Pathways to next-generation redox flow batteries

Redox flow batteries (RFBs) provide a promising pathway towards grid-scale energy storage but are inhibited from widespread implementation due to high costs. RFBs are divided into aqueous (Aq) and nonaqueous (NAq) redox flow batteries, both of which show distinct challenges to build low-cost RFBs with battery prices less than 100 per kWh-1. Overcoming these cost challenges requires a detailed electrolyte techno-economic (TE) model, which explicitly quantifies RFB redox active material, salt, and solvent costs. TE model results identify active species concentration and cell voltage as critical cost-constraining parameters for nonaqueous and aqueous RFBs respectively. Active species concentration targets for NAqRFBs are decreased by increasing cell voltage, and by decreasing area-specific resistance, redox active material molecular weight, and salt molecular weight and concentration. Similarly, cell voltage targets for AqRFBs are decreased by decreasing area-specific resistance and redox active material cost per unit mass and molecular weight. Alternative design pathways for nonaqueous and aqueous RFBs are proposed which decrease NAqRFB redox active material molality targets to 1.1 mol kg-1 and AqRFB cell voltage targets to 0.6 V, and which could potentially decrease RFB battery price to 90 per kWh-1. This TE model is used to analyze a group of experimentally tested nitrobenzene derivatives to find optimal redox active material potential, molecular weight, and salt molecular weight for next-generation nonaqueous RFBs. Nitrobenzene derivatives are found to have a battery price of 260 per kWh-1 when used with TBAPF6 salt, but on switching to TMABF4 salt with lower molecular weight, the battery price can be reduced further to 160 per kWh-1 albeit with higher active material molality targets. Finally, an analytical model of redox active species crossover in nonaqueous RFBs is developed and implemented in order to reduce coulombic inefficiencies in RFBs by selecting optimal operating parameters. The degree of crossover is found to be highly sensitive to current density and separator permeability, and can be decreased by an order of magnitude using thicker separators and higher current densities.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2016

Author dc:creator

• Dmello, Rylan Doyle

Contributors dc:contributor

• Smith, Kyle C.

• electrochemistry
• nitrobenzene
• crossover
• Redox flow battery (RFB)
• NAqRFB
• AqRFB
• NAqRFBs
• Techno economic model

Statement dc:rights

• Copyright 2016 Rylan Dmello

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/90840

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/90840