Università degli studi di Modena e Reggio Emilia

Silicon anodes typically suffer from poor intrinsic conductivity and dramatic volume change during charge/discharge cycles, which hinders their commercialization in high energy density lithium-ion batteries (LiBs). This issue can be alleviated by embedding particles of the active material in an adhesive matrix, such as a polymer binder, that can accommodate large volume changes during lithiation and delithiation. Several research efforts have aimed at enhancing the adhesive, elastic, electrical, and ionic properties of binders for use in silicon anodes. Therefore, stable silicon/polymer interfaces are crucial for the performance of high capacity silicon-based LiBs. In this research, we focused on the definition of the mechanisms that determine the adhesion properties of a couple of recently proposed self-healing polymers, on Si-surfaces. The structural and electronic properties as well as the energetics of boronic acid-doped polyaniline and polyvinyl alcohol monomers absorbed on Si (110) and Si (111) surfaces have been investigated through first-principles calculations based on the density functional theory. We showed that the coabsorption of these two monomers increases the absorption energy and in general improves the adhesion properties of both polymers on both Si-surfaces, especially on the Si (111) facet.

Pyrrolidinium-based (Pyr) ionic liquids (ILs) have been proposed as electrolyte components in lithium-ion batteries (LiBs), mainly due to their higher electrochemical stability and wider electrochemical window. Since they are not naturally electroactive, in order to allow their use in LiBs, it is necessary to mix the ionic liquids with lithium salts (Li). Li-PF6, Li-BF4, and Li-TFSI are among the lithium salts more frequently used in LiBs, and each anion, namely PF6 (hexafluorophosphate), BF4 (tetrafluoroborate), and TFSI (bis(trifluoromethanesulfonyl)azanide), has its own solvation characteristics and interaction profile with the pyrrolidinium ions. The size of Pyr cations, the anion size and symmetry, and cation-anion combinations influence the Li-ion solvation properties. In this work, we used molecular dynamics calculations to achieve a comprehensive view of the role of each cation-anion combination and of different fractions of lithium in the solutions to assess their relative advantage for Li-ion battery applications, by comparing the solvation and structural properties of the systems. This is the most-comprehensive work so far to consider pyrrolidinium-based ILs with different anions and different amounts of Li: from it, we can systematically determine the role of each constituent and its concentration on the structural and dynamic properties of the electrolyte solutions.