Electrostatically driven self-assembly of charged block-copolymers:

stabilization and ion dynamics

Chang Yun Son

Pohang University of Science and Technology

Abstract

High concentration liquid electrolytes, such as water-in-salt electrolytes and ionic liquids, as well as solid state polymer electrolytes are rapidly emerging materials to replace the flammable organic electrolytes widely used in industrial lithium ion batteries. Molecular dynamics (MD) simulation of these systems is challenging due to a number of reasons, including lack of predictive force fields, complex polarization effects occurring both in electrolytes and on electrodes, highly correlated ion motion due to high concentration and strong electrostatic interactions, to name a few.

In this talk, I’ll present our ongoing efforts to enable predictive molecular simulations of these highly charged interfacial systems. Two major advances will be highlighted – the development of predictive multi-scale force field for ILs and polymers based entirely on first-principle calculations, and the development of simulation algorithms to treat surface polarization and proper thermal equilibrium in polarizable MD simulations. New physical insights gained from the new simulation model and simulation algorithms will be discussed, which are successfully applied to design novel polymer electrolytes with unique phase behavior and ionic conduction suitable to energy applications.

Another important study investigates polymer electrolytes (PE) with high ion conduction and mechanical stability for energy applications. PEs with network morphologies can show high ion conductivity but the development of stable network morphologies in charged block-copolymer system has been limited due to the narrow stability window. We present a molecular dynamics (MD) simulation study of an acid-tethered block-copolymer system comprising ionic liquid, which was shown to offer high ion conductivity and interesting morphological transition including the low-symmetry A15 phase. Simulations revealed strong conformational anisotropy between the double-shell forming randomly acid-tethered block and the neutral core block, which stabilized the low symmetry A15 structure. Analyzing ion dynamics based on the proximity to the polymers (bulk, interface) revealed the diffusion of bulk area ion is much faster than the diffusion of interfacial area. This quantitative result shows the controlling electrostatic interaction at the interfacial area is important to get high ion conductivity at network morphology system. Our work provides novel routes to develop functional PEs with peculiar network morphologies which can further facilitate next generation PEs with high ionic conductivity.