Dendrite-Free Sodium Metal Anodes Via Solid Electrolyte Interphase Engineering With a Covalent Organic Framework Separator

摘要

Solid electrolyte interphases (SEIs) play a crucial role in keeping sodiummetal anodes (SMAs) intact and improving battery life. However, the SEIsarising from irreversible reactions between metallic Na and electrolytes failto suppress Na dendrite growth and have sluggish Na~+ kinetics. Herein,a functionalized separator modified by a sp~2 carbon conjugated-covalentorganic framework (sp~2c-COF) is proposed to induce a robust SEI. X-rayphotoelectron spectroscopy (XPS) analyses and theoretical calculationsdemonstrate that the SEI is rich in NaF because the structure of NaPF6 isunstable due to influences from the COF separator. In situ observations showthat the Na dendrite is effectively suppressed even at a high current densityof 20 mA cm~（?2）. Satisfactorily, the COF separator exhibits a high transferencenumber of 0.78, achieving a fast Na plating/stripping process. Based onthese superiorities, a symmetric cell Na|COF|Na shows stable cycling for over1500 h at 20 mA cm~（?2）. In addition, full cells Na|COF|NaTi_2(PO_4)_3 (NTPO) presentgood rate performance (30 and 50 C) and excellent cycling stability over5000 cycles at 5 and 10 C. The application of COFs to improve SMAs in thiswork demonstrates a new strategy for improving sodium metal batteries.