Confinement-enhanced Li⁺ ion dynamics in an ionic liquid-based electrolyte in porous material

Area of Science:

• Materials Science
• Electrochemistry
• Physical Chemistry

Background:

• Ionic liquids (ILs) offer stable electrolytes for Li-ion batteries but suffer from poor Li+ transport due to ion clustering.
• Confinement within nanoporous materials can alter IL properties, potentially improving ion transport.

Purpose of the Study:

• To investigate the effects of confinement in mesoporous silica (SBA-15) and a metal-organic framework (ZIF-8) on Li+ dynamics and ion clustering in an IL electrolyte.
• To understand how pore size and material interface influence Li+ coordination and mobility.

Main Methods:

• Utilized Raman spectroscopy to analyze Li-anion coordination and ion-wall interactions.
• Employed temperature-dependent 7Li spin relaxation rates (analyzed via Bloembergen, Purcell, and Pound model) to probe Li+ dynamics and local environment.

Main Results:

• Confinement in SBA-15 (8 nm and 4 nm pores) did not alter Li+ coordination or break Li-TFSA clusters, and reduced Li+ dynamics.
• Confinement in ZIF-8 (1.16 nm pores) surprisingly enhanced Li+ local dynamics and asymmetry, correlating with reduced Li+-TFSA coordination and suggesting cluster breakup.
• Differences were attributed to pore wall interactions: TFSA- with SBA-15 and Pyr14+ with ZIF-8.

Conclusions:

• Nanoporous material interfaces significantly influence IL structure and ion dynamics.
• ZIF-8 confinement demonstrates potential for overcoming poor Li+ transport in IL electrolytes by disrupting ion clusters.
• Tailoring pore surface chemistry offers a strategy for optimizing ion dynamics in advanced battery electrolytes.