Global climate change, energy crisis, and the need for strict climate action plan, have paved the way towards sustainable energy storage, and green energy transportation. Since their advent in the year 1991, Lithium – ion batteries (LIB) are sought as the most promising energy storage technology due to their potential use in portable electronics, electric vehicles (EVs), and stationary grid storage solutions. Therefore, it is of common conscious to develop high energy/power density, safe, cheap and recyclable LIBs. Binders are electrochemically inactive and form a small part of electrode components. However, with the aim of realizing a high energy density LIB, it is of utmost importance to investigate the role of binders, since they strongly affect mechanical integrity and electrochemical performance of a battery cell. The present thesis work focuses on the role of polymeric binders, especially styrene-butadiene rubber (SBR), in water – based anodes for LIBs. Water – based anode slurries including Graphite, Carbon black, Carboxymethyl cellulose (CMC) and SBR, were investigated regarding the effect of adhesion strength on mechanical properties and electrochemical performance of LIBs. Anode slurries with varying SBR concentrations were produced to achieve different degrees of adhesion to the current collector (copper foil). Anodes with two different loadings (2.15 & 3.5 mAh/cm2) were investigated in this study. Peel tests were conducted to measure adhesive strength, and resulting data indicated a rise in adhesion with increasing SBR content, thus lowering the probability of delamination of electrode layer from the current collector. The anode samples were optically examined during processing steps such as calendaring, cutting and punching. A similar systematic trend was observed, wherein the anode samples with higher SBR content were less prone to delamination and fracturing during processing. LIB cells were characterized electrochemically for their performance using methodologies such as rate capability, cycling, and DC internal resistance (DCIR) tests. Anodes (both loadings) with higher SBR concentration performed poorly during rate tests. Likewise, cells with higher SBR content were susceptible to drastic capacity fade during long-term cycling test. While examining internal resistance evolution, more binder content resulted in higher resistance of the cell. Consequently, it lead to premature reaching of cell voltage and capacity fade. Thus, a trade-off between mechanical integrity and electrochemical performance was carefully analyzed, since improved adhesion strength at the expense of cell performance was noted; however, this work was in alignment with the benchmark tests, and confirmed its industrial relevance. Finally, this thesis provides the groundwork for fine-tuning of the slurry recipe to optimize mechanical properties of electrodes, and subsequent electrochemical performance of the cell.
Il cambiamento climatico globale, la crisi energetica e la necessità di un rigoroso pi-ano d'azione per il clima hanno spianato la strada allo stoccaggio sostenibile dell'en-ergia e al trasporto di energia verde. Dal loro avvento nell'anno 1991, le batterie agli ioni di litio (LIB) sono ricercate come la tecnologia di accumulo di energia più promettente a causa del loro potenziale utilizzo nell'elettronica portatile, nei veicoli elettrici (EV) e nelle soluzioni di stoccaggio della rete fissa. Pertanto, è di comune consapevolezza sviluppare LIB ad alta densità di energia/potenza, sicuri, economici e riciclabili. I leganti sono elettrochimicamente inattivi e costituiscono una piccola parte dei componenti degli elettrodi. Tuttavia, con l'obiettivo di realizzare un LIB ad alta densità di energia, è della massima importanza studiare il ruolo dei leganti, poi-ché influenzano fortemente l'integrità meccanica e le prestazioni elettrochimiche di una cella della batteria. Il presente lavoro di tesi si concentra in particolare sul ruolo dei leganti polimerici gomma stirene-butadiene (SBR), in anodi a base d'acqua per LIB. Sono stati studiati gli impasti anodici a base d'acqua tra cui grafite, nerofumo, carbossimetilcellulosa (CMC) e SBR per quanto riguarda l'effetto della forza di ade-sione sulle proprietà meccaniche e sulle prestazioni elettrochimiche dei LIB. Sono state prodotte impasti anodici con concentrazioni di SBR variabili per ottenere diver-si gradi di adesione al collettore di corrente (foglio di rame). In questo studio sono stati studiati anodi con due diversi carichi (2,15 e 3,5 mAh/cm2). Sono stati condotti test di peeling per misurare la forza adesiva e i dati risultanti hanno indicato un au-mento dell'adesione con l'aumento del contenuto di SBR, riducendo così la probabil-ità di delaminazione dello strato di elettrodo dal collettore di corrente. I campioni di anodi sono stati esaminati otticamente durante le fasi di lavorazione come calandra-tura, taglio e punzonatura. È stata osservata una tendenza sistematica simile, in cui i campioni di anodi con contenuto di SBR più elevato erano meno inclini alla delami-nazione e alla frattura durante gli esperimenti. Le celle LIB sono state caratterizzate elettrochimicamente per le loro prestazioni utilizzando metodologie come test di ca-pacità di velocità, ciclazione e resistenza interna DC (DCIR). Gli anodi (entrambi i carichi) con una maggiore concentrazione di SBR hanno funzionato male durante i test di velocità. Allo stesso modo, le celle con un contenuto di SBR più elevato erano suscettibili di un drastico riduzione della capacità durante il test di ciclazione a lungo termine. Durante l'esame dell'evoluzione della resistenza interna, più contenuto di legante ha comportato una maggiore resistenza della cella. Di conseguenza, porta al raggiungimento prematuro della tensione della cella e alla diminuzione della capacità. È stata notata una maggiore forza di adesione a scapito delle prestazioni di cella. Infine, questa tesi fornisce le basi per la messa a punto della ricetta dell'impasto liquido per ottimizzare le proprietà meccaniche degli elettrodi e le successive prestazioni elettrochimiche della cella.
Effect of coating adhesion strength on processing behavior and electrochemical performance of water-based anodes for Lithium-ion batteries
Hegde, Akshay Dattatraya
2021/2022
Abstract
Global climate change, energy crisis, and the need for strict climate action plan, have paved the way towards sustainable energy storage, and green energy transportation. Since their advent in the year 1991, Lithium – ion batteries (LIB) are sought as the most promising energy storage technology due to their potential use in portable electronics, electric vehicles (EVs), and stationary grid storage solutions. Therefore, it is of common conscious to develop high energy/power density, safe, cheap and recyclable LIBs. Binders are electrochemically inactive and form a small part of electrode components. However, with the aim of realizing a high energy density LIB, it is of utmost importance to investigate the role of binders, since they strongly affect mechanical integrity and electrochemical performance of a battery cell. The present thesis work focuses on the role of polymeric binders, especially styrene-butadiene rubber (SBR), in water – based anodes for LIBs. Water – based anode slurries including Graphite, Carbon black, Carboxymethyl cellulose (CMC) and SBR, were investigated regarding the effect of adhesion strength on mechanical properties and electrochemical performance of LIBs. Anode slurries with varying SBR concentrations were produced to achieve different degrees of adhesion to the current collector (copper foil). Anodes with two different loadings (2.15 & 3.5 mAh/cm2) were investigated in this study. Peel tests were conducted to measure adhesive strength, and resulting data indicated a rise in adhesion with increasing SBR content, thus lowering the probability of delamination of electrode layer from the current collector. The anode samples were optically examined during processing steps such as calendaring, cutting and punching. A similar systematic trend was observed, wherein the anode samples with higher SBR content were less prone to delamination and fracturing during processing. LIB cells were characterized electrochemically for their performance using methodologies such as rate capability, cycling, and DC internal resistance (DCIR) tests. Anodes (both loadings) with higher SBR concentration performed poorly during rate tests. Likewise, cells with higher SBR content were susceptible to drastic capacity fade during long-term cycling test. While examining internal resistance evolution, more binder content resulted in higher resistance of the cell. Consequently, it lead to premature reaching of cell voltage and capacity fade. Thus, a trade-off between mechanical integrity and electrochemical performance was carefully analyzed, since improved adhesion strength at the expense of cell performance was noted; however, this work was in alignment with the benchmark tests, and confirmed its industrial relevance. Finally, this thesis provides the groundwork for fine-tuning of the slurry recipe to optimize mechanical properties of electrodes, and subsequent electrochemical performance of the cell.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/195098