Nature-Derived Sodium-Ion Battery: Mechanistic Insights into Na-Ion Coordination within Sustainable Molecular Cathode Materials

Ongoing research in sustainable battery technologies aims to implement the sodium-ion battery (SIB) as a lower-cost alternative to the lithium-ion battery (LIB), thus reducing the susceptibility of materials to volatility in the supply chain and resource scarcity. However, delving into the design paradigm for a stable cathode host material for efficient SIBs is highly challenging because of the greater radius of sodium ions in comparison to lithium. This study explores the chemical and electrochemical sodium-ion coordination properties of tetrakislawsone (TKL), a tetrameric derivative of the lawsone molecule responsible for the dye properties of henna. TKL exhibits stable capacity in electrolytes with facile and reversible Na-ion coupled redox, allowing it to maintain its performance over hundreds of cycles of charging and discharging. Characterization of the Na-ion coordination mechanism in TKL was performed with solid-state NMR and DFT computations, in conjunction with other spectroscopic methods. It was demonstrated that the chemical binding of Na ions occurs via an eight-membered coordination sphere between hydrogen bonded hydroxyl and carbonyl functional groups, forming an interface across two distinct lawsone subunits. This process is accommodated by the three-dimensional structuring of TKL wherein the lawsone units shift out of plane from the aromatic core. This nature-inspired SIB cathode material provides avenues to build fast, stable, high-capacity electrodes using organic molecular systems.