Nanoconfinement-Induced Electrochemical Ion-Solvent Cointercalation in Pillared Titanate Host Materials

Abstract

Electrochemical ion-solvent cointercalation reactions are an avenue to reach improved kinetics compared to the corresponding intercalation of desolvated ions. Here, we demonstrate the impact of different structural pillar molecules on the electrochemical Li⁺ intercalation mechanism in expanded hydrogen titanate (HTO) electrode materials. We show that interlayer-expansion of HTO with organic pillars can enable cointercalation reactions. Their electrochemical reversibility is drastically improved when non-cross-linking pillars are employed that expand and separate the host material's individual layers, underlining the impact of the electrochemo-mechanics of the nanoconfined interlayer space. This pillared HTO structure results in an increased Li⁺ storage capacity and reversibility compared to pristine HTO. We derive structural models of the pillared HTO host materials based on combined experiments and theoretical calculations, and employ electrochemical operando experiments to unambiguously demonstrate the nanoconfinement-induced cointercalation mechanism in pillared HTO electrode materials. The work demonstrates the potential of nanoconfined pillar molecules to modify host materials and enable highly reversible cointercalation reactions with improved capacity and kinetics.