Deciphering SN2-Type Nucleophilic Substitution via Halogen-Free Intermediates for High-Energy Zinc-Iodine Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• High-valence halogen conversion reactions are key for high-energy-density aqueous batteries.
• Stable and reversible iodine (I) 0/I+ conversion remains a challenge compared to I-/I0 conversion.
• Existing methods using interhalogen chemistry introduce corrosion and toxicity issues.

Purpose of the Study:

• To propose a novel SN2-type nucleophilic substitution mechanism for activating the I0/I+ redox process.
• To develop halogen-free intermediates for efficient four-electron halogen reactions.
• To establish a structure-kinetics relationship for imide-containing molecules in iodine redox processes.

Main Methods:

• Investigated SN2-type nucleophilic substitution mechanism for I0/I+ redox.
• Synthesized and tested halogen-free imide intermediates.
• Elucidated structure-kinetics relationship using hydrogen dissociation energy (Ed) and local nucleophilicity (LN).
• Fabricated and cycled a Zn-I2 battery with a theobromine intermediate.

Main Results:

• Imide intermediates effectively promote four-electron halogen reactions via conjugation-stabilized nitrogen anions.
• A structure-kinetics relationship was established using Ed and LN descriptors.
• The Zn-I2 battery with theobromine intermediate showed stable cycling with 93.9% capacity retention over 1000 cycles at 5 A g-1.

Conclusions:

• The proposed SN2 mechanism and imide intermediates offer a new pathway for I0/I+ redox activation.
• This work provides insights into the I0/I+ redox mechanism for developing high-capacity multielectron iodine cathodes.
• Halogen-free imide intermediates are promising for advanced aqueous battery applications.