Solvate Structures and Computational/Spectroscopic Characterization of LiClO₄ Electrolytes

Abstract

A Raman spectral evaluation of numerous crystalline solvates with lithium perchlorate (LiClO4) has been conducted over a wide temperature range. Two new solvate crystal structures(PMDETA)1:LiClO4 and (THF)1:LiClO4 with N,N,N′,N″,N″-pentamethyldiethylenetriamine and tetrahydrofuranhave been determined to aid in this study. With a help of density functional theory (DFT) and molecular dynamics (MD) simulations, the spectroscopic data have been correlated with varying modes of ClO4 –···Li+ cation coordination within the solvate structures to create a characterization tool to facilitate the Raman band assignments for the determination of ionic association interactions within solid and liquid electrolytes containing LiClO4. This study demonstrates that many of the spectroscopic evaluation conclusions reported in the scientific literature for LiClO4-based electrolytes are inaccurate.

Solvate Structures and Computational/Spectroscopic Characterization of LiCF3SO3 Electrolytes

“…The present study continues the exploration of these factorsas has been done for other lithium salts including LiPF 6 , LiTFSI (i.e., lithium bis­(trifluoromethanesulfonyl)­imide: LiN­(SO 2 CF 3 ) 2 ), LiClO 4 , − LiBF 4 , and LiDFOB (i.e., lithium difluoro­(oxalato)­borate: LiBF 2 (C 2 O 4 ))with a present focus on lithium trifluoromethanesulfonate or “triflate” (i.e., LiCF 3 SO 3 ). This latter salt is generally not used in commercial secondary Li-ion batteries, but it has been and continues to be widely used for fundamental evaluations of liquid and polymer electrolytes, including for Li-ion, Li-O 2 , and Li–S batteries; dye-sensitized solar cells; light-emitting electrochemical cells; and other applications.…”

“…This does not exclude such coordination from occurring in liquid electrolytes, but this suggests that monodentate coordination predominates. This is in accordance with the results for other lithium salts such as LiPF 6 , LiClO 4 , and LiBF 4 . ,, …”

“…This is likely attributable, at least in part, to solid-state packing effects with neighboring solvent molecules. Similar results were noted for LiClO 4 solvates …”

“…This is in accordance with the results for other lithium salts such as LiPF 6 , LiClO 4 , and LiBF 4 . 1,5,6 3.2. Raman Spectroscopic Analysis of Crystalline Solvates.…”

“…Similar results were noted for LiClO 4 solvates. 5 T h e t w o k n o w n C I P -I c r y s t a l l i n e s o l v a t e -s�(PHEN) 2 :LiCF 3 SO 3 and (G3) 1 :LiCF 3 SO 3 �have a Raman band at low temperatures at 755 and 760 cm −1 , respectively (Figure S8). The speculative (G1) 2 :LiCF 3 SO 3 solvate has a band at 759 cm −1 (at −20°C) (Figure 4).…”