Synergistic enhancement of lithium storage in biomass-derived hard carbon anodes via structure and phosphorus doping engineering

Conventional lithium-ion batteries (LIBs) anodes suffer from critical drawbacks including severe volume expansion, inferior conductivity, insufficient initial Coulombic efficiency (ICE), and limited cycling life. Biomass-based hard carbon (HC) features low cost, abundant sources, stable cyclability, and minor volume variation, making it ideal to overcome the bottlenecks of traditional anodes. In this work, hierarchical porous HC was synthesized via high-temperature pyrolysis and carbonization with walnut shells, reed stalks, and corn stalks as raw precursors. The morphology and structural properties were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and nitrogen adsorption-desorption. Electrochemical lithium storage performance was evaluated by cyclic voltammetry (CV) and constant current charge-discharge tests. Results indicate that walnut shell-derived HC shows a more ordered carbon skeleton and low impurities, improving material yield and cycling stability. Phosphorus doping enhances conductivity and electron transport, increases active sites, and reduces side reactions with electrolytes, thus boosting ICE and stability. The 5% phosphorus-doped sample exhibits excellent lithium storage performance via the triple synergistic effect of structure, interface, and electronic conductivity. At 0.5 C for 100 cycles, it delivers an ICE of 82.81%, reversible capacity of 242.6 mA h g-1, and capacity retention of 80.15%. Even at 1.86 A g-1, a rate capability of 129.1 mA h g-1 is achieved. These findings provide a feasible route for constructing advanced hard carbon HC electrodes with superior lithium-storage capability.