Weakly polar additives boost Li+ diffusion kinetics and alleviate electrolyte solvent decomposition for lithium metal batteries

Abstract

The performance of lithium metal batteries (LMBs) is greatly hampered by the unstable solid electrolyte interphase (SEI) and uncontrollable growth of Li dendrites. To address this question, we developed a weak polar additive strategy to develop stable and dendrite-free electrolyte for LMBs. In this paper, the effects of additives on the Li⁺ solvation kinetics and the electrode-electrolyte interphases (EEI) formation are discussed. The function of synergistically boosting the superior Li⁺ kinetics and alleviating solvent decomposition on the electrodes is confirmed. From the thermodynamic view, the exothermic process of defluorination reaction for 3, 5-difluoropyridine (3, 5-DFPy) results in the formation of LiF-rich SEI layer for promoting the uniform Li nucleation and deposition. From the dynamic view, the weakened Li⁺ solvation structure induced by weak polar 3, 5-DFPy contributes to better Li⁺ kinetics through the easier Li⁺ desolvation. As expected, Li||Li cell with 1.0 wt% 3, 5-DFPy exhibits 400 cycles at 1.0 mA cm⁻² with a deposition capacity of 0.5 mAh cm⁻², and the Li||LiNi_0.6Mn_0.2Co_0.2O₂ batteries delivers the highly reversible capacity after 200 cycles.