Waste-Towel-Derived Hard Carbon as High Performance Anode for Sodium Ion Battery

Developing cost-effective yet high-performance hard carbon anodes is critical for advancing the commercialization of sodium-ion batteries (SIBs), as they offer a balance of low cost, high capacity, and compatibility with Na⁺ storage mechanisms. Herein, waste towels, an abundant, low-cost precursor with a high carbon yield (>49%), were utilized to synthesize hard carbons via a two-step process: pre-oxidation at 250 °C to stabilize the fibrous structure, followed by carbonization at 1100 °C (THC-1100), 1300 °C (THC-1300), or 1500 °C (THC-1500). Electrochemical evaluations revealed that THC-1300, carbonized at an intermediate temperature, exhibited superior Na⁺ storage performance compared to its counterparts: it delivered a high reversible specific capacity of ~320 mAh/g at 1.0 C (1 C = 320 mA/g), with 78% capacity retention after 200 cycles, demonstrating excellent long-term cyclic stability. Its rate capability was equally impressive, achieving specific capacities of 341.5, 331.2, 302.0 and 234.8 mAh/g at 0.2, 0.5, 2.0 and 5.0 C, respectively, indicating efficient Na⁺ diffusion even at high current densities. Notably, THC-1300 also showed an improved initial Coulombic efficiency (ICE) of 75.4%, reflecting reduced irreversible Na⁺ consumption during the first cycle. These enhancements are attributed to the synergistic effects of THC-1300's optimized structural and textural properties: a balanced interlayer spacing (d₍₀₀₂₎ = 0.387 nm) that facilitates rapid Na⁺ intercalation, a low BET surface area (1.62 m²/g) helps to minimize electrolyte side reactions. The combined advantages of high specific capacity, improved ICE, and remarkable cycling stability position this waste-towel-derived hard carbon as a highly viable and sustainable candidate for anode materials in next-generation SIBs, addressing both performance and cost requirements for large-scale energy storage applications.