B,N Co-doped Polyacrylonitrile-Derived Carbon-Coated LiMn0.6Fe0.4PO4 Cathode for Enhanced Battery Performance

Abstract

To address the low conductivity and manganese dissolution of lithium manganese iron phosphate (LMFP), a boron and nitrogen co-doped graphitic carbon coating strategy are developed. With PAN and boric acid mixture as the carbon source, a continuous, dense, and highly conductive B,N co-doped carbon layer was fabricated on LMFP via a two-step sintering process. LMFP@B/N–C exhibits outstanding electrochemical performance, delivering a capacity of 152.7 mA h/g at 0.1C and 122.8 mA h/g at 1C, with 80.4% capacity and 79.2% retention after 300 and 500 cycles at 1C, outperforming both glucose-derived LMFP@C and PAN-only-derived LMFP@N–C. Boric acid serves as both a cross-linker and a graphitization catalyst, greatly improving the uniformity, compactness, and conductivity of carbon layer. Density functional theory calculations show that B,N co-doping induces interfacial charge redistribution and a built-in electric field, which lowers the Li+ migration barrier and optimizes the interfacial electronic structure. The dense carbon layer acts as a protective barrier, suppressing Mn dissolution, reducing lattice expansion, and enhancing structural stability. This synergistic modification effectively boosts electronic conductivity and ion transport kinetics, leading to superior electrochemical performance of LMFP.