Polysiloxane‐based Electrolytes: Influence of Salt Type and Polymer Chain Length on the Physical and Electrochemical Properties

Abstract

An oligo/poly(methyl(2‐(tris(2‐H methoxyethoxy)silyl)ethyl)siloxane)), 390EO, and 2550EO, were synthesized. Dilute electrolyte solutions of 390EO and 2550EO were prepared using LiTFSI, LiFSI, and LiPF6. The influence of the length of the siloxane polymer chain, salt type, and Si‐tripodand centers at the side chain on ionic conductivity, tLi+, and physical properties were examined. Both electrolyte systems showed high values of tLi+ (0.35 for 2550EO/LiTFSI and 0.64 for 390EO/LiTFSI). Alternatively 390EO/LiPF6 and 2550EO/LiPF6 displayed high tLi+ values of 0.61 and 0.44, respectively, while 390EO/LiFSI displayed the smallest tLi+ (0.25). To clarify the role played by the Li+ environment in Li+ transport, the solvation states of electrolytes were examined. It was observed that anion solvation can be achieved using siloxane‐based solvent in all systems. Walden plot analysis demonstrates that ionic diffusion was not controlled by either macroviscosity/microviscosity in the siloxane‐based polymer electrolytes. Ions instead move along a relatively smooth ion‐pathway without complete full segmental reorientation in 2550EO as a result of decoupling and high ion solvation behavior. Conversely, in 390EO, ions might move to available sites by a jumping after decoupling with low ion solvation behavior. Consequently, a high t Li+ was achieved, and the oxidative stability of the salt was ensured.

Salt-Concentrated Siloxane-Based Electrolytes for Lithium Metal Batteries: Physical Properties, Electrochemical Properties, and Cell Performance

“…This increase is only two times larger when the salt concentration is increased from 20/1 to 10/1; however, it is almost five times larger when it is increased from 10/1 to 5/1 and almost nine times larger when it is increased from 5/1 to 2.5/1. However, all electrolyte systems showed a slight increase in T g compared to the neat polymer of 390EO . Moreover, the electrolyte systems have almost the same T g value at ∼ −25 °C (starting point, Supporting Information, Figure S1b) (Table ).…”

“…Recently, a siloxane-based oligomer (390EO) grafted with Si-tripodant centers was verified through chemical synthesis, electrochemical, and physical property characterization . The reported results are highly significant in showing that LiTFSI does not cause Al current collector corrosion when used with polysiloxane solvents .…”

“…The mixtures were stirred at 50 °C, and all steps were conducted in an inert atmosphere. The structural characterization of the 390EO was confirmed using Fourier transform infrared spectroscopy (FTIR) and 1 H and 29 Si nuclear magnetic resonance (NMR), and the positional relationships between protons and silicon atoms were confirmed using 2D NMR ( 1 H– 1 H COSY and 1 H– 29 Si HMBC) …”

“…Conductivity, viscosity, and transference number measurements were conducted several times and their average values were determined. The data of conductivity, viscosity, and transference number related to 20/1 (390EO/LiTFSI; EO/Li = 20/1) have been previously published …”

“…In addition, superior conductivities of liquid electrolytes can be achieved in a single system using low viscosity and nonflammable siloxane-based salt-concentrated electrolyte systems. In contrast, organosiloxane polymers are durable under overcharge and high-voltage conditions; , moreover, they can be nonflammable, even under harsh and extreme conditions, , owing to their high antioxidative ability, ,, excellent thermal resistance, , and facile chemical modifications. − Furthermore, organosiloxane polymers are compatible with lithium metal anodes, , with a passive film formation ability at the electrode–electrolyte interface. , The individual structure of the macromolecular organosilicon member, double-decker silsesquioxane (DDSQ), was first used as a proton conducting member for fuel cells in 2011 and, until recently, organosilicon materials have not received significant research attention. In the last five years, polysiloxanes have become increasingly popular in various battery technologies by being used as a single-ion conducting polymer electrolyte , or a coating material for Li metal, and even as a scaffold for LIB ionic liquids .…”