An All‐Organic Non‐aqueous Lithium‐Ion Redox Flow Battery

Abstract

A non-aqueous lithium-ion redox fl ow battery employing organic molecules is proposed and investigated. 2,5-Di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene and a variety of molecules derived from quinoxaline are employed as initial high-potential and low-potential active materials, respectively. Electrochemical measurements highlight that the choice of electrolyte and of substituent groups can have a signifi cant impact on redox species performance. The charge-discharge characteristics are investigated in a modifi ed coin-cell confi guration. After an initial break-in period, coulombic and energy effi ciencies for this unoptimized system are ∼ 70% and ∼ 37%, respectively, with major charge and discharge plateaus between 1.8-2.4 V and 1.7-1.3 V, respectively, for 30 cycles. Performance enhancements are expected with improvements in cell design and materials processing.

A Membrane‐Free Redox Flow Battery with Two Immiscible Redox Electrolytes

“…The coulombic efficiency of this battery was close to 100 % demonstrating that this first example of a Membrane-Free battery, although far from being optimized, already behaves similar to common RFBs employing expensive ion-exchange membranes. [12] As expected, the ionic liquid anolyte (green curve in Figure 3 a) contributes with a larger polarization to the battery overpotential due to its higher viscosity, lower ionic conductivity, smaller diffusion coefficients and slower kinetics of the active species in comparison with aqueous catholyte. Remarkably, during the OCV step the voltage drop at the interphase, which is one of the key issues of this innovative concept, was found to be negligible revealing the high mobility of charge carriers, probably protons, through the interphase.…”

“…It is worth mentioning that this high value, which has been obtained from a proof-of-concept cell that is not optimized in any respect, is already comparable with recent examples of organic RFBs using membranes. [12] Further improvements in energy density may be realized by increasing organic molecules solubility and enhancing cell voltages via molecular design and electrolyte choice. Although the concept has been validated for one biphasic system in particular, this technology is very versatile and can be applied to other pairs of redox molecules and immiscible solvents.…”

“…[9] Another encouraging research line is the substitution of aqueous electrolytes by non-aqueous electrolytes [10] or even ionic liquids, [11] which are more electrochemically stable and would allow achieving higher battery voltages and energy densities. [12,13] In the last few years, RFBs based on organic redox molecules, such as quinones, phenothiazine, nitroxides, viologens, and pyridines [14][15][16][17] have experienced a great deal of interest, becoming one of the hottest topics in electrochemical energy storage (see Table S1 in the Supporting Information). [18,19] Regardless of the chemical nature of the electroactive species and the type of electrolytes, most RFBs rely on ion-selective membranes to separate the two redox electrolytes and to prevent the crossover of active compounds while allowing the migration of charge carriers.…”

An Investigation of the Ionic Conductivity and Species Crossover of Lithiated Nafion 117 in Nonaqueous Electrolytes

“…Recently, lithiated perfluorinated ionomer has been used as a cation-exchange membrane in a nonaqueous RFB 39 and lithium ion battery. 40 However, the "ion selective" mechanism of these membranes has yet to be demystified.…”

A chemistry and material perspective on lithium redox flow batteries towards high-density electrical energy storage

“…À0.75-1.25 V vs. SHE at neutral pH environment. Therefore, a regular cell provides a relatively low operating voltage in the range of 1.2-1.6 V. 19 Another important category of rechargeable batteries is the Li-ion battery and Li-ion polymer batteries. In a Li-ion battery (Fig.…”