Calix[4]pyrrole-Based Wavy Covalent Organic Framework: A Protective Layer for High Performance Lithium-Metal...

Practical applications of lithium metal batteries are often limited by low cycling efficiencies and uncontrolled lithium dendrite growth caused by unstable and heterogeneous lithium-electrolyte interfaces. To address this issue, a calix[4]pyrrole-based wavy covalent organic framework (WCOF) is developed that acts as a protective layer to suppress Li dendrite growth and reduce side reactions on the Li anode. The present WCOF is porous and contains calix[4]pyrrole units acting as "molecular traps" that allow efficient PF₆ ^- anion capture while allowing for uniform Li⁺ diffusion. This provides structurally stable artificial protective layers that permit high Li⁺ transference numbers. The resulting solid electrolyte interphases permit ultralong-term stable cycling at a current density of 1 mA cm^-2 and reversible lithium plating/stripping (over 2500 h) at an areal capacity of 2 mAh cm^-2. The protected anodes of this study also demonstrated excellent cell stability through 260 cycles when paired with high-voltage cathodes (NCM811 with high mass loading: 20 mg cm^-2).