A long-lasting dual-function electrolyte additive for stable lithium metal batteries

Abstract

Solid electrolyte interphases (SEI) plays a vital role in stabilizing lithium (Li) metal anodes for rechargeable batteries. However, forming robust SEI layers is challenging in the state-of-the-art electrolytes. Herein, we report a long-lasting and dual-function additive (potassium nonafluoro-1-butanesulfonate or KPBS) for dual-salt LiFSI-LiTFSI ether electrolyte. Our work suggests that the electrostatic shield effect from potassium ion (K + ) and the F-rich PBS − anions with a middle lowest unoccupied molecular orbital (LUMO) level together promote the formation of a LiF-rich SEI during the Li plating/striping process, which effectively restricts Li dendrite growth and suppresses electrolyte consumption. As a consequence, the designed electrolyte endows small nucleation overpotential, highly reversible Li plating/stripping, and excellent cycling stability. Specifically, with such an electrolyte, Li–Cu cells can maintain stable cycling during 400 cycles at 1 mA cm −2 for 1 mA h cm −2 with a high coulombic efficiency (CE) of 99.1%. Li–LiFePO 4 full cells displayed dramatically improved cycling stability after 100 cycles with high CE of 99.6% under relatively lean electrolyte condition (7.5 μL mA h −1 ), limited Li supply (N/P = 1.2) and high areal capacity (4.1 mA h cm −2 ). • A long-lasting electrolyte additive, KPBS, promoting the formation of robust LiF-rich SEI layer on the anode side was discovered. • The K + cations can offer effective electrostatic shielding that prevents the formation of Li-metal “hot-spots”. • The F-rich PBS − anions with a unique lowest unoccupied molecular orbital (LUMO) level is responsible for the formation of LiF-rich SEI layer. • Li–LiFePO 4 full cells with KPBS showed improved cycling stability with relatively lean electrolyte, limited Li supply and high areal capacity. • The electrolyte additive shows promise for practical Li-metal cell applications.