A series of well-defined cationic hepta-coordinate bismuth halides [BiX2(py)5][B(3,5-(CF3)2-C6H3)4] (X = Cl, Br, I), stabilized only by substitutionally labile solvent molecules, were synthesized and fully characterized. Their apparent D5h symmetry...
In recent years, the interest in the development of highly concentrated electrolyte solutions for battery applications has increased enormously. Such electrolyte solutions are typically characterized by a low flammability, a high thermal and electrochemical stability and by the formation of a stable solid electrolyte interphase (SEI) in contact to electrode materials. However, the classification of concentrated electrolyte solutions in terms of the classical scheme “strong” or “weak” has been controversially discussed in the literature. In this paper, a comprehensive theoretical framework is presented for a more general classification, which is based on a comparison of charge transport and mass transport. By combining the Onsager transport formalism with linear response theory, center‐of‐mass fluctuations and collective translational dipole fluctuations of the ions in equilibrium are related to transport properties in a lithium‐ion battery cell, namely mass transport, charge transport and Li+ transport under anion‐blocking conditions. The relevance of the classification approach is substantiated by showing that i) it is straightforward to classify highly concentrated electrolytes and that ii) both fast charge transport and fast mass transport are indispensable for achieving fast Li+ transport under anion‐blocking conditions.
The conventional classification of electrolyte solutions as “strong” or “weak” accounts for their charge transport properties, but neglects their mass transport properties, and is not readily applicable to highly concentrated solutions. Here, we use the Onsager transport formalism in combination with linear response theory to attain a more general classification taking into account both charge and mass transport properties. To this end, we define a molar mass transport coefficient , which is related to equilibrium center‐of‐mass fluctuations of the mobile ions and which is the mass‐transport analogue of the molar ionic conductivity . Three classes of electrolyte solution are then distinguished: (i) “Strong electrolytes” with ; (ii) “weak charge transport electrolytes” with ; and (iii) “weak mass transport electrolytes” with . While classes (i) and (ii) encompass the classical “strong” and “weak” electrolytes, respectively, many highly concentrated electrolytes fall into class (iii) and thus exhibit transport properties clearly distinct from classical strong and weak electrolytes.
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