Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Patent
1997-09-19
2000-04-04
Kalafut, Stephen
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
429314, 429317, 429330, 252 622, H01M 1040
Patent
active
060459514
DESCRIPTION:
BRIEF SUMMARY
This invention is related to a non-aqueous electrolyte system for use in batteries, capacitors or electrochromic devices, said system essentially consisting of an alkali or ammonium salt, a solvent mixture and optionally a polymer.
Liquid, solid and immobilized non-aqueous electrolytes are of considerable interest for use in lithium batteries, supercapacitors and other electrochemical devices.
Recently, lithium secondary batteries have been developed based on lithium insertion materials for both the negative electrode and the positive electrode. Such electrochemical cells have a cell voltage in excess of 4V in the charged state and an energy density of more than 100 Wh/kg. Similarly for the recently developed supercapacitor cells, voltages higher than 3V give considerable improvement with respect to the energy storage capability. However, electrolyte compositions used in these devices are traditionally limiting the device performance because of low ionic conductivity and low electrochemical stability. The demands for electrolytes in batteries and supercapacitors have been sufficiently fulfilled only with few organic carbonates or in particular with mixtures thereof.
U.S. Pat. No. 5,192,629 of Bell Communication Research Inc. describes an electrolyte system comprising a solution of LiPF.sub.6 in a mixture of dimethyl carbonate and ethylene carbonate.
EP 541 889 of Sanyo Electric Co. describes for lithium-ion graphite-based batteries the combination of a separator with a liquid electrolyte comprising one or more of the solvents ethylene carbonate, propylene carbonate, lactones and sulfolanes.
U.S. Pat. No. 5,240,790 of Alliant Techsystems Inc. describes the use of a polyacrylonitrile-based gelled polymer system, which includes as an immobilised liquid phase a ternary plasticifier mixture of ethylene carbonate, .gamma.-butyrolactone and polyethylene glycol dimethyl ether, in lithium-based electrode batteries.
U.S. Pat. No. 5,326,657 of Nippon Oil Co. describes a polymeric solid ionic electrolyte having good mechanical properties. The polymeric solid electrolyte is a radiation crosslinked network based on a polyfunctional acrylate compound, containing a non-aqueous organic solvent and an alkali metal and/or an ammonium salt.
EP 651 455 of Matsushita Electrical Industrial Co Ltd. describes the use of a separator based on polyethylene and/or polypropylene to prevent lithium secondary batteries from shortcircuiting.
Although electrolyte systems showing high conductivity and which are stable against oxidation are known, there still exists a need for an electrolyte system which in addition to said high conductivity and high oxidation stability display a high stability against reduction.
Accordingly, it is an object of the invention to provide a non-aqueous electrolyte system for use in batteries, capacitors or electrochromic devices (including so-called "smart windows") which can be applied in a broad voltage range, which has a conductivity higher than 10.sup.-3 S/cm at room temperature, and which shows a high stability against reduction.
Now it has been found that this object is accomplished by an electrolyte system consisting essentially of an alkali or ammonium salt, a solvent mixture, and optionally a polymer, wherein said solvent mixture comprises a mixture of ethylene carbonate and .gamma.-valerolactone, optionally containing one or more additional solvents selected from other organic carbonates, other lactones, esters and glymes, said system optionally being confined in a separator.
Whereas the pure .gamma.-valerolactone is electrochemically stable against coke and graphite, the passivation layer formed upon reaction with the lithium containing negative electrode structures is poor, the lithium conductivity is poor, the reaction product is neither thermodynamically nor kinetically stable, and the cell balance is severely distorted as large amounts of active material is consumed in the passivation reaction.
In contrast, the ethylene carbonate displays good properties of the passivation layer formed, high cond
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Consigny Marine
Wendsjo .ANG.sa
Yde-Andersen Steen
Danionics A/S
Kalafut Stephen
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