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 PF$_6$$^−$ anions (Li$^+$–NMe$_2$–PF$_6$$^−$). Results show that the electrolyte with optimal 3 mg mL$^{−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–LiFePO$_4$ 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.