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. (C) 2011 Elsevier B.V. All rights reserved.