Concentration-Driven Li⁺ Solvation Engineering with TDMAP-Based Porphyrin Additives for Dendrite-Free Li Metal Batteries

The performance of lithium metal batteries is strongly influenced by Li⁺ solvation and solid electrolyte interphase (SEI), which governs dendrite growth, cycling stability, and Coulombic efficiency. Herein, to modulate Li⁺ solvation structure, the tetrakis(4-N, N-dimethylaminophenyl)porphyrin (TDMAP) is introduced as an additive in carbonate-based electrolyte, further reinforcing SEI stability. Spectroscopical measurements reveal that TDMAP displaces ethylene carbonate (EC) molecules from the first solvation shell, partially forming mixed coordination environments and acting as a ligand that modulates the Li⁺ solvation shell and alters its interaction with PF₆^- anions (Li⁺-NMe₂-PF₆^-). Results show that the electrolyte with optimal 3 mg mL^-1 TDMAP (TDMAP-3) enables and promotes smooth, dense Li deposition and a LiF-rich and nitrogen-rich SEI on the condition of the expected Li⁺ solvation structure shell, in contrast to the dendritic and porous Li plating morphology as observed in the base electrolyte. Consequently, the cell with TDMAP-3 additive reduces the nucleation overpotential from 62 to 20 mV, achieves high Coulombic efficiency (∼99%), and the Li-LiFePO₄ full cell maintains capacity retention of 97.3% over 450 cycles, demonstrating that porphyrin additive effectively regulates Li⁺ solvation and SEI composition for high-performance Li metal batteries.