Non-Aqueous Redox Flow Batteries: Challenges &...

Non-Aqueous Redox Flow Batteries: Challenges & Opportunities

11/18/14

Fikile Brushett Department of Chemical Engineering

Massachusetts of Institute of Technology, Cambridge, MA

2nd Annual MRES Conference, Northeastern University, Boston MA August 19th, 2014

Need for Distributed Grid Energy

2

Solar Wind Tidal

Power control & generation

Storage

Community Power grid

How can excess electricity be

utilized?

Batteries are <1% of Grid-scale EES

11/18/14 3

DOE, Report on the First Quadrennial Technology Review, 2012

“To accelerate widespread adoption…installed cost of electrochemical grid storage systems fall to the low $100’s/kWh range.” (US Dept. of Energy)

Redox Flow Batteries for Grid Storage

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Xn+ + e- ↔ X(n-1)+ Y(m-1)+ ↔ Ym+ + e-

Xn+

X(n-1)+ Ym+

Y(m-1)+ Y(m-1)+

Ym+

Xn+

X(n-1)+ C+

e-

Charge – solid line Discharge – dotted line

only charge shown

11/18/14

May contain trade secrets or commercial or financial informa7on that is privileged or confiden7al and exempt from public disclosure.

5

Why Non-Aqueous Flow Batteries? Benefits: (+) Expanded voltage window may enable higher energy (and power)

densities and increased round-trip energy efficiency

(+) Broad design space facilitated by wide range of electrolyte options

(+) A greater selection of redox couples available based on solvent choice and/or wider voltage window

(+) Smaller footprint may enable specific high-value urban applications

Challenges: (-) Higher solvent costs may hamper cost-competitiveness

(-) Reduced electrolyte conductivity may decrease performance and limit cell stack design options

(-) Undesirable solvent properties (e.g., volatility, flammability, toxicity)

(-) Unknowns (not a well-studied area)

Towards Cost-effective Energy Storage

11/18/14


6

( ) d

bopaddsmm

smm

dvertqdsysddvdvdsys

a

d tcc

Sc

cMsSc

cMsUFntU

RcEP +

+⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛++⎟⎟

⎠

⎞⎜⎜⎝

⎛++

−=

−

−−

−

−−

+

++

+

++ ,,

,,

,,,,,2

,

0 11 χχεεεεεε

Power Energy All Else

( ) 1,0

−+++= ∑ ddbopaddi

iima tEccmcAcP

Price = area + materials + overhead + system

•  5 h storage •  $120/kWh*

*includes inverter

•  7000 cycles •  20 year life

Linking performance & cost (as simply as possible):

In collaboration with R. Darling (UTRC) & K. Gallagher(ANL)

Flow Battery Component Cost Inputs

11/18/14 7

Component Year 2014 Cost, $/m2

Ref. Future State Cost, $/m2

Ref.

Graphite flow field plate 55 1 25-35 1

Stainless-steel flow field plate 40 2 10-20 2

Carbon fiber felt / paper electrode

70 1 10-30 2

Fluorinated ion-exchange membrane

500 1 25-75 3

Polyolefin microporous separator

10 1 1-3 Est.

Frames, seals, and manifolds 6 Est. 1-3 Est.


1.  V. Viswanathan et al., J. Power Sources, 2014

2.  B.D. James and A.B. Spisak, Report from Strategic Analysis Inc., October 2012

3.  M. Mathias et al., The Electrochemical Society Interface, Fall 2005

$120/kWh Flow Battery Designs (includes inverter)

11/18/14


8

Both Nonaqueous & Aqueous Flow Batteries have the potential for $120/kWh!

Assumes: §  75% roundtrip

efficiency

§  5 hr discharge

§  10% - 90% SOC

§  MW = 100 g/mol

§  Specific volume = 0.1 L/kg

reactor cost

actives, salts,

solvents, & storage vessels

What might success look like?

11/18/14


9

§  Tailored redox molecules are an attractive pathway if…

Properties Non-aqueous Aqueous Uavg. (V) 3 1.5

ASR (Ω-cm2) 5 0.5

Capacity (g/mol*e-) 150 (~180 mAh/g) 150 (~180 mAh/g)

Solubility (kg/kg) 0.8 0.05

Concentration (mol/L)* ~4-5 ~1-2

Material Cost ($/kg) 5 5

Electrolyte Cost ($/kg) 5 0.1

*Assuming 1 g/mL electrolyte density

§  Metal anodes are promising but cycle life (> 7000 cycles with 20% irreversible capacity fade) and charging current may limit adoption.

Non-Aqueous Flow Battery Materials

11/18/14

Redox-Active Organic Molecules

Brushett et al., Adv. Energy Mater., 2012

DBBB

Shinkle et al., J. Power Sources, 2012

Metal-centered Coordination Complexes Metal-centered Ionic Liquids

Anderson et al., Dalton Trans., 2010

Semi-solid Slurry Suspension

Duduta et al., Adv. Energy Mater., 2011

Why Redox Active Organic Molecules?

11/18/14 11

Benefits: (+) High storage capacity (low MWs & multi e-)

(+) Structural tunability (e.g., activity, solubility)

(+) Cheap & abundant raw materials

(+) Potential low “CO2” footprint

Challenges: (-) Low mass density (e.g., 1-2 g/cm3)

(-) Low electronic conductivity

(-) Solubility in organic electrolytes

(-) Unproven long term stability

Armand & Tarascon, Nature, 2008

Overcharge Protection Materials

Zhang et al., LIBs– New Developments, 2012

A Wide Range of Candidate Materials

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Reductive Decomposition

Oxidative Decomposition

~4.0 V

Non-Aqueous Window

Aqueous Window

~1.23 V

A Wide Range of Candidate Materials

11/18/14 13

~180 mAh/g

overcharge materials

discovery materials

goal

goal: validate chemistry

DBBB (Overcharge Material)

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2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene (DBBB)

MW: 338.5 g/mol electrolyte A: 1.2 M LiPF6 in EC:EMC (3:7 by vol)

Brushett et al., Adv. Energy Mater., 2012; Zhang et al., Energy & Environ. Sci., 2012; Zhang et al., J. Power Sources, 2010

A successful overcharge protection material developed which has shown remarkable reversibility, stability, & longevity in LIB applications

- e-

+ e-

Molecular Accounting: Addition by Subtraction

11/18/14


15

n = 1 electron MW: 338.5 g/mol

Density: 0.9 g/cm3

Capacity: 79 mAh/g [DBBB]neat = 2.7 M

Do we need the long ether chains?

Redox-active core

Do we need tert-butyl protective group?

Can this core support multi-electron transfer?

Would methyl groups suffice?

Can we maintain solubility without it?

𝑞= 𝑛𝐹/3.6∗𝑀𝑊 

n – # of electron transfer F – Faraday constant MW – molecular weight

Derivatization of Substituted Alkoxybenzenes

11/18/14


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DBBB: ~79 mAh/g

O

O

O

asymmetric structures

O

O

P

O

P

O

alternate substituents

O

O

simpler structures

O

O

other structures

In collaboration with J. Huang & L. Zhang (ANL)

Just a few examples…

Towards higher capacity materials…

11/18/14


17

𝑞= 𝒏𝑭/3.6∗𝑀𝑊  What are the next steps…

-0.8

-0.4

0

0.4

0.8

3.5 3.7 3.9 4.1 4.3

Cur

rent

(mA/

cm2 )

Potential (V vs. Li/Li+)

1005020105

scan rate(mV/s)

oxidation

reduction

Experimental: 0.01 M redox species / 1 M LiClO4 / PC, GCE/Au/Li

-1

-0.5

0

0.5

1

3.5 3.7 3.9 4.1 4.3

Cur

rent

(mA/

cm2 )

Potential (V vs. Li/Li+)

1005020105

scan rate(mV/s)

oxidation

reduction

~79 mAh/g ~162 mAh/g

Quinoxalines (Discovery Material)

11/18/14


18

Substituent groups can impart favorable and unfavorable traits on the base molecule

Can we validate the observed chemistry and better understand how the value proposition of this discovery material

MW: 130.15 g/mol Solubility: ~7 M

Capacity: 412 mAh/g

Effect of Substituent Group on Redox Behavior

11/18/14 19

5 mM redox, 0.2 M LiBF4/PC in Pt/Li/Li cell, 20 mV/s

- 2e-

+ 2e-

Compounds Lower Redox (V vs. Li/Li+)

Upper Redox (V vs. Li/Li+)

Quinoxaline 2.649 ± 0.005 3.07 ± 0.02

2-methylquinoxaline 2.609 ± 0.006 2.94 ± 0.02

2,3-dimethylquinoxaline 2.525 ± 0.007 2.85 ± 0.02

2,3,6-trimethylquinoxaline 2.484 ± 0.008 2.80 ± 0.02

Brushett et al., Adv. Energy Mater., 2012

Unusual Redox Behavior of Quinoxalines

11/18/14 20

Barqawi & Atfah, Electrochim. Acta, 1987

quinoxaline

2,3,6,7-tetramethylquinoxaline

cyclopentano{b}quinoxaline

Prior reports show different CV behavior Unexpected Anion Sensitivity

A Quick Detour into Li-ion Battery Degradation

11/18/14 21

Xu, Chem. Soc. Rev., 2004

§  At moderate temperatures (> 55°C), capacity fades after a few months

§  Decomposition primarily driven by Lewis acid equilibrium products

LiPF6 ↔ LiF + PF5

§  Mitigation strategy: Bind with a Lewis base (e.g. pyridine)

What can this tell us about Quinoxaline activity? Li et al., J. Electrochem. Soc., 2005

Quantum Calculations to Understand Redox Potential

11/18/14 22

LiBF4 Li+ + BF4- + LiF + BF3 Salt dissociation:

In collaboration with R. Assary & L. Curtiss (ANL)

11/18/14


23

Validation of BF3-enabled Redox Behavior

Pre-synthesized Adduct Direct spike of BF3 into the electrolyte

In collaboration with C. Diesendruck & J. Moore (UIUC)

§  Leads to an order of magnitude increase in the observed current §  Activation in previously inert electrolytes §  Complex electrochemical behavior (still under investigation…)

DFT Prediction

DFT Prediction

Concluding Remarks

11/18/14


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§  Non-aqueous (and aqueous) flow batteries have the potential to meet $100/kWh grid storage targets

§  Non-aqueous solvents loosen one constraint (voltage) but take on another (solubility from electrolyte cost)

§  Organic molecules offer unique design opportunities through substituent modification and electrolyte interactions

§  A flow battery is more than the redox materials (electrolyte, membranes, electrodes) all of which need developmental work

Acknowledgements

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Funding:

Not shown: Kyler Carroll (PD), Apurba Sakti (PD), John Barton (GS), Steven Brown (GS), Jeff Kowalski (GS), Jarrod Milshtein (GS)

T-E Modeling: §  Rob Darling (UTRC) §  Seungbum Ha, Kevin Gallagher (ANL)

Organic Synthesis: §  Jinhua Huang, Lu Zhang (ANL) §  Charles Diesendruck, Jeff Moore (UIUC)

Quantum Calculations: §  Rajeev Assary, Larry Curtiss (ANL)

Flow Cell Testing: §  Larry Pederson, Xiaoliang Wei, Wei

Wang (PNNL)

We gratefully acknowledge the Materials Engineering Research Facility and the ABR program providing scaled-up materials.

BACK-UP SLIDES

11/18/14


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Range of Grid Storage Options & Applications

11/18/14 27

Adapted from the original figure in Sandia National Laboratory report, SAND 2013-5131, 2013

UPS-Power Quality T & D Grid Support – Load Shifting Bulk Power Mgmt.

Pumped Hydro

Flow Batteries

NaS Battery

Li-ion Battery

Lead-Acid Battery

High-Power Flywheels

High-Power Supercapacitors SMES

Advanced Pb-Acid battery High-Energy Supercapacitors

1 kW 1 GW 100 MW 10 MW 1 MW 100 kW 10 kW

Seco

nds

Min

utes

H

ours

Dis

char

ge T

ime

at R

ated

Pow

er

System Power Ratings, Module Size

Molten Salt

CAES

11/18/14 28

3.8

4

4.2

4.4

4.6

0 1 2 3 4 5 6 7 8 9 10

E0' (V

vs.

Li/L

i+ )

Redox Potential

0.0

1.0

2.0

3.0

0 1 2 3 4 5 6 7 8 9 10

k0(×10

-4cm/s) Rate Constant

MW 338 248 402 346 294 338 427 166 166

0

0.5

1

1.5

2

0 1 2 3 4 5 6 7 8 9 10

D0(×10

-6cm2/s) Diffusion

1 M LiClO4 / PC (Similar trends observed in LiTFSI/DME)


11/18/14 29

(But high cost of inac7ve materials and manufacturing, >40%)

V-‐redox

Target range

Goal: Lower cost chemistries at higher concentra7ons and higher voltage

Flow BaUeries: Cost of energy ($/kWh) is func7on of cost of materials ($/kg) and concentra7on of redox-‐ac7ve species (M) and hardware cost*

(Plot assumes 40% of system cost is hardware)

JCESR goal

Li-‐ion electrodes

Non-Aqueous vs. Aqueous Power Performance

11/18/14


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Interesting Trends as Function of Concentration

11/18/14


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Peak currents were obtained from CV measurements taken in a GC / Pt / Ag/Ag+ cell at a scan rate of 10 mV/s. PC was used as a solvent.

§  For 0.005 M → 0.05 M 2,3,6-TMQ, leads to a 2-fold increase in peak current

§  Increasing the [LiBF4] is directly proportional to increased peak current

§  Similar results observed with quinoxaline (Q)

An All-‐Organic Non-‐Aqueous Redox Couple

11/18/14


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V

2DBBB

2[DBBB+A-‐]

TMQ

TMQ2-‐ [C+]2

Note: Only showing charging

2e-‐

2C+

Can we transition this electrochemical redox couple to a prototype flow cell?

2e-‐

JCESR’s 10 cm2 Flow Cell Prototype

11/18/14


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Test Conditions in Ar-glovebox: Electrolyte = 0.1 M DBBB & 0.2 M TMQ / 0.6 M LiBF4 / PC Electrolyte Volume = 10 mL each Flow rate = 40 mL/min Li+-Nafion 212 membrane ic/id = 0.0625 mA/cm2, 0.2 – 2.5 V

0th order Energy Density based on Li metal

11/18/14


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Based only on the capacity of the

organic material

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Non-Aqueous Redox Flow Batteries: Challenges &...

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