Les accumulateurs commerciaux à base de lithium-ion (LIB) utilisent des matériaux à base de carbone (graphite) comme électrode négative; cependant, la technologie atteint sa limite en raison de la faible capacité spécifique théorique. L'objectif de cette thèse est d'étudier le comportement électrochimique de trois nouvelles anodes à haute capacité (SnSb microsturé, Ti3SiC2 anodisé et nanotubes de Si poreux) comme alternatives au graphite, d'identifier les principaux paramètres responsables de la perte de capacité et de proposer une solution commune pour améliorer leurs performances électrochimiques. Ces matériaux d'électrode présentent une bonne performance électrochimique qui les rend prometteurs pour remplacer le carbone en tant qu'électrode négative pour batteries au Li-ion. Cependant, ils présentent une perte de capacité initiale importante qui doit être résolue avant la commercialisation. Les limitations observées sont attribuées à de nombreux facteurs, et en particulier à la formation et la croissance d’une SEI à la surface des matériaux. En raison de la forte perte de la capacité et du manque d’études détaillées sur les matériaux à base d’étain, en particulier le SnSb, nous avons concentré la suite du travail à la formation et la croissance de la SEI sur cette électrode négative. L'évolution des propriétés électriques, de la composition chimique et de la morphologie du SnSb microstructuré a été étudiée en détail pour comprendre son comportement électrochimique. Pour limiter l’effet de la SEI, nous avons proposé d’appliquer un film protecteur à la surface de l'électrode. / Currently, commercial lithium ion batteries (LIBs) use carbon based materials as negative electrode; however the technology is reaching its limit because of the low theoretical specific capacity. The objective of this thesis is to study the electrochemical behaviour of three different new high capacity anodes (SnSb alloy, anodized Ti3SiC2, and Si nanotubes) as alternative to graphite, identify the main parameters responsible for the capacity fading, and propose a versatile solution to improve their electrochemical performance. These electrode materials exhibit good electrochemical performance which makes them promising candidates to replace carbon as a negative electrode for LIBs. However, their limitation due to capacity fading and the large initial irreversible capacity loss must be resolved before commercialization. The observed limitations are attributed to many factors, and particularly, to the formation and growth of SEI layer which is the common factor for all the three electrode materials. Because of the strong capacity fade and lack of many detailed studies on the Sn-based materials, specifically SnSb, we focus our study to investigate the formation and growth of SEI layer on SnSb electrode. The evolution of the electrical, compositional, and morphological properties have been investigated in detail to understand the electrochemical behavior of micron-sized SnSb. To limit the capacity fade, we propose the use of a protective film on the electrode surface. The electrochemical performance of micron-sized SnSb electrode coated with thermoplastic elastomer protective film, namely poly(styrene-b-2-hydroxyethyl acrylate) PS-b-PHEA has been achieved.

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This study sought to improve the performance of Si-based anodes through the use of hierarchically structured electrodes to provide the nanoscale framework needed to accommodate large volume changes while controlling the interfacial area – which affects solid-electrolyte interphase (SEI) formation. To accomplish this, electrodes were fabricated from vertically aligned carbon nanotubes (VACNT) infiltrated with silicon. On the nanoscale, these electrodes allowed us to adjust the surface area, tube diameter, and silicon layer thickness. On the micro-scale, we have the ability to control the electrode thickness and the incorporation of micro-sized features. Treatment of the interfacial area between the electrolyte and the electrode by encapsulating the electrode controls the stabilization and reduction of unstable SEI. Si-VACNT composite electrodes were prepared by first synthesizing VACNTs on Si wafers using photolithography for catalyst patterning, followed by aligned CNT growth. Nano-layers of silicon were then deposited on the aligned carbon nanotubes via LPCVD at 200mTorr and 535°C. A thin copper film was used as the current collector. Electrochemical testing was performed on the electrodes assembled in a CR2025 coin cell with a metallic Li foil as the counter electrode. The impact of the electrode structure on the capacity at various current densities was investigated. Experimental results demonstrated the importance of control over the superficial area between the electrolyte and the electrode on the performance of silicon-based electrodes for next generation lithium ion batteries. In addition, the results show that Si-VACNT height does not limit Li transport for the range of the conditions tested.

Lithium ion batteries (LIBs) are widely used for storing and converting chemical energy into electrical energy. During battery operation, lithium ions move between electrode materials, enabling energy storage. However, aging mechanisms like lithium plating can negatively impact battery performance and lifetime. Lithium plating occurs when lithium ions are reduced to metallic lithium on the graphite electrode. The undesired Li plating in LIBs leads to dendrite formation that may puncture the separator, causing internal short-circuit and ultimately thermal runaway. This study aims to investigate the internal processes of LIBs during charge and discharge. Two analysis methods are employed: online electrochemical mass spectrometry (OEMS) and acoustic emission monitoring (AEM). OEMS is a gas analysis technique that combines electrochemical measurements with mass spectrometry to provide real-time testing of cells. OEMS allows identifying and quantifying gas evolution/consumption of chemical species. AE is a diagnostic tool, offering monitoring the health of LIBs through detection and characterisation of stress waves produced by parasitic mechano-electrochemical events. The results indicates that the formation of SEI thin film layer, generated gases like hydrogen and ethylene, while consuming carbon dioxide. During induced lithium plating, hydrogen and carbon dioxide were consumed, and ethylene gas was produced, due to new SEI film formation process. The acoustic emission analysis indicated that lithium plating was an active process, whereas SEI formation was less AE active. Further research is needed to understand the relationships and significance of these processes for battery performance and safety. Overall, this study highlighted the importance of investigating aging mechanisms in LIBs to enhance their performance and longevity. By combining OEMS and AE, it was possible to analyse the batteries behaviour during cycling. The evolution of gas and acoustic signals provided insights into the reactions and processes occurring inside the battery during cycling.

Silicon (Si) has been considered as a promising negative electrode material for lithium ion batteries (LIBs) because of its high theoretical capacity, low discharge voltage, and low cost. However, the utilization of Si electrode has been hampered by problems such as slow ionic transport, large stress/strain generation, and unstable solid electrolyte interphase (SEI). These problems severely influence the performance and cycle life of Si electrodes. In general, ionic conduction determines the rate performance of the electrode, while electron leakage through the SEI causes electrolyte decomposition and, thus, causes capacity loss. The goal of this thesis research is to design Si electrodes with high current efficiency and durability through a fundamental understanding of the ionic and electronic conduction in Si and its SEI. Multi-scale physical and chemical processes occur in the electrode during charging and discharging. This thesis, thus, focuses on multi-scale modeling, including developing new methods, to help understand these coupled physical and chemical processes. For example, we developed a new method based on ab initio molecular dynamics to study the effects of stress/strain on Li ion transport in amorphous lithiated Si electrodes. This method not only quantitatively shows the effect of stress on ionic transport in amorphous materials, but also uncovers the underlying atomistic mechanisms. However, the origin of ionic conduction in the inorganic components in SEI is different from that in the amorphous Si electrode. To tackle this problem, we developed a model by separating the problem into two scales: 1) atomistic scale: defect physics and transport in individual SEI components with consideration of the environment, e.g., LiF in equilibrium with Si electrode; 2) mesoscopic scale: defect distribution near the heterogeneous interface based on a space charge model. In addition, to help design better artificial SEI, we further demonstrated a theoretical design of multicomponent SEIs by utilizing the synergetic effect found in the natural SEI. We show that the electrical conduction can be optimized by varying the grain size and volume fraction of two phases in the artificial multicomponent SEI.

This dissertation is focus on the study of solid-electrolyte interphases (SEIs) on advanced lithium ion battery (LIB) anodes. The purposes of this dissertation are to a) develop a methodology to study the properties of SEIs; and b) provide guidelines for designing engineered SEIs. The general knowledge gained through this research will be beneficial for the entire battery research community.

Limiter le vieillissement des accumulateurs lithium-ion est un challenge pour optimiser leur utilisation notamment dans le domaine spatial. La qualité de la couche de passivation (SEI), formée à la surface de l’électrode négative de graphite lors des premiers cycles de vie de la batterie, est déterminante pour ses performances futures. Celle-ci est composée de polymères et de divers sels de lithium dont la dissolution, la précipitation et la migration affectent les performances. Cette étude vise à comprendre l’impact de ces composés sur la cyclabilité et de proposer des solutions à l’effet néfaste de ces sels sur le bon fonctionnement et le vieillissement de l’accumulateur Li-ion. La première partie de ce travail aborde l’impact de divers sels de lithium de la SEI (LiF, Li2CO3, LiOH, LiOCH3, LiOC2H5) sur le comportement en cyclage des accumulateurs. Par la suite, nous avons proposé des solutions pour améliorer le comportement qu’engendre la présence de ces sels sur les performances à travers deux approches. La première concerne l’utilisation de co-solvants complexants de la famille des glymes. La seconde approche consiste à modifier les propriétés interfaciales électrodes/électrolyte par l’ajout d’additifs tensioactifs à l’électrolyte. Les résultats montrent dans les deux cas des améliorations notables de la cyclabilité des dispositifs en demi-pile et en cellule complète. / Limiting the lithium-ion batteries ageing is a challenge to overcome in the field of spatial applications. The quality of the solid electrolyte interfaces (SEI), created at the electrode surface during the first cycles of the battery, is decisive for its future performances. The SEI is composed of polymers and several lithium salts which are able to dissolve, precipitate and migrate in the electrolyte and hence modify the battery performances. This study aims to understand the impact of the dissolution of these compounds on the cell cycling ability and to propose solutions to avoid the harmful effects of these salts on the battery ageing. The first part of this study is devoted to the study of the effect of dissolved SEI lithium salts (LiF, LiOH, Li2O, Li2CO3 , LiOCH3, LiOC2H5) on the cycling ability of half and full cells.In order to improve the battery performances in spite of the presence of these SEI salts in the electrolyte, two solutions have been examined. The first one is to add a co-solvent belonging to the glyme family which is able to form complexes with lithium ions and the second to use a surfactant additive which will modify the interfacial electrode/electrolyte properties. Results show that in both cases an improvement in half-cell or full-cell cycling ability was achieved.

<p>  </p> <p>Room-temperature sodium-sulfur (RT Na-S) batteries are an emergent new technology that are highly attractive due to their low raw materials cost and large theoretical specific energy. However, many fundamental problems still plague RT Na-S batteries that prevent their progression from the research and development phase to the commercial phase. Sulfur and its final discharge product are insulators, and intermediate polysulfide discharge products are soluble in commonly used liquid electrolytes. As a result, RT Na-S cells exhibit large capacity defects, low coulombic efficiencies, and rapid capacity fading. Additionally, the reactive sodium metal anode can form dendrites during cycling, which reduces capacity and shortens cell life. One way to combat these issues is the judicious selection of electrolyte components. In this study, the effects of monoglyme (G1), diglyme (G2), and tetraglyme (G4) glyme ether electrolyte solvents on RT Na-S cell performance are investigated. Galvanostatic cycling of Na/Na symmetric coin cells reveals that the G2 solvent enable stable cycling at low overpotentials over a wide range of current densities. In contrast, the G1-based cells show evidence of dendritic plating, and G4-based cells are not suitable for use at high current densities. Electrochemical impedance spectroscopy during cycling confirms that the G2 solvent facilitates the formation of a strong, stable SEI on the Na electrode surface. Results from galvanostatic cycling of RT Na-S full coin cells demonstrates that G1-based cells deliver the highest initial specific discharge capacities among the three cell types, but G4-based cells are the most reversible. Infinite charging, the indefinite accrual of charge capacity at the high charge voltage plateau, affects all cell types at different cycle numbers and to different extents. This behavior is linked to the strength of the polysulfide shuttle during charge. Optical microscopy experiments show that G2 and G4 facilitate the formation of the S3•- sulfur radical, which reduces capacity. G1 minimizes the radical formation and thus delivers higher initial specific discharge capacity. In order to fully optimize the electrolyte for RT Na-S cells, future work should study glyme solvent blends, additives, and concentrated salts.</p>

<p>Sodium (Na)-ion battery displays many properties similar to Lithium (Li)-ion battery, such as operating principles and capacity, which noticeably compressed the Na-ion battery cathode exploration period. Having said that, anode materials of Na-ion battery is still underperforming as commercial graphite is inadequate in storing bulky Na ions. In the search for anode materials, both alloy-type and Na metal anode materials have gained popularity as these materials can absorb more charges and have higher storage capacity. It is essential to remember that such materials exhibit massive volume expansion upon sodiation and hence experience considerable mechanical stress upon cycling, leading to fractures and pulverization of the electrodes. In addition to electrode stability, ionic motions between the electrode and electrolyte are pivotal in determining the battery response. The decomposition of the electrolyte cocktails forms a passivation layer on the electrode surface, known as solid electrolyte interphase (SEI), which can rupture and regenerate in unstable cycles. Rickety SEI can cause the consumption of active Na and the formation of local hotspots for notorious dendrite growth, leading to short battery durability.</p> <p><br></p> <p>In the first part of the thesis, Tin (Sn) has been selected as an exemplar system to study the dynamic changes in a Na-ion battery. Higher ion-uptake capabilities of Sn electrode come with a price of large structural and morphological changes and can be controlled by careful charting of non-active phases such as binder and suitable electrolyte solution. This work comprehensively studies the technical challenges associated with Sn with different binder domains and in different liquid electrolyte environments. Parallelly, the sensitivity of the Na-Sn system towards the operating potential window and the crosstalk between the working electrode (alloying and de-alloying) and the counter electrode (plating and stripping) has been untied. Also, a fundamental understanding of the materials-transport-interface interactions during thermal abuse tests and their implication on the safety aspects of Na-ion batteries has been addressed. </p> <p><br></p> <p>Following that, the morphological stability of the Na metal anode is investigated based on the distinct electrochemical reactions arising from the composition of different liquid electrolytes. The role heterogeneity in the SEI layer of Na metal for the growth of dendritic patterns has been discussed. A unified framework incorporating a detailed electrochemical study of various electrolyte formulations, cognizant of the reactions and kinetics at the electrode-electrolyte interface, has been developed. To mechanistically counter the heterogeneity implications and synergistically leverage the electrolyte-additive-driven improvement in ionic transport, a flux-homogenizing separator has been introduced to extend the battery cycling. Based on this synergistic approach, the complex interplay between the homogeneity in SEI composition, electrodeposition/dissolution morphology, and cell performance in Na-metal-based batteries has been identified.</p> <p><br></p> <p>This work tried to offer fresh insights on fundamental mechanisms governing the evolution of the electrode-electrolyte interphases and their role in determining electro-chemo-mechano-thermal stability for future research endeavors in the Na-ion battery field. </p>

Les matériaux dits de conversion à base de Sb et Sn, utilisés comme électrodes, apparaissent comme des composés particulièrement intéressants compte tenu de leur forte capacité théorique. Le matériau TiSnSb a été récemment développé en tant qu’électrode négative pour batteries lithium-ion. Ce matériau est capable d’accueilir, de façon réversible, 6,5 Li par unité formulaire, ce qui correspond à une capacité spécifique de 580 mAh/g. Dans le domaine des batteries lithium-ion, les propriétés de l’interface électrode/électrolyte (« solid electrolyte interphase », SEI), formant une couche de passivation protectrice à la surface des électrodes sont considérées comme essentielles pour les performances au sens large des batteries. Cet aspect représente le sujet majeur traité dans ce travail de thèse. Dans cet optique, nous avons tout d'abord étudié les propriétés électrochimiques de l'électrode TiSnSb sous divers aspects, dont les effets du régime de cyclage, l’influence de la nature des additifs au sein de l’électrolyte ainsi que l’utilisation de liquides ioniques à température ambiante (RTILs). En particulier, un système d'électrolyte à base de RTILs a été développé et optimisé vis-à-vis des performances électrochimiques. Afin de caractériser l’interface électrode-électrolyte, deux techniques de caractérisation majeures ont été utilisées : la Spectroscopie Photoélectronique à Rayonnement X (XPS) et la Spectroscopie d'Impédance électrochimique (EIS). Cette étude a permis de cibler certains paramètres essentiels liant les aspects performances électrochimiques à la nature de l’interface électrode-électrolyte. / In the past decades, the need for portable power has accelerated due to the miniaturization of electronic appliances. It continues to drive research and development of advanced energy systems, especially for lithium ion battery systems. As a consequence, conversion materials for lithium-ion batteries, including Sb and Sn-based compounds, have attracted much intense attention for their high storage capacities. Among conversion materials, TiSnSb has been recently developed as a negative electrode for lithium-ion batteries. This material is able to reversibly take up 6.5 Li per formula unit which corresponds to a specific capacity of 580 mAh/g. In the field of lithium-ion battery research, the solid electrolyte interphase (SEI) as a protective passivation film formed at electrode surface owing to the reduction of the electrolyte components, has been considered as a determinant factor on the performances of lithium-ion battery. Thus it has been a focused topic of many researches. However, little information can be found about the formation and composition of the SEI layer formed on TiSnSb conversion electrode at this time. With the aim to investigate the influences of the SEI layer on the performances of composite TiSnSb electrode, we first studied the electrochemical properties of the electrode from various aspects, including the effects of cycling rates, electrolyte additives, as well as room temperature ionic liquids (RTILs). Especially, a RTILs-based electrolyte system was developed and optimized by evaluating its physicochemical properties to be able to further improve the performances of TiSnSb electrode. In order to characterize the SEI layer formed at electrode surface, we performed X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). This study allowed to target some essential parameters concerning electrochemical performances linked with the nature of the solid electrolyte interphase.*