Electrolytes enriched by potassium perfluorinated sulfonates for lithium metal batteries

Abstract

Lithium (Li) metal is widely considered as a promising anode for next-generation lithium metal batteries (LMBs) due to its high theoretical capacity and lowest electrochemical potential. However, the uncontrollable formation of Li dendrites has prevented its practical application. Herein, we propose a kind of multi-functional electrolyte additives (potassium perfluorinated sulfonates) from the multi-factor principle for electrolyte additive molecular design (EDMD) view to suppress the Li dendrite growth. The effects of these additives are revealed through experimental results, molecular dynamics simulations and first-principles calculations. Firstly, K+ can form an electrostatic shield on the surface of Li anode to prevent the growth of Li dendrites. Secondly, potassium perfluorinated sulfonates can improve the activity of electrolytes as co-conductive salts, and lower the electro-potential of Li nucleation. Thirdly, perfluorinated sulfonate anions not only can change the Li+ solvation sheath structure to decrease the desolvation energy barrier and increase the ion migration rate, but also can be partly decomposed to form the superior solid electrolyte interphase (SEI). Benefited from the synergistic effects, an outstanding cycle life over 250 h at 1 mA cm−2 is achieved in symmetric Li||Li cells. In particular, potassium perfluorinated sulfonate additives (e.g., potassium perfluorohexyl sulfonate, denoted as K+PFHS) can also contribute to the formation of high-quality cathode electrolyte interphase (CEI). As a result, Li||LiNi0.6Mn0.2Co0.2O2 full cells exhibit significantly enhanced cycling stability. This multi-factor principle for EDMD offers a unique insight on understanding the electrochemical behavior of ion-type electrolyte additives on both the Li metal anode and high-voltage cathode.