Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Patent
1996-02-20
1997-08-26
Gorgos, Kathryn L.
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
429194, 429197, 429198, 429201, 429199, H01M 616, H01M 614, H01M 604
Patent
active
056609477
DESCRIPTION:
BRIEF SUMMARY
This is a national stage application of PCT/EP94/01366 filed Apr. 29, 1994.
BACKGROUND OF THE INVENTION AND FIELD OF THE INVENTION
The present invention concerns new electrolytes for use in galvanic cells, in particular lithium cells. In this paper a lithium cell is defined as follows: Essentially a lithium cell consists of an anode, a cathode, and an electrolyte. The anode consists of lithium, a lithium alloy, or a compound which is able to intercalate lithium ions, for example carbon. In general the cathode consists of a substance which is able to intercalate lithium ions or reacts electrochemically with lithium ions, where the potential of the cathode is markedly higher than the potential of the anode. The electrolyte consists of one or more salts which are dissolved in a suitable solvent, a mixture of solvents, a polymer, or a mixture of a polymer with one or more solvents. A distinction is made between primary and secondary lithium cells.
This definition includes the so-called `rocking chair batteries`. Recent investigations in this field are described in a review of B. Scrosati (J. Electrochem. Soc. Vol. 139, 2776, (1992)).
Typical solvents currently in use include:
Organic carbonates such as propylene carbonate (PC) or ethylene carbonate (EC). Linear and cyclic ethers and polyethers such as dimethoxyethane (DME), diethoxyethane (DEE), tetrahydrofurane (THF), 2-methyltetrahydrofurane (2-Me-THF), dioxolane, and the polymer polyethylene oxide as well.
Typical salts currently in use include:
Lithium perchlorate (LiClO.sub.4), lithium tetrafluoroborate (LiBF.sub.4), lithium hexafluorophosphate (LiPF.sub.6) lithium hexafluoroarsenate (LiAsF.sub.6), lithium trifluoromethylsulfonate (LiCF.sub.3 SO.sub.3), and lithium bis(trifluoromethylsulfonyl)imid (Li(CF.sub.3 SO.sub.2).sub.2 N).
The above-mentioned salts show some serious drawbacks. Lithium perchlorate has a tendency to explode in combination with some solvents such as dioxolane. Compounds with fluorinated inorganic anions, such as lithium hexafluorophosphate, are of low thermal stability, and generate Lewis acids by dissociation which are able to polymerized the solvent. Because of its arson content lithium hexafluoroarsenate is environmentally damaging, and generates carcinogenic by-products by reaction with lithium. Lithium bis(trifluoromethylsulfonyl)imide is comparatively expensive.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an electrolyte for use in a galvanic cell which is non-explosive, stable, and ecologically harmless and a galvanic cell using the electrolyte.
This is achieved by an electrolyte comprising borates of the formula ABL.sub.2, wherein A is lithium or a quarternary ammonium ion. The bidentate chelate ligand L is bonded to the central boron atom via two oxygen atom. In general chelate complexes of this type are of high thermal stability. There is little risk of an exothermic reaction with the solvent or with lithium, because borates are no highly oxidizing agents. Therefore, the electrolytes in accordance with the invention are non-explosive. Furthermore, the salts in accordance with the invention are not able to form Lewis acids, which would polymerized the solvent. Therefore, the electrolytes are stable for a long time and can be used over a wide temperature range. The salts in accordance with the invention comprise no elements which are able to form toxic compounds during combustion. In general hydrolytic products of the salts are harmless and of low toxicity. Therefore, the electrolytes in accordance with the invention are environmentally harmless.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 to 9 show cyclic voltammograms of the residual current of some systems of the electrolyte of the disclosed invention:
FIGS. 10 to 12 show magnification of the anodic region for two systems of the electrolyte of the disclosed invention; and
FIGS. 13 to 16 show galvanostatic cycling experiments of the electrolyte of the disclosed invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The conductivity of the
REFERENCES:
patent: 4808282 (1989-02-01), Gregory
B. Scrosati, J. Electrochem. Soc. vol. 139, 2776 (1992), Lithium Rocking Chair Batteries: An Old Concept?.
Barthel, J. et al., J. Electrochem. Soc. vol. 140,6 (1993), The Influence of Water on the Cycleability of Lithium in 2-Methyltetrahydrofuran-Based Electrolytes.
Yilmaz, H. et al., J. Electroanal. Chem. vol. 261,105-112 (1989), Correlation of Anodic Peak Potentials with the Semi-Empirical orbital and HOMO Energies of Various Vinyl Compounds.
Gorgos Kathryn L.
Wong Edna
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