Influence of the Polymer Structure and its Crystallization on the Interface Resistance in Polymer-LATP and Polymer-LLZO Hybrid Electrolytes

For many years, composite electrolytes (CEs) consisting of a mixture of inorganic solid electrolytes (ISEs) and polymer electrolytes (PEs) have been investigated as promising materials for the scalable production of solid-state batteries (SSBs). It is believed that CEs can overcome limitations of the single components, namely the low room-temperature conductivity and lithium ion transference number of PEs and the poor mechanical properties and high temperature processing necessary for ISE ceramics. To facilitate ion transport in the CE between the electrodes a low and stable charge transfer resistance between PEs and ISEs is required. In this study, we investigate by means of electrochemical impedance spectroscopy (EIS) how polymer crystallinity influences the charge-transfer resistance of hetero-ionic interfaces between polyethylene oxide (PEO)-based electrolytes and Li$_{1.5}$Al$_{0.5}$Ti$_{1.5}$(PO$_4$)$_3$ (LATP) as well as Li$_{6.25}$Al$_{0.25}$La$_3$Zr$_2$O$_{12}$ (LLZO) as ISEs. Crystallization of PEO based electrolytes below their melting temperature leads to an increased charge-transfer resistance. On the other hand, electrolytes based on the amorphous poly[2-(2-(2-methoxyethoxy)ethoxy)ethyl glycidyl ether (PTG) do not show an increased charge transfer resistance. Finally, the conductivity of ISE-rich CEs is measured as a function of their temperature and composition for elucidating how the interface resistance influences charge transport in ISE-rich composite electrolytes

Designing Cathodes and Cathode Active Materials for Solid‐State Batteries

Solid-state batteries (SSBs) currently attract great attention as a potentially safe electrochemical high-energy storage concept. However, several issues still prevent SSBs from outperforming today\u27s lithium-ion batteries based on liquid electrolytes. One major challenge is related to the design of cathode active materials (CAMs) that are compatible with the superionic solid electrolytes (SEs) of interest. This perspective, gives a brief overview of the required properties and possible challenges for inorganic CAMs employed in SSBs, and describes state-of-the art solutions. In particular, the issue of tailoring CAMs is structured into challenges arising on the cathode-, particle-, and interface-level, related to microstructural, (chemo-)mechanical, and (electro-)chemical interplay of CAMs with SEs, and finally guidelines for future CAM development for SSBs are proposed

Designing Cathodes and Cathode Active Materials for Solid State Batteries

Solid state batteries SSBs currently attract great attention as a potentially safe electrochemical high energy storage concept. However, several issues still prevent SSBs from outperforming today s lithium ion batteries based on liquid electrolytes. One major challenge is related to the design of cathode active materials CAMs that are compatible with the superionic solid electrolytes SEs of interest. This perspective, gives a brief overview of the required properties and possible challenges for inorganic CAMs employed in SSBs, and describes state of the art solutions. In particular, the issue of tailoring CAMs is structured into challenges arising on the cathode , particle , and interface level, related to microstructural, chemo mechanical, and electro chemical interplay of CAMs with SEs, and finally guidelines for future CAM development for SSBs are propose

Analysis of the Temperature impact on Reliability of GaN-based Light Emitting Diodes

This thesis reports the results of the three-year research activity on Light Emitting Diodes (LEDs) for Solid State Lighting. In particular, the research project was focused on the study of thermal characterization of Gallium Nitride (GaN) based LEDs, and the impact of the temperature on the reliability of devices. The work starts from an overview of the State of the art of III-V optoelectronic devices and on reliability aspects of such devices. Afterwards, different characterization methods for thermal characterization of LEDs are presented and discussed with the description of some experimental implementations designed. In the remaining chapters three reliability approaches on different LED structures are presented: (i) an Accelerated Lifetime Testing (ALT) on low-flux Phosphors Converted LEDs, (ii) an ALT on High Brightness LEDs with Chip-on-Board technology, and (iii) a reliability analysis on Deep UV AlGaN-LEDs. In all case studies, the thermal aspects have been stressed in the analysis of the results. The different activities started from an in-depth knowledge of the device structure and the related issues, and aimed at (i) extrapolating the degradation model that can provide an accurate lifetime estimation, (ii) investigating on physical mechanisms responsible for degradation, (iii) finding a correlation between thermal behaviour and reliability. The present work permitted to collect new results concerning the mechanisms that still limit the reliability of LEDs, and will provide the experimental and analytical tools suitable for ALT design and implementation.Con il presente lavoro di tesi vengono riportati i risultati dell'attività di ricerca triennale su Light Emitting Diode (LED) per illuminazione allo stato solido. In particolare, il progetto di ricerca è stato incentrato sullo studio della caratterizzazione termica di LED in nitruro di gallio (GaN) e sull'impatto della temperatura sull'affidabilità dei dispositivi. Il lavoro comincia da una panoramica sullo stato dell'arte di dispositivi optoelettronici a semiconduttore composito di tipo III-V e sugli aspetti affidabilistici ad essi legati. In seguito vengono presentati diversi metodi per la caratterizzazione termica dei LED, insieme alla descrizione dettagliata delle diverse implementazioni sperimentali per ottenere tali misure. Nei capitoli restanti vengono presentati e discussi tre diversi approcci di analisi affidabilistica: (i) un test di vita accelerato su LED bianchi a basso flusso luminoso, (ii) un test di vita accelerato su LED ad alto flusso con tecnologia Chip On Board, e (iii) un'analisi affidabilistica di LED in AlGaN con emissione nel profondo ultravioletto. In tutti questi studi, sono stati sottolineati gli aspetti termici nell'analisi dei risultati. Queste analisi partono da un'approfondita conoscenza della struttura dei dispositivi e delle problematiche relative, con l'obiettivo di (i) trovare un modello di degrado in grado di fornire una corretta stima del tempo di vita, (ii) indagare i meccanismi fisici alla base del degrado, e (iii) individuate una correlazione tra le proprietà termiche e l'affidabilità del dispositivo. Il lavoro presentato ha permesso di mettere insieme nuovi risultati relativi ai meccanismi che attualmente limitano l'affidabilità dei LED, e ha reso disponibile diversi strumenti sperimentali e analitici utili per la progettazione e l'implementazione di test di vita accelerati futuri

Long-term Survival after TAVR of Patients with Low Flow - Low Gradient vs High Gradient Aortic Valve Stenosis

reservedL’impianto transcatetere della valvola aortica (TAVI) è diventato il trattamento di scelta nei pazienti affetti da stenosi aortica (AS) severa sintomatica con più di 75 anni di età. Tra questi, fino ad un terzo, presentano parametri emodinamici discordanti: questo sottotipo viene definito low flow – low gradient (LFLG). In base alla frazione d’eiezione, le stenosi aortiche LFLG sono ulteriormente classificate in classical LFLG (con FE < 50%) e paradoxical LFLG (FE ≥ 50%). Nonostante le solide evidenze di beneficio della TAVI rispetto al trattamento conservativo nei pazienti con LFLG AS, la forma classica è stata correlata a risultati post-procedurali e al follow up a medio termine peggiori rispetto alle stenosi aortiche ad alto gradiente (HG). Al contrario, i pazienti con una forma paradossa o con HG AS sottoposti a TAVI sembrano presentare tassi di sopravvivenza simili ad un anno di follow up. Attualmente non si hanno ancora evidenze consolidate sui risultati a lungo termine delle LFLG AS trattate con TAVI. Scopo dello studio Valutare la sopravvivenza a lungo termine, fino a 10 anni, dopo l’impianto valvolare aortico transcatetere sia nei pazienti con cLFLG AS che pLFLG rispetto a quelli con HG AS. Materiali e metodi È stata svolta un’analisi retrospettiva dei dati dal registro dell’Università di Padova REVALVing Experience, che comprende tutti i pazienti sottoposti a TAVI a partire da giugno 2007 nel nostro centro. Sono stati inclusi nello studio 574 soggetti sottoposti a TAVI con un follow – up di almeno 5 anni. Di questi, il 73% soddisfaceva i criteri per HG AS, 15% per pLFLG AS e 11% per cLFLG AS. L’endpoint primario dello studio è la mortalità per qualsiasi causa. Risultati I pazienti con cLFLG AS hanno presentato una prognosi peggiore al follow-up a lungo termine, con una rapida diminuzione della sopravvivenza entro il primo anno, mentre i pazienti con pLFLG e HG AS avevano tassi di sopravvivenza a lungo termine simili. È stata effettuata un’analisi della sopravvivenza pesata con propensity score (PS) e si è visto che i tassi di sopravvivenza a lungo termine non aggiustati nei soggetti con cLFLG AS erano significativamente inferiori rispetto a quelli con HG AS (p=0,02), mentre i tassi di sopravvivenza a lungo termine aggiustati risultavano simili (p = 0,77). Invece, i pazienti affetti da pLFLG o HG AS hanno mostrato tassi di sopravvivenza a lungo termine comparabili sia con l’analisi non pesata che pesata (p = 0,34 e p = 0,10 rispettivamente). È stata eseguita poi un’analisi di sensibilità con tutte le covariate incluse nel PS che ha confermato l’assenza di un impatto significativo dello stato di cLFLG o pLFLG sulla sopravvivenza (p=0,20 e p=0,11 rispettivamente). Infine, si è indagato il possibile impatto del LV-EF sulla sopravvivenza a lungo termine nelle cLFLG AS. La frazione d’eiezione pre-procedurale non ha dimostrato un impatto significativo sulla sopravvivenza (p=0,67) diversamente dal miglioramento della LV-EF (Δ>15%) ad un anno dalla procedura (p=0,04). I pazienti con cLFLG AS con miglioramento della LV-EF hanno avuto una sopravvivenza significativamente più lunga rispetto a quelli con nessuno o minimo recupero della LV-EF (p=0,02). Conclusioni Il maggior tasso di mortalità, nei pazienti con cLFLG AS sottoposti a TAVI, può essere correlato al maggior rischio cardiovascolare di base piuttosto che al mero stato emodinamico. Al contrario, i pazienti con pLFLG AS rappresentano una popolazione più simile ai soggetti con HG AS in termini di caratteristiche pre-procedurali e tassi di sopravvivenza post-procedurale. Il presente studio ha confermato che il recupero della frazione d’eiezione dopo TAVI è comune tra i pazienti affetti da cLFLG AS ed ha un potenziale impatto sul tempo di sopravvivenza post-procedurale. Eseguire la TAVI in pazienti accuratamente selezionati con stenosi aortica LFLG sembra essere un approccio sicuro ed efficace.Background Transcatheter aortic valve implantation (TAVI) has become the treatment of choice in patients affected by severe, symptomatic aortic stenosis (AS). Up to one-third of patients with severe AS present discordant hemodynamic data: this status is defined as low flow – low gradient (LFLG). According to LV-EF, LFLG AS are further classified in classical LFLG (cLFLG, presenting an EF 50%). Despite a clear benefit of TAVI over conservative treatment in patients with LFLG AS, cLFLG status has been related to worse post-procedural outcomes at mid-term follow-up compared to high-gradient aortic stenosis (HG AS). On the contrary, patients either with pLFLG AS or HG AS undergoing TAVI seem to present similar survival rates at 1-year follow-up. However, at present little is known about long-term outcomes of LFLG AS treated with TAVI. Objectives To evaluate long-term survival, up to 10 years, after TAVI both in pLFLG and cLFLG AS compared to HG AS. Methods This study was conducted as a retrospective analysis from the ongoing Padua University REVALVing Experience (PUREVALVE) registry, including all consecutive patients undergoing TAVI since June 2007. Given the purpose of our study, only subjects with at least 5-year follow up were considered for the analysis (from June 2007 to December 2016). A total of 574 subjects resulted eligible and were included in the analysis. Of them, 73% fulfilled the criteria for HG-AS 15% for pLF-LG AS and 11% for cLF-LG AS. The primary endpoint was death from any cause. Results Patients with cLFLG AS presented the worst prognosis at long-term follow-up while pLFLG and HG AS had similar long-term survival rates. We then performed a propensity score weighted survival analysis to evaluate long-term survival of the three groups adjusting the results for possible baseline confounders. Even if patients with cLFLG AS presented significantly lower unadjusted survival rates compared to those affected by HG AS (p=0.02), when considering weighted curves similar long-term survival between groups was observed (p=0.77). Conversely, patients affected either by pLFLG or HG AS showed comparable long-term survival rates both at unadjusted and adjusted analyses (p=0.34 and p=0.10 respectively). Then, we performed a sensitivity analysis with all the covariates included in the PS, which confirmed the absence of a significant impact of both cLFLG and pLFLG status on survival (p=0,20 and p=0,11 respectively). Finally, we aimed to investigate the possible impact of LV-EF on long-term survival of patients with cLFLG AS. Baseline EF did not show significant impact on survival time p=0.67) in cLFLG AS patients. On the contrary, we demonstrated a significant relation between an LV-EF improvement detected within 1-year after the procedure and survival time p=0.04). Patients with cLFLG AS presenting a significant LV-EF improvement after the procedure, had a significantly longer post-procedural survival time compared to those with no or slighter EF recovery (p=0.02). Conclusions The higher mortality rates characterizing patients with cLFLG-AS undergoing TAVI, may be more related to the higher baseline CV risk rather than the mere hemodynamic status. On the contrary, pLFLG patients represent a population more similar to HG-AS subjects in terms of both baseline characteristics and post-procedural survival rates. The present study confirmed that LV-EF recovery after TAVI is a common finding among patients affected by cLFLG AS and has a potential impact on post-procedural survival time. Performing TAVI in carefully selected patients with LFLG AS seems to be the most reasonable, effective and safest approach

Optimization of robot working cycles through Travelling Salesman Problem

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