In situ synthesized free-standing LiCoPO4@C nanofibers with multifunctional electrochemical activity for lithium-ion and lithium-sulfur batteries.

Abstract

Free-standing LiCoPO₄@C (LCP@C) nanofibers were synthesized by one-pot electrospinning of precursor salts followed by controlled pre-oxidation and carbonization at 400-460 °C. Pre-oxidation temperature controlled a trade-off between crystallinity and carbon retention: moderate treatment (440 °C) yielded uniformly dispersed nanoparticles within a continuous carbon fiber network, while lower and higher temperatures led to compositional heterogeneity and severe carbon depletion, respectively. Notably, bulk electrical conductivity did not scale with carbon content or graphitization degree; LCP@C-440 exhibited the highest conductivity (6.37 × 10^-5 S cm^-1) among the series despite a lower carbon content and graphitization degree, indicating that fiber-network connectivity, rather than carbon quantity, dominates electronic transport. As a high-voltage lithium-ion cathode paired with a fully fluorinated electrolyte, LCP@C-440 delivered an initial capacity of 80 mAh g^-1 with 75% retention after 100 cycles, outperforming literature composites, using the same electrolyte, in cycling stability despite their higher initial capacities. As a multifunctional host for a 1 M Li₂S₆ catholyte, LCP@C-440 retained a discharge capacity of 467 mAh g^-1 after 250 cycles at 0.2C with a coulombic efficiency of ∼98%, and delivered 350 mAh g^-1 at 1C, fully recovering to 534 mAh g^-1 upon returning to 0.1C. These results demonstrate that a one-pot electrospun LCP@C architecture yields a structurally robust, multifunctional electrode, combining improved cycling stability with a fully fluorinated electrolyte in a high-voltage lithium-ion configuration and sustained long-term performance as a lithium-sulfur host.