JP2004139954A - Negative electrode for non-aqueous electrolytic solution secondary battery and its manufacturing method as well as non-aqueous electrolytic solution secondary battery - Google Patents

Negative electrode for non-aqueous electrolytic solution secondary battery and its manufacturing method as well as non-aqueous electrolytic solution secondary battery Download PDF

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JP2004139954A
JP2004139954A JP2003092419A JP2003092419A JP2004139954A JP 2004139954 A JP2004139954 A JP 2004139954A JP 2003092419 A JP2003092419 A JP 2003092419A JP 2003092419 A JP2003092419 A JP 2003092419A JP 2004139954 A JP2004139954 A JP 2004139954A
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coating layer
negative electrode
secondary battery
electrolyte secondary
aqueous electrolyte
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JP3664402B2 (en
JP2004139954A5 (en
Inventor
Kiyotaka Yasuda
安田 清隆
Yoshiki Sakaguchi
坂口 善樹
Kazuko Taniguchi
谷口 和子
Makoto Dobashi
土橋 誠
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Mitsui Mining and Smelting Co Ltd
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Mitsui Mining and Smelting Co Ltd
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode for non-aqueous electrolytic solution secondary battery in which long life of the electrode can be achieved and energy density per unit volume and unit weight is greatly improved, and its manufacturing method, and a non-aqueous electrolytic solution secondary battery using the negative electrode. <P>SOLUTION: In the negative electrode for non-aqueous electrolytic solution secondary battery, a first covering layer containing tin, tin alloy, aluminum, or aluminum alloy is formed on the current collector surface and a second covering layer containing a metal that has low formation ability of lithium compound is formed on the top of it. Here, the first covering layer may be further formed on the top of the second covering layer. Furthermore, a covering layer containing copper or the like may be further formed as the uppermost layer. By forming each covering layer by heat treatment, a desired performance can be obtained. Since the heat treatment can be carried out in a very short time, cost merit is great. <P>COPYRIGHT: (C)2004,JPO

Description

【0001】
【発明の属する技術分野】
本発明は、リチウム等のアルカリ金属を多量に吸蔵、脱蔵することができる非水電解液二次電池用負極及びその製造方法に関し、詳しくは特定構成の負極を用いることによって、電極の長寿命化が達成でき、かつ単位体積及び単位重量当たりのエネルギー密度を飛躍的に向上させた非水電解液二次電池用負極及びその製造方法、並びに該負極を用いた非水電解液二次電池に関する。
【0002】
【従来の技術及び発明が解決しようとする課題】
携帯用の小型電気・電子機器の普及に伴い、小型で高容量の非水電解液(電解質)二次電池の開発が盛んに行われている。この非水電解液二次電池は、マンガン酸リチウム、コバルト酸リチウム、ニッケル酸リチウム等を正極材料とし、炭素質材料、リチウム金属等を負極材料としたものが一般的である。
【0003】
しかし、炭素質材料は、理論的放電容量が372mAh/gと低く、今後予想される小型電気・電子機器の多機能化による消費電力の増大に対して、現行の炭素材料では、そのニーズに対応は困難である。
【0004】
一方、リチウム金属は、理論的放電容量が3860mAh/gと高いものの、非水電解液とリチウム金属との反応によるリチウムの劣化や充放電の繰り返しにより負極からリチウム金属がデンドライト状に成長し、絶縁体であるセパレーターを貫通して正極と短絡が生じたり、サイクル寿命特性が短いという問題があった。
【0005】
このような問題を解決するために、銅板等の集電体の表面に、スズ又はスズ合金の被膜を電気メッキ法により積層した負極が提案されている(特許文献1及び2並びに非特許文献1参照)。しかし、このような負極は、リチウムの吸蔵、脱蔵に伴い、スズ又はスズ合金が割れて、銅板等からなる集電体より剥離、脱落し、電極の長寿命化が図れないという問題がある。特に、通常は、集電体とスズ又はスズ合金のメッキは別途に行うため、集電体表面に酸化被膜が形成された後に、スズ又はスズ合金メッキを行うため、スズ又はスズ合金は集電体から容易に剥離、脱落してしまう。
【0006】
【特許文献1】
特開2001−68094号公報
【特許文献2】
特開2001−68094号公報
【非特許文献1】
第42回電池討論会予稿集p282,284,288
【0007】
また、非水電解液二次電池用負極には、高い単位体積及び単位重量当たりのエネルギー密度が求められている。
【0008】
従って、本発明の目的は、電極の長寿命化が達成でき、かつ単位体積及び単位重量当たりのエネルギー密度を飛躍的に向上させた非水電解液二次電池用負極及びその製造方法、並びに該負極を用いた非水電解液二次電池を提供することにある。
【0009】
【課題を解決するための手段】
本発明者らは、検討の結果、集電体の表面にスズ等のリチウムの吸蔵が可能な元素を含む第1被覆層及びリチウム化合物の形成能の低い金属を含む第2被覆層が形成されてなる負極が、上記目的が達成し得ることを知見した。
【0010】
本発明は、上記知見に基づきなされたもので、集電体表面に、スズ、スズ合金、アルミニウム又はアルミニウム合金を含む第1被覆層が形成され、次に該第1被覆層の上に、リチウム化合物の形成能の低い金属を含む第2被覆層が形成されていることを特徴とする非水電解液二次電池用負極を提供するものである。
【0011】
また、本発明は、集電体表面に、スズ、スズ合金、アルミニウム又はアルミニウム合金を含む第1被覆層及びリチウム化合物の形成能の低い金属を含む第2被覆層をそれぞれ電解又は乾式法による表面処理によって順次析出させ、次いで120〜350℃で10分〜24時間熱処理する非水電解液二次電池用負極の製造方法を提供するものである。
【0012】
また、本発明は、多数のスリットが設けられた集電体表面に、スズ、スズ合金、アルミニウム又はアルミニウム合金を含む第1被覆層、リチウム化合物の形成能の低い金属を含む第2被覆層、さらに上記第1被覆層と同種又は異種の第1被覆層をそれぞれ電解又は乾式法による表面処理により析出させた3層構造を基本とする多層被覆層を設け、得られた上記集電体及び上記多層被覆層からなる複合体に、外側方向への引張力を付与することによって、該多層被覆層に1mm以下の間隔で直径2mm以下の空孔を形成させることを特徴とする非水電解液二次電池用負極の製造方法を提供するものである。
【0013】
また、本発明は、集電体表面に、スズ、スズ合金、アルミニウム又はアルミニウム合金を含む第1被覆層、リチウム化合物の形成能の低い金属を含む第2被覆層、さらに上記第1被覆層と同種又は異種の第1被覆層をそれぞれ電解又は乾式法による表面処理により析出させた3層構造を基本とする多層被覆層を設け、得られた上記集電体及び上記多層被覆層からなる複合体に、該多層被覆層側からレーザー処理をすることによって、該多層被覆層に1mm以下の間隔で直径2mm以下の空孔を形成させることを特徴とする非水電解液二次電池用負極の製造方法を提供するものである。
【0014】
さらに、本発明は、集電体表面に、スズ、スズ合金、アルミニウム又はアルミニウム合金を含む第1被覆層、リチウム化合物の形成能の低い金属を含む第2被覆層、さらに上記第1被覆層と同種又は異種の第1被覆層をそれぞれ電解又は乾式法による表面処理により析出させた3層構造を基本とする多層被覆層を設け、得られた上記集電体及び上記多層被覆層からなる複合体に、該多層被覆層側からピンを用いて穿孔することによって、該多層被覆層に1mm以下の間隔で直径2mm以下の空孔を形成させることを特徴とする非水電解液二次電池用負極の製造方法を提供するものである。
【0015】
また、本発明は、上記負極を用いた非水電解液二次電池を提供するものである。
【0016】
【発明の実施の形態】
以下、本発明の実施の形態について詳述する。
【0017】
本発明の非水電解液二次電池用負極における集電体としては、例えば銅、ニッケル、ステンレス等の導電性材料の箔が用いられる。例えば集電体として銅箔を用いる場合、この銅箔は銅含有溶液を用いた電解により得られ、その厚みは10〜30μmが望ましい。特に特開2000−90937号公報に記載の方法より得られた銅箔は、厚みが12μm以下と極めて薄いことから好ましく用いられる。
【0018】
本発明の負極は、上記集電体の表面に、スズ、スズ合金、アルミニウム又はアルミニウム合金を含む第1被覆層が形成され、該第1被覆層の上に、リチウム化合物の形成能の低い金属を含む第2被覆層が形成されてなる多層被覆層を有している。
【0019】
本発明における多層被覆層は、上記のように第1被覆層及び第2被覆層からなる2層構造を必須としている。第1被覆層上に第2被覆層を形成することで、第1被覆層の作用によって放電容量が高まると同時に、第1被覆層の剥離や脱落が効果的に防止され、電極の長寿命化を図ることができる。本発明の別の実施形態においては、負極は、第2被覆層上に更に第1被覆層が形成されてなる3層構造であってもよい。この3層構造の実施形態によれば、集電体の表面に形成された第1被覆層の剥離や脱落が一層効果的に防止され、電極の一層の長寿命化が図れる。本発明の更に別の実施形態においては、上記の3層構造の上に、第2被覆層及び第1被覆層をこの順で1組とした1組以上の被覆層が更に形成されていてもよい。すなわち、3層構造のみならず、5層構造、7層構造等としてもよい。これら多層被覆層を構成する2以上の第1被覆層及び第2被覆層は、それぞれ同種の材料から構成されていてもよく、或いは異なる材料から構成されていてもよい。
【0020】
本発明の負極が、上記の3層構造(第1被覆層、第2被覆層及び第1被覆層)を有している場合や、該3層構造の上に、第2被覆層及び第1被覆層を1組とした1組以上の被覆層が更に形成されている場合、更に最上層としてリチウム化合物の形成能の低い金属を含む被覆層が形成されていることが好ましい。例えば本発明の負極が、上記の3層構造を有している場合には、上側の第1被覆層(つまり、第2被覆層上に形成された第1被覆層)上に、リチウム化合物の形成能の低い金属を含む被覆層が更に形成された4層構造であることが好ましい。最上層としてリチウム化合物の形成能の低い金属を含む被覆層が形成されていることで、スズなどからなる第1被覆層の酸化が抑制され、不可逆容量が低減される。また、第1被覆層の脱落が防止され、負極の寿命特性が向上するという効果が奏される。この効果を一層顕著なものとする観点から、最上層として形成されるリチウム化合物の形成能の低い金属を含む被覆層は、その厚みが0.01〜20μm、特に0.02〜10μm、とりわけ0.5〜5μmという極薄であることが好ましい。「リチウム化合物の形成能が低い」とは、リチウムと金属間化合物若しくは固溶体を形成しないか、又は形成したとしてもリチウムが微量であるか若しくは非常に不安定であることを意味する。該金属の例としては銅、鉄、コバルト、クロム、ニッケル等が挙げられる。逆にリチウム化合物の形成能の高い金属としては、スズ、シリコン、アルミニウム等があり、これらの金属はリチウムと金属間化合物を形成する。リチウム化合物の形成能の低い金属として特に銅を用いると、第1被覆層の酸化及び脱落が一層防止され、不可逆容量が一層低減し、負極の寿命特性が一層向上する点から好ましい。
【0021】
第1被覆層において、スズ合金としてはスズ−ビスマス、スズ−鉄、スズ−コバルト、スズ−銅等が挙げられ、アルミニウム合金としては、アルミニウム−リチウム、アルミニウム−マンガン、アルミニウム−チタン、アルミニウム−クロム、アルミニウム−バナジウム、アルミニウム−銅等が挙げられる。これらの第1被覆層は、好ましくは電解メッキ又は乾式法による表面処理により得られ、その厚みは0.5〜50μmが好ましく、1〜50μmが更に好ましく、2〜20μmが一層好ましい。
【0022】
第2被覆層は、リチウム化合物の形成能の低い金属を含んで構成されている。「リチウム化合物の形成能の低い金属」の詳細については、先に述べた、最上層として形成されるリチウム化合物の形成能の低い金属からなる被覆層に関する説明が適用される。リチウム化合物の形成能の低い金属を含む第2被覆層は、スズ等を含む第1被覆層の担持材としての役割を果たすため、リチウムの吸蔵、脱蔵に伴うサイクル寿命特性の向上に貢献する。この観点から、リチウム化合物の形成能の低い金属として、特に銅又はニッケルを用いることが好ましい。第2被覆層は、例えば上記の金属を含有する溶液を用いた電解により得られ、その厚みは0.02〜50μmが望ましく、0.2〜20μmがさらに望ましい。
【0023】
第2被覆層は、第1被覆層の全域を連続して被覆していてもよく、或いは第1被覆層を断続的に被覆していてもよい。第2被覆層が第1被覆層上を断続的に被覆している状態の具体例を図1及び図2に示す。図1及び図2は何れも第1被覆層、第2被覆層及び第1被覆層を有する3層構造の負極の断面を走査型電子顕微鏡(SEM)で観察した組成像である。図1及び図2における第1被覆層はスズから、第2被覆層は銅からそれぞれ構成されている。また集電体は銅箔から構成されている。これらの図においては、理解の助けとするために、各被覆層の境界を、線でなぞり強調してある。これらの図から明らかなように、集電体の表面に第1被覆層が連続的に形成され、その上に第2被覆層が断続的に形成されている。尚、第2被覆層上に形成された第1被覆層は第2被覆層と同様に不連続の層となっている。従って、第2被覆層上に形成された第1被覆層が不連続になっている部分においては、第2被覆層が表面に露出していることがある。断続した第2被覆層を形成するためには、例えば第2被覆層を形成するときの電解条件を適切に選択したり、集電体である銅箔の表面粗さを適切に制御すればよい。また、連続した第2被覆層を形成して負極を作製した後に、該負極に対して充放電を行い、集電体上に形成された第1被覆層を膨張収縮させることで、連続した第2被覆層を不連続な状態に変化させることもできる。第2被覆層が第1被覆層上を断続的に被覆している場合には、断続した第2被覆層間が、電解液が進入する経路となる。
【0024】
電解液の進入を更に促進させるために、被覆層を貫通する空孔を形成することも有利である。例えば、本発明の負極が集電体上の第1被覆層、その上の第2被覆層及びその上の第1被覆層を有している場合、これらの被覆層に、1mm以下の間隔で2mm以下、望ましくは500μm以下の空孔が存在していることが好ましい。つまり、これら3層を貫通する貫通孔が存在していることが好ましい。このような空孔が存在することによって、電解液が一層効果的に空孔中に入るため、いずれの第1被覆層も負極として一層良好に機能する。また、体積膨張、収縮をこの空孔によって緩和することができる。
【0025】
また、本発明の負極が集電体上の第1被覆層、その上の第2被覆層及びその上の第1被覆層を有している場合、上記第2被覆層は、各第1被覆層との界面において、2mm以下の間隔で、ランダム、かつ微細な破断部を有していることが望ましい。このような破断部を有することによって第1被覆層の負極としての有効利用をさらに図ることができる。この破断部は、各被覆層に上記空孔が形成されていない場合にも設けてもよい。
【0026】
本発明の非水電解液二次電池用負極の構成の例を図3及び図4に模式的に示す。図3は、本発明の非水電解液二次電池用負極の一例を模式的に示す断面図であり、図4は他の例を模式的に示す断面図である。図3及び図4に示されるように、非水電解液二次電池用負極は、集電体(銅箔)2と多層被覆層5からなり、多層被覆層5は第1被覆層3、第2被覆層4及び第1被覆層3の3層構造である。多層被覆層5には、一定間隔で空孔6が設けられている。また、図4では、第2被覆層4の第1被覆層3の界面に破断部7が設けられている。尚、図3及び図4においては、第2被覆層4は連続層で示されているが、これはあくまでも模式的なものであり、第2被覆層4は上述の通り不連続の層であってもよい。
【0027】
本発明の非水電解液二次電池用負極の別の実施形態として、集電体の直ぐ上に形成された第1被覆層が、スズ又はアルミニウムと、上記第2被覆層の構成元素及び/又は上記集電体の構成元素との合金からなる実施形態が挙げられる。例えば、集電体が銅箔からなり且つ第2被覆層が銅を含む場合、第1被覆層をスズ−銅合金とすることができる。この実施形態の場合には、第1被覆層と集電体及び/又は第2被覆層との密着性が良好になり、活物質の脱落が防止されるという利点がある。また本発明の非水電解液二次電池用負極の更に別の実施形態として、第2被覆層が、リチウム化合物の形成能の低い金属と、該第2被覆層に隣接する第1被覆層の構成元素との合金からなることが好ましい。更に本発明の非水電解液二次電池用負極のまた別の実施形態として、最上層が、リチウム化合物の形成能の低い金属と、該最上層と隣接する第2被覆層の構成元素との合金からなることが好ましい。これら2つの実施形態の場合には、電極の集電機能を維持しつつ、リチウムの吸脱蔵に起因する体積変化が緩和され、合金の微粉化が抑制されるという利点がある。
【0028】
上記の実施形態の電極は好ましくは次に述べる方法で製造される。先ず集電体表面に、スズ、スズ合金、アルミニウム又はアルミニウム合金を含む被覆層(A層という)、リチウム化合物の形成能の低い金属を含む被覆層(B層という)、上記A層と同種又は異種のA層およびリチウム化合物の形成能の低い金属を含む被覆層(C層という)を順次、電解又は乾式法による表面処理により析出させ、4層構造の多層被覆層を設ける。この状態を図5に示す。なお図5においては集電体は銅箔からなり、2つのA層はスズからなり、B層及びC層は銅からなっている。次に、この多層被覆層及び集電体からなる複合体を熱処理する。熱処理は各層を構成する元素を拡散させる目的で行われる。この目的のため、熱処理条件は120〜350℃で10分〜24時間、特に160〜250℃で10分〜6時間であることが好ましい。熱による元素の拡散は通常時間を要するものであるが、A層〜C層の厚みを薄くすることで、非常に短時間で元素を拡散させることができ、コストメリットが大きい。熱処理の雰囲気は窒素ガスやアルゴンガスなどの不活性ガス雰囲気でもよく、或いは空気中でもよい。また10−1Torr以下の真空度の真空中でもよい。特に被覆層の過剰な酸化を防止する点から不活性ガス雰囲気中又は真空中であることが好ましい。
【0029】
所定時間の熱処理による元素拡散によって、上記実施形態の電極が得られる。図5に示す多層被覆層を用いて得られた本発明の電極の一例を図6に示す。図6においては、集電体に隣接して形成されたA層に由来するスズと、集電体及び/又はB層に由来する銅とを含むスズ−銅合金からなる第1被覆層が形成されている。なお、熱処理条件をコントロールすることで元素の拡散をコントロールできることから、第1被覆層においてはスズ及び銅の濃度を所望の値にコントロールできる。具体的には、第1被覆層はスズリッチのスズ−銅合金層となっている。第1被覆層の上には、B層に由来する銅と、二つのA層に由来するスズとを含むスズ−銅合金からなる第2被覆層が形成されている。第2被覆層は銅リッチとなっている。第2被覆層上には、上側のA層に由来するスズと、B層及びC層に由来する銅とを含むスズ−銅合金からなる第1被覆層が形成されている。第1被覆層はスズリッチとなっている。この第1被覆層上には、上側のA層に由来するスズと、C層に由来する銅とを含むスズ−銅合金からなる最上層が形成されている。最上層は銅リッチとなっている。
【0030】
なお図6においては、各層の境界は比較的明確に観察されるが、熱処理条件によっては元素の拡散に勾配が生じ、それに起因して各層の境界が明確ではない場合もある。例えば、図5に示す多層被覆層における各層の厚みや熱処理条件によっては、熱処理の結果得られる電極は、スズ−銅合金からなる第1被覆層と、銅リッチのスズ−銅合金からなる第2被覆層とから構成され、第1被覆層が銅リッチのスズ−銅合金の層とスズリッチのスズ−銅合金の層との2層構造となっている場合もある(後述する実施例参照)。
【0031】
次に本発明の非水電解液二次電池用負極の別の好ましい製造方法(製造方法A〜C)を、3層構造の負極の製造を例にとり説明する。
【0032】
<製造方法A>
製造方法Aの製造工程を図7に示す。製造方法Aでは、図7(a)のように、集電体2にスリット8を設ける。集電体が例えば銅箔からなる場合、この銅箔は電解等によって得られる。スリット8は、交差状に、かつ間隔が3mm以下となるように設けるのが望ましい。
【0033】
次に、図7(b)に示されるように、この集電体2の表面に、上記第1被覆層、上記第2被覆層及び上記第1被覆層をそれぞれ電解又は乾式法による表面処理により析出させた3層構造からなる多層被覆層5を設ける。
【0034】
そして、図7(c)に示されるように、得られた上記集電体及び上記多層被覆層からなる複合体に、外側方向への引張力Fを付与する。このことによって、図7(d)のごとく、多層被覆層5に1mm以下の間隔で直径2mm以下の空孔6を形成した非水電解液二次電池用負極が製造される。
【0035】
<製造方法B>
製造方法Bでは、集電体の上に、3層構造からなる多層被覆層を形成する。集電体が例えば銅箔からなる場合、銅含有溶液を電解してドラム上に集電体としての銅箔を析出させる。この電解工程においては、銅箔の表面処理、にかわ処理、防錆処理等を行うが、これと平行して電解により、上記集電体上に、上記第1被覆層、上記第2被覆層及び上記第1被覆層をそれぞれ電解又は乾式法による表面処理により析出させた3層構造からなる多層被覆層を設ける。
【0036】
次に、得られた上記集電体及び上記多層被覆層からなる複合体に、多層被覆層側からレーザー処理する。このことによって、多層被覆層に1mm以下の間隔で直径2mm以下の空孔を形成した非水電解液二次電池用負極が製造される。
【0037】
<製造方法C>
製造方法Cは、製造方法Bと同様に、集電体の上に、3層構造からなる多層被覆層を形成する。集電体が例えば銅箔からなる場合には、銅箔の電解工程において層構造からなる多層被覆層を形成する。
【0038】
次に、得られた上記集電体及び上記多層被覆層からなる複合体に、多層被覆層側からピンを用いて穿孔する。このことによって、多層被覆層に1mm以下の間隔で直径2mm以下の空孔を形成した非水電解液二次電池用負極が製造される。
【0039】
上記製造方法A〜Cでは、上記のようにして空孔を形成する処理の前後に、上記複合体の多層被覆層側からプレス又はロール圧延処理を施してもよい。これによって、上記第2被覆層には、上記第1被覆層の界面において、2mm以下の間隔で、ランダム、かつ微細な破断部が形成される。また、後述する実施例からも明らかなように、このプレス又はロール圧延処理は、上記空孔を設けない場合にも行ってもよい。
【0040】
上記製造方法A〜Cでは、上記のようにして空孔を形成する処理の前後に、上記集電体及び3層構造からなる上記多層被覆層を具備する複合体に対して上述した熱処理が施されていることも望ましい。熱処理条件は上述した通りである。複合体に熱処理を施すことの利点は前述した通りである。
【0041】
上記した本発明の製造方法では、集電体として例えば銅箔を用いると、従来より用いられている電解銅箔の製造設備をそのまま使用することもできる。従って、上記負極を安価に、かつ簡便に製造することができる。また、集電体及び多層被覆層を一連の工程で製造できるので、集電体や第2被覆層を構成する銅の表面に酸化被膜が形成されることがないので、スズ等の第1被覆層が割れても、酸化していない銅とスズ等が強固に結合し、例えばCu−Sn合金界面がスズ等の剥離、脱落を防止する。
【0042】
次に、本発明の非水電解液二次電池について説明する。本発明の非水電解液二次電池は、基本構造として、負極、正極、セパレータ、非水系電解液を含んでおり、負極としては上記のように本発明の負極を使用するが、他の正極、セパレータ、非水電解液については特に制限されず、従来よりリチウム二次電池等の非水電解液二次電池に公知のものが使用される。
【0043】
正極は、正極活物質、必要により導電剤及び結着剤を適当な溶媒に懸濁し、正極合剤を作製し、これを集電体に塗布、乾燥した後、ロール圧延、プレスし、さらに裁断、打ち抜きすることにより得られる。
【0044】
正極活物質としては、リチウムニッケル複合酸化物、リチウムマンガン複合酸化物、リチウムコバルト複合酸化物等の従来公知の正極活物質が用いられる。
【0045】
また、正極に用いられる導電剤としては、カーボンブラック、アセチレンブラック、グラファイト等が用いられる。結着剤としては、スチレンブタジエンゴム、ポリテトラフルオロエチレン、ポリフッ化ビニリデン、フッ素系ポリマー、カルボキシメチルセルロース、ポリビニルアルコール等が用いられる。また、溶媒としてはN−メチルピロリドン、ジメチルホルムアミド等が使用される。また、集電体としてはアルミニウム又はアルミニウム合金が好ましく用いられる。
【0046】
セパレーターとしては、合成樹脂製不織布、ポリエチレン又はポリプロピレン多孔質フイルム等が好ましく用いられる。
【0047】
非水電解液は、リチウム二次電池の場合、一般的な非水電解液は、支持電解質であるリチウム塩を有機溶媒に溶解した溶液からなる。リチウム塩としては、例えば、LiC1O、LiA1Cl、LiPF、LiAsF、LiSbF、LiSCN、LiC1、LiBr、LiI、LiCFSO、LiCSO等が例示され、特にLiPFを含む電解質が好ましい。
【0048】
有機溶媒としては、エチレンカーボネート、プロピレンカーボネート、ビニレンカーボネート等の環状カーボネート類;ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネート等の鎖状カーボネート類;ギ酸メチル、酢酸エチル、プロピオン酸メチル等の脂肪族カルボン酸エステル類;γ−ブチロラクトン等のγ−ラクトン類;1,2−ジメトキシエタン等の鎖状エーテル類;テトラヒドロフラン等の環状エーテル類;その他ジメチルスルホキシド、ジオキソラン類、アミド類、ニトリル類、スルホラン類等の各種の非プロトン性溶媒を使用することが好ましい。特に、環状カーボネートと鎖状カーボネートとの混合系、及びこれにさらに脂肪族カルボン酸エステルを混合した系が好ましく用いられ、とりわけエチレンカーボネートとエチルメチルカーボネートとの混合溶媒が好ましい。
【0049】
非水電解液二次電池の形状は特に制限されず、円筒型、角形、コイン型、ボタン型等のいずれでもよい。本発明の非水電解液二次電池は、例えば携帯情報端末、携帯電子機器、自動車の用途に好適に用いることができる。
【0050】
【実施例】
以下、実施例等に基づき本発明を具体的に説明する。
【0051】
〔比較例1〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる第1被覆層を電解により厚さ2μm析出させ、非水電解液二次電池用負極とした。
【0052】
〔実施例1〕
集電体として用いられる厚さ30μmの電解銅箔に、1mm間隔で交差状のスリットを設けた。次に、スズからなる第1被覆層を電解により厚さ2μm析出させた。続いて銅からなる第2被覆層を電解により厚さ1μm析出させた。最後にスズからなる第1被覆層を電解により厚さ2μm析出させ、多層被覆層を形成した。
【0053】
得られた上記集電体及び上記多層被覆層からなる複合体に、外側方向への引張力を付与した。このことによって、多層被覆層に0.1mmの間隔で直径0.05mmの空孔を形成した非水電解液二次電池用負極を製造した。
【0054】
〔実施例2〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる第1被覆層を電解により厚さ2μm析出させた。続いて銅からなる第2被覆層を電解により厚さ1μm析出させた。最後にスズからなる第1被覆層を電解により厚さ2μm析出させ、多層被覆層を形成した。
【0055】
得られた上記集電体及び上記多層被覆層からなる複合体に、多層被覆層側からレーザー処理を行った。このことによって、多層被覆層に0.1mmの間隔で直径0.05mmの空孔を形成した非水電解液二次電池用負極を製造した。
【0056】
〔実施例3〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる第1被覆層を電解により厚さ2μm析出させた。続いて銅からなる第2被覆層を電解により厚さ1μm析出させた。最後にスズからなる第1被覆層を電解により厚さ2μm析出させ、多層被覆層を形成した。
【0057】
得られた上記集電体及び上記多層被覆層からなる複合体に、多層被覆層側からピンを用いて穿孔した。このことによって、多層被覆層に0.1mmの間隔で直径0.5mmの空孔を形成した非水電解液二次電池用負極を製造した。
【0058】
〔実施例4〜6〕
実施例1〜3において、多層被覆層に空孔を形成した後、複合体の多層被覆層をロール圧延し、第2被覆層の第1被覆層との界面において、0.1mmの間隔でランダム、かつ微細な破断部を設け、非水電解液二次電池用負極とした。
【0059】
〔実施例7〕
多層被覆層を5層構造(第1被覆層+第2被覆層+第1被覆層+第2被覆層+第1被覆層)とした以外は、実施例1と同様にして非水電解液二次電池用負極を製造した。
【0060】
〔実施例8〕
多層被覆層に空孔を形成する前に、集電体及び多層被覆層からなる集電体に、200℃、3時間熱処理を施した以外は、実施例6と同様にして非水電解液二次電池用負極を製造した。
【0061】
〔実施例9〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる第1被覆層を電解により厚さ2μm析出させた。続いて銅からなる第二被覆層を電解により0.02μm析出させ非水電解液二次電池用負極を製造した。
【0062】
〔実施例10〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる第1被覆層を電解により厚さ2μm析出させた。続いて銅からなる第2被覆層を電解により厚さ1μm析出させた。最後にスズからなる第1被覆層を電解により厚さ2μm析出させ、多層被覆層を形成し、非水電解液二次電池用負極を製造した。
【0063】
〔実施例11〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる第1被覆層を電解により厚さ2μm析出させた。続いてニッケルからなる第2被覆層を電解により厚さ1μm析出させた。最後にスズからなる第1被覆層を電解により厚さ2μm析出させ、多層被覆層を形成した。次いで多層被覆層をロール圧延し、第2被覆層の第1被覆層との界面において、0.1mmの間隔でランダム、かつ微細な破断部を設け、非水電解液二次電池用負極を製造した。
【0064】
〔実施例12〕
第2被覆層としてニッケルに代えて銅を用いる以外は実施例11と同様にして非水電解液二次電池用負極を製造した。
【0065】
〔実施例13〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる第1被覆層を電解により厚さ2μm析出させた。続いて銅からなる第2被覆層を電解により厚さ1μm析出させた。その上に、スズからなる第1被覆層を電解により厚さ2μm析出させた。最後に、銅からなる被覆層を電解により厚さ0.02μm析出させ、多層被覆層を形成し、非水電解液二次電池用負極を製造した。
【0066】
〔実施例14〕
実施例13において、4層構造の多層被覆層を形成した後、該多層被覆層をロール圧延し、第2被覆層の第1被覆層との界面において、0.1mmの間隔でランダム、かつ微細な破断部を設ける以外は実施例13と同様にして非水電解液二次電池用負極を製造した。
【0067】
〔実施例15〕
実施例13において、銅からなる最上層の被覆層の厚みを0.05μmとする以外は実施例13と同様にして非水電解液二次電池用負極を製造した。
【0068】
〔実施例16〕
実施例15において、4層構造の多層被覆層を形成した後、該多層被覆層をロール圧延し、第2被覆層の第1被覆層との界面において、0.1mmの間隔でランダム、かつ微細な破断部を設ける以外は実施例15と同様にして非水電解液二次電池用負極を製造した。
【0069】
〔実施例17〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる被覆層を電解により厚さ2μm析出させた。続いて銅からなる被覆層を電解により厚さ2μm析出させた。次にスズからなる被覆層を電解により厚さ2μm析出させた。最後に銅からなる被覆層を電解により厚さ0.05μm析出させ、多層被覆層を形成した。次に、この多層被覆層及び集電体からなる複合体を、アルゴン雰囲気下、200℃で1時間熱処理した。このようにして得られた負極は、電子顕微鏡観察の結果、スズ−銅合金からなる第1被覆層と、銅リッチのスズ−銅合金からなる第2被覆層とから構成されていた。第1被覆層は、銅リッチのスズ−銅合金の層上にスズリッチのスズ−銅合金の層が形成されている2層構造となっていた。
【0070】
〔実施例18〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる被覆層を電解により厚さ4μm析出させた。続いて銅からなる被覆層を電解により厚さ4μm析出させ、多層被覆層を形成した。次に、この多層被覆層及び集電体からなる複合体を、アルゴン雰囲気下、200℃で3時間熱処理した。このようにして得られた負極は、電子顕微鏡観察の結果、スズ−銅合金からなる第1被覆層と、ほぼ銅からなり、スズ−銅合金を一部含む第2被覆層とから構成されていた。第1被覆層は、スズリッチのスズ−銅合金の層上に銅リッチのスズ−銅合金の層が形成されている2層構造となっていた。
【0071】
〔実施例19〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる被覆層を電解により厚さ2μm析出させた。続いて銅からなる被覆層を電解により厚さ2μm析出させた。次にスズからなる被覆層を電解により厚さ2μm析出させた。最後に銅からなる被覆層を電解により厚さ2μm析出させ、多層被覆層を形成した。次に、この多層被覆層及び集電体からなる複合体を、アルゴン雰囲気下、200℃で1時間熱処理した。このようにして得られた負極は、電子顕微鏡観察の結果、スズ−銅合金からなる第1被覆層と、銅リッチのスズ−銅合金からなる第2被覆層とから構成されていた。第1被覆層は、銅リッチのスズ−銅合金の層上にスズリッチのスズ−銅合金の層が形成されている2層構造となっていた。
【0072】
〔実施例20〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる被覆層を電解により厚さ2μm析出させた。続いて銅からなる被覆層を電解により厚さ2μm析出させた。次にスズからなる被覆層を電解により厚さ2μm析出させた。最後に銅からなる被覆層を電解により厚さ5μm析出させ、多層被覆層を形成した。次に、この多層被覆層及び集電体からなる複合体を、アルゴン雰囲気下、200℃で1時間熱処理した。このようにして得られた負極は、電子顕微鏡観察の結果、スズ−銅合金からなる第1被覆層と、銅リッチのスズ−銅合金からなる第2被覆層とから構成されていた。第1被覆層は、銅リッチのスズ−銅合金の層上にスズリッチのスズ−銅合金の層が形成されている2層構造となっていた。
【0073】
〔実施例21〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる被覆層を電解により厚さ1μm析出させた。続いて銅からなる被覆層を電解により厚さ1μm析出させた。次にスズからなる被覆層を電解により厚さ1μm析出させた。最後に銅からなる被覆層を電解により厚さ1μm析出させ、多層被覆層を形成した。次に、この多層被覆層及び集電体からなる複合体を、アルゴン雰囲気下、200℃で30分間熱処理した。このようにして得られた負極は、電子顕微鏡観察の結果、スズ−銅合金からなる第1被覆層と、銅リッチのスズ−銅合金からなる第2被覆層とから構成されていた。第1被覆層は、銅リッチのスズ−銅合金の層上にスズリッチのスズ−銅合金の層が形成されている2層構造となっていた。
【0074】
〔実施例22〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる被覆層を電解により厚さ2μm析出させた。続いて銅からなる被覆層を電解により厚さ2μm析出させた。次にスズからなる被覆層を電解により厚さ2μm析出させた。最後にニッケルからなる被覆層を電解により厚さ2μm析出させ、多層被覆層を形成した。次に、この多層被覆層及び集電体からなる複合体を、アルゴン雰囲気下、200℃で1時間熱処理した。このようにして得られた負極は、電子顕微鏡観察の結果、スズ−銅合金からなる第1被覆層と、ニッケルリッチのスズ−ニッケル合金からなる第2被覆層とから構成されていた。第1被覆層は、銅リッチのスズ−銅合金の層上にスズリッチのスズ−銅合金の層が形成されている2層構造となっていた。
【0075】
〔実施例23〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる被覆層を電解により厚さ2μm析出させた。続いて銅からなる被覆層を電解により厚さ2μm析出させた。次にスズからなる被覆層を電解により厚さ2μm析出させた。最後にクロムからなる被覆層を電解により厚さ2μm析出させ、多層被覆層を形成した。次に、この多層被覆層及び集電体からなる複合体を、アルゴン雰囲気下、200℃で1時間熱処理した。このようにして得られた負極は、電子顕微鏡観察の結果、スズ−銅合金からなる第1被覆層と、クロムリッチのスズ−クロム合金からなる第2被覆層とから構成されていた。第1被覆層は、銅リッチのスズ−銅合金の層上にスズリッチのスズ−銅合金の層が形成されている2層構造となっていた。
【0076】
〔実施例24〕
集電体として用いられる厚さ12μmの電解銅箔に、スズからなる被覆層を電解により厚さ4μm析出させた。続いて銅からなる被覆層を電解により厚さ4μm析出させた。次にスズからなる被覆層を電解により厚さ4μm析出させた。最後に銅からなる被覆層を電解により厚さ4μm析出させ、多層被覆層を形成した。次に、この多層被覆層及び集電体からなる複合体を、アルゴン雰囲気下、200℃で1時間熱処理した。このようにして得られた負極は、電子顕微鏡観察の結果、スズ−銅合金からなる第1被覆層と、銅リッチのスズ−銅合金からなる第2被覆層とから構成されていた。第1被覆層は、銅リッチのスズ−銅合金の層上にスズリッチのスズ−銅合金の層が形成されている2層構造となっていた。
【0077】
実施例1〜24及び比較例1で得られた負極を用いて下記の通り非水電解液二次電池を作成した。そして、下記に準拠して、不可逆容量(%)、初期容量(mAh/g)、10〜20∞及び100〜200∞の劣化率(%)を評価した。結果を表1に示す。充放電条件は、電流密度0,05mA/cm、電圧範囲0〜1.5Vである。尚、実施例9〜16の負極について、充放電の後にSEMによる組成像観察を行った結果、第2被覆層が断続的に形成されていたことが確認された。
【0078】
<非水電解液二次電池の作成>
負極として上記した多層構造を有する銅箔用い、陽極(対極)として金属リチウムを用いてセパレーターを介して対向させ、非水電解液としてLiPF/エチレンカーボネートとジエチルカーボネートの混合溶液(1:1容量比)を用いて通常の方法によって非水電解液二次電池を作成した。
【0079】
(不可逆容量)
〔1−(初回放電容量/初回充電容量)〕×100
すなわち、充電したが放電できず、活物質に残存した容量を示す。
【0080】
(初期容量)
第1被覆層及び第2被覆層を含めた活物質当たりの初回の放電容量を示す。
【0081】
(劣化率)
(1)劣化率(10−20∞)
10サイクル目の容量を基準とする。10−20サイクルの10サイクルの間において、1サイクル当たり、10サイクル目の容量に対して何%の劣化があったのかを示す。
(2)劣化率(100−200∞)
10サイクル目の容量を基準とする。100−200サイクルの100サイクルの間において、1サイクル当たり、10サイクル目の容量に対して何%の劣化があったのかを示す。
【0082】
【表1】

Figure 2004139954
【0083】
【表2】
Figure 2004139954
【0084】
【発明の効果】
本発明の非水電解液二次電池用負極は、電極の長寿命化が達成でき、かつ単位体積及び単位重量当たりのエネルギー密度を飛躍的に向上する。このため、上記負極を用いた非水電解液二次電池は、高容量で、優れた充放電特性及びサイクル寿命特性を有する。また、本発明の製造方法によって、上記負極が従来の既存設備を利用して安価に、かつ簡便に製造できる。
【図面の簡単な説明】
【図1】図1は、本発明の非水電解液二次電池用負極の一例の断面を示す走査型電子顕微鏡による組成像である。
【図2】図2は、本発明の非水電解液二次電池用負極の他の例の断面を示す走査型電子顕微鏡による組成像である。
【図3】図3は、本発明の非水電解液二次電池用負極の一例を模式的に示す断面図である。
【図4】図4は、本発明の非水電解液二次電池用負極の他の例を模式的に示す断面図である。
【図5】図5は、熱処理前の多層被覆層の断面を示す走査型電子顕微鏡像である。
【図6】図6は、熱処理によって得られた本発明の非水電解液二次電池用負極の断面を示す走査型電子顕微鏡像である。
【図7】図7は、本発明の製造方法(製造方法A)の一例を示す工程図である。
【符号の説明】
1:非水電解液二次電池
2:集電体(銅箔)
3:第1被覆層
4:第2被覆層
5:多層被覆層
6:空孔
7:破断部
8:スリット
F:引張力[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery capable of inserting and extracting a large amount of an alkali metal such as lithium, and a method for producing the same. For a non-aqueous electrolyte secondary battery, in which the energy density per unit volume and unit weight can be dramatically improved, and a method for producing the same, and a non-aqueous electrolyte secondary battery using the negative electrode .
[0002]
Problems to be solved by the prior art and the invention
2. Description of the Related Art With the spread of small portable electric and electronic devices, small and high capacity non-aqueous electrolyte (electrolyte) secondary batteries have been actively developed. This non-aqueous electrolyte secondary battery generally uses lithium manganate, lithium cobaltate, lithium nickelate, or the like as a positive electrode material, and uses a carbonaceous material, lithium metal, or the like as a negative electrode material.
[0003]
However, the carbonaceous material has a low theoretical discharge capacity of 372 mAh / g, and the current carbon material meets the needs against the expected increase in power consumption due to the multifunctionalization of small electric and electronic devices. It is difficult.
[0004]
On the other hand, although lithium metal has a high theoretical discharge capacity of 3860 mAh / g, lithium metal grows in a dendrite form from the negative electrode due to the degradation of lithium due to the reaction between the nonaqueous electrolyte and lithium metal and repeated charge / discharge, resulting in insulation. There is a problem that a short circuit may occur with the positive electrode through the separator as a body or the cycle life characteristics may be short.
[0005]
In order to solve such a problem, a negative electrode has been proposed in which a tin or tin alloy film is laminated on a surface of a current collector such as a copper plate by an electroplating method (Patent Documents 1 and 2 and Non-Patent Document 1). reference). However, such a negative electrode has a problem that tin or a tin alloy is cracked due to occlusion and desorption of lithium, peeled and dropped from a current collector formed of a copper plate or the like, and the life of the electrode cannot be extended. . In particular, since the current collector and the tin or tin alloy are usually separately plated, the tin or tin alloy is plated after the oxide film is formed on the current collector surface. It easily peels off from the body and falls off.
[0006]
[Patent Document 1]
JP 2001-68094 A
[Patent Document 2]
JP 2001-68094 A
[Non-patent document 1]
Proceedings of the 42nd Battery Symposium p282, 284, 288
[0007]
In addition, a high energy density per unit volume and unit weight is required for a negative electrode for a non-aqueous electrolyte secondary battery.
[0008]
Accordingly, an object of the present invention is to provide a negative electrode for a non-aqueous electrolyte secondary battery and a method for producing the same, which can achieve a long electrode life and dramatically improve the energy density per unit volume and unit weight. An object of the present invention is to provide a non-aqueous electrolyte secondary battery using a negative electrode.
[0009]
[Means for Solving the Problems]
As a result of the study, the present inventors have found that a first coating layer containing an element capable of absorbing lithium such as tin and a second coating layer containing a metal having a low ability to form a lithium compound are formed on the surface of the current collector. It was found that the above-described negative electrode can achieve the above object.
[0010]
The present invention has been made based on the above-described findings, and a first coating layer containing tin, a tin alloy, aluminum or an aluminum alloy is formed on a surface of a current collector, and then a lithium coating is formed on the first coating layer. An object of the present invention is to provide a negative electrode for a non-aqueous electrolyte secondary battery, wherein a second coating layer containing a metal having a low ability to form a compound is formed.
[0011]
Also, the present invention provides a method in which a first coating layer containing tin, a tin alloy, aluminum or an aluminum alloy, and a second coating layer containing a metal having a low ability to form a lithium compound are formed on the current collector surface by electrolytic or dry methods, respectively. An object of the present invention is to provide a method for producing a negative electrode for a non-aqueous electrolyte secondary battery, which is sequentially deposited by a treatment and then heat-treated at 120 to 350 ° C. for 10 minutes to 24 hours.
[0012]
In addition, the present invention provides a first coating layer containing tin, a tin alloy, aluminum or an aluminum alloy, a second coating layer containing a metal having a low ability to form a lithium compound, Further, a multilayer coating layer based on a three-layer structure in which a first coating layer of the same type or a different type as the first coating layer is deposited by electrolysis or surface treatment by a dry method, respectively, is provided. Non-aqueous electrolyte solution characterized in that pores having a diameter of 2 mm or less are formed at intervals of 1 mm or less by applying a tensile force in an outward direction to a composite comprising the multilayer coating layer. It is intended to provide a method for producing a negative electrode for a secondary battery.
[0013]
Further, the present invention provides a method according to the present invention, wherein a first coating layer containing tin, a tin alloy, aluminum or an aluminum alloy, a second coating layer containing a metal having a low ability to form a lithium compound, and the first coating layer are formed on the current collector surface. A composite comprising the above-mentioned current collector and the above-mentioned multilayer coating layer provided with a multilayer coating layer based on a three-layer structure in which the same or different first coating layers are respectively deposited by electrolytic or surface treatment by a dry method. Producing a negative electrode for a non-aqueous electrolyte secondary battery, wherein pores having a diameter of 2 mm or less are formed in the multilayer coating layer at an interval of 1 mm or less by performing a laser treatment from the multilayer coating layer side. It provides a method.
[0014]
The present invention further provides a first coating layer containing tin, a tin alloy, aluminum or an aluminum alloy, a second coating layer containing a metal having a low ability to form a lithium compound, and the first coating layer on the current collector surface. A composite comprising the above-mentioned current collector and the above-mentioned multilayer coating layer provided with a multilayer coating layer based on a three-layer structure in which the same or different first coating layers are respectively deposited by electrolytic or surface treatment by a dry method. A negative electrode for a non-aqueous electrolyte secondary battery, wherein pores having a diameter of 2 mm or less are formed in the multilayer coating layer at intervals of 1 mm or less by piercing with a pin from the multilayer coating layer side. Is provided.
[0015]
The present invention also provides a non-aqueous electrolyte secondary battery using the negative electrode.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0017]
As the current collector in the negative electrode for a non-aqueous electrolyte secondary battery of the present invention, for example, a foil of a conductive material such as copper, nickel, and stainless steel is used. For example, when a copper foil is used as the current collector, the copper foil is obtained by electrolysis using a copper-containing solution, and its thickness is desirably 10 to 30 μm. In particular, the copper foil obtained by the method described in JP-A-2000-90937 is preferably used because it has a very small thickness of 12 μm or less.
[0018]
In the negative electrode of the present invention, a first coating layer containing tin, a tin alloy, aluminum or an aluminum alloy is formed on the surface of the current collector, and a metal having a low ability to form a lithium compound is formed on the first coating layer. And a multilayer coating layer formed by forming a second coating layer containing
[0019]
The multilayer coating layer in the present invention has a two-layer structure composed of the first coating layer and the second coating layer as described above. By forming the second coating layer on the first coating layer, the discharge capacity is increased by the action of the first coating layer, and at the same time, peeling and falling off of the first coating layer are effectively prevented, and the life of the electrode is extended. Can be achieved. In another embodiment of the present invention, the negative electrode may have a three-layer structure in which a first coating layer is further formed on a second coating layer. According to the embodiment having the three-layer structure, the first coating layer formed on the surface of the current collector is more effectively prevented from peeling off and falling off, and the life of the electrode can be further extended. In still another embodiment of the present invention, one or more sets of a coating layer having a second coating layer and a first coating layer in this order as one set are further formed on the three-layer structure. Good. That is, not only a three-layer structure but also a five-layer structure, a seven-layer structure, or the like may be used. The two or more first coating layers and the second coating layers constituting these multilayer coating layers may be made of the same material, or may be made of different materials.
[0020]
When the negative electrode of the present invention has the above three-layer structure (the first coating layer, the second coating layer, and the first coating layer), or on the three-layer structure, the second coating layer and the first coating layer When one or more sets of the coating layers are further formed as one set of the coating layers, it is preferable that a coating layer containing a metal having a low ability to form a lithium compound is further formed as the uppermost layer. For example, when the negative electrode of the present invention has the above three-layer structure, a lithium compound is formed on the upper first coating layer (that is, the first coating layer formed on the second coating layer). It is preferable to have a four-layer structure in which a coating layer containing a metal having low forming ability is further formed. By forming a coating layer containing a metal having low ability to form a lithium compound as the uppermost layer, oxidation of the first coating layer made of tin or the like is suppressed, and the irreversible capacity is reduced. In addition, the first coating layer is prevented from falling off, and the life characteristics of the negative electrode are improved. From the viewpoint of making this effect more remarkable, the coating layer containing a metal having a low ability to form a lithium compound formed as the uppermost layer has a thickness of 0.01 to 20 μm, particularly 0.02 to 10 μm, and particularly preferably 0 to 10 μm. It is preferable that the thickness is as thin as 0.5 to 5 μm. "Low ability to form a lithium compound" means that no intermetallic compound or solid solution is formed with lithium, or even if formed, the amount of lithium is very small or very unstable. Examples of the metal include copper, iron, cobalt, chromium, nickel and the like. Conversely, metals having a high ability to form lithium compounds include tin, silicon, and aluminum, and these metals form intermetallic compounds with lithium. It is preferable to use copper as the metal having a low ability to form a lithium compound, in particular, since oxidation and falling off of the first coating layer are further prevented, the irreversible capacity is further reduced, and the life characteristics of the negative electrode are further improved.
[0021]
In the first coating layer, tin alloys include tin-bismuth, tin-iron, tin-cobalt, tin-copper, and the like. Aluminum alloys include aluminum-lithium, aluminum-manganese, aluminum-titanium, and aluminum-chromium. , Aluminum-vanadium, aluminum-copper and the like. These first coating layers are preferably obtained by electrolytic plating or surface treatment by a dry method, and the thickness is preferably 0.5 to 50 μm, more preferably 1 to 50 μm, and still more preferably 2 to 20 μm.
[0022]
The second coating layer is configured to include a metal having a low ability to form a lithium compound. For the details of the “metal having a low ability to form a lithium compound”, the above description regarding the coating layer formed of a metal having a low ability to form a lithium compound, which is formed as the uppermost layer, applies. Since the second coating layer containing a metal having a low ability to form a lithium compound serves as a support material for the first coating layer containing tin or the like, it contributes to an improvement in the cycle life characteristics associated with occlusion and desorption of lithium. . From this viewpoint, it is particularly preferable to use copper or nickel as the metal having a low ability to form a lithium compound. The second coating layer is obtained by, for example, electrolysis using a solution containing the above-mentioned metal, and the thickness is preferably 0.02 to 50 μm, more preferably 0.2 to 20 μm.
[0023]
The second coating layer may continuously cover the entire area of the first coating layer, or may cover the first coating layer intermittently. FIGS. 1 and 2 show specific examples of a state in which the second coating layer intermittently covers the first coating layer. 1 and 2 are composition images obtained by observing a cross section of a three-layered negative electrode having a first coating layer, a second coating layer, and a first coating layer with a scanning electron microscope (SEM). 1 and 2, the first coating layer is made of tin, and the second coating layer is made of copper. The current collector is made of copper foil. In these figures, the boundaries of each coating layer are highlighted by lines to aid understanding. As is clear from these figures, the first coating layer is continuously formed on the surface of the current collector, and the second coating layer is formed intermittently thereon. Note that the first coating layer formed on the second coating layer is a discontinuous layer like the second coating layer. Therefore, in portions where the first coating layer formed on the second coating layer is discontinuous, the second coating layer may be exposed on the surface. In order to form the intermittent second coating layer, for example, the electrolysis conditions for forming the second coating layer may be appropriately selected or the surface roughness of the copper foil as the current collector may be appropriately controlled. . In addition, after forming the negative electrode by forming a continuous second coating layer, the negative electrode is charged and discharged, and the first coating layer formed on the current collector is expanded and contracted, so that the continuous second coating layer is formed. 2 The coating layer can be changed to a discontinuous state. When the second coating layer covers the first coating layer intermittently, the intermittent second coating layer becomes a path for the electrolyte to enter.
[0024]
It is also advantageous to form holes through the coating layer to further facilitate the entry of the electrolyte. For example, when the negative electrode of the present invention has a first coating layer on a current collector, a second coating layer thereon, and a first coating layer thereon, these coating layers are provided at an interval of 1 mm or less. It is preferable that pores of 2 mm or less, desirably 500 μm or less exist. That is, it is preferable that there are through holes penetrating these three layers. The presence of such pores allows the electrolyte to enter the pores more effectively, so that any of the first coating layers functions better as a negative electrode. Further, volume expansion and contraction can be reduced by the holes.
[0025]
Further, when the negative electrode of the present invention has a first coating layer on the current collector, a second coating layer thereon, and a first coating layer thereon, the second coating layer comprises It is desirable to have random and fine breaks at an interface of 2 mm or less at the interface with the layer. By having such a broken portion, the first coating layer can be further effectively used as a negative electrode. This broken portion may be provided even when the above-mentioned holes are not formed in each coating layer.
[0026]
Examples of the configuration of the negative electrode for a non-aqueous electrolyte secondary battery of the present invention are schematically shown in FIGS. FIG. 3 is a cross-sectional view schematically showing one example of the negative electrode for a non-aqueous electrolyte secondary battery of the present invention, and FIG. 4 is a cross-sectional view schematically showing another example. As shown in FIGS. 3 and 4, the negative electrode for a non-aqueous electrolyte secondary battery includes a current collector (copper foil) 2 and a multilayer coating layer 5, and the multilayer coating layer 5 includes a first coating layer 3, It has a three-layer structure of two coating layers 4 and a first coating layer 3. In the multilayer coating layer 5, holes 6 are provided at regular intervals. In FIG. 4, a break 7 is provided at the interface between the second coating layer 4 and the first coating layer 3. 3 and 4, the second coating layer 4 is shown as a continuous layer, but this is only a schematic one, and the second coating layer 4 is a discontinuous layer as described above. You may.
[0027]
As another embodiment of the negative electrode for a non-aqueous electrolyte secondary battery of the present invention, the first coating layer formed directly on the current collector includes tin or aluminum, and the constituent elements of the second coating layer and / or Alternatively, an embodiment including an alloy with the constituent elements of the current collector may be used. For example, when the current collector is made of copper foil and the second coating layer contains copper, the first coating layer can be a tin-copper alloy. In the case of this embodiment, there is an advantage that adhesion between the first coating layer and the current collector and / or the second coating layer is improved, and the active material is prevented from falling off. Further, as still another embodiment of the negative electrode for a nonaqueous electrolyte secondary battery of the present invention, the second coating layer includes a metal having a low ability to form a lithium compound and a first coating layer adjacent to the second coating layer. It is preferable to be made of an alloy with the constituent elements. In yet another embodiment of the negative electrode for a non-aqueous electrolyte secondary battery of the present invention, the uppermost layer is formed of a metal having a low ability to form a lithium compound and a constituent element of a second coating layer adjacent to the uppermost layer. Preferably, it is made of an alloy. In the case of these two embodiments, there is an advantage that the change in volume due to the absorption and desorption of lithium is reduced while the current collecting function of the electrode is maintained, and the pulverization of the alloy is suppressed.
[0028]
The electrodes of the above embodiments are preferably manufactured by the following method. First, a coating layer containing tin, a tin alloy, aluminum or an aluminum alloy (referred to as an A layer), a coating layer containing a metal having a low ability to form a lithium compound (referred to as a B layer), A different layer A and a coating layer containing a metal having a low ability to form a lithium compound (referred to as layer C) are sequentially deposited by electrolytic or dry surface treatment to provide a multilayer coating layer having a four-layer structure. This state is shown in FIG. In FIG. 5, the current collector is made of copper foil, the two A layers are made of tin, and the B and C layers are made of copper. Next, the composite including the multilayer coating layer and the current collector is heat-treated. The heat treatment is performed for the purpose of diffusing the elements constituting each layer. For this purpose, the heat treatment conditions are preferably from 120 to 350 ° C. for 10 minutes to 24 hours, particularly from 160 to 250 ° C. for 10 minutes to 6 hours. Diffusion of an element by heat usually requires time, but by reducing the thickness of the A layer to the C layer, the element can be diffused in a very short time, and there is a great cost advantage. The atmosphere for the heat treatment may be an inert gas atmosphere such as a nitrogen gas or an argon gas, or may be an air atmosphere. Also 10 -1 It may be in a vacuum having a degree of vacuum of Torr or less. In particular, it is preferable to be in an inert gas atmosphere or in a vacuum in order to prevent excessive oxidation of the coating layer.
[0029]
The electrode of the above embodiment is obtained by element diffusion by heat treatment for a predetermined time. FIG. 6 shows an example of the electrode of the present invention obtained by using the multilayer coating layer shown in FIG. In FIG. 6, a first coating layer made of a tin-copper alloy containing tin derived from the layer A formed adjacent to the current collector and copper derived from the current collector and / or the layer B is formed. Have been. Since the diffusion of the element can be controlled by controlling the heat treatment conditions, the tin and copper concentrations in the first coating layer can be controlled to desired values. Specifically, the first coating layer is a tin-rich tin-copper alloy layer. On the first coating layer, a second coating layer made of a tin-copper alloy containing copper derived from the B layer and tin derived from two A layers is formed. The second coating layer is rich in copper. A first coating layer made of a tin-copper alloy containing tin derived from the upper A layer and copper derived from the B and C layers is formed on the second coating layer. The first coating layer is tin-rich. An uppermost layer made of a tin-copper alloy containing tin derived from the upper A layer and copper derived from the C layer is formed on the first coating layer. The top layer is copper rich.
[0030]
In FIG. 6, the boundaries between the layers are observed relatively clearly, but depending on the heat treatment conditions, a gradient may occur in the diffusion of the element, which may cause the boundaries between the layers to be unclear. For example, depending on the thickness of each layer and the heat treatment conditions in the multilayer coating layer shown in FIG. 5, the electrode obtained as a result of the heat treatment has a first coating layer made of a tin-copper alloy and a second coating layer made of a copper-rich tin-copper alloy. In some cases, the first coating layer has a two-layer structure of a copper-rich tin-copper alloy layer and a tin-rich tin-copper alloy layer (see Examples described later).
[0031]
Next, another preferred method for producing the negative electrode for a non-aqueous electrolyte secondary battery of the present invention (production methods A to C) will be described with reference to the production of a negative electrode having a three-layer structure as an example.
[0032]
<Production method A>
FIG. 7 shows a manufacturing process of the manufacturing method A. In the manufacturing method A, the slit 8 is provided in the current collector 2 as shown in FIG. When the current collector is made of, for example, a copper foil, the copper foil is obtained by electrolysis or the like. The slits 8 are desirably provided in an intersecting manner and at an interval of 3 mm or less.
[0033]
Next, as shown in FIG. 7 (b), the first coating layer, the second coating layer, and the first coating layer are formed on the surface of the current collector 2 by electrolytic or dry surface treatment. A multilayer coating layer 5 having a three-layer structure is provided.
[0034]
Then, as shown in FIG. 7C, an outward tensile force F is applied to the obtained composite comprising the current collector and the multilayer coating layer. As a result, as shown in FIG. 7D, a negative electrode for a non-aqueous electrolyte secondary battery in which holes 6 having a diameter of 2 mm or less are formed at intervals of 1 mm or less in the multilayer coating layer 5 is manufactured.
[0035]
<Production method B>
In the manufacturing method B, a multilayer coating layer having a three-layer structure is formed on the current collector. When the current collector is made of, for example, a copper foil, the copper-containing solution is electrolyzed to deposit a copper foil as a current collector on a drum. In this electrolysis step, the copper foil is subjected to surface treatment, glue treatment, rust prevention treatment, and the like. In parallel with this, the first coating layer, the second coating layer, There is provided a multilayer coating layer having a three-layer structure in which each of the first coating layers is deposited by electrolytic or surface treatment by a dry method.
[0036]
Next, the resulting composite comprising the current collector and the multilayer coating layer is subjected to laser treatment from the multilayer coating layer side. As a result, a negative electrode for a non-aqueous electrolyte secondary battery in which holes having a diameter of 2 mm or less are formed at intervals of 1 mm or less in the multilayer coating layer is manufactured.
[0037]
<Production method C>
In the manufacturing method C, similarly to the manufacturing method B, a multilayer covering layer having a three-layer structure is formed on the current collector. When the current collector is made of, for example, a copper foil, a multilayer coating layer having a layer structure is formed in the copper foil electrolysis step.
[0038]
Next, a hole is made in the obtained composite comprising the current collector and the multilayer coating layer using a pin from the multilayer coating layer side. As a result, a negative electrode for a non-aqueous electrolyte secondary battery in which holes having a diameter of 2 mm or less are formed at intervals of 1 mm or less in the multilayer coating layer is manufactured.
[0039]
In the above-mentioned production methods A to C, a press or roll rolling treatment may be performed from the side of the multilayer coating layer of the composite before and after the treatment for forming pores as described above. As a result, random and fine breaks are formed in the second coating layer at an interface of 2 mm or less at the interface with the first coating layer. Further, as is clear from the examples described later, this press or roll rolling may be performed even when the holes are not provided.
[0040]
In the manufacturing methods A to C, the heat treatment described above is applied to the composite including the current collector and the multilayer coating layer having a three-layer structure before and after the processing for forming the holes as described above. It is also desirable that it is done. The heat treatment conditions are as described above. The advantages of subjecting the composite to heat treatment are as described above.
[0041]
In the above-described production method of the present invention, when a copper foil is used as the current collector, for example, a conventionally used facility for producing an electrolytic copper foil can be used as it is. Therefore, the negative electrode can be manufactured inexpensively and easily. Further, since the current collector and the multilayer coating layer can be manufactured in a series of steps, no oxide film is formed on the surface of the copper constituting the current collector and the second coating layer. Even if the layer is cracked, unoxidized copper and tin are firmly bonded, and for example, the Cu-Sn alloy interface prevents peeling and falling off of tin and the like.
[0042]
Next, the non-aqueous electrolyte secondary battery of the present invention will be described. The non-aqueous electrolyte secondary battery of the present invention includes a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte as its basic structure. The negative electrode uses the negative electrode of the present invention as described above. The separator, the non-aqueous electrolyte and the non-aqueous electrolyte are not particularly limited, and those conventionally known for non-aqueous electrolyte secondary batteries such as lithium secondary batteries are used.
[0043]
The positive electrode is prepared by suspending a positive electrode active material and, if necessary, a conductive agent and a binder in an appropriate solvent to prepare a positive electrode mixture, applying this to a current collector, drying the roll, rolling, pressing, and further cutting. , By punching.
[0044]
As the positive electrode active material, a conventionally known positive electrode active material such as a lithium nickel composite oxide, a lithium manganese composite oxide, and a lithium cobalt composite oxide is used.
[0045]
As the conductive agent used for the positive electrode, carbon black, acetylene black, graphite, or the like is used. As the binder, styrene-butadiene rubber, polytetrafluoroethylene, polyvinylidene fluoride, a fluoropolymer, carboxymethyl cellulose, polyvinyl alcohol, or the like is used. Further, N-methylpyrrolidone, dimethylformamide and the like are used as the solvent. Aluminum or an aluminum alloy is preferably used as the current collector.
[0046]
As the separator, a synthetic resin nonwoven fabric, a polyethylene or polypropylene porous film, or the like is preferably used.
[0047]
When a non-aqueous electrolyte is a lithium secondary battery, a general non-aqueous electrolyte is a solution in which a lithium salt as a supporting electrolyte is dissolved in an organic solvent. As the lithium salt, for example, LiC1O 4 , LiA1Cl 4 , LiPF 6 , LiAsF 6 , LiSbF 6 , LiSCN, LiCl, LiBr, LiI, LiCF 3 SO 3 , LiC 4 F 9 SO 3 Etc., and in particular, LiPF 6 An electrolyte containing is preferred.
[0048]
Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and aliphatic carboxylic acids such as methyl formate, ethyl acetate, and methyl propionate. Esters; γ-lactones such as γ-butyrolactone; chain ethers such as 1,2-dimethoxyethane; cyclic ethers such as tetrahydrofuran; other dimethyl sulfoxides, dioxolanes, amides, nitriles, sulfolanes and the like. It is preferred to use various aprotic solvents. In particular, a mixed system of a cyclic carbonate and a chain carbonate and a system in which an aliphatic carboxylic acid ester is further mixed are preferably used, and a mixed solvent of ethylene carbonate and ethyl methyl carbonate is particularly preferable.
[0049]
The shape of the nonaqueous electrolyte secondary battery is not particularly limited, and may be any of a cylindrical shape, a square shape, a coin shape, a button shape, and the like. The nonaqueous electrolyte secondary battery of the present invention can be suitably used, for example, for portable information terminals, portable electronic devices, and automobiles.
[0050]
【Example】
Hereinafter, the present invention will be specifically described based on examples and the like.
[0051]
[Comparative Example 1]
A first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm on an electrolytic copper foil having a thickness of 12 μm used as a current collector to obtain a negative electrode for a nonaqueous electrolyte secondary battery.
[0052]
[Example 1]
Crossed slits were provided at 1 mm intervals in a 30 μm thick electrolytic copper foil used as a current collector. Next, a first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm. Subsequently, a second coating layer made of copper was deposited by electrolysis to a thickness of 1 μm. Finally, a first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm to form a multilayer coating layer.
[0053]
An outward tensile force was applied to the obtained composite comprising the current collector and the multilayer coating layer. As a result, a negative electrode for a non-aqueous electrolyte secondary battery in which pores having a diameter of 0.05 mm were formed in the multilayer coating layer at intervals of 0.1 mm was produced.
[0054]
[Example 2]
On a 12 μm-thick electrolytic copper foil used as a current collector, a first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm. Subsequently, a second coating layer made of copper was deposited by electrolysis to a thickness of 1 μm. Finally, a first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm to form a multilayer coating layer.
[0055]
The obtained composite comprising the current collector and the multilayer coating layer was subjected to laser treatment from the multilayer coating layer side. As a result, a negative electrode for a non-aqueous electrolyte secondary battery in which pores having a diameter of 0.05 mm were formed in the multilayer coating layer at intervals of 0.1 mm was produced.
[0056]
[Example 3]
On a 12 μm-thick electrolytic copper foil used as a current collector, a first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm. Subsequently, a second coating layer made of copper was deposited by electrolysis to a thickness of 1 μm. Finally, a first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm to form a multilayer coating layer.
[0057]
The resulting composite comprising the current collector and the multilayer coating layer was perforated with a pin from the multilayer coating layer side. As a result, a negative electrode for a non-aqueous electrolyte secondary battery in which pores having a diameter of 0.5 mm were formed in the multilayer coating layer at intervals of 0.1 mm was produced.
[0058]
[Examples 4 to 6]
In Examples 1-3, after forming pores in the multilayer coating layer, the multilayer coating layer of the composite was roll-rolled, and at the interface of the second coating layer with the first coating layer, random at intervals of 0.1 mm. In addition, a fine broken portion was provided to obtain a negative electrode for a non-aqueous electrolyte secondary battery.
[0059]
[Example 7]
A non-aqueous electrolyte solution was prepared in the same manner as in Example 1 except that the multilayer coating layer had a five-layer structure (first coating layer + second coating layer + first coating layer + second coating layer + first coating layer). A negative electrode for a secondary battery was manufactured.
[0060]
Example 8
Before forming the holes in the multilayer coating layer, the nonaqueous electrolyte solution was prepared in the same manner as in Example 6 except that the current collector comprising the current collector and the multilayer coating layer was subjected to a heat treatment at 200 ° C. for 3 hours. A negative electrode for a secondary battery was manufactured.
[0061]
[Example 9]
On a 12 μm-thick electrolytic copper foil used as a current collector, a first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm. Subsequently, a second coating layer made of copper was deposited by electrolysis at 0.02 μm to produce a negative electrode for a non-aqueous electrolyte secondary battery.
[0062]
[Example 10]
On a 12 μm-thick electrolytic copper foil used as a current collector, a first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm. Subsequently, a second coating layer made of copper was deposited by electrolysis to a thickness of 1 μm. Finally, a first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm to form a multilayer coating layer, thereby producing a negative electrode for a non-aqueous electrolyte secondary battery.
[0063]
[Example 11]
On a 12 μm-thick electrolytic copper foil used as a current collector, a first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm. Subsequently, a second coating layer made of nickel was deposited by electrolysis to a thickness of 1 μm. Finally, a first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm to form a multilayer coating layer. Then, the multilayer coating layer is roll-rolled, and random and fine breaks are provided at intervals of 0.1 mm at the interface between the second coating layer and the first coating layer to produce a negative electrode for a non-aqueous electrolyte secondary battery. did.
[0064]
[Example 12]
A negative electrode for a non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 11 except that copper was used instead of nickel as the second coating layer.
[0065]
[Example 13]
On a 12 μm-thick electrolytic copper foil used as a current collector, a first coating layer made of tin was deposited by electrolysis to a thickness of 2 μm. Subsequently, a second coating layer made of copper was deposited by electrolysis to a thickness of 1 μm. A first coating layer of tin was deposited thereon by electrolysis to a thickness of 2 μm. Finally, a coating layer made of copper was deposited by electrolysis to a thickness of 0.02 μm to form a multilayer coating layer, thereby producing a negative electrode for a non-aqueous electrolyte secondary battery.
[0066]
[Example 14]
In Example 13, after forming a multilayer coating layer having a four-layer structure, the multilayer coating layer was roll-rolled, and random and fine at an interface of 0.1 mm at the interface between the second coating layer and the first coating layer. A negative electrode for a non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 13 except that a sharp break was provided.
[0067]
[Example 15]
A negative electrode for a non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 13, except that the thickness of the uppermost coating layer made of copper was 0.05 μm.
[0068]
[Example 16]
In Example 15, after forming a multilayer coating layer having a four-layer structure, the multilayer coating layer was roll-rolled, and the interface between the second coating layer and the first coating layer was random and fine at an interval of 0.1 mm. A negative electrode for a non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 15 except that a sharp break was provided.
[0069]
[Example 17]
A coating layer made of tin was deposited by electrolysis to a thickness of 2 μm on a 12 μm thick electrolytic copper foil used as a current collector. Subsequently, a coating layer made of copper was deposited by electrolysis to a thickness of 2 μm. Next, a coating layer made of tin was deposited by electrolysis to a thickness of 2 μm. Finally, a coating layer made of copper was deposited by electrolysis to a thickness of 0.05 μm to form a multilayer coating layer. Next, the composite including the multilayer coating layer and the current collector was heat-treated at 200 ° C. for 1 hour in an argon atmosphere. As a result of electron microscopic observation, the negative electrode thus obtained was composed of a first coating layer made of a tin-copper alloy and a second coating layer made of a copper-rich tin-copper alloy. The first coating layer had a two-layer structure in which a tin-rich tin-copper alloy layer was formed on a copper-rich tin-copper alloy layer.
[0070]
[Example 18]
A coating layer made of tin was deposited by electrolysis to a thickness of 4 μm on an electrolytic copper foil having a thickness of 12 μm used as a current collector. Subsequently, a coating layer made of copper was deposited by electrolysis to a thickness of 4 μm to form a multilayer coating layer. Next, the composite including the multilayer coating layer and the current collector was heat-treated at 200 ° C. for 3 hours in an argon atmosphere. As a result of electron microscopic observation, the negative electrode thus obtained was composed of a first coating layer made of a tin-copper alloy and a second coating layer made of substantially copper and partially containing a tin-copper alloy. Was. The first coating layer had a two-layer structure in which a copper-rich tin-copper alloy layer was formed on a tin-rich tin-copper alloy layer.
[0071]
[Example 19]
A coating layer made of tin was deposited by electrolysis to a thickness of 2 μm on a 12 μm thick electrolytic copper foil used as a current collector. Subsequently, a coating layer made of copper was deposited by electrolysis to a thickness of 2 μm. Next, a coating layer made of tin was deposited by electrolysis to a thickness of 2 μm. Finally, a coating layer made of copper was deposited by electrolysis to a thickness of 2 μm to form a multilayer coating layer. Next, the composite including the multilayer coating layer and the current collector was heat-treated at 200 ° C. for 1 hour in an argon atmosphere. As a result of electron microscopic observation, the negative electrode thus obtained was composed of a first coating layer made of a tin-copper alloy and a second coating layer made of a copper-rich tin-copper alloy. The first coating layer had a two-layer structure in which a tin-rich tin-copper alloy layer was formed on a copper-rich tin-copper alloy layer.
[0072]
[Example 20]
A coating layer made of tin was deposited by electrolysis to a thickness of 2 μm on a 12 μm thick electrolytic copper foil used as a current collector. Subsequently, a coating layer made of copper was deposited by electrolysis to a thickness of 2 μm. Next, a coating layer made of tin was deposited by electrolysis to a thickness of 2 μm. Finally, a coating layer made of copper was deposited by electrolysis to a thickness of 5 μm to form a multilayer coating layer. Next, the composite including the multilayer coating layer and the current collector was heat-treated at 200 ° C. for 1 hour in an argon atmosphere. As a result of electron microscopic observation, the negative electrode thus obtained was composed of a first coating layer made of a tin-copper alloy and a second coating layer made of a copper-rich tin-copper alloy. The first coating layer had a two-layer structure in which a tin-rich tin-copper alloy layer was formed on a copper-rich tin-copper alloy layer.
[0073]
[Example 21]
A coating layer made of tin was electrolytically deposited to a thickness of 1 μm on a 12 μm thick electrolytic copper foil used as a current collector. Subsequently, a coating layer made of copper was deposited by electrolysis to a thickness of 1 μm. Next, a coating layer made of tin was deposited by electrolysis to a thickness of 1 μm. Finally, a coating layer made of copper was deposited by electrolysis to a thickness of 1 μm to form a multilayer coating layer. Next, the composite including the multilayer coating layer and the current collector was heat-treated at 200 ° C. for 30 minutes in an argon atmosphere. As a result of electron microscopic observation, the negative electrode thus obtained was composed of a first coating layer made of a tin-copper alloy and a second coating layer made of a copper-rich tin-copper alloy. The first coating layer had a two-layer structure in which a tin-rich tin-copper alloy layer was formed on a copper-rich tin-copper alloy layer.
[0074]
[Example 22]
A coating layer made of tin was deposited by electrolysis to a thickness of 2 μm on a 12 μm thick electrolytic copper foil used as a current collector. Subsequently, a coating layer made of copper was deposited by electrolysis to a thickness of 2 μm. Next, a coating layer made of tin was deposited by electrolysis to a thickness of 2 μm. Finally, a coating layer made of nickel was deposited by electrolysis to a thickness of 2 μm to form a multilayer coating layer. Next, the composite including the multilayer coating layer and the current collector was heat-treated at 200 ° C. for 1 hour in an argon atmosphere. As a result of electron microscopic observation, the negative electrode thus obtained was composed of a first coating layer made of a tin-copper alloy and a second coating layer made of a nickel-rich tin-nickel alloy. The first coating layer had a two-layer structure in which a tin-rich tin-copper alloy layer was formed on a copper-rich tin-copper alloy layer.
[0075]
[Example 23]
A coating layer made of tin was deposited by electrolysis to a thickness of 2 μm on a 12 μm thick electrolytic copper foil used as a current collector. Subsequently, a coating layer made of copper was deposited by electrolysis to a thickness of 2 μm. Next, a coating layer made of tin was deposited by electrolysis to a thickness of 2 μm. Finally, a coating layer made of chromium was deposited by electrolysis to a thickness of 2 μm to form a multilayer coating layer. Next, the composite including the multilayer coating layer and the current collector was heat-treated at 200 ° C. for 1 hour in an argon atmosphere. As a result of electron microscopic observation, the negative electrode thus obtained was composed of a first coating layer made of a tin-copper alloy and a second coating layer made of a chromium-rich tin-chromium alloy. The first coating layer had a two-layer structure in which a tin-rich tin-copper alloy layer was formed on a copper-rich tin-copper alloy layer.
[0076]
[Example 24]
A coating layer made of tin was deposited by electrolysis to a thickness of 4 μm on an electrolytic copper foil having a thickness of 12 μm used as a current collector. Subsequently, a coating layer made of copper was deposited by electrolysis to a thickness of 4 μm. Next, a coating layer made of tin was deposited by electrolysis to a thickness of 4 μm. Finally, a coating layer made of copper was deposited by electrolysis to a thickness of 4 μm to form a multilayer coating layer. Next, the composite including the multilayer coating layer and the current collector was heat-treated at 200 ° C. for 1 hour in an argon atmosphere. As a result of electron microscopic observation, the negative electrode thus obtained was composed of a first coating layer made of a tin-copper alloy and a second coating layer made of a copper-rich tin-copper alloy. The first coating layer had a two-layer structure in which a tin-rich tin-copper alloy layer was formed on a copper-rich tin-copper alloy layer.
[0077]
Using the negative electrodes obtained in Examples 1 to 24 and Comparative Example 1, nonaqueous electrolyte secondary batteries were prepared as follows. Then, the irreversible capacity (%), the initial capacity (mAh / g), and the deterioration rates (%) of 10 to 20 ° and 100 to 200 ° were evaluated based on the following. Table 1 shows the results. The charge and discharge conditions were as follows: current density: 0.05 mA / cm 2 , And the voltage range is 0 to 1.5V. In addition, the composition images of the negative electrodes of Examples 9 to 16 were observed by SEM after charging and discharging, and it was confirmed that the second coating layer was formed intermittently.
[0078]
<Preparation of non-aqueous electrolyte secondary battery>
A copper foil having the above-described multilayer structure is used as a negative electrode, metallic lithium is used as an anode (counter electrode), and a metal foil is used as a nonaqueous electrolyte. 6 / A non-aqueous electrolyte secondary battery was prepared by a usual method using a mixed solution of ethylene carbonate and diethyl carbonate (1: 1 volume ratio).
[0079]
(Irreversible capacity)
[1- (initial discharge capacity / initial charge capacity)] × 100
That is, it indicates the capacity that was charged but could not be discharged and remained in the active material.
[0080]
(Initial capacity)
The first discharge capacity per active material including the first coating layer and the second coating layer is shown.
[0081]
(Deterioration rate)
(1) Deterioration rate (10-20∞)
Based on the capacity at the 10th cycle. It shows what percentage of the capacity of the 10th cycle has deteriorated per cycle during 10 cycles of 10-20 cycles.
(2) Degradation rate (100-200∞)
Based on the capacity at the 10th cycle. It shows what percentage of the capacity of the 10th cycle has deteriorated per cycle during 100 cycles of 100-200 cycles.
[0082]
[Table 1]
Figure 2004139954
[0083]
[Table 2]
Figure 2004139954
[0084]
【The invention's effect】
ADVANTAGE OF THE INVENTION The negative electrode for non-aqueous electrolyte secondary batteries of this invention can achieve a long life of an electrode, and improves the energy density per unit volume and unit weight dramatically. Therefore, a non-aqueous electrolyte secondary battery using the above-described negative electrode has high capacity and excellent charge / discharge characteristics and cycle life characteristics. Further, according to the production method of the present invention, the above-mentioned negative electrode can be produced inexpensively and easily using conventional existing equipment.
[Brief description of the drawings]
FIG. 1 is a composition image by a scanning electron microscope showing a cross section of an example of a negative electrode for a non-aqueous electrolyte secondary battery of the present invention.
FIG. 2 is a composition image by a scanning electron microscope showing a cross section of another example of the negative electrode for a non-aqueous electrolyte secondary battery of the present invention.
FIG. 3 is a cross-sectional view schematically showing one example of a negative electrode for a non-aqueous electrolyte secondary battery of the present invention.
FIG. 4 is a cross-sectional view schematically showing another example of the negative electrode for a non-aqueous electrolyte secondary battery of the present invention.
FIG. 5 is a scanning electron microscope image showing a cross section of the multilayer coating layer before heat treatment.
FIG. 6 is a scanning electron microscope image showing a cross section of the negative electrode for a non-aqueous electrolyte secondary battery of the present invention obtained by heat treatment.
FIG. 7 is a process chart showing an example of the manufacturing method (manufacturing method A) of the present invention.
[Explanation of symbols]
1: Non-aqueous electrolyte secondary battery
2: current collector (copper foil)
3: First coating layer
4: Second coating layer
5: Multilayer coating layer
6: void
7: broken part
8: slit
F: tensile force

Claims (23)

集電体表面に、スズ、スズ合金、アルミニウム又はアルミニウム合金を含む第1被覆層が形成され、次に該第1被覆層の上に、リチウム化合物の形成能の低い金属を含む第2被覆層が形成されていることを特徴とする非水電解液二次電池用負極。A first coating layer containing tin, a tin alloy, aluminum or an aluminum alloy is formed on the surface of the current collector, and a second coating layer containing a metal having a low ability to form a lithium compound is formed on the first coating layer. A negative electrode for a non-aqueous electrolyte secondary battery, wherein a negative electrode is formed. 上記第2被覆層の上に、上記第1被覆層と同種又は異種の第1被覆層が更に形成されている3層構造の多層被覆層を有する請求項1記載の非水電解液二次電池用負極。2. The non-aqueous electrolyte secondary battery according to claim 1, further comprising a multilayer coating layer having a three-layer structure, wherein a first coating layer of the same type or different from the first coating layer is further formed on the second coating layer. For negative electrode. 上記多層被覆層に1mm以下の間隔で直径2mm以下の空孔が存在している請求項2記載の非水電解液二次電池用負極。3. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 2, wherein pores having a diameter of 2 mm or less exist at intervals of 1 mm or less in the multilayer coating layer. 上記3層構造の上に、上記第2被覆層及び上記第1被覆層とそれぞれ同種又は異種の第2被覆層及び第1被覆層をこの順で1組とした1組以上の被覆層が更に形成されている請求項2又は3記載の非水電解液二次電池用負極。On the three-layer structure, one or more sets of coating layers, in which the second coating layer and the first coating layer, which are the same or different from the second coating layer and the first coating layer, respectively, are in this order as one set, are further provided. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 2, wherein the negative electrode is formed. 最上層として、リチウム化合物の形成能の低い金属を含む被覆層が更に形成されている請求項2〜4の何れかに記載の非水電解液二次電池用負極。The negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 2 to 4, wherein a coating layer containing a metal having a low ability to form a lithium compound is further formed as an uppermost layer. 上記最上層の厚みが0.01〜20μmである請求項2〜5の何れかに記載の非水電解液二次電池用負極。The negative electrode for a non-aqueous electrolyte secondary battery according to claim 2, wherein the thickness of the uppermost layer is 0.01 to 20 μm. 上記第1被覆層の厚みが0.5〜50μmであり、上記第2被覆層の厚みが0.02〜50μmである請求項1〜6の何れかに記載の非水電解液二次電池用負極。The non-aqueous electrolyte secondary battery according to claim 1, wherein the thickness of the first coating layer is 0.5 to 50 μm, and the thickness of the second coating layer is 0.02 to 50 μm. Negative electrode. 上記第2被覆層に、2mm以下の間隔で、ランダム、かつ微細な破断部を有している請求項1〜7の何れかに記載の非水電解液二次電池用負極。The negative electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the second coating layer has random and fine breaks at an interval of 2 mm or less. 上記リチウム化合物の形成能の低い金属が銅、鉄、コバルト、クロム又はニッケルである請求項1又は5記載の非水電解液二次電池用負極。6. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the metal having a low ability to form a lithium compound is copper, iron, cobalt, chromium, or nickel. 上記第1被覆層が、スズ又はアルミニウムと、上記第2被覆層の構成元素及び/又は上記集電体の構成元素との合金からなる請求項1記載の非水電解液二次電池用負極。The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the first coating layer is made of an alloy of tin or aluminum and a constituent element of the second coating layer and / or a constituent element of the current collector. 上記第2被覆層が、銅、鉄、コバルト、クロム若しくはニッケルからなるか、又は銅、鉄、コバルト、クロム若しくはニッケルと、該第2被覆層に隣接する第1被覆層の構成元素との合金からなる請求項1又は2記載の非水電解液二次電池用負極。The second coating layer is made of copper, iron, cobalt, chromium, or nickel, or an alloy of copper, iron, cobalt, chromium, or nickel, and a constituent element of the first coating layer adjacent to the second coating layer. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, comprising: 上記最上層が、銅、鉄、コバルト、クロム若しくはニッケルからなるか、又は銅、鉄、コバルト、クロム若しくはニッケルと、該最上層と隣接する第1被覆層の構成元素との合金からなる請求項5に記載の非水電解液二次電池用負極。The uppermost layer is made of copper, iron, cobalt, chromium or nickel, or an alloy of copper, iron, cobalt, chromium or nickel and a constituent element of the first coating layer adjacent to the uppermost layer. 6. The negative electrode for a non-aqueous electrolyte secondary battery according to 5. 集電体表面に、スズ、スズ合金、アルミニウム又はアルミニウム合金を含む第1被覆層及びリチウム化合物の形成能の低い金属を含む第2被覆層をそれぞれ電解又は乾式法による表面処理によって順次析出させ、次いで120〜350℃で10分〜24時間熱処理する非水電解液二次電池用負極の製造方法。A first coating layer containing tin, a tin alloy, aluminum or an aluminum alloy, and a second coating layer containing a metal having a low ability to form a lithium compound are sequentially deposited on the current collector surface by electrolytic or dry surface treatment, respectively. Next, a method for producing a negative electrode for a non-aqueous electrolyte secondary battery, which is heat-treated at 120 to 350 ° C for 10 minutes to 24 hours. 上記熱処理が不活性ガス雰囲気中又は真空中で行われる請求項13記載の非水電解液二次電池用負極の製造方法。14. The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 13, wherein the heat treatment is performed in an inert gas atmosphere or in a vacuum. 上記不活性ガスが窒素又はアルゴンである請求項14記載の非水電解液二次電池用負極の製造方法。The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 14, wherein the inert gas is nitrogen or argon. 上記熱処理が空気中で行われる請求項13記載の非水電解液二次電池用負極の製造方法。14. The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 13, wherein the heat treatment is performed in air. 多数のスリットが設けられた集電体表面に、スズ、スズ合金、アルミニウム又はアルミニウム合金を含む第1被覆層、リチウム化合物の形成能の低い金属を含む第2被覆層、さらに上記第1被覆層と同種又は異種の第1被覆層をそれぞれ電解又は乾式法による表面処理により析出させた3層構造を基本とする多層被覆層を設け、得られた上記集電体及び上記多層被覆層からなる複合体に、外側方向への引張力を付与することによって、該多層被覆層に1mm以下の間隔で直径2mm以下の空孔を形成させることを特徴とする非水電解液二次電池用負極の製造方法。A first coating layer containing tin, a tin alloy, aluminum or an aluminum alloy, a second coating layer containing a metal having a low ability to form a lithium compound, and the first coating layer on a surface of the current collector provided with a number of slits. A composite comprising the above-mentioned current collector and the above-mentioned multilayer coating layer provided with a multilayer coating layer based on a three-layer structure in which first coating layers of the same or different types are respectively deposited by electrolytic or surface treatment by a dry method. Producing a negative electrode for a non-aqueous electrolyte secondary battery, wherein pores having a diameter of 2 mm or less are formed at intervals of 1 mm or less in the multilayer coating layer by applying a tensile force to the body in an outward direction. Method. 集電体表面に、スズ、スズ合金、アルミニウム又はアルミニウム合金を含む第1被覆層、リチウム化合物の形成能の低い金属を含む第2被覆層、さらに上記第1被覆層と同種又は異種の第1被覆層をそれぞれ電解又は乾式法による表面処理により析出させた3層構造を基本とする多層被覆層を設け、得られた上記集電体及び上記多層被覆層からなる複合体に、該多層被覆層側からレーザー処理をすることによって、該多層被覆層に1mm以下の間隔で直径2mm以下の空孔を形成させることを特徴とする非水電解液二次電池用負極の製造方法。A first coating layer containing tin, a tin alloy, aluminum or an aluminum alloy, a second coating layer containing a metal having a low ability to form a lithium compound, and a first coating layer of the same type or different from the first coating layer on the current collector surface. A multilayer coating layer based on a three-layer structure in which each coating layer is deposited by electrolytic or dry surface treatment is provided, and the resulting composite comprising the current collector and the multilayer coating layer is provided with the multilayer coating layer. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery, comprising forming pores having a diameter of 2 mm or less in the multilayer coating layer at an interval of 1 mm or less by performing laser treatment from the side. 集電体表面に、スズ、スズ合金、アルミニウム又はアルミニウム合金を含む第1被覆層、リチウム化合物の形成能の低い金属を含む第2被覆層、さらに上記第1被覆層と同種又は異種の第1被覆層をそれぞれ電解又は乾式法による表面処理により析出させた3層構造を基本とする多層被覆層を設け、得られた上記集電体及び上記多層被覆層からなる複合体に、該多層被覆層側からピンを用いて穿孔することによって、該多層被覆層に1mm以下の間隔で直径2mm以下の空孔を形成させることを特徴とする非水電解液二次電池用負極の製造方法。A first coating layer containing tin, a tin alloy, aluminum or an aluminum alloy, a second coating layer containing a metal having a low ability to form a lithium compound, and a first coating layer of the same type or different from the first coating layer on the current collector surface. A multilayer coating layer based on a three-layer structure in which each coating layer is deposited by electrolytic or dry surface treatment is provided, and the resulting composite comprising the current collector and the multilayer coating layer is provided with the multilayer coating layer. A method for producing a negative electrode for a non-aqueous electrolyte secondary battery, wherein pores having a diameter of 2 mm or less are formed at intervals of 1 mm or less in the multilayer coating layer by piercing with a pin from the side. 上記3層構造の上に、上記第2被覆層及び第1被覆層とそれぞれ同種又は異種の第2被覆層及び第1被覆層をこの順で1組みとした1組以上の被覆層を更に設け、その後に上記空孔を形成させる請求項17〜19の何れかに記載の非水電解液二次電池用負極の製造方法。On the three-layer structure, there is further provided one or more sets of coating layers in which the second coating layer and the first coating layer, which are the same or different from the second coating layer and the first coating layer, respectively, constitute one set in this order. 20. The method for producing a negative electrode for a non-aqueous electrolyte secondary battery according to claim 17, wherein the pores are formed thereafter. 上記複合体の多層被覆層側からプレス又はロール圧延処理を施すことによって、上記第2被覆層に、2mm以下の間隔で、ランダム、かつ微細な破断部を設ける請求項17〜20の何れかに記載の非水電解液二次電池用負極の製造方法。21. The composite according to any one of claims 17 to 20, wherein the composite is subjected to a press or roll rolling treatment from the side of the multilayer coating layer, and the second coating layer is provided with random and fine breaks at intervals of 2 mm or less. The method for producing a negative electrode for a nonaqueous electrolyte secondary battery according to the above. 上記集電体及び上記多層被覆層からなる複合体を、上記空孔を形成する前又は後に、120〜350℃で10分〜24時間熱処理する請求項17〜21の何れかに記載の非水電解液二次電池用負極の製造方法。The non-aqueous solution according to any one of claims 17 to 21, wherein the composite comprising the current collector and the multilayer coating layer is heat-treated at 120 to 350 ° C for 10 minutes to 24 hours before or after forming the pores. A method for producing a negative electrode for an electrolyte secondary battery. 請求項1〜12の何れかに記載の負極を用いた非水電解液二次電池。A non-aqueous electrolyte secondary battery using the negative electrode according to claim 1.
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