Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Cell enclosure structure – e.g. – housing – casing – container,...
Reexamination Certificate
1998-07-22
2002-01-08
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Cell enclosure structure, e.g., housing, casing, container,...
C429S320000, C429S178000
Reexamination Certificate
active
06337153
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to non-aqueous electrolyte cells and is particularly concerned with sealed non-aqueous electrolyte cells having electric energy generating elements sealed within a casing that is formed from a laminated material made from a metal foil and a resin film.
(2) Description of the Prior Art
Heretofore, metal sheets such as stainless steel sheets (SUS) have been used as casing materials for sealed cells. However, such a metal sheet has high rigidity and therefore cannot be easily formed into an extremely thin flat shape. In addition, the metal sheet has high specific gravity which causes a decrease in energy density per unit weight of the cell when used in the fabrication of extremely thin cells.
For these reasons, lately developed sheet-like (i.e., extremely thin flat plate type) sealed non-aqueous electrolyte cells use, as a casing material, a laminated material comprising a metal foil laminated to a resin film. Such a laminated material is lightweight and flexible compared to stainless steel sheets etc., and therefore can be easily formed into an extremely thin flat shape. The laminated material can be fused by heat, which facilitates the sealing of cells. Additionally, it has a structure in which a metal foil layer having low gas permeability and a resin layer having excellent chemical stability are laminated together, and the former (i.e., the metal foil) functions to inhibit permeation of moisture, oxygen and others while the latter (i.e., the resin layer) functions as a protective layer against oxygen and alkali. With this structure, the laminated material, as a whole, excels in gas permeability as well as in chemical stability. Accordingly, the laminated material has been regarded as a useful material for forming a casing for sheet-like cells which accommodate highly reactive electric energy generating elements.
Despite the above advantages, there has not been developed yet a sheet-like sealed non-aqueous electrolyte cell which has a casing made from a laminated material and provides satisfactory service life, because the degree of sealing in the prior art electric cells decreases with time.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming the above-described problem presented by the prior art sealed non-aqueous electrolyte cells having a casing made from a laminated material. One of the objects of the invention is therefore to provide a sheet-like sealed non-aqueous electrolyte cell having a laminated material casing, which cell includes a means for preventing a trace amount of water present therein from causing deterioration in the performance of the cell.
The above object can be achieved by a sealed non-aqueous electrolyte cell according to the invention having: a casing that is made from a laminated material comprising a metal foil and a resin film; and an inorganic oxide fine powder that is not an electrode active material and is accommodated within the casing together with electric energy generating elements.
Generally, sealed non-aqueous electrolyte cells are apt to be damaged by moisture but it is difficult to completely exclude moisture from the cells in the fabrication process. Therefore, a finished product often includes water which was originally contained, for example, in an organic solvent (a component of the electrolyte) or derived from moisture on the cell members. Water entrapped in the cell reacts with the electrolyte salt and the active material and becomes a direct cause of deterioration in the performance of the cell. Hydrofluoric acid or the like, which is a product of the reaction between cell components and water entrapped within the cell, acts on the sealing parts of the casing, decreasing adhesive strength and therefore the degree of sealing in the parts. This causes a vicious circle in which the decreased degree of sealing allows penetration of moisture and oxygen from the outside of the cell and the penetrating moisture causes a further decrease in the degree of sealing. Finally, there occurs leakage, resulting in the expiration of the cell's life.
It is understood from the above that the decreased degree of sealing is a cause of shortening the service life of the prior art sheet-like sealed non-aqueous electrolyte cells.
As opposed to the prior art cell, the present invention having the above-described structure includes an inorganic oxide fine powder which is not an electrode active material and this fine powder adsorbs and inactivates a trace amount of water which has been present in the cell since completion of the fabrication or moisture which has penetrated into the cell after the fabrication. The fine powder also adsorbs hydrofluoric acid etc. produced by the reaction between the water within the cell and the cell components. Additionally, the inorganic oxide fine powder contained in the cell enhances the viscosity of the cell components thereby restricting scatter and evaporation of the cell components and the reaction products including hydrofluoric acid. With this arrangement, the extent to which hydrofluoric acid and others come in direct contact with the sealing parts of the casing can be reduced, which, in consequence, reduces the possibility of degradation in the sealing parts.
By virtue of the inorganic oxide fine powder favourably functioning as described above, it is possible to prevent a decrease in the performance of the cell directly caused by the reaction between the cell components and water and to prevent a decrease in the degree of sealing caused by the reaction products of the electrolyte salt etc. and water. This leads to an increase in the cycling capability of the cell. In short, the invention has the capability to prevent a decrease in the performance of a cell, which decrease is attributable to the reaction between water penetrated into the cell and the components of the cell.
The sealing parts defined herein are the parts where the opposed seal edges of the laminated material are bonded to each other to seal the cell. Bonding of these edges is usually achieved by thermal fusion but may be achieved by an adhesive agent, because the use of an adhesive agent does not spoil the effects of adding the inorganic oxide fine powder.
In the invention, the inorganic oxide fine powder may be contained in an electrolyte.
The electrolyte of a non-aqueous electrolyte cell is usually composed of an organic solvent and an electrolyte salt such as lithium salt, and the organic solvent contains trace amounts of water while the electrolyte salt is highly reactive with water. In cases where the electrolyte includes the inorganic oxide fine powder, the fine powder absorbs water contained in the organic solvent so that the hydrolysis reaction between the water in the organic solvent and the electrolyte salt can be restrained. Even if reaction products are produced to some extent by hydrolysis, the reaction products will be adsorbed by the inorganic oxide fine powder. In addition, the inorganic oxide fine powder contained in the electrolyte enhances the viscosity of the electrolyte so that scatter and evaporation of the components of the electrolyte and the reaction products can be restrained. Accordingly, when blended with the electrolyte, the inorganic oxide fine powder can work effectively to restrain a decrease in the degree of sealing.
In the invention, the inorganic oxide fine powder may have an average particle diameter of 5 &mgr;m or less.
When the inorganic oxide fine powder has a particle diameter of 5 &mgr;m or less, the total surface area of the fine powder is large enough to provide a strong power for adsorbing water, hydrofluoric acid and others and to favourably increase the viscosity of the electrolyte. This arrangement restrains the degree of sealing from decreasing and as a result, improved cycling capability can be ensured.
In the invention, the inorganic oxide fine powder may be contained in amounts of 0.05 to 20% by weight of the electrolyte.
When the amount of the inorganic oxide fine powder contained in th
Fujii Takanori
Kodama Yasunobu
Maeda Shiori
Naijo Shuichi
Nakane Ikuro
Armstrong Westerman Hattori McLeland & Naughton LLP
Kalafut Stephen
Sanyo Electric Co,. Ltd.
Tsang Susy
LandOfFree
Sealed non-aqueous electrolyte cell having a casing of a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sealed non-aqueous electrolyte cell having a casing of a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sealed non-aqueous electrolyte cell having a casing of a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2860944