JP2004234994A

JP2004234994A - Lithium secondary battery, battery pack of same, and electrode of same

Info

Publication number: JP2004234994A
Application number: JP2003021568A
Authority: JP
Inventors: Masanori Yoshikawa; 正則吉川; Juichi Arai; 寿一新井; Yoshimi Yanai; 吉美矢内; Takenori Ishizu; 竹規石津
Original assignee: Hitachi Ltd; Shin Kobe Electric Machinery Co Ltd
Current assignee: Hitachi Ltd; Resonac Corp
Priority date: 2003-01-30
Filing date: 2003-01-30
Publication date: 2004-08-19

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light lithium secondary cell with high power density, and a battery pack and an electrode of the same. <P>SOLUTION: The lithium secondary cell, composed of a positive electrode, a negative electrode, a separator, and nonaqueous electrolyte solution containing lithium salt, has a plurality of current collecting lead pieces arranged. One lead piece 5, 6 at every electrode area of 10 to 100 cm<SP>2</SP>is arranged at least at either the positive electrode or the negative electrode, and a width of the lead piece is made the same with or shorter than the width of an interval 16 between two adjacent lead pieces. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、新規なリチウム二次電池とその組電池及びその正極と負極に関する。
【０００２】
【従来の技術】
【特許文献１】特開平９−９２３３５号公報
【特許文献２】特開２００１−１４８２３８号公報
【０００３】
情報化社会の発達に伴ってパソコン、携帯電話等の普及が、今後益々増大することが予想される。リチウム二次電池は電池電圧が高く高エネルギー密度であるため、開発が盛んであり、パソコン、携帯電話等の電源として実用化されている。
【０００４】
しかしながら、携帯用機器以外の用途については、電力貯蔵用、電気自動車等の電源が考えられるが、これら用途に適用するには電池の大型化、長寿命化、高出力化、低コスト化が不可欠である。近年では、環境問題の観点から、特に電気自動車、ハイブリッド自動車へのリチウム電池の実用化が期待されている。このような自動車分野への適用には電池の高出力化及び軽量化が重要な課題である。高出力電池を得るには大電流が取れる電池構造、あるいは正極板、負極板の構造の改良が電池実用化のポイントとなる。リチウム電池の高出力化に関する技術が特許文献１及び特許文献２に開示されている。
【０００５】
特許文献１では電極板の集電体箔を側縁方向に沿って電極活物質を塗布していない未塗布部を設け、この未塗布部の一部を短冊上に切断し、未塗布部の大半を複数の集電リードとした構造の電池が開示されている。
【０００６】
又、特許文献２では、電極板の集電体箔を側縁方向に沿って電極活物質を全面的に塗布していない未塗布部を設け、これに切れ目を入れ、集電リードとして大電流を得る方式が開示されている。
【０００７】
【発明が解決しようとする課題】
しかし、いずれの特許文献においても、未塗布部の集電体箔の大部分を利用し、集電リードとした構造とするとリチウム電池の特長である軽量性が損なわれ、又出力密度が低下する恐れがある。リチウム電池で一般的に用いられる集電箔は、アルミニウム、銅であり、その密度は、それぞれ、２．７ｇ／ｃｍ^３、８．９ｇ／ｃｍ^３である。
【０００８】
一方、正極活物質のリチウム遷移金属複合酸化物の密度は４．３〜５．１ｇ／ｃｍ^３程度であり、また負極活物質である非晶質炭素材、黒鉛は１．５〜２．２ｇ／ｃｍ^３程度である。したがって、活物質層を相対密度６０％程度で集電体箔の厚さの１０倍設けたとしても、正極板での集電体箔の占める重量の割合は２０〜２５％程度となり、負極板ではその割合は実に４０〜５０％程度となり、電極板全体重量に占めるその割合は大きく、決して無視できるものではない。正負極板の側縁方向に全面的に未塗布部を設けこれを集電リードする構造、あるいは未塗布部の大部分を利用し集電リード片を設ける構造では、集電効率は良いが、さらに正負極板に占める集電箔の割合は増大し、リチウム電池の特長である軽量性が損なわれる。電池の軽量性が要求される電気自動車、ハイブリッド自動車への適用は困難となる。
【０００９】
本発明の目的は、出力密度が高く、軽量なリチウム二次電池とその組電池及びその電極を提供することにある。
【００１０】
【課題を解決するための手段】
本発明は、遷移金属複合酸化物を主体としリチウムの吸蔵放出が可能な正極活物質が集電体箔の両面に形成された正極と、リチウムの吸蔵放出が可能な負極活物質が集電体箔の両面に形成された負極と、リチウム塩を含む非水電解液とを有し、前記正極及び負極がセパレータを介して巻回又は積層されたリチウム二次電池において、前記正極及び負極は正極活物質及び負極活物質を有するその片面の面積１０〜１００ｃｍ^２、好ましくは２０〜７０ｃｍ^２、より好ましくは２０〜５０ｃｍ^２当たりの正極活物質及び負極活物質が設けられていない集電リード片が１個設けられ、該集電リード片の幅は隣接する集電リード片間の間隔のスペース幅と同等以下であることを特徴とする。
【００１１】
又、本発明は、正極と負極とを前記セパレータを介して捲回され、各電極幅が２５ｃｍ以下、好ましくは５〜２０ｃｍである円筒状であること、正極と負極とが前記セパレータを介して積層された角形であることが好ましい。又、前記集電リード片は、短冊条に前記正極及び負極のいずれも３〜２０ｍｍ、好ましくは５〜１０ｍｍの幅に前記集電体箔によって一体に形成されていること、集電リード片が正極及び負極となる各々に設けられた集電リード部に溶接によって接合されていること、正極集電リード部が電池蓋に溶接によって接合され負極集電リード部が電池缶に溶接によって接合されていることが好ましい。前述に記載のリチウム二次電池を直列及び並列の少なくとも一方によって接続した組電池が構成される。
【００１２】
集電リード片は、正極活物質及び負極活物質が設けられていない集電体箔によって一体に構成され、正極及び負極の各々に対して各片面の電極面積１０〜１００ｃｍ^２当たり１個設けることにより高出力密度でかつ軽量なリチウム二次電池が提供できるものである。発明者らは、集電リード片の数と、正極及び負極に対して各面積との関係を検討した結果、電極面積が１００ｃｍ^２以下では出力密度に対して影響が極めて小さく、それを過ぎると急激に出力密度が低下、特に５０ｃｍ^２以下では全く影響がないことを見出したものである。従って、集電リード片はできるだけ少なくすることが必要であり、そのため１０ｃｍ^２以上であれば出力密度に対して全く影響がなく、そして、リード片の幅は隣接するリード片間の間隔のスペース幅と同等以下とすることが、軽量化に大きな効果が得られるものである。
【００１３】
集電リード片を導出する手法としては、集電体箔の一部をリード片として取り出すのが好適であり、集電リード片の幅は、製造する電池容量、出力によって適度な幅にする。特に、前記集電リード片は、集電体箔の一部をリード片として取り出し、２〜５ｃｍ当たり５〜１０ｍｍの幅のリード片を１個形成することにより軽量で且つ高い出力密度を得ることができる。
【００１４】
電解質としては、例えばプロピレンカーボネート、エチレンカーボネート、ブチレンカーボネート、ビニレンカーボネート、ジメチルカーボネート、ジエチルカーボネート、メチルエチルカーボネート、テトラヒドロフラン、１，２−ジエトキシエタン等より少なくとも１種以上選ばれた非水溶媒に、例えばＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＢＦ４、ＬｉＰＦ６等より少なくとも１種以上選ばれたリチウム塩を溶解させた有機電解液あるいはリチウムイオンの伝導性を有する固体電解質あるいはゲル状電解質あるいは溶融塩等、一般に炭素系材料、リチウム金属、あるいはリチウム合金を負極活物質として用いた電池で使用される既知の電解質を用いることができる。また、電池の構成上の必要性に応じて微孔性セパレータを用いることができる。
【００１５】
本発明のリチウム二次電池は、電気自動車用、ハイブリッド自動車に限らず、更に高出力が必要とされる電動工具などの電源として適用可能である。
【００１６】
【発明の実施の形態】
本発明は以下に述べる実施例に限定されるものではない。
【００１７】
（実施例１）
図１は、本実施例に係るリチウム二次電池用電極の平面図である。正極材料にはスピネルマンガン酸化物を、導電剤には黒鉛を、結着剤にはポリフッ化ビニリデンを用い、８５：１０：５の重量比で、混練機で３０分混練し正極合剤を得た。正極合剤を、厚さ２０μｍ、幅１３ｃｍのアルミニウム箔にアルミニウム箔の側縁部の一方に沿って未塗布部１４を約３ｃｍにして両面に塗布した。負極材料には非晶質炭素を、結着剤にはポリフッ化ビニリデンを用い、９０：１０の重量比で正極と同様に混練し、負極合剤を厚さ２０μｍの銅箔に正極板と同様に側縁部の一方に沿って未塗布部１４を約３ｃｍにして両面に塗布した。得られた正負極板は、プレス機で圧延成型した後、１５０℃で５時間真空乾燥し、正極１及び負極２を得た。本実施例では、各活物質が形成されている塗布部１５が電極幅であり、１０ｃｍとした。
【００１８】
図１に示すように、正極板の正極合剤の未塗布部１４、及び負極板の負極合剤の未塗布部１４を、正極集電リード片５、負極集電リード片６として短冊状の所定の幅とスペース間隔１６で切断した。正極集電リード片５、負極集電リード片６として、正極板及び負極板のいずれも正負極板片面の電極面積１０ｃｍ^２（１−１）、２０ｃｍ^２（１−２）、５０ｃｍ^２（１−３）、１００ｃｍ^２（１−４）、１５０ｃｍ^２（１−５）、２００ｃｍ^２（１−６）、３００ｃｍ^２（１−７）毎に、面積１０ｃｍ^２（１−１）に対しては幅５ｍｍ、他の面積に対しては幅１０ｍｍとし、等間隔に１個設けると共に、各集電リード片の幅を電極面積１０ｃｍ^２（１−１）では隣接する集電リード片間の間隔のスペース幅と同等であるが、それ以外ではスペース幅以下である。これらの正負極板をセパレータとともに捲回し、捲回群を円筒形の電池缶４に挿入した。
【００１９】
負極リード片６はニッケルの集電リード部８に集めて超音波溶接し、集電リード部８を電池缶４の缶底に溶接した。一方、正極リード片５はアルミニウムの集電リード部７に超音波溶接した後、アルミニウムの集電リード部７を二枚の電池蓋９の下側に超音波溶接した。電解液を注入後、電池蓋９を電池缶４によってかしめて電池を得た。二枚の電池蓋９の下側には貫通孔１３を有し、その上に破裂片１０が弾性体のパッキン１１によって固定され、その上をもう一方の電池蓋９によって密封される。又、電池蓋９はガスケット１２を介して電池缶４によって固定される。二枚の電池蓋９には空隙が設けられる。
【００２０】
図２は、得られたリチウム二次電池の断面図である。充電終止電圧４．３Ｖ、放電終止電圧３．０Ｖ、充放電レート０．２５Ｃ（定格容量の４時間率）で充放電した後、満充電の状態で、１０秒間、電流を印加し、１０秒後の電圧を測定し、出力性能を調べた。
【００２１】
図３は、電池電圧と放電電流レートとの関係を示す線図である。電池の放電終止電圧（Ｖ）と電流電圧特性の直線を放電終止電圧まで外挿したときの電流値（Ｉ）及び電池重量（Ｗｔ）より、出力密度（Ｐ）を式Ｐ＝（Ｖ×Ｉ）／Ｗｔを用いて求めた。
【００２２】
表１は、リード片１個当たりの電極板面積と出力密度を示したものである。電池番号１−７の出力密度は１０００Ｗ／ｋｇ未満であり、十分な出力は得られなかった。一方、電池番号１−１は集電リード片を電池番号１−２に比較して２倍の数設けたにもかかわらず、出力密度は１％弱とわずかしか大きくならず、集電リード片の数を多くした効果はほとんど認められなかった。取り出せる最大電流の増加が認められないことは、電池番号１−２の集電リード片の数で十分に電池性能を引き出していることを示しており、これ以上の数の集電リード片を設けることは、電池重量を増加させるだけであり、リチウム電池の軽量化を損なう結果となる。
【００２３】
本実施例では、等間隔に集電リード片を設けたが、円筒形捲回群の同じ半径上の位置に集電リード片が揃うように、集電リード片の取り出し位置を中心部に近くなるに従って、隣接集電リード片の間隔が短くなるように配置した構成にしても良い。また、偏平状に捲回した電極群を用いて電池を構成してもその効果はなんら変わらない。
【００２４】
【表１】

【００２５】
図４は、集電リード片１個当たりの出力密度と電極面積との関係を示す線図である。図４に示すように、電極面積が１００ｃｍ^２以下では電極面積の増加と共に出力密度がやや低下するが大きな影響がなく、それを過ぎると急激に出力密度が低下することが明らかである。特に、電極面積が５０ｃｍ^２以下では出力密度に対して極めて影響が少ないことが明らかである。従って、集電リード片はできるだけ少なくすることが必要であり、そのため１０〜１００ｃｍ^２当たり集電リード片を１個としても出力密度に対して影響が極めて小さく、軽量化に大きな効果が得られるものである。
【００２６】
（実施例２）
本実施例は、実施例１と同様に正極及び負極を形成し、電極面積３０ｃｍ^２を一定にし、電極幅５〜４０ｃｍに種々変えて、実施例１と同等に充放電試験を行い、電極幅と出力密度との関係を調べた。又、集電リード片の幅は、電極幅５〜３０ｃｍでは５ｍｍとし、電極幅４０ｃｍでは３．５ｍｍとした。
【００２７】
【表２】

【００２８】
図５は、電極幅と出力密度との関係を示す線図である。図５に示すように、電極幅が２５ｃｍまではその幅が大きくなるに従ってやや出力密度が低下するが、１２００Ｗ／ｋｇ以上の高い出力密度を有する。しかし、それを超える幅では１０００Ｗ／ｋｇ以下の低い出力密度に急激に低下する。
【００２９】
（実施例３）
電極活物質、電極合剤などの作製法を実施例１と同様にして、電極面積３０ｃｍ^２の角形の正負極板を作製し、それぞれの正負極板１枚ごとに集電リード片を１枚設けた。作製した正負極板を、セパレータを介して積層し、角形電池を製造した。実施例１と同様に出力を調べた。その結果、出力密度１４９２Ｗ／ｋｇを得た。
【００３０】
（実施例４）
正極活物質にＬｉＣｏＯ２を用い、負極活物質に黒鉛を用いて実施例１と同様に電極板を作製した。集電リード片は５０ｃｍ^２毎に設け、電池を作製した。得られた電池の出力特性を実施例１と同様に調べた。その結果、出力密度１６３４Ｗ／ｋｇを得た。
【００３１】
（実施例５）
実施例１と同仕様の電池を４本直列に接続し組電池を構成した。集電リード片１個を導出した正負極板の片面の面積１０ｃｍ^２、２０ｃｍ^２、３０ｃｍ^２、５０ｃｍ^２、８０ｃｍ^２、１００ｃｍ^２、１３０ｃｍ^２の順に組電池の番号を５−１、５−２、５−３、５−４、５−５、５−６、５−７とする。実施例１と同様に出力を調べた。ただし、放電終止電圧を１２Ｖとして出力密度を求めた。その結果を表３に示す。
【００３２】
【表３】

【００３３】
本実施例においても、実施例１と同様に、集電リード片１個当たりの電極面積が１００ｃｍ^２以下では出力密度に対して大きな影響がなく、それを過ぎると急激に出力密度が低下することが明らかであった。
【００３４】
図６は、出力密度と電極面積との関係を示す線図である。図６に示すように、電極面積が１００ｃｍ^２以下ではその面積が大きくなるにしたがって出力密度がやや低下するが、１１００Ｗ／ｋｇ以上の高い出力密度を有する。しかし、それを過ぎると急激に出力密度が低下することが明らかである。
【００３５】
従って、電極面積を１０〜１００ｃｍ^２において出力密度に対して影響が極めて小さく、軽量化に大きな効果が得られるものである。又、集電リード片の幅は、各電極に対して接している長さが実施例２と同様な傾向であることが明らかであった。
【００３６】
（実施例６）
実施例３と同仕様の電池を４本直列に接続し組電池を構成した。実施例１と同様に出力を調べた。ただし、放電終止電圧を１２Ｖとして出力密度を求めた。その結果、出力密度１３１０Ｗ／ｋｇを得た。
【００３７】
【発明の効果】
本発明によれば、高出力密度でかつ軽量なリチウム二次電池及びその組電池を提供できるものであり、電気自動車、ハイブリッド自動車等の大容量、高出力、かつ軽量化が要求される分野への適用、更に、電動工具等の高出力かつ軽量な性能を必要とする分野への幅広い適用が可能となる。
【図面の簡単な説明】
【図１】本発明に係るリチウム二次電池の正極及び負極の平面図。
【図２】本発明に係るリチウム二次電池の断面図。
【図３】リチウム二次電池の放電電流レートと電池電圧との関係を示す線図。
【図４】出力密度と電極面積との関係を示す図。
【図５】出力密度と電極幅との関係を示す図。
【図６】出力密度と電極面積との関係を示す図。
【符号の説明】
１…正極、２…負極、３…セパレータ、４…電池缶、５…正極集電リード片、６…負極集電リード片、７…正極集電リード部、８…負極集電リード部、９…電池蓋、１０…破裂弁、１１、１２…パッキン、１４…未塗布部、１５…塗布部、１６…スペース間隔。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a novel lithium secondary battery, its assembled battery, and its positive electrode and negative electrode.
[0002]
[Prior art]
[Patent Document 1] JP-A-9-92335 [Patent Document 2] JP-A-2001-148238
With the development of the information society, the spread of personal computers and mobile phones is expected to increase further in the future. Lithium secondary batteries have a high battery voltage and a high energy density, and have been actively developed, and have been put to practical use as power sources for personal computers, mobile phones, and the like.
[0004]
However, for applications other than portable devices, power sources for power storage, electric vehicles, etc. are conceivable, but for these applications, larger batteries, longer life, higher output, and lower cost are indispensable. It is. In recent years, practical use of lithium batteries for electric vehicles and hybrid vehicles has been expected from the viewpoint of environmental problems. For such applications in the automotive field, it is important to increase the output and weight of the battery. In order to obtain a high-power battery, improvement of the battery structure capable of providing a large current, or the structure of the positive electrode plate and the negative electrode plate is an important point of practical use of the battery. Patent Literature 1 and Patent Literature 2 disclose technologies related to increasing the output of lithium batteries.
[0005]
In Patent Literature 1, the collector foil of the electrode plate is provided with an uncoated portion on which the electrode active material is not applied along the side edge direction, and a part of the uncoated portion is cut into strips. A battery having a structure in which most of the plurality of current collecting leads are used is disclosed.
[0006]
In Patent Document 2, a current collector foil of an electrode plate is provided with an uncoated portion where the electrode active material is not entirely coated along a side edge direction, and a cut is made in the uncoated portion to form a large current as a current collecting lead. Have been disclosed.
[0007]
[Problems to be solved by the invention]
However, in any of the patent documents, when the current collector lead is formed by using a large part of the current collector foil in the uncoated portion, the lightness characteristic of the lithium battery is impaired, and the output density is reduced. There is fear. Current collecting foils generally used in lithium batteries are aluminum and copper, and their densities are 2.7 g / cm ³ and 8.9 g / cm ³ , respectively.
[0008]
On the other hand, the density of the lithium transition metal composite oxide as the positive electrode active material is about 4.3 to 5.1 g / cm ³ , and the amorphous carbon material and graphite as the negative electrode active material are 1.5 to 2.2 g. / Cm ³ . Therefore, even if the active material layer is provided at a relative density of about 60% and the thickness of the current collector foil is 10 times the thickness of the current collector foil, the weight ratio of the current collector foil to the positive electrode plate is about 20 to 25%, In this case, the ratio is actually about 40 to 50%, and the ratio to the total weight of the electrode plate is large and cannot be ignored. In a structure in which an uncoated portion is entirely provided in the side edge direction of the positive / negative electrode plate and a current collecting lead is provided, or a structure in which a current collecting lead piece is provided by using most of the uncoated portion, the current collecting efficiency is good, Furthermore, the proportion of the current collector foil in the positive and negative electrode plates increases, and the light weight characteristic of the lithium battery is impaired. It becomes difficult to apply the battery to an electric vehicle or a hybrid vehicle that requires light weight.
[0009]
It is an object of the present invention to provide a light-weight lithium secondary battery having a high output density, a battery assembly thereof, and an electrode thereof.
[0010]
[Means for Solving the Problems]
The present invention relates to a positive electrode in which a positive electrode active material mainly composed of a transition metal composite oxide and capable of inserting and extracting lithium is formed on both sides of a current collector foil, and a negative electrode active material capable of inserting and extracting lithium is formed of a current collector In a lithium secondary battery having a negative electrode formed on both sides of a foil and a non-aqueous electrolyte containing a lithium salt, and wherein the positive electrode and the negative electrode are wound or laminated via a separator, the positive electrode and the negative electrode are positive electrodes active material and one side of the area 10 to 100 cm ² having a negative electrode active material, preferably 20～70Cm ^2, more preferably per 20 to 50 cm ² positive active material and the anode active material is not disposed current collecting lead pieces One current collecting lead piece is provided, and the width of the current collecting lead piece is equal to or less than the space width of the interval between adjacent current collecting lead pieces.
[0011]
Further, the present invention, the positive electrode and the negative electrode are wound through the separator, each electrode width is 25 cm or less, preferably 5 to 20 cm cylindrical, the positive electrode and the negative electrode through the separator It is preferably a laminated square shape. In addition, the current collecting lead piece is such that each of the positive electrode and the negative electrode is integrally formed in a strip with a width of 3 to 20 mm, preferably 5 to 10 mm by the current collector foil. The positive and negative electrode current collecting leads are joined to each other by welding, the positive electrode current collecting lead is joined to the battery lid by welding, and the negative electrode current collecting lead is joined to the battery can by welding. Is preferred. An assembled battery in which the above-described lithium secondary batteries are connected by at least one of series and parallel is formed.
[0012]
The current collecting lead piece is integrally formed by a current collector foil not provided with the positive electrode active material and the negative electrode active material, and one piece is provided for each of the positive electrode and the negative electrode for each electrode surface of 10 to 100 cm ^{2 on} each side. Accordingly, a lithium secondary battery having a high output density and a light weight can be provided. The present inventors have studied the relationship between the number of current collecting lead pieces and the respective areas for the positive electrode and the negative electrode. As a result, when the electrode area is 100 cm ² or less, the effect on the output density is extremely small. It has been found that the output density is sharply reduced, and in particular, there is no effect at 50 cm ² or less. Therefore, it is necessary to reduce the number of current collecting lead pieces as much as possible. Therefore, if it is 10 cm ² or more, the power density is not affected at all, and the width of the lead pieces is equal to the space width between adjacent lead pieces. When it is equal to or less than the above, a great effect on weight reduction can be obtained.
[0013]
As a method for deriving the current collecting lead piece, it is preferable to take out a part of the current collector foil as a lead piece, and the width of the current collecting lead piece is set to an appropriate width depending on the battery capacity and output to be manufactured. In particular, the current collecting lead piece is lightweight and has a high output density by taking out a part of the current collector foil as a lead piece and forming one lead piece having a width of 5 to 10 mm per 2 to 5 cm. Can be.
[0014]
As the electrolyte, for example, propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, tetrahydrofuran, at least one or more non-aqueous solvents selected from 1,2-diethoxyethane and the like, For example, generally, a carbon-based material such as an organic electrolyte solution in which at least one lithium salt selected from LiClO4, LiAsF6, LiBF4, and LiPF6 is dissolved or a solid electrolyte or a gel electrolyte or a molten salt having lithium ion conductivity, Known electrolytes used in batteries using lithium metal or a lithium alloy as a negative electrode active material can be used. Further, a microporous separator can be used according to the necessity of the battery configuration.
[0015]
The lithium secondary battery of the present invention is applicable not only to electric vehicles and hybrid vehicles, but also to a power source for an electric tool or the like that requires a higher output.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention is not limited to the embodiments described below.
[0017]
(Example 1)
FIG. 1 is a plan view of the electrode for a lithium secondary battery according to the present embodiment. Spinel manganese oxide was used as the positive electrode material, graphite was used as the conductive agent, and polyvinylidene fluoride was used as the binder. The mixture was kneaded at a weight ratio of 85: 10: 5 with a kneader for 30 minutes to obtain a positive electrode mixture. Was. The positive electrode mixture was applied to both surfaces of an aluminum foil having a thickness of 20 μm and a width of 13 cm along one of the side edges of the aluminum foil with an uncoated portion 14 of about 3 cm. Amorphous carbon is used for the negative electrode material, polyvinylidene fluoride is used for the binder, and the mixture is kneaded at a weight ratio of 90:10 in the same manner as the positive electrode. Then, the uncoated portion 14 was applied to both sides along one of the side edge portions at about 3 cm. The obtained positive and negative electrode plates were roll-formed by a press machine, and then dried in vacuum at 150 ° C. for 5 hours to obtain a positive electrode 1 and a negative electrode 2. In this embodiment, the width of the coating portion 15 on which each active material is formed has an electrode width of 10 cm.
[0018]
As shown in FIG. 1, the non-coated portion 14 of the positive electrode mixture of the positive electrode plate and the non-coated portion 14 of the negative electrode mixture of the negative electrode plate are strip-shaped as the positive current collecting lead piece 5 and the negative current collecting lead piece 6. Cutting was performed at a predetermined width and a space interval of 16. As the positive electrode current collecting lead piece 5 and the negative electrode current collecting lead piece 6, both the positive electrode plate and the negative electrode plate have an electrode area of 10 cm ² (1-1), 20 cm ² (1-2), 50 cm ² (1 -3), 100 cm ² (1-4), 150 cm ² (1-5), 200 cm ² (1-6), and 300 cm ² (1-7) every 10 cm ² (1-1) A width of 5 mm and a width of 10 mm for other areas are provided, one at a regular interval, and the width of each current collecting lead piece is set to the width of the gap between adjacent current collecting lead pieces at an electrode area of 10 cm ² (1-1). Same as the space width, but otherwise less than the space width. These positive and negative electrode plates were wound together with the separator, and the wound group was inserted into the cylindrical battery can 4.
[0019]
The negative electrode lead piece 6 was collected on a nickel current collecting lead 8 and ultrasonically welded, and the current collecting lead 8 was welded to the bottom of the battery can 4. On the other hand, the positive electrode lead piece 5 was ultrasonically welded to the aluminum current collecting lead portion 7, and then the aluminum current collecting lead portion 7 was ultrasonically welded to the lower side of the two battery lids 9. After injecting the electrolyte, the battery lid 9 was swaged with the battery can 4 to obtain a battery. A through hole 13 is provided below the two battery lids 9, on which a rupture piece 10 is fixed by an elastic packing 11, and the rupture piece 10 is hermetically sealed by the other battery lid 9. The battery cover 9 is fixed by the battery can 4 via the gasket 12. A gap is provided in the two battery lids 9.
[0020]
FIG. 2 is a cross-sectional view of the obtained lithium secondary battery. After charging and discharging at a charge end voltage of 4.3 V, a discharge end voltage of 3.0 V, and a charge / discharge rate of 0.25 C (4 hours of rated capacity), a current is applied for 10 seconds in a fully charged state, and then 10 seconds. The subsequent voltage was measured and the output performance was examined.
[0021]
FIG. 3 is a diagram showing the relationship between the battery voltage and the discharge current rate. From the current value (I) and the battery weight (Wt) obtained by extrapolating a straight line between the discharge end voltage (V) and the current-voltage characteristic of the battery to the discharge end voltage, the output density (P) is expressed by the formula P = (V × I ) / Wt.
[0022]
Table 1 shows the electrode plate area and the output density per lead piece. The output density of Battery No. 1-7 was less than 1000 W / kg, and a sufficient output was not obtained. On the other hand, the output density of battery number 1-1 is slightly less than 1%, although the number of current collecting lead pieces is twice as large as that of battery number 1-2. The effect of increasing the number was almost unrecognizable. The fact that no increase in the maximum current that can be taken out is recognized indicates that the battery performance is sufficiently derived from the number of the current collecting lead pieces of the battery number 1-2, and more current collecting lead pieces are provided. This only increases the weight of the battery, which impairs the weight saving of the lithium battery.
[0023]
In the present embodiment, the current collecting lead pieces are provided at equal intervals.However, so that the current collecting lead pieces are aligned at the same radial position of the cylindrical winding group, the position where the current collecting lead pieces are taken out is close to the center. A configuration may be adopted in which the distance between the adjacent current collecting lead pieces is reduced as much as possible. Further, even if a battery is formed by using a flatly wound electrode group, the effect is not changed at all.
[0024]
[Table 1]

[0025]
FIG. 4 is a diagram showing a relationship between an output density per one current collecting lead piece and an electrode area. As shown in FIG. 4, when the electrode area is 100 cm ² or less, the output density slightly decreases with an increase in the electrode area, but there is no significant effect, and after that, the output density sharply decreases. In particular, when the electrode area is 50 cm ² or less, it is apparent that the influence on the output density is extremely small. Therefore, it is necessary to reduce the number of current collecting lead pieces as much as possible. Therefore, even if one current collecting lead piece per 10 to 100 cm ² , the influence on the output density is extremely small, and a great effect on weight reduction can be obtained. It is.
[0026]
(Example 2)
In this example, a positive electrode and a negative electrode were formed in the same manner as in Example 1, the electrode area was kept constant at 30 cm ² , and the electrode width was variously changed to 5 to 40 cm. And the relationship between power density. The width of the current collecting lead piece was 5 mm when the electrode width was 5 to 30 cm, and was 3.5 mm when the electrode width was 40 cm.
[0027]
[Table 2]

[0028]
FIG. 5 is a diagram showing the relationship between the electrode width and the output density. As shown in FIG. 5, the output density slightly decreases as the electrode width increases up to an electrode width of 25 cm, but has a high output density of 1200 W / kg or more. However, when the width exceeds the above range, the power density sharply decreases to a low power density of 1000 W / kg or less.
[0029]
(Example 3)
A method for producing an electrode active material, an electrode mixture, and the like was performed in the same manner as in Example 1 to fabricate a square positive / negative electrode plate having an electrode area of 30 cm ² , and one current collecting lead piece for each positive / negative electrode plate. Provided. The produced positive and negative electrode plates were laminated with a separator interposed therebetween to produce a prismatic battery. The output was examined in the same manner as in Example 1. As a result, an output density of 1492 W / kg was obtained.
[0030]
(Example 4)
An electrode plate was produced in the same manner as in Example 1, except that LiCoO2 was used as the positive electrode active material and graphite was used as the negative electrode active material. A current collecting lead piece was provided every 50 cm ² to produce a battery. The output characteristics of the obtained battery were examined in the same manner as in Example 1. As a result, an output density of 1634 W / kg was obtained.
[0031]
(Example 5)
Four batteries of the same specifications as in Example 1 were connected in series to form an assembled battery. The current collecting lead pieces one one side of the area 10cm ² of the positive and negative electrode plate was ^{^{derived, 20cm 2, 30cm 2, 50cm}} 2, 80cm 2, 100cm 2, the number of the order to the battery pack of 130cm ² 5-1,5-2 , 5-3, 5-4, 5-5, 5-6, 5-7. The output was examined in the same manner as in Example 1. However, the output density was determined by setting the discharge end voltage to 12 V. Table 3 shows the results.
[0032]
[Table 3]

[0033]
Also in this embodiment, as in the case of the first embodiment, when the electrode area per one current collecting lead piece is 100 cm ² or less, there is no significant effect on the output density, and after that, the output density rapidly decreases. Was evident.
[0034]
FIG. 6 is a diagram showing the relationship between the output density and the electrode area. As shown in FIG. 6, when the electrode area is 100 cm ² or less, the output density slightly decreases as the area increases, but has a high output density of 1100 W / kg or more. However, it is clear that the power density drops sharply after that.
[0035]
Therefore, when the electrode area is 10 to 100 cm ² , the influence on the output density is extremely small, and a great effect on weight reduction can be obtained. Further, it was clear that the width of the current collecting lead piece had the same length as that of Example 2 in the length in contact with each electrode.
[0036]
(Example 6)
Four batteries of the same specifications as in Example 3 were connected in series to form an assembled battery. The output was examined in the same manner as in Example 1. However, the output density was determined by setting the discharge end voltage to 12 V. As a result, an output density of 1310 W / kg was obtained.
[0037]
【The invention's effect】
According to the present invention, it is possible to provide a lithium secondary battery having a high output density and a light weight and an assembled battery thereof, and to a field where a large capacity, a high output and a light weight are required such as an electric vehicle and a hybrid vehicle. , As well as a wide range of applications to fields requiring high output and lightweight performance, such as power tools.
[Brief description of the drawings]
FIG. 1 is a plan view of a positive electrode and a negative electrode of a lithium secondary battery according to the present invention.
FIG. 2 is a cross-sectional view of a lithium secondary battery according to the present invention.
FIG. 3 is a diagram showing a relationship between a discharge current rate of a lithium secondary battery and a battery voltage.
FIG. 4 is a diagram showing a relationship between an output density and an electrode area.
FIG. 5 is a diagram showing a relationship between an output density and an electrode width.
FIG. 6 is a diagram showing a relationship between an output density and an electrode area.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator, 4 ... Battery can, 5 ... Positive current collecting lead piece, 6 ... Negative current collecting lead piece, 7 ... Positive current collecting lead part, 8 ... Negative electrode current collecting lead part, 9 ... battery lid, 10 ... burst valve, 11, 12 ... packing, 14 ... uncoated part, 15 ... coated part, 16 ... space interval.

Claims

A positive electrode in which a positive electrode active material mainly composed of a transition metal composite oxide and capable of inserting and extracting lithium is formed on both sides of the current collector foil, and a negative electrode active material capable of inserting and extracting lithium is formed on both sides of the current collector foil. In a lithium secondary battery comprising the formed negative electrode and a non-aqueous electrolyte containing a lithium salt, wherein the positive electrode and the negative electrode are wound or laminated via a separator, each of the positive electrode and the negative electrode has an area of 10 A lithium secondary battery, wherein one current collecting lead piece is provided per 100 cm ² , and the width of the lead piece is equal to or less than the space width of the space between adjacent lead pieces.

2. The lithium secondary battery according to claim 1, wherein the positive electrode and the negative electrode have a cylindrical shape wound with the separator interposed therebetween, and the width of each of the positive electrode and the negative electrode is 25 cm or less. 3.

2. The lithium secondary battery according to claim 1, wherein the positive electrode and the negative electrode have a prismatic shape laminated with the separator interposed therebetween. 3.

An assembled battery, wherein the lithium secondary batteries according to claim 1 are connected by at least one of series and parallel.

A positive electrode active material mainly composed of a transition metal composite oxide and capable of inserting and extracting lithium is formed on both surfaces of a current collector foil, and one current collecting lead piece is provided for an area of one surface of 10 to 100 cm ^2. A positive electrode for a lithium secondary battery, wherein a width of the piece is equal to or less than a space width of a space between adjacent lead pieces.

A negative electrode active material capable of inserting and extracting lithium is formed on both surfaces of the current collector foil, and one current collecting lead piece is provided per 10 to 100 cm ^{2 of} one surface of the current collector foil, and the width of the lead pieces is adjacent to each other. A negative electrode for a lithium secondary battery, wherein the negative electrode has a width equal to or less than a space width of an interval between the two.