Résumé
Through two redox molecules, mono- and dicarboxylic ferrocene anions (FcMono and FcDi, respectively), interleaved between the lamellae of a layered double hydroxide Mg2Al(OH)6 (LDH), have been synthesized and investigated as electrode materials inwater in salt electrolyte using lithium bis-(trifluoromethanesulfonyl)-imide Li+[N(SO2CF3)2]- (LiTFSI) mixed in different amount of H2O. The redox activities of the composite electrode materials including Mg2Al(OH)6[FcMono]1.0 and Mg2Al(OH)6[FcDi]0.5 suffer from the dissolution of the active redox species migrating out of the host structure in water based electrolyte when low molalities are used. However, while increasing the molality of the electrolyte solution Mg2Al(OH)6[FcDi]0.5 electrode material performs better than Mg2Al(OH)6[FcMono]1.0 ones according to the cycling stability For Mg2Al(OH)6[FcDi]0.5, an optimum behavior is observed for a concentration of LITFSI of at least of 10 m. The electrode exhibits a stable capacity of 25 mAh g-1 which is maintained after more than 100 cycles with 100 % coulombic efficiency. Such stability during cycling is explained by two complementary processes: the preservation of the lamellar structure of Mg2Al(OH)6[FcDi]0.5, FcDi molecule being tethered by its two ends (unlike FcMono tethered at one end only), in connection with the high concentration of the electrolyte in LiTFSI, which helps slowing down the migration of the interleaved redox species out of the structure. This opens the route to re-evaluate LDH-based hybrid materials for water-based energy storage devices.