Electrochemical characterization of electrospun SnOₓ-embedded carbon nanofibers anode for lithium ion battery with EXAFS analysis

SnOₓ-embedded carbon nanofibers (SnOₓ/CNF) were synthesized by electrospinning a composite solution of Sn(II) acetate, polyacrylonitrile (PAN), and polyvinylpyrrolidone (PVP) in N,N-dimethylformamide (DMF), followed by stabilization and carbonization. The SnOₓ for SnOₓ/CNF-700 was distributed about below 2nm in diameter, whereas that for SnOₓ/CNF-800 represented around below 4nm. The fine structure of SnOₓ for SnOₓ/CNF was confirmed by analysis of extended X-ray absorption fine structure (EXAFS). The diameter of the fibers decreased with increasing temperature, whereas both SnOₓ particles and electrical conductivity of SnOₓ/CNF increased. Both SnOₓ/CNF-700 and SnOₓ/CNF-800 were prepared as disordered structures, whereas SnOₓ/CNF-900 was synthesized as an SnO₂-like structure. The disordered transformation inducing excellent electrochemical performance originated form CNF prepared by electrospinning and proper heat treatment. Pure SnO₂ displayed low electrochemical performance, indicating a typical large volume change and high mechanical stress. On the contrary, SnOₓ/CNF-800 represented outstanding specific discharge capacity and exceptional cycle retention at the same time, representing a coulomb efficiency of 71% even in the initial cycle. The specific discharge capacity for SnOₓ/CNF-800 slightly decreased by the 20th cycle, and then gradually increased by the 100th cycle. The CNF plays an important role as a buffering agent to prevent SnOₓ particles from agglomerating. The CNF having 1D pathway with high electrical conductivity leads to the promotion of charge transfer as well as mass transfer.