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Hexafluorophosphate-Bis(trifluoromethanesulfonyl)imide anion co-intercalation for increased performance of dual-carbon battery using mixed salt electrolyte

2020    Madrid, Jose C. Madrid; Nakamura, Kotaro; Inda, Keisuke; Haneke, Lukas; Heckmann, Andreas; Frerichs, Joop Enno; Hansen, Michael Ryan; Placke, Tobias; Winter, Martin; Watanabe, Motonori; Takagaki, Atsushi; Akbay, Taner; Ishihara, Tatsumi

Co-intercalation of Hexafluorophosphate(PF6-) and Bis(trifluoromethane sulfonyl)imide (TFSI-) anions as a result of the use of a mixed salt of LiPF6 and LiTFSI is studied for the increased performance of a dual-carbon battery (DCB). Unlike the fluorineor the imide-based anions (e.g., PF6- and TFSI-), the cluster formation between co intercalated PF6- and TFSI- in the positive electrode of a DCB results in achieving high discharge capacities with significantly increased cycle properties. A reversible discharge capacity of 85 mAh/g-cathode over 350 cycles with no significant degradation is presented. The Coulombic efficiency of almost 100% is reached after the initial 10 cycles and suitable rate property is also observed. F NMR analysis on graphitic carbon intercalated with PF6- and TFSI- suggests the interaction between two anions and ratio of intercalated PF6 and TFSIwas changed by applied voltage, resulting in the increased stability of the intercalated structure which is also supported by the first principles calculations.