Lithium Storage Mechanism: A Review of Perylene Diimide N-Substituted with a 1,2,4-Triazol-3-yl Ring for Organic Cathode Materials

The demand for lithium-ion batteries (LIBs) has increased rapidly. However, commercial inorganic-based cathode materials have a low theoretical capacity and inherent disadvantages, such as high cost and toxicity. Redox-active organic cathodes with a high theoretical capacity, eco-friendly properties, and sustainability have been developed to overcome these limitations. Herein, perylene diimide derivatives N-substituted with 1,2,4-triazol-3-yl rings (PDI-3AT) were developed to apply as a cathode material for LIBs. The PDI-3AT cathode exhibited discharge capacities of 85.2 mAh g –1 (50 mA g –1 over 100 cycles) and 64.5 mAh g –1 (500 mA g –1 over 1000 cycles) with ratios to the theoretical capacities of 84 and 64%, respectively. Electrochemical kinetics analysis showed capacitive behaviors of the PDI-3AT cathode with efficient pathways for lithium-ion transport. Also, the activation step of the PDI-3AT cathode was demonstrated by improving the charge transfer resistance and lithium-ion diffusion coefficient during the initial few charge–discharge cycles. Furthermore, DFT calculations at the B3LYP/6-311+G** level and ex situ analysis of various charge states of the PDI-3AT electrode using attenuated total reflection Fourier transform infrared (ATR FT-IR) analysis, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were conducted for the further study of the lithium-ion storage mechanism. The results showed that the lithiation process formed the lithium enolate (═C–O–Li) coordinated with the N atoms of the 1,2,4-triazole ring. It is expected that our study results will encourage the production and use of redox-active perylene diimide derivatives as next-generation cathode materials.