Increase in Positive Active Material Utilization in

1
Increase in Positive Active Material Utilization
in Lead-Acid BatteriesSimon McAllister, Rubha
Ponraj, I. Francis Cheng, Dean B.
EdwardsDepartment of Chemistry, University of
Idaho, Moscow, ID 83844-2343Email
ifcheng_at_uidaho.edu, Tel [phone]

• Experimental
• Preparation of the Positive plate
• Lead Strips - Pb and 4-6 Sb with Teflon ring
  attached.
• Paste contains PbO, 0.5 Dynel fibers, additives
  for total mass of 10 g, 1 ml of 1.4 specific
  gravity H2SO4 1.2 ml of DI water
• Teflon ring is filled with paste
• Hydroset for 24 hours to convert Pb0 to PbII
• Dried overnight

Background
Results
The lead-acid battery is a highly successful
rechargeable electrochemical storage system.
Despite its design dating from Plante in 1859 the
system can benefit from new approaches. The
basic electrode reactions during charge and
discharge of a lead-acid battery with 1.3
specific gravity H2SO4 are shown in reactions 1-3
1,2
Formation and Conditioning
Figure 7 - Performance changes due to the
diatoms. Specific capacity is the amount of
charge that can be produced for a given mass, in
mAh g-1.
Figure 1 Schematic of lead-acid battery
Purpose The performance of these batteries is
limited by the positive plate reaction due to low
PbO2 positive active material (PAM) utilization
which is around 30 or less at the 1 hour rate.
Utilization is the amount of charge we obtain at
a certain discharge rate relative to the
theoretical charge. Reasons for low utilization
include slow diffusion of electrolyte into the
interior, and electrical isolation from the
buildup of PbSO4 3,4. To improve PAM
utilization 4-8 1) Porosity and conductivity
of the PAM have to be increased. 2) The
unreacted material has to be replaced with a
filler. Porosity of PAM is increased by the
addition of highly porous additives thereby
enhancing the diffusion of acid to the interior
of active material and providing fine local
reservoirs of acid within porous particles.

• Formation step with 1.1 specific gravity H2SO4
  to convert Pb0, PbO, and PbSO4 to PbO2
• Theoretical capacity - 0.2241 Ah/g
• Fast charge with constant current to obtain 100
  theoretical capacity in 24 hrs
• Slow charge with constant current (half of fast
  charge) applied for 12 hrs to reach 125
  theoretical.

• The addition of 3 diatoms of 53-74 µm exhibited
  the best performance and they are believed to
  favor acid diffusion inside the active mass.
• The scanning electron micrographs (Figure 8a, b)
  show the porous structure of diatoms.
• The SEM of diatoms recovered from the active
  material after the performance tests (Figure 8d)
  proves that diatoms survive in the battery
  environment.

• Conditioning
• Acid is changed to 1.3 specific gravity H2SO4
  and plates are cycled individually 4 to 5 times
  in a cylindrical cell.
• Discharged at 10 mA g-1
• Charged at fast rate to 125 previous discharge
  capacity

Performance measurements Four size fractions,
20-30 µm, 30-53 µm, 53-74 µm and 74-90 µm, at 3
wt and 5 wt were tested. 4 plates in each group
were pasted. Capacity measurements are taken at a
50 mA cm-2 discharge and a 10 mA cm-2 discharge.
Plates are cycled at each rate until the capacity
reaches a maximum.

• Conclusion
• Diatoms are an inexpensive filler material that
  increases positive active material utilization by
  replacing unreacted active material, while
  maintaining pores for diffusion.
• Utilization increases by over 12.7 at a fast
  rate discharge of 50 mA cm-2 with a corresponding
  9.3 increase in specific capacity.

Figure 2 Diagram of porous lead dioxide with
diffusion of HSO4

• Characteristics of Ideal Additives
• Lead-acid batteries have a harsh acid and
  oxidative environment, therefore the following
  characteristics have to be considered while
  selecting additives 4
• Increase utilization
• Chemically and oxidatively stable
• Good adhesion to active material
• Increase PAM utilization without affecting
  cycle life
• Low cost
• Light weight
• Diatoms are our choice as an additive because of
  its porosity, abundance and stability towards
  battery conditions. In this work, we added size
  sorted diatoms (Melosira) at different loadings
  and studied their effect on the positive plate
  performance.

• References
• H. Bode, Lead-Acid Batteries, translated by R.J.
  Brodd and K.V. Kordesch, 1997, page 4.
• S.V. Baker, P.T. Moseley and A.D. Turner, J.
  Power Sources, 27 (1989) 127.
• P.T.Moseley, J. Power Sources, 64 (1997) 47.
• K.McGregor, J. Power Sources, 59 (1996) 31.
• H.Dietz, J.Garche, K.Weisner, J. Power Sources,
  14 (1985) 305.
• D.Berndt, Maintenance-Free Batteries, second
  edition 1997, page 103.
• P.W. Appel, D.B. Edwards, J. Power Sources, 55
  (1995) 81.
• D.B. Edwards, V.S. Srikanth, J. Power Sources,
  34 (1991) 217.

• Future work
• Duplicate diatoms effect in full positive plate.
• Add conductive additives to increase electron
  flow

Acknowledgement Office of Naval Research Award
Number  N00014-04-1-0612, Department of
Chemistry, Microelectronics Research and
Communications Institute (MRCI), Dr. and Mrs.
Renfrew.