Recent Progress in Using Covalent Organic Frameworks to Stabilize Metal Anodes for Highly-Efficient Rechargeable Batteries

Alkali metals (Li, Na, and K) and multivalent metals (Zn, Mg, Ca, and Al) have become star anodes for developing high-energy-density rechargeable batteries due to their high theoretical capacity and excellent conductivity. However, the inevitable dendrites and unstable interfaces of metal anodes pose challenges to the safety and stability of batteries. To address these issues, covalent organic frameworks (COFs), as emerging materials, have been widely investigated due to their regular porous structure, flexible molecular design, and high specific surface area. In this minireview, we summarize the research progress of COFs in stabilizing metal anodes. First, we present the research origins of metal anodes and delve into their advantages and challenges as anodes based on the physical/chemical properties of alkali and multivalent metals. Then, special attention has been paid to the application of COFs in the host design of metal anodes, artificial solid electrolyte interfaces, electrolyte additives, solid-state electrolytes, and separator modifications. Finally, a new perspective is provided for the research of metal anodes from the molecular design, pore modulation, and synthesis of COFs.

Competitive Coordination Structure Regulation in Deep Eutectic Electrolyte for Stable Zinc Batteries

Rechargeable zinc-based batteries are finding their niche in energy storage applications where cost, safety, scalability matter, yet they are plagued by rapid performance degradation due to the lack of suitable electrolytes to stabilize Zn anode. Herein, we report a competitive coordination structure to form unique quaternary hydrated eutectic electrolyte with ligand-cation-anion cluster. Unraveled by experiment and calculation results, the competing component can enter initial primary coordination shell of Zn2+ ion, partially substituting Lewis basic eutectic ligands and reinforcing cation-anion interaction. The hydration-deficient complexes induced between competing eutectic as hydrogen bond donor-accepter and water also broaden the electrochemical window and confine free water activity. The altered coordination further leads to robust hybrid organic-inorganic enriched solid electrolyte interphase, enabling passivated surface and suppressed dendrite growth. Noticeably, stable Zn plating/stripping for 8000 cycles with high Coulombic efficiencies of 99.6 % and long cycling life of 10000 cycles for Zn-organic batteries are obtained. Even under harsh conditions (small N/P ratio, low temperature), the profits brought by the competitive eutectic electrolyte are still very prominent. This design principle leveraged by eutectic electrolytes with competitive coordination offers a new approach to improve battery performance.