Three-Motif Molecular Junction Covalent Organic Frameworks for Symmetric All-Organic Lithium-Ion Battery.

The symmetric all-organic batteries (SAOBs) based on the same organic electrode materials for both cathode and anode are promising in achieving an efficient battery system with excellent electrode compatibility, compensable volume change, full discharge ability, low preparation cost, and simple operation procedure, etc. Herein, for the first time, we have designed a kind of anhydride-based three-motif molecular junction COFs (i.e., TAT-AZO-COF) through a melt polymerization method that can serve as dual-electrode active materials for SAOBs. The prepared TAT-AZO-COF with three-motif molecular junction units, resulting from the integration of a cathode-active carbonyl group, an anode-active azo group, and a changeably bipolar-active triazin group, could provide a tunable voltage inductive effect to simultaneously meet the requirements of SAOBs. Thus-assembled SAOBs display excellent rate performance, high energy density (125 Wh kg-1) at 1 A g-1 and superior long-cycle property (90 mAh g-1 over 10 000 cycles) at 10 A g-1, which is represented to be the best high-current density performance among all the organic electrode materials in dual-electrode available SAOBs. The Li+ storage mechanisms of three-motif molecular junction COFs are thoroughly scrutinized by experimental and theoretical identification, and the feasibility in practical application has been validated by a successfully assembled pouch cell.