Understanding and Enhancing the Cycling Stability of Layered Double Hydroxides with Intercalated Ferrocene Anions for Energy Storage Application

Abstract In this work, the layered double hydroxide (LDH) Mg 2 Al(OH) 6 was intercalated with redox active ferrocene carboxylate anions in order to implement charge storage capability to the interlayer spaces of the LDH structure. Two sets of anions, namely mono‐ and dicarboxylic ferrocene, were intercalated to produce two different active materials: MgAl‐FcMono and MgAl‐FcDi. The electrochemical investigation of these two materials was performed in two model electrolytes: 1 M LiTFSI in H 2 O and Pyr 13 TFSI. In the aqueous electrolyte, the first charge reaches the full theoretic capacity of ca. 60 and 40 mAh g −1 for both materials. However, significantly less capacity is stored and delivered during subsequent cycles. In‐situ UV/vis experiments identified the loss as a release of charged ferrocene anions from the LDH during oxidation in the charging process, which is more severe for MgAl‐FcMono. It is possible to prevent this release of redox species by the use of the ionic liquid Pyr 13 TFSI as a high concentrated electrolyte. Subsequently, both materials cycled very steadily with high coulombic efficiency for 150 cycles. This better understanding of the capacity degradation of the LDH‐ferrocene active material is key to improving this new and promising concept of using modified LDHs as active material in energy storage application.