Non-Aqueous Flow Battery Development

Rangachary Mukundan (mukundan@lanl.gov), Sandip Maurya, and Benjamin L DavisMPA-11: Materials Synthesis and Integrated Devices, Los Alamos National Laboratory, Los Alamos, NM 87545, United States

• Iron Pyridylimide complexes show potential for NARFB application. A single complex supports multi electron redox and can be cycled up to 2.35V• Redox active organic molecules (ROMs) display wide potential window (> 3V) for NARFB applications. Collaboration with SNL (Travis Anderson) to incorporate them into NARFBs. Joint

publication with SNL planed. Objective of > 3V redox potential met.• Anion exchange membranes developed and demonstrated in aqueous flow battery. Compatibility with Non-aqueous electrolytes to be evaluated• Membrane transport number determined with commercial membranes and anion/cation exchange membranes from SNL (Cy Fujimoto). Membranes also obtained for evaluation

from ORNL (Jagjit Nanda). Joint publication with SNL planned. Objective of transport number determination met.

Objectives

Acknowledgments• Dr. Imre Gyuk, Director of Energy Storage Research, Office of Electricity• Sarah Eun Joo Park, Yu Seung Kim, Shikha Sharma, Nathan Smythe and John C Gordon, Laboratory Directed

Research & Development, MPA Division, and Feynman Center for Innovation (Work till February 2020)

Summary and Collaborations

Flow batteries are among the 3 core R&D technologies prioritized by OE, as part of their mission to create a resilient, reliable, and flexible electrical grid. A NARFB Workshop conducted in 2019 concluded that “While non-aqueous flow batteries hold promise of high energy and power density durable grid-scale energy storage, significant research effort is required to realize this potential.” The two primary long-term objectives of this project based on the conclusion of the workshop are:1. Development of stable low-cost redox couples that exhibit a > 3V potential window2. Development of high conductivity durable membranes/separators

Introduction

Redox Active Molecule Development Characterization

Flow batteries utilizing Non-aqueous electrolytes enable cell operation at higher potential compared to aqueous electrolyte, leading to higher energy density and energy efficiency. Non-aqueous redox flow batteries (NARFBs) are ideally suited to take advantage of low-cost, multi-electron, metal/ligand and organic molecule based chemistries if they can address long term stability.

Membrane Development and Characterization

Bulk electrolysis

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Synthesis

Cyclic Voltammetry

Multi electron redox separated by > 2VMetal center (> 0.5V), multiple electrons on ligand (< -1.5V)

Stable charge/discharge cycles demonstrated in a flow battery. Potential for higher energy density compared to Vanadium flow batteries

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Quaternized poly(arylene ether benzonitrile) membranessynthesized and characterizedPerformance comparable or better than SOA Nafionmembrane in aqueous VRFB.

Thickness can be adjusted to provide optimal power density and cycling stability50 µm membrane demonstrates significantly improved capacity retention and good power density

• Capability: Membrane synthesis and characterization of conductivity, transport number, and selectivity• Prior Work: Stable anion exchange membranes

developed. Highly selective for Vanadium ions in aqueous electrolyte with no crossover in 500 h• Current Work: Set up established to determine

membrane transport number• Future Work: Evaluate/Modify membranes for NARFBs

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t-Membrane Transport number determination

E. J. Park, S. Maurya, U. Martinez, Y. S. Kim and R. Mukundan, Journal of Membrane Science, 2020, 617, 118565.

• Capability: Synthesis and evaluation of non aqueous flow battery chemistries.

• Cyclic voltammetry to establish potential window• Bulk Electrolysis to establish

redox stability• Flow battery testing (5 - 50cm2)

to evaluate energy and power density

• Prior Work: Potential for high voltage in Iron based methyl pyridylimine chemistry established• Current Work: Instability of 2nd

electron on ligand determined. 1st

electron on ligand and metal center can be cycled reversibly• Future Work: Developing Redox

active organic molecules (ROMs) with > 3V potential window. Stability in NARFB to be established.

Approach1. Synthesize/Evaluate metal-ligand and organic redox active molecules for NARFB

applicationsa) Multi-electron supporting metal/ligand molecules developedb) Organic molecules with >3V being developed

2. Synthesize/evaluate membranes for flow battery applicationsa) Developed transference number measurement apparatusb) In collaboration with SNL and ORNL, develop and evaluate membranes for

NARFB applications

S. Sharma et al, Iron-Iminopyridine Complexes as Charge Carriers for Non-Aqueous Redox Flow Battery Applications, To be submitted to Applied Energy Materials

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Potential (V vs. Ag/AgNO3)

3.3 V

Diphenyl oxadiazole-Thianthrene couple displays voltage of 3.3V. Cycled 20 times with 80% voltage efficiency

Flow battery testing

2,5-Diphenyl-1,3,4-oxadiazole(ODZ/ODZ·-)

Anolyte

Thianthrene (TH/TH·+)Catholyte

(TH/TH·+)

(ODZ/ODZ·-)

Bulk cycling demonstrates stability of metal (+ve) and first ligand (-ve) redox reations