Ion conductors

Details Ion conductors Ion conductors

1990-02-05

1991-08-20

Kalafut, Stephen J.

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Include electrolyte chemically specified and method

252 622, H01M 1040

Patent

active

050413465

DESCRIPTION:

BRIEF SUMMARY
This invention relates to polymeric electrolytes, methods of making these, and to their use in electrolytic cells and batteries of such cells.
Solid polymeric electrolytes have been investigated in recent years as alternatives to liquid electrolytes in batteries as their use allows greater flexibility in battery design and manufacture. The most widely studied material for this application has been high molar mass poly(ethylene oxide) ("PEO") combined with a dissolved salt to enhance conductivity.
The polymer PEO is able to form stable solvates with a number of salts, however the electrical and morphological properties of such electrolytes require improvement before they are suitable for use in cells which operate effectively at or about room temperature. In particular high molar mass PEO tends to crystallise at about 65.degree. C. considerably reducing the content of the amorphous component needed for high ion conductivity.
Recent advances, e.g. as described in UK patent application GB-2164047A have attempted to overcome this disadvantage of PEO whilst retaining an essentially oxyethylene-based polymer, by modification of the PEO structure such that crystallinity at ambient temperatures is essentially moved. In GB-2164 047A linking groups eg (CH.sub.3)SiO and CH.sub.2 O (`oxymethylene`) are introduced between short sequences of oxyethylene groups, thereby disrupting the PEO backbone so that crystallisation is inhibited.
The polymeric electrolytes described in GB-216047A typically have conductivities at 25.degree. C. of 10.sup.-4 to 10.sup.-5 S cm.sup.-1 (.OMEGA..sup.-1 cm.sup.-1), a considerable improvement over PEO itself. These conductivities are appropriate for certain battery applications, particularly where the electrolyte is in the form of a thin film, e.g. 50 .mu.m thick, thereby permitting the relatively low current densities over a higher active surface area and maintaining the required overall current needed for the device.
The present invention seeks to improve the current densities that may be carried by a polymer-based electrolyte at ambient temperatures by increasing the conductivity of the electrolyte and altering its temperature dependence, particularly at a low temperatures (e.g. less than 0.degree. C.), this latter being an important object of this invention.
According to the present invention an ion-conducting polymeric material comprises a mixture of at least three components (a), (b) and (c):
The material may also contain a fourth component (d) one or more ionic salts.
Preferably the polymeric material contains only one structural material.
The structural material(s) (a) primarily provide mechanical support for the polymeric material of the invention, and is/are preferably polymer(s), which may be natural or synthetic, thermosetting or thermoplastic. The structural materials may themselves be ion-solvating, and examples of structural materials are the polymers poly(ethylene oxide) i.e. `PEO` preferably of molar mass range 1.times.10.sup.6 to 5.times.10.sup.6, epoxy resins, polyurethanes and polyvinylchloride.
The plasticiser(s) is/are preferably also ion-solvating and should be compatible with other polymer(s) in the polymeric material, particularly with component (c). Preferred plasticisers are dipolar aprotic solvents such as acetonitrile, .gamma.-butyrlacetone, dioxolane, 2-methyltetrahydrofuran, tetrahydrofuran, dimethyl sulfhoxide, low molar mass polyethylene glycol (e.g., of molar mass 300-500 especially ca 400) or derivatives thereof, and in particular alkylene carbonates such as propylene carbonate and ethylene carbonate.
The ion-solvating polymers (c) are those polymers which contain (CH.sub.2 CH.sub.2 O) units in their repeat units, in particular those described in GB-2164047A. These include:
(i) graft copolymers having amorphous sidechains which contain the unit (CH.sub.2 CH.sub.2 O).sub.k where k has an average value between 3 and 20 and the mainchain is selected from a carbon-carbon or siloxane or a phosphazene backbone, where there may be a linkage group between the sidec

REFERENCES:
patent: 4471037 (1984-09-01), Bannister
patent: 4840856 (1989-06-01), Nakacho
patent: 4886716 (1989-12-01), Roggero et al.

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