Framework Electronegativity Governs Interfacial Transport Kinetics in Lithium-Metal Batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• Separator engineering is crucial for improving lithium metal battery (LMB) performance.
• Current methods for tuning separator polarity lack a clear link to transport kinetics, making optimization empirical.

Purpose of the Study:

• To establish a quantitative descriptor for ion-selective transport in battery separators.
• To rationally design advanced separators for enhanced LMB performance.

Main Methods:

• Synthesized a series of isoreticular covalent organic frameworks (COFs) with tunable framework electronegativity (χ).
• Investigated the relationship between framework electronegativity and ion transport kinetics (Sand's time).
• Fabricated and tested TFCOF@PP separators in LiFePO4 and NCM811 full cells.

Main Results:

• Framework electronegativity (χ) was identified as a quantitative descriptor for ion-selective transport.
• Optimized TFCOF@PP separators increased the Li+ transference number by 73% and suppressed concentration polarization.
• Achieved stable cycling at 5 C with 83.1% capacity retention after 4000 cycles in LiFePO4 cells.

Conclusions:

• Framework electronegativity provides a rational basis for designing separators that mitigate kinetic failure in metal batteries.
• The developed descriptor-based strategy enables significant improvements in LMB rate capability and cycle life.
• Demonstrated robust performance under demanding conditions, highlighting practical applicability.