Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-04-10
2003-09-09
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S162000, C429S161000, C429S127000, C429S128000, C429S300000, C429S301000, C429S302000, C429S303000
Reexamination Certificate
active
06617074
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a lithium ion polymer secondary battery composed of a lamination of a positive-electrode sheet, a negative-electrode sheet, and a polymer electrolyte layer provided therebetween, and to a gelatinous polymer electrolyte for sheet batteries which is used in the polymer electrolyte layer.
2. Description of the Related Art
In recent years, thin batteries have been in increasing demand with the spread of portable devices, such as video cameras and notebook personal computers. A typical thin battery is a lithium ion polymer secondary battery which is formed by laminating a positive-electrode sheet and a negative-electrode sheet. The positive-electrode sheet is prepared by forming an active material on a surface of a positive-electrode collector foil, and the negative-electrode sheet is prepared by forming an active material on a surface of a negative-electrode collector foil. A polymer electrolyte layer is disposed between the active material on the positive-electrode sheet and the active material on the negative-electrode sheet. The positive-electrode collector foil and the negative-electrode collector foil are provided with a positive-electrode terminal and a negative-electrode terminal, respectively, from which a current generated by a potential between these two active materials is extracted. Such a laminate is hermetically packed to form a lithium ion polymer secondary battery. The positive-electrode terminal and the negative-electrode terminal are led out from the package and are used as terminals to supply a predetermined potential from the lithium ion polymer secondary battery.
Polymer solid electrolytes using ion-conducting polymers have been used as electrolytes for such sheet batteries in order to prevent leakage of electrolyte solutions. In polymer solid electrolytes, electrolytes are homogeneously dissolved into polymers. The polymer solid electrolytes are flexible and are suitable for use in sheet batteries. A problem of the polymer solid electrolytes is significantly low ion conductivity compared to electrolyte solutions. Thus, batteries using the polymer solid electrolytes exhibit low charging current densities and high electrical resistance.
In order to solve such a problem, Japanese Unexamined Patent Publication No. 10-321210 discloses a separator for nonaqueous batteries. In this separator, an electrolyte solution having high ion conductivity is impregnated in open pores formed on two surfaces of a membrane electrolyte. As a result, ion conductivity of batteries is improved and the batteries maintain high current densities.
However, the areas of the positive-electrode sheet and the negative-electrode sheet must be increased in order to increase the discharge capacity of the lithium ion polymer secondary batteries. If the areas of these sheets are simply increased, the resulting batteries have large areas compared to the thicknesses thereof and will not be readily used. When the sheets are folded to solve such a problem, deflection occurs between the positive-electrode sheet and the negative-electrode sheet at folded portions, so that these sheets become detached from the electrolyte layer. Thus, the effective surface area of the interface between the electrodes and the electrolyte is reduced, resulting in a decreased discharge capacity and deterioration of discharge capacity characteristics after a number of discharge-charge cycles due to increased internal resistance. When the deflection is significant, direct contact between the positive-electrode sheet and the negative-electrode sheet, so-called “internal short-circuiting” will occur at the deflected portion.
Since the polymer electrolyte layer disposed between the two active materials is relatively thin, these two active materials or collector foils, which are laminated at ends of the polymer electrolyte layer, may come into contact with each other by misalignment of lamination or by an external force applied to the laminate, resulting in internal short-circuiting.
As described above, the separator for nonaqueous batteries has open pores on the two surfaces thereof. If the separator insufficiently comes into contact with the positive-electrode sheet or the negative-electrode sheet, the electrolyte solution impregnated in these pores may leak. Moreover, intercalate/deintercalate cycles of ions in the electrodes cause a change in volume, and thus a gap may be formed between the separator and the positive- and/or negative-electrode sheets. Such a gap also causes leakage of the electrolyte solution. Because the sheet battery is bent according to the shape of the space for the battery in some cases, a gap may be formed between the between the separator and the positive- and/or negative-electrode sheets due to the stress during bending, resulting in leakage of the electrolyte solution. In addition, gas is produced in the battery during the charging/discharging cycles. When the gas is trapped on the surfaces of the positive and/or negative electrodes, the gas precludes ion mobility in the battery. Thus, the effective surface area at the interface between the electrodes and the electrolyte decreases, resulting in increased internal resistance and deterioration of discharge capacity characteristics after a number of discharge-charge cycles.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a lithium ion polymer secondary battery which does not cause internal short-circuiting, and which has a large discharge capacity and improved discharge capacity characteristics after a number of discharge-charge cycles.
It is another object of the present invention to provide a lithium ion polymer secondary battery which does not cause internal short-circuiting without a decreased discharge capacity.
It is still another object of the present invention to provide a gelatinous polymer electrolyte for sheet batteries, which is free from leakage of an electrolyte solution, which has improved discharge capacity characteristics after a number of discharge-charge cycles, and which exhibits high ion conductivity.
According to a first aspect of the present invention, a lithium ion polymer secondary battery includes a laminate of a strip of positive-electrode sheet having a positive-electrode collector foil and a first active material provided on the positive-electrode collector foil, a plurality of negative-electrode sheets, each including a negative-electrode collector foil and a second active material provided on the negative-electrode collector foil, and at least one polymer electrolyte layer. The polymer electrolyte layer is provided on at least one surface of the first active material, the strip of positive-electrode sheet is fan-folded at least one time, each of the negative-electrode sheets has a predetermined area corresponding to the area of flat portions of the folded positive-electrode sheet and is interposed between the flat portions of the folded positive-electrode sheet, and the polymer electrolyte layer is interposed between the first active material and the second active material.
According to a second aspect of the present invention, a lithium ion polymer secondary battery includes a laminate of a strip of negative-electrode sheet having a negative-electrode collector foil and a second active material provided on the negative-electrode collector foil, a plurality of positive-electrode sheets, each including a positive-electrode collector foil and a first active material provided on the positive-electrode collector foil, and at least one polymer electrolyte layer. The polymer electrolyte layer is provided on at least one surface of the second active material, the strip of negative-electrode sheet is fan-folded at least one time, each of the positive-electrode sheets has a predetermined area corresponding to the area of flat portions of the folded negative-electrode sheet and is interposed between the flat portions of the folded negative-electrode sheet, and the polymer electrolyte layer is interposed
Higami Akihiro
Kobayashi Tadashi
Minakuchi Akio
Takeuchi Sawako
Watarai Yusuke
Martin Angela J.
Mitsubishi Materials Corporation
Ryan Patrick
LandOfFree
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