Mechanism of Exact Transition between Cationic and Anionic Redox Activities in Cathode Material Li2FeSiO4.

The discovery of anion redox activity is promising for boosting the capacity of lithium ion battery (LIB) cathodes. However, fundamental understanding of the mechanisms that trigger the anionic redox is still lacking. Here, using hybrid density functional study combined with experimental soft X-ray absorption spectroscopy (sXAS) measurements, we unambiguously proved that Li(2- x)FeSiO4 performs sequent cationic and anionic redox activity through delithiation. Specifically, Fe2+ is oxidized to Fe3+ during the first Li ion extraction per formula unit (f.u.), while the second Li ion extraction triggered the oxygen redox exclusively. Cationic and anionic redox result in electron and hole polaron states, respectively, explaining the poor conductivity of Li(2- x)FeSiO4 noted by previous experiments. In contrast, other cathode materials in this family exhibit diversity of the redox process. Li2MnSiO4 shows double cationic redox (Mn2+-Mn4+) during the whole delithiation, while Li2CoSiO4 shows simultaneous cationic and anionic redox. The present finding not only provides new insights into the oxygen redox activity in polyanionic compounds for rechargeable batteries but also sheds light on the future design of high-capacity rechargeable batteries

Bulk-Sensitive Soft X-ray Edge Probing for Elucidation of Charge Compensation in Battery Electrodes

To this day, elucidating the charge transfer process in electrode materials upon electrochemical cycling remains a challenge, primarily due to the complexity of chemical reactions at the electrode surfaces. Here, we present an elegant and reliable method to probe bulk-sensitive soft edges for elucidating anodic and cathodic charge compensation contribution via X-ray Raman scattering spectroscopy. By using a hard X-ray incident beam, this technique circumvents surface limitations and is practically free of self-absorption due to its nonresonant nature. In addition, it does not require complex sample preparation or experimental setups, making it an ideal tool for potential in situ analysis of the electronic structure of electrode materials. In this study, we monitored, for the first time, bulk soft edges of both oxygen and transition metal (iron) of the cathode material $Li_2FeSiO_4$ during one complete electrochemical cycle concurrently. Our results reveal that the redox mechanism relies primarily on the iron (cathodic) contribution. Nevertheless, a change in electron confinement of the oxygen suggests its active involvement in the charge compensation process (anodic). Moreover, we were able to support the experimentally observed changes in the electronic structure with ab initio-based simulation

Compositional and Structural Aspects of Li-rich Anti-perovskites as Li-ion Battery Cathodes

Alkali-metal ion battery cathode is the part which mostly defines its specific characteristics, thus, studies in this field are always important, to make the batteries fulfill the needs of the rapidly accelerating progress and growing market. Current dissertation represents a comprehensive physicochemical study of novel inorganic compounds with general formula of Li2MChO (M – Mn, Fe, Co; Ch– S, Se) and Pm-3m anti-perovskite structure. One of their key properties is the electrochemical activity, and rather high specific capacity, explained by a high amount of lithium which can be reversibly extracted per formula unit. Although the practical application of these materials as Li-ion battery cathodes is limited due to relatively low operation voltage and high requirements to synthetic conditions, outstanding chemical flexibility of the crystal structure turns the cubic anti-perovskites into excelsior model for studying the synergetic effects of various transition metal cations on the structural stability against lithium removal, as well as on the mechanism of charge compensation. The named investigations are mostly based on operando methods, using synchrotron radiation facilities, and the electrochemical activity of anti-perovskites provides an opportunity to conduct such experiments: while lithium is removed or inserted into the crystal lattice, the electrochemical cell is irradiated, allowing to observe the changes constantly. Such studies may bring use for the battery research in general and give certain hints for creation of new battery materials, in particular, high-entropy ones (if two transition metal cations, or two chalcogenide anions are combined in Li2MChO formula, the compound formally becomes a high-entropy one). Besides, an attempt to extend the research topic was done, introducing the double anti-Ruddlesden-Popper phases (double anti-perovskites). Their structure is layered, which is favorable for the reversible electrochemical alkali-metal, which is in this specific case sodium, extraction, however, as their cationic and anionic sublattices are formed by the same transition metal cations and by the same anions, as in cubic anti-perovskites, they suffer from the same issue of low operation voltage. Nevertheless, from this type of structure it is also possible to expect chemical flexibility, which makes them model compounds as well, but for investigations on layered cathode materials, which are rather common nowadays: one of the most typical examples of those is NMC, which is commercialized, but still has much of unrealized potential. In the end, this dissertation is considered by its author as primarily fundamental research, which is supposed to expand the knowledge in the field of physical chemistry of novel battery compounds, and to give certain keys for their development

Synthesis, Structure and Electrochemistry of Positive Electrode Materials for Rechargeable Magnesium and Lithium Ion Batteries: Mechanistic Investigations

To meet the requirements for high energy density storage systems, rechargeable batteries based on the “beyond lithium ion” technologies have been widely investigated. The magnesium battery is a promising candidate benefiting from the utilization of a Mg metal negative electrode, which offers high volumetric capacity (3833 mAh mL-1), low redox potential (-2.37 V vs. S.H.E.), non-dendritic growth, low price and safe handling in atmosphere. However, the discovery of potential positive electrode materials beyond the seminal Mo6S8 has been limited, mainly due to the sluggish mobility of a divalent Mg2+ ion in solid frameworks. This thesis presents the research on both finding new positive electrode materials and investigating mechanisms to understand the limitation. Two structures of titanium sulfide are identified as the second family of Mg2+ insertion positive electrodes, offering almost twice the capacity of the benchmark Mo6S8. The facile Mg2+ solid diffusion is mainly supported by the polarizable lattices, while the crystal structure plays a critical rule on the specific diffusion mechanism, which further influences the electrochemistry. While sulfides provide moderate energy density, it can be largely increased by shifting to oxide materials. However, poor electrochemistry has been widely observed for oxide based Mg positive electrode materials. In the present thesis work, a case study with birnessite MnO2 identifies desolvation as a key factor limiting Mg2+ insertion into oxides from nonaqueous electrolytes, while another study with Mg2Mo3O8 demonstrates the strong influence of transition states on setting the magnitude of migration barriers. Those limitations have to be overcome to allow facile Mg2+ insertion into oxides. Alternative setups which would accomplish the advantages of a Mg negative electrode and avoid the sluggish Mg2+ solid diffusion include the Mg-Li hybrid system. Two “high voltage” Prussian blue analogues (average 2.3 V vs. Mg/Mg2+) are investigated as positive electrode materials in the thesis, both showing promising energy density and cycle life. Finally, novel positive electrode materials for Li-ion batteries are examined. The possibility of stabilizing lithium transition-metal silicate in the olivine structure is studied by combined atomistic scale simulation and solid state synthesis, suggesting a potential solution by cation substitution

New polyanion-based cathode materials for alkali-ion batteries

A number of new materials have been discovered through exploratory synthesis with the aim to be studied as the positive electrode (cathode) in Li-ion and Na-ion batteries. The focus has been set on the ease of synthesis, cost and availability of active ingredients in the battery, and decent cycle-life performance through a combination of iron and several polyanionic ligands. An emphasis has been placed also on phosphite (HPO32-) as a polyanionic ligand, mainly due to the fact that it has not been studied seriously before as a polyanion for cathode materials. The concept of mixed polyanions, for example, boro-phosphate and phosphate-nitrates were also explored. In each case the material was first made and purified via different synthetic strategies, and the crystal structure, which dominantly controls the performance of the materials, has been extensively studied through Single-Crystal X-ray Diffraction (SCXRD) or synchrotron-based Powder X-ray Diffraction (PXRD). This investigation yielded four new compositions, namely Li3Fe2(HPO3)3Cl, LiFe(HPO3)2, Li0.8Fe(H2O)2B[P2O8]·H2O and AFePO4NO3 (A = NH4/Li, K). Furthermore, for each material the electrochemical performance for insertion of Li+ ion has been studied by means of various electrochemical techniques to reveal the nature of alkali ion insertion. In addition Na-ion intercalation has been studied for boro-phosphate and AFePO4NO3. Additionally a novel synthesis procedure has been reported for tavorite LiFePO4F1-x(OH)x, where 0≤ x ≤1, an important class of cathode materials. The results obtained clearly demonstrate the importance of crystal structure on the cathode performance through structural and compositional effects. Moreover these findings may contribute to the energy storage community by providing insight into the solid-state science of electrode material synthesis and proposing new alternative compositions based on sustainable materials --Abstract, page iv

Design and synthesis of new insertion electrode materials for Li-ion and Na-ion batteries identified via the Bond Valence Energy Landscape approach.

365 p.Las baterías se consideran un elemento clave para la descarbonización de nuestra sociedad. Las baterías de litio-ion dominan actualmente el mercado de los dispositivos portátiles y de los vehículos híbridos y eléctricos gracias a su ligereza y a su extraordinaria densidad y rendimiento energéticos. Sin embargo, la creciente demanda de litio y el inestable contexto mundial hacen que aumente la preocupación por su disponibilidad y precio, por lo que las baterías de sodio-ion han generado mucho interés en los últimos años. La abundancia y el bajo coste del sodio lo convierten en una atractiva alternativa al litio. Además, aparte de su gran abundancia, el sodio está bien distribuido por toda la Tierra, lo que reduce considerablemente el impacto económico y geopolítico. El material del cátodo es el componente clave de la batería, ya que es el que más influye en el rendimiento final de la misma y en su coste. El material catódico seleccionado debe proporcionar una rápida inserción/extracción del catión móvil y una capacidad reversible estable. Además, el material de cátodo ideal debería poseer una alta capacidad específica y ofrecer un alto potencial. Se han desarrollado continuamente un gran número de químicas diferentes con numerosos análogos que pueden aplicarse con éxito tanto a las baterías de iones de litio como a las de iones de sodio. Sin embargo, el aumento constante de la demanda de mayor rendimiento y sostenibilidad exige el desarrollo de nuevos materiales mejorados.El objetivo de esta tesis es identificar nuevos materiales catódicos que puedan ser utilizados en baterías recargables de Li-ion y Na-ion. El reto es encontrar nuevos compuestos que puedan mejorar tanto la capacidad específica como el voltaje. Por ello, esta tesis responde a las necesidades actuales de desarrollo de materiales avanzados para baterías. En la búsqueda de nuevos materiales para electrodos pueden aplicarse dos enfoques diferentes. El primero es el diseño de nuevos materiales no reportados, y el segundo implica la revisión de estructuras ya conocidas con características compositivas y estructurales atractivas (o que requieran pequeñas modificaciones compositivas) necesarias para materiales de electrodos cuyo rendimiento electroquímico aún no ha sido evaluado. En nuestro trabajo, decidimos aplicar el segundo enfoque. El diseño de los nuevos materiales catódicos se basa en la modelización computacional y la metodología experimental

Surface Modification of Nickel-Rich Layered Cathode by Perovskite Oxides towards Enhanced Electrochemical Performance

Cathode is the key component in lithium-ion batteries (LIBs) and it determines the performance of LIBs to a large extent. Recently, layered-structure Ni-rich cathode has attracted concentrated research attention due to its high theoretical capacity and energy density, which showed great potential as an alternative for the current dominant LiCoO2 in the energy market. Intrinsically, the high Ni content led to an excellent discharge capacity; however, the high reactivity of Ni also caused an capacity fading resulting from the undesired side reactions during prolonged cycling. Therefore, a trade-off between high capacity and long cycle life obstruction of the commercializing process of Ni-rich cathode in modern LIBs. In this case, this work attempt to employing surface modification strategy to stabilize the cyclability of Ni-rich cathodes by perovskite oxides. Because they provide a variety of outstanding physical and chemical properties. Most importantly, several materials, including metal oxide, fluoride, phosphate, etc. have been investigated as surface coating layer for the electrochemical property enhancement; however, perovskite oxide is still rarely mentioned. THus, this work firstly used a typical perovskite oxide, strontium titanate (STO) and its diverse modified forms, as surface modifier coated onto Ni-rich cathodes, respectively. In detail, chapter 4 demonstrates that the STO surface coating on NCM811 could effectively enhance its cycling stability. The effect of the heat treatment after perovskite oxide surface coating is studied and disclosed in chapter 5. In chapter 6, NCA is covered by STO with the defect-rich surface, exhibiting a better rate performance due to the higher electronic and ionic conductivity possessed by the coating layer. At last, as-prepared Nb-doped STO onto NCM811 could act as a buffer layer to suppress the dissolution of transition metal ions resulting from the electrolyte decomposed HF attacking and robust the Li diffusion channel during the charge-discharge process. The current study offers a systematically understanding of the positive effect of perovskite oxide materials-based surface modification on Ni-rich cathodes. It confirms the feasibility of improving the electrochemical performances of Ni-rich oxides by preventing the deleterious side reactions accompanied by reducing Li residues on the cathode surface, which is of great significance to the optimization of the cathode material for next-generation LIB for electric vehicles

Management and Applications of Energy Storage Devices

This book reviews recent trends, developments, and technologies of energy storage devices and their applications. It describes the electrical equivalent circuit model of batteries, the technology of battery energy storage systems in rooftop solar-photovoltaic (PV) systems, and the implementation of second-life batteries in hybrid electric vehicles. It also considers a novel energy management control strategy for PV batteries operating in DC microgrids, along with the present state and opportunities of solid-state batteries. In addition, the book examines the technology of thin-film energy storage devices based on physical vapor deposition as well as the challenges of ionic polymer-metal composite membranes. Furthermore, due to the novel battery technology in energy storage devices, this book covers the structural, optical, and related electrical studies of polyacrylonitrile (PAN) bearing in mind the applications of gel polymer electrolytes in solid-state batteries. Since energy storage plays a vital role in renewable energy systems, another salient part of this book is the research on phase change materials for maximum solar energy utilization and improvement. This volume is a useful reference for readers who wish to familiarize themselves with the newest advancements in energy storage systems

Pushing the boundaries of lithium battery research with atomistic modelling on different scales

Computational modelling is a vital tool in the research of batteries and their component materials. Atomistic models are key to building truly physics-based models of batteries and form the foundation of the multiscale modelling chain, leading to more robust and predictive models. These models can be applied to fundamental research questions with high predictive accuracy. For example, they can be used to predict new behaviour not currently accessible by experiment, for reasons of cost, safety, or throughput. Atomistic models are useful for quantifying and evaluating trends in experimental data, explaining structure-property relationships, and informing materials design strategies and libraries. In this review, we showcase the most prominent atomistic modelling methods and their application to electrode materials, liquid and solid electrolyte materials, and their interfaces, highlighting the diverse range of battery properties that can be investigated. Furthermore, we link atomistic modelling to experimental data and higher scale models such as continuum and control models. We also provide a critical discussion on the outlook of these materials and the main challenges for future battery research

The Fifteenth Annual Conference YUCOMAT 2013: Programme and the Book of Abstracts

The First Conference on materials science and engineering, including physics, physical chemistry, condensed matter chemistry, and technology in general, was held in September 1995, in Herceg Novi. An initiative to establish Yugoslav Materials Research Society was born at the conference and, similar to other MR societies in the world, the programme was made and objectives determined. The Yugoslav Materials Research Society (Yu-MRS), a nongovernment and non-profit scientific association, was founded in 1997 to promote multidisciplinary goal-oriented research in materials science and engineering. The main task and objective of the Society has been to encourage creativity in materials research and engineering to reach a harmonic coordination between achievements in this field in our country and analogous activities in the world with an aim to include our country into global international projects. Until 2003, Conferences were held every second year and then they grew into Annual Conferences that were traditionally held in Herceg Novi in September of every year. In 2007 Yu-MRS formed two new MRS: MRS-Serbia (official successor of Yu-MRS) and MRS-Montenegro (in founding). In 2008, MRS – Serbia became a member of FEMS (Federation of European Materials Societies)