[17,18]. In the former case, the Co3O4 powder electrode needs to be
fabricated by traditional slurry-coating technique for electrochem-
ical measurement. Despite much progress, the binder involved will
greatly decrease the electrical conductivity of the electrode
materials and undermine the nanoscale advantage. For the latter
case, electro-active Co3O4 nanostructures (such as arrays and
films) are directly grown on conductive substrates forming binder-
free electrodes. This kind of electrode architectures avoids the use
of auxiliary components like conductive agents and binders and
exhibit good electrochemical properties due tot well-defined
electrode network with tailored porosity and good mechanical
stability [19]. In addition, to further increase electronic conductiv-
ity of Co3O4, the typical way is to combine Co3O4 with various
conductive components (such as graphene [20,21], carbon
nanotube [22], carbon nanofibre [23]) for forming a hybrid
nanostructure. In recent years, construction of metal shell or
coating on the metal oxides arrays is considered as a new type of
modification strategy to enhance the performance of LIBs [5].
Typically, ultrathin porous metal shell possesses higher electrical
conductivity than the carbon, and meanwhile, will not block the
fast transfer of ions. Nevertheless, the conformal deposition of
ultrathin metal shell still remains challenge, and needs to be
further explored.
In this paper, different from previous metal modified works,
herein we report a facile method for controllable synthesis of
ultrathin Co on the preformed Co3O4 nanowires forming composite
nanowire arrays. High electrical conductivity and porosity * are