Bipolar Polymeric Protective Layer for Dendrite-Free and Corrosion-Resistant Lithium Metal Anode in Ethylene Carbonate Electrolyte

The unstable interface between Li metal and ethylene carbonate (EC)-based electrolytes triggers continuous side reactions and uncontrolled dendrite growth, significantly impacting the lifespan of Li metal batteries (LMBs). Herein, a bipolar polymeric protective layer (BPPL) is developed using cyanoethyl (−CH₂CH₂C≡N) and hydroxyl (−OH) polar groups, aiming to prevent EC-induced corrosion and facilitating rapid, uniform Li⁺ ion transport. Hydrogen-bonding interactions between −OH and EC facilitates the Li⁺ desolvation process and effectively traps free EC molecules, thereby eliminating parasitic reactions. Meanwhile, the −CH₂CH₂C≡N group anchors TFSI⁻ anions through ion-dipole interactions, enhancing Li⁺ transport and eliminating concentration polarization, ultimately suppressing the growth of Li dendrite. This BPPL enabling Li|Li cell stable cycling over 750 cycles at 10 mA cm⁻² for 2 mAh cm⁻². The Li|LiNi_0.8Mn_0.1Co_0.1O₂ and Li|LiFePO₄ full cells display superior electrochemical performance. The BPPL provides a practical strategy to enhanced stability and performance in LMBs application.