JP3933573B2 - Aluminum foil for current collector of lithium ion battery, current collector of lithium ion battery and lithium ion battery - Google Patents
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Description
【０００１】
【発明の属する技術分野】
この発明は、集電体用アルミニウム箔、集電体および二次電池に関し、特に、リチウムイオン電池やポリマー電池などに用いられる集電体用アルミニウム箔とそれを備えた集電体および二次電池に関するものである。
【０００２】
【従来の技術】
近年、高いエネルギ効率の二次電池として、リチウムイオン電池やポリマー電池などが携帯電話機、パーソナルコンピュータ、カメラまたは自動車の電源として使用されてきている。
【０００３】
二次電池の例としてリチウムイオン電池やリチウムイオンポリマー電池では、正極材料として、たとえばカーボン、リチウム金属酸化物塩、フッ素系バインダからなる活物質を集電体としてのアルミニウム箔にコーティングしたものが使用される。また、ポリマー電池では、正極材料または負極材料としてポリアニリン、ポリアセチレン等の導電性の高分子電極活物質を、集電体としてのアルミニウム箔にコーティングしたものが使用されている。
【０００４】
上述のように二次電池の集電体の材料としてアルミニウム箔が使用されている理由としては、以下の点が挙げられる。
【０００５】
（１） アルミニウム箔は、自然酸化膜が形成されるため、電解液に侵されにくく、支持体として比較的安定である。
【０００６】
（２） アルミニウム箔は、電気伝導性に優れ、電気的抵抗値が小さいため、二次電池の電気効率に悪影響を与えない。
【０００７】
（３） アルミニウム箔は、電気的抵抗値が低いため、抵抗による発熱が少ない。
【０００８】
（４） アルミニウム箔は、製造コストが安価であり、経済的な材料である。ところで、二次電池の正極または負極の電極を構成するために、集電体としてのアルミニウム箔の表面に電極活物質やバインダが塗布加工される。このような塗布加工されるコーティング材はアルミニウム箔の表面との密着性が不十分で、アルミニウム箔と電極活物質との間の接触抵抗が大きくなるという問題があった。また、コーティング材とアルミニウム箔の表面との間の密着性が不十分であるため、二次電池の充電・放電時に電極活物質の膜が剥離するという現象が生じ、これが二次電池の寿命等の特性に大きな影響を与えるという問題があった。
【０００９】
これらの問題を解決するために、工業的には、コーティング材の塗布加工後、圧着処理等が行なわれているが、必ずしも十分ではなかった。逆に、塗布加工された膜が圧着時に剥離するなどの問題が生じる場合もあった。この問題を解決するために、特開平５−７４４７９号公報（特許文献１参照）では、機械的・化学的に表面を粗化した金属箔が開示されている。また、特開平１１−９７０３２号公報（特許文献２参照）では、高純度アルミニウム箔で特定の金属イオンを抑えたアルミニウム箔材料が開示されている。また、特開平１１−１３５１３０号公報（特許文献３参照）では、圧延の方法により表面を粗化したアルミニウム箔が開示されている。また、特開２０００−１１３８２号公報（特許文献４参照）では、陽極酸化した後脱膜処理したアルミニウム箔材料が提案されている。
【００１０】
【特許文献１】
特開平５−７４４７９号公報
【００１１】
【特許文献２】
特開平１１−９７０３２号公報
【００１２】
【特許文献３】
特開平１１−１３５１３０号公報
【００１３】
【特許文献４】
特開２０００−１１３８２号公報
【００１４】
【発明が解決しようとする課題】
これらはいずれもアルミニウム箔の表面を機械的、化学的、電気化学的にエッチングし表面改質することにより、塗布加工される膜とアルミニウム箔の表面との間の接着強度を高めようとするものである。しかしながら、高純度アルミニウム箔を主に用いるため機械強度が低く、粗化することで強度がさらに低下し、電池の高容量化に必要なアルミニウム箔の薄膜化には問題があった。また、これらの処理膜で表面状態の経時変化が認められ、処理後長時間保管した処理アルミニウム箔に電極活物質を塗布すると、電池の耐久性で問題があった。すなわち、上述の特許文献１から４で示されたアルミニウム箔では、必ずしも塗布される物質との密着性を向上することが達成できていなかった。
【００１５】
そこで、この発明は上述のような問題点を解決するためになされたものであり、電極活物質との密着性を高めることが可能な集電体用アルミニウム箔を提供することである。
【００１６】
この発明の別の目的は、電極活物質との間の接触抵抗を低下させることが可能な集電体用アルミニウム箔を提供することである。
【００１７】
この発明の別の目的は、電極活物質との間の密着性が高く、かつ接触抵抗値が小さい集電体を提供することである。
【００１８】
この発明の別の目的は、寿命などのような特性を高めるように寄与し得る集電体を備えた二次電池を提供することである。
【００１９】
【課題を解決するための手段】
本発明者は、これまでの提案された処理方法での処理膜が保管の環境・時間により特性が変化するという事実を把握した。また、集電体の用途に適するアルミニウム箔には、純度・表面粗度および酸化被膜に関係なく、表面状態の調整が必要であることを発見した。この発見に基づき、本発明では表面処理工程を施すことにより経時安定性に優れたリチウムイオン電池用のアルミニウム集電体を発明するに至った。これにより、アルミニウム箔と電極活物質との密着性を高め、電極活物質の接触抵抗を低く保持することが可能なだけでなく、必ずしも高純度アルミニウム箔が必要でなくなり、合金箔が活用できることにより薄膜化に必要な高強度の集電体用アルミニウム箔を提供できるようになった。
リチウムイオン電池の集電体用アルミニウム箔は、リチウムイオン電池の集電体に使用するアルミニウム箔であって、表面にフッ素が存在し、アルミニウムを９６．５質量％以上９９．９質量％以下、マンガンを１．５質量％以下、鉄を１．５質量％以下、シリコンを０．７質量％以下および銅を０．２質量％以下含み、マンガン、鉄、シリコンおよび銅の合計の含有率が０．１質量％以上３．５質量％未満であり、表面に残存する炭素量は０．３ｍｇ／ｍ 2 以下であり、膜耐電圧が０．２Ｖ以上１．５Ｖ以下の酸化膜が表面に形成されている。
【００２３】
この発明の別の局面に従った集電体用アルミニウム箔は、フッ酸を含む酸性溶液で最終洗浄された表面を有する。このようにフッ酸を含む酸性溶液で表面洗浄された表面は、電極活物質との密着性が高く、かつ電極活物質との接触抵抗を低く保たれる。
【００２４】
具体的には、集電体用アルミニウム箔を、フッ酸を主成分とし、これに他の酸や非イオン界面活性剤を配合した混合溶液系で表面処理する。これにより、表面に分布する鉄を取除き水洗することにより、集電体用アルミニウム箔表面に残存するカーバイド、圧延油が表面に残存することに起因する炭素量を０．３ｍｇ／ｍ2以下に保ち、その表面に膜耐電圧が０．２Ｖ以上１．５Ｖ以下の酸化膜が形成される。このようにアルミニウム箔の表面を改質することにより、特にその油膜質量および酸化被膜の厚みを限定することにより、電極活物質等からなる膜を塗布加工する際にその膜の密着性を改善することができる。これにより、本来のアルミニウム箔の特性を十分に活かすことができる。ここで、表面の炭素の残存量が０．３ｍｇ／ｍ2を超える場合には、アルミニウム箔の表面の上に形成される活物質の膜の密着性が良好でなく、その結果として膜とアルミニウム箔との間の接触抵抗が増大する。また、膜耐電圧が０．２Ｖ未満の場合には、アルミニウム箔の表面が安定ではなく、集電体として使用中に集電体が電解質中に溶解しやすい。また、膜耐電圧が１．５Ｖを超える場合には、集電体の表面の内部抵抗が上昇し、電気効率の悪化や発熱などの弊害が生じる。
【００２５】
より好ましくは、集電体用アルミニウム箔の引張強度は９８ＭＰａ以上である。引張強度が９８ＭＰａ未満の場合には、電極塗工時、ピッチ電極塗工時において加工のために、変形による不具合が（材料延び）生じ、特に薄膜化する際に箔切れなどの問題が生じやすい。
【００２６】
より好ましくは、集電体用アルミニウム箔の厚みは９μｍ以上１００μｍ以下である。厚みが９μｍ未満の場合、アルミニウム箔の表面を処理加工するときや他の製造工程中においてアルミニウム箔の破断や亀裂を生じるおそれがある。また、厚みが１００μｍを超える場合には、特性上の不都合はないが、体積や質量の面で不都合が顕著になるばかりでなく、製造コストの点で不利となる。
【００２７】
アルミニウム箔は、アルミニウムを９６．５質量％以上９９．９質量％以下、マンガンを１．５質量％以下、鉄を１．５質量％以下、シリコンを０．７質量％以下および銅を０．２質量％以下含み、マンガン、鉄、シリコンおよび銅の合計の含有率が０．１質量％以上３．５質量％未満である。ここで、銅、鉄およびシリコンの含有率が多くなるほど化学処理が速くなり制御が困難となる。一方、マンガンはこれに対して化学処理速度を抑える働きがあり、アルミニウム純度および添加元素の配合割合により、反応速度およびエッチング処理表面の形状を制御し得る。また、表面に残存する鉄、シリコンおよび銅は、アルミニウム箔を二次電池の集電体として用いた場合に腐食の原因となる。具体的には、充放電時に電解質によるアルミニウムの腐食量が大きくなり、これにより電極の寿命が低下し、また特性が大きく劣化するために、化学処理が終了した後ではこれらの元素は極力少ない方が好ましい。
【００２８】
この発明に従った集電体は、上述のいずれかのアルミニウム箔を備える。この発明に従った二次電池は、上述の集電体を備え、これを用いることにより二次電池の寿命等の特性を高めることができる。
【００２９】
【実施例】
以下に述べるように、リチウムイオン電池に用いられるアルミニウム箔として、表面処理やアルミニウムの純度を変えたものを、実施例１から３と比較例１から３で準備した。各材料の成分分析値はＩＣＰ（分光分析法）により分析された値を示す。
【００３０】
（実施例１）
公称純度が９８．４５質量％、成分分析値としてシリコンが１４５０ｐｐｍ、鉄が１２５００ｐｐｍ、銅が４０ｐｐｍ、厚みが２０μｍ、引張強度が１８９ＭＰａのアルミニウム硬質箔（ＪＩＳ呼称Ａ８０２１−Ｈ１８）を、フッ酸を含む酸性溶液としてのＴ処理液（フッ酸を０．３質量％含み、ノニオン界面活性剤を０．５質量％含む酸性溶液であり、温度２５℃）に２０秒含浸して最終洗浄を行なった。その後アルミニウム硬質箔を水洗い処理した後に温度７０℃で２０秒乾燥処理した。
【００３１】
（実施例２）
公称純度９９．３質量％、成分分析値として銅が５００ｐｐｍ、鉄が４０００ｐｐｍ、シリコンが２０００ｐｐｍ、厚みが３０μｍ、引張強度が１７５ＭＰａのアルミニウム硬質箔（ＪＩＳ呼称１Ｎ３０−Ｈ１８）を、Ａ処理液（苛性ソーダの濃度が２５ｇ／リットルのアルカリ性溶液であり、温度が２５℃）に２５秒浸漬した。その後アルミニウム硬質箔を水洗い処理した後にフッ酸を含む酸性溶液であるＳ処理液（Ｔ処理液に硫酸を５質量％となるように調整したものであって、温度が２５℃）に浸漬することにより最終洗浄を行なった。その後再度水洗いして温度７０℃で２０秒間乾燥処理を行なった。
【００３２】
（実施例３）
公称純度が９６．７５質量％、成分分析値としてマンガンが１００００ｐｐｍ（表中には記載せず）、銅が２０００ｐｐｍ、鉄が６５００ｐｐｍ、シリコンが６５００ｐｐｍ、厚みが１５μｍ、引張強度が２４０ＭＰａのアルミニウム硬質箔（ＪＩＳ呼称Ａ３００３−Ｈ１８）を、Ｔ処理液（フッ酸を０．３質量％含み、ノニオン界面活性剤を０．５質量％含む酸性溶液で温度が２５℃）に２０秒浸漬して最終洗浄を行なった。その後アルミニウム硬質箔を水洗い処理し温度７０℃で２０秒間乾燥処理した。
【００３３】
（比較例１）
公称純度が９９．３質量％、成分分析値として銅が５００ｐｐｍ、鉄が４０００ｐｐｍ、シリコンが２０００ｐｐｍ、厚みが３０μｍ、引張強度が５０ＭＰａのアルミニウム軟質箔（ＪＩＳ呼称１Ｎ３０−Ｏ）を使用した。
【００３４】
（比較例２）
公称純度が９９．３質量％、成分分析値として銅が５００ｐｐｍ、鉄が４０００ｐｐｍ、シリコンが２０００ｐｐｍ、厚みが３０μｍ、引張強度が１７５ＭＰａのアルミニウム硬質箔（ＪＩＳ呼称１Ｎ３０−Ｈ１８）の表面を塩化メチレンで脱脂処理した。
【００３５】
（比較例３）
公称純度が９９．８５質量％、成分分析値として銅が１０ｐｐｍ、鉄が２５０ｐｐｍ、シリコンが１５０ｐｐｍ、厚みが２０μｍ、引張強度が７２ＭＰａのアルミニウム軟質箔の表面をメタノールで洗浄処理した。
【００３６】
上述の実施例１から３と比較例１から３で準備したアルミニウム箔の組成、アルミニウム、引張強度と、表面処理によって得られたカーボン残存量（最終洗浄された表面に残存する炭素量）を表１に示す。また、アルミニウム箔の表面に形成された酸化膜の被膜耐電圧の測定結果も表１に示す。
【００３７】
【表１】
なお、実施例１では、フッ素を含む無機化合物としてのフッ化物無機金属塩がアルミニウム箔の表面に存在した。実施例２および３では、フッ素と炭素とを含む化合物がアルミニウム箔の表面に存在した。
【００３９】
以上のようにして準備された集電体用アルミニウム箔を用いて、以下に示す試験を行なうことにより、集電体としての性能を確認した。
【００４０】
まず、実施例１から３と比較例１から３で準備した、各集電体用材料の表面にリチウムイオン電池の正極活物質を塗布した後に、集電体用材料を加工した。リチウムイオン電池の正極活物質の組成は、コバルト酸リチウムが５０質量％、アセチレンブラックが１０質量％、ＰＶＤＦ（ポリビニルジフロライド）が５質量％、ＮＭＰ（Ｎメチルピロリドン）が３５質量％であった。その後、正極活物質を温度１００℃で１０分間乾燥処理した。このようにして、乾燥後の厚みが８０μｍとなるように、正極活物質の膜を各集電体用材料の表面に形成した。その後、圧延ロールにて約２０％の圧下を加えて、塗膜を各集電体材料の表面に圧着させた。このようにして圧延後の塗膜の密着性を観察した。
【００４１】
また、集電体用材料と活物質の塗膜との接触抵抗値を測定した。接触抵抗値の測定は図１に示すように、黄銅製の上部電極１（質量：５００ｇ）と、下部電極２の間に各試料を挟んだ状態で、ＡＢ間をデジタルマルチメータにより測定することで行なわれた。この場合、厳密には接触抵抗のみを測定するものではないが、電極や試料の体積抵抗は無視し得るほどに小さいものであるので、その測定値を接触抵抗値と見なすことができる。
【００４２】
塗膜の密着性の観察結果と接触抵抗値の測定結果を表２に示す。
【００４３】
【表２】
実施例１から３で準備した集電体材料は、圧延後においても塗膜の良好な密着性を示し、また塗膜との接触抵抗値も低いことがわかる。
【００４５】
以上に開示された実施例はすべての点で例示であって制限的なものではないと考慮されるべきである。本発明の範囲は上記の実施例ではなくて特許請求の範囲によって示され、特許請求の範囲と均等の意味および範囲内でのすべての修正や変形を含むものであると解釈されるべきである。
【００４６】
【発明の効果】
以上のように、この発明によれば、集電体用アルミニウム箔は電極活物質やバインダとの接着強度に優れ、二次電池の集電体として使用中に電解質への溶出量も少ないため、長期間安定した性能を要求される二次電池に有用である。また、本発明に従った集電体用アルミニウム箔の製造方法は、安全かつ経済的であるので工業生産に適している。
【図面の簡単な説明】
【図１】 実施例で行なわれた接触抵抗値の測定方法を概略的に示す図である。
【符号の説明】
１ 上部電極、２ 下部電極。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a current collector aluminum foil, a current collector, and a secondary battery, and in particular, a current collector aluminum foil used in a lithium ion battery, a polymer battery, and the like, and a current collector and a secondary battery including the same. It is about.
[0002]
[Prior art]
In recent years, lithium ion batteries, polymer batteries, and the like have been used as power sources for mobile phones, personal computers, cameras, and automobiles as high energy efficient secondary batteries.
[0003]
As an example of a secondary battery, a lithium ion battery or a lithium ion polymer battery uses, as a positive electrode material, an active material made of, for example, carbon, a lithium metal oxide salt, or a fluorine-based binder coated on an aluminum foil as a current collector. Is done. In polymer batteries, a positive electrode material or a negative electrode material in which a conductive polymer electrode active material such as polyaniline or polyacetylene is coated on an aluminum foil as a current collector is used.
[0004]
As described above, the reason why the aluminum foil is used as the material for the current collector of the secondary battery is as follows.
[0005]
(1) Since a natural oxide film is formed on the aluminum foil, the aluminum foil is not easily attacked by the electrolytic solution, and is relatively stable as a support.
[0006]
(2) Aluminum foil is excellent in electrical conductivity and has a small electrical resistance value, and therefore does not adversely affect the electrical efficiency of the secondary battery.
[0007]
(3) Since aluminum foil has a low electrical resistance value, heat generation due to resistance is small.
[0008]
(4) Aluminum foil is an economical material with a low manufacturing cost. By the way, in order to constitute a positive electrode or a negative electrode of a secondary battery, an electrode active material or a binder is applied to the surface of an aluminum foil as a current collector. Such a coating material to be coated has a problem that the adhesion between the surface of the aluminum foil is insufficient and the contact resistance between the aluminum foil and the electrode active material is increased. In addition, since the adhesion between the coating material and the surface of the aluminum foil is insufficient, a phenomenon occurs in which the electrode active material film peels off during charging / discharging of the secondary battery, which may lead to the life of the secondary battery, etc. There was a problem of having a great influence on the characteristics of the.
[0009]
In order to solve these problems, industrially, a crimping process or the like is performed after the coating process of the coating material, but it is not always sufficient. Conversely, there may be a problem that the coated film is peeled off during pressure bonding. In order to solve this problem, Japanese Patent Laid-Open No. 5-74479 (see Patent Document 1) discloses a metal foil whose surface is mechanically and chemically roughened. Japanese Patent Application Laid-Open No. 11-97032 (see Patent Document 2) discloses an aluminum foil material in which specific metal ions are suppressed with a high-purity aluminum foil. Japanese Unexamined Patent Publication No. 11-135130 (see Patent Document 3) discloses an aluminum foil whose surface is roughened by a rolling method. Japanese Unexamined Patent Publication No. 2000-11382 (see Patent Document 4) proposes an aluminum foil material that has been anodized and then removed.
[0010]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-74479
[Patent Document 2]
Japanese Patent Laid-Open No. 11-97032 [0012]
[Patent Document 3]
Japanese Patent Laid-Open No. 11-135130
[Patent Document 4]
JP 2000-11382 A [0014]
[Problems to be solved by the invention]
All of these are intended to increase the adhesive strength between the coating film and the surface of the aluminum foil by mechanically, chemically and electrochemically etching the surface of the aluminum foil to modify the surface. It is. However, since the high-purity aluminum foil is mainly used, the mechanical strength is low, and the strength is further lowered by roughening, and there is a problem in thinning the aluminum foil necessary for increasing the capacity of the battery. Further, the surface state of these treated films was changed over time, and when an electrode active material was applied to the treated aluminum foil stored for a long time after the treatment, there was a problem in battery durability. That is, the aluminum foils disclosed in Patent Documents 1 to 4 described above have not necessarily achieved improvement in adhesion with the substance to be applied.
[0015]
Accordingly, the present invention has been made to solve the above-described problems, and it is an object of the present invention to provide an aluminum foil for a current collector that can improve adhesion with an electrode active material.
[0016]
Another object of the present invention is to provide an aluminum foil for a current collector that can reduce the contact resistance with an electrode active material.
[0017]
Another object of the present invention is to provide a current collector having high adhesion to an electrode active material and a small contact resistance value.
[0018]
Another object of the present invention is to provide a secondary battery including a current collector that can contribute to enhancing characteristics such as lifetime.
[0019]
[Means for Solving the Problems]
The present inventor has grasped the fact that the properties of the treated film in the previously proposed treatment methods change depending on the storage environment and time. It was also discovered that the aluminum foil suitable for the current collector needs to be adjusted in surface condition regardless of purity, surface roughness and oxide film. Based on this discovery, the present invention has invented an aluminum current collector for a lithium ion battery excellent in stability over time by performing a surface treatment step. As a result, not only can the adhesion between the aluminum foil and the electrode active material be improved and the contact resistance of the electrode active material can be kept low, but a high-purity aluminum foil is not necessarily required, and the alloy foil can be utilized. It has become possible to provide a high-strength aluminum foil for current collectors required for thinning.
An aluminum foil for a current collector of a lithium ion battery is an aluminum foil used for a current collector of a lithium ion battery, wherein fluorine is present on the surface, and aluminum is 96.5% by mass or more and 99.9% by mass or less, Contains 1.5% by mass or less of manganese, 1.5% by mass or less of iron, 0.7% by mass or less of silicon and 0.2% by mass or less of copper, and the total content of manganese, iron, silicon and copper is 0.1% by mass or more and less than 3.5% by mass, the amount of carbon remaining on the surface is 0.3 mg / m 2 or less, and an oxide film having a withstand voltage of 0.2 V or more and 1.5 V or less is formed on the surface. Is formed.
[0023]
An aluminum foil for a current collector according to another aspect of the present invention has a surface finally cleaned with an acidic solution containing hydrofluoric acid. Thus, the surface cleaned with an acidic solution containing hydrofluoric acid has high adhesion to the electrode active material and low contact resistance with the electrode active material.
[0024]
Specifically, the aluminum foil for current collector is surface-treated with a mixed solution system in which hydrofluoric acid is a main component and other acids and nonionic surfactants are blended. Thus, by removing the iron distributed on the surface and washing with water, the amount of carbon resulting from the remaining carbide and rolling oil remaining on the surface of the aluminum foil for the current collector is 0.3 mg / m 2 or less. An oxide film having a withstand voltage of 0.2 V to 1.5 V is formed on the surface. By modifying the surface of the aluminum foil in this way, particularly by limiting the mass of the oil film and the thickness of the oxide film, the adhesion of the film is improved when coating a film made of an electrode active material or the like. be able to. Thereby, the characteristic of the original aluminum foil can fully be utilized. Here, when the residual amount of carbon on the surface exceeds 0.3 mg / m 2 , the adhesion of the active material film formed on the surface of the aluminum foil is not good, and as a result, the film and The contact resistance with the aluminum foil is increased. Moreover, when the film withstand voltage is less than 0.2 V, the surface of the aluminum foil is not stable, and the current collector is easily dissolved in the electrolyte during use as a current collector. On the other hand, when the withstand voltage of the film exceeds 1.5 V, the internal resistance of the surface of the current collector is increased, causing problems such as deterioration of electric efficiency and heat generation.
[0025]
More preferably, the aluminum foil for current collector has a tensile strength of 98 MPa or more. If the tensile strength is less than 98 MPa, a problem due to deformation (elongation of material) occurs due to processing during electrode coating and pitch electrode coating, and problems such as foil breakage are likely to occur particularly when thinning the film. .
[0026]
More preferably, the thickness of the aluminum foil for current collector is 9 μm or more and 100 μm or less. When the thickness is less than 9 μm, the aluminum foil may break or crack when the surface of the aluminum foil is processed or during other manufacturing processes. Further, when the thickness exceeds 100 μm, there is no inconvenience in characteristics, but not only inconvenient in terms of volume and mass but also in terms of manufacturing cost.
[0027]
A aluminum foil, aluminum 96.5 wt% 99.9 wt% or less, manganese of 1.5 wt% or less, iron 1.5% by mass or less, the silicon below 0.7 wt% and copper 0 .2% by mass or less, and the total content of manganese, iron, silicon and copper is 0.1% by mass or more and less than 3.5% by mass. Here, as the content of copper, iron and silicon increases, the chemical treatment becomes faster and the control becomes more difficult. On the other hand, manganese has a function of suppressing the chemical treatment rate, and the reaction rate and the shape of the etching treatment surface can be controlled by the aluminum purity and the mixing ratio of the additive element. Further, iron, silicon and copper remaining on the surface cause corrosion when an aluminum foil is used as a current collector of a secondary battery. Specifically, the amount of corrosion of aluminum by the electrolyte during charging / discharging increases, thereby reducing the life of the electrode and greatly degrading its characteristics. Is preferred.
[0028]
The current collector according to the present invention includes any one of the aluminum foils described above. The secondary battery according to the present invention includes the above-described current collector, and by using this, characteristics such as the life of the secondary battery can be improved.
[0029]
【Example】
As described below, Examples 1 to 3 and Comparative Examples 1 to 3 were prepared as the aluminum foil used in the lithium ion battery in which the surface treatment and the purity of aluminum were changed. The component analysis value of each material indicates a value analyzed by ICP (spectroscopic analysis).
[0030]
Example 1
Aluminum hard foil (JIS name A8021-H18) having a nominal purity of 98.45 mass%, silicon analysis of 1450 ppm, iron of 12500 ppm, copper of 40 ppm, thickness of 20 μm, and tensile strength of 189 MPa, containing hydrofluoric acid The T treatment solution (containing 0.3% by mass of hydrofluoric acid and 0.5% by mass of nonionic surfactant and containing 25% by mass of nonionic surfactant) was impregnated for 20 seconds as an acidic solution for final cleaning. Thereafter, the aluminum hard foil was washed with water and then dried at a temperature of 70 ° C. for 20 seconds.
[0031]
(Example 2)
An aluminum hard foil (JIS name 1N30-H18) having a nominal purity of 99.3% by mass, component analysis values of copper of 500 ppm, iron of 4000 ppm, silicon of 2000 ppm, thickness of 30 μm, and tensile strength of 175 MPa is treated with A treatment liquid (caustic soda). Was immersed in an alkaline solution at a temperature of 25 ° C. for 25 seconds. Then, after the aluminum hard foil is washed with water, it is immersed in an S treatment solution that is an acidic solution containing hydrofluoric acid (T treatment solution is adjusted so that sulfuric acid is 5% by mass and the temperature is 25 ° C.). The final washing was performed. Thereafter, it was washed again with water and dried at a temperature of 70 ° C. for 20 seconds.
[0032]
(Example 3)
Aluminum hard foil having a nominal purity of 96.75% by mass, a component analysis value of 10,000 ppm manganese (not shown in the table), 2000 ppm copper, 6500 ppm iron, 6500 ppm silicon, 15 μm thickness, and 240 MPa tensile strength (JIS name A3003-H18) is immersed in a T treatment liquid (acid solution containing 0.3% by mass hydrofluoric acid and 0.5% by mass nonionic surfactant at a temperature of 25 ° C.) for 20 seconds for final cleaning. Was done. Thereafter, the aluminum hard foil was washed with water and dried at a temperature of 70 ° C. for 20 seconds.
[0033]
(Comparative Example 1)
An aluminum soft foil (JIS name 1N30-O) having a nominal purity of 99.3% by mass, copper analysis of 500 ppm, iron of 4000 ppm, silicon of 2000 ppm, thickness of 30 μm, and tensile strength of 50 MPa was used.
[0034]
(Comparative Example 2)
The surface of an aluminum hard foil (JIS name 1N30-H18) having a nominal purity of 99.3% by mass, component analysis values of copper of 500 ppm, iron of 4000 ppm, silicon of 2000 ppm, thickness of 30 μm, and tensile strength of 175 MPa is methylene chloride. Degreased.
[0035]
(Comparative Example 3)
The surface of an aluminum flexible foil having a nominal purity of 99.85% by mass, component analysis values of copper of 10 ppm, iron of 250 ppm, silicon of 150 ppm, thickness of 20 μm, and tensile strength of 72 MPa was washed with methanol.
[0036]
The composition, aluminum, and tensile strength of the aluminum foil prepared in Examples 1 to 3 and Comparative Examples 1 to 3 described above, and the remaining carbon amount obtained by the surface treatment (the amount of carbon remaining on the final cleaned surface) are shown. It is shown in 1. Table 1 also shows the measurement results of the withstand voltage of the oxide film formed on the surface of the aluminum foil.
[0037]
[Table 1]
In Example 1, a fluoride inorganic metal salt as an inorganic compound containing fluorine was present on the surface of the aluminum foil. In Examples 2 and 3, a compound containing fluorine and carbon was present on the surface of the aluminum foil.
[0039]
The performance as a current collector was confirmed by performing the following test using the aluminum foil for current collector prepared as described above.
[0040]
First, after applying the positive electrode active material of the lithium ion battery to the surface of each current collector material prepared in Examples 1 to 3 and Comparative Examples 1 to 3, the current collector material was processed. The composition of the positive electrode active material of the lithium ion battery was 50% by mass of lithium cobaltate, 10% by mass of acetylene black, 5% by mass of PVDF (polyvinyl difluoride), and 35% by mass of NMP (N-methylpyrrolidone). It was. Thereafter, the positive electrode active material was dried at a temperature of 100 ° C. for 10 minutes. In this way, a film of the positive electrode active material was formed on the surface of each current collector material so that the thickness after drying was 80 μm. Then, about 20% reduction was applied with the rolling roll, and the coating film was crimped | bonded to the surface of each collector material. Thus, the adhesion of the coated film after rolling was observed.
[0041]
Further, the contact resistance value between the current collector material and the active material coating was measured. As shown in FIG. 1, the contact resistance value is measured with a digital multimeter between AB with each sample sandwiched between the upper electrode 1 (mass: 500 g) made of brass and the
[0042]
Table 2 shows the observation results of the adhesion of the coating film and the measurement results of the contact resistance value.
[0043]
[Table 2]
It can be seen that the current collector materials prepared in Examples 1 to 3 show good adhesion of the coating film even after rolling, and the contact resistance value with the coating film is low.
[0045]
The embodiments disclosed above are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the scope of claims for patent, and should be construed to include all modifications and variations within the scope and meaning equivalent to the scope of claims for patent.
[0046]
【The invention's effect】
As described above, according to the present invention, the current collector aluminum foil has excellent adhesion strength with the electrode active material and the binder, and the amount of elution into the electrolyte during use as a current collector for a secondary battery is small. This is useful for secondary batteries that require stable performance over a long period of time. Moreover, the method for producing an aluminum foil for a current collector according to the present invention is suitable for industrial production because it is safe and economical.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a method of measuring a contact resistance value performed in an example.
[Explanation of symbols]
1 Upper electrode, 2 Lower electrode.
Claims (6)
表面にフッ素が存在し、There is fluorine on the surface,
アルミニウムを９６．５質量％以上９９．９質量％以下、マンガンを１．５質量％以下、鉄を１．５質量％以下、シリコンを０．７質量％以下および銅を０．２質量％以下含み、マンガン、鉄、シリコンおよび銅の合計の含有率が０．１質量％以上３．５質量％未満であり、96.5% by mass or more and 99.9% by mass or less of aluminum, 1.5% by mass or less of manganese, 1.5% by mass or less of iron, 0.7% by mass or less of silicon and 0.2% by mass or less of copper Including, the total content of manganese, iron, silicon and copper is 0.1 mass% or more and less than 3.5 mass%,
前記表面に残存する炭素量は０．３ｍｇ／ｍThe amount of carbon remaining on the surface is 0.3 mg / m 22 以下であり、膜耐電圧が０．２Ｖ以上１．５Ｖ以下の酸化膜が前記表面に形成されている、リチウムイオン電池の集電体用アルミニウム箔。An aluminum foil for a current collector of a lithium ion battery, wherein an oxide film having a withstand voltage of 0.2 V to 1.5 V is formed on the surface.
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