Synthesis and characterization of liquid and polymer electrolytes for rechargeable lithium batteries.

摘要

With the aim of designing new liquid and polymer electrolytes for practical uses in rechargeable Li-Metal/Li-Ion batteries, thirteen molecular sulfones, thirteen polyether esters, two polyether sulfides and corresponding polysulfoness and eleven anion-trapping polymers containing under-coordinated boron atoms in the main chain have been synthesized. These electrolytes are characterized by the technique of glass transition, ionic conductivity, cation transport number, solid electrolyte interface, electrochemical stability window and reversibility, as well as their performance in actual voltaic cells.; In the first part of this study, methoxy or ethoxy terminated ethylene glycol segments and cyclo alkyl groups, such as cyclo pentyl and cyclo hexyl, are used to synthesize new sulfones in which a methyl or ethyl group constitutes the other half part. Most of these synthesized sulfones have melting points below room temperature, and their best conductivities and electrochemical windows are comparable with that of the well-known cyclic molecule tetramethylene sulfone (TMS). Lithium metal cells using the best sulfone electrolytes show that more than 50mAh/g discharge capacity can be maintained even after 200 cycles.; In the second part of this study, a series of polyesters with variable spacers are synthesized and characterized. The best conductivity with lithium imide (LiIm) is comparable with that of polyethylene oxide (PEO)/LiIm complex reported in the literature. The electrochemical stability range of the polyesters is as wide as 4.7v versus lithium. A typical good cell constructed using lithium metal as the anode and LiCr_0.015Mn_1.985O₄ as the cathode shows that the discharge capacity can be maintained around 90mAh/g after 25 cycles while the coulomb efficiency is above 80%.; In the third part of this study, a series of anion-trapping and single-ion-conducting polymer electrolytes has been prepared by reaction of certain lithium salts with a polymer host containing under-coordinated in-chain boron atoms, which are separated from each other by variable-length polyethylene glycols. The ionic conductivity of the majority of the electrolytes is observed to exhibit Vogel-Tammann-Fulcher (VTF) behavior, indicating that the segmental movement of the polymer chains facilitates the ion motion. The electrochemical stability window is found to be around 4.5v versus lithium, which is wide enough for practical applications.