The 50 most-cited articles in Journal of The Electrochemical Society, 2016

This year, the battery industry celebrates the 25 th anniversary of the introduction of the lithium ion rechargeable battery by Sony Corporation. The discovery of the system dates back to earlier work by Asahi Kasei in Japan, which used a combination of lower temperature carbons for the negative electrode to prevent solvent degradation and lithium cobalt dioxide modified somewhat from Goodenough's earlier work. The development by Sony was carried out within a few years by bringing together technology in film coating from their magnetic tape division and electrochemical technology from their battery division. The past 25 years has shown rapid growth in the sales and in the benefits of lithium ion in comparison to all the earlier rechargeable battery systems. Recent work on new materials shows that there is a good likelihood that the lithium ion battery will continue to improve in cost, energy, safety and power capability and will be a formidable competitor for some years to come.

Lithium ion batteries have become an integral part of our daily lives. Among a number of different cathode materials nickel-rich LiNi x Co y Mn z O 2 is particularly interesting. The material can deliver high capacities of ∼195 mAh g −1 putting it on the map for electric vehicles. With an increasing nickel content, a number of issues arise in the material limiting its performance. The Li/Ni mixing, highly reactive surface and formation of micro cracks are the most pressing ones. An overview of recent literature exploring these phenomena is herein summarized and were applicable solutions will be highlighted.

Lithium ion battery performance at high charge/discharge rates is largely determined by the ionic resistivity of an electrode and separator which are filled with electrolyte. Key to understand and to model ohmic losses in porous battery components is porosity as well as tortuosity. In the first part, we use impedance spectroscopy measurements in a new experimental setup to obtain the tortuosities and MacMullin numbers of some commonly used separators, demonstrating experimental errors of <8%. In the second part, we present impedance measurements of electrodes in symmetric cells using a blocking electrode configuration, which is obtained by using a non-intercalating electrolyte. The effective ionic resistivity of the electrode can be fit with a transmission-line model, allowing us to quantify the porosity dependent MacMullin numbers and tortuosities of electrodes with different active materials and different conductive carbon content. Best agreement between the transmission-line model and the impedance data is found when constant-phase elements rather than simple capacitors are used.

In this study, the influence of ionomer content in IrO 2 /TiO 2 anode electrodes for a proton exchange membrane (PEM) electrolyzer is investigated (Nafion 212 membrane; 2.0 mg Ir cm −2 / 0.35 mg Pt cm −2 (anode/cathode)) and the contributions of ohmic losses, kinetic losses, proton transport losses in the electrodes, and mass transport losses to the overall cell voltage are analyzed. Electrolysis tests are performed with an in-house designed high pressure electrolyzer cell at differential pressure up to 30 bar. The best performance is obtained for an ionomer content of 11.6 wt% and a cell voltage of 1.57 V at 1 A cm −2 and less than 2 V at 6 A cm −2 (ambient pressure, 80°C). Performance losses at lower ionomer contents are the result of a higher proton conduction resistance. For higher ionomer contents, on the other hand, performance losses can be related to a filling of the electrode void volume by ionomer, leading to a higher O 2 mass transport resistance, an increased electronic contact resistance, and the electronic insulation of parts of the catalyst by ionomer. At high…

Herein, we present the synthesis and characterization of negative (a hard carbon/carbon black composite) and positive (K 0.3 MnO 2 ) active materials for K-ion batteries as well as their combination in a non-aqueous K-ion cell. The hard carbon/carbon black composite can deliver up to 200 mAh g −1 while the layered birnessite K 0.3 MnO 2 delivers up to 136 mAh g −1 . The K-ion cell exhibits an interesting and encouraging cycling performance for 100 cycles. These exciting new insights demonstrate the potential of K-ion batteries, which are worth to be further investigated in greater detail.

Gassing in lithium-ion batteries (LIBs) is a serious challenge, especially at high voltage and elevated temperature. In this study, we use On-line Electrochemical Mass Spectrometry (OEMS) and a two-compartment cell with a newly developed aluminum edge-seal to elucidate the origin of H 2 evolution in LIBs. We demonstrate that the new sealing is entirely impermeable for gaseous and liquid species, thus allowing us to measure the true H 2 evolution from H 2 O reduction at a graphite electrode, without interference from the lithium counter-electrode. We further report that graphite//NMC full-cells without any diffusion barrier between anode and cathode show enhanced H 2 generation, especially for high charging potentials and at elevated temperature. We propose that the diffusion of protic electrolyte oxidation species (R-H + ) from the cathode to the anode and their subsequent reduction is the origin of enhanced H 2 gassing. To prove this hypothesis, methanesulfonic acid is added to the electrolyte as a chemical source of protons. At the negative graphite electrode, all H + can be…

Ion–solvent interactions play a crucial role in secondary battery systems: the desolvation of ions at an electrode/electrolyte interface can be the rate-determining step of a battery reaction, for instance. The present theoretical study investigates the interactions between K ions and organic electrolyte solvents for application in non-aqueous K-ion batteries, which have recently drawn interest as novel rechargeable batteries. Compared to Li, Na, and Mg ions, K ions display the lowest interaction energy, reflecting the large ionic radius and weak Lewis acidity of K. The weak interaction of K ions with solvents is consistent with the high rate capability exhibited by K-ion batteries and the relatively low solubility of K-ion salts observed experimentally.

MXene-based materials are promising electrode materials for electrochemical capacitors (ECs) due to their unique two-dimensional layered structure, high surface area, remarkable chemical stability, and electrical conductivity. TiO 2 nanoparticles decorated Ti 3 C 2 MXene were synthesized through a simple in situ hydrolysis and heat-treatment process and subsequently fabricated as an electrode for ECs. The as-prepared Ti 3 C 2 , TiO 2 , and TiO 2 -Ti 3 C 2 were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results indicated that TiO 2 nanoparticles with a diameter of less than 30 nm were decorated onto the Ti 3 C 2 MXene nanosheets. The resulting composites exhibited significantly higher specific capacitance of 143 F g −1 at 5 mV s −1 , which was 1.5 times that of pure Ti 3 C 2 (93 F g −1 ). Moreover, TiO 2 -Ti 3 C 2 showed excellent cycling stability, retaining ∼92% of its initial capacitance after 6000 cycles. These results suggest that TiO 2 -Ti 3 C 2 nanocomposite has the potential as…

Water electrolysis is a promising technology for enabling the storage of surplus electricity produced by intermittent renewable power sources in the form of hydrogen. At the core of this technology is the electrolyte, and whether this is acidic or alkaline affects the reaction mechanisms, gas purities and is of significant importance for the stability and activity of the electrocatalysts. This article presents a simple but precise physical model to describe the voltage-current characteristic, heat balance, gas crossover and cell efficiency of water electrolyzers. State-of-the-art water electrolysis cells with acidic and alkaline electrolyte are experimentally characterized in order to parameterize the model. A rigorous comparison shows that alkaline water electrolyzers with Ni-based catalysts but thinner separators than those typically used is expected be more efficient than acidic water electrolysis with Ir and Pt based catalysts. This performance difference was attributed mainly to a similar conductivity but approximately 38-fold higher diffusivities of hydrogen and oxygen in the…

The increasing usage of electrical drive systems and stationary energy storage worldwide lead to a high demand of raw materials for the production of lithium-ion batteries. To prevent further shortage of these crucial materials, ecological and efficient recycling processes of lithium-ion batteries are needed. Nowadays industrial processes are mostly pyrometallurgical and as such energy and cost intensive. The LithoRec projects, funded by the Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (BMUB), aimed at a realization of a new energy-efficient recycling process, abstaining high temperatures and tracing mechanical process-steps. The conducted mechanical processes were thoroughly investigated by experiments in a laboratory and within technical scale, describing gas release of aged and non-aged lithium-ion batteries during dry crushing, intermediates, and products of the mechanical separation. Conclusively, we found that applying a second crushing step increases the yield of the coating materials, but also enables more selective separation. This…

Improvement of life-time is an important issue in the development of Li-ion batteries. Aging mechanisms limiting the life-time can efficiently be characterized by physico-chemical analysis of aged cells with a variety of complementary methods. This study reviews the state-of-the-art literature on Post-Mortem analysis of Li-ion cells, including disassembly methodology as well as physico-chemical characterization methods for battery materials. A detailed scheme for Post-Mortem analysis is deduced from literature, including pre-inspection, conditions and safe environment for disassembly of cells, as well as separation and post-processing of components. Special attention is paid to the characterization of aged materials including anodes, cathodes, separators, and electrolyte. More specifically, microscopy, chemical methods sensitive to electrode surfaces or to electrode bulk, and electrolyte analysis are reviewed in detail. The techniques are complemented by electrochemical measurements using reconstruction methods for electrodes built into half and full cells with reference electrode.…

The electrolyte additive fluoroethylene carbonate (FEC) is known to significantly improve the lifetime of Li-ion batteries with silicon anodes. In this work, we show that FEC can indeed improve the lifetime of silicon-carbon composite anodes but is continuously consumed during electrochemical cycling. By the use of 19 F-NMR spectroscopy and charge/discharge cycling we demonstrate that FEC is only capable to stabilize the cell performance as long as FEC is still remaining in the cell. Its total consumption causes a significant increase of the cell polarization leading to a rapid capacity drop. We show with On-line Electrochemical Mass Spectrometry (OEMS) that the presence of FEC in the electrolyte prohibits the reduction of other electrolyte components almost entirely. Consequently, the cumulative irreversible capacity until the rapid capacity drop correlates linearly with the specific amount of FEC (in units of μmol FEC /mg electrode ) in the cell. The latter quantity therefore determines the lifetime of silicon anodes rather than the concentration of FEC in the electrolyte. By…

Consumer electronics, wearable and personal health devices, power networks, microgrids, and hybrid electric vehicles (HEVs) are some of the many applications of lithium-ion batteries. Their optimal design and management are important for safe and profitable operations. The use of accurate mathematical models can help in achieving the best performance. This article provides a detailed description of a finite volume method (FVM) for a pseudo-two-dimensional (P2D) Li-ion battery model suitable for the development of model-based advanced battery management systems. The objectives of this work are to provide: ( i ) a detailed description of the model formulation, ( ii ) a parametrizable Matlab framework for battery design, simulation, and control of Li-ion cells or battery packs, ( iii ) a validation of the proposed numerical implementation with respect to the COMSOL MultiPhysics commercial software and the Newman's DUALFOIL code, and ( iv ) some demonstrative simulations involving thermal dynamics, a hybrid charge-discharge cycle emulating the throttle of an HEV, a model predictive…

Despite the extensive commercial use of Li 1- x Ni 1-y-z Mn z Co y O 2 (NMC) as the positive electrode in Li-ion batteries, and its long research history, its fundamental transport properties are poorly understood. These properties are crucial for designing high energy density and high power Li-ion batteries. Here, the transport properties of NMC 333 and NMC 523 are investigated using impedance spectroscopy and DC polarization and depolarization techniques. The electronic conductivity is found to increase with decreasing Li-content (increasing state-of-charge) from ∼10 −7 Scm −1 to ∼10 −2 Scm −1 over Li concentrations x = 0.00 to 0.75, corresponding to an upper charge voltage of 4.8 V with respect to Li/Li + . The lithium ion diffusivity is at least one order of magnitude lower, and decreases with increasing x to at x = ∼0.5. The ionic conductivity and diffusivity obtained from the two measurements techniques (EIS and DC) are in good agreement, and chemical diffusion is limited by lithium transport over a wide state-of-charge range.

The chemical and electrochemical instabilities of LiPF 6 in carbonate electrolytes for Li-ion batteries were studied with online electrochemical mass spectrometry (OEMS). Decomposition of carbonate electrolytes based on LiPF 6 eventually results in the formation of POF 3 , which is readily detected and followed in situ during operation of Li-rich HE-NCM-based Li-ion cells. Electrode potentials above ∼4.2 V leads to carbonate solvent oxidation and presumably the formation of ROH species, which subsequently hydrolyze the LiPF 6 salt and initiate a thermally activated autocatalytic electrolyte decomposition cycle involving POF 3 as a reactive intermediate. Activation of the Li 2 MnO 3 domains of the Li-rich cathode contributes along with electrolyte and separator impurities to further POF 3 generation. Electrode potentials below ∼2.5 V vs. Li + /Li impede POF 3 formation and presumably also further electrolyte decomposition by scavenging reactive intermediate species. As a result, much less POF 3 gas was detected upon the 2 nd charge when using Li metal counter electrode, contrary to…

The Solid electrolyte interphase (SEI), either naturally formed or artificially designed, plays a critical role in the stability and durability of Li-ion batteries (LIBs). It is even more important for high energy density electrodes such as Li metal anodes, which is subjected to large volumetric and interfacial variations due to Li deposition/stripping cycles during operation. Currently, there is a lack of understanding of the role of SEI/Li interfaces and their mechanical and electrochemical properties. In this paper, we present an interfacial study to evaluate the two major SEI components, LiF and Li 2 CO 3 , based on density functional theory (DFT) calculations. The calculated interfacial energy results show that the Li 2 CO 3 /Li interface has higher interfacial mechanical strength. The density of states (DOS) and electrostatic potential results demonstrate that the LiF/Li interface has higher electron tunneling energy barrier from Li metal to SEI. These results provide quantitative inputs for related meso-scale simulations and valuable insights for advanced electrode protective…

The degradation behaviors of bare and Al-oxide coated LiCoO 2 in the high-voltage phase transition region were investigated at the charge voltage of 4.7 V. In both materials, two voltage plateaus that indicate phase transitions from the O3 to H1-3 and O1 phases were observed in the first charge/discharge. Bare LiCoO 2 exhibited considerably decreased capacity, and increased polarization and charge transfer resistance in the cycle test, whereas these changes were remarkably suppressed in the coated LiCoO 2 . The phase transitions of the coated LiCoO 2 can be assumed to be fairly reversible, since the voltage plateaus remained even after 20 cycles. After the cycle tests, stacking faults were observed throughout the bare LiCoO 2 particle. Pitting corrosion occurred on the faults, and the formation of a spinel-like layer was observed on the surface of the cycled bare LiCoO 2 . The pitting corrosion caused intrinsic capacity fading by Co dissolution. The formation of the spinel-like layer also resulted in effective capacity fading due to the increased polarization. Both the pitting…

Renewable energy sources such as solar and wind power are important for the future energy supply chain, but require suitable energy storage and conversion technologies due to the nature of the intermittency in electricity generation. Solid oxide cell (SOC) is such a highly efficient device which can store the renewable electricity into chemical energy of fuels under solid oxide electrolysis cell (SOEC) operation mode and to regenerate the electricity using the stored fuels under solid oxide fuel cell (SOFC) operation mode. However, there are significant technological barriers for the commercial viability of SOCs, one of them is the significant performance degradation under the SOEC mode. This paper reviews critically the durability and performance degradation issues of SOCs under SOEC operation conditions and the emphasis is mainly on the physical, chemical and microstructural processes that cause the degradation and their dependence on the operation conditions and nature of the oxygen and hydrogen electrodes and electrolyte materials. The degradation due to the contaminants such as…

Iridium is the main element in modern catalysts for the oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWE), which is predominantly due to its relatively good activity and tolerable stability in harsh PEMWE conditions. Limited abundance of iridium, however, poses limitations on widespread applications of these devices, in particular in the large scale conversion and storage of renewable energy. In this work we investigate if the electrocatalytic performance of iridium can be fine-tuned by thermal treatment of catalysts at different temperatures. The OER activity and the dissolution of two different iridium electrodes, viz. (a) flat metallic iridium surfaces prepared by electron beam physical vapor deposition (EBPVD) and (b) electrochemically prepared porous hydrous iridium oxide films (HIROF) are studied. The range of applied annealing temperatures is 100°C–600°C, with a general trend of decreasing activity and increasing stability the higher the temperature. Numerous peculiarities in the trend are however observed. These are discussed considering…

The formation of copper oxides and hydroxides from metallic copper and underpotentially deposited copper atoms on platinum nanoparticles, when it is subjected to a potential scan between the hydrogen evolution potential and the oxygen evolution potential in alkaline solution as a function of scan rate and the pH of the solution has been investigated. Cyclic voltammetry of bulk copper electrodes in alkaline solution reveal that oxidation proceeds in steps leading to formation of Cu 2 O, Cu(OH) 2 and CuO on the surface as well as some soluble oxides which corroborates well with X-ray photoelectron spectroscopy (XPS) analysis. Furthermore, interesting needle like formations on copper surface was observed in a scanning electron microscope (SEM), which can explain the unusual relation between the peak current and scan rate. On the other hand, the oxidation of copper monolayer on platinum nanoparticles leads primarily to formation of Cu 2 O and shows the effect of nobility imparted by the underlying platinum in terms of increased potential.

We have demonstrated the repeated cycling of a redox flow cell based on water-soluble organic redox couples (ORBAT) at high voltage efficiency, coulombic efficiency and power density. These cells were successfully operated with 4,5-dihydroxybenzene-1,3-disulfonic acid (BQDS) at the positive electrode and anthraquinone-2,6-disulfonic acid (AQDS) at the negative electrode. Reduction of the voltage losses arising from mass transport limitations, and understanding of the chemical transformations of BQDS during charging have led to these improvements in performance. The specific advances reported here include the use of organic redox couples in the free-acid form, improvements to the flow field configuration, and novel high-surface-area graphite-felt electrode structures. We have identified various steps in the chemical and electrochemical transformations of BQDS during the first few cycles. We have also confirmed that the crossover of the reactants through the membrane was not significant. The performance improvements and new understanding presented here will hasten the development of…

Deposition of metallic Li is a severe aging mechanism in Lithium-ion cells. This study evaluates the influence of the main operating parameters leading to deposition of Li: temperature, charging C-rate, and end-of-charge voltage. Therefore both, graphite anodes and NMC cathodes from commercial 16Ah pouch cells are reconstructed into 3-electrode full cells. The position of the reference electrode between anode and cathode allows acquiring anode potentials vs. (Li/Li + ). Extensive evaluations of data reveal critical combinations of operating parameters to avoid Li deposition. The results from the reconstructed 3-electrode cells are compared with independently performed aging tests of the original 16Ah cells.

Unsupported iridium (Ir) nanoparticles, that serve as standard oxygen evolution reaction (OER) catalysts in acidic electrolyzers, were investigated for electrochemical performance and durability in rotating disk electrode (RDE) half-cells. Fixed potential holds and potential cycling were applied to probe the durability of Ir nanoparticles, and performance losses were found to be driven by particle growth (coarsening) at moderate potential (1.4 to 1.6 V) and Ir dissolution at higher potential (≥1.8 V). Several different commercially available samples were evaluated and standardized conditions for performance comparison are reported. The electrocatalyst RDE results have also been compared to results obtained for performance and durability in electrolysis cells.

Na-ion batteries have regained attention because they offer sustainability advantages over the Li-ion technology, hence their interest for massive electrochemical storage. Although the Na-ion electrochemistry is analogous to that of the Li-ion concept, there are a few notable differences such as the stability of carbonated-based electrolytes toward the Li or Na metal anodes. Herein we report on the positive effect of FEC as electrolyte additive on the efficiency of Na-half cells which unfortunately comes with a side effect involving the sudden onset of polarization during discharge at unpredictable capacity values. We show that these anomalies, associated to an inefficient plating-stripping at the sodium metal anode, do not appear in full Na-ion cells. Therefore, FEC-based electrolytes are not the panacea and alternative additives must be sought to enable building of reliable half cells with metal anodes.

One of the biggest causes of degradation in lithium-ion batteries is elevated temperature. In this study we explored the effects of cell surface cooling and cell tab cooling, reproducing two typical cooling systems that are used in real-world battery packs. For new cells using slow-rate standardized testing, very little difference in capacity was seen. However, at higher rates, discharging the cell in just 10 minutes, surface cooling led to a loss of useable capacity of 9.2% compared to 1.2% for cell tab cooling. After cycling the cells for 1,000 times, surface cooling resulted in a rate of loss of useable capacity under load three times higher than cell tab cooling. We show that this is due to thermal gradients being perpendicular to the layers for surface cooling leading to higher local currents and faster degradation, but in-plane with the layers for tab cooling leading to more homogenous behavior. Understanding how thermal management systems interact with the operation of batteries is therefore critical in extending their performance. For automotive applications where 80%…

The hydrogen and oxygen evolved during alkaline water electrolysis with liquid KOH electrolytes are typically separated using porous separators such as Zirfon PERL (Agfa), a commercially available composite of zirconium oxide and polysulfone. In this study, the hydrogen diffusivity (driven by concentration differences) and electrolyte permeability (driven by differential pressures) of the Zirfon PERL separator were characterized as a function of the temperature and molarity of the KOH filling. The diffusivity of hydrogen in the separator was found to be approximately 16% of that of the electrolyte filling inside its pores. With respect to water electrolysis conditions, the extent of hydrogen cross-permeation caused by the convection of the cross-permeating electrolyte was estimated and compared to that caused by diffusion. On the basis of the physically characterized mechanisms, smaller pores were predicted to reduce the differential pressure driven gas cross-permeation.

Impedance measurements of lithium-ion batteries are a powerful tool to investigate the electrolyte/electrode interface. To separate the contributions of anode and cathode to the full-cell impedance, a reference electrode is required. However, if the reference electrode is placed inappropriately, the impedance response can easily be biased and lead to erroneous conclusions. In this study, we present a novel micro-reference electrode for Swagelok-type T-cells which is suitable for long-term impedance and reference potential measurements. The reference electrode consists of a thin insulated gold wire, which is placed centrally between cathode and anode and is in-situ electrochemically alloyed with lithium. The resulting lithium-gold alloy reference electrode shows remarkable stability (>500 h) even during cycling or at elevated temperatures (40°C). The accuracy of impedance measurements with this novel reference electrode is carefully validated. Further, we investigate the effect of different vinylene carbonate (VC) contents in the electrolyte on the charge transfer resistance of…

Layered transition metal oxides Na x Ni 1/3 Fe 1/3 Mn 1/3 O 2 are promising cathode materials for sodium ion batteries. Here we report the large scale synthesis of NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NaNFM) by using hydroxide co-precipitation combined with solid-state reaction method. The obtained NaNFM showed good electrochemical performance with 1C rate (130 mA g −1 ) capacities of 125 mAh g −1 (55°C), 122 mAh g −1 (25°C), 95 mAh g −1 (−10°C), and 72 mAh g −1 (−20°C), respectively. 1 Ah soft-packed batteries using the prepared NaNFM as cathode and hard carbon as anode were prepared and investigated. Electrochemical tests showed that the as prepared 1 Ah soft-packed batteries exhibited excellent cycling performance with capacity retention over 73% after 500 cycles at 1C rate. The ex situ XRD experiments revealed that the charge/discharge process of Na x Ni 1/3 Fe 1/3 Mn 1/3 O 2 cathode showed excellent reversibility and the layered crystallographic structure of the NaNFM electrode remained stable after 500 cycles. This work demonstrates the NaNi 1/3 Fe 1/3 Mn 1/3 O 2 is a promising cathode…

A new device concept, Na-Ion Desalination (NID), is introduced to desalinate NaCl from water using Na-ion battery (NIB) intercalants. A two-dimensional porous-electrode model is used to predict the performance of NID cells operating at sea- and brackish-water salinity-levels by simulating electrolyte transport, membrane polarization, and simultaneous electrochemistry. Anion-selective membranes are used to isolate electrodes in NID cells because simulations showed substantial drop from influent salinity (63%) compared to porous separators used in conventional NIBs (22%). Symmetric NIB intercalants and energy recovery were used to minimize energy consumption. A Na 0.44 MnO 2 -based NID-cell with 0.5 mm-thick electrodes desalinated 700 mM influent by 63% while consuming only 50% more energy (0.74 kWh/m 3 ) than thermodynamic minimum when cycled at C/2 rate. The high volumetric charge-capacity of NIB intercalants enabled 59–64% drop in influent salinity with water-recovery levels up to 80% and 95% for 700 mM and 70 mM influent, respectively. The present predictions of NID performance…

Potassium tetratitanate (K 2 Ti 4 O 9 ) has been synthesized by solid state method using K 2 CO 3 and TiO 2 , and studied as an anode material for potassium ion batteries for the first time. A discharge capacity of 80 mAh g −1 has been obtained at a current density of 100 mA g −1 (0.8 C rate) and 97 mAh g −1 at 30 mA g −1 (0.2 C rate), initially. The discharge capacity is stable at low rates of cycling. The uptake of K + on charging K 2 Ti 4 O 9 electrodes is quantitatively studied. The proposed mechanism of charging involves reduction of two Ti ions from 4+ oxidation state to 3+ oxidation state, which facilitates insertion of two K + ions per formula unit. The rate capability experiments suggest that K 2 Ti 4 O 9 is capable of undergoing charge-discharge cycling at high rates (up to 15 C rate), but with a low discharge capacity. Thus K 2 Ti 4 O 9 is a promising anode material for future K-ion batteries.

Electrochemical impedance spectroscopy is a convenient and powerful tool in characterizing porous electrodes in electrochemical systems. The full potential of impedance characterization can only be achieved when a physically meaningful impedance model is used. This study aims to build a theoretically-consistent framework and to develop a series of impedance models for porous electrodes with different properties. The framework starts from a full problem formulated with the concentrated solution theory and then simplifies it to four limiting cases. In-plane, through-plane, multi-dimensional inhomogeneities are considered. In addition, based on the analytical Fourier transform, the impedance response during dynamic process is numerically calculated. The models developed in this study are then applied to three typical cases: blocking electrode, electrode with faradaic reactions, and electrode constituted of particles with insertion reactions, corresponding to their practical counterparts in electrochemical capacitors, polymer electrolyte fuel cells, and lithium-ion batteries,…

Energy density of full cells containing layered-oxide positive electrodes can be increased by raising the upper cutoff voltage above the present 4.2 V limit. In this article we examine aging behavior of cells, containing LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523)-based positive and graphite-based negative electrodes, which underwent up to ∼400 cycles in the 3–4.4 V range. Electrochemistry results from electrodes harvested from the cycled cells were obtained to identify causes of cell performance loss; these results were complemented with data from X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) measurements. Our experiments indicate that the full cell capacity fade increases linearly with cycle number and results from irreversible lithium loss in the negative electrode solid electrolyte interphase (SEI) layer. The accompanying electrode potential shift reduces utilization of active material in both electrodes and causes the positive electrode to cycle at higher states-of-charge. Full cell impedance rise on aging arises primarily at the positive electrode…

The Li + transference numbers of three different liquid electrolytes for Li-ion batteries were measured in a symmetrical Li | electrolyte | Li cell by means of very-low-frequency impedance spectroscopy (VLF-IS). The electrolytes were: (i) The standard battery electrolyte LP30; (ii) an equimolar mixture of tetraglyme (G4) and lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI); (iii) Li-TFSI dissolved in the ionic liquid 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-TFSI). We found that the Li + transference numbers of the two electrolytes LP30 and G4/Li-TFSI are much smaller than the Li + transport numbers t L i + NMR obtained from pulsed-field gradient NMR measurements. On the other hand, in the case of BMP-TFSI/Li-TFSI, the values for t L i + current and t L i + NMR are more similar. In order to rationalize the large differences between t L i + current and t L i + NMR found for LP30 and G4/Li-TFSI, we combined the Onsager reciprocal relations with linear response theory, and we derived expressions for t L i + current , which take into account all…

Li-rich layered oxides, e.g. Li[Li 0.20 Ni 0.13 Mn 0.54 Co 0.13 ]O 2 (LR-NMC), lead high energy density Li-ion battery cathodes, thanks to the reversible redox of oxygen anions that boost charge storage capacity. Unfortunately, their commercialization has been stalled by practical issues (i.e. voltage hysteresis, poor rate capability, and voltage fade) and hence it is necessary to investigate whether these problems are intrinsically inherent to anionic redox and its structural consequences. To this end, the 'model' Li-rich layered oxide Li 2 Ru 0.75 Sn 0.25 O 3 (LRSO) is here used as a fertile test-bed for scrutinizing the effects of cationic and anionic redox independently since they are neatly isolated at low and high potentials, respectively. Through an arsenal of electrochemical techniques, we demonstrate that voltage hysteresis is triggered by anionic redox and grows progressively with deeper oxidation of oxygen in conjunction with the deterioration of both interfacial charge-transfer kinetics and bulk diffusion coefficient. We equally show that this anionic-driven poor…

In this article, a two-dimensional, multiphase, transient model is introduced and used to explore the impact of catalyst-layer thickness on performance. In particular, the tradeoffs between water production and removal through transport or evaporation are highlighted, with a focus on low-temperature performance. For the latter, a case study of an ultra-thin catalyst layer is undergone to explore how various material properties alter the steady-state and startup performance of a cell. The findings provide understanding and guidance to optimize fuel-cell performance with thin electrodes.

In this work we employ the advanced scanning flow cell based analytical techniques, viz. inductively coupled plasma mass spectrometry (SFC-ICP-MS) and on-line electrochemical mass-spectrometry (SFC-OLEMS) to directly detect the amounts of dissolved platinum and evolved carbon dioxide in two protocols that are commonly used in the fuel cell community to simulate load cycle and start-stop conditions in proton exchange membrane fuel cells (PEMFCs). In contrast to previous assumptions, claiming a separation between carbon corrosion and platinum dissolution, in both standard protocols platinum dissolution and carbon corrosion are present at low rates, which is also reflected by a comparably low ECSA decrease. On the other hand, a huge increase in rate of both processes is observed during transitions from low to high potential regimes experienced by a PEMFC in operation, here studied in a third protocol covering the whole potential range from 0.6 to 1.5 V RHE . The latter is typically not addressed in literature. This finding is explained by taking into account platinum catalyzed carbon…

Li[Ni 0.42 Mn 0.42 Co 0.16 ]O 2 (NMC442)/graphite pouch cells demonstrate superb performance at high voltage when ethylene carbonate (EC)-free electrolytes, using a solvent mixture that is >95% ethyl methyl carbonate (EMC) and between 2 and 5% of an "enabler", are used. The "enablers", required to passivate graphite during formation, can be vinylene carbonate (VC), methylene-ethylene carbonate (MEC), fluoroethylene carbonate (FEC) or difluoro ethylene carbonate (DiFEC), among others. In order to optimize the amount of "enabler" added to EMC, gas chromatography coupled with mass spectrometry (GC-MS) was used to track the consumption of "enabler" during the formation step. Storage tests, electrochemical impedance spectroscopy (EIS), ultrahigh precision coulometry (UHPC), long-term cycling, differential voltage analysis and isothermal microcalorimetry were used to determine the optimum amount of enabler to add to the cells. It was found that the graphite negative electrode cannot be fully passivated when the amount of "enabler" is too low resulting in gas production and capacity fade.…

This study deals with the decomposition of ethylene carbonate (EC) by H 2 O in the absence and presence of catalytically active hydroxide ions (OH − ) at reaction conditions close to lithium-ion battery operation. We use On-line Electrochemical Mass Spectrometry (OEMS) to quantify the CO 2 evolved by these reactions, referred to as H 2 O-driven and OH − -driven EC hydrolysis. By examining both reactions at various temperatures (10 – 80°C) and water concentrations (<20 ppm or 200, 1000, and 5000 ppm H 2 O) with or without catalytically active OH − ions in EC with 1.5 M LiClO 4 , we determine an Arrhenius relationship between the CO 2 evolution rate and the cell temperature. While the apparent activation energy for the base electrolyte (<20 ppm H 2 O) is very large (app. E a ≈153 kJ/mol), substantially lower values are obtained in the presence of H 2 O (app. E a ≈99 ± 3 kJ/mol), which are even further decreased in the presence of catalytically active OH − (app. E a ≈43 ± 5 kJ/mol). Our data show that OH − -driven EC hydrolysis is relevant already at room temperature, whereas H 2…

A guide is offered to new researchers (and their supervisors) of the most promising topics to explore in market-driven or curiosity-driven dielectrophoresis (DEP) research. Based on an analysis of publications since 2000, contributions from electronic engineers and materials scientists are likely to be maintained, with increasing emphasis on the development of DEP-based protocols for chemical and biochemical analyses that involve nanoparticles. Two modes of DEP are likely to dominate, namely metal-electrode based (eDEP) and insulator-based (iDEP). Where high values of the electric field and its gradient are required, such as the spatial manipulation of nanoparticles (e.g., exosomes, proteins, viruses, carbon-nanotubes), eDEP would in many cases be the preferred choice. This would also be the case for the selective isolation of biological cells; the development of cell-based drug discovery protocols; electronic sensors and the assembly of nanoparticles (e.g., carbon nanotubes). Applications of iDEP would be particularly suited for the separation or detection of bioparticles such as…

Raman spectroscopy in a confocal microscope was used to study electrochemically synthesized corrosion products from sour gas experiments. When exposed to oxygen-containing atmosphere, the initial mackinawite FeS corrosion product transformed under laser irradiation to hematite, Fe 2 O 3 . Measurements with a thin water layer on top of the corrosion products prevented the transformation, as drying was prevented. In situ Raman measurements of mackinawite formation avoided the problem of transformation completely. In situ and operando, the initially formed mackinawite showed two Raman peaks in the wavenumber range > 180 cm − 1 centered around 200–215 cm − 1 and 285–300 cm − 1 . On an empirical basis, these modes were assigned to a B 1g mode of the iron sublattice and an A 1g mode of the sulfur sublattice, respectively. A comparison with a literature assignment for aged mackinawite suggests that the aging observed involves significant changes in the sulfur sublattice.

The study of particle size effect provides the fundamental understanding of the active sites that is necessary for guiding the design and development of better catalysts. Here we report a systematic investigation of particle size effect of hydrogen oxidation and evolution reaction (HOR/HER) on carbon supported Pd nanoparticles with sizes ranging from 3 to 42 nm in both acidic and alkaline electrolytes using rotating disk electrode (RDE) method. Similar particle size effect was obtained in both acid and base: the HOR/HER activity in terms of specific exchange current density increases as Pd particle size increases from 3 to 19 nm, and then reaches a plateau with activity similar to that of bulk Pd. The enhanced activity with rising particle size could be attributed to the increased ratio of the sites with weaker hydrogen binding energy revealed in cyclic voltammograms (CVs). Pd catalysts with different Pd particle sizes all showed much higher HOR/HER activity in acid than in base, which is largely attributed to their smaller hydrogen binding energy in acid evidenced by the lower…

When NMC/graphite Li-ion cells are operated at elevated temperature or at a cutoff potential above 4.2 V, electrolyte oxidation becomes increasingly severe leading to gaseous products and other oxidized species. These generated gas products and oxidized species can migrate to, and then interact with, the negative electrode. A variety of cell formats (pouch cells, symmetric cells and coin cells) as well as pouch bags, containing only a delithiated positive electrode or a lithiated negative electrode, were used to investigate electrode/electrode interactions. Open circuit potential measurements during high temperature storage, ex-situ measurements of gas volume produced versus time, gas chromatography-mass spectrometry (GC-MS) of the gases produced and electrochemical impedance spectroscopy (EIS) of the electrodes versus time were performed. During storage at 60°C, pouch bags containing only a lithiated negative electrode and electrolyte produced no gas while charged full pouch cells produced some gas and pouch bags containing only a delithiated positive electrode and electrolyte…

The local corrosion behavior of additive manufactured AlSiMg specimens was studied using the SEM and SKPFM techniques. A morphological characterization of corroded areas revealed that crystallographic pitting developed in the aluminum grains inside the melt pool borders, from where corrosion spread to adjacent zones. The local Volta potential analysis showed that there is a close relation between the cellular grain size and the potential difference between the silicon and the aluminum phase. SKPFM measurements explained why the melt pool borders were more severely attacked by corrosion than other regions in the surface of the AM specimens. In regions with larger and coarser microstructures, greater potential difference between the phases was found, which represents a higher driving force for galvanic corrosion.

The Effect of Common Airborne Impurities and Mixtures on PEMFC Performance and Durability

Membranes based on poly(2,2 ' -( m -phenylene)-5,5-bibenzimidazole) ( m -PBI) can dissolve large amounts of aqueous KOH to give electrolyte systems with ion conductivity in a practically useful range. The conductivity of the membrane strongly depends on the concentration of the aqueous KOH phase, reaching about 10 −1 S cm −1 or higher in 15–25 wt% KOH. Herein, m -PBI membranes are systematically characterized with respect to performance and short-term stability as electrolyte in a zero-gap alkaline water electrolyzer at different KOH concentrations. Using plain uncatalyzed nickel foam electrodes, the cell based on m -PBI outperforms the cell based on the commercially available state-of-the-art diaphragm and reaches a current density of 1500 mA cm −2 at 2.4 V in 20 wt% KOH at 80°C. The cell performance remained stable during two days of operation, though post analysis of the membrane using size exclusion chromatography and spectroscopy reveal evidence of oxidative degradation of the base polymer at KOH concentrations of 15 wt% and higher.

Symmetric cells with porous La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) electrodes on Gd 0.1 Ce 0.9 O 1.95 (GDC) electrolytes were aged at 800°C for 800 hours in ambient air. Electrochemical impedance spectroscopy (EIS) measurements performed periodically at 700°C showed a continuous increase of the polarization resistance from 0.15 to 0.34 Ω·cm 2 . Three-dimensional (3D) tomographic analysis using focused ion beam–scanning electron microscopy (FIB-SEM) showed negligible changes due to the ageing, suggesting that the observed resistance increase was not caused by electrode morphological evolution. However, an increased amount, by a factor of 3, of a water-soluble Sr rich surface phase on the aged LSCF electrode was detected by an etching procedure coupled with inductively coupled plasma-optical emission spectrometry (ICP-OES). The electrochemical analysis in combination with the microstructural parameters determined by FIB-SEM was used to examine the effect of Sr segregation on the rate of oxygen surface exchange, based on the Adler-Lane-Steele (ALS) model.

Mechanical constraints have been widely used experimentally to prevent the growth of dendrites within lithium metal. The only article known to the authors that tries to theoretically understand how mechanical forces prevent dendrite growth was published by Monroe and Newman [ J. Electrochem. Soc. , 150 (10) A1377 (2005)]. Based on the assumption that surface tension prevents the growth of interfacial roughness, Monroe and Newman considered pre-stressed conditions of the lithium electrodes. This scenario indicates that prevention of dendrite growth by mechanical means is only possible by using electrolytes with shear modulus at least two times larger than that of lithium metal. A different scenario of relaxed lithium metal (without any pre-existing surface stresses) has been considered in the present analysis. Deposition of lithium due to electrochemical reaction at the lithium/electrolyte interface induces compressive stress at the electrode, the electrolyte, and the newly deposited lithium metal. Present simulations indicate that during operation at low current densities, the…

The choice of cathode material critically influences the performance, cost and energy density in a Li ion battery. LiMn 2 O 4 (LMO) cathode is an attractive cathode material because of its high rate capability, low cost, safety and non-toxicity. However, low cycle life or capacity fading with cycling is a big hurdle in the practical application of LMO cathodes. The dominant cause of the capacity fading, Mn dissolution from LMO, is still a challenge to overcome. In this review, we attempt to emphasize the loopholes in the understanding related to the Mn dissolution phenomenon in LMO cathodes in the presence of both aqueous and non-aqueous electrolytes. The underlying mechanism behind the dissolution process is often explained with the help of ionic charge disproportionation argument. Nevertheless, there are experimental and theoretical evidence in the literature to counter the simplistic view of dissolution due to charge disproportionation. Moreover, the correlation between the metal dissolution and the capacity fading is not causally established yet in the literature which hinders…

The capacity fade mechanisms of LiCoO 2 /Si-alloy:graphite pouch cells filled with a 1M LiPF 6 EC:EMC:FEC (27:63:10) electrolyte were studied using galvanostatic cycling, electrochemical impedance spectroscopy on symmetric cells, gas-chromatography and differential voltage analysis. Analysis of the gas generated during the first cycle indicated that FEC reacts at the negative electrode following a 1-electron reduction pathway and other pathways that do not lead to the formation of gaseous products. An analysis of the electrolyte showed that FEC is continuously consumed during the first 80% of the first charge (formation cycle). Typical cells charged and discharged at 40°C showed a gradual capacity loss for the first 250 cycles followed by a sudden capacity drop associated with a large polarization growth. Analysis of the electrolyte showed that this sudden failure is associated with the depletion of FEC. The capacity loss as well as the consumption of FEC prior to the sudden failure was fitted using a model that includes a time dependence and a cycle number dependence. The time…

The practically available specific energy of Li ion batteries (LIB) is highly depending on the used specific charge/discharge current, since the respective overpotentials of each electrode affect the two vital specific energy parameters, specific capacity and voltage. Focusing on the positive composite electrode as the specific energy bottleneck, the overall nature of the overpotential is discussed for the LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM) active material. It is shown that the characteristic overpotentials during charge (delithiation) and discharge (lithiation) is state of charge (SOC) and depth of discharge (DOD) dependent, respectively. It was demonstrated that the discharge characteristics are intertwined with the previous charge conditions, particularly with the charging time and the specific charge capacity. Increasing both in parallel can even lead to a deterioration of the subsequent specific discharge capacity. Furthermore, Li + transport pathways within the NCM composite electrode are discussed and their influence on the observed overpotential evaluated. Changes of the…