Advanced anode design with PAN-lignin fiber and B, P-co-doped graphitic carbon nitride composites for sustainable lithium-ion battery applications

This study introduces a sustainable anode material for lithium-ion batteries (LIBs) by integrating boron-phosphorus co-doped graphitic carbon nitride (BPCN) into a polyacrylonitrile-lignin (PAN-Lignin) matrix. The composite leverages lignin’s renewable nature and BPCN’s heteroatom-rich structure to address critical challenges in conventional LIB anodes, such as reliance on fossil-derived materials and limited electrochemical performance. Centrifugal spinning and controlled carbonization (800 °C under argon) yielded hierarchically porous PAN-Lignin/BPCN fibers with expanded interlayer spacing (0.34-0.38 nm), as confirmed by XRD and FTIR. The optimized 75:25 PAN-Lignin/BPCN composite demonstrated exceptional lithium-ion storage, achieving an initial discharge capacity of 522.46 mAh g⁻¹ at 0.5 A/g, 1.4× higher than undoped PAN-Lignin anodes—and retained 72.3% capacity (178 mAh g⁻¹) over 50 cycles. Electrochemical analysis revealed synergistic effects: BPCN enhanced electronic conductivity via polarized B-N/P-N bonds, while the lignin-derived carbon framework provided interconnected porosity for efficient ion diffusion. EIS showed low initial interfacial resistance (7.319 Ω) and charge transfer resistance (303 Ω), though post-cycling R_ct increased to 710 Ω due to SEI formation. The composite outperformed single-doped analogs (BCN: 467 mAh g⁻¹; PCN: 498 mAh g⁻¹) and conventional lignin-based carbons, attributed to BPCN’s dual role in stabilizing the SEI layer and introducing active sites. Sustainability was emphasized through lignin’s carbon-negative sourcing and a 200 °C reduction in carbonization temperature compared to graphite anodes. This work advances sustainable LIB technology by replacing >75% fossil-based components with biomass-derived materials while achieving performance metrics rivaling synthetic graphite. The 75:25 PAN-Lignin/BPCN composite sets a benchmark for biomass anodes, aligning with global decarbonization goals. Future efforts should focus on SEI stabilization and full-cell integration to bridge the gap between lab-scale innovation and commercial energy storage systems.