Polymer Electrolyte Thesis

In pursuit of safer and more flexible solid-state lithium ion batteries, solid polymer electrolytes have emerged as a promising candidate.The present dissertation entails exploration of solid plasticized, photopolymerized (i.e.In order to improve the mechanical toughness of the highly conductive PEGDA/Li TFSI/SCN PEM, effects of prepolymer molecular weight on mechanical and electrochemical properties of PEMs were further investigated.

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Finally, the investigation of the charge/discharge cycling performance of solid-state Li Fe PO half-cells at an elevated temperature of 60 °C is discussed in Chapter VII.

In the half-cells, particularly, SCN plasticized PEMs with and without electrolyte modifier lithium bis(oxalato)borate (Li BOB) were respectively employed.

Rapid decline of capacity and increase of cell resistance were found in the unmodified PEM containing cell; however, these deteriorations were greatly suppressed upon Li BOB modification.

Electrochemical and thermal compatibility of PEMs towards different electrodes were examined in several symmetric cells and half-cells.

Upon SCN incorporation, these two peaks merged into one that was further suppressed below the T of the pure network, whereas σ improved to the superionic conductor level.

The role of SCN on the σ enhancement as both plasticizer for the polymer network and ionizer for the salt is discussed in Chapter V.

Lithium bis(trifluoromethanesulfonyl)imide (Li TFSI) was incorporated as a source of lithium ions, while a solid plasticizer succinonitrile (SCN) and a liquid plasticizer tetraethylene glycol dimethyl ether (TEGDME) were incorporated in the respective systems.

The important role of plasticizer on the enhancement of ionic conductivity (σ) to the superionic conductive level (10 S/cm) was revealed in both systems.

We further used graphene oxide to enhance the crystal orientation, hence the conductivity anisotropy.

To quantitatively characterize the crystallization effect, a model electrolyte system consists of PEO single crystals with well controlled crystal structure, size, crystallinity and orientation were fabricated.