Understanding a Single-Li-Ion COF Conductor for Being Dendrite Free in a Li-Organic Battery

In addition to improving ion conductivity and the transference number, single-Li-ion conductors (SLCs) also enable the elimination of interfacial side reactions and concentration difference polarization. Therefore, the SLCs can achieve high performance in solid-state batteries with Li metal as anode and organic molecule as cathode. Covalent organic frameworks (COFs) are leading candidates for constructing SLCs because of the excellent 1D channels and accurate chemical-modification skeleton. Herein, various contents of lithium-sulfonated covalently anchored COFs (denoted as LiO₃S-COF1 and LiO₃S-COF2) are controllably synthesized as SLCs. Due to the directional ion channels, high Li contents, and single-ion frameworks, LiO₃S-COF2 shows exceptional Li-ion conductivity of 5.47 × 10^-5 S · cm^-1, high transference number of 0.93, and low activation energy of 0.15 eV at room temperature. Such preeminent Li-ion-transported properties of LiO₃S-COF2 permit stable Li⁺ plating/stripping in a symmetric lithium metal battery, effectively impeding the Li dendrite growth in a liquid cell. Moreover, the designed quasi-solid-state cell (organic anthraquinone (AQ) as cathode, Li metal as anode, and LiO₃S-COF2 as electrolyte) shows high-capacity retention and rate behavior. Consequently, LiO₃S-COF2 implies a potential value restraining the dissolution of small organic molecules and Li dendrite growth.