Cyclized Polyacrylonitrile (cPAN): A Critical Structure Review and Its Application as Active Cathode Material in Lithium Batteries

Cyclized polyacrylonitrile (cPAN) synthesis entails a multistep process encompassing cyclization, the elimination of NH₃, H₂, and hydrogen cyanate (HCN) gases, and graphitization. This process yields a semiconducting polymer that, when paired with sulfur, is used as cathode materials in Li–S batteries or, under elevated temperatures, produces carbon fibers. Within this framework, we comprehensively characterized cPAN obtained through varying temperature regimes. Utilizing scanning electron microscopy (SEM) and transmission electron microscopy (TEM), alongside infrared and Raman spectroscopies, we scrutinized the samples subjected to thermal treatment. Together, employing density functional theory (DFT), we investigated the potential reaction pathways implicated in the heat treatment of cPAN, while also investigating its viability as a cathode material through DFT calculations and electrochemical characterization using a pontetiostat. Our inquiry emphasizes pivotal insights concerning the structural nuances of cPAN, with a critical state of the structure commonly proposed in the literature. Finally, we assembled and characterized the cPAN as an active material for lithium batteries in a range between 0.2 and 4.6 V, inducing, at high voltage, overpotential reactions that modify the capacity of the cPAN. Thus, cPAN can be considered a material that can be used as anode and cathode material in lithium batteries, according to the electrochemical conditions.