Nature-Inspired Purpurin Polymer for Li-Ion Batteries: Mechanistic Insights into Energy Storage via Solid-State NMR and Computational Studies

Organic electrode materials for lithium-ion batteries provide an enticing solution to alleviate the challenges of sustainability, costliness, and humanitarian impact associated with the sourcing and recycling of current inorganic-based technologies. However, recent research efforts have focused on curtailing the instability of readily soluble organic molecules in electrolytes, which results in rapid capacity fading and short cycling lifetimes. Quinones, such as the naturally occurring red dye purpurin, exhibit electrochemical properties competitive with commercial LIB cathodes, and attributed tothe coordination of Li ions with redox-active carbonyl and hydroxyl functional groups. In order to overcome solubility problems, this study successfully appends purpurin to the widely available and inexpensive polymer, 4-chloromethyl polystyrene. The resulting purpurin-functionalized polystyrene exhibits a stable capacity of 150 mAh g(-1) at a current density of 50 mA g(-1) for over 60 cycles. To validate the performance of this material, in-depth Li-ion binding mechanisms are elucidated through a unique comparison of solution-state characterization of soluble analogs and solid-state NMR spectroscopy performed on the polymer, supplemented by computational studies.