 Graphene nanoplatelet (GnP), which consists of small stacks of graphene, is used as a reinforcement to enhance the performance of the poly(acrylonitrile-butyl acrylate) (PANBA) binder in a lithium ion battery (LIB). To the best of our knowledge, this is the first time that a conductive nanofiller such as GnP has been used in a conventional water-dispersed polymer and applied as a binder for LIB. Our so-called PANBA/GnP nanocomposites are made with either 0.5 wt%, 1 wt%, or 2 wt% of GnP. The nanocomposites are synthesized via an in situ emulsion polymerization technique and are very well-dispersed, homogeneous, and stable for at least 6 months. The elongation and electrical conductivity of the PANBA/GnP nanocomposites exceed those of the PANBA non-filled polymer, and the PANBA/GnP nanocomposite binder ultimately enhances the electrochemical performance of the high-capacity silicon/graphite mixture anode.