Note: Descriptions are shown in the official language in which they were submitted.
1111495
The present invention is concerned with negative elec-
trode structures for lead-acid storage batteries. It is a
companion invention to an invention described in Canadian
application S.N. 315,760 filed November 2, 1978 by the same
inventors entitled Battery and Electrolytic Cell Electrodes.
In general, regardless of the particular type of mechanical
design employed in a lead-acid battery, the negative electrode
of current, state of the art batteries comprises a base of
pure lead upon the surface of which is pasted or otherwise
deposited and adhered an active mass which in the charged
state essentially comprises spongy lead and in the discharged
state approaches lead sulfate. The lead base of the negative
electrode is heavy and is mechanically very weak.
It has now been discovered that by means of a composite
structure a highly advantageous negative electrode for a lead
acid battery can be provided.
It is an object of the present invention to provide a
novel negative lead-acid storage battery electrode.
Other objects and advantages will be observed from the
following description, taken in conjunction with the drawing
in which:
The figure depicts a cross section of a negative lead acid
storage battery electrode of the present invention.
Generally speaking the present invention contemplates a
negative lead-acid storage battery electrode having a compositely
structured base comprising a sintered matrix of metal substan-
tially less dense than lead at least partially infiltrated with
lead, an alloy of lead or a metal wetted by lead in the liquid
state and bearing on at least part of the surface thereof and
metallurgically bonded thereto a layer of pure lead. The total
1111495
electrode includes this base, the layer of pure lead and active
mass adherent to the layer of pure lead.
Referring now to the drawing, negative electrode base 11
comprises a matrix 12 of metal less dense than lead having lead
13 at least partially infiltrated through pores in matrix 12.
At least a portion, and advantageously the whole of the surface
of base 11, has pure lead 14 coated thereon and metallurgically
bonded thereto. Active mass 15 is adhered to pure lead 14 in
any convenient manner well known to those of normal skill in
the art.
The metal of matrix 12 can be any strong metal less dense
than lead which can be formed into a sintered powdered compact
and is in the solid state at lead infiltration temperatures
(e.g., 400C-550C). Examples of such metals include iron,
nickel, copper, titanium, zirconium, manganese and aluminum and
alloys of these metals. Particular advantage is found in the
use of titanium which has a density of 4.5 g/cc and which in
powder form can be readily compacted, sintered and infiltrated
with lead. Lead 13 as an infiltrant can be pure lead or lead-
rich alloy or in some instances can be replaced by a lightermetal which is wetted by pure lead in the molten state.
When the base of the lead-acid battery negative electrode
of the present invention is made of sintered titanium infiltrated
with lead excellent mechanical characteristics (compared to pure
lead) can be achieved. Table I sets forth some mechanical char-
acteristics of sheet form composites having a matrix of titanium
sintered at about 980C for 1 hour in an argon atmosphere and
thereafter infiltrated with a melt containing 0.5~ tin,balance
lead at 550C for 1 hour.
1111495
_ BLE I
Vol. % Vol. % Vol. % Y. S. UTS Elong
Infil- 2 2
Ti trant Pores Kg/Cm Kg/Cm % in 2.54cm
; 84.24 12.84 2.93 2094 2924 2.0
83.10 12.72 4.16 2195 2700 2.0
83.05 13.68 3.26 2108 2632 3.0
75.70 20.92 3.39 1761 2203 3.0
75.54 23.39 1.08 1693 2229 2.0
67.98 28.66 3.36 1353 1748 2.0
69.04 27.43 3.52 1401 1754 2.0
68.63 27.74 3.63 1306 1659 1.0
; 61.06 34.95 3.96 1068 1374 <1.0
62.46 32.81 4.73 1162 1489 1.0
Room temperature electrical resistivities of composite materials
similar to those for which mechanical test results are given in
Table I but of rod form rather than sheet form range within the
limits of about 30 to about 100 microhm-centimeter. Additionally,
the sheet-form titanium-lead composites giving the mechanical
test results set forth in Table I have densities ranging from
Ibout 45~ to about 60% of lead. Totally the mechanical charac-
teristics, the electrical resistivities and the densities of
titanium-lead composites enable negative lead-acid battery
electrode structures to be made which are much lighter than, much
stronger than, and have equal or better electric current carrying
capacity than conventional structures made of pure lead.
When titanium-lead composites are used as base 11 of
negative electrodes of the present invention, it is advantageous
to maintain the volume per cent of titanium of the composite
within the range of about 50~ to about 90%, the balance of the
composite being lead or lead alloy infiltrant and up to about
~111495
5% pores. Generally, the composite can be made by grinding
sponge titanium into powder, forming the powder into any
desired shape by conventional powder metallurgical means, sin-
tering the formed powder shape and thereafter infiltrating the
thus sintered shape with molten lead or other infiltrant.
Table II sets forth the volume per cent porosity which has been
observed in sintered bodies of titanium, prior to infiltration,
which have been compacted under the indicated pressure.
TABLE II
Compacting2Pressure
Kg/cm Volume % Voids
0 (loose powder) 58.6
140.6 39.1
281.2 37.4
562.4
843.6 31.6
1125 29.1
1400 25.6
2812 18.3
3500 1~.2
4218 15.3
4920 11.3
Greater detail regarding the formation of titanium-lead com-
posite structures is set forth in Canadian application Serial
No. 315,760, referred to hereinbefore and filed iNov. 2, 1978.
For use in a negative lead-acid storage battery electorde,
it is essential that any surface of the composite structure
which bears negative active mass must be separated from that
active mass by layer of pure lead 14. Ordinarily th.is layer,
111~495
~.
.002 and .015 cm thick, completely envelopes the infiltrated
matrix base, serves to anchor negative active mass to the base
and, more importantly, serves to protect the base from corrosion
by the acid electrolyte of the battery. The layer of pure lead
is most conveniently applied by merely dipping the composite
base into molten pure lead, removing the thus coated base and
allowing the pure lead to freeze on the surface. If portions
of base must be exposed, these portions can be stopped off
before immersion or scraped clean after immersion. If desired,
the pure lead can also be the infiltrant and coating and infil-
tration can occur simultaneously. Alternatively, pure lead in
foil form can be cold bonded to the surface of the infiltrated
composite base. Lead or lead alloy at least partly infiltrated
into pores in matrix 12 provides a means to firmly metallurgi-
cally bond protective pure lead layer 14 to base 11 in contrast
to relatively weak bonding between pure lead and solid metal
cores of negative electrodes which have heretofore been suggested
in the prior art.
Alternatively, normal atomic bonding to the lead in the
; 20 matrix can also be achieved by electroplating a layer of lead
over the negative core.
Although the present invention has been described in con-
junction with preferred embodiments, it is to be understood that
modifications and variations may be resorted to without departing
from the spirit and scope of the invention, as those skilled in
the art will readily understand. Such modifications and varia-
tions are considered to be within the purview and scope of the
invention and appended claims.
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