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  • The performance of the qCPA approaches is similar

    2020-02-13

    The performance of the qCPA approaches is similar with regards to the derivative properties of CO2 and for mixtures of CO2+self-associating compounds. For CO2+n-alkanes the four-parameter versions of qCPA both perform somewhat better than the three-parameter version. Nevertheless this modest improvement may not justify the increased model flexibility and uncertainty in the parameter estimation. Unless the primary focus is binary CO2+n-alkane mixtures the most promising approach is thus considered to be qCPA with three adjustable parameters.
    Acknowledgements The authors gratefully acknowledge the Danish Research Council for Independent Research for funding this work as part of the project; ‘CO2 Hydrates – Challenges and Possibilities’.
    Introduction Lithium-ion battery materials are still considered to be the most promising Edaravone converter/charger due to their excellent electrochemical parameters, and their industrial applications especially for power electronic devices are extremely important [1,2,3,4,5]. Moreover, outstanding commercial success of Li-ion cathode materials based on lithium cobaltate (LiCoO2) caused that they became materials for personal use, which in turn demands more efficient functional parameters such as high energy density, long life-cycle, light-weight and safety. In recent years, in order to have a deeper insight into electrochemical properties of Li-ion battery cathode materials, theoretical investigations based on DFT electronic band structure calculations have been undertaken in systematic way [6,7,8,9,10,11]. For instance, the impact of electronic structure features on the discharge curve in the series of compounds as AMO2 (A = Li, Na; M = Mn, Co, Ni, Fe) and their solid solutions, have been recently notified based on detailed experimental and theoretical investigations [11,13,14]. Also, the step-like vs. continuous-like character of the discharge curve have been interpreted in terms of correlations between electronic structure and electrochemical properties in selected Li- and Na-ion cathode materials, respectively. Quite recently, it was found that substitution of Ni by lower cost and more accessible elements such as Co and Mn in LiNiCoMnO2 cathode material, improved its electrochemical properties, namely crystal stability, initial capacity and life cycle [15,16,17,18]. The fact that experimentally investigated Li-ion battery materials commonly contain 3d transition metal elements (M = Mn, Fe, Co, Ni) directs attention to their possible magnetic properties. More precisely one can ask about local magnetic moments appearance in such materials and how magnetism can be affected when Li concentration changes. The aim of this work is to show the evolution of total-, site-decomposed and l-decomposed density of states (DOS) in the whole range of Li concentration, starting our analysis from the reference LiCoO2, next considering electronic and magnetic properties of 3d dopants (Mn and Ni) and then ending with highly disordered Li(Co-Ni-Mn)O cathode material. We show that electronic structure features and resulting magnetic properties strongly depend on the chemical composition of the considered system. The enlightening of spin-polarised electronic structure behaviours, especially in the vicinity of the Fermi level, seems to be important to better understand the mechanisms responsible for electrochemical properties, if these systems exhibit magnetic order near battery operating temperature.
    Computational details The layered LiMO2 with M = Co and Ni were reported to crystallize in the rhombohedral unit cell (α-NaFeO2-type, space group ) [19], whereas the crystal structure of LiMnO2 was found to belong to orthorhombic (space group Pnma). In this work, we restrict our discussion to the rhombohedral structure only, and experimental lattice constants as well as atomic positions have been used to calculate electronic structure of ordered LiMO2 compounds. In the case of disordered Li(Co-Ni-Mn)O2 alloys, recently refined crystal data in two compositions LiNi0.65Co0.25Mn0.1O2 and LiNi0.55Co0.35Mn0.1O2 were employed [11] in KKR-CPA computations.