Carbon-Enhanced VRLA Batteries

October 20th, 2011

David G. Enos, Summer R. Ferreira, Wes E. Baca

Sandia National Laboratories

Rod Shane

East Penn Manufacturing

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation,

a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s

National Nuclear Security Administration under contract DE-AC04-94AL85000.

The Advanced VRLA Battery • Recently, there are several manners in which carbon has been

added to a Pb-Acid battery

The work presented here deals with the Advanced Battery,

where carbon has been added to the negative active material

Lead-Acid

Cell

Asymmetric

Supercapacitor

PbO2 Pb PbO2 Carbon

PbO2Ultrabattery

PbO2 Pb + CSeparator

Advanced VRLA Battery

Why add excess carbon to the NAM?

• Carbon additions to the negative active material

(NAM) can substantially reduce hard sulfation

Fernandez, 2010*

Standard Carbon Addition

*M.Fernandez, J.Valenciano, F.Trinidad, N. Munoz, Journal of Power Sources, Vol. 195 (2010), pp. 4458-4469.

• The overall goal of this work is to quantitatively define the

role that carbon plays in the electrochemistry of a VRLA

battery.

What reactions/changes take place on the surface of the

carbon particles?

What processes govern the increase and then eventual

decrease in capacity with increasing # of cycles?

Are the kinetics of the charge/discharge process different

when carbon is present vs. when it is not?

Why are some carbons effective additions while others are

not? Are there any distinguishing characteristics of effective

additions? Is the effectiveness controlled by aspects of the

plate production method? etc.

Research Goals

Constituent Material Analysis

• Given the limited understanding of what characteristics yield an

effective carbon addition, a broad spectrum approach is being

taken to quantify the carbon particle properties.

Carbon Black Graphite Actetylene

Black

Activated

Carbon

Particle size 20 nm 20+ µm 20 nm 100+ µm

Effective surface area

(BET) 75 m2/g 6 m2/g 75 m2/g >2000 m2/g

Structure (XRD) Semicrystalline Crystalline Semicrystalline Amorphous

Acid Soluble

Contamination Clean Clean Very Clean Na, PO4

6 Month Self Dischage (%)

0 10 20 30 40

Cu

mu

lati

ve

Pro

ba

bil

ity

0.0

0.2

0.4

0.6

0.8

1.0

Alber Impedance ()

1950 2000 2050 2100 2150

Cu

mu

lati

ve P

rob

ab

ilit

y

0.0

0.2

0.4

0.6

0.8

1.0

Float Voltage (V)

2.26 2.28 2.30 2.32 2.34 2.36 2.38 2.40 2.42 2.44 2.46

Flo

at

Cu

rre

nt

(mA

)

0

50

100

150

200

250

Capacity (Ah)

9.5 10.0 10.5 11.0 11.5 12.0 12.5

Cu

mu

lati

ve P

rob

ab

ilit

y

0.0

0.2

0.4

0.6

0.8

1.0

Control

Carbon Black + Graphite

Acetylene Black

Activated Carbon

Performance Testing Shows Some Differentiation

between Control and Carbon Modified Batteries

Capacity

Impedance

Float Current Self Discharge

Depth of Discharge (%)

0 20 40 60 80 100

Pu

lse

Po

wer

Cap

acit

y (

W)

100

120

140

160

180

200

220

240

260

280

300

Control

Carbon Black + Graphite

Acetylene Black

Activated Carbon

Performance Testing Shows Similarities Between

Control and Carbon Modified Batteries

HPPC Discharge Capacity HPPC Charge Capacity

Depth of Discharge (%)

0 20 40 60 80 100

Pu

lse

Po

we

r C

ap

ac

ity (

W)

160

180

200

220

240

260

280

300

320

Note: These HPPC data are for new cells

More Dramatic Differentiation Observed as the

Batteries are Cycled

• Comparable behavior observed for all four battery

types at 1k cycles

• At 10k cycles, capacity loss was evident in the

control, acetylene black, and activated carbon

batteries (but not in the carbon black + graphite cell)

• Control battery failed at 11,292 cycles

Failure defined as a capacity loss of greater than

20% after three discharge/charge cycles in an

attempt to recover.

Pore Size Diameter (m)

0.01 0.1 1 10 100

Lo

g D

iffe

ren

tial In

tru

sio

n (

mL

/g)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Control

Carbon Black + Graphite

Acetylene Black

Activated Carbon

Pore Size Diameter (m)

0.01 0.1 1 10 100

Lo

g D

iffe

ren

tial

Intr

usio

n (

mL

/g)

0.0

0.1

0.2

0.3

0.4

0.5

Porosity and Pore Size Distribution

Formed

Raw

Porosity and Pore Size Distribution

Pore Size Diameter (m)

0.01 0.1 1 10 100

Lo

g D

iffe

ren

tial

Intr

usio

n (

mL

/g)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Control

Carbon Black + Graphite

Acetylene Black

Activated Carbon

1k Cycles

Pore Size Diameter (m)

0.01 0.1 1 10 100

Lo

g D

iffe

ren

tia

l In

tru

sio

n (

mL

/g)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

10k Cycles

Minimal Sulfation at 1k Cycles

100 microns

Control

Carbon Black + Graphite

Activated Carbon

Acetylene Black

Significant Sulfation at 10k Cycles for

Two of the Batteries

100 microns

Control

Carbon Black + Graphite

Activated Carbon

Acetylene Black

250 microns

20% Capacity Loss 15% Capacity Loss

15% Capacity Loss 4% Capacity Gain

Summary/Conclusions to Date

• Battery performance

Pb-C batteries had lower initial capacity, higher initial internal

resistance, higher float current, comparable HPPC performance,

and superior HRPSoC cycling performance

• Material Characterization

Pore structure in Pb-C batteries notably smaller (order of

magnitude), but comparable in overall volume

Hard sulfation becoming significant after 10k cycles with the

control battery and activated carbon battery

Future Tasks

• Cycle testing will continue

50k and 100k cycles

Cycle to end of life

Analysis of cycled battery materials

• Program will conclude in August 2012