A molecular dynamics study of a fully zwitterionic copolymer/ionic liquid-based electrolyte: Li⁺ transport mechanisms...

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Polymer electrolytes (PEs) are vital for developing safer, high-energy density batteries.
• Achieving a balance between mechanical stiffness and ionic conductivity in PEs remains challenging.
• Zwitterionic (ZI) gel electrolytes offer promising properties for lithium-metal and beyond lithium-ion battery chemistries.

Purpose of the Study:

• To investigate the fundamental structure-dynamic relationships governing ionic transport in ZI gel electrolytes.
• To clarify the Li+ coordination environment within these advanced battery materials.
• To elucidate the impact of ZI polymer addition on ionic conductivity and ion dynamics.

Main Methods:

• Molecular dynamics (MD) simulations were employed.
• Two IL-based electrolyte systems were studied: [BMP][TFSI] with LiTFSI salt, and a ZI gel electrolyte with a ZI copolymer (poly(MPC-co-SBVI)).
• Structural analyses and ionic transport properties were examined.

Main Results:

• ZI polymer addition decreased [TFSI]- -[Li]+ interactions and increased IL ion diffusivities, enhancing overall ionic conductivity.
• Lithium ions preferentially interacted with polymer phosphonate groups.
• [TFSI]- anions interacted with the sulfonate group, while [BMP]+ cations showed secondary interactions with the polymer.

Conclusions:

• MD simulations provide insights into ion coordination and transport mechanisms in ZI gel electrolytes.
• Simulated transference numbers indicated smaller [Li]+ contributions than experimental data suggested, attributed to lithium aggregates and strong Li+-polymer interactions.
• These findings aid in optimizing ZI gel electrolytes for advanced battery applications.