Recent Progress in Developing a LiOH‐Based Reversible Nonaqueous Lithium–Air Battery

Abstract

By replacing the conventional graphite-based anode (372 mAh g −1 for LiC 6 , on the basis of mass of C) with silicon (3579 mAh g −1 for Li 15 Si 4 , on the basis of mass of Si) or lithium metal (3860 mAh g −1 ; based on the mass of Li) anodes, the practical energy density of LIB single cells can be increased to 300-400 Wh kg −1 . [4] Nevertheless, to surpass the commonly targeted goal of 500 Wh kg −1 , [5] alternative cathodic chemistries beyond Li-ion intercalation are required. Using O 2 as an active material for electrochemical energy storage is appealing in terms of cost and availability, and when coupled to Li metal, lithium-air batteries (LABs) could deliver energy densities up to 3505 Wh kg −1 (theoretical value). [1c,6] Several studies have demonstrated nonaqueous Li-O 2 batteries with energy densities of up to 1230 Wh kg −1 using novel cell designs, [7] although the cycle life needs to be improved. Table S1, Supporting Information, summarizes the high-energy lithium-air full cells reported to date.The theoretical energy density of nonaqueous LABs depends on the specific cathodic half-cell reaction (Equations ( 1)-( 4), note that all voltages are referred to against Li/Li + ), and thus the chemical composition of the discharge product. [8] Thus far, successfully tested discharge products for aprotic LABs include LiO 2 , Li 2 O 2 , Li 2 O, and LiOH. Both Li 2 O 2 and Li 2 O are thermodynamically stable compounds (Equations ( 1) and ( 2)), whereas LiO 2 is unstable at standard conditions but has been reported to form in LABs assisted by Ir-and Pd-catalytic systems (Equation ( 3)). [8a-d] Formation of Li 2 O during discharge involves rupture of the OO bond and is thus less kinetically favorable than Li 2 O 2 formation, unless discharge occurs in the presence of a catalyst such as nickel at above 150 °C. 2 2 1 8b,9 (4) Notably, one issue that LiO 2 , Li 2 O 2 , and Li 2 O have in common is their moisture and carbon dioxide sensitivity, as The realization of practical nonaqueous lithium-air batteries (LABs) calls for novel strategies to address their numerous theoretical and technical challenges. LiOH formation/decomposition has recently been proposed as a promising alternative route to cycling LABs via Li 2 O 2 . Herein, the progress in developing LiOH-based nonaqueous LABs is reviewed. Various catalytic systems, either soluble or solid-state, that can activate a LiOH-based electrochemistry are compared in detail, with emphasis in providing an updated understanding of the oxygen reduction and evolution reactions in nonaqueous media. We identify the key factors that can switch the cell chemistry between Li 2 O 2 and LiOH and highlight the debate around these routes, as well as rationalize potential causes for these opposing opinions. The identities of the reaction intermediates, activity of redox mediators and additives, location of reaction interfaces, causes of parasitic reactions, as well as the effect of CO 2 on the LiOH electrochemistry, all play a critical role in altering the relative rates of ...

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

“…In the early stage, solid catalysts (e.g., carbonbased materials, metals, and metal oxides) were proposed, which can promote Li x O y decomposition by enhancing charge transfer within Li x O y or delithiation kinetics. 6,7 Very recently, Chen's group and our previous study both display that the solid catalyst Co 3 O 4 can suppress 1 O 2 formation in LOBs to some extent. 8,9 Nevertheless, such catalysts act only near their surface and the active sites are gradually buried in the formed insulating products.…”

“…Rechargeable aprotic Li–O 2 batteries (LOBs) have been considered as one of the most promising energy storage systems because of their ultrahigh energy densities (3505 Wh kg –1 based on Li 2 O 2 , 3707 Wh kg –1 based on LiOH) . However, the practical application has been limited by their numerous drawbacks.…”

“…R echargeable aprotic Li−O 2 batteries (LOBs) have been considered as one of the most promising energy storage systems because of their ultrahigh energy densities (3505 Wh kg −1 based on Li 2 O 2 , 3707 Wh kg −1 based on LiOH). 1 However, the practical application has been limited by their numerous drawbacks. In particular, the high charge overpotential caused by decomposition of insulating discharge products Li x O y (e.g., LiO 2 , Li 2 O 2 , and Li 2 O) severely increases side reactions.…”

“…To the best of our knowledge, in LOBs the oxidation or disproportionation of superoxide intermediate causes 1 O 2 formation, which leads to the degradation of the carbon electrode and the electrolyte. At present, RMs have been reported to promote intersystem crossing and suppress 1 O 2 generation.…”

“…Compared with Li x O y , LiOH is more torpid with the electrolyte and carbon support. Besides, reversible LiOH chemistry in LOBs has been achieved by some catalysts (e.g., LiI, Ru/SP, Ru@CNT) together with a trace amount of water. , However, to date, it is unclear whether the formation/decomposition of LiOH in LOBs can be a chemical step to avoid the 1 O 2 generation …”