oxide fuel cell (SOFC), a symmetric cell (cathode/YSZ/cathode), and a thick pellet half-cell. Large discrepancies were observed in the measurements, with the electrode showing a current-independent area-specific resistance (ASR) of ∼0.2 Ω cm 2 as an SOFC cathode, while nearly identical electrodes in the other two configurations exhibited nonlinear behavior, with ASR as large as 12 Ω cm 2 . The discrepancies are partly explained by electrode polarization effects. This has important implications for cathode characterization in SOFC.