Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
2000-08-22
2001-10-23
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S323000, C429S188000, C429S189000, C429S231950
Reexamination Certificate
active
06306540
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electrolytic solution used in a battery and to a battery using the electrolytic solution.
BACKGROUND ART
A lithium ion secondary battery has been developed as a secondary battery, which can achieve high voltage and high energy density.
The main components thereof are positive and negative electrodes, and an ion conductive layer disposed between these electrodes. It is possible to obtain a battery, which can be charged and discharged in a larger amount of current by decreasing the resistance with an ion conductive layer. Therefore, an ion conductive layer is required to decrease ion conductive resistance, and the electrodes must be arranged with an appropriate distance therebetween to prevent short-circuit.
In lithium ion secondary batteries in practical use, as disclosed in Japanese Unexamined Patent Publication No. 8-83608 (1996), a porous separator film is used to separate the electrodes from each other by an appropriate distance, and an electrolytic solution for ion conduction is charged between these two electrodes to realize ion migration between them.
A lithium ion secondary battery in practical use has a structure, wherein the above-mentioned components are stored in a solid outer can comprising metal or the like.
A solution obtained by dissolving a lithium salt into a mixed solvent of a main solvent and a sub solvent is employed as the electrolytic solution for the above-mentioned lithium ion secondary battery of prior art, and lithium hexafluorophosphate (LiPF
6
) is employed as a salt of the electrolytic solution, since the solution and the salt bring about extremely high ion conductivity and high electrochemical stability. Since a non-aqueous electrolytic solution having inferior ion conductivity relative to an aqueous solution needs to be employed in a lithium ion secondary battery, the above mentioned salts securing high ion conductivity are employed without exception.
However, LiPF
6
has a disadvantage of thermal unstability, as it has been pointed out that a LiPF
6
type electrolytic solution begins to decompose at a lower temperature than an electrolytic solution containing a salt such as LiBF
4
through the decomposing reaction shown in the following chemical reaction formula (1).
LiPF
6
→PFs(gas)+LiF (1)
In the publication 1 (ELECTROCHEMISTRY AND INDUSTRIAL PHYSICAL CHEMISTRY, 65, No. 11, pp. 900-908, 1997), it is described that PF
5
formed by the above decomposition reaction is a gas itself, and a decomposition gas is evolved by reacting with solvent molecules. The formation of the gas inside the battery may cause deformation or breakage of the battery outer can.
For this reason, from the viewpoint of a battery design, it is necessary to use a solid outer can, which is difficult to deform or break. But a solid outer can is not preferable from the viewpoint of a battery energy density because of its heavy weight and large volume.
Moreover, as the decomposition reaction shown in the formula (1) proceeds, the concentration of LiPF
6
undesirably decreases, which reduces ion conductivity of an electrolytic solution.
The present invention has been contrived to solve these problems, and an object of the present invention is to provide a battery electrolytic solution having excellent stability, and also to provide a battery with excellent battery characteristics and a lightweight outer structure.
DISCLOSURE OF INVENTION
The first battery electrolytic solution of the present invention comprises a solvent, a supporting electrolyte and an additive, which additive contains a decomposition product of the supporting electrolyte in the solvent. Since decomposition of the supporting electrolyte is inhibited by the electrolytic solution, it prevents ion conductivity of the electrolytic solution from decreasing to improve the stability thereof.
The second battery electrolytic solution of the present invention comprises a solvent, a supporting electrolyte, and a gas formation inhibitor, which gas formation inhibitor contains a decomposition product of the supporting electrolyte with the formation of a gas in the solvent. Because of the electrolytic solution, stability of the supporting electrolyte is improved, and it prevents gas from forming, which improves the stability thereof.
The third battery electrolytic solution of the present invention comprises the second battery electrolytic solution, wherein the supporting electrolyte is a salt dissociating fluoro complex ions in the solvent, and the gas formation inhibitor is a fluoride-ion-dissociating salt in the solvent. By the electrolytic solution, ion conductivity becomes excellent, and it prevents gas from forming, which improves the stability thereof.
The fourth battery electrolytic solution of the present invention comprises the third battery electrolytic solution, wherein the supporting electrolyte is LiPF
6
. By the electrolytic solution, ion conductivity becomes extremely high, electrochemical stability becomes excellent, and the gas formation is inhibited, which improves the stability of the electrolytic solution.
The fifth battery electrolytic solution of the present invention comprises the third battery electrolytic solution, wherein the supporting electrolyte is LiPF
6
, and the gas formation inhibitor is a salt that dissociates fluoride ions and cations, which constitute a battery reaction in the solvent. By the electrolytic solution, the gas formation is inhibited without adversely effecting the battery reaction, which improves the stability and achieves excellent electrochemical stability.
The sixth battery electrolytic solution of the present invention comprises the fifth battery electrolytic solution, wherein the gas formation inhibitor is LiF. By the electrolytic solution, the gas formation is inhibited without adversely effecting battery reaction when the electrolytic solution is used as the electrolytic solution in a lithium ion secondary battery to improve its' stability.
The seventh battery electrolytic solution of the present invention comprises the second battery electrolytic solution, which contains the gas formation inhibitor in an amount more than its solubility at room temperature. By the electrolytic solution, the effect of inhibiting the gas formation at a high temperature becomes large. Furthermore, a safer battery can be obtained, which has small possibility of deformation or breakage when the battery is maintained at a high temperature.
The first battery of the present invention is the battery, which is obtained by filling the electrolytic solution of any one of the above-mentioned 1 to 7 between a positive electrode and a negative electrode. By the electrolytic solutions, battery characteristics become stable, and the outer structure becomes light.
BEST MODE FOR CARRYING OUT THE INVENTION
The battery electrolytic solution of the present invention comprises a solvent, a supporting electrolyte and an additive.
The additive contains a decomposition product of the supporting electrolyte in the solvent, and also contains a material participating in the decomposition reaction of the supporting electrolyte. Equilibrium in the electrolytic solution is controlled to the direction wherein the supporting electrolyte is not decomposed. As a result, ion conductivity of the electrolytic solution is prevented from decreasing, the electrolytic solution is stabilized, and a safe battery having high performance can be obtained by using the electrolytic solution. This is the fundamental principle of inhibiting decomposition of the supporting electrolyte in the electrolytic solution.
Another battery electrolytic solution of the present invention comprises a solvent, a supporting electrolyte, and a gas formation inhibitor.
The gas formation inhibitor corresponds to the above-mentioned additive, and contains a material formed with the formation of a gas during the decomposition of the supporting electrolyte to control the solution equilibrium in the electrolytic solution participating in the decomposing reaction of the supporting elec
Adachi Hiroshi
Aihara Shigeru
Aragane Jun
Hamano Kouji
Hiroi Osamu
Kalafut Stephen
Martin Angela J.
Mitsubishi Denki & Kabushiki Kaisha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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