Showing papers in "Journal of The Electrochemical Society in 2012"
TL;DR: In this paper, a review of the modeling and simulation of lithium-ion batteries and their use in the design of better batteries is presented and likely future directions in battery modeling and design including promising research opportunities are outlined.
Abstract: The lithium-ion battery is an ideal candidate for a wide variety of applications due to its high energy/power density and operating voltage. Some limitations of existing lithium-ion battery technology include underutilization, stress-induced material damage, capacity fade, and the potential for thermal runaway. This paper reviews efforts in the modeling and simulation of lithium-ion batteries and their use in the design of better batteries. Likely future directions in battery modeling and design including promising research opportunities are outlined.
586 citations
380 citations
Abstract: A new MXene phase, Ti2C, obtained by aluminum extraction from Ti2AlC and exfoliation of the reaction product, was electrochemically studied vs. Lithium. Li-ions insertion into the 2-D structure was characterized by in situ XRD measurements. Additional electrochemical kinetic characterizations of Ti2C, using a cavity micro-electrode, showed that the electrochemical reactions involve two different phenomena: one diffusion-limited, the other not. A Ti2C/activated carbon asymmetric cell was assembled to highlight the high rate performance of the MXene. The cell was cycled between 1.0 V and 3.5 V, and showed good capacity retention during 1000 galvanostatic charge/discharge cycles at rates up to 10C.
314 citations
TL;DR: A combined experimental and computational study on Na3V2(PO4)3 has been carried out to investigate its structural, electrochemical, and thermal properties as a sodium battery cathode as discussed by the authors.
Abstract: A combined experimental and computational study on Na3V2(PO4)3 has been carried out to investigate its structural, electrochemical, and thermal properties as a sodium battery cathode. The synthesized material by a sol-gel process was well-indexed to the R-3m space group in the framework of a rhombohedral NASICON structure. Galvanostatic measurements indicate that at 3.4 V vs. Na/Na+, 1.4 Na reversibly reacts with each Na3V2(PO4)3, which corresponds to a specific capacity of 84.8 mAh/g. Moreover, this material shows excellent rate capabilities and good cycling performance. Ex-situ XRD analyzes indicate that this material reacts with Na ions based on a reversible two-phase reaction. Thermal analyzes employing TGA/DSC and In-situ XRD at various temperatures show that this material maintains good thermal stability up to 450°C even in the desodiated state. The promising electrochemical and thermal properties suggest that this material with the well-defined NASICON structure is a promising cathode for large-scale sodium rechargeable batteries.
302 citations
297 citations
TL;DR: In this paper, irreversible capacity loss in a graphite-LiFePO 4 cell is attributed to diffusion induced stresses that cause pre-existing cracks on the electrode surfaces to grow gradually upon cycling, leading to the growth of SEI on the newly exposed electrode surfaces.
Abstract: Coupled mechanical-chemical degradation of electrodes upon charging and discharging has been recognized as a major failure mechanism in lithium ion batteries. The instability of commonly employed electrolytes results in solid electrolyte interphase (SEI) formation. Although the SEI layer is necessary, as it passivates the electrode-electrolyte interface from further solvent decomposition, SEI formation consumes lithium and thus contributes to irreversible capacity loss. In this paper, we study irreversible capacity loss in a graphite-LiFePO 4 cell. Our results support the mechanism of irreversible capacity loss due to the consumption of lithium in forming SEI. We attribute irreversible capacity loss to diffusion induced stresses (DISs) that cause pre-existing cracks on the electrode surfaces to grow gradually upon cycling, leading to the growth of SEI on the newly exposed electrode surfaces. Because lithium is consumed in forming the new SEI, irreversible capacity loss continues with cycling. Along with the SEI formation upon newly exposed (cracked) surfaces, the existing SEI thickness also grows with cycling, resulting in additional loss of lithium. In this study, we provide, a simple mathematical model, based on the Paris' Law formulation of mechanical fatigue, in combination with chemical degradation to explain battery life. We compare the predicted capacity at different temperatures with the experimental data obtained from electrochemical measurements on graphite-LiFePO 4 cells.
292 citations
TL;DR: In this paper, the electrochemistry and structural changes that occur during sodium insertion and removal from tin are studied by in-situ X-ray diffraction at 30°C.
Abstract: The electrochemistry and the structural changes that occur during sodium insertion and removal from tin are studied by in-situ X-ray diffraction at 30°C. The Sn vs. Na voltage curve has four distinct plateaus, corresponding to four two-phase regions during sodiation, and indicating that four Na-Sn binary alloys are formed. The alloy formed at full sodiation was found to be Na15Si4, as expected from the Na-Sn binary system at equilibrium. The three intermediate Na-Sn phases that form during sodiation have X-ray diffraction patterns that do not correspond to any known equilibrium phase of Na-Sn. More work is needed to characterize these new binary Na-Sn phases.
291 citations
290 citations
TL;DR: In this article, the effect of cathode platinum loading on oxygen transport resistance in a fuel cell electrode was determined by measuring limiting current in fuel cells over a wide range of platinum loadings (0.03 to 0.40 mgPt/cm2).
Abstract: The effect of cathode platinum loading on oxygen transport resistance in a fuel cell electrode was determined by measuring limiting current in fuel cells over a wide range of platinum loadings (0.03 to 0.40 mgPt/cm2). The measurements show that the electrode oxygen transport resistance is inversely proportional to platinum loading or, equivalently, platinum surface area, and is mathematically similar to a 12 s/cm resistive film coating the active platinum sites. At low platinum loading this anomalous resistance significantly reduces the partial pressure of oxygen at the platinum surface and seriously degrades fuel cell performance at high power conditions. The magnitude of this film-like resistance is equivalent to ~35 nm of bulk-like ionomer but only 4–10 nm, assuming uniform coating, is present in the electrode. Alternatively, 380 nm diameter agglomerates with 20 nm of ionomer coating their external surface would create the same resistance, but such agglomerates are not apparent in SEM micrographs. As a result, the source of this resistance remains unknown, and further investigations are required to understand and mitigate it.
285 citations
TL;DR: In this paper, a 2D transient, isothermal model of a vanadium redox flow battery that can predict the species crossover and related capacity loss during operation is presented, and the model further improves upon the accuracy of existing models by incorporating a more complete version of the Nernst equation, which enables accurate prediction of the cell potential without the use of a fitting voltage.
Abstract: This paper presents a 2-D transient, isothermal model of a vanadium redox flow battery that can predict the species crossover and related capacity loss during operation. The model incorporates the species transport across the membrane due to convection, diffusion, and migration, and accounts for the transfer of water between the half-cells to capture the change in electrolyte volume. The model also accounts for the side reactions and associated changes in species concentration in each half-cell due to vanadium crossover. A set of boundary conditions based on the conservations of flux and current are incorporated at the electrolyte|membrane interfaces to account for the steep gradients in concentration and potential at these interfaces. In addition, the present model further improves upon the accuracy of existing models by incorporating a more complete version of the Nernst equation, which enables accurate prediction of the cell potential without the use of a fitting voltage. A direct comparison of the model predictions with experimental data shows that the model accurately predicts the measured voltage of a single charge/discharge cycle with an average error of 1.83%, and estimates the capacity loss of a 45 cycle experiment with an average error of 4.2%.
283 citations
TL;DR: In this article, a simplified electrochemical and thermal model of LiFePO4-graphite based Li-ion batteries is developed based on the Pseudo Two-Dimensional mathematical structure.
Abstract: Derived from the Pseudo Two-Dimensional mathematical structure, a simplified electrochemical and thermal model of LiFePO4-graphite based Li-ion batteries is developed in this paper. Embedding the porous electrode theory, this model integrates the main design parameters of Li-ion systems and its partial differential equations mathematical structure makes it a promising candidate for battery management system (BMS) applications and comprehensive aging investigations. Based on a modified Single-Particle approach, the model is used to simulate and discuss capacity restitution in galvanostatic charges and discharges at various rates and temperatures. Constant high-rate solicitations similar to fast charge of plug-in electric vehicles or electric vehicles, are experimentally tested and simulated with the present model. Also, thermal issues occurring during these specific operating conditions are quantitatively pointed out. The concept of current-dependent spherical particle radius is used to obtain good agreement with experimental data related to galvanostatic charges and discharges. The capabilities and limits of this preliminary modeling work are discussed in detail and ways to extend the potentialities of this approach to BMS applications are proposed.
TL;DR: In this article, the performance of silicon thin film electrodes was investigated in the presence of anode solid electrolyte interphase (SEI) forming additives, such as Vinylene Carbonate (VC), flouroethylene carbonate (FEC), and lithium difluorooxalatoborate (LiFOB), which improved the cycling efficiency and capacity retention of cells.
Abstract: The cycling performance of silicon thin film electrodes was investigated in the presence of anode solid electrolyte interphase (SEI) forming additives. Incorporation of vinylene carbonate (VC), flouroethylene carbonate (FEC), and lithium difluorooxalatoborate (LiFOB) improve the cycling efficiency and capacity retention of cells. Ex-situ surface analysis of the silicon anodes after cycling indicates that incorporation of the additives changes the structure of the SEI. Additives decrease the concentration of LiF on the anode surface consistent with inhibition of LiPF6 decomposition. The changes in surface structure correlate with improved cycling performance.
TL;DR: In this article, a hierarchical porous Ni-Co oxide powder is successfully synthesized by a facile chemical bath deposition method and its structure and composition is confirmed by transmission electron microscopy and energy dispersive X-ray analysis.
Abstract: Hierarchically porous Ni-Co oxide powder is successfully synthesized by a facile chemical bath deposition method. The structure and composition of Ni-Co oxide are confirmed by transmission electron microscopy and energy dispersive X-ray analysis. Scanning electron microscopy characterization indicates that the Ni-Co oxide has architecture of numerous microflowers with porous flakes. The pseudocapacitive behavior of the Ni-Co oxide powder is investigated by cyclic voltammgrams (CVs) and galvanostatic charge-discharge tests in alkali solution. The Ni-Co oxide shows a good reversibility with a high specific capacitance (834.93 Fg−1 at 1 mVs−1 scan rate). This active material was also used to manufacture a Ni-Co oxide//AC (Active Carbon) asymmetric supercapacitor. The Ni-Co oxide//AC asymmetric supercapacitor shows not only a high specific capacitance (60 Fg−1 with 1 mVs−1 scan rate), but also a high reversibility where its specific capacitance remains at 37 Fg−1 at a high current density of 20 mAcm−2.
TL;DR: In this article, the authors use microkinetic modeling to demonstrate that deviations from ideal Tafel kinetics, which assume a linear relationship between overpotential and log-current, are an inherent property of multi-step heterogeneous electrocatalytic reactions.
Abstract: We use microkinetic modeling to demonstrate that deviations from ideal Tafel kinetics, which assume a linear relationship between overpotential and log-current, are an inherent property of multi-step heterogeneous electrocatalytic reactions. We show that in general, deviations from ideal Tafel behavior can often be attributed to a simultaneous increase in the rate of the rate-limiting elementary step and a change in the number of available active sites on the electrode as overpotential is induced. Our analysis shows that in the oxygen reduction reaction (ORR) on Pt electrodes, which exhibits nonlinear Tafel behavior, changing electrode potential affects not only the rate-limiting step (the initial electron transfer to molecular oxygen), but also the concentration of surface intermediates—mainly OH and H 2 O. Based on comparison of measured and predicted changes in Tafel slope (as well as pH dependence), we show that alternative interpretations of the non-ideal Tafel behavior of ORR on Pt, such as changes in rate-limiting step or adsorbate repulsion effects, are inconsistent with the observed ORR kinetics.
TL;DR: In this article, the effect of discharge cutoff voltage on the reversibility of Li/S battery with a LiNO3-contained electrolyte was evaluated, and it was shown that deep discharge must be avoided for a long cycle life Li2S battery when Li NO3 is used as an additive or a co-salt of the electrolyte.
Abstract: LiNO3 is unique in suppressing the redox shuttle of lithium polysulfides in Li/S battery. In this paper we evaluate the effect of discharge cutoff voltage on the reversibility of Li/S battery with a LiNO3-contained electrolyte. Based on a study of the liquid Li/S cells with a 0.05 m Li2S9 solution as the catholyte, we find that the highly reversible discharge and charge cycling of Li/S cells occurs at higher than 1.8 V vs. Li/Li+, which corresponds to a multistage redox process of the sulfur cathode between elemental sulfur and insoluble Li2S2. At lower potentials, not only the Li2S2 is reduced into poorly reversible Li2S, but also the LiNO3 is reduced irreversibly. Moreover, the irreversible reduction of LiNO3 further reduces the reversibility of the poorly reversible Li2S, resulting in a significant slowdown in the electrode reaction kinetics and a permanent loss in the reversibility of the Li/S cell. This work suggests that deep discharge must be avoided for a long cycle life Li/S battery when LiNO3 is used as an additive or a co-salt of the electrolyte.
TL;DR: In this article, a model of concurrent reaction and plasticity is presented to accommodate the reaction-induced volumetric expansion by plastic deformation of the lithiated silicon in an electrochemical cell.
Abstract: In an electrochemical cell, crystalline silicon and lithium react at room temperature, forming an amorphous phase of lithiated silicon. The reaction front—the phase boundary between the crystalline silicon and the lithiated silicon—is atomically sharp. Evidence has accumulated recently that the velocity of the reaction front is limited by the rate of the reaction at the front, rather than by the diffusion of lithium through the amorphous phase. This paper presents a model of concurrent reaction and plasticity. We identify the driving force for the movement of the reaction front, and accommodate the reaction-induced volumetric expansion by plastic deformation of the lithiated silicon. The model is illustrated by an analytical solution of the co-evolving reaction and plasticity in a spherical particle. We derive the conditions under which the lithiation-induced stress stalls the reaction. We show that fracture is averted if the particle is small and the yield strength of lithiated silicon is low. Furthermore, we show that the model accounts for recently observed lithiated silicon of anisotropic morphologies.
TL;DR: In this article, the electrolyte solution structure for acetonitrile (AN)-lithium salt mixtures has been examined for highly dissociated salts, and phase diagrams are reported for (AN)n-LiN(SO2CF3)2 (LiTFSI) and -LiPF6 electrolytes.
Abstract: The electrolyte solution structure for acetonitrile (AN)-lithium salt mixtures has been examined for highly dissociated salts. Phase diagrams are reported for (AN)n-LiN(SO2CF3)2 (LiTFSI) and -LiPF6 electrolytes. Single crystal structures and Raman spectroscopy have been utilized to provide information regarding the solvate species present in the solid-state and liquid phases, as well as the average solvation number variation with salt concentration. Molecular dynamics (MD) simulations of the mixtures have been correlated with the experimental data to provide additional insight into the molecular-level interactions. Quantum chemistry (QC) calculations were performed on (AN)n-Li-(anion)m clusters to validate the ability of the developed many-body polarizable force field (used for the simulations) to accurately describe cluster stability (ionic association). The combination of these techniques provides tremendous insight into the solution structure within these electrolyte mixtures.
TL;DR: In this article, the authors reformulate and extend porous electrode theory for non-ideal active materials, including those capable of phase transformations, using principles of non-equilibrium thermodynamics, and relate the cell voltage, ionic fluxes and Faradaic charge transfer kinetics to the variational electrochemical potentials of ions and electrons.
Abstract: We reformulate and extend porous electrode theory for non-ideal active materials, including those capable of phase transformations. Using principles of non-equilibrium thermodynamics, we relate the cell voltage, ionic fluxes, and Faradaic charge-transfer kinetics to the variational electrochemical potentials of ions and electrons. The Butler-Volmer exchange current is consistently expressed in terms of the activities of the reduced, oxidized and transition states, and the activation overpotential is defined relative to the local Nernst potential. We also apply mathematical bounds on effective diffusivity to estimate porosity and tortuosity corrections. The theory is illustrated for a Li-ion battery with active solid particles described by a Cahn-Hilliard phase-field model. Depending on the applied current and porous electrode properties, the dynamics can be limited by electrolyte transport, solid diffusion and phase separation, or intercalation kinetics. In phase-separating porous electrodes, the model predicts narrow reaction fronts, mosaic instabilities and voltage fluctuations at low current, consistent with recent experiments, which could not be described by existing porous electrode models.
TL;DR: In this paper, the solid components deposited in sulfur cathode during cycling for Li-S battery are studied by Fourier transform infrared (FTIR), Raman spectra and X-ray photoelectron spectroscopy (XPS).
Abstract: The solid components deposited in sulfur cathode during cycling for Li-S battery is studied in this work. ROLi, HCO2Li, LixSOy and Li2S (or Li2S2) are proved to be the main components by the methods of Fourier transform infrared (FTIR), Raman spectra and X-ray photoelectron spectroscopy (XPS). ROLi and HCO2Li are solvent degradation products existed in electrolyte. The reversibility of Li2S and Li2S2 are not serious as in previous reports. ROLi, HCO2Li and LixSOy co-deposited with Li2S or Li2S2 in discharge process lead to the cathodes performance deterioration. Lithium salts such as LiNO3 and LiTFSI can oxidize sulfur compounds to higher oxidation states, and LixSOy species increased with cycling indicates the active mass irreversible oxidation that may be another important reason for the capacity fading of Li-S battery.
TL;DR: In this article, the performance of a vanadium flow battery with no-gap architecture was significantly improved via several techniques, including variation of the overall electrode thickness, membrane thickness, and electrode thermal treatment.
Abstract: The performance of a vanadium flow battery with no-gap architecture was significantly improved via several techniques. Specifically, gains arising from variation of the overall electrode thickness, membrane thickness, and electrode thermal treatment were studied. There is a trade-off between apparent kinetic losses, mass transfer losses, and ionic resistance as the electrode thickness is varied at the anode and cathode. Oxidative thermal pretreatment of the carbon paper electrode increased the peak power density by 16%. Results of the pretreatment in air showed greater improvement in peak power density compared to that obtained with pretreatment in an argon environment. The highest peak power density in a VRB yet published to the author s knowledge was achieved at a value of 767 mW cm 2 with optimized membrane and electrode engineering. 2012 The Electrochemical Society. [DOI: 10.1149/2.051208jes] All rights reserved.
TL;DR: A nano-scaled coating of titanium oxide (TiO2) on graphene (G) has been achieved via a novel atomic layer deposition (ALD) method as discussed by the authors, achieving a capacity of 75 F/g and 84 F /g at a scan rate of 10 mV/s for composites grown using 50 and 100 ALD cycles.
Abstract: A nano-scaled coating of titanium oxide (TiO2) on graphene (G) has been achieved via a novel atomic layer deposition (ALD) method. As a potential supercapacitor material, the TiO2-G composites exhibited a capacity of 75 F/g and 84 F/g at a scan rate of 10 mV/s for composites grown using 50 and 100 ALD cycles, respectively. The nearly identical Nyquist plots of the TiO2-G composites compared with those of pure graphene demonstrated that the composites possess excellent conductivity for charge transfer and open structures for ion diffusion. In addition, even with 3-4 times additional mass loading (maximum 3.22 mg/cm2), the composites exhibit no obvious degradation with respect to the electrochemical performance. This ALD approach presents a promising route to synthesize advanced graphene-based nanocomposites for supercapacitor applications. © 2012 The Electrochemical Society. [DOI: 10.1149/2.025204jes] All rights reserved.
TL;DR: In this paper, a physically motivated equivalent circuit model of LiFePO4-cathode was proposed to evaluate the rate determining processes of Li-Ion batteries in order to separate performance limiting factors.
Abstract: Lithium iron phosphate is a promising candidate material for Li-Ion batteries. In this study, the rate determining processes are assessed in more detail in order to separate performance limiting factors. Electrochemical impedance spectroscopy (EIS) data of experimental LiFePO4/Lithium-cells are deconvoluted by the method of distribution of relaxation times (DRT), what necessitates a pre-processing of the capacitive branch. This results in a separation into cathode and anode polarization processes and in a proposition of a physically motivated equivalent circuit model. We identify three different polarization processes of the LiFePO4-cathode (i) solid state diffusion, (ii) charge transfer (cathode/electrolyte) and (iii) contact resistance (cathode/current collector). Our model is then applied to EIS data sets covering varied temperature (0° to 30°C) and state of charge (10% to 100%). Activation energy, polarization resistance and frequency range are determined separately for all cathode processes involved. Finally, the tape-casted LiFePO4–cathode sheet is modified in porosity, thickness and contact area between cathode/electrolyte and cathode/current collector by a calendering process. Charge transfer resistance and contact resistance respond readily in polarization and relaxation frequency.
TL;DR: Liu et al. as discussed by the authors investigated lithium-ion electrode laminates as polymer composites to explain their performance variation due to changes in formulation and introduced a physical model in which AB and AM particles compete for polymer binder, which forms fixed layers of polymer on their surfaces.
Abstract: Author(s): Liu, G; Zheng, H; Song, X; Battaglia, VS | Abstract: This paper investigates lithium-ion electrode laminates as polymer composites to explain their performance variation due to changes in formulation. There are three essential components in a positive electrode laminate: active material (AM) particles, acetylene black (AB) particles, and the polymer binder. The high filler content and discrete particle sizes make the electrode laminate a very unique polymer composite. This work introduces a physical model in which AB and AM particles compete for polymer binder, which forms fixed layers of polymer on their surfaces. This competition leads to the observed variations in electrode morphology and performance for different electrode formulations. The electronic conductivities of the cathode laminates were measured and compared to an effective conductivity calculation based on the physical model to probe the interaction among the three components to reveal the critical factors controlling electrode conductivity and electrochemical performance. The data and effective conductivity calculation results agree very well with each other. This developed physical model provides a theoretical guideline for optimization of electrode composition for most polymer binder-based Li-ion battery electrodes. © 2012 The Electrochemical Society.