Tandem Design of Functional Separators for Li Metal Batteries with Long‐Term Stability and High‐Rate Capability

Abstract The lithium (Li) dendrite growth seriously hinders the applications of lithium metal batteries (LMBs). Numerous methods have been proposed to restrict the formation of Li dendrites by improving the Li‐ion transference number (t_Li⁺) through separator modification according to Sand's time equation. However, ignoring the positive contribution of anion motion to solid electrolyte interphase (SEI) formation will result in insufficient inorganic components, which impedes practical implementation of LMBs. Herein, a “tandem” separator is constructed (ZSM‐5‐Poly dimethyl diallyl ammonium chloride (PDDA)/Polyethylene (PE)/SbF₃), which anchored anions and built an inorganic‐rich SEI at the same time. The resulting SEI from SbF₃ (SBF) coating on side facing Li is rich in Li‐Sb alloy (Li₃Sb) and LiF. Li₃Sb can significantly reduce the migration energy barrier of Li ion (Li⁺) and facilitate Li⁺ transport. Simultaneously, ZSM‐5‐PDDA (Z5P) coating at the other side can effectively immobilize anions and increase the t_Li⁺. Moreover, the regular pore structure is conducive to homogenizing Li⁺ flux and also capable to uniform temperature distribution, significantly improving safety. Hence, the lifespan of Li|Li and Li|Cu cells assemble with Z5P/PE/SBF separator is significantly extended. In addition, full cells with LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) and LiFePO₄ (LFP) cathodes show excellent cycle stability and superior rate performance.