Highly Thermally/Electrochemically Stable I⁻/I3⁻ Bonded Organic Salts with High I Content for Long-Life Li–I₂ Batteries

Rechargeable lithium–iodine batteries are highly attractive energy storage systems featuring high energy density, superior power density, sustainability, and affordability owing to the promising redox chemistries of iodine. However, severe thermodynamic instability and shuttling issues of the cathode have plagued the active iodine loading, capacity retention and cyclability. Here the development of highly thermally and electrochemically stable I⁻/I₃⁻-bonded organic salts as cathode materials for Li–I₂ batteries is reported. The chemical bonding of iodine/polyiodide ions with organic groups allows up to 80 wt% iodine to be effectively stabilized without sacrificing fast and reversible redox reaction activity. Thus, the shuttle effect is significantly inhibited, which improves cathode capacity and restrains side-reactions on the Li anode. As a result, such cathodes afford Li–I₂ batteries a specific capacity of 173.6 mAh g⁻¹_{methylamine hydroiodide (MAI)} (217 mAh g⁻¹_I) at 0.5 C, superior rate capability of 133.1 mAh g⁻¹_MAI at 50 C, and ultrahigh capacity retention rate of 98.3% over 10000 cycles (5 months). In-situ, ex-situ spectral characterizations and density functional theory calculations clarify the robust chemical interaction between iodides and organic groups. The cathode chemistries elucidated here propel the development of Li–I₂ batteries and are expected to be extended to other metal-iodine battery technology.