Electrochemical Modification of Methane Plasma-Derived Recovered Carbon by Phosphorus Doping as an Anode Material for Sodium-Ion Batteries

High-capacity and sustainable anode materials are critical for the commercial advancement of sodium-ion batteries (SIBs). In this study, red phosphorus was integrated into a carbon framework using high-energy ball milling to create a phosphorus-doped recovered carbon (PRC) composite. Structural characterization through HRTEM and XRD confirms that phosphorus incorporation induces a significant lattice expansion (d002 = 0.358 nm), providing widened pathways for sodium-ion (Na+) transport. Electrochemical evaluations reveal that the PRC anode has an outstanding reversible capacity of 250 mAh/g at 0.1 A/g and sustains around 100 mAh/g at a high current density of 5.0 A/g, significantly outperforming the pristine recovered carbon (55 mAh/g). Kinetic analysis using the Randles-Sevcik equation indicates an order-of-magnitude boost in the diffusion coefficient 3.5 × 10−13 cm2/s compared to the undoped precursor. Furthermore, b-value analysis demonstrates that the superior rate capability is driven by dominant pseudocapacitive charge storage and enhanced structural stability over 200 cycles. These findings underscore the potential of heteroatom-doped recovered carbon as a robust, low-cost platform for high-power density SIBs.