Dual-Compartment Electrocatalytic Oxidation of Polystyrene: Insights into Anode–Cathode Degradation Mechanisms and Differences

Electrolytes and additives for batteries Part I: fundamentals and insights on cathode degradation mechanisms

General considerations on degradation of Solid Oxide Fuel Cell anodes and cathodes due to impurities in gases

Introduction Lithium-ion battery life is expected to increase, and the need for degradation analyses has grown [1]. Among the degradation mechanism, the change in the electrode surface state has significant influence on lithium-ion battery performance. In this study, a long-term cycle test was conducted using commercial 18650-type lithium ion cells for a current rate of 1 C at 25 °C. The electrode surface state was investigated by X-ray photoelectron spectroscopy (XPS), hard X-ray photoelectron spectroscopy (HAXPES), and transmission electron microscopy (TEM). Experimental The cycle test was performed using a 18650-type commercial lithium-ion cell equipped with a Li(Ni1/3Mn1/3Co1/3)O2 cathode and a graphite anode. After cycle test completion, the cell was analyzed at a state-of-charge of 50% (= 3.694 V) by electrochemical impedance spectroscopy at 25 °C. The degraded single electrode property was measured by preparing a half cell against lithium metal. The electrode surface state was characterized by XPS and HAXPES. HAXPES measurements were performed at the BL46XU beamline of SPring-8. The cathode surface state was also investigated by TEM. The electrolytic solution was analyzed by 1H- and 19F-NMR. Results and discussion During the cycle test, the discharge capacity decreased gradually and then drastically above 1500 cycles. The capacity retention measured at 1 C reached below 10% after 1700 cycles. Nyquist plots before and after cycle test showed an increase in electrolyte and charge transfer resistances (Fig. 1). To understand the degradation mechanism, the degraded cell was disassembled after the cell was discharged at C/20, and their electrodes and electrolytic solution were removed under argon atmosphere. Half cells were prepared, and measured electrodes were characterized. After the first cycle, the degraded cathode exhibited a coulombic efficiency of 186%, indicating that it was partially charged when the cell was opened. Conversely, the degraded anode displayed a coulombic efficiency of about 100%, showing it was fully discharged. This mismatch between cathode and anode state-of-charge may explain the decrease in cell capacity. In addition, charge/discharge curves in the second cycle showed a capacity loss of about 20% at the cathode compared to initial condition. XPS and HAXPES spectra of Mn 2p, Co 2p, and Ni 2p were measured to investigate the cathode surface state. XPS and HAXPES detection depths are approximately 6 and 30 nm, respectively. No spectral changes were observed for Mn 2p 1/2 and Co 2p 1/2. Figure 2 shows the XPS and HAXPES spectra of Ni 2p 1/2. Ni 2p 1/2 XPS peak shifted toward higher energies (around 1.9 eV), indicative of the higher valence state of Ni at the cathode. Ni 2p 1/2 HAXPES peak only slightly shifted (around 0.7 eV) as a potential result of the oxidation of Ni2+, consistent with the partially charged state of the cathode. The difference between XPS and HAXPES suggests that the cycle test changed the cathode surface state. The structural properties of the cathode surface were evaluated by TEM. The lattice fringes of the layered rock-salt Li(Ni1/3Mn1/3Co1/3)O2 structure disappeared from the active material surface, and the electron diffraction pattern of the surface was unclear. These results indicate that amorphization occurred at the cathode surface (about 3 nm), augmenting the charge transfer resistance. Moreover, electrolyte analysis revealed that LiPF6was decomposed, explaining the increase in electrolyte resistance. In summary, the long-term cycle test revealed that the capacity loss stemmed from the shift of cathode and anode reaction regions and cathode degradation. Furthermore, the increase in impedance spectrum resulted from cathode surface amorphization and LiPF6decomposition. Acknowledgment Synchrotron radiation experiments were performed at the BL46XU of SPring-8 with the approval of the Japan Synchrotron Radiation Institute (JASRI) (Proposal No. 2013A1234, 2014A1558, 2014B1015, and 2014B1594) [1] T. Matsuda et al. 226th ECS meeting A5-343 Figure 1

While impressive solid oxide fuel cell (SOFC) performance has been achieved, durability under “real world” conditions is still an issue for commercial deployment. In particular cathode exposure to H2O and CO2 can result in long-term performance degradation issues. Therefore, we have embarked on a multi-faceted fundamental investigation of the effect of these contaminants on cathode degradation mechanisms in order to establish cathode composition/structures and operational conditions to enhance cathode durability. Using a Focused Ion Beam (FIB)/SEM we are quantifying in 3-D the microstructural changes of the cathode before and after the onset of cathode performance degradation. This includes changes in TPB density, phase-connectivity, and tortuosity, as well as tertiary phase formation. This is then linked to heterogeneous catalysis methods to elucidate the cathode oxygen reduction reaction (ORR) mechanism to determine how H2O and CO2 affect the ORR as a function of temperature, time, and composition. By use of in-situ 18O-isotope exchange of labeled contaminants we are investigating whether oxygen incorporated in the lattice of LSM and LSCF, and their composites with YSZ and GDC, respectively, originated from ambient O2 or the contaminant, as well as intermediate adsorbed species and mechanisms that lead to degradation. The results will be used to develop a cohesive and overarching theory that explains the microstructural and compositional cathode performance degradation mechanisms.

While impressive solid oxide fuel cell (SOFC) performance has been achieved, durability under “real world” conditions is still an issue for commercial deployment. In particular cathode exposure to H2O and CO2 results in long-term performance degradation issues. Therefore, we have embarked on a multi-faceted fundamental investigation of the effect of these contaminants on cathode degradation mechanisms in order to establish cathode composition/structures and operational conditions to enhance cathode durability Using a dual Focused Ion Beam (FIB)/SEM) we are quantifying in 3-D the microstructural changes of cathode before and after the onset of cathode performance degradation. This includes changes in TPB density, phase-connectivity, and tortuosity, as well as tertiary phase formation. This is linked to heterogeneous catalysis methods to elucidate the cathode oxygen reduction reaction (ORR) mechanism to determine how H2O and CO2 affect the ORR as a function of temperature, time, and composition. By use of in-situ 18O-isotope exchange of labeled contaminants we will determine whether oxygen incorporated in the lattice of LSM and LSCF, and their composites with YSZ, originated from ambient O2 or the contaminant as well as intermediate adsorbed species and mechanisms that lead to degradation. The results will be used to develop a cohesive and overarching theory that explains the microstructural and compositional cathode performance degradation mechanisms.

Degradation diagnosis of lithium-ion batteries with a LiNi0.5Co0.2Mn0.3O2 and LiMn2O4 blended cathode using dV/dQ curve analysis

Introduction Currently conducted lithium-ion batteries (LIBs) degradation analyses aim to improve the LIBs' life expectancy for electronic vehicles (EVs). As LIB for EVs are used in various environments, life tests at various conditions must be conducted. To clarify the relationship between test conditions and degradation mechanisms, as many LIBs as test conditions and cycle numbers must be analyzed. Hence, non-destructive analyses during life tests are needed for efficient and non-expensive degradation analyses. The dV/dQ curve analysis has been reported as a non-destructive degradation analytical method[1-2]. However, research on the relationship between test conditions (temperature, SOC range, and C-rate) and degradation factors through dV/dQ analysis has not been reported. In the present study, cycle-life tests on LIB with a composite cathode were conducted under several conditions, and the relationship between test conditions and degradation factors was quantitatively investigated using dV/dQ curve analyses. Experimental A commercially available lithium-ion cell with a composite cathode (18650-type, 1.4 Ah) was used for the cycle tests. The cathode and anode consist of LiNi0.5Co0.2Mn0.3O2 + LiMn2O4 (75:25 wt.%) and graphite as active materials, respectively. Cycle tests were conducted at the following conditions: one charge/discharge C-rate (C/3), two SOC ranges (100–0%, 100–70%), and three temperatures (0°C, 25°C, 45°C). The low-current (C/20) charge/discharge test with the SOC range of 100–0% at 25°C was periodically executed during cycle tests for measuring the battery performance and calculating the dV/dQ curve from the discharge curve. The cathode (x LiNi0.5Co0.2Mn0.3O2・y LiMn2O4) and anode (graphite) dV/dQ curves were also obtained, which were calculated by the discharge curves of the half-cell against lithium metal electrode. The degraded cathode capacity, anode capacity, and the cathode/anode reaction region slip were diagnosed by curve fitting the cell's dV/dQ curve using the cathode and anode curves. Results and discussion Figure 1 shows the low-current discharge curves and dV/dQ curves of the cell, the cathode, and the anode of the initial cell (dotted line) and the degraded cell (solid line). Here, the degraded cell at test conditions of 45°C and 100–0% SOC range, after 480 cycles, is shown as an example. The capacity retention of the cell was 82.6%, and the anode reaction region's shift and the cathode capacity's decrease were observed. Figure 2 shows the cathode degradation and the cathode/anode reaction region slip during the tests at SOC range of 100–0% and 45°C. Both result in a decrease of the cell's capacity, and the cathode/anode reaction region slip progress faster. The conducted dV/dQ analyses for all the test conditions indicate that the influence of the various degradation factors (cathode degradation, anode degradation, and cathode/anode reaction region slip) differs according to the cycle test conditions. When the SOC range is wide, the cathode degradation proceeds faster. This may be due to the cathode material's (especially LiNi0.5Co0.2Mn0.3O2) degradation, which is caused by the electronic isolation and/or inactivation by expansion and contraction in the charge/discharge tests. In contrast, when the temperature is high, the cathode/anode reaction region slip accelerates the cell's capacity decrease, probably because the reaction region slip results from the rechargeable lithium-ion consumption through electrolyte decomposing (as a side reaction), which is accelerated by temperature. In conclusion, dV/dQ curve analyses were applied on LIBs with a composite cathode. The results indicate that the cathode degradation and the cathode/anode reaction region slip cause the cell's capacity to decrease, and their effect differs according to the test conditions. Reference [1] I. Bloom, A. N. Jansen, D. P. Abraham, J. Knuth, S. A. Jones, V. S. Battaglia, and G. L. Henriksen, J. Power Sources, 139, 295 (2005). [2] K. Honkura, K. Takahashi, and T. Horiba, J. Power Sources, 196, 10141 (2011). Figure 1

Next-generation lithium ion batteries are expected to demonstrate superior energy and power density with longer cycle life for successful electrification of the automobile, aviation, and marine industries. Adoption of lithium metal anodes with solid electrolytes can help to achieve that goal given that the dendrite-related issues are solved eventually. Another possibility is to use Ni-rich high-capacity NMC cathode materials with liquid and/or solid electrolytes, which presently experiences rapid capacity fade while charged to higher voltages. Several mechanical and chemical degradation mechanisms are active within these NMC-based cathode particles. Recent experimental research activities attempted to correlate the mechanical damage with the capacity fade experienced by Ni-rich LiNixMnyCozO2 (x+y+z = 1) (NMC) cathodes. A computational framework is developed in this study capable of quantifying the evolution of inter primary particle and cathode/electrolyte interfacial fracture experienced by the poly- and single-crystalline NMC cathodes during charge/discharge operation. Influences of mechanical degradation on the overall cell capacity, while operating with liquid and/or solid electrolytes, are successfully characterized. Decreasing the size of the cathode primary particles, or the size of the single-crystalline cathodes, can mitigate the overall mechanical degradation, and subsequent capacity fade, experienced by NMC cathodes. The developed theoretical methodology can help the engineers and scientists to better understand the mechanical degradation mechanism prevalent in Ni-rich NMC cathodes and build superior lithium ion-based energy storage devices for the application in next-generation devices.

The volume of end-of-life lithium-ion batteries (LIBs) is expected to increase rapidly over the coming decade. Consequently, it is of great interest to recycle and reuse cathode materials due to their high value in LIBs. Direct cathode recycling, which aims to regenerate cathode materials without destroying their original functional structures, could potentially maximize the return value from end-of-life LIBs compared to pyrometallurgical- and hydrometallurgical-based recycling processes. Here, we fundamentally investigate the effectiveness of cathode regeneration by regenerating chemically-degraded cathodes at different levels of delithiation, which are analogous to spent cathodes at different states of health (SOH). To evaluate whether direct recycling is effective in regenerating spent cathodes at different degrees of degradation, regenerated cathodes are thoroughly compared with pristine and chemically delithiated cathodes. The use of chemically delithiated samples provides the opportunity to fundamentally examine how the disordered, lithium-deficient cathode from used LIBs is regenerated while preventing the complications associated with other cathode degradation mechanisms, including surface layer formation and particle cracking.

We present a cryogenic photoelectron gun, developed for the target section of the Test Storage Ring (TSR) of the Max Planck Institute of Nuclear Physics (MPIK). Cooled to cryogenic temperatures by liquid nitrogen, the photocathode source provides an electron gas with an initial thermal energy spread of around 10 meV. The beam optics of the target section reduce the electron temperatures to much lower values in the comoving frame of the beam. Recently the photocathode source has seen significant improvements regarding its reliability. By controlling several cathode degradation mechanisms, including cryosorption, vacuum degrading leak electron currents, and backstream of ionised restgas particles, cathode lifetime and currents have been subject to substantial improvements. Presently the photoelectron gun can deliver currents of up to 1 mA at lifetimes of about 24h. The ability of the photoelectron beam to cool slow, heavy molecular ion beams was demonstrated by cooling a 3 MeV CF+ beam in the TSR. At an electron cooling energy of only 53 eV and a perveance-limited current of 0.34 mA, a cooling time below 2 s has been achieved, with a very small transverse relative momentum spread of 2.5 · 10−5 and final ion beam cross-section of 0.5×0.1 mm2.

Today, stationary energy storage systems utilizing lithium-ion batteries account for the majority of new storage capacity installed. In order to meet technical and economic requirements, the specified system’s lifetime has to be ensured. For reliable lifetime predictions, models for cell degradation are necessary. Physicochemical models that include ageing mechanisms are based on a detailed set of parameters, which are often not available, and require parametrization of the degradation rates. Instead, purely empirical models can be parametrized without knowledge of internal cell setup through extensive testing, however are prone to extrapolation errors due to the utilized mathematical functions. In this work, a semi-empirical model based on a reduced set of internal cell parameters and physically supported degradation functions is used (1). Due to the limited knowledge about degradation mechanisms, purely empirical models as well as semi-empirical models tend to lump multiple degradation effects into single functions. This leads to prediction errors when deviating from the parametrization test conditions. E.g. for cycle ageing, Waldmann et al. reported a transition of dominating ageing mechanisms at 25°C (2). The ageing above 25°C was attributed to SEI-growth and cathode degradation, for temperatures below 25°C to lithium plating. Model development therefore should aim for a separation of the degradation mechanisms where possible. The respective mechanisms then can be modelled through functions that are suitable for the degradation driving factors, which is the focus of this work: A semi-empirical cell degradation model is developed that separates one calendar and several cycle ageing effects. Emphasis is placed on the varying degradation at different temperatures. Degradation for cycle ageing at high and low temperatures is thus calculated separately, a novel approach in semi-empirical models. As such models require parametrization, a lifetime test study is conducted. Cell type and experimental parameters are in accordance with an application in stationary systems. Lithium iron phosphate batteries have shown capacity retention for more than 5,000 full cycles before usable capacities fall below 80%, which is suitable for stationary applications (3). The parametrization is based on a commercial 26650 lithium iron phosphate cell with a nominal capacity of 3 Ah. The lifetime study is separated into parametrization and validation tests. Validation tests are excluded from model parametrization and thus show the model performance in deviating, more realistic conditions. Temperatures in the tests are 0°C, 10°C, 15°C, 25°C, 35°C, 45°C and 55°C to accurately describe varying degradation mechanisms. Parametrization for calendar ageing consists of storage tests of cells at varying State of Charge (SOC) in steps of 12.5%. Cycle ageing parametrization is based on constant current full cycle tests at C-Rates of 0.5C, 1C and 1.7C with and without CV-phases at the end of charging. For validation, a dynamic profile representative for a summer and a winter day of a residential photovoltaic-battery system is tested. Regular characterization tests were performed at 25°C. As experimental results for the degradation in terms of capacity loss showed to be more severe than an impedance increase, we focused on modelling the battery capacity. Calendar ageing is modelled with temperature and anode-potential dependency based on the storage tests. Figure 1a shows the Arrhenius-dependency of the capacity loss rate at SOC of 100% for temperatures between 10°C and 45°C. Figure 1b shows the relation between anode open circuit potential and calendar ageing at a storage temperature of 25°C for SOC between 0% and 100%. For cycle ageing, degradation mechanisms are separated in low and high temperature effects and parametrized based on the constant-current tests. Cell degradation can thus be given as the linear combination of separate mechanisms. Figure 2 shows the cycle-induced capacity loss rate occurring additionally to comparative storage tests over temperatures from 0°C to 55°C. High and low temperature mechanisms are separately calculated. Summarizing, the model enables a cell degradation simulation over a wide temperature range. Through independent, yet temperature-dependent calculation of calendar and cycle ageing effects detailed studies on the effect of thermal management are enabled. Details on the prediction performance against the validation tests and model limitations are given in the presentation. Finally, model results for real-world grid applications as well as strategies for optimized operation temperatures are presented and evaluated.

Considering the expected lifetimes for Solid Oxide Fuel Cells of 5 to 10 years, durability is still a major issue. Even though quite a number of research institutions and companies have proven an acceptable degradation rate of cells, stacks and systems for periods ranging from a few hundred hours to several years, neither reliable degradation models nor methodologies to evaluate the durability in a short timeframe are available. Thus any kind of modification on the cell or stack level, which might affect the durability, requires an expensive and time consuming repetition of the durability test. Accelerated lifetime tests, which enable a rapid degradation analysis, and degradation models, that enable an extrapolation of the results, would be highly desirable. In most durability investigations a cumulative degradation rate is evaluated from the cell voltage decrease in a galvanostatic operating mode. In addition, extensive post test analysis is performed to detect the failure causes. This approach does not reveal any quantitative information on the different underlying degradation mechanisms. If aggravated stress is applied by increasing operating temperature, current density or gas utilization, the degradation of cathode, electrolyte, anode, contact layers and interconnects is accelerated in different ways. Therefore the cell voltage alone is insufficient to understand the performance degradation and its acceleration due to aggravated stress. To deconvolute the degradation of cathode, electrolyte and anode (i) electrochemical impedance spectroscopy, (ii) impedance data analysis by the distribution of relaxation times and, (iii) a subsequent CNLS-Fit to a physically meaningful equivalent circuit model is suggested. Cell tests were performed at different stress levels by varying temperature and current density as well as fuel and oxidant composition. Based on this extensive data set, the interplay between stress level and impact of the different stresses on degradation mechanisms in cathode, electrolyte and anode will be presented and guidelines for the design of accelerated tests will be discussed.

Solid-state lithium batteries (SSLBs) are the promising next-generation energy storage systems because of their attractive advantages in terms of energy density and safety. However, the interfacial engineering and battery building are of huge challenges, especially for stiff oxide-based electrolytes. Herein, we construct SSLBs by a cosintering method using Li3BO3 as a sintering agent to bind the cathode materials LiNi0.6Mn0.2Co0.2O2 (NMC) and solid-state electrolytes Li6.4La3Zr1.4Ta0.6O12. Small NMC primary particles are compared with large secondary particles to study the effects on interfacial adhesion, mechanical retention, internal resistance evolution, and electrochemical performance. Our results reveal that the interfacial resistance decreases during charging and increases during discharging, resulting in an overall increase in the interfacial resistance after one cycle. The main reason is attributed to the microcracks induced by the volumetric changes of NMC during the electrochemical process. The mechanical degradations at the interfaces accumulated upon cycling can cause capacity decay and low Coulombic efficiency. The SSLB constructed from small NMC primary particles shows regulation of particle distribution, mitigation in local volumetric change, and alleviation in mechanical degradation at the interfaces, leading to smaller resistance change and better electrochemical performance. The findings shed lights on designing SSLBs with good mechanical retention and electrochemical performance.

The scope of this paper is focused on analyzing the chemical degradation of LSCF cathode induced from many sources by GCI technique both from theoretical and experimental sides. As you know, electrochemical reaction occurring in the SOFC cathode is the reduction of oxygen, therefore cathode materials for SOFC have to posses many properties. It is necessary to evaluate the performance and degradation of SOFC cathode since improvement of long-term stability is one of the major issues during SOFC commercialization process. This research is important toward the commercialization of SOFC because efforts are being made to clarify the mechanisms of cell performance degradation and to improve durability effectively.

ABSTRACTLeakage degradation under DC stresses in epitaxially-grown Ba1−xSrxTiO3/SrRuO3 capacitors with various top electrodes was examined. Epitaxial capacitors employed in this study exhibit higher dielectric constant arising from optimized lattice deformation caused by lattice mismatch between Ba1−xSrxTiO3 and SrRuO3; dielectric constant for SrRuO3/30nm thick Bal-xSrxTiO3/SrRuO3 all oxide capacitor was 550, which corresponds SiO2 equivalent thickness of 0.21 nm. In addition, this type of capacitors have interfaces of higher cleanliness between dielectrics and electrodes, which are expected to provide opportunities of more simplified discussions on reliability issues for thin film capacitors. Dielectric breakdown properties and DC stress-induced leakage degradation properties were examined in room temperature and elevated temperatures. Various kinds of leakage degradation were observed and categorized in anode degradation and cathode degradation. The degradation in capacitors with oxide electrodes was markedly suppressed compared to that in capacitors with metal electrodes such as Pt or Ru. This higher degradation resistance yielded longer lifetime in capacitors of this type and the estimated life time at 458K for SrRuOS/ Bal-xSrxTiO3/SrRuO3 capacitor was 3E8 seconds, which exceeds required specification for DRAM application. These differences were discussed on the basis of a supposed degradation mechanism in which oxygen vacancy generation at anode interface is taken into account as well as vacancy accumulation at cathode interface.