Potassium\nHexafluorophosphate Additive Enables Stable\nLithium–Sulfur Batteries

Abstract

Uncontrollable dendrite growth and\nlow Coulombic efficiency are\nthe two main obstacles that hinder the application of rechargeable\nLi metal batteries. Here, an optimized amount of potassium hexafluorophosphate\n(KPF₆, 0.01 M) has been added into the 2 M LiTFSI/ether-based\nelectrolyte to improve the cycling stability of lithium–sulfur\n(Li–S) batteries. Due to the synergistic effect of self-healing\nelectrostatic shield effect from K⁺ cations and the LiF-rich\nsolid electrolyte interphases derived from PF₆^– anions, the KPF₆ additive enables a high Li Coulombic\nefficiency of 98.8% (1 mA cm^–2 of 1 mAh cm^–2). The symmetrical Li cell can achieve a stable cycling performance\nfor over 200 cycles under a high Li utilization up to 33.3%. Meanwhile,\nthe polysulfide shuttle has been restrained due to the higher concentration\nof the LiTFSI in the electrolyte. As a result, the assembled Li–S\nfull cell displays excellent capacity retention with only 0.25% decay\nper cycle in the final electrolyte. Our work offers a smart approach\nto improve both the anode and cathode performance by the electrolyte\nmodification of rechargeable Li–S batteries.