Manufacture of Active Material for Accumulator Batteries.
Year: 1898

page_text: Date of Application, 26th May, 1898-Accepted, 9th July, 1898
COMPLETE SPECIFICATION.
Manufacture of Active Material for Accumulator Batteries.
We, HENRI TOBLER, of No. 3, Beim Bahnhof, Muttenz, near Bâle, Switzerland,
Official, and JACOB HEINRICH GRAEBER, of 26, Petersgasse, Bale, Switzerland, Electrical
Engineer, do hereby declare the nature of this invention and in what manner the
same is to be performed, to be particularly described and ascertained in and by the
following statement:-
This invention relates to the manufacture of an active material of perfect con-
sistency for accumulator batteries, which. maintains its cohesion also during the
activity of the element, so that the lead gratings or other appliances for retaining the
active material can be entirely dispensed with.
These
With accumulator batteries as at present employed, red lead is generally employed
for the positive electrode while white lead is used for the negative electrode.
lead compounds, after being mixed with suitable binding materials, are generally
stirred up with dilute sulphuric acid of about 10 p.c. to form a paste, which is then
applied to the lead gratings and dried, after which the finished plate is formed or
rendered active. In forming, there is produced on the positive plate peroxide of lead
together with a thin layer f sulphate of lead, the latter being only slightly porous
and causing considerable resistance which correspondingly reduces the current
pressure of the accumulator. To this is added the fact that the inner part of the
electrode has become converted into soft lead peroxide which of course behaves very
differently from the sulphate layer as to resistance &c. This explains the reason why
these plates so readily crumble away.
According to the present invention these disadvantages are obviated by forming
the active material entirely of lead sulphate; in this case the change which occurs
during the charging of the cell produces lead peroxide on the anode and spongy lead
superficially on the cathode, while during the discharging of the cell the sulphate is
re-formed; the known equations express the changes
The itau peroxide and read produced are converted into sulphate when
is discharged.
For the purpose of this invention lead oxide is mixed with graphite and made into
a paste with distilled water; dilute sulphuric acid is then added to this paste until
its colour is brown and the mass moulded to the desired form and dried. When
dry the plates thus prepared are laid for several days in dilute sulphuric acid, after
which they are again dried and transferred to a second bath of sulphuric acid, some-
what stronger than that first employed. The plates are left in this bath until they
are white and hard all through. If necessary the drying and treatment with
sulphuric acid are repeated until the whole mass has been converted into sulphate.
The plates are next put together as electrodes and formed in the known manner,
whereby lead peroxide is produced on the positive electrode and spongy lead on the
negative electrode as shewn above.

page_text: The addition of graphite renders it possible to use every part of the plate as a
source of current without the plate being disintegrated by the action of the electric
current. At the same time the difficulty which heretofore subsisted owing to the
use of a binding material producing a high internal resistance, is overcome, since
the graphite is itself a conductor so that every particle of the plate will be fully used
without its coherency being destroyed.
Such an element gives a terminal pressure of 2.6 volts and its efficiency is three
times as great as that of the known accumulators of equal electrode surface in conse-
quence of the absence of the inner resistance. At the same time the periods of rest
are avoided which have heretofore been necessary for enabling the charging of an
element to be efficiently effected moreover, an important feature consists in that the
concentration of the acid in this element remains unchanged, whereas in the
elements hitherto used the concentration is altered during the first charging by
the formation of sulphate.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
A manufacture of active material, free from non-conducting binding material for
accumulators produced by mixing a paste of finely powdered lead oxide and graphite
with dilute sulphuric acid, moulding the inass to the desired form and alternately
drying the material and treating it with dilute sulphuric acid until the mass is hard
and coherent so as not to require a supporting frame substantially as described.