Quantification of the Voltage Losses in the Minimal Architecture Zinc-Bromine Battery Using GITT and EIS

Abstract

The sources of voltage loss in the minimal architecture zinc bromine battery are characterized using the galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) on a cell with a three electrode setup. Monitoring of the electrode voltages during charge/discharge indicate the full cell capacity is limited by the Zn/Zn 2+ negative electrode. From GITT, the losses in voltage due to mass transport are shown to be relatively small in comparison to the IR resistance in the cell. In addition, it is shown that decreases in the open circuit voltage with respect to theory are likely caused by the complexation of Br 2 into Br X − . Using EIS, the charge transfer resistances at each electrode and ohmic resistances of each component are determined. Overall, the main factors restricting the voltage of the cell are the ohmic resistances in the carbon cloth current collectors and in the electrolyte. Additionally, significant charge transfer resistances are observed at the negative electrode near the start of charge and end of discharge, when the amount of zinc plated on the carbon cloth electrode is minimal. The major design criteria for electrochemical energy storage on the grid-scale are low cost and long lifetime. To accomplish this, research efforts have largely focused on the development of lowcost active materials which are incorporated into traditional battery designs.1-10 These designs typically contain a considerable amount of passive components that are necessary for extending the lifetime of the battery. An undesired consequence of combining inexpensive materials with passive components is the balance-of-plant cost far outweighs the active material cost.For example, zinc-bromine redox flow batteries have been shown to perform with less than 20% capacity fade for 2,500 cycles. 11,12 However, the cost of this technology (>$200 kWh) is still prohibitive even though the active materials and carbon electrodes only account for ∼$8 kWh. 13 The majority of the cost comes from the system level, where complexing agents, separation membranes, and flow systems are used to prevent the corrosive bromine from reacting with the zinc electrode. [14][15][16][17][18][19][20][21][22][23] In light of this fact, our lab has recently developed a minimal architecture zinc-bromine battery (MA-ZBB), which utilizes the same chemistry from commercial zinc-bromine flow batteries, but does not require the need of any passive components, significantly reducing the cost (projected ∼$94/kWh).24 The MA-ZBB is composed of two carbon based electrodes, which are spatially separated in the vertical direction, in an aqueous electrolyte containing zinc-bromide salt. The battery does not contain any passive components for controlling bromine/zinc interaction (i.e. pumps, membranes or complexing agents). Instead, the electrodes are vertically separated to utilize the variations in density between bromine and the aqueous electrolyte as an advantage to minimize self-discharge. At the negative electrode on top of th...

Advanced Materials for Zinc‐Based Flow Battery: Development and Challenge

“…However, some common issues still exist that all the ZFBs have encountered on account of the similar plating‐stripping process of the zinc couple in the negative half‐cell, which occurs during charging‐discharging of the battery. These issues include zinc dendrite and accumulation, a limited areal capacity and a relatively low working current density. In the following, we will briefly introduce how these issues impede the development of ZFB applications.…”

A One-Dimensional Stack Model for Redox Flow Battery Analysis and Operation

“…For example, in the case that V 2+ crosses over to the high potential (positive) side, or VO 2+ crosses to the low potential (negative) side, the ions will interact with those already present to achieve the intermediate oxidation state, V 3+ , as described by Equation (14). Similar self-discharge reactions are also listed in Equations (15) and 16, and the combination of these three reactions describe the self-discharge events that are assumed to occur quickly and allow each side of the battery system to maintain mass and charge balances. Additionally, inclusion of these reactions simplifies the system by allowing for the consideration of only one electrochemical reaction for each side of the cell as no more than two oxidation states of vanadium will exist for any significant length of time.…”

“…Since we consider the special case of the VRFB, we couple crossover to our mass balance through three homogeneous redox reactions, Equations (14)(15)(16). We assume that each of these reactions occur instantaneously, which is synonymous with having large or well-mixed reservoirs as this would enable the respective solutions to reach a composition with only two oxidation states of vanadium present.…”

“…0.09 USD kg −1 ) and the use of a common redox-active species on both sides of the cell, enabling recovery from crossover-driven capacity fade [4,9,10]. Related RFB research areas that seek to increase energy density and/or employ inexpensive reactants, such as nonaqueous systems [11][12][13], and bromine- [14][15][16], sulfur- [17][18][19], and iron-based chemistries [20][21][22][23], generally focus on development of materials that overcome the undesirable VRFB performance attributes, namely the cell voltage (E θ = 1.26 V) and the cost of vanadium (ca. 20 USD kg −1 ) [1,4,24,25].…”

Modeling the Performance of a Zinc/Bromine Flow Battery

“…Manla et al [27] analyzed and modeled a zinc bromide energy storage for vehicular applications and showed that the open-circuit voltage and internal resistance of the battery are the functions of the battery's state of charge (SOC) and they adopted a Kalman filtering technique to adjust the estimated SOC according to battery current. Knehr et al [28] quantified the sources of voltage loss in the minimal architecture zinc bromine battery based on the experimental data obtained by using the galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) on a cell with a three electrode setup. Among the modeling works on the Zn/Br 2 flow battery mentioned above [20][21][22][23][24][25][26][27][28], references [20,21,[23][24][25][26] belong to the electrochemical models, references [28] uses an equivalent circuit model to quantify the voltage losses, and references [22,27] are based on simple algebraic equation models.…”