Coupling Water‐Proof Li Anodes with LiOH‐Based Cathodes Enables Highly Rechargeable Lithium–Air Batteries Operating in Ambient Air

Abstract

Realizing an energy-dense, highly rechargeable nonaqueous lithium-oxygen battery in ambient air remains a big challenge because the active materials of the typical high-capacity cathode (Li 2 O 2 ) and anode (Li metal) are unstable in air. Herein, a novel lithium-oxygen full cell coupling a lithium anode protected by a composite layer of polyethylene oxide (PEO)/lithium aluminum titanium phosphate (LATP)/wax to a LiOH-based cathode is constructed. The protected lithium is stable in air and water, and permits reversible, dendrite-free lithium stripping/plating in a wet nonaqueous electrolyte under ambient air. The LiOH-based full cell reaction is immune to moisture (up to 99% humidity) in air and exhibits a much better resistance to CO 2 contamination than Li 2 O 2 , resulting in a more consistent electrochemistry in the long term. The current approach of coupling a protected lithium anode with a LiOH-based cathode holds promise for developing a long-life, high-energy lithium-air battery capable of operating in the ambient atmosphere.

Unraveling the Reaction Interfaces and Intermediates of Ru-Catalyzed LiOH Decomposition in DMSO-Based Li–O2 Batteries

“…Indeed, oxidation of DMSO to DMSO 2 was confirmed using Fourier transformed infrared spectroscopy (Figure 3B), showing two new peaks that appeared at 1285 and 1135 cm −1 , corresponding to the asymmetric stretching (ν as SO 2 ) and symmetrical stretching (ν s SO 2 ) of the SO 2 group of dimethyl sulfone, 45 respectively, consistent with the result during a battery charge. 19,27,45 In order to evaluate in an operating cell whether hydroxyl radical, as an reaction intermediate, is indeed generated during charge, an in situ three-electrode UV−vis cell 46,47 was set up (Figure 4A), and a radical trap, pnitrosodimethylaniline (RNO), specific to • OH, 48−50 was used to reveal any electrochemical generation of hydroxyl radical at the cathode. Other potential reactive oxygen species, such as O 2 − , 1 O 2 , and H 2 O 2 , may also be formed, although probably at a later stage of oxygen evolution reaction.…”

“…The four-electron OER in aprotic media is important for alkali metal (i.e., Li, Na, and K)–air batteries, where cell operation in air inevitably incurs formation of hydroxide phases (due to reactions of typical discharge products, Li 2 O 2 , NaO 2 , and KO 2 , with moisture) − and requires hydroxide decomposition on cell recharging. In the presence of added water in aprotic electrolytes, LiOH formation/decomposition (2H 2 O + 4e – + 4Li + + O 2 ↔ 4LiOH) itself can also solely form a basis for discharge/charge reactions. − A series of in situ Raman and isotope-assisted nuclear magnetic resonance (NMR) spectroscopic studies ,,− suggest that LiOH forms first via electrochemical formation of HO 2 – /H 2 O 2 , which are then chemically disproportionated by catalysts to O 2 and LiOH, overall leading to a nominal reduction reaction of four electrons per O 2 . Nevertheless, the reversibility of the charge reaction is usually poor: although the discharge product LiOH can be thoroughly decomposed upon recharging, only a little or even no O 2 is released. ,,, …”

Advances in Lithium–Oxygen Batteries Based on Lithium Hydroxide Formation and Decomposition

“…Therefore, protection of Li metal anode is needed for LiOH chemistry. Recently, water-proof Li metal anodes have been developed, such as wax-infiltrated solid-state electrolyte layer (Wu et al, 2017;Lei et al, 2022). Besides the protection of Li anode, alternative reference electrodes have been developed for studying the effect of water or redox mediators on battery chemistry and performance.…”

“…Since then, the research and development of Li−O 2 batteries have blossomed (Aurbach et al, 2016;Chang et al, 2017;Lim et al, 2017;Song et al, 2017). Three types of battery chemistries have been reported, including 1e − lithium superoxide (LiO 2 ) (Lu et al, 2016), 2e − lithium peroxide (Li 2 O 2 ) (McCloskey et al, 2013), and 4e − lithium oxide (Li 2 O) and lithium hydroxide (LiOH) (Liu et al, 2015;Lei et al, 2022). The corresponding reactions are summarized below.…”

“…Li 2 O 2 is the most reported discharge product in non-aqueous Li−O 2 batteries because, under ambient conditions, LiO 2 is thermodynamically unstable against disproportionation (Zhang et al, 2017), and Li 2 O is thermodynamically unfavorable owing to a lower electrode potential of E 0 (O 2 /Li 2 O) = 2.91 V. It is also noted that Li 2 O can be thermodynamically more favorable over Li 2 O 2 as discharge product in a molten-salt electrolyte at >150 °C (Xia et al, 2018), which is beyond the scope of this study. When compared with Li 2 O 2 chemistry, Li−O 2 batteries based on LiOH chemistry can be operated in humid environments and demonstrate better resistance toward CO 2 (Lei et al, 2022), which might enable the operation of Li−O 2 batteries in the air. Liu et al (2015) reported high-performance Li−O 2 batteries based on LiOH formation and decomposition via iodide catalysis (Figure 1B).…”