Multifunctional Silicon‐Based Composite Electrolyte Additive Enhances the Stability of the Lithium Metal Anode/Electrolyte Interface

Abstract The high energy density of lithium metal batteries (LMBs) makes them a promising battery research target. However, the solid electrolyte interphase (SEI) instability causes dendrite formation/growth and short circuits. Electrolyte engineering can regulate the intrinsic properties of the SEI due to the composition and properties of the SEI strongly depend on the electrolyte component. In this work, 2,4,6,8‐tetramethyl‐2,4,6,8‐tetravinylcyclotetra‐siloxane (V4) is paired with vinyl‐triethoxy‐silane (VTEO) to obtain a novel ester‐based electrolyte additive. Decomposition of V4 molecules into silicon‐based polymer‐rich SEI on the Li metal anode surface has been predicted theoretically and verified experimentally. Through ─CH═CH 2 addition polymerization on the preformed silicon‐based polymer layers which originates from the decomposition of V4, VTEO molecules can be integrated into SEI films due to their “molecular bridge” structure. The organic functional group (─OCH 2 CH 3 ) on VTEO molecules promotes Li + transport kinetics and forms Si─O─Li bonds under the presence of OH − , improving anode interface stability. The experimental results show that the cycle life of the LFP‐Li full batteries is over 1000 and 500 cycles at 5 C and 10 C, respectively. This research elucidates a reliable strategy for constructing SEI film with high adhesion and long‐term viability on the Li metal anode.