State Of Cathode Surface Research Articles

Parameter sensitivity analysis of electrochemical model-based battery management systems for lithium-ion batteries

Accurate identification of physical parameters of a lithium-ion electrochemical model is of critical importance for next-generation battery management systems. The complexity of the electrochemical model increases the difficulty of the identification process, and hence the analysis of parameter identifiability is the cornerstone for accurate parameter identification. The overarching goal of this paper is to analyze the parameter sensitivity of an electrochemical model under both the charging process and real-world driving cycles. The boundaries for the sensitivity analysis of 26 physical parameters are determined with a systematic benchmarking of published parameters for lithium Nickel-Manganese-Cobalt-Oxide/graphite cells. In particular, the sensitivity of the parameters is analyzed not only for terminal voltage but also for essential states in an electrochemical model-based battery management system, e.g., cathode bulk state of charge, cathode surface state of charge and anode potential. The sensitivity matrices of the parameters under different C-rates and depth of discharge regions clearly show their different influences on capacity-related parameters and other parameters. Furthermore, the rankings of the normalized parameter sensitivity index provide us the identifiability of the parameters, as well as the influence of parameter inaccuracy on the main functionalities in an electrochemical model-based battery management system.

Cathode Surface State and Cathode Temperature Distribution After Current Zero of Different AMF-Contacts

The objective of this paper is to compare the state of cathode surface of different axial magnetic field (AMF) contact systems (CSs) during arcing and after arc extinction. The arcs were ignited by opening of electrodes and were fed by sine half-wave current pulses with a duration of 10 ms. Investigations were performed in the range of arc currents up to the levels of guaranteed failure. The measurements were done by a high-speed Phantom M310 video camera. The cathode surface state during arcing was studied using a set of neutral density filters. It was discovered that melting of a part of the cathode surface during arc burning takes place in high-current vacuum arcs. A changing relief in the form of hillocks and hollows forms on the melted surface. We found out that there are two components in droplet erosion of the cathode, when its surface is partially melted: in addition to droplets formed directly in the cathode spot (which can be called droplets of the first type), the liquid part of the surface also emits droplets (which can be called droplets of the second type) significantly different in their sizes and velocities. The formation mechanisms of droplets of the first and the second type are different. The cathode surface temperature distribution immediately after current zero was obtained by comparing the results of cathode surface filming to the results of calibrated band-lamp filming in identical conditions. Reflection of anode radiation from cathode surface was analyzed by mathematical simulation. The filming was carried out using an interference filter. We found that the distribution of the cathode surface temperature is substantially nonuniform. The axial region is the most heated. We conclude that in all investigated CSs with the same amplitude value of the current, the temperature of the most heated parts of the cathode surface is significantly lower than the temperature of the most heated parts of the anode surface. Analysis of obtained results shows that switching failure can be provoked by the cathode and by the anode processes depending on CS design.

Carbon adsorption on tungsten and electronic field emission

Electronic emission taking place at the electrodes of high voltage systems and responsible for detrimental breakdown processes is known to be strongly dependent on the cathode surface state and in particular on the presence of carbon contamination. To understand better the effect of carbon adsorption on cathode electronic emission, density functional theory calculations are reported for bulk bcc tungsten as well as for clean and carbon-covered W(100) surfaces for several coverages up to 2ML. Adsorption geometries and energies, work functions and electronic densities of states are analyzed to assess the effect of the presence of adlayers on surface electronic field emission properties. It is shown that flat carbon adlayer deposition on clean W(100) surfaces induces an increase of the surface work function and a decrease of electronic density near the Fermi level. Both factors contribute to reducing electronic field emission levels.

Degradation Mechanism of Nickel Manganese Cobalt Oxide-Type Commercial Lithium-Ion Cells By Long-Term Cycle Tests

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

Estimation of cathode-initiated breakdown in vacuum

Cathode initiation of vacuum breakdown in DC and pulse modes is considered. New criteria and methods for evaluating the cathode initiation mechanism are proposed. They are based on consideration of relative changes in cathode surface state and electric strength. The elaborated criteria and methods have been verified with experiments results using DC and pulse modes of high-voltage treatment of electrodes. Accuracy of the proposed methods exceeds known methods precision. It is shown that optimum modes of pulsed conditioning can be used for definition of top boundary of cathode initiation mechanism applicability in DC mode.

Effect of cathode surface state on the characteristics of pulsed hollow-cathode glow discharges

A study is made of the effect of pulse repetition rate (0.1−103 s−1) and average discharge current (0–1 A) on the breakdown delay time and burning voltage of low-pressure glow discharges (p<0.1 Pa) in an electrode system of the reverse magnetron type with a large cathode surface area (≈103 cm2). It is shown that increasing the repetition rate leads to a many-fold reduction in the statistical spread in the delay time and in the discharge formation time, while the average discharge current has a significant effect on the burning voltage. The mechanism for the observed phenomena is interpreted qualitatively in terms of the presence of thin dielectric films on the cathode surface.

Influence of the deposition parameters controlled by OES on PZT thin film properties deposited by RF magnetron sputtering

Lead zirconate titanate (PZT) thin films have been deposited, in a reactive argon/oxygen gas mixture, from a metallic target of nominal composition Pb1.1(Zr0.4 Ti0.6) by rf magnetron sputtering on Si substrates and Pt/TiN/Ti/SiO2/Si structures. During plasma deposition, in situ Optical Emission Spectroscopy (OES) measurements show clearly a correlation between the oxygen emission line evolution and the thin film composition. As a result, the cathode surface state can be controlled by OES to ensure a good compositional transferability from the target to the film and reproducibility of thin film properties for given values of deposition parameters. Using this approach, and after annealing of as-deposited thin films by Rapid Thermal Annealing (RTA), the PZT films exhibited a well-saturated hysteresis loop at an applied electric field of 300 kV/cm with Pr of 48 μC/cm2; the dielectric constant and dissipator factor at a frequency of 100 kHz were 914 and 0.04, respectively.

Effect of Annealing Treatment on PZT Thin Fiilm Properties Using Oxygen 18 Depth Profiling Technique

AbstractLead zirconate titanate (PZT) thin films have been deposited in a reactive argon/oxygen gas mixture from a metallic target of nominal composition Pb1.1(Zr0.4Ti0.6)O3 by rf magnetron sputtering on Si substrates and RuO2/SiO2/Si structures. During plasma deposition, in situ Optical Emission Spectroscopy (OES) measurements clearly show a correlation between the evolution of characteristic atomic emission line intensities and the thin film composition determined by simultaneous Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA). As a result, the cathode surface state can be monitored by OES to ensure a good compositional transferability from the target to the film and reproducibility of thin film properties for given values of deposition parameters. Electrical properties and crystallization have been optimized with a 90 nm PZT thin film grown on RuO2 electrodes. These PZT films, annealed with a very modest thermal budget (550°C) are fatigue-free and show very low leakage currents (J=2.10−8 A/cm2 at 1 V). The use of a metallic target allows us to control the oxygen incorporation in the PZT thin film and also, using 18O as a tracer, to study the oxygen vacancy migration which plays a key role in fatigue, leakage current, and electrical degradation/breakdown in PZT thin films.

真空中の電圧‐電流特性に及ぼす陰極表面状態の効果について

真空中の電圧‐電流特性に及ぼす陰極表面状態の効果について

タウンゼント放電域の火花電圧に及ぼす陰極表面状態の影響[II

タウンゼント放電域の火花電圧に及ぼす陰極表面状態の影響[II

Influence of cathode surface state on spark voltage in townsend discharge [II

Influence of cathode surface state on spark voltage in townsend discharge [II