REDOX FLOW BATTERIESREDOX FLOW BATTERIESA storage system for the future

Anita Gurbani Gurbani

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Energ storage technologiesEnergy storage technologies

Flow batteries can cover a wide range of power and

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time rates providing high storage capacity.

Redo Flo BatterRedox Flow Battery

- Redox flow battery concept was introduced by Thaler (1974)

RFB electrochemically store/release electricity by thevalence change of the species in the electrolyte that circulatethrough the anode and cathode, separated by an ion exchangeg , p y gmembrane.

Th ti ll d lTheoretically, many redox couples are possible, but some of them are notapplicable d e to side reactions

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applicable due to side reactions.

VRB orking principlesVRB – working principles

-Vanadium Redox Flow Battery proposed by Skyllas-Kazacos & co-workers at UNSW (1983) Fi t All V di b tt t t d b UNSW/U i h (1986)-First All-Vanadium battery patented by UNSW/Unisearch (1986)

-Many industrial trials and demonstrations units of VRB around the world since 1991since 1991.-Commercial companies: Prudent Energy & Cellstrom.

~ 3 M Vanadium in 4-6 M H2SO4. Cathode:

VO2+ + H O VO + + 2H+ + e-VO + H2O VO2 + 2H + e

Anode:Anode:V3+ + e- V2+

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TOTAL = 1,2 V

Ad antages of the VRBAdvantages of the VRB

- ENERGY STORED IN TANKS, POWER STORED IN STACK: independent system design for power and capacity.p y g p p yOutput power range: kW-MWEnergy Storage Capacity: kWh 10 MWh

SAME SOLUTION OF BOTH HALF

Energy Storage Capacity: kWh-10 MWh

- SAME SOLUTION OF BOTH HALF CELLS: reduced cross-mixing of active especies across membrane andactive especies across membrane and not irreversible

- INDEFINITE LIFE of electrolyte:

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reduced replacement costs.

Ad antages of the VRBAdvantages of the VRB

- MORE ADVANTAGES:

- High efficiency (> 75-80%)- Long lifetime- Deep discharge ability- Deep discharge ability- Low self-discharge- Fast response- Environmental friendly- Operation safety

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Disd antages of the VRBDisdvantages of the VRB

- DISADVANTAGES:

- Limited solubility in some acidsLow energy density (~ 25

Wh/kg)- Limited temperature range (10-

40ºC)0 C)- High vanadium costs

V(V) th l i it ti- V(V) thermal precipitationduring operation.

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Other RFB technologiesOther RFB technologies

VRB i th t d fl t h lVRB is the most common redox flow technology.Others are:

Bromine/polysulfide flow battery (THE REGENESYS SYSTEM)

Energy efficiency: ~ 70%Estimated costs: ~ 175 €/kWh

Negative: Na2S4 2Na2S2

Positive: 3NaBr NaBr3Little Barford, South England

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3TOTAL: 1,5 V

Little Barford, South England120 MWh/15 MW

(Project stopped in Dec. 2003)

Other RFB technologiesOther RFB technologies

VRB i th t d fl t h lVRB is the most common redox flow technology.Others are:

Zinc/bromine system (ZBB)

“Hybrid” RFB. -Stack size influences energy content too !!

-Zn is critical for lifetime.

Zn2+(aq)+ 2e- → Zn (s)Zn2+(aq)+ 2e → Zn (s)2Br- (aq) → Br2 (aq) + 2e-

TOTAL 1 8 V

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TOTAL: 1,8 V

Other RFB technologiesOther RFB technologies

VRB i th t d fl t h lVRB is the most common redox flow technology.Others are:

Cerium/zinc system (PLURION’S RFB)

Also limitations by zincAlso limitations by zinc.

Solvent electrolyte:Solvent electrolyte: Methane Sulfonic Acid (CH3SO3H)

OCV = 2 4 V

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1 m2 pilot cell (2002)OCV 2,4 V

Components of the RFBComponents of the RFB

- Main stack components are:

- Graphite electrodes on conducting plastic substrate (bipolarplate) as anode and cathodeplate) as anode and cathode

- Ion-exchange membrane to prevent cross mixing of solutionsFl f- Flow-frames

Oth t- Other components are:

- Tanks, pumps, tubes …- Control system

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Co t o systeThe vanadium Redox Battery Website (www. Unsw.au)

Costs of RFBCosts of RFB

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Costs of RFB2 kW/30 kWh Cost estimation

Costs of RFB

Data Unit Cost Total CostC t d it 52 A/ 2

2 kW/30 kWh Cost estimation

Current density 52 mA/cm2

Electrode area 1,75 m2/kWV2O5 – Energy 6,0 kg/kWh

2 2Activation film 3,5 m2/kW 50 €/ m2 350 €Bipolar plate 65 €/kW 130 €Frames, etc. 435 €/k 870 €Membrane 2,1 m2/kW 25 €/ m2 105 €Tanks 185 € cada uno 370 €Pumps 160 € cada uno 320 €Pumps 160 € cada uno 320 €Control 500 € 500 €V2O5 14,0 €/kg 2520 €Electrolyte production 3 €/kg 540 €Electrolyte production 3 €/kg 540 €

TOTAL 5745 € → 192 €/kW

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Challenges of VRBChallenges of VRB

TO IMPROVE PERFORMANCE AND COST DOWNTO IMPROVE PERFORMANCE AND COST DOWN

-Electrolyte: StabilitySolubilityy

-Ion exchange membrane: StabilityIon exchange membrane: StabilityDurabilitySelectivity

OR No membrane Single Tank RFBSelectivity

CostSingle Tank RFB

-Electrode/Bipolar plate: Electrical conductivity

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Cost

O r approachOur approach

BENCH-SCALE STUDIES Charge/Discharge strategies

Different applications simulations e e app ca o s s u a o s(programmable discharge profiles)

LAB SCALE STUDIES New concepts of manufacturing redox flow batteries

Design concepts

Assembly procedures

Monitoring

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O r approachOur approachBENCH SCALEBENCH SCALE

First generation vanadium redoxflow battery made of commercialcomponents which is able to runwith 10 to 40 cells, so from 25 to100Ah.Power electronics unit(RedoxBatGen) with an advancedcontrol to manage energy flowsb th f d t th b tt Thiboth from and to the battery. Thisunit has been developed toemulate different grid conditionsemulate different grid conditions,from different renewable energyconnection scenarios to grid

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connection scenarios to gridregulation ones.

O r approachOur approachBENCH SCALE

• Flow rate: small differences in charge/discharge cycles:

90

100

(%)

BENCH SCALE

charge/discharge cycles:

70

80

ge E

ffic

ienc

y (

65

D)

100 200

50

55

60

70

1,5 L/min 3 L/min6 L/min

Vol

tag

60

Discharge volge

vol

tage

(V

45

20 40 60 80 100 12050

6 L/min

Time (min)

1,5 L/min 3 L/min6 L/min

ltage (V)C

harg

50 i

40

A flow rate from whichdifferences in efficiency are

556 L/min

Time (min)

50 min35

differences in efficiency arenegligible.

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O r approachOur approachLAB SCALE – SINGLE CELL ACTIVITIES

Various single cell and 2 to 4 cell-stack have been designed.

LAB SCALE – SINGLE CELL ACTIVITIES

g g

-Dimensions: 150 mm x 150 mmDimensions: 150 mm x 150 mm

-Voltage: 2,4 V

-Fluid connection in serial (parallel d l d d lmodel under development

Inter electrode distance: 2 mm-Inter electrode distance: 2 mm

-Electrical connection in serial

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(allows stack and single-cell studies)

O r approachOur approachLAB SCALE – SINGLE CELL ACTIVITIES

• Activities are focused to:– ELECTROLYTE:

LAB SCALE – SINGLE CELL ACTIVITIES

• SOC monitoring of the electrolyte to improve EFFICIENCY

MODELING AND SIMULATION:– MODELING AND SIMULATION:• Fluid-dynamic simulation before designing of all configurations

– DESIGNING AND MANUFACTURING:• Electrolyte entrance and flow field design• Electric contact• Electric contact• Electrode size and composition

– MANUFACTURING THINKING IN MAINTENANCE

Main objective of the study: to achieve a compromise between single

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component efficiency and overall stack performance and costs.

O r approachOur approachLAB SCALE – SINGLE CELL ACTIVITIES

In order to flow the electrolyte through the cell, channels may bemachined to the bipolar plate

LAB SCALE – SINGLE CELL ACTIVITIES

machined to the bipolar plate.

Various channel designs have been machined in order toVarious channel designs have been machined, in order tocompare the performances of the single cell.

Cost-effective design must:Avoid leakages of electrolyte- Avoid leakages of electrolyte

- Assure high contact time in “electrode-electrolyte-membrane”systemsystem.

- Allow same machining to both bipolar plates of each celleasier maintenance quicker exchange of defective or broken

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easier maintenance, quicker exchange of defective or brokencomponents.

O r approachOur approachLAB SCALE – SINGLE CELL ACTIVITIES

Channel /electrode /plate configurations:Each one of the designs has been

LAB SCALE – SINGLE CELL ACTIVITIES

Each one of the designs has been optimized in terms of:

Channel size- Channel size- Channel depth- Electrode sizeElectrode size

Also Fluid-dynamic MODELING andAlso Fluid dynamic MODELING and SIMULATION has been performed and VALIDATION with experimental data V O w e pe e dhas been done to optimize: Flow rate, avoid stagnant fluid, fluid homogeneity, -Good homogeneity of the fluid.

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g , g y,maximum contact in all electrode area -Reduced electrode area less

expensive.

O r approachOur approach

SERIAL OR PARALLEL CONFIGURATION:

SERIAL CONFIGURATION:Limited leakage (bypass) current bypass potential limited toLimited leakage (bypass) current bypass potential limited toone cellMore power needed ({Qcell = Qtotal/no.cells} - ideally)More power needed ({Qcell Qtotal/no.cells} ideally)Voltage not uniform inside the stack (each cell has a differentvoltage)g )

Both configurations are being analyzedBoth configurations are being analyzedthe most COST-EFFECTIVE

solution will be chosen

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solution will be chosen.

S mmarSummary

Vanadium redox battery: efficient energy storage system.

Different systems are being investigated in R&D teams most ofDifferent systems are being investigated in R&D teams most ofthem on vanadium technology.

The flexible independent sizing of storage capability and power is animportant advantage in comparison to other technologies.

There is still high potential for reducing costs mainly in design aspectsof all components of the VRB.

In Tekniker, different efficiency calculations have been obtained bystudying charge/discharge strategies still a normalization is needed.

Optimization of parameters obtained in the single cell such aselectrolyte income, size of electrode and so on; have to be validated inth t t b h t ti i i l fi l d i

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the test-bench to optimize economical final design.