TY - JOUR
T1 - Analysis of crossover-induced capacity fade in redox flow batteries with non-selective separators
AU - Nemani, Venkat Pavan
AU - Smith, Kyle C.
N1 - This work was partially supported by the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. Additional support was provided by the Department of Mechanical Science and Engineering at the University of Illinois at Urbana-Champaign.
PY - 2018
Y1 - 2018
N2 - Redox flow batteries (RFBs) are candidates for grid-scale energy storage. For RFBs mechanistic understanding of redox-active species crossover is needed to optimize electrolyte composition (both of inert salt ions and redox-active species) especially when low-cost separators are used instead of ion-selective membranes. We simulate these effects using a multi-component porous electrode model with Nernst-Planck fluxes and Marcus-Hush-Chidsey kinetics to predict capacity utilization and fade. The molar ratio of inert salt to redox species and the ratio of their diffusivities are used to parameterize different electrolytes in RFBs with non-selective separators. Irrespective of whether redox couples use a common charge-balancing counterion (rocking chair configuration) or not (salt splitting configuration) the molar ratio of inert salt to redox species must exceed 50% to cycle with substantial capacity. Using Damköhler numbers (characteristic scales of reaction rates to transport rates) for both inert salt Dasalt and redox-active species Daredox we classify three RFB operating regimes: redox shuttle limited, ohmic polarized, and sufficient supporting electrolyte. In the sufficient supporting electrolyte regime capacity fade is found to scale inversely with Daredox, resulting in capacity fade per cycle less than 0.01% for Daredox larger than 105 and capacity utilization of approximately 80% for Dasaltsmaller than 12.
AB - Redox flow batteries (RFBs) are candidates for grid-scale energy storage. For RFBs mechanistic understanding of redox-active species crossover is needed to optimize electrolyte composition (both of inert salt ions and redox-active species) especially when low-cost separators are used instead of ion-selective membranes. We simulate these effects using a multi-component porous electrode model with Nernst-Planck fluxes and Marcus-Hush-Chidsey kinetics to predict capacity utilization and fade. The molar ratio of inert salt to redox species and the ratio of their diffusivities are used to parameterize different electrolytes in RFBs with non-selective separators. Irrespective of whether redox couples use a common charge-balancing counterion (rocking chair configuration) or not (salt splitting configuration) the molar ratio of inert salt to redox species must exceed 50% to cycle with substantial capacity. Using Damköhler numbers (characteristic scales of reaction rates to transport rates) for both inert salt Dasalt and redox-active species Daredox we classify three RFB operating regimes: redox shuttle limited, ohmic polarized, and sufficient supporting electrolyte. In the sufficient supporting electrolyte regime capacity fade is found to scale inversely with Daredox, resulting in capacity fade per cycle less than 0.01% for Daredox larger than 105 and capacity utilization of approximately 80% for Dasaltsmaller than 12.
UR - http://www.scopus.com/inward/record.url?scp=85064455453&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85064455453&partnerID=8YFLogxK
U2 - 10.1149/2.0701813jes
DO - 10.1149/2.0701813jes
M3 - Article
AN - SCOPUS:85064455453
SN - 0013-4651
VL - 165
SP - A3144-A3155
JO - Journal of the Electrochemical Society
JF - Journal of the Electrochemical Society
IS - 13
ER -