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<p>Recently, energy storage systems have become more focused towards sustainable energy sources like LIBs due to attractive attributes like high energy density and volumetric density which make them extremely competitive compared to other energy sources for many portable and non-portable applications (smartphones, eVTOLs, stationary storage systems, electric vehicle and so on). Longer cycling stability, capacitance retentive power, lower self-discharge rate and high voltage window are qualitative features in LIB. Even though LIBs are rechargeable energy storage systems, all cells decay and degrade over time causing capacity and power fade due to a number of factors such as manufacturing defects, usage outside the normal operating conditions, and other abuse conditions like overcharge, over-discharge and indentation. This work presents a systematic investigation of several off-nominal conditions which are typically observed in LIBs such as overcharge, over-discharge, nail indentation, periodic overcharge, and over-discharge in order to form a comparative analysis on the effect of each of these conditions on cycle life aging, morphological changes on the cell components and also to evaluate potential internal short circuit (ISC) mechanisms. The cell failure mechanism induced by each condition and its negative impact on the electrochemical performance has been rigorously analyzed in this work based on the proper protocols. The correlation of the galvanostatic performance with the morphological change of the individual electrodes was also scrutinized under SEM and EDS to demarcate the severity of the defect into Li-ion cells. The practical off-nominal condition analysis of LIB will pave the way for more reliable cell functioning and recommendations to be considered to effectively analyze these off-nominal conditions. The analysis was divided into two parts; 1) curve-based analysis which included capacity fade, internal resistance, Incremental & Differential capacity analysis and EIS analysis 2) disassembly-based analysis which consisted of post-mortem visual inspection, morphology-based analysis using electron microscopy and composition analysis. From the capacity fade and IR evolution study, it was observed that periodic off-nominal conditions exhibited the highest rate of capacity fade and the greatest increase in DC internal resistance consistently. The least rate of capacity loss was shown by overcharged and no defect cells and a similar trend for DCIR values as well indicating that there was a positive correlation between capacity fade and internal resistance evolution. From the EIS study a slightly different trend was observed with the overcharged cell exhibiting the highest ohmic resistance and the no defect cell XV </p> <p>the least indicating ORI as an aging mechanism in overcharged and periodic overcharge/over-discharged cells. Another interesting observation was that the highest change in change transfer resistance was shown by over-discharged cell followed by nail-indented and overcharged cells and the least for cells subjected to periodic off-nominal conditions. This was attributed to a large amount of delamination caused by particle cracking in no defect cells causing LAM in these cells, lithium plating in Overcharged, copper current collector dissolution in over-discharged cells which resulted in LLI as the primary aging mechanism in these cells. This was further confirmed by ICA-DVA curve analysis at various capacity fades, postmortem inspection and SEM-EDS analysis. The periodic overcharged cells underwent a combination of degradation mechanisms including LAM from delamination, LLI through lithium deposition on the separators and Contact loss due to electrolyte vaporization causing active material adhesion on the separator and vice versa. The last degradation mechanism exacerbated the rate of increase of internal resistance by blocking pathways for Li+ ion diffusion. To summarize, while no defect and nail-indented cells exhibited primarily one aging mechanism (ORI) other cells exhibited a combination of degradation modes and the decoupling of these modes became increasingly indistinguishable for the cells subjected to periodic off-nominal conditions. Interestingly, no manifestation of soft or hard Internal short circuits was observed in the tested cells. However, it should be noted that for the periodic overcharged cells which underwent excessive lithium plating on the separators and charring of electrodes, dendrite formation could potentially have caused ISC upon further cycling. This cements the fact that periodic off-nominal conditions exacerbate the possibility of sudden failures and accelerate degradation in Li-ion cells. </p>

<p>Energy storage devices have become an integral part of the digital infrastructure of the 21st century. Li-ion batteries are a widely used chemical form of energy storage devices comprising components with varied chemical, mechanical and electrochemical properties. Over long-term usage, the anode and cathode experience spatially heterogeneous Li reaction, mechanical degradation, and reversible capacity loss. The small particle size and environmental sensitivity of materials used in Li-ion battery materials make investigating electrodes' electrochemical and mechanical properties an arduous task. Nevertheless, understanding the effect of electrochemical fatigue load (during the battery's charging and discharging process) on composite electrodes' mechanical stability is imperative to design and manufacture long-lasting energy storage devices.</p><p>Due to the low-symmetry lattice, Lithium Nickel Manganese Cobalt Oxide (NMC) cathode materials exhibit direction-dependent (anisotropic) mechanical properties. In this Dissertation, we first measure the anisotropic elastic stiffness of NMC cathode material using nano-indentation. We also determine the effect of Ni stoichiometry on the indentation modulus, hardness, and fracture toughness of NMC materials. The complete information on the mechanical properties of cathode materials will enable accurate computational results and the design of robust cathodes.</p><p>Further, using operando optical experiments, we report that NMC porous composite cathode experiences asynchronous reactions only during the 1st charging process. Non-uniform carbon binder network coverage across the cathode and Li concentration-dependent material properties of NMC results in the initial asynchronous phenomenon. The information on the degree of electrochemical conditioning of Li-ion battery cathode obtained from optical microscopy can test the consistency of product quality in the industrial manufacturing process. We also investigate the effects of non-uniform reactions on active material’s local morphology change and study the evolution of particle network over long-term cycling. Reported data from experiments depicts that in the early cycles, individual particles’ characteristics significantly influence the degree of damage across the cathode.</p><p>However, the interaction with neighboring particles becomes more influential in later cycles. Computational modeling uses a multiphysics-based theoretical framework to explain the interplay between electrochemical activity and mechanical damage. The methodology, theoretical framework, and experimental procedure detailed here will enable the design of efficient composite electrodes for long-lasting batteries.</p>

<p dir="ltr">Li-ion batteries are ubiquitous in today’s world with portable electronics, EVs making inroads into daily lives, and electric aircraft at the cusp of becoming reality. These and many more applications revolutionize the world with improvements in batteries at scales from materials, manufacturing, electrode architectures, cell design, and protocols. The various challenges associated with the current generation of batteries include the fast-charging capabilities, economic return of the longevity of the battery, and thermal safety characteristics. The aging and degradation of LIBs appears to be a key pain point particularly when exposed to harsh operating temperature and fast charging conditions. LIBs undergo aging due to numerous chemical and physical degradation processes throughout their lifetime owing to their operation. These challenges are exacerbated by the presence of stringent operating conditions including extreme fast charging, and sub-zero temperature resulting in severe degradation and short cycle life. The LIBs also face challenges in their thermal stability characteristics, failing catastrophically when exposed to high temperature or mechanical abuse conditions. The onset and intensity of these thermal runaway behaviors are further modified when batteries undergo varied aging leading to increased heat and gas generation potentially causing fire or explosions. Overall, a comprehensive characterization to delineate the interconnected role and implications of operating extremes and electrode design on electrochemical performance, cell aging, and thermal runaway behavior is critical for better batteries. </p><p dir="ltr">To this end, the role of electrode microstructure in mitigating lithium plating behavior under various operating conditions, including extreme fast charging has been examined. Further, these multi-length scale characteristics of the electrode microstructure are explored via data-driven approaches to study the complex interaction of transport and kinetic limitations on the microstructure designs. A third study is undertaken for in-operando characterization of the LIB degradation, probing the multi-length scale degradation using pulse voltammetry. Here an accurate degradation descriptors dataset is identified and accurately parametrized, throughout its cycling lifespan. These aging behaviors are translated to physio-chemical degradation mechanisms via a reduced-order coupled electrochemical-thermal-aging interactions model. Lastly, the implication of aging behavior on thermal-safety interactions is delineated. Overall the dissertation is focused on developing a fundamental understanding of the LIB performance, degradation, and safety interactions.</p>

Die vorliegende Arbeit konzentriert sich auf die Synthese von neuartigen hohlen MoSx-Nanomaterialien mit kontrollierbarer Größe und Form durch die kolloidale Template Methode. Ihre möglichen Anwendungen in wässrigen Energiespeichersystemen, einschließlich Superkondensatoren und Li-Ionen-Batterien (LIBs), wurden untersucht. Im ersten Teil wurde eine neue Nanostruktur aus hohlen Kohlenstoff-MoS2-Kohlenstoff-nanoplättchen erfolgreich durch eine L-Cystein unterstützte hydrothermale Methode unter Verwendung von Gibbsit als Templat und Polydopamin (PDA) als Kohlenstoffvorläufer synthetisiert. Nach dem Kalzinieren und Ätzen des Gibbsit Templates wurden gleichförmige Hohlplättchen erhalten, die aus einer sandwichartigen Anordnung von teilweise graphitischem Kohlenstoff und zweidimensional geschichteten MoS2 Flocken bestehen. Die Plättchen haben eine ausgezeichnete Dispergierbarkeit und Stabilität in Wasser sowie eine gute elektrische Leitfähigkeit aufgrund des durch die Kalzinierung von Polydopaminbeschichtungen erzeugten Kohlenstoffs gezeigt. Das Material wird dann in einem symmetrischen Superkondensator mit 1 M Li2SO4 als Elektrolyt aufgebracht, der eine spezifische Kapazität von 248 F/g (0.12 F/cm2) bei einer konstanten Stromdichte von 0.1 A/g und eine ausgezeichnete elektrochemische Stabilität über 3000 Zyklen aufweist, was darauf hindeutet, dass hohle Kohlenstoff-MoS2-Kohlenstoffnanoplättchen vielversprechende Materialien als Kandidaten für Superkondensatoren sind. Im zweiten Teil wurde 21 molare LiTFSI, das sogenannte "Wasser-in-Salz" (WIS) Elektrolyt, in Superkondensatoren mit hohlen Kohlenstoffnanoplättchen als Elektrodenmaterial untersucht. Im Vergleich zu dem im ersten Teil verwendeten 1 molaren Li2SO4-Elektrolyten wurden bei dem vorliegenden WIS Elektrolyt signifikante Verbesserungen in einem breiteren und stabilen Potentialfenster festgestellt, das durch die geringere Leitfähigkeit mit dem Gegenstück leicht beeinflusst wird. Die elektrochemische Impedanzspektroskopie (EIS) wurde ausgiebig eingesetzt, um einen Einblick in die Reaktionsmechanismen der WIS-Superkondensatoren zu erhalten. Zusätzlich wurde auch der Einfluss der Temperatur auf die elektrochemische Leistung im Temperaturbereich zwischen 15 und 55 °C untersucht, was eine hervorragende spezifische Kapazität von 128 F/g bei dem optimierten Zustand von 55 °C ergab. Die EIS-Messungen deckten die Abnahme der angepassten Widerstände mit der Temperaturerhöhung und umgekehrt auf und beleuchteten direkt die Beziehung zwischen elektrochemischer Leistung und Arbeitstemperatur von Superkondensatoren für zuverlässige praktische Anwendungen. Im dritten Teil wurde MoS3, ein amorphes, kettenförmig strukturiertes Übergangsmetall Trichalcogenid, als vielversprechende Anode in "Wasser-in-Salz" Li-Ionen-Batterien (WIS-LIBs) nachgewiesen. Die in diesem Teil verwendeten hohlen MoS3-Nanosphären wurden mittels einer skalierbaren Säurefällungsmethode bei Raumtemperatur synthetisiert, wobei sphärische Polyelektrolytbürsten (SPB) als Schablonen verwendet wurden. Beim Einsatz in WIS-LIBs mit LiMn2O4 als Kathodenmaterial erreicht das präparierte MoS3 eine hohe spezifische Kapazität von 127 mAh/g bei einer Stromdichte von 0.1 A/g und eine gute Stabilität über 1000 Zyklen sowohl in Knopf- als auch in Pouch-Zellen. Der Arbeitsmechanismus von MoS3 in WIS-LIBs wurde auch durch Ex-situ-Röntgenbeugungsmessungen (XRD) untersucht. Während des Betriebs wird MoS3 während der anfänglichen Li-Ionen-Aufnahme irreversibel in Li2MoO4 umgewandelt und dann allmählich in eine stabilere und reversible LixMoOy-Phase (2≤y≤4)) entlang der Zyklen umgewandelt. Amorphes Li-defizientes Lix-mMoOy/MoOz wird bei der Delithiierung gebildet. Die Ergebnisse der vorliegenden Studie zeigen einfache Ansätze zur Synthese hohler MoSx-Nanomaterialien mit kontrollierbarer Morphologie unter Verwendung einer Template-basierten Methode, die auf die vielversprechende Leistung von MoSx für wässrige Energiespeicheranwendungen zurückzuführen sind. Die elektrochemischen Untersuchungen von hohlen MoSx-Nanomaterialien in wässrigen Elektrolyten geben Einblick in die Reaktionsmechanismen von wässrigen Energiespeichersystemen und treiben die Entwicklung von Metallsulfiden für wässrige Energiespeicheranwendungen voran. / The present thesis focuses on the synthesis of novel hollow MoSx nanomaterials with controllable size and shape through the colloidal template method. Their possible applications in aqueous energy storage systems, including supercapacitors and Li-ion batteries (LIBs), have been studied. In the first part, hollow carbon-MoS2-carbon nanoplates have been successfully synthesized through an L-cysteine-assisted hydrothermal method by using gibbsite as the template and polydopamine (PDA) as the carbon precursor. After calcination and etching of the gibbsite template, uniform hollow platelets, which are made of a sandwich-like assembly of partial graphitic carbon and two-dimensional layered MoS2 flakes, have been obtained. The platelets have shown excellent dispersibility and stability in water, and good electrical conductivity due to carbon coating generated by the calcination of polydopamine. The material is then applied in a symmetric supercapacitor using 1 M Li2SO4 as the electrolyte, which exhibits a specific capacitance of 248 F/g (0.12 F/cm2) at a constant current density of 0.1 A/g and an excellent electrochemical stability over 3000 cycles, suggesting that hollow carbon-MoS2-carbon nanoplates are promising candidate materials for supercapacitors. In the second part, 21 m LiTFSI, so-called “water-in-salt” (WIS) electrolyte, has been studied in supercapacitors with hollow carbon nanoplates as electrode materials. In comparison with 1 M Li2SO4 electrolyte used in the first part, significant improvements on a broader and stable potential window have been revealed in the present WISE, which is slightly influenced by the lower conductivity with the counterpart. The electrochemical impedance spectroscopy (EIS) has been extensively employed to provide an insight look on the formation of solid electrolyte interphase in the WIS-supercapacitors. Additionally, the effect of temperature on the electrochemical performance has also been investigated in the temperature range between 15 and 55 °C, yielding eminent specific capacitance of 128 F/g at the optimized condition of 55 °C. The EIS measurements disclosed the decrease of fitted resistances with the increase of temperature and vise versa, directly illuminating the relationship between electrochemical output and working temperature of supercapacitors for reliable practical applications. In the third part, MoS3, an amorphous chain-like structured transitional metal trichalcogenide, has been demonstrated as a promising anode in the “water-in-salt” Li-ion batteries (WIS-LIBs). Hollow MoS3 nanospheres used in this part have been synthesized via a scalable room-temperature acid precipitation method using spherical polyelectrolyte brushes (SPB) as the template. When applied in WIS-LIBs with LiMn2O4 as the cathode material, the prepared MoS3 achieves a high specific capacity of 127 mAh/g at the current density of 0.1 A/g and good stability over 1000 cycles in both coin cells and pouch cells. The working mechanism of MoS3 in WIS-LIBs has also been studied by ex-situ X-ray diffraction (XRD) measurements. During operation, MoS3 undergoes irreversible conversion to Li2MoO4 during the initial Li ion uptake, and is then gradually converted to a more stable and reversible LixMoOy (2≤y≤4)) phase along cycling. Amorphous Li-deficient Lix-mMoOy/MoOz is formed upon delithiation. The results in the present thesis demonstrate facile approaches for synthesizing hollow MoSx nanomaterials with controllable morphologies using a template-based method, which attribute to the promising performance of MoSx for aqueous energy storage applications. The electrochemical studies of hollow MoSx nanomaterials in aqueous electrolytes provide insight into the reaction mechanisms of aqueous energy storage systems and push forward the development of metal sulfides for aqueous energy storage applications.

Die Röntgenabsorptionsspektroskopie (XAS) ist eine element-spezifische Charakterisierungs-methode, welche es erlaubt die elektronische und chemische Struktur der SEI zu untersuchen. In dieser Arbeit stelle ich ein neues Verfahren vor, das die Transmissions-XAS von Flüssigkeiten und Dünnschicht-Batterieelektroden unter in-situ Bedingungen mit weicher Röntgenstrahlung ermöglicht. Thematisch ist die Arbeit in zwei Teile gegliedert. Das neuartige Verfahren wird zunächst umfangreich vorgestellt und dann zur Untersuchung der Solid Electrolyte Interphase (SEI) auf Silizium angewendet. Das Verfahren basiert auf einer elektrochemischen Halbzelle, die mit einem Stapel aus zwei Siliziumnitrid-Membranfenster ausgestattet ist, um den Elektrolyten einzuschließen. Eines der Membranfenster ist gleichzeitig der Träger für die Dünnschicht-Siliziumanode, die Ladezyklen mit einer Kathode aus metallischem Lithium durchläuft. Nachdem sich die SEI gebildet hat, wird mittels eines Röntgenstrahls von hoher Intensität vorsätzlich eine Blase erzeugt, um überschüssigen Elektrolyten abzudrängen und einen dünnen Elektrolytfilm über der SEI zu stabilisieren. Durch den Elektrolytfilm bleibt die SEI in-situ. Das erzeugte System aus Blase, Elektrolytfilm, SEI und Siliziumanode wird dann mittels Transmissions-XAS untersucht. Im zweiten Teil meiner Arbeit werden dann Silizium Dünnschicht-Anoden mit dem vorgestellten Verfahren am Elektronenspeicherring BESSY II in Berlin untersucht. Bei der elektrochemischen Charakterisierung zeigen die Dünnschicht-anoden alle für die De-/Lithiierung von Silizium üblichen Merkmale. Als Hauptbestandteile der SEI wurden Lithiumacetat, Li Ethylendicarbonat oder -monocarbonat, Li Acetylacetonat, LiOH und LiF ermittelt. Darüber hinaus deuten Anzeichen von Aldehyden auf flüssige Einschlüsse in einer möglich-erweise porösen SEI Struktur hin. / X-ray Absorption Spectroscopy (XAS) is an element-specific technique, which allows to probe the electronic and chemical structure of the SEI. In this work, I introduce a novel approach for transmission XAS on liquids and thin-film battery electrode materials under in-situ conditions in the soft X-ray regime. Thematically, this work is divided into two parts: 1) the introduction of this novel method and 2) its application to investigate the Solid Electrolyte Interphase (SEI) on silicon thin film anodes. The presented technique is based on an electrochemical half-cell equipped with a sandwich of two silicon nitride membrane windows to encapsulate the electrolyte. One of the membranes acts as substrate for the silicon thin-film anode, which is cycled with a metallic lithium counter-electrode. After the SEI has formed, a gas bubble is intentionally introduced through radiolysis by a high intensity X-ray to push out excessive electrolyte and stabilize a thin electrolyte layer on top of the SEI, keeping it in-situ. The obtained stack comprised of bubble, electrolyte thin-layer, SEI and anode, is then probed with transmission XAS. The second part of this work utilizes the presented method to investigate the SEI on amorphous silicon anodes at the BESSY II synchrotron facility in Berlin. The anodes’ electrochemical characterization shows all significant features of silicon’s de-/lithiation. The SEI’s main components are determined as Li acetate, Li ethylene di-carbonate or Li ethylene mono-carbonate, Li acetylacetonate, LiOH, and LiF. Additionally, the evidence for aldehyde species indicates possible liquid inclusions within a presumably porous SEI morphology.

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LIBs have become an ideal choice in the EVs batteries and stationary storage applications due to their invaluable advantages. The demand for LIBs is projected to increase due to the growth in the sale of EVs. But an average lifespan of LIBs is expected to be around 8 years, thus resulting in the generation of a huge pile of spent batteries after their end of life. The disposal of spent LIBs has several environmental impacts and also results in the loss of valuable metals as a waste. So, efficient, and sustainable recycling methods should also grow at the same pace as of the EVs industries. Li is one of the vital elements for the modern energy revolution and there is a growing demand for its usage in the battery applications. High demand for Li along with supply risks due to its uneven distribution in different geographical locations will increase the Li price. Also, Li was added to the list of EUs critical materials. Currently, only 1% of Li from the end of life products is being recovered. The hydrometallurgy processes based on acid leaching followed by recovery steps are found to be efficient in the recovery of a considerable amount of Li yet there are many drawbacks. Therefore, a combined method such as a thermal treatment followed by water leaching is found to be a promising route to first selectively separate Li from the other valuable metals. The purpose of this research is to investigate the selective leaching of Li from thermally pretreated waste LIBs (by pyrolysis and incineration processes between 400 – 700 ºC for 30, 60, 90min) with water as a leaching agent at high temperature and low L/S ratio. Al salts were also leached along with Li with an efficiency not higher than 3.5%. The finding showed that the time of thermal pretreatment did not have a significant change in Li leaching efficiency. The effect of the S/L ratio showed that the leaching efficiency of Li was higher with an increase in liquid content, keeping the mass of solid constant. At a higher leaching temperature, the leaching efficiency of Li was higher due to an increase in the solubility of Li salts. The highest Li leaching efficiency of nearly 60% was observed from the sample pyrolyzed at 700 ºC for 60 min with the leaching condition S/L ratio = 1:20 g/mL, 80 ºC, 300 rpm, 3 hrs. Furthermore, the tests such as addition of 10% excess carbon during thermal treatment or use of carbonated water during leaching were carried out to enhance the leaching efficiency of Li. However, the test results did not have a significant increase in the leaching efficiency of Li. / LIB har blivit ett idealiskt val i EV-batterier och stationära lagringsapplikationer på grund av deras ovärderliga fördelar. Efterfrågan på LIB bedöms öka på grund av tillväxten i försäljningen av elbilar. Men en genomsnittlig livslängd på LIB förväntas vara cirka 8 år, vilket resulterar i att en enorm hög med förbrukade batterier genereras efter deras livslängd. Bortskaffande av förbrukade LIB har flera miljöpåverkan och resulterar också i förlust av värdefulla metaller som avfall. Så effektiva och hållbara återvinningsmetoder borde också växa i samma takt som inom elbranschen. Li är ett av de viktigaste elementen för den moderna energirevolutionen och det finns en växande efterfrågan på dess användning i batteritillämpningarna. Hög efterfrågan på Li tillsammans med utbudsrisker på grund av dess ojämna fördelning på olika geografiska platser kommer att öka Li-priset. Li läggs också till i listan över EU: s kritiska material. För närvarande återvinns endast 1% av Li från uttjänta produkter. Hydrometallurgiprocesserna baserade på syraläckning följt av återvinningssteg har visat sig vara effektiva vid utvinningen av en betydande mängd Li men det finns många nackdelar. Därför har en kombinerad metod, såsom en termisk behandling följt av vattenlakning, visat sig vara en lovande väg att först selektivt separera Li från de andra värdefulla metallerna. Syftet med denna forskning är att undersöka den selektiva urlakningen av Li från termiskt förbehandlade avfall LIB (genom pyrolys och förbränningsprocesser mellan 400 - 700 ºC under 30, 60, 90 minuter) med vatten som läckmedel vid hög temperatur och låg L / S förhållande. Al-salter lakades också ut tillsammans med Li med en verkningsgrad som inte var högre än 3,5%. Resultatet visade att tiden för termisk förbehandling inte hade någon signifikant förändring av Li-utlakningseffektiviteten. Effekten av S / L-förhållandet visade att urlakningseffektiviteten för Li var högre med en ökning av vätskeinnehållet, vilket höll massan av fast ämne konstant. Vid en högre urlakningstemperatur var urlakningseffektiviteten för Li högre på grund av en ökning av lösligheten av Li-salter. Den högsta Li-lakningseffektiviteten på nästan 60% observerades från provet pyrolyserat vid 700 ° C under 60 minuter med läckningsförhållandet S / L-förhållande = 1:20 g / ml, 80 ° C, 300 rpm, 3 timmar. Vidare utfördes testerna såsom tillsats av 10% överskott av kol under termisk behandling eller användning av kolsyrat vatten under lakning för att förbättra lakningseffektiviteten för Li. Emellertid hade testresultaten ingen signifikant ökning av utlakningseffektiviteten för Li.