Biphenylene Concentric Nanorings as High-Performance Anode Materials for Sodium Ion Batteries: A DFT and AIMD Study

Sodium-ion batteries (SIBs) are emerging as cost-effective and sustainable candidates for large-scale energy storage due to the natural abundance and low cost of sodium. However, conventional graphite anodes are intrinsically unsuitable for SIBs because Na ion intercalation is thermodynamically unfavorable, motivating the exploration of alternative anode materials. Inspired by the recent experimental realization of the biphenylene network (BPN), encourages to explore its low-dimensional analogues as potential anode materials for alkali-ion batteries. In this study, we therefore rationally design and investigate biphenylene concentric nanorings (BPNCRs), a zero-dimensional (0D) derivative of BPN, as a potential anode material for SIBs using first-principles density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. The BPNCR anode exhibits a high theoretical capacity of 483 mAhg –1 and energy density of 1236 mWhg –1, which can be further enhanced by increasing the inter-ring separation. The average open-circuit voltage is 0.15 V under vacuum and becomes significantly higher (0.76 V) under electrolyte-screened conditions, which is beneficial for practical operation. Charge analysis reveals significant electron transfer from Na to the carbon framework, indicating strong Na–C interaction and also all Na atoms are charged, thereby reducing the possibility of Na plating. BPNCRs also exhibit excellent mechanical stability, with slight volume expansion (∼1.06%) during sodiation and a low Na-ion diffusion barrier (