Lead Acid Batteries in VRLA/AGM Design

Allen XiangMarch. 2012

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• The VRLA/AGM revolution of 1971• Key VRLA/AGM features and outlook• Essential technologies

Technology Issues - The topics

• Positive grid alloy and grid manufacturing technology• Electrolyte management in the cell• Positive active mass stabilization• Plastic material and AGM stability• Thermal management and RAPS applications• Asset management with anti-theft GPS module

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What makes the world go ‘round?

4

Petrol ?

5

Tires ?

6

Batteries!

BSS

7

1971

This invention concerns a maintenance-free type lead acid cell which is in a normally sealed condition. The cell is characterized by structurally free, non-self-supporting plates separated from one another with highly absorbent flexible separators containing electrolyte and constrained within a container such that mechanical integrity is imparted to obtain a unitary self-supporting structure. Means are provided for maximum recombination of evolved gases and for discharge of excessively high pressure gas. A centroid element allows for operation in any indiscriminate attitude.

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1971

• Maintenance-free operation• Electrolyte leak proof design• Grid plates• Electrolyte absorbed in glass fiber

matrix• Internal gas recombination • Self stable battery case • Overpressure vent valve • Position independent operation

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1971

• Maintenance-free operation• Electrolyte leak proof design• Grid plates• Electrolyte absorbed in glass fiber

matrix• Internal gas recombination • Self stable battery case • Overpressure vent valve • Position independent operation

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1971

1981

• Maintenance-free operation• Electrolyte leak proof design• Grid plates• Electrolyte absorbed in glass fiber

matrix• Internal gas recombination • Self stable battery case • Overpressure vent valve • Position independent operation• Prismatic cell design• 2V cells and 6V/12V monoblocs

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1971

1981Today

AcmeMP

Eos

REX

HTB

12

The „official“ family name

Valve Regulated Lead Acid battery with Absorbent Glass Mat

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What offers power, Pb/PbO2/H2SO4?

FLA

Pb+PbO2+2H2SO4↔2PbSO4+2H2O+2e

6 KgDilution of acid

11 KgExcess of acid

13 Kg

Excess of active material

26 Kg

Grids, case, cover, terminals

43 Kg

166 Wh Kg

theory

23 Wh Kg

effective

Materialfor 1 kWh

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What makes the VRLA/AGM attractive?

VRLAAGM

166 Wh Kg

6.0 Kg

Higheracid

density

Lessactive

mass perAh

Thinnercorrosion resistantlead alloy

grids

Less electrolyteMore efficient

material use

35 Kg

28 Wh Kg

Materialfor 1 KW for 1h

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What is a key VRLA/AGM feature?

VRLAAGM

Internaloxygen

recombination

_ +

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The valve of a VRLA cell

VRLAAGM

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What is a key VRLA feature?

Delicate charge balance

due to internal oxygen recombination

100mA 100mA

4mA ? 1mA ?

O2 cycle

Pb corrosionSelfdischarge

+_

O2 venting/capture

e

2mA ?

1mA ?Selfdischarge

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VRLAAGM

Less volume&

floor surfaceoccupied

What made VRLA/AGM based power back-up so attractive?

89

10111213141516171819202122

2VOPzS125

12VOGi105

12OPzSbloc

2VEOS 300 12NDF 155 12NDT 100

KW

for

1h

per m

2

1KW x h x m2

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• ≈ 32% lower weight per Ah• ≈ 45% smaller volume per Ah• ≈ 36 % better high rate performance• Position independent operation• Only 1/6 of air exchange volume needed• No water top-up needed• No electrolyte leakage• Fast on site – air freight capable• No activation procedure needed• > 1 year storage capability• Low cost of ownership• Worldwide availability• Attractive form factors (H x W x L)

VRLAAGM

The additional benefits of VRLA/AGM batteries

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• ≈ 32% lower weight per Ah• ≈ 45% smaller volume per Ah• ≈ 36 % better high rate performance• Position independent operation• Only 1/6 of air exchange volume needed• No water top-up needed• No electrolyte leakage• Fast on site – air freight capable• No activation procedure needed• > 1 year storage capability• Low cost of ownership• Worldwide availability• Attractive form factors (H x W x L)

VRLAAGM

The additional benefits of VRLA/AGM batteries

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• ≈ 32% lower weight per Ah• ≈ 45% smaller volume per Ah• ≈ 36 % higher 1h rate current capability• Position independent operation• Only 1/6 of air exchange volume need• No water top-up needed• No electrolyte leakage• Fast on site – air freight capable• No activation procedure needed• > 1 year storage capability• Low cost of ownership• Worldwide availability• Attractive form factors (H x W x L)

How did the stationary lead acid battery evolve?

VRLAAGM

FLA

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What makes a VRLA battery more sensitive?

VRLAAGM

Less coolingby air flow

Morewaste heat per cell675mW vs. 92mW30%

less electrolyte

High-techplastics

Reduceddiagnostics

Delicatewelds

Thinner grids

MoreKW power

Less skilledoperators

Acidstratification

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• ≈ 32% lower weight per Ah• ≈ 45% smaller volume per Ah• ≈ 36 % higher 1h rate current capability• Position independent operation• Only 1/6 of air exchange volume need• No water top-up needed• No electrolyte leakage• Fast on site – air freight capable• No activation procedure needed• > 1 year storage capability• Low cost of ownership• Worldwide availability• Attractive form factors (H x W x L)

How should the VRLA/AGM battery evolve?

VRLAAGM

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VRLAAGM

• ≈ 32% lower weight per Ah• ≈ 45% smaller volume per Ah• ≈ 36 % higher 1h rate current capability• Position independent operation• Only 1/6 of air exchange volume need• No water top-up needed• No electrolyte leakage• Fast on site – air freight capable• No activation procedure needed• > 1 year storage capability• Low cost of ownership• Worldwide availability• Attractive form factors (H x W x L)

Narada Ranges of VRLA

OPzS HR Eos REX, HTBOPzV NV Acme, MP

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Critical components and technologies for dependable service

• Positive grid alloy and grid manufacturing technology

• Electrolyte management in the cell • Positive active mass stabilization

• Plastic material and AGM stability

• Thermal management and RAPS applications

• Asset management with anti-theft GPS module

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Pb

PbCa

Sn

• Positive grid alloy and grid manufacturing technology

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• Positive grid alloy and grid manufacturing technology

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• Pb as bulk material 99.996%

• Sn as passivation preventer >3000ppm

• Ca as hardener ≈ 600ppm

• Bi as cycle life enhancer ≈ 300ppm

• Ag as creep strength enhancer ≈ 100ppm• Al as sacrificial element ≈

300ppm

Pb

PbSn

PbCaSn

Ag

Bi

Al

• Pb is too soft• Sn enhances GB corrosion• Ca enhances GB corrosion• Ag enhances water loss

• Positive grid alloy and grid manufacturing technology

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• Positive grid alloy and grid manufacturing technology

Pb

PbSn

PbCa

Ag

Bi

Al

Continuous strip caster

400p.min-1

1.5mm

Continuous strip roller400p.min-1

2mm

Book moldcaster

15p.min-1

5mm

Grid shapepuncher

+-0.2mm+-6%/g

+-0.06mm+-3%/g

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• Positive grid alloy and grid manufacturing technology

Pb99.997

%

PbSn0.3-

2.0%

PbCaSn

2.0%

Continuous strip casterstructure

Continuous strip rollingstructure

Book moldcast structure

PbSn

PbSnPb

PbSnPbCaSn

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GB

• Positive grid alloy and grid manufacturing technology

PbCaSn

Pb → PbO2

1mol volume Pb

1.39 mol volume PbO2

GB

Pb0.3%Sn

PbO2

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• Basic features of the corrosion attack of lead and lead alloys

Pb0.4Sn

Pb0.9Sn0.01Ca

4 G 2 G 1 G

Pb pure

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• In VRLA compatible alloys, the corrosion attack proceeds predominantly via grain boundaries

• At the same alloy composition, the least grid damage occurs in the alloy with the smallest number of grain boundaries per volume of alloy

• Single or large grained alloys perform thus the best and fine grained the worst

• Only pure lead is immune to a predominant grain boundary centered attack

• Grid alloy stock manufacturing plays a key role with the corrosion resistance decreasing from book mold cast to continuous cast to continuous rolled material

• Basic features of the corrosion attack of lead and lead alloys

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• Electrolyte management in the cells – a delicate equilibrium

• Assure a maximum of available H2SO4 for capacity

• Assure a maximum of available water for life

• Assure 3-4% open pores for gas transport

• Assure maximum absorption of the acid on the glass fibers

• Prevent gravity induced acid movements (de-wicking)

• Prevent density gradient induced electrolyte movement

• Balance acid storage in AGM vs. in active mass

H2O

+-

Dil. H2SO4

H2SO4 H2SO4

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• Electrolyte management in the cells

Impact of acid quantity

• dosing of “life” acid

• density of “life” acid

• formation efficiency

< 2mmO2

Horizontal O2

> 200mm

Vertical

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• Positive active mass stabilization

Pb++

Pb++

Pb++

Pb++Pb++

Pb++SO4

- -

SO4- -

SO4- -

SO4- -

SO4- -

SO4- -

Pb++

Pb++

Pb++

e

Pb++ Pb++SO4

- -

SO4- -

SO4- -

SO4- -

Pb++

SO4- -

SO4- -

PbSO4 (sol)

PbSO4

• Schematic view of the dissolution-precipitation reaction in an active mass pore during the discharge of the positive mass in a lead acid battery

e

PbSO4

PbSO4

SO4- -

SO4- -

SO4- -

SO4- -

SO4- -

SO4- -

SO4- -

SO4- -

Pb++

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• Positive active mass stabilization

PAM volume50% PbO2

50% pores

PAM volume<50% PbO2

>50% pores

PAM volume30% PbO2

38% PbSO4

32% pores

Pb → PbO2

+39% volume need

PbO2 → PbSO4

+92% volume need

PbSO4 → PbO2

-92% +X% volume gain – Y% volume loss

Pb Pb Pb

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• Plastic material and AGM stability

+- -

100%

73%

100%

• The AGM (Absorbent glass mat) in a VRLA cell has to be compressed in thickness by about 25 to 30% to assure adequate electrolyte continuity between the plates

• This compressed AGM exercises, not unlike a spring, a force of about 40KPa or 70 to 110Kg on the interior walls of a 100Ah cell

• Two factors, AGM shrinkage and plastic deformation by heath, destabilize this assembly and can led to dramatic cell capacity losses

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• Plastic material and AGM stability

35°C

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Coolstar• Thermal management and RAPS applications

• Focus on not only cooling down, but also cooling management and temperature uniformity.

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• Adapting the positive plate design to achieve a lower Pavlov γ factor and increased active mass loading

γ 1.34 γ 0.77

• Thermal management and RAPS applications

γ = g PbO2 / cm2 grid surface

γ 0.7717.7g.Ah

γ 1.3414.3g.Ah

• Capture and recombine oxygen with hydrogen on a Pd-on-Carbon catalyst bed

• Decrease the oxygen recombination duty of the negative active mass and thus polarize the negative plate stronger

• Increased negative plate polarization reduces the float current and associated internal heating 42

• Thermal management and RAPS applications

140mA200mA

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• Asset management with anti-theft GPS module

Anti-theft GPS module

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• Asset management with anti-theft GPS module

Anti-theft GPS module

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In power need?….call on

VRLA/AGM batteries!

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Thank you for your attention!