Precise Regulation of Intrachannel Negative Charge Density in Metal-Organic Frameworks for Efficient Alkali-Ion...

Charged nanochannels are critical for efficient cation transport in metal-organic frameworks (MOFs); however, the relationship between intrachannel negative charge density and ionic conductivity remains poorly understood. Here, we report structurally analogous MOFs with nanochannels of precisely tunable negative charge density: neutral N-MOF, moderately charged M-MOF, and highly charged H-MOF. Our results show that intrachannel negative charge density regulates the electrostatic microenvironment and host-guest interactions, thereby controlling ion-pair dissociation, cation hopping, and the concentration of mobile charge carriers. Fixed negatively charged groups within the MOF nanochannels promote salt dissociation and provide hopping sites for ion migration. However, excessive charge density in H-MOF causes electrostatic anchoring that restricts Li⁺ mobility, whereas the moderate charge density in M-MOF provides the optimal balance between ion dissociation and ion transport. Accordingly, ionic conductivity follows the order M-MOF > H-MOF > N-MOF for both Li⁺ and Na⁺ transport. M-MOF achieved ionic conductivities of 1.56 mS cm^-1 for Li⁺ and 1.38 mS cm^-1 for Na⁺ at 30°C, establishing precise intrachannel charge regulation as a design principle for next-generation solid-state electrolytes.