Boosting Ion Transport in Manganese Dioxide Cathodes through Electronically Tuned Molecular Intercalants

Interlayer engineering has been extensively investigated in cathode materials for aqueous zinc-ion batteries (AZIBs). However, current efforts have primarily focused on structural modifications of host materials with limited attention to the molecular properties of intercalants. Herein, we introduce two types of organic molecular intercalants, relatively functionalized with electron-withdrawing groups and electron-donating groups, into MnO2 to modulate the cathode's intrinsic electronic structure. Resonant inelastic X-ray scattering (RIXS) spectroscopy reveals that both intercalants regulate Mn 3d orbitals to different extents. In contrast to the electron-donating group, the electron-withdrawing groups strengthen the interactions with lattice oxygen and promote the Mn 3d-O 2p orbital hybridization, resulting in a reduced crystal field splitting energy and enhanced interactions with Zn. As a result, the molecule with electron-withdrawing groups intercalated with MnO2 exhibits improved ion transport kinetics, delivering a 10-fold increase in the ionic diffusion value as compared to the electron-donating one, and excellent rate performance (172.7 mA h g-1 at 8 C) outperforming commercial MnO2 by a factor of 10.3. Notably, in situ and ex situ X-ray techniques confirm the reversible and stable interlayer structure evolution during cycling, attributed to the strong interaction between Zn and MnO2 intercalated by molecules with electron-withdrawing groups. This study provides new insights into molecular-level electronic modulation in layered materials toward advanced cathode materials.