Rechargeable battery with solid electrolyte

Details Rechargeable battery with solid electrolyte Rechargeable battery with solid electrolyte

1991-06-25

1992-12-29

Skapars, Anthony

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Include electrolyte chemically specified and method

429218, H01M 1040, H01M 618

Patent

active

051750660

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a cathode material for a rechargeable battery with solid electrolyte and to the rechargeable batteries comprising said material as cathode material.
The development of batteries with solid electrolyte has constituted a significant progress in the area of rechargeable batteries. Lithium batteries with solid electrolyte are a particularly interesting class of rechargeable batteries. These batteries comprise two reversible lithium electrodes, one of which acts as a source of lithium ions during the discharge and the other as host of lithium ions, the two being separated by a thin film of polymer electrolyte which acts as a lithium ion support. The process is reversed during recharging.
In the know batteries, the lithium source can be a metallic lithium (or lithium alloy) sheet, a structure for intercalating lithium ions at low potential (for example WO.sub.2) or a conjugated polymer n-doped with lithium. The host is generally a structure for intercalation lithium ions (TiS.sub.2, V.sub.6 O.sub.13, MoO.sub.2, and the like), a transition metal compound which can be reduced by lithium (for example FeS.sub.2, NiS.sub.2) or a p-doped conjugated polymer. The lithium ion support is obtained by dissolving a lithium salt (for example LiClO.sub.4, LiCF.sub.3 SO.sub.3) in a solvating aprotic polymer, such as a polyethylene oxide.
Batteries of this type have favorable performance levels. Nevertheless, their capacity is insufficient. Thus, for a battery comprising TiS.sub.2, the calculated capacity is in the order of 200 A.h/kg; for a battery comprising V.sub.6 O.sub.13, it is in the order of 300 A.h/kg.
Furthermore, various compounds for intercalation lithium ions are known as cathode materials in nonrechargeable batteries.
Thus, lithium batteries with solid electrolyte are known in which the cathode material is a carbon fluoride CF.sub.x obtained by reaction of fluorine with graphite at a temperature in the order of 350 to 650.degree. C. Such a cathode material is suitable for batteries. However, the reversibility of intercalation of lithium ions in such a material is virtually zero and it cannot be used in rechargeable batteries.
In addition, the use of carbon fluorides obtained at ambient temperature as cathode material has been described, on the one hand, in batteries with solid polymer electrolyte, and, on the other, in an electrochemical system with liquid electrolyte (propylene carbonate). The reversibility of intercalation of the lithium ions in the liquid system has been found to be very poor. The C-F bond of the graphite fluorides obtained at low temperature indeed has a partial ionic character, which facilitates the formation of LiF between the graphite planes upon discharge according to the scheme Li.sup.+ +F.sup.- .fwdarw. LiF. During discharge, the dissociation reaction LiF .fwdarw. Li.sup.+ +F.sup.- should take place. In theory, this reaction is difficult to imagine, since the enthalpy is very strongly positive.
Indeed, LiF is formed which precipitates. The solvent contributes to entraining LiF formed at the outside of the electrochemically active zones, especially outside the electrolyte, by dissolution and nucleation.
The present inventors have now found that, contrary to the liquid systems, the electrochem.ical systems with solid electrolyte gave good reversibility of intercalation of lithium ions in a material composed of a graphite fluoride obtained at ambient temperature and they have developed a new rechargeable battery with solid electrolyte.
The present invention relates to a rechargeable battery comprising a solid polymer electrolyte, an anode composed of a lithium source and a cathode comprising a lithium-receiving material, characterized in that the lithium-receiving material is a compound of the formula CF.sub.x M.sub.7 where M is chosen from I, Cl, Br, Re, W, Mo, B and 0.3.ltoreq.x .ltoreq.0.9, 0.02.ltoreq.y.ltoreq.0.06, and the structure of this material is such that the carbon atoms form planar hexagons.


BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, 3 and

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