Hexachloro-1,3-butadiene as a Functional Additive for Constructing an Efficient Solid Electrolyte Interface Layer for Long-Life Stable Li Anodes

Lithium (Li) metal is considered as one of the attractive anodes for next-generation high-energy-density batteries due to its ultrahigh theoretical specific capacity and low potential. However, many great challenges including uncontrolled dendrite growth and undesired side reactions during repeated cycling still seriously hinder its practical application in Li metal secondary batteries. Herein, we report the hexachloro-1,3-butadiene (HCBD) molecule as a functional additive to stabilize the Li anode by forming a stable solid electrolyte interface (SEI) layer with high Li ion conductivity via in situ surface and electrochemical reactions. Density functional theory calculations demonstrate that HCBD can preferentially react with the Li anode, which generates an ionic conducting species (LiCl) into an SEI layer. The LiCl-rich SEI layer effectively regulates Li⁺ deposition/stripping kinetics and then induces uniform nucleation of Li⁺ and reduces the side reactions between the Li anode and electrolyte. With an optimal amount of HCBD in an ether-based electrolyte, an excellent cycling lifespan (7000 h) was achieved with a low hysteresis voltage of similar to 10 mV at 1.0 mA cm^-2 in a Li||Li symmetrical cell. Furthermore, the LiFePO₄-based cell with the additive-functionalized Li anode displays obviously improved cycling stability (with a high specific capacity of 141.1 mAh g^-1 after 350 cycles at 1 C).