Highly Porous Polyimide Gel for Use as a Battery Separator with Room-Temperature Ionic Liquid Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Advanced aerospace vehicles require enhanced energy storage with improved specific energy and safety.
• Current lithium-ion batteries use flammable carbonate electrolytes and polyolefin separators, limiting safety and performance.
• Room-temperature ionic liquids (RTILs) offer nonflammable alternatives but often show poor compatibility with conventional separators.

Purpose of the Study:

• To develop and evaluate novel polyimide (PI) gel separators for enhanced compatibility with RTIL electrolytes.
• To create safer, nonflammable energy storage systems for demanding applications like aerospace.

Main Methods:

• Synthesized cross-linked polyimide (PI) gel separators using ODA, BPDA, and Desmodur N3300A with varying lengths (n=30, 60).
• Characterized PI gel separators for porosity, thermal stability, and morphology.
• Screened six imidazolium-based RTILs with LiTFSI, evaluating ionic conductivity and long-term stability in the PI gel systems.

Main Results:

• PI gel separators exhibited high porosity (>85%), excellent thermal stability (>561 °C), and a stable fibrillar network.
• Nonflammable separator/electrolyte systems achieved room-temperature ionic conductivities in the 10^-3 S/cm range.
• The 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) RTIL showed optimal performance, with good conductivity retention after prolonged storage.

Conclusions:

• Cross-linked polyimide gel separators are effective in enabling carbonate-free, nonflammable RTIL electrolytes.
• These PI gel separators maintain suitable ionic conductivity for lithium-based cells, addressing key safety and performance challenges.
• The developed systems show promise for advanced energy storage solutions in aerospace and other high-demand fields.