High Performance Lithium Metal Batteries Enabled by Surface Tailoring of Polypropylene Separator with a Polydopamine/Graphene Layer

Lithium (Li) metal batteries suffer from the intrinsic issues associated with poor Coulombic efficiency and dendritic Li growth. Herein, a multifunctional trilayer membrane is reported first by depositing a dual layer of a polydopamine (PDA) and a graphene-carboxymethyl cellulose (Gr-CMC) on top of the standard polypropylene separator in order to enhance the cycle performance and electrochemical stabilities of Li metal electrodes. The Gr-CMC layer of the designed separator has an excellent electrolyte wettability, enhanced electrical conductivity, and additional capacity for Li storage. These strong benefits facilitate the excellent and effective electrochemical reactions and kinetics in both the Li/Cu half-cell and the Li/LiFePO₄ (LFP) full cell. When the PDA/Gr-CMC separator is employed in both systems, the cycle stability and Coulombic efficiency are dramatically improved and the interfacial impedance between the electrode and the separator is significantly reduced. Electrochemical stability tests at 0 °C further demonstrate the positive potential of the designed separator for facilitating the stable operation of Li metal batteries. The approach not only serves as an effective way of enhancing the life-time and capacity of Li metal batteries but also can broaden the material options for the development of advanced Li metal batteries.