A Non-Stabilized Supersaturated High-Energy-Density Storage Concept for the Redox Flow Battery and Its Demonstration in an H2-V System

Abstract

Redox Flow Batteries are ideal for grid-scale energy storage but have low energy density. In an effort to resolve this issue, this work presents an H2-vanadium RFB system that operates with the catholyte above the solubility limit of vanadium ions in the supersaturated regime without the use of chemical stabilizers, necessary for the operation of a novel solid/liquid storage concept. Initial charge/discharge testing was performed at constant potential (1.35 V charge and 0.65 V discharge) increasing Vanadium concentrations from 1.5 M to 2.5 M. Coulometric capacity increased 67% (40.2 Ah l−1 to 67.0 Ah l−1) while average current density decreased 35% (48 mA cm−2 to 31 mA cm−2) with charge/discharge limited to SOC (20%–80%). Continuing charge/discharge with a cutoff current of 5.56 mA cm−2 increased coulombic capacity by 43% (36.4 Ah l−1 to 51.9 Ah l−1) while average current density decreased 17% (27.7 mA cm−2 to 22.9 mA cm−2). Additional testing was performed with constant current charge/discharge (75 mA cm−2), limited by cutoff potential (1.35 V charge and 0.60 V discharge). Coulometric capacity increased 73.5% (26.5 Ah l−1 to 46.0 Ah l−1) with higher working potential for the 2.5 M Vanadium solution. Energy capacity increased 79.1% (25.3 Wh l−1 to 45.3 Wh l−1) with minimal change in charge/discharge power (90.7/−70.9 mW cm−2 to 92.1/−72.8 mW cm−2) and efficiency (77.1% to 78.4%).