LU85669A1 - SECONDARY ELECTRICAL ENERGY ACCUMULATION DEVICE AND ELECTRODE FOR THIS DEVICE - Google Patents

Description

Secondary device for the accumulation of electric energy! * plate and electrode for this device.

The invention resides in the use of a carbonaceous material in conjunction with an electron collector 5 as an electrode for secondary devices 1 for the accumulation of electrical energy.

The carbonaceous material of the electrode is stable in the presence of an electrolytic system containing anions such as perchlorates, hexafluoro-arsenates and the like at ambient or normal operating temperatures at which the electrode is used. In other words, the carbonaceous material does not undergo a significant swelling or a significant irreversible contraction during deep electric charge and discharge cycles, for example, the cycles which can be carried out during the commissioning of a secondary electrical energy storage device.

In numerous patents and in the technical literature, storage devices are described! mulation of electrical energy in which a carbonaceous material such as carbon or graphite is used as the electrode material. Of course, one of the very first of these devices was the Leclanché battery (1866) in which carbon was used as an electron collector in a! Zn / NH4C1 / Mn02 primary battery. Since carbon has been widely used as an electrode component in primary batteries, primary fuel cells, secondary fuel cells, secondary batteries and capacitors. The function of carbon or graphite in! r- the aforementioned devices was mainly that * of a current collector or a reactive material 5 35 in order to form, with fluorine, new compounds

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2 having properties and structures different from those of the initial carbon / graphite and, more recently, the function of semiconductor materials forming salts with ions of the electrolyte. These 5 devices of the prior art can be classified as follows: primary batteries like. described in U.S. Patent No. 2,597,451 to Coleman et al, "Panasonic Lithium Battery Literature" and in U.S. Patents No. 4,271,242, 3,700,502 and 4,224,389; fuel cells as described in Japanese patent publication No. 54-082043; secondary fuel cells having a limited ability to recharge as described in US Patent No. 4,037,025 to Dey et al .; * a rechargeable fuel cell in which - an activated graphite is used (specific high surface area); secondary rechargeable batteries (accumulators) as described in United States patent No. 4,251,568 in the name of Hart, in which graphite is used as a current collector, in the United States patents America No. 3,844,837 and 4,009,323 in the name of Bennion, as well as the capacitors described in the patent of the Federal Republic of Germany No. 3,231,243 or in the patent of the United States of America No. 3,700 .975 in the names of Butherus et al., In which a carbon (graphite) with a high specific surface is used.

In some of these devices, ionizable salts dissolved in a non-conductive solvent are also used.

The carbonaceous materials described in these patents and in the literature are materials treated with graphite or carbon until they become electrically conductive. These L · 3 materials are derived from polyacetylenes, polyphenylenes, polyacrylonitriles and petroleum pitch which have been heated to "carbonize and / or graphitize" the material constituting the precursor in order to impart a certain degree of electrical conductivity. Some of the graphites used according to the literature of the. prior art are graphites such as RPG (reinforced pyrolytic graphite), quality graphite for Rl nuclear reactors, PGCP (carbon graphitic pyrolytic paper 10) and GRAFOIL (trademark of "Union Carbide Corporation") comprising an expanded and compressed graphite , and the like.

The doping of similar carbonaceous materials was also mentioned in "Chemical and Enginee-15 ring News", volume 60, n ° 16, pages 29-33, April 19, 1982, in an article entitled "Conducting Polymers R & D Continues to Grow "; "Journal Electrochem * Society, Electrochemical Science", 118, N ° 12, pages 1886-1890, December 1971; and in "Chemical & Engi-20 neering News", 59, No. 41, pages 34-35, October 12, 1981, under the title "Polymer Cell Offers More Power, Less Weight".

The problems with the above-mentioned elements are that they do not have a long life, since the electrode made from this carbonaceous material is likely to become degrade when subjected to repeated cycles of electric charge and discharge.

For example, in U.S. Patent No. 3,844,837 (Bennion et al.), There is described

a battery using graphite - nuclear grade impregnated with Li ^ O shavings

as a positive electrode, as well as copper as a negative electrode in a LiCFgSOg- electrolyte

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4 dimethyl sulfite. The graphite electrode was formed from R-1 nuclear grade graphite (sold by "Great Lakes Carbon Company") and was reported to flake after 95 cycles of electrical charge and discharge. This patent also tested a gra-4 phite canvas and concluded that it was unsatisfactory.

Several other graphites were used with equally unsatisfactory results, the best results being obtained from pyrolytic graphite which failed after 33 cycles. Dey et al use a carbonaceous or graphitic material with a high specific surface in the 15 pores of which a chemical reaction takes place Λ but, as a general rule, it is thought that this material - has a low conductivity due to the lack of - continuity of the carbon surface. In addition, it is believed that these materials do not retain their dimensional stability and structural integrity which are necessary for the reversible formation of carbon complexes essential for ensuring a long service life of secondary batteries after recharging cycles.

In the experiments carried out during the development of the present invention, GRAFOIL (trade mark) which suffered a fault during the first electrical charge, was used, as well as RPG (Super Temp) graphite electrodes. who also failed. We cons-ç. It is known that more than 20% of the positive electrode consisting of RPG graphite was lost * in the form of flakes, chips and powder after only 27 cycles of electric charge and discharge.

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It should be noted that the prior art mentions the disintegration and deterioration of the electrode following swelling and withdrawal from the body thereof and it should also be noted that this swelling and withdrawal increases with each cycle of electric charge and discharge, thus giving rise to a deformation of the graphite plates which flake as a result of the stress due to swelling and shrinking. When these experiments were carried out during the development of the present invention, it was confirmed that this flaking of the graphite wafers occurred when the aforementioned graphitic materials were subjected to repeated cycles of electric charge and discharge. 15 ques.

According to a first aspect, the present invention provides an electrode intended to be used in a secondary device for the accumulation of electrical energy, this electrode comprising a body made of a carbonaceous material electrically conductive and having a skeletal orientation at the less on or near the surface, as well as a current collector electrically associated with this electrode, the carbonaceous material having a Young's modulus 25 greater than 6.9 GPa, while undergoing a physical dimensional change less than 5% during repeated cycles of electric charge and discharge.

In another aspect, the invention provides a secondary electrical energy storage device comprising a housing having an interior surface that is not electrically conductive, as well as a lamellar body or an exterior surface that is impervious to humidity, at least one element being placed in this housing, each element comprising at least one pair of electrodes conducting the electrode

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/ 6 tricity and electrically isolated from any contact with each other, this housing containing a practically non-aqueous electrolyte, at least one electrode; of each element being an electrode of the invention.

According to another aspect, the invention resides in a secondary device for accumulating electrical energy comprising a housing having an interior surface that is not electrically conductive, as well as a laminated body or an exterior surface 10 impermeable to humidity, at least one element being placed in this housing, each element comprising at least one pair of electrodes conducting electricity and electrically insulated from any contact with each other, this housing containing an electro-lyte practically non-aqueous, each of the electrodes of each element being an electrode according to claim 1, 2 or 3, each of these electrodes also having the freedom of choice of polarity during recharging and the possibility of being partially and / or completely subjected reverse polarization without prejudice. The electrodes can be separated from each other by a certain distance or by a material which is not electrically conductive and permeable to ions.

25 Physical properties

Preferably, the electrically conductive carbonaceous material of the electrode must meet the following criteria concerning the physical properties: (1) A Young's modulus greater than 6.9 GPa, -3 30 preferably, from 69 GPa to 380 GPa and, better still, - 5 from 138 GPa to 311 GPa.

(2) An aspect ratio greater than 100: 1.

^ In this specification, the aspect ratio is defined by the length / diameter ratio 1 / d of a / 35 fibrous or filamentary strand of carbonaceous material

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7 or by the length / depth ratio when the carbonaceous material is produced in the form of a flat sheet.

(3) Whatever the form in which the carbonaceous material can be manufactured (woven, knitted or nonwoven from fibers in wicks or with continuous filaments, or in the form of a film), its structural integrity and mechanical must be such that it does not require the presence of a support such as a pressure plate (canvas or face films) to maintain it in the desired form of a sheet or plate at the at least 100 charge / discharge cycles.

(4) A specific surface of at least 0.1 15 m2 / g, but less than 1, in combination with absorbed activated carbon, advantageously less than 50 m2 / g, preferably less than 10 m2 / g and, better still, less than 5 m2 / g.

. (5) Sufficient integrity of the shape of the carbonaceous material so that it can retain its shape of plate or sheet when it has a dimension greater than 6.45 cm2 to more than 930 cm2 without support other than a metal frame current collector forming the marginal part 25 of the electrode.

(6) The secondary device for accumulating electrical energy in which the electrode of the present invention is used, must be practically free of water, at a rate of less than 100 parts per 30 million. Preferably, the water content should be less than 20 parts per million and more preferably less than 10 parts per million. The device of the invention can operate with a water content of up to 300 parts per million, but it will then have a somewhat reduced lifespan all through cycles 8. In addition, it is understood that, if the water content becomes expensive, the device can be dismantled, dried and reassembled in the dry state without significantly altering its possibilities for continuous operation.

Criteria, performance (7) The carbonaceous material of an electrode must be able to withstand more than 100 cycles of electrical charge and discharge without undergoing significant deterioration due to its flaking. Preferably, no significant deterioration should occur after more than 100 electrical charge and discharge cycles at a discharge capacity of more than 150 coulombs / g of carbonaceous material from an electrode.

(8) The coulometric (coulombic) efficiency of the carbonaceous material of the electrode should be greater than 70%, preferably greater than 80% and more preferably greater than 90%.

(9) The carbonaceous material of the electrode must be able to withstand deep electric discharges of more than 70% of its electric charge capacity for at least 100 cycles of electric charge and discharge and, preferably, more than 80% during more than 500 electric charge and discharge cycles.

Accordingly, the carbonaceous material of an electrode having the physical properties described above should preferably be able to withstand discharge and electrical recharge for more than 100 cycles at a discharge capacity of more than 150 coulombs / g of carbonaceous material in an electrode and at a coulometric efficiency of more than ~ 70% without undergoing any significant irreversible change in dimensions (dimensional change of less than about 5%).

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Usually, the carbonaceous material will be obtained by heating a precursor material at a temperature above 850 ° C until it is electrically conductive. The starting carbon materials forming precursors capable of forming the oriented and electrically conductive carbon material for the electrode can be obtained from pitch (petroleum or coal tar), polyacetylene, polyacrylonitrile, 10 de polyphenylene, SARAN (trademark) and the like. The starting carbonaceous material forming the precursor must have a certain degree of skeletal orientation, that is to say that a good number of these materials have high concentrations of oriented benzenooid structural frac-tions or frac-rations which can be transformed, upon heating, into a slow benzenoid or equiva-E skeletal orientation at or near the surface due to the skeletal orientation of the starting material.

Among the preferred carbonaceous materials as precursors and having this skeletal orientation upon heating, there are, for example, assemblies of multifilament or monofilament fibers or strands which are prepared from petroleum pitch or polyacrylonitrile. These multifilament or monofilament fibers or strands are easily transformed into yarns or yarns which can then be transformed into a product similar to a canvas. A suitable technique for making fibers suitable for monofilaments is described in United States Patent No. 4,005,183, in which the fibers are made into a yarn which is then woven into a fabric. The fabric is then subjected to a temperature (usually more than 1,000 ° C.) sufficient to carbonize it by rendering the material

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10 carbon conductive of electricity and so as to give the material the physical properties described above in paragraphs (l) to (6). In conjunction with an electron collector, this fabric is particularly suitable for use as an electrode in the secondary electrical energy storage device of the present invention.

According to an advantageous characteristic, the carbonaceous material forming a precursor is in the form of fibers with continuous filaments, one or more threads consisting of one or more continuous filaments or a bundle of non-continuous fibers (spun), that it can be transformed into assemblies such as woven, non-woven or knitted assemblies, or else the fibers in wicks as such can be layered to form a canvas or a flat member similar to paper or felt. However, acceptable results are obtained when yarns formed from short fibers of 1 to 10 cm in length are woven into a fabric-like product (as long as these short fibers are always subjected to a heat treatment, the required physical properties mentioned above sub (1) to (6)). Obviously, although it is advantageous to form the precursor material, preferably in a stabilized state (obtained by oxidation) in a desired form (knitted, woven or felt) before carbonization, this structuring can be carried out after carbonization if the modulus is less than about 380 GPa, J1- preferably, less than about 269 GPa for manufacturing at It is obviously understood that the carbonaceous material can be formed from a film precursor.

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The degree of carbonization and / or graphitization does not seem to be a controlling factor in the yield of the material as an electrode element in an electrical storage device, with the exception that it must be sufficient to that the material is sufficiently electrically conductive and that it must also be sufficient to confer the above-mentioned physical and mechanical properties under the conditions of use envisaged.

Carbonaceous materials having a degree of carbonization of about 90% are called in the literature "partially carbonized materials". Carbonaceous materials having a degree of carbonization of 91 to 98% are called in the literature "carbonized materials", while materials having a degree of carbonization of more than 98% are called "graphitized materials". Surprisingly, carbonaceous materials having a degree of carbonization of 90 to 99% have been found to fail as electrode materials, unless they have the dimensional stability required during charge cycles and electrical discharge. For example, although having the specific surface, the electrical conductivity and the degree of carbonization required, the graphite RPG and the "GRAFOIL" do not have the required physical properties regarding the Young's modulus and the aspect ratio, if although they are failing.

According to the present invention, it is possible to realize a reversible electric storage device in polarity and rechargeable by aligning, in, a housing, at least one pair of electrodes produced from the carbonaceous material described above, as well as the associated electron collector (conductors of electricity). The housing has a non-conductive interior surface 12 and is impervious to moisture. The electrodes are immersed in a non-aqueous fluid (water being present in an amount less than about 100 parts per million) contained in this housing. The fluid itself must be capable of forming at least one ionizable metal salt or it contains this salt in solution. Each electrode consists of the carbonaceous material heat treated according to the present invention, in assoit) ciation with an electron collector which, preferably, is isolated against any contact with the electrolytic fluid.

The secondary electrical energy storage device of the invention can be produced without having the possibility of being reversed in polarity by aligning the above-mentioned assembly of carbon fibers. electrically conductive, for example, a canvas and its electron collector as an electrode i | positive · alternately with a negative electrode, i, which can be made of a metal such as lithium, i or of a metal alloy, then by immersing the electrodes in a practically non-aqueous fluid; which is itself capable of forming at least one soluble ionizable metal salt or which contains this salt in solution to supply electrolyte ions.

In the construction of a preferred embodiment of the secondary electrical energy storage device of the present invention, conventional porous separators such as glass fibers, polymeric materials or composite structures of polymeric materials to separate the positive electrode and the negative electrode from each other. More preferably, as a separator, a non-woven sheet of polypropylene is used since it has Λ; 13 the desired degree of porosity and that it nevertheless includes a winding path sufficient to prevent the carbonaceous fibers from entering it, thus preventing any electrical short-circuit. Likewise, the porous separators will advantageously act as stiffeners or supports for the electrodes.

Energy storage devices which are confined in fluid tight housings are generally known in the art.

Such housings can be advantageously used in the present invention provided that their material is non-conductive of electricity and impermeable to gases and / or humidity (water or water vapor).

15 Among the materials which have been found to be chemically compatible for these housings are polyvinyl chloride, polyethylene, polypropylene, polytrifluoroethylene and related perfluorinated polymers, an instant setting polymer. , a mixture of rapidly solidifying reactive urethanes, aramids, a metal coated with a non-conductive polymeric material such as an epoxy resin, for example, "DER 331" or "DERAKANE" (trademarks of "Dow Chemical Company "," ZETABON "25 (trademark of" Dow Chemical Company ") and / or glass or metal oxide, fluoride or the like. Among the housing materials which have been found suitable in the preferred system of propylene carbonate, there are acrylic resins, polycarbonates and nylon. Acrylic resins crack, polycarbonates crack and become extremely brittle, while nylon (except aramids) is chemically reactive.

In addition to being compatible, 35 a housing material must also form an Λ 14 absolute barrier layer of less than 2.15 g I ^ O / yr / m2 against the transmission of water vapor from the environment outside the accommodation. No currently known thermoplastic material alone forms this absolute moisture barrier to a thickness which would be useful for battery housing. Currently only; metals, for example, aluminum or mild steel, form an absolute moisture barrier layer 10 at thicknesses on the order of a sheet. It has been found that an aluminum sheet with a thickness greater than 0.038 mm is essentially impermeable to the transmission of water vapor. It has also been found that by laminating it with other materials, an aluminum sheet as thin as 0.009 mm can provide adequate protection against the transmission of water vapor.

Appropriate housings made from a metal / plastic laminate, from a metal coated with an epoxy resin by cathodic plating, or from a metal having an interior lining of plastic or glass currently meet the required conditions. with regard to chemical compatibility and the ability to form a barrier layer against moisture. Most of the cells and batteries that have been produced so far have been tested in a dry box with an H20 content of less than 5 parts per million, in a glass element or in a double-walled housing in which the space between the walls was filled with an activated molecular sieve, for example, zeolite 5A.

„Preferably, the electrolytic fluid consists of a non-aqueous solvent, chemically stable and non-conductive for one or more salts

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15; ionizable which is or are dissolved in the solvent.

,, As solvents, the compounds generally known in the art can be used, for example, "compounds containing oxygen, sulfur 5 and / or nitrogen atoms bound to carbon atoms in an electrochemically state not reactive. Preferably, nitriles such as acetonitrile can be used; ! amides such as dimethylformamide; ethers | such as tetrahydrofuran; sulfur compounds | Such as dimethyl sulfite; as well as other compounds such as propylene carbonate. It is obviously understood that the solvent itself can be ionizable under conditions of use sufficient to provide the necessary ions in the soil. Thus, the ionizable salt must be at least partially soluble and ionizable when it is dissolved and enters into solution in the solvent or during liquefaction. It being understood that one; may use slightly soluble salts, it will be appreciated that the rate of electric charge and discharge may be adversely affected by a low concentration of these salts in solution.

Among the ionizable salts which can be used when practicing the invention, there are those described in the prior art, in particular salts of the more active metals such as, for example, the alkali metal salts preferably lithium, sodium or potassium salts, or mixtures thereof containing stable anions such as perchlorate (C10 ^ =), tetrafluoroborate (BF ^ =), hexafluoro-arsenate (AsFg =), hexafluoro anions -antimonate (SbFg =) or hexafluorophosphate (PFg =).

Λ The electrolyte (solvent and salt) must be practically free of water, that is to say, it must contain less than 100 parts per million, preferably! (___: 16 rence, less than 20 parts per million and, better still, less than 10 parts per million of water. Of course, the electrolyte can be prepared by containing \ n water beyond the amount desired and it can be dried, for example, on activated zeolite 5A molecular sieves. These agents can also be combined in the final battery in order to maintain the required low water content. The electro lyte must also allow, to the ions (anions and; 10 cations) of the ionizable salt, to move freely 'through the solvent when the electric potential • of the charge and of the discharge displaces the ions towards and away from their respective poles (electrodes ).

When made in the form of a fabric or a sheet, the electrode comprises an electron reader conductively associated with at least one of the edges of the sheet or of carbonaceous fibers. Preferably, the edge (s) is or are further protected by a material in order to isolate the collector and practically protect the electron collector against contact with the fluid and its electrolytic ions. Of course, the protective material must not be altered by the fluid, nor by the electrolytic ions.

The current collector comes intimately into contact with the carbonaceous material of the electrode at least along one edge and, preferably, on all four edges when the carbonaceous material is in the form of an assembly such that a canvas, sheet or planar felt. The electrode can also be produced in other forms, for example, in the form of a cylindrical or tubular bundle of fibers, threads or yarns, the ends of this bundle comprising a current collector. It is also evident that an electrode in the form of a planar body

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17 (canvas, sheet or felt) can be wound with a porous separator between the layers of the carbonaceous material, the opposite edges of the wound material being connected to a current collector. Although metallic copper has been used as the current collector, any electrically conductive metal or alloy can be used, for example, silver, gold, platinum, cobalt, palladium and their alloys. Likewise, although electroplating has been adopted to bond a metal or metal alloy to carbonaceous material, other coating techniques (including melt applications) or others may be used. electrodeposition methods, provided that the edges or ends of the electrode, including the majority of the ends of the fibers at the edges of the carbonaceous material, are sufficiently impregnated with the metal to establish a current path and a practically low resistance electrical contact.

The collectors made from a common metal such as copper, nickel, silver or alloys of these metals, must be protected against the electrolyte and, therefore, they are preferably coated with a synthetic resin or an oxide, a fluoride or the like, this material not being attacked by the electrolyte or not undergoing significant degradation under the operating conditions of an element.

The electrodes of the present invention, made from the electrically conductive carbonaceous material, as well as its current collector can be used as a positive electrode in a secondary energy storage device.

No significant deterioration of the electrode itself, nor of the electrolyte, that is to say the solvent and the ionizable salt, is observed under the effect of repeated charges at a capacity greater than 150. coulombs / g of active carbonaceous material, no more than under deep discharges at more than 80% of the total capacity of the electrode at speeds, fast or slow of charge / discharge.

As a variant, the electrodes of the invention, produced from the electrically conductive carbonaceous material 10, as well as their current collectors can also be used both as positive electrodes and negative electrodes in an accumulator (secondary battery ) with the same advantageous operating characteristics as those described above.

A specific surface of at least 0.5 m2 / g and a low resistivity of less than 0.05 ohm / cm for the carbonaceous material used for the electrode of the invention are desirable properties.

20 ° ès consequently, a battery produced with the carbon material electrodes of the invention has an extremely low internal resistance and a very high corresponding coulometric efficiency which is usually greater than 80%.

During the study period devoted to finding the limits of the present invention, it was found that initial current densities (under load) of more than 15.5 to 31 mA / cm2 could lead to a deterioration of the carbonaceous material 30 of the electrode.

- „EXAMPLE 1„ * '* A pair of electrodes was formed, each having a surface of 71 cm 2 from a "Panex" fabric (trade mark) PWB-6 (fabric subjected to heat treatment at a temperature superior

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/ / 19 at 100 ° C by the manufacturer, which made this canvas electrically conductive), sold by "Stackpole Fibers Industry Company". The fabric was woven from a polyacrylonitrile precursor in which the yarn was formed from non-continuous filaments (woven fibers) having an average length of about 5 cm, a diameter of 7 to 8 micrometers and an aspect ratio of around 700: 1. The fabric was heat treated by the manufacturer 10 after weaving. The edges of the heat treated fabric were coated with copper by electrolytic deposition to form a current collector.

A wire was soldered to one end of the copper coated edges. All four edges of each electrode (current collector and wire connector) were coated with an amine curable epoxy resin ("DER (trademark) 331", manufactured by "The Dow Chemical Company") to isolate the metal against the corrosive effects of elec-20 trolyte under the conditions of use. The pair of electrodes was immersed in an electrolyte comprising a 15% solution of LiClO 4 in propylene carbonate, this electrolyte being contained in a housing made of polyvinyl chloride. The 25 electrodes were spaced less than 0.6 cm apart. The electrode assembly in the housing was transferred to a dry box. The housing was sealed while in the dry box, the metal wires extending out of the housing. The water content of the accommodation. assembled was less than 10 parts per million.

= ,; · The fibers had a Young's modulus of around 230 - · GPa and a surface / weight ratio of 0.6 to 1 m2 / g.

The total electrical capacity of the active carbonaceous material of the electrode was determined to be

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20 of about 250 coulombs / g.

The element thus prepared was electrically charged to a maximum voltage of 5.3 volts, the current not exceeding 5.4 milliamps / cm 2 of electrode area. The element was electrically charged and discharged for 1,250 cycles over an 11 month period and had a coulometric efficiency greater than 90%, with a discharge capacity of more than 85%. The element was then disassembled and the fibers of each of the canvas electrodes were examined under a microscope with a magnification of 1,000 times. As far as can be measured, the fibers have the same diameter as those of the same batch which have not been used in the element. The element was reassembled and the test was continued in the same manner as that described above. To date, the element has undergone more than 2800 charge and discharge cycles over a period of 23 months without undergoing a reduction in coulometric efficiency which was always greater than 90%.

EXAMPLE 2

Six electrodes similar to those of Example 1 were made and connected in a three-element unit so that each of the three pairs of electrodes was sealed in separate polyethylene bags (bags). The electrodes were connected in series. The three-element unit was operated in the same manner as in Example 30 1, except that the voltage was approximately 16 volts. The initial open circuit voltage was approximately 13.5 volts. After 228 cycles of electrical charge and discharge, during which the discharge was carried out at more than 78% of the total capacity, the elements were dismantled and removed

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21 the electrodes of their pocket and the fibers were examined for signs of deterioration, ie flaking, as well as excessive swelling and removal of the fibers. Examination did not reveal any detectable change in the diameter of the fibers from that measured in the same batch of fibers which were not used to make the electrode of this example. The measurements were made with a laser interferometer.

10 EXAMPLE 3

Several flat sheets of a woven fabric were cut from a yarn formed from fibers with essentially continuous monofilaments constituting a precursor and obtained from 15 pitch of petroleum. These fibers are manufactured by "Union Carbide Company" and they are sold under the trade name "Thornel" (trade mark).

The yarn consisting of a bundle of fibers forming a precursor and having an aspect ratio of about 20,800: 1 was woven into a fabric which was then subjected to a heat treatment at a temperature above 2,000 ° C. The flat sheets each had an area of approximately 930 cm2. The fibers had a Young's modulus of 315 GPa and a specific surface of approximately 1 m2 / g after the heat treatment. The leaves have received an electrolytic deposit of metallic copper along their four edges,. so that all of the fibers were electrically connected to form an electron collecting frame. An insulated copper wire was attached to a "collector edge near a corner by means of a solder joint which, together with the copper collector, received a coating of" DERAKANE "(trademark of" Dow Chemical Company "for a curable vinyl ester resin). The pairs of sheets 22 have been aligned parallel to one another, the welded metal wires being situated at the opposite ends of the edges adapted to each other, while being separated by a perforated, nonwoven composite sheet. and fibrous polypropylene having a thickness of 0.1 mm. As a receptacle for the element, a polyethylene pocket (bag) with a dimension of approximately 930 cm 2 was used. Three elements were assembled in a dry box by placing a pair of the carbon fiber sheets and their separator in each of the three bags and filling each bag with about 500 g of an electrolyte consisting of a 15% solution in weight of LiClO 4 in propylene carbonate. The level of electrolyte in the pocket was determined to obtain 21 g of active fibers per electrode (surface of the electrode exposed to the electrolyte). The remainder of the carbon fibers of each electrode extended out of the solution or was covered by the frame 20 of "Derakane" (trademark) resin / metallic copper.

The assembly of the elements in a dry box kept the water content at less than 20 parts per million of electrolyte solution. Each pouch was sealed while it was in the dry box so that the ends of the welded wire can extend through the seal to the opposite ends of the sealed edge. The three elements thus produced were placed in a clear plastic box and the metal wires were connected in series. g- A quantity of activated zeolite 5A molecular sieves (to absorb moisture) was added over the top of the elements and the assembly was removed from the dry box. Metallic wires

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23 at the end of the two end plates of the series of „three elements were connected to terminals extending through the cover of the box and the cover was also sealed on the latter.

The assembly was charged at a potential of 15 to 16 volts and at a current of 1.8 to 2 amps for 45 minutes. Next, the device was discharged by means of a 12 volt automobile headlight 10 drawing an average current of 2 to 2.5 amps. The device was discharged to 90% of its capacity in 30 minutes. The electrical charge and discharge cycles have been performed more than 850 times. The element was then disassembled and the fibers were examined under the microscope with a magnification of 1,000 times; no detectable signs of swelling or deterioration following flaking were observed. The device accepted an electrical charge and a deep discharge at 90% of its capacity for each cycle.

EXAMPLE 4

A canvas based on polyacrylonitrile (precursor fibers) was supplied by "R.K. Textile, Ltd.", Heaton Moor, United Kingdom. This fabric is sold under the trade name "Panox" (trade mark) and is made of non-conductive carbon fibers having an aspect ratio greater than 250: 1 and processed into a spun yarn and a woven fabric without being heated at a temperature above 400 ° C. This fabric was subjected to a heat treatment at a temperature of about ,, * · 1,000 ° C for a period of time sufficient for it to become electrically conductive.

The canvas subjected to the heat treatment had a Young's modulus of 160 GPa and a specific surface / 24 of approximately 1 m2 / g. Two samples with a width of 5 cm on one side and an area of 26 cm2 were cut from the heat treated fabric and the four edges of each fabric sample received an electrolytic deposit of metallic copper to form a current collector for the electrode.

A wire was soldered to a corner of the current collector of each electrode. On the copper solder and current collector, a coating composition based on a vinyl ester resin of the brand "Derakane" (trademark) was applied. A composite nonwoven sheet of polypropylene ("Celgard (trademark) 5511") was placed between the two electrodes which were inserted into a plastic bag (envelope). This assembly was placed in a dry box in which. the water content was kept below 20 parts per million of the electrolyte solution.

A 10% by weight solution of LiClO 4 in a solution of propylene carbonate was used to fill the envelope until the two electrodes were submerged in the electrolyte solution. The metal wires of each electrode were connected to a bipolar switch, one terminal of which was connected to a source of 5.3 volts electrical voltage.

The other terminal was connected to an electrical resistance load of 10 ohms. The element was subjected to deep discharge at more than 80% of its total charge and it operated for more than 800 cycles of electric charge and discharge with efficiency. . coulometric greater than 80%. The capacity of this element was about 70% of that of Example 1, 1 (polyacrylonitrile) on a total weight basis of electrode.

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It has been found that elements made in accordance with the present invention have an internal resistance which, on average, is less than 0.41 ohm / m2 of electrode area in a six-cell element. This value, initially measured below 1 ohm, included the lead wires going to the charging system and having a length of about 6 m. By measuring the resistance of the conductors and then again measuring the total resistance of the system from the load, it was calculated that the resistance of the accumulator (secondary battery) proper was 0.41 ohm / m2.

Confirmation of the results of the above examples was provided by a collaborator in a two-electrode element made from "Thornel VCB-45" fabric having a Young's modulus of 315 GPa, r a specific surface of 1 m2 / g and an aspect ratio greater than 10,000: 1, each canvas having a dimension of 15.2 cm x 15.2 cm. An electro-lytic deposit of copper was applied to all four edges of the fabrics to form the current collector. The current collector was then coated with "DERAKANE (trademark) 470-36". The edges of the current collector were about 2.6 cm wide, leaving areas of active carbonaceous about 10 cm x 10 cm. The surface, ie 100 cm2, of each electrode contained approximately 6 g of carbon fibers.

The electrodes were separated by placing an electrode in a thermally sealed bag made of a microporous polypropylene film "Celgard - (trademark) 5511".

> The assembly consisting of the electrodes and the separator was placed in a polyethylene bag which was filled with a dry electrolyte of 15% by weight of LiClO. in propylene carbonate (approximately

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26 100 cm3), then the assembly was pressed between two marginal plastic pressure plates supporting the sides of the bag containing the electrolyte. The thickness of the copper current collector coated with "DERAKANE" prevented the fibrous part of the two electrodes from being pressed in the minimum distance separating them from each other. In subsequent tests, a 10 cm x 10 cm spacer plate was inserted between the IQ marginal pressure plates in order to more firmly press the electrode / separator combination, which lowered the resistance of the element by approximately 0.9 ohm to about 0.7 ohm.

Discharge results at different speeds were noted for two of the element configurations described above. In one case (element at 0.9 ohm), the separation between the electrodes was - limited to approximately 4 mm by the epoxy coating deposited on the current collector. In the other case (elements at 0.7 ohm), the electrodes were forced together in the center by simply interposing, between them, the porous polypropylene separator (less than 1 mm).

The graph in Figure 1 illustrates the terminal voltage across the discharge, in coulombs per g of fiber for the element at 0.9 ohm at different discharge rates between 6 hours and three quarters of a 'hour. These discharges correspond to what is called a first plateau (2 volt cut-off). If it is assumed that the total capacity of the first plate is 180 coulombs / g at the cut-off voltage of 2 volts, the values entered on the abscissa can be replaced by "% discharged", the value of "180 coulombs / g "equivalent to" 100% discharged ".

The total energy recovered at a speed of 3 hours under a constant load is almost the same as at the speed of 6 hours. In the rapid discharge> 27 of the speed of three quarters of an hour, inefficiencies are observed due to the resistance of the element and to the polarization of the electrodes. The current densities of the electrodes corresponding to these discharge rates are as follows:

Speed (hours) Average current density at constant load (mA / cm2) 6 0.5 3 1.0; 10 1.5 2.0! 0.75 4.0! The value in "coulombs per g of fibers" is based on the weight of the active carbonaceous material of one electrode only. FIG. 2 illustrates the results i 15 obtained for the element at 0.7 ohm. Obviously,! i more energy is available i for the element with lower resistance. FIG. 3 illustrates the comparison of the two elements at the higher discharge speed (speed: 3/4 20 hours).

| A reference electrode i of metallic lithium was introduced into the element in order to determine which of the electrodes was in polarization regime. The voltage drops between each electrode and the reference electrode were determined during charging and discharging and when opening the circuit.

When the circuit was opened, the voltages existing between the negative electrode and the reference electrode were generally less than 100 mv and they only changed slightly over time.

In the long run, measured between the positive electrode and the reference electrode, the voltage changed, decreasing after each charge and increasing after each discharge.

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The maximum power capacities of a battery cell at different charge stages have been determined by a pulsed discharge of the cell at charges giving voltages across 5 of half the open circuit voltage. The "pulses" had a duration of 10 seconds and the power was calculated by the average power for 10 seconds.

The element was first charged to 344 10 coulombs per g of active carbonaceous material in an electrode. This value was considered as a state of charge at 100%. The maximum current drawn from the 10 cm x 10 cm electrode element at 100% charge was 2.5 to 3 amps. Subsequent power determinations were made at 247 coulombs per gram (72% load) and 224 coulombs per gram (65% load). Figure IV

ir illustrates the results obtained.

The maximum power delivered by this element was about 0.48 watt per gram of fiber at 100% charge, falling to about 0.31 watt per gram of fiber at 72% charge . Thereafter, the power capacitances drop rapidly since the voltage decreases and the polarization comes into play. A pulsed discharge of more than 10 seconds does not necessarily reduce the final power to a great extent.

Figure V illustrates the voltage plot of a power discharge at maximum speed of 40 seconds. 30 After the first 10 seconds, the voltage drop u - is small.

"EXAMPLE 5 l A three-element battery was produced from 12 plates (four per element) of fibers of the brand" Thornel "as described in Example 3.

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29

Each plate had an area of approximately 930 cm2 and - it had an electrolytic deposit of copper on each edge. The copper plating formed along the edges has been coated with a curable vinyl ester resin of the brand name "Derakane" (trademark). The plates had an active area of approximately 852 cm2. The four plates of each element were assembled with a perforated separator of a polypropylene scrim between each plate. Pairs of plates of each element were connected in parallel so that, during the charge / discharge cycles, the plates were alternately +, -, +, -. The four plates and their separators were contained in a polypropylene bag measuring 33 cm x 33 cm and containing about 600 cm3 of a solution of electrolyte made up, of 15% by weight of LiClO 4 in propylene carbonate. This electrolyte content in each bag was sufficient to provide about 37 g of active fibers per electrode plate.

The battery was initially charged over a period of 1,000 minutes at a capacity of 7.9 amp hours at a potential of 14-16 volts.

The element was then discharged over a period of 200 minutes using a 12 volt automobile headlight with an average capacity of 6.2 ampere hours, which represents a discharge of more than 80 %. Recharging was performed over an 800 minute period. An average coulometric efficiency of about 90% was observed during the charge / - - discharge cycles.

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Claims (22)

1. An electrode intended to be used in a secondary device for the accumulation of electric energy, this electrode comprising a body of a carbonaceous material conducting electricity having a skeletal orientation, at least at or near the surface, as well as a current collector electrically associated with this electrode, characterized in that the carbonaceous material has a Young's modulus greater than 6.9 GPa and undergoes a physical dimensional change of less than 5% during repeated charge cycles and electrical discharge. 2. Electrode according to claim 1, characterized in that the assembly in carbonaceous material 15. a Young's modulus from 6.9 GPa to 380 GPa, while ^ the carbonaceous material derives from a material forming a precursor and chosen from a polyacrylonitrile or a pitch. 3. An electrode according to claim 2, ca-20 characterized in that the carbonaceous material has a Young's modulus of 69 GPa to 380 GPa. 4. An electrode according to claim 2, characterized in that the carbonaceous material has a Young's modulus of 138 GPa to 311 GPa. 5. Electrode according to any one of claims 1 to 4, characterized in that the carbonaceous material has a specific surface of 0.1 to 50 m2 / g. 6. Electrode according to claim 5, ca-30 characterized in that the carbonaceous material has a specific <- »- surface of 0.1 to 10 m2 / g. 7. An electrode according to claim 5, characterized in that the carbonaceous material has a specific surface of 0.1 to 6 m2 / g. 4 35 31 8. An electrode according to any one of - claims 1 to 7, characterized in that the carbonaceous material has an aspect ratio (1 / d) or an - equivalent ratio greater than 100: 1. 9. An electrode according to any one of claims 1 to 8, characterized in that the carbonaceous material has an autonomous structural integrity in dimensions from 6.45 cm2 to more than 930 cm2. 10. An electrode according to any one of claims 10 to 9, characterized in that the carbonaceous material is in the form of a canvas, a film, a paper, a flat sheet similar to paper or felt, or in the form of other assemblies. 11. Electrode according to any one of claims 1 to 9, characterized in that the carbonaceous material is in the form of a canvas or a • • · sheet or a canvas similar to a felt comprising an assembly of at least one bundle of continuous yarns or woven fibers having a length of 1 to 10 cm. 12. An electrode according to any one of claims 1 to 9, characterized in that the carbonaceous material is a woven or knitted fabric produced from an assembly of a bundle of yarns of continuous filaments or of fibers in rovings having a length of 1 to 10 cm. 13. An electrode according to any one of claims 1 to 9, characterized in that the carbonaceous material is a cloth, a sheet or a cloth similar to a felt formed from a bundle of fibers in wicks. or assembled continuous filaments. ^ 14. An electrode according to any one of claims 1 to 13, characterized in that the electron collector is an electrically conductive metal 32 deposited electrolytically at least on one edge of the carbonaceous material, while the edge V having received the electrolytic deposit is coated with a non-reactive and non-conductive protective material. 15. An electrode according to any one of claims 1 to 14, characterized in that the carbonaceous material can withstand more than 100 cycles of electric discharge from more than 70% to more than 70% of the coulometric efficiency without significant deterioration. 10 aunt of the structural integrity of the material. 16. Secondary electrical energy storage device comprising a housing having an interior surface that is not electrically conductive and a lamellar body or an exterior surface impermeable to moisture, as well as at least one element arranged in this housing, each element comprising two electrodes which are electrically conductive and electrically isolated from any contact with one another, this housing containing a practically non-aqueous electrolyte, characterized in that at least one of the electrodes of each element is an electrode according to any one of claims 1 to 15. 17. Device according to claim '16, characterized in that the electrolyte comprises a non-aqueous, chemically stable and non-conductive solvent, as well as an ionizable salt dissolved in this solvent. 18. Device according to claim 16 or 17, characterized in that the solvent of the electrolyte is chosen from compounds comprising oxygen, sulfur and / or nitrogen atoms linked to w - carbon atoms in an electrochemically non-reactive state, while the salt is a salt of an alkali metal. v 19. Device according to claim 18, characterized in that the solvent of the electrolyte is / (t 33 propylene carbonate, while the salt of an alkali metal is lithium perchlorate. 20. Secondary accumulation device 'i. of electrical energy comprising a housing having an interior surface non-conductive of electricity, as well as a laminated body or an external surface impermeable to moisture, as well as at least one element installed in this housing, each element comprising at least two electrodes conducting the electricity and electrically isolated from any contact with each other, this housing containing a practically non-aqueous electrolyte, characterized in that each of the electrodes of each element is an electrode according to the any of claims 15 to 15. 21. Device according to claim 20, characterized in that each electrode of an element with freedom of choice of polarity during recharging and the possibility of being partially and / or completely subjected to reverse polarization without prejudice. 22. Device according to claim 20 or 21, this device having a maximum power density of more than 0.31 watt per gram of active carbon positive electrode during a pulse period of 40 seconds at full load . ^ AA-Ua