Showing papers in "Journal of The Electrochemical Society in 2010"
TL;DR: In this article, the Butler-Volmer equation was fitted to the HOR/HER exchange current densities on polycrystalline platinum and high surface area carbon-supported platinum nanoparticles using rotating disk electrode (RDE) measurements.
Abstract: The kinetics of the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) on polycrystalline platinum [Pt(pc)] and high surface area carbon-supported platinum nanoparticles (Pt/C) were studied in 0.1 M KOH using rotating disk electrode (RDE) measurements. After corrections of noncompensated solution resistance from ac impedance spectroscopy and of hydrogen mass transport in the HOR branch, the kinetic current densities were fitted to the Butler-Volmer equation using a transfer coefficient of α = 0.5, from which HOR/HER exchange current densities on Pt(pc) and Pt/C were obtained, and the HOR/HER mechanisms in alkaline solution were discussed. Unlike the HOR/HER rates on Pt electrodes in alkaline solution, the HOR/HER rates on a Pt electrode in 0.1 M HClO 4 were limited entirely by hydrogen diffusion, which renders the quantification of the HOR/HER kinetics impossible by conventional RDE measurements. The simulation of the hydrogen anode performance based on the specific exchange current densities of the HOR/HER at 80°C illustrates that in addition to the oxygen reduction reaction cell voltage loss on the cathode, the slow HOR kinetics are projected to cause significant anode potential losses in alkaline fuel cells for low platinum loadings (> 130 mV at 0.05 Mg pt /CM 2 anode and 1.5 A/cm 2 anode ), contrary to what is reported for proton exchange membrane fuel cells.
1,304 citations
TL;DR: Hirschorn et al. as mentioned in this paper proposed a method to solve the problem of chemical engineering by using the theory of theory of I.I. Theory Bryan Hirschorn,* Mark E. Orazem,** Bernard Tribollet,** Vincent Vivier,** Isabelle Frateur, and Marco Musiani.
Abstract: I. Theory Bryan Hirschorn,* Mark E. Orazem,** Bernard Tribollet,** Vincent Vivier,*** Isabelle Frateur, and Marco Musiani*** Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, USA Laboratoire Interfaces et Systemes Electrochimiques, UPR 15 du CNRS, Université Pierre et Marie Curie, 75252 Paris cedex 05, France Laboratoire de Physico-Chimie des Surfaces, UMR CNRS-ENSCP 7045, Ecole Nationale Supérieure de Chimie de Paris, Chimie ParisTech, 75005 Paris, France Istituto per l’Energetica e le Interfasi, Consiglio Nazionale delle Ricerche, 35127 Padova, Italy
403 citations
TL;DR: In this paper, density functional theory (DFT) is used to reveal that the polycrystalline Young's modulus (E) of graphite triples as it is lithiated to LiC 6 is captured in a linear relationship between E and lithium concentration suitable for predicting diffusion-induced deformation in battery electrode materials.
Abstract: Density functional theory (DFT) is used to reveal that the polycrystalline Young's modulus (E) of graphite triples as it is lithiated to LiC 6 This behavior is captured in a linear relationship between E and lithium concentration suitable for continuum-scale models aimed at predicting diffusion-induced deformation in battery electrode materials Alternatively, Poisson's ratio is concentration-independent Charge-transfer analyses suggest simultaneous weakening of carbon-carbon bonds within graphite basal planes and strengthening of interlayer bonding during lithiation The variation in bond strength is shown to be responsible for the differences between elasticity tensor components, C ij , of lithium-graphite intercalation (Li-GIC) phases Strain accumulation during Li intercalation and deintercalation is examined with a core-shell model of a Li-GIC particle assuming two coexisting phases The requisite force equilibrium uses different Young's moduli computed with DFT Lithium-poor phases develop tensile strains, whereas Li-rich phases develop compressive strains Results from the core-shell model suggest that elastic strain should be defined relative to the newest phase that forms during lithiation of graphite, and Li concentration-dependent mechanical properties should be considered in continuum level models
387 citations
TL;DR: In this article, LiCoO 2 powders were coated with conformal Al 2 O 3 ALD films with thicknesses of only ∼ 3 to 4 A established using two ALD cycles.
Abstract: Ultrathin atomic layer deposition (ALD) coatings enhance the performance of lithium-ion batteries (LIBs). Previous studies have demonstrated that LiCoO 2 cathode powders coated with metal oxides with thicknesses of ∼100 to 1000 A grown using wet chemical techniques improved LIB performance. In this study, LiCoO 2 powders were coated with conformal Al 2 O 3 ALD films with thicknesses of only ∼ 3 to 4 A established using two ALD cycles. The coated LiCoO 2 powders exhibited a capacity retention of 89% after 120 charge-discharge cycles in the 3.3-4.5 V (vs Li/Li + ) range. In contrast, the bare LiCoO 2 powders displayed only a 45% capacity retention. Al 2 O 3 ALD films coated directly on the composite electrode also produced improved capacity retention. This dramatic improvement may result from the ultrathin Al 2 O 3 ALD film acting to minimize Co dissolution or reduce surface electrolyte reactions. Similar experiments with ultrathin ZnO ALD films did not display enhanced performance.
343 citations
TL;DR: In this paper, a methodology was developed to compare the ORR activities of submicrometer-sized transition-metal oxides, and the projection of LaNiO 3 in the actual fuel cell cathode was presented, which was shown to be competitive with current platinum-based cathodes.
Abstract: Transition-metal oxides can exhibit high electrocatalytic activity for reactions such as the oxygen reduction reaction (ORR) in alkaline media. It is often difficult to measure and compare the activities of oxide catalysts on either per mass or per surface area basis, because of the poorly defined oxygen transport to and within porous oxide electrodes of several tens of micrometers thickness. In this study, a methodology was developed to compare the ORR activities of submicrometer-sized transition-metal oxides. Thin films of LaNiO 3 , LaCu 0.5 Mn 0.5 O 3 , and La 0.75 Ca 0.25 FeO 3 oxide particles were bonded to glassy carbon via an ion-exchanged Nafion binder, and their mass and specific ORR activities were extracted from rotating disk electrode measurements. We found that the specific activity of LaNi0 3 was much higher than that of La 0.75 Ca 0.25 FeO 3 and LaCu 0.5 Mn 0.5 O 3 . The projection of LaNiO 3 in the actual fuel cell cathode was presented, which was shown to be competitive with current platinum-based cathodes.
342 citations
TL;DR: Li 7 La 3 Zr zr z O 12 (LLZ) pellet with a garnet-like structure was obtained, and its conductivity was 1.8 × 10−4 S cm−1 at room temperature.
Abstract: Electrochemical properties of Li 7 La 3 Zr z O 12 (LLZ) were investigated to reveal its availability as a solid electrolyte for all-solid-state rechargeable batteries with a Li metal anode. After calcination at 1230°C, a well-sintered LLZ pellet with a garnet-like structure was obtained, and its conductivity was 1.8 × 10 ―4 S cm ―1 at room temperature. The cyclic voltammogram of the Li/LLZ/Li cell showed that the dissolution and deposition reactions of lithium occurred reversibly without any reaction with LLZ. This indicates that a Li metal anode can be applied for an LLZ system. A full cell composed of a LiCoO 2 /LLZ/Li configuration was also operated successfully at expected voltage estimated from the redox potential of Li metal and LiCoO 2 . Simultaneously, an irreversible behavior was observed at the first discharge and charge cycle due to an interfacial problem between LiCoO 2 and LLZ. The discharge capacity of the full cell was 15 μA h cm ―2 . These results reveal that LLZ is available for all-solid-state lithium batteries.
332 citations
TL;DR: In this paper, the microstructural changes of the membrane electrode assembly (MEA) cathode and the compositional changes along the MEA cathode thickness and within individual Pt x Co nanoparticles before and after voltage cycling were investigated.
Abstract: Electrochemical measurements showed an ≈75% Pt surface area loss and an ≈40% specific activity loss for a membrane electrode assembly (MEA) cathode with acid-treated "Pt 3 Co" catalyst particles in a H 2 /N 2 proton exchange membrane fuel cell after 24 h voltage cycling between 0.65 and 1.05 V vs reversible hydrogen electrode. Transmission electron microscopy, scanning transmission electron microscopy, associated X-ray energy dispersive spectroscopy, and high angle annular dark-field techniques were used to probe the microstructural changes of the MEA cathode and the compositional changes along the MEA cathode thickness and within individual Pt x Co nanoparticles before and after voltage cycling. Further Co dissolution from acid-treated Pt x Co particles that leads to an increased thickness of a Pt-enriched surface layer and the development of core/shell Pt x Co particles was largely responsible for the reduction in the specific activity of Pt x Co nanoparticle after potential cycling. The Pt weight loss associated with the formation of Pt crystallites near the cathode/membrane interface largely contributed to the measured electro- chemical surface area loss, while particle growth of the Pt x Co particles via Ostwald ripening played a lesser role.
325 citations
TL;DR: In this article, the effects of carbon microstructure and carbon loading on the performance of Li/air batteries were investigated, and a dry rolling method was optimized to prepare air electrodes with high mesopore volume.
Abstract: The effects of carbon microstructure and carbon loading on the performance of Li/air batteries were investigated. The active carbons from various sources were compared, and a dry rolling method was optimized to prepare air electrodes with high mesopore volume. It is found that the capacities of air electrodes improve significantly when the mesopore volume of the carbon source is high. However, for carbons with low mesopore volumes, other factors such as surface activity also play an important role in determining the electrochemical performances of the Li/air batteries. A practical criterion, area-specific capacity, was used to optimize the carbon loading for air electrode. The best area-specific capacity of 13.1 mAh/cm2 was obtained at a carbon loading of 15.1 mg/cm2. Further increasing or decreasing the carbon loading led to a reduced area- specific capacity. Finally, at fixed carbon loading and discharge rates, electrolyte amount was another key factor governing cell performance. A spring mechanism is proposed to explain the formation of the tri-phase regions in air electrodes. After optimizing the parameters listed above, a high capacity of 1,756 mAh/g carbon corresponding to a specific energy of 4,614 Wh/kg carbon was obtained for Li/air batteries operated in a dry air environment.
322 citations
TL;DR: In this article, an analysis of the dependence of electric potential on the state of stress of a lithiated-silicon electrode is presented, and the importance of the coupling is discussed in interpreting the hysteresis observed in the potential vs state of charge plots and the role of stress in modifying the maximum charge capacity of a silicon electrode under stress.
Abstract: An analysis of the dependence of electric potential on the state of stress of a lithiated-silicon electrode is presented. Based on the Larche and Cahn chemical potential for a solid solution, a thermodynamic argument is made for the existence of the stresspotential coupling in lithiated silicon; based on the known properties of the material, the magnitude of the coupling is estimated to be 60 mV/GPa in thin-film geometry. An experimental investigation is carried out on silicon thin-film electrodes in which the stress is measured in situ during electrochemical lithiation and delithiation. By progressively varying the stress through incremental delithiation, the relation between stress change and electric-potential change is measured to be 100–120 mV/GPa, which is of the same order of magnitude as the prediction of the analysis. The importance of the coupling is discussed in interpreting the hysteresis observed in the potential vs state-of-charge plots and the role of stress in modifying the maximum charge capacity of a silicon electrode under stress.
316 citations
TL;DR: In this paper, the authors describe an instrument designed to make high precision coulombic efficiency measurements and give examples of its use on commercial Li-ion cells and Li half-cells.
Abstract: Undesired reactions in Li-ion batteries, which lead to capacity loss, can consume or produce charge at either the positive or negative electrode. For example, the formation and repair of the solid electrolyte interphase consumes Li + and e - at the negative electrode. High purity electrolytes, elimination of water, various electrolyte additives, electrode coatings, and special electrode materials are known to improve cycle life and therefore must impact coulombic efficiency. Careful measurements of coulombic efficiency are needed to quantify the impact of trace impurities, additives, coatings, etc., in only a few charge-discharge cycles and in a relatively short time. The effects of cycle-induced and time-related capacity loss could be probed by using experiments carried out at different C-rates. In order to make an impact on Li-ion cells for automotive and energy storage applications, where thousands of charge-discharge cycles are required, coulombic efficiency must be measured on the order of 0.01 %. In this paper, we describe an instrument designed to make high precision coulombic efficiency measurements and give examples of its use on commercial Li-ion cells and Li half-cells. High precision coulombic efficiency measurements can detect problems occurring in half-cells that do not lead to capacity loss, but would in full cells, and can measure the impact of electrolyte additives and electrode coatings.
315 citations
TL;DR: In this paper, the authors derived a fracture mechanics failure criterion for individual electrode particles and demonstrate its utility with a model system, galvanostatic charging of Li x Mn 2 O 4.
Abstract: Fracture of electrode particles due to diffusion-induced stress has been implicated as a possible mechanism for capacity fade and impedance growth in lithium-ion batteries. In brittle materials, including many lithium intercalation materials, knowledge of the stress profile is necessary but insufficient to predict fracture events. We derive a fracture mechanics failure criterion for individual electrode particles and demonstrate its utility with a model system, galvanostatic charging of Li x Mn 2 O 4 . Fracture mechanics predicts a critical C-rate above which active particles fracture; this critical C-rate decreases with increasing particle size. We produce an electrochemical shock map, a graphical tool that shows regimes of failure depending on C-rate, particle size, and the material's inherent fracture toughness K Ic . Fracture dynamics are sensitive to the gradient of diffusion-induced stresses at the crack tip; as a consequence, small initial flaws grow unstably and are therefore potentially more damaging than larger initial flaws, which grow stably.
TL;DR: In this article, the performance loss of lithium-ion batteries with lithium iron phosphate positive chemistry was analyzed using electrochemical characterization techniques such as galvanostatic charge-discharge at different rates, ac impedance, and hybrid pulse power characterization measurements.
Abstract: The performance loss of lithium-ion batteries with lithium iron phosphate positive chemistry was analyzed using electrochemical characterization techniques such as galvanostatic charge-discharge at different rates, ac impedance, and hybrid pulse power characterization measurements. Differentiation analysis of the discharge profiles as well as in situ reference electrode measurement revealed loss of lithium as well as degradation of the carbon negative; the cell capacity, however, was limited by the amount of active lithium. Destructive physical analyses and ex situ electrochemical analyses were performed at test completion on selected cells. While no change in positive morphology and performance was detected, significant cracking and delamination of the carbon negative was observed. In addition, X-ray diffraction analysis confirmed the changes in the crystal structure of the graphite during cycling. The degradation of the carbon negative is consistent with the observations from the electrochemical analysis. Ex situ electrochemical analysis confirmed that active lithium controlled cell capacity and its loss with cycling directly correlated with cell degradation. The relationship between carbon negative degradation and loss of active lithium is discussed in the context of a consistent overall mechanism.
TL;DR: In this paper, a plasma-enhanced ALD of Al 2 O 3, TiO 2, and Ta 2 O 5 has been investigated at 25-400°C using [Al(CH 3 ) 3 ], [Ti(O i Pr) 4 ],[Ti(Cp Me )(Oi Pr) 3], [TiCp*(OMe) 3 ], and [Ta(NMe 2 ) 5 ] as precursors.
Abstract: Many reported atomic layer deposition (ALD) processes are carried out at elevated temperatures (>150°C), which can be problematic for temperature-sensitive substrates. Plasma-enhanced ALD routes may provide a solution, as the ALD temperature window can, in theory, be extended to lower deposition temperatures due to the reactive nature of the plasma. As such, the plasma-enhanced ALD of Al 2 O 3 , TiO 2 , and Ta 2 O 5 has been investigated at 25-400°C using [Al(CH 3 ) 3 ], [Ti(O i Pr) 4 ], [Ti(Cp Me )(O i Pr) 3 ], [TiCp*(OMe) 3 ], and [Ta(NMe 2 ) 5 ] as precursors. An O 2 plasma was employed as the oxygen source in each case. We have demonstrated metal oxide thin-film deposition at temperatures as low as room temperature and compared the results with corresponding thermal ALD routes to the same materials. The composition of the films was determined by Rutherford backscattering spectroscopy. Analysis of the growth per cycle data and the metal atoms deposited per cycle revealed that the growth per cycle is strongly dependent on the film density at low deposition temperatures. Comparison of these data for Al 2 O 3 ALD processes in particular, showed that the number of Al atoms deposited per cycle was consistently high down to room temperature for the plasma-enhanced process but dropped for the thermal process at substrate temperatures lower than 250°C.
TL;DR: In this paper, the authors describe a totally solid-state, rechargeable, long cycle life lithium-oxygen battery cell, which is comprised of a Li metal anode, a highly Li-ion conductive solid electrolyte membrane laminate fabricated from glass-ceramic (GC) and polymerceramic materials.
Abstract: This paper describes a totally solid-state, rechargeable, long cycle life lithium-oxygen battery cell. The cell is comprised of a Li metal anode, a highly Li-ion conductive solid electrolyte membrane laminate fabricated from glass-ceramic (GC) and polymer-ceramic materials, and' a solid-state composite air cathode prepared from high surface area carbon and ionically conducting GC powder. The cell exhibited excellent thermal stability and rechargeability in the 30-105°C temperature range. It was subjected to 40 charge-discharge cycles at current densities ranging from 0.05 to 0.25 mA/cm 2 . The reversible charge/discharge voltage profiles of the Li―O 2 cell with low polarizations between the discharge and charge are remarkable for a displacement-type electrochemical cell reaction involving the reduction of oxygen to form lithium peroxide. The results represent a major contribution in the quest of an ultrahigh energy density electrochemical power source. We believe that the Li―O 2 cell, when fully developed, could exceed specific energies of 1000 Wh/kg in practical configurations.
TL;DR: In this article, a new electrochemical cell has been designed for operando experiments at synchrotron facilities both for X-ray diffraction and Xray absorption, which allows the investigation of insertion materials under high current densities (up to 5C rate) and hence to study complex phenomena of structural and electronic changes out of equilibrium.
Abstract: A new electrochemical cell has been specially designed for operando experiments at synchrotron facilities both for X-ray diffraction and X-ray absorption. It allows the investigation of insertion materials under high current densities (up to 5C rate) and hence to study complex phenomena of structural and electronic changes out of equilibrium. The LiFePO 4 -FePO 4 system has been chosen as a case study to validate this cell, and tricky phenomena, with apparent delays in phase formation compared with the number of electrons exchanged, have been spotted.
TL;DR: In this article, the intrinsic ORR activity on glassy carbon (GC) as well as polycrystalline Au and Pt electrodes, where Au is the most active with an activity trend of Au ≫ GC > Pt Rotating disk electrode (RDE) measurements were used to obtain the kinetic current of the ORR and the reaction order with respect to oxygen partial pressure in 1 M LiClO 4 propylene carbonate: 1,2-dimethoxyethane (1:2 v/v)
Abstract: Rechargeable lithium-air batteries have the potential to provide ≈3 times higher specific energy of fully packaged batteries than conventional lithium rechargeable batteries However, very little is known about the oxygen reduction reaction (ORR) and oxygen evolution in the presence of lithium ions in aprotic electrolytes, which hinders the improvement of low round-trip efficiencies of current lithium-air batteries We report the intrinsic ORR activity on glassy carbon (GC) as well as polycrystalline Au and Pt electrodes, where Au is the most active with an activity trend of Au ≫ GC > Pt Rotating disk electrode (RDE) measurements were used to obtain the kinetic current of the ORR and the reaction order with respect to oxygen partial pressure in 1 M LiClO 4 propylene carbonate: 1,2-dimethoxyethane (1:2 v/v) In addition, air electrodes with Vulcan carbon or Au or Pt nanoparticles supported on Vulcan were examined in Li-O 2 single cells, where the observed discharge cell voltages follow the catalytic trend established by RDE measurements The ORR mechanism and the rate-determining steps were discussed and contrasted with the ORR activity trend in acid and alkaline solutions
TL;DR: In this article, the degradation of Ni/yttria-stabilized zirconia (YSZ)-based solid oxide electrolysis cells operated at high current densities was studied.
Abstract: The degradation of Ni/yttria-stabilized zirconia (YSZ)-based solid oxide electrolysis cells operated at high current densities was studied. The degradation was examined at 850 degrees C, at current densities of -1.0, -1.5, and -2.0 A/cm(2), with a 50:50 (H(2)O:H(2)) gas supplied to the Ni/YSZ hydrogen electrode and oxygen supplied to the lanthanum, strontium manganite (LSM)/YSZ oxygen electrode. Electrode polarization resistance degradation is not directly related to the applied current density but rather a consequence of adsorbed impurities in the Ni/YSZ hydrogen electrode. However, the ohmic resistance degradation increases with applied current density. The ohmic resistance degradation is attributed to oxygen formation in the YSZ electrolyte grain boundaries near the oxygen electrode/electrolyte interface. (C) 2010 The Electrochemical Society. [DOI:10.1149/1.3447752] All rights reserved.
TL;DR: Hirschorn et al. as mentioned in this paper proposed a method to detect the presence of interference in the process of chemical engineering applications by using the Hirschorn-Orazem algorithm.
Abstract: II. Applications Bryan Hirschorn,* Mark E. Orazem,** Bernard Tribollet,** Vincent Vivier,*** Isabelle Frateur, and Marco Musiani*** Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, USA Laboratoire Interfaces et Systemes Electrochimiques, UPR 15 du CNRS, Université Pierre et Marie Curie, 75252 Paris cedex 05, France Laboratoire de Physico-Chimie des Surfaces, UMR CNRS-ENSCP 7045, Ecole Nationale Supérieure de Chimie de Paris, Chimie ParisTech, 75005 Paris, France Istituto per l’Energetica e le Interfasi, Consiglio Nazionale delle Ricerche, 35127 Padova, Italy
TL;DR: In this article, it is shown that the use of fluorinated binders can be replaced with greener and cost-effective polymers derived from cellulose, which can be used in hybrid electric vehicles.
Abstract: The stringent environmental requirements regarding the mobility energy usage are forcing most automakers to develop hybrid electric vehicles, which allows for a more efficient and thus less polluting use of fossil combustibles. A vast deployment of such vehicles involves producing and recycling of batteries on the thousand tons per year scale. Present Li-ion technologies involve the use of fluorinated binders, which are costly, and the use of environmentally unfriendly volatile organic compounds for the processing, which are difficult to recycle. In this paper, it is shown that the fluorinated binders can be replaced with greener and cost-effective polymers derived from cellulose. .
TL;DR: In this paper, a mathematical model to simulate the generation of mechanical stress during the discharge process in a dual porous insertion electrode cell sandwich comprised of lithium cobalt oxide and carbon is presented.
Abstract: A mathematical model to simulate the generation of mechanical stress during the discharge process in a dual porous insertion electrode cell sandwich comprised of lithium cobalt oxide and carbon is presented. The model attributes stress buildup within intercalation electrodes to two different aspects: changes in the lattice volume due to intercalation and phase transformation during the charge/discharge process. The model is used to predict the influence of cell design parameters such as thickness, porosity, and particle size of the electrodes on the magnitude of stress generation. The model developed in this study can be used to understand the mechanical degradation in a porous electrode during an intercalation/deintercalation process, and the use of this model results in an improved design for battery electrodes that are mechanically durable over an extended period of operation.
TL;DR: In this paper, a symmetric cell configuration with Na Superionic CONductor (NASICON)-type A 3 V 2 (PO 4 ) 3 (where A is Li or Na) as both cathode and anode was tried in a coin-type cell (type 2320).
Abstract: To improve the thermal stability of lithium- and sodium-ion batteries, the room-temperature molten salts LiBF 4 /1-ethyl-3-methyl imidazolium tetrafluoroborate (EMIBF 4 ) and NaBF 4 /EMIBF 4 were used as ionic liquid (IL) electrolytes instead of flammable carbonate-type organic electrolyte solvents. To avoid cathodic decomposition of the IL electrolytes, a symmetric cell configuration with Na Superionic CONductor (NASICON)-type A 3 V 2 (PO 4 ) 3 (where A is Li or Na) as both cathode and anode was tried in a coin-type cell (type 2320). As a result, both the polyanionic-based Li 3 V 2 (PO 4 ) 3 (LVP) as well as Na 3 V 2 (PO a ) 3 (NVP) symmetric cells using organic electrolytes were found to operate as secondary batteries and exhibited satisfactory electrochemical performances. The substitution of the organic electrolytes by the appropriate IL electrolytes in both cases resulted in the reduction in the first discharge capacities. However, the IL-based cells revealed better cyclability and a more stable behavior at elevated temperatures. The obtained electrochemical behavior of the symmetric cells was confirmed by the complex impedance measurements at 25 and 80°C. In addition, the thermal stability of LVP and NVP with the IL electrolytes was also examined.
TL;DR: In this paper, the microstructural strain in a composite electrode during lithium insertion using a side-by-side cell geometry was measured using a digital image correlation analysis, displaying both dilation and contraction.
Abstract: The mechanics and microstructure of electrodes are critical in determining the performance and durability of lithium-ion batteries, especially the new large format cells and packs developed for transportation applications. During battery operation, Li diffuses into and out of the electrode particles, causing microstructural changes and deformation-induced degradation. A variety of models have been proposed to interpret these mechanical and microstructural changes, but they have no direct experimental support. We report direct in situ measurements of the microstructural strain in a composite electrode during lithium insertion using a side-by-side cell geometry. The color variation in graphite with Li concentration creates lithium spatial maps. A digital image correlation analysis provides corresponding deformation and strain fields, displaying both dilation and contraction. Through a combination of experimental measurement and theoretical analysis, the unexpected contraction during lithiation is explained by the stiffening of graphite upon lithiation. The result confirms the change in modulus that we recently predicted. Quantification of local strains shows that an increased graphite crystallite volume during lithiation is accommodated primarily by a decrease in the composite (or particle) porosity. The change in porosity can substantially impact battery power; however, this effect has generally been ignored in cell performance models for lithium-ion batteries.
TL;DR: In this article, the authors developed analytical solutions for the evolution of concentration and stresses within a spherical electrode element under charging-discharging conditions when the system thermodynamics are ideal (e.g., no repulsion forces are significant between intercalate species).
Abstract: Most lithium-ion battery electrodes experience large volume changes caused by concentration changes within the host particles during charging and discharging. Electrode failure, in the form of fracture or decrepitation, can occur as a result of repeated volume changes. In this work, we first develop analytic solutions for the evolution of concentration and stresses within a spherical electrode element under charging-discharging conditions when the system thermodynamics are ideal (e.g., no repulsion forces are significant between intercalate species). Both interfacial (electrochemical) kinetics and intercalate diffusion are comprehended. Based on the analytic solutions, we propose tensile stress-based criteria for the initiation of cracks within a spherical insertion electrode. These criteria may help guide the development of new materials for lithium-ion batteries with enhanced mechanical durability and identify battery operating conditions that, when maintained, keep the mechanical stresses below acceptable values, thereby increasing cell life.
TL;DR: Li-air cells based on Li foil as an anode electrode, freestanding carbon nanotube/nanofiber mixed buckypaper as an air (cathode) electrode, and organic electrolyte were assembled.
Abstract: Li-air cells based on Li foil as an anode electrode, freestanding carbon nanotube/nanofiber mixed buckypaper as an air (cathode) electrode, and organic electrolyte were assembled. The air electrode was made with single-wall carbon nanotube (SWNT) and carbon nanofiber (CNF) without any binder. The discharge capacity was strongly dependent on both the discharge current density and the thickness of the air electrode. A discharge capacity as high as 2500 mAh/g was obtained for an air electrode at a thickness of 20 μm with a discharge current density of 0.1 mA/cm 2 ; however, it was reduced to 400 mAh/g when the thickness of the air electrode was increased to 220 μm. For a 66 μm thick air electrode, the discharge capacity decreased from 1600 to 340 mAh/g when the discharge current density increased from 0.1 to 0.5 mA/cm 2 . The scanning electron microscope images on surfaces of the air electrode from a fully discharged cell showed that the voids at the air side were almost fully filled by the solid deposition; however, the voids at the membrane side were still wide open.
TL;DR: In this paper, a mathematical model for diffusion-induced stress generation in spherical Li-ion active materials has been incorporated into Dualfoil, a Li ion cell-sandwich model with porous electrodes, and the model is used to examine differences in the electrochemomechanical response of "power" vs "energy" cells at high currents.
Abstract: A mathematical model for diffusion-induced stress generation in spherical Li-ion active materials has been incorporated into Dualfoil, a Li-ion cell-sandwich model with porous electrodes. The model is used to examine differences in the electrochemomechanical response of "power" vs "energy" cells at high currents. Porous electrode effects, particularly in "energy-type" cells with thick electrodes, amplify the peak stresses encountered during lithium insertion and extraction and may result in nonuniform decrepitation or disordering through the depth of the electrode. We also elucidate the roles of fragment connectivity, volume expansion factors, nonlinear lattice expansion, and variable solid-state diffusion on diffusion-induced stress, stress-induced diffusion, and the voltage response of dual-intercalation cells with porous electrodes. In conventional electrode materials (with small volume expansion), pressure diffusion plays a limited role in determining the galvanostatic voltage response but becomes important in determining the stress response. Pressure diffusion and nonlinear lattice expansion play an important role in determining both the voltage and stress response in large-volume-expansion materials (e.g., alloys and perhaps graphite at low utilization).
TL;DR: In this article, the synthesis of "layered-layered" integrated xLi 2 Mno 3 ·(1 ― x)LiMn 1/3 Ni1/3 Co 1/ 3 O 2 materials (x = 0.3, 0.5, and 0.7) using the self-combustion reaction in solutions containing metal nitrates and sucrose was reported.
Abstract: We report herein on the synthesis of "layered-layered" integrated xLi 2 Mno 3 ·(1 ― x)LiMn 1/3 Ni 1/3 Co 1/3 O 2 materials (x = 0.3, 0.5, and 0.7) using the self-combustion reaction in solutions containing metal nitrates and sucrose. The nanoparticles of these materials were obtained by further annealing of the as-prepared product in air at 700°C for 1 h and submicrometric particles were obtained by further annealing at 900°C for 22 h. The effect of composition on the electrochemical performance was explored in this work. By a rigorous study with high resolution transmission electron microscopy (HRTEM), it became clear that the syntheses with the above stoichiometries produce two-phase materials comprising nanodomains of both rhombohedral LiNiO 2 -like and monoclinic Li 2 MnO 3 structures, which are closely integrated and interconnected with one another at the atomic level. Stable reversible capacities ∼220 mAh/g were obtained with composite electrodes containing submicrometer particles of 0.5Li 2 MnO 3 ·0.5LiMn 1/3 Ni 1/3 Co 1/3 O 2 . Structural aspects, activation of the monoclinic component, and stabilization mechanisms are thoroughly discussed using Raman spectroscopy, solid-state NMR, HRTEM, and X-ray diffraction (including Rietveld analysis) in conjunction with electrochemical measurements. This work provides a further indication that this family of integrated compounds contains the most promising cathode materials for high energy density Li-ion batteries.
TL;DR: In this paper, thin films of copper sulfide (CuS, 200 nm thick) were deposited over thin film of tin sulfide by sequential chemical deposition, and the grazing incidence X-ray diffraction analysis of these layers established the formation of thin films with ternary composition.
Abstract: Thin films of copper sulfide (CuS, 200 nm thick) were deposited over thin films of tin sulfide (SnS, 180 nm thick) by sequential chemical deposition. The layers were heated in nitrogen atmosphere at 350 and 400°C. The grazing incidence X-ray diffraction analysis of these layers established the formation of thin films of ternary composition, Cu 2 SnS 3 and Cu 4 SnS 4 . Optical bandgaps of the films are direct, 0.95 eV for Cu 2 SnS 3 and 1.2 eV for Cu 4 SnS 4 , and the electronic transitions are of the forbidden type in both cases. The films are p-type, with electrical conductivities of 0.5-10 Ω ―1 cm ―1 and hole concentrations of 10 17 ―10 18 cm ―3 . Based on the optical absorption coefficients, the light generated current density (J L ) as a solar cell absorber was evaluated for these materials for air mass 1.5 (1000 W/m 2 ) global solar radiation. For a film thickness of 0.5 μm. Cu 2 SnS 3 and Cu 4 SnS 4 could offer J L of 34 and 27 mA/cm 2 , respectively. Corresponding optical conversion efficiencies of solar energy into electron-hole pairs are 32 and 24%. The built-in potential for CdS/Cu 2 SnS 3 and CdS/Cu 4 SnS 4 junctions would be above 0.9 V and above 1.1 V when ZnO replaces CdS as the window layer.
TL;DR: In this article, the authors proposed an oxygen reduction reaction (ORR) mechanism that occurs on non-platinum electrocatalysts, specifically materials derived from pyrolyzed cobalt tetramethoxyphenyl porphyrin in acidic media.
Abstract: A study on the oxygen reduction reaction (ORR) mechanism that occurs on non-platinum electrocatalysts, specifically materials derived from pyrolyzed cobalt tetramethoxyphenyl porphyrin in acidic media, is presented here. Reactant and product flux analysis is performed on rotating ring-disk electrode (RRDE) data to evaluate the non-platinum-based materials. An in-depth X-ray photelectron spectroscopy surface characterization analysis is performed and discussed in the context of structure-to-property correlations that are established using a multivariant analysis technique. Pyrolyzed cobalt porphyrin catalysts are highly heterogeneous materials that include both Co species that are associated with nitrogen (CoN x ) and Co nanoparticles coated by "native" Co oxides. This study proposes an ORR mechanism that occurs on this class of non-Pt electrocatalysts based on structure-to-property correlations and qualitative analysis of the RRDE flux data. The combined flux analysis and structural characterization suggests that the series type, 2 × 2 peroxide ORR pathway is supported on the bifunctional catalyst materials. In this model, two distinct active sites are involved following a bifunctional catalysis scheme. It is suggested that oxygen is initially adsorbed and reduced to peroxide on a CoN x -type site. The intermediate product, peroxide, can be further reduced to water in a series reaction step on a decorating active cobalt oxide species on the catalyst surface.
TL;DR: In this article, structural and morphological changes in composite sulfur electrodes were studied due to their cycling in rechargeable Li-S cells produced by Sion Power Inc. The gradual changes in the structure of sulfur cathodes due to cycling was described and discussed.
Abstract: In this work, structural and morphological changes in composite sulfur electrodes were studied due to their cycling in rechargeable Li-S cells produced by Sion Power Inc. Composite sulfur cathodes, comprising initially elemental sulfur and carbon, undergo pronounced structural and morphological changes during discharge-charge cycles due to the complicated redox behavior of sulfur in nonaqueous electrolyte solutions that contain Li ions. Nevertheless, Li―S cells can demonstrate prolonged cycling. To advance this technology, it is highly important to understand the evolution of the structure and morphology of sulfur cathodes as cycling proceeds. High resolution scanning and tunneling microscopy, scanning probe microscopy, and Raman spectroscopy were used in conjunction with the electrochemical measurements. A special methodology for slicing composite sulfur electrodes and their cross sectioning and depth profiling was developed. The gradual changes in the structure of sulfur cathodes due to cycling is described and discussed herein. Important phenomena include changes in the surface electrical conductivity of sulfur electrodes and pronounced morphological changes due to the irreversibility of the sulfur redox reactions. Based on the observations presented in this work, it may be possible to outline guidelines for improving Li-S battery technology and extending its cycle life.
TL;DR: In this article, an experimentally validated model was developed to analyze the polarization of a LiNi0.8Co0.15Al0.05O2 vertical bar 1.2 M LiPF6 in ethylene carbonate.
Abstract: An experimentally validated model was developed to analyze the polarization of a LiNi0.8Co0.15Al0.05O2 vertical bar 1.2 M LiPF6 in ethylene carbonate (EC):ethyl methyl carbonate (EMC) (3:7)vertical ...