|
GENERICALLY considered, a "battery"
is a device which generates electric current.
There are two distinct species of battery, one
being known as "primary," and the other as
"storage," although the latter is sometimes
referred to as a "secondary battery" or
"accumulator." Every type of each of these
two species is essentially alike in its general
make-up; that is to say, every cell of battery
of any kind contains at least two elements of
different nature immersed in a more or less
liquid electrolyte of chemical character. On
closing the circuit of a primary battery an
electric current is generated by reason of the
chemical action which is set up between the
electrolyte and the elements. This involves a
gradual consumption of one of the elements and a
corresponding exhaustion of the active properties
of the electrolyte. By reason of this, both
the element and the electrolyte that have been
used up must be renewed from time to time, in
order to obtain a continued supply of electric
current.
The storage battery also generates electric
current through chemical action, but without
involving the constant repriming with active
materials to replace those consumed and exhausted
as above mentioned. The term "storage," as
applied to this species of battery, is,
however, a misnomer, and has been the cause of
much misunderstanding to nontechnical persons.
To the lay mind a "storage" battery presents
itself in the aspect of a device in which
electric energy is STORED, just as
compressed air is stored or accumulated in a
tank. This view, however, is not in
accordance with facts. It is exactly like the
primary battery in the fundamental circumstance
that its ability for generating electric current
depends upon chemical action. In strict
terminology it is a "reversible" battery, as
will be quite obvious if we glance briefly at its
philosophy. When a storage battery is
"charged," by having an electric current
passed through it, the electric energy produces
a chemical effect, adding oxygen to the positive
plate, and taking oxygen away from the negative
plate. Thus, the positive plate becomes
oxidized, and the negative plate reduced.
After the charging operation is concluded the
battery is ready for use, and upon its circuit
being closed through a translating device, such
as a lamp or motor, a reversion
("discharge") takes place, the positive
plate giving up its oxygen, and the negative
plate being oxidized. These chemical actions
result in the generation of an electric current
as in a primary battery. As a matter of fact,
the chemical actions and reactions in a storage
battery are much more complex, but the above
will serve to afford the lay reader a rather
simple idea of the general result arrived at
through the chemical activity referred to.
The storage battery, as a commercial article,
was introduced into the market in the year
1881. At that time, and all through the
succeeding years, until about 1905, there
was only one type that was recognized as
commercially practicable--namely, that known
as the lead-sulphuric-acid cell, consisting of
lead plates immersed in an electrolyte of dilute
sulphuric acid. In the year last named Edison
first brought out his new form of nickel-iron
cell with alkaline electrolyte, as we have
related in the preceding narrative. Early in
the eighties, at Menlo Park, he had given
much thought to the lead type of storage
battery, and during the course of three years
had made a prodigious number of experiments in
the direction of improving it, probably
performing more experiments in that time than the
aggregate of those of all other investigators.
Even in those early days he arrived at the
conclusion that the lead-sulphuric-acid
combination was intrinsically wrong, and did not
embrace the elements of a permanent commercial
device. He did not at that time, however,
engage in a serious search for another form of
storage battery, being tremendously occupied
with his lighting system and other matters.
It may here be noted, for the information of
the lay reader, that the lead-acid type of
storage battery consists of two or more lead
plates immersed in dilute sulphuric acid and
contained in a receptacle of glass, hard
rubber, or other special material not acted upon
by acid. The plates are prepared and "formed"
in various ways, and the chemical actions are
similar to those above stated, the positive
plate being oxidized and the negative reduced
during "charge," and reversed during
"discharge." This type of cell, however,
has many serious disadvantages inherent to its
very nature. We will name a few of them
briefly. Constant dropping of fine particles of
active material often causes short-circuiting of
the plates, and always necessitates occasional
washing out of cells; deterioration through
"sulphation" if discharge is continued too far
or if recharging is not commenced quickly
enough; destruction of adjacent metal- work by
the corrosive fumes given out during charge and
discharge; the tendency of lead plates to
"buckle" under certain conditions; the
limitation to the use of glass, hard rubber, or
similar containers on account of the action of
the acid; and the immense weight for electrical
capacity. The tremendously complex nature of
the chemical reactions which take place in the
lead-acid storage battery also renders it an
easy prey to many troublesome diseases.
In the year 1900, when Edison undertook to
invent a storage battery, he declared it should
be a new type into which neither sulphuric nor
any other acid should enter. He said that the
intimate and continued companionship of an acid
and a metal was unnatural, and incompatible with
the idea of durability and simplicity. He
furthermore stated that lead was an unmechanical
metal for a battery, being heavy and lacking
stability and elasticity, and that as most
metals were unaffected by alkaline solutions, he
was going to experiment in that direction. The
soundness of his reasoning is amply justified by
the perfection of results obtained in the new
type of storage battery bearing his name, and
now to be described.
The essential technical details of this battery
are fully described in an article written by one
of Edison's laboratory staff, Walter E.
Holland, who for many years has been closely
identified with the inventor's work on this cell
The article was published in the Electrical
World, New York, April 28, 1910;
and the following extracts there- from will
afford an intelligent comprehension of this
invention:
"The `A' type Edison cell is the outcome of
nine years of costly experimentation and
persistent toil on the part of its inventor and
his associates....
"The Edison invention involves the use of an
entirely new voltaic combination in an alkaline
electrolyte, in place of the
lead-lead-peroxide combination and acid
electrolyte, characteristic of all other
commercial storage batteries. Experience has
proven that this not only secures durability and
greater output per unit-weight of battery, but
in addition there is eliminated a long list of
troubles and diseases inherent in the lead-acid
combination....
"The principle on which the action of this new
battery is based is the oxidation and reduction
of metals in an electrolyte which does not
combine with, and will not dissolve, either the
metals or their oxides; and an electrolyte,
furthermore, which, although decomposed by the
action of the battery, is immediately re-formed
in equal quantity; and therefore in effect is a
CONSTANT element, not changing in
density or in conductivity.
"A battery embodying this basic principle will
have features of great value where lightness and
durability are desiderata. For instance, the
electrolyte, being a constant factor, as
explained, is not required in any fixed and
large amount, as is the case with sulphuric acid
in the lead battery; thus the cell may be
designed with minimum distancing of plates and
with the greatest economy of space that is
consistent with safe insulation and good
mechanical design. Again, the active materials
of the electrodes being insoluble in, and
absolutely unaffected by, the electrolyte, are
not liable to any sort of chemical deterioration
by action of the electrolyte--no matter how
long continued....
"The electrolyte of the Edison battery is a
21 per cent.
solution of potassium hydrate having, in
addition, a small amount of lithium hydrate.
The active metals of the electrodes --which
will oxidize and reduce in this electrolyte
without dissolution or chemical
deterioration--are nickel and iron. These
active elements are not put in the plates AS
METALS; but one, nickel, in the form of
a hydrate, and the other, iron, as an oxide.
"The containing cases of both kinds of active
material (Fig. 1), and their supporting
grids (Fig. 2), as well as the bolts,
washers, and nuts used in assembling (Fig.
3), and even the retaining can and its cover
(Fig. 4), are all made of nickel-plated
steel--a material in which lightness,
durability and mechanical strength are most
happily combined, and a material beyond
suspicion as to corrosion in an alkaline
electrolyte....
"An essential part of Edison's discovery of
active ma- setials for an alkaline storage
battery was the PREPARATION of these
materials. Metallic powder of iron and nickel,
or even oxides of these metals, prepared in the
ordinary way, are not chemically active in a
sufficient degree to work in a battery. It is
only when specially prepared iron oxide of
exceeding fineness, and nickel hydrate
conforming to certain physical, as well as
chemical, standards can be made that the
alkaline battery is practicable. Needless to
say, the working out of the conditions and
processes of manufacture of the materials has
involved great ingenuity and endless
experimentation."
The article then treats of Edison's
investigations into means for supporting and
making electrical connection with the active
materials, showing some of the difficulties
encountered and the various discoveries made in
developing the perfected cell, after which the
writer continues his description of the "A"
type cell, as follows:
"It will be seen at once that the construction
of the two kinds of plate is radically
different. The negative or iron plate (Fig.
5) has the familiar flat-pocket construction.
Each negative contains twenty-four pockets--a
pocket being 1/2 inch wide by 3 inches long,
and having a maximum thickness of a little more
than 1/8 inch. The positive or nickel plate
(Fig. 6) is seen to consist of two rows of
round rods or pencils, thirty in number, held
in a vertical position by a steel
support-frame. The pencils have flat flanges
at the ends (formed by closing in the metal
case), by which they are supported and
electrical connection is made. The frame is
slit at the inner horizontal edges, and then
folded in such a way as to make individual
clamping-jaws for each end- flange. The
clamping-in is done at great pressure, and the
resultant plate has great rigidity and strength.
"The perforated tubes into which the nickel
active material is loaded are made of
nickel-plated steel of high quality. They are
put together with a double-lapped spiral seam to
give expansion-resisting qualities, and as an
additional precaution small metal rings are
slipped on the outside. Each tube is 1/4
inch in diameter by 4 1/8 inches long, add
has eight of the reinforcing rings.
"It will be seen that the `A' positive plate
has been given the theoretically best design to
prevent expansion and overcome trouble from that
cause. Actual tests, long continued under very
severe conditions, have shown that the
construction is right, and fulfils the most
sanguine expectations."
Mr. Holland in his article then goes on to
explain the development of the nickel flakes as
the conducting factor in the positive element,
but as this has already been described in
Chapter XXII, we shall pass on to a later
point, where he says:
"An idea of the conditions inside a loaded tube
can best be had by microscopic examination.
Fig. 7 shows a magnified section of a
regularly loaded tube which has been sawed
lengthwise. The vertical bounding walls are
edges of the perforated metal containing tube;
the dark horizontal lines are layers of nickel
flake, while the light-colored thicker layers
represent the nickel hydrate. It should be
noted that the layers of flake nickel extend
practically unbroken across the tube and make
contact with the metal wall at both sides.
These metal layers conduct current to or from
the active nickel hydrate in all parts of the
tube very efficiently. There are about three
hundred and fifty layers of each kind of material
in a 4 1/8 -inch tube, each layer of nickel
hydrate being about 0.01 inch thick; so it
will be seen that the current does not have to
penetrate very far into the nickel
hydrate--one-half a layer's thickness being
the maximum distance. The perforations of the
containing tube, through which the electrolyte
reaches the active material, are also shown in
Fig. 7."
In conclusion, the article enumerates the chief
characteristics of the Edison storage battery
which fit it pre- eminently for transportation
service, as follows: 1. No loss of active
material, hence no sediment short-circuits.
2. No jar breakage. 3. Possibility of
quick disconnection or replacement of any cell
without employment of skilled labor. 4.
Impossibility of "buckling" and harmlessness
of a dead short-circuit. 5. Simplicity of
care required. 6. Durability of materials and
construction. 7. Impossibility of
"sulphation." 8. Entire absence of
corrosive fumes. 9. Commercial advantages of
light weight. 10. Duration on account of its
dependability. 11. Its high practical
efficiency.
|
|
