Silicon, as the most common semiconductor material, has widespread applications in computer chips and solar cells. Additionally, it has demonstrated superior specific capacity compared to graphite when used in lithium battery anodes, leading to extensive research by scientists. However, silicon undergoes an approximate threefold volume expansion during lithiation. As a brittle material at room temperature, silicon cannot withstand such significant volume changes and tends to fracture, ultimately resulting in battery short circuits and rapid capacity decay within a few cycles. Among the various studies, nanoscale silicon and silicon composites have shown promising application prospects. The former possesses a large specific surface area and can form porous structures, which effectively buffer the volume changes during battery use. The latter typically involves incorporating flexible materials, such as the commonly used carbon, into silicon to mitigate the volume expansion. Moreover, silicon anodes have gained attention in all-solid-state batteries. In this study, silicon films and silicon-carbon composite films with various structures were prepared using pulsed laser deposition (PLD) at room temperature. PLD, a physical vapor deposition (PVD) technique, leverages the interaction between laser and materials to achieve material deposition. This research comprises two main parts. The first part involves the deposition of pure silicon films. These films were deposited on metallic-coated silicon wafers to characterize the properties under different parameters, including pressure (ranging from vacuum to 150 Pa), laser fluence (3 to 5 J/cm²), and deposition atmosphere (pure argon and a mixture of argon and hydrogen). The morphology, elemental composition, thickness distribution, and crystallinity of the films were characterized using scanning electron microscopy (SEM) and Raman spectroscopy. Post-deposition annealing treatments were conducted, and the annealed films were further analyzed to understand thermal-induced crystallization and other potential thermal effects. Optical emission spectroscopy (OES) was employed to study plume dynamics under varying deposition pressures. Based on the properties of the silicon films, those with the potential for good electrochemical performance were further deposited on dendritic copper foil. These films were sent to the Helmholtz Institute Ulm (HIU) in Germany for application in all-solid-state lithium-ion batteries, with cell assembly and electrochemical testing conducted by Professor A. Varzi's research group. The electrochemical results from this collaboration are also introduced and analyzed in this study. The second part focuses on silicon-carbon composite films. Three types of films were investigated: double-layer, multilayer, and mixture films. The deposition process of these films, particularly the target orientation, is detailed, followed by characterization using SEM and Raman spectroscopy. In addition to the silicon component, the structure of carbon in the films was also analyzed. The electrochemical performance of the composite films was not tested. However, based on the results from the silicon films and the morphology of the composite films, their potential electrochemical behaviour is briefly discussed. In conclusion, silicon films and silicon-carbon composite films were synthesized using PLD, and their properties under various deposition parameters were investigated. Electrochemical tests indicated that high porosity in the films could enhance cyclic performance, although specific capacity might be adversely affected due to poorer contact and utilization of Si material. Future research will focus on further characterizing the electrochemical performance of the composite films, particularly the multilayered ones, which show potential for excellent performance in all-solid-state lithium-ion batteries.
Il silicio, essendo il materiale semiconduttore più comune, ha applicazioni diffuse nei chip per computer e nelle celle solari. Inoltre, ha dimostrato una capacità specifica superiore rispetto alla grafite quando è utilizzato come anodo in batterie agli ioni di litio, stimolando ricerche estensive da parte degli scienziati. Tuttavia, il silicio subisce un'espansione volumetrica di circa tre volte durante la reazione di litiazione. Essendo un materiale fragile a temperatura ambiente, il silicio tende a non tollerare significativi cambiamenti di volume e a fratturarsi, causando infine cortocircuiti della batteria e un rapido calo della sua capacità entro pochi cicli. Tra i vari studi, il silicio nanostrutturato e i compositi di silicio si sono dimostrati promettenti dal punto di vista applicativo. Il primo possiede una grande superficie specifica e può formare strutture porose, che compensano efficacemente i cambiamenti di volume durante l'uso della batteria. Il secondo, tipicamente, prevede l'incorporazione di materiali duttili, come il carbonio, comunemente usato insieme al silicio per mitigare l'espansione volumetrica. Inoltre, gli anodi di silicio hanno attirato l'attenzione nelle batterie allo stato solido. In questo studio, film di silicio e film compositi di silicio-carbonio con varie strutture sono stati preparati utilizzando la deposizione laser pulsata (PLD) a temperatura ambiente. La PLD, tra le tecniche di deposizione fisica da vapore (PVD), sfrutta l'interazione tra laser e materiali per ottenere la deposizione di film sottili. Questa ricerca comprende due parti principali. La prima parte riguarda la deposizione di film di silicio puro. Questi film sono stati depositati su wafer di silicio metallizzati per caratterizzarne le proprietà sotto diversi parametri, inclusi la pressione di deposizione (da vuoto a 150 Pa), la fluenza del laser (3-5 J/cm²) e l’atmosfera di deposizione (argon puro e una miscela di argon e idrogeno). La morfologia, la composizione elementale, la distribuzione dello spessore e la cristallinità dei film sono stati caratterizzati utilizzando la microscopia elettronica a scansione (SEM) e la spettroscopia Raman. Inoltre, sono stati effettuati trattamenti termici post-deposizione, e i film corrispondenti sono stati ulteriormente analizzati per comprendere la cristallizzazione indotta dalla temperatura e altri potenziali effetti termici. La spettroscopia di emissione ottica (OES) è stata impiegata per studiare la dinamica della piuma di ablazione in funzione della pressione di deposizione. Basandosi sulle proprietà dei film di silicio, quelli con il potenziale per una buona performance elettrochimica sono stati ulteriormente depositati su fogli di rame dendritico. Questi film sono stati poi inviati all'Helmholtz Institute Ulm (HIU), in Germania, per l'applicazione in batterie al litio allo stato solido, con l'assemblaggio delle celle e i test elettrochimici condotti dal gruppo di ricerca del Professor A. Varzi. I risultati elettrochimici di questa collaborazione sono discussi in questo studio. La seconda parte si concentra invece sui film compositi di silicio-carbonio. Sono stati studiati tre tipi di film: a doppio strato, multistrato e misti. Il processo di deposizione di questi film, in particolare la configurazione del target, è descritto in dettaglio, seguito dalla caratterizzazione tramite SEM e spettroscopia Raman. Oltre alla componente di silicio, è stata analizzata anche la struttura del carbonio nei film. La performance elettrochimica dei film compositi non è stata ancora testata. Tuttavia, basandosi sui risultati dei film di silicio e sulla morfologia dei film compositi, il loro potenziale comportamento elettrochimico è brevemente discusso. In conclusione, film di silicio e film compositi di silicio-carbonio sono stati sintetizzati utilizzando la PLD, e le loro proprietà sotto vari parametri di deposizione sono state investigate. I test elettrochimici hanno indicato che un'alta porosità nei film potrebbe migliorare la performance durante i cicli elettrochimici, sebbene la capacità specifica potrebbe essere negativamente influenzata dalla minore area di contatto con l’elettrolita solido e dalla minore utilizzazione del materiale attivo. Le ricerche future si concentreranno sull'ulteriore caratterizzazione elettrochimiche dei film compositi, in particolare quelli multistrato, che mostrano potenziale per una performance eccellente in batterie al litio allo stato solido.
Nanostructured silicon thin films as anode materials for solid-state lithium-ion batteries
Li, Shuang
2023/2024
Abstract
Silicon, as the most common semiconductor material, has widespread applications in computer chips and solar cells. Additionally, it has demonstrated superior specific capacity compared to graphite when used in lithium battery anodes, leading to extensive research by scientists. However, silicon undergoes an approximate threefold volume expansion during lithiation. As a brittle material at room temperature, silicon cannot withstand such significant volume changes and tends to fracture, ultimately resulting in battery short circuits and rapid capacity decay within a few cycles. Among the various studies, nanoscale silicon and silicon composites have shown promising application prospects. The former possesses a large specific surface area and can form porous structures, which effectively buffer the volume changes during battery use. The latter typically involves incorporating flexible materials, such as the commonly used carbon, into silicon to mitigate the volume expansion. Moreover, silicon anodes have gained attention in all-solid-state batteries. In this study, silicon films and silicon-carbon composite films with various structures were prepared using pulsed laser deposition (PLD) at room temperature. PLD, a physical vapor deposition (PVD) technique, leverages the interaction between laser and materials to achieve material deposition. This research comprises two main parts. The first part involves the deposition of pure silicon films. These films were deposited on metallic-coated silicon wafers to characterize the properties under different parameters, including pressure (ranging from vacuum to 150 Pa), laser fluence (3 to 5 J/cm²), and deposition atmosphere (pure argon and a mixture of argon and hydrogen). The morphology, elemental composition, thickness distribution, and crystallinity of the films were characterized using scanning electron microscopy (SEM) and Raman spectroscopy. Post-deposition annealing treatments were conducted, and the annealed films were further analyzed to understand thermal-induced crystallization and other potential thermal effects. Optical emission spectroscopy (OES) was employed to study plume dynamics under varying deposition pressures. Based on the properties of the silicon films, those with the potential for good electrochemical performance were further deposited on dendritic copper foil. These films were sent to the Helmholtz Institute Ulm (HIU) in Germany for application in all-solid-state lithium-ion batteries, with cell assembly and electrochemical testing conducted by Professor A. Varzi's research group. The electrochemical results from this collaboration are also introduced and analyzed in this study. The second part focuses on silicon-carbon composite films. Three types of films were investigated: double-layer, multilayer, and mixture films. The deposition process of these films, particularly the target orientation, is detailed, followed by characterization using SEM and Raman spectroscopy. In addition to the silicon component, the structure of carbon in the films was also analyzed. The electrochemical performance of the composite films was not tested. However, based on the results from the silicon films and the morphology of the composite films, their potential electrochemical behaviour is briefly discussed. In conclusion, silicon films and silicon-carbon composite films were synthesized using PLD, and their properties under various deposition parameters were investigated. Electrochemical tests indicated that high porosity in the films could enhance cyclic performance, although specific capacity might be adversely affected due to poorer contact and utilization of Si material. Future research will focus on further characterizing the electrochemical performance of the composite films, particularly the multilayered ones, which show potential for excellent performance in all-solid-state lithium-ion batteries.| File | Dimensione | Formato | |
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2024_07_Li_Thesis_01.pdf
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Descrizione: Master Thesis
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2024_07_Li_Executive Summary_02.pdf
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Descrizione: Executive Summary
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https://hdl.handle.net/10589/222836