IE851017L - An electrochemical generator with composite electrode - Google Patents

Abstract

Electrochemical generator, the electrolyte of which is made of a macromolecular material comprising a salt in solution and of which the positive electrode is a composite electrode which comprises as active material a metallic compound adapted to be reduced by the cation of the salt in solution by generating during this reduction new species which can include the zero oxidation degree metal, said generator being able to operate reversibly at ambient temperature.

Description

6 1 9 - 1 - The present invention relates to an electrochemical generator operating reversibly at ambient temperature, of which the electrolyte is a solid solution of an ionic compound in a macrornolecular material, the said generator being characterised by the active material of its positive electrode.

European Patent No. 13 199 has already proposed electrochemical generators of the thin film type, of which the electrolyte is a solid solution of an ionic compound in a macrornolecular material. According to this patent, the positive electrode may consist of the product of agglomeration in a composite mass of the electrochemically active material, of an inert compound possessing ionic conductivity and of a macrornolecular material identical or similar to that of which the electrolyte is constituted. In this same European Patent, the preferred material for producing the electrolyte is an ethylene polyoxide. Numerous materials have been suggested as the electrochemically active material. The choice of these materials is more restricted when it Is desired to produce rechargeable generators which are capable of providing high and stable voltages in keeping with the charging and discharging cycles.

To produce generators which operate at ambient temperature, it is preferable to choose a macrornolecular material consisting of an ethylene oxide copolymer and a cyclic oxide ether, substituted or otherwise, having a chain of the polyether type, so producing a material which takes the form of a single theraiodynamically stable phase which Is very favourable to satisfactory operation of these generators at ambient temperature. In association with these electrolytes, there are a certain number of electrochemically active materials which can be used and which permit of reversible operation at ambient temperature. For example, molybdenum dioxide, vanadium oxide and titanium disulphide may be quoted. These compounds have in common, the property of giving rise reactions with the cation of the electrolyte material. essentially to insertion salt in solution in the The use of these materials, hereinafter referred to as insertion materials since they give rise mainly to insertion reactions, does have a number of drawbacks. Generally, they are expensive materials which are difficult to synthesise. Furthermore, insertion reactions involve only about one single electron per molecule of active material (between 1 and 1.5). Therefore, the theoretical capacity of the electrode is low. For example, when the active material is vanadium oxide this capacity is around 420 ampere hours per kilogramme of active material. It is around 250 Ah/kg for TiSa.

Various electrode materials other than insertion materials have been proposed, though without much success, for the production of electrochemically secondary generators but they involve associating these materials with electrolytes which are vastly different from those Involved with the generators according to the invention. For example, molten salts or organic solvents are involved. So far, the best example proposed is that of a generator using an iron pyrite as an active electrode material, the said electrode being associated with an organic electrolyte functioning at ambient temperature (AMBIENT TEMPERATURE SECONDARY Li/FeSa CELLS G.H. NEWMANi L.P. KLEMANN, Proceedings of the 29th Power Sources Conference June 1980). According to this article, an attempt has been made to produce a rechargeable generator operating at ambient temperature. The authors of this article have tested quite a range of organic .electrolytes such as for example the dioxolanedimethoxyethane mixture comprising in solution a lithium organoborate or such as lithium triethy1(N-pyrroly 1 -borate dioxolane, these tests being aimed at finding a pairing of electrolyte and electrode materials permitting of satisfactory cycling of the accumulator at ambient temperature. Referring to this article, it can be seen that the tests were - 3 - not -favourable because the best cyclic result achieved made it possible only to achieve 22 cycles with discharge capacities diminishing notably as the number o-f cycles increased. For example, there was a graduation -from 128 mA-hours -for the -first 5 cycle to 71 mA-hours for the 22nd cycle which represents a considerable diminution in capacity. The authors o-f this article concluded that they were still not in a position to make ^ a generator operate in a reversible -fashion, according to a considerable number o-f cycles and at ambient temperature when , 10 the material o-f the electrode is FeSa, that is to say a material which, upon being reduced, gives rise to the nucleation o-f new species. To explain the various reactions involved in this reduction, reference may for example be made to the article by M.B. CLARK LITHIUM BATTERIES, PUBLISHED BY J.M. CABANO 1983, 15 ACADEMIC PRESS.

Without wishing to bring forth a limitative scientific theory, the authors of the present invention think they can explain this impossibility of using FeSa as an electrode material for a reversible accumulator comprising a liquid 20 electrolyte at ambient temperature by the fact that during reduction, mechanisms are created which transport new species from these electrolytes which are capable of migrating or diffusing due to the absence of any selectivity! this absence of selectivity modifies the electrochemical processes or the? 25 availability of active materials upon discharge or recharging of the generator.

In contrast, the inventors have discovered that it was possible to have an electrochemical generator operate at ambient temperature in a reversible manner over a considerable number of 30 cycles on condition that a generator according to the invention is used.

The present invention accordingly provides an electrochemical generator capable of operating reversibly at ambient temperature comprising 35 electrolyte consisting of a solid in solution a negative electrode, an solution of at least one salt in a macrornolecular material, the said solid solution consisting -For the most part of an amorphous structure o-f the polyether type and possessing sufficient ionic conductivity to allow operation o-f the generator at ambient temperature, and a composite positive electrode constituted by the agglomeration product o-f a solid solution of at least one salt in solution in a macrornolecular material consisting for the most part o-f an amorphous structure o-f the polyether type, an electrochemically active material and possibly an electronic conductor wherein the active material of the electrode is a metal compound capable of being reduced by the cation of the salt in solution in the electrolyte, this reduction occurring during the discharges, the said metal compound generating during the said reduction one or more species including the metal with an oxidation degree equal to zero, the said metal compound being a displacement compound consisting either of a chalcogenide of a metal chosen from among cobalt, nickel, manganese, lead, bismuth, copper, silver and mercury or of iron monosulphide, or copper phosphate. According to the nomenclature adopted in "Material for Advanced Batteries* NATO CONFERENCES, 197? MURPHY, pages 343, 347, such materials are referred to as displacement materials. The man skilled in the art will readily appreciate that when one speaks of a displacement material, such materials may include those which are not solely displacement materials and which exhibit certain characteristics of insertion materials, the important point being that the displacement characteristics predominate. By way of illustration, it is considered that manganese dioxide Mn02 is a displacement material although it is capable of giving rise to insertion reactions.

In comparison with composite electrodes produced with an electrochemically active material of the insertion type, the electrodes of the generators according to the invention exhibit the following particular feature. - 5 - Insertion type composite electrodes may be described as being formed from grains coated with the macrornolecular material constituting the electrolyte, whether they are grains of active material or grains o-f electronically conductive material. 5 During a discharge, the ions corresponding to the material o-f the negative electrode become inserted into the active material ^ o-f the positive electrode, causing an increase in its volume, while during charging, this volume reduces and it should be remembered that this insertion reaction as well as the reverse 10 reaction reveals no new phase. The said variations in volume are perfectly o-f-fset by the macrornolecular material which is an elastomer. Thus, at any time, that is to say during bath charging and discharging, at the end o-f a charging or at the end o-f a discharging operation, one is in the presence of grains of' 15 electrochemically active material coated with the macrornolecular material of the electrolyte and directly in contact therewith.

For the electrodes according to the invention, during the course of charging or discharging, one is in the presence o-f unitary grains of electrochemically active material or 20 agglomerates of these grains, the said grains or the said agglomerates each being in contact with or even completely surrounded by new phases corresponding to the secondary species generated', these new phases appearing at the periphery of unitary grains and at the periphery or at the heart of 25 agglomerates. The whole is enclosed in macrornolecular material.

This appearance of new phases or, conversely, their disappearance, creates fluctuations in volume which are compensated by the elastomeric nature of the macrornolecular materia! of the electrolyte. Since diffusion and convection 30 phenomena can only Involve the peripheral phases, that is to say , those which are in direct contact with the macrornolecular material of the electrolyte, it will therefore be appreciated that in the electrode according to the invention, convection and diffusion are greatly limited and that these phenomena are far 35 less marked than in cases where the active materials are in contact with a liquid electrolyte. In particular, this phenomenon does not affect the species situated at the heart of the agglomerates of grains of active material.

The present invention further provides an electrochemical generator capable of operating reversibly at ambient temperature, comprising a negative electrode, an electrolyte constituted by a solid solution of at least one salt in solution in a macrornolecular material, the said solid solution being constituted to a large extent by an amorphous structure of the polyether type and possessing sufficient ionic conductivity to allow operation of the generator at ambient temperature, and a composite positive electrode constituted by the agglomeration product of a solid solution of at least one salt in solution in a macrornolecular material constituted to a large extent by an amorphous structure of the polyether type with an electrochemically active material and optionally an electronic conductor, wherein the active material of the composite positive electrode is a displacement material constituted either by a chalcogenide of a metal selected from among cobalt, nickel, manganese, lead, bismuth, copper, silver and mercury or by iron monosulphide or copper phosphate and wherein at least during the charge and discharge cycles of said generator, the said composite positive electrode comprises unitary grains of active material and/or agglomerates of grains of active material, the said unitary grains or grains of the said agglomerates being in contact with phases that correspond to species generated during the electrochemical process, the whole being embedded in the macrornolecular material with ionic conduction.

In the case of the electrode comprising solely unitary grains, each grain is enclosed in a coating comprising new phases. - 7 - By way o-f macrornolecular materiel used for producing the solid solution of the electrolyte or that of the electrode, the two solutions may be identical or different. To carry out the invention in an advantageous way, a copolymer of ethylene oxide 5 and a second constituent selected -from the cyclic ether oxides, substituted or otherwise, may be used.

The second constituent o-f the copolymer may be chosen -from among the substituted cyclic ether oxides represented by the formula (I) CHa-CH-0 10 I (I> R in which R represents: either an alkyl or alkenyl radical Ra comprising in particular from 1 to 42 and preferably from I to 4 carbon atoms, - or a radical The radical R may be an alkyl radical, preferably a methyl radical, and the second constituent is present at the rate o-f 0 not included - to 25% in a molar percentage in relation to the total number o-f moles. Preferably, this percentage is comprised between 1.5 and 25% when the salt is lithium perchlorate and is greater than 5% when the salt is a lithium trifluoromethane-su1phate.

The radical R may also be a radical -CHa-0-Re-Ra or 0-CH=CHa or -CH3-0-CHh-CH=CH= and the second constituent is present at the rate of zero - not included - to 30%, the percentage being a molar percentage expressed in proportion to the total number of moles of electrolyte. Preferably, this percentage is between 1.5 and 30% when the salt is lithium perchlorate and is greater than 5% when it is lithium trifluoromethane sulphonate.

In accordance with a particular embodiment of the invention, the second constituent of the copolymer is chosen from the cyclic ether oxides, substituted or otherwise, of which the cycle comprises more than three links,, Its molar percentage is preferably between zero - not included - and 30%.

By way of non-1imitative example, these cyclic ether oxides of which the cycle comprises more than three links may be: oxethane, tetrahydrofuranne, 1-3 dioxane, dioxolane and their substituted derivatives.

In the event of the second monomeric constituent being chosen from the ether oxides to formula (I), the chain obtained has an ethylene polyoxide structure of which certain hydrogens are substituted by radicals. This chain is characterised by a regular alternation of two carbon atoms and one oxygen atom: R I CHa-CHs CHh-CHk CHs-CH CHs-CH= / \/ \! \l \ 0 0 0 0 0 In the event of the second constituent being chosen from the cyclic ether oxides with a cycle comprising more than three links, a polyether chain is obtained in which the oxygen atoms may be separated by more than two carbon atoms or by a single carbon atom according to the nature of the second starting constituent.

For example, an ethylene-methy1-3-oxethane oxide copolymer will have this structure CjHs CHn-CHs CHs-CH-CHa / V \ 0 0 0 an ethylene oxide, dioxolans copolymer: CHa-CH® CHS CHa-CHs / \/\/ \ 0 0 0 an ethylene oxide methyl 4-THF copolymer: CHaCHs CHs-CHa-CH-CH® CHs / V I \/ 0 o CH3 o - 10 - According to a preferred embodiment of the invention, the cation of the salt in solution in the macrornolecular material of the electrolyte and of the electrode is a cation Li*" and the metallic displacement compound reducible by lithium is a 5 chalcogenide of an element chosen from iron, cobalt, nickel, manganese, lead, bismuth, copper, silver and mercury.

According to a first embodiment of the invention, the metallic displacement compound is a sulphide and preferably a mono- or disulphide. 10 According to a second embodiment of the invention, this metallic displacement compound is a manganese oxida MnOS| a copper oxide CuO or Cux0, a lead oxida or a bismuth oxide.

According to a third embodiment, the metallic compound is a phosphate. 15 Thus, according to the invention, an electrochemical current generator is obtained which is capable of operating in a reversible manner over a considerable number of cycles at temperatures up to ambient temperature, the said generator employing as an electrode material materials which do not give 20 rise mainly to displacement reactions, that is to say reactions which generate new species, the said reactions possibly involving more than one electron and being concomitant with insertion reactions.

Without wishing at this point to provide limitative 25 explanations, the Applicants feel that the ready rechargeabi1ity at ambient temperature of generators produced according to the invention can be attributed to the fact that the active material of the electrode is contained in a composite electrode comprising as an electrolyte a copolymer which permits of 30 operation at ambient temperature but also due to the fact that the selectivity of transport in the electrolyte and the solid nature of the electrolyte block convection of the intermediate species and block or at least restrict the diffusion of these species. In particular, the ionic species of a charge exceeding or equal to 2 diffuse very slowly in such an electrolyte, which is due to their cross-1 inking action. Furthermore, the absence of fluidity and the elastomeric properties of this electrolyte are favourable to maintenance of contact between them, of species generated during the electrochemical displacement process.

The generators according to the invention therefore make it possible to use as an electrode material the readily available conventional material which can in some cases release more than one electron per atom of active material.

But the invention will be better understood from reading the following examples which are given solely by way of illustration and which are not in any vway to be regarded as limitative, the examples being read with reference to the appended drawings all of which represent discharge-charge curves for accumulators, that is to say the fluctuation in voltage as a function of the rate of usage, the said rate being equal to the proportion of energy recovered in relation to the total energy. These various drawings relate to various electrode materials: Fig. 1 FeSa Fig. 2 Ni Si.?s Fig. 3 NiS Fig. 4 FeS Fig. 5 CoSa Fig. 6 MnOa Fig. 7 Cu„0(PO«) First series of examples The following generator, identified as generator A, was produced with the following components: a negative electrode consisting of a 100 micron thick lithium strip. A polymer electrolyte consisting of a solid solution of lithium perchlorate in an ethylene oxide-methyl glycidyl ether (OE-MGE) oxide copolymer comprising 10% by weight of MGE. In this solution, the ratio of the number of hetero-atoms of the copolymer to the number of atoms of the cation is equal to 20:1. The positive electrode is a composite electrode produced by spreading the following mixture on an aluminium strip: - Electrolyte OE-MGE, 15% MGE by weight, comprising in solution LiClO* at 20:1 (73% by volume) - Carbon black (7% by volume) - FeSa in the form of a powder of a granular size comprised between 10 and 15 microns obtained from natural pyrite used without any processing.

The positive electrode has a capacity of 3.61 C/mK (coulombs per cma); the total thickness of the generator is 200 p. The generator A was cycled at 26"C under a constant current density equal to 7 fjiA/cm® and Fig. 1 shows the curve (1) for the first discharge of the accumulator. It can be seen that the accumulator is discharged down to about 30% of use which, as a function of the electrode capacity, makes it possible to say that approx. 3.4 electrons have been released. The curve (2) represents the first recharge of the accumulator. This curve clearly shows the two steps characteristic of FeSa. Finally, the curve (3) shows the evolution of the voltage in the event of the 35th discharge. This 35th discharge made it possible tD release 3.2 electrons and, as in the first recharge, these electrodes are counted in relation to one molecule of FeSs* This high number of electrons clearly shows that the final species are mainly Li3S and metallic iron, which was confirmed by X-ray analysis. Finally, it can be seen that the curves (1) and (3) are common over a major part of the rate of use, which shows the easy rechargeabi1ity of the accumulator since it was possible to carry out thirty-five cycles without any drop in activity. - 13 - Within the same series of examples, the accumulator A' was produced which was identical to the accumulator A except that the FeSs powder was replaced by a mixture o-f iron powder and lithium sulphide LizS powder in proportions such that the 5 -following stoichiometric ratio might be preserved: 2 LiaS, 1 Fe and with a bottom granulometry o-f 5 fi, the generator was cycled at the same temperature and under the same current density. For this, the -first step was to charge A' in such a way as to raise its potential to the value o-f EO = 3.05 V 10 (as for the accumulator A). The -fact of being able to charge this accumulator A' clearly shows that the reactions involved are displacement reactions between LiaS and iron. Then the accumulator A' was cycled and the curve (5) shows the second charge while the curve (6) shows the 35th discharge. 15 It will be evident that for this accumulator A' the rate of use is 30% (whereas A was about 80%) but that the same number of cycles can be achieved as for A. The results can be explained as follows. The good recharging qualities can be attributed to the limitation of transports within the 20 electrolyte. For their part, the low rates of use obtained can be attributed to the fact that one does not enjoy the same properties of maintenance of contact as with the accumulator A. In the accumulator A', the two initial components are not in perfect contact during the electrochemical processes as the 25 species are for FeSa.

From this comparative example, one may draw the conclusions that the rechargeable generators according to the invention function well on the one hand by reason of the limitation of transports in the electrolyte but on the other by 30 virtue of the fact that the species generated during the transport reactions are maintained in contact.

Finally, within the same series of examples, the accumulator A' was reproduced and made to operate at 75°C. - 14 - There was a notable drop in the rate of use and potential of the reaction, this drop increasing during the course of cycling. Therefore, this would seem to confirm that the diffusion phenomena which exist at high temperature are penalising and 5 that in contrast the invention makes it possible for satisfactory operation at ambient temperature.

If the same test is conducted with the accumulator A, it is seen that the phenomenon noted for A' is far more limited.

Second series of examples 10 An accumulator B was produced identical to accumulator A but in which the displacement material was NiSi.?s, for which the positive electrode capacity is 2.33 C/cm®. A series of charges and discharges were carried out and graphs drawn in Fig. 2. The graph for the first discharge 410) starts from 2.5 V 15 and shows a discharge of up to 90% of usage. The graph for the first charge does not provide cause for any special comment. The graph (12) represents the second discharge and the graph (14) the hundredth discharge. The graphs (10), (12) and (14) show a very long portion which is common to all and if there is 20 an evident substantial evolution between the first and second discharges, there is very littl© evolution to be seen between the second discharge and the hundredth discharge.

Finally, this example shows clearly that there are displacement reactions because if there were insertion 25 reactions it would be necessary to respect the stoichiometric formula for NiS9.

Third series of examples Two accumulators were produced, C and D, identical to the accumulator A but with the following characteristic •features: C D Electrode material Nis FeS Capacity C/cms 2.3 1.6 these accumulators were cycled under a constant current strength (d = 7.5 |JLA/cma) at 26°C.

For the accumulator C, Fig. 3 shows the graph (20) for the -first discharge, the graph (21) for the recharge while in Fig. 4 there is shown -for D the graph (22) for the first discharge, the curve (23) for the tenth discharge.

It should be noted that the pattern of these graphs shown in Figs. 3 and 4 is very similar to that of the graphs obtained for the same materials used with molten salt electrolytes for which it is perfectly well known that NiS and FeS function by the displacement process. The study of these molten salt materials is reported in IREQ No. 2779 "Recherche et developpement sur les accumulateurs en sels fondus"/"Research and development into molten salt accumulators" G. V/ASSORT, M. 6AUTHIER, D. FAUTEUX, R. BELLEMARE.

This example clearly shows that the invention relates not only to displacement disulphides but also to displacement monosulphides.

Fourth series of examples In this example, an accumulator E identical to the accumulator A but having a positive electrode comprising cobalt disulphide CoSn and of which the macrornolecular material of the electrolyte is a propylene oxide-ethylene oxide copolymer is - 16 - cycled. Cycling is carried aut at 26"C with a current density o-f 7 nA/cma.

Fig. 5 shows the graph (30) -for- the tenth discharge which clearly demonstrates that at the tenth discharge 85% o-f use is 5 still available, that is to say that 3.4 electrons are recovered and that the discharge plateau is around 1.5 V. The discharge graphs obtained -for about a hundred cycles are identical to the graph (30).

Fifth example 10 In this example, the accumulator F, identical to A, but in which the electrode material is manganese dioxide MnOa, was cycled (75 cycles) at Z6°C with a current density o-f 8 fiA/cms.

Fig. 6 shows the cycling graphs obtained.

The graph (31) is the -first discharge, the graph (32) the 15 2nd, (33) the 25th and (34) the 75th.

After the -first discharge down to 60%, the accumulator was recharged to 52% o-f use. The second discharge provides about 50% o-f use which is tantamount to saying that there is a ratio of 1 between the charge and the discharge. This ratio can 20 also be -found in the other cycles.

This cycling obtained with materials which are not optimised shows one surprising effect o-f the. invention because MnOs had always been regarded as unable to give rise to reversible cycles in association with a polymer electrolyte. 05 Sixth example This example relates to a generator of which the active - 17 - material is a copper oxyphosphate Cu«sO(PO«)s. The generator o-f this example is made up as follows: - Positive electrode: the following are spread onto an aluminium collector (a leaf 15 microns thick): 5 65% by weight of Cu40(P04)x 5% by weight acetylene black 31% by weight of copolymer OE-MGE and 24% by weight LiC10.«.

- Electrolyte. Ethylene oxide-butylene oxide copolymer < 10 (OE-QB) comprising 18% by weight of LiClO.*.

- Negative electrode: lithium strip 60 microns thick.

The positive electrode was 20 microns thick and the electrolyte 65 microns and the assembly took the form of a circular pellet 1 cm in diameter. 15 Therefore, the capacity of the positive electrode was 7.4 mAh/cm2 (23.6 mA in all).

This generator was subjected to successive discharging and charging cycles at a constant current density of 16 nA/cra® at a temperature of 40»c (in other words a regime of C/470). 20 The stabilised operating graphs (more than 50 cycles) ar© shown in Fig. 7 (graph 40 for the discharges and graph 50 for the charges). They show a discharge plateau at 2.36 V. By stopping the discharge at 1 V, rates of 30% usage are seen, considering the passage of 2 electrons per capper atom., 25 corresponding to an effective anergy recovery of 8 Cb/cma.

However, the invention is not confined to the embodiments mentioned: in contrast, it embraces all variations. Far example, it is quite obvious that the macrornolecular material may be crass-1 inked or not. r - 18 -

Claims (12)

1. CLAIMS: 1. An electrochemical generator capable o-f operating reversibly at ambient temperature, comprising a negative electrode, an electrolyte constituted by a solid solution o-f ft 5 at least one salt in solution in a macrornolecular material, the said solid solution being constituted to a large extent by an amorphous structure of the polyether type and possessing sufficient ionic conductivity to allow operation of the generator at ambient temperature, and a composite 10 positive electrode constituted by the agglomeration product o-f a solid solution of at least one salt in solution in a macrornolecular material constituted to a large extent by an amorphous structure of the polyether type with an electrochemically active material and optionally an 15 electronic conductor, wherein the active material of the electrode is a metal compound able to be reduced by the cation of the salt in solution within the electrolyte, this reduction occurring during the discharges, the said metal compound generating during the 20 said reduction one or more species including the metal with an oxidation degree equal to zero, the said metal compound being a displacement compound constituted either by a chalcogenide of a metal selected from among cobalt9 nickel, manganese, lead, bismuth, copper, silver and mercury or by 25 iron monosulphide or copper phosphate.

2. The electrochemical generator according to Claim 1, wherein the chalcogenide is a sulphide. «

3. The electrochemical generator according to Claim 2, wherein the sulphide is a monosulphide or a disulphide. 5 - 19 -

4. The electrochemical generator according to Claim 1, wherein the sulphide is selected from among CoS2/ NiS and NiSl.75.

5. The electrochemical generator according to Claim 1, 5 wherein the chalcogenide is an oxide.

6. The electrochemical generator according to Claim 5, wherein manganese dioxide MnOj is used as the oxide.

7. An electrochemical generator capable of operating reversibly at ambient temperature, comprising a negative 10 electrode, an electrolyte constituted by a solid solution of at least one salt in solution in a macrornolecular material, the said solid solution being constituted to a large extent by an amorphous structure of the polyether type and possessing sufficient ionic conductivity to allow operation ^ of the generator at ambient temperature, and a composite positive electrode constituted by the agglomeration product of a solid solution of at least one salt in solution in a macrornolecular material constituted to a large extent by an amorphous structure of the polyether type with an 2 0 electrochemically active material and optionally an electronic conductor, wherein the active material of the composite positive electrode is a displacement material constituted either by a chalcogenide of a metal selected from among cobalt, nickel, manganese, lead, bismuth, copper, 25 silver and mercury or by iron monosulphide or copper phosphate and wherein, at least during the charge and discharge cycles of said generator, the r - 20 - said composite positive electrode comprises unitary grains o-f active material and/or agglomerates o-f grains o-f active material, the said unitary grains or grains o-f the said agglomerates being in contact with phases that correspond to species generated during the electrochemical process, the whole being embedded in the macrornolecular material with ionic conduction.

8. The electrochemical generator according to Claim 7, wherein the composite positive electrode comprises only unitary grains as the chemically active material, each grain being coated with a layer constituted by the said new phases.

9. The electrochemical generator according to Claim 7, wherein the composite positive electrode comprises only agglomerates o-f grains as the electrochemical ly active material, further wherein the phases that correspond to the species generated during the electrochemical process are located within the said agglomerates and/or at the periphery thereof.

10. The electrochemical generator according to Claim 7, wherein the displacement material is a chalcogenide and in particular a sulphide or an oxide. - 21 -

11. The electrochemical generator according to Claim 7, wherein the copper phosphate consists of CU40(P04)2-

12. An electrochemical generator according to Claim 1 or Claim 7, substantially as described. MACLACHLAN & DONALDSON, Applicants' Agents, 47, Merrion Square, DUBLIN 2.