A Polyionic, Large-Format Energy Storage Device Using an Aqueous Electrolyte and Thick-Format Composite NaTi2(PO4)3/Activated Carbon Negative Electrodes

A composite anode comprising blended NASICON-structured NaTi2(PO4)(3) and activated carbon has been implemented in an aqueous electrolyte electrochemical energy storage device. A simple solid-state synthetic route based on lowcost precursors was used to produce the NaTi2(PO4)(3), and thick (> 1 mm) freestanding electrodes were fabricated with a range of activated carbon mass fractions. Electrochemical analyses showed the efficacy and stability of this composite anode combination in a functional paradigm where both Na+ and Li+ cations can participate in the charge storage reactions. Use of this composite anode in concert with a lambda-MnO2 based cathode results in an energy storage device that is low cost, robust, and of sufficient energy density to be implemented in stationary applications. Data from large-format units that contain many cells in series indicate that string-level self-balancing occurs, an effect that can be relied on for making cycle-stable high-voltage strings of cells.