Critical Factors Affecting the Catalytic Activity of Redox Mediators on Li–O₂ Battery Discharge

Abstract

Redox mediators (RMs) have a substantial ability to govern oxygen reduction reaction (ORR) in Li–O2 batteries, which can realize large capacity and high-rate capability. However, studies on understanding RM-assisted ORR mechanisms are still in their infancy. Herein, a quinone-based molecule, vitamin K1 (VK1), is first used as the ORR RM for Li–O2 batteries, together with 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ), to elucidate key factors on the catalytic activity of RMs. By combining experiments and first-principle computations, we demonstrate that the reduced VK1 has strong oxygen affinity and can effectively retard the deposition of Li2O2 films on the electrode surface, thereby guaranteeing enough active sites for electron transfer. Besides, the low reaction free energy of disproportionation of the Li­(VK1)­O2 intermediate into Li2O2 also significantly accelerates the ORR process. Consequently, the catalytic activity of VK1 is significantly boosted, and the discharge capacity of VK1-assisted batteries is 3.2–4.5 times that of DBBQ-assisted batteries. This study provides new insight for better understanding the working roles of RMs in Li–O2 batteries.

Advanced Li/Na–CO2 Batteries Enabled by the γ-MnO2 Catalyst with Enhanced Carbonate Decomposition

“…Meanwhile, it is momentous to develop environmentally friendly and sustainable advanced energy storage and efficient energy conversion systems to meet the increasing energy demand. The traditional lithium-ion battery (LIB) is considered an efficient energy storage system, which is widely used in various aspects of life, such as consumer electronics and electric vehicles. , Nevertheless, the limited theoretical capacity of traditional LIBs is difficult to meet the demands of long time, long distance, and high energy density for energy storage devices. − …”

The Surface Electronic Structure Reconstruction of Co2.85Mn0.15O4 with High Active Sites for High-Efficient Lithium–Oxygen Batteries

“…But the stability of the Li–O 2 cell with RMs is commonly worse than that with cathode catalysts, which can be attributed to the shuttle effect of RMs. Researchers have came up with some strategies to suppress the shuttle effect such as equipping a selective separator which can hinder RMs instead of Li + . , Designing a cathode catalyst with as high an ORR/OER activity as the RMs is also an important direction to enhance efficiency and stability of Li–O 2 batteries.…”

“…Researchers have came up with some strategies to suppress the shuttle effect such as equipping a selective separator which can hinder RMs instead of Li + . 16,17 Designing a cathode catalyst with as high an ORR/OER activity as the RMs is also an important direction to enhance efficiency and stability of Li−O 2 batteries.…”

Completely Eradicating Singlet Oxygen in Li–O2 Battery via Cobalt(II)-Porphyrin Complex-Catalyzed LiOH Chemistry

“…Redox mediators (RMs), soluble catalysts in an electrolyte, have been confirmed to be high-efficiency diffusive catalysts for the cathode reactions. , They act as electron–hole “carriers” between the electrode surface and Li x O y , facilitating the decomposition of Li x O y , irrespective of the size and the structure of Li x O y . Since Bruce et al reported tetrathiafulvalene (TTF) as an effective RM for LOBs in 2013, various kinds of RMs (organic, organometallic, and halide) have been developed. − Among them, organometallic RMs are particularly attractive because their redox properties can be flexibly tuned by replacing the center active transition metal ions and/or modifying the organic ligands. , In addition, recent studies have revealed that RMs can induce an increased intersystem crossing rate and suppress 1 O 2 formation during the ORR and OER processes, thereby reducing parasitic reactions. , Notably, the organic RMs themselves can also be predominantly decomposed and deactivated by 1 O 2 , leading to limited efficiencies of 1 O 2 suppression. , Thus, it is essential to find a way to operate LOBs via a chemical step that does not form 1 O 2 . Compared with Li x O y , LiOH is more torpid with the electrolyte and carbon support.…”