Effect of monomer composition on the formation of hybrid polymer-liquid electrolytes for lithium-ion batteries

Abstract

The electrolyte plays a key role in the performance of novel lithium-ion battery concepts. Hybrid polymer-liquid electrolytes (HEs) are suitable candidates for novel concepts of lithium-ion batteries (LIBs) and lithium-metal batteries (LMBs), where high ionic conductivity coupled with mechanical integrity are required at the same time. HEs are produced through polymerization-induced phase separation (PIPS) of a monomer/electrolyte mixture which allows for the formation of a two-phase system where the domains create a bicontinuous structure. Electrochemical performance and thermomechanical behavior can be tailored through several variables e.g., monomer and solvent chemistries, solvent concentration, and curing conditions. The present study is focused on the chemical structure of the monomer where methacrylate and acrylate monomers are compared as homopolymers or copolymers in HEs. The number of ethylene oxide (EO) units in the backbone of the monomers are furthermore analyzed as a structural parameter. The results show that the monomer structure not only affects the electrochemical and thermomechanical properties, but also defines the morphology of the HEs obtained, which can be in the form of a bicontinuous structure, a gel, or a mixture of the two, according to the kinetic and thermodynamic variables affecting the phase separation and the ultimate T_g of the polymer.