Exploring polycyclic aromatic hydrocarbons for sodium- and potassium-ion battery anodes: a DFT approach

Abstract

The growing demand for sustainable, cost-effective, and high-performance energy storage technologies has intensified research into alternative systems beyond lithium-ion batteries (LIBs). Sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) have emerged as promising candidates due to the abundance and affordability of Na and K. In this study, density functional theory (DFT) methods were employed to systematically investigate the potential of twenty-three polycyclic aromatic hydrocarbons (PAHs) as organic anode materials for SIBs and PIBs. A detailed analysis of the interaction between PAHs and alkali metal cations (M⁺ = Na⁺, K⁺) and atoms (M = Na, K) was performed using molecular electrostatic potential (MESP) analysis, adsorption energy calculations, charge transfer analysis, and spin density distribution analysis. The results reveal that the interaction between PAHs and M leads to charge transfer, resulting in the formation of PAH˙⁻⋯M⁺ complexes, which are crucial for anode activity. Cell voltages (V_cell) were computed from adsorption energetics, highlighting a strong dependence on the structure and size of the PAH. Compact and highly conjugated PAHs like naphthalene, phenanthrene, coronene, and circumbiphenyl show superior electrochemical performance, with several candidates demonstrating V_cell > 1.00 V for LIBs and SIBs and V_cell > 0.60 V for PIBs. This study establishes key structure–property relationships, underscoring the importance of molecular geometry, π-conjugation, and electron-donating ability in tailoring organic anode materials for post-lithium battery systems.