Polymer Gel Electrolyte Prepared by “Salting-In” Poly(ethylene glycol) into a Phosphonium-Based Ionic Liquid with a Lithium Salt

Abstract

We report the synthesis of an ion gel electrolyte based on a tetra-arm poly(ethylene glycol) (TetraPEG) network in a phosphonium-based ionic liquid (IL) solution utilizing the "salting-in" effect with a Li salt. Poly(ethylene glycol) (PEG) chains are insoluble in phosphonium-based ILs (such as triethylpentylphosphonium bis(trifluoromethanesulfonyl)amide, [P 2225 ][TFSA]); however, the addition of LiTFSA enabled complete solvation of TetraPEG into a [P 2225 ][TFSA] solution. The Li salt and polymer concentration dependences for PEG solubility in a [P 2225 ][TFSA] system were investigated, and the optimum concentrations for polymer gel electrolyte preparation were elucidated. The gelation reaction (Michael addition between tetra-maleimide-terminated and tetra-thiol-terminated PEGs) of TetraPEG prepolymers in LiTFSA/[P 2225 ][TFSA] solutions was characterized via chemical reaction kinetics to determine the apparent gelation rate constant (k gel ′), and the reaction efficiency (p) was estimated to be p ∼ 95% at the end of the reaction. The resulting nearly defect-free TetraPEG gel electrolyte polymer network showed high ionic conductivity, comparable to the corresponding solution electrolyte. The TetraPEG gel electrolyte containing LiTFSA/[P 2225 ][TFSA] also possessed a wide electrochemical window (∼4.2 V vs Li/Li + ), thus allowing the reversible Li deposition/dissolution reaction to be performed using typical metal negative electrodes.

Ionic Liquid-Based Gels for Applications in Electrochemical Energy Storage and Conversion Devices: A Review of Recent Progress and Future Prospects

“…In the same year, Singh et al [ 53 ] tested IL-GPE P(VDF-HFP)/PYR 13 FSI/LiTFSI on a LiNi 0.33 Mn 0.33 Co 0.33 O 2 (LNMC) coated Li 2 CuO 2 cathode to study the structural and cyclical stability of the cathode and found a twofold increase in its ionic conductivity compared to Yang et al [ 49 ]. Another report submitted in 2020 by Matsuura et al [ 85 ] shows the synthesis of tetra-arm poly(ethylene glycol) (TetraPEG) in triethylpentylphosphonium (P 225 ) with Li-TFSI salt solution with an increased electrochemical window up to 4.2 V with 95% efficiency.…”

Polyether-based solid electrolytes with a homogeneous polymer network: effect of the salt concentration on the Li-ion coordination structure

“…[24][25][26][27][28] The resulting TetraPEG gels exhibit high mechanical strength even at low polymer concentrations (o5 wt%) and can be used to realize Li-ion battery gel electrolytes with a high ionic conductivity comparable to that of liquid electrolytes. [28][29][30][31] Recently, Tosa et al reported a solid polymer electrolyte based on a homogeneous TetraPEG network and Li salt, which they synthesized via a Michael addition reaction between TetraPEG-MA and TetraPEG-NH 2 prepolymers in organic electrolyte solutions at high temperature (333 K). 32 They investigated the effect of the network structure on the mechanical and electrochemical properties by controlling the network homogeneity in the solid TetraPEG electrolyte at a fixed ratio of Li salt-to-ether oxygen (Li/O PEG ) of 1 : 10.…”

Enhanced crystallization of poly(lactic acid) bioplastics by a green and facile approach using liquid poly(ethylene glycol)

“…The increase in the viscosity of PEG may covert the samples with high PEG composition to exhibit the gel‐like behaviors. The PEG “gels” have various energy storage and biomedical applications, including battery electrolytes, phase change materials, drug delivery systems, controlled release matrices, and regenerative medicine scaffolds 37–40 . Our prepared green composite materials with high PEG composition may also be used in the applications mentioned above.…”