JP3652550B2

JP3652550B2 - Lithium secondary battery and manufacturing method thereof

Info

Publication number: JP3652550B2
Application number: JP17222299A
Authority: JP
Inventors: 宏根本; 賢信鬼頭; 真治大坪
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 1999-06-18
Filing date: 1999-06-18
Publication date: 2005-05-25
Anticipated expiration: 2019-06-18
Also published as: JP2001006654A

Description

【０００１】
【発明の属する技術分野】
本発明は、内部電極体からの集電抵抗を低減することにより安定な大電流放電を可能ならしめたリチウム二次電池及び生産性に優れたリチウム二次電池の製造方法に関する。
【０００２】
【従来の技術】
近年、環境保護運動の高まりを背景として、二酸化炭素等の排出規制が望まれる中、自動車業界ではガソリン車等の化石燃料を使用する自動車に替えて、電気自動車（ＥＶ）やハイブリッド電気自動車（ＨＥＶ）の導入を促進する動きが活発になっている。
【０００３】
ＥＶ、ＨＥＶ用電池には、電池容量が大きいことのみならず、自動車の加速性能や登坂性能に大きな影響を及ぼす電池出力が大きいことも求められる。このような要求特性から、現在、実用化されている電池の中では、リチウム二次電池が最も適した電池と考えられている。
【０００４】
一般的に、リチウム二次電池の内部電極体は、正極板と負極板とを多孔性ポリマーフィルムからなるセパレータを介して正極板と負極板とが直接に接触しないように捲回又は積層して構成されている。例えば、図１に示すように、捲回型の内部電極体１は、正極板２と負極板３とをセパレータ４を介して捲回して作製され、正極板２及び負極板３（以下、「電極板２・３」という。）のそれぞれに正極用の集電タブ５Ａ及び負極用の集電タブ５Ｂ（以下、「タブ５Ａ・５Ｂ」と記す。）が配設される。
【０００５】
そして、タブ５Ａ・５Ｂの、電極板２・３と接続された反対側の端部は、外部端子１１又は外部端子１１に導通する内部端子部材１２等の電流取出端子１３に取り付けられる。即ち、タブ５Ａ・５Ｂは、電極板２・３からの集電を行うと共に、電流取出端子１３と導通するリード線としての役割を担っている。
【０００６】
なお、外部端子は電流を電池外部に取り出す為の電極端子を指し、内部端子部材は電池内部において一時的に電流を集電する部材を指すものであり、電流取出端子とはこれらを総称したものである。従って、外部端子と内部端子部材とを一体化して、電流取出端子を構成することも可能である。
【０００７】
電極板２・３は、正極板２についてはアルミニウム等、負極板３については銅等の金属箔等を集電基板として用い、それぞれに電極活物質を塗布して形成されており、タブ５Ａ・５Ｂは、このような集電基板の少なくとも一辺に配設される。そこで、タブ５Ａ・５Ｂとして短冊状のものを用いると、電極板２・３を捲回する際に、タブ５Ａ・５Ｂの部分で部分的に外周に向けて膨らむといった形状むらが発生し難く、また、集電基板と集電タブとの接触抵抗を低減することができる。
【０００８】
【発明が解決しようとする課題】
ところで、ＥＶ又はＨＥＶ用のリチウム二次電池では、電池１本当たりに、頻繁に１００Ａ、２００Ａといった大電流を流す必要のある場面が想定される。このような大電流が流れた場合に電池の出力ロスが小さくなるように、電池全体の内部抵抗をできるだけ小さくする必要がある。
【０００９】
そこで、発明者らは先に特願平１１−１３５２０号において、生産性が高い集電タブの接続方法を提案し、集電タブの接続が関与する部分の抵抗及び抵抗分布幅を低減したリチウム二次電池を開示している。
【００１０】
しかしながら、特願平１１−１３５２０号に開示した発明中、電池の生産性に優れた「かしめ加工」のみを用いて集電タブを内部電極端子に接続した構造を有する電池を用いて、更に大きな電流による放電、例えば、２００Ａ超の電流による放電を行った場合には、一部の電池に、その後の充放電曲線が所定の特性曲線から外れる挙動を示すものが現れることが明らかとなってきた。
【００１１】
つまり、特願平１１−１３５２０号に開示されたかしめ加工のみによる集電タブの接続という方法を用いた場合には、勿論、電池の組立作業性が良好であり、また所定の抵抗ばらつきの範囲内に集電タブの抵抗が納められる為に、高い生産性と信頼性が得られるが、より過酷な大電流放電を行った場合であっても電池特性が維持されるという、更に高い信頼性を確保することを目的とした場合には、結果的に不良品の発生率が高くなって、生産歩留りが低下するおそれがある。
【００１２】
【課題を解決するための手段】
本発明は、上述した大電流放電による一部の電池の特性劣化と生産歩留りの低下という新たに生じた問題に対処すべくなされたものである。
即ち、本発明によれば、正極板及び負極板がセパレータを介して捲回又は積層された内部電極体と、電流を集電するか又は外部に取り出すための電流取り出し端子と、一端が前記正極板又は負極板にかつ他端が前記電流取り出し端子に電気的に接続された複数の短冊状集電タブとを備えたリチウム二次電池であって、前記複数の短冊状集電タブの他端の前記電流取り出し端子への接続が、それぞれが厚み方向に積層された状態でかつ前記電流取り出し端子によって挟持された状態で、積層方向に圧着されることによるものであるとともに、前記複数の短冊状集電タブの少なくとも長辺部分のそれぞれの側面上に溶接が施されてなることを特徴とするリチウム二次電池、が提供される。また、本発明においては、正極板及び負極板がセパレータを介して捲回又は積層された内部電極体と、電流を集電するか又は外部に取り出すための電流取り出し端子と、一端が前記正極板又は負極板にかつ他端が前記電流取り出し端子に電気的に接続された複数の短冊状集電タブとを備えたリチウム二次電池を製造する方法であって、前記複数の短冊状集電タブのそれぞれを厚み方向に積層した状態でかつ前記電流取り出し端子によって挟持させた状態で、積層方向に圧着して、前記複数の短冊状集電タブの他端を前記電流取り出し端子に接続するとともに、前記複数の短冊状集電タブの少なくとも長辺部分のそれぞれの側面上に溶接を施すことを特徴とするリチウム二次電池の製造方法が提供される。
【００１３】
ここで、複数の短冊状集電タブの少なくとも長辺部分のそれぞれの側面上への溶接は、抵抗溶接により行うことが好ましく、抵抗スポット溶接を用いることが更に好ましい。このような抵抗溶接においては、３００Ｗ・ｓ〜２０００Ｗ・ｓ又は５０００Ａ〜３００００Ａの容量により、１回〜１００回の範囲で行うことが、溶接によって生ずる熱から集電タブや内部電極体を保護する観点、及び作業性の観点から好ましい。なお、この抵抗溶接は、５００Ｗ・ｓ〜１０００Ｗ・ｓ又は７０００Ａ〜２００００Ａの容量により、２回〜１０回の範囲で行うと、生産性が高まり、更に好ましい。
【００１４】
本発明においては、複数の短冊状集電タブの１枚の厚みが５μｍ以上１００μｍ以下であり、かつ接続された枚数が少なくとも２０枚であることが好ましい。本発明は、電池容量が２Ａｈ以上といった電極板１枚当たり複数の集電タブを設けることが好ましい電池に好適に適用される。また、大電流の放電を頻繁に行う電気自動車用又はハイブリッド電気自動車用として、好適に用いられる。
【００１５】
【発明の実施の形態】
以下、本発明の実施形態について図面を参照しながら説明するが、本発明が以下の実施形態に限定されるものではない。
本発明におけるリチウム二次電池（以下、「電池」という。）の内部電極体は、正極板と負極板とを多孔性ポリマーフィルムからなるセパレータを介して正極板と負極板とが直接に接触しないように捲回又は積層して構成されている。具体的には、捲回型の内部電極体１は、先に図１に示したように、正極板２と負極板３とをセパレータ４を介して捲回して形成され、電極板２・３にそれぞれ集電タブ５Ａ・５Ｂが接続される。
【００１６】
一方、積層型の内部電極体７は、図２に示すように、正極板８と負極板９とをセパレータ１０を介しながら交互に積層し、正負各電極板８・９（以下、「電極板８・９」という。）のそれぞれに正極用の集電タブ６Ａ及び負極用の集電タブ６Ｂが接続されて構成される。
【００１７】
正極板２・８及び負極板３・９は、共に集電基板にそれぞれの電極活物質を塗布して薄板状に形成される。集電基板の形態としては、箔、メッシュ等が挙げられ、本発明においては、正極板２・８用の集電基板としてアルミニウム箔が、負極板３・９用の集電基板としては銅箔が、それぞれ好適に用いられる。
【００１８】
そして、上記いずれの構造を有する電池であっても、一般的に、正極活物質としては、コバルト酸リチウム（ＬｉＣｏＯ₂）やニッケル酸リチウム（ＬｉＮｉＯ₂）或いはマンガン酸リチウムスピネル（ＬｉＭｎ₂Ｏ₄）等のリチウム遷移金属複合酸化物が用いられる。なお、これら正極活物質の導電性を向上させる為に、アセチレンブラックやグラファイト粉末等のカーボン粉末を電極活物質に混合することも好ましい。一方、負極活物質としては、ソフトカーボンやハードカーボンといったアモルファス系炭素質材料や天然黒鉛、人造黒鉛等の炭素質粉末が用いられる。
【００１９】
セパレータ４・１０としては、マイクロポアを有するリチウムイオン透過性のポリエチレンフィルムを、多孔性のリチウムイオン透過性のポリプロピレンフィルムで挟んだ三層構造としたものが好適に用いられる。これは、内部電極体の温度が上昇した場合に、ポリエチレンフィルムが約１３０℃で軟化してマイクロポアが潰れてリチウムイオンの移動、即ち電池反応を抑制する安全機構を兼ねたものである。そして、このポリエチレンフィルムを、より軟化温度の高いポリプロピレンフィルムで挟持することによって、電極板２・３間、電極板８・９間の接触・溶着を防止することができる。
【００２０】
次に、図１に示した捲回型内部電極体１の場合を例に、集電タブ５Ａの接続方法、接続形態について説明するが、図１における負極側の集電タブ５Ｂについても、また、図２に示した集電タブ６Ａ・６Ｂについても、同様である。
【００２１】
前述したように、集電タブ５Ａとしては短冊状のものが用いられるが、ここで、集電タブ５Ａは、正極板２等を捲回する際に超音波溶接等の方法を用いて正極板２に取り付けられて電気的に接続される。つまり、電流取出端子に集電タブ５Ａを接続する際には、集電タブ５Ａの一端は既に内部電極体１と接続された状態にある。
【００２２】
短冊状の集電タブ５Ａは、それぞれを厚み方向に積層して束ねた状態として、内部電極体１と接続されていない一端（他端）を電流取出端子と接続することが好ましい。図３（ａ）の側面図及び（ｂ）の正面図は、電流取出端子１３としてリベットを用い、リベットにおける圧着を行う部分に、集電タブ５Ａを束ねて挿入した圧着前の状態を示すものである。こうして、圧着作業が容易となり、また、集電タブ５Ａの電池ケース内への収納も容易となる。なお、集電タブ５Ａの接続を図３に示した形態で行う為には、集電タブ５Ａは、内部電極体１が作製された時点で、内部電極体１の径方向にほぼ直線上に並ぶように、正極板２との接続位置を定めることが好ましい。
【００２３】
本発明においては、束ねられた集電タブ５Ａの一端（他端）と電流取出端子１３との接続は、圧着により行われる（以降、圧着が行われた部分を「圧着部」ということとする。）。ここでの圧着には、かしめ加工、はとめ加工といった種々の圧着方法を用いることができる。そして、図４（ａ）の断面図、（ｂ）の正面図に示すように、束ねられた集電タブ５Ａの積層方向に圧力が掛かるようにして圧着し、強固に電流取出端子１３と集電タブ５Ａとを接続し、圧着部１４を形成することが好ましい。
【００２４】
このような圧着を行った上で、更に、図５（ａ）の側面図及び（ｂ）の正面図に示すように、圧着された短冊状の集電タブ５Ａの少なくとも長辺部分の側面を溶接して一体化する（溶接が行われた部分を「溶接部」ということとする。）。溶接部１５は、束ねられた集電タブ５Ａの側面近傍が熔解し、互いに溶接された状態であれば十分であり、必ずしも集電タブ５Ａの圧着部１４域内にある一部分が、その内部まで熔解して溶接されていることを必要とするものではない。
【００２５】
なお、束ねられた集電タブ５Ａの側面のみならず、電流取出端子１３もまた集電タブ５Ａと同時に溶接されていると、圧着部１４の抵抗の低減が図られ、更に好ましい。こうして、圧着後に溶接を行うことにより、圧着のみを行った場合と比較して、接続に関する接触抵抗が低減され、かつ抵抗分布幅をも狭まる為に、大電流放電による電池特性の劣化を抑制することが可能となる。
【００２６】
溶接は電子ビーム溶接、抵抗溶接、超音波溶接、ＴＩＧ溶接等の種々の溶接方法を用いて行うことが可能である。ここで、溶接を行う際には、前述したように集電タブ５Ａの一端は、内部電極体１と接続された状態となっているので、内部電極体１の取り扱いの容易さ、集電タブ５Ａの溶断の危険性、内部電極体１への熱伝達による内部電極体１の損傷といった事項を含めて、溶接作業性を考慮することが好ましい。
【００２７】
表１は、各種の溶接方法を用いた場合の溶接の条件及び結果を示している。表１内に示した「抵抗」は、長さ５０ｍｍ、厚み５０μｍのアルミニウム（Ａｌ）製集電タブ５０枚をＡｌ製のリベットを用いて圧着した後、溶接を行った場合の集電タブの開放された一端からリベットまでの抵抗値を、また長さ５０ｍｍ、厚み５０μｍの銅（Ｃｕ）タブ５０枚をＣｕ製のリベットを用いて圧着した後溶接した場合の集電タブの開放された一端からリベットまでの抵抗値を示している。
【００２８】
【表１】

【００２９】
また、表１中、溶接方向における「タブ平行」は、集電タブの主平面の幅方向に平行な方向、例えば、スポット溶接では、集電タブの側面間を挟み込むように圧力をかけた状態で電流を流して溶接を行った場合を指す。一方、「タブ直角」は、集電タブの積層方向に平行に、リベットにおいて圧着を行う部分の一部を含めて溶接を行った場合を示している。
【００３０】
電子ビーム溶接は、電流取出端子１３と束ねられた集電タブ５Ａの全体について、均一に金属を熔解させ、溶接することが可能であり、集電タブ５Ａと電流取出端子１３との接触抵抗を極めて小さくすることができると共に、発熱量も小さいという優れた特徴を有する。しかし、装置が高価であり、作業環境を高真空に保持する必要がある等、装置コストやランニングコストの面で必ずも好ましいものとは言えない。
【００３１】
超音波溶接では、圧着部１４の抵抗が十分に低減され、また溶接時の発生熱も内部電極体１へ悪影響が及ぶと考えられるほどは発生しないが、最適な溶接条件の設定が難しいとうい点で不便である。また、装置が一般的に高価であるという問題もある。
【００３２】
ＴＩＧ溶接は、装置が安価で作業も容易であるという利点はあるが、溶接の進行程度の制御が行い難く、また、供給熱量が多く、集電タブ５Ａの溶断が起こり易い問題ある。この為、生産歩留りが極めて低くなり、また、内部電極体１への熱伝導による悪影響が懸念されるという問題が内在する。
【００３３】
これらに対して、抵抗溶接は、作業が容易でしかも装置が安価であり、１回当たりの溶接の容量を制御して発熱量を制御することが容易であることから、本発明において最も好適に用いられる。抵抗溶接にも種々の方法があるが、最も好適に採用される方法はスポット溶接である。
【００３４】
スポット溶接を行うに当たって、１回当たりの溶接の容量が小さい場合には、１回当たりの発熱量が小さく、集電タブ５Ａへ与える損傷は小さくなるが、溶接回数を多くする必要が生ずる点で、作業性、生産性がよいものとは言い難い。一方、１回の溶接に供する容量を大きくすると、溶接回数を低減することはできるが、発生熱が大きくなり、集電タブの変色（酸化）による劣化や溶断による生産歩留りの低下、更に内部電極体１の溶接熱による特性劣化が懸念される。
【００３５】
そこで、１回当たりのスポット溶接の容量は、コンデンサタイプの溶接機を用いる場合には３００Ｗ・ｓ〜２０００Ｗ・の範囲で行い、又はインバータタイプの場合には５０００Ａ〜３００００Ａの範囲で行うと、溶接回数が１回〜１００回の範囲で、十分に圧着部１４の抵抗を低減することができる。この程度の作業回数では、生産性を極端に低下させることはない。
【００３６】
なお、より好ましくは、コンデンサタイプの溶接機を用いる場合には５００Ｗ・ｓ〜１０００Ｗ・の範囲で行い、又はインバータタイプの場合には７０００Ａ〜２００００Ａの範囲で行うと、溶接回数を２回〜１０回の範囲とすることができ、生産性の向上が図られ、好ましい。この容量は、集電タブ５Ａの材質によって、適宜好適な値に設定することが好ましい。
【００３７】
ところで、スポット溶接は、電極を集電タブ５Ａに一定の圧力で押し当てた加圧状態で行われるが、その圧力としては５〜１００ｋｇｆの範囲で行うことが好ましく、２０〜６０ｋｇｆの範囲で行うことが更に好ましい。５ｋｇｆ未満の場合には熔解が進まないために、集電タブ５Ａどうしの熔解接続が十分に進まず、また１００ｋｇｆを超える場合には、圧着部の過剰変形等が発生することがあり、好ましくない。
【００３８】
なお、本発明を適用するに好ましい集電タブの厚みや枚数は前述した条件に限定されるものではないが、集電タブの１枚の厚みは、５μｍ以上１００μｍ以下のものを用いることが好ましく、かつ、少なくとも２０枚の集電タブを接続する場合に、本発明は顕著な効果を奏する。
【００３９】
上述のように、本発明は複数の集電タブを用いることが好ましい電池容量の比較的大きい電池に好適に用いられ、具体的には、２Ａｈｒ以上の容量を有するリチウム二次電池に好適に採用される。また、集電タブと電流取出端子との圧着部の抵抗が低減されることから、大電流の放電を安定して行うことが可能となる。このような特性を活かして、本発明は、ＥＶ或いはＨＥＶ用のバッテリーとして好適に用いられる。
【００４０】
【発明の効果】
以上、本発明によれば、安定な大電流放電を可能ならしめたリチウム二次電池を提供することが可能となると共に、生産性を低下させることがない為、安定に大電流の放電を可能ならしめた電池を、歩留りよく生産することが可能となる。また、圧着部の抵抗が低減されることから、圧着部における各集電タブの抵抗分布のばらつきも低減され、電池のサイクル劣化の抑制にも効果を奏する。
【図面の簡単な説明】
【図１】捲回型内部電極体の構造の一実施形態を示す斜視図である。
【図２】積層型内部電極体の構造の一実施形態を示す斜視図である。
【図３】集電タブと電流取出端子の圧着前の状態を示す説明図であり、図３（ａ）は側面図、図３（ｂ）は正面図である。
【図４】集電タブと電流取出端子との圧着後の接続の一実施形態を示す説明図であり、図４（ａ）は側面図、図４（ｂ）は正面図である。
【図５】集電タブと電流取出端子との圧着部に溶接を施した例を示す説明図であり、図５（ａ）は側面図、図５（ｂ）は正面図である。
【符号の説明】
１…内部電極体、２…正極板、３…負極板、４…セパレータ、５Ａ・６Ａ…正極用集電タブ、５Ｂ・６Ｂ…負極用集電タブ、７…内部電極体、８…正極板、９…負極板、１０…セパレータ、１１…外部端子、１２…内部端子部材、１３…電流取出端子、１４…圧着部、１５…溶接部。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a lithium secondary battery excellent in possibly tighten a lithium secondary battery and productivity stable large current discharge by reducing the collector resistance of the internal electrode body.
[0002]
[Prior art]
In recent years, due to the increasing environmental protection movement, carbon dioxide and other emission regulations are desired. In the automobile industry, instead of automobiles that use fossil fuels such as gasoline cars, electric vehicles (EV) and hybrid electric vehicles (HEV) ) Is being actively promoted.
[0003]
EV and HEV batteries are required not only to have a large battery capacity but also to have a large battery output that greatly affects the acceleration performance and climbing performance of an automobile. Due to such required characteristics, lithium secondary batteries are considered to be the most suitable batteries among the batteries in practical use at present.
[0004]
Generally, an internal electrode body of a lithium secondary battery is formed by winding or laminating a positive electrode plate and a negative electrode plate with a separator made of a porous polymer film so that the positive electrode plate and the negative electrode plate are not in direct contact with each other. It is configured. For example, as shown in FIG. 1, the wound internal electrode body 1 is manufactured by winding a positive electrode plate 2 and a negative electrode plate 3 with a separator 4 interposed therebetween, and the positive electrode plate 2 and the negative electrode plate 3 (hereinafter “ Each of the electrode plates 2 and 3 "is provided with a positive current collecting tab 5A and a negative current collecting tab 5B (hereinafter referred to as"

tabs

5A and 5B ").
[0005]
The opposite ends of the

tabs

5A and 5B connected to the electrode plates 2 and 3 are attached to the current extraction terminals 13 such as the external terminal 11 or the internal terminal member 12 that conducts to the external terminal 11. That is, the tabs 5 </ b> A and 5 </ b> B collect current from the electrode plates 2 and 3 and also serve as lead wires that are electrically connected to the current extraction terminals 13.
[0006]
The external terminal refers to an electrode terminal for taking out the current outside the battery, the internal terminal member refers to a member that temporarily collects current inside the battery, and the current extraction terminal is a generic term for these. It is. Therefore, it is possible to configure the current extraction terminal by integrating the external terminal and the internal terminal member.
[0007]
The electrode plates 2 and 3 are formed by applying a metal foil such as aluminum for the positive electrode plate 2 and copper for the negative electrode plate 3 and applying an electrode active material to each of the current collectors. 5B is disposed on at least one side of such a current collector board. Therefore, when the

tabs

5A and 5B are strip-shaped, when winding the electrode plates 2 and 3, it is difficult to generate uneven shapes such as the

tabs

5A and 5B partially swell toward the outer periphery. Further, Ru can reduce contact resistance between the current collector substrate and collector tab.
[0008]
[Problems to be solved by the invention]
By the way, in the lithium secondary battery for EV or HEV, the scene where it is necessary to frequently flow a large current such as 100 A and 200 A per battery is assumed. It is necessary to make the internal resistance of the entire battery as small as possible so that the output loss of the battery is reduced when such a large current flows.
[0009]
In view of this, the inventors previously proposed a method of connecting a current collecting tab with high productivity in Japanese Patent Application No. 11-13520, and reduced the resistance and the resistance distribution width of the portion related to the connection of the current collecting tab. A secondary battery is disclosed.
[0010]
However, in the invention disclosed in Japanese Patent Application No. 11-13520, a battery having a structure in which a current collecting tab is connected to an internal electrode terminal using only “caulking” with excellent battery productivity is used. It has been clarified that when a discharge due to a current, for example, a discharge due to a current exceeding 200 A, is performed, some of the batteries exhibit a behavior in which a subsequent charge / discharge curve deviates from a predetermined characteristic curve. .
[0011]
In other words, when using the method of connecting the current collecting tabs only by caulking disclosed in Japanese Patent Application No. 11-13520, of course, the assembly workability of the battery is good, and the range of the predetermined resistance variation Since the resistance of the current collecting tab is contained in the inside, high productivity and reliability can be obtained, but the battery characteristics are maintained even when more severe large current discharge is performed. As a result, there is a risk that the production rate of defective products increases and the production yield decreases.
[0012]
[Means for Solving the Problems]
The present invention has been made to cope with the newly generated problems such as deterioration of characteristics of some batteries and reduction of production yield due to the large current discharge.
That is, according to the present invention, the internal electrode body is wound or laminated via the positive electrode plate and a negative electrode plate Gase separator, and current extraction terminal for taking out current or external to the collector, one end the A lithium secondary battery comprising a plurality of strip-like current collecting tabs, the other end of which is electrically connected to the positive electrode plate or the negative electrode plate, and the other end of which is electrically connected to the current extraction terminal. The connection of the end to the current extraction terminal is performed by crimping in the stacking direction in a state where each is stacked in the thickness direction and sandwiched by the current extraction terminal, and the plurality of strips There is provided a lithium secondary battery characterized in that welding is performed on each side surface of at least the long side portion of the current collector tab . In the present invention, the positive electrode plate and the negative electrode plate are wound or laminated with a separator interposed therebetween, a current extraction terminal for collecting current or taking out the current, and one end of the positive electrode plate Or a method for producing a lithium secondary battery comprising a plurality of strip-shaped current collecting tabs, the other end of which is electrically connected to the negative electrode plate and the other current extracting terminal, the plurality of strip-shaped current collecting tabs In a state where each of these is laminated in the thickness direction and sandwiched by the current takeout terminal, and crimped in the lamination direction, the other ends of the plurality of strip-like current collecting tabs are connected to the current takeout terminal, A method for manufacturing a lithium secondary battery is provided, wherein welding is performed on each side surface of at least a long side portion of the plurality of strip-like current collecting tabs.
[0013]
Here, welding onto each side of at least the long sides of the plurality of strip-shaped current collector tab is preferably carried out by resistance welding, it is more preferable to use a resistor spot welding. In such resistance welding, the current collecting tab and the internal electrode body are protected from heat generated by welding by performing the welding in a range of 1 to 100 times with a capacity of 300 W · s to 2000 W · s or 5000 A to 30000 A. From the viewpoint of viewpoint and workability, it is preferable. In addition, when this resistance welding is performed in the range of 2 times to 10 times with a capacity of 500 W · s to 1000 W · s or 7000 A to 20000 A, productivity is further increased .
[0014]
Oite the present invention preferably a plurality of a thickness of one strip-shaped current collector tabs is at 5μm least 100μm or less, and the connected number is at least 20 sheets. The present invention is suitably applied to a battery that preferably has a plurality of current collecting tabs per electrode plate having a battery capacity of 2 Ah or more. Further, it is suitably used for an electric vehicle or a hybrid electric vehicle that frequently discharges a large current.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments .
In the internal electrode body of the lithium secondary battery (hereinafter referred to as “battery”) in the present invention, the positive electrode plate and the negative electrode plate are not in direct contact with each other through a separator made of a porous polymer film. Thus, it is configured by winding or stacking. Specifically, the wound type internal electrode body 1 is formed by winding a positive electrode plate 2 and a negative electrode plate 3 with a separator 4 interposed therebetween as shown in FIG. Are connected to current collecting

tabs

5A and 5B, respectively.
[0016]
On the other hand, as shown in FIG. 2, the laminated internal electrode body 7 is formed by alternately laminating positive and negative electrodes 8 and 9 with separators 10 therebetween, and positive and negative electrode plates 8 and 9 (hereinafter referred to as “electrode plates”). 8 and 9 ") are connected to a current collecting tab 6A for a positive electrode and a current collecting tab 6B for a negative electrode.
[0017]
Both the positive plates 2 and 8 and the negative plates 3 and 9 are formed in a thin plate shape by applying the respective electrode active materials to the current collecting substrate. Examples of the form of the current collecting substrate include foil and mesh. In the present invention, aluminum foil is used as the current collecting substrate for the positive plates 2 and 8, and copper foil is used as the current collecting substrate for the negative plates 3 and 9. Are preferably used.
[0018]
In any battery having any of the above structures, the positive electrode active material generally includes lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), or lithium manganate spinel (LiMn ₂ O ₄ ). Lithium transition metal composite oxides such as are used. In addition, in order to improve the electroconductivity of these positive electrode active materials, it is also preferable to mix carbon powders, such as acetylene black and a graphite powder, with an electrode active material. On the other hand, as the negative electrode active material, amorphous carbonaceous materials such as soft carbon and hard carbon, and carbonaceous powders such as natural graphite and artificial graphite are used.
[0019]
As the separators 4 and 10, a three-layer structure in which a lithium ion permeable polyethylene film having micropores is sandwiched between porous lithium ion permeable polypropylene films is preferably used. This also serves as a safety mechanism that suppresses the migration of lithium ions, that is, the battery reaction, when the temperature of the internal electrode body rises, the polyethylene film softens at about 130 ° C. and the micropores collapse. Then, by sandwiching the polyethylene film with a polypropylene film having a higher softening temperature, contact / welding between the electrode plates 2 and 3 and between the electrode plates 8 and 9 can be prevented.
[0020]
Next, the connection method and connection form of the current collecting tab 5A will be described by taking the case of the wound type internal electrode body 1 shown in FIG. 1 as an example. The current collecting tab 5B on the negative electrode side in FIG. The same applies to the

current collecting tabs

6A and 6B shown in FIG .
[0021]
As described above, although as a collector tab 5A is needed use those strip, where the current collecting tabs 5A, at the time of winding the positive electrode plate 2 and the like by using a method of ultrasonic welding positive It is attached to the plate 2 and electrically connected . That is, when the current collecting tab 5A is connected to the current extraction terminal, one end of the current collecting tab 5A is already connected to the internal electrode body 1.
[0022]
Strip-shaped electrode tabs 5A as being integrated by laminating respectively in the thickness direction, it is preferable that one end that is not connected to the internal electrode body 1 (the other end) connected to the current extracting terminal. The side view of Fig.3 (a) and the front view of (b) show the state before the crimping | compression-bonding which used the rivet as the electric current extraction terminal 13, and bundled and inserted the current collection tab 5A in the part which crimps | bonds in a rivet. It is. Thus, the crimping operation is facilitated, and the current collecting tab 5A can be easily housed in the battery case. In order to connect the current collecting tab 5A in the form shown in FIG. 3, the current collecting tab 5A is substantially linear in the radial direction of the internal electrode body 1 when the internal electrode body 1 is manufactured. It is preferable to determine the connection position with the positive electrode plate 2 so as to line up.
[0023]
In the present invention, the connection between one end (the other end) of the bundled current collecting tabs 5A and the current extraction terminal 13 is performed by pressure bonding (hereinafter, the portion where pressure bonding has been performed is referred to as a “pressure bonding portion”). .) Various crimping methods such as caulking and crimping can be used for the crimping here. Then, as shown in the cross-sectional view of FIG. 4A and the front view of FIG. 4B, the current collecting tabs 13A and the current collecting terminals 13 and the current collecting terminals 13 are firmly bonded by pressure in the stacking direction of the bundled current collecting tabs 5A. It is preferable to connect the electric tab 5 </ b> A to form the crimp portion 14.
[0024]
After performing such crimping, as shown in the side view of FIG. 5A and the front view of FIG. 5B, the side surface of at least the long side portion of the crimped strip-shaped current collecting tab 5A is applied. Weld and integrate (the welded part is called “welded part”). The welded portion 15 is sufficient if the vicinity of the side surface of the bundled current collecting tabs 5A is melted and welded to each other, and a part of the current collecting tab 5A in the crimping portion 14 region is melted to the inside thereof. It does not need to be welded.
[0025]
Note that it is more preferable that not only the side surfaces of the bundled current collecting tabs 5A but also the current extraction terminals 13 are welded simultaneously with the current collecting tabs 5A because the resistance of the crimping portion 14 is reduced. In this way, by performing welding after crimping, the contact resistance related to connection is reduced and the resistance distribution width is narrowed compared to the case where only crimping is performed, so that deterioration of battery characteristics due to large current discharge is suppressed. It becomes possible.
[0026]
Welding electron beam welding, resistance welding, ultrasonic welding, it can be performed using a variety of welding methods such as TIG welding. Here, when welding is performed, since one end of the current collecting tab 5A is connected to the internal electrode body 1 as described above, it is easy to handle the internal electrode body 1, and the current collecting tab. It is preferable to consider welding workability including matters such as the risk of 5A fusing and damage to the internal electrode body 1 due to heat transfer to the internal electrode body 1.
[0027]
Table 1 shows welding conditions and results when various welding methods are used. “Resistance” shown in Table 1 is the value of the current collecting tab when welding is performed after pressing 50 aluminum (Al) current collecting tabs having a length of 50 mm and a thickness of 50 μm using rivets made of Al. The open end of the current collecting tab when the resistance value from the open end to the rivet is welded after 50 copper (Cu) tabs having a length of 50 mm and a thickness of 50 μm are crimped using Cu rivets. The resistance value from to rivet is shown.
[0028]
[Table 1]

[0029]
In Table 1, “Tab parallel” in the welding direction is a direction parallel to the width direction of the main surface of the current collecting tab. For example, in spot welding, pressure is applied so as to sandwich the side surfaces of the current collecting tab. This refers to the case where welding is performed with an electric current. On the other hand, “tab right angle” indicates a case where welding is performed including a part of the rivet that is crimped in parallel to the stacking direction of the current collecting tabs.
[0030]
In the electron beam welding, the entire current collecting tab 5A bundled with the current extraction terminal 13 can be uniformly melted and welded, and the contact resistance between the current collection tab 5A and the current extraction terminal 13 can be reduced. It has an excellent feature that it can be made extremely small and the calorific value is small. However, it is not necessarily preferable in terms of apparatus cost and running cost because the apparatus is expensive and the working environment needs to be maintained at a high vacuum.
[0031]
In ultrasonic welding, the resistance of the crimping portion 14 is sufficiently reduced, and the heat generated during welding is not generated to the extent that the internal electrode body 1 may be adversely affected, but it is difficult to set optimum welding conditions. Inconvenient in terms. There is also a problem that the apparatus is generally expensive.
[0032]
TIG welding has the advantage that the apparatus is inexpensive and easy to operate, but it is difficult to control the degree of progress of welding, and there is a problem that the amount of supplied heat is large and the current collecting tab 5A is likely to melt. For this reason, the production yield becomes extremely low, and there is a problem that there is a concern about an adverse effect due to heat conduction to the internal electrode body 1.
[0033]
On the other hand, resistance welding is most suitable in the present invention because it is easy to work and is inexpensive, and it is easy to control the amount of heat generated by controlling the welding capacity per time. Used. There are various methods for resistance welding, but the most preferably employed method is spot welding.
[0034]
In spot welding, when the welding capacity per one time is small, the heat generation amount per time is small and damage to the current collecting tab 5A is small, but it is necessary to increase the number of times of welding. It is hard to say that workability and productivity are good. On the other hand, if the capacity to be used for one welding is increased, the number of weldings can be reduced, but the generated heat increases, the deterioration of the current collecting tab due to discoloration (oxidation), the decrease in production yield due to fusing, and the internal electrode There is a concern about the characteristic deterioration due to the welding heat of the body 1.
[0035]
Therefore, the capacity of spot welding per one time is 300 W · s to 2000 W · when using a capacitor type welding machine, or 5000 A to 30000 A in the case of an inverter type. In the range of 1 to 100 times, the resistance of the crimping part 14 can be sufficiently reduced. With this number of operations, productivity is not drastically reduced.
[0036]
More preferably, when a capacitor type welding machine is used, the welding is performed in the range of 500 W · s to 1000 W ·, or in the case of the inverter type, in the range of 7000 A to 20000 A, the number of welding is 2 to 10 times. This is preferable because the productivity can be improved. This capacity is preferably set to an appropriate value depending on the material of the current collecting tab 5A.
[0037]
By the way, spot welding is performed in a pressurized state in which the electrode is pressed against the current collecting tab 5A at a constant pressure. The pressure is preferably in the range of 5 to 100 kgf, and is preferably in the range of 20 to 60 kgf. More preferably. If less than 5 kgf, melting does not proceed, so the melting connection between the current collecting tabs 5A does not proceed sufficiently. If it exceeds 100 kgf, excessive deformation of the crimping part may occur, which is not preferable. .
[0038]
Note that the thickness and the number of current collecting tabs preferable for applying the present invention are not limited to the above-described conditions, but it is preferable to use one current collecting tab having a thickness of 5 μm to 100 μm. And when connecting at least 20 current collection tabs, this invention has a remarkable effect.
[0039]
As described above, the present invention is preferably used for a battery having a relatively large battery capacity, preferably using a plurality of current collecting tabs, and specifically, suitably used for a lithium secondary battery having a capacity of 2 Ahr or more. Is done. In addition, since the resistance of the crimping portion between the current collecting tab and the current extraction terminal is reduced, it is possible to stably discharge a large current. Taking advantage of such characteristics, the present invention is suitably used as a battery for EV or HEV.
[0040]
【The invention's effect】
As described above, according to the present invention, it becomes possible to provide a possibly tighten a lithium secondary battery a stable large current discharge, since it does not reduce the productivity, the discharge of stable large current if possible tighten the battery, it is possible to yield good productivity. In addition, since the resistance of the crimping portion is reduced, the variation in the resistance distribution of each current collecting tab in the crimping portion is also reduced, which is effective in suppressing the cycle deterioration of the battery.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an embodiment of a structure of a wound internal electrode body.
FIG. 2 is a perspective view showing an embodiment of a structure of a multilayer internal electrode body.
FIGS. 3A and 3B are explanatory views showing a state before crimping of a current collecting tab and a current extraction terminal , FIG. 3A is a side view, and FIG. 3B is a front view;
4A and 4B are explanatory views showing an embodiment of a connection after crimping between a current collecting tab and a current extraction terminal, in which FIG. 4A is a side view and FIG. 4B is a front view.
5A and 5B are explanatory views showing an example in which welding is performed on a crimping portion between a current collecting tab and a current extraction terminal , FIG. 5A is a side view, and FIG. 5B is a front view.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Internal electrode body, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4 ... Separator, 5A * 6A ... Current collection tab for positive electrodes, 5B * 6B ... Current collection tab for negative electrodes, 7 ... Internal electrode body, 8 ... Positive electrode plate , 9 ... negative electrode plate, 10 ... separator, 11 ... external terminal, 12 ... internal terminal member, 13 ... current extraction terminal, 14 ... crimping part, 15 ... welding part.

Claims

Others and the internal electrode body is wound or laminated via the positive electrode plate and a negative electrode plate Gase separator, and current extraction terminal for taking out current or external to the collector, the one end the positive electrode plate or negative electrode plate A lithium secondary battery comprising a plurality of strip-like current collecting tabs whose ends are electrically connected to the current extraction terminals ,
The connection of the other end of the plurality of strip-shaped current collecting tabs to the current extraction terminal is crimped in the stacking direction in a state where each is stacked in the thickness direction and sandwiched between the current extraction terminals. The lithium secondary battery is characterized in that welding is performed on each side surface of at least the long side portion of the plurality of strip-like current collecting tabs .

Each welding onto side surfaces, the lithium secondary battery according to claim 1, characterized in that due to the resistance welding of at least the long sides of said plurality of strip-shaped current collector tab.

3. The lithium secondary battery according to claim 2 , wherein the resistance welding is performed in a range of 1 to 100 times with a capacity of 300 W · s to 2000 W · s or 5000 A to 30000 A. 4.

Wherein the plurality of a thickness of one strip-shaped current collector tabs is at 5μm least 100μm or less, and, according to any one of claims 1 to 3, connected number is equal to or at least 20 sheets Lithium secondary battery.

The lithium secondary battery according to any one of claims 1 to 4 , wherein the battery capacity is 2 Ah or more.

The lithium secondary battery according to any one of claims 1 to 5, characterized in that used as or hybrid electric automobile for electric vehicles.

An internal electrode body in which a positive electrode plate and a negative electrode plate are wound or stacked with a separator interposed therebetween, a current extraction terminal for collecting current or extracting the current to the outside, one end on the positive electrode plate or the negative electrode plate and the other end Is a method of manufacturing a lithium secondary battery comprising a plurality of strip-like current collecting tabs electrically connected to the current extraction terminal,
In the state where each of the plurality of strip-like current collecting tabs is laminated in the thickness direction and sandwiched by the current extraction terminals, the other ends of the plurality of strip-like current collecting tabs are bonded to each other in the lamination direction. A method for manufacturing a lithium secondary battery, comprising: connecting to a current extraction terminal; and welding on each side surface of at least a long side portion of the plurality of strip-like current collecting tabs.