Battery and supercapacitor materials in flow cells. Electrochemical energy storage in a LiFePO(4)/reduced graphene oxide aqueous nanofluid

Exploring conceptual frontiers between batteries, supercapacitors, redox flow batteries (RFBs) and fuel cells (FCs), we have used a battery material (i.e. LiFePO₄) and a supercapacitor material (i.e. graphene) in the form of nanoparticles dispersed in an aqueous electrolyte to characterize the electrochemical activity of the resulting electroactive nanofluids. X-ray diffraction, TEM, Raman, XPS and AFM analyses were carried out to characterize the solid LiFePO₄ and RGO components. The corresponding electroactive nanofluids were prepared by dispersion in an aqueous Li₂SO₄ electrolyte and stabilized with Diaminobenzoic Acid (DABA). Cyclic voltammetry measurements were used to analyze their electrochemical behavior in three-electrode cells. Charge-discharge tests of the LiFePO₄/RGO (positive) vs. RGO (negative) nanofluids were also performed. Effective utilization of dispersed electroactive particles (ca. 100 mAh/g(LFP) at 1C) was demonstrated, which turned out to be superior to the same LFP material used as solid electrode. A charge-transfer percolation effect provided by the RGO dispersion is proposed as the mechanism for the good performance of LiFePO₄ (not coated with carbon!) and RGO Nanofluids. Our results constitute a first step and proof of concept of the possible application of electroactive nanofluid electrodes in alternative flow batteries.Daniel Rueda-Garcia, Zahilia Cabán-Huertas, Sergi Sánchez-Ribot, Carlos Marchante, Raul Benages, Deepak P. Dubal, Omar Ayyad, Pedro Gómez-Romer