Enhancing the capacity and discharge times of flexible graphene batteries by decorating their anodes with magnetic alloys NiMnMx (Mx=Ga, In, Sn)

This work reports the electrochemical performance of flexible batteries whose graphene anodes were decorated with magnetic alloy microparticles of Ni50Mn35In15 (NiMnIn), Ni50Mn30Ga20 (NiMnGa), and Ni50Mn40Sn10 (NiMnSn). The X-ray diffraction patterns indicated that all the magnetic alloys present a martensite phase. According to the scanning electron microscopy analysis, the NiMnGa and NiMnIn microparticles presented a diameter size of 1.5-30 mu m and high porosity. These anodes decorated with magnetic alloy microparticles were subjected to an acid treatment with phosphoric acid to induce the oxidation of the magnetic microparticles. As result, several oxides were simultaneously formed on their surface as confirmed by XPS and FTIR analysis. The presence of these oxides (active sites for the charge storage) enhanced the capacity, energy density and discharge times of the graphene batteries (GBs). The highest energy density (343.5 W h/kg) and capacity (621.7 mA h/g) were obtained for the GB that contained NiMnGa microparticles. In addition, all the GBs demonstrated a discharge voltage >1 V after 10 h, which suggests that they could be suitable to provide energy in portable applications.