Converting a Metal-Coordinating Polymer to a Polymerized Ionic Liquid Improves Li⁺ Transport

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Solid polymer electrolytes (SPEs) offer mechanical strength and reduced flammability for next-generation lithium-ion (Li+) batteries.
• Conventional SPEs face limitations in Li+ conductivity, hindering their widespread application.
• Imidazole-functionalized polymers (PMS-Im) show promise but require further optimization for improved ionic transport.

Purpose of the Study:

• To investigate the effect of polymer quaternization on lithium salt solvation and Li+ transport in SPEs.
• To enhance the ionic conductivity of imidazole-based polymers for high-performance Li+ battery applications.
• To explore the relationship between polymer structure, ion transport mechanisms, and overall battery performance.

Main Methods:

• Synthesis of an imidazolium functionalized polymer (PMS-Im+) through quaternization of PMS-Im.
• Characterization of Li+ solvation properties and polymer plasticization.
• Measurement of ionic conductivity and analysis of Li+ transport using inverse Haven ratios.

Main Results:

• Quaternization of PMS-Im to PMS-Im+ significantly improved lithium salt solvation and polymer plasticization.
• Inverse Haven ratios as high as 10 indicated positively correlated Li+ transport, suggesting nanochannel percolation.
• PMS-Im+ achieved a Li+ conductivity of 2.1 × 10^-5 S/cm at 90 °C, over an order of magnitude higher than PMS-Im (1.6 × 10^-6 S/cm).

Conclusions:

• Quaternized imidazolium polymers (PMS-Im+) are superior solid polymer electrolytes compared to their imidazole counterparts.
• Enhanced solvation and ion transport mechanisms in PMS-Im+ lead to significantly improved Li+ conductivity.
• The findings pave the way for developing high-performance SPEs for advanced lithium-ion batteries.