Recent advances in understanding of the mechanism and control of Li₂O₂formation in aprotic Li–O₂batteries

Abstract

Aprotic Li-O batteries represent promising alternative devices for electrical energy storage owing to their extremely high energy densities. Upon discharge, insulating solid LiO forms on cathode surfaces, which is usually governed by two growth models, namely the solution model and the surface model. These LiO growth models can largely determine the battery performances such as the discharge capacity, round-trip efficiency and cycling stability. Understanding the LiO formation mechanism and controlling its growth are essential to fully realize the technological potential of Li-O batteries. In this review, we overview the recent advances in understanding the electrochemical and chemical processes that occur during the LiO formation. In the beginning, the oxygen reduction mechanisms, the identification of O/LiO intermediates, and their influence on the LiO morphology have been discussed. The effects of the discharge current density and potential on the LiO growth model have been subsequently reviewed. Special focus is then given to the prominent strategies, including the electrolyte-mediated strategy and the cathode-catalyst-tailoring strategy, for controlling the LiO growth pathways. Finally, we conclude by discussing the profound implications of controlling LiO formation for further development in Li-O batteries.

Promoting Li–O2 Batteries With Redox Mediators

“…However,L i-O 2 batteries still face many challenges,s uch as lowp ractical specific energy,h igh overpotentials, poor rate capability,e lectrolyte decomposition,a nd limited cycle life. [2] Most problems are caused by the side reactions occurring on discharge/charge and the insulating nature of the Li 2 O 2 solid discharge product.…”

Defect Chemistry in Discharge Products of Li–O2 Batteries

“…A typical aprotic Li–O 2 cell is composed of two electrodes (a porous cathode and a lithium anode) and an aprotic electrolyte facilitating Li + transport. Upon discharge, the discharge product of Li 2 O 2 forms on the cathode surface via the oxygen reduction reaction (ORR); upon charge, Li 2 O 2 is electrochemically decomposed in the oxygen evolution reaction (OER) . Since charge behavior largely depends on the structure and morphology of the as‐formed discharge product, understanding the Li 2 O 2 formation mechanism is of crucial importance.…”

“…Since charge behavior largely depends on the structure and morphology of the as‐formed discharge product, understanding the Li 2 O 2 formation mechanism is of crucial importance. There are two widely adopted Li 2 O 2 growth models, the solution model and the surface model, that largely determine the discharge capacity and charge overpotential by controlling the structure and morphology of Li 2 O 2 . However, a series of parasitic reactions can occur during discharge and charge and lead to carbon‐based cathode decomposition and electrolyte decomposition to form irreversible carbonates, resulting in low coulombic efficiency and cyclability deterioration .…”

A Safe Organic Oxygen Battery Built with Li‐Based Liquid Anode and MOFs Separator

“…And the inhomogeneous distribution of current density on Li surface and Li ion in SEI layer would inevitably result in dendrite growth, which causes circuit shortage phenomenon, sometimes even severe accidents 9,10. At the cathode side, the ideal electrochemistry based on reversible formation and decomposition of Li 2 O 2 is always challenged by the solid–solid contact mode between Li 2 O 2 and the carbon cathode, which leads to sluggish reaction kinetics and parasitic reactions, and is responsible for the high overpotential and poor durability of Li‐O 2 batteries 11,12…”