Simultaneously Generating Redox Mediator and Hybrid SEI for Lithium–oxygen Batteries by Lewis Acid Catalyzed Ring‐opening Reaction of Organic Iodine

Abstract Facing high overpotential, severe Li corrosion and degradation of electrolytes caused by the reactive oxygen species, the development of lithium–oxygen batteries is seriously limited. Although the iodine species have been considered to be effective redox mediators (RMs) for lowering the charging overpotential, the shuttling of oxidized I 3 − may attack the Li metal anode, compromising the number of RMs, cycling stability and energy efficiency. Here the intend to introduce 3‐Iodooxetane (C 3 H 5 OI, IOD) into TEGDME‐based electrolyte to form a protective SEI layer on the Li surface for defending against the attack of I 3 − . However, the iodine in IOD is found difficult to dissociate. To solve this problem, hard Lewis acid, aluminum trichloride (AlCl 3 ) is proposed as the catalytic agent for dissociating the I − and triggering the ring‐opening reaction of the detached C 3 H 5 O + ions. The former can dissociate redox couple I 3 − /I − while the latter can form oligomers or polymers under the attack of a nucleophile. Meanwhile, AlCl 3 can form Al 2 O 3 and LiCl inorganic species. Taking together, the introduction of IOD and AlCl 3 into electrolytes can effectively derive reduced overpotential and in situ SEI layers consisting of flexible organics and rigid inorganics, endowing lithium–oxygen batteries over 150 cycles with significantly enhanced stability and lifespan.