Current lithium-ion batteries face severe safety challenges including thermal-runaway, flaming, and explosion/leakage issues. Safer batteries could be developed by exchanging the highly-flammable liquid electrolytes to advanced electrolytes with lower flammability. Ionic liquids, polymers, and inorganic solid-state electrolytes (SSEs) are three commonly-applied categories of the possible safer electrolytes. Ionic liquids and polymers can be applied for flexible batteries with less flaming and leakage concerns. Inorganic SSEs have even higher intrinsic safety and are suitable high-energy Li-metal batteries with improved thermal stability and batteries for extreme high-temperature applications. Despite the safety improvement, these advanced electrolytes have not been widely applied today. The challenges include the parasitic reactions and the high electrolyte/electrode interfacial resistivity. These issues result in limited energy/power densities and low durability of a cell.

This work attempts to understand the mechanical contact and electrochemical stability of the advanced electrolytes against various electrodes and integrate these electrolytes into high-energy solid-state batteries with improved safety.

The analysis and integration strategies of different types of electrolytes are separately studied due to their distinct mechanical properties. This work covers the following topics. (1). The ionic liquid electrolyte was tailored to a flexible battery by additives. Based on the ionic liquid, flexible polymer batteries without flaming or leakage concerns were developed. (2). UV-cured solid polymer electrolytes were integrated into high-power polymer batteries by 3D-printing techniques. The 3D-electrode/polymer interface and the cell performance were evaluated. (3). The interfaces between the inorganic SSEs and the electrodes were studied and modified to mitigate the interfacial resistance, to assess Li metal batteries for room-temperature and high-temperature applications. (4). High-energy solid-state batteries were developed based on the structural design of the SSE and interfacial treatment. In conclusion, this work studies novel routes for integrating advanced electrolytes into lithium-ion batteries by interfacial treatment and structural design, and explores the application of the lithium-ion batteries with both high safety and improved energy densities.