Improvements in Secondary Batteries.
Year: 1888

page_text: COMPLETE SPECIFICATION.
Improvements in Secondary Batteries.
PIERRE, ANATOLE FICHET, and ALBERT NODON, both of 12 rue Cassette in
Paris Republic of France, Engineers, 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 :-
The ways of construction of secondary batteries which form the object of the
present patent are intended to obtain several advantages among which may be
mentioned the long duration of the apparatus and great power with slight weight. In
the greater part of the secondary batteries known, electrodes are liable to rapid
alterations because they are constituted with metallic pieces which take part in the
chemical reactions. In order to avoid these alterations of clectrodes, we constitute
them with electrical conductors, but we manage so as they take no part in the chemical
reactions which intervene during the action of the apparatus. To obtain that result
our electrodes are formed now with pieces of agglomerated carbon, now with metallic
pieces covered with an adherent and sufficiently thick layer of the active metal. The
thickness of this layer is such as to be never completely dissolved, and in that way the
metallic electrode on which the layer is applied being never bare undergoes no
alteration. For example we may inention the use of electrodes of galvanised iron
with a strong layer of zinc. The iron is the conductor, and the layer zinc alone takes
part to the reactions.
In order to make one easily understand the way of construction of the apparatus
and the whole of the chemical reactions which makes them distinct from the other
systems of reversible batteries, we will begin by explaining the meaning we attach to
certain expressions, such as primary and secondary, which will be employed in the
course of the following explanations.
By analogy with what takes place in the ordinary elements often called primary
elements, we call primary current that which is produced by the internal chemical
action which dissolves a metal and changes it in a soluble salt; we call primary period
that which corresponds to this action, and primary combinations those formed by the

page_text: metal which is dissolved. At the end of the primary period the element is discharged
and ready to be charged anew.
We call secondary period that which comes after the preceeding one.
During this
secondary period, the apparatus is transversed by a current, called secondary current,
in the opposite direction to the first, and produced by an exterior source such as a
dynamo. The secondary current is meant to recharge or regenerate the clement;
under its influence the primary combinations are destroyed, the metal dissolved in the
first period is deposited anew, and the active substance which formed a salt with this
metal, enters into new chemical combinations, called secondary combinations. At the
end of the secondary period, the substances go back to their primitive state, and the
element is afresh ready to produce a primary current as before.
:
In order that the two preceeding characterised periods may succeed each other
indefinitely, several conditions are necessary; among which we may mention the
following 1° The reactions of the secondary period must be exactly opposite to those
of the primary one. 20 The whole must take place without loss or elimination of
any part of the active substances. 3° At the end of the secondary period the active
substances are to be brought back to the same physical state as at the beginning of the
primary period, so the metal which has been dissolved during the primary period is to
be brought back to the metallic state at the end of the secondary one. If at the
beginning of the primary period this metal had formed an adherent layer at
the surface of the negative electrode, it should, when the element has been regenerated
by the secondary current, he brought back to the same state and the regeneration
would be imperfect if the metal was in a pulveurlent state in suspension in the liquids
or if it lay at the bottom of the vase.
We are now to explain the way by which we realise, in the construction "of our
reversible batteries, the conditions above enumerated. In order to obtain simple
reactions indefinitely reversible we give preference to primary combinations which
take place only by two elements, a metal and an halogen chlorine, bromine or iodine.
Our primary current is then generated by the formation of a metallic chloride, Bromide,
or Iodide.
The halogen which is to combine with the metal is not employed in the free state,
but by precaution beforehand, we make it take place in a chemical combination which
will be destroyed by degrees to furnish the halogen to the metal when wanted so that
the halogen may never be free in the liquid. This is to assure the regularity of
the current and to prevent the attack in open circuit; at the same time by those means,
we avoid during the secondary period any loss of halogen.
In fact, if we consider the beginning of the primary action, we remark that at that
moment the metal is deposited in an adherent layer at the surface of the negative
electrode whilst the positive one is dipped into an aqueous solution of the secondary
combination formed by the halogen and another substance purposely chosen. When
the exterior circuit is closed, the secondary combination vanishes by degrees, and gives
up the halogen to the metal which begins being dissolved. At the end of the primary
period, the halogen is combined with the metal, and the substance which formed with it
the secondary combination is in its turn spread in the liquid of the element. If-then,
in the discharged element, we send the regenerating current coming from the dynamo,
we electrolyse the primary metallic combination. The metal deposits itself on the
negative electrode to reconstitute the primitive layer, and at the same time the halogen
going to the positive pole regenerates the secondary combination. The reaction which
gives birth to the primary current produces itself in account of the difference between
two chemical affinities; one of these powerful between the halogen and the metal, the
other one weak between the halogen and 'the substance which forms with it the
secondary combination.
It is known that the electromotive force of the current engendered by a chemical
reaction is proportional to the heat of formation of this reaction. The result is that
in our apparatus the electromotive force of the primary current. corresponds to the
difference between the heat of formation of the primary combination which takes
place, and the heat of formation of the secondary combination which is destroyed.

page_text: The greatest interest lies in this that the difference be maximum. There is then a
great advantage in choosing among the metals those which may be combined with
halogens with great evolution of heat, and in another way to choose, to form the
secondary combinations, substances, which are united to the halogen with weak
evolution of heat. It is moreover necessary that the metal set free by the secondary
current do not decompose the water at the ordinary temperature and may deposit
itself easily as an adherent layer on the surface of the negative electrode. A good
many metals may satisfy these two conditions; but by experience, we have been
brought to know that zinc is preferable. Its combinations with the halogens emit
much heat, they are very soluble in water and crystallize with difficulty ; moreover tho
zine may be usely amalgamated and in that state, the attack in open circuit is very
weak; and in closed circuit very regular. · Concerning the choice of the substances
that are to become united to the halogen to form the secondary combinations, it is
fixed by certain qualities that are to be met with in the secondary combinations
such as:
Weak heat of formation, great solubility, and sufficient stability in presence of water.
As a principle, a large number of substances may be employed to form the secondary
combinations. Among the metals, we may mention copper which in presence of
predominance of halogen, forms soluble and stable products; the heat of formation
of these being approximately the half of that of the corresponding zinc products.
With the copper and zinc couple combined with the halogen an electromotive force of
about one volt is obtained; other metals, such as iron, mercury, silver, gold, etc., give
analogous results. As the electromotive force of one volt is not sufficient to make the
apparatus practically useful, we must conclude from it that the elements constituted
with two metals do not present a great interest for an industrial design and we must
search for secondary combinations which may give a greater electromotive force.
Among the substances which may he united to the halogens with a slight evolution
of heat we may mention several compounds of alkaline or alkaline-earth metals; so
the alkaline chlorides may, under certain conditions, of temperature and pressure
combine with an exceeding quantity of chlorine; the alkaline and alkaline earth
bromides dissolved in water combine at the ordinary temperature and without pressure
with an excess of bromide to form bibromides and iribromides; the alkalino and
alkaline earth iodides form in the same conditions biiodides and triiodides. All these
reactions take place with very slight evolution of heat and we have observed how
advantageous is the use of them for the construction of our reversible batteries. In
short leaving entirely aside the metals and metallic salts for the metalloids we have
ascertained that some of them may unite to the halogens with very little evolution of
heat. The number of these products is pretty large, let us mention to begin the
combinations of the halogens with each other, that is to say the chlorides of bromine,
the chlorides of iodine, and the bromides of iodine, and subsequently the chloridles,
Bromides, and Iodides of sulphur and the chlorides of selenium and of tellurium.
The heat of formation of these several products is so weak that their stability is not
always sufficient to prevent their spontaneous decomposition in presence of water at
the ordinary temperature, and the greater part of those among them which keep stable
at a low temperature decompose themselves when it ascends some degrees. It would
then have been impossible to make use of these composits of halogens and metalloids
for the construction of our reversible batteries, if we had not ressorted to a process
which increases their stability in presence of water. This process consists in the uso
to dissolve these instable combinations not of pure water but of a concentrated
solution of a particular salt which has combined with water with great evolution
of heat.
The following example will explain what takes place.
Let us admit that the element be constructed with zinc chloride for the primary
combination and with iodine to obtain the secondary combination.
Under the influence of the current of charge the zinc chloride will be destroyed.
The zinc will deposite itself on the negative electrode whilst the chlorine making its
appearance on the positive pole will meet there the iodine and combining with it will

page_text: form in the first place chloride of iodine (I cl) and soon after Perchloride of iodine (I cl₂).
These combinations are decomposed in presence of water and the reaction is repre-
sented by
These is formation of hydrochloric acid, emission of oxygen and procipitation of
iodine. In analyzing this reaction at the thermo chemical point of view one may see
that the energy by which the decomposition takes place is represented by 0,4 caloric,
the fact is that the heats of formation are:
For I el 4,4 calories, for HO 34,5 cal., and for H cl dissolved 39,3 cal.; this gives
then for the first part 4,4 + 34,5 38,9 cal, and for the second 39,3 cal., the
difference (39,3
0,4 cal.) represents the coefficient of instability of I cl in
presence of water.
38,9
=
To make I cl stable, it is necessary to augment the value of the first member of
the preceeding expression and we obtain that result by the means we have indicated.
Supposing in fact that instead of employing pure water, we have used for a solvent
chloride of magnesium (Mg cl), which is dissolved in 6 equivalents of water to form
Mg cl 6 (Ho) with evolution of heat of 18 calories, the decomposition of this Mg cl 6
(Ho) would require 18 cal., but as the decomposition of I cl by water gives only 0,4 cal.,
this reaction will not take place unless there be a useless excess of water.
One might multiply the examples, and demonstrate that this method may be
generally applied, but the preceeding one is sufficient to show how it is applied to the
construction of our secondary batteries.
The preceeding explications show that we may apply in many differents ways the
principle of the construction of our elements by making a judicious choice of the
halogen and of the secondary combination. Let us demonstrate by three examples
taken among many; firstly we will choose for a halogen chlorine, secondly bromine,
and thirdly iodine, and uniting them with zine we will form the primary combination.
1° the primary combination is the chloride of zinc and the secondary one the
trichloride of iodine; the primary et secondary reactions are in that case:
3 Zn cl + J = 3 Zn + I cl3..
The compound K Br, being stable pure water may be employed as a solvent.
3° the primary combination is the iodide of zinc and the secondary one the
triiodide of magnesium. The reactions are in that case represented by the formula:
These three examples are sufficient to indicate the way by which we apply these
principles to the construction of cur reversible batteries, and one may see that the
electrodes fulfil simply the part of conductors of current without interfering chemically
in the reactions.
Till now we have avoided to mention any particular mode of construction, and we
have endeavoured only to show that the action of the reversible batteries in which the
halogen is never free, but goes alternately from one combination to another, may be
realized by means of a great variety of chemical reactions provided they satisfy to
certain conditions that we have enumerated.

page_text: Let us
now explain how we are to proceed in the pratical construction of the
batteries according to the indicated principles.
The recipients may be made with glass, earthen-ware, stone, or any substance able
to resist the corroding action of the liquid, such as wood covered with an appropriate
varnish etc. sometimes we make use of recipients of carbon which in that case form
at the same time electrodes.
The greater number of the modes of construction usually employed for tho
primary elements may be used for the construction of our secondary batteries
however we have experienced some others especially to obtain certain advantages such
as economy in the construction, lightness, easy transporting, etc. The shape of these
apparatus differ whether we want to construct single elements or batteries formed by
the connection of a certain number of elements.
A single element is composed for its essential part of a recipient and two electrodes
generally separated by a porous diaphragm.
It is often advantageous to have for a recipient a substance able to constitute
the negative electrode, such as carbon, or galvanised iron, or any other suitable
substance.
.
The insulation is obtained by an enamel coat or any other appropriate varnish.
In this recipient is a porous vase containing the positive electrode made of
agglomerated carbon; this electro:le may have a channeled surface. The cover and
joints have a packing of plaster, asbestos, cement, or any other substance resisting
the attack of liquid; the impermeability of the joints is made sure by a sound impreg-
nation of any substance which is suitable to fill the pores. If Paraffine is the substance
employed it is sometimes preferable to submit it before making use of it the paraffine to
the prolonged action of chlorine.
The amalgamation of the zinc is easily obtained by pouring a small quantity of
mercury or of amalgamated nine into the element. When the apparatus is entirely
ready, the liquid is introduced into it. The preparation of this liquid has been made
conformably to the preceeding indications by mixing each substance, according to the
chemical equivalents, and with the smallest quantity of water necessary for the solution,
but avoiding however the possibility of crystallization. The liquid must not fill up the
vase to the brim; a small space above is left for its expansion. An operture if necessary
is left for the emission of gas.
The batteries of several elements when connected in series are often advantageously
employed. In this case we prefer giving to the electrodes the shape of plates; the
arrangement presents the following disposition.
The plates of carbon made impermeable by impregnation of paraffine or any other
appropriate substance able to fill the pores receive by the action of the secondary
current the layer of zine on one of their faces which becomes the negative electrodes;
the other face constituting the positive pole of the following element bathes in the
active liquid. All the plates of carbon are separated, one from another, by porous
diaphragms, and all the elements so constructed are placed in the same vase.
The extreme plates of carbon form the two poles of the battery; in order to spread
uniformly the current on the whole surface of the electrodes we cover with a thick layer
of galvanised copper the exterior faces of these.
In the single elements we cover also with copper top end of the carbon in order to
make sure the best electric contact.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is:
1° The application to the construction of reversible batteries of the differential
reactions such as it has been described and which results from the fact that the
halogen which is used as an active substance is never set free but alternately
passes from a secondary combination to a primary one and vice versa according
that the element produces a primary current or that it undergoes the action of the
current of charge.

page_text: 2° The use as secondary combinations of the compounds formed by the halogens
combined with each other or with the sulphur or the selenium, or even with the
alkaline, or alkaline earth chlorides, Bromides, and Iodides.
3° The means of preventing the decomposition by water of the instable secondary
combinations which consists in making use as a solvent of these combinations of
concentrated solutions of salts which unite to the water with sufficient evolution
of heat.
4° The use of electrodes taking no part in the chemical reactions, but simply
behaving as electrical conductors and supports for the active substances which deposit
themselves on their surface.
5° The use of suitable metal covered with zinc or an amalgam of zinc and especially
of galvanised iron, the metal fulfilling the part of conductor and the zine which covers
it keeping a uniform layer of mercury on the whole surface.
6° The use for the halogen secondary elements, (characterised by the above
mentioned chemical reactions) of the mode of construction of batteries formed by
several successive elements connected in series by means of plates alternately of
carbon and of porous substances, each plate of carbon forming on
positive electrode of an element and on the other one the negative electrode of the
following element.
one face the
7° The galvanic coppering of the external faces of the extreme electrodes of the
secondary batteries connected in series.
80 The use to impregnate the carbon electrodes and the joints of the apparatus in
order to make them impermeable to the liquids, of any unalterable substance proper
to fill the pores and especially of the products of substitution obtained by the
prolonged action of the chlorine on the paraffine in order to saturate sufficiently the
paraffine with the halogens before the construction of the apparatus.
Dated this 20th day of October 1888.
A. FICHET.
ALBERT NODOR,