A 2D covalent organic framework with ultra-large interlayer distance as high-rate anode material for lithium-ion batteries

Covalent organic frameworks (COFs) have been broadly investigated for energy storage systems. However, many COF-based anode materials suffer from low utilization of redox-active sites and sluggish ions/electrons transport caused by their densely stacked layers. Thus, it is still a great challenge to obtain COF-based anode materials with fast ions/electrons transport and thus superior rate performance. Herein, a redox-active piperazine-terephthalaldehyde (PA-TA) COF with ultra-large interlayer distance is designed and synthesized for high-rate anode material, which contains piperazine units adopting a chair-shaped conformation with the nonplanar linkages of a tetrahedral configuration. This unique structure renders PA-TA COF an ultra-large interlayer distance of 6.2 Å, and further enables it to achieve outstanding rate and cycling performance. With a high specific capacity of 543 mAh·g−1 even after 400 cycles at 1.0 A·g−1, it still could afford a specific capacity of 207 mAh·g−1 even at a high current density of 5.0 A·g−1. Our study indicates that expanding the interlayer distance of COFs by rational molecular design would be of great importance to develop high-rate electrode materials for lithium-ion batteries.