Interfacial Stabilization of Li2O-Based Cathodes by Malonic-Acid-Functionalized Fullerenes as a Superoxo-Radical Scavenger for Suppressing Parasitic Reactions.

Abstract

The utilization of an anionic redox reaction as an innovative strategy for overcoming the limitations of cathode capacity in lithium-ion batteries has recently been the focus of intensive research. Li2O-based materials using the anionic (oxygen) redox reaction have the potential to deliver a much higher capacity than commercial cathodes using cationic redox reactions based on transition-metal ions. However, parasitic reactions attributed to the superoxo species (such as LiO2), derived from the Li2O active material of the cathode, deteriorate the stability of the interface between the cathode and electrolyte, which has limited the commercialization of Li2O-based cathodes. To address this issue, malonic-acid-functionalized fullerenes (MC60) were applied in the electrolyte as an additive for scavenging the superoxo radicals (O21- in LiO2) that trigger parasitic reactions. MC60 can efficiently capture superoxo radicals using the π-conjugated surface and the malonate functionality on the surface. As a result, MC60 considerably enhanced the available capacity and cycling performance of the Li2O-based cathodes, decreased the interfacial layer formed on the cathode surface, and hindered the generation of byproducts, such as Li2CO3, CO2, and C-F3, derived from parasitic reactions. In addition, the loss of Li2O from the cathode surface during cycling was also suppressed, validating the ability of MC60 to capture superoxo radicals. This result confirms that the introduction of MC60 can effectively alleviate the parasitic reactions at the cathode/electrolyte interface and improve the electrochemical performance of Li2O-based cathodes by scavenging the superoxo species.