WO1983003322A1

WO1983003322A1 - Electrolytes formed of solid solutions of closoboranes in a plastic macromolecular material and electrochemical generators containing such electrolytes

Info

Publication number: WO1983003322A1
Application number: PCT/EP1983/000076
Authority: WO
Inventors: Nationale De Valorisation De La Recherche ... Agence; Nationale Elf Aquitaine Societe
Original assignee: Societe National Elf Aquitaine; Agence National de Valorisation de la Recherche ANVAR
Current assignee: Societe National Elf Aquitaine; Bpifrance Financement SA
Priority date: 1982-03-18
Filing date: 1983-03-16
Publication date: 1983-09-29
Anticipated expiration: 1984-09-18
Also published as: EP0090710A1; JPS59500493A; AU1377283A; CA1197085A

Abstract

Un électrolyte polymère solide consiste au moins en partie en une solution solide d'un closoborane d'un métal alcalin dans un polymère ou copolymère comprenant des hétéroatomes susceptibles de former des liaisons du type donneur-récepteur avec le cation dudit closoborane. Dans des batteries, ledit électrolyte est associé à une électrode négative comprenant un matériau d'électrode susceptible de fournir le même cation à son interface avec l'électrolyte, alors qu'une électrode positive forme un récepteur à un potentiel chimique inférieur pour l'espèce non-ionisée correspondant audit cation alcalin.A solid polymer electrolyte consists at least in part of a solid solution of a closoborane of an alkali metal in a polymer or copolymer comprising heteroatoms capable of forming bonds of the donor-receptor type with the cation of said closoborane. In batteries, said electrolyte is associated with a negative electrode comprising an electrode material capable of providing the same cation at its interface with the electrolyte, while a positive electrode forms a receptor at a lower chemical potential for the species. non-ionized corresponding to said alkaline cation.

Description

Electrolytes formed of solid solutions of closoboranes in a plastic macromolecular material and electrochemical generators containing such electrolytes.

The invention relates to new electrolytes formed of a solid solution of at least one ionic compound in a macromolecular polymeric material.

U.S. patent 4.303.7^8 titled. "Electrochemical generators for producing current and new materials for their manufacture" discloses an electrochemical generator having at least one cell-element comprising an electrolyte separating a.positive electrode and a negative electrode from each other. Said electrolyte was formed at least in part of a solid solution of a ionic compound within a plastic macromolecular material formed of one or several homo- and/or co- polymers derived from one or several monomers comprising at least one heteroatom, for instance oxygen or^" nitrogen, said ionic compound comprising an alkali or ammonium cation and an anion derived from a strong acid. The negative electrode comprised an electrode- material forming a source capable of supplying an alkali or ammonium cation at its interface with the electrolyte, said cation corresponding to the metal of the ionic compound in said electrolyte, and the positive electrode comprised an electrode material^' forming a sink at a lower chemical potential for the corresponding cation. In other words the electrolyte in such generator enables the trans¬ fer of the alkali or ammonium cation by ionic conduction from the negative electrode to the positive electrode when the electrochemical reaction resulting in the production of current takes place in said generator.

As concerns the sόlubilized ionic compound, the same application discloses several anion-and cation- combinations in which the anion exhibits an ionic radius o higher than or equal to 1.81 A, for instance I (iodine) or more complex anions in which the negative charge is distributed over several atoms, for instance SCN , CIO^, ^• BF^, BFjJ, PFg,. AsF~, CF^O^", CF-_jSO^".

It has now been found that an electrolyte comprising a solid solution of a closoborane of an alkali metal or of ammonium in polymeric macromolecular materials of the type defined in the above US patent could be advantageously substituted for the electrolytes disclosed in the US patent in electrochemical generators of the type disclosed he eabove.

It is true that the use of closoboranes in different electrochemical generators had already been

■suggested, for instance in the French Patent Application 2.460.625 titled "Rechargeable -electrochemical generator comprising an electrolyte containing closoborane" . The electrolyte contemplated in that patent consisted of a liquid solution of a closoborane in an aprotic solvent.

However the presence of a chelating agent and, in practice, an additional joint .solvent common to the closoborane and to the chelating agent were .required both for improving the solubility characteristics of said chlosoboranes in the aprotic solvent and for favoring the migration of the^" ions from the positive electrode to the negative electrode.

It was therefore most surprising that similar or same closoboraneswere found able to dissolve in macro- molecular materials of the abovesaid type, in the absence of chelating agents and/or joint solvents, to yield solid solutions capable of containing very high proportions of such closoboranes. ^*

The new solid polymeric electrolyte of this invention is thus formed at least in part by a solid

OMPI solution of a closoborane dissolved within a macromole¬ cular material formed at least in part by one or several homo- and/or co- polymers derived from one or several monomer units comprising at least one heteroatom, particularly oxygen or nitrogen, capable of forming donor-acceptor bonds with an alcali cation, said closoborane having the general formula M_p-B -X -Y. ^"ⁿ which M represents an alkali metal or ammonium, n is an integer equal to 8, 10 or 12, X and Y which are identica or di.fferent, each represent a radical selected from the group consisting of hydrogen, halogens, .CN, a hydro- ^• carbon radical, comprising from 1 to 25, preferably from 1 to 3 carbon atoms and a^' and b are integers the sum of which is equal to n. Preferred compounds according to the invention are.those in which X and Y are identical and represent hydrogen or an halogen, particularly chlorine, and in which n is equal to 10 or 12.

Advantageously the ratio of the number of heteroatoms in- said monomer unit or units to the number of atoms of the alkali metal or of the ammonium ions ranges from 4 to 30, preferably from 4 to 16, the proportion of closoborane in said solution not being in excess of that for which the solubilit limit would be reached.

The alkali metal is preferably lithium or sodium.

The plastic materials in which the closobo¬ ranes are solubilized advantageously consist of hom.o- and/or co- polymers derived from any of the monomeric units represented : - either by the following formula :

in which R' represents a hydrogen atom or one of the groups Ra, -CH -0-R_a- -CH_p-0-Re-Ra.-CH_p-N = (CE )₂ with Ra representing _. an alkyl or cycloalkyl radical comprising from 1 to 16, preferably 1 to 4 carbon atoms,. Re representing a polyether radical of the general formula -(CH_p-CH₂-0) -, p having a value from 1 to 100, notably from 1 to 2 - or by the following formula :

in which R" represents Ra, -Re-Ra, with Ra and Re having respectively one of the above-indicated meanings, or by the following^"formula :

in which ^"Ra and Re have respectively one of the above indicated meanings

- or by the following formula :•

in which R., and R„ are identical or different and repre¬ sent each one of the above defined groups^' Re, Re-Ra as defined hereabove, Re however possibly also representing a poly-ether of formula :

O

W Vr The preparation of the ionic compound can be carried out according to any method known per se. For instance in order to produce a sodium dodecarborane of formula (NaB₁₂H₁₂) the method of synthesis at high ^•'• temperature startin ' rom sodium borate (NapB^O-) as disclosed in NATURFORSCHU G 25 B, 1970, pp. 6-10 can be used.

Compounds in which X and Y are different can be obtained by carrying out any of the methods disclosed n US patent 3-551.120. For instance closoboranes in. which X is hydrogen and Y a hydrocarbon radical may be obtained by the action of an olefine on the acid ^-^ 12^12 _* in the presence of a diluent, the alkaline salt then being obtainable by neutralization by the suitable alkaline metal hydroxyde. Similarly those cloboranes in which X is a CN radical can be obtained by the action of CNC1 on (H,0)B₁₂H₁₂, said reaction being carried out under a pressure of 16 x I r Pascals at a temperature of . about 25°C. The preparation of the solid polymer electrolyte can be carried, ut according to several methods. Both the macromolecular material and the selected closoborane can be dissolved .in a common- solvent, such as acetonitrile or methanol, the solvent then being removed such as by evaporation. The relative proportion of closoborane selec¬ ted should not exceed the solubility limit thereof in the selected macromolecular material used. If need be that solubilit limit will be .determined beforehand. Another method of preparing the abovesaid electrolyte consists of grinding a mixture of the macromolecular material and of the ionic compound and of melting the mixture at a tem¬ perature equal to or higher than the melting temperature of the polymer and by malaxing the mixture in the molten state until complete dissolution is achieved.

OMPI ; The solid electrolytes obtained are suitable for the production of electrochemical generators of the primary and secondary types, particularly rechargeable batteries. The invention thus also pertains to the electrochemical generators so formed. Accordingly a generator according to the invention can be defined as comprising the new^" electrolyte of the invention associated with at least one negative electrode and at least one positive electrode separated from each other by means of said solid electrolyte, the negative electrode comprising an electrode material forming a source of species capable of supplying a cation corresponding to the metal of the closoborane in said electrolyte at the interface thereof with the negative electrode, the positive electrode forming a sink at a lower chemical potential for the corresponding cation.

In advantageous embodiments of the. generator according to^' the invention, the negative electrode is formed either of the corresponding alkali metal, or of an alloy thereof or of an intermetallic or insertion compound containing said metal. An advantageous positive electrode comprises a compound including; a transition metal, particularly insertion compounds such as chalcogenides, in the structure of which said alkali metal atoms are liable of being inserted and of diffusing throughout their lattices.

Other .examples of macromolecules liable of being used for preparing the conductive solid solutions and- of electrode materials for making the electro¬ chemical generators of this invention are described in US patent 4.303.748 which is incorporated herein by reference. Other examples of closoboranes as such for making the electrolyte of this invention are also identified in French patents 76 26677/2-323-238 and

79 27042/2.440.525 which are also incorporated herein by reference.

The abovesaid solid solution is also suitable ^' for the production of electrodes, whose electrode material is in the form of particles, said electrodes forming a substantially homogenous agglomeration composit product of its electrode material and of said solid solution. The composite electrode can further contain a particulate component having electronical conduction. Such electrode, can be manufactured according to the principles set forth in USP 4.303-748 in relation to • solid solutions- containing ionic compounds of a different type. The use of the electrolyte according to- this invention in generators of the above type has proven of particular interest, particularly in relation to the inert character of the closoboranes with respect to most of the electrode materials liable of being used. This property enables, a stable electrochemical storage of electrical current and when- said generators consist of rechargeable batteries, a large number of loading- unloading cycles. In addition the abovesaid chemical inertia confers on said generators an improved resistance to.thermal shock.

Other features and advantages of the polymer solid electrolytes according to this invention will appear in the following disclosure of preferred embo¬ diments, it being understood that these examples do not have a limitative character.

Fig. 1 is representative of the results of a series of tests carried out with the different electro- . lytes of the examples. The diagrams of the drawing are representative of the variation in the electrical conductivity (expressed in ohm —1.cm—1-as a function of

OMPI the reciprocal of the temperature expressed in degrees Kelvin) .

In all of these examples, the macromolecular material used was a poly- (ethylene oxide) having a molecu- lar weight of 900.000. The electrolyte was o.btained by

■dissolving 1 g of poly(ethylene oxide) in 35 ml of aceto- nitrile, then adding the closoborane in amounts according as the .indications provided in the examples hereafter.

The solutions so obtained were casted on a poly- tetrafluorethylene support to a thickness of 5 mm and the layer so obtained was stoved at 6θ°C for 3 hours.

Conductivity measurements -were made in each example according as temperatures in order to determine the temperature at which said conductivity equalled 10 ³Ω .cm (TσlO ³). These measurements were carried out under vacuum so as to remove any trace of humidity and of solvent. First series of examples

The closoborane solubilized in the pol (ethylene oxide) was ^2^12^12 _' ^{Tiιe solu}bilized amounts were such as to obtain atomic ratios O/Li ranging from 4 to 16. The results obtained are indicated in the table hereafter.

The number of each test and the corresponding values of the 0/Li ratio and of the temperatures tσlO - are indicated in the table

The curves illustrative of the variation of conductivity according as the reciprocal of temperature do not comprise a transition point for polymers 1 and 2, whereby their amorphous character is established. Second series.of examples

Polymeric solid electrolytes containing sodium ciosoborane of formula NapB.pH.,₂characterized by O/Na ratios ranging from 6 to 8 were tested under similar conditions. The following results were obtained :

Third series of examples In this series the closoborane tested had the

^•following formula i_pB^_pCl.,₂. The ratios O/Li in the solid solutions obtained ranged from 6 to 14. The results ob¬ tained are reported in the following table. The tempera- tures at which a conductivity of 10 —4Ω—1.cm—1was reached are also indicated in the .following table :

The curves representative of the variations of conductivity as a function of the reciprocal of temperature are indicated in fig. 1. It will be appreciated that starting from test n° 12, the conductivity curves show that the solid solution obtained exhibited a

OMP dominently cristalline structure throughout the tempe¬ rature range which was used.

The results in relation to the temperature for

-5 -1 which the conductivity σ equals 10 ^Ω show that these electrolytes are indeed suitable for the production of electrochemical generators of the primary and secondary types.

Similarly it has been found that decaboranes of general formula ^M ₂ ^B10^X10 ""^{n wn}^-^{ch M and x} have the above indicated general meanings were compatible with the above use, inasmuch as solid solutions obtained therewith exhibit a temperature σlO -5 lower than 100°C.

A cell representative of an electro chemical generator of the secondary type was produced under the following conditions.

The electrolyte of this cell was formed with the solid solution used in test N° 5 (first series of examples). It was associated with a positive electrode formed of a substantially homogenous agglomerate of the same solid solution with 60 % (volume/volume) of a particulate TiS₂ forming the initial active material of the electrode. The negative electrode consisted of an alloy of lithium and of aluminium containing 60 % of lithium (atomic percentage). The cell so constituted was operative for the production of electrical current and yielded the following results : voltage in open circuit : 2.3 V at 100°C p discharge current : > 1 m A/cm . ^' In a similar manner a primary cell was formed using a solid solution of ^Li ₂ ^B12^H12 ^{in a c}° ^oly^{mer of} ethylene oxide ^'(70 % volume/volume) and of glycidyl methyl ether (30 % volume/volume) of formula

O It was verified first that the conductivity of this

_c _ _ι solid solution was above.10 ^Ω .cm at 70°C.

The electrodes associated with this electrolyte in said cell were a negative electrode consisting of lithium and a positive electrode consisting initially of an iron disulfide (FeS_p) . The following results were obtained : voltage in open circuit : 1.9 V at 25°C

2 discharge current : > 1 A/cm .

The invention also relates to the new electrolyte formed

10 of a solid solution of a ionic compound. in a polymeric material of the class consisting of homopolymers derived of the monomeric unit de ined hereafter or of copolymers derived of the abovesaid monomeric unit and of another monomeric unit, wherein the first mentioned monomeric unit

15. is represented by the following formula :

in which

meanings which have, been 0 indicated earlier. In case of copolymers, the other mono¬ meric unit referred to hereabove may be any one of those which have also been identified herein or in USP 4.303-748.

As a matter of fact the abovesaid solid solutions containing the monopolymers or copolymers of the abovesaid 5 class are new and inventive .per se, whatever the ionic compound dissolved therein. The solubilized ionic compound may. be any of those which have been referred to herein or in- the above said US -patent, in addition to the closo¬ boranes more specifically contemplated therein. . 0 The homopolymers or copolymers of this invention are preferably in the amorphous state. Their molecular weight is higher than 10,000, _.preferably higher than 100,000. These solid solutions can be prepared according to the same techniques as those which have been defined earlier in this application or in the abovesaid US patent with, respect to other homo- or co-polymers. The electrolytes comprising said_. solid solution, or consisting of said solid solution, can be associated with positive and negative electrodes, similar to those which are contemplated herein. Accordingly the invention also concerns the batteries so formed. In addition these solid solutions are also liable of being used to produce electrodes, whose electrode material is -in the form of particles, said electrodes forming a substantially homogenous agglomeration composite product of its electrode material and of said solid solution.

Other features and advantages of said solutions are further exa plified hereafter. Fourth example

Lithium iodide was dissolved in a poly-(dimethoxy- ethylene) having a molecular weight higher than 100,000.

This was achieved by polymerizing cis-l,2-dimethoxyethylene in toluol at a temperature of -68°C. The polymerization reaction" was initiated by a complex of boron-trifluoride and of dimethylether. The polymer was recovered and dissolved. in acetonitril in the presence of lithium iodide under proportions such as to finally obtain a ratio of the oxygen atoms to the lithium atoms O/Li equal to 8.

The solution. as deposited on a polytetrafluor- ethylene plate and the solvent evaporated, thereby obtaining a film of solid electrolyte. The conductivity of the film so formed was higher than 10 -5Ω—1.cm—1 at a temperature of

80°C.

Fifth example

An electrolyte was formed upon admixing with the same poly-(dimethoxyethylene) a sodium perchlorate N ClO.... .- . . 13 . ^'

Sixth example

Similar results were obtained with the same macro¬ molecular material associated with a potassium trifluoro- ethane-sulfonate (CF,S0-.K) under a ratio of O/K equal to

3 3

^•5 12. - _. ^•

Seventh example

An electrochemical generator cell^_of the secondary type was formed upon associating the electrolyte film obtained in example 1 with two electrodes of opposite sign. 0 The negative electrode was formed of an alloy of lithium and aluminium containing 50 % .(atomic percentage) of lithium and -the^' positive electrode was formed of a composite agglomeration product of TiS_p and of the solid electrolyte (60 vol. % of solid electrolyte). 5 After, a first loading, the. voltage in open circuit and the discharge current at a temperature of 8θ°C were .measured. The following results were obtained :

- voltage in open circuit : 2.3 V. ^• - discharge current : > 0.1 m A/cm 2. 0 The preceding examples are of course not limitative of this invention. It must be understood that all alterna-^' tives making use of the same principles or of any components included within any_.of the above classes of compounds or: materials, as well as those departing from said formulae, 5 yet having similar properties, are considered to be equi¬ valents which must be considered as falling within the scope of the. claims attached herewith.

Claims

1. A solid polymeric electrolyte comprising at least in part a solid solution of one or several ionic compounds including each at least one cation and one anion, said anionic compounds being dissolved within a plastic macro- molecular material formed at least in part by one or several homo- and/or co- polymers derived from one or several monomers including a heteroatom capable of forming donor-acceptor type bonds with the cation of the ionic compound, wherein said ionic compounds are selected among ^' the closoboranes of formula

M-2Bn aY.b in which n is an integer equal to 8, 10 or 12, M is an alkali metal or the ammonium.ion, X and Y, which are identical or different, represent each a group selected from among hydrogen, halogens, CN and hydrocarbon groups, a and b^: are integers, the sum .of which equals n.

2. The solide electrolyte of claim 1 wherein either X or Y or both consist of hydrocarbon groups and wherein said hydrocarbon groups comprise form 1 to 3 carbon atoms. 3- The solid electrolyte of claim 1 wherein X and Y are identical and are hydrogen or a halogen.

4. The solid electrolyte of claim 3 wherein X and Y are both chlorine.

5. The electrolyte of claim 4 wherein n is either 10 or 12.

6. The electrolyte of claim 1 wherein the ratio of the number of heteroatoms from said homo- and/or co- polymers to the number of alkali metal atoms or NH, ions ranges from 4 to 30. ^' 7 - The solid electrolyte of claim 6 wherein said ratio ranges from 4 to 16.

8. The electrolyte of claim 1 wherein the macromolecular material is a poϊy(ethylene oxyde) . 9. The electrolyte of claim 1 wherein the macromole¬ cular material is a copolymer of ethylene oxide and of glycidylmethyl. ether.

10. Electrochemical generator for producing electrical current comprising at least one negative electrode and at least one positive electrode separated from each other by means of a solid electrolyte, the negative electrode comprising an electrode material forming a source of species having a higher chemical potential capable of supplying an alkali or-an ammonium cation at its inter¬ face with the electrolyte and the positive electrode forming a sink at a lower chemical potential for the non- ionized species corresponding to the abovesaid alkaline cation, wherein the electrolyte which enables the transfer of this alkali cation by ionic conduction from the negative electrode to the positive electrode is formed at least in part by a solid solution of at least one ^• -closoborane in a plastic macromolecular material, said closoborane being selected from the group of closoboranes of formula : ^{' "}

M2₀Bn aY.b in which n is an integer equal to 8, 10 or 12, M is an alkali metal or the ammonium ion, X and Y, which are identical or different, represent each a group selected from- among hydrogen, halogens,.CN and hydrocarbon groups, a and b are integers, the sum^" of which equals .n, and said macromolecular- material being formed at least in part by one or several monomers including a heteroatom capable of forming donor-acceptor type bonds with the cation M of said closoboranes.

11.. The generator of claim 10 wherein the positive electrode is formed at least in part by a compound based on a titanium disulfide. 12. The generator of claim 10 wherein the positive electrode is formed at least in part by a compound based on an iron disulfide. 13- The generator of claim 10 wherein the positive electrode is formed by an alkali metal or by ^'an alloy containing said alkali metal, or by an intermetallic compound or insertion compound containing said alkali metal, wherein said alkali metal is sodium or lithium.

Electrolytes formed of solid solutions of closoboranes in a plastic, macromolecular material and electrochemical generators containing such electrolytes.