  Lithium-ion batteries have attracted enormous interests recently as promising
power sources. However, the safety issue associated with the employment of
highly flammable liquid electrolyte impedes the further development of
next-generation lithium-ion batteries. Recently, researchers reported the use
of electrospun core-shell fiber as the battery separator consisting of polymer
layer as protective shell and flame retardants loaded inside as core. In case
of a typical battery shorting, the protective polymer shell melts during
thermal-runaway and the flame retardants inside would be released to suppress
the combustion of the electrolyte. Due to the use of a single precursor
solution for electrospinning containing both polymer and flame retardants, the
weight ratio of flame retardants is limited and dependent. Herein, we developed
a dual-nozzle, coaxial electrospinning approach to fabricate the core-shell
nanofiber with a greatly enhanced flame retardants weight percentage in the
final fibers. The weight ratio of flame retardants of triphenyl phosphate in
the final composite reaches over 60 wt.%. The LiFePO4-based cell using this
composite nanofiber as battery separator exhibits excellent flame-retardant
property without compromising the cycling stability or rate performances. In
addition, this functional nanofiber can also be coated onto commercial
separators instead of being used directly as separators.
