Unraveling multi-level porous carbon negative electrode materials based on <i>Rosa roxburghii</i> pomace for high-performance sodium-ion batteries

A key hurdle in optimizing sodium-ion battery (SIB) performance is developing cost-effective, highly stable anode materials. Biomass-derived carbon has emerged as a leading candidate due to its recyclability and structural benefits. As a cellulose-rich biomass waste, <i>Rosa roxburghii</i> pomace (RRP) can be transformed into hard carbon materials with porous structures and suitable interlayer spacing through carbonization and structural regulation, exhibiting excellent sodium storage performance. In this study, we developed high-performance hard carbon materials through a straightforward thermal decomposition method, starting with RRP as the primary feedstock. To fine-tune the structure, melamine served as a nitrogen source, effectively weaving nitrogen heteroatoms into the carbon framework. Boasting a sizable interlayer carbon distance (0.69 nm), RRP-800-N exhibits a remarkable reversible capacity (223.7 mAh g^-1 at 31 mA g^-1). It also showcases a high initial coulombic efficiency, clocking in at 99.11% at 31 mA g^-1, and demonstrates a stable cycling life, retaining 237.1 mAh g^-1 after 100 cycles at 31 mA g^-1. The experimental results indicate that the high-activity N groups and disordered amorphous structure of RRP-800-N offer sufficient active sites and enhance conductivity. In addition, the abundant mesopores provide continuous ion transport pathways, shortening the diffusion distance of Na⁺ from the electrolyte to the bulk material. This research shows how RRP biomass waste can be transformed into affordable, sustainable hard carbon, proving its potential as a durable sodium-ion battery anode.