Exploring the Effects of Amphiphilic Fluorinated Copolymer on the Structures and Ion Dynamics at the Electrolyte-Cathode Interface of Lithium Ion Battery via Molecular Simulations

  • 李 韋勳

Student thesis: Master's Thesis

Abstract

A recently developed amphiphilic co-polymer binder poly(PEGMA-block-PFHEMA) which consists Li+ conducting ethylene oxide (EO) segments has been shown to improve the lithium ion battery efficiency In this work we utilized molecular dynamics (MD) simulations to explore the effects of amphiphilic fluorinated copolymer composed of PEGMA and PFHEMA at the cathode/electrolytes interface We found that varying the molecular weight the ratio of PEGMA to PFHEMA and the monomer block sizes of the co-polymer can alter the surface density of EO-segments The radial distribution function and Li+ coordination analyses showed the interaction between Li+ and PF6- is reduced on the binder surface The coordination around Li+ have gradually changed from EC and DEC solvent to polymer EO-segments as Li+ approaching the binder surface Furthermore the diffusivity of the bound Li+ are in the same order as the coordinated ether oxygens illustrating the cooperative motion of the Li+ and EO-chains In contrast the intrachain Li+ conduction is absent in this binder system due to the short EO-segments; while the occurrence of interchain Li+ conduction increases with the EO-chain surface density Yet the overall diffusivity of the surface bound Li+ is reduced as the surface EO-chain density increases The combined results conclude that the addition of the EO chains can reduce the interaction between Li+ and PF6- but decrease the overall Li+ diffusivity on the binder surface The two competing effects provide microscopic insights into the experimental observation of the optimal ratio of PEGMA to PFHEMA
Date of Award2017 Aug 5
Original languageEnglish
SupervisorChi-cheng Chiu (Supervisor)

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