JP2005071649A

JP2005071649A - Flat nonaqueous electrolyte secondary battery

Info

Publication number: JP2005071649A
Application number: JP2003209215A
Authority: JP
Inventors: Munehito Hayami; 宗人早見
Original assignee: Toshiba Battery Co Ltd
Current assignee: FDK Twicell Co Ltd
Priority date: 2003-08-28
Filing date: 2003-08-28
Publication date: 2005-03-17
Anticipated expiration: 2023-08-28
Also published as: JP4466905B2

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the rise of internal resistance in a flat nonaqueous electrolyte secondary battery with enhanced service capacity. <P>SOLUTION: In this flat nonaqueous electrolyte secondary battery, a metal negative electrode case also serving as a negative terminal and a metal positive electrode case also serving as a positive electrode terminal are fitted, caulked and sealed through an insulating gasket 2, and a wound electrode group is contained in it so that the service capacity is large. Two sheets metal plate 3 between which a spring 4 is interposed are arranged on the insulating gasket to sandwich an upper part of the gasket so that a current collection part of one electrode of the electrode group and the inside metal plate 3 can surely contact each other with the interposed spring. Thereby, even when the electrode group expands, the contact does not become unstable, and the increment in the internal resistance can be prevented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は放電容量を高めた扁平形非水電解質二次電池に関し、さらに詳しくは内部抵抗の上昇を阻止した上記電池に関する。
【０００２】
【従来の技術】
携帯電話やＰＤＡなどの小型情報端末を中心に使用機器の小型化が加速しており、主電源である二次電池についても小型化を図ることが要求されている。これに対し、扁平形非水電解質二次電池において、小型化した状態でありながら放電容量を高める改良が行われた。すなわち、限られた容積内で正負極対向面積を大きくすることによって放電容量を高めたものであって、例えば電極群を捲回電極群や積層電極群とすることによって、少なくとも３面以上の正極と負極がセパレータを介し対向している正負極対向面を有するようにし、電極群内の正負極対向面積の総和が絶縁ガスケットの開口面積よりも大きくなるようにしたものである。（例えば特許文献１および特許文献２参照。）
【０００３】
しかしながらこれらの電池系においては、正負極電極ケースと電極群の最外周部分が直接接触するため、電池内で電極が動いたり、充放電時に電極群の膨張・収縮が起こると、電気的に接触が悪くなり、電池の内部抵抗が上昇して電池特性が低下するという問題が生じる。
【０００４】
【特許文献１】
特開２００１−０６８１４３号公報
【特許文献２】
特開２００１−０６８１６０号公報
【０００５】
【発明が解決しようとする課題】
本発明は上記の問題を解決するためになされたもので、上記放電容量を高めた扁平形非水電解質二次電池における内部抵抗の上昇や、それに伴う電池特性の低下を防止することを目的とする。
【０００６】
【課題を解決するための手段】
本発明は、上記電池の絶縁ガスケットを改良することによって上記目的を達成したものである。すなわち本発明は、負極端子を兼ねる金属製の負極ケースと、正極端子を兼ねる金属製の正極ケースが絶縁ガスケットを介し嵌合され、さらに加締め加工により封口された封口構造を有し、その内部に少なくともセパレータを介して帯状の正極および負極が捲回されている電極群と、非水電解質とを包含している扁平形非水電解質二次電池において、上記絶縁ガスケットの上部にばねを介した２枚の金属板がガスケット上部を挟むように配置されていることを特徴とする。
【０００７】
本発明は絶縁ガスケットの上部に２枚の金属板を配置してその２枚の金属板でガスケット上部を挟むようにしており、しかも２枚の金属板はその間にばねを配しているので、その圧力によって電極群を安定して保持することができる。またばねを介した２枚の金属板によって電極群の通電部と負極ケースおよび正極ケースとが一体化し、通電性が向上して内部抵抗の上昇を抑制することができる。また、これらが一体化したことによって、生産性も向上する。
【０００８】
本発明が適用される扁平形非水電解質二次電池には種々の外形のものがあるが、例えば負極ケースと正極ケースはそれぞれその外周が２辺以上の直線部とそれらを結ぶ曲線とからなる形状をしているものが挙げられる。
【０００９】
【発明の実施の形態】
以下に本発明の実施例を説明する。
図１は本発明の電池に使用される電極群の斜視図を示す図である。この電極群は、各帯状の正極と負極の間にポリエチレン微多孔膜からなるセパレータを介し渦巻状に捲回し、次に一定方向に捲回電極の中心部の空間がなくなるまで加圧して、電池扁平面に対し水平方向に正負極対向部をもつようにしたものである。この電極群の最外周部の正極および負極には電極作用物質が塗工されておらず、金属製集電板が剥き出しとなっていて通電部を形成している。以下にこの電極群の製造方法について詳細に説明する。
【００１０】
まず、ＬｉＣｏＯ_２１００質量部に対し導電材としてアセチレンブラック５質量部と黒鉛粉末５質量部を加え、結着剤としてポリフッ化ビニリデンを５質量部加え、Ｎ−メチルピロリドンで希釈、混合し、スラリー状の正極合剤を得た。次にこの正極合剤を、正極集電体である厚さ０．０２ｍｍのアルミ箔の片面にドクターブレード法により塗工、乾燥を行い、アルミ箔表面に正極作用物質含有層を形成した。以後、正極作用物質含有層の塗膜厚さが両面で０．１５ｍｍとなるまで塗工、乾燥を繰り返し、両面塗工正極を作製した。次に、この電極体の片面の端から正極ケースに接する部分の作用物質含有層を除去し、アルミ層を剥き出して通電部とし、幅２１ｍｍ、長さ１９０ｍｍ、厚さ０．１５ｍｍの長さに切り出した正極板を作製した。
【００１１】
次に黒鉛化メソフェーズピッチ炭素繊維粉末１００質量部に結着剤としてスチレンブタジエンゴム（ＳＲＢ）とカルボキシメチルセルロース（ＣＭＣ）をそれぞれ２．５質量部を添加し、イオン交換水で希釈、混合し、スラリー状の負極合剤を得た。得られた負極合剤を負極集電体である厚さ０．０２ｍｍの銅箔に作用物質含有層の厚さが０．１５ｍｍとなるように正極の場合と同様に塗工、乾燥を繰り返し実施し、両面塗工負極を作製した。次に、この電極体の片面の端から負極ケースに接する部分の作用物質含有層を除去し、銅層を剥き出して通電部とし、幅２１．５ｍｍ、長さ２１２ｍｍ、厚さ０．１５ｍｍの長さに切り出した負極板を作製した。
【００１２】
次に正負極各通電部面を外周巻き終わり側とし、これら正極と負極の間に厚さ２５μｍのポリエチレン微多孔膜からなるセパレータを介して渦巻き状に捲回し、これを扁平形電池の扁平面に対し水平方向に正負極対向部をもつような方向に加圧した。加圧は捲回電極の中心部の空間がなくなるまで行った。
【００１３】
図２は本発明において使用される絶縁ガスケットの断面図であって、図１のＸ−Ｘ線に沿う断面を示している。図３は絶縁ガスケットのＹ−Ｙ断面図、図４はこの絶縁ガスケットを用い捲回電極群を内包した電池のＸ−Ｘ断面図であり、図５はこの絶縁ガスケットの上面図である。
【００１４】
図２に示すように、この絶縁ガスケットは、ガスケットの内面部２辺が捲回した電極群の湾曲と同じ形になっており、その部分に電極群を嵌め込むと、電極群がしっかりと納まり、ガスケットから抜けなくなる。またガスケットの上部には２枚の金属板３がばね４を介してガスケット上部を挟むように配置しており、電極と電極ケースとの通電の役割を果たしている。また、ばねがあることにより、電極群を一定の圧力で加圧することができ、充放電を繰り返した場合に起こる電極群の膨張を抑えることができる。
【００１５】
本発明のガスケットの材質に関しては、一般的に用いられている電気絶縁性のある樹脂であればよいが、ＰＰＳ（ポリフェニレンスルファイド）などの耐熱性のある樹脂を用いると電極群、絶縁ガスケットおよび電極ケースを一体化して乾燥することができるので、生産性向上の面から好ましい。
また、上部に用いられる金属板の材質については、特に限定するものではないが、電気伝導性のよいものが好ましく、例えばニッケル等が好ましい。
【００１６】
【発明の効果】
以上説明したとおり、本発明において改良した絶縁ガスケットは、正極ケースと負極ケースとの絶縁という本来の役割を保ちつつ、電極群を確実に保持して電池の内部抵抗増加を抑制することができた。したがって本発明によれば、電池特性の向上した扁平形非水電解質二次電池を提供することができる。また、一電極ケース−ガスケット−電極群の一体化が可能であるので、生産性の向上にもつながる。
【図面の簡単な説明】
【図１】本発明の一実施例である電池の電極群を示す斜視図。
【図２】本発明の一実施例である絶縁ガスケットの図１におけるＸ−Ｘ断面図。
【図３】本発明の一実施例である絶縁ガスケットの図１におけるＹ−Ｙ断面図。
【図４】図２および図３に示す絶縁ガスケットを用いた電池のＸ−Ｘ断面図。
【図５】本発明の一実施例である絶縁ガスケットの上面図。
【符号の説明】
１…電極群、２…絶縁ガスケット、３…金属板、４…ばね、５…負極ケース、６…正極ケース。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flat non-aqueous electrolyte secondary battery having an increased discharge capacity, and more particularly to the above-described battery in which an increase in internal resistance is prevented.
[0002]
[Prior art]
Miniaturization of devices used is accelerating mainly on small information terminals such as mobile phones and PDAs, and it is required to reduce the size of secondary batteries as main power sources. On the other hand, the flat nonaqueous electrolyte secondary battery has been improved to increase the discharge capacity while being in a miniaturized state. That is, the discharge capacity is increased by increasing the positive and negative electrode facing area within a limited volume. For example, by forming the electrode group as a wound electrode group or a laminated electrode group, the positive electrode has at least three surfaces. And the negative electrode are opposed to each other with a separator interposed therebetween, and the sum of the positive and negative electrode facing areas in the electrode group is larger than the opening area of the insulating gasket. (For example, refer to Patent Document 1 and Patent Document 2.)
[0003]
However, in these battery systems, the positive and negative electrode case and the outermost peripheral part of the electrode group are in direct contact with each other. This causes a problem that the internal resistance of the battery increases and the battery characteristics deteriorate.
[0004]
[Patent Document 1]
JP 2001-068143 A [Patent Document 2]
JP 2001-068160 A
[Problems to be solved by the invention]
The present invention has been made to solve the above problems, and aims to prevent an increase in internal resistance in the flat nonaqueous electrolyte secondary battery having an increased discharge capacity and a decrease in battery characteristics associated therewith. To do.
[0006]
[Means for Solving the Problems]
The present invention achieves the above object by improving the insulating gasket of the battery. That is, the present invention has a sealing structure in which a metal negative electrode case also serving as a negative electrode terminal and a metal positive electrode case also serving as a positive electrode terminal are fitted via an insulating gasket and further sealed by caulking. In a flat nonaqueous electrolyte secondary battery including an electrode group in which a belt-like positive electrode and a negative electrode are wound at least through a separator and a nonaqueous electrolyte, a spring is interposed above the insulating gasket. Two metal plates are arranged so as to sandwich the upper portion of the gasket.
[0007]
In the present invention, two metal plates are arranged on the top of an insulating gasket, and the upper portion of the gasket is sandwiched between the two metal plates, and a spring is disposed between the two metal plates. Thus, the electrode group can be stably held. Further, the current-carrying part of the electrode group and the negative electrode case and the positive electrode case are integrated by the two metal plates via the spring, so that the electrical conductivity can be improved and the increase in internal resistance can be suppressed. Moreover, productivity is improved by integrating these.
[0008]
There are various types of flat nonaqueous electrolyte secondary batteries to which the present invention is applied. For example, each of the negative electrode case and the positive electrode case has a linear portion having two or more sides and a curve connecting them. The thing which has a shape is mentioned.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Examples of the present invention will be described below.
FIG. 1 is a perspective view of an electrode group used in the battery of the present invention. This electrode group is spirally wound through a separator made of a polyethylene microporous membrane between each strip-like positive electrode and negative electrode, and then pressurized in a certain direction until there is no space in the center of the wound electrode, It has positive and negative electrode facing portions in the horizontal direction with respect to the flat surface. The positive electrode and the negative electrode at the outermost peripheral portion of this electrode group are not coated with an electrode active substance, and a metal current collector plate is exposed to form a current-carrying portion. Hereinafter, a method for producing this electrode group will be described in detail.
[0010]
First, 5 parts by mass of acetylene black and 5 parts by mass of graphite powder are added as conductive materials to 100 parts by mass of LiCoO ₂ , 5 parts by mass of polyvinylidene fluoride is added as a binder, diluted and mixed with N-methylpyrrolidone, slurry. A positive electrode mixture was obtained. Next, this positive electrode mixture was applied to one side of a 0.02 mm thick aluminum foil as a positive electrode current collector by a doctor blade method and dried to form a positive electrode active substance-containing layer on the aluminum foil surface. Thereafter, coating and drying were repeated until the coating film thickness of the positive electrode active material-containing layer became 0.15 mm on both sides, to produce a double-sided coated positive electrode. Next, the part containing the active substance in contact with the positive electrode case is removed from one end of the electrode body, and the aluminum layer is peeled off to form a current-carrying part, having a width of 21 mm, a length of 190 mm, and a thickness of 0.15 mm. A cut-out positive electrode plate was produced.
[0011]
Next, 2.5 parts by mass of styrene butadiene rubber (SRB) and carboxymethyl cellulose (CMC) as binders are added to 100 parts by mass of graphitized mesophase pitch carbon fiber powder, diluted with ion-exchanged water, mixed, and slurry A negative electrode mixture was obtained. The obtained negative electrode mixture was repeatedly applied and dried in the same manner as in the case of the positive electrode so that the thickness of the active substance-containing layer was 0.15 mm on a 0.02 mm thick copper foil as a negative electrode current collector. Then, a double-sided coated negative electrode was produced. Next, the part containing the active substance in contact with the negative electrode case is removed from one end of the electrode body, and the copper layer is peeled off to form a current-carrying part. The length is 21.5 mm, length 212 mm, and thickness 0.15 mm. A negative electrode plate cut out was prepared.
[0012]
Next, each energization part surface of the positive and negative electrodes is set as the outer circumferential winding end side, and is wound between the positive electrode and the negative electrode in a spiral shape through a separator made of a polyethylene microporous film having a thickness of 25 μm. On the other hand, the pressure was applied in such a direction as to have a positive and negative electrode facing portion in the horizontal direction. Pressurization was performed until there was no space in the center of the wound electrode.
[0013]
FIG. 2 is a cross-sectional view of the insulating gasket used in the present invention, and shows a cross section taken along line XX of FIG. 3 is a YY sectional view of the insulating gasket, FIG. 4 is an XX sectional view of a battery using the insulating gasket and including a wound electrode group, and FIG. 5 is a top view of the insulating gasket.
[0014]
As shown in FIG. 2, this insulating gasket has the same shape as the curve of the electrode group in which the two inner side portions of the gasket are wound, and when the electrode group is fitted in that portion, the electrode group is firmly stored. , It will not come out of the gasket. In addition, two metal plates 3 are arranged on the upper part of the gasket so as to sandwich the upper part of the gasket through the spring 4 and play a role of energization between the electrode and the electrode case. Further, the presence of the spring makes it possible to pressurize the electrode group at a constant pressure, and to suppress the expansion of the electrode group that occurs when charging and discharging are repeated.
[0015]
As for the material of the gasket of the present invention, any generally used electrically insulating resin may be used. However, when a heat resistant resin such as PPS (polyphenylene sulfide) is used, an electrode group, an insulating gasket and The electrode case can be integrated and dried, which is preferable from the viewpoint of improving productivity.
Further, the material of the metal plate used in the upper part is not particularly limited, but a material having good electrical conductivity is preferable, for example, nickel or the like is preferable.
[0016]
【The invention's effect】
As described above, the insulating gasket improved in the present invention can maintain the original role of insulation between the positive electrode case and the negative electrode case, and can reliably hold the electrode group and suppress an increase in the internal resistance of the battery. . Therefore, according to the present invention, a flat nonaqueous electrolyte secondary battery having improved battery characteristics can be provided. In addition, since one electrode case-gasket-electrode group can be integrated, productivity is improved.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a battery electrode group according to an embodiment of the present invention.
2 is a cross-sectional view taken along line XX in FIG. 1 of an insulating gasket according to an embodiment of the present invention.
3 is a cross-sectional view taken along line YY in FIG. 1 of an insulating gasket according to an embodiment of the present invention.
4 is an XX cross-sectional view of a battery using the insulating gasket shown in FIGS. 2 and 3. FIG.
FIG. 5 is a top view of an insulating gasket according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Electrode group, 2 ... Insulating gasket, 3 ... Metal plate, 4 ... Spring, 5 ... Negative electrode case, 6 ... Positive electrode case.

Claims

A metal negative electrode case that also serves as a negative electrode terminal and a metal positive electrode case that also serves as a positive electrode terminal are fitted via an insulating gasket and further sealed by caulking, and at least a separator is interposed in the interior. In a flat nonaqueous electrolyte secondary battery including an electrode group in which strip-shaped positive and negative electrodes are wound and a nonaqueous electrolyte, two metal plates with springs above the insulating gasket Is arranged so as to sandwich the upper portion of the gasket.

2. The flat nonaqueous electrolyte secondary battery according to claim 1, wherein each of the negative electrode case and the positive electrode case has a shape in which an outer periphery is formed by a straight portion having two or more sides and a curve connecting them.