Versatile Approach Combining Theoretical and Experimental, the case of of LiNi 0.5 Mn 1.5 O 4 spinel

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Solid state properties rationalization by means of ab initio calculation

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Versatile Approach Combining Theoretical and Experimental Aspects of Raman Spectroscopy ToInvestigate Battery Materials

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Rationalization of the electrochemical properties of A x Sb negative electrodes in Li/Na-ion batteries

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Influence of polymorphism on the electrochemical behavior of MxSb negative electrodes in Li/Na batteries

International audienceRecently, different and unexpected electrochemical behaviours have been demonstrated for MxSb electrodes (M = Li, Na) in Li/Na ion batteries. Despite a similar thermodynamic stability of the hexagonal and cubic polymorphs of Li3Sb, only cubic Li3Sb is observed at the end of discharge. In contrast, both cubic and hexagonal Na3Sb polymorphs may be observed albeit they exhibit very different thermodynamic stabilities. This polymorph selectivity is here investigated by means of simple thermodynamic and electrostatic considerations using first-principles Density Functional Theory (DFT) calculations. We show that the Na-based polymorphs are more ionic than their Li-based homologues, despite less ionic Na/Sb interactions. We establish a direct correlation between the relative compactness and stability of the M3Sb polymorphs to rationalize the preference of the hexagonal structure type for the most ionic compounds of the M3Sb series (M = Li, Na, K, Rb, Cs). The M-Sb interactions are further linked to the different electrochemical behaviours of the MxSb electrodes through Madelung constant calculations. This method is based on the knowledge of only one given MxSb composition and thus allows rationalizing the different intermediate compositions achieved through electrochemical cycling. To validate our method, we finally provide the first-principles computed phase stability diagrams which further reveal two new phases for both Li-Sb and Na-Sb systems

Design of Electrode Materials for Lithium-Ion Batteries: The Example of Metal-Organic Frameworks

International audienceIn the field of energy storage and Li-ion batteries, searching for new (positive) electrode materials with better electrochemical performances than those of transition-metal oxides is of permanent concern. To that aim, very simple concepts of chemical bonding can be used to find out the origin of the electrode limitations and to guide experimentalists for the design of new promising materials. This local approach was recently applied to hybrid architectures, such as metal-organic frameworks (MOFs), and allowed some of us to demonstrate the first reversible lithium insertion into the MIL53(Fe) positive electrode. In this paper, we combine firstprinciples density functional calculations and local chemical bond analyses to fully interpret the redox mechanism of this material. Its reactivity versus elemental lithium is investigated as a function of (i) the lithium composition from xLi/Fe ) 0-1, (ii) the lithium distribution over the most probable Li sites, and (iii) the OH/F substitution ratio along the redox chains. The results show that the MIL53(Fe) is a weak antiferromagnet at T ) 0 K with iron ions in the high-spin state (Fe3+, S ) 5/2). It reacts with lithium through a two-step insertion/conversion mechanism. The insertion reaction is perfectly reversible and proceeds in two steps: first, a single-phase reaction whose capacity increases linearly with the fluorine content in the starting material, then a two-phase reaction that ends around xLi/Fe ) 0.5 due to the stabilization of a localized Fe2+/Fe3+ mixed-valence state along the inorganic chains. Further lithium insertion into Li0.5MIL53(Fe) is shown to provoke an irreversible conversion reaction due to a complete loss of the local interactions between the inorganic and organic networks of the MOF architecture. On the basis of this interpretation, several alternatives to improve the capacity of these materials can be proposed by means of appropriate ligand functionalization and/or use of electrochemically active molecules within the large open space occurring in such porous materials

Unified picture of anionic redox in Li/Na-ion batteries

International audienceAnionic redox in Li-rich and Na-rich transition metal oxides (A-rich-TMOs) has emerged as a new paradigm to increase the energy density of rechargeable batteries. Ever since, numerous electrodes delivering extra anionic capacity beyond the theoretical cationic capacity have been reported. Unfortunately, most often the anionic capacity achieved in charge is partly irreversible in discharge. A unified picture of anionic redox in A-rich-TMOs is designed here to identify the electronic origin of this irreversibility and to propose new directions to improve the cycling performance of the electrodes. The electron localization function is introduced as a holistic tool to unambiguously locate the oxygen lone pairs in the structure and follow their participation in the redox activity of A-rich-TMOs. The charge-transfer gap of transition metal oxides is proposed as the pertinent observable to quantify the amount of extra capacity achievable in charge and its reversibility in discharge, irrespective of the material chemical composition. From this generalized approach, we conclude that the reversibility of the anionic capacity is limited to a critical number of O holes per oxygen, hO ≤ 1/3

An intuitive and efficient method for cell voltage prediction of lithium and sodium-ion batteries

International audienceThe voltage delivered by rechargeable Lithium- and Sodium-ion batteries is a key parameter to qualify the device as promising for future applications. Here we report a new formulation of the cell voltage in terms of chemically intuitive quantities that can be rapidly and quantitatively evaluated from the alkaliated crystal structure with no need of first-principles calculations. The model, which is here validated on a wide series of existing cathode materials, provides new insights into the physical and chemical features of a crystal structure that influence the material potential. In particular, we show that disordered materials with cationic intermixing must exhibit higher potentials than their ordered homologues. The present method is utilizable by any solid-state chemist, is fully predictive and allows rapid assessement of material potentials, thus opening new directions for the challenging project of material design in rechargeable batteries

FeII/FeIII mixed-valence state induced by Li-insertion into the metal-organic-framework Mil53(Fe): A DFT+U study

International audienceThe iron-based metal-organic-framework MIL53(Fe) has recently been tested as a cathode materials for Li-Ion batteries, leading to promising cycling life and rate capability. Despite a poor capacity of 70mAhg−1 associated with the exchange of almost 0.5Li/Fe, this result is the first evidence of a reversible lithium insertion never observed in a MOF system. In the present study, the MIL53(Fe) redox mechanism is investigated through first-principles DFT+U calculations. The results show that MIL53(Fe) is a weak antiferromagnetic charge transfer insulator at T = 0K, with iron ions in the high-spin S = 5/2 state. Its reactivity vs elemental lithium is then investigated as a function of lithium composition and distribution over the most probable Li-sites of theMOFstructure. The redox mechanism is fully interpreted as a two-step insertion/ conversion mechanism, associated with the stabilization of the Fe3+/Fe2+ mixed-valence state prior to the complete decomposition of the inorganic-organic interactions within the porousMOFarchitecture

Non linear power amplifier effects on post-OFDM waveforms

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