JP4565812B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

【００２９】
上記表１の結果から明らかなように、セパレータの上下に溶着部を形成しなかった電極群ｘ１を用い、かつ電解液ｅ１を用いた電池Ｙ２においては、全ての電池に内部短絡が発生していたことが分かる。また、セパレータの上下に溶着部１３ｃ，１３ｄを形成した電極群ａ１を用いても、電解液ｅ１を用いた電池Ｙ１においては、内部短絡の発生個数が多いことが分かる。これは、溶着部が未形成の電極群ｘ１に電解液ｅ１が充填された電池Ｙ２を充電状態で高温放置すると、高温によりセパレータの熱収縮が発生して、電極群ｘ１の上下端部での短絡が発生したためと考えられる。
【００３０】
一方、セパレータ１３の上下に溶着部１３ｃ，１３ｄが形成された電極群ａ１に電解液ｅ１が充填された電池Ｙ１を充電状態で高温放置して、セパレータ１３の熱収縮が起こり始めると、電極群上下の溶着部間でのセパレータ１３のテンションが大きくなって、電極群の内部のセパレータ１３に皺が発生するようになる。この結果、僅かな刺激で破膜したり、裂けが生じるようになって、破膜や裂けが生じた部分で短絡が発生したと考えられる。
【００３１】
これらに対して、セパレータ１３の上下に溶着部を形成しなかった電極群ｘ１を用いても、ゲル状電解質（ｅ２）を用いてゲル化された電池Ｘ１においては、セパレータ１３の上下に溶着部１３ｃ，１３ｄを形成した電極群ａ１に電解液ｅ１が充填された電池Ｙ１よりも内部短絡の発生個数が減少していることが分かる。さらに、セパレータ１３の上下に溶着部１３ｃ，１３ｄを形成した電極群ａ１を用い、かつゲル状電解質（ｅ２）を用いた電池Ａ１においては、内部短絡が発生していないことが分かる。
【００３２】
これは、溶着部が未形成の電極群ｘ１にゲル状電解質（ｅ２）が充填された電池Ｘ１においては、ゲル状電解質（ｅ２）の接着力により、セパレータ１３と各電極１１，１２との密着性が向上し、セパレータ１３の熱収縮が抑制されたからであると考えられる。しかしながら、ゲル状電解質によるセパレータ１３の熱収縮の抑制だけでは、液状電解液を使用した電池Ｙ１，Ｙ２よりは内部短絡の発生を減少できているが、それでも十分であるとは言えない。
【００３３】
一方、セパレータ１３の上下に溶着部１３ｃ，１３ｄが形成された電極群ａ１にゲル状電解質（ｅ２）が充填された電池Ａ１においては、ゲル状電解質（ｅ２）の接着力によるセパレータ１３と各電極１１，１２とが密着することによってセパレータの熱収縮が抑制されると共に、セパレータ１３の上部１３ａおよび下部１３ｂにそれぞれ溶着部１３ｃ，１３ｄが形成されているので、高温放置しても、電極群ａ１上下の溶着部間でのセパレータ１３のテンションが大きくなり、電極群ａ１の内部のセパレータ１３に皺が発生することがなく、内部短絡が発生しなかったと考えられる。
【００３４】
６．セパレータの溶着幅の検討
ついで、セパレータ１３の溶着部１３ｃ，１３ｄの溶着幅ｘ，ｙについて検討を行った。そこで、上突出部１３ａに溶着部を形成することなく、下突出部１３ｂに溶着幅ｙが扁平状電極群１０ａの幅Ｘに対して５％となるように溶着部１３ｄを形成した電極群を作製し、これを電極群ａ２とした。また、上突出部１３ａに溶着幅ｘが扁平状電極群１０ａの幅Ｘに対して５％となるように溶着部１３ｃを形成し、下突出部１３ｂに溶着部を形成することなく電極群を作製し、これを電極群ａ３とした。また、上突出部１３ａに溶着幅ｘが扁平状電極群１０ａの幅Ｘに対して４０％となるように溶着部１３ｃを形成し、下突出部１３ｂに溶着部を形成することなく電極群を作製し、これを電極群ａ４とした。
【００３５】
また、上突出部１３ａに溶着幅ｘが扁平状電極群１０ａの幅Ｘに対して６０％となるように溶着部１３ｃを形成し、下突出部１３ｂに溶着部を形成することなく電極群を作製し、これを電極群ａ５とした。また、上突出部１３ａに溶着幅ｘが扁平状電極群１０ａの幅Ｘに対して９５％となるように溶着部１３ｃを形成し、下突出部１３ｂに溶着部を形成することなく電極群を作製し、これを電極群ａ６とした。また、上突出部１３ａに溶着幅ｘが扁平状電極群１０ａの幅Ｘに対して９５％となるように溶着部１３ｃを形成し、かつ下突出部１３ｂに溶着幅ｙが扁平状電極群１０ａの幅Ｘに対して６０％となるように溶着部１３ｄを形成して電極群を作製し、これを電極群ａ７とした。
【００３６】
さらに、上突出部１３ａに溶着幅ｘが扁平状電極群１０ａの幅Ｘに対して１００％となるように溶着部１３ｃを形成し、下突出部１３ｂに溶着部を形成することなく電極群を作製し、これを電極群ｘ２とした。また、上突出部１３ａに溶着幅ｘが扁平状電極群１０ａの幅Ｘに対して１００％となるように溶着部１３ｃを形成し、かつ下突出部１３ｂに溶着幅ｙが扁平状電極群１０ａの幅Ｘに対して１００％となるように溶着部１３ｄを形成して電極群を作製し、これを電極群ｘ３とした。
【００３７】
ついで、これらの電極群ａ２〜ａ７およびｘ２，ｘ３を用いるとともに、上述のように調製したゲル用非水電解液ｅ２を用いて、上述と同様にして非水電解質電池Ａ２〜Ａ７，Ｘ２，Ｘ３をそれぞれ作製した。なお、電極群ａ２を用いたものを電池Ａ２とし、電極群ａ３を用いたものを電池Ａ３とし、電極群ａ４を用いたものを電池Ａ４とし、電極群ａ５を用いたものを電池Ａ５とし、電極群ａ６を用いたものを電池Ａ６とし、電極群ａ７を用いたものを電池Ａ７とした。また、電極群ｘ２を用いたものを電池Ｘ２とし、電極群ｘ３を用いたものを電池Ｘ３とした。
【００３８】
ついで、これらの各電池Ａ２〜Ａ７，Ｘ２，Ｘ３をそれぞれ５０個ずつ用いて、上述と同様にして高温放置試験を行った後、これらの各電池Ａ２〜Ａ７，Ｘ２，Ｘ３の電圧を測定して、試験前後の電圧差が０．５Ｖ以上（試験後の電池電圧が３．７Ｖ以下）のものを内部短絡が発生した電池と判定すると、下記の表２に示すような結果が得られた。なお、表２には上述した電池Ａ１と電池Ｘ１の結果も併せて示している。
【００３９】
【表２】

【００４０】
上記表２の結果から明らかなように、電池Ｘ１，Ｘ２，Ｘ３は内部短絡の発生個数が多いことが分かる。これは、ゲル状電解質が充填された場合、セパレータ１３の上下の全幅に亘って溶着部１３ｃ，１３ｄが形成された電極群ｘ３を用いた電池Ｘ３を充電状態で高温放置すると、正極１１から発生したガスが電極群ｘ３内から放散しにくくなって、電極群ｘ３内に滞留するようになる。この結果、電極群ｘ３に変形を生じたり、歪みが生じるようになって内部短絡が発生しやすくなったと考えられる。また、セパレータ１３の上部の全幅に亘って溶着部１３ｃが形成された電極群ｘ２を用いた電池Ｘ２を充電状態で高温放置しても、同様の理由で内部短絡が発生しやすくなったと考えられる。
【００４１】
一方、電池Ａ１〜Ａ７は内部短絡の発生個数が激減していることが分かる。これは、ゲル状電解質が充填された場合、セパレータ１３の上部あるいは下部もしくは上下部の一部に溶着部１３ｃ（１３ｄ）が形成されていると、充電状態で高温放置してセパレータ１３の熱収縮が起こり始めても、ゲル状電解質（ｅ２）の接着力により、セパレータ１３と各電極１１，１２との密着性が向上しているため、セパレータ１３の熱収縮が抑制され、内部短絡の発生個数が減少することとなる。この場合、電極群の幅方向の中央部近傍は両端部近傍よりも構成圧が低いため、セパレータ１３の収縮が起こりやすくなる。このため、溶着部１３ｃ（１３ｄ）は電極群の幅方向の中央部近傍に形成するのが望ましい。
【００４２】
これらのことから、ゲル状電解質が充填された場合、セパレータ１３の上部あるいは下部もしくは上下部の一部に形成する溶着部１３ｃ（１３ｄ）の幅寸法ｘ，ｙは、電極群の幅寸法Ｘに対して５％以上で、９５％以下にするのが望ましいということができる。
【００４３】
【発明の効果】
上述したように、本発明の非水電解質二次電池１０においては、外装体１４内にゲル状非水電解質を備え、かつ渦巻状電極群の各電極１１，１２より上下方向に突出してセパレータ１３が配設されているとともに、突出した部分１３ａ（１３ｂ）の少なくとも一方の一部はセパレータ１３ａ（１３ｂ）同士が溶着により一体的に接合されている。このため、高温放置してセパレータ１３に熱収縮が発生しても、ゲル状電解質の接着力により、セパレータ１３と各電極１１，１２との密着性が向上しているため、セパレータ１３の熱収縮が抑制され、内部短絡の発生個数が減少することとなる。
【００４４】
なお、上述した実施の形態においては、非水電解質の有機溶媒として、エチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）との混合溶媒を用いる例について説明したが、有機溶媒としては、カーボネート類、ラクトン類、エーテル類、ケトン類、ニトリル類、アミド類、スルホン系化合物、エステル類、芳香族炭化水素などを用いるようにしてもよいし、これら溶媒の２種類以上を混合して用いるようにしてもよい。これらの中でカーボネート類、ラクトン類、エーテル類、ケトン類、ニトリル類、エステル類などが好ましく、好適にはカーポネート類が望ましい。
【００４５】
具体例としては、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、γ−ブチロラクトン、γ−バレロラクトン、γ−ジメトキシエタン、テトラヒドロフラン、アニソール、１，４−ジオキサン、４−メチルー２−ペンタノン、シクロヘキサノン、アセトニトリル、プロピオニトリル、ジエチルカーボネート、ジメチルホルムアミド、スルホラン、蟻酸メチル、蟻酸エチル、酢酸メチル、酢酸エチル、酢酸プロピル、プロピオン酸エチルなどを挙げることができ、充放電効率を高める点からプロピレンカーボネート、エチレンカーボネートが好適である。
【００４６】
また、上述した実施の形態においては、電解質として六フッ化リン酸リチウム（ＬｉＰＦ₆）を用いる例について説明したが、これ以外の電解質としては、過塩素酸リチウム（ＬｉＣｌＯ₄）、ホウフッ化リチウム（ＬｉＢＦ₄）、六フッ化珪酸リチウム（ＬｉＡｓＦ₆）、トリフルオロメチルスルホン酸リチウム（ＬｉＣＦ₃ＳＯ₃）、ビストリフルオロメチルスルホニルイミドリチウム（ＬｉＮ（ＣＦ₃ＳＯ₂）₂）などのリチウム塩を用いるのが望ましい。中でも、ＬｉＰＦ₆、ＬｉＢＦ₄を用いるのが好ましく、有機溶媒に対する溶解量としては、０．５〜２．０モル／リットルとするのが好ましい。
【００４７】
また、電極界面の被膜安定化、低被膜抵抗化などの目的で、ビニレンカーボネート、ビニルエチレンカーボネート、トリフルオロメチルビニレンカーボネート、トリフルオロプロピレンカーボネート、無水マレイン酸、無水コハク酸、カテコール、レゾルシンなどを上記の如き電解液に添加するようにしてもよい。
【００４８】
さらに、上述した実施の形態においては、ゲル用非水電解液を調製するに際して、熱重合性モノマー材料としてテトラエチレングリコールジアクリレートとトリメチロールプロパントリアクリレートを用い、重合開始剤としてｔ−ヘキシルパーオキシピバレートを用いる例について説明したが、これに限られることはない。例えば、機械的強度の高いＰＶｄＦなどの物理架橋ポリマーを用いても良く、ＰＥＯ、ＰＰＯ系のポリエーテル系、ポリエステル系、ポリカーボネート系などの高いイオン導電性を兼ね備える化学架橋ポリマーを用いても良い。
【００４９】
また、モノマーを重合させる際には、重合開始剤を加えることなく電子線やγ線などの放射線を照射する方法、光増感剤などの紫外線重合開始剤を添加して紫外線を照射する方法、酸化還元系の開始剤を用いたレドックス系常温硬化法などが適用できるが、特別な装置を必要としない点で熱硬化法が好ましい。例えば、熱重合開始剤として有機過酸化物などを用いて恒温槽中で保持し、硬化することができる。電解液の質量に対するモノマーの量は１〜３０質量％の範囲で添加することが好ましい。少なすぎる場合にはポリマーマトリックスの架橋密度が減少し、機械的強度が不足する結果、セパレータと電極との密着強度が得にくくなる。一方、多すぎる場合にはイオン伝導度が低下するため、急速充放電特性が低下してしまう。
【図面の簡単な説明】
【図１】 本発明の非水電解液二次電池に用いられる電極群を模式的に示す図であり、図１（ａ）は上面図であり、図１（ｂ）は正面図であり、図１（ｃ）は下面図である。
【図２】 本発明の非水電解液二次電池を模式的に示す図であり、図２（ａ）は斜視図であり、図２（ｂ）は図２（ａ）のＡ−Ａ断面を示す断面図である。
【符号の説明】
１０…非水電解液二次電池、１１…正極、１１ａ…正極リード、１２…負極、１２ａ…負極リード、１３…セパレータ、１３ａ…上突出部、１３ｂ…下突出部、１３ｃ…上溶着部、１３ｄ…下溶着部、１４…外装体[0001]
BACKGROUND OF THE INVENTION
In the present invention, a belt-like positive electrode in which a positive electrode mixture is applied to a positive electrode current collector and a belt-like negative electrode in which a negative electrode mixture is applied to a negative electrode current collector are wound in a spiral shape facing each other via a belt-like separator. The present invention relates to a non-aqueous electrolyte secondary battery including a spiral electrode group and a gel-like non-aqueous electrolyte in an outer package.
[0002]
[Prior art]
In recent years, a positive electrode active material capable of occluding and releasing lithium ions (for example, lithium cobalt oxide (LiCoO) as a battery used in portable electronic / communication equipment such as a mobile phone, a notebook computer, and a small video camera. ₂ ), Lithium manganate (LiMn) ₂ O _Four Non-aqueous electrolyte secondary battery comprising a lithium-containing transition metal oxide)) and a negative electrode active material capable of occluding and releasing lithium ions (eg, graphite, carbon, etc.) It has come to be widely used as a battery.
[0003]
This type of non-aqueous electrolyte secondary battery is generally produced as follows. That is, first, a positive electrode mixture containing a positive electrode active material is applied to a positive electrode current collector to produce a strip-shaped positive electrode, and a negative electrode mixture containing a negative electrode active material is applied to a negative electrode current collector to form a strip-shaped negative electrode. Make it. Thereafter, the obtained belt-like positive electrode and the belt-like negative electrode are laminated so as to face each other via a belt-like separator, and then wound into a spiral shape to form a spiral electrode group having a perfectly circular cross section. Then, this is accommodated in a cylindrical outer can, or a circular spiral electrode group is pressure-molded into an elliptical shape with a flat cross-sectional shape, and this is formed into a rectangular tube outer can or a film-like outer body. The nonaqueous electrolyte secondary battery is made by injecting a nonaqueous electrolyte.
[0004]
By the way, as a function of the separator that separates the positive electrode and the negative electrode, the battery reaction basically has a function of preventing a short circuit to prevent a direct short circuit between the positive electrode and the negative electrode and allows ions to permeate through the microporous structure. It is a necessary condition to have an ion permeation function that enables the above. However, a separator having a shutdown function (SD function) has been adopted as a separator used in this type of non-aqueous electrolyte secondary battery from the viewpoint of improving safety. This SD function has a function to stop the battery reaction by synthesizing the plastic material of the separator material as the battery internal temperature rises to melt and deform to block the micropores when an abnormal current is generated due to incorrect connection or the like. Means.
[0005]
However, at the time of abnormal heat generation of the battery, an internal short circuit due to the contraction of the separator occurs, and there is a possibility that safety is lowered. For this reason, in order to suppress the shrinkage of the separator, a means of using high molecular weight polyethylene or mixing polypropylene has been taken. However, there is a problem that the shutdown temperature rises and the current interrupt function becomes difficult to operate. In addition, when a separator uniaxially stretched in the width direction is used, shrinkage in the width direction can be suppressed, but there is a problem that the film tends to tear in the stretch direction.
[0006]
Therefore, Patent Document 1 discloses a battery in which an internal short circuit in which the electrode and the outer can are in contact with each other even if the separator is thermally contracted by attaching a short circuit prevention tape to the uppermost part of the outermost periphery of the spiral electrode group. (Japanese Unexamined Patent Publication No. 2000-251866) has come to be proposed. However, in the battery proposed in Patent Document 1, since the shrinkage of the separator disposed on the inner peripheral portion of the spiral electrode group cannot be prevented, both electrodes facing the shrunk separator are the electrode group. There was a problem of short circuiting at the top or bottom.
[0007]
For this reason, Patent Document 2 (Japanese Patent Laid-Open No. 2003-22794) proposes welding the upper and lower ends of the separator in order to prevent an internal short circuit due to the shrinkage of the separator at a high temperature. According to this, the separator is welded in the vicinity of the lead portion, or when the battery is exposed to high temperature, the separator is welded together to wrap the electrode. As a result, it is possible to prevent an internal short circuit due to the shrinkage of the separator at a high temperature.
[Patent Document 1]
JP 2000-251866 A
[Patent Document 2]
JP 2003-22794 A
[0008]
[Problems to be solved by the invention]
However, in the non-aqueous electrolyte secondary battery proposed in the above-mentioned Japanese Patent Application Laid-Open No. 2003-22794, a liquid electrolyte (electrolytic solution) is used as the non-aqueous electrolyte. For this reason, when the battery temperature rises and thermal contraction of the separator begins to occur, the tension between the welded portions above and below the spiral electrode group increases, and wrinkles are generated in the separator inside the electrode group. As a result, the membrane breaks or tears with a slight stimulus, causing a problem that a short circuit occurs at the portion where the membrane is broken or torn.
[0009]
Further, as proposed in the above-mentioned Japanese Patent Application Laid-Open No. 2003-22794, in the method of thermally welding the separators, if the electrode group is slightly deformed due to the influence of gas generated from the electrodes, a substantial welding effect is obtained. Caused the problem of being unable to obtain. It has also been found that it is almost impossible to uniformly weld the electrodes so as to enclose them.
[0010]
Furthermore, in recent years, development of a laminate-type battery using a laminate film as an exterior material has been advanced in response to the demand for higher energy density of this type of non-aqueous electrolyte secondary battery. However, in such a laminate type battery, since the pressing force is extremely smaller than that in the case of using a metal outer can such as aluminum, there is a problem that the electrode group is likely to be deformed. In particular, when the battery is exposed to a high temperature, a large amount of gas is generated. Therefore, the deformation / distortion of the electrode group becomes more significant than when a metal outer can is used. For this reason, even if it comprised the electrode group as mentioned above, the problem that an effect was hardly acquired with respect to an internal short circuit arose.
[0011]
Therefore, the present invention has been made to solve the above problems, and even if the battery heats up abnormally and the separator contracts, the occurrence of internal short circuit at the upper and lower ends of the electrode group is suppressed. An object of the present invention is to provide a non-aqueous electrolyte secondary battery with improved safety so that the battery does not rupture or ignite.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, in the nonaqueous electrolyte secondary battery of the present invention, a strip-shaped positive electrode and a strip-shaped negative electrode are wound in a spiral shape facing each other via a strip-shaped separator. Flat An electrode group and a gel-like nonaqueous electrolyte are provided in the exterior body, and the strip separator Flat Protruding vertically from each electrode of the electrode group And At least one part of the protruding part is formed by joining the separators together by welding or bonding. In addition, the width dimension of the joint portion is not less than 5% and not more than 95% of the width dimension of the flat electrode group. It is characterized by that.
[0013]
Thus, a gel-like nonaqueous electrolyte is provided in the exterior body, and Flat When separators are disposed so as to protrude vertically from each electrode of the electrode group, and at least one part of the protruding portions is integrally bonded to each other by welding or adhesion, the separator is left at a high temperature. Even when the thermal contraction of the separator starts to occur, the adhesion between the separator and each electrode is improved by the adhesive force of the gel electrolyte. For this reason, it is possible to suppress the thermal contraction of the separator and reduce the occurrence of an internal short circuit. in this case, Flat Since the component pressure in the vicinity of the central portion in the width direction of the electrode group is lower than that in the vicinity of both end portions, the separator tends to contract. For this reason, the joint is Flat It is desirable to form near the center of the electrode group in the width direction.
[0014]
In addition If the width of the joint is too short, the effect of preventing internal short circuit is insufficient, and if the width of the joint is too long, the generated gas stays in the electrode group, and the electrode The deformation / distortion of the group increases, and conversely an internal short circuit occurs. For this reason, when the gel electrolyte is filled, the width dimension of the joint formed on the upper or lower part of the separator or part of the upper and lower parts is Flat It is desirable to set it to 5% or more and 95% or less with respect to the width dimension of the electrode group.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to FIGS. 1 and 2 below. However, the present invention is not limited to these embodiments, and may be appropriately changed within a range not changing the object of the present invention. Can be implemented. FIG. 1 is a diagram schematically showing an electrode group used in the non-aqueous electrolyte secondary battery of the present invention, FIG. 1 (a) is a top view, and FIG. 1 (b) is a front view. FIG. 1C is a bottom view. FIG. 2 is a diagram schematically showing a nonaqueous electrolyte secondary battery of the present invention, FIG. 2 (a) is a perspective view, and FIG. 2 (b) is a cross-sectional view taken along line AA of FIG. 2 (a). It is sectional drawing shown.
[0016]
1. Fabrication of positive electrode
Lithium cobaltate (LiCoO) as positive electrode active material ₂ ) And a carbon-based powder (for example, 5% by mass) such as acetylene black or graphite as a conductive agent were mixed to prepare a positive electrode mixture. This positive electrode mixture is kneaded with a binder solution in which a binder (for example, 3% by mass) made of polyvinylidene fluoride (PVdF) is dissolved in an organic solvent made of N-methyl-2-pyrrolidone (NMP). Thus, a positive electrode active material slurry or a positive electrode active material paste was prepared.
[0017]
Next, a positive electrode current collector made of aluminum foil (for example, having a thickness of 15 μm and a width of 54.0 mm) was prepared, and the positive electrode active material slurry or the positive electrode active material paste prepared as described above was used as the positive electrode current collector. The positive electrode mixture layer was formed by uniformly applying to both sides of the film. Here, the slurry was applied using a die coater or a doctor blade, and the paste was applied by a roller coating method. Then, it was made to pass through a drier to remove the organic solvent (NMP) that was necessary when making the slurry or paste, and dried. After drying, it was rolled with a roll press until the thickness became 0.17 mm, and cut into a predetermined shape to produce a strip-like positive electrode 11. In the strip-like positive electrode 11, the positive electrode slurry is not applied to the portion arranged on the outermost periphery during winding, and the positive electrode lead 11 a is formed by ultrasonically welding an aluminum current collecting tab.
[0018]
Note that the above-described LiCoO is used as the positive electrode active material. ₂ In addition to Li _x MO ₂ (Wherein M is at least one of Co, Ni, and Mn, and 0.45 ≦ x ≦ 1.20), for example, a lithium transition metal composite oxide such as LiNiO ₂ , LiNi _y Co _1-y O ₂ (However, 0.01 ≦ y ≦ 0.99), Li _0.5 MnO ₂ , LiMnO ₂ These may be used alone or as a mixture of two or more.
[0019]
2. Production of negative electrode
A binder solution in which natural graphite powder as a negative electrode active material and a binder (for example, 3% by mass) made of polyvinylidene fluoride (PVdF) are dissolved in an organic solvent made of N-methyl-2-pyrrolidone (NMP). Were kneaded to prepare a negative electrode active material slurry or a negative electrode active material paste. Next, a negative electrode current collector made of copper foil (for example, having a thickness of 12 μm and a width of 56.0 mm) was prepared, and the negative electrode active material slurry or the negative electrode active material paste produced as described above was used as the negative electrode current collector. The negative electrode mixture layer was formed by uniformly coating both sides of the film.
[0020]
Here, the slurry was applied using a die coater or a doctor blade, and the paste was applied by a roller coating method. Then, it was made to pass through a drier to remove the organic solvent (NMP) necessary for making the slurry or paste and dry it. After drying, it was rolled with a roll press machine until the thickness became 0.14 mm, cut into a predetermined shape, and a strip-like negative electrode 12 was produced. In the strip-shaped negative electrode 12, the negative electrode slurry is not applied to the portion disposed on the outermost periphery during winding, and a nickel current collecting tab is ultrasonically welded to form the negative electrode lead 12a.
[0021]
As the negative electrode active material, in addition to the above-mentioned natural graphite, a carbon-based material capable of occluding and desorbing lithium ions, such as artificial graphite, carbon black, coke, glassy carbon, carbon fiber, or a fired body thereof. Or lithium alloy such as metallic lithium, lithium-aluminum alloy, lithium-lead alloy, lithium-tin alloy, SnO ₂ , SnO, TiO ₂ , Nb ₂ O _Three A base metal oxide having a lower potential than the positive electrode active material may be used.
[0022]
3. Fabrication of electrode group
Next, a belt-like positive electrode 11 and a belt-like negative electrode 12 produced as described above are prepared, and a belt-like separator made of a polyethylene microporous film (thickness of 0.025 mm and width of 59.0 mm) is prepared between them. 13 and were overlapped so that the center lines in the width direction coincided with each other. Then, after winding these in a spiral shape with a winder, the outermost periphery was taped to form a spiral electrode group. Subsequently, this was crushed so that the cross-sectional shape became a flat ellipse, and the flat electrode group 10a was produced.
[0023]
Here, the width direction of the strip separator 13 (It becomes the height direction in FIG. 1 (b)) The upper end portion of the negative electrode 12 is formed with an upper protrusion portion 13a protruding upward by 1.5 mm from the upper end portion of the negative electrode 12, and the lower protrusion portion 13b is formed protruding downward by 1.5 mm from the lower end portion. Become. Next, the x portion (60% of the width X of the flat electrode group 10a) at the center in the width direction of the upper protruding portion 13a is welded to each other and joined together, and the lower protruding portion 13b The y portion (60% of the width X of the flat electrode group 10a) in the center in the width direction is heat-welded to each other and joined together to form an electrode group a 1 It was. Further, the projections 13a and 13b are not welded to each other as they are, but the electrodes x 1 It was. Instead of integrating by heat welding, an adhesive that does not adversely affect the battery reaction (for example, an epoxy adhesive, an acrylic adhesive, or the like) may be integrally bonded.
[0024]
4). Preparation of non-aqueous electrolyte secondary battery
First, LiPF is used as an electrolyte in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 3: 7. ₆ Was dissolved at a rate of 1 mol / liter to prepare a non-aqueous electrolyte, which was defined as an electrolyte e1. Moreover, while adding 3.0 mass% of tetraethylene glycol diacrylate as a thermopolymerizable monomer material and 1.0 mass% of trimethylol propane triacrylate to the electrolyte solution e1 prepared in this way, A non-aqueous electrolyte for gel was prepared by adding 0.3% by mass of t-hexylperoxypivalate, and this was designated as electrolyte e2.
[0025]
Next, the flat electrode group 10a (a 1 , X 1 ) Was accommodated in an exterior body 14 made of an aluminum laminate film, and placed in a dry box, and then the electrolytes e1 and e2 prepared as described above were injected into the exterior body 14. Next, the inside of the dry box was sucked with a vacuum pump to create a reduced pressure atmosphere. As a result, the electrolyte injected into the exterior body 14 is impregnated in the electrode group. Then, the opening part of the exterior body 14 was temporarily sealed and taken out from the dry box. Next, in the case of using the electrolytic solution e2, after being placed in the heating device, the inside of the heating device was kept at a temperature of 60 ° C. and heated for 5 hours. Thereby, the thermopolymerizable monomer material was polymerized, and the electrolytic solution was cured by gelation.
[0026]
Next, after the first charge was performed to disperse the generated gas, the openings of the exterior body 14 were fully sealed to prepare nonaqueous electrolyte batteries A1, X1, Y1, and Y2, respectively. At this time, main sealing was performed so that the positive electrode lead 11 a extending from the positive electrode 11 and the negative electrode lead 12 a extending from the negative electrode 12 were liquid-tightly sealed in the upper opening of the outer package 14. Here, the electrode group a 1 A battery A1 was prepared using the nonaqueous electrolyte e2 for gel. Similarly, electrode group x 1 And a non-aqueous electrolyte for gel e2 is used as battery X1, and electrode group a 1 And a non-aqueous electrolyte e1 is used as a battery Y1, and an electrode group x 1 A battery Y2 was prepared using the nonaqueous electrolyte e1.
[0027]
5). High temperature storage test
Next, 50 batteries A1, X1, Y1, and Y2 were used and discharged at room temperature (about 25 ° C.) with a discharge current of 1 ItmA until the battery voltage reached 2.75V. After this, the battery is charged at a constant current until the battery voltage reaches 4.2 V at a room temperature (about 25 ° C.) with a charging current of 1 ItmA, and after reaching 4.2 V, the voltage is constant until the current value becomes 30 mA or less. Was charged. Then, after each battery A1, X1, Y1, Y2 in such a charged state was heated to 150 ° C. at a temperature rising rate of 5 ° C./min, a high temperature standing test was performed in which the temperature of 150 ° C. was maintained for 3 hours. went. Thereafter, the voltage of each of these batteries A1, X1, Y1, and Y2 was measured, and an internal short circuit occurred when the voltage difference before and after the test was 0.5 V or more (the battery voltage after the test was 3.7 V or less). When judged to be a battery, the results shown in Table 1 below were obtained.
[0028]
[Table 1]

[0029]
As is clear from the results in Table 1 above, in the battery Y2 using the electrode group x1 in which the welded portions were not formed above and below the separator and using the electrolytic solution e1, an internal short circuit occurred in all the batteries. I understand that. Moreover, even if it uses the electrode group a1 which formed the welding parts 13c and 13d on the upper and lower sides of a separator, in the battery Y1 using the electrolyte solution e1, it turns out that there are many occurrence numbers of an internal short circuit. This is because when the battery Y2 filled with the electrolytic solution e1 in the electrode group x1 in which the welded portion is not formed is left in a charged state at a high temperature, thermal contraction of the separator occurs due to the high temperature, and the upper and lower ends of the electrode group x1 This is probably because a short circuit occurred.
[0030]
On the other hand, when the battery Y1 in which the electrolyte solution e1 is filled in the electrode group a1 in which the welded portions 13c and 13d are formed on the upper and lower sides of the separator 13 is left at a high temperature in a charged state, The tension of the separator 13 between the upper and lower welded portions is increased, and wrinkles are generated in the separator 13 inside the electrode group. As a result, it is considered that a film is broken or ruptured by a slight stimulus, and a short circuit occurs at a portion where the film is broken or ruptured.
[0031]
On the other hand, in the battery X1 gelled using the gel electrolyte (e2) even if the electrode group x1 in which the welded portions are not formed above and below the separator 13, the welded portions are formed above and below the separator 13 in the battery X1. It can be seen that the number of occurrences of internal short circuits is reduced as compared with the battery Y1 in which the electrode group a1 in which the electrodes 13c and 13d are formed is filled with the electrolytic solution e1. Furthermore, it can be seen that an internal short circuit does not occur in the battery A1 using the electrode group a1 in which the welds 13c and 13d are formed above and below the separator 13 and using the gel electrolyte (e2).
[0032]
This is because, in the battery X1 in which the electrode group x1 in which the weld portion is not formed is filled with the gel electrolyte (e2), the adhesion between the separator 13 and the electrodes 11 and 12 is caused by the adhesive force of the gel electrolyte (e2). This is considered to be because the heat shrinkage of the separator 13 was suppressed. However, the suppression of the thermal contraction of the separator 13 by the gel electrolyte alone can reduce the occurrence of internal short circuits as compared with the batteries Y1 and Y2 using the liquid electrolyte, but it cannot be said to be sufficient.
[0033]
On the other hand, in the battery A1 in which the electrode group a1 in which the welded portions 13c and 13d are formed above and below the separator 13 is filled with the gel electrolyte (e2), the separator 13 and each electrode due to the adhesive force of the gel electrolyte (e2) 11 and 12, the thermal contraction of the separator is suppressed, and the welded portions 13 c and 13 d are formed on the upper portion 13 a and the lower portion 13 b of the separator 13, respectively. It is considered that the tension of the separator 13 between the upper and lower welded portions was increased, no wrinkles were generated in the separator 13 inside the electrode group a1, and no internal short circuit occurred.
[0034]
6). Examination of welding width of separator
Next, the welding widths x and y of the welded portions 13c and 13d of the separator 13 were examined. Therefore, an electrode group in which the welded portion 13d is formed so that the weld width y is 5% of the width X of the flat electrode group 10a without forming the welded portion on the upper projecting portion 13a. The electrode group a2 was produced. Further, the welded portion 13c is formed on the upper protruding portion 13a so that the welding width x is 5% of the width X of the flat electrode group 10a, and the electrode group is formed without forming the welded portion on the lower protruding portion 13b. The electrode group a3 was produced. Further, the welded portion 13c is formed on the upper protruding portion 13a so that the welding width x is 40% of the width X of the flat electrode group 10a, and the electrode group is formed without forming the welded portion on the lower protruding portion 13b. The electrode group was formed as electrode group a4.
[0035]
Further, the welded portion 13c is formed on the upper protruding portion 13a so that the welding width x is 60% of the width X of the flat electrode group 10a, and the electrode group is formed without forming the welded portion on the lower protruding portion 13b. The electrode group a5 was produced. Further, the welded portion 13c is formed on the upper protruding portion 13a so that the welding width x is 95% of the width X of the flat electrode group 10a, and the electrode group is formed without forming the welded portion on the lower protruding portion 13b. The electrode group was formed as electrode group a6. Further, the welded portion 13c is formed on the upper protruding portion 13a so that the welding width x is 95% of the width X of the flat electrode group 10a, and the welding width y is formed on the lower protruding portion 13b with the flat electrode group 10a. The welded portion 13d was formed so as to be 60% with respect to the width X of the electrode group to produce an electrode group, which was designated as an electrode group a7.
[0036]
Further, the welded portion 13c is formed on the upper protruding portion 13a so that the welding width x is 100% of the width X of the flat electrode group 10a, and the electrode group is formed without forming the welded portion on the lower protruding portion 13b. The electrode group x2 was prepared. Further, the welded portion 13c is formed on the upper protruding portion 13a so that the welding width x is 100% of the width X of the flat electrode group 10a, and the welding width y is formed on the lower protruding portion 13b with the flat electrode group 10a. The welded portion 13d was formed so as to be 100% with respect to the width X of the electrode group to produce an electrode group, which was designated as an electrode group x3.
[0037]
Next, while using these electrode groups a2 to a7 and x2 and x3, the nonaqueous electrolyte batteries A2 to A7, X2 and X3 were prepared in the same manner as described above using the nonaqueous electrolyte e2 for gel prepared as described above. Were prepared. A battery using the electrode group a2 is referred to as a battery A2, a battery using the electrode group a3 as a battery A3, a battery using the electrode group a4 as a battery A4, a battery using the electrode group a5 as a battery A5, A battery using electrode group a6 was designated as battery A6, and a battery using electrode group a7 was designated as battery A7. A battery using the electrode group x2 is referred to as a battery X2, and a battery using the electrode group x3 is referred to as a battery X3.
[0038]
Then, using each of these batteries A2 to A7, X2, and X3, a high temperature storage test was performed in the same manner as described above, and then the voltages of these batteries A2 to A7, X2, and X3 were measured. When the voltage difference before and after the test was 0.5 V or more (the battery voltage after the test was 3.7 V or less) was determined to be a battery in which an internal short circuit occurred, the results shown in Table 2 below were obtained. . Table 2 also shows the results of the battery A1 and the battery X1 described above.
[0039]
[Table 2]

[0040]
As is apparent from the results in Table 2, the batteries X1, X2, and X3 have a large number of internal short circuits. This is generated from the positive electrode 11 when the battery X3 using the electrode group x3 in which the welded portions 13c and 13d are formed over the entire upper and lower width of the separator 13 is left in a charged state when charged with a gel electrolyte. It becomes difficult for the gas thus discharged to diffuse from the electrode group x3, and the gas stays in the electrode group x3. As a result, it is considered that the electrode group x3 is deformed or distorted and an internal short circuit is likely to occur. Further, even when the battery X2 using the electrode group x2 in which the welded portion 13c is formed over the entire width of the upper portion of the separator 13 is left at a high temperature in a charged state, an internal short circuit is likely to occur for the same reason. .
[0041]
On the other hand, it can be seen that the number of internal short circuits in the batteries A1 to A7 is drastically reduced. This is because, when the gel electrolyte is filled, if the welded portion 13c (13d) is formed on the upper portion, the lower portion or a part of the upper and lower portions of the separator 13, it is left at a high temperature in a charged state and the heat shrinkage of the separator 13 However, since the adhesion between the separator 13 and the electrodes 11 and 12 is improved by the adhesive force of the gel electrolyte (e2), the thermal contraction of the separator 13 is suppressed, and the number of internal short-circuits is reduced. Will decrease. In this case, since the component pressure in the vicinity of the center portion in the width direction of the electrode group is lower than that in the vicinity of both end portions, the separator 13 is likely to contract. For this reason, it is desirable to form the welding part 13c (13d) in the vicinity of the center part in the width direction of the electrode group.
[0042]
From these facts, when the gel electrolyte is filled, the width dimensions x and y of the welded portion 13c (13d) formed on the upper portion or the lower portion of the separator 13 or part of the upper and lower portions are equal to the width dimension X of the electrode group. On the other hand, it can be said that it is desirable to set it to 5% or more and 95% or less.
[0043]
【The invention's effect】
As described above, in the non-aqueous electrolyte secondary battery 10 of the present invention, the outer body 14 includes the gel-like non-aqueous electrolyte, and protrudes in the vertical direction from the electrodes 11 and 12 of the spiral electrode group, thereby separating the separator 13. And at least one part of the protruding portion 13a (13b) is integrally joined to each other by welding the separators 13a (13b). For this reason, even if the separator 13 is left at a high temperature and heat shrinkage occurs, the adhesion between the separator 13 and the electrodes 11 and 12 is improved by the adhesive force of the gel electrolyte. Is suppressed, and the number of internal short-circuit occurrences is reduced.
[0044]
In the embodiment described above, an example in which a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) is used as the organic solvent for the nonaqueous electrolyte has been described. Examples of the organic solvent include carbonates and lactones. , Ethers, ketones, nitriles, amides, sulfone compounds, esters, aromatic hydrocarbons, etc., or a mixture of two or more of these solvents may be used. Good. Among these, carbonates, lactones, ethers, ketones, nitriles, esters and the like are preferable, and carbonates are preferable.
[0045]
Specific examples include propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, γ-dimethoxyethane, tetrahydrofuran, anisole, 1,4-dioxane, 4-methyl-2-pentanone, cyclohexanone, acetonitrile, pro Examples include pionitrile, diethyl carbonate, dimethylformamide, sulfolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, and ethyl propionate. Propylene carbonate and ethylene carbonate are preferred from the standpoint of increasing charge and discharge efficiency. It is.
[0046]
In the embodiment described above, lithium hexafluorophosphate (LiPF) is used as the electrolyte. ₆ ) Is described, but other electrolytes include lithium perchlorate (LiClO). _Four ), Lithium borofluoride (LiBF) _Four ), Lithium hexafluorosilicate (LiAsF) ₆ ), Lithium trifluoromethylsulfonate (LiCF) _Three SO _Three ), Bistrifluoromethylsulfonylimide lithium (LiN (CF _Three SO ₂ ) ₂ It is desirable to use a lithium salt such as Among them, LiPF ₆ , LiBF _Four Is preferably used, and the amount dissolved in the organic solvent is preferably 0.5 to 2.0 mol / liter.
[0047]
In addition, vinylene carbonate, vinyl ethylene carbonate, trifluoromethyl vinylene carbonate, trifluoropropylene carbonate, maleic anhydride, succinic anhydride, catechol, resorcin, etc. are used for the purpose of stabilizing the film at the electrode interface and reducing film resistance. You may make it add to such electrolyte solution.
[0048]
Furthermore, in the above-described embodiment, when preparing the non-aqueous electrolyte for gel, tetraethylene glycol diacrylate and trimethylolpropane triacrylate are used as the thermopolymerizable monomer material, and t-hexylperoxy is used as the polymerization initiator. Although an example using pivalate has been described, the present invention is not limited to this. For example, a physical cross-linked polymer such as PVdF having a high mechanical strength may be used, and a chemical cross-linked polymer having high ionic conductivity such as PEO, PPO polyether, polyester, and polycarbonate may be used.
[0049]
In addition, when polymerizing the monomer, a method of irradiating radiation such as an electron beam or γ-ray without adding a polymerization initiator, a method of irradiating ultraviolet rays by adding an ultraviolet polymerization initiator such as a photosensitizer, Although a redox-type room temperature curing method using a redox-based initiator can be applied, a thermosetting method is preferable in that a special apparatus is not required. For example, it can be held and cured in a thermostatic bath using an organic peroxide as a thermal polymerization initiator. It is preferable to add in the range of 1-30 mass% of monomers with respect to the mass of the electrolytic solution. When the amount is too small, the crosslink density of the polymer matrix decreases, resulting in insufficient mechanical strength. As a result, it is difficult to obtain adhesion strength between the separator and the electrode. On the other hand, when the amount is too large, the ionic conductivity is lowered, so that the rapid charge / discharge characteristics are lowered.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing an electrode group used in a non-aqueous electrolyte secondary battery of the present invention, FIG. 1 (a) is a top view, and FIG. 1 (b) is a front view; FIG. 1C is a bottom view.
2 is a diagram schematically showing a non-aqueous electrolyte secondary battery of the present invention, FIG. 2 (a) is a perspective view, and FIG. 2 (b) is a cross-sectional view taken along line AA in FIG. 2 (a). FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Non-aqueous electrolyte secondary battery, 11 ... Positive electrode, 11a ... Positive electrode lead, 12 ... Negative electrode, 12a ... Negative electrode lead, 13 ... Separator, 13a ... Upper protrusion part, 13b ... Lower protrusion part, 13c ... Upper welding part, 13d ... lower welding part, 14 ... exterior body

Claims (2)

A non-aqueous electrolyte secondary battery comprising a flat electrode group in which a belt-like positive electrode and a belt-like negative electrode are spirally wound with a belt-like separator facing each other and a gel-like non-aqueous electrolyte,
The strip separator is arranged to protrude in the vertical direction from each electrode of the flat electrode group ,
At least one part of the projecting part is integrally joined to each other by welding or adhesion, and the width dimension of the joined part is not less than 5% and not more than 95% of the width dimension of the flat electrode group. non-aqueous electrolyte secondary battery characterized in that it. The non-aqueous electrolyte secondary battery according to claim 1, wherein the outer package is a film-shaped outer package.

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