JP2004247192A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery excellent in productivity and space saving capability, reduced in internal resistance, and suitable for heavy-current discharge. <P>SOLUTION: This lithium secondary battery is provided with: a rolled type internal electrode body 1 composed by rolling a positive electrode plate 2 and a negative electrode plate 3 by interlaying a separator; and a positive electrode current collection member 4A and a negative electrode current collection member 4B connected to ends of the electrode plate 2 and the electrode plate 3 for leading out currents from the ends, respectively; and is formed by welding connection parts 10 between the collection member 4A and/or the collection member 4B, and connection edges 11 of the electrode plate 2 and/or the electrode plate 3. The ratio of the number of rolling units with one or more of the connection parts 10 formed to the total number of rolling of the electrode body 1 is above 70% for every rolling unit composed by one-time rolling the electrode plate 2 and the electrode plate 3 by interposing the separator. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】本発明はリチウム二次電池に関し、更に詳しくは、生産性及び省スペース性に優れているとともに内部抵抗が低減され、かつ大電流放電に適したリチウム二次電池に関する。
【０００２】
【従来の技術】リチウム二次電池は、近年、携帯型の通信機器やノート型パーソナルコンピュータ等の電子機器の電源を担う、小型でエネルギー密度の大きな充放電可能な二次電池として広く用いられている。また、国際的な地球環境の保護を背景として省資源化や省エネルギー化に対する関心が高まる中、リチウム二次電池は、自動車業界において積極的な市場導入が検討されている電気自動車（ＥＶ）、ハイブリッド電気自動車（ＨＥＶ）用のモータ駆動用バッテリー、又は夜間電力の保存による電力の有効利用手段としても期待されており、これらの用途に適する大容量リチウム二次電池の実用化が急がれている。
【０００３】リチウム二次電池には、一般的にリチウム遷移金属複合酸化物等が正極活物質として、またハードカーボンや黒鉛といった炭素質材料が負極活物質としてそれぞれ用いられる。リチウム二次電池の反応電位は約４．１Ｖと高いために、電解液として従来のような水系電解液を用いることができず、このため電解質であるリチウム化合物を有機溶媒に溶解した非水電解液が用いられる。そして、充電反応は正極活物質中のリチウムイオンが、非水電解液中を通って負極活物質へ移動して捕捉されることで起こり、放電時には逆の電池反応が起こる。
【０００４】これらの中で、ＥＶ、ＨＥＶ等に好適に用いられる比較的容量の大きいリチウム二次電池においては、内部電極体として図２に示すような、リード線として機能する集電タブ（正極集電タブ５、負極集電タブ６）が取り付けられた電極板（正極板２、負極板３）を、互いに接触しないように、間にセパレータ７を介しつつ、巻芯１３の外周に捲回してなる捲回型内部電極体１が好適に用いられている。なお、正極板２及び負極板３は、金属箔体等の集電基板の両表面に電極活物質（正極活物質と負極活物質の両方を指す）層を形成したものであり、正極集電タブ５及び負極集電タブ６は、正極板２及び負極板３の端部の金属箔体が露出した部分に所定間隔で取り付けられている（例えば、特許文献１参照）。
【０００５】しかしながら、これらの集電タブは、電極体を捲回又は積層するときに、一つずつ電極板にスポット溶接等して取り付ける必要があるために、その工程は煩雑であるという問題があった。また、集電タブの、電極板と接続された反対側の端部は、それら複数の集電タブを揃えて束ね、内部端子にリベット等を用いて打ち込み接続等して取り付ける必要があるために、その工程も同様に煩雑であり、また低抵抗に接続することは容易ではないという問題があった。更に、複数枚の集電タブを用いて内部電極体と内部端子とを接続する構造を採用するには、この接続構造を収納するためのより大きなスペースが必要となり、電池自体が大型化してしまうといった問題があった。
【０００６】このような問題を解消するため、図３に示すような構造的特徴を有するリチウム二次電池６８が開示されている（例えば、特許文献２参照）。このリチウム二次電池６８は、捲回型内部電極体１を構成する正極板及び負極板の端部における、金属箔体が露出した部分に集電タブを取り付けることなく、正極集電部材４Ａと負極集電部材４Ｂ（集電部材）のそれぞれに溶接によって直接に接続する構造の電池（タブレス構造型のリチウム二次電池）であるために、生産性及びスペース性の向上が図られ、電池自体が小型化されている。
【０００７】しかしながら、例えば、車載用、電力保存用等の比較的大容量のリチウム二次電池に関しては、その利用目的や使用状況に応じてより大電流の充放電が要求される場合があるが、特許文献２において開示されたタブレス構造型のリチウム二次電池であっても、想定される全ての場合において十分に満足し得る性能を発揮するものであるとはいいきれず、その内部抵抗を低減し、より大電流放電を可能とすべく更なる改良を図る余地がある。
【０００８】
【特許文献１】
特開２００１−８５０４２号公報
【特許文献２】
欧州特許出願公開第１２５５３１０号明細書
【０００９】
【発明が解決しようとする課題】本発明は、このような従来技術の有する問題点に鑑みてなされたものであり、その目的とするところは、生産性及び省スペース性に優れているとともに内部抵抗が低減され、かつ大電流放電に適したリチウム二次電池を提供することにある。
【００１０】
【課題を解決するための手段】即ち、本発明によれば、少なくとも１枚の金属箔体からそれぞれ構成された正極板及び負極板がセパレータを介して捲回されてなる捲回型内部電極体と、前記正極板及び前記負極板の端部に、前記端部から電流を導出するためにそれぞれ接続された正極集電部材及び負極集電部材とを備え、前記正極集電部材及び／又は前記負極集電部材と、前記正極板及び／又は前記負極板の前記端部のうちの、前記正極集電部材及び／又は前記負極集電部材と接続されるべく立体的に配列された端縁（接続端縁）との接続箇所が、溶接されることにより形成されてなるリチウム二次電池であって、前記正極板及び前記負極板が前記セパレータを介して１回の捲回により構成される捲回単位当り、１箇所以上の前記接続箇所が形成された前記捲回単位の数の、前記捲回型内部電極体の全捲回数に対する割合が、７０％以上であることを特徴とするリチウム二次電池が提供される。
【００１１】本発明においては、捲回型内部電極体の全捲回数ｎ（ｎは１以上の実数）と、接続箇所の数ｍ（ｍは自然数）とが、ｍ≧ｎの関係を満たすことが好ましく、任意の位置の捲回単位における、捲回単位当りの接続箇所の数が、任意の位置の捲回単位の内周側に位置する捲回単位における、捲回単位当りの接続箇所の数以上であることが好ましい。
【００１２】本発明においては、正極板を構成する金属箔体及び正極集電部材が、アルミニウム又はアルミニウム合金からなることが好ましく、負極板を構成する金属箔体及び負極集電部材が、銅又は銅合金からなることが好ましい。
【００１３】本発明においては、正極集電部材及び／又は負極集電部材の形状が、十字形状、Ｙ字形状、Ｉ字形状、又は一部に切り欠きを有する円板形状であることが好ましい。
【００１４】本発明のリチウム二次電池は、電池容量が２Ａｈ以上の大型電池に好適に採用され、また、大電流の放電が頻繁に行われる電気自動車又はハイブリッド電気自動車のモータ駆動用電源等として好適に用いられる。
【００１５】
【発明の実施の形態】以下、本発明の実施の形態について説明するが、本発明は以下の実施の形態に限定されるものではなく、本発明の趣旨を逸脱しない範囲で、当業者の通常の知識に基づいて、適宜、設計の変更、改良等が加えられることが理解されるべきである。
【００１６】本発明は、少なくとも１枚の金属箔体からそれぞれ構成された正極板及び負極板がセパレータを介して捲回されてなる捲回型内部電極体と、正極板及び負極板の端部に、端部から電流を導出するためにそれぞれ接続された正極集電部材及び負極集電部材とを備え、正極集電部材及び／又は負極集電部材と、正極板及び／又は負極板の端部のうちの、正極集電部材及び／又は負極集電部材と接続されるべく立体的に配列された端縁（接続端縁）との接続箇所が、溶接されることにより形成されてなるリチウム二次電池であり、正極板及び負極板がセパレータを介して１回の捲回により構成される捲回単位当り、１箇所以上の接続箇所が形成された捲回単位の数の、捲回型内部電極体の全捲回数に対する割合が、７０％以上であることを特徴とする。以下、図１に示す模式図を例に挙げ、本発明の実施の形態について具体的に説明する。
【００１７】図１は、本発明のリチウム二次電池に用いられる捲回型内部電極体における、集電部材と電極板との接続状態を説明する模式図である。図１に示すように、捲回型内部電極体１は、金属箔体から構成された正極板２及び負極板３が、セパレータ（図示せず）を介して巻芯（図示せず）の外周にｎ回（ｎは１以上の実数）捲回されることにより構成されている。電極板（正極板２、負極板３）の表面には電極活物質が塗工されているが、電極板の端部には電極活物質が塗工されずに金属箔体が露出しており、電極集電部材（正極集電部材４Ａ、負極集電部材４Ｂ）と接続されるべく立体的に配列されている。このように立体的に配列された電極板の端縁（接続端縁１１）と当接するように電極集電部材（正極集電部材４Ａ、負極集電部材４Ｂ）が配置され、電極集電部材と接続端縁１１とが溶接によって接続され、接続箇所１０が形成されている。ここで、捲回型内部電極体１について、正極板２及び負極板３がセパレータを介して１回の捲回により構成される単位を「捲回単位」とした場合、本発明のリチウム二次電池は、１箇所以上の接続箇所１０が形成された捲回単位の数の、捲回型内部電極体１の全捲回数ｎに対する割合が、７０％以上である。
【００１８】捲回型内部電極体１の全捲回数ｎに対して、１箇所以上の接続箇所１０が形成された捲回単位が所定の割合以上含まれている場合には、電極板（正極板２、負極板３）の全域において均等に電流の導出入が効率的に行われることとなる。本実施形態のリチウム二次電池は、前記割合が７０％以上であるため、電極板の全域に渡って均等に接続箇所が分布しており、電流の導出入が効率的に行われ、その内部抵抗の低減がなされている。前記割合が７０％未満であると、接続箇所の分布が疎らとなり、電流導出入の効率が低下し、内部抵抗が上昇するために好ましくない。
【００１９】また、電極集電部材と電極板を形成する金属箔体とを溶接することにより直接的に接続して電流を導出入する構造であるため、集電タブが不要である。従って、本発明のリチウム二次電池は、煩雑な集電タブの取り付け工程が不要となるため生産性の向上が図られる。更に、集電タブを収納するためのスペースを省くことができるために、電池全体がコンパクトである。
【００２０】より電流の導出入が効率的に行われ、内部抵抗を低減するといった観点からは、前記割合が８０％以上であることが好ましく、８５％以上であることが更に好ましい。なお、本発明においては、１箇所以上が溶接によって接続されてなる捲回単位の数の、全捲回数に対する割合の上限値については特に限定されないが、１００％であることが最も好ましいことはいうまでもない。但し、溶接作業工程等を含む実質的な製造可能性を考慮すれば、概ね９０％程度であれば十分に低内部抵抗であるとともに、大電流充放電に対応し得るものとなる。
【００２１】また、本発明のリチウム二次電池に用いられる捲回型内部電極体１は、その全捲回数をｎ（ｎは１以上の実数）、接続箇所１０の数をｍ（ｍは自然数）とした場合に、これらがｍ≧ｎの関係を満たすことが好ましい。即ち、このような関係を満たすと、捲回型内部電極体１からの電流導出入のパスとなる溶接箇所１０の数が十分に確保されることとなるため、低内部抵抗であり、より大電流の充放電に対応し得る電池とすることができる。
【００２２】ここで、図１に示すように、立体的に配列された接続端縁１１と当接するように十字形状の正極集電部材４Ａを配置した場合を想定すると、捲回型内部電極体１の全捲回数がｎ回である場合、形成される接続箇所１０は最大で４ｎ箇所となる。また、正極集電部材の形状がＹ字形状、Ｉ字形状である場合には、最大で各々３ｎ箇所、２ｎ箇所の接続箇所が形成される。
【００２３】より低内部抵抗であり、更なる大電流の充放電への対応を可能にするといった観点からは、本発明のリチウム二次電池においては、捲回型内部電極体の全捲回数ｎ（ｎは１以上の実数）と、接続箇所の数ｍ（ｍは自然数）とが、ｍ≧１．５ｎの関係を満たすことが好ましく、ｍ≧２ｎの関係を満たすことが更に好ましい。なお、本発明においては、捲回型内部電極体の全捲回数ｎとの関係における、接続箇所の数ｍの上限値については特に限定されないが、ｎ≦ｍ≦２ｎの関係を満たしていれば、十分な低内部抵抗とすることができる。
【００２４】また、本発明においては、任意の位置の捲回単位（以下、「基準捲回単位」と記す）における、捲回単位当りの接続箇所の数が、基準捲回単位の内周側に位置する捲回単位（以下、「内周側捲回単位」と記す）における、捲回単位当りの接続箇所の数以上であることが好ましい。通常、捲回単位当りの電極板の面積は、捲回型内部電極体の内周から外周へ移行するに従って漸次増加する。このため、基準捲回単位における捲回単位当りの接続箇所の数が、その内周側に位置する内周側捲回単位における、捲回単位当りの接続箇所の数以上であると、捲回単位当りの電極板の面積がより広い外周側に位置する捲回単位においても、電流の導出入がより効率的に行われることとなり、その内部抵抗の低減を図ることができる。
【００２５】なお、基準捲回単位が捲回型内部電極体の最内周に位置する場合には、内周側捲回単位は存在しないこととなる。従って、本発明における「基準捲回単位」は、捲回型内部電極体の最内周に位置する捲回単位を除くものとする。
【００２６】本発明においては、リチウム二次電池の構成部材として良好な特性を発揮させるといった観点から、正極板を構成する金属箔体及び正極集電部材は、アルミニウム又はアルミニウム合金からなることが好ましく、負極板を構成する金属箔体及び負極集電部材は、銅又は銅合金からなることが好ましい。更に、負極集電部材と、負極板の端部との接続部分において、負極板から負極集電部材の方向に延びる柱状晶が形成されてなることが好ましい。一般に溶接金属は、溶融金属が母材（未溶融部）の結晶粒上に同一結晶方位をもって成長（エピタキシャル成長）する。このように形成された固相は熱源の移動に伴い、溶接ビード（溶融部分）内部へ成長する。この成長は、温度勾配の最も大きい方向に成長し易く、その方向へほぼ一方向に延びた形態で成長し、このように成長した結晶は柱状晶と呼ばれる。
【００２７】負極集電部材から垂れ下がった溶融部は、冷却に伴い再結晶化するが、負極板（金属箔体）を通じて溶融部の熱が急速に拡散する。即ち、負極板に密着した部分の溶融部の温度が低下し、負極板と溶融部との界面が核となって負極板から負極集電部材の方向へと柱状晶が形成し易くなると考えられる。更に、本発明では負極板の接続端縁近傍の側面部が負極集電部材の第一凸部の突出端面と隙間なく密着して接触状態が良好であり、負極板を通じた冷却効果によって柱状晶が形成し易い状態である。従って、接続部分において、負極板から負極集電部材の方向に延びる柱状晶が形成されている場合には、負極板と負極集電部材との接続状態が良好、即ち、負極集電部材と負極板との接続に十分な強度が確保されているために好ましい。
【００２８】また、本発明においては、正極集電部材４Ａ及び／又は負極集電部材４Ｂの形状が、図５（ａ）、図５（ｅ）に示すような十字形状、図５（ｂ）、図５（ｆ）に示すようなＹ字形状、図５（ｃ）、図５（ｇ）に示すようなＩ字形状、又は図５（ｄ）、図５（ｈ）に示すような、一部に切り欠きを有する円板形状であることが好ましい。正極集電部材４Ａ、負極集電部材４Ｂの形状がこれらの形状である場合には、溶接により形成された接続箇所の、接続状態の検査がし易く、また余剰部ができるだけ含まれない形状であるために電池を軽量化することができる。また、電解液を充填する際等において、電解液が全体に回り易い構造であるために好ましい。
【００２９】電極集電部材と電極板の接続端縁との溶接状態は、集電部材の形状、照射するレーザーの出力、溶接速度、捲回型内部電極体を構成する電極板の接続端縁に対する、電極集電部材の押付け量等の条件設定により左右される。即ち、これらの諸条件を適宜設定することにより、捲回単位当り１箇所以上の接続箇所が形成された捲回単位の数の、捲回型内部電極体の全捲回数に対する割合が所定の割合以上である、本発明に係るリチウム二次電池を製造することができる。
【００３０】次に、本発明のリチウム二次電池に用いられる捲回型内部電極体における、電極集電部材と電極板の接続端縁とを溶接により接続する具体的方法について、正極集電部材と正極板の接続端縁との溶接（正極側）、負極集電部材と負極板の接続端縁との溶接（負極側）とに分けて説明する。
【００３１】正極側については、図６に示すように、正極板２の狭幅端面を含む面の法線８Ａに対して、角度θ_１（０°＜θ_１≦９０°）で、正極集電部材４Ａの第二突条部３２にエネルギー線５３を照射し、第二突条部３２、本体部１２の一部、及び第一突条部３１を溶解して、正極集電部材４Ａと、正極板２（金属箔体２０）の端部１５とを溶接によって接続すればよい。このような状態でエネルギー線５３を照射することで、正極板２と正極集電部材４Ａとの接続状態をより確実なものとすることができ、正極集電部材４Ａに穴等の製品欠陥が生じ難くなる。なお、正極板と正極集電部材との接続状態をより確実とし、正極集電部材に穴等の製品欠陥を更に生じ難くするといった観点からは、前述の角度θ_１は５°≦θ_１≦８０°であることが更に好ましく、１０°≦θ_１≦６０°であることが特に好ましく、１５°≦θ_１≦４５°であることが最も好ましい。
【００３２】また、正極集電部材４Ａを、その第一突条部３１が狭幅端面２１に略垂直に交差するように配置し、狭幅端面２１に略垂直に交差するように、エネルギー線発生装置を用いて、第二突条部３２を走査して照射すればよい。このとき、上述した、狭幅端面を含む面の法線８Ａに対して角度θ_１（０°＜θ_１≦９０°）で第二突条部３２にエネルギー線５３を照射することに加え、エネルギー線５３を、狭幅端面２１に略垂直に交差する線に対して、角度が略垂直となるように第二突条部３２に照射することが好ましい。このことにより、ろう材を用いることなく、簡易な操作によって正極板２の端部１５と正極集電部材４Ａとを接続することができる。また、正極板２を構成する金属箔体２０に損傷を与えずに、正極集電部材４Ａのみを溶解させて接続することができるために、正極集電部材４Ａと正極板２との接続に十分な強度が確保される。
【００３３】なお、本発明にいう「接続端縁」とは、１枚の電極板を構成する金属箔体における複数箇所の接続される端縁、又は複数枚の電極板を構成する金属箔体における複数箇所に渡る各金属箔体の接続される端縁を意味する。また、「狭幅端面に略垂直に交差する」とは、複数の接続端縁における狭幅端面の全てについて略垂直に交差することを意味する。
【００３４】正極集電部材の第二突条部に照射するエネルギー線のパワー密度は、５ｋＷ／ｍｍ^２以上であることが好ましく、６ｋＷ／ｍｍ^２以上であることが更に好ましく、７ｋＷ／ｍｍ^２以上であることが特に好ましい。３ｋＷ／ｍｍ^２未満であると、接続状態が良好ではなく、機械的強度が不十分となる場合が想定されるために好ましくない。なお、パワー密度の上限については特に限定されないが、使用する各部材への損傷発生を回避する等の観点から適宜決定すればよく、例えば６０ｋＷ／ｍｍ^２以下であればよい。ここで、本発明にいうエネルギー線の「パワー密度」とは、エネルギー線のパワー（ｋＷ）を、エネルギー線が照射される照射点のスポット面積（ｍｍ^２）で除して得た値を意味する。
【００３５】負極側については、図７に示すように、負極板３の側面部を含む面の法線８Ｂに対して、角度θ_２（０°≦θ_２≦３０°）で、負極集電部材４Ｂの第二突条部３２にエネルギー線５３を照射し、第二突条部３２、本体部１２の一部、及び第一突条部３１を溶解して、負極集電部材４Ｂと、負極板３の端部１５とを溶接によって接続すればよい。このような状態でエネルギー線５３を照射することにより、負極板３と負極集電部材４Ｂとの接続状態をより確実なものとすることができ、負極集電部材４Ｂに穴等の製品欠陥が生じ難くなる。なお、負極板と負極集電部材との接続状態をより確実とし、負極集電部材に穴等の製品欠陥を更に生じ難くするといった観点からは、前述の角度θ_２は０°≦θ_２≦１０°であることが更に好ましく、０°≦θ_２≦５°であることが特に好ましい。また、熱効率の観点からは、負極集電部材４Ｂの第二突条部３２の表面又はその近傍にエネルギー線５３を合焦させることが好ましく、更に、負極を構成する金属箔体２０に対して、エネルギー線５３を実質的に照射しないことが好ましい。
【００３６】更に、負極集電部材４Ｂを、その第一突条部３１が側面部１３に略垂直に交差するように配置し、側面部１３に略垂直に交差するように、エネルギー線発生装置を用いて、第二突条部３２を走査して照射すればよい。このとき、上述した、側面部を含む面の法線８Ｂに対して角度θ_２（０°≦θ_２≦３０°）で第二突条部３２にエネルギー線５３を照射することに加え、エネルギー線５３を、側面部１３に略垂直に交差する線に対して、角度が略垂直となるように第二突条部３２に照射することが好ましい。このことにより、ろう材を用いることなく、簡易な操作によって負極板３の端部１５と負極集電部材４Ｂとを接続することができる。また、負極板３を構成する金属箔体２０に損傷を与えずに、負極集電部材４Ｂのみを溶解させて接続することができるために、負極集電部材４Ｂと負極板３との接続に十分な強度が確保される。なお、「側面部に略垂直に交差する」とは、複数の接続端縁における側面部の全てについて略垂直に交差することを意味する。
【００３７】負極集電部材の第二突条部に照射するエネルギー線のパワー密度は、３ｋＷ／ｍｍ^２以上であることが好ましく、６ｋＷ／ｍｍ^２以上であることが更に好ましく、８ｋＷ／ｍｍ^２以上であることが特に好ましい。３ｋＷ／ｍｍ^２未満であると、接続状態が良好ではなく、機械的強度が不十分となる場合が想定されるために好ましくない。なお、パワー密度の上限については特に限定されないが、使用する各部材への損傷発生を回避する等の観点から適宜決定すればよく、例えば６０ｋＷ／ｍｍ^２以下であればよい。
【００３８】また、エネルギー線の乱反射を抑制して負極板を構成する金属箔体への損傷発生を抑制する観点から、負極集電部材の第二突条部のうちの、エネルギー線を照射する部分が平面状であることが好ましく、少なくとも照射点よりも広い範囲が平面状であることが好ましい。更に、照射するエネルギー線のスポット径を、１ｍｍ以下とすることが好ましく、０．８ｍｍ以下とすることが更に好ましい。このことにより、不要な箇所へのエネルギー線の照射が抑制され、特に負極を構成する金属箔体への損傷発生を抑制することができる。
【００３９】なお、エネルギー密度が高く発熱量も小さい、レーザー又は電子ビームによるエネルギー線を照射して溶接することが好ましく、更に、エネルギー線が連続波であることが、第二突条部の表面にエネルギーを集中させて照射することができ、電極板を構成する金属箔体への損傷発生を抑制することができるために好ましい。なお、レーザーの中でも、ＹＡＧレーザーは焦点を良好に絞ることができ、焦点以外に配置された金属箔体への損傷発生を更に抑制することができるために好ましい。
【００４０】また、正極集電部材の第二突条部にエネルギー線を照射するに際しては、連続照射が可能なエネルギー線発生装置を用いることが好ましく、このときの走査速度は、０．１〜１００ｍ／ｍｉｎであることが好ましく、１〜３０ｍ／ｍｉｎであることが更に好ましく、２〜１０ｍ／ｍｉｎであることが特に好ましい。更に、配列された正極板の枚数に応じ、正極集電部材を複数個用意し、複数の正極集電部材を、それらの第一突条部が狭幅端面に略垂直に交差するようにして連続的に配置することが好ましく、このことにより複数枚の正極板を一度の照射によって接続することができる。
【００４１】一方、負極集電部材の第二突条部にエネルギー線を照射するに際しては、連続照射が可能なエネルギー線発生装置を用いることが好ましい。更に、配列された負極板の枚数に応じ、負極集電部材を複数個用意し、複数の負極集電部材を、それらの第一突条部が側面部に略垂直に交差するようにして連続的に配置することが好ましく、このことにより、複数枚の負極板を一度の照射によって接続することができる。
【００４２】なお、電極集電部材と電極板の接続端縁とを溶接して接続するに際して、ろう材等の接合補助材料は不要ではあるが、用いても構わない。接合補助材料を用いる場合には、これを電極板を構成する金属箔体及び／若しくは電極集電部材の所定箇所に塗布し、又は金属箔体と電極集電部材の所定箇所との間に挟持した状態でエネルギー線を照射すればよい。
【００４３】また、捲回型内部電極体を構成する電極板の接続端縁に対して、電極集電部材を押し付けることによっても、電極集電部材と電極板の接続端縁との溶接状態を良好にすることができる。このときの押付け量は、０．０５〜３ｍｍの範囲内で適宜設定すればよい。なお、本発明にいう「押付け量」とは、電極集電部材が押し付けられることにより、電極板の接続端縁が、押し付けられる前の位置（初期位置）から引き込んだ分の長さ（ｍｍ）をいう。
【００４４】次に、本発明のリチウム二次電池を構成する主要部材及び構造、並びに製造方法について説明する。
【００４５】正極板は、集電基板となる金属箔体の両面に正極活物質を塗工することによって作製される。金属箔体を構成する金属としては、アルミニウムやチタン等の正極電気化学反応に対する耐蝕性が良好な金属が用いられる。正極活物質としては、マンガン酸リチウム（ＬｉＭｎ_２Ｏ_４）やコバルト酸リチウム（ＬｉＣｏＯ_２）、ニッケル酸リチウム（ＬｉＮｉＯ_２）等のリチウム遷移金属複合酸化物が好適に用いられるが、立方晶スピネル構造を有するマンガン酸リチウムを用いると、他のリチウム遷移金属複合酸化物を用いた場合と比較して、内部電極体の抵抗を小さくすることができるために好ましい。なお、正極活物質には、アセチレンブラック等の炭素微粉末を導電助剤として加えることが好ましく、２〜１０質量％の範囲で任意に添加すればよい。
【００４６】マンガン酸リチウムの化学量論組成はＬｉＭｎ_２Ｏ_４で表されるが、このような化学量論組成のものに限られず、遷移元素Ｍｎの一部を、Ｔｉを含み、その他に、Ｌｉ、Ｆｅ、Ｎｉ、Ｍｇ、Ｚｎ、Ｂ、Ａｌ、Ｃｏ、Ｃｒ、Ｓｉ、Ｓｎ、Ｐ、Ｖ、Ｓｂ、Ｎｂ、Ｔａ、Ｍｏ及びＷからなる群より選択される１種類以上の元素からなる、２種類以上の元素で置換してなるＬｉＭ_ＸＭｎ_２−ＸＯ_４（但し、Ｍは置換元素で、Ｘは置換量を示す）も好適に用いられる。
【００４７】上述のような元素置換を行った場合には、そのリチウム（Ｌｉ）／マンガン（Ｍｎ）比（モル比）は、マンガンをリチウムで置換したリチウム過剰の場合には（１＋Ｘ）／（２−Ｘ）となる。一方、リチウム以外の置換元素Ｍで置換した場合には１／（２−Ｘ）となる。従って、いずれの場合であっても常にリチウム（Ｌｉ）／マンガン（Ｍｎ）比＞０．５となるが、本発明においてはこのようなマンガン酸リチウムを用いることが好ましく、化学量論組成（ＬｉＭｎ_２Ｏ_４）のものを用いた場合と比較して結晶構造が更に安定化されているため、電池に優れたサイクル特性を付与することができる。
【００４８】なお、置換元素Ｍにあっては、理論上、Ｌｉは＋１価、Ｆｅ、Ｍｎ、Ｎｉ、Ｍｇ、Ｚｎは＋２価、Ｂ、Ａｌ、Ｃｏ、Ｃｒは＋３価、Ｓｉ、Ｔｉ、Ｓｎは＋４価、Ｐ、Ｖ、Ｓｂ、Ｎｂ、Ｔａは＋５価、Ｍｏ、Ｗは＋６価のイオンとなり、ＬｉＭｎ_２Ｏ_４中に固溶する元素であるが、Ｃｏ、Ｓｎについては＋２価の場合、Ｆｅ、Ｓｂ及びＴｉについては＋３価の場合、Ｍｎについては＋３価、＋４価の場合、Ｃｒについては＋４価、＋６価の場合もあり得る。従って、各種の置換元素Ｍは混合原子価を有する状態で存在する場合があり、また、酸素の量については、必ずしも理論化学組成で表されるように４であることを必要とせず、結晶構造を維持するための範囲内で欠損して、又は過剰に存在していても構わない。
【００４９】正極活物質の塗工は、正極活物質粉末に溶剤や結着剤等を添加して作製したスラリー又はペーストを、ロールコータ法等を用いて、集電基板に塗布・乾燥することで行われ、その後に必要に応じてプレス処理等が施される。
【００５０】負極板は、正極板と同様にして作製することができる。負極板を構成する集電基板としては、銅箔又はニッケル箔等の負極電気化学反応に対する耐蝕性が良好な金属箔体が好適に用いられる。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人造黒鉛や天然黒鉛等の高黒鉛化炭素材料が、更には、前記高黒鉛化炭素材料としては繊維状のものが好適に用いられる。
【００５１】セパレータとしては、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（ＰＥ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（ＰＰ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、電極体の温度が上昇した場合に、ＰＥフィルムが約１３０℃で軟化してマイクロポアが潰れ、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ＰＥフィルムをより軟化温度の高いＰＰフィルムで挟持することによって、ＰＥフィルムが軟化した場合においても、ＰＰフィルムが形状を保持して正極板と負極板の接触・短絡を防止し、電池反応の確実な抑制と安全性の確保が可能となる。このようなセパレータを介して正極板と負極板とを巻芯の外周に捲回して、捲回型内部電極体を作製することができる。
【００５２】捲回型内部電極体の全捲回数ｎは、作製しようとする電池の大きさ・電池容量等に応じて適宜設定すればよく、ｎ＝１０〜３００の範囲内で任意に設定すればよい。また、巻芯の全長についても、３〜５０ｃｍの範囲内で任意に設定すればよい。なお、ｎ＝１０〜３００、かつ、巻芯の全長が３〜５０ｃｍである場合、捲回単位当りの電極板（正極板及び負極板）の面積は、捲回型内部電極体の内周から外周へ移行するに従って１８〜３２００ｃｍ^２の範囲で漸次増加することとなる。
【００５３】次に、非水電解液について説明する。非水電解液を構成する溶媒（有機溶媒）としては、エチレンカーボネート（ＥＣ）、ジエチルカーボネート（ＤＥＣ）、ジメチルカーボネート（ＤＭＣ）、プロピレンカーボネート（ＰＣ）といった炭酸エステル系のものや、γ−ブチロラクトン、テトラヒドロフラン、アセトニトリル等の単独溶媒又は混合溶媒が好適に用いられる。
【００５４】電解質としては、六フッ化リン酸リチウム（ＬｉＰＦ_６）やホウフッ化リチウム（ＬｉＢＦ_４）等のリチウム錯体フッ素化合物、又は過塩素酸リチウム（ＬｉＣｌＯ_４）といったリチウムハロゲン化物を挙げることができ、これらのうちの１又は２種類以上を上述した有機溶媒（混合溶媒）に溶解して用いることができる。なお、酸化分解が起こり難く非水電解液の導電性の高い六フッ化リン酸リチウム（ＬｉＰＦ_６）を用いることが好ましい。
【００５５】集電部材と、電極板を構成する金属箔体との溶接方法（捲回型内部電極体の製造方法）は既述の通りであり、図３に示すように、製造した捲回型内部電極体１を電池ケース７３に挿入し、電極リード部材７２と集電部材（正極集電部材４Ａ、負極集電部材４Ｂ）、及び電極内部端子（正極内部端子６９Ａ、負極内部端子６９Ｂ）を接合して安定な位置にホールドする。その後、電池蓋（正極電池蓋７１Ａ、負極電池蓋７１Ｂ）により電池ケース７３を封ずるとともに前述の非水電解液を含浸することにより、本実施形態のリチウム二次電池（タブレス構造型のリチウム二次電池）を得ることができる。
【００５６】本実施形態においては、電極リード部材７２は、接続される正極集電部材４Ａ、正極内部端子６９Ａ、及び負極集電部材４Ｂ、負極内部端子６９Ｂと、同種金属又はその合金により構成されていることが好ましい（図３）。具体的には、正極内部端子６９Ａ及び正極集電部材４Ａにアルミニウム又はアルミニウム合金を用いた場合には、正極の電極リード部材７２にアルミニウム又はアルミニウム合金を採用し、負極内部端子６９Ｂ及び負極集電部材４Ｂに銅又は銅合金を用いた場合には、負極の電極リード部材７２に銅又は銅合金を採用することが好ましい。
【００５７】電極リード部材７２を用いなくとも、正極集電部材４Ａと正極内部端子６９Ａ、負極集電部材４Ｂと負極内部端子６９Ｂとを直接的に接続し、通電させてもよい。また、これまで述べてきたタブレス構造を有する部分を正極及び負極に用いてもよいし、正極又は負極のいずれかに用いてもよい。なお、図３中、符号７０Ａは正極外部端子、符号７０Ｂは負極外部端子、符号７５は放圧孔を示す。
【００５８】また、図４に示すように、集電部材５４が、電極蓋を兼用している構成であってもよい。図４では、片端が開放された円筒形の電池ケース７３を用い、その電池ケース７３の片端にくびれ加工を形成した例を示しているが、集電部材５４が電極蓋を兼用している構成であれば電池の形状に特に制限はなく、例えば電池ケース７３の両端がくびれ加工されているもの、電池ケース７３の両端が開放されたもの等を使用しても構わない。また、図４においては、正極側に放圧孔７５を有する例を示しているが、負極側に放圧孔を有する構成でも構わない。
【００５９】図３に示すように、本実施形態のリチウム二次電池６８は、捲回型内部電極体１からの電流導出部分に、電極板を構成する金属箔体と、集電部材（正極集電部材４Ａ、負極集電部材４Ｂ）とを直接的に接続した構成を採用することにより、従来の電流導出手段である集電タブを用いる必要がない。従って、煩雑な集電タブの取り付け工程が不要であり、生産性の向上を図ることができる。また、集電タブの長さの分のスペースを省くことができるため、電池全体がコンパクトである。
【００６０】以上、本発明に係るリチウム二次電池について、その実施形態を示しながら説明してきたが、本発明が上記の実施形態に限定されるものでないことはいうまでもない。また、本発明に係るリチウム二次電池は、特に、電池容量が２Ａｈ以上である大型の電池に好適に採用されるが、このような容量以下の電池に適用することを妨げるものではない。また、本発明のリチウム二次電池は、大容量でありながらも小型化されているため、特に省スペース性が要求される車載用電池として、更には、電気自動車又はハイブリッド電気自動車のモータ駆動用電源に用いることが好ましいとともに、高電圧を必要とされるエンジン起動用としても好適に用いることができる。
【００６１】
【実施例】以下、本発明を実施例により具体的に説明するが、本発明はこれら実施例に限定されるものではない。
【００６２】
（捲回型内部電極体の作製）
Ｌｉ／Ｍｎ＞０．５であるＬｉ_１．０５Ｍｎ_１．９５Ｏ_４スピネルを正極活物質とし、これに導電助剤としてアセチレンブラックを外比で２〜１０質量％の範囲で添加したものに、更に溶剤、バインダを加えて調製した正極剤スラリーを、厚さ２０μｍのアルミニウム箔の両面にそれぞれ約１００μｍの厚みとなるように塗工して作製した正極板と、繊維状高黒鉛化炭素粉末を負極活物質として、厚さ１０μｍの銅箔の両面にそれぞれ約８０μｍの厚みとなるように塗工して作製した負極板を作製した。次いで、得られた正極板と負極板を、セパレータを介して捲回（ｎ＝６５）することにより捲回型内部電極体を作製した。
【００６３】
（非水電解液の調製）
ＥＣ、ＤＭＣ、及びＥＭＣの各種有機溶媒を、ＥＣ：ＤＭＣ：ＥＭＣ＝１：１：１（体積比）で混合して混合溶媒を調製し、それぞれに１ｍｏｌ／ｌの濃度となるように電解質であるＬｉＰＦ_６を溶解して非水電解液を調製した。
【００６４】
（実施例１〜１４）
図１に示すように、捲回型内部電極体１の、アルミニウムからなる金属箔体により構成された正極板２の接続端縁１１上に、断面形状が、Ｌ字、逆Ｔ字、又は十字形状である、厚み０．２〜５ｍｍ程度のアルミニウムからなる十字形状の正極集電部材４Ａを載置するとともに、表１に示す押付け量（ｍｍ）となるように、適当な圧力をかけて正極集電部材４Ａを正極板２の接続端縁１１に押し付けた。次いで、正極集電部材４Ａの上方からエネルギー密度５〜６０ＫＷ／ｍｍ^２のＹＡＧレーザーを４方向に走査速度０．１〜１００ｍ／ｍｉｎで照射して溶接することにより、正極集電部材４Ａと、正極板２の接続端縁１１との接続体を得た。なお、押付け量とは、正極集電部材４Ａが押し付けられることにより、正極板２の接続端縁１１が、押し付けられる前の位置（初期位置）から引き込んだ分の長さ（ｍｍ）をいう。
【００６５】得られた接続体を電池ケースに収納後、所定の電解液注入孔を通じて電池ケース内部の減圧（１Ｐａ）処理をしながら加熱（１００℃、２４時間）後、非水電解液を含浸（真空含浸）した。次いで電解液注入孔を封止することにより、リチウム二次電池を作製した（実施例１〜１４）。なお、その他の部材、試験環境は全ての試料について同じとし、電池の封止不良等による電池外部からの水分の浸入等の影響も排除した。
【００６６】
（比較例１，２）
正極集電部材４Ａを正極板２の接続端縁１１に押し付けない（押付け量＝０）こと以外は（図１参照）、前述の実施例１〜１４と同様の方法により、リチウム二次電池を作製した（比較例１，２）。
【００６７】
（電池の動作確認）
大電流試験（１Ｃ〜１０００Ａ）、及び低温試験（２５℃〜−４０℃）動作確認を行った。
【００６８】
（溶接状態の評価）
各電池を分解して正極集電部材が接続した状態の捲回型内部電極体を取り出し、正極集電部材を強制的に金属箔体の先端部から引き剥そうとした場合に、金属箔体がちぎれ、正極集電部材側にその先端部が残った箇所の数を「ｍ（溶接箇所の数）」としてカウントした。また、１箇所以上の接続箇所が形成された捲回単位の数の、捲回型内部電極体の全捲回数（ｎ＝６５）に対する割合（％）を「溶接割合（％）」として算出した。結果を表１に示す。
【００６９】
【表１】

【００７０】
（結果）
電池の動作確認（大電流試験、及び低温試験）の結果、実施例１〜１４の電池については良好な動作を示すことが確認できたのに対し、比較例１，２の電池については動作不良を示すことが確認できた。従って、電池の動作確認、及び表１に示す結果から明らかなように、溶接割合（１箇所以上の接続箇所が形成された捲回単位の数の、捲回型内部電極体の全捲回数に対する割合）が７０％以上である本発明に係る実施例１〜１４の電池は、生産性及び省スペース性に優れるといった特性を備え、良好な電池動作を示すとともに内部抵抗の低減がなされており、大電流放電に適していることが判明した。
【００７１】
【発明の効果】以上説明したように、本発明のリチウム二次電池は、正極板及び負極板がセパレータを介して１回の捲回により構成される捲回単位当り、１箇所以上の接続箇所が形成された捲回単位の数の、捲回型内部電極体の全捲回数に対する割合が、所定の割合以上であるため、集電部材と集電基板を構成する金属箔体との接続状態が良好であり、生産性及び省スペース性に優れているとともに内部抵抗の低減がなされ、かつ大電流放電に適したものである。
【図面の簡単な説明】
【図１】本発明のリチウム二次電池に用いられる捲回型内部電極体における、集電部材と電極板との接続状態を説明する模式図である。
【図２】タブ構造型のリチウム二次電池に用いられる捲回型内部電極体の一例を示す斜視図である。
【図３】タブレス構造型のリチウム二次電池の一例を示す断面図である。
【図４】タブレス構造型のリチウム二次電池の他の例を示す断面図である。
【図５】図５（ａ）〜（ｈ）は、本発明のリチウム二次電池を構成する集電部材の形状の例を示す模式図である。
【図６】本発明のリチウム二次電池に用いられる、正極集電部材と正極板の接続端縁との溶接方法を模式的に示す斜視図である。
【図７】本発明のリチウム二次電池に用いられる、負極集電部材と負極板の接続端縁との溶接方法を模式的に示す斜視図である。
【符号の説明】
１…捲回型内部電極体、２…正極板、３…負極板、４Ａ…正極集電部材、４Ｂ…負極集電部材、５…正極集電タブ、６…負極集電タブ、７…セパレータ、８Ａ…狭幅端面を含む面の法線、８Ｂ…側面部を含む面の法線、１０…接続箇所、１１…接続端縁、１２…本体部、１３…巻芯、１５…端部、２０…金属箔体、２１…狭幅端面、３１…第一突条部、３２…第二突条部、５３…エネルギー線、５４…集電部材、６８…リチウム二次電池、６９Ａ…正極内部端子、６９Ｂ…負極内部端子、７０Ａ…正極外部端子、７０Ｂ…負極外部端子、７１Ａ…正極電池蓋、７１Ｂ…負極電池蓋、７２…電極リード部材、７３…電池ケース、７５…放圧孔。[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery which is excellent in productivity and space saving, has low internal resistance, and is suitable for large-current discharge.
[0002]
2. Description of the Related Art In recent years, lithium secondary batteries have been widely used as small, chargeable / dischargeable secondary batteries having a large energy density and serving as power supplies for electronic devices such as portable communication devices and notebook personal computers. I have. Also, amid increasing interest in resource saving and energy saving against the background of international protection of the global environment, lithium secondary batteries are being considered for active market introduction in the automotive industry, such as electric vehicles (EV) and hybrid vehicles. It is also expected to be used as a motor driving battery for an electric vehicle (HEV) or as a means for effectively using electric power by storing electric power at night, and there is an urgent need to commercialize a large-capacity lithium secondary battery suitable for these uses. .
In a lithium secondary battery, a lithium transition metal composite oxide or the like is generally used as a positive electrode active material, and a carbonaceous material such as hard carbon or graphite is used as a negative electrode active material. Since the reaction potential of a lithium secondary battery is as high as about 4.1 V, a conventional aqueous electrolyte cannot be used as an electrolyte. Therefore, a non-aqueous electrolyte in which a lithium compound as an electrolyte is dissolved in an organic solvent is used. Liquid is used. Then, the charging reaction occurs when lithium ions in the positive electrode active material move to the negative electrode active material through the non-aqueous electrolyte and are captured, and the opposite battery reaction occurs during discharging.
Among these, in a lithium secondary battery having a relatively large capacity suitably used for an EV, an HEV, etc., a current collecting tab (a positive electrode) functioning as a lead wire as shown in FIG. The electrode plates (the positive electrode plate 2 and the negative electrode plate 3) to which the current collecting tabs 5 and the negative electrode current collecting tabs 6 are attached are wound around the outer periphery of the core 13 with the separator 7 interposed therebetween so as not to contact each other. The wound internal electrode body 1 is preferably used. The positive electrode plate 2 and the negative electrode plate 3 are each formed by forming an electrode active material (refers to both a positive electrode active material and a negative electrode active material) layers on both surfaces of a current collecting substrate such as a metal foil body. The tab 5 and the negative electrode current collecting tab 6 are attached at predetermined intervals to portions where the metal foil body at the ends of the positive electrode plate 2 and the negative electrode plate 3 are exposed (for example, see Patent Document 1).
However, these current collecting tabs need to be attached to the electrode plate by spot welding or the like at the time of winding or laminating the electrode body, so that the process is complicated. there were. In addition, the end of the current collecting tab on the opposite side connected to the electrode plate needs to be bundled by aligning the plurality of current collecting tabs, and to be attached to the internal terminals by driving connection using rivets or the like. However, there is a problem that the process is similarly complicated, and it is not easy to connect to a low resistance. Further, in order to adopt a structure in which the internal electrode body and the internal terminal are connected by using a plurality of current collecting tabs, a larger space for accommodating the connection structure is required, and the battery itself becomes large. There was a problem.
In order to solve such a problem, a lithium secondary battery 68 having a structural characteristic as shown in FIG. 3 is disclosed (for example, see Patent Document 2). This lithium secondary battery 68 has a positive electrode current collecting member 4A without attaching a current collecting tab to a portion where the metal foil body is exposed at the ends of the positive electrode plate and the negative electrode plate constituting the wound type internal electrode body 1. Since the battery (tableless lithium secondary battery) has a structure that is directly connected to each of the negative electrode current collecting members 4B (current collecting members) by welding, productivity and space are improved, and the battery itself is improved. Has been downsized.
However, for a relatively large-capacity lithium secondary battery for use in a vehicle, for storing power, or the like, charging and discharging of a larger current may be required depending on the purpose of use and the state of use. However, even the tabless structure type lithium secondary battery disclosed in Patent Document 2 cannot exhibit sufficiently satisfactory performance in all conceivable cases, and its internal resistance is reduced. There is room for further improvements to reduce and allow higher current discharge.
[0008]
[Patent Document 1]
JP 2001-85042 A
[Patent Document 2]
European Patent Publication No. 12555310
[0009]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. An object of the present invention is to provide a lithium secondary battery having reduced resistance and suitable for large-current discharge.
[0010]
That is, according to the present invention, there is provided a wound internal electrode body in which a positive electrode plate and a negative electrode plate each composed of at least one metal foil are wound via a separator. And a positive electrode current collecting member and a negative electrode current collecting member respectively connected to ends of the positive electrode plate and the negative electrode plate to derive a current from the ends, and the positive electrode current collecting member and / or A negative electrode current collector, and an edge of the end of the positive electrode plate and / or the negative electrode plate that is three-dimensionally arranged to be connected to the positive electrode current collector and / or the negative electrode current collector ( A connection portion between the positive electrode plate and the negative electrode plate, wherein the positive electrode plate and the negative electrode plate are formed by a single winding with the separator interposed therebetween. One or more connection points per time unit It made a number of said wound units, relative to the total winding number of the wound-type internal electrode body, a lithium secondary battery, characterized by at least 70% is provided.
In the present invention, the total number of turns n (n is a real number of 1 or more) of the wound internal electrode body and the number m of connection points (m is a natural number) satisfy a relationship of m ≧ n. Preferably, in the winding unit at any position, the number of connection points per winding unit, in the winding unit located on the inner peripheral side of the winding unit at any position, the number of connection points per winding unit It is preferable that the number is not less than the number.
In the present invention, the metal foil and the positive electrode current collector constituting the positive electrode plate are preferably made of aluminum or an aluminum alloy. The metal foil and the negative electrode current collector constituting the negative electrode plate are preferably made of copper or aluminum. It is preferred to be made of a copper alloy.
In the present invention, the shape of the positive electrode current collecting member and / or the negative electrode current collecting member is preferably a cross shape, a Y-shape, an I-shape, or a disc shape having a cutout in a part. .
The lithium secondary battery of the present invention is suitably used for a large battery having a battery capacity of 2 Ah or more, and is used as a power source for driving a motor of an electric vehicle or a hybrid electric vehicle in which a large current is frequently discharged. It is preferably used.
[0015]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below, but the present invention is not limited to the following embodiments, and is within the scope of the present invention. It should be understood that design changes, improvements, etc. may be made as appropriate based on the knowledge of
The present invention is directed to a wound internal electrode body formed by winding a positive electrode plate and a negative electrode plate each composed of at least one metal foil body with a separator interposed therebetween, and an end portion of the positive electrode plate and the negative electrode plate. A positive current collecting member and a negative current collecting member connected to each other to derive a current from an end portion; and a positive current collecting member and / or a negative current collecting member, and a positive electrode plate and / or a negative electrode plate. Lithium formed by welding a portion of the portion connected to an edge (connection edge) that is three-dimensionally arranged to be connected to the positive electrode current collecting member and / or the negative electrode current collecting member. A secondary battery in which the number of winding units in which one or more connection points are formed per winding unit in which a positive electrode plate and a negative electrode plate are formed by one winding via a separator, The ratio of the internal electrode body to the total number of turns is 70% or more. The features. Hereinafter, embodiments of the present invention will be specifically described with reference to the schematic diagram shown in FIG. 1 as an example.
FIG. 1 is a schematic diagram illustrating a connection state between a current collecting member and an electrode plate in a wound internal electrode body used in a lithium secondary battery of the present invention. As shown in FIG. 1, in a wound type internal electrode body 1, a positive electrode plate 2 and a negative electrode plate 3 made of a metal foil are formed by a separator (not shown) and an outer periphery of a winding core (not shown). (N is a real number of 1 or more). An electrode active material is coated on the surfaces of the electrode plates (the positive electrode plate 2 and the negative electrode plate 3), but a metal foil body is exposed at the end of the electrode plate without being coated with the electrode active material. , Are three-dimensionally arranged to be connected to the electrode current collectors (the positive electrode current collector 4A and the negative electrode current collector 4B). The electrode current collecting members (the positive electrode current collecting member 4A and the negative electrode current collecting member 4B) are arranged so as to be in contact with the edges (connection edges 11) of the three-dimensionally arranged electrode plates. And the connection edge 11 are connected by welding to form a connection portion 10. Here, with respect to the wound internal electrode body 1, when the unit in which the positive electrode plate 2 and the negative electrode plate 3 are formed by a single winding via a separator is referred to as a “winding unit”, the lithium secondary battery of the present invention is used. In the battery, the ratio of the number of winding units in which one or more connection points 10 are formed to the total number n of windings of the wound internal electrode body 1 is 70% or more.
When the winding unit in which one or more connection portions 10 are formed is included in a predetermined ratio or more with respect to the total number n of windings of the wound internal electrode body 1, the electrode plate (positive electrode) Current can be efficiently led in and out uniformly over the entire area of the plate 2 and the negative electrode plate 3). In the lithium secondary battery of the present embodiment, the connection ratio is evenly distributed over the entire area of the electrode plate because the ratio is 70% or more, so that current can be efficiently drawn in and out. The resistance has been reduced. If the ratio is less than 70%, the distribution of the connection points becomes sparse, the efficiency of current supply / reception decreases, and the internal resistance increases, which is not preferable.
Further, since the electrode current collecting member and the metal foil body forming the electrode plate are directly connected to each other by welding, and a current is drawn in and out, a current collecting tab is unnecessary. Therefore, the lithium secondary battery of the present invention does not require a complicated step of attaching a current collecting tab, thereby improving productivity. Furthermore, since the space for accommodating the current collection tab can be omitted, the whole battery is compact.
From the viewpoint that the current can be more efficiently introduced and reduced and the internal resistance is reduced, the ratio is preferably 80% or more, and more preferably 85% or more. In the present invention, the upper limit value of the ratio of the number of winding units formed by welding at one or more locations to the total number of winding times is not particularly limited, but 100% is most preferable. Not even. However, in consideration of substantial manufacturability including a welding operation step and the like, an internal resistance of about 90% is sufficiently low and can cope with large current charging and discharging.
In the wound internal electrode body 1 used in the lithium secondary battery of the present invention, the total number of windings is n (n is a real number of 1 or more), and the number of connection points 10 is m (m is a natural number). ), It is preferable that these satisfy the relationship of m ≧ n. That is, when such a relationship is satisfied, the number of welding portions 10 serving as paths for drawing and entering current from the wound-type internal electrode body 1 is sufficiently ensured. A battery capable of responding to current charging and discharging can be obtained.
Here, as shown in FIG. 1, it is assumed that a cross-shaped positive current collector 4A is arranged so as to abut the connection edges 11 arranged three-dimensionally. When the total number of turns of 1 is n, the number of connection points 10 to be formed is 4n at maximum. When the shape of the positive electrode current collector is Y-shaped or I-shaped, 3n connection points and 2n connection points are formed at the maximum.
The lithium secondary battery of the present invention has a lower internal resistance and is capable of coping with the charging and discharging of a larger current. (N is a real number of 1 or more) and the number m of connection points (m is a natural number) preferably satisfy the relationship m ≧ 1.5n, and more preferably satisfy the relationship m ≧ 2n. In the present invention, the upper limit of the number m of connection points in relation to the total number n of windings of the wound internal electrode body is not particularly limited, as long as the relation of n ≦ m ≦ 2n is satisfied. , And a sufficiently low internal resistance.
Further, in the present invention, the number of connection points per winding unit in a winding unit at an arbitrary position (hereinafter referred to as a “reference winding unit”) is determined on the inner circumferential side of the reference winding unit. It is preferable that the number of connection points per winding unit in the winding unit (hereinafter referred to as “inner circumference side winding unit”) is equal to or more than the number of connection points per winding unit. Usually, the area of the electrode plate per unit of winding gradually increases as it moves from the inner circumference to the outer circumference of the wound internal electrode body. Therefore, if the number of connection points per winding unit in the reference winding unit is equal to or greater than the number of connection points per winding unit in the inner circumference side winding unit located on the inner circumference side, Even in the winding unit located on the outer peripheral side where the area of the electrode plate per unit is larger, the current can be more efficiently led in and out, and the internal resistance can be reduced.
When the reference winding unit is located at the innermost circumference of the wound internal electrode body, the inner winding unit does not exist. Therefore, the “reference winding unit” in the present invention excludes the winding unit located at the innermost circumference of the wound internal electrode body.
In the present invention, the metal foil and the positive electrode current collector constituting the positive electrode plate are preferably made of aluminum or an aluminum alloy from the viewpoint of exhibiting good characteristics as a component of the lithium secondary battery. It is preferable that the metal foil body and the negative electrode current collector constituting the negative electrode plate are made of copper or a copper alloy. Further, it is preferable that columnar crystals extending in the direction from the negative electrode plate toward the negative electrode current collector be formed at a connection portion between the negative electrode current collector and the end of the negative electrode plate. Generally, in a weld metal, a molten metal grows (epitaxial growth) with the same crystal orientation on crystal grains of a base material (unmelted portion). The solid phase thus formed grows inside the weld bead (molten portion) as the heat source moves. This growth is easy to grow in the direction of the largest temperature gradient, and grows in a form extending in almost one direction in that direction. The crystal thus grown is called a columnar crystal.
The melted portion hanging down from the negative electrode current collector recrystallizes with cooling, but the heat of the melted portion diffuses rapidly through the negative electrode plate (metal foil). That is, it is considered that the temperature of the molten portion of the portion in close contact with the negative electrode plate decreases, and the interface between the negative electrode plate and the molten portion becomes a nucleus and columnar crystals are easily formed from the negative electrode plate toward the negative electrode current collector. . Furthermore, in the present invention, the side surface portion near the connection edge of the negative electrode plate is in close contact with the protruding end surface of the first convex portion of the negative electrode current collector without any gap, and the contact state is good. Are easy to form. Therefore, when columnar crystals extending in the direction from the negative electrode plate to the negative electrode current collecting member are formed at the connection portion, the connection state between the negative electrode plate and the negative electrode current collecting member is good, that is, the negative electrode current collecting member and the negative electrode This is preferable because sufficient strength is secured for connection with the plate.
In the present invention, the shape of the positive electrode current collecting member 4A and / or the negative electrode current collecting member 4B has a cross shape as shown in FIGS. 5 (a) and 5 (e), and FIG. 5 (f), I-shape as shown in FIGS. 5 (c) and 5 (g), or as shown in FIGS. 5 (d) and 5 (h). It is preferably a disk shape having a notch in a part. When the shape of the positive electrode current collecting member 4A and the shape of the negative electrode current collecting member 4B are these shapes, it is easy to inspect the connection state of the connection portion formed by welding, and the shape should include a surplus portion as little as possible. Because of this, the weight of the battery can be reduced. In addition, when the electrolyte is filled or the like, it is preferable because the electrolyte has a structure that can easily go around the whole.
The welding state between the electrode current collector and the connection edge of the electrode plate depends on the shape of the current collector, the output of the laser to be irradiated, the welding speed, and the connection edge of the electrode plate constituting the wound internal electrode body. And the amount of pressing of the electrode current collecting member. That is, by appropriately setting these various conditions, the ratio of the number of winding units in which one or more connection points are formed per winding unit to the total number of turns of the wound internal electrode body is a predetermined ratio. As described above, the lithium secondary battery according to the present invention can be manufactured.
Next, a specific method for connecting the electrode current collecting member and the connection edge of the electrode plate by welding in the wound internal electrode body used in the lithium secondary battery of the present invention will be described. And the connection edge of the positive electrode plate (positive electrode side) and the welding of the negative electrode current collector and the connection edge of the negative electrode plate (negative electrode side).
On the positive electrode side, as shown in FIG. 6, an angle θ with respect to a normal line 8A of the surface including the narrow end face of the positive electrode plate 2 is shown. ₁ (0 ° <θ ₁ ≦ 90 °), the energy beam 53 is irradiated to the second ridge 32 of the positive electrode current collecting member 4A to melt the second ridge 32, a part of the main body 12, and the first ridge 31. Then, the positive electrode current collecting member 4A and the end 15 of the positive electrode plate 2 (metal foil body 20) may be connected by welding. By irradiating the energy beam 53 in such a state, the connection state between the positive electrode plate 2 and the positive electrode current collecting member 4A can be made more reliable, and product defects such as holes in the positive electrode current collecting member 4A can be reduced. It is unlikely to occur. In addition, from the viewpoint of making the connection state between the positive electrode plate and the positive electrode current collecting member more reliable and making it more difficult for product defects such as holes to occur in the positive electrode current collecting member, the above-described angle θ is used. ₁ Is 5 ° ≦ θ ₁ ≦ 80 °, more preferably 10 ° ≦ θ ₁ ≦ 60 ° is particularly preferable, and 15 ° ≦ θ ₁ It is most preferred that ≦ 45 °.
Further, the positive current collector 4A is disposed so that the first ridge portion 31 intersects the narrow end face 21 substantially perpendicularly, and the energy beam is arranged so as to intersect the narrow end face 21 substantially perpendicularly. What is necessary is just to scan and irradiate the 2nd protrusion part 32 using a generator. At this time, the angle θ with respect to the normal line 8A of the surface including the narrow end surface described above. ₁ (0 ° <θ ₁ In addition to irradiating the energy beam 53 to the second ridge 32 at ≦ 90 °), the angle of the energy beam 53 is set to be substantially perpendicular to a line that intersects perpendicularly to the narrow end face 21. It is preferable to irradiate the second ridge portion 32. Thus, the end 15 of the positive electrode plate 2 and the positive electrode current collector 4A can be connected by a simple operation without using a brazing material. Further, since only the positive electrode current collector 4A can be melted and connected without damaging the metal foil body 20 constituting the positive electrode plate 2, the connection between the positive electrode current collector 4A and the positive electrode plate 2 can be made. Sufficient strength is secured.
In the present invention, the term "connection edge" refers to an edge to be connected at a plurality of locations in a metal foil body constituting one electrode plate, or a metal foil body constituting a plurality of electrode plates. Means the connected edge of each metal foil body over a plurality of locations. Further, “intersects substantially narrowly with the narrow end face” means that all of the narrow end faces at the plurality of connection edges intersect substantially vertically.
The power density of the energy beam applied to the second ridge of the positive electrode current collector is 5 kW / mm ² And more preferably 6 kW / mm ² More preferably, it is 7 kW / mm ² It is particularly preferable that the above is satisfied. 3 kW / mm ² If it is less than 1, the connection state is not good and the mechanical strength may be insufficient, which is not preferable. The upper limit of the power density is not particularly limited, but may be appropriately determined from the viewpoint of avoiding the occurrence of damage to each member used, for example, 60 kW / mm. ² The following may be sufficient. Here, the “power density” of the energy ray referred to in the present invention means that the power (kW) of the energy ray is determined by changing the spot area (mm) of the irradiation point irradiated with the energy ray. ² ) Means the value obtained.
On the negative electrode side, as shown in FIG. 7, an angle θ with respect to a normal line 8 B of the surface including the side surface of the negative electrode plate 3. ₂ (0 ° ≦ θ ₂ ≦ 30 °), the energy beam 53 is applied to the second ridge 32 of the negative electrode current collecting member 4B to melt the second ridge 32, a part of the main body 12, and the first ridge 31. Then, the negative electrode current collecting member 4B and the end 15 of the negative electrode plate 3 may be connected by welding. By irradiating the energy beam 53 in such a state, the connection state between the negative electrode plate 3 and the negative electrode current collecting member 4B can be made more reliable, and product defects such as holes in the negative electrode current collecting member 4B can be reduced. It is unlikely to occur. In addition, from the viewpoint of making the connection state between the negative electrode plate and the negative electrode current collecting member more reliable and making it more difficult to produce a product defect such as a hole in the negative electrode current collecting member, the above-described angle θ is used. ₂ Is 0 ° ≦ θ ₂ ≦ 10 °, more preferably 0 ° ≦ θ ₂ It is particularly preferred that ≦ 5 °. Further, from the viewpoint of thermal efficiency, it is preferable to focus the energy beam 53 on or near the surface of the second ridge portion 32 of the negative electrode current collecting member 4B. It is preferable that the energy ray 53 is not substantially irradiated.
Further, the negative electrode current collecting member 4B is arranged so that the first ridge portion 31 intersects the side surface 13 substantially perpendicularly, and the energy ray generating device is arranged so as to intersect the side surface approximately perpendicularly. It is sufficient to scan and irradiate the second ridge portion 32 by using. At this time, the angle θ with respect to the normal line 8B of the surface including the side surface portion described above. ₂ (0 ° ≦ θ ₂ In addition to irradiating the energy beam 53 to the second ridge portion 32 at ≦ 30 °), the energy beam 53 is irradiated so that the angle is substantially perpendicular to a line that intersects the surface portion 13 substantially perpendicularly. It is preferable to irradiate the two protrusions 32. Thus, the end 15 of the negative electrode plate 3 and the negative electrode current collecting member 4B can be connected by a simple operation without using a brazing material. Further, since the negative electrode current collector 4B alone can be dissolved and connected without damaging the metal foil body 20 constituting the negative electrode plate 3, the connection between the negative electrode current collector 4B and the negative electrode plate 3 can be made. Sufficient strength is secured. Note that “intersects substantially perpendicularly to the side surface” means that all of the side surfaces at the plurality of connection edges intersect approximately perpendicularly.
The power density of the energy beam applied to the second ridge of the negative electrode current collector is 3 kW / mm ² And more preferably 6 kW / mm ² More preferably, it is 8 kW / mm ² It is particularly preferable that the above is satisfied. 3 kW / mm ² If it is less than 1, the connection state is not good and the mechanical strength may be insufficient, which is not preferable. The upper limit of the power density is not particularly limited, but may be appropriately determined from the viewpoint of avoiding the occurrence of damage to each member used, for example, 60 kW / mm. ² The following may be sufficient.
Further, from the viewpoint of suppressing the irregular reflection of the energy ray and the occurrence of damage to the metal foil constituting the negative electrode plate, the energy ray is irradiated from the second ridge of the negative electrode current collector. The portion is preferably flat, and at least a range wider than the irradiation point is preferably flat. Furthermore, the spot diameter of the energy beam to be irradiated is preferably set to 1 mm or less, more preferably 0.8 mm or less. Thus, irradiation of unnecessary portions with energy rays can be suppressed, and in particular, occurrence of damage to the metal foil body constituting the negative electrode can be suppressed.
It is preferable that welding is performed by irradiating an energy beam with a high energy density and a small amount of heat generated by a laser or an electron beam, and that the energy beam is a continuous wave. This is preferable because irradiation can be performed with energy concentrated on the metal foil, and the occurrence of damage to the metal foil constituting the electrode plate can be suppressed. Among the lasers, a YAG laser is preferable because the focus can be satisfactorily narrowed, and the occurrence of damage to the metal foil disposed outside the focus can be further suppressed.
When irradiating the second projecting portion of the positive electrode current collecting member with an energy beam, it is preferable to use an energy beam generator capable of continuous irradiation. It is preferably 100 m / min, more preferably 1 to 30 m / min, and particularly preferably 2 to 10 m / min. Furthermore, in accordance with the number of the arranged positive electrode plates, a plurality of positive electrode current collecting members are prepared, and a plurality of positive electrode current collecting members are arranged so that their first ridges intersect substantially perpendicularly with the narrow end surface. It is preferable to arrange them continuously, whereby a plurality of positive plates can be connected by one irradiation.
On the other hand, when irradiating the second projecting portion of the negative electrode current collector with energy rays, it is preferable to use an energy ray generator capable of continuous irradiation. Further, according to the number of the arranged negative electrode plates, a plurality of negative electrode current collecting members are prepared, and a plurality of negative electrode current collecting members are continuously arranged such that their first ridges substantially perpendicularly intersect the side surface. It is preferable that the plurality of negative electrodes be connected by a single irradiation.
When the electrode current collecting member and the connection edge of the electrode plate are connected by welding, a joining auxiliary material such as a brazing material is not necessary, but may be used. When a joining auxiliary material is used, it is applied to a predetermined portion of the metal foil body and / or the electrode current collecting member constituting the electrode plate, or is sandwiched between the metal foil body and a predetermined portion of the electrode current collecting member. It is sufficient to irradiate the energy beam in the state in which it is performed.
The welding state between the electrode current collecting member and the connection edge of the electrode plate can also be changed by pressing the electrode current collecting member against the connection edge of the electrode plate constituting the wound internal electrode body. Can be good. The pressing amount at this time may be appropriately set within the range of 0.05 to 3 mm. The term "amount of pressing" as used in the present invention refers to the length (mm) of the amount by which the connection edge of the electrode plate is pulled in from the position (initial position) before being pressed by the pressing of the electrode current collecting member. Say.
Next, the main members and structure of the lithium secondary battery of the present invention and the manufacturing method will be described.
The positive electrode plate is manufactured by applying a positive electrode active material to both surfaces of a metal foil body serving as a current collecting substrate. As the metal constituting the metal foil, a metal having good corrosion resistance to a positive electrode electrochemical reaction, such as aluminum or titanium, is used. As the positive electrode active material, lithium manganate (LiMn ₂ O ₄ ) Or lithium cobaltate (LiCoO) ₂ ), Lithium nickelate (LiNiO) ₂ ) Is preferably used. However, when lithium manganate having a cubic spinel structure is used, the use of a lithium transition metal composite oxide as compared with the case where other lithium transition metal composite oxides are used is preferred. This is preferable because the resistance can be reduced. In addition, it is preferable to add carbon fine powder such as acetylene black to the positive electrode active material as a conductive auxiliary agent, and it may be arbitrarily added in the range of 2 to 10% by mass.
The stoichiometric composition of lithium manganate is LiMn ₂ O ₄ Is not limited to such a stoichiometric composition, a part of the transition element Mn contains Ti, and in addition, Li, Fe, Ni, Mg, Zn, B, Al, Co, LiM substituted by two or more elements consisting of one or more elements selected from the group consisting of Cr, Si, Sn, P, V, Sb, Nb, Ta, Mo and W _X Mn _2-X O ₄ (Where M is a substitution element and X indicates the substitution amount) is also suitably used.
When the above-described element substitution is performed, the lithium (Li) / manganese (Mn) ratio (molar ratio) is (1 + X) / ( 2-X). On the other hand, when it is substituted with a substitution element M other than lithium, it becomes 1 / (2-X). Therefore, in any case, the ratio of lithium (Li) / manganese (Mn) is always> 0.5. However, in the present invention, it is preferable to use such lithium manganate, and the stoichiometric composition (LiMn) ₂ O ₄ Since the crystal structure is further stabilized as compared with the case of using (1), excellent cycle characteristics can be imparted to the battery.
In the substitution element M, Li is + 1-valent, Li, Mn, Ni, Mg and Zn are + 2-valent, B, Al, Co and Cr are + 3-valent, Si, Ti and Sn in theory. Is +4, P, V, Sb, Nb and Ta are +5, Mo and W are +6, and LiMn ₂ O ₄ It is an element that forms a solid solution therein, but Co and Sn have +2 valence, Fe, Sb and Ti have +3 valence, Mn has +3 valence and +4 valence, and Cr has +4 valence and +6. It can be valuable. Accordingly, the various substitution elements M may exist in a state having a mixed valence, and the amount of oxygen does not necessarily need to be 4 as represented by the theoretical chemical composition, and the crystal structure May be deficient or excessive in the range for maintaining the above.
The coating of the positive electrode active material is performed by applying a slurry or paste prepared by adding a solvent, a binder, or the like to the positive electrode active material powder to a current collecting substrate by using a roll coater method or the like and drying. Then, a pressing process or the like is performed as necessary.
The negative electrode plate can be manufactured in the same manner as the positive electrode plate. As the current collecting substrate constituting the negative electrode plate, a metal foil having good corrosion resistance to a negative electrode electrochemical reaction, such as a copper foil or a nickel foil, is preferably used. As the negative electrode active material, amorphous carbonaceous materials such as soft carbon and hard carbon, and highly graphitized carbon materials such as artificial graphite and natural graphite, and more preferably, the highly graphitized carbon material is preferably a fibrous material. Used.
The separator preferably has a three-layer structure in which a lithium ion permeable polyethylene film having micropores (PE film) is sandwiched between porous lithium ion permeable polypropylene films (PP film). Used. When the temperature of the electrode body rises, the PE film softens at about 130 ° C. and the micropores are crushed, which also serves as a safety mechanism for suppressing the movement of lithium ions, that is, the battery reaction. By sandwiching the PE film with a PP film having a higher softening temperature, even when the PE film is softened, the PP film retains its shape to prevent contact and short circuit between the positive electrode plate and the negative electrode plate, It is possible to reliably suppress the reaction and ensure safety. By winding the positive electrode plate and the negative electrode plate around the outer periphery of the core through such a separator, a wound internal electrode body can be manufactured.
The total number of turns n of the wound type internal electrode body may be appropriately set according to the size and battery capacity of the battery to be manufactured, and may be arbitrarily set within the range of n = 10 to 300. Just fine. Also, the total length of the winding core may be arbitrarily set within a range of 3 to 50 cm. When n = 10 to 300 and the total length of the winding core is 3 to 50 cm, the area of the electrode plate (the positive electrode plate and the negative electrode plate) per unit of winding is determined from the inner circumference of the wound type internal electrode body. 18-3200cm as you move to the outer circumference ² Gradually increases in the range.
Next, the non-aqueous electrolyte will be described. Solvents (organic solvents) constituting the non-aqueous electrolyte include carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC) and propylene carbonate (PC), and γ-butyrolactone. A single solvent such as tetrahydrofuran and acetonitrile or a mixed solvent is suitably used.
As the electrolyte, lithium hexafluorophosphate (LiPF) ₆ ) And lithium borofluoride (LiBF) ₄ ) Or lithium perchlorate (LiClO) ₄ ), And one or more of them can be used by dissolving them in the above-mentioned organic solvent (mixed solvent). It should be noted that lithium hexafluorophosphate (LiPF), which is unlikely to undergo oxidative decomposition and has high conductivity in the nonaqueous electrolyte, ₆ ) Is preferably used.
The method of welding the current collecting member and the metal foil constituting the electrode plate (the method of manufacturing the wound internal electrode body) is as described above, and as shown in FIG. The internal electrode body 1 is inserted into the battery case 73, and the electrode lead member 72, the current collecting members (the positive current collecting member 4A, the negative current collecting member 4B), and the electrode internal terminals (the positive internal terminal 69A, the negative internal terminal 69B). And hold in a stable position. Thereafter, the battery case 73 is sealed with a battery cover (a positive battery cover 71A, a negative battery cover 71B) and impregnated with the above-described non-aqueous electrolytic solution, whereby the lithium secondary battery (tabless structure type lithium Battery).
In the present embodiment, the electrode lead member 72 is made of the same kind of metal or an alloy thereof as the positive current collector 4A, the positive internal terminal 69A, the negative current collector 4B, and the negative internal terminal 69B to be connected. (FIG. 3). Specifically, when aluminum or an aluminum alloy is used for the positive electrode internal terminal 69A and the positive electrode current collecting member 4A, aluminum or an aluminum alloy is used for the positive electrode lead member 72, and the negative electrode internal terminal 69B and the negative electrode current collecting member are used. When copper or a copper alloy is used for the member 4B, it is preferable to use copper or a copper alloy for the electrode lead member 72 of the negative electrode.
Even if the electrode lead member 72 is not used, the positive current collector 4A and the positive internal terminal 69A, and the negative current collector 4B and the negative internal terminal 69B may be directly connected and energized. Further, the portion having the tabless structure described above may be used for the positive electrode and the negative electrode, or may be used for either the positive electrode or the negative electrode. In FIG. 3, reference numeral 70A denotes a positive electrode external terminal, reference numeral 70B denotes a negative electrode external terminal, and reference numeral 75 denotes a pressure release hole.
Further, as shown in FIG. 4, the current collecting member 54 may be configured to also serve as an electrode cover. FIG. 4 shows an example in which a cylindrical battery case 73 having one open end is used, and necking is formed on one end of the battery case 73. However, the configuration in which the current collecting member 54 also serves as an electrode cover is shown. If so, the shape of the battery is not particularly limited. For example, a battery case 73 in which both ends are constricted, a battery case 73 in which both ends are open, and the like may be used. Further, FIG. 4 shows an example in which the pressure release hole 75 is provided on the positive electrode side, but a configuration having a pressure release hole on the negative electrode side may be employed.
As shown in FIG. 3, in the lithium secondary battery 68 of this embodiment, a metal foil body constituting an electrode plate and a current collecting member (positive electrode) are provided at a portion where current is drawn from the wound internal electrode body 1. By employing a configuration in which the current collecting member 4A and the negative electrode current collecting member 4B) are directly connected, it is not necessary to use a current collecting tab which is a conventional current deriving unit. Therefore, a complicated current collecting tab mounting step is not required, and productivity can be improved. Further, since the space corresponding to the length of the current collecting tab can be omitted, the whole battery is compact.
As described above, the lithium secondary battery according to the present invention has been described with reference to the embodiments, but it goes without saying that the present invention is not limited to the above embodiments. In addition, the lithium secondary battery according to the present invention is particularly preferably used for a large battery having a battery capacity of 2 Ah or more, but does not prevent application to a battery having such a capacity or less. In addition, the lithium secondary battery of the present invention has a large capacity but is miniaturized, so that it is particularly used as an on-vehicle battery that requires space saving, and further for driving a motor of an electric vehicle or a hybrid electric vehicle. It is preferably used for a power supply, and can also be suitably used for starting an engine that requires a high voltage.
[0061]
EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.
[0062]
(Preparation of wound internal electrode body)
Li with Li / Mn> 0.5 _1.05 Mn _1.95 O ₄ A positive electrode slurry prepared by adding a solvent and a binder to a material obtained by adding spinel as a positive electrode active material and acetylene black as a conductive additive in an external ratio in a range of 2 to 10% by mass to a thickness of 20 μm is added. A positive electrode plate prepared by coating both sides of an aluminum foil so as to have a thickness of about 100 μm, respectively, and a fibrous highly graphitized carbon powder as a negative electrode active material, and about 80 μm of a copper foil having a thickness of 10 μm on both sides. A negative electrode plate was prepared by coating so as to have a thickness. Next, the obtained positive electrode plate and negative electrode plate were wound (n = 65) with a separator interposed therebetween to produce a wound internal electrode body.
[0063]
(Preparation of non-aqueous electrolyte)
Various organic solvents of EC, DMC, and EMC are mixed at EC: DMC: EMC = 1: 1: 1 (volume ratio) to prepare a mixed solvent, and the mixed solvent is adjusted so that each has a concentration of 1 mol / l. A certain LiPF ₆ Was dissolved to prepare a non-aqueous electrolyte.
[0064]
(Examples 1 to 14)
As shown in FIG. 1, the cross-sectional shape of the wound internal electrode body 1 is L-shaped, inverted T-shaped, or cross-shaped on the connection edge 11 of the positive electrode plate 2 formed of a metal foil body made of aluminum. A cross-shaped positive electrode current collector 4A made of aluminum having a thickness of about 0.2 to 5 mm is placed, and a suitable pressure is applied so that the pressing amount (mm) shown in Table 1 is obtained. The current collecting member 4A was pressed against the connection edge 11 of the positive electrode plate 2. Next, the energy density is 5 to 60 KW / mm from above the positive electrode current collecting member 4A. ² The YAG laser was irradiated in four directions at a scanning speed of 0.1 to 100 m / min and welded to obtain a connection body between the positive electrode current collector 4A and the connection edge 11 of the positive electrode plate 2. The pressing amount refers to the length (mm) of the amount by which the connection edge 11 of the positive electrode plate 2 is pulled in from the position (initial position) before being pressed by the pressing of the positive electrode current collecting member 4A.
After the obtained connection body is housed in the battery case, it is heated (100 ° C., 24 hours) while reducing the pressure (1 Pa) inside the battery case through a predetermined electrolyte injection hole, and then impregnated with a non-aqueous electrolyte. (Vacuum impregnation). Next, a lithium secondary battery was fabricated by sealing the electrolyte injection hole (Examples 1 to 14). The other components and the test environment were the same for all the samples, and the influence of intrusion of moisture from the outside of the battery due to poor sealing of the battery and the like was eliminated.
[0066]
(Comparative Examples 1 and 2)
Except that the positive electrode current collecting member 4A is not pressed against the connection edge 11 of the positive electrode plate 2 (the pressing amount = 0) (see FIG. 1) (see FIG. 1), the lithium secondary battery is manufactured in the same manner as in Examples 1 to 14 described above. It was produced (Comparative Examples 1 and 2).
[0067]
(Check battery operation)
A large current test (1C to 1000A) and a low temperature test (25C to -40C) were confirmed.
[0068]
(Evaluation of welding condition)
When each battery is disassembled and the wound internal electrode body with the positive current collector connected is taken out and the positive current collector is forcibly peeled off from the tip of the metal foil, the metal foil The number of places where the tip was torn and the tip end remained on the positive electrode current collecting member side was counted as "m (number of welded parts)". Further, the ratio (%) of the number of winding units in which one or more connection points were formed to the total number of windings (n = 65) of the wound internal electrode body was calculated as “welding ratio (%)”. . Table 1 shows the results.
[0069]
[Table 1]

[0070]
(result)
As a result of battery operation confirmation (high current test and low-temperature test), it was confirmed that the batteries of Examples 1 to 14 exhibited good operation, whereas the batteries of Comparative Examples 1 and 2 were defective. Could be confirmed. Therefore, as is clear from the operation check of the battery and the results shown in Table 1, the welding ratio (the number of winding units in which one or more connection points are formed, with respect to the total number of windings of the wound internal electrode body) The batteries of Examples 1 to 14 according to the present invention having a ratio of 70% or more have characteristics such as excellent productivity and space saving, exhibit good battery operation, and have a reduced internal resistance. It turned out to be suitable for large current discharge.
[0071]
As described above, in the lithium secondary battery of the present invention, the positive electrode plate and the negative electrode plate have one or more connection points per winding unit formed by one winding with the separator interposed therebetween. Since the ratio of the number of winding units in which is formed to the total number of turns of the wound internal electrode body is equal to or greater than a predetermined ratio, the connection state between the current collecting member and the metal foil body forming the current collecting substrate And is excellent in productivity and space saving, has a reduced internal resistance, and is suitable for large-current discharge.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a connection state between a current collecting member and an electrode plate in a wound internal electrode body used in a lithium secondary battery of the present invention.
FIG. 2 is a perspective view showing an example of a wound internal electrode body used in a tab structure type lithium secondary battery.
FIG. 3 is a cross-sectional view illustrating an example of a tabless structure type lithium secondary battery.
FIG. 4 is a cross-sectional view showing another example of a tabless structure type lithium secondary battery.
FIGS. 5A to 5H are schematic views showing examples of the shape of a current collecting member constituting the lithium secondary battery of the present invention.
FIG. 6 is a perspective view schematically showing a method for welding a positive electrode current collector and a connection edge of a positive electrode plate used in the lithium secondary battery of the present invention.
FIG. 7 is a perspective view schematically showing a method of welding the negative electrode current collector and the connection edge of the negative electrode plate used in the lithium secondary battery of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Wound type internal electrode body, 2 ... Positive electrode plate, 3 ... Negative electrode plate, 4A ... Positive electrode current collecting member, 4B ... Negative electrode current collecting member, 5 ... Positive electrode current collecting tab, 6 ... Negative electrode current collecting tab, 7 ... Separator 8A: normal line of the surface including the narrow end surface, 8B: normal line of the surface including the side surface portion, 10: connection point, 11: connection edge, 12: body portion, 13: core, 15: end portion, Reference Signs List 20: Metal foil body, 21: Narrow end face, 31: First ridge, 32: Second ridge, 53: Energy ray, 54: Current collecting member, 68: Lithium secondary battery, 69A: Inside of positive electrode Terminal, 69B: negative electrode internal terminal, 70A: positive electrode external terminal, 70B: negative electrode external terminal, 71A: positive electrode battery cover, 71B: negative electrode battery cover, 72: electrode lead member, 73: battery case, 75: pressure release hole.

Claims (10)

少なくとも１枚の金属箔体からそれぞれ構成された正極板及び負極板がセパレータを介して捲回されてなる捲回型内部電極体と、前記正極板及び前記負極板の端部に、前記端部から電流を導出するためにそれぞれ接続された正極集電部材及び負極集電部材とを備え、前記正極集電部材及び／又は前記負極集電部材と、前記正極板及び／又は前記負極板の前記端部のうちの、前記正極集電部材及び／又は前記負極集電部材と接続されるべく立体的に配列された端縁（接続端縁）との接続箇所が、溶接されることにより形成されてなるリチウム二次電池であって、
前記正極板及び前記負極板が前記セパレータを介して１回の捲回により構成される捲回単位当り、１箇所以上の前記接続箇所が形成された前記捲回単位の数の、前記捲回型内部電極体の全捲回数に対する割合が、７０％以上であることを特徴とするリチウム二次電池。A wound internal electrode body formed by winding a positive electrode plate and a negative electrode plate each composed of at least one metal foil body with a separator interposed therebetween; and the end portions at the end portions of the positive electrode plate and the negative electrode plate. A positive electrode current collecting member and a negative electrode current collecting member respectively connected to derive a current from the positive electrode current collecting member and / or the negative electrode current collecting member, and the positive electrode plate and / or the negative electrode plate The end portion is formed by welding a connection point with an edge (connection edge) that is three-dimensionally arranged to be connected to the positive electrode current collecting member and / or the negative electrode current collecting member. A lithium secondary battery comprising:
The number of the winding units in which one or more connection points are formed per winding unit in which the positive electrode plate and the negative electrode plate are formed by one winding with the separator interposed therebetween, A lithium secondary battery, wherein the ratio of the internal electrode body to the total number of turns is 70% or more. 前記捲回型内部電極体の全捲回数ｎ（ｎは１以上の実数）と、前記接続箇所の数ｍ（ｍは自然数）とが、ｍ≧ｎの関係を満たす請求項１に記載のリチウム二次電池。The lithium according to claim 1, wherein a total number of turns n (n is a real number of 1 or more) of the wound internal electrode body and a number m (m is a natural number) of the connection points satisfy a relationship of m ≧ n. Secondary battery. 任意の位置の前記捲回単位における、前記捲回単位当りの前記接続箇所の数が、
前記任意の位置の前記捲回単位の内周側に位置する前記捲回単位における、前記捲回単位当りの前記接続箇所の数以上である請求項１又は２に記載のリチウム二次電池。In the winding unit at an arbitrary position, the number of the connection points per the winding unit,
3. The lithium secondary battery according to claim 1, wherein the number of the connection points per the winding unit in the winding unit located on the inner peripheral side of the winding unit at the arbitrary position is equal to or more than the number of the connection points. 前記正極板を構成する前記金属箔体及び前記正極集電部材が、アルミニウム又はアルミニウム合金からなる請求項１〜３のいずれか一項に記載のリチウム二次電池。The lithium secondary battery according to any one of claims 1 to 3, wherein the metal foil body and the positive electrode current collector constituting the positive electrode plate are made of aluminum or an aluminum alloy. 前記負極板を構成する前記金属箔体及び前記負極集電部材が、銅又は銅合金からなる請求項１〜４のいずれか一項に記載のリチウム二次電池。The lithium secondary battery according to any one of claims 1 to 4, wherein the metal foil body and the negative electrode current collector constituting the negative electrode plate are made of copper or a copper alloy. 前記正極集電部材及び／又は前記負極集電部材の形状が、十字形状、Ｙ字形状、Ｉ字形状、又は一部に切り欠きを有する円板形状である請求項１〜５のいずれか一項に記載のリチウム二次電池。The shape of the positive electrode current collecting member and / or the negative electrode current collecting member is a cross shape, a Y-shape, an I-shape, or a disc shape having a cutout in a part thereof. Item 7. The lithium secondary battery according to Item 1. 電池容量が２Ａｈ以上である請求項１〜６のいずれか一項に記載のリチウム二次電池。The lithium secondary battery according to any one of claims 1 to 6, wherein the battery capacity is 2 Ah or more. 車載用電池である請求項１〜７のいずれか一項に記載のリチウム二次電池。The lithium secondary battery according to any one of claims 1 to 7, which is a vehicle-mounted battery. 電気自動車用又はハイブリッド電気自動車用である請求項８に記載のリチウム二次電池。The lithium secondary battery according to claim 8, which is for an electric vehicle or a hybrid electric vehicle. エンジン起動用である請求項８又は９に記載のリチウム二次電池。The lithium secondary battery according to claim 8, which is for starting an engine.

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