Are electrospun carbon/metal oxide composite fibers relevant electrode materials for Li-ion batteries?

Self-standing and flexible paper-like electrodes consisting of nano-sized Co3O4 nanoparticles encapsulated in nitrogen-doped graphite-like carbon fibers are synthesized by electrospinning followed by thermal treatment. Several studies have recently reported that encapsulating nano-sized metal oxides that display conversion reaction, such as manganese, iron and cobalt oxides, within the three-dimensional network of electrospun carbon fibers allows to remarkably improve the performances of lithium-ion batteries. In the present work, we challenge these reports with a study based on the optimization of the preparation and post-synthesis treatment parameters, and a very precise characterization of the structural, morphological and chemical properties of the composite materials leading to clear structure-electrochemical properties correlations. In particular, it is found that the electrochemical properties of a physical mixture of cobalt oxide nanoparticles and electrospun carbon nanofibers are equivalent to the ones of the electrospun nanocomposites, proving that the benefit of electrospun metal oxide-carbon nanocomposites is limited and that the "enhanced properties" claimed in the literature arise from imprudent comparisons.