Ultrastable Gel Polymer Lithium Metal Batteries With Novel Nitro-Substituted Hexafluoride SEI-Forming Additive

Abstract

Employing functional additives can facilitate the formation of stable solid electrolyte interphase (SEI), which has emerged as a promising strategy to improve the electrochemical properties of lithium metal batteries (LMBs). Typical SEI containing inorganic components, such as lithium fluoride (LiF) and lithium nitride (LiN_xO_y and Li₃N), have been confirmed to construct an ideal SEI for LMBs. Here, we designed and synthesized a novel molecule named BTFN to act as an SEI-forming additive containing fluorine and nitro groups. The strong electron-withdrawing effect greatly reduces the lowest unoccupied molecular orbital (LUMO) energy, facilitating its preferential decomposition during the SEI-forming process. An SEI with rich LiF, LiN_xO_y, and Li₃N forms after its preferential and complete decomposition, greatly enhancing stabilization and uniformity. The lifespan of symmetric LMBs with BTFN significantly increases more than 12 times under the same conditions; the Li/SPE/LFP full batteries cycle more than four times the contrast batteries with a capacity retention of 99.7%. This work provides some experiences and opinions for exploring complex SEI-forming additives.