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Network-based solid polymer electrolytes (SPEs) for lithium metal batteries (LMBs) and beyond
Dissertation   Open access

Network-based solid polymer electrolytes (SPEs) for lithium metal batteries (LMBs) and beyond

Yongwei Zheng
Doctor of Philosophy (Ph.D.), Drexel University
Dec 2020
DOI:
https://doi.org/10.17918/00000279
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Abstract

Lithium ion batteries Polymer networks Sodium ion batteries Polyelectrolytes Solid state batteries
Lithium metal batteries (LMBs) are regarded as the next-generation energy storage devices due to the high theoretical energy density. Conventional organic-based liquid electrolytes are not compatible with LMBs because of the safety issues that are caused by the high flammability and Li dendrites-induced short-circuit. Recently, solid polymer electrolytes (SPEs) have received attention due to the mechanical properties, and flexibility. Compared with different SPEs structures, the network structure stands out. The network based SPEs exhibit both good ionic conductivity and mechanical stability. They also perform well in inhibiting Li dendrites growth and extend the cell cycling lifetime. In this dissertation, a series of network based SPEs were synthesized and characterized. The network chemistry selection was based on polymer physics and electrochemistry. A typical example is the crosslinked poly (ethylene oxide) (PEO) network. A systematic characterization has been conducted on this single network platform. Then, the network structure was transited from single network to interpenetrating network (IPN) in order to address some of the issues. For example, poly (propylene carbonate) (PPC) was incorporated to liberate the Li⁺ and increase the cation transference number. Ultra-high molecular weight PEO was incorporated to increase the toughness of the SPE. Poly (acrylonitrile) (PAN) was incorporated to improve the anodic stability voltage. In cell level, the performance of the SPEs was evaluated in a series setup such as symmetrical cell, half cell, and full cell. In this dissertation, the design of SPEs is to pursue the extended cell cycling lifetime and increased Li metal anode cycling efficiency. So, the formation, composition, and evolution of the solid electrolyte interface (SEI) were specially characterized, analyzed and correlated with the chemistry of SPE, salts and additives. The results demonstrated the concept of IPN is feasible in designing the SPEs for LMBs.

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