Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2002-03-19
2004-05-25
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S215000, C029S623500, C141S001100
Reexamination Certificate
active
06740452
ABSTRACT:
BACKGROUND OF THE INVENTION
Electrochemical storage batteries, and in particular, lead sulfuric acid storage batteries are ubiquitous in automotive applications. These batteries have electrochemical cells developing about 2.25 Volts each. A generic lead acid battery cell has a positive plate, a negative plate, and an electrolyte, typically aqueous sulfuric acid. The plates are held in a parallel orientation and electrically isolated by a porous separator to allow free movement of charged ions. Generally, six of these cells are connected in series to produce the 12 Volts (12 V) common in automobile systems.
The positive battery plate (also known as a positive electrode) contains a current collector (i.e., a metal plate or grid, hereinafter grid), covered with a layer of positive active material (hereinafter PAM) on the surface. PAM is essentially all electrically conductive lead dioxide (PbO
2
). The negative battery plate contains a current collector (grid), and it is covered with a negative active material, typically lead metal referred to in the art as “spongy lead.”
Lead acid battery cells are quite unique because the electrolyte actively participates in the energy storage and release process, as represented schematically in Equations 1, 2, 3, and 4 below:
Equation
1
Electrolyte
H
2
SO
4
⇌
H
+
+
HSO
4
-
Equation
2
Negative
Electrode
Pb
(
metal
)
+
HSO
4
-
⇌
Charge
Discharge
PbSO
4
+
H
+
+
2
e
-
Equation
3
Positive
Electrode
Pb
O
2
+
3
H
+
+
HSO
4
-
+
2
e
-
⇌
Charge
Discharge
Pb
SO
4
+
2
H
2
O
Equation
4
Total
Reaction
Pb
(
metal
)
+
Pb
O
2
+
2
H
2
SO
4
⇌
Charge
Discharge
2
Pb
SO
4
+
2
H
2
O
Discharge within the electrochemical cell results in lead metal (Pb) supplied by the negative plate reacting with the ionized sulfuric acid electrolyte to form lead sulfate (PbSO
4
) on the surface of the negative plate (see Equation 2). Discharge also results in the PbO
2
located on the positive plate being converted into PbSO
4
on or near the positive plate. Charging of the battery cell (via an electron supply from an external electrical current) converts PbSO
4
into spongy lead metal on the surface of the negative plate, and converts PbSO
4
into PbO
2
(PAM) on the surface of the positive plate. In effect, charging converts PbSO
4
into PAM and lead metal; discharging releases the stored electrical potential by converting PAM and lead metal back into PbSO4.
Lead acid batteries, to function properly, require the negative electrode to remain porous. However, the surface of the spongy lead on the negative plate can become covered by an impenetrable film of lead sulfate that forms during discharge. This film “pacifies” the spongy lead by forming a film over the negative active material (known in the art as “sintering”). Accordingly, an expander is added in small amounts to the negative active material to prevent the contraction and solidification of the spongy lead of the negative plate and thus preventing the contraction or the closing of the pores in the negative plate. Expanders are typically acid resistant materials able to function in the presence of the sulfuric acid electrolyte.
The common process to manufacture lead acid battery plates includes pasting (i.e., preparing a suitable paste and applying the paste to a grid), followed by curing and forming steps, in which the active materials are converted from the paste applied to the grids. The paste applied to the grids typically includes the combination of dry powders, sulfuric acid, and water. To maximize the utilization of negative plates, the paste must be uniform in both composition and consistency. To be evenly applied to the grids, the powders used to make the paste must have a pre-defined particle size distribution and the paste cannot contain either an insufficient or an excess of water. Of particular significance is the uniform distribution of the expander in the negative paste, which must be evenly distributed once applied to the surface of the grid.
To produce a uniform paste, the materials are mixed typically in a batch type operation and then applied to the grids. However, a batch type operation is not as efficient as a continuous process would be. As such, a method of making a uniform paste from a material that eliminates at least some of the mixing of powdered materials used to form the paste is desirable, as is the use of such materials wherein paste is made and applied to grids in a continuous process.
SUMMARY OF THE INVENTION
Provided for herein is a process of forming a negative battery paste including combining a barium containing material at least partially dissolved in water with an organic expander, carbon black, and a lead oxide containing material to form a first mixture; followed by combining the first mixture with an amount of sulfuric acid to form the negative battery paste.
REFERENCES:
patent: 944822 (1909-12-01), Rodman
patent: 2644023 (1953-06-01), Rasch
patent: 6203943 (2001-03-01), Bennett et al.
patent: 6346347 (2002-02-01), McNally et al.
patent: 6454977 (2002-09-01), Kwok et al.
patent: 6018262 (1985-09-01), None
Delphi Technologies Inc.
Funke Jimmy L.
Maples John S.
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