Note: Descriptions are shown in the official language in which they were submitted.
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MAGNESIUM-BASED PRIMARY (NON-RECHARGEABLE) AND SECONDARY
(RECHARGEABLE) BATTERIES
Scope of the invention
The present invention regards primary (i.e., non-rechargeable) and secondary
s (i.e., rechargeable) batteries in which at least the anode contains
magnesium, and
optionally also the electrolyte and cathode contain magnesium, as well as
methods for making said batteries.
Prior art
As is known, the enormous and rapid development of digital electronics that
has
io taken place in recent years has enabled the creation of a large number of
new
portable devices, such as computers, cellphones, videocameras, etc. These
devices are almost exclusively equipped with storage batteries built according
to a
single technology; namely nickel-cadmium (Ni-Cd) batteries.
The need to produce ever smaller and lighter portable devices, together with
the
is need for long operating autonomy of these devices, has pushed numerous
private
firms operating in the sector, as well as public research bodies, to carry out
research aimed at developing new technologies capable of meeting the
requirements referred to above.
In the late eighties and early nineties, two new types of batteries appeared
on the
2o market: nickel-metal hydride (Ni-MH) and lithium-ion (Li-ion) batteries.
In just a few years, the performance of batteries produced using these
technologies has improved considerably, to the extent that today the
performance
of these batteries is superior to that of nickel-cadmium batteries.
A further advantage of the batteries produced using these new technologies is
the
2s absence of cadmium, which, since it is a heavy metal, has quite a serious
detrimental impact on the environment.
As is known, lithium-ion batteries are, in energy terms, still the most
promising
ones, but their production cost is relatively high. However, if the cost per
cycle of
these systems is considered, it may be noted that they become competitive as
3o compared to the more economical nickel-cadmium batteries. On the basis of
the
technical characteristics, environmental impact, and cost per cycle, a
considerable
growth is expected for the lithium-ion system on the world market.
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On the other hand, nickel-metal hydride batteries are likely to have a more
modest
growth, whilst it is estimated that nickel-cadmium batteries are unlikely to
maintain
their current production levels.
The international scenario witnesses a concentration of the majority of
production
s in the sector of lithium-ion batteries, which are an evolution of lithium
systems.
Primary lithium batteries, which are widely used in calculators, clocks and
watches, cardiac pacemakers, etc., are made with a lithium anode and a cathode
made of transition metal oxide (e.g., Mn02). Thanks to the high
electrochemical
potential supplied by the lithium anode, these batteries provide high cell
voltages,
io and consequently also high energy densities.
However, these systems are not reversible, or at the most are usable for just
a few
cycles.
The idea of exploiting lithium to make secondary batteries has given rise to a
first
technology known as lithium-polymer (Li-polymer) technology. This method,
which
is exploits metallic lithium for making the anode, presents, however, serious
difficulties in terms of reversibility. In fact, during the recharging phase,
dendritic
deposits are formed on the surface of the anode, which are the result of the
reaction of the lithium with the organic polymeric electrolyte and are
responsible
for the fast deterioration of this type of battery.
2o At best, the number of cycles obtained using systems of this type thus
amounts to
just a few dozens or hundreds.
On the other hand, the reactivity of the lithium in regard to the polymeric
electrolyte
may also become a cause of serious problems of safety in the operating phase
of
the battery itself.
zs The next step in the development of these devices was that of the
introduction of
the so-called lithium-ion or rocking-chair technology, which is based on
solutions
that tend to solve the problem of formation of dendrites on the lithium anode
by
replacing the lithium with composite materials capable of intercalating Li+ in
their
structure via insertion reactions.
3o In recent years, it has been possible to produce anodes based on carbon
with
properties of intercalation. Certain carbons with a regular structure
(turbostatic or
graphitizable) or with a highly crystalline structure (natural or synthetic
graphites)
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can in fact intercalate the Li+ ion in their layers in a reversible manner,
thus giving
rise to complexes of the LiXCs type.
Other lithium-ion batteries are provided with an intercalated titanium
disulphide-
based (LixTiS2) anode. The latter has a behaviour similar to that of a carbon
s electrode.
Usually the cathode is instead made using oxides of lithium and transition
metals,
among which the most widely used up to now is lithium cobaltate (LiCo02),
which,
for reasons of cost, availability, and toxicity, tends to be replaced by
lithium
nickelate (LiNi02) or lithium manganate (LiMn04).
io The number of cycles achievable using the rocking-chair technology reaches
one
thousand.
Usually, in these systems the electrolyte consists of an organic polymer with
solvent properties, which is rendered ionic-conductive by being doped with
special
lithium salts (e.g., LiPFs, LiCl04, etc.).
is Notwithstanding the fact that the above-mentioned technological advances
tend to
solve the problems linked to the use of lithium on account of the high
reactivity of
this element, and in particular the main problem linked to the formation of
dendrites on the anode, research for a complete solution to these problems is
still
very much in progress. The problem of the formation of dendrites has not yet
been
2o completely solved, whilst likewise the problem of high reactivity of
lithium, together
with the known problems of safety referred to previously, and the problem of
reversibility still remain open.
Magnesium could be an element usable for overcoming these problems, and in
particular as a replacement for lithium.
2s As reported in the literature, a number of researchers, such as Farrington
and
Cherng have sought to develop magnesium-based polymeric electrolyte systems
for the possible development of magnesium batteries, with, however, somewhat
meagre results. The polymeric electrolytes obtained had, in fact,
conductivities
which, at room temperature, were too high (i.e., with conductivity lower than
10-6
3o siemens/cm) for the production of primary and/or secondary batteries.
Nevertheless, in the patent US44575 Moulton suggests the possibility of making
magnesium batteries, without, however, specifying the procedure, in particular
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without specifying how to make the anode, cathode and polymeric electrolyte.
Polymeric electrolytes doped with magnesium salts are cited, which, when
tested,
yielded resistivities higher than 10' ohm~cm at room temperature, whereas in
order to be able to make the batteries it. is necessary for the resis_ tivity
values to
s drop below than 105 ohm~cm.
The main task of the present invention is to succeed in developing primary
(non-
rechargeable) batteries andlor secondary (rechargeable) batteries that
overcome
the problems of reactivity and reversibility typical of lithium-based
batteries.
In the framework of the above-mentioned task, a consequent primary purpose is
to
io develop batteries with high-level technical characteristics allied to a
reduction in
production costs.
Another important purpose is to develop miniaturized and lightweight
batteries.
Yet a further purpose is to develop batteries suitable for use in portable
digital
electronic equipment.
1 s A further important purpose is to arrive at the almost total elimination
of
environmental impact.
Summary of the invention
These and other purposes, which will appear more clearly in what follows, are
achieved by primary (non-rechargeable) and secondary (rechargeable) batteries
2o that form the object of the present invention, of the type comprising at
least one
anode, at least one cathode, at least one electrolyte, and current collectors,
said
batteries being characterized' in that, at least the anode and preferentially
also the
electrolyte contain magnesium. Also the cathode of the batteries that form the
object of the present invention may optionally incorporate magnesium.
Zs The anode included in the present invention is characterized in that it
uses
magnesium in the various states of oxidation Mg"+ t°5"~I, optionally
combined with
metallic magnesium, and the electrolyte, possibly containing. magnesium, is
characterized in that it comprises any ionic species of magnesium in solvents,
including polymeric solvents, that are capable of producing electrolytes
having
3o good ionic conductivity and capable of solvation of the said ionic species.
When the cathode contains magnesium, this is a species of magnesium in the
state of oxidation 2+ and may have a substrate of highly conductive inorganic
or
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s
organic materials, or else may be intercalated or embedded in highly
conductive
inorganic or organic materials.
Forming a further object of the present invention are methods for the
production of
said primary and secondary batteries of the type comprising at least one
anode, at
s least one cathode, at least one electrolyte set between anode and cathode,
and
electrical-connection collectors, said batteries being characterized in that
at least
the anode and the electrolyte contain magnesium and even the cathode can
optionally contain magnesium.
Further characteristics and advantages will emerge more clearly from the
ensuing
io detailed description of the invention, an embodiment of which is
illustrated, merely
for the purpose of providing a non-limiting example, in the attached plate of
drawing.
Brief description of the figure
Figure 1 is a schematic sectional view of a battery built according to the
present
is invention, where:
designates an anode which has the characteristics and is made as is
described in detail in what follows;
- 11 designates a cathode which has the characteristics and is made as is
described in detail in what follows; and
- 12 designates an electrolyte which has the characteristics and is made as is
described in detail in what follows.
Detailed description of the invention
Notwithstanding the fact that the attempts referred to above failed to lead to
promising results, the present inventors have now surprisingly found that
2s magnesium is an element that can be usefully employed in making primary and
secondary batteries.
Following on extensive and ample research, the present inventors have in fact
found that, for the purposes of the present invention, i.e., for obtaining
primary and
secondary batteries with technical performance comparable, if not superior, to
that
of lithium batteries at present in use or known, reference being made to the
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aforementioned Figure, the batteries that form the object of the present
invention
may be primary and secondary batteries of the type comprising at least one
anode, at least one cathode, at least one electrolyte set between anode and
cathode, and current collectors, said batteries being characterized in that at
least
s the anode and preferentially also the electrolyte contain magnesium.
In the batteries that form the object of the present invention also the
cathode may
optionally incorporate magnesium.
When the cathode does not contain magnesium, it is a conventional cathode, and
hence is in itself known, and consequently will not be described further
herein.
~o The primary and secondary batteries that form the object of the present
invention
may moreover comprise possible dielectric spacers, not illustrated in the
Figure.
In particular, the batteries according to the present invention may be made up
of:
- An anode 10 characterized in that it comprises magnesium in the various
states of oxidation Mg"+~osns2)~ optionally combined with metallic magnesium.
~s In said anode, the magnesium may be included as such or may also have a
substrate of highly conductive inorganic or organic materials, or else of
highly
conductive inorganic or organic materials that are capable of englobing, by
intercalation or embedding into their own matrices, magnesium crystallites of
reduced dimensions or magnesium monocrystals.
2o in particular, the anode 10 may consist of metallic magnesium as such, and
in this
case the magnesium may be used in laminated or sintered form.
In the case, instead, where the magnesium has a substrate of highly conductive
materials, these may be inorganic materials chosen from the group made up of
metals, for example aluminium, copper, and other equivalent metals, or oxides,
Zs alloys, and fabrics made of the same. The said highly conductive substrate
materials may also be organic, and also of a polymeric type; in the latter
case,
they are chosen from among materials such as carbon-fibre fabrics, graphite,
or
even graphite-based composite materials, or other equivalent materials
suitable
for the purposes.
3o Also in the case where intercalation or embedding materials are used for
the
anode, this may be either organic or inorganic. The intercalation or embedding
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materials that may be used for the purposes of the present invention are
transition-
metal compounds, alkaline-metal compounds, and alkaline earth-metal
compounds, as well as non-metal compounds, chosen from among oxides,
sulphides, phosphates or phosphides, such as tungsten oxides (WYOx), ferric
s oxides (FeyOX), titanium sulphides (TiySx), cobalt oxides (CoYOX), nickel
oxides
(NiyOX), manganese oxide (MnyOX), or else other equivalent compounds, or
carbon-based materials with intercalation properties and with a highly
crystalline
structure or an irregular structure, or equivalent materials, or else a
material of a
polymeric type, such as carbon-based polymers or equivalent polymers that are
io capable of englobing, by intercalation or embedding into their own
matrices,
magnesium crystallites of reduced dimensions or magnesium monocrystals.
Furthermore said anode 10 may be optionally oxidized with oxidizing agents
such
as oxygen gas or peroxide, such as H202, or organic peroxides and stabilized
by
treatment with stabilizing agents such as alkoxides, (e.g. tetra-alkoxy
titanium,
is tetra-alkoxy silanes, trialkoxy aluminium, tetra-alkoxy zirconium, or
magnesium
dialkoxide, or equivalent compounds).
A cathode 11 characterized in that it contains magnesium species with state
of oxidation 2+.
In the case where the cathode contains magnesium, the latter may have a
Zo substrate of highly conductive inorganic or organic materials, including
polymeric
materials, or else the magnesium may be intercalated or embedded in inorganic
or
organic materials. The materials that may be used both in the case where the
magnesium has a substrate and in the case where the magnesium is intercalated
or embedded are the same as the materials mentioned previously for the anode.
2s This type of cathode may be used, dispersing the active material in a
porous and
conductive matrix. This use affords the advantage of improving the
electrochemical properties of the batteries.
Also the cathode may be optionally oxidized with the same oxidizing agents.
The
oxidation of the cathode may be, like the anode, in situ and following on its
3o preparation or, unlike the anode, the cathode may be prepared with
electrochemically active materials that have been partially oxidized prior to
its
preparation.
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When the cathode 11 does not contain magnesium, it is a conventional cathode
and is in itself known; consequently, it is not further described herein. In
this case,
anyway, the cathode contains electrochemically active materials having a base
of
metallic mixtures in appropriate proportions in a reduced or oxidized form.
For this
s purpose, as is known from the prior art, materials containing transition
metals may
be used, such as, but not exclusively, manganese with state of oxidation
ranging
from 7+ to 2+, and other equivalent metals.
- An electrolyte 12 characterized in that it comprises any ionic species of
magnesium in solvents, including polymeric solvents, capable of producing
io electrolytes with good ionic conductivity and capable of solvating said
species.
The electrolyte according to the present invention comprises, as ionic species
of
magnesium, magnesium salts or complexes of the general formula Mg(R)yX2_y,
with 0<_y<_2, having a very low charge/volume ratio.
The radical R may be chosen from the group consisting, for example, of alkyls
with
is C~-C~ chains, whilst X may be chosen from among halides, CI04,
(CF3)~+XSO3_X ,
with Osx<_2, SCN', P043', or chlorides in 8 form, or other equivalents.
The compounds of the general formula Mg(R)yX2_y, with 0<_y<_2, usable for
doping
the electrolyte, may moreover be preferentially magnesium salts or magnesium
complexes with lattice energy lower than 500 kcal/mol.
2o The solvents used for the electrolyte may be of various types, since the
essential
characteristic required is that they should possess good ionic conductivity
and in
any case that they should at the same time be able to solvate the magnesium
salts
or magnesium complexes that have been chosen. For the purpose, they may
therefore be liquid solvents or solvents in the solid or viscous state.
2s In the case of liquid solvents, these are chosen from among materials
having polar
groups which are able to co-ordinate and dissociate the ionic magnesium salts
or
complexes and which contain oxygen, nitrogen, sulphur and carbon. These
solvents may therefore be chosen from among ethers, alcohols, di-alcohols,
esters, amines and amides, thioethers, thioalcohols, thioesters, alkyl
carbonates
3o and alkyl thiocarbonates, or other equivalents.
In the case where the solvent for the electrolyte is solid or viscous, it may
be of a
polymeric type.
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Usable for the purpose are all the polymers or copolymers of the same having
different molecular weights, which are capable of solvating magnesium salts or
complexes suitable for the purpose. Such polymers and/or copolymers may be
chosen from among polyalkylene oxides, polyalkylene glycols, polycarbonates,
s polyalkyl siloxanes, polyethylene diaminotetra-acetate, or equivalent
polymers or
copolymers of the same macromolecular frameworks having different molecular
weights, also containing, in their chains, hetero-atoms of the oxygen,
nitrogen,
silicon, and phosphorus types.
Also usable for the purpose are polyphosphazene polymers functionalized with
the
1o polymers and/or copolymers mentioned previously.
To provide examples, among polyalkylene oxides, the following may be
mentioned: polymethylene oxide, polyethylene oxide, polypropylene oxide and
others; among polyalkylene glycols, the following may be mentioned:
polymethylene glycols, polyethylene glycols, polypropylene glycols and
fluorinated
is derivatives of the same and others; among polycarbonates, the following may
be
mentioned: polymethylene carbonates, polyethylene carbonates, and
polypropylene carbonates and others; among the polyalkyl siloxanes, the
following
may be mentioned: polymethyl siloxane, polyethyl siloxane, and polypropyl
siloxane and others.
2o Also usable for the purpose are copolymers derived from the polyalkylene
oxides
and polyalkylene glycols, polycarbonates, polyalkyl siloxanes, polyethylene
diaminotetra-acetate; polyalkylene glycols and polycarbonates, polyalkyl
siloxanes, polyethylene diaminotetra-acetate; polycarbonates and polyalkyl
siloxanes, polyethylene diaminotetra-acetate; polyalkyl siloxanes and
polyethylene
2s diaminotetra-acetate such as, as example, polyethylene oxide-polypropylene
oxide, polymethylene oxide-polyethylene oxide, and polymethylene oxide
polypropylene oxide; polyethylene oxide-polymethylene carbonate, polypropylene
oxide-polyethylene carbonate, and polyethylene oxide- polypropylene carbonate;
polyethylene glycol- polymethyl polysiloxane, polyethylene oxide-polymethyl
3o siloxane, and polyethylene oxide- polyethylene diaminotetra-acetate, etc.
It is also possible to use for the purpose, for instance, polyphosphazene
polymers
functionalized with polymers and/or copolymers of the polyethylene-oxide type
or
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the like having different molecular weights.
The polymers and/or copolymers that may be used for the preparation of the
electrolyte may moreover be functionalized with groups that bond or co-
ordinate
magnesium so as to improve their interaction with the salts or complexes of
the
s latter.
For the purpose of improving the ionic conductivity of the electrolyte, this
may also
be optionally acidified or alkalinized according to known procedures, which,
consequently, will not be described in greater detail herein.
In the case where the electrolyte is acidified, however, the preferential
acidifying
to agents for the electrolyte are compounds with a base of phosphorus,
polyphosphates, P205, or equivalents of the orthophosphoric-acid type. In the
case
where the electrolyte is alkalinized, the compounds that may be used are
nitrogen
based ones and, in this case, are preferentially amines or ammonia, as well as
basic derivatives of sulphur and phosphorus.
is Acidification improves the conductivity of the electrolyte, and this
process is to be
carried out whenever the performance of the electrolyte is not adequate for
the
application. This process is to be preferred in the case of stabilized
electrodes.
Also alkalinization improves the conductivity of the electrolyte and is
carried out
with the purpose of favouring the electrochemical functioning of the
electrodes.
2o This process is, however, to be preferred in the case where non-stabilized
electrodes are used.
- Spacers (not shown in the Figure) consisting of inorganic or organic
materials which are permeable to ions and have high dielectric
characteristics;
these are appropriately functionalized, if necessary, in order to eliminate
the polar
2s groups that may be present on the surfaces of the fibres. For the purpose
it is
possible to use, for example, cellulose, glass-fibre fabrics, organic
membranes, or
other equivalent materials.
- Current collectors 13, either metallic or non-metallic, with conductive
characteristics and with a resistivity of not more than 10 ohm~m for
collecting the
3o electrons and for electrical connection of the poles of the battery
element. For the
purpose, it is possible, for example, to use metals, even in the form of
oxides,
alloys, and fabrics made of the same, such as aluminium, copper, steel, brass,
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etc., or organic materials made of carbon or carbon-fibre fabrics, or similar
materials.
The method for making the primary and/or secondary batteries according to the
present invention envisages at least one of the following steps:
s - preparation of an anode characterized in that it comprises magnesium in
the
various states of oxidation Mg"+ co<-"sz~, optionally combined with metallic
Mg, said
anode having a base of metallic magnesium as such, or else of magnesium on a
substrate of highly conductive inorganic or organic materials, or in inorganic
or
organic materials for intercalation or embedding of the magnesium;
to - preparation of a cathode characterized in that it comprises species of
magnesium
in the state of oxidation 2+ having a substrate of highly conductive inorganic
or
organic materials or in inorganic or organic composite materials for
intercalation or
embedding of the magnesium;
- preparation of an electrolyte characterized in that it comprises any ionic
species
is of magnesium in solvents that are capable of producing electrolytes having
good
ionic conductivity and of solvating said species.
The electrolyte may moreover optionally be reinforced with spacers as
described
previously.
The above three components are put in contact with one another, the layer of
2o electrolyte 12 being set in between the anode 10 and the cathode 11. The
intimate
contact between anode 10, electrolyte 12, and cathode 11 may also be obtained
by exerting a slight pressure on the ensemble of components at temperatures of
between room temperature and approximately 150°C.
To obtain batteries with adequate performance, the same technologies may be
zs adopted as those used for the preparation of the already known lithium
batteries.
In particular, it is possible to:
- use single-layer or multi-layer button battery technology;
- connect the multi-layer films in parallel (parallel stacking), or else
connect the
multi-layer films in series (bipolar stacking), for non-folded structures;
30 - use flat-roll design technology or jelly-roll design technology, or flat-
stack design
technology for folded structures.
Described in detail in what follows are the methodologies for the preparation
of the
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individual components when these contain magnesium, and hence are not
conventional and so known, both in terms of characteristics and in terms of
production methodologies, to any person skilled in the branch.
A - General methodolocties for the preparation of the components
s A.1 - Preparation of the anode 10
For the purposes of the present invention, three types of anode 10 may be
used: a
magnesium-based anode having the characteristics already mentioned previously,
(i) as such or (ii) on a substrate of highly conductive organic or inorganic
materials,
or (iii) intercalated or embedded in material for intercalation or embedding
of
to magnesium.
The magnesium as such may be laminated starting from Grignard-grade
magnesium, or may be in the form of powder of appropriate grain size, or else
in
the form of a ribbon of varying length, which is commercially available. In
addition,
the magnesium may also be sintered.
is The anode may also consist of magnesium on a substrate of highly conductive
organic or inorganic materials, including polymeric materials, as described
previously. This type of anode may be prepared by chemical, thermal vapour,
electrolytic, or electrochemical deposition methods of magnesium species.
The other type of anode 10 is made with intercalation or embedding material
for
2o magnesium. Particularly this anode is prepared by suspending, in a solvent
such
as benzene, toluene, N-N dimethyl acetamide, dimethyl formamide, or
tetrahydrofuran or the like, a mixture of polyethylene or polyvinyl chloride,
or
polyacrylamide, or polyacrylonitrile, or some other, with intercalation
material
previously extended up to complete homogenization with magnesium. The system
2s is treated until complete and homogeneous distribution of the above
described
materials in the solvent itself is obtained. The composite film with a base of
intercalation or embedding material is then obtained by slow evaporation of
the
solvent.
Other methods of intercalation, in addition to the ones described previously,
for
30 obtaining the anode, may be based on physical methodologies, such as plasma
spraying or sputtering of the magnesium into the intercalation or embedding
material chosen.
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Whatever the type of anode, this may possibly be subsequently oxidized with
oxygen gas or peroxide, such as H202, or organic peroxides. The anode may,
moreover, be subjected to a further and possible stabilization treatment. As
stabilizing agents may be used alkoxides, such as tetra-alkoxy titanium, tetra-
s alkoxy silanes, trialkoxy aluminium, tetra-alkoxy zirconium, or magnesium
dialkoxide, or other equivalent compounds.
With the above further processes it is possible to obtain an anode that
presents
better characteristics of stability, reversibility, and exchange currents.
A.2 - Preparation of the cathode 11
to The cathode 11 may be prepared either providing a substrate for the
magnesium
or with a composite having a base of intercalation or embedding material,
adopting
methodologies that are similar to the ones already described for the anode 10,
and
which, for this reason, will not be described further herein. The
intercalation
materials are the same as those usable for the anode and may be, for example,
is but not exclusively, with a base of carbon, graphite, titanium disulphide
(TiS2),
cobalt dioxide (Co02), nickel dioxide (Ni02), manganese dioxide (Mn02), or
other
equivalents chosen from among the ones already mentioned previously.
Like the anode, also the cathode may undergo further processes of oxidation in
situ and following on its preparation, these processes having already been
2o described previously. Unlike the anode, however, the cathode may be
prepared
with electrochemically active materials that have been partially oxidized
prior to the
preparation of the cathode.
A.3 - Preparation of the intercalation material
The intercalation material is chosen from among the materials that may be used
2s for this purpose in the anode or in the cathode, and is prepared according
to the
general procedure described in what follows. The intercalation material is
ground
in a ball mill until complete structural disorder of the material is achieved.
Subsequently, the material is brought into intimate contact with magnesium
carbonates or magnesium oxides. The mixture thus obtained, after
3o homogenization and pelletization is brought up to a temperature of
approximately
100°C to 400°C for a period of between 1 and 3 hours, and
subsequently to a
temperature of between 800°C and 1200°C under a inert atmosphere
(for
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14
example, an argon atmosphere), and then kept at the temperature range
indicated
in vacuum conditions for 1 to 5 days.
A.4 - Preparation of the electrolyte 12
The electrolyte 12 according to the present invention may be prepared using
s solvents, including, but not exclusively, polymeric solvents, capable of
solvating
any ionic species of magnesium and of producing electrolytes having good ionic
conductivity. The electrolyte according to the present invention comprises, as
ionic
species, magnesium salts or magnesium complexes of the general formula
Mg(R)YX2_Y, with 0<_y_<2, having a very low charge/volume ratio. The radical R
may
to be chosen from the group consisting, for example, of alkyls with C~-C7
chains,
whilst X may be chosen from among halides, CI04, (CF3)~+XSO3_X, with 0<_x_<2,
SCN-, PO43~, or chlorides in b form. The compounds of the general formula
Mg(R)YX2_y, with Osy<_2, usable for doping the electrolyte, may moreover be
preferentially magnesium salts or ionic complexes of magnesium with lattice
Is energy lower than 500 kcal/mol.
The preparation is according to the following reaction:
solvent + salt / inorganic complex --> electrolyte
The mode of preparation of the electrolyte 12 according to the above reaction
can
follow three general procedures. The first regards the direct dissolution of
the
2o magnesium salt or complex in the liquid solvent or in the melted polymer
(when
the latter so permits). The second procedure regards the dissolution of the
polymer solvent and the magnesium salt or complex in a common solvent to
obtain the polymeric film through slow evaporation of the solvent (solvent-
casting).
The third procedure regards obtaining polymeric electrolytes which can have a
2s high conductivity and which are based on polymeric electrolytes having a
high
degree of crosslinking. In these circumstances, the polymeric electrolyte, for
obvious reasons, must be prepared obtaining solutions of the monomer and of
the
magnesium salt or complex preliminarily, and carrying out the polymerization
reaction subsequently.
3o The solvents usable for the purpose are all those already mentioned
previously,
and in particular, to provide an example, any liquid material having polar
groups
containing oxygen, nitrogen, sulphur, and carbon, which co-ordinate and
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dissociate the ionic magnesium salts or complexes, such as ethers, alcohols,
di-
alcohols, esters, amines and amides, thioethers, thioalcohols, thioesters,
alkyl
carbonates and alkyl thiocarbonates, or else polymers and/or copolymers with
different molecular weights, polyalkylene oxides, polyalkylene glycols,
s polycarbonates, polyalkyl siloxanes, polyethylene diaminotetra-acetate,
derivatives
thereof in which one or more atoms in the chain are substituted with one or
more
hetero-atoms chosen from among oxygen, nitrogen, silicon, and phosphorus and
polyphosphazene polymers functionalized with the polymers or copolymers
mentioned previously.
to Among the magnesium salts or complexes that may be used for the purposes of
the present invention, particularly advantageous is 8-MgCl2, which, since it
has a
very low lattice energy, i.e., close to 0 kcal/mol., may be solubilized in
organic
solvents that are capable of co-ordinating the magnesium, and Grignard
magnesium as species generating cations for the electrolyte.
is The electrolyte obtained according to one of the processes described above
may
also be acidified or alkalinized with the use of procedures and means known
for
the purpose. In the case where the electrolyte is acidified, it may be
preferential 'for
the purposes of the present invention to add appropriate amounts of phosphorus-
based compounds, such as P205, or other equivalents, under stirring and up to
2o complete dissolution. A similar procedure is followed in the case where the
electrolyte is alkalinized with nitrogen-based compounds or with basic
derivatives
of sulphur and phosphorus.
A.5 - Preparation of the dielectric spacers
The dielectric spacers may be made of any ion-permeable insulating materials
2s having good characteristics of insulating strength and dielectric constant.
In the
case where the material has polar groups on its surface, chemical inertization
is
performed by means of appropriate functionalization to prevent interaction
with the
magnesium ions or with ionic complexes of magnesium. In the case of glass
fibres, for example, the hydroxyl groups present on the surface are de-
activated by
3o reaction with triethoxyalkyl silane, thus rendering the surface of the
spacer highly
apolar.
B - General examples for the production of the components
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The invention is hereinafter further clarified in its general aspects and
through a
few examples of practical implementation, which have the sole purpose of
illustrating the invention without limiting the scope thereof in any way.
8.1 - Example of preparation of the anode 10 by sintering
s The anode 10 is prepared starting from metallic magnesium which is finely
ground
and sintered applying a pressure of 1400 MPa. In this way, after applying the
pressure for approximately 10 minutes, a metallic film is obtained having the
desired thickness.
B.2 - Preparation of graphite thermally pre-intercalated with magnesium
to A mixture of magnesium oxide and graphite, in a weight ratio ca of 3% is
rendered
disordered using a ball mill. This mechanical mixing proceeds for
approximately
thirty minutes and has the purpose of intimately homogenizing the two
components. The mechanical action of the min moreover increases the
crystallographic disorder of the graphite. The material thus obtained is next
is introduced into a quartz tube and subjected to six nitrogen-vacuum cycles
to
eliminate any traces of air.
Subsequently, the tube is subjected to a vacuum by means of a diffusion pump
at
a pressure of 10'6 mbar and brought up to a temperature of 700°C, at
which it is
kept for approximately 14 hours.
ao 8.3 - Preparation of the composite cathode 11
The intercalated graphite, referred to in Example B.2, is suspended in a
xylene
solution containing, dissolved therein, 10 wt% of polyethylene. From the
mixture
thus obtained the solvent is made to evaporate slowly (solvent-casting method)
to
obtain a black, slightly gummy film, which is broken up into tiny flakes and
2s subsequently converted into a sintered cathode 11 by application of a
pressure of
1400 MPa.
8.4 - Examples of preparation of the polymers for the electrolyte
Example B.4.1
Commercially available polyethylene glycols with molecular weights from 200 up
to
30 1000 may be used.
Example B.4.2
For the preparation of the polymer, it is possible to use commercially
available
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polymers, such as polycarbonates, or equivalent ones.
Example B.4.3 - (Synthesis of polyethylene glycol-polydimethyl polysiloxane
copolymers)
An aliquot of approximately 3 grams of dimethyl dichlorosilane is made to
react in
s toluene with 50 mol% of polyethylene glycol 400. The reaction is conducted
in
nitrogen for approximately 10 hours. A transparent polymer is obtained having
a
high viscosity. After eliminating the toluene and the residue of dimethyl
dichlorosilane in vacuum conditions (10-3 bar) at a temperature of
approximately
120°C, a thick liquid polymer is obtained that resembles honey in
appearance. The
to analyses have shown that the material thus synthesized is a copolymer with
blocks of polyethylene oxide and polydimethyl siloxane.
Example B.4.4 - (Synthesis of the di-anhydride monomer of ethylene-
diaminotetra-
acetate acid)
Approximately 3 grams of ethylene-diaminotetra-acetate acid are made to react
in
is toluene with acetic anhydride in the presence of small amounts of pyridine.
After
approximately two hours of refluxing, the white precipitate of the anhydride
of the
ethylene-diaminotetra-acetate acid is first filtered and then washed with
toluene in
a rigorously inert nitrogen atmosphere. The white solid thus obtained is
subsequently vacuum-dried for approximately one day. The analyses have shown
2o that the product is the anhydride of pure ethylene-diaminotetra-acetate
acid.
Example B.4.5 - (Synthesis of copolymer with blocks of ethylene-diaminotetra-
acetate - polyethylene glycol)
The anhydride of the ethylene-diaminotetra-acetate acid is made to a react
with a
1:1 aliquot of polyethylene glycol having a molecular weight of from 400 to
800.
2s 8. 5 - Example of preparation of 8 magnesium chloride
One gram of metallic magnesium is introduced into a 250-ml flask in a
rigorously
inert argon atmosphere. The flask is prepared in an argon dry box with reflux
drip
and vacuum cocks. Approximately 100 ml of n-chlorobutane are added to the
magnesium using the drip. The mixture thus obtained is made to react for
3o approximately 8 hours under argon flow at the boiling temperature of the
chlorobutane. After two hours' reaction, a greyish solid is obtained having a
floury
appearance. After vacuum-drying for six hours, a white powder is obtained.
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Analyses have shown that this is magnesium chloride in 8 form.
8.6 - Examples of preparation of magnesium-based polymeric electrolytes
Example B.6.1 - (Preparation of the polymeric electrolyte polyethylene
glycol/(MgCl2)x)
s The magnesium salt is previously dissolved in ethyl acetate. In the same
solvent, a
polyethylene-glycol solution is prepared separately. The two solutions thus
obtained are mixed together. After heating for approximately one hour under
reflux, the solvent is removed by subjecting it to a vacuum (10-3 mbar) and to
heating to a temperature of approximately 100°C. Any traces of solvents
that are
to left are subsequently eliminated under high-vacuum conditions (10-6 mbar)
for
approximately two days.
Example B.6.2 - (Synthesis of electrolitic polymer polyethilene glycol-
poymethilsiloxane)
An amount of polymer polyethilene glycol-poymethilsiloxane is dissolved in
ethyl
is alcohol perfectly anhydrous. Separately in the same solvent is prepared a
solution
of b magnesium chloride. Then the two solutions obtained are mixed together .
the
solvent is subsequently removed under vacuum (10-3 mbar)at temperatures from
80° to 100°C.
Example B.6.3 - (Synthesis of the electrolytic polymer obtained by doping the
2o polyethylene-diaminotetra-acetate-polyethereal copolymer with magnesium
salts)
The synthesized polyethylene-diaminotetra-acetate-polyethereal copolymer is
doped directly with magnesium salts at the melting temperature of the
copolymer.
Example B.6.4 - (Direct synthesis, i.e., without solvents, of polymeric
electrolytes
with a base of polyethylene glycols or polyethylene oxides and 8 magnesium
2s chloride)
The polyether polymers of various molecular weights (200 to 200.000) are
directly
treated with 8-MgCl2. The heterogeneous system thus obtained is homogenized
for complete dissolution of the salt in the polymer by means of heating and
continuous stirring.
3o Example B.6.5. - (Direct synthesis, i.e., without solvents, of polymeric
electrolytes
having a base of polyethylene glycols or polyethylene oxides and 8 magnesium
chloride, acidified with P205)
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The polymeric electrolyte obtained according to the foregoing Example B.6.4 is
treated with 8 wt% of P20$. The time required for obtaining a polymeric
electrolyte
by means of stirring and complete dissolution of the P205 is approximately 4
hours. The addition of P205 increases the viscosity of the polymer.
s B.7 - Example of preparation of the polymeric electrolyte 72 reinforced,
with glass
fibres
The liquid polymeric electrolyte or solid polymeric electrolyte in the molten
state is
used for impregnating a glass-fibre fabric. in this way, a thin layer of
polymeric
electrolyte is obtained which is reinforced with glass fibres.
~ o C - Examples of prototvaes produced
Practical tests carried out on prototypes revealed that the task and purposes
set
had been achieved.
In particular, in one first case (single-element button battery with polymeric
electrolyte reinforced with a porous paper filter), an anodic disk (anode 10)
made
is of sintered metallic magnesium and having a diameter of 8 mm was interfaced
with a film of polymeric electrolyte PEG 400 (MgCl2)X reinforced with a paper
disk
having the same diameter, after prior heating of the two compounds. On top of
the
polymeric-electrolyte film was laid a composite cathodic film (cathode 11 )
having a
base of intercalation material consisting of metal oxides with graphite in
liquid
2o suspension subsequently dried, prepared according to the previous examples.
The
element thus obtained was housed on a system consisting of two current
collectors 13. A few instants after assembly, this prototype revealed a
voltage of
approximately 0.8 V. Within approximately 5-6 hours, the voltage of the
battery
prototype increased until it reached approximately 1.8 V. After a few
rechargings
2s were carried out at a constant current of between 5 and 150 p.A, the
prototype
presented a threshold voltage between 2 and 3 V. After discharge, the voltage
returned to 1.8 V.
In a second case (single-element button battery with polymeric electrolyte
reinforced with glass fibre), the anode 10 and cathode 11 were prepared
according
3o to the same procedures as for the first prototype. In the present case, as
reinforcement for the polymeric electrolyte 12, glass fibre having a thickness
of
0.02 mm was used. The characteristics of this prototype were the same as for
AMENDED SHEET
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those of the first prototype, but the reversibility was considerably superior.
In a third case (single-element button battery with polymeric electrolyte
acidified
with P205 and reinforced with glass fibres), the anode 10 and cathode 11 were
prepared following the same procedures as for the first prototype.
Acidification of
s the polymeric electrolyte 12 by means of P205 enabled a voltage of
approximately
2.2 V to be obtained, together with excellent reversibility, a high specific
energy
density, and a considerable charge capacity.
From the examples given above there clearly emerge the advantages that may be
obtained using magnesium for the production of the batteries that form the
object
io of the present invention. In addition, when compared to lithium, magnesium,
which
is a very light element, presents characteristics of better workability,
together with
a good reactivity and oxide-reducing voltage. The possibility for magnesium to
exchange two electrons may enable an efficiency of 100%, and, given the same
volumes, magnesium may reach 80% more in terms of charge and 45% more in
is terms of energy as compared to lithium.
The systems developed according to the technology described herein enable, in
fact, excellent technical performance to be achieved, allied to the advantage
of a
reduction in production costs and to the practically total absence of
environmental
impact, given that the component materials are all non-polluting and that
2o magnesium is a safe element as demonstrated by its medical and clinical
uses.
The invention thus conceived may undergo numerous modifications and
variations, and, without departing from the scope of the inventive idea of the
present invention, it is possible for a person skilled in the branch to make,
to the
primary (non-rechargeable) and secondary (rechargeable) batteries that form
the
2s object of the present invention, all the modifications and improvements
resulting
from normal technical know-how and experience in the sector, as well as from
the
natural evolution of the state of the art.
