JP4428796B2

JP4428796B2 - Non-aqueous secondary battery

Info

Publication number: JP4428796B2
Application number: JP2000074551A
Authority: JP
Inventors: 史朗加藤; 肇木下; 静邦矢田; 治夫菊田
Original assignee: Osaka Gas Co Ltd
Current assignee: Osaka Gas Co Ltd
Priority date: 2000-03-16
Filing date: 2000-03-16
Publication date: 2010-03-10
Anticipated expiration: 2020-03-16
Also published as: JP2001266812A

Description

【０００１】
【発明の属する技術分野】
本発明は、非水系二次電池に関し、特に、蓄電システム用非水系二次電池に関する。
【０００２】
【従来の技術】
近年、省資源を目指したエネルギーの有効利用及び地球環境問題の観点から、深夜電力貯蔵及び太陽光発電の電力貯蔵を目的とした家庭用分散型蓄電システム、電気自動車のための蓄電システム等が注目を集めている。例えば、特開平６−８６４６３号公報には、エネルギー需要者に最適条件でエネルギーを供給できるシステムとして、発電所から供給される電気、ガスコージェネレーション、燃料電池、蓄電池等を組み合わせたトータルシステムが提案されている。このような蓄電システムに用いられる二次電池は、エネルギー容量が１０Ｗｈ以下の携帯機器用小型二次電池と異なり、容量が大きい大型のものが必要とされる。このため、上記の蓄電システムでは、複数の二次電池を直列に積層し、電圧が例えば５０〜４００Ｖの組電池として用いるのが常であり、ほとんどの場合、鉛電池を用いていた。
【０００３】
一方、携帯機器用小型二次電池の分野では、小型及び高容量のニーズに応えるべく、新型電池としてニッケル水素電池、リチウム二次電池の開発が進展し、１８０Ｗｈ／ｌ以上の体積エネルギー密度を有する電池が市販されている。特に、リチウムイオン電池は、３５０Ｗｈ／ｌを超える体積エネルギー密度の可能性を有すること、及び、安全性、サイクル特性等の信頼性が金属リチウムを負極に用いたリチウム二次電池に比べ優れることから、その市場を飛躍的に延ばしている。
【０００４】
これを受け、蓄電システム用大型電池の分野においても、高エネルギー密度電池の候補として、リチウムイオン電池をターゲットとし、リチウム電池電力貯蔵技術研究組合（ＬＩＢＥＳ）等で精力的に開発が進められている。
【０００５】
これら大型リチウムイオン電池のエネルギー容量は、１００Ｗｈから４００Ｗｈ程度であり、体積エネルギー密度は、２００〜３００Ｗｈ／ｌと携帯機器用小型二次電池並のレベルに達している。その形状は、直径５０ｍｍ〜７０ｍｍ、長さ２５０ｍｍ〜４５０ｍｍの円筒型、厚さ３５ｍｍ〜５０ｍｍの角形又は長円角形等の扁平角柱形が代表的なものである。
【０００６】
また、薄型のリチウム二次電池については、薄型の外装に、例えば、金属とプラスチックをラミネートした厚さ１ｍｍ以下のフィルムを収納したフィルム電池（特開平５−１５９７５７号公報、特開平７−５７７８８号公報等）、厚さ２ｍｍ〜１５ｍｍ程度の小型角型電池（特開平８−１９５２０４号公報、特開平８−１３８７２７号公報、特開平９−２１３２８６号公報等）が知られている。これらのリチウム二次電池は、いずれも、その目的が携帯機器の小型化及び薄型化に対応するものであり、例えば携帯用パソコンの底面に収納できる厚さ数ｍｍでＪＩＳＡ４サイズ程度の面積を有する薄型電池も開示されているが（特開平５−２８３１０５号公報）、エネルギー容量が１０Ｗｈ以下であるため、蓄電システム用二次電池としては容量が小さ過ぎる。
【０００７】
【発明が解決しようとする課題】
扁平形状の電池の場合、放熱性を向上させる目的から電池の厚みを薄くするに従い、電池表裏面積は大きくなる。又高いエネルギー密度を維持するためには、特に、蓄電システムに用いられる大型リチウム二次電池（エネルギー容量３０Ｗｈ以上）において扁平形状の電池を試作する場合は、その傾向が強く、例えば、１００Ｗｈ級の厚さ６ｍｍのリチウムイオン電池の場合、電池表裏面の大きさは、６００ｃｍ²（片面）と非常に大きい。
【０００８】
一般的に携帯機器用の小型リチウムイオン電池においては、機器の故障による誤作動や使用者側の誤用によって過充電や外部短絡といった状態になると、電池内部が加熱されて電解液が分解されたり蒸発したりすることにより内部でガスが発生する。よって内圧上昇に伴う事故を防止するためには、例えば特開平６−３６７５２に記載されている様に動作圧が高い範囲１〜２ＭＰａで設計されている安全弁が容器の蓋や底に備えられている。
【０００９】
しかしながら電池表裏面が大きくかつ容器厚さが薄い大型電池に上述のような一般的な安全機構を設けた場合、電池内部でガスが発生し内圧が上昇するような異常事態において小型電池では問題にならない低い圧力であっても容器、特にその表裏面が容易に膨らみ、安全機構が充分に働かないまま発火や爆発を誘発しかねない危険な状態におちいるという問題があった。
【００１０】
本発明の目的は、上記問題点を解決すべく、異常時に発火や爆発といった事故を確実に防止できる安全性の高い扁平形状の非水系二次電池を提供することにある。
【００１１】
本発明の更なる目的は、３０Ｗｈ以上の大容量且つ１８０Ｗｈ／ｌ以上の体積エネルギー密度を有し、放熱特性に優れた安全性の高い非水系二次電池を提供する事にある。
【００１２】
【課題を解決するための手段】
本発明の上記目的は、正極、負極、セパレータ、及びリチウム塩を含む非水系電解質を備える扁平形状の電池容器にて密閉されエネルギー容量が３０Ｗｈ以上且つ体積エネルギー密度が１８０Ｗｈ／ｌ以上で作動圧が５ｋＰａ以上５００ｋＰａ未満である非水系二次電池であって、前記扁平形状をなす電池容器の広平面部に配置され容器外周から該広平面部の重心に至る距離の６０％以内の外周寄りの範囲に少なくともその一部分を含み前記作動圧により破断する薄肉部と、前記広平面部の重心と前記薄肉部両端の各々とを通る２本の直線で区画された広平面内部の内、前記薄肉部を含む領域内であって該薄肉部より外側の範囲に少なくともその一部分が含まれるように形成された変形防止部とを有することを特徴とする非水系二次電池により達成される。
【００１３】
前記変形防止部は、前記領域内であって容器外周から前記広平面の重心に至る距離の３０％以内の外周寄りの範囲に少なくともその一部が形成されていることが好ましい。
【００１４】
前記薄肉部は、少なくとも一つの直線状又は曲線状の溝で形成されていることが好ましい。
【００１５】
前記変形防止部は、電池容器の一部を薄肉とすることにより形成されていることが好ましく、少なくとも一つの直線状又は曲線状の溝により形成されていることが好ましい。
【００１６】
前記変形防止部は、電池容器に設けられた直線状又は曲線状のリブにより形成しても良い。
【００１７】
前記電池容器が多角形の扁平形状をなし、前記薄肉部を構成する溝は、該多角形の重心と角部とを結ぶ仮想直線を横切るように配置されており、前記溝のなす曲線の接線又は直線と、前記仮想直線の垂線との交角が±６０度の範囲内に設定されていることが好ましい。
【００１８】
前記変形防止部を構成する曲線状溝の接線又は直線状溝が、前記扁平平面の外周線に対して±２０度以内の角度をなすように設けられていることが好ましい。
【００１９】
前記変形防止部は、前記仮想直線を挟んで対向配置され、且つ、対向配置された変形防止部同士が互いに離隔配置されるとともに、各々の変形防止部が前記薄肉部とも離隔配置されていることが好ましい。
【００２０】
前記電池容器の広平面の形状は、矩形であることが好ましい。
【００２１】
前記非水系二次電池は、厚さが１２ｍｍ未満の扁平形状であることが好ましい。
【００２２】
前記電池容器の板厚は、０．２ｍｍ以上１ｍｍ以下であることが好ましい。
【００２３】
【発明の実施の形態】
以下、本発明の一実施の形態の非水系二次電池について図面を参照しながら説明する。図１は、本発明の一実施の形態の扁平な矩形（ノート型）の蓄電システム用非水系二次電池の平面図及び側面図を示す図であり、図２は、図１に示す電池の内部に収納される電極積層体の構成を示す側面図である。
【００２４】
図１及び図２に示すように、本実施の形態の非水系二次電池は、上蓋１及び底容器２からなる電池ケース（電池容器）と、該電池ケースの中に収納されている複数の正極１０１ａ、負極１０１ｂ、１０１ｃ、及びセパレータ１０４からなる電極積層体とを備えている。本実施の形態のような扁平型非水系二次電池の場合、正極１０１ａ、負極１０１ｂ（又は積層体の両外側に配置された負極１０１ｃ）は、例えば、図２に示すように、セパレータ１０４を介して交互に配置されて積層されるが、本発明は、この配置に特に限定されず、積層数等は、必要とされる容量等に応じて種々の変更が可能である。
【００２５】
各正極１０１ａの正極集電体１０５ａは、正極端子３に電気的に接続され、同様に、各負極１０１ｂ、１０１ｃの負極集電体１０５ｂは、負極端子４に電気的に接続されている。正極端子３及び負極端子４は、電池ケースすなわち上蓋１と絶縁された状態で取り付けられている。上蓋１及び底容器２は、図１中の拡大図に示したＡ点で全周を上蓋を溶かし込み、溶接されている。上蓋１には、電解液の注液口５が開けられており、電解液注液後、アルミニウム-変性ポリプロピレンラミネートフィルム、アルミニウム-変性ポリエチレンラミネートフィルムに代表される水分透過率の低い熱可塑性フィルム６を用いて、熱融着にて封口される。
【００２６】
封口工程においては、電池内の圧力を大気圧未満とすることが好ましい。好ましくは６５０ｔｏｒｒ以下、更に好ましくは５５０ｔｏｒｒ以下で行う。この圧力は、使用するセパレータ、電解液の種類、電池缶の素材、厚み、電池の形状を加味して決定されるものである。内圧が大気圧以上の場合、電池が設計厚みより大きくなる、あるいは、厚みバラツキが大きくなり、電池の内部抵抗、容量がばらつく原因となる。
【００２７】
図１及び図２に示す非水系二次電池の形状は、例えば縦３００ｍｍ×横２１０ｍｍ×厚さ６ｍｍであり、正極１０１ａにＬｉＭｎ₂Ｏ₄、負極１０１ｂ、１０１ｃに炭素材料を用いるリチウム二次電池の場合、例えば、蓄電システムに用いることができる。
【００２８】
正極１０１ａに用いられる正極活物質としては、リチウム系の正極材料であれば、特に限定されず、リチウム複合コバルト酸化物、リチウム複合ニッケル酸化物、リチウム複合マンガン酸化物、或いはこれらの混合物、更にはこれら複合酸化物に異種金属元素を一種以上添加した系等を用いることができ、高電圧、高容量の電池が得られることから、好ましい。また、安全性を重視する場合、熱分解温度が高いマンガン酸化物が好ましい。このマンガン酸化物としてはＬｉＭｎ₂Ｏ₄に代表されるリチウム複合マンガン酸化物、更にはこれら複合酸化物に異種金属元素を一種以上添加した系、さらにはリチウム、酸素等を量論比よりも過剰にしたＬｉＭｎ₂Ｏ₄が挙げられる。
【００２９】
負極１０１ｂ、１０１ｃに用いられる負極活物質としては、リチウム系の負極材料であれば、特に限定されず、リチウムをドープ及び脱ドープ可能な材料であることが、安全性、サイクル寿命などの信頼性が向上し好ましい。リチウムをドープ及び脱ドープ可能な材料としては、公知のリチウムイオン電池の負極材として使用されている黒鉛系物質、炭素系物質、錫酸化物系、ケイ素酸化物系等の金属酸化物、或いはポリアセン系有機半導体に代表される導電性高分子等が挙げられる。特に、安全性の観点から、１５０℃前後の発熱が小さいポリアセン系物質又はこれを含んだ材料が望ましい。
【００３０】
セパレータ１０４の構成は、特に限定されるものではないが、単層又は複層のセパレータを用いることができ、少なくとも1枚は不織布を用いることが好ましく、サイクル特性が向上する。また、セパレータ１０４の材質は、特に限定されるものではないが、例えばポリエチレン、ポリプロピレンなどのポリオレフィン、ポリアミド、クラフト紙、ガラス等が挙げられるが、ポリエチレン、ポリプロピレンが、コスト、含水などの観点から好ましい。また、セパレータ１０４として、ポリエチレン、ポリプロピレンを用いる場合、セパレータの目付量は、好ましくは５ｇ／ｍ²以上３０ｇ／ｍ²以下であり、より好ましくは５ｇ／ｍ²以上２０ｇ／ｍ²以下であり、さらに好ましくは８ｇ／ｍ²以上２０ｇ／ｍ²以下である。セパレータの目付量が３０ｇ／ｍ²を越える場合、セパレータが厚くなり過ぎたり、又は気孔率が低下し、電池の内部抵抗が高くなるので好ましくなく、５ｇ／ｍ²未満の場合、実用的な強度が得られないので好ましくない。
【００３１】
本実施の形態の非水系二次電池の電解質としては、公知のリチウム塩を含む非水系電解質を使用することができ、正極材料、負極材料、充電電圧等の使用条件により適宜決定され、より具体的にはＬｉＰＦ₆、ＬｉＢＦ₄、ＬｉＣｌＯ₄等のリチウム塩を、プロピレンカーボネート、エチレンカーボネート、ジエチルカーボネート、ジメチルカーボネート、メチルエチルカーボネート、ジメトキシエタン、γーブチルラクトン、酢酸メチル、蟻酸メチル、或いはこれら２種以上の混合溶媒等の有機溶媒に溶解したもの等が例示される。また、電解液の濃度は特に限定されるものではないが、一般的に０．５ｍｏｌ／ｌから２ｍｏｌ／ｌが実用的であり、該電解液は当然のことながら、水分が１００ｐｐｍ以下のものを用いることが好ましい。なお、本明細書で使用する非水系電解質とは、非水系電解液、有機電解液を含む概念を意味するものであり、また、ゲル状又は固体の電解質も含む概念を意味するものである。
【００３２】
上記のように構成された非水系二次電池は、家庭用蓄電システム（夜間電力貯蔵、コージェネレション、太陽光発電等）、電気自動車等の蓄電システム等に用いることができ、大容量且つ高エネルギー密度を有することができる。この場合、エネルギー容量は、好ましくは３０Ｗｈ以上、より好ましくは５０Ｗｈ以上であり、且つエネルギー密度は、好ましくは１８０Ｗｈ／ｌ以上、より好ましくは２００Ｗｈ／ｌである。エネルギー容量が３０Ｗｈ未満の場合、或いは、体積エネルギー密度が１８０Ｗｈ／ｌ未満の場合は、蓄電システムに用いるには容量が小さく、充分なシステム容量を得るために電池の直並列数を増やす必要があること、また、コンパクトな設計が困難となることから蓄電システム用としては好ましくない。
【００３３】
ところで、一般に、蓄電システム用の大型リチウム二次電池（エネルギー容量３０Ｗｈ以上）においては、高エネルギー密度が得られるものの、その電池設計が携帯機器用小型電池の延長にあることから、直径又は厚さが携帯機器用小型電池の３倍以上の円筒型、角型等の電池形状とされる。この場合には、充放電時の電池の内部抵抗によるジュール発熱、或いはリチウムイオンの出入りによって活物質のエントロピーが変化することによる電池の内部発熱により、電池内部に熱が蓄積されやすい。このため、電池内部の温度と電池表面付近の温度差が大きく、これに伴って内部抵抗が異なる。その結果、充電量、電圧のバラツキを生じ易い。また、この種の電池は複数個を組電池にして用いるため、システム内での電池の設置位置によっても蓄熱されやすさが異なって各電池間のバラツキが生じ、組電池全体の正確な制御が困難になる。更には、高率充放電時等に放熱が不十分な為、電池温度が上昇し、電池にとって好ましくない状態におかれることから、電解液の分解等よる寿命の低下、更には電池の熱暴走の誘起など信頼性、特に、安全性に問題が残されていた。
【００３４】
本実施の形態の扁平形状の非水系二次電池は、放熱面積が大きくなり、放熱に有利であるため、上記のような問題も解決することができる。すなわち、本実施の形態の非水系二次電池は、扁平形状をしており、その厚さは、好ましくは１２ｍｍ未満、より好ましくは１０ｍｍ未満、さらに好ましくは８ｍｍ未満である。厚さの下限については電極の充填率、電池サイズ（薄くなれば同容量を得るためには面積が大きくなる）を考慮した場合、２ｍｍ以上が実用的である。電池の厚さが１２ｍｍ以上になると、電池内部の発熱を充分に外部に放熱することが難しくなること、或いは電池内部と電池表面付近での温度差が大きくなり、内部抵抗が異なる結果、電池内での充電量、電圧のバラツキが大きくなる。なお、具体的な厚さは、電池容量、エネルギー密度に応じて適宜決定されるが、期待する放熱特性が得られる最大厚さで設計するのが、好ましい。
【００３５】
また、本実施の形態の非水系二次電池の形状としては、例えば、扁平形状の表裏面が角形、円形、長円形等の種々の形状とすることができ、角形の場合は、一般に矩形であるが、三角形、六角形等の多角形とすることもできる。さらに、肉厚の薄い円筒等の筒形にすることもできる。筒形の場合は、筒の肉厚がここでいう厚さとなる。また、製造の容易性の観点から、電池の扁平形状の表裏面が矩形であり、図１に示すようなノート型の形状が好ましい。
【００３６】
電池ケースとなる上蓋１及び底容器２に用いられる材質は、電池の用途、形状により適宜選択され、特に限定されるものではなく、鉄、ステンレス鋼、アルミニウム等が一般的であり、実用的である。また、電池ケースの厚さも電池の用途、形状或いは電池ケースの材質により適宜決定され、特に限定されるものではない。好ましくは、その電池表面積の８０％以上の部分の厚さ（電池ケースを構成する一番面積が広い部分の厚さ）が０．２ｍｍ以上である。上記厚さが０．２ｍｍ未満では、電池の製造に必要な強度が得られないことから望ましくなく、この観点から、より好ましくは０．３ｍｍ以上である。また、同部分の厚さは、１ｍｍ以下であることが望ましい。この厚さが１ｍｍを超えると、電極面を押さえ込む力は大きくなるが、電池の内容積が減少し充分な容量が得られないこと、或いは、重量が重くなることから望ましくなく、この観点からより好ましくは０．７ｍｍ以下である。
【００３７】
上記のように、非水系二次電池の厚さを１２ｍｍ未満に設計することにより、例えば、該電池が３０Ｗｈ以上の大容量且つ１８０Ｗｈ／ｌの高エネルギー密度を有する場合、高率充放電時等においても、電池温度の上昇が小さく、優れた放熱特性を有することができる。従って、内部発熱による電池の蓄熱が低減され、結果として電池の熱暴走も抑止することが可能となり信頼性、安全性に優れた非水系二次電池を提供することができる。
【００３８】
次に、上記の様に構成された本発明の非水系二次電池に具備する安全機構について詳細に説明する。安全機構は電池容器に形成された薄肉部を有しており、この薄肉部は、電池容器に一定以上の内部圧力が生じると破断する安全弁として作用する。この安全弁の作動圧（電池内部の上昇した圧力と大気圧との差）は、下限が、好ましくは、５ｋＰａ以上、より好ましくは２０ｋＰａ以上、上限が、好ましくは５００ｋＰａ未満、より好ましくは１２０ｋＰａ未満、特に好ましくは８０ｋＰａ未満である。この作動圧は、電池の形状、厚み、電池容器の素材、電池の容量、使用するセパレータ、電解液の種類等により適宜設計されるが、作動圧が上記下限未満であると通常使用時にも作動してしまう可能性があり好ましくない。又作動圧が上記上限以上の場合、電池内部にガスが発生する異常事態においても安全弁が働かず容易に膨張変形し発火や爆発を誘発させる危険性がある。本発明において安全弁の個数は、少なくとも１個以上であればよく、特に２個以上の複数の安全弁を設けてもよい。
【００３９】
安全弁を配置させる場所については、図３（ａ）の斜線領域５１に示す様に扁平形状をなす電池容器の広平面部内に配置し、広平面の外周から所定距離の範囲に少なくともその一部分を含むように設けるのが望ましい。その外周寄りの範囲は、容器外周から該広平面部の重心に至る距離の６０％以内の外周寄りの範囲とするのが望ましく、４０％以内の範囲とするのがさらに望ましい。電池の広平面が大きくかつ容器厚さが薄い場合、上述の通り容器は膨らみ安い。その度合いは使用する電池の形状、厚み、電池容器の素材に依存するが、特に外周から広平面部の重心に至る距離の６０％以内の外周寄りの範囲に容器の膨らみに伴う歪みが発生し易い。この歪みは、外周から重心に至る距離の４０％以内の外周寄りの範囲においてさらに大きくなる傾向を示す。これは、上記範囲において、容器壁を変形させる力が大きく作用していることを意味する。また、内圧の上昇に伴って容器壁全体に作用する応力が、この範囲に伝搬して集中的に作用しているとも言える。したがって、これらの範囲に安全弁を設けると、容器内圧が低圧でも、安全弁を設けた箇所には集中した大きな応力が作用し、確実に作動させることができる。逆に、上記範囲より重心よりの範囲にのみ安全弁を設けると、その範囲は、容器が膨らんだときにあまり変形せずにそのまま持ち上げられる傾向を示し、変形曲率が小さく平らに近い状態を保つため、安全弁を作動させる力が作用し難い。
【００４０】
電池容器の広平面部の形状が矩形等、多角形の場合には、そのコーナー部近傍に設けると、そこに歪みが集中するので、その歪みを有効に利用でき、確実な作動を得る上で好ましい。また、このように、電池容器の内圧の集中による歪みを利用して作動さる安全弁であるので、内部ガスにより容器が膨らむというような異常事態でない通常状態においては、多少の外圧によっては不用意な開口は起こらない。
【００４１】
さらに、図４に示すように、広平面部の重心と前記薄肉部（６４）両端の各々とを通る２本の直線ｍ、ｎで区画された広平面内部の内、前記薄肉部を含む領域内であって該薄肉部より外側の範囲に少なくともその一部分が含まれるように形成された変形防止部（６５）とを備え、該変形防止部は、図３（ｂ）の斜線領域５２に示す様に前記扁平形状をなす電池容器の広平面部に配置され、容器外周から該広平面の重心に至る距離の３０％以内の外周寄りの範囲に少なくともその一部分を含んだ前記薄肉部とは異なる少なくとも一つ以上の薄肉により形成した変形防止部が形成されていると、内圧が上昇し前記電池容器の中央部が持ち上がるように膨らんだときに、より外周側の変形を抑制する効果がある。膨張する部分と外周側の変形歪み度合いの差が大きい程、前記安全弁の開口面積を広くさせ、異常時内部の蓄熱を素早く外部へ放出させることができより好ましい。この抑制効果は、外周から重心に至る距離の２０％以内の外周寄りの範囲においてさらに大きい。変形防止部は、前記薄肉部と同様の薄肉により形成することができ、或いは、リブを設けることにより形成することができる。
【００４２】
薄肉部を備えた安全弁としては、薄い金属箔を冷間圧接させたラプチャーディスク部品を取り付ける方式や、容器の一部を薄肉加工して弱くさせる方法等を採用することができるが、好ましくは前記薄肉部が、容器広平面部側に形成された少なくとも一つの直線又は曲線の溝とされる。この溝は、例えば切溝加工により形成することができる。
【００４３】
図４を用いて、線状溝の配置を説明する。図４に示す電池容器は広平面が矩形形状であり、直線状溝６４又は曲線状溝６４の接線６４ａは、矩形の重心（中心）Ｇ及び角部とを結ぶ仮想直線６１を横切るように配置されており、前記溝のなす直線又は曲線の接線が、前記仮想直線の垂線に対して±６０度以内の角度をなすように設けられているのが望ましい。これは、容器が膨らむときに生じる広平面部での歪みは、仮想直線６１を横切る方向において大きいからである。したがって、角６２を上記範囲とすることにより、大きな歪みが生じる方向に溝を沿わすことができ、その結果低い容器内圧で破断開口し易い安全弁とすることができるのである。溝のなす角６２が３０度未満では、容器が膨らむときに大きな歪みを生じずに持ちあがることとなり、低圧で確実に作動させることが難しい。この例のように容器広平面が矩形の場合は、その重心と角部とを結ぶ仮想直線は、勿論対角線となる。なお、容器広平面部が、矩形以外の多角形の場合でも、直線状溝又は曲線状溝の接線が、多角形の重心（中心）及び角部を結ぶ仮想直線を横切るように配置され、前記溝のなす直線又は曲線の接線が、前記仮想直線の垂線に対して±６０度以内の角度をなすように設けられることにより、上記と同様の作用が得られる。
【００４４】
前述のように広平面部側に上記の角度範囲内で安全弁の溝を形成することにより、弁開放時に電池内容物が周囲へ飛散することも防止できる。安全弁の溝は、その形状、薄肉部厚さの設計により予め決定された前記所定圧力の範囲で開口させることができる。また、安全弁を容器広平面部側に設けることにより大きな開口面積を持たせて素早く内部ガスを抜き出すことが可能となる。さらに、保護カバーが必要でかつ設備投資も大きいラプチャーディスクと比較して、コストを低減することができる点でもより好ましい。
【００４５】
また前記薄肉部とは異なる少なくとも一つ以上の歪みを抑制させるための変形防止部は、前記容器扁平平面側に少なくとも一つの直線状又は曲線状の溝であることが望ましい。さらには歪みを抑制させる効果のある前記一つの直線状溝又は曲線状溝の接線が、前記扁平平面の外周線に対して±２０度以内の角度をなすように設けられていることがより好ましい。なぜならば外周線に対して２０度以上の角度をなすと、前記容器が膨れてきたときに膨れを抑制する効果がなくそのまま持ち上げられ、開口面積を大きくすることができないからである。図４を用いて、前記歪みを抑制させるための線状溝の配置を説明する。図４に示す電池容器は広平面が矩形形状であり、直線状溝６５又は曲線状溝６５の接線６５ａは、前記安全弁より角部側の外周に沿う位置にあり、前記溝のなす直線又は曲線の接線が、前記外周線との平行線に対して±２０度以内の角度をなすように設けられている。
【００４６】
安全弁の製造方法は特に限定されないが、前述した切溝加工方式の場合エッチングやプレスなどの方式により、任意の形状で所定の厚さを残し薄肉部の切り溝加工を行う事が出来る。図５には溝加工式の安全弁と歪みを抑制させる溝部とを組み合せた種々の例を示す。上蓋1表面の周囲近傍でかつコーナー付近７１に大きな薄肉部切り溝加工部７２を設けより外周側に外周線に沿った溝加工部８２を設けると、低い圧力でかつ大きな開口面積を持つ安全弁となる。図中７２ａは直線状、７２ｂは円弧状、７２ｃは円の一部のみ残した形状、７２ｄはＸ印形状の溝方式安全弁である。
【００４７】
【実施例】
以下、本発明の実施例を示し、本発明をさらに具体的に説明する。
（実施例１）
（１）図１に示すように、底容器２は、０．５ｍｍのＳＵＳ３０４製薄板を深さ５ｍｍに絞り作成し、電池の上蓋１も厚さ０．５ｍｍのＳＵＳ３０４製薄板で作成した。電池外形寸法は短辺側で２１０ｍｍ、長辺側で３００ｍｍとおよそＪＩＳ規格Ａ４サイズと同等とした。該上蓋には、アルミ製の正極端子及び銅製の負極端子３、４（６ｍｍφ、先Ｍ3のねじ切り）を取り付けた。正極及び負極端子３、４は、ポリプロピレン製ガスケットで上蓋１と絶縁した。該底容器２内へ電極積層体を挿入せずに上蓋１を配置し、図１の角部Ａを全周に亘りレーザー溶接して電池外装体のみの組立品を作製した。
【００４８】
（２）該上蓋１のコーナー部（図５のコーナー部７１）に図５に溝７２ａとしてした形状及び幅０．５ｍｍ深さ０．０４ｍｍ長さ６０ｍｍの寸法の直線状溝をエッチング加工により形成し安全弁とした。この溝は、コーナー部の両辺より１０ｍｍずつ内側を結び、矩形状上蓋の重心及び角部を結ぶ直線を横切るように形成されており、前記直線状溝が、前記直線（対角線）の垂線に対して短辺側で角部の方へ１０度の角度をなすように設けられている。また該上蓋１のコーナー部（図５のコーナー部７１部のより外周側）に図５に溝８２として形状及び幅０．５ｍｍ深さ０．０３ｍｍ長さ２０ｍｍの寸法の直線状溝２本をエッチング加工により歪みを抑制させる溝を形成させた。この溝はコーナーより８ｍｍずつ入った内側から両辺に並行に形成された直線状溝である。
【００４９】
（３）上記のようにして得られた電池外装体のみの組立品に、注液口５を使って電池内圧を上昇させていき安全弁の開口試験を行ったところ、４０ｋＰａと低い圧力で素早く作動し電池の膨張後厚さも１８ｍｍでとどまった。また開口部の幅は２ｍｍと大きかった。尚前記歪みを抑制させる溝を形成させずに同様の電池外装体のみの組立品を作製し、注液口５を使って電池内圧を上昇させていき安全弁の開口試験を行ったところ、同様に４０ｋＰａと低い圧力で素早く作動し電池の膨張後厚さも１８ｍｍでとどまった。しかし開口部の幅は０．５ｍｍであった。
【００５０】
（実施例２）
実施例1の（２）の安全弁構造以外は実施例1と同様に電池外装体のみの組立品を作製した。電池上蓋１のコーナー部に、図５のコーナー部７１部における溝７２ｂのような位置及び形状、幅０．５ｍｍ、深さ０．０４ｍｍの寸法で、両辺より５０ｍｍ内側の点を中心とし半径４０ｍｍ内角９０度の、コーナー側への凸をなす円弧状切溝をエッチング加工して安全弁を作製した。上記のようにして得られた電池外装体のみの組立品に、注液口５を使って電池内圧を上昇させ安全弁の開口試験を行ったところ、５０ｋＰａと低い圧力で素早く作動し電池の膨張後厚さも２２ｍｍでとどまった。また開口部の幅は１．５ｍｍであった。
【００５１】
（実施例３）
実施例1の（２）の安全弁構造及び歪みを抑制させる溝を電池上蓋１のコーナー部に作製して実際の電池を以下の様に組み立てた。
【００５２】
（１）ＬｉＣｏ２Ｏ４１００重量部、アセチレンブラック８重量部、ポリビニリデンフルオライド（ＰＶＤＦ）３重量部をＮ−メチルピロリドン（ＮＭＰ）１００重量部と混合し正極合材スラリーを得た。該スラリーを集電体となる厚さ２０μｍのアルミ箔の両面に塗布、乾燥した後、プレスを行い、正極を得た。図４は電極の説明図である。本実施例において正極１０１aの塗布面積（Ｗ１×Ｗ２）は、262.5×192ｍｍ２であり、２０μｍの集電体１０5aの両面に103μｍの厚さで塗布されている。その結果、電極厚さｔは226μｍとなっている。また、電極の短辺側には電極が塗布されていない耳部分があり、φ3の穴が開けられている。
【００５３】
（２）黒鉛化メソカーボンマイクロビーズ（ＭＣＭＢ、大阪ガスケミカル製、品番６−２８）１００重量部、ＰＶＤＦ１０重量部をＮＭＰ９０重量部と混合し、負極合材スラリーを得た。該スラリーを集電体となる厚さ１４μｍの銅箔の両面に塗布、乾燥した後、プレスを行い、負極を得た。図４を用いて説明する。負極１０１ｂ又は101ｃの塗布面積（Ｗ１×Ｗ２）は、267×195ｍｍ２であり、18μｍの集電体１０5ｂの両面に108μｍの厚さで塗布されている。その結果、電極厚さｔは２３４μｍとなっている。また、電極の短辺側には電極が塗布されていない耳部分があり、φ3の穴が開けられている。更に、同様の手法で片面だけに塗布し、それ以外は同様の方法で厚さ126μｍの片面電極を作成した。片面電極は（３）項の電極積層体において外側に配置される（図２中１０１ｃ）。
【００５４】
（３）上記（１）項で得られた正極８枚、負極９枚（内片面２枚）を図２に示すようにセパレータ１０４a（ポリプロピレン不織布:ニッポン高度紙工業、ＭＰ1050、目付10ｇ/ｍ2）とセパレータ104ｂ（ポリエチレン製微孔膜；旭化成工業HIPORE6022,目付13.3ｇ/ｍ2)を介して（図2中104として標記されている）、交互に積層し電極積層体を作成した。セパレータ104ｂは正極側に配置した。また、容器との絶縁の為、積層体の外側の負極板101ｃの更に外側にセパレーター104ｂを配置した。
【００５５】
（４）電池の底容器２（図１参照）は、０．５ｍｍのＳＵＳ３０４製薄板を深さ５ｍｍに絞り作成した。また、電池の上蓋１も厚さ０．５ｍｍのＳＵＳ３０４製薄板で作成した。該上蓋には、アルミ製の正極端子及び銅製の負極端子３、４（６ｍｍφ、先Ｍ3のねじ切り）を取り付けるた。正極及び負極端子３、４は、ポリプロピレン製ガスケットで上蓋１と絶縁されている。
【００５６】
（５）上記（３）項で作成した電極積層体の各正極耳の穴を正極端子３に、各負極耳１の穴を負極端子４に入れ、それぞれ、アルミ、銅のボルトで接続した。電極積層体を絶縁テープで固定し、図１の角部Ａを全周に亘りレーザー溶接した。その後、電解液注液孔5（6ｍｍφ）から電解液としてエチレンカーボネートとジエチルカーボネートを１：１重量比で混合した溶媒に１ｍｏｌ／ｌの濃度にＬｉＰＦ６を溶解した溶液を注液した。この電池を、12ｍｍφに打ち抜いた厚さ０．08ｍｍのアルミ箔-変性ポリプロピレンラミネートフィルムを300torrの減圧下で熱融着する事により、電解液注液孔5を封口した。
（６）上記のようにして得られた電池を５Ａの電流で４．１Ｖまで充電し、その後４．１Ｖの定電圧を印加する定電流定電圧充電を１２時間行い、続いて５Ａの低電流で２．５Ｖまで放電したところ、放電容量は２３．５Ａｈであり、エネルギー容量は８５Ｗｈであった。容量を確認後再び上記同様の充電を行い充電末状態とした。次に安全性を確認するため、１０Ａの定電流充電での過充電試験を社団法人電池工業会指針ＳＢＡＧ１１０１に準じて行った。約７０％分過充電した時点で電池内部でのガス発生によるためか電池容器が膨張し出したが、図５中７１部の安全弁７２ａが広く開口し蒸気が素早く放出され、大容量型電池であるにもかかわらず発熱発火等には至らず安全性の高いことがわかった。電池の膨張後厚さも１８ｍｍでとどまっていた。
【００５７】
（比較例１）
実施例３で使用した安全弁構造以外は実施例３と同様に電池を作製した。該上蓋１のコーナー部に、図５のコーナー部７１における溝７２ａのような位置及び形状、幅１ｍｍ深さ０．０４８ｍｍ長さ６０ｍｍの直線状溝をエッチング加工により形成した。この溝は、コーナー部の両辺より１０ｍｍずつ内側を結び、矩形状上蓋の重心及び角部を結ぶ仮想直線（対角線）を横切るように形成されており、前記直線状溝が、前記直線の垂線に対して短辺側で角部の方へ１０度の角度をなすように設けられ、作動圧１ｋＰａの安全弁を形成した。しかしレーザ溶接工程において、取り付けていた放熱板などの冶具を脱着する際に既に安全弁の一部が破損して開口していた。作動圧がこの様に低すぎると、通常使用時にも容易に開口してしまうことが予想された。
【００５８】
（比較例２）
実施例３で使用した安全弁構造以外は実施例３と同様に電池を作製した。該上蓋１のコーナー部に、図５のコーナー部７１における溝７２ａのような位置及び形状、幅０．８ｍｍ深さ０．０４６ｍｍ長さ６０ｍｍの直線状溝をエッチング加工により形成した。この溝は、コーナー部の両辺より１０ｍｍずつ内側を結び、矩形状上蓋の重心及び角部を結ぶ仮想直線（対角線）を横切るように形成されており、前記直線状溝が、前記直線の垂線に対して短辺側で角部の方へ１０度の角度をなすように設けられ、作動圧２ｋＰａの安全弁を形成した。しかし注液工程において、減圧状態から常圧に戻すことにより電解液を注入される際に安全弁の一部から液漏れし開口していることがわかった。作動圧がこの様に低すぎると一般的な製造工程においても容易に開口してしまうことが予想された。
【００５９】
（比較例３）
実施例1の（２）の安全弁構造以外は実施例1と同様に電池外装体のみの組立品を作製した。図６に示すように、底容器２の上部側面８１に示すような幅０．５ｍｍ、深さ０．４ｍｍで短辺５ｍｍ長辺４０ｍｍで十字刻印状の安全弁８２を作製した。上記のようにして得られた電池外装体のみの組立品に、注液口５を使って電池内圧を上昇させ安全弁の開口試験を行ったところ、低圧では安全弁が作動せず５００ｋＰａに到達した時点で厚さ１２０ｍｍまで大きく膨張して変形歪みのためか突然溶接部の一部が開口した。電池内容物を含んでいた場合非常に危険な事態が予想された。
【００６０】
【発明の効果】
以上から明らかな通り、本発明によれば、扁平型電池、特に、大容量且つ高体積エネルギー密度を有する扁平型電池において、低い内部圧力上昇によって開口する安全機構を具備し、安全性が高い非水系二次電池を提供することができる。
【図面の簡単な説明】
【図１】本発明の一実施の形態の蓄電システム用非水系二次電池の平面図（上）及び側面図（下）を示す図である。
【図２】図１に示す電池の内部に収納される電極積層体の構成を示す側面図である。
【図３】本発明の構成要素である（ａ）薄肉部及び（ｂ）変形防止部の配置領域を示す説明図である。
【図４】本発明の切溝加工方式安全弁及び歪みを抑制させる溝の配置角度を示す説明図である。
【図５】本発明の非水系二次電池の実施例に用いた安全弁及び歪みを抑制させる溝の説明図である。
【図６】比較例としての非水系二次電池に用いた安全弁の説明図であり、（ａ）は平面図、（ｂ）は側面図、（ｃ）は側面の拡大図、（ｄ）は（ｃ）のＥ−Ｅ線断面図である。
【符号の説明】
１上蓋
２底容器
３正極端子
４負極端子
５注液口
６封口フィルム
５１安全弁配置範囲
６１仮想直線（対角線）
６２直線状切溝式安全弁例
６３対角線と直線状切溝式安全弁で挟まれた狭角
７１上蓋コーナー部
７２ａ、７２ｂ，７２ｃ，７２ｄ安全弁
８１底容器上部側面側
８２安全弁
１０１ａ正極（両面）
１０１ｂ負極（両面）
１０１ｃ負極（片面）
１０４、１０４ａ、１０４ｂセパレータ
１０５ａ正極集電体
１０５ｂ負極集電体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous secondary battery, and more particularly to a non-aqueous secondary battery for a power storage system.
[0002]
[Prior art]
In recent years, from the viewpoint of effective use of energy aiming at resource saving and global environmental problems, attention has been focused on home-use distributed storage systems for the storage of late-night power storage and solar power generation, storage systems for electric vehicles, etc. Collecting. For example, Japanese Patent Laid-Open No. 6-86463 proposes a total system that combines electricity, gas cogeneration, fuel cells, storage batteries, and the like supplied from a power plant as a system that can supply energy to energy consumers under optimum conditions. ing. A secondary battery used in such a power storage system requires a large battery having a large capacity, unlike a small secondary battery for portable equipment having an energy capacity of 10 Wh or less. For this reason, in the above power storage system, a plurality of secondary batteries are usually stacked in series and used as an assembled battery having a voltage of 50 to 400 V, for example, and in most cases, lead batteries are used.
[0003]
On the other hand, in the field of small secondary batteries for portable devices, the development of nickel-metal hydride batteries and lithium secondary batteries as new batteries has progressed to meet the needs for small size and high capacity, and has a volumetric energy density of 180 Wh / l or more. Batteries are commercially available. In particular, a lithium ion battery has a possibility of a volume energy density exceeding 350 Wh / l, and reliability such as safety and cycle characteristics is superior to a lithium secondary battery using metallic lithium as a negative electrode. , Has dramatically expanded its market.
[0004]
In response, in the field of large-scale batteries for power storage systems, lithium-ion batteries are targeted as candidates for high-energy density batteries, and development is actively underway by the Lithium Battery Power Storage Technology Research Association (LIBES) and others. .
[0005]
The energy capacity of these large-sized lithium ion batteries is about 100 Wh to 400 Wh, and the volume energy density is 200 to 300 Wh / l, the same level as a small secondary battery for portable devices. The shape is typically a cylindrical shape having a diameter of 50 mm to 70 mm, a length of 250 mm to 450 mm, and a flat prismatic shape such as a square or oblong square having a thickness of 35 mm to 50 mm.
[0006]
As for a thin lithium secondary battery, for example, a film battery (Japanese Patent Laid-Open Nos. 5-159757 and 7-57788, in which a film having a thickness of 1 mm or less obtained by laminating metal and plastic is housed in a thin exterior. And a small prismatic battery having a thickness of about 2 mm to 15 mm (Japanese Patent Laid-Open Nos. 8-195204, 8-138727, 9-213286, etc.) are known. Each of these lithium secondary batteries has a purpose corresponding to the miniaturization and thinning of portable devices. For example, the lithium secondary battery has a thickness of several millimeters that can be stored on the bottom of a portable personal computer and has an area of about JIS A4 size. Although the thin battery which has is also disclosed (Unexamined-Japanese-Patent No. 5-283105), since an energy capacity is 10 Wh or less, a capacity | capacitance is too small as a secondary battery for electrical storage systems.
[0007]
[Problems to be solved by the invention]
In the case of a flat battery, the front and back areas of the battery increase as the battery thickness is reduced for the purpose of improving heat dissipation. In order to maintain a high energy density, in particular, when a flat battery is prototyped in a large lithium secondary battery (energy capacity of 30 Wh or more) used in a power storage system, the tendency is strong. In the case of a lithium ion battery having a thickness of 6 mm, the size of the battery front and back surfaces is 600 cm. ² Very large (one side).
[0008]
In general, in a small lithium ion battery for portable devices, if the battery is overcharged or externally short-circuited due to malfunction due to device failure or misuse by the user, the inside of the battery is heated and the electrolyte is decomposed or evaporated. Gas is generated inside. Therefore, in order to prevent an accident caused by an increase in internal pressure, for example, as described in JP-A-6-36752, a safety valve designed in a high operating pressure range of 1-2 MPa is provided on the lid or bottom of the container. Yes.
[0009]
However, when the general safety mechanism as described above is installed on a large battery with a large battery front and back and a thin container thickness, it is a problem with a small battery in an abnormal situation where gas is generated inside the battery and the internal pressure rises. Even at low pressures, the container, especially the front and back surfaces, swells easily, and there is a problem in that it is in a dangerous state that may cause ignition or explosion without the safety mechanism working sufficiently.
[0010]
In order to solve the above problems, an object of the present invention is to provide a flat non-aqueous secondary battery with high safety that can reliably prevent accidents such as ignition and explosion at the time of abnormality.
[0011]
A further object of the present invention is to provide a highly safe non-aqueous secondary battery having a large capacity of 30 Wh or more and a volume energy density of 180 Wh / l or more and excellent heat dissipation characteristics.
[0012]
[Means for Solving the Problems]
The above object of the present invention is to be sealed in a flat battery container including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt, and has an energy capacity of 30 Wh or more and a volumetric energy density of 180 Wh / l or more and an operating pressure. A non-aqueous secondary battery of 5 kPa or more and less than 500 kPa, which is disposed on the wide flat surface portion of the flat battery container and is close to the outer periphery within 60% of the distance from the outer periphery of the container to the center of gravity of the wide flat surface portion A thin portion that includes at least a portion thereof and is broken by the operating pressure; and within the wide plane that is partitioned by two straight lines that pass through the center of gravity of the wide planar portion and both ends of the thin portion. A non-aqueous secondary, characterized in that it has a deformation preventing portion formed so that at least a part thereof is included in a region outside the thin-walled portion within a region including the thin-walled portion Battery Achieved.
[0013]
It is preferable that at least a part of the deformation preventing portion is formed in a range near the outer periphery within 30% of the distance from the outer periphery of the container to the center of gravity of the wide plane in the region.
[0014]
The thin portion is preferably formed of at least one linear or curved groove.
[0015]
The deformation preventing portion is preferably formed by thinning a part of the battery container, and is preferably formed by at least one linear or curved groove.
[0016]
The deformation preventing portion may be formed by a linear or curved rib provided on the battery container.
[0017]
The battery container has a polygonal flat shape, and the grooves constituting the thin-walled portion are arranged so as to cross a virtual straight line connecting the center of gravity and the corners of the polygon, and the tangent line of the curve formed by the grooves Alternatively, it is preferable that the angle of intersection between the straight line and the perpendicular to the virtual straight line is set within a range of ± 60 degrees.
[0018]
It is preferable that the tangent or straight groove of the curved groove constituting the deformation preventing portion is provided so as to form an angle within ± 20 degrees with respect to the outer peripheral line of the flat plane.
[0019]
The deformation prevention parts are arranged opposite to each other across the virtual straight line, and the deformation prevention parts arranged opposite to each other are spaced apart from each other, and each deformation prevention part is also arranged apart from the thin wall part. Is preferred.
[0020]
The wide plane shape of the battery container is preferably rectangular.
[0021]
The non-aqueous secondary battery preferably has a flat shape with a thickness of less than 12 mm.
[0022]
The plate thickness of the battery container is preferably 0.2 mm or more and 1 mm or less.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a nonaqueous secondary battery according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a plan view and a side view of a flat rectangular (note type) non-aqueous secondary battery for an electricity storage system according to an embodiment of the present invention, and FIG. 2 is a diagram of the battery shown in FIG. It is a side view which shows the structure of the electrode laminated body accommodated in an inside.
[0024]
As shown in FIGS. 1 and 2, the non-aqueous secondary battery according to the present embodiment includes a battery case (battery container) including an upper lid 1 and a bottom container 2, and a plurality of cases accommodated in the battery case. And an electrode laminate including a positive electrode 101a, negative electrodes 101b and 101c, and a separator 104. In the case of a flat type non-aqueous secondary battery as in the present embodiment, the positive electrode 101a and the negative electrode 101b (or the negative electrode 101c disposed on both outer sides of the laminate) have separators 104, for example, as shown in FIG. However, the present invention is not particularly limited to this arrangement, and the number of layers and the like can be variously changed according to the required capacity and the like.
[0025]
The positive electrode current collector 105 a of each positive electrode 101 a is electrically connected to the positive electrode terminal 3. Similarly, the negative electrode current collector 105 b of each negative electrode 101 b, 101 c is electrically connected to the negative electrode terminal 4. The positive terminal 3 and the negative terminal 4 are attached in a state insulated from the battery case, that is, the upper lid 1. The upper lid 1 and the bottom container 2 are welded by melting the upper lid all around the point A shown in the enlarged view of FIG. The upper lid 1 is provided with an electrolytic solution injection port 5. After the electrolytic solution is injected, a thermoplastic film 6 having a low moisture permeability represented by an aluminum-modified polypropylene laminate film and an aluminum-modified polyethylene laminate film. And sealed by heat fusion.
[0026]
In the sealing step, the pressure in the battery is preferably less than atmospheric pressure. Preferably it is 650 torr or less, more preferably 550 torr or less. This pressure is determined in consideration of the separator to be used, the type of electrolyte, the material of the battery can, the thickness, and the shape of the battery. When the internal pressure is equal to or higher than the atmospheric pressure, the battery becomes larger than the design thickness or the thickness variation becomes large, which causes the internal resistance and capacity of the battery to vary.
[0027]
The shape of the nonaqueous secondary battery shown in FIGS. 1 and 2 is, for example, 300 mm long × 210 mm wide × 6 mm thick. ₂ O _Four In the case of a lithium secondary battery using a carbon material for the negative electrodes 101b and 101c, for example, it can be used in a power storage system.
[0028]
The positive electrode active material used for the positive electrode 101a is not particularly limited as long as it is a lithium-based positive electrode material, and lithium composite cobalt oxide, lithium composite nickel oxide, lithium composite manganese oxide, or a mixture thereof, A system in which one or more different metal elements are added to these composite oxides can be used, and a high voltage and high capacity battery can be obtained, which is preferable. Further, when safety is important, manganese oxide having a high thermal decomposition temperature is preferable. As this manganese oxide, LiMn ₂ O _Four Lithium composite manganese oxide, a system in which one or more different metal elements are added to these composite oxides, and LiMn in which lithium, oxygen, etc. are made in excess of the stoichiometric ratio ₂ O _Four Is mentioned.
[0029]
The negative electrode active material used for the negative electrodes 101b and 101c is not particularly limited as long as it is a lithium-based negative electrode material, and is a material capable of doping and dedoping lithium, such as safety and reliability such as cycle life. Is preferable. Examples of materials that can be doped and dedoped with lithium include graphite-based materials, carbon-based materials, tin oxide-based, silicon oxide-based metal oxides, and polyacene, which are used as negative electrode materials for known lithium ion batteries. Examples thereof include conductive polymers represented by organic organic semiconductors. In particular, from the viewpoint of safety, a polyacene-based substance that generates a small amount of heat at around 150 ° C. or a material containing the same is desirable.
[0030]
Although the structure of the separator 104 is not particularly limited, a single-layer or multi-layer separator can be used, and at least one sheet is preferably a non-woven fabric, which improves cycle characteristics. The material of the separator 104 is not particularly limited, and examples thereof include polyolefins such as polyethylene and polypropylene, polyamide, kraft paper, and glass. Polyethylene and polypropylene are preferable from the viewpoints of cost, moisture content, and the like. . When polyethylene or polypropylene is used as the separator 104, the basis weight of the separator is preferably 5 g / m. ² 30 g / m ² Or less, more preferably 5 g / m ² 20 g / m or more ² Or less, more preferably 8 g / m ² 20 g / m or more ² It is as follows. Separator weight is 30g / m ² Is not preferable because the separator becomes too thick or the porosity is lowered and the internal resistance of the battery is increased. ² If it is less than 1, practical strength cannot be obtained, which is not preferable.
[0031]
As the electrolyte of the non-aqueous secondary battery of this embodiment, a non-aqueous electrolyte containing a known lithium salt can be used, which is appropriately determined depending on the use conditions such as the positive electrode material, the negative electrode material, and the charging voltage, and more specifically. LiPF ₆ , LiBF _Four LiClO _Four A lithium salt such as propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxy ethane, γ-butyl lactone, methyl acetate, methyl formate, or a mixed solvent of two or more thereof. Etc. are exemplified. Further, the concentration of the electrolytic solution is not particularly limited, but generally 0.5 mol / l to 2 mol / l is practical, and naturally the electrolytic solution has a water content of 100 ppm or less. It is preferable to use it. In addition, the non-aqueous electrolyte used in this specification means a concept including a non-aqueous electrolyte solution and an organic electrolyte solution, and also refers to a concept including a gel-like or solid electrolyte.
[0032]
The non-aqueous secondary battery configured as described above can be used for a household power storage system (night power storage, cogeneration, solar power generation, etc.), a power storage system such as an electric vehicle, and the like. It can have an energy density. In this case, the energy capacity is preferably 30 Wh or more, more preferably 50 Wh or more, and the energy density is preferably 180 Wh / l or more, more preferably 200 Wh / l. When the energy capacity is less than 30 Wh or when the volumetric energy density is less than 180 Wh / l, the capacity is small for use in the power storage system, and it is necessary to increase the number of series-parallel batteries to obtain sufficient system capacity. In addition, it is not preferable for a power storage system because a compact design becomes difficult.
[0033]
By the way, in general, a large lithium secondary battery (energy capacity of 30 Wh or more) for a power storage system can obtain a high energy density, but its battery design is an extension of a small battery for portable devices. However, the shape of the battery is a cylindrical shape, a rectangular shape or the like that is three times or more that of a small battery for portable devices. In this case, heat is likely to be accumulated inside the battery due to Joule heat generation due to the internal resistance of the battery during charging and discharging, or internal heat generation of the battery due to change in entropy of the active material due to the entry and exit of lithium ions. For this reason, the temperature difference between the temperature inside the battery and the vicinity of the battery surface is large, and the internal resistance differs accordingly. As a result, variations in charge amount and voltage are likely to occur. In addition, since this type of battery is used as a plurality of assembled batteries, the ease of heat storage differs depending on the installation position of the batteries in the system, resulting in variations among the batteries, and accurate control of the entire assembled battery is possible. It becomes difficult. In addition, because of insufficient heat dissipation during high-rate charging / discharging, etc., the battery temperature rises, leaving the battery unfavorable, resulting in a decrease in life due to decomposition of the electrolyte, and thermal runaway of the battery. Problems such as induction of reliability, particularly safety, remained.
[0034]
The flat non-aqueous secondary battery according to the present embodiment has a large heat radiation area and is advantageous for heat radiation, and thus can solve the above-described problems. That is, the nonaqueous secondary battery of the present embodiment has a flat shape, and the thickness thereof is preferably less than 12 mm, more preferably less than 10 mm, and further preferably less than 8 mm. As for the lower limit of the thickness, 2 mm or more is practical in consideration of the filling factor of the electrode and the battery size (the area becomes larger in order to obtain the same capacity as the thickness is reduced). When the thickness of the battery is 12 mm or more, it becomes difficult to sufficiently dissipate the heat generated inside the battery to the outside, or the temperature difference between the inside of the battery and the vicinity of the battery surface increases, resulting in different internal resistances. The variation in the amount of charge and voltage in the battery increases. The specific thickness is appropriately determined according to the battery capacity and the energy density, but it is preferable to design with the maximum thickness that provides the expected heat dissipation characteristics.
[0035]
In addition, as the shape of the non-aqueous secondary battery of the present embodiment, for example, the flat front and back surfaces can be various shapes such as a square, a circle, an oval, etc. However, it may be a polygon such as a triangle or a hexagon. Furthermore, it can also be made into cylindrical shapes, such as a thin cylinder. In the case of a cylinder, the thickness of the cylinder is the thickness referred to here. Further, from the viewpoint of ease of manufacture, the flat front and back surfaces of the battery are rectangular, and a notebook shape as shown in FIG. 1 is preferable.
[0036]
The materials used for the top lid 1 and the bottom container 2 that serve as the battery case are appropriately selected depending on the use and shape of the battery, and are not particularly limited, and iron, stainless steel, aluminum, etc. are common and practical. is there. Further, the thickness of the battery case is appropriately determined depending on the use and shape of the battery or the material of the battery case, and is not particularly limited. Preferably, the thickness of the portion of 80% or more of the battery surface area (the thickness of the portion having the largest area constituting the battery case) is 0.2 mm or more. If the thickness is less than 0.2 mm, it is not desirable because the strength required for manufacturing the battery cannot be obtained. From this viewpoint, it is more preferably 0.3 mm or more. The thickness of the same part is desirably 1 mm or less. If this thickness exceeds 1 mm, the force to hold down the electrode surface increases, but it is not desirable because the internal volume of the battery is reduced and a sufficient capacity cannot be obtained, or the weight increases. Preferably it is 0.7 mm or less.
[0037]
As described above, by designing the thickness of the non-aqueous secondary battery to be less than 12 mm, for example, when the battery has a large capacity of 30 Wh or more and a high energy density of 180 Wh / l, a high rate charge / discharge, etc. However, the rise in battery temperature is small, and it can have excellent heat dissipation characteristics. Therefore, the heat storage of the battery due to internal heat generation is reduced, and as a result, it is possible to suppress the thermal runaway of the battery, and it is possible to provide a non-aqueous secondary battery excellent in reliability and safety.
[0038]
Next, the safety mechanism provided in the non-aqueous secondary battery of the present invention configured as described above will be described in detail. The safety mechanism has a thin part formed in the battery container, and this thin part acts as a safety valve that breaks when an internal pressure exceeding a certain level is generated in the battery container. The operating pressure of this safety valve (the difference between the increased pressure inside the battery and the atmospheric pressure) has a lower limit of preferably 5 kPa or more, more preferably 20 kPa or more, and an upper limit of preferably less than 500 kPa, more preferably less than 120 kPa, Particularly preferably, it is less than 80 kPa. This operating pressure is appropriately designed according to the shape and thickness of the battery, the material of the battery container, the capacity of the battery, the separator to be used, the type of the electrolyte, etc. If the operating pressure is less than the above lower limit, it operates even during normal use. This is not preferable. When the operating pressure is higher than the above upper limit, there is a risk that even in an abnormal situation in which gas is generated inside the battery, the safety valve does not work and easily expands and deforms to cause ignition or explosion. In the present invention, the number of safety valves may be at least one, and in particular, two or more safety valves may be provided.
[0039]
As for the place where the safety valve is arranged, as shown in the hatched area 51 in FIG. 3A, the safety valve is arranged in the wide flat portion of the battery container having a flat shape, and at least a part thereof is included within a predetermined distance from the outer periphery of the wide flat surface. It is desirable to provide as follows. The range closer to the outer periphery is preferably a range closer to the outer periphery within 60% of the distance from the outer periphery of the container to the center of gravity of the wide flat portion, and more preferably within 40%. When the wide plane of the battery is large and the container thickness is thin, the container swells and is cheap as described above. The degree depends on the shape and thickness of the battery used, and the material of the battery container. In particular, distortion due to the swelling of the container occurs in the vicinity of the outer periphery within 60% of the distance from the outer periphery to the center of gravity of the wide flat surface portion. easy. This distortion tends to become larger in a range near the outer periphery within 40% of the distance from the outer periphery to the center of gravity. This means that in the above-mentioned range, a force that deforms the container wall is acting greatly. It can also be said that the stress acting on the entire container wall as the internal pressure increases propagates to this range and acts intensively. Therefore, when a safety valve is provided in these ranges, even if the internal pressure of the container is low, a large concentrated stress acts on the location where the safety valve is provided, and the valve can be reliably operated. Conversely, when a safety valve is provided only in the range from the center of gravity to the above range, the range tends to be lifted as it is without much deformation when the container swells, and the deformation curvature is small and keeps the flat state. The force that operates the safety valve is difficult to act.
[0040]
If the shape of the wide flat part of the battery container is a rectangle or other polygonal shape, if it is provided near the corner, distortion concentrates there, so that the distortion can be used effectively to obtain reliable operation. preferable. In addition, as described above, the safety valve is operated by utilizing the distortion caused by the concentration of the internal pressure of the battery container. No opening occurs.
[0041]
Furthermore, as shown in FIG. 4, a region including the thin portion within the wide plane defined by two straight lines m and n passing through the center of gravity of the wide flat portion and both ends of the thin portion (64). And a deformation preventing portion (65) formed so that at least a part thereof is included in a range outside the thin portion, and the deformation preventing portion is indicated by a hatched region 52 in FIG. 3 (b). In this way, it is arranged on the wide flat part of the battery container having the flat shape, and is different from the thin part including at least a part thereof in a range near the outer periphery within 30% of the distance from the outer periphery of the container to the center of gravity of the wide flat surface. When the deformation prevention part formed of at least one thin wall is formed, there is an effect of suppressing the deformation on the outer peripheral side when the internal pressure rises and the central part of the battery container swells up. It is more preferable that the difference in the degree of deformation distortion between the expanding portion and the outer peripheral side is larger because the opening area of the safety valve can be widened, and heat storage inside the abnormality can be quickly released to the outside. This suppression effect is even greater in a range near the outer periphery within 20% of the distance from the outer periphery to the center of gravity. The deformation preventing part can be formed by a thin wall similar to the thin wall part, or can be formed by providing a rib.
[0042]
As a safety valve having a thin part, a method of attaching a rupture disk part cold-welded with a thin metal foil, a method of thinning a part of a container to weaken it, etc. can be adopted. The thin portion is at least one straight or curved groove formed on the container wide flat surface side. This groove can be formed by, for example, kerf processing.
[0043]
The arrangement of the linear grooves will be described with reference to FIG. The battery container shown in FIG. 4 has a rectangular shape on a wide plane, and the straight groove 64 or the tangent line 64a of the curved groove 64 is arranged so as to cross a virtual straight line 61 connecting the center of gravity (center) G and corners of the rectangle. It is preferable that the straight line or the tangent line of the curved line is provided so as to form an angle within ± 60 degrees with respect to the perpendicular line of the virtual straight line. This is because the distortion in the wide plane portion that occurs when the container swells is large in the direction across the virtual straight line 61. Therefore, by setting the angle 62 within the above range, the groove can be along the direction in which a large strain is generated, and as a result, the safety valve can be easily opened at a low container internal pressure. If the angle 62 formed by the groove is less than 30 degrees, the container will be lifted without causing a large distortion when it swells, making it difficult to reliably operate at low pressure. When the container wide plane is rectangular as in this example, the virtual straight line connecting the center of gravity and the corner is of course a diagonal line. In addition, even when the container wide plane portion is a polygon other than a rectangle, the tangent of the straight groove or the curved groove is arranged so as to cross the virtual straight line connecting the center of gravity (center) and the corner of the polygon. Record By providing the straight line formed by the groove or the tangent line of the curved line so as to form an angle within ± 60 degrees with respect to the perpendicular line of the virtual straight line, the same action as described above can be obtained.
[0044]
As described above, by forming the groove of the safety valve within the above angle range on the wide plane portion side, it is possible to prevent the battery contents from being scattered around when the valve is opened. The groove of the safety valve can be opened within the predetermined pressure range determined in advance by designing the shape and thickness of the thin portion. In addition, by providing a safety valve on the side of the container wide flat surface, it is possible to quickly extract the internal gas with a large opening area. Furthermore, it is more preferable in that the cost can be reduced as compared with a rupture disk that requires a protective cover and has a large equipment investment.
[0045]
Further, it is desirable that the deformation preventing part for suppressing at least one or more distortions different from the thin part is at least one linear or curved groove on the container flat plane side. Furthermore, it is more preferable that the tangent line of the one straight groove or the curved groove having an effect of suppressing the distortion is provided so as to form an angle within ± 20 degrees with respect to the outer peripheral line of the flat plane. . This is because if the angle of 20 degrees or more is formed with respect to the outer peripheral line, the container is lifted as it is without any effect of suppressing the expansion, and the opening area cannot be increased. The arrangement of the linear grooves for suppressing the distortion will be described with reference to FIG. The battery container shown in FIG. 4 has a rectangular shape with a wide plane, and the tangent 65a of the straight groove 65 or the curved groove 65 is located along the outer periphery on the corner side from the safety valve, and the straight line or the curve formed by the groove. Is formed so as to form an angle of ± 20 degrees or less with respect to a parallel line with the outer peripheral line.
[0046]
The manufacturing method of the safety valve is not particularly limited, but in the case of the above-described grooving method, the grooving of the thin portion can be performed by leaving a predetermined thickness in an arbitrary shape by a method such as etching or pressing. FIG. 5 shows various examples in which a grooved safety valve and a groove for suppressing distortion are combined. A safety valve having a low pressure and a large opening area can be obtained by providing a large thin wall grooving portion 72 near the periphery of the surface of the upper lid 1 and near the corner 71 and providing a groove processing portion 82 along the outer peripheral line on the outer peripheral side. Become. In the figure, 72a is a straight line, 72b is a circular arc shape, 72c is a shape with only a part of a circle left, and 72d is a grooved safety valve with an X mark shape.
[0047]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
(1) As shown in FIG. 1, the bottom container 2 was made by drawing a 0.5 mm SUS304 thin plate to a depth of 5 mm, and the battery top lid 1 was also made of a SUS304 thin plate having a thickness of 0.5 mm. The external dimensions of the battery were 210 mm on the short side and 300 mm on the long side, approximately the same as the JIS standard A4 size. An aluminum positive electrode terminal and copper negative electrode terminals 3 and 4 (6 mmφ, threaded M3) were attached to the upper lid. The positive and negative terminals 3 and 4 were insulated from the upper lid 1 by a polypropylene gasket. The upper lid 1 was disposed without inserting the electrode laminate into the bottom container 2, and the corner portion A in FIG. 1 was laser welded over the entire circumference to produce an assembly including only the battery outer casing.
[0048]
(2) In the corner portion of the upper lid 1 (corner portion 71 in FIG. 5), a straight groove having the shape of the groove 72a in FIG. 5 and the dimensions of width 0.5mm depth 0.04mm length 60mm is formed by etching. A safety valve was used. This groove is formed so as to cross the straight line connecting the center of gravity and the corner of the rectangular upper lid by 10 mm from both sides of the corner part, and the straight groove is perpendicular to the straight line (diagonal line). The angle is 10 degrees toward the corner on the short side. Further, two linear grooves having a shape and a width of 0.5 mm, a depth of 0.03 mm, and a length of 20 mm are formed as a groove 82 in FIG. 5 at the corner portion of the upper lid 1 (more peripheral side of the corner portion 71 portion in FIG. 5). A groove for suppressing distortion was formed by etching. This groove is a straight groove formed in parallel on both sides from the inside, 8 mm from the corner.
[0049]
(3) A safety valve opening test was performed on the assembly of only the battery outer casing obtained as described above by increasing the internal pressure of the battery using the liquid injection port 5, and quickly operated at a low pressure of 40 kPa. However, the thickness after expansion of the battery remained at 18 mm. The width of the opening was as large as 2 mm. In addition, when the same battery exterior body only assembly was produced without forming the groove for suppressing the distortion, and the battery internal pressure was increased using the liquid injection port 5 and the safety valve opening test was performed. It operated quickly at a low pressure of 40 kPa, and the thickness after expansion of the battery remained at 18 mm. However, the width of the opening was 0.5 mm.
[0050]
(Example 2)
Except for the safety valve structure of Example 1 (2), an assembly including only the battery outer package was produced in the same manner as in Example 1. The corner portion of the battery top lid 1 has a position and shape like the groove 72b in the corner portion 71 in FIG. 5, a width of 0.5 mm, a depth of 0.04 mm, and a radius of 40 mm centered on a point 50 mm inside from both sides. A safety valve was manufactured by etching an arcuate groove having an inner angle of 90 degrees and projecting toward the corner. When the battery internal pressure was increased using the liquid injection port 5 and the safety valve opening test was performed on the assembly of the battery outer casing obtained as described above, the quick operation was performed at a low pressure of 50 kPa. The thickness stayed at 22mm. The width of the opening was 1.5 mm.
[0051]
(Example 3)
The safety valve structure of Example 1 (2) and the groove for suppressing distortion were produced in the corner portion of the battery top lid 1 to assemble an actual battery as follows.
[0052]
(1) 100 parts by weight of LiCo 2 O 4, 8 parts by weight of acetylene black and 3 parts by weight of polyvinylidene fluoride (PVDF) were mixed with 100 parts by weight of N-methylpyrrolidone (NMP) to obtain a positive electrode mixture slurry. The slurry was applied to both sides of a 20 μm thick aluminum foil serving as a current collector, dried, and then pressed to obtain a positive electrode. FIG. 4 is an explanatory diagram of electrodes. In this embodiment, the application area (W1 × W2) of the positive electrode 101a is 262.5 × 192 mm 2 and is applied to both surfaces of a 20 μm current collector 10 5a with a thickness of 103 μm. As a result, the electrode thickness t is 226 μm. Further, there is an ear portion on which the electrode is not applied on the short side of the electrode, and a hole of φ3 is formed.
[0053]
(2) 100 parts by weight of graphitized mesocarbon microbeads (MCMB, manufactured by Osaka Gas Chemical Co., No. 6-28) and 10 parts by weight of PVDF were mixed with 90 parts by weight of NMP to obtain a negative electrode mixture slurry. The slurry was applied to both sides of a 14 μm thick copper foil serving as a current collector, dried, and then pressed to obtain a negative electrode. This will be described with reference to FIG. The application area (W1 × W2) of the negative electrode 101b or 101c is 267 × 195 mm 2 and is applied to both surfaces of an 18 μm current collector 10 5b with a thickness of 108 μm. As a result, the electrode thickness t is 234 μm. Further, there is an ear portion on which the electrode is not applied on the short side of the electrode, and a hole of φ3 is formed. Further, a single-sided electrode having a thickness of 126 μm was prepared by the same method except that the coating was applied to only one side. The single-sided electrode is arranged on the outer side in the electrode laminate of item (3) (101c in FIG. 2).
[0054]
(3) Eight positive electrodes and nine negative electrodes (two inner surfaces) obtained in the above item (1) are separators 104a as shown in FIG. And separator 104b (polyethylene microporous membrane; Asahi Kasei HIPORE 6022, weight per unit: 13.3 g / m 2) (labeled as 104 in FIG. 2) were alternately laminated to form an electrode laminate. The separator 104b was disposed on the positive electrode side. Further, a separator 104b was disposed on the outer side of the negative electrode plate 101c outside the laminated body for insulation from the container.
[0055]
(4) The bottom container 2 of the battery (see FIG. 1) was prepared by drawing a 0.5 mm SUS304 thin plate to a depth of 5 mm. Further, the upper lid 1 of the battery was also made of a thin plate made of SUS304 having a thickness of 0.5 mm. The positive electrode terminal made of aluminum and the negative electrode terminals 3 and 4 made of copper (6 mmφ, threaded M3) were attached to the upper lid. The positive and negative terminals 3 and 4 are insulated from the upper lid 1 by a polypropylene gasket.
[0056]
(5) The holes of each positive electrode ear of the electrode laminate prepared in the above item (3) were put into the positive electrode terminal 3 and the holes of each negative electrode ear 1 were put into the negative electrode terminal 4 and connected with aluminum and copper bolts, respectively. The electrode laminate was fixed with an insulating tape, and the corner A in FIG. 1 was laser welded over the entire circumference. Thereafter, a solution in which LiPF6 was dissolved at a concentration of 1 mol / l was poured into a solvent in which ethylene carbonate and diethyl carbonate were mixed at a 1: 1 weight ratio as an electrolytic solution from the electrolytic solution injection hole 5 (6 mmφ). This battery was heat-sealed with an aluminum foil-modified polypropylene laminate film having a thickness of 0.08 mm punched to 12 mmφ under a reduced pressure of 300 torr to seal the electrolyte injection hole 5.
(6) The battery obtained as described above is charged to 4.1 V with a current of 5 A, and then a constant current and constant voltage charge for applying a constant voltage of 4.1 V is performed for 12 hours, followed by a low current of 5 A. When discharged to 2.5 V, the discharge capacity was 23.5 Ah, and the energy capacity was 85 Wh. After confirming the capacity, the same charging as described above was performed again to obtain the end-of-charge state. Next, in order to confirm safety, an overcharge test with a constant current charge of 10 A was performed in accordance with the Association of Battery Industry Association Guidelines SBA G1101. When the battery was overcharged by about 70%, the battery container expanded due to gas generation inside the battery, but the safety valve 72a at 71 in FIG. Despite the fact, it was found that it was safe because it did not cause exothermic ignition. After expansion, the thickness of the battery remained at 18 mm.
[0057]
(Comparative Example 1)
A battery was produced in the same manner as in Example 3 except for the safety valve structure used in Example 3. A straight groove having a position and shape like the groove 72a in the corner portion 71 of FIG. 5, a width of 1 mm, a depth of 0.048 mm, and a length of 60 mm was formed in the corner portion of the upper lid 1 by etching. This groove connects the inside by 10 mm from both sides of the corner portion, and connects the center of gravity and corner portion of the rectangular upper lid. Virtual It is formed so as to cross a straight line (diagonal line), and the linear groove is provided so as to form an angle of 10 degrees toward the corner part on the short side with respect to the perpendicular of the straight line, 1 kPa Formed a safety valve. However, in the laser welding process, when a jig such as a heat sink attached was removed, a part of the safety valve was already damaged and opened. If the operating pressure was too low, it was expected that the opening would easily occur during normal use.
[0058]
(Comparative Example 2)
A battery was produced in the same manner as in Example 3 except for the safety valve structure used in Example 3. A straight groove having a position and shape like the groove 72a in the corner portion 71 of FIG. 5 and a width of 0.8 mm, a depth of 0.046 mm, and a length of 60 mm was formed by etching in the corner portion of the upper lid 1. This groove connects the inside by 10 mm from both sides of the corner portion, and connects the center of gravity and corner portion of the rectangular upper lid. Virtual It is formed so as to cross a straight line (diagonal line), and the linear groove is provided so as to form an angle of 10 degrees toward the corner part on the short side with respect to the perpendicular of the straight line, and the working pressure is 2 kPa. A safety valve was formed. However, in the liquid injection process, it was found that the electrolyte leaked from a part of the safety valve and opened when the electrolytic solution was injected by returning from the reduced pressure state to the normal pressure. When the operating pressure is too low, it is expected that the opening easily occurs even in a general manufacturing process.
[0059]
(Comparative Example 3)
Except for the safety valve structure of Example 1 (2), an assembly including only the battery outer package was produced in the same manner as in Example 1. Figure 6 As shown in Fig. 5, a safety valve 82 having a cross-shaped shape with a width of 0.5 mm, a depth of 0.4 mm, a short side of 5 mm and a long side of 40 mm as shown on the upper side surface 81 of the bottom container 2 was produced. When the battery internal pressure was raised using the liquid injection port 5 and the safety valve opening test was performed on the assembly of the battery exterior body obtained as described above, the safety valve did not operate at low pressure and reached 500 kPa. A large portion of the welded portion was opened due to deformation distortion or sudden expansion. A very dangerous situation was expected when the battery contents were included.
[0060]
【The invention's effect】
As is apparent from the above, according to the present invention, a flat battery, particularly a flat battery having a large capacity and a high volumetric energy density, is equipped with a safety mechanism that opens due to a low internal pressure rise, and has high safety. An aqueous secondary battery can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing a plan view (top) and a side view (bottom) of a nonaqueous secondary battery for an electricity storage system according to an embodiment of the present invention.
2 is a side view showing a configuration of an electrode laminate housed in the battery shown in FIG. 1. FIG.
FIG. 3 is an explanatory view showing an arrangement region of (a) a thin portion and (b) a deformation prevention portion which are components of the present invention.
FIG. 4 is an explanatory view showing a groove arrangement type safety valve of the present invention and an arrangement angle of grooves for suppressing distortion.
FIG. 5 is an explanatory diagram of a safety valve used in an example of a non-aqueous secondary battery of the present invention and a groove for suppressing distortion.
6 is an explanatory view of a safety valve used in a non-aqueous secondary battery as a comparative example, (a) is a plan view, (b) is a side view, (c) is an enlarged side view, and (d) is a side view. It is EE sectional view taken on the line of (c).
[Explanation of symbols]
1 Upper lid
2 Bottom container
3 Positive terminal
4 Negative terminal
5 Injection port
6 Sealing film
51 Safety valve arrangement range
61 Virtual straight line (diagonal line)
62 Example of linear kerf type safety valve
63 Narrow angle between diagonal and straight kerf type safety valve
71 Upper lid corner
72a, 72b, 72c, 72d Safety valve
81 Top side of bottom container
82 Safety valve
101a Positive electrode (both sides)
101b Negative electrode (both sides)
101c Negative electrode (single side)
104, 104a, 104b Separator
105a Positive electrode current collector
105b Negative electrode current collector

Claims

The battery is sealed in a flat battery container including a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte containing a lithium salt, and has an energy capacity of 30 Wh or more, a volume energy density of 180 Wh / l or more, and an operating pressure of 5 kPa or more and less than 500 kPa. An aqueous secondary battery,
Broken by the working pressure comprises at least a portion thereof near the outer periphery of the range within 60% of the distance from disposed container periphery to the wide flat portion to the centroid of the wide flat portion of the battery container forming the flat shape, at least a A thin portion formed by two linear or curved grooves ,
The inside of the wide plane defined by two straight lines passing through the center of gravity of the wide flat portion and each of both ends of the thin portion is within the region including the thin portion and outside the thin portion. possess a deformation preventing portion formed to include a portion,
The deformation preventing portion is formed so as to be at least partially included in a range near the outer periphery within 30% of the distance from the outer periphery of the container to the center of gravity of the wide plane in the region.
The deformation preventing portion is formed by making a part of the battery container thin,
The deformation preventing part is formed by at least one linear or curved groove,
The battery container has a polygonal flat shape, and the grooves constituting the thin-walled portion are arranged so as to cross a virtual straight line connecting the center of gravity and the corners of the polygon, and the tangent line of the curve formed by the grooves Alternatively, the intersection angle between the straight line and the perpendicular of the virtual straight line is set within a range of ± 60 degrees,
A tangent or straight groove of the curved groove constituting the deformation preventing portion is provided so as to form an angle of ± 20 degrees or less with respect to the outer peripheral line in the region in the wide plane portion,
The deformation prevention parts are arranged opposite to each other across the virtual straight line, and the deformation prevention parts arranged opposite to each other are spaced apart from each other, and each deformation prevention part is also arranged apart from the thin wall part. A non-aqueous secondary battery.

The battery is sealed in a flat battery container including a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte containing a lithium salt, and has an energy capacity of 30 Wh or more, a volume energy density of 180 Wh / l or more, and an operating pressure of 5 kPa or more and less than 500 kPa. An aqueous secondary battery,
The battery container having the flat shape is disposed on the wide flat surface portion and includes at least a part thereof in a range near the outer periphery within 60% of the distance from the outer periphery of the container to the center of gravity of the wide flat surface portion. A thin portion formed by two linear or curved grooves,
The inside of the wide plane defined by two straight lines passing through the center of gravity of the wide flat portion and each of both ends of the thin portion is within the region including the thin portion and outside the thin portion. A deformation preventing part formed to include a part,
The said deformation | transformation prevention part is formed of the linear or curved rib provided in the battery container, The non-aqueous secondary battery characterized by the above-mentioned.

The deformation preventing portion is formed so as to be at least partially included in a range near the outer periphery within 30% of the distance from the outer periphery of the container to the center of gravity of the wide plane in the region. Item 3. A nonaqueous secondary battery according to Item 2 .

The battery container has a polygonal flat shape, and the grooves constituting the thin-walled portion are arranged so as to cross a virtual straight line connecting the center of gravity and the corners of the polygon, and the tangent line of the curve formed by the grooves Alternatively, the non-aqueous secondary battery according to claim 2 , wherein an intersection angle between the straight line and the perpendicular to the virtual straight line is set within a range of ± 60 degrees.

The tangent or straight rib of the curved rib constituting the deformation preventing portion is provided so as to form an angle of ± 20 degrees or less with respect to the outer peripheral line in the region in the wide plane portion. The non-aqueous secondary battery according to claim 2 .

The deformation prevention parts are arranged opposite to each other across the virtual straight line, and the deformation prevention parts arranged opposite to each other are spaced apart from each other, and each deformation prevention part is also arranged apart from the thin wall part. The non-aqueous secondary battery according to claim 4 .

The non-aqueous secondary battery according to any one of claims 1 to 6 , wherein a shape of a wide plane of the battery container is a rectangle.

The non-aqueous secondary battery according to claim 1 , wherein the non-aqueous secondary battery has a flat shape with a thickness of less than 12 mm.

The thickness of the battery container, a non-aqueous secondary battery according to claim 1, characterized in that at 0.2mm to 1mm.