WO1992002571A1

WO1992002571A1 - Cation conductive solid polymers

Info

Publication number: WO1992002571A1
Application number: PCT/US1991/005521
Authority: WO
Inventors: Subhash Narang; Sivapackia Ganapathiappan
Original assignee: SRI International Inc; Stanford Research Institute
Current assignee: SRI International Inc
Priority date: 1990-08-03
Filing date: 1991-08-02
Publication date: 1992-02-20
Anticipated expiration: 1993-02-03

Abstract

An amorphous ionically conductive macromolecular solid having improved ambient temperature ionic conductivity. It comprises a macromolecular solid which carries a negative charge and has a positively charged ionic species associated with it. The macromolecular material comprises a polymer or copolymer having a plurality of side chains having distal constituents having the formula: -X-Y- M+, where X = CF¿2?, CFCN, CFR, or CCNR or C6FaRb where a is 1-4, b is 0-3 and a + b is 4 and where R is virtually any organic or substituted organic group, for example, alkyl, alkenyl, aryl, aralkyl, haloalkyl, CN, a polymer such as a polyether, a polyester, a polyamine, a polyimine, etc., Y = SO3, CO2 or POc where c is 2, 3 or 4, and M = a cation.

Description

Description CATION CONDUCTIVE SOLID POLYMERS

Technical Field

The present invention relates to a broad class of cation conductive solid polymers useful in batteries, fuel cells, sensors, supercapacitors, electrochromic devices and the like. Background Of The Invention

A number cf solvent-free polymer

electrolytes are known and there has been considerable interest in the possible utilization of the

electrolytes in electrochemical devices such as batteries, fuel cells, sensors, supercapacitors and eiectrochromic devices. Among the polymers which have been tested for such use are those based upon the linear-chain polyethers, poly (ethyleneoxide) and poly(propyieneoxide) with alkali metal salts. Cation conductive phosphazene and siloxane polymers have also been reported which exhibit better conductivity at room temperature than do the linear-chain polyether electrolytes. One class of polymers of interest are the pclyphosphazene sulfonates as reported by S.

Ganapathiappan, Kaisin Chen and D.F. Shriver,

Macromolecules, 1988, 21, 2299, in Journal of the American Chemical Society, 1989, 111. 4091 and

Chemistry of Materials, 1989, 1 , 483. The polyether electrolytes reported in, for example, Polymer

Communications, 1987, 28, 302. Polyester conductive polymers are reported in, for example, Macromolecules 1988, 21, 96. Cation conductive siloxane comb

polymers are reported in Polymer Communications, 1989, 30, 52 and in Journal of Polymer Science: Part C:

Polymer letters, 28, 187-191, 1990. Anion

conductivity is also known in solid polymer

electrolytes as is reported, for example, in

Macromolecules 1984, 17 , 975. Single ion conductive polymers have an advantage over double (positive and negative) ion conductive polymers in that they can charge and discharge more completely as limitations on charging and discharging due to DC polarization is obviated.

While the various polymer electrolytes set forth in the above publications have shown promise, such promise has generally not been enough to make them practical choices for use in, for example high energy batteries and for other applications wherein it is desirable to have particularly high ionic

conductivity for the polymer electrolyte and wherein it is desirable to use relatively thin films of the polymer electrolyte. Basically, the polymer

electrolytes of the prior art do not exhibit

sufficient ionic conductivity. Furthermore, the polymer electrolytes of the prior art have generally not exhibited desirable physical properties for incorporation in electrolytic devices. For example, the films may be too sticky, the polymers may be too close to being liquid, the polymers may be too

brittle, or the polymers may be too heat sensitive.

The present invention is directed to

overcoming one or more of the problems as set forth above. Disclosure Of Invention

In accordance with an embodient of the present invention an amorphous lomcally conductive macromolecular solid is set forth which has improved ambient temperature ionic conductivity. The

macromolecular solid carries a negative charge and has a positively charged ionic species associated with it. The macromolecular material comprises a polymer or copolymer having a polymer backbone having a plurality of side chains extending therefrom having distal constituents having the formula:

-X-Y- M⁺

wherein

X = CF₂, CFCN, CFR, or CCNR or C₆F_aR_b where a is 1-4, b is 0-3 and a + b is 4 and wnere R is

virtually any organic or substituted organic group, for example, alkyl, alkenyl, aryl, aralkyl, haloalkyl, CN, a polymer such as a polyether, a polyester, a polyamme, a polyimine, etc.

Y = SO₃, CO₂ or PO_c where c is 2, 3 or 4, and

M = a cation.

An lomcally conductive macrcroiecular solid m accordance with the present invention nas a number of advantages over prior art lomcally conductive macromolecular solids. First of all, the conductivity of the macromolecular solid in accordance with the present invention is generally significantly higher than tnat of the prior art macromolecular solids.

Second, the macromolecular solids of the present invention have desirable physical properties in that tney can be formulated in relatively thin but still relatively highly conducting films which have

desiraole mechanical properties sucn as

and lack of stickiness. Furthermore, side cnams of the nature required by the present invention can be relatively readily added to polymers of substantially any backbone so long as such polymers have at least one active or labile hydrogen. Or, alternatively, the required side chains of the present invention can be added to the monomers which are later polymerized or copolymerized to form a polymer system. Since any of a number of different polymer backbones can be

utilized the designer of a battery, fuel cell,

supercapacitor, electrochromic device, sensor or the like can, to a greater extent, choose the physical properties desired for the particular application thus providing significant added flexibility to the design of such devices. In accordance with a preferred embodiment of the present invention a plasticizer carbe added leading to a further increase m the

conductivity of the macromolecular solid as well as adjustment of its mechanical properties as by adding flexibility.

Brief Description Of Drawings

The invention will be better understood by reference to the figures of the drawings wherein like partes denote like parts throughout and wherein:

Figure 1 illustrates a cell assembly as used for measuring conductivity;

Figure 2 illustrates a cell and vacuum chamber as used for measuring conductivities; and

Figure 3 illustrates, schematically, an experimental, setup as used for AC impedance

(conductivity) measurements. Best Mode For Carrying Out Invention

The present invention provides a broad class of iomcally conductive macromolecular solids. Such macromolecular solids (polymers or copolymers) can have any of a great number of polymer backbones (made up of repetitive units) but are all characterized by having a plurality of side chains which have distal constituents having the formula:

-X-Y-M⁺

wherein

X = CF₂, CFCN, CFR, or CCNR or C₆F_aR_b where a is 1-4, b is 0-3 and a - b is 4 and where R is

virtually any organic or substituted organic group, for example, alkyi, alkenyl, aryl, aralkyl, CN, haloalkyl, a polymer such as a polyether, a polyester, a polyamine, a polyimine, etc.

Y = SO₃, CO₂ or PO_c where c is 2, 3 or 4 , and M = a cation.

The term cation is used broadly herein to include virtually every species which can bear a positive charge and includes the elements of Groups IA, IB, IIA, IIB, IIIA, IIIB, IVA, IVB, VA, VB , VIA, VIB, VIIA, VIIB, AND VIII of the Periodic Table of the Elements.

Examples of useful polymer backbones include polyether polymers, polyester polymers,

poly(ethylene) imine polymers, polyphasphazene

polymers, siloxane polymers, and the like. The just set forth list of polymer backbones is not meant to be exhaustive buz is merely illustrative of a few of the polymers to which the side chains required by the present invention may be appended. The polymers which make up the backbone of the macromolecular solid of the invention can be polymerized by the methods of the prior art. The polymer backbone may also comprise a copolymer of two or more polymers with repeating units of the individual monomers.

Generally the number of side chains on the macromolecular solid should be such as to provide from 0.04 to about 4 side chains per monomer unit. More preferably, the number of side chains per monomer unit falls within the range from about 0.04 to about 2.

The preferred compounds are those wherein X = CF₂ or C₆F₄

Alternatively, some, but not all of the fluorines may be replaced with an organic group. Virtually any organic or substituted organic group can be present, for example, alkyl, aikenyl, aryl, aralkyl, haloalkyl, a polymer such as a polyether, a polyesrer, a

polyamine, a polyimine, etc.

The cation, M, can be virtually any desired catioin for a desired use, e.g., as a sensor, battery, fuel cell, supercapacitor, electrochromic device, ofr the like. Batteries can be based upon, for example, having the cation be an hydrogen, a quarternary ammonium ion (NR¹ ₄ ⁺ where R¹ can be hydrogen, alkyl, aryl, aralkyl, aikenyl or the like), or an alkali metal cation, such as lithium, sodium, potassium, rubidium or cesium, with lithium and sodium generally being preferred.

In accordance with the present invention the _^macromolecular solid can further include an effective amount for enhancing the ionic conductivity cf the solid of a plasticizer. Virtually any plasticizer which does not significantly lower the ionic

conductivity can be utilized. However, the preferred plasticizer can be represented by the formula:

R² ₃C (OC₂R² ₄)_nCN wherein each R² const. tuent is independently hydrogen, alkyl, aryl, aikenyl- or aralkyl with hydrogen, methyl and ethyl being preferred and wherein n = 1 to 8 inclusive.

One method of preparing polymers with the desired side chains is as follows: a desired polymer, for example, a poly (ethylene) imine polymer, can be reacted with a compound of the formula R³COCl in an amount sufficient to react with only a portion of the imine hydrogen to add COR³ groups. The remainder of the poly (ethylene) imine polymer backbone wili then still have imine hydrogens present. Thereafter, the -COR containing ethyleneimme polymer can be reacted to an excess of FSO₂CF₂COF to provide the required side chains in accordance with the present invention, but with a fluorine attached to the terminal SO₂ group. Thereafter the polymer can be reacted with a metal carbonate, for example sodium carbonate, to convert it to its ionic form. The polymer can then be dialyzed in the presence of an excess of sodium chloride. All of the CO groups in the side chains can then be reduced using, for example, BH₃·SMe₂ followed by HCl and a base such as LiOH, NaOH or KOH . A typical R³ group would be -CH₂O(C₂H₄O)_m,CH₃ but R³ may have a multitude of other structures.

Cation conductive polymers with polyether side chains can be made by the following reaction scheme

1 . CH₃ ( OC₂H₄ ) ₂OH → CH₃OC₂H₄OCH₂CHO

CH₂Cl₂

( COCl ) ₂ ↓ [ O ]

DMSO

N ( C₂H₅) ₃

CH₃OC₂H₄OCH₂COOH 2. CH₃(OC₂H₄)₂OH - CH₃OC₂H₄OCH₂COOH

Mln₂O₇

-78ºC

CH₃(OC₂H₄)_mOH + Na → NaO(C₂H₄)_mCH₃

THF

NaO(C₂H₄₀)_mCH₃ → CH₃(OC₂H₄)_mOCH₂COOCH₃

BrCH₂COOCH₃

-NaBr

CH₃(OC₂H₄)_mOCH₂COOCH₃ → CH₃(OC₂H₄)_mOCH₂COOH

acid or base

hydrolysis

where m may be an integer or an average of integers

Single ion conductive ionic conducting polymers can also be prepared as set forth in

following:

x

where R = CH₂O ( C₂H₄O )_mCH₃ , m is an integer or average of integers and M can suitably be Li or Na. As an alternative poly(ethylene) imine based electrolyte can be synthesized from monomers as per the following reaction scheme:

Poly (phosphazenef luorosulf cnate) home- and copolymers can be prepared as fellows: 1) [NPCl₂]_n 2Na⁺[SO,CF₂CH₂O] ^2- →

THF

[NP(OCH₂CF₂SO₃Na-)_xCl_2-x]_n →

NaOR

(excess )

[NP(OCH₂CF₂SO₃Na⁺)_χ(OR)_2-x]_n →

LiCl

(excess)

( NP ( OCH₂CF₂SO₃Li ⁺ )_x ( OR ) _2-x ]_n

where R is C₂H₄OC₂K₄OCH₃ and x lies between 0 and 1. 2) [NPCl₂]_n + 2Na⁺[SO₃CF₂CH₂O]^2-

THF

[ NP(OCH₂CF₂SO₃-Na⁺ ) ₂] _n

Siloxane homo- and copolymers having the required side chains can be made as follows:

wherein M = Na or Li;

R = (C₂H₄O)_mCH₃ where m is an integer or average of integers; and

x = 0 to 1.

More generally, the compound

where X, Y and R are as previously defined can be reacted with virtually any polymer which has an available hydrogen, for example a hydrogen attached to nitrogen, sulfur or oxygen, to provide the desired side chains. As pointed out previously, the group R can be virtually any alkyl, aryl, aralkyl, aikenyl, fluoroalkvl, fluoroarvl or fluoroalkenyl group or can be an oligomer such

polyethyleneoxide or polypropyleneoxide.

An alternative side chain m accordance with the present invention can be added by reacting the compound

with an active hydrogen on a polymer backbone. Such might be carried out, for example, by converting the above compound to its acid chloride and then reacting the acid chloride with poly (ethyieneimine) as set forth previously.

The invention will be setter understood by reference to the illustrative examples which follow. It should be noted that these examples are meant to be illustrative only and are not exhaustive of the polymer backbones and side chains of the invention.

Equipment And Measurement Technique

Conductivities of the polymers were evaluated by AC impedance spectroscopy. Referring to the Figures, a film 6 of the dried polymer electrolyte was sandwiched between two stainless steel blocking electrodes 7,8 that each had an area of 0.7854 cm².

The thickness cf the polymer film 6, which typically varied between 0.51 mm and 1.02 mm, was measured with a micrometer. The assemoly 9, composed of the

blocking electrode-polymer sandwich cell 10 inside a Delrin cup 12 (Figure 1), was transferred to a vacuun chamber 14 that had provision for heating (Figure 2) and for applying a constant pressure of 65-97 lb/in² across the polymer film 6. The electrodes 7,8 were connected to a potentiostat (PAR 173) operating in the gaivanostatic mode.

The cell 10 was then perturbed with a small AC signal generated by a Solartron 1250 Frequency Response Analyzer, and the real and imaginary

components of the cell impedance were measured as a function of frequency at each of the desired

temperatures. The setup was allowed to stabilize overnight after the temperature was changed. The AC impedance data were plotted in both the Nyquist and 3ode planes to identify the high frequency relaxation arising due to the polymer electrolyte. Typically, the frequency of the AC signal was scanned from 65 KHz down to 10 mHz. The intercept at the real axis of the high frequency relaxation was assumed to represent the resistive component of the polymer electrolyte

impedance. This was then converted to the resistivity of the polymer (the thickness and the area of the polymer film 6 were known). The reciprocal of

resistivity gave the conductivity, σ, having units of Ω-cm^-1. In cases where high frequency relaxation occurred above 65 KHz, a Hewlett Packard 4192A

Impedance Analyzer was used to measure the polymer electrolyte resistance. This instrument has a

frequency range capability of 13 MHz to 5 Hz. The experimental setup 16 used for conductivity

measurements is shown in Figure 3. Preparation Of Polymer Films

Solutions of polymer films were prepared by dissolving a known quantity of polymer in dry solvent. For conductivity measurements, the polymer solution was added dropwise into the Delrin cup to cast a film. The film was then dried for 3 days in a glass vacuum apparatus at 120ºC at <0.01 torr. Film thickness was measured using a micrometer. Example 1

Poly (ethyleneimine) polymers in accordance with the present invention were synthesized as

described herein and the ionic conductivity of their lithium and sodium salts were determined at 24 'C and 80 'C. Table 1 reports the results of this study.

Example 2

The effects of the presence of the plasticizer CH₃ ( OC₂H₄)₄CN were determined for lithium forms of modified poly (ethyleneimine) polymers in accordance with the present invention. The results are recorded in Table 2. These can be compared viz: the entries in Table 1 wherein X = 0.66 and X = 0.93 and wherein M is Li. It will be noted that the conductivity increased from low (which amounts to less than 10^-7) to the order of magnitude of 10^-5 to 10^-6. Thus, significant effect has been found for adding plasticizer.

Example 3

Polyphosphazene polymers in accordance with the invention in the manner previously described and the effect of the presence of a plasticizer on the conductivity of such polymers was determined. Table 3 presents the results of such experiments.

Example 4

The variation in the conductivity of

siloxane polymers in accordance with the invention and synthesized as previously described was determined and is reported in Table 4 .

Industrial Applicability

Cation conductive solid polymers are provided in accordance with the present invention which have good physical properties and which are relatively high in conductivity whereby they are useful in the manufacture of batteries, sensors, fuel cells and the like.

While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable cf further

modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention and the limits of the appended claims.

Claims

Claims That Which Is Claimed Is:

1. An amorphous ionicaily conductive macromolecular solid having improved ambient

temperature ionic conductivity, said solid carrying a negative charge and having at least one positively charged ionic species dissolved associated with it, said macromolecular material comprising a polymer or copolymer having a plurality of side chains having distal constituents having the forsula:

-X-Y- M⁺

wherein

X = CF₂, CFCN, CFR, or CCNR or C₆F_aR_b where a is 1-4, b is 0-3 and a - b is 4 and where R is an organic or substituted organic grcup,

Y = SO₃, CO₂ cr PO_c where c is 2, 3 or 4, and M = a cation.

2. A macromolecular solid as set forth in claim 1, wherein said polymer or copolymer has a phosphazine, poly (ethyleneimine) cr siloxane backbone.

3. A macromolecular sciid as set forth in claim 2, further including:

an effective amount for enhancing the ionic conductivity of said solid of a plasticizer. A macromolecular solid as set forth in claim 3, wherein said plasticizer comprises

R² ₃C(OC₂R² ₄)_nCN wherein each R² constituent is independently hydrogen, alkyl, aryl, aikenyl or aralkyl and n = 1-8.