JP2004220871A

JP2004220871A - Material of lithium cell anode and its manufacturing method

Info

Publication number: JP2004220871A
Application number: JP2003005145A
Authority: JP
Inventors: Toshihisa Hara; 利久原
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2003-01-10
Filing date: 2003-01-10
Publication date: 2004-08-05
Anticipated expiration: 2023-01-10
Also published as: JP4136674B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a material of lithium cell anode with high energy density, excellent cycle characteristics and stable cell characteristics. <P>SOLUTION: A surface plated layer made of an Ni layer, a Cu-Sn alloy layer and an Sn layer is formed in that order on the surface of a parent material made of Cu or a Cu alloy, with the Cu-Sn alloy layer made of a η layer (Cu<SB>6</SB>Sn<SB>5</SB>) of a thickness of 0.5 to 100 μm. After the surface of the parent material is coated with the Ni plated layer, it is coated with the Cu plated layer and the Sn plated layer in that order once, twice or more, and then is given a heat treatment to complete the Cu-Sn alloy layer. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、自動車、携帯電話等に使用されるリチウム二次電池の負極用材料に関する。さらに詳しくは、高エネルギー密度で充放電サイクル性に優れ、さらに電池特性の安定したリチウム二次電池の負極用材料に関する。
【０００２】
【従来の技術】
現在、リチウム電池に用いられている負極活物質は黒鉛であり、銅箔の表面に厚さ１００μｍ程度の黒鉛の薄膜を形成したものが負極として用いられている。リチウム二次電池は、鉛蓄電池やニッケル水素蓄電池などに比べ、エネルギー密度が高いが、さらにエネルギー密度が高く、軽量化や小型化に対応できる二次電池が望まれている。しかし、黒鉛材料では、さらなる小型化と高エネルギー密度化に限界があり、コストも高かった。
【０００３】
エネルギー密度を向上させるため、負極活物質として黒鉛粒子などとともにＳｎやＳｉを混合した粉末を用いたり、インジウムやアンチモンなどの希少金属を用いることが提案されているが、コストが高くなる問題があった（特開２００１−２６６８９１，特開２０００−２１４０４，特開平１０−２１９１３号公報）。また、特開２００２−１５１０５６には、ＳｎとＩｎの合金膜を形成した銅箔を負極とすることが提案されているが、Ｉｎをめっきするのは難しかった。さらに鉛やビスマス、カドミウムなどを負極活物質として用いる提案もあるが、これらは環境規制物質であり、使用が規制されるという問題がある。
【０００４】
【発明が解決しようとする課題】
一方、黒鉛より理論的にエネルギー密度を高くできる錫が、次世代リチウム電池の負極活物質として従来より研究されている。しかし、錫は満充電時に体積が約３倍に膨張し、体積変化により集電体である銅箔が断絶されるため、充放電サイクル性が悪く、数回のサイクルで放電容量が低下するという問題があった。
これに対し、体積膨張を吸収するため、例えば銅箔に錫を間隔をあけてポーラスにめっきする技術が検討されたが、これは実用化にいたっていない。
また、錫めっきした銅箔を熱処理したものを負極に用いると、サイクル性が向上すると報告されているが、これは錫への銅の拡散を制御していないために性能が不安定であり、実用化できなかった。
【０００５】
本発明は、Ｓｎをリチウム電池の負極活物質として用いる場合の上記問題点に鑑みなされたもので、高エネルギー密度で、サイクル性に優れ、電池特性が安定しているリチウム電池負極用材料を提供することを目的とする。
【０００６】
【課題を解決するための手段】
Ｃｕ母材に、Ｓｎ又はＳｎ合金からなる表面めっき層を形成した後（図１１に表面めっき構造の概念図を示す）、熱処理を行うと、母材成分のＣｕがＳｎ中に拡散し、最初にＳｎとＣｕの合金層であるη層（Ｃｕ_６Ｓｎ_５）が形成され、熱処理を続けるとε層（Ｃｕ_３Ｓｎ）が形成され（図１２に表面めっき構造の概念図を示す）、最終的にはε層のみとなってしまう。η層形成時にＣｕは約２倍の体積のＳｎと相互拡散する過程で結晶内に空孔及びそれが集積したボイドができ、これが、Ｓｎがリチウムと反応するときの体積変化による歪を緩和し、電池のサイクル特性を向上させる。しかし、ε層が形成されるとボイドがε層とＣｕ母材の界面に集まり、Ｃｕ−Ｓｎ合金層の剥離を起こす問題があり、また、ε層となったＳｎはリチウムとの充放電に寄与しないため、電気特性が低下する。
本発明は、このような知見に基づき、表面めっき層におけるε層の形成を抑制し、η層を含むＣｕ−Ｓｎ合金層を安定化させることにより、リチウム電池負極としての性能を向上させたものである。
【０００７】
その１つは、Ｃｕ母材にＮｉ層をめっきしてＣｕ母材からのＣｕの拡散を抑制し、η層を含むＣｕ−Ｓｎ合金層を安定化させたものである。
すなわち、このリチウム電池負極用材料は、Ｃｕ又はＣｕ合金からなる母材表面に、Ｎｉ層及びＣｕ−Ｓｎ合金層からなる表面めっき層がこの順に形成され、前記Ｃｕ−Ｓｎ合金層はη層（Ｃｕ_６Ｓｎ_５）を含み、その厚さが０．５〜１００μｍであることを特徴とする。あるいは前記母材表面に、Ｎｉ層、Ｃｕ−Ｓｎ合金層及びＳｎ層からなる表面めっき層がこの順に形成され、前記Ｃｕ−Ｓｎ層はη層を含み、Ｃｕ−Ｓｎ合金層及びＳｎ層の合計厚さが０．５〜１００μｍであることを特徴とする。上記Ｃｕ−Ｓｎ合金層のＣｕ含有量は５〜７０ａｔ％で、全てη層からなるのが望ましい。また、Ｃｕ−Ｓｎ合金層又は／及びＳｎ層は、Ｓｉ、Ｚｎ、Ａｌ、Ｎｉ、Ｆｅ、Ｃｒ、Ｔｉ、Ｚｒ、Ｃｏ、Ｓ、Ｐ、Ｂ、Ｍｇ、Ｃ、Ｏ、Ｈのうち少なくとも１種類を含むことができる。
【０００８】
上記リチウム電池負極用材料は、Ｃｕ又はＣｕ合金からなる母材表面にＮｉめっき層を形成した後、Ｃｕ層とＳｎ層のめっきをこの順に１回又は２回以上繰り返し形成し、熱処理を行うことで製造できる。Ｎｉ層が母材から拡散するＣｕ量を制限するので、熱処理後η相が形成されるように計算された量のＣｕとＳｎをＮｉ層上にめっきすることにより安定したη層が形成される。具体的には、Ｃｕ層とＳｎ層の合計中、Ｃｕ含有量を５〜７０ａｔ％に制御することにより、ε層の形成を防止する。図１に熱処理前の表面めっき層の構造、図２に熱処理後の表面めっき層の構造の概念図を示す。最上層に形成されたＳｎ層が十分厚ければ、熱処理後にＳｎ層が残留する。
Ｃｕ−Ｓｎ合金層又はＣｕ−Ｓｎ合金層及びＳｎ層の厚さは、例えば、Ｎｉ層上に約０．１〜０．５μｍのＣｕ層と０．２〜１．５μｍのＳｎ層を交互に１〜１００回繰り返し多層にめっきした後、熱処理することにより調整することができる。
【０００９】
上記リチウム電池負極用材料では、熱処理条件と使用条件によって、下地ＮｉがＣｕ−Ｓｎ層に拡散する。また、Ｃｕめっき層及び／又はＳｎめっき層に第３元素、具体的にはＳｉ、Ｚｎ、Ｓｎ、Ａｌ、Ｎｉ、Ｆｅ、Ｃｒ、Ｔｉ、Ｚｒ、Ｃｏ、Ｓ、Ｐ、Ｂ、Ｍｇ、Ｃ、Ｏ、Ｈのいずれか１種以上を、２元合金又は多元合金めっきの形で、又は添加剤を含むめっき浴を用いることで添加することができる。あるいは、Ｃｕめっき層とＳｎめっき層のほかに上記元素からなるめっき層又は上記元素を含むめっき層を形成し、又は上記元素を蒸着し、熱処理によりＣｕ−Ｓｎ層に（熱処理後Ｓｎ層が残留する場合はＳｎ層にも）取り込むことができる。例えば第３元素がＮｉであれば、Ｃｕ又はＣｕ合金母材上にＮｉ、Ｃｕ、Ｓｎ又はそれらの合金をこの順に１回又は２回以上めっきし、第３元素がＺｎであれば、Ｃｕ又はＣｕ合金母材上にＮｉめっき層を形成した後、Ｚｎ、Ｃｕ、Ｓｎ又はそれらの合金をこの順に１回又は２回以上めっきし、熱処理を行い、それぞれＮｉ層上にＣｕ−Ｓｎ−Ｎｉ合金層、Ｃｕ−Ｓｎ−Ｚｎ合金層を得る。なお、Ｃｕ層とＳｎ層の間に挟まれるＮｉ層の厚さは、めっき密着性を確保するため０．２μｍ以上とするのが望ましい。
第３元素の含有量は０．００１〜２０ａｔ％の範囲である。これらの元素は、炭素よりもエネルギー容量が高いか（特にＳｉ、Ｚｎ、Ａｌ）又は合金のマトリックス（η層）中のＳｎの分布状態を安定化させ（特にＮｉ、Ｃｒ、Ｃｏ、Ｓ、Ｐ、Ｂ）、いずれもリチウム電池負極用材料の特性を向上させる。
図３〜図６に第３元素を含む場合の表面めっき層の構造（熱処理後）の概念図を示す。
【００１０】
なお、前記製造方法では、Ｃｕ層とＳｎ層を別々にめっきで形成した後、熱処理することによりη層を含むＣｕ−Ｓｎ合金層を形成したが、Ｃｕ−Ｓｎ合金めっきを行い、これを熱処理してη層を含むＣｕ−Ｓｎ合金層を形成する方法によっても、目的を達成することができる。鉛フリーはんだめっきとして知られているＳｎ−Ｃｕ合金めっきは、Ｃｕを３．５ａｔ％程度含有するものが一般的であるが、めっき条件によりＣｕ濃度を高くめっきすることができ、その場合、めっき層構造はＳｎリッチ層とＣｕリッチ層が交互に重なった構造となる。Ｃｕ濃度を５〜７０ａｔ％に制御したＣｕ−Ｓｎ合金めっき層を形成し、これを熱処理することにより、ε層を形成させず、η層を含むＣｕ−Ｓｎ合金層を形成することができ、η層形成時に空孔及びボイドが形成される。
また、Ｃｕ−Ｓｎだけでなく、先に示した元素、Ｓｉ、Ｚｎ、Ｓｎ、Ａｌ、Ｎｉ、Ｆｅ、Ｃｒ、Ｔｉ、Ｚｒ、Ｃｏ、Ｓ、Ｐ、Ｂ、Ｃ、Ｏ、Ｍｇの１種以上を、前記と同様の方法により添加することができる。
図７に第３元素を含む場合の表面めっき層の構造（熱処理前）の概念図を示す。
【００１１】
もう１つは、特定の添加元素を含むＣｕ母材を使用して、ε層の形成を抑制し、η層を含むＣｕ−Ｓｎ合金層を安定化させたものである。
すなわち、このリチウム電池負極材料は、Ｓｉ、Ｚｎ、Ｓｎ、Ａｌ、Ｎｉ、Ｆｅ、Ｃｒ、Ｔｉ、Ｚｒ、Ｃｏ、Ｓ、Ｐ、Ｂ、Ｍｇのうち少なくとも１種類の添加元素を含むＣｕ合金からなる母材表面に、当該添加元素を含むＣｕ−Ｓｎ合金層からなる表面めっき層が形成され、前記Ｃｕ−Ｓｎ合金層はη層を含み、その厚さが０．５〜１００μｍであることを特徴とする。あるいは、前記母材表面に、前記添加元素を含むＣｕ−Ｓｎ合金層及びＳｎ層からなる表面めっき層がこの順に形成され、前記Ｃｕ−Ｓｎ合金層はη層を含み、Ｃｕ−Ｓｎ合金層及びＳｎ層の合計厚さが０．５〜１００μｍであることを特徴とする。上記Ｃｕ−Ｓｎ合金層のＣｕ含有量は５〜７０ａｔ％で、全てη層からなるのが望ましい。
また、Ｃｕ−Ｓｎ合金層は、母材に含まれる前記添加元素を含め、Ｓｉ、Ｚｎ、Ａｌ、Ｎｉ、Ｆｅ、Ｃｒ、Ｔｉ、Ｚｒ、Ｃｏ、Ｓ、Ｐ、Ｂ、Ｍｇ、Ｃ、Ｏ、Ｈのうち少なくとも１種類を含むことができ、Ｓｎ層も前記元素のうち少なくとも１種類を含むことができる。
【００１２】
上記リチウム電池負極用材料は、Ｓｉ、Ｚｎ、Ｓｎ、Ａｌ、Ｎｉ、Ｆｅ、Ｃｒ、Ｔｉ、Ｚｒ、Ｃｏ、Ｓ、Ｐ、Ｂ、Ｍｇのうち少なくとも１種類を含むＣｕ合金からなる母材表面にＳｎめっき層を形成し、熱処理を行うことで製造できる。熱処理によりη層を含むＣｕ−Ｓｎ合金層が形成されるが、この形成時にＣｕとともにη層中にＣｕ合金中の添加元素が拡散し、Ｃｕ−Ｓｎ−α（αは母材中の前記添加元素）の三元又は多元合金層を形成する。図８及び図９に熱処理後の表面めっき層の構造の概念図を示す。
上記添加元素はＳｎ層とη層及びη層と母材の界面に濃縮層を形成し、Ｃｕ−Ｓｎ−αの三元又は多元合金が成長することによって、ε層の形成が抑制されη層が安定化する。前記添加元素は、炭素よりもエネルギー容量が高いか、合金のマトリックス（η層）を安定化させる効果があり、いずれもリチウム電池負極用材料の特性を向上させる。
さらに、上記リチウム電池負極用材料を製造する場合に、Ｓｎめっき層に第３元素、具体的にはＳｉ、Ｚｎ、Ａｌ、Ｎｉ、Ｆｅ、Ｃｒ、Ｔｉ、Ｚｒ、Ｃｏ、Ｓ、Ｐ、Ｂ、Ｍｇ、Ｃ、Ｏ、Ｈのいずれか１種以上を、２元合金又は多元合金めっきの形で、あるいは添加剤を含むめっき浴を用いることで添加することができる。
【００１３】
【発明の実施の形態】
Ｎｉ層、Ｃｕ層、Ｓｎ層の形成は電気めっき、無電解めっき、その他のめっき手段を利用できる。
次亜リン酸等を還元剤とする無電解めっきでは、還元剤成分のＰ（リン）やＢ（ボロン）などがめっき皮膜中に取り込まれる。また、無電解めっきでは還元剤がめっき皮膜中に取り込まれ、加熱処理後に空孔やボイドを増加する傾向がある。表面めっき層に形成された空孔やボイドは充放電のサイクル性を向上させる。
【００１４】
電気めっき製造方法としては、Ｎｉめっきはワット浴やスルファミン酸浴を用い、めっき温度４０〜５５℃、電流密度３〜３０Ａ／ｄｍ^２で行う。Ｎｉめっき厚みは０．１〜５μｍである、加工性を考えると０．２〜１μｍが望ましい。めっき条件によりＮｉ粒径を粗く変化させ、表面積を大きくすることができる。
Ｃｕめっきには一般にはシアン浴が使われているが、錫めっき液へのシアン混入による液劣化や廃水処理の問題があるため、硫酸銅浴を使用し、電流密度２．５〜１５Ａ／ｄｍ^２で行う。めっき条件によってＣｕめっき粒形を制御することができ、例えばめっき温度が４０℃を超えるとＣｕめっき粒が大きくなる。また、Ｎｉめっき上にＣｕめっきを行う場合、電流密度２．５Ａ／ｄｍ^２未満及び１０Ａ／ｄｍ^２超の場合にもＣｕめっき粒が大きくなる。めっき粒が大きくなることで表面積が大きくなり、その方が、熱処理後のＣｕ−Ｓｎ合金層及びＳｎ層がリチウム電池負極に適したものとなる。また、Ｃｕめっき浴に光沢剤を入れると熱処理後にボイドが増加する。
電気Ｓｎめっきは、めっき温度２５℃以下、めっき電流密度２〜２０Ａ／ｄｍ^２で施した後に熱処理を行う。めっき液中に光沢剤を添加すると、光沢剤中のＳやＣ成分がめっき皮膜中へ取り込まれ、サイクル性の向上に寄与する。
【００１５】
充放電サイクル性が良くなる原因のひとつとして、Ｃｕ−Ｓｎ合金層又はＳｎ層内にできる空孔が挙げられる。めっき液中の添加剤と加熱後の空孔及びボイドの発生を断面観察によって調査した結果、めっき浴中に光沢剤等の添加剤を含む方が空孔及びボイドの発生が多いことが見出された。めっき浴中に添加剤を入れることにより、添加剤の成分であるＣやＳなどの第３元素がめっき皮膜中に取り込まれ、めっき欠陥が増加し、これが熱処理後の空孔及びボイドの増加につながるものと考えられる。なお、添加剤としては、ＣやＳなど電池性能、サイクル性を向上させる元素を含むものが望ましい。
【００１６】
リチウムと反応するＣｕ−Ｓｎ合金層及びＳｎ層の厚みは薄いほど生産性が良く、低コストであるが、薄いと電池容量が小さくなるため、０．５μｍ以上が必要である。一方、高容量のためにはＣｕ−Ｓｎ合金層及びＳｎ層厚みは１０μｍ以上が望ましく、多層構造や合金めっきを行えば１００μｍ形成することも可能である。厚いほど電池容量は大きくなるが、厚くするほど製造コストは高くなるためＣｕ−Ｓｎ合金層及びＳｎ層の合計厚さは１００μｍを上限とする。
【００１７】
Ｃｕ又はＣｕ合金母材は、圧延銅板条や電解銅箔を用いることができる。Ｓｉ、Ｚｎ、Ｓｎ、Ａｌ、Ｎｉ、Ｆｅ、Ｃｒ、Ｔｉ、Ｚｒ、Ｃｏ、Ｓ、Ｐ、Ｂ、Ｏ、Ｃ、Ｍｇ等の添加元素を含む母材は圧延銅板条である。添加元素を含むＣｕ合金圧延板は純銅板にくらべ軟化しにくいため、充放電時の発熱による板の破断やめっき層の剥離が起こりにくいという利点を持つ。
圧延銅板条の厚みは例えば８０〜３００μｍのものが利用できる。もちろん、１０〜２１０μｍ厚みの電解銅箔を用いてもよい。電解銅箔は表面を粗面化したものでもよい。
【００１８】
銅板条の表面粗さについて、圧延銅板条の表面粗さは一般的にＲｍａｘ＝０．８μｍ、Ｒａ＝０．１μｍ程度であるが、電解銅箔と同様に、表面積を多くとるために粗くしたい場合は研磨仕上げやエッチング仕上げにより所望の粗さ（ＲＺ＝１μｍ以上）に仕上げることができる。さらに、ＮｉめっきやＣｕめっきを粗く仕上げることにより表面粗さを制御し、Ｓｎめっきをまったく金属光沢の無い粗い表面状態にすることもできる。
【００１９】
本発明では、めっき後の熱処理により、Ｃｕ層とＳｎ層、又はＣｕ母材中のＣｕとＳｎ層を合金化させ、Ｃｕ−Ｓｎ合金層を形成するが、ＣｕとＳｎの相互拡散は２５℃の室温でも進行し、また電池の発熱によっても合金化するため、熱処理により完全に合金化させておく必要はない。例えばＣｕ層とＳｎ層の多層構造を形成してこれを合金化させる場合、部分的にＣｕとＳｎの多層構造が残った表面めっき層でも、電池負極材料として使用できる。
【００２０】
本発明の製造方法において、生産性良く熱処理するには２００℃以上の高温での短時間加熱が望ましい。熱処理温度が２３０℃以上ではＳｎが溶融するため拡散がすばやく進行する。６００℃以上になると、Ｃｕ母材が軟化し、歪が発生する。よって、高温で熱処理する場合は２３０℃〜６００℃とする。熱処理を行うことにより、表面のＳｎ結晶粒子が大きくなり、Ｃｕ−Ｓｎ合金層が形成され、ウイスカが発生しにくくなる。高温で熱処理する場合の加熱時間については、３秒以下では、材料の熱伝達が不均一であり、熱処理後の外観ムラが発生する。６０秒以上では、表層のＳｎ層の酸化が進行するため、加熱時間は３〜６０秒とする。還元雰囲気や不活性雰囲気中で加熱することが望ましい。
【００２１】
また、熱処理は２００℃以下の温度で時間をかけてＣｕ−Ｓｎ系合金層を成長させることもできる。２００℃以下の加熱では錫の溶融による結晶粒変化がないため、熱処理後も金属光沢の無い表面状態を保持することができる。
さらに、Ｃｕ層とＳｎ層を繰り返し積層して熱処理する場合、ＣｕめっきとＳｎめっきの１サイクルごと又は複数サイクル毎に熱処理を行う（めっき工程の中間で熱処理を行う）こともでき、まためっき工程終了後に熱処理を複数回に分けて行うこともできる。電池組み立て後に電池性能に影響を与えない１２０℃以下の温度での熱を加えても構わない。
【００２２】
なお、熱処理によるＳｎへのＣｕの拡散は均一ではなく、Ｓｎの結晶粒界への拡散は結晶粒内への拡散より早いため、Ｃｕ−Ｓｎ合金層は波状に成長する。また、波状状態は下地めっき粒によって変化する。そのため、加熱後に一部は完全にη層（Ｃｕ_６Ｓｎ_５）となり、一部にＳｎ層やＣｕ層が残った状態も観察されるが、一部合金化していなくても電池特性としては良好である。図１０にその表面めっき構造（熱処理後）の概念図を示す。
【００２３】
【実施例】
＜供試材の作成条件＞
Ｃｕ又はＣｕ合金母材として表１のＮｏ．１〜１４に示す種々の組成の板材（厚さ１００μｍ）を用い、Ｎｏ．１〜３，６〜９については、母材上にＮｉめっきを施し、続いてＣｕめっき及びＳｎめっきを順次１又は２回以上繰り返し施し、Ｎｏ．４はＮｉめっきの上にＺｎめっきを形成した後、ＣｕめっきとＳｎめっきを１回ずつ施し、Ｎｏ．５はＮｉめっき、Ｃｕめっき及びＳｎめっきを２回繰り返し施した（いずれも各めっき層の厚みは熱処理後のＣｕ−Ｓｎ合金層がすべてη層になるように計算した）。Ｎｏ．１０〜１４については、Ｓｎめっきのみを施した。Ｎｉめっき、Ｃｕめっき及びＳｎめっきの各めっき浴を表２〜表４に示す。ただし、光沢剤はＮｏ．３，６のみで添加した。
続いて、Ｎｏ．１〜１３の板材に熱処理を施し、Ｃｕ合金母材の上に表面めっき層（Ｎｉ層、Ｃｕ−Ｓｎ合金層、Ｓｎ層）をもつリチウム電池負極用材料（供試材）が得られた。
表１に各供試材（Ｎｏ．１〜１４）の母材組成、熱処理後の表面めっき層構成及び各層厚、熱処理条件をあわせて示す。
【００２４】
【表１】

【００２５】
【表２】

【００２６】
【表３】

【００２７】
【表４】

【００２８】
なお、各供試材の各めっき層厚さは下記要領で測定した。また、各供試材について、エネルギー密度、充放電サイクル性、電池安定性試験を行った。その結果を表１にあわせて示す。
［Ｓｎ及びＮｉ層厚さ測定］
Ｓｎ及びＮｉ層厚さは、蛍光Ｘ線膜厚計（セイコー電子工業株式会社；型式ＳＦＴ１５６Ａ）を用いて測定した。
［Ｃｕ−Ｓｎ合金層厚さ測定］
Ｃｕ−Ｓｎ合金層厚さは、蛍光Ｘ線膜厚計（セイコー電子工業株式会社；型式ＳＦＴ１５６Ａ）を用いてＳｎ量を測定し、Ｓｎを含む合金層のめっき厚みとした。また、めっきをミクロトーム法にて加工し、表面層の断面をＳＥＭ観察し、層厚さを調査した。
【００２９】
［放電容量及び充放電サイクル数］
放電容量は、供試材を負極とし、Ｌｉ箔を正極とし、電解液を１ＭＬｉＣｌＯ_４／ＥＣ＋ＰＣとしたセルで、充放電範囲０〜１Ｖで測定した。充放電サイクル数は、定電圧定電流で充放電を繰り返し、初期の放電容量が維持できる回数とした。
［電池安定性］
１６０℃×１２０ｈｒ高温放置した材料を用い、エネルギー密度を測定した。電池安定性評価基準は、加熱前の８０％以上のエネルギー密度を持つレベルを○とし、エネルギー密度がそれ以下に低下したレベルを×と評価した。
【００３０】
表１に示すように、めっき層構成にＮｉ層を持つＮｏ．１〜９は、いずれも放電容量が高く、充放電サイクル性が良好であり、電池安定性が高かった。また、Ｎｏ．１０、１１はＮｉ層をもたないが、母材が特定の添加元素を含み、該添加元素によりε層の成長が抑制されたため、高い放電容量を得ることができた。Ｎｉ層をもつと同時にＣｕ−Ｓｎ合金層中にリチウムと錫の反応を助ける成分を含むＮｏ．３〜６は、サイクル性が特に良好であった。
一方、Ｎｏ．１２〜１４はＮｉ層がなく、母材に特定の添加元素も含まれていないので、充放電サイクル時や高温使用環境でε層が成長し、電池性能が低下した。
【００３１】
なお、Ｃｕ層とＳｎ層を熱処理することによりＣｕ−Ｓｎ合金層を形成する代わりに、Ｃｕ−Ｓｎ合金めっきを行うことによっても同様の効果を得ることができる。その際のめっき浴を表５に示す。
【００３２】
【表５】

【００３３】
【発明の効果】
本発明によれば、高エネルギー密度で、サイクル性に優れ、低コストのリチウム電池負極用材料を提供することができる。また、高温で使用される場合（エンジンルーム等）においても優れた電池安定性が保持できる。
【図面の簡単な説明】
【図１】表面めっき層の加熱前の断面の概念図である。
【図２】その加熱後の断面の概念図である。
【図３】第３元素を含む表面めっき層の断面の概念図である。
【図４】第３元素を含む表面めっき層の断面の概念図である。
【図５】第３元素を含む表面めっき層の断面の概念図である。
【図６】第３元素を含む表面めっき層の断面の概念図である。
【図７】第３元素を含む表面めっき層の断面の概念図である。
【図８】第３元素を含む表面めっき層の断面の概念図である。
【図９】多元素を含む表面めっき層の断面の概念図である。
【図１０】熱処理後も部分的にＣｕ層やＳｎ層が残っている表面めっき層の断面の概念図である。
【図１１】従来技術による表面めっき層の断面の概念図である。
【図１２】従来技術による表面めっき層の断面の概念図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a material for a negative electrode of a lithium secondary battery used for an automobile, a mobile phone, and the like. More specifically, the present invention relates to a negative electrode material for a lithium secondary battery having high energy density, excellent charge / discharge cycleability, and stable battery characteristics.
[0002]
[Prior art]
At present, the negative electrode active material used in lithium batteries is graphite, and a copper foil having a graphite thin film with a thickness of about 100 μm formed on the surface is used as the negative electrode. A lithium secondary battery has a higher energy density than a lead storage battery, a nickel-metal hydride storage battery, or the like, but a secondary battery that has a higher energy density and can be reduced in weight and size is desired. However, graphite materials have limitations in further miniaturization and high energy density, and have high costs.
[0003]
In order to improve the energy density, it has been proposed to use a powder in which Sn or Si is mixed together with graphite particles or the like as a negative electrode active material, or to use a rare metal such as indium or antimony. (JP-A-2001-268991, JP-A-2000-21404, and JP-A-10-21913). Japanese Patent Application Laid-Open No. 2002-151056 proposes that a copper foil on which an alloy film of Sn and In is formed be used as a negative electrode, but it is difficult to plate In. Further, there are proposals to use lead, bismuth, cadmium, and the like as a negative electrode active material, but these are environmentally regulated substances, and there is a problem that their use is regulated.
[0004]
[Problems to be solved by the invention]
On the other hand, tin, which can theoretically have a higher energy density than graphite, has been studied as a negative electrode active material for next-generation lithium batteries. However, the volume of tin expands about three times when fully charged, and the change in volume breaks the copper foil, which is a current collector, so that the charge / discharge cycleability is poor and the discharge capacity is reduced in several cycles. There was a problem.
On the other hand, in order to absorb the volume expansion, for example, a technique of plating tin on a copper foil at intervals has been studied, but this has not been put to practical use.
In addition, it is reported that the use of a heat-treated tin-plated copper foil for the negative electrode improves cycleability.However, this is because the performance of the copper is not controlled because the diffusion of copper into tin is unstable. It could not be put to practical use.
[0005]
The present invention has been made in view of the above problems when Sn is used as a negative electrode active material of a lithium battery, and provides a lithium battery negative electrode material having a high energy density, excellent cycleability, and stable battery characteristics. The purpose is to do.
[0006]
[Means for Solving the Problems]
After forming a surface plating layer made of Sn or an Sn alloy on a Cu base material (a conceptual diagram of the surface plating structure is shown in FIG. 11), when a heat treatment is performed, Cu of the base material component diffuses into Sn, An η layer (Cu ₆ Sn ₅ ), which is an alloy layer of Sn and Cu, is formed, and an ε layer (Cu ₃ Sn) is formed by continuing the heat treatment (FIG. 12 shows a conceptual diagram of the surface plating structure). Ultimately, only the ε layer is formed. In the process of interdiffusion of Sn with approximately twice the volume of Sn during the formation of the η layer, voids and voids in which the vacancies accumulate are formed in the crystal, which alleviate the strain due to the volume change when Sn reacts with lithium. And improve the cycle characteristics of the battery. However, when the ε layer is formed, voids collect at the interface between the ε layer and the Cu base material, causing a problem that the Cu—Sn alloy layer is peeled off. Since it does not contribute, the electrical characteristics are degraded.
The present invention has improved the performance as a lithium battery negative electrode by suppressing the formation of the ε layer in the surface plating layer and stabilizing the Cu-Sn alloy layer including the η layer based on such findings. It is.
[0007]
One is that a Cu layer is plated with a Ni layer to suppress the diffusion of Cu from the Cu matrix and stabilize the Cu—Sn alloy layer including the η layer.
That is, in this lithium battery negative electrode material, a surface plating layer composed of a Ni layer and a Cu—Sn alloy layer is formed in this order on the surface of a base material composed of Cu or a Cu alloy, and the Cu—Sn alloy layer is an η layer ( Cu ₆ Sn ₅ ), and has a thickness of 0.5 to 100 μm. Alternatively, a surface plating layer composed of a Ni layer, a Cu-Sn alloy layer and a Sn layer is formed in this order on the surface of the base material, the Cu-Sn layer includes an η layer, and a total of the Cu-Sn alloy layer and the Sn layer. The thickness is 0.5 to 100 μm. It is desirable that the Cu-Sn alloy layer has a Cu content of 5 to 70 at%, and that all of the Cu-Sn alloy layer be an η layer. The Cu—Sn alloy layer and / or Sn layer is at least one of Si, Zn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, Mg, C, O, and H. Can be included.
[0008]
The above-mentioned lithium battery negative electrode material is obtained by forming a Ni plating layer on the surface of a base material made of Cu or a Cu alloy, and then repeating the plating of the Cu layer and the Sn layer one or more times in this order, and performing heat treatment. It can be manufactured by Since the Ni layer limits the amount of Cu diffused from the base material, a stable η layer is formed by plating the calculated amount of Cu and Sn on the Ni layer so that the η phase is formed after the heat treatment. . Specifically, by controlling the Cu content in the total of the Cu layer and the Sn layer to 5 to 70 at%, the formation of the ε layer is prevented. FIG. 1 shows a conceptual diagram of the structure of the surface plating layer before the heat treatment, and FIG. 2 shows a conceptual diagram of the structure of the surface plating layer after the heat treatment. If the Sn layer formed on the uppermost layer is sufficiently thick, the Sn layer remains after the heat treatment.
The thickness of the Cu-Sn alloy layer or the Cu-Sn alloy layer and the Sn layer is, for example, about 0.1 to 0.5 µm Cu layer and 0.2 to 1.5 µm Sn layer alternately on the Ni layer. It can be adjusted by performing heat treatment after repeatedly plating the multilayer for 1 to 100 times.
[0009]
In the lithium battery negative electrode material, the base Ni diffuses into the Cu—Sn layer depending on the heat treatment conditions and the use conditions. Further, the Cu plating layer and / or the Sn plating layer has a third element, specifically, Si, Zn, Sn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, Mg, C, One or more of O and H can be added in the form of a binary alloy or multi-element alloy plating, or by using a plating bath containing an additive. Alternatively, in addition to the Cu plating layer and the Sn plating layer, a plating layer made of the above element or a plating layer containing the above element is formed, or the above element is vapor-deposited, and heat treatment is performed on the Cu-Sn layer (the Sn layer remains after the heat treatment). If so, it can be taken into the Sn layer as well. For example, if the third element is Ni, Ni, Cu, Sn or an alloy thereof is plated once or twice or more in this order on Cu or a Cu alloy base material, and if the third element is Zn, Cu or After forming a Ni plating layer on a Cu alloy base material, Zn, Cu, Sn or an alloy thereof is plated once or twice or more in this order, and heat treatment is performed, and a Cu—Sn—Ni alloy is formed on the Ni layer, respectively. To obtain a Cu—Sn—Zn alloy layer. Note that the thickness of the Ni layer sandwiched between the Cu layer and the Sn layer is desirably 0.2 μm or more in order to ensure plating adhesion.
The content of the third element is in the range of 0.001 to 20 at%. These elements have a higher energy capacity than carbon (particularly Si, Zn, Al) or stabilize the distribution of Sn in the matrix (η layer) of the alloy (particularly Ni, Cr, Co, S, P). And B) both improve the characteristics of the material for a negative electrode of a lithium battery.
FIGS. 3 to 6 show conceptual diagrams of the structure (after heat treatment) of the surface plating layer when the third element is included.
[0010]
In the above manufacturing method, the Cu layer and the Sn layer were separately formed by plating, and then heat treatment was performed to form the Cu—Sn alloy layer including the η layer. However, Cu—Sn alloy plating was performed, and this was heat-treated. The object can also be achieved by a method of forming a Cu—Sn alloy layer including an η layer. Sn-Cu alloy plating, which is known as lead-free solder plating, generally contains about 3.5 at% of Cu, but can be plated at a high Cu concentration depending on plating conditions. The layer structure is a structure in which Sn-rich layers and Cu-rich layers alternately overlap. By forming a Cu-Sn alloy plating layer in which the Cu concentration is controlled at 5 to 70 at% and heat-treating the same, a Cu-Sn alloy layer including an η layer can be formed without forming an ε layer, Voids and voids are formed when the η layer is formed.
Not only Cu-Sn but also one or more of the above-mentioned elements, Si, Zn, Sn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, C, O, and Mg Can be added in the same manner as described above.
FIG. 7 shows a conceptual diagram of the structure (before heat treatment) of the surface plating layer when the third element is included.
[0011]
The other is to suppress the formation of an ε layer and stabilize a Cu—Sn alloy layer including an η layer by using a Cu base material containing a specific additive element.
That is, this lithium battery negative electrode material is made of a Cu alloy containing at least one additional element among Si, Zn, Sn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, and Mg. A surface plating layer made of a Cu-Sn alloy layer containing the additive element is formed on the base material surface, and the Cu-Sn alloy layer includes an η layer and has a thickness of 0.5 to 100 µm. And Alternatively, on the surface of the base material, a Cu—Sn alloy layer containing the additive element and a surface plating layer composed of an Sn layer are formed in this order, the Cu—Sn alloy layer includes an η layer, and a Cu—Sn alloy layer and The total thickness of the Sn layer is 0.5 to 100 μm. It is desirable that the Cu-Sn alloy layer has a Cu content of 5 to 70 at%, and that all of the Cu-Sn alloy layer be an η layer.
Further, the Cu—Sn alloy layer includes Si, Zn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, Mg, C, O, including the additional element contained in the base material. At least one of H may be included, and the Sn layer may include at least one of the above elements.
[0012]
The lithium battery negative electrode material is formed on a surface of a base material made of a Cu alloy containing at least one of Si, Zn, Sn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B and Mg. It can be manufactured by forming an Sn plating layer and performing heat treatment. A Cu-Sn alloy layer including an η layer is formed by the heat treatment. At the time of this formation, the additive element in the Cu alloy diffuses into the η layer together with Cu, and Cu-Sn-α (α is Element) to form a ternary or multi-element alloy layer. 8 and 9 are conceptual diagrams of the structure of the surface plating layer after the heat treatment.
The above-mentioned additive element forms a concentrated layer at the interface between the Sn layer and the η layer and the interface between the η layer and the base material. By growing a ternary or multi-element alloy of Cu—Sn—α, the formation of the ε layer is suppressed, and Is stabilized. The additional elements have an energy capacity higher than that of carbon or an effect of stabilizing the matrix (η layer) of the alloy, and all of them improve the characteristics of the material for a negative electrode of a lithium battery.
Further, when producing the material for a negative electrode of a lithium battery, a third element, specifically, Si, Zn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, One or more of Mg, C, O, and H can be added in the form of a binary alloy or multi-element alloy plating, or by using a plating bath containing an additive.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
For the formation of the Ni layer, Cu layer and Sn layer, electroplating, electroless plating and other plating means can be used.
In electroless plating using hypophosphorous acid or the like as a reducing agent, a reducing agent component such as P (phosphorus) or B (boron) is incorporated into the plating film. Further, in the electroless plating, a reducing agent is taken into the plating film, and the pores and voids tend to increase after the heat treatment. The holes and voids formed in the surface plating layer improve the charge / discharge cycleability.
[0014]
As an electroplating method, Ni plating is performed using a Watt bath or a sulfamic acid bath at a plating temperature of 40 to 55 ° C. and a current density of 3 to 30 A / dm ² . The Ni plating thickness is 0.1 to 5 μm, and preferably 0.2 to 1 μm in consideration of workability. The Ni particle size can be roughly changed depending on the plating conditions to increase the surface area.
Although a cyan bath is generally used for Cu plating, there is a problem of liquid deterioration and wastewater treatment due to mixing of cyan into a tin plating solution. Therefore, a copper sulfate bath is used and a current density of 2.5 to 15 A / dm. Perform in ² . The Cu plating grain shape can be controlled by the plating conditions. For example, if the plating temperature exceeds 40 ° C., the Cu plating grains become large. Further, when Cu plating is performed on Ni plating, the Cu plating grains are large even when the current density is less than 2.5 A / dm ^{2 and more} than 10 A / dm ² . The surface area is increased by increasing the size of the plated particles, and the Cu—Sn alloy layer and the Sn layer after the heat treatment are more suitable for the negative electrode of the lithium battery. When a brightener is added to the Cu plating bath, voids increase after heat treatment.
The electric Sn plating is performed at a plating temperature of 25 ° C. or lower and a plating current density of ² to 20 A / dm ² , followed by heat treatment. When a brightener is added to the plating solution, the S and C components in the brightener are taken into the plating film, which contributes to an improvement in cycleability.
[0015]
One of the causes for improving the charge / discharge cycle property is a hole formed in the Cu—Sn alloy layer or the Sn layer. As a result of investigating the additives in the plating solution and the generation of voids and voids after heating by cross-sectional observation, it was found that the inclusion of additives such as brighteners in the plating bath generated more voids and voids. Was done. By putting the additive into the plating bath, the third element such as C or S, which is a component of the additive, is taken into the plating film and plating defects increase, which increases the number of pores and voids after the heat treatment. It is considered to be connected. It is desirable that the additive contains an element such as C or S that improves battery performance and cycleability.
[0016]
The thinner the Cu—Sn alloy layer and the Sn layer that react with lithium, the better the productivity and the lower the cost. However, the thinner the battery capacity, the smaller the thickness. On the other hand, for high capacity, the thickness of the Cu—Sn alloy layer and the Sn layer is desirably 10 μm or more, and a multilayer structure or alloy plating can be formed to 100 μm. The battery capacity increases as the thickness increases, but the manufacturing cost increases as the thickness increases. Therefore, the upper limit of the total thickness of the Cu—Sn alloy layer and the Sn layer is 100 μm.
[0017]
As the Cu or Cu alloy base material, a rolled copper strip or an electrolytic copper foil can be used. The base material containing additional elements such as Si, Zn, Sn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, O, C, and Mg is a rolled copper strip. Since a rolled Cu alloy sheet containing an additive element is harder to soften than a pure copper sheet, there is an advantage that breakage of the sheet and peeling of the plating layer due to heat generated during charging and discharging hardly occur.
The thickness of the rolled copper strip can be, for example, 80 to 300 μm. Of course, an electrolytic copper foil having a thickness of 10 to 210 μm may be used. The electrolytic copper foil may have a roughened surface.
[0018]
Regarding the surface roughness of the copper strip, the surface roughness of the rolled copper strip is generally about Rmax = 0.8 μm and Ra = 0.1 μm, but, like the electrolytic copper foil, it is desired to increase the surface area. In this case, a desired roughness (RZ = 1 μm or more) can be obtained by polishing or etching. Further, the surface roughness can be controlled by roughly finishing the Ni plating or the Cu plating, and the Sn plating can be brought into a rough surface state without any metallic luster.
[0019]
In the present invention, the Cu layer and the Sn layer, or the Cu and Sn layers in the Cu base material are alloyed by heat treatment after plating to form a Cu—Sn alloy layer, but the mutual diffusion of Cu and Sn is 25 ° C. It proceeds at room temperature and alloys due to the heat generated by the battery, so that it is not necessary to completely alloy by heat treatment. For example, when a multilayer structure of a Cu layer and a Sn layer is formed and alloyed, a surface plating layer partially having a multilayer structure of Cu and Sn can also be used as a battery negative electrode material.
[0020]
In the manufacturing method of the present invention, short-time heating at a high temperature of 200 ° C. or more is desirable for heat treatment with high productivity. If the heat treatment temperature is 230 ° C. or higher, the diffusion of Sn proceeds quickly because Sn is melted. When the temperature is 600 ° C. or higher, the Cu base material is softened, and distortion occurs. Therefore, when heat treatment is performed at a high temperature, the temperature is set to 230 ° C to 600 ° C. By performing the heat treatment, Sn crystal grains on the surface become large, a Cu—Sn alloy layer is formed, and whiskers are not easily generated. If the heating time in the case of performing the heat treatment at a high temperature is 3 seconds or less, the heat transfer of the material is not uniform, and the appearance unevenness after the heat treatment occurs. If the time is 60 seconds or longer, the oxidation of the surface Sn layer proceeds, so the heating time is 3 to 60 seconds. It is desirable to heat in a reducing atmosphere or an inert atmosphere.
[0021]
In addition, the heat treatment can be performed at a temperature of 200 ° C. or less for a long time to grow the Cu—Sn based alloy layer. Since heating at 200 ° C. or less does not cause a change in crystal grains due to melting of tin, a surface state having no metallic luster can be maintained even after the heat treatment.
Further, when the Cu layer and the Sn layer are repeatedly laminated and subjected to the heat treatment, the heat treatment can be performed for each cycle of the Cu plating and the Sn plating or for each of a plurality of cycles (the heat treatment is performed in the middle of the plating process). After the completion, the heat treatment may be performed a plurality of times. After the battery is assembled, heat at a temperature of 120 ° C. or less that does not affect the battery performance may be applied.
[0022]
Note that the diffusion of Cu into Sn due to the heat treatment is not uniform, and the diffusion of Sn into the crystal grain boundaries is faster than the diffusion into the crystal grains. Therefore, the Cu—Sn alloy layer grows in a wave shape. In addition, the wavy state changes depending on the grains of the base plating. Therefore, after heating, part of the layer completely becomes an η layer (Cu ₆ Sn ₅ ), and a state in which an Sn layer or a Cu layer remains partially is observed. However, even if the alloy is not partially alloyed, good battery characteristics are obtained. It is. FIG. 10 shows a conceptual diagram of the surface plating structure (after the heat treatment).
[0023]
【Example】
<Conditions for preparing test materials>
As the Cu or Cu alloy base material, Nos. 1 to 14 having various compositions (thickness: 100 μm) were used. With respect to Nos. 1 to 3 and 6 to 9, Ni plating was applied to the base material, and then Cu plating and Sn plating were sequentially repeated one or more times. For No. 4, after forming Zn plating on Ni plating, Cu plating and Sn plating were performed once each. In No. 5, Ni plating, Cu plating, and Sn plating were repeatedly performed twice (in each case, the thickness of each plating layer was calculated so that the Cu—Sn alloy layer after the heat treatment became an η layer). No. About 10-14, only Sn plating was given. Tables 2 to 4 show the respective plating baths of Ni plating, Cu plating and Sn plating. However, the brightener was No. Only 3, 6 was added.
Then, No. Heat treatment was performed on the plate materials 1 to 13 to obtain a lithium battery negative electrode material (test material) having a surface plating layer (Ni layer, Cu-Sn alloy layer, Sn layer) on the Cu alloy base material.
Table 1 also shows the base material composition of each test material (Nos. 1 to 14), the configuration of the surface plating layer after heat treatment, the thickness of each layer, and the heat treatment conditions.
[0024]
[Table 1]

[0025]
[Table 2]

[0026]
[Table 3]

[0027]
[Table 4]

[0028]
The thickness of each plating layer of each test material was measured in the following manner. In addition, energy density, charge / discharge cycleability, and battery stability test were performed on each test material. The results are shown in Table 1.
[Sn and Ni layer thickness measurement]
The thicknesses of the Sn and Ni layers were measured using a fluorescent X-ray film thickness meter (Seiko Instruments Inc .; Model SFT156A).
[Cu-Sn alloy layer thickness measurement]
The thickness of the Cu-Sn alloy layer was determined by measuring the amount of Sn using a fluorescent X-ray film thickness meter (Seiko Denshi Kogyo Co., Ltd .; Model SFT156A) and defining the plating thickness of the alloy layer containing Sn. Further, the plating was processed by a microtome method, the cross section of the surface layer was observed by SEM, and the layer thickness was examined.
[0029]
[Discharge capacity and number of charge / discharge cycles]
The discharge capacity was measured in a charge / discharge range of 0 to 1 V in a cell in which a test material was used as a negative electrode, a Li foil was used as a positive electrode, and an electrolyte was 1 M LiClO ₄ / EC + PC. The number of charge / discharge cycles was defined as the number of times charge / discharge was repeated at a constant voltage and constant current and the initial discharge capacity could be maintained.
[Battery stability]
The energy density was measured using a material left at a high temperature of 160 ° C. for 120 hours. Regarding the battery stability evaluation criteria, a level having an energy density of 80% or more before heating was evaluated as 、, and a level at which the energy density was reduced below that was evaluated as ×.
[0030]
As shown in Table 1, No. 1 having a Ni layer in the plating layer configuration. All of Nos. 1 to 9 had high discharge capacity, good charge / discharge cyclability, and high battery stability. No. Although Nos. 10 and 11 have no Ni layer, the base material contained a specific additive element, and the growth of the ε layer was suppressed by the additive element, so that a high discharge capacity could be obtained. No. 1 having a component that assists the reaction between lithium and tin in the Cu—Sn alloy layer while having a Ni layer. In Nos. 3 to 6, the cyclability was particularly good.
On the other hand, No. In Nos. 12 to 14, the Ni layer was not included, and the base material did not contain a specific additive element. Therefore, the ε layer grew during a charge / discharge cycle or in a high-temperature use environment, and the battery performance deteriorated.
[0031]
A similar effect can be obtained by performing Cu-Sn alloy plating instead of forming a Cu-Sn alloy layer by heat-treating the Cu layer and the Sn layer. Table 5 shows the plating bath at that time.
[0032]
[Table 5]

[0033]
【The invention's effect】
According to the present invention, it is possible to provide a low-cost lithium battery negative electrode material having high energy density, excellent cycleability, and low cost. Also, excellent battery stability can be maintained even when used at a high temperature (such as an engine room).
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a cross section of a surface plating layer before heating.
FIG. 2 is a conceptual diagram of a cross section after the heating.
FIG. 3 is a conceptual diagram of a cross section of a surface plating layer containing a third element.
FIG. 4 is a conceptual diagram of a cross section of a surface plating layer containing a third element.
FIG. 5 is a conceptual diagram of a cross section of a surface plating layer containing a third element.
FIG. 6 is a conceptual diagram of a cross section of a surface plating layer containing a third element.
FIG. 7 is a conceptual diagram of a cross section of a surface plating layer containing a third element.
FIG. 8 is a conceptual diagram of a cross section of a surface plating layer containing a third element.
FIG. 9 is a conceptual diagram of a cross section of a surface plating layer containing multiple elements.
FIG. 10 is a conceptual diagram of a cross section of a surface plating layer in which a Cu layer or a Sn layer remains partially even after heat treatment.
FIG. 11 is a conceptual diagram of a cross section of a surface plating layer according to a conventional technique.
FIG. 12 is a conceptual diagram of a cross section of a surface plating layer according to a conventional technique.

Claims

A surface plating layer composed of a Ni layer and a Cu-Sn alloy layer is formed in this order on a surface of a base material composed of Cu or Cu alloy, and the Cu-Sn alloy layer includes an η layer (Cu ₆ Sn ₅ ), and has a thickness of Material for a lithium battery negative electrode, having a thickness of 0.5 to 100 μm.

On the surface of the base material made of Cu or Cu alloy, a surface plating layer made of a Ni layer, a Cu—Sn alloy layer and a Sn layer is formed in this order, and the Cu—Sn alloy layer includes an η layer (Cu ₆ Sn ₅ ). And a total thickness of the Cu—Sn alloy layer and the Sn layer is 0.5 to 100 μm.

The Cu-Sn alloy layer includes at least one of Si, Zn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, Mg, C, O, and H. The material for a negative electrode of a lithium battery according to claim 1.

The Cu-Sn alloy layer and / or the Sn layer contains at least one of Si, Zn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, Mg, C, O, and H. 3. The material for a negative electrode of a lithium battery according to claim 2, comprising:

Si, Zn, Sn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, Mg A surface plating layer made of a Cu—Sn alloy layer including the η layer (Cu ₆ Sn ₅ ) and a thickness of 0.5 to 100 μm. Material for battery negative electrode.

Si, Zn, Sn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, Mg A Cu—Sn alloy layer and a surface plating layer composed of a Sn layer are formed in this order, the Cu—Sn alloy layer includes an η layer (Cu ₆ Sn ₅ ), and the total thickness of the Cu—Sn alloy layer and the Sn layer Material for a lithium battery negative electrode, having a thickness of 0.5 to 100 μm.

The Cu-Sn alloy layer includes at least one of Si, Zn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, Mg, C, O, and H. The material for a negative electrode of a lithium battery according to claim 5.

The Cu-Sn alloy layer and / or the Sn layer contains at least one of Si, Zn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, Mg, C, O, and H. The material for a negative electrode of a lithium battery according to claim 6, comprising:

The material for a negative electrode of a lithium battery according to any one of claims 1 to 8, wherein the Cu content in the Cu-Sn alloy layer is 5 to 70 at%.

After forming a Ni plating layer on the surface of a base material made of Cu or a Cu alloy, a Cu plating layer and a Sn plating layer are repeatedly formed one or more times in this order, and heat treatment is performed to perform an η layer (Cu ₆ Sn ₅ ). A method for producing a negative electrode material for a lithium battery, comprising forming a Cu-Sn alloy layer containing:

The Cu plating layer contains at least one of Si, Zn, Sn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, Mg, C, O, H, and / or The Sn plating layer includes at least one of Si, Zn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, Mg, C, O, and H. The method for producing a material for a negative electrode of a lithium battery described in 1.

Forming a Sn plating layer on the surface of a base material made of a Cu alloy containing at least one of Si, Zn, Sn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B and Mg, To form a Cu—Sn alloy layer including an η layer (Cu ₆ Sn ₅ ).

The Sn plating layer includes at least one of Si, Zn, Al, Ni, Fe, Cr, Ti, Zr, Co, S, P, B, Mg, C, O, and H. 13. The method for producing a negative electrode material for a lithium battery according to 12 above.

The method for producing a negative electrode material for a lithium battery according to any one of claims 10 to 13, wherein the Cu content in the Cu-Sn alloy layer is 5 to 70 at%.

A Ni or Ni alloy plating layer, a Cu or Cu alloy plating layer, a Sn or a Sn alloy plating layer are repeatedly formed on the surface of a base material made of Cu or Cu alloy twice or more in this order, and heat treatment is performed to obtain η A method for producing a negative electrode material for a lithium battery, comprising forming a Cu-Sn-Ni alloy layer including a layer.

After forming a Ni or Ni alloy plating layer on the surface of a base material made of Cu or Cu alloy, the Zn or Zn alloy plating layer, the Cu or Cu alloy plating layer, and the Sn or Sn alloy plating layer are repeated once or twice in this order. A method for producing a negative electrode material for a lithium battery, comprising forming a Cu—Sn—Zn alloy layer including an η layer on a Ni layer by repeatedly forming and performing heat treatment.