Few-Layered Fluorinated Triazine-Based Covalent Organic Nanosheets for High-Performance Alkali Organic Batteries.

In order to fulfill the increasing demand for renewable energy, besides the lithium-ion batteries, other alkali (Na, K)-ion batteries are extensively investigated. However, the difficulty to find universal and environmentally benign electrodes for these alkali (Na, K)-ion batteries still severely restricts their development. Promising characteristics, including molecular diversity, low cost, and operation safety, endow the organic electrodes more advantages for applications in alkali-ion batteries. However, organic electrodes usually deliver a reversible capacity smaller than that of their inorganic counterparts due to sluggish ion/electron diffusion and possible dissolution in organic electrolytes. This work introduces fluorine atoms into the covalent triazine frameworks (CTF) to obtain two-dimensional layered fluorinated CTF (FCTF) and its exfoliated few-layered product (E-FCTF) and uses them as anodes of Li, Na, and K organic batteries. Exfoliated E-FCTF electrode delivers high reversible capacities, as well as excellent cycle life for alkali organic batteries (1035 mAh g-1 at 100 mA g-1 after 300 cycles and 581 mAh g-1 at 2 A g-1 after 1000 cycles for lithium organic batteries). In view of the experimental probing and the theoretical calculation, the Li storage mechanism for the E-FCTF can be determined to be an intriguing multielectronic redox reaction originated from lithium storage on the benzene ring and triazine ring units.