Unveiling the Complex Effects of H₂O on Discharge–Recharge Behaviors of Aprotic Lithium–O₂ Batteries

Abstract

The addition of HO, even trace amount, in aprotic Li-O batteries has a remarkable impact on achieving high capacity by triggering solution mechanism, and even reducing charge overpotential. However, the critical role of HO in promoting solution mechanism still lacks persuasive spectroscopic evidence, moreover, the origin of low polarization remains incompletely understood. Herein, by in situ spectroscopic identification of reaction intermediates, we directly verify that HO additive is able to alter oxygen reduction reaction (ORR) pathway subjected to solution-mediated growth mechanism of LiO. In addition, ingress of HO also induces to form partial LiOH, resulting in reduced charging polarization due to its higher conductivity; however, LiOH could not contribute to O evolution upon recharge. These original results unveil the complex effects of HO on cycling the aprotic Li-O batteries, which are instructive for the mechanism study of aprotic Li-O batteries with protic additives or soluble catalysts.

Promoting Li–O2 Batteries With Redox Mediators

“…Li + is exchanged with H + in LiO 2 and Li 2 O 2 , forming soluble intermediates (Scheme b) . Aetukuri et al.…”

Protecting the Li‐Metal Anode in a Li–O2 Battery by using Boric Acid as an SEI‐Forming Additive

“…The cell with BA exhibited larger discharge capacity and higher coulombic efficiency, which is probably due to a small amount of water produced by reactions and (2). It has been reported that small amount of water has such positive effects in LOBs . SEM, X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS) results show that the discharge product is always Li 2 O 2 particles, which are oxidized after charge (Figures S3 and S5, Supporting Information).…”

Defect Chemistry in Discharge Products of Li–O2 Batteries

“…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 . 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 .…”

“…Unfortunately, humidity can also limit the cycling ability and rate performance because of its negative effect on Li 2 O 2 /O 2 conversion . In the case of Li–O 2 batteries with H 2 O, the discharge products can be Li 2 O 2 and/or LiOH, depending on the catalysts, electrolytes and H 2 O concentration. Li et al studied the mechanism of water catalysis based on the Ru/MnO 2 /SP cathode of Li–O 2 batteries.…”

“…In contrast to the charge mechanism above, Liu et al stated that oxidation of LiOH was anoxygenic and that the reaction should be LiOH → Li + + e − + ·OH, while the obtained ·OH radicals were consumed by DMSO to irreversibly form DMSO 2 , catalyzed by Ru . Recently, Ma et al also verified that no O 2 was released by combining an isotope‐labeling technique with DEMS. Regardless of the catalyst effect, the charge potential depends on the concentration of H 2 O.…”