Elektrochemische Impedanzspektroskopie an alternden Lithium-Ionen Batterien

The change of Lithium-ion Battery (LiB) model parameters during cyclic ageing is analysed in order to relate it to the capacity of the cell. Therefore, approaches to distinguish between anode and cathode contributions to the full cell impedance spectrum are developed. The results from a new measurement routine, using temperature gradients across a full cell, show that a successful assignment of the charge transfer processes at the cathode and anode is possible. For the analysed cell the cathode charge transfer processes occur at a lower time constant than the related anode processes. With the information of such an assignment, ageing of a 30 mAh pouch cell is analysed with Electrochemical Impedance Spectroscopy (EIS). A Newman-type LiB-model for this cell is extended by a physical ageing model including a Solid Electrolyte Iterphase (SEI), loss of active surface area and loss of active material. The simulation results of this model in combination with the related measurement results are used with a parameter identification algorithm to quantify the thickness of the SEI, the amount of isolated surface area and the loss of active material. The results show that the impedance increase is caused by a decrease of active surface area while the capacity decrease is caused by a loss of active material at the anode and cathode. The SEI thickness has found to increase to 45 nm while the active surface areas of the anode and cathode decrease by 20% and 57% respectively until the End Of Life (EOL) of the cell after 400 cycles. The change of the ageing parameters occurs in correlation to the decrease of the capacity of the analysed cell. Finally, the identifiability of kinetic, transport and ageing parameters, identified using this approach, has been quantified using Fisher-Information-Matrices (FIMs) showing that the impedance spectra are sensitive enough to the ageing parameters to ensure their precise identifiability.Die Veränderung von Parametern eines Lithium-Ionen Batteriemodels während zyklischer Alterung wird analysiert, um Rückschlüsse auf die Kapazität der Zelle zu ziehen. Hierfür werden Ansätze vorgestellt, die es ermöglichen zwischen den Beiträgen von Anode und Kathode zur Vollzellimpedanz zu unterscheiden. Die Ergebnisse einer neuen Messroutine, bei der ein Temperaturgradient auf die Vollzelle aufgeprägt wird, zeigen, dass eine erfolgreiche Zuordnung der Ladungstransferprozesse an Anode und Kathode möglich ist. Für die untersuchte Zelle finden die Ladungstransferprozesse an der Kathode mit einer kleineren Zeitkonstante statt als die entsprechenden Prozesse an der Anode. Mit der Information einer solchen Zuordnung wird die Alterung einer 30 mAh Pouchzelle mit der Elektrochemischen Impedanz Spektroskopie (EIS) analysiert. Hierfür wird ein Newman-Model einer LiB um ein physikalisches Alterungsmodel erweitert, das eine Solid Electrolyte Interphase (SEI), den Verlust von aktiver Oberfläche und den Verlust von Aktivmaterial enthält. Die Ergebnisse zeigen, dass der Impedanzanstieg durch einen Verlust an aktiver Oberfläche und der Kapazitätsverlust durch einen Verlust an Aktivmaterial in Anode und Kathode verursacht wird. Bis zum Ende der Lebensdauer der Batterie nach 400 Zyklen, erhöht sich die Dicke der SEI auf 45 nm, während die aktiven Oberflächen von Anode und Kathode um 20% und 57% abnehmen. Die Veränderung der Alterungsparameter ist bei der untersuchten Zelle mit der Abnahme der Zellkapazität korreliert. Abschließend wurde die Identifizierbarkeit von kinetischen-, Transport- und Alterungsparametern mathematisch mit Fischerinformationsmatrizen untersucht undgezeigt, dass die Impedanzspektren sensitiv genug auf eine Änderung der Alterungsparameter reagieren, um diese präzise zu identifizieren

Single-chamber Versus Dual-chamber Implantable Cardioverter Defibrillators: Do We Need Physiologic Pacing in The Course?

Background: Many patients with ICD receive different antiarrhythmic drugs (e.g. sotalol, amiodarone, β-blockers) because of ventricular or atrial tachycardias. These drugs can cause AV-block or chronotropic incompetence resulting in a higher percentage of ventricular pacing. Methods: We analyzed in a retrospective study the impact of DDD(R) versus VVI(R) mode on subjective (NYHA classification) and objective parameters [brain natriuretic peptide (BNP), 6 minute walk test, echocardiography] in 12 of 120 patients (age 60.2 ± 11.2 years; 10 males, 2 females) who needed an upgrading of a single to a dual chamber ICD. The ICD had to be upgraded because of chronotropic incompetence in all patients with signs of progressing heart failure. Data were collected in VVI(R)-pacing and after 6 and 12 months in DDD(R)-pacing with a long AV-interval and AV hysteresis to reduce ventricular pacing. Results: The 6 minute walk test (392.4 ± 91.4 vs. 324.6 ± 93.3 m, P < 0.001), NYHA-classification (1.4 ± 0.3 vs. 2.6 ± 0.8, P < 0.0001), BNP (234.1 ± 73.5 vs. 410.4 ± 297.0 pg/ml, P < 0.001), left ventricular ejection fraction (49.8 ± 9.6 vs. 36.5 ± 10.9 %, P < 0.0001) and A-wave (73.6 ± 13.7 vs. 41.0 ± 14.0 cm/sec, P < 0.0001) improved with DDD(R)-pacing after 12 months. The ventricular pacing decreased (84.2 ± 18.1 vs. 1.1 ± 1.7 %, P < 0.0001) after 12 months by DDD(R)-pacing with long AV-interval (220.0 ± 10.4 ms) and AV hysteresis. Conclusion: Our data show a superiority of DDD(R) mode versus VVI(R) mode regarding subjective and objective parameters as NYHA-classification, BNP, 6 minute walk test, left ventricular ejection fraction and left ventricular endsystolic volume after 12 months. The improvements seem to depend on the reduction of ventricular pacing with advanced atrial contraction. But only a small number of patients needed the upgradation

Best reply structure and equilibrium convergence in generic games

Game theory is widely used as a behavioral model for strategic interactions in biology and social science. It is common practice to assume that players quickly converge to an equilibrium, e.g. a Nash equilibrium. This can be studied in terms of best reply dynamics, in which each player myopically uses the best response to her opponent's last move. Existing research shows that convergence can be problematic when there are best reply cycles. Here we calculate how typical this is by studying the space of all possible two-player normal form games and counting the frequency of best reply cycles. The two key parameters are the number of moves, which defines how complicated the game is, and the anti-correlation of the payoffs, which determines how competitive it is. We find that as games get more complicated and more competitive, best reply cycles become dominant. The existence of best reply cycles predicts non-convergence of six different learning algorithms that have support from human experiments. Our results imply that for complicated and competitive games equilibrium is typically an unrealistic assumption. Alternatively, if for some reason "real" games are special and do not possess cycles, we raise the interesting question of why this should be so.Comment: Main paper + Supplemental Informatio

Medicinal Flora of the Popoluca, Mexico: A botanical systematical perspective

We studied the medicinal plants used by the Popoluca of the Sierra de Santa Marta (eastern Mexico). Using Moerman's method of regression analysis we determined which ethnomedically used taxa are over-represented in the Popolucan pharmacopoeia (e.g., Asteraceae) and which are underrepresented (e.g., Orchidaceae). Moerman et al. (1999) found high correlation between the holarctic pharmacopoeias and assumed that apart from the relatedness of the northern floras a "global pattern of human knowledge" may account for this finding. Although the Popoluca dwell in a habitat dominated by a neotropical flora but intermixed with important holarctic elements, they include considerably fewer neotropical taxa in their pharmacopoeia as one would expect if the historical transmitted knowledge were influencing their selection. This finding confirms the theory stated by Moerman et al. However, the Popoluca include some neotropical taxa in their pharmacopoeia and thus a moderate correlation exists between the Popolucan pharmacopoeia and the neotropical pharmacopoeia analysed by Moerman et al. We therefore conclude that apart from historically transmitted knowledge about specific taxa the "global pattern of human knowledge” addressed by Moerman et al. is largely based on "common selection criteria.

Identifying Anode and Cathode Contributions in Li-Ion Full-Cell Impedance Spectra

Measured impedance spectra of Li-ion battery cells are often reproduced with equivalent circuits or physical models to determine losses due to charge transfer processes at the electrodes. The identified model parameters can usually not readily or unambiguously be assigned to the anode and the cathode. A new measurement method is presented that enables the assignment of features of impedance spectra of full cells to single electrodes. To this end, temperature gradients are imprinted perpendicular to the electrode layers of a single-layered Li-ion battery cell while impedance spectra are measured. The method exploits different dependences of the charge transfer processes at the electrodes on temperature. An equivalent circuit model of RC-elements and the effect of temperature on the related electrode properties is discussed to demonstrate the feasibility of the method. A reliable assignment of the change of impedance spectra to the electrode processes is shown to be possible. The assignment can be used to identify if changes in an impedance spectrum originate from the anode or the cathode

The prediction of ICD therapy in multicenter automatic defibrillator implantation trial (MADIT) II like patients: a retrospective analysis

Objectives MADIT II like patients have not been compared to patients without an electrophysiological study, patients in whom ventricular tachycardia or fibrillation were induced in an electrophysiological study (EPS) and patients without an inducibility in EPS in one study. Background The multicenter automatic defibrillator implantation trial (MADIT) II showed a benefit of ICD implantation in patients with ischemic heart disease.Methods We performed a retrospective analysis in 93 patients with an ischemic heart disease and an ejection fraction ≤30% who had an ICD implanted with a follow-up at least an 18 months. Patients were divided into 3 groups according to the primary indication for ICD implantation: without EPS (group I), patients in whom ventricular tachycardia or fibrillation were inducible in EPS (group II) or patients without an inducibility in EPS (group III). Results During the mean follow-up of 32.9 ± 16.1 months 289 appropriate ICD therapies and 10 deaths occurred. The incidence of appropriate ICD therapies did not differ significantly between the groups (group I 40%, group II 54% and group III 48% of patients). We found in group II a higher risk of appropriate ICD therapies with occurrence of a specific constellation of EPS values. These patients showed a 15-fold risk (P = 0.005) of an appropriate ICD therapy. Furthermore a brain natriuretic peptide value of 265 pg/ml also predicted an appropriate ICD therapy with a 3.5-fold risk (P = 0.017).Conclusion In the present retrospective study the results of MADIT II were affirmed in the case of incidence of ventricular arrhythmias in patients with an EF < 30% and coronary heart disease. The prediction of an appropriate ICD therapy with EPS was only achieved in patients with inducibility in the EPS