Doctoral Dissertations

Date of Award

5-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Sheng Dai

Committee Members

Alexei P. Sokolov, Bhavya Sharma, Bin Hu

Abstract

The commercial success of lithium-ion batteries (LIBs) revolutionized human life. The advancement of LIBs with superior performances would be essential for vehicle electrification and grid-scale application. However, current LIBs technology with liquid electrolytes limits this because of leakage, flammability, and safety issues such as fire and explosion. On the other hand, the energy storage capacity of current electrodes will not deliver the energy to drive the large scale application. Extensive research efforts have been focused on optimizing each component of LIBs. To address the safety threats posed by liquid electrolytes, polymer electrolytes were proposed. Due to lightweight, flexibility, the thermal stability of polymer electrolytes, it will significantly reduce the safety issues and size of the battery, increasing the energy density. However, the low ionic conductivity of the polymer electrolytes inhibits its practical application. Gel polymer electrolytes were developed to solve the issues of ionic conductivity which cost the mechanical strength as these parameters are inversely coupled with each other.The first part of the dissertation works was focused on to solve the dilemma about high ionic conductivity vs. high mechanical strength. Herein, we proposed a strategy for simultaneously boosting ionic conductivity and mechanical strength of polymer gel electrolytes via a smart engineering approach with novel synthetic design. Uniquely designed hollow silica nanospherical architecture was used to confine the ionic liquids into its nanocavity, creating the nanodomain of the liquids into the polymer matrix. This confinement strategy increases the mechanical strength by reducing the plasticizing behavior and enhances the ionic conductivity providing non-disturbed nanochannel for the fast lithium-ion conduction. Similarly, layer by layer assembly approach was developed to enhance the mechanical strength preserving the liquid-like dynamics of gel electrolytes. The ultrathin alternating sequence of polyanions and polycations on gel electrolytes enhanced the mechanical strength via strong coulombic interaction.The second part of the dissertation was focused on the development of the high capacity anode from the conversion type electrode using a direct fluorination approach. The formation of the oxyfluoride phase as a result of fluorination enhances the capacity and facilitates the reversible conversion reaction. This strategy solves the inherent problems of conversion materials.

Comments

Chapters 3, 4 and 5 of this dissertation were already published in journal Batteries &Supercaps, ACS applied energy materials, and ChemSusChem, respectively.

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