Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2001-03-23
2004-01-27
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C029S623300, C429S094000
Reexamination Certificate
active
06682853
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
The present application claims priority to Japanese Application No. P2000-081577 filed Mar. 6, 2000 which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nonaqueous-electrolyte secondary battery and a method of manufacturing the same, more particularly, to a lithium ion battery such as a lithium ion polymer secondary battery having a gel-type or plasticizing macromolecular electrolyte layer.
2. Description of the Related Art
In recent years, accompanying by a situation that portable small electric equipment such as small, lightweight mobile phones, or portable computers, has been popularized, secondary batteries having small, reliable output characteristics and capable of longtime-use by re-charging many times such as nickel-cadmium batteries, nickel-metal hydride batteries and lithium ion batteries have been studied and developed vastly as an electric source for supplying electric power to drive the electric equipment.
Among the secondary batteries, the lithium ion secondary battery has characteristics capable of outputting stable electric power despite its being small, lightweight and thin in size, and the battery has been studied and developed for the purpose of being employed as a foldable secondary battery by taking advantage of suitable structural characteristics for its thin size. For realizing a thinner size or a foldable shape as described above, it is suggested that a technique employ a gel-type electrolyte including plasticizer, to achieve flexibility, and a technique which employs macromolecular solid electrolyte, in which a lithium salt is dissolved in a macromolecular material, is used.
With a gel-type electrolyte or macromolecular solid electrolyte, excellent characteristics as a so-called dry cell, which is free of leakage unlike the case of using liquid-type electrolyte. However, there is a tendency such that enough electrical contact between positive and negative electrodes, can not be attained by only laminating the positive and negative electrodes and electrolyte corresponding to those electrodes. This is attributed to the reason that the gel-type, or macromolecular solid electrolyte does not have flowability the same as the liquid-type electrolyte do, so that the electrolyte and the electrodes does not contact hermetically.
In the case that a satisfactory electrical contact between the electrodes and the electrolyte can not be achieved, contact resistance inside the battery increases, thereby increasing electrical loss, which is undesirable for battery characteristics. In the case that a sufficient contact area between the electrolyte and the electrodes can not be achieved, desired ion mobility can not be gained therebetween, which decreases battery capacity less than the ordinal capacity. Accordingly, in the lithium ion battery employing the gel-type electrolyte or the macromolecular solid electrolyte as the electrolyte, it is preferable that electrolyte layers and active material layers of the electrodes contact hermetically in order to realize excellent electrical contact, which reduces the inside resistance to a minimum, and obtains the best battery capacity.
For obtaining excellent electrical contact between the electrolyte layers and the active material layers of the electrodes, it is suggested that a technique is used for changing parts where the electrolyte layers and the active material layers do not contact, or where the electrolyte layers and the active material layers do not contact partly, such that desirable contact is achieved by applying pressure from the outside, when laminating the electrolyte layers and the active material layers of the electrodes in order to form a laminating structure comprising contents inside the battery.
An invention using positive mixed materials with doped macromolecular solid electrolyte to positive electrode active layers, is suggested in Laid Open JP. No. Hei 2 (1990)-40867, for instance. This is a technique such that part of a macromolecular solid electrolyte is mixed with the positive electrode active material layers, which improves electrical contact between the macromolecular solid electrolyte and the positive electrode active material layers. However, in the case that such technique is employed for improving contact from the chemical point of view, if a satisfactory structural (physical) contact between the electrolyte layers and the electrodes is not achieved, electrical contact therebetween tends to be poor. For this reason, pressure is desirable to be applied to the laminating structure from the outside in order to gain sufficient structural contact.
Recently, as for an appropriate battery for cellular phones, portable computers and portable game machines, which has been popularized dramatically, a thin lithium ion battery has been noticed. For realizing the best appropriate thin lithium ion battery for this use, it is suggested that a structure is made in a manner that film-like electrolyte or foil-like electrodes and so on are laminated to form a laminating structure inside the battery, or are further rolled and compressed, and accommodated into film-like or thin-board like package members.
In the above-mentioned method, however, when the electrolyte layers and the electrodes are laminated and is applied pressure from the outside, a position exposed toward the outside without being covered with the electrolyte layers at an end of either the positive electrode or the negative electrode is pressurized or folded with pressure generated at this moment,to contact the other electrode, which causes short circuit between both electrodes.
Particularly, in the thin lithium ion battery, when a user adds strong force in order to put the battery into the main body of electrical equipment after manufacturing, or drops, or applies pressure to the battery, pressure is likely to be applied to the laminating structure of the battery, and in the case of the foldable thin battery, pressure attributed to that folded shape is applied to the laminating structure. As a result of this, in ends of the electrodes, specifically, parts exposed toward the outside without being covered with the electrolyte layers, contact the other electrode, thereby causing a short circuit between both electrodes.
In addition, in the lithium ion battery including the gel-type electrolyte layer, which has high flowability and poor strength, inside the laminating structure, when pressure is applied to the laminating structure from the outside, the gel-type electrolyte layer is likely to be deformed physically, thereby the ends of one electrode tends to contact the other electrode.
With the reason that excellent throughput achieves cost reduction, the positive electrode, the negative electrode and the lead electrode are stamped out (a cutting process) with a metal mold and so on, however, a protrusion such as cutting burr or curling is likely to occur in cutting ends thereon. In the case that such a protrusion occurs in one electrode, when manufacturing or using the battery, the protrusion contacts the other electrode, thereby causing a short circuit.
As another case, internal stress is generated in the electrolyte or the electrodes, which changes positions of the ends of the electrode due to seclusion change or temperature variation, thereby causing a short circuit between the both electrodes.
In the case of instigating a short circuit between both electrodes as mentioned above, effective electromotive force or battery capability of the battery seriously decreases, and much worse, no electric power output results.
SUMMARY OF THE INVENTION
The invention has been achieved in consideration of the above problems and its object is to provide a lithium ion battery capable of preventing a short circuit between both electrodes when manufacturing or using the battery as a product, and a method of manufacturing the same.
A nonaqueous-electrolyte secondary battery according to the present invention inc
Kimijima Takaaki
Sugiyama Tsuyoshi
Parsons Thomas H.
Ryan Patrick
Sonnenschein Nath & Rosenthal LLP
LandOfFree
Nonaqueous electrolyte secondary battery and method of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nonaqueous electrolyte secondary battery and method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nonaqueous electrolyte secondary battery and method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3228935