Reduced graphene oxide decorated with SnO2 nanoparticles as negative electrode for lithium ion capacitors

The effort to increase the energy density of conventional electric double-layer capacitors (EDLCs) goes through the development of lithium-ion capacitors (LICs). Herein, we report a self-standing, binder-free composite as the battery-type negative electrode obtained by a low-cost and easily scalable method. Tin(IV) oxide nanoparticles (<10 nm) embedded in a reduced graphene oxide matrix (SnO2-rGO) were prepared by an in-situ synthetic approach that involves the freeze/freeze-drying of a graphene oxide suspension in the presence of a tin precursor and its subsequent thermal reduction under argon atmosphere. Physicochemical and electrochemical characterization confirmed the optimum nano-structuration of the composite showing ultrafast response at high current densities. Its coupling with a highly porous olive pits waste-derived activated carbon (AC) as the capacitor-type positive electrode, enables the fabrication of a LIC with an excellent energy density output. The newly designed LIC is able to deliver 60 Wh kg−1 at 2.9 kW kg−1 (tdischarge ≈ 1 min) and still 27 Wh kg−1 at 10.6 kW kg−1 (tdischarge ≈ 10 s).