JP4827112B2

JP4827112B2 - Flat non-aqueous electrolyte secondary battery

Info

Publication number: JP4827112B2
Application number: JP2000231653A
Authority: JP
Inventors: 広隆酒井; 宗人早見; 正美鈴木
Original assignee: Hitachi Maxell Energy Ltd
Current assignee: Hitachi Maxell Energy Ltd
Priority date: 2000-07-31
Filing date: 2000-07-31
Publication date: 2011-11-30
Anticipated expiration: 2020-07-31
Also published as: JP2002042744A

Description

【０００１】
【発明の属する技術分野】
本発明は重負荷放電特性に優れた扁平形非水電解質二次電池に関する。
【０００２】
【従来の技術】
正極作用物質にＭｎＯ₂やＶ₂Ｏ₅などの金属酸化物、あるいはフッ化黒鉛などの無機化合物、あるいはポリアニリンやポリアセン構造体などの有機化合物を用い、負極に金属リチウム、あるいはリチウム合金、あるいはポリアセン構造体などの有機化合物、あるいはリチウムを吸蔵、放出可能な炭素質材料、あるいはチタン酸リチウムやリチウム含有珪素酸化物のような酸化物を用い、電解質にプロピレンカーボネート、エチレンカーボネート、ブチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、メチルエチルカーボネート、ジメトキシエタン、γ−ブチルラクトンなどの非水溶媒にＬｉＣｌＯ₄、ＬｉＰＦ₆、ＬｉＢＦ₄、ＬｉＣＦ₃ＳＯ₃、ＬｉＮ（ＣＦ₃ＳＯ₂）₂、ＬｉＮ（Ｃ₂Ｆ₅ＳＯ₂）₂等の支持塩を溶解した非水電解質を用いたコイン形やボタン形などの扁平形非水電解質二次電池は、放電電流が数〜数十μＡ程度の軽負荷で放電が行われるＳＲＡＭやＲＴＣのバックアップ用電源や電池交換不要腕時計の主電源といった用途に用いられている。
【０００３】
これら従来のコイン形やボタン形などの扁平形非水電解質二次電池は製造が簡便であり、量産性に優れ、長期信頼性や安全性に優れるという長所をもっている。また、構造が簡便であることから小型化が可能である。
【０００４】
しかし、その反面、電極面積が制限されるため中〜重負荷放電に不可能であり、小型電池のニーズが大きい携帯電話やＰＤＡなどの情報端末の主電源としては採用することができなかった。
【０００５】
【発明が解決しようとする課題】
そこで、本発明者らは種々検討した結果、電池形状は変更せず、電極面積を大きくすることで重負荷放電が可能なコイン形やボタン形の扁平形非水電解質二次電池を提供するものである。すなわち、扁平形電池の扁平面に垂直な方向の断面をみた場合、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電極群を配し、かつ電極群内の正負極対向面積の総和を絶縁ガスケットの開口面積よりも大きくすることで重負荷放電特性を著しく向上させた扁平形非水電解質二次電池を提供することができたが、大電流放電時に電圧が低下するという不具合があった。
【０００６】
この電圧低下の原因は電極群と電池容器の接触にあることが分かった。このような非水電解質二次電池では、充放電に伴う作用物質の体積変化が大きく、放電時に電極群が収縮して電池容器との接触が保てなくなり、内部抵抗の増加につながるためである。
【０００７】
従来型の円筒形や角形の非水電解質二次電池では電極群からタブ端子を引き出し、電気容器等の外部端子に溶接することにより電気的接続を確保している。そのため電極群の体積変化の際にも接触不良による内部抵抗の上昇は起こらなかった。
【０００８】
しかし、扁平形の電池では電極ケースと電極群は接触により電気的接続をとっているため、電極群の収縮時には内部抵抗が上昇することになる。従来はエキスパンドメタルなどの金属網を電気容器内面に抵抗溶接することにより電極群と電気容器との接触を確保することで上記の内部抵抗の上昇を押さえていたが、電池構成部品点数が増加することと、正極ケースについては抵抗溶接部分から腐食し漏液事故が発生する恐れがあった。
本発明は上記問題を解消するためになされたもので、優れた放電性能を有する扁平形非水電解質二次電池を提供することを目的とするものである。
【０００９】
【課題を解決するための手段】
上記課題を解決するために、本発明の扁平形非水電解質二次電池では正極ケースと負極ケースのいずれか一方の内側に、もしくは正極ケースと負極ケースの両者の内側に凹凸を設けることにより、放電時に電極群が収縮しても電池容器との接触は保たれるように構成したものである。
【００１０】
従来のペレット状に成形した作用物質を用いた扁平型一次電池では、電池ケースと外部端子の接触抵抗を軽減するために電池ケース外面にエンボス加工のような凹凸を設けた例は知られている。
【００１１】
本発明のように電池ケース内面に凹凸を設けて電極群との接触を向上させた例はなかった。またペレット状に成形した作用物質は、それ自身の抵抗値が１０〜５０Ωと高く大電流放電は不可能であり、そのため接触抵抗値は問題とされなかった。しかし、本発明の電極群は表面積が大きく、内部抵抗が低くなるため、電池全体の内部抵抗に対して接触抵抗の占める比重が大きく、大電流放電を行うにはこの接触抵抗値の改善が必要であるということに気付いた。また、ペレット状の扁平形一次電池の場合は、放電のみ行われるため充放電に伴う作用物質の体積変化が問題とならなかった。
【００１２】
なお、凹凸を突起形状で正負極ケース内部に設けた場合、突起寸法としては径φが０．２〜２．０ｍｍ、高さが０．０１〜０．５０ｍｍの範囲にあれば十分な効果が得られる。突起の個数は単数であっも複数であってもよい。
【００１３】
【発明の実施の形態】
以下、本発明の実施例及び比較例について詳細に説明する。
（実施例１）
本発明の実施例１の電池の製造方法を図１の断面図を参照して説明する。
まず、ＬｉＣｏＯ₂１００質量部に対し、導電剤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５質量部を加え、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のアルミ箔の両面にドクターブレード法により塗工、乾燥を行い、正極作用物質含有層の塗膜厚さが両面で０．１５ｍｍの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１０ｍｍ部分の作用物質含有層を除去し、アルミ層を剥き出しにし通電部とし、幅１５ｍｍ，長さ１２０ｍｍに切り出し正極板２を作製した。
【００１４】
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（ＳＢＲ）とカルボキシメチルセルロース（ＣＭＣ）をそれぞれ２．５質量部添加し、イオン交換水で希釈、混合してスラリー状の負極合剤を得た。この負極合剤を負極集電体である厚さ０．０２ｍｍの銅箔両面にドクターブレード法により塗工、乾燥を行い、作用物質含有層の塗膜厚さが０．１５ｍｍの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１０ｍｍ部分の作用物質含有層を除去し、銅層を剥き出しにし通電部とし、幅１５ｍｍ，長さ１２０ｍｍに切り出し負極板４を作製した。
【００１５】
次に、正負極板通電部面を外周巻き終り側とし、これら正極板と負極板の間に厚さ２５μｍのポリエチレン微多孔膜からなるセパレータ３を介して渦巻状に捲回し、扁平形電池の扁平面に対し水平方向に正負極対抗部を持つよう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偏平状の電極群を作製した。
【００１６】
作製した電極群を８５℃で１２ｈ乾燥した後、絶縁ガスケット６を一体化した負極金属ケース１の内底面に電極群の負極板の作用物質含有層除去部が接するように配置し、エチレンカーボネートとメチルエチルカーボネートを体積比１：１の割合で混合した溶媒に支持塩としてＬｉＰＦ₆を１ｍｏｌ／ｌの割合で溶解せしめた非水電解質を注液し、さらに電極群の正極板の作用物質含有層除去部に接するようにステンレス製の正極ケース５を嵌合し、上下反転後、正極ケースに径方向および高さ方向の加締め加工を実施し、封口した。前記負極ケース１中央部には容器外面から内面に向けてφ１．０ｍｍ、高さ０．２ｍｍの突起１ａが設けられている。これにより厚さ３ｍｍ、直径φ２４．５ｍｍの実施例１の扁平形非水電解質二次電池を５０個製作した。
【００１７】
（実施例２）
負極ケースに突起を設けず、正極ケースの中央部に容器外面から内面に向けて１．０ｍｍ、高さ０．２ｍｍの突起１ａが設けられている以外は実施例１と同様の、図１に示す構造の電池を５０個作製した。
【００１８】
（実施例３）
正極ケースと負極ケース両者の中央部に容器外面から内面に向けてφ１．０ｍｍ、高さ０．２ｍｍの突起１ａが設けられている以外は実施例１と同様の、図１に示す構造の電池を５０個作製した。
【００１９】
（比較例１）
突起のない負極ケースを用いたこと以外は実施例１と同様の、図１に示す構造の電池を５０個作製した。
【００２０】
これらの電池について、４．２Ｖ、３ｍＡの定電流定電圧で、４８時間初充電を実施後、１５０ｍＡの定電流で３．０Ｖまで放電を実施し、放電容量を求めた。この試験結果を表１に示す。
【００２１】
【表１】

【００２２】
この表１から本実施例の電池に対し、比較例の電池では著しく放電容量が劣っている。これは放電時に電極が収縮することにより電極群と電池容器の接触が不安定になり、内部抵抗が上昇したためである。本実施例のように突起を設ければ、接触が確保されるため、このような容量低下は生じない。実施例１、２、３の比較から、突起を正極側、負極側のいずれか、もしくは両者に設けた場合でも効果は同じであることが分かる。したがって、本発明によれば、優れた放電性能を示す扁平形非水電解質二次電池を得ることができる。
なお、本発明の実施例は、ケース内面に突起を１つ設けた場合で説明したが、エンボス加工のような凹凸をケース内面に施した場合でも同様の効果が得られる。
【００２３】
また、非水電解質に非水溶液を用いた扁平形非水電解質二次電池を用いて説明したが、非水電解質にポリマー電解質を用いたポリマー二次電池や固体電解質を用いた固体電解質二次電池についても同様の効果が得られる。さらに、樹脂製セパレータの代わりにポリマー薄膜や固体電解質膜を用いることも可能である。
【００２４】
電池形状については正極ケースのかしめ加工により封口するコイン形非水電解質二次電池を用いて説明したが、正負極電極を入れ替え、負極ケースのかしめ加工により封口することも可能である。さらに、電池形状についても円形のコイン型である必要はなく小判形、角形などの特殊形状を有する扁平形非水電解質二次電池においても適用可能である。
【００２５】
【発明の効果】
以上説明したように、本発明によれば、優れた放電性能の扁平形非水電解質二次電池を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例１の電池の断面図。
【図２】図１の負極ケースの上面図。
【符号の説明】
１…負極ケース、１ａ…負極ケース突起部、２…正極板、３…セパレータ、４…負極板、５…正極ケース、６…絶縁ガスケット。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flat nonaqueous electrolyte secondary battery excellent in heavy load discharge characteristics.
[0002]
[Prior art]
A metal oxide such as MnO ₂ or V ₂ O ₅ , an inorganic compound such as fluorinated graphite, or an organic compound such as polyaniline or a polyacene structure is used as the positive electrode active material, and metal lithium, lithium alloy, or polyacene is used as the negative electrode Organic compounds such as structures, carbonaceous materials capable of occluding and releasing lithium, or oxides such as lithium titanate and lithium-containing silicon oxide, and propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate as electrolytes LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ ) in a non-aqueous solvent such as dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, and γ-butyl lactone. soluble support salt such as SO ₂₎ ₂ A flat non-aqueous electrolyte secondary battery such as a coin type or button type using a non-aqueous electrolyte is a backup power source or battery for SRAM or RTC that discharges with a light load with a discharge current of several to several tens of μA. It is used for applications such as the main power source of wristwatches that do not require replacement.
[0003]
These conventional coin-type and button-type flat non-aqueous electrolyte secondary batteries have the advantages of being easy to manufacture, excellent in mass productivity, and excellent in long-term reliability and safety. Further, since the structure is simple, the size can be reduced.
[0004]
However, on the other hand, the electrode area is limited, so that it is impossible for medium to heavy load discharge, and it cannot be used as a main power source for information terminals such as mobile phones and PDAs that have a large need for small batteries.
[0005]
[Problems to be solved by the invention]
Accordingly, as a result of various studies, the present inventors provide a coin-type or button-type flat non-aqueous electrolyte secondary battery capable of heavy load discharge by increasing the electrode area without changing the battery shape. It is. That is, when a cross section in a direction perpendicular to the flat surface of the flat battery is viewed, an electrode group having positive and negative electrode facing surfaces in which at least three positive electrodes and a negative electrode face each other with a separator interposed therebetween, and A flat nonaqueous electrolyte secondary battery with significantly improved heavy load discharge characteristics can be provided by making the sum of the positive and negative electrode opposing areas larger than the opening area of the insulating gasket. There was a problem that decreased.
[0006]
It was found that the cause of this voltage drop was the contact between the electrode group and the battery container. In such a non-aqueous electrolyte secondary battery, the volume change of the active substance accompanying charging / discharging is large, and the electrode group contracts at the time of discharging, so that the contact with the battery container cannot be maintained, leading to an increase in internal resistance. .
[0007]
In a conventional cylindrical or rectangular nonaqueous electrolyte secondary battery, electrical connection is ensured by pulling out a tab terminal from an electrode group and welding it to an external terminal such as an electric container. Therefore, even when the volume of the electrode group was changed, the internal resistance did not increase due to poor contact.
[0008]
However, in a flat battery, since the electrode case and the electrode group are electrically connected by contact, the internal resistance increases when the electrode group contracts. Conventionally, the increase in internal resistance was suppressed by securing the contact between the electrode group and the electric container by resistance-welding a metal net such as expanded metal to the inner surface of the electric container, but the number of battery components increased. In addition, the positive electrode case was corroded from the resistance welded portion, and there was a risk of a liquid leakage accident.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a flat nonaqueous electrolyte secondary battery having excellent discharge performance.
[0009]
[Means for Solving the Problems]
In order to solve the above problem, in the flat nonaqueous electrolyte secondary battery of the present invention, by providing irregularities inside either the positive electrode case and the negative electrode case, or both the positive electrode case and the negative electrode case, Even when the electrode group contracts during discharge, the contact with the battery container is maintained.
[0010]
In a flat type primary battery using an active substance formed into a conventional pellet shape, an example in which unevenness such as embossing is provided on the outer surface of the battery case is known in order to reduce the contact resistance between the battery case and the external terminal. .
[0011]
There was no example in which the contact with the electrode group was improved by providing irregularities on the inner surface of the battery case as in the present invention. In addition, the active substance formed into a pellet has a high resistance value of 10 to 50Ω and cannot be discharged with a large current, so that the contact resistance value is not a problem. However, since the electrode group of the present invention has a large surface area and low internal resistance, the specific gravity of the contact resistance is large with respect to the internal resistance of the entire battery, and it is necessary to improve the contact resistance value in order to perform a large current discharge. I realized that. Further, in the case of a pellet-shaped flat primary battery, only the discharge is performed, so the volume change of the active substance accompanying charging / discharging has not been a problem.
[0012]
In addition, when unevenness is provided in the positive and negative electrode cases in the shape of protrusions, sufficient effects can be obtained if the diameter φ is in the range of 0.2 to 2.0 mm and the height is in the range of 0.01 to 0.50 mm. can get. The number of protrusions may be singular or plural.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, examples and comparative examples of the present invention will be described in detail.
Example 1
A battery manufacturing method according to Example 1 of the present invention will be described with reference to the cross-sectional view of FIG.
First, to 100 parts by mass of LiCoO ₂ , 5 parts by mass of acetylene black and 5 parts by mass of graphite powder are added as a conductive agent, 5 parts by mass of polyvinylidene fluoride is added as a binder, and diluted and mixed with N-methylpyrrolidone. A slurry-like positive electrode mixture was obtained. Next, this positive electrode mixture was applied to both sides of a 0.02 mm thick aluminum foil as a positive electrode current collector by a doctor blade method and dried, so that the coating thickness of the positive electrode active material-containing layer was on both sides. A 0.15 mm double-coated positive electrode was produced. Next, the active substance-containing layer of 10 mm was removed from the end of one side of the electrode body, and the aluminum layer was stripped to form a current-carrying part, which was cut into a width of 15 mm and a length of 120 mm to produce the positive electrode plate 2.
[0014]
Next, 2.5 parts by mass of styrene butadiene rubber (SBR) 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 slurried. A negative electrode mixture was obtained. This negative electrode mixture is applied to both sides of a 0.02 mm thick copper foil, which is a negative electrode current collector, by a doctor blade method and dried, and a double-sided coated negative electrode having an active substance-containing layer coating thickness of 0.15 mm Was made. Next, the active substance containing layer of 10 mm portion was removed from the end of one side of this electrode body, and the copper layer was stripped to form a current-carrying part, which was cut into a width of 15 mm and a length of 120 mm to produce the negative electrode plate 4.
[0015]
Next, the positive and negative electrode plate current-carrying surface is set to the end of the outer periphery winding, and is wound spirally between the positive electrode plate and the negative electrode plate with a separator 3 made of a polyethylene microporous film having a thickness of 25 μm. On the other hand, the flat electrode group was produced by applying pressure so that the space in the central part of the wound electrode disappears in a certain direction so as to have the positive and negative electrode opposing parts in the horizontal direction.
[0016]
After the produced electrode group was dried at 85 ° C. for 12 hours, the active substance-containing layer removing portion of the negative electrode plate of the electrode group was in contact with the inner bottom surface of the negative electrode metal case 1 integrated with the insulating gasket 6, and ethylene carbonate and A non-aqueous electrolyte prepared by dissolving LiPF ₆ as a supporting salt in a ratio of 1 mol / l in a solvent in which methyl ethyl carbonate is mixed at a volume ratio of 1: 1 is injected, and further, an active substance-containing layer of the positive electrode plate of the electrode group A stainless steel positive electrode case 5 was fitted so as to be in contact with the removal portion, and after turning upside down, the positive electrode case was subjected to caulking in the radial direction and the height direction and sealed. A projection 1a having a diameter of 1.0 mm and a height of 0.2 mm is provided at the central portion of the negative electrode case 1 from the outer surface to the inner surface of the container. As a result, 50 flat nonaqueous electrolyte secondary batteries of Example 1 having a thickness of 3 mm and a diameter of 24.5 mm were manufactured.
[0017]
(Example 2)
FIG. 1 is the same as in Example 1 except that the negative electrode case is not provided with a protrusion, and a protrusion 1a having a height of 0.2 mm and a height of 1.0 mm is provided from the outer surface to the inner surface of the positive electrode case. 50 batteries having the structure shown were manufactured.
[0018]
(Example 3)
The battery having the structure shown in FIG. 1 is the same as that of Example 1 except that a projection 1a having a diameter of 1.0 mm and a height of 0.2 mm is provided from the outer surface to the inner surface of the positive electrode case and the negative electrode case. 50 were produced.
[0019]
(Comparative Example 1)
50 batteries having the structure shown in FIG. 1 were produced in the same manner as in Example 1 except that a negative electrode case without protrusions was used.
[0020]
About these batteries, after carrying out 48 hours initial charge with the constant current constant voltage of 4.2V and 3mA, it discharged to 3.0V with the constant current of 150mA, and calculated | required the discharge capacity. The test results are shown in Table 1.
[0021]
[Table 1]

[0022]
From Table 1, the discharge capacity of the battery of the comparative example is significantly inferior to that of the battery of this example. This is because the contact between the electrode group and the battery container becomes unstable due to contraction of the electrode during discharge, and the internal resistance increases. If a protrusion is provided as in the present embodiment, contact is ensured, and such a capacity reduction does not occur. From the comparison of Examples 1, 2, and 3, it can be seen that the effect is the same even when the protrusion is provided on either the positive electrode side, the negative electrode side, or both. Therefore, according to the present invention, a flat nonaqueous electrolyte secondary battery exhibiting excellent discharge performance can be obtained.
Although the embodiment of the present invention has been described in the case where one protrusion is provided on the inner surface of the case, the same effect can be obtained even when unevenness such as embossing is provided on the inner surface of the case.
[0023]
In addition, a flat nonaqueous electrolyte secondary battery using a nonaqueous solution as a nonaqueous electrolyte has been described, but a polymer secondary battery using a polymer electrolyte as a nonaqueous electrolyte or a solid electrolyte secondary battery using a solid electrolyte The same effect can be obtained for. Further, a polymer thin film or a solid electrolyte membrane can be used instead of the resin separator.
[0024]
The battery shape has been described using a coin-type non-aqueous electrolyte secondary battery that is sealed by caulking the positive electrode case, but it is also possible to replace the positive and negative electrodes and seal the negative electrode case by caulking. Further, the battery shape need not be a circular coin type, and can be applied to a flat nonaqueous electrolyte secondary battery having a special shape such as an oval shape or a square shape.
[0025]
【The invention's effect】
As described above, according to the present invention, a flat nonaqueous electrolyte secondary battery having excellent discharge performance can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a battery according to Example 1 of the present invention.
2 is a top view of the negative electrode case of FIG. 1. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Negative electrode case, 1a ... Negative electrode case protrusion part, 2 ... Positive electrode plate, 3 ... Separator, 4 ... Negative electrode plate, 5 ... Positive electrode case, 6 ... Insulating gasket.

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 the positive electrode case is further crimped by crimping to compress the insulating gasket. In a flat type non-aqueous electrolyte secondary battery having a structure and containing therein a positive electrode of lithium-containing oxide, a separator, a negative electrode of a carbonaceous material, and a non-aqueous electrolyte,
The band-like positive electrode and the negative electrode wound with a separator, or a multi-layer laminate, or by Rukoto is returned in fold, in the vertical direction of the cross section to the flat surface of the flat-shaped non-aqueous electrolyte secondary battery, and the positive electrode A flat electrode group having at least three or more positive and negative electrode facing surfaces facing each other with the separator interposed therebetween is housed, and a positive electrode constituent material having conductivity on the outer side of one flat surface of the electrode group. Contact with the positive electrode case by exposing, contacting the negative electrode case by exposing the negative electrode constituent material having conductivity outside the other flat surface of the electrode group,
Provide unevenness on the inside of the positive electrode case, the convex portion on the inner side of the positive electrode case and the exposed portion of the positive electrode constituent material are in contact,
Irregularities on the inside of the negative electrode case, whether the the exposed portion of the inner convex portion of the negative electrode case and the negative electrode constituting material is in contact, or,
Protrusions are provided on the inner side of the positive electrode case, the convex portions on the inner side of the positive electrode case are in contact with the exposed portions of the positive electrode constituent material, and the convex portions on the inner side of the negative electrode case are provided with irregularities on the inner side of the negative electrode case. And a flat nonaqueous electrolyte secondary battery , wherein the exposed portion of the negative electrode constituent material is in contact .

The flat nonaqueous electrolyte secondary battery according to claim 1, wherein a protrusion is provided inside either one of the positive electrode case and the negative electrode case, or inside both the positive electrode case and the negative electrode case.