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 2 nm in diameter, whereas that for SnOx/CNF-800 represented around below 4 nm. 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.