Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
1999-10-22
2002-03-12
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231500, C429S245000, C429S209000, C204S192120, C204S192150, C029S623100
Reexamination Certificate
active
06355376
ABSTRACT:
TECHNOLOGICAL FIELD
The object of this invention is a material based on titanium oxysulphide, which can be used, in particular as a positive electrode in an electrochemical generator or an electrochromatic cell.
In a more precise way, it relates to the creation of electrochemical generators or electrochromatic cells in particular in thin layers, whose principle of operation is based on the insertion and the removal of alkali metal ions or protons into and from the positive electrode.
Electrochemical generators of this type can find numerous applications, for example, in the form of micro-generators having a total thickness of a few &mgr;m in systems for providing back-up to the memories of micro-systems during a power failure or as integrated systems in cards with a memory of the bank card type.
These generators can also be used as an electrochromatic system when the positive electrode changes colour during the insertion, which makes them interesting for the display of information or better still when the negative electrode is transparent, for glazing that changes color according to needs.
STATE OF THE PRIOR TECHNOLOGY
Electrochemical generators of this type using a chalcide or an oxychalcide of titanium as a positive electrode, are described in particular, in the document WO-A-90/05387. In this document, the positive electrode material is made up of a layer of compound corresponding to the formula:
TiO
a
X
b
in which X represents an atom of sulphur, selenium or tellurium and a and b are such that a is at the most equal to 2, b is at the most equal to 3 and (a+b) is between 2 and 3.
The layer is prepared by magnetron type cathode sputtering, from a titanium disulphide TiS
2
target containing 5% of oxygen atoms.
This electrode material has interesting electrochemical properties but its deposition by cathode sputtering, in the form of a thin layer, has the disadvantage of requiring the manufacture of TiS
2
targets, from commercial TiS
2
powders which always contain a few percent of oxygen. Indeed, because of the lamellar structure of TiS
2
, the powder compacts rather easily but the sintering is delicate since there is a loss of sulphur whatever temperature is used. Because of this, during the cathode sputtering, the power applied to the titanium sulphide target has to be limited to a value below 2 Watts/cm
2
otherwise one risks seeing the target cleaved depending on the thickness.
Furthermore, although the performance of an electrochemical generator using this electrode material in the form of a thin layer is satisfactory, it would be of interest to further improve this performance, in particular the capacity of the generator per unit mass. Hence research has been undertaken to provide electrode materials of the same type under better conditions and to further improve the performance of the electrochemical generator using such electrodes.
The document U.S. Pat. No. 4,508,608 describes a method of preparation of a cathode based on a high porosity chalcide, by cathode sputtering of molecules of a transition metal chalcide onto and into a high porosity current collector substrate. The chalcide can be, in particular, a titanium sulphide such as titanium disulphide or trisulphide.
The energy per unit mass of titanium trisulphide (840 Wh/kg) is very high in relation to that of titanium disulphide (485 Wh/kg) but the use of TiS
3
poses certain problems since the insertion of lithium is only weakly reversible in TiS
3
.
The precise object of this invention is a positive electrode material, based on titanium oxysulphide which gets around these disadvantages and which leads to a notable improvement in the performance of the micro-generator, in addition having the advantage that the electrodes in thin layers are suitable for manufacture on an industrial scale.
DESCRIPTION OF THE INVENTION
According to the invention, the positive electrode material for an electrochemical generator is made up of a thin layer of an amorphous compound of formula:
TiO
a
S
3+b
in which a and b are such that:
0<a≦0.5
0<b≦0.7
According to the invention, thanks to the choice of an electrode material of the type TiO
a
S
3+b
which can be deposited by cathode sputtering, one obtains a layer of isotropic and amorphous material of much lower density than that of massive TiS
3
, which, because of this, stands up to the insertion and removal of alkali metal ions or protons very well. In effect, its low density corresponds to an expanded amorphous structure and there is no swelling of the material during the insertion of the ions. Hence, the layer does not deteriorate since the transport of the ions occurs without any change in the morphology. This isotropic layer also offers the advantage of allowing good diffusion of lithium in all directions.
According to the invention, this thin layer of titanium oxysulphide corresponding to the formula mentioned above can be prepared by radiofrequency cathode sputtering from a TiS
3
target. In the TiS
3
compound, the titanium atom is tetravalent as in TiS
2
and the sulphur is present in the form of a sulphide and a disulphide group: Ti
4+
S
2−
S
2
2−
.
For this deposition, the use of a TiS
3
target is of particular interest since TiS
3
can be obtained easily by chemical reaction of titanium and sulphur in powder form, in stoichiometric quantities, in a sealed tube under vacuum at 500° C. Under these conditions, a black coloured TiS
3
powder is obtained, the spectrum X of which corresponds to that of TiS
3
. This powder can be easily compacted, for example, under a pressure of 294 MPa (3 tonnes/cm
2
) and sintered, for example, at a temperature of 500° C., in a sealed tube under vacuum. Hence, one can manufacture targets of much larger diameter, for example from 50 to 75 mm diameter, than is the case for TiS
2
targets. Also, this method can be implemented on an industrial scale for the manufacture of electrodes in thin layers, which was not possible with the method of the prior art using a TiS
2
target, because of the need to limit the power applied to the TiS
2
targets.
An object of the invention is also an electrochemical generator using the positive electrode material mentioned above. This generator comprises a positive electrode, a negative electrode capable of liberating a proton or an alkali metal ion and an ion conducting electrolyte arranged between the two electrodes, and is characterised in that the positive electrode is formed from a thin layer of an amorphous compound of formula:
TiO
a
S
3+b
in which a and b are such that:
0<a≦0.5
0<b≦0.7
said layer being arranged on a substrate.
The substrates used to support the thin layer of amorphous compound can be very diverse, conductors or insulators, flexible or rigid. Generally, one uses a substrate that conducts electricity or an insulating substrate covered with a layer of an electrically conductive material onto which the thin layer of the compound TiO
a
S
3+b
is arranged.
The electrically conductive material can be, in particular, a metal, for example Cr, Pt, Ni, Al etc. monocrystalline silicon or an oxide conductor of electricity like the mixed oxides of indium and tin (ITO).
The insulating support can be a ceramic material, Pyrex, a glass or a plastic material resistant to the cathode sputtering conditions, for example, a flexible plastic material such as a polyester like the polyterephthalate of ethylene glycol or a polyimide.
These flexible substrates allow, in particular, continuous production of large surface area electrodes since they can be passed continuously into the cathode sputtering deposition enclosure.
In the generator described above, the negative electrode can be produced, in particular, in lithium or in a material containing lithium. The material containing lithium can be an alloy of lithium or a lithium compound.
The negative electrode is preferably in the form of a thin layer deposited by traditional methods, for example by evaporation under vacuum or by cathode sputtering. Thin layers obtained by such methods are highly adv
Centre Nationale de la Recherche
Chaney Carol
Dove Tracy
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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