The role of iodide in the formation of lithium hydroxide in lithium–oxygen batteries

Abstract

Iodide ions promote deprotonation of water; in consequence LiOH/LiOH·H2O is formed as a final discharge product.

Defect Chemistry in Discharge Products of Li–O2 Batteries

“…Seeking alternative energy carriers with a low charge overpotential is one of the most effective ways to minimize the negative effects caused by Li 2 O 2 such as the nucleophilic attack of cell components and the resulting high charge overpotential. Two promising strategies have been developed, including stabilizing intermediates of LiO 2 by suppressing Li 2 O 2 formation and converting Li 2 O 2 into other promising energy carriers such as LiOH, and Li 2 CO 3 . In this section, we will focus on the mechanistic study of Li–O 2 batteries using LiO 2 or LiOH/Li 2 CO 3 as alternative energy carriers.…”

“…It is widely accepted that LiOH is one of the main side products in Li–O 2 batteries, where H 2 O is the dominant proton source in humid oxygen and electrolytes. In contrast to conventional Li–O 2 batteries, which work via Li 2 O 2 formation, a novel Li–O 2 battery employing LiOH as the energy carrier has attracted extensive interest . The Li–O 2 battery that works via LiOH formation, 4Li + 2H 2 O + O 2 ⇌ 4LiOH ( E ° = 3.32 V), delivers a low charge potential and high cycling stability because of the enhanced conductivity of LiOH and the alleviation of side reactions caused by the high nucleophilicity of Li 2 O 2 .…”

“…The Li–O 2 battery that works via LiOH formation, 4Li + 2H 2 O + O 2 ⇌ 4LiOH ( E ° = 3.32 V), delivers a low charge potential and high cycling stability because of the enhanced conductivity of LiOH and the alleviation of side reactions caused by the high nucleophilicity of Li 2 O 2 . Additives such as H 2 O and lithium iodide (LiI) greatly impact the conversion of the aforementioned Li–O 2 batteries, acting as either initiators or catalysts to promote the formation of LiOH . The complex effects of H 2 O and LiI on LiOH chemistry will be discussed in this section, mainly focusing on the reaction mechanism.…”

“…With H 2 O as the dominant proton source, the voltage gap was reduced to 0.2 V with 0.05 m LiI via LiOH formation based on rGO in 0.25 m LiTFSI/DME electrolyte. The possibility of this reaction was disputed, specifically in regard to whether LiOH can be thermodynamically oxidized by triiodide () . Shen et al observed that ions were not consumed with the significant accumulation of LiOH.…”

“…Indeed, different H 2 O:LiI ratios can change the pH values and thus exhibit a noteworthy impact on the product composition. Tutodziecki et al suggested that the high acidity by strong I − –H 2 O interactions at low H 2 O:LiI ratios (<5) promotes LiOH formation instead of Li 2 O 2 formation, while a mixture of Li 2 O 2 , LiOOH·H 2 O and LiOH·H 2 O was observed at high H 2 O:LiI ratios (>5). Similarly, Zhu et al also indicated that LiOOH·H 2 O (in neutral conditions) and LiOH·H 2 O (in weakly acidic conditions) can be the primary discharge products .…”