Design of a bipolar organic small-molecule cathode with mesoporous nanospheres structure for long lifespan and high-rate Li-storage performance

Organic small-molecule compounds have become promising cathode materials for high-performance lithium-ion batteries (LIBs) due to their high theoretical capacity, efficient utilization of active sites, low cost, and sustainability. However, severe dissolution and poor electronic conductivity limit their further practical applications. Herein, we have synthesized an insoluble organic small molecule, ferrocenyl-3-(lambda 1-azazyl) pyrazinyl [2,3-f] [1,10] phenanthrolino-2-amine (FCPD), by grafting ferrocene onto pyrazino[2,3-f] [1,10] phenanthroline-2,3-diamine (PPD). The combination of ferrocene (p-type Fe2+ moiety) and PPD (n-type C00000000000000000000000000000000111111110000000011111111000000000000000000000000N groups) in a bipolar manner endows the target FCPD cathode with an increased theoretical capacity and a wide voltage window. The highly conjugated pi-pi aromatic skeleton inside enhances FCPD's electron delocalization and promotes strong interaction between FCPD units. Additionally, the mesoporous structure within the FCPD can provide numerous electroactive sites, contact area, and ion diffusion channels. Benefiting from the bipolar feature, aromatic, and mesoporous structure, the FCPD cathode demonstrates a large capacity of 250 mA h g-1 at 0.1 A g-1, a long lifespan of 1000 cycles and a high-rate capability of 151 mA h g-1 at 5 A g-1 along with a wide voltage window (1.2-3.8 V). Additionally, in situ synchrotron FT-IR and ex situ XPS reveal its dual ion storage mechanism in depth. Our findings provide essential insights into exploring the molecular design of advanced organic small molecules. We designed a bipolar organic small-molecule cathode ferrocenyl-3-(lambda 1-azazyl) pyrazinyl [2,3-f] [1,10] phenanthrolino-2-amine (FCPD). This unique molecular design successfully boosts its Li+/anion storage performance.

Automated summary

Organic small-molecule compounds have shown promise as cathode materials for high-performance lithium-ion batteries due to their high theoretical capacity, efficient utilization of active sites, low cost, and sustainability. However, challenges such as dissolution and poor electronic conductivity hinder their practical application. In this study, a new insoluble organic small molecule, FCPD, was synthesized by grafting ferrocene onto PPD. The FCPD cathode exhibited a large capacity, long lifespan, high-rate capability, and wide voltage window, thanks to its bipolar feature, aromatic, and mesoporous structure.