Interfacial Stabilization of Li 2 O-Based Cathodes by Malonic-Acid-Functionalized Fullerenes as a Superoxo-Radical Scavenger for Suppressing Parasitic Reactions.

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. Li ₂ O-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 LiO ₂ ), derived from the Li ₂ O active material of the cathode, deteriorate the stability of the interface between the cathode and electrolyte, which has limited the commercialization of Li ₂ O-based cathodes. To address this issue, malonic-acid-functionalized fullerenes (MC ₆₀ ) were applied in the electrolyte as an additive for scavenging the superoxo radicals (O ₂ ^1- in LiO ₂ ) that trigger parasitic reactions. MC ₆₀ can efficiently capture superoxo radicals using the π-conjugated surface and the malonate functionality on the surface. As a result, MC ₆₀ considerably enhanced the available capacity and cycling performance of the Li ₂ O-based cathodes, decreased the interfacial layer formed on the cathode surface, and hindered the generation of byproducts, such as Li ₂ CO ₃ , CO ₂ , and C-F ₃ , derived from parasitic reactions. In addition, the loss of Li ₂ O from the cathode surface during cycling was also suppressed, validating the ability of MC ₆₀ to capture superoxo radicals. This result confirms that the introduction of MC ₆₀ can effectively alleviate the parasitic reactions at the cathode/electrolyte interface and improve the electrochemical performance of Li ₂ O-based cathodes by scavenging the superoxo species.