(774f) Fractional Degradation Cost for Cycling a Zinc/Bromine Flow Cell Battery

Bistrika, A., Oregon State University
Antonishen, M., Oregon State University
Davidson, J., Oregon State University
Halamay, D., Oregon State University
Naviaux, D., Oregon State University
Song, J., Oregon State University
Brekken, T., Oregon State University
von Jouanne, A., School of Electrical Engineering and Computer Science, Oregon State University

It is widely understood that intermittent resources
such as solar and wind are dependent on environmental factors outside our
ability to control.  This allows for the possibility of either power output
exceeding or falling short of forecast levels which leads to more frequent
cycling of regional hydro generators and greater overall grid instability under
the current infrastructure.  Quantifying the cost associated with added
maintenance attributed to an increased penetration of wind and the physical
limitations of a growing dependence on Pumped Hydro Energy Storage (PHES),
becomes essential in painting a more complete picture.  However, alternative means
of Large Scale Energy Storage (LSES), for storing excess power when the outputs
exceeds demand and to supplement output power when it falls short of demand, is
a widely accepted route for mitigating intermittent power generation.1 
Thus, it is crucial to establish an accurate and relative cost function for the
commercially available and most economically viable storage technologies.  The
most promising electrical energy storage technology, to replace PHES, is flow
cell batteries.2 
This begs the question what are the degradation mechanisms in these building
size chemical systems and what do we do when they stop working.  In this study
we report on the key degradation mechanisms that could be expected for standard
operation of a zinc/bromine flow cell battery using graphite electrodes and
assign a cost function dependent of system operating parameters.  In a previous
study we reported the oxidation (or charging) reaction as the most damaging to
the electrode material, see Figure 1
We discuss aging trends and electrode performance by considering surface
chemistry as observed by Raman spectroscopy and scanning electron microscopy. 
Theoretical system performance based on steady state current density measurements
is used to establish a normalized operating cost function for a zinc/bromine battery,
as can be seen in Figure 2.

Figure 1
Oxidation and reduction exchange current; measured for both the cathode and
anode in 6 [M] NH4Br. The x-axis represents the electrode aging, depicted by
total coulombs passed through the electrode per unit surface.

Figure 2 Cost of a 10 % state of charge cycle with respect to a
representative operating parameter (current density factor).

1.             Yang Z, Zhang J, Kintner-Meyer MCW, et
al. Electrochemical Energy Storage for Green Grid. Chemical Reviews. 2012/04/07

2.             Soloveichik
GL. Battery Technologies for Large-Scale Stationary Energy Storage. Annual
Review of Chemical and Biomolecular Engineering.
2012/04/24 2011;2(1):503-527.