JP2004063145A - Secondary battery using non-aqueous electrolyte - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery using non-aqueous electrolyte, whose gas generation quantity during initial charging is reduced and whose cycle life is improved. <P>SOLUTION: The secondary battery using the non-aqueous electrolyte comprises a positive electrode 3, a negative electrode 4 containing carbonaceous material which can absorb/emit lithium ions, and the non-aqueous electrolyte including non-aqueous solvent. The non-aqueous solvent contains ethylene carbonate, chain carbonate including at least methyl ethyl carbonate (MEC), and sultone compound having at least a double bond in its ring. <P>COPYRIGHT: (C)2004,JPO

Description

【００５９】
化１において、Ｃ_ｍＨ_ｎは直鎖状の炭化水素基で、ｍとｎは、２ｍ＞ｎを満たす２以上の整数である。
【００６０】
環内に少なくとも一つの二重結合を有するスルトン化合物は、負極との還元反応により二重結合が開いて重合反応が起こるため、負極表面に保護被膜を形成することができる。ところで、ＥＣとγ−ブチロラクトン（ＧＢＬ）と前記スルトン化合物とを含む非水溶媒を用いると、ＥＣによる保護被膜の生成がＧＢＬにより阻害される。その結果、スルトン化合物の被膜生成反応が優先的に生じ、スルトン化合物の添加量を少量にしても被膜が厚くなるため、界面抵抗の増大を招く。
【００６１】
本願発明のような、ＥＣと、少なくともＭＥＣを含む鎖状カーボネートと、前記スルトン化合物とを含む非水溶媒によると、スルトン化合物はＥＣによる保護被膜を補修するように働くため、スルトン化合物を含まないときよりもさらに良好な保護被膜を形成することができる。これにより、初充電時のガスの発生を抑止することができる。さらに、この保護被膜は、リチウムイオン透過性が高いものの、溶媒の透過性については低いため、負極の炭素質材料に吸蔵されたリチウムイオン（Ｌｉ^＋）と溶媒との充電時の副反応を抑制することができる。従って、充放電サイクルの進行に伴う放電電気量の減少を抑制することができるため、充放電サイクル寿命を向上することができる。
【００６２】
スルトン化合物の中でも好ましいのは、スルトン化合物Ａのうちｍ＝３、ｎ＝４である化合物、即ち１，３−プロペンスルトン（ＰＲＳ）、または、ｍ＝４、ｎ＝６である化合物、即ち１，４−ブチレンスルトン（ＢＴＳ）である。スルトン化合物としては、１，３−プロペンスルトン（ＰＲＳ）あるいは１，４−ブチレンスルトン（ＢＴＳ）を単独で用いても、これらＰＲＳとＢＴＳを併用しても良い。ＰＲＳ及びＢＴＳのうちの少なくとも一方のスルトン化合物によると、少なくともＭＥＣを含む鎖状カーボネートとＥＣとの共存下で、負極表面に良好な保護被膜を形成することができると共に、溶媒との充電時の副反応を抑制する効果を最も高くすることができる。
【００６３】
スルトン化合物の比率（ｚ）は、１０体積％以下にすることが望ましい。これは、スルトン化合物の比率（ｚ）が１０％体積を超えると、上記の保護被膜が極めて厚くなってリチウムイオン透過性が低下し、常温よりも低い温度における放電容量が低下するからである。更に、例えば−２０℃等の低い温度でも放電容量を高く保つためには、スルトン化合物が含まれる割合（ｚ）は４％体積以下であることが望ましい。また、保護被膜の形成量を十分に確保するためには、スルトン化合物の比率（ｚ）を最低でも０．０１体積％確保することが望ましい。更に、スルトン化合物の比率（ｚ）が０．１体積％以上あれば、例えば６５℃等の更に高い温度でも保護被膜による保護機能を充分に示すことができる。
【００６４】
ｄ．副成分
非水溶媒中には、ＥＣ、鎖状カーボネート、スルトン化合物以外の他の溶媒を含有させることができる。
【００６５】
副成分としては、例えば、ビニレンカーボネート（ＶＣ）、ビニルエチレンカーボネート（ＶＥＣ）、フェニルエチレンカーボネート（ｐｈＥＣ）、プロピレンカーボネート（ＰＣ）、γ−バレロラクトン（ＶＬ）、プロピオン酸メチル（ＭＰ）、プロピオン酸エチル（ＥＰ）、２−メチルフラン（２Ｍｅ−Ｆ）、フラン（Ｆ）、チオフェン（ＴＩＯＰ）、カテコールカーボネート（ＣＡＴＣ）、エチレンサルファイト（ＥＳ）、１２−クラウン−４（Ｃｒｏｗｎ）、テトラエチレングリコールジメチルエーテル（Ｅｔｈｅｒ）等を挙げることができる。副成分の種類は、１種類もしくは２種類以上にすることができる。
【００６６】
中でも、ビニレンカーボネート（ＶＣ）を含む副成分は、負極のリチウムイオン透過性を損なわずに、負極表面の保護被膜の緻密性を高めることができる。よって、ＶＣとスルトン化合物を併用することによって、少量のスルトン化合物で充放電サイクル寿命を改善することが可能になる。つまり、低温放電特性へ悪影響をほとんど及ぼさずに、充放電サイクル寿命を向上することができる。
【００６７】
非水溶媒中の副成分の体積比率（ｗ）は、１０体積％以下の範囲内にすることが望ましい。これは、副成分の体積比率（ｗ）を１０体積％よりも多くすると、負極表面の保護被膜のリチウムイオン透過性が低下して低温放電特性が大幅に損なわれる可能性があるからである。また、副成分の分解によるガス発生を生じる恐れもある。副成分の体積比率（ｗ）のさらに好ましい範囲は、０．０１〜５体積％である。
【００６８】
前記非水溶媒に溶解される電解質としては、例えば、過塩素酸リチウム（ＬｉＣｌＯ_４）、六フッ化リン酸リチウム（ＬｉＰＦ_６）、四フッ化ホウ酸リチウム（ＬｉＢＦ_４）、六フッ化砒素リチウム（ＬｉＡｓＦ_６）、トリフルオロメタスルホン酸リチウム（ＬｉＣＦ_３ＳＯ_３）、ビストリフルオロメチルスルホニルイミドリチウム［ＬｉＮ（ＣＦ_３ＳＯ_２）_２］、ＬｉＮ（Ｃ_２Ｆ_５ＳＯ_２）_２などのリチウム塩を挙げることができる。使用する電解質の種類は、１種類または２種類以上にすることができる。
【００６９】
中でも、ＬｉＰＦ_６あるいはＬｉＢＦ_４を含むものが好ましい。また、ＬｉＮ（ＣＦ_３ＳＯ_２）_２およびＬｉＮ（Ｃ_２Ｆ_５ＳＯ_２）_２のうち少なくとも一方からなるイミド塩と、ＬｉＢＦ_４及びＬｉＰＦ_６のうち少なくともいずれか一方からなる塩とを含有する混合塩Ａか、あるいはＬｉＢＦ_４及びＬｉＰＦ_６を含有する混合塩Ｂを用いると、高温でのサイクル寿命をより向上することができる。また、電解質の熱安定性が向上されるため、高温環境下で貯蔵時の自己放電による電圧低下を抑えることができる。
【００７０】
特に、混合塩Ｂが好ましい。また、混合塩Ｂにおいては、ＬｉＢＦ_４の存在比を５〜４０ｍｏｌ％、より好ましくは１０〜３０ｍｏｌ％の範囲内にすることが望ましい。
【００７１】
前記電解質の前記非水溶媒に対する溶解量は、０．５〜２．５モル／Ｌとすることが望ましい。さらに好ましい範囲は、１〜２．５モル／Ｌである。
【００７２】
前記液状非水電解質には、セパレータとの濡れ性を良くするために、トリオクチルフォスフェート（ＴＯＰ）のような界面活性剤を含有させることが望ましい。界面活性剤の添加量は、３％以下が好ましく、さらには０．１〜１％の範囲内にすることが好ましい。
【００７３】
前記液状非水電解質の量は、電池単位容量１００ｍＡｈ当たり０．２〜０．６ｇにすることが好ましい。液状非水電解質量のより好ましい範囲は、０．２５〜０．５５ｇ／１００ｍＡｈである。
【００７４】
６）容器（収納容器）
容器の形状は、例えば、有底円筒形、有底矩形筒型、袋状、カップ状等にすることができる。
【００７５】
この容器は、例えば、樹脂層を含むシート、金属板、金属フィルム等から形成することができる。
【００７６】
前記シートに含まれる樹脂層は、例えば、ポリオレフィン（例えば、ポリエチレン、ポリプロピレン）、ポリアミド等から形成することができる。前記シートとしては、金属層と、前記金属層の両面に配置された保護層とが一体化されたシートを用いることが望ましい。前記金属層は、水分を遮断する役割と容器の形状保持を担う。前記金属層は、例えば、アルミニウム、ステンレス、鉄、銅、ニッケル等を挙げることができる。中でも、軽量で、水分を遮断する機能が高いアルミニウムが好ましい。前記金属層は、１種類の金属から形成しても良いが、２種類以上の金属層を一体化させたものから形成しても良い。前記２つの保護層のうち、外部と接する保護層は前記金属層の損傷を防止する役割をなす。この外部保護層は、１種類の樹脂層、もしくは２種類以上の樹脂層から形成される。一方、内部保護層は、前記金属層が非水電解質により腐食されるのを防止する役割を担う。この内部保護層は、１種類の樹脂層、もしくは２種類以上の樹脂層から形成される。また、かかる内部保護層の表面に、容器をヒートシールにより封止するための熱可塑性樹脂を配することができる。
【００７７】
前記シートの厚さは、０．３ｍｍ以下にすることが望ましい。これは、厚さが０．３ｍｍより厚いと、高い重量エネルギー密度及び体積エネルギー密度を得られ難くなるからである。シートの厚さの好ましい範囲は、０．２５ｍｍ以下で、更に好ましい範囲は０．１５ｍｍ以下で、最も好ましい範囲は０．１２ｍｍ以下である。また、厚さが０．０５ｍｍより薄いと、変形や破損し易くなることから、シートの厚さの下限値は０．０５ｍｍにすることが好ましい。
【００７８】
前記シートの表面の少なくとも一部に接着層を形成し、前記接着層により前記電極群を前記シートの内面に接着することが望ましい。このような構成にすると、前記電極群の表面に前記シートを固定することができるため、電解液が電極群と容器の間に浸透するのを抑えることができる。
【００７９】
前記金属板及び前記金属フィルムは、例えば、鉄、ステンレス、アルミニウムから形成することができる。
【００８０】
前記金属板及び金属フィルムの厚さは、０．４ｍｍ以下にすることが望ましい。これは、厚さが０．４ｍｍより厚いと、高い重量エネルギー密度及び体積エネルギー密度を得られ難くなるからである。金属板及び金属フィルムの厚さの好ましい範囲は、０．３ｍｍ以下で、最も好ましい範囲は０．２５ｍｍ以下である。また、厚さが０．０５ｍｍより薄いと、十分な強度を得られなくなることから、金属板及び金属フィルムの厚さの下限値は０．０５ｍｍにすることが好ましい。
【００８１】
容器の厚さは、以下に説明する方法で測定される。すなわち、容器の封止部を除く領域において、互いに１ｃｍ以上離れて存在する３点を任意に選択し、各点の厚さを測定し、平均値を算出し、この値を容器の厚さとする。なお、前記容器の表面に異物（例えば、樹脂）が付着している場合、この異物を除去してから厚さの測定を行う。例えば、前記容器の表面にＰＶｄＦが付着している場合、前記容器の表面をジメチルホルムアミド溶液で拭き取ることによりＰＶｄＦを除去した後、厚さの測定を行う。
【００８２】
本発明に係る非水電解質二次電池の一例である薄型、角形、円筒形非水電解質二次電池を図１〜図４を参照して詳細に説明する。
【００８３】
図１は、本発明に係わる非水電解質二次電池の一例である薄型非水電解質二次電池を示す斜視図、図２は図１の薄型非水電解質二次電池を短辺方向に沿って切断した部分断面図で、図３は本発明に係る非水電解質二次電池の一例である角形非水電解質二次電池を示す部分切欠斜視図、図４は本発明に係る非水電解質二次電池の一例である円筒形非水電解質二次電池を示す部分断面図である。
【００８４】
まず、薄型非水電解質二次電池について説明する。
【００８５】
図１に示すように、矩形のカップ状をなす容器本体１内には、電極群２が収納されている。電極群２は、正極３と、負極４と、正極３と負極４の間に配置されるセパレータ５を含む積層物が偏平形状に捲回された構造を有する。非水電解質は、電極群２に保持されている。容器本体１の縁の一部は幅広になっており、蓋板６として機能する。容器本体１と蓋板６は、それぞれ、ラミネートフィルムから構成される。このラミネートフィルムは、外部保護層７と、熱可塑性樹脂を含有する内部保護層８と、外部保護層７と内部保護層８の間に配置される金属層９とを含む。容器本体１には蓋体６が内部保護層８の熱可塑性樹脂を用いてヒートシールによって固定され、それにより容器内に電極群２が密封される。正極３には正極タブ１０が接続され、負極４には負極タブ１１が接続され、それぞれ容器の外部に引き出されて、正極端子及び負極端子の役割を果たす。
【００８６】
次いで、角形非水電解質二次電池について説明する。
【００８７】
図３に示すように、例えばアルミニウムのような金属製の有底矩形筒状容器１２内には、電極群１３が収納されている。電極群１３は、正極１４、セパレータ１５及び負極１６がこの順序で積層され、扁平状に捲回されたものである。中央付近に開口部を有するスペーサ１７は、電極群１３の上方に配置されている。
【００８８】
非水電解質は、電極群１３に保持されている。防爆機構１８ａを備え、かつ中央付近に円形孔が開口されている封口板１８ｂは、容器１２の開口部にレーザ溶接されている。負極端子１９は、封口板１８ｂの円形孔にハーメチックシールを介して配置されている。負極１６から引き出された負極タブ２０は、負極端子１９の下端に溶接されている。一方、正極タブ（図示しない）は、正極端子を兼ねる容器１２に接続されている。
【００８９】
次いで、円筒形非水電解質二次電池について説明する。
【００９０】
ステンレスからなる有底円筒状の容器２１は、底部に絶縁体２２が配置されている。電極群２３は、前記容器２１に収納されている。前記電極群２３は、正極２４、セパレータ２５、負極２６及びセパレータ２５を積層した帯状物を前記セパレータ２５が外側に位置するように渦巻き状に捲回した構造になっている。
【００９１】
前記容器２１内には、非水電解質が収容されている。中央部が開口された絶縁紙２７は、前記容器２１内の前記電極群２３の上方に配置されている。絶縁封口板２８は、前記容器２１の上部開口部に配置され、かつ前記上部開口部付近を内側にかしめ加工することにより前記封口板２８は前記容器２１に固定されている。正極端子２９は、前記絶縁封口板２８の中央に嵌合されている。正極リード３０の一端は、前記正極２４に、他端は前記正極端子２９にそれぞれ接続されている。前記負極２６は、図示しない負極リードを介して負極端子である前記容器２１に接続されている。
【００９２】
以上説明した本発明に係る非水電解質二次電池は、正極と、リチウムイオンを吸蔵・放出可能な炭素質物を含む負極と、非水溶媒を含む非水電解質とを具備した非水電解質二次電池であり、
前記非水溶媒は、エチレンカーボネート（ＥＣ）と、少なくともメチルエチルカーボネート（ＭＥＣ）を含む鎖状カーボネートと、環内に少なくとも一つの二重結合を有するスルトン化合物とを含むことを特徴とするものである。
【００９３】
このような二次電池によれば、負極表面にリチウムイオン透過性に優れる緻密な保護被膜を形成することができるため、実用的な低温放電特性を維持しつつ、充電時の負極と非水溶媒との副反応を抑えることができる。その結果、初充電時のガス発生量が低減され、かつ実用的な低温放電特性と優れた充放電サイクル寿命を有する非水電解質二次電池を実現することができる。
【００９４】
ところで、前記スルトン化合物は、負極表面全体を覆うように保護被膜を形成しやすいため、保護被膜の界面抵抗が高くなる傾向がある。一方、ビニレンカーボネート（ＶＣ）による保護被膜は、負極の端部（エッジ）に選択的に形成されやすいため、リチウムイオン透過性に優れるものの、緻密性にやや劣る。メソフェーズピッチ系炭素材料または黒鉛材料のような炭素質物を負極に用いる際、ＥＣと前記鎖状カーボネートと前記スルトン化合物とＶＣとを含む非水溶媒を使用することによって、負極の界面抵抗を増大させることなく、負極表面に緻密で、かつリチウムイオン透過性に優れる保護被膜を形成することができる。その結果、二次電池の充放電サイクル寿命をさらに向上することができる。
【００９５】
【実施例】
以下、本発明の実施例を前述した図面を参照して詳細に説明する。
【００９６】
（実施例１）
＜正極の作製＞
まず、リチウムコバルト酸化物（Ｌｉ_ｘＣｏＯ_２；但し、Ｘは０＜Ｘ≦１である）粉末９０重量％に、アセチレンブラック５重量％と、ポリフッ化ビニリデン（ＰＶｄＦ）５重量％のジメチルフォルムアミド（ＤＭＦ）溶液とを加えて混合し、スラリーを調製した。前記スラリーを厚さが１５μｍのアルミニウム箔からなる集電体の両面に塗布した後、乾燥し、プレスすることにより、正極層が集電体の両面に担持された構造の正極を作製した。なお、正極層の厚さは、片面当り６０μｍであった。
【００９７】
＜負極の作製＞
炭素質材料として３０００℃で熱処理したメソフェーズピッチ系炭素繊維（粉末Ｘ線回折により求められる（００２）面の面間隔（ｄ_００２）が０．３３６ｎｍ）の粉末を９５重量％と、ポリフッ化ビニリデン（ＰＶｄＦ）５重量％のジメチルフォルムアミド（ＤＭＦ）溶液とを混合し、スラリーを調製した。前記スラリーを厚さが１２μｍの銅箔からなる集電体の両面に塗布し、乾燥し、プレスすることにより、負極層が集電体に担持された構造の負極を作製した。なお、負極層の厚さは、片面当り５５μｍであった。
【００９８】
なお、炭素質物の（００２）面の面間隔ｄ_００２は、粉末Ｘ線回折スペクトルから半値幅中点法によりそれぞれ求めた。この際、ローレンツ散乱等の散乱補正は、行わなかった。
【００９９】
＜セパレータ＞
厚さが２５μｍの微多孔性ポリエチレン膜からなるセパレータを用意した。
【０１００】
＜非水電解液の調製＞
エチレンカーボネート（ＥＣ）、メチルエチルカーボネート（ＭＥＣ）および１，３−プロペンスルトン（ＰＲＳ）を体積比率（ＥＣ：ＭＥＣ：ＰＲＳ）が３３：６６：１になるように混合して非水溶媒を調製した。得られた非水溶媒に六フッ化リン酸リチウム（ＬｉＰＦ_６）をその濃度が１．０モル／Ｌになるように溶解させて、液状非水電解質を調製した。
【０１０１】
＜電極群の作製＞
前記正極の集電体に帯状アルミニウム箔（厚さ１００μｍ）からなる正極リードを超音波溶接し、前記負極の集電体に帯状ニッケル箔（厚さ１００μｍ）からなる負極リードを超音波溶接した後、前記正極及び前記負極をその間に前記セパレータを介して渦巻き状に捲回した後、偏平状に成形し、電極群を作製した。
【０１０２】
アルミニウム箔の両面をポリエチレンで覆った厚さ１００μｍのラミネートフィルムを、プレス機により矩形のカップ状に成形し、得られた容器内に前記電極群を収納した。
【０１０３】
次いで、容器内の電極群に８０℃で真空乾燥を１２時間施すことにより電極群及びラミネートフィルムに含まれる水分を除去した。
【０１０４】
容器内の電極群に前記液状非水電解質を電池容量１Ａｈ当たりの量が４．８ｇとなるように注入し、ヒートシールにより封止することによって、前述した図１、２に示す構造を有し、厚さが３．６ｍｍ、幅が３５ｍｍ、高さが６２ｍｍの薄型非水電解質二次電池を組み立てた。
【０１０５】
（実施例２〜５）
非水溶媒中のＰＲＳ含有量（ｚ）を下記表１に示すように変更すること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１０６】
（実施例６）
ＰＲＳの代わりに、１，４−ブチレンスルトン（ＢＴＳ）を用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１０７】
（実施例７〜８）
非水溶媒中のＢＴＳ含有量（ｚ）を下記表１に示すように変更すること以外は、前述した実施例６と同様にして非水電解質二次電池を製造した。
【０１０８】
（実施例９）
エチレンカーボネート（ＥＣ）、メチルエチルカーボネート（ＭＥＣ）、ジエチルカーボネート（ＤＥＣ）および１，３−プロペンスルトン（ＰＲＳ）を体積比率（ＥＣ：ＭＥＣ：ＤＥＣ：ＰＲＳ）が３３：４９．５：１６．５：１になるように混合して非水溶媒を調製した。得られた非水溶媒に六フッ化リン酸リチウム（ＬｉＰＦ_６）をその濃度が１．０モル／Ｌになるように溶解させて、液状非水電解質を調製した。
【０１０９】
かかる液状液状非水電解質を用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１１０】
（実施例１０〜１１）
非水溶媒中のＰＲＳ含有量（ｚ）を下記表１に示すように変更すること以外は、前述した実施例９と同様にして非水電解質二次電池を製造した。
【０１１１】
（実施例１２）
エチレンカーボネート（ＥＣ）、メチルエチルカーボネート（ＭＥＣ）、ジメチルカーボネート（ＤＭＣ）および１，３−プロペンスルトン（ＰＲＳ）を体積比率（ＥＣ：ＭＥＣ：ＤＭＣ：ＰＲＳ）が３３：４９．５：１６．５：１になるように混合して非水溶媒を調製した。得られた非水溶媒に六フッ化リン酸リチウム（ＬｉＰＦ_６）をその濃度が１．０モル／Ｌになるように溶解させて、液状非水電解質を調製した。
【０１１２】
かかる液状液状非水電解質を用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１１３】
（実施例１３〜１４）
非水溶媒中のＰＲＳ含有量（ｚ）を下記表１に示すように変更すること以外は、前述した実施例１２と同様にして非水電解質二次電池を製造した。
【０１１４】
（実施例１５）
エチレンカーボネート（ＥＣ）、メチルエチルカーボネート（ＭＥＣ）、１，３−プロペンスルトン（ＰＲＳ）及び１，４−ブチレンスルトン（ＢＴＳ）を体積比率（ＥＣ：ＭＥＣ：ＰＲＳ：ＢＴＳ）が３３：６６：０．５：０．５になるように混合して非水溶媒を調製した。得られた非水溶媒に六フッ化リン酸リチウム（ＬｉＰＦ_６）をその濃度が１．０モル／Ｌになるように溶解させて、液状非水電解質を調製した。
【０１１５】
かかる液状非水電解質を用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１１６】
（実施例１６）
エチレンカーボネート（ＥＣ）、メチルエチルカーボネート（ＭＥＣ）、１，３−プロペンスルトン（ＰＲＳ）及び１，４−ブチレンスルトン（ＢＴＳ）を体積比率（ＥＣ：ＭＥＣ：ＰＲＳ：ＢＴＳ）が３０：６０：５：５になるように混合して非水溶媒を調製した。得られた非水溶媒に六フッ化リン酸リチウム（ＬｉＰＦ_６）をその濃度が１．０モル／Ｌになるように溶解させて、液状非水電解質を調製した。
【０１１７】
かかる液状非水電解質を用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１１８】
（実施例１７）
エチレンカーボネート（ＥＣ）、ビニレンカーボネート（ＶＣ）、メチルエチルカーボネート（ＭＥＣ）及び１，３−プロペンスルトン（ＰＲＳ）を体積比率（ＥＣ：ＶＣ：ＭＥＣ：ＰＲＳ）が３３：０．５：６６：０．５になるように混合して非水溶媒を調製した。得られた非水溶媒に六フッ化リン酸リチウム（ＬｉＰＦ_６）をその濃度が１．０モル／Ｌになるように溶解させて、液状非水電解質を調製した。
【０１１９】
かかる液状非水電解質を用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１２０】
（実施例１８）
エチレンカーボネート（ＥＣ）、ビニレンカーボネート（ＶＣ）、メチルエチルカーボネート（ＭＥＣ）及び１，４−ブチレンスルトン（ＢＴＳ）を体積比率（ＥＣ：ＶＣ：ＭＥＣ：ＢＴＳ）が３３：０．５：６６：０．５になるように混合して非水溶媒を調製した。得られた非水溶媒に六フッ化リン酸リチウム（ＬｉＰＦ_６）をその濃度が１．０モル／Ｌになるように溶解させて、液状非水電解質を調製した。
【０１２１】
かかる液状非水電解質を用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１２２】
（実施例１９）
エチレンカーボネート（ＥＣ）、ビニレンカーボネート（ＶＣ）、メチルエチルカーボネート（ＭＥＣ）、ジエチルカーボネート（ＤＥＣ）及び１，３−プロペンスルトン（ＰＲＳ）を体積比率（ＥＣ：ＶＣ：ＭＥＣ：ＤＥＣ：ＰＲＳ）が３３：０．５：４９．５：１６．５：０．５になるように混合して非水溶媒を調製した。得られた非水溶媒に六フッ化リン酸リチウム（ＬｉＰＦ_６）をその濃度が１．０モル／Ｌになるように溶解させて、液状非水電解質を調製した。
【０１２３】
かかる液状非水電解質を用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１２４】
（実施例２０）
ジエチルカーボネート（ＤＥＣ）の代わりにジメチルカーボネート（ＤＭＣ）を用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１２５】
（実施例２１）
実施例１で説明したのと同様な組成の非水溶媒に、四フッ化ホウ酸リチウム（ＬｉＢＦ_４）と六フッ化リン酸リチウム（ＬｉＰＦ_６）をそれぞれの濃度が０．２モル／Ｌ（ＬｉＢＦ_４）、０．８モル／Ｌ（ＬｉＰＦ_６）になるように溶解させて、液状非水電解質を調製した。
【０１２６】
かかる液状非水電解質を用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１２７】
（比較例１〜７）
下記表２に示す組成の非水溶媒を用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１２８】
（比較例８）
ＰＲＳの代わりに、プロパンスルトン（ＰＳ）を用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１２９】
（比較例９）
負極に金属リチウムを用いること以外は、前述した実施例１と同様にして非水電解質二次電池を製造した。
【０１３０】
得られた実施例１〜２１および比較例１〜９の二次電池について、初充電前後における電池厚みの変化、充放電サイクル特性および低温放電特性を下記に説明する条件で評価し、その結果を下記表１〜２に示す。
【０１３１】
（初充電前後における電池厚みの変化）
各二次電池について、初充電直前の電池の厚さを測定した。その後、室温で０．２Ｃ（１３０ｍＡ）で４．２Ｖまで定電流・定電圧充電を１５時間行い、再度電池の厚さを測定した。初充電後の電池の厚さを初充電前の電池の厚さで割った値を、厚みの変化率とした。
【０１３２】
（充放電サイクル特性）
各二次電池について、初充放電工程として、室温で０．２Ｃ（１３０ｍＡ）で４．２Ｖまで定電流・定電圧充電を１５時間行い、その後、室温で０．２Ｃで３．０Ｖまで放電した。
【０１３３】
次に、充放電サイクル特性として、充放電レート１Ｃ、充電終止電圧４．２Ｖ、放電終止電圧３．０Ｖの充放電試験を行い、温度２０℃の環境中において充放電を５００回繰り返した後の放電容量維持率（１回目の放電の容量を１００％とする）を求めた。
【０１３４】
（低温放電特性）
各二次電池について、初充放電工程として、室温で０．２Ｃ（１３０ｍＡ）で４．２Ｖまで定電流・定電圧充電を１５時間行い、その後、室温で０．２Ｃで３．０Ｖまで放電した。
【０１３５】
次に、温度−２０℃の環境下で、放電レート１Ｃ、放電終止電圧３．０Ｖの条件で放電させることにより、低温での放電容量を測定した。室温において同条件で放電した場合の放電容量を１００％として低温放電容量を表わし、その結果を−２０℃での放電容量維持率とした。
【０１３６】
ここで、１Ｃとは公称容量（Ａｈ）を１時間で放電するために必要な電流値である。よって、０．２Ｃは、公称容量（Ａｈ）を５時間で放電するために必要な電流値である。
【０１３７】
【表１】

【０１３８】
【表２】

【０１３９】
表１及び表２から明らかなように、少なくともＭＥＣを含む鎖状カーボネートとＥＣと環内に少なくとも一つの二重結合を有するスルトン化合物とを含む非水溶媒を備えた実施例１〜２１の二次電池は、比較例１〜８の二次電池に比較して、初充電による容器の膨れが少なく、かつ５００サイクル後の容量維持率が高いことがわかる。
【０１４０】
また、実施例１〜５を比較することによって、スルトン化合物の体積比率ｚが多い方が初充電による容器の膨れが少なくなり、かつ５００サイクル後の容量維持率が高くなるものの、−２０℃における放電容量が低くなることがわかる。よって、実用的な低温放電特性を確保しつつ、初充電による容器の膨れとサイクル寿命とを改善するためには、スルトン化合物の体積比率ｚを０＜ｚ≦１０にすることが望ましい。
【０１４１】
実施例１〜３と実施例９〜１１を比較することによって、ＥＣ、ＭＥＣ、ＤＥＣ及びＰＲＳを含む非水溶媒を備えた実施例９〜１１は、５００サイクル後の容量維持率をより高くできることが理解できる。また、実施例１〜３と実施例１２〜１４を比較することによって、ＥＣ、ＭＥＣ、ＤＭＣ及びＰＲＳを含む非水溶媒を備えた実施例１２〜１４は、−２０℃での放電容量維持率がより高くなることが理解できる。
【０１４２】
さらに、５００サイクル後の容量維持率の点では、ＰＲＳまたはＢＴＳとＥＣとＶＣとＭＥＣとを含む非水溶媒を備える実施例１７〜１８の二次電池が最も高くなることがわかる。一方、−２０℃での放電容量維持率の点では、ＥＣ、ＶＣ、ＭＥＣ、ＤＭＣ及びＰＲＳを含む非水溶媒を備える実施例２０の二次電池が最も高くなる。
【０１４３】
これに対し、初充電前後での電池の厚みの変化率から、スルトン化合物が無添加の非水溶媒を用いる比較例１、３〜７の二次電池は、初充電後にラミネートの電池外装体が著しく変形し、二次電池として使用するには不適当であることが明らかである。また、スルトン化合物を１０体積％含むものの、ＥＣの量が９体積％と少ない非水溶媒を備えた比較例２の二次電池も、初充電による電池の厚みの増加率が大きかった。
【０１４４】
さらに、比較例８のような、プロパンスルトンのように二重結合を持たないスルトン化合物によると、すべての試験項目において、無添加の時よりも悪くなる結果が得られた。
【０１４５】
一方、比較例９に示すように、金属リチウムからなる負極を用いる際に、実施例１と同様な組成の非水電解質を使用すると、初充電による電池厚さの増加率を少なくすることができるものの、５００サイクル後の容量維持率が１２％と著しく低くなる。これは、金属リチウムからなる負極の方が、炭素質物を含む負極に比べて、非水電解質に対する反応性が著しく高いため、スルトン化合物由来の保護皮膜とＥＣ添加では負極と非水電解質との反応を十分に抑えることができないためであると推測される。
【０１４６】
（実施例２２）
ポリエチレングリコールジアクリレート（分子量１０００）と、実施例１で説明したのと同様な組成の液状非水電解質とを重量比１：１０の割合で混合し、さらにこれに熱重合開始剤としてｔ−ヘキシルパーオキシピバレートを５０００ｐｐｍ添加することにより、プレゲル溶液を調製した。
【０１４７】
前述した実施例１で説明したのと同様にして電極群を作製し、この電極群を容器内に収納し、真空乾燥を施した後、プレゲル溶液を電池容量１Ａｈあたり５．２ｇの量で注液した。次いで、ヒートシールにより封止した後、６０℃で３時間加熱することによりプレゲル溶液を重合・架橋してゲル状非水電解質とし、薄型非水電解質二次電池を得た。
【０１４８】
（比較例１０）
プレゲル溶液中に１，３−プロペンスルトンを添加しないこと以外は前述した実施例２２と同様にして非水電解質二次電池を製造した。
【０１４９】
得られた実施例２２及び比較例１０の二次電池について、初充電前後における電池厚みの変化、充放電サイクル特性および低温放電特性を前述した実施例１で説明したのと同様な条件で評価し、その結果を下記表３に示す。
【０１５０】
【表３】

【０１５１】
表３から明らかなように、エチレンカーボネートとメチルエチルカーボネートとスルトン化合物とを含むゲル状非水電解質を備えた実施例２２の二次電池は、スルトン化合物が無添加の比較例１０に比較して、初充電前後での電池の厚みの変化率が小さく、かつ充放電サイクル特性と低温放電特性に優れていることが理解できる。
【０１５２】
（実施例２３）
肉厚が０．２５ｍｍのアルミニウム製の角形缶に、実施例１で説明したのと同様な電極群を収納した。
【０１５３】
次いで、金属缶内の電極群に８０℃で真空乾燥を１２時間施すことにより電極群及び金属缶に含まれる水分を除去した。
【０１５４】
引き続き、金属缶内の電極群に前述した実施例１で説明したのと同様な液状非水電解質を電池容量１Ａｈ当たりの量が４．８ｇとなるように注入し、注液孔を溶接により封止することにより、前述した図３に示す構造を有し、厚さが４．８ｍｍ、幅が３０ｍｍ、高さが４８ｍｍの角形非水電解質二次電池を組み立てた。
【０１５５】
（比較例１１）
非水溶媒にスルトン化合物を添加しないこと以外は、前述した実施例２３と同様にして非水電解質二次電池を製造した。
【０１５６】
（実施例２４）
前述した実施例１で説明したのと同様な正極と負極とセパレータを用意し、正極と負極の間にセパレータを介して渦巻き状に捲回することにより電極群を作製した。得られた電極群を肉厚が０．２２ｍｍのステンレス製の円筒形缶に収納した。
【０１５７】
次いで、金属缶内の電極群に８０℃で真空乾燥を１２時間施すことにより電極群及び金属缶に含まれる水分を除去した。
【０１５８】
金属缶内の電極群に前述した実施例１で説明したのと同様な液状非水電解質を電池容量１Ａｈ当たりの量が４．８ｇとなるように注入し、かしめ固定により封止することによって、前述した図４に示す構造を有し、径が１８ｍｍ、高さが６５ｍｍの円筒形非水電解質二次電池を組み立てた。
【０１５９】
（比較例１２）
非水溶媒にスルトン化合物を添加しないこと以外は、前述した実施例２４と同様にして非水電解質二次電池を製造した。
【０１６０】
得られた実施例２３〜２４及び比較例１１〜１２の二次電池について、初充電前後における電池厚みの変化、充放電サイクル特性および低温放電特性を下記に説明する条件で評価し、その結果を下記表４に示す。
【０１６１】
（初充電前後における電池厚みの変化）
角形二次電池について、初充電直前の電池の厚さを測定した。その後、室温で０．２Ｃ（１２４ｍＡ）で４．２Ｖまで定電流・定電圧充電を１５時間行い、再度電池の厚さを測定した。初充電後の電池の厚さを初充電前の電池の厚さで割った値を、厚みの変化率とした。なお、円筒形二次電池では、初充電の際にガスが発生しても金属缶がほとんど膨れないため、初充電前後における電池厚みの変化度合いを評価することができなかった。
【０１６２】
（充放電サイクル特性）
各二次電池について、初充放電工程として、室温で０．２Ｃ（角形：１２４ｍＡ、円筒形：３６０ｍＡ）で４．２Ｖまで定電流・定電圧充電を１５時間行い、その後、室温で０．２Ｃで３．０Ｖまで放電した。
【０１６３】
次に、充放電サイクル特性として、充放電レート１Ｃ、充電終止電圧４．２Ｖ、放電終止電圧３．０Ｖの充放電試験を行い、温度２０℃の環境中において充放電を５００回繰り返した後の放電容量維持率（１回目の放電の容量を１００％とする）を求めた。
【０１６４】
（低温放電特性）
各二次電池について、初充放電工程として、室温で０．２Ｃで４．２Ｖまで定電流・定電圧充電を１５時間行い、その後、室温で０．２Ｃで３．０Ｖまで放電した。
【０１６５】
次に、温度−２０℃の環境下で、放電レート１Ｃ、放電終止電圧３．０Ｖの条件で放電させることにより、低温での放電容量を測定した。室温において同条件で放電した場合の放電容量を１００％として低温放電容量を表わし、その結果を−２０℃での放電容量維持率とした。
【０１６６】
【表４】

【０１６７】
実施例２３及び比較例１１の角形非水電解質二次電池において、初充電前後の電池厚みの変化率は、外装体が金属缶であるために、実施例２３よりも小さくなっているが、この場合もスルトン化合物を含まない比較例１１よりも実施例２３の方が良い値を示している。また、角形、円筒形共に、スルトン化合物の添加により、５００サイクル後の容量維持率と−２０℃放電容量維持率が改善されていることが明らかである。
【０１６８】
（ＰＲＳとＶＣの検出方法）
また、実施例１７の二次電池について、前記初充放電工程後、５時間以上回路を開放して十分に電位を落ち着かせた後、Ａｒ濃度が９９．９％以上、かつ露点が−５０℃以下のグローブボックス内で分解し、電極群を取り出した。前記電極群を遠沈管につめ、ジメチルスルホキシド（ＤＭＳＯ）−ｄ_６を加えて密封し、前記グローブボックスより取り出し、遠心分離を行った。その後、前記グローブボックス内で、前記遠沈管から前記電解液と前記ＤＭＳＯ−ｄ_６の混合溶液を採取した。前記混合溶媒を５ｍｍφのＮＭＲ用試料管に０．５ｍｌ程度入れ、ＮＭＲ測定を行った。前記ＮＭＲ測定に用いた装置は日本電子株式会社製ＪＮＭ−ＬＡ４００ＷＢであり、観測核は^１Ｈ、観測周波数は４００ＭＨｚ、ジメチルスルホキシド（ＤＭＳＯ）−ｄ_６中に僅かに含まれる残余プロトン信号を内部基準として利用した（２．５ｐｐｍ）。測定温度は２５℃とした。^１ＨＮＭＲスペクトルではＥＣに対応するピークが４．５ｐｐｍ付近、ＶＣに対応するピークが７．７ｐｐｍ付近に観測された。一方、ＰＲＳに対応するピークが、図５に示すスペクトルのように５．１ｐｐｍ付近（Ｐ_１）、７．０５ｐｐｍ付近（Ｐ_２）及び７．２ｐｐｍ付近（Ｐ_３）に観測された。これらの結果から、初充放電工程後の実施例１７の二次電池に存在する非水溶媒中にＶＣとＰＲＳが含まれていることを確認できた。
【０１６９】
また、観測周波数を１００ＭＨｚとし、ジメチルスルホキシド（ＤＭＳＯ）−ｄ_６（３９．５ｐｐｍ）を内部基準物質として^１３ＣＮＭＲ測定を行ったところ、ＥＣに対応するピークが６６ｐｐｍ付近、ＶＣに対応するピークが１３３ｐｐｍ付近、ＰＲＳに対応するピークが７４ｐｐｍ付近と１２４ｐｐｍ付近と１４０ｐｐｍ付近に観測され、この結果からも、初充放電工程後の実施例１７の二次電池に存在する非水溶媒中にＶＣとＰＲＳが含まれていることを確認できた。
【０１７０】
さらに、^１ＨＮＭＲスペクトルにおいて、ＥＣのＮＭＲ積分強度に対するＶＣのＮＭＲ積分強度の比と、ＥＣのＮＭＲ積分強度に対するＰＲＳのＮＭＲ積分強度の比を求めたところ、非水溶媒全体に対するＶＣの割合、ＰＲＳの割合がいずれも二次電池組立て前より減少していることを確認することができた。
【０１７１】
なお、本発明は、上記の実施例に限るものではなく、他の種類の正極・負極・セパレータ・容器の組合わせにおいても同様に適用可能である。
【０１７２】
【発明の効果】
以上詳述したように本発明によれば、初充電時のガス発生量が低減され、実用的な低温放電特性と高い充放電サイクル寿命を有する非水電解質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】本発明に係わる非水電解質二次電池の一例である薄型非水電解質二次電池を示す斜視図。
【図２】図１の薄型非水電解質二次電池を短辺方向に沿って切断した部分断面図。
【図３】本発明に係る非水電解質二次電池の一例である角形非水電解質二次電池を示す部分切欠斜視図。
【図４】本発明に係る非水電解質二次電池の一例である円筒形非水電解質二次電池を示す部分断面図。
【図５】実施例１７の非水電解質二次電池の非水電解質に含まれるＰＲＳについての^１ＨＮＭＲスペクトルを示す特性図。
【符号の説明】
１…容器本体、
２…電極群、
３…正極、
４…負極、
５…セパレータ、
６…蓋板、
７…外部保護層、
８…内部保護層、
９…金属層、
１０…正極端子、
１１…負極端子。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
In recent years, in order to reduce the size and weight of electronic devices such as mobile communication devices, notebook computers, palmtop computers, integrated video cameras, portable CD (MD) players, and cordless telephones, these electronic devices have been developed. In particular, a small-sized and large-capacity battery is demanded as a power source for the battery.
[0003]
Examples of batteries that are widely used as power supplies for these electronic devices include primary batteries such as alkaline manganese batteries, and secondary batteries such as nickel cadmium batteries and lead storage batteries. Among them, a non-aqueous electrolyte secondary battery using a lithium composite oxide for the positive electrode and a carbonaceous material capable of occluding and releasing lithium ions for the negative electrode is small, lightweight, has a high unit cell voltage, and can obtain a high energy density. Attention has been paid to this.
[0004]
In the negative electrode, lithium or a lithium alloy can be used instead of the carbonaceous material. However, in this case, by repeating the charging and discharging operations of the secondary battery, the dissolution and precipitation of lithium are repeated, and a so-called dendrite which grows into a needle shape is formed, and the dendrite penetrates through the separator. There is a problem that a short circuit may occur. On the other hand, the negative electrode containing a carbonaceous material can suppress the formation of dendrites as compared with a negative electrode containing lithium or a lithium alloy.
[0005]
By the way, in recent years, as a container for accommodating an electrode group including a positive electrode and a negative electrode as described above, a container formed by laminating a metal foil such as aluminum and a resin into a bag shape or a cup shape is used. Have been. This has made it possible to further reduce the weight and size of the nonaqueous electrolyte secondary battery.
[0006]
On the other hand, as an electrolyte for a non-aqueous electrolyte secondary battery, a supporting salt is dissolved in a non-aqueous solvent in which a solvent having a high dielectric constant such as ethylene carbonate or propylene carbonate and a low-viscosity solvent such as methyl ethyl carbonate or diethyl carbonate are mixed. It is known that the use of such a material improves discharge characteristics at low temperatures.
[0007]
However, when a mixed non-aqueous solvent of a solvent having a high dielectric constant and a low-viscosity solvent is used, a large amount of gas is generated at the time of initial charging, so that in a non-aqueous electrolyte secondary battery including a container made of a laminated film, the container is There is a problem that the battery swells and deforms. Further, in a non-aqueous electrolyte secondary battery using a cylindrical or square metal can as a container, although the amount of deformation of the metal can due to gas generation at the time of initial charging is small, there is a possibility that the current cutoff valve may malfunction. .
[0008]
When a nonaqueous solvent mixture of a solvent having a high dielectric constant and a low viscosity solvent as described above is used, in a so-called charge / discharge cycle in which charging and discharging are repeated, a cyclic carbonate such as EC is formed on the carbonaceous material of the negative electrode. A decomposition reaction is caused to cause an inhibition of a charge / discharge reaction by a decomposition product and a deterioration of a carbonaceous material. This phenomenon is particularly remarkable when a substance such as highly crystallized graphite is used as the carbonaceous material. As a result, in the charge / discharge cycle, a phenomenon occurs in which the amount of discharged electricity gradually decreases, and the life of the charge / discharge cycle is shortened.
[0009]
[Problems to be solved by the invention]
An object of the present invention is to provide a non-aqueous electrolyte secondary battery in which the amount of gas generated during initial charging is reduced and the cycle life is improved.
[0010]
[Means for Solving the Problems]
The non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode including a carbonaceous material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte including a non-aqueous solvent. ,
The non-aqueous solvent contains ethylene carbonate (EC), a chain carbonate containing at least methyl ethyl carbonate (MEC), and a sultone compound having at least one double bond in a ring. is there.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
A non-aqueous electrolyte secondary battery according to the present invention includes a container, an electrode group housed in the container, and a non-aqueous electrolyte held by the electrode group and containing a non-aqueous solvent.
[0012]
The non-aqueous solvent includes ethylene carbonate (EC), a chain carbonate containing at least methyl ethyl carbonate (MEC), and a sultone compound having at least one double bond in a ring.
[0013]
The electrode group, positive electrode, negative electrode, separator, non-aqueous electrolyte, and container will be described.
[0014]
1) Electrode group
This electrode group may be, for example, whether (i) the positive electrode and the negative electrode are spirally wound with a separator interposed therebetween, or (ii) the positive electrode and the negative electrode are wound in a flat shape with a separator interposed therebetween. (Iii) the positive electrode and the negative electrode are spirally wound with a separator interposed therebetween, and then compressed in the radial direction; or (iv) the positive electrode and the negative electrode are bent at least once with a separator interposed therebetween. Alternatively, it is produced by a method of (v) laminating a positive electrode and a negative electrode with a separator interposed therebetween.
[0015]
The electrode group need not be pressed, but may be pressed to increase the integration strength of the positive electrode, the negative electrode, and the separator. In addition, heating can be performed at the time of pressing.
[0016]
The electrode group may contain an adhesive polymer in order to increase the integration strength of the positive electrode, the negative electrode, and the separator. It is desirable that the polymer having adhesiveness can maintain high adhesiveness while holding the non-aqueous electrolyte. Further, such a polymer is more preferably high in lithium ion conductivity. Specific examples include polyacrylonitrile (PAN), polyacrylate (PMMA), polyvinylidene fluoride (PVdF), polyvinyl chloride (PVC), and polyethylene oxide (PEO).
[0017]
2) Positive electrode
The positive electrode includes a current collector and a positive electrode layer supported on one or both surfaces of the current collector and containing an active material.
[0018]
The positive electrode layer includes a positive electrode active material, a binder, and a conductive agent.
[0019]
Examples of the positive electrode active material include various oxides such as manganese dioxide, lithium manganese composite oxide, lithium-containing nickel oxide, lithium-containing cobalt oxide, lithium-containing nickel-cobalt oxide, lithium-containing iron oxide, and lithium. Vanadium oxides and chalcogen compounds such as titanium disulfide and molybdenum disulfide can be exemplified. Among them, lithium-containing cobalt oxides (for example, LiCoO₂), Lithium-containing nickel cobalt oxide (eg, LiNi_0.8Co_0.2O₂), Lithium manganese composite oxide (eg, LiMn)₂O₄, LiMnO₂) Is preferable because a high voltage can be obtained. As the positive electrode active material, one kind of oxide may be used alone, or two or more kinds of oxides may be mixed and used.
[0020]
Examples of the conductive agent include acetylene black, carbon black, and graphite.
[0021]
The binder has a function of holding the active material on the current collector and connecting the active materials. As the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyethersulfone, ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), or the like is used. be able to.
[0022]
The mixing ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.
[0023]
As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, aluminum, stainless steel, or nickel.
[0024]
The positive electrode is manufactured, for example, by suspending a conductive agent and a binder in a suitable solvent in a positive electrode active material, applying the suspension to a current collector, and drying to form a thin plate.
[0025]
3) Negative electrode
The negative electrode includes a current collector and a negative electrode layer supported on one or both surfaces of the current collector.
[0026]
The negative electrode layer includes a carbonaceous material that stores and releases lithium ions and a binder.
[0027]
Examples of the carbonaceous material include a graphite material or a carbonaceous material such as graphite, coke, carbon fiber, spherical carbon, pyrolysis gas-phase carbonaceous material, and resin fired product; thermosetting resin, isotropic pitch, mesophase pitch Graphitic material obtained by performing a heat treatment at 500 to 3000 ° C. on a base carbon, a mesophase pitch-based carbon fiber, a mesophase small sphere or the like (in particular, a mesophase pitch-based carbon fiber is preferable because the capacity and charge / discharge cycle characteristics are increased) or Carbonaceous material; and the like. Among them, the plane distance d of the (002) plane₀₀₂It is preferable to use a graphitic material having a graphite crystal having a particle size of 0.34 nm or less. A nonaqueous electrolyte secondary battery provided with a negative electrode containing such a graphite material as a carbonaceous material can significantly improve the battery capacity and large current discharge characteristics. The surface distance d₀₀₂Is more preferably 0.337 nm or less.
[0028]
Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC). Can be used.
[0029]
The mixing ratio of the carbonaceous material and the binder is preferably in the range of 90 to 98% by weight of the carbonaceous material and 2 to 20% by weight of the binder.
[0030]
As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. These conductive substrates can be formed from, for example, copper, stainless steel, or nickel.
[0031]
The negative electrode is, for example, kneading a carbonaceous material that absorbs and releases lithium ions and a binder in the presence of a solvent, applies the obtained suspension to a current collector, and after drying, applies a desired pressure. By pressing once or multi-stage pressing 2 to 5 times.
[0032]
4) Separator
As the separator, a microporous membrane, a woven fabric, a nonwoven fabric, a laminate of the same material or a different material among them, or the like can be used. Examples of the material forming the separator include polyethylene, polypropylene, an ethylene-propylene copolymer, and an ethylene-butene copolymer. As the material for forming the separator, one or more kinds selected from the above-mentioned kinds can be used.
[0033]
The thickness of the separator is preferably 30 μm or less, and more preferably 25 μm or less. The lower limit of the thickness is preferably 5 μm, and more preferably 8 μm.
[0034]
The separator preferably has a heat shrinkage at 120 ° C. for one hour of 20% or less. More preferably, the heat shrinkage is 15% or less.
[0035]
The separator preferably has a porosity in the range of 30 to 60%. A more preferred range of porosity is 35-50%.
[0036]
The separator has an air permeability of 600 seconds / 100 cm.³The following is preferred. Air permeability is 100cm³Means the time (seconds) required for the air to pass through the separator. The upper limit of air permeability is 500 seconds / 100cm³Is more preferable. The lower limit of the air permeability is 50 seconds / 100 cm.³The lower limit is more preferably 80 seconds / 100 cm.³It is.
[0037]
It is desirable that the width of the separator be wider than the width of the positive electrode and the width of the negative electrode. With such a configuration, it is possible to prevent the positive electrode and the negative electrode from directly contacting each other without passing through the separator.
[0038]
5) Non-aqueous electrolyte
As the non-aqueous electrolyte, those having a substantially liquid or gel form can be used. The gel non-aqueous electrolyte can reduce the possibility that the non-aqueous electrolyte leaks to the outside when the container is broken by some external force. On the other hand, the liquid non-aqueous electrolyte can increase the ionic conductivity as compared with the gelled non-aqueous electrolyte, so that the capacity when discharging the non-aqueous electrolyte secondary battery with a large current and the capacity when discharging at a low temperature The capacity can be improved.
[0039]
The non-aqueous electrolyte is prepared, for example, by the methods described in the following (I) to (IV).
[0040]
(I) A non-aqueous electrolyte is obtained by dissolving an electrolyte (eg, lithium salt) in the above-described non-aqueous solvent (liquid non-aqueous electrolyte).
[0041]
(II) An organic polymer compound and a lithium salt are dissolved in a solvent to prepare a polymer solution. Next, the polymer solution is applied or impregnated to the electrode (at least one of the positive electrode and the negative electrode), the separator, or both the electrode and the separator, and the solvent is evaporated to be cast. Next, an electrode group is obtained by interposing a separator between the positive electrode and the negative electrode. This is accommodated in a container, and a non-aqueous electrolytic solution is injected and held on a cast polymer film to obtain a secondary battery including a gelled non-aqueous electrolyte.
[0042]
(III) In the above method (II), a crosslinked polymer may be used instead of the organic polymer compound. For example, (a) a prepolymer solution is prepared from a compound having a crosslinkable functional group, a lithium salt, and a solvent, and the prepolymer solution is used as an electrode (at least one of a positive electrode and a negative electrode), a separator, or an electrode and a separator. After coating or impregnating both, the compound having a crosslinkable functional group is crosslinked. Next, an electrode group is obtained by interposing a separator between the positive electrode and the negative electrode. The crosslinking step may be performed before or after the solvent is volatilized. In the case of crosslinking by heating, for example, the crosslinking may be performed while the solvent is volatilized. Alternatively, (b) the prepolymer solution is applied or impregnated on the electrode (at least one of the positive electrode and the negative electrode), the separator, or both the electrode and the separator, and then the separator is interposed between the positive electrode and the negative electrode. An electrode group is obtained. Thereafter, a cross-linking step can be performed.
[0043]
The method of crosslinking is not particularly limited, but heat polymerization or photopolymerization with ultraviolet rays is preferred from the viewpoint of simplicity and cost of the apparatus. When crosslinking is performed by heating or irradiation with ultraviolet rays, it is necessary to add a polymerization initiator suitable for the polymerization method to the prepolymer solution. Further, the polymerization initiator is not limited to one kind, and two or more kinds may be used as a mixture.
[0044]
(IV) An organic polymer compound and a lithium salt are directly dissolved in a non-aqueous electrolyte to obtain a gel electrolyte. This gel electrolyte is applied or impregnated to the electrode (at least one of the positive electrode and the negative electrode), the separator, or both the electrode and the separator, and subsequently, a separator is interposed between the positive electrode and the negative electrode to obtain an electrode group. Thus, a secondary battery including the gelled non-aqueous electrolyte is obtained.
[0045]
(V) In the method (IV) described above, a crosslinked polymer can be used instead of the organic polymer compound. For example, a pregel solution is prepared from a compound having a crosslinkable functional group, a lithium salt, and an electrolytic solution, and is applied to an electrode (at least one of a positive electrode and a negative electrode), a separator, or both an electrode and a separator. Alternatively, after impregnation, the compound having a crosslinkable functional group is crosslinked. This cross-linking step may be performed before or after manufacturing the electrode group.
[0046]
The method of crosslinking is not particularly limited, but heat polymerization or photopolymerization with ultraviolet rays is preferred from the viewpoint of simplicity and cost of the apparatus. When crosslinking is performed by heating or irradiation with ultraviolet rays, it is necessary to add a polymerization initiator suitable for the polymerization method to the pregel solution. Further, the polymerization initiator is not limited to one kind, and two or more kinds may be used as a mixture.
[0047]
(VI) An electrode group in which a separator is interposed between a positive electrode and a negative electrode is housed in a container. Next, after impregnating the electrode group with the gelled nonaqueous electrolyte of the above (IV), the container is sealed to obtain a secondary battery including the gelled nonaqueous electrolyte. Alternatively, after the electrode group is impregnated with the pregel solution of (V), the pregel solution is crosslinked before or after sealing the container to obtain a secondary battery including the gelled nonaqueous electrolyte.
[0048]
Examples of the organic polymer compound in the above (II) and (IV) include a polymer having a skeleton of an alkylene oxide such as polyethylene oxide or polypropylene oxide or a derivative thereof; {vinylidene fluoride, propylene hexafluoride, tetrafluoroethylene} , Perfluoroalkyl vinyl ether, or a copolymer thereof; polyacrylate-based polymer having polyacrylonitrile or a polyacrylonitrile as a main component and having a skeleton of a copolymer of methyl acrylate, vinyl pyrrolidone, vinyl acetate, or the like; Polycarbonate polymer; Polyacrylonitrile polymer; Polyethylene terephthalate, polybutylene terephthalate or derivatives thereof as a skeleton; ethyl methacrylate, styrene, biacetic acid Polyester polymer is a copolymer of such le; fluororesin; polyolefin resins; polyether resins; and a copolymer of two or more thereof; and the like. Further, a prepolymer solution (III) and a pregel solution (V) can be prepared from monomers or oligomers which are precursors of these polymers.
[0049]
Next, the non-aqueous solvent and the electrolyte contained in the liquid non-aqueous electrolyte and the gel non-aqueous electrolyte will be described.
[0050]
Various solvents constituting the non-aqueous solvent will be described.
[0051]
a. Ethylene carbonate
Ethylene carbonate has the advantage that (EC) has a high lithium ion conductivity and forms a good surface protective film on the negative electrode surface.
[0052]
It is desirable that the ratio (x) of EC to the total volume of the nonaqueous solvent is in the range of 20 to 50% by volume. This is due to the following reasons. If the ratio (x) of EC to the total volume of the nonaqueous solvent is less than 20% by volume, there is a possibility that a good surface protective film cannot be formed. EC contributes to the formation of a good surface protective film, but has a high freezing point and viscosity. Therefore, when the EC ratio (x) exceeds 50% by volume, the ionic conductivity of the non-aqueous electrolyte decreases and the low-temperature discharge characteristics are reduced. In this case, the charge / discharge cycle life may be significantly reduced.
[0053]
A more preferable range of the EC ratio (x) is in a range of 25 to 50% by volume, and a further preferable ratio (x) is in a range of 25 to 45% by volume.
[0054]
b. Chain carbonate
The chain carbonate contains methyl ethyl carbonate (MEC) as an essential component, and MEC alone may be used as the chain carbonate, or another chain carbonate may be used in combination with the MEC. Other chain carbonates used in combination with MEC preferably have a low freezing point and a low viscosity. Further, a solvent having a relatively low molecular weight is desirable. This is because the discharge characteristics at low temperatures are improved. As another chain carbonate, at least one of diethyl carbonate (DEC) and dimethyl carbonate (DMC) is preferable. Particularly, from the viewpoint of obtaining excellent charge / discharge cycle characteristics, a chain-like carbonate containing MEC and DEC is preferable, while from the viewpoint of obtaining excellent low-temperature discharge characteristics, a chain-like carbonate containing MEC and DMC is preferable.
[0055]
It is desirable that the ratio (y) of the chain carbonate to the total volume of the nonaqueous solvent is in the range of 40 to 80% by volume. This is due to the following reasons. If the ratio (y) of the chain carbonate to the total volume of the nonaqueous solvent is less than 40% by volume, sufficient low-temperature discharge characteristics may not be obtained. On the other hand, when the ratio (y) of the chain carbonate exceeds 80% by volume, gas generation becomes remarkable, and the battery characteristics at high temperatures may be deteriorated.
[0056]
A more preferred range of the ratio (y) of the chain carbonate is within a range of 50 to 80% by volume, and a still more preferable range (y) is within a range of 55 to 75% by volume.
[0057]
c. Sultone compounds having at least one double bond in the ring
Here, as the sultone compound having at least one double bond in the ring, the sultone compound A represented by the following general formula 1 or at least one H of the sultone compound A is substituted with a hydrocarbon group. Sultone compound B can be used. In the present application, the sultone compound A or the sultone compound B may be used alone, or both the sultone compound A and the sultone compound B may be used.
[0058]
Embedded image

[0059]
In Chemical Formula 1, C_mH_nIs a linear hydrocarbon group, and m and n are integers of 2 or more that satisfy 2m> n.
[0060]
The sultone compound having at least one double bond in the ring can form a protective film on the surface of the negative electrode because the double bond is opened by a reduction reaction with the negative electrode to cause a polymerization reaction. By the way, when a non-aqueous solvent containing EC, γ-butyrolactone (GBL) and the sultone compound is used, the formation of a protective film by EC is inhibited by GBL. As a result, a film-forming reaction of the sultone compound occurs preferentially, and even if the amount of the sultone compound added is small, the film becomes thick, so that the interface resistance is increased.
[0061]
According to the non-aqueous solvent containing EC, a chain carbonate containing at least MEC, and the sultone compound as in the present invention, the sultone compound does not contain a sultone compound because it acts to repair a protective film formed by EC. A better protective film can be formed than when. Thereby, generation of gas at the time of initial charging can be suppressed. Further, this protective coating has high lithium ion permeability but low solvent permeability, and thus lithium ions (Li) absorbed in the carbonaceous material of the negative electrode.⁺) And the solvent during the charging can be suppressed. Therefore, a decrease in the amount of discharge electricity accompanying the progress of the charge / discharge cycle can be suppressed, so that the charge / discharge cycle life can be improved.
[0062]
Among the sultone compounds, a compound having m = 3 and n = 4 in the sultone compound A, that is, 1,3-propene sultone (PRS) or a compound having m = 4 and n = 6, that is, 1 , 4-butylene sultone (BTS). As the sultone compound, 1,3-propene sultone (PRS) or 1,4-butylene sultone (BTS) may be used alone, or these PRS and BTS may be used in combination. According to the sultone compound of at least one of PRS and BTS, a good protective film can be formed on the negative electrode surface in the presence of EC and a chain carbonate containing at least MEC, and at the time of charging with a solvent. The effect of suppressing side reactions can be maximized.
[0063]
It is desirable that the ratio (z) of the sultone compound be 10% by volume or less. This is because, when the ratio (z) of the sultone compound exceeds 10% by volume, the protective coating becomes extremely thick, the lithium ion permeability is reduced, and the discharge capacity at a temperature lower than room temperature is reduced. Further, in order to keep the discharge capacity high even at a low temperature such as -20 ° C, the ratio (z) containing the sultone compound is desirably 4% by volume or less. In addition, in order to sufficiently secure the formation amount of the protective film, it is desirable to secure the ratio (z) of the sultone compound at least 0.01% by volume. Further, when the ratio (z) of the sultone compound is 0.1% by volume or more, the protective function of the protective film can be sufficiently exhibited even at a higher temperature such as 65 ° C.
[0064]
d. Minor component
The non-aqueous solvent may contain a solvent other than EC, chain carbonate, and sultone compound.
[0065]
Examples of the auxiliary component include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), phenylethylene carbonate (phEC), propylene carbonate (PC), γ-valerolactone (VL), methyl propionate (MP), and propionic acid. Ethyl (EP), 2-methylfuran (2Me-F), furan (F), thiophene (TIOP), catechol carbonate (CATC), ethylene sulfite (ES), 12-crown-4 (crown), tetraethylene glycol Dimethyl ether (Ether) and the like can be mentioned. The types of subcomponents can be one or two or more.
[0066]
Above all, the auxiliary component containing vinylene carbonate (VC) can increase the denseness of the protective coating on the negative electrode surface without impairing the lithium ion permeability of the negative electrode. Therefore, by using VC and the sultone compound in combination, it becomes possible to improve the charge / discharge cycle life with a small amount of the sultone compound. That is, the charge / discharge cycle life can be improved with almost no adverse effect on the low-temperature discharge characteristics.
[0067]
It is desirable that the volume ratio (w) of the subcomponent in the non-aqueous solvent is in the range of 10% by volume or less. This is because, when the volume ratio (w) of the subcomponent is more than 10% by volume, the lithium ion permeability of the protective film on the negative electrode surface may be reduced and the low-temperature discharge characteristics may be significantly impaired. In addition, gas may be generated due to decomposition of subcomponents. A more preferable range of the volume ratio (w) of the accessory component is 0.01 to 5% by volume.
[0068]
Examples of the electrolyte dissolved in the non-aqueous solvent include lithium perchlorate (LiClO₄), Lithium hexafluorophosphate (LiPF)₆), Lithium tetrafluoroborate (LiBF₄), Lithium arsenic hexafluoride (LiAsF)₆), Lithium trifluorometasulfonate (LiCF₃SO₃), Lithium bistrifluoromethylsulfonylimide [LiN (CF₃SO₂)₂], LiN (C₂F₅SO₂)₂And the like. The type of electrolyte used can be one or more.
[0069]
Among them, LiPF₆Or LiBF₄Is preferred. In addition, LiN (CF₃SO₂)₂And LiN (C₂F₅SO₂)₂An imide salt comprising at least one of₄And LiPF₆Mixed salt A containing at least one of the following, or LiBF₄And LiPF₆When the mixed salt B containing is used, the cycle life at a high temperature can be further improved. Further, since the thermal stability of the electrolyte is improved, a voltage drop due to self-discharge during storage in a high-temperature environment can be suppressed.
[0070]
Particularly, mixed salt B is preferable. In the mixed salt B, LiBF₄Is preferably in the range of 5 to 40 mol%, more preferably 10 to 30 mol%.
[0071]
The amount of the electrolyte dissolved in the non-aqueous solvent is desirably 0.5 to 2.5 mol / L. A more preferred range is 1 to 2.5 mol / L.
[0072]
It is desirable that the liquid nonaqueous electrolyte contains a surfactant such as trioctyl phosphate (TOP) in order to improve the wettability with the separator. The amount of the surfactant added is preferably 3% or less, and more preferably in the range of 0.1 to 1%.
[0073]
It is preferable that the amount of the liquid non-aqueous electrolyte is 0.2 to 0.6 g per 100 mAh of battery unit capacity. A more preferable range of the mass of the liquid non-aqueous electrolyte is 0.25 to 0.55 g / 100 mAh.
[0074]
6) Container (storage container)
The shape of the container can be, for example, a cylindrical shape with a bottom, a rectangular tube with a bottom, a bag shape, a cup shape, or the like.
[0075]
This container can be formed from, for example, a sheet including a resin layer, a metal plate, a metal film, or the like.
[0076]
The resin layer included in the sheet can be formed from, for example, polyolefin (for example, polyethylene or polypropylene), polyamide, or the like. As the sheet, it is desirable to use a sheet in which a metal layer and protective layers disposed on both sides of the metal layer are integrated. The metal layer plays a role of blocking moisture and a shape of the container. Examples of the metal layer include aluminum, stainless steel, iron, copper, and nickel. Among them, aluminum that is lightweight and has a high function of blocking moisture is preferable. The metal layer may be formed from one type of metal, or may be formed from a combination of two or more types of metal layers. Of the two protective layers, a protective layer in contact with the outside serves to prevent damage to the metal layer. This external protective layer is formed from one type of resin layer or two or more types of resin layers. On the other hand, the inner protective layer plays a role of preventing the metal layer from being corroded by the non-aqueous electrolyte. This internal protective layer is formed from one type of resin layer or two or more types of resin layers. In addition, a thermoplastic resin for sealing the container by heat sealing can be provided on the surface of the internal protective layer.
[0077]
The thickness of the sheet is desirably 0.3 mm or less. This is because when the thickness is more than 0.3 mm, it is difficult to obtain a high weight energy density and a high volume energy density. A preferred range of the sheet thickness is 0.25 mm or less, a more preferred range is 0.15 mm or less, and a most preferred range is 0.12 mm or less. When the thickness is smaller than 0.05 mm, the sheet is easily deformed or broken. Therefore, the lower limit of the thickness of the sheet is preferably set to 0.05 mm.
[0078]
It is preferable that an adhesive layer is formed on at least a part of the surface of the sheet, and the electrode group is adhered to an inner surface of the sheet by the adhesive layer. With such a configuration, since the sheet can be fixed to the surface of the electrode group, it is possible to suppress the electrolyte from permeating between the electrode group and the container.
[0079]
The metal plate and the metal film can be formed from, for example, iron, stainless steel, and aluminum.
[0080]
It is desirable that the thickness of the metal plate and the metal film be 0.4 mm or less. This is because when the thickness is more than 0.4 mm, it becomes difficult to obtain a high weight energy density and a high volume energy density. The preferable range of the thickness of the metal plate and the metal film is 0.3 mm or less, and the most preferable range is 0.25 mm or less. If the thickness is less than 0.05 mm, sufficient strength cannot be obtained. Therefore, the lower limit of the thickness of the metal plate and the metal film is preferably set to 0.05 mm.
[0081]
The thickness of the container is measured by the method described below. That is, in the region except for the sealed portion of the container, three points existing at a distance of 1 cm or more from each other are arbitrarily selected, the thickness of each point is measured, an average value is calculated, and this value is used as the container thickness . When foreign matter (for example, resin) adheres to the surface of the container, the thickness is measured after removing the foreign matter. For example, when PVdF adheres to the surface of the container, the thickness is measured after removing the PVdF by wiping the surface of the container with a dimethylformamide solution.
[0082]
A thin, square, cylindrical non-aqueous electrolyte secondary battery as an example of the non-aqueous electrolyte secondary battery according to the present invention will be described in detail with reference to FIGS.
[0083]
FIG. 1 is a perspective view showing a thin non-aqueous electrolyte secondary battery which is an example of the non-aqueous electrolyte secondary battery according to the present invention. FIG. 2 shows the thin non-aqueous electrolyte secondary battery of FIG. FIG. 3 is a partially cutaway perspective view showing a rectangular non-aqueous electrolyte secondary battery which is an example of the non-aqueous electrolyte secondary battery according to the present invention, and FIG. 4 is a non-aqueous electrolyte secondary battery according to the present invention. FIG. 2 is a partial cross-sectional view illustrating a cylindrical non-aqueous electrolyte secondary battery as an example of a battery.
[0084]
First, a thin nonaqueous electrolyte secondary battery will be described.
[0085]
As shown in FIG. 1, an electrode group 2 is accommodated in a container body 1 having a rectangular cup shape. The electrode group 2 has a structure in which a laminate including a positive electrode 3, a negative electrode 4, and a separator 5 disposed between the positive electrode 3 and the negative electrode 4 is wound into a flat shape. The non-aqueous electrolyte is held by the electrode group 2. A part of the edge of the container body 1 is wide and functions as a cover plate 6. The container body 1 and the lid plate 6 are each formed of a laminated film. The laminate film includes an outer protective layer 7, an inner protective layer 8 containing a thermoplastic resin, and a metal layer 9 disposed between the outer protective layer 7 and the inner protective layer 8. The lid 6 is fixed to the container main body 1 by heat sealing using the thermoplastic resin of the inner protective layer 8, whereby the electrode group 2 is sealed in the container. A positive electrode tab 10 is connected to the positive electrode 3, and a negative electrode tab 11 is connected to the negative electrode 4. Each of the negative electrodes 4 is drawn out of the container and serves as a positive electrode terminal and a negative electrode terminal.
[0086]
Next, the prismatic nonaqueous electrolyte secondary battery will be described.
[0087]
As shown in FIG. 3, an electrode group 13 is accommodated in a bottomed rectangular cylindrical container 12 made of metal such as aluminum. The electrode group 13 has a structure in which a positive electrode 14, a separator 15, and a negative electrode 16 are laminated in this order and wound flat. The spacer 17 having an opening near the center is disposed above the electrode group 13.
[0088]
The non-aqueous electrolyte is held by the electrode group 13. A sealing plate 18b having an explosion-proof mechanism 18a and having a circular hole opened near the center is laser-welded to the opening of the container 12. The negative electrode terminal 19 is arranged in a circular hole of the sealing plate 18b via a hermetic seal. The negative electrode tab 20 pulled out from the negative electrode 16 is welded to the lower end of the negative electrode terminal 19. On the other hand, a positive electrode tab (not shown) is connected to the container 12 also serving as a positive electrode terminal.
[0089]
Next, the cylindrical non-aqueous electrolyte secondary battery will be described.
[0090]
A cylindrical container 21 made of stainless steel and having a bottom has an insulator 22 disposed at the bottom. The electrode group 23 is housed in the container 21. The electrode group 23 has a structure in which a band formed by laminating the positive electrode 24, the separator 25, the negative electrode 26, and the separator 25 is spirally wound so that the separator 25 is located outside.
[0091]
The container 21 contains a non-aqueous electrolyte. The insulating paper 27 having a central opening is disposed above the electrode group 23 in the container 21. The insulating sealing plate 28 is disposed in the upper opening of the container 21, and the sealing plate 28 is fixed to the container 21 by caulking the vicinity of the upper opening inward. The positive terminal 29 is fitted in the center of the insulating sealing plate 28. One end of the positive electrode lead 30 is connected to the positive electrode 24, and the other end is connected to the positive electrode terminal 29. The negative electrode 26 is connected to the container 21 as a negative terminal via a negative lead (not shown).
[0092]
The non-aqueous electrolyte secondary battery according to the present invention described above has a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode including a carbonaceous material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte including a non-aqueous solvent. Battery,
The non-aqueous solvent contains ethylene carbonate (EC), a chain carbonate containing at least methyl ethyl carbonate (MEC), and a sultone compound having at least one double bond in a ring. is there.
[0093]
According to such a secondary battery, since a dense protective film having excellent lithium ion permeability can be formed on the surface of the negative electrode, the negative electrode and the nonaqueous solvent during charging can be maintained while maintaining practical low-temperature discharge characteristics. Can be suppressed. As a result, a non-aqueous electrolyte secondary battery having a reduced amount of gas generated during initial charging and having practical low-temperature discharge characteristics and excellent charge / discharge cycle life can be realized.
[0094]
By the way, since the sultone compound easily forms a protective film so as to cover the entire negative electrode surface, the interface resistance of the protective film tends to increase. On the other hand, since the protective film made of vinylene carbonate (VC) is easily formed selectively on the edge of the negative electrode, the protective film is excellent in lithium ion permeability but slightly inferior in denseness. When a carbonaceous material such as a mesophase pitch-based carbon material or a graphite material is used for the negative electrode, the interface resistance of the negative electrode is increased by using a non-aqueous solvent containing EC, the chain carbonate, the sultone compound, and VC. Thus, a dense protective film having excellent lithium ion permeability can be formed on the negative electrode surface. As a result, the charge / discharge cycle life of the secondary battery can be further improved.
[0095]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings described above.
[0096]
(Example 1)
<Preparation of positive electrode>
First, lithium cobalt oxide (Li_xCoO₂X is 0 <X ≦ 1); 90% by weight of the powder, 5% by weight of acetylene black, and a solution of 5% by weight of polyvinylidene fluoride (PVdF) in dimethylformamide (DMF) are added and mixed; A slurry was prepared. The slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm, dried, and pressed to produce a positive electrode having a structure in which a positive electrode layer was supported on both sides of the current collector. In addition, the thickness of the positive electrode layer was 60 μm per side.
[0097]
<Preparation of negative electrode>
Mesophase pitch-based carbon fiber heat-treated at 3000 ° C. as a carbonaceous material (plane spacing (d) determined by powder X-ray diffraction (d)₀₀₂) Was mixed with 95% by weight of a powder of 0.336 nm) and a solution of 5% by weight of polyvinylidene fluoride (PVdF) in dimethylformamide (DMF) to prepare a slurry. The slurry was applied on both sides of a current collector made of a copper foil having a thickness of 12 μm, dried, and pressed to produce a negative electrode having a structure in which a negative electrode layer was supported on the current collector. The thickness of the negative electrode layer was 55 μm per one side.
[0098]
The spacing d of the (002) plane of the carbonaceous material₀₀₂Was determined from the powder X-ray diffraction spectrum by the half width midpoint method. At this time, scattering correction such as Lorentz scattering was not performed.
[0099]
<Separator>
A separator made of a microporous polyethylene membrane having a thickness of 25 μm was prepared.
[0100]
<Preparation of non-aqueous electrolyte>
A non-aqueous solvent is prepared by mixing ethylene carbonate (EC), methyl ethyl carbonate (MEC) and 1,3-propene sultone (PRS) such that the volume ratio (EC: MEC: PRS) is 33: 66: 1. did. Lithium hexafluorophosphate (LiPF) is added to the obtained non-aqueous solvent.₆) Was dissolved at a concentration of 1.0 mol / L to prepare a liquid non-aqueous electrolyte.
[0101]
<Preparation of electrode group>
The positive electrode current collector of the positive electrode is ultrasonically welded to a positive electrode lead made of a band-shaped aluminum foil (thickness: 100 μm), and the negative electrode current collector is ultrasonically welded to a negative electrode lead made of a band-shaped nickel foil (thickness: 100 μm). After the positive electrode and the negative electrode were spirally wound between the positive electrode and the negative electrode with the separator interposed therebetween, the positive electrode and the negative electrode were formed into a flat shape to form an electrode group.
[0102]
A 100 μm-thick laminated film in which both surfaces of an aluminum foil were covered with polyethylene was formed into a rectangular cup shape by a press machine, and the electrode group was housed in the obtained container.
[0103]
Next, moisture contained in the electrode group and the laminated film was removed by subjecting the electrode group in the container to vacuum drying at 80 ° C. for 12 hours.
[0104]
The liquid non-aqueous electrolyte was injected into the electrode group in the container so that the amount per 1 Ah of the battery capacity was 4.8 g, and was sealed by heat sealing, thereby having the structure shown in FIGS. A thin non-aqueous electrolyte secondary battery having a thickness of 3.6 mm, a width of 35 mm, and a height of 62 mm was assembled.
[0105]
(Examples 2 to 5)
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the PRS content (z) in the non-aqueous solvent was changed as shown in Table 1 below.
[0106]
(Example 6)
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that 1,4-butylene sultone (BTS) was used instead of PRS.
[0107]
(Examples 7 and 8)
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 6 except that the BTS content (z) in the non-aqueous solvent was changed as shown in Table 1 below.
[0108]
(Example 9)
Ethylene carbonate (EC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC) and 1,3-propene sultone (PRS) have a volume ratio (EC: MEC: DEC: PRS) of 33: 49.5: 16.5. : 1 to prepare a non-aqueous solvent. Lithium hexafluorophosphate (LiPF) is added to the obtained non-aqueous solvent.₆) Was dissolved at a concentration of 1.0 mol / L to prepare a liquid non-aqueous electrolyte.
[0109]
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that such a liquid non-aqueous electrolyte was used.
[0110]
(Examples 10 to 11)
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 9 except that the PRS content (z) in the non-aqueous solvent was changed as shown in Table 1 below.
[0111]
(Example 12)
Ethylene carbonate (EC), methyl ethyl carbonate (MEC), dimethyl carbonate (DMC) and 1,3-propene sultone (PRS) have a volume ratio (EC: MEC: DMC: PRS) of 33: 49.5: 16.5. : 1 to prepare a non-aqueous solvent. Lithium hexafluorophosphate (LiPF) is added to the obtained non-aqueous solvent.₆) Was dissolved at a concentration of 1.0 mol / L to prepare a liquid non-aqueous electrolyte.
[0112]
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that such a liquid non-aqueous electrolyte was used.
[0113]
(Examples 13 and 14)
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 12 except that the PRS content (z) in the non-aqueous solvent was changed as shown in Table 1 below.
[0114]
(Example 15)
Ethylene carbonate (EC), methyl ethyl carbonate (MEC), 1,3-propene sultone (PRS) and 1,4-butylene sultone (BTS) have a volume ratio (EC: MEC: PRS: BTS) of 33: 66: 0. 0.5: 0.5 to prepare a non-aqueous solvent. Lithium hexafluorophosphate (LiPF) is added to the obtained non-aqueous solvent.₆) Was dissolved at a concentration of 1.0 mol / L to prepare a liquid non-aqueous electrolyte.
[0115]
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the liquid non-aqueous electrolyte was used.
[0116]
(Example 16)
Ethylene carbonate (EC), methyl ethyl carbonate (MEC), 1,3-propene sultone (PRS) and 1,4-butylene sultone (BTS) have a volume ratio (EC: MEC: PRS: BTS) of 30: 60: 5. : 5 to prepare a non-aqueous solvent. Lithium hexafluorophosphate (LiPF) is added to the obtained non-aqueous solvent.₆) Was dissolved at a concentration of 1.0 mol / L to prepare a liquid non-aqueous electrolyte.
[0117]
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the liquid non-aqueous electrolyte was used.
[0118]
(Example 17)
Ethylene carbonate (EC), vinylene carbonate (VC), methyl ethyl carbonate (MEC) and 1,3-propene sultone (PRS) have a volume ratio (EC: VC: MEC: PRS) of 33: 0.5: 66: 0. The mixture was mixed to give a non-aqueous solvent. Lithium hexafluorophosphate (LiPF) is added to the obtained non-aqueous solvent.₆) Was dissolved at a concentration of 1.0 mol / L to prepare a liquid non-aqueous electrolyte.
[0119]
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the liquid non-aqueous electrolyte was used.
[0120]
(Example 18)
Ethylene carbonate (EC), vinylene carbonate (VC), methyl ethyl carbonate (MEC) and 1,4-butylene sultone (BTS) have a volume ratio (EC: VC: MEC: BTS) of 33: 0.5: 66: 0. The mixture was mixed to give a non-aqueous solvent. Lithium hexafluorophosphate (LiPF) is added to the obtained non-aqueous solvent.₆) Was dissolved at a concentration of 1.0 mol / L to prepare a liquid non-aqueous electrolyte.
[0121]
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the liquid non-aqueous electrolyte was used.
[0122]
(Example 19)
Ethylene carbonate (EC), vinylene carbonate (VC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC) and 1,3-propene sultone (PRS) have a volume ratio (EC: VC: MEC: DEC: PRS) of 33. : 0.5: 49.5: 16.5: 0.5 to prepare a non-aqueous solvent. Lithium hexafluorophosphate (LiPF) is added to the obtained non-aqueous solvent.₆) Was dissolved at a concentration of 1.0 mol / L to prepare a liquid non-aqueous electrolyte.
[0123]
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the liquid non-aqueous electrolyte was used.
[0124]
(Example 20)
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that dimethyl carbonate (DMC) was used instead of diethyl carbonate (DEC).
[0125]
(Example 21)
Lithium tetrafluoroborate (LiBF) was added to a non-aqueous solvent having the same composition as that described in Example 1.₄) And lithium hexafluorophosphate (LiPF)₆) At a concentration of 0.2 mol / L (LiBF₄), 0.8 mol / L (LiPF₆) To prepare a liquid non-aqueous electrolyte.
[0126]
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the liquid non-aqueous electrolyte was used.
[0127]
(Comparative Examples 1 to 7)
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that a non-aqueous solvent having a composition shown in Table 2 below was used.
[0128]
(Comparative Example 8)
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that propane sultone (PS) was used instead of PRS.
[0129]
(Comparative Example 9)
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that lithium metal was used for the negative electrode.
[0130]
Regarding the obtained secondary batteries of Examples 1 to 21 and Comparative Examples 1 to 9, the change in battery thickness before and after the initial charge, the charge / discharge cycle characteristics and the low-temperature discharge characteristics were evaluated under the conditions described below. The results are shown in Tables 1 and 2 below.
[0131]
(Change in battery thickness before and after initial charging)
For each secondary battery, the thickness of the battery immediately before the first charge was measured. Thereafter, constant-current / constant-voltage charging was performed for 15 hours at room temperature at 0.2 C (130 mA) to 4.2 V, and the thickness of the battery was measured again. The value obtained by dividing the thickness of the battery after the first charge by the thickness of the battery before the first charge was defined as the rate of change of the thickness.
[0132]
(Charge / discharge cycle characteristics)
For each secondary battery, as a first charge / discharge step, constant-current / constant-voltage charging was performed at room temperature at 0.2 C (130 mA) to 4.2 V for 15 hours, and then discharged at room temperature to 0.2 V at 3.0 V. .
[0133]
Next, as charge / discharge cycle characteristics, a charge / discharge test was performed at a charge / discharge rate of 1 C, a charge end voltage of 4.2 V, and a discharge end voltage of 3.0 V, and after charge / discharge was repeated 500 times in an environment at a temperature of 20 ° C. The discharge capacity retention ratio (the capacity of the first discharge was defined as 100%) was determined.
[0134]
(Low temperature discharge characteristics)
For each secondary battery, as a first charge / discharge step, constant-current / constant-voltage charging was performed at room temperature at 0.2 C (130 mA) to 4.2 V for 15 hours, and then discharged at room temperature to 0.2 V at 3.0 V. .
[0135]
Next, the discharge capacity was measured at a low temperature by discharging under an environment of a temperature of −20 ° C. and a discharge rate of 1 C and a discharge end voltage of 3.0 V. The discharge capacity at low temperature was expressed assuming that the discharge capacity when discharged under the same conditions at room temperature was 100%, and the result was defined as the discharge capacity retention rate at -20 ° C.
[0136]
Here, 1C is a current value required to discharge the nominal capacity (Ah) in one hour. Therefore, 0.2C is a current value required to discharge the nominal capacity (Ah) in 5 hours.
[0137]
[Table 1]

[0138]
[Table 2]

[0139]
As is clear from Tables 1 and 2, Examples 1-21 provided with a non-aqueous solvent containing a chain carbonate containing at least MEC, EC and a sultone compound having at least one double bond in the ring. It can be seen that the secondary battery has less swelling of the container due to the first charge and a higher capacity retention rate after 500 cycles than the secondary batteries of Comparative Examples 1 to 8.
[0140]
Further, by comparing Examples 1 to 5, the larger the volume ratio z of the sultone compound, the smaller the blister of the container due to the first charge, and the higher the capacity retention after 500 cycles, but at -20 ° C. It can be seen that the discharge capacity decreases. Therefore, in order to secure the practical low-temperature discharge characteristics and to improve the swelling of the container due to the initial charge and the cycle life, it is desirable that the volume ratio z of the sultone compound be 0 <z ≦ 10.
[0141]
By comparing Examples 1 to 3 with Examples 9 to 11, Examples 9 to 11 having a non-aqueous solvent containing EC, MEC, DEC and PRS can have higher capacity retention after 500 cycles. Can understand. In addition, by comparing Examples 1 to 3 with Examples 12 to 14, Examples 12 to 14 having a non-aqueous solvent containing EC, MEC, DMC and PRS showed that the discharge capacity retention ratio at -20 ° C was reduced. Can be understood to be higher.
[0142]
Further, it can be seen that the secondary batteries of Examples 17 and 18 including the non-aqueous solvent containing PRS or BTS, EC, VC and MEC have the highest capacity retention after 500 cycles. On the other hand, the secondary battery of Example 20 including the non-aqueous solvent containing EC, VC, MEC, DMC and PRS has the highest discharge capacity retention rate at -20 ° C.
[0143]
On the other hand, from the rate of change of the thickness of the battery before and after the first charge, the secondary batteries of Comparative Examples 1 and 3 to 7 using the non-aqueous solvent to which the sultone compound was not added had the laminated battery outer body after the first charge. It is apparent that the battery is significantly deformed and is unsuitable for use as a secondary battery. The secondary battery of Comparative Example 2 including the non-aqueous solvent containing 10% by volume of the sultone compound but having a small amount of EC of 9% by volume also showed a large increase in the thickness of the battery due to the first charge.
[0144]
Furthermore, according to the sultone compound having no double bond such as propane sultone as in Comparative Example 8, the results were worse in all the test items than in the case of no addition.
[0145]
On the other hand, as shown in Comparative Example 9, when a nonaqueous electrolyte having the same composition as in Example 1 is used when using a negative electrode made of metallic lithium, the rate of increase in battery thickness due to initial charging can be reduced. However, the capacity retention after 500 cycles is extremely low at 12%. This is because the negative electrode made of metallic lithium has a much higher reactivity with the nonaqueous electrolyte than the negative electrode containing a carbonaceous material. It is presumed that this is because it is not possible to sufficiently suppress.
[0146]
(Example 22)
Polyethylene glycol diacrylate (molecular weight: 1000) and a liquid non-aqueous electrolyte having the same composition as described in Example 1 were mixed at a weight ratio of 1:10, and t-hexyl was added thereto as a thermal polymerization initiator. A pregel solution was prepared by adding 5000 ppm of peroxypivalate.
[0147]
An electrode group was prepared in the same manner as described in Example 1 described above, and this electrode group was housed in a container, dried under vacuum, and then the pregel solution was poured in an amount of 5.2 g per 1 Ah of battery capacity. Liquid. Next, after sealing by heat sealing, the pregel solution was polymerized and crosslinked by heating at 60 ° C. for 3 hours to obtain a gel nonaqueous electrolyte, thereby obtaining a thin nonaqueous electrolyte secondary battery.
[0148]
(Comparative Example 10)
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 22 except that 1,3-propene sultone was not added to the pregel solution.
[0149]
With respect to the obtained secondary batteries of Example 22 and Comparative Example 10, the change in battery thickness, charge / discharge cycle characteristics, and low-temperature discharge characteristics before and after the initial charge were evaluated under the same conditions as described in Example 1 described above. The results are shown in Table 3 below.
[0150]
[Table 3]

[0151]
As is clear from Table 3, the secondary battery of Example 22 including the gelled non-aqueous electrolyte containing ethylene carbonate, methyl ethyl carbonate, and the sultone compound was compared with Comparative Example 10 in which the sultone compound was not added. It can be understood that the rate of change in the thickness of the battery before and after the initial charge is small, and the charge / discharge cycle characteristics and the low-temperature discharge characteristics are excellent.
[0152]
(Example 23)
An electrode group similar to that described in Example 1 was housed in an aluminum square can having a thickness of 0.25 mm.
[0153]
Next, moisture contained in the electrode group and the metal can was removed by subjecting the electrode group in the metal can to vacuum drying at 80 ° C. for 12 hours.
[0154]
Subsequently, a liquid non-aqueous electrolyte similar to that described in Example 1 was injected into the electrode group in the metal can so that the amount per battery capacity of 1 Ah was 4.8 g, and the injection hole was sealed by welding. By stopping, a rectangular non-aqueous electrolyte secondary battery having the structure shown in FIG. 3 described above, having a thickness of 4.8 mm, a width of 30 mm, and a height of 48 mm was assembled.
[0155]
(Comparative Example 11)
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 23 except that the sultone compound was not added to the non-aqueous solvent.
[0156]
(Example 24)
The same positive electrode, negative electrode, and separator as those described in Example 1 were prepared, and an electrode group was produced by spirally winding the positive electrode and the negative electrode with a separator interposed therebetween. The obtained electrode group was housed in a stainless steel cylindrical can having a thickness of 0.22 mm.
[0157]
Next, moisture contained in the electrode group and the metal can was removed by subjecting the electrode group in the metal can to vacuum drying at 80 ° C. for 12 hours.
[0158]
A liquid non-aqueous electrolyte similar to that described in Example 1 described above was injected into the electrode group in the metal can so that the amount per battery capacity 1Ah was 4.8 g, and sealing was performed by caulking and fixing. A cylindrical non-aqueous electrolyte secondary battery having the structure shown in FIG. 4 described above and having a diameter of 18 mm and a height of 65 mm was assembled.
[0159]
(Comparative Example 12)
A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 24, except that the sultone compound was not added to the non-aqueous solvent.
[0160]
Regarding the obtained secondary batteries of Examples 23 to 24 and Comparative Examples 11 to 12, the change in battery thickness before and after the initial charge, the charge / discharge cycle characteristics and the low-temperature discharge characteristics were evaluated under the conditions described below. It is shown in Table 4 below.
[0161]
(Change in battery thickness before and after initial charging)
For the prismatic secondary battery, the thickness of the battery immediately before the first charge was measured. Thereafter, constant-current / constant-voltage charging was performed for 15 hours at room temperature at 0.2 C (124 mA) to 4.2 V, and the thickness of the battery was measured again. The value obtained by dividing the thickness of the battery after the first charge by the thickness of the battery before the first charge was defined as the rate of change of the thickness. In addition, in the case of the cylindrical secondary battery, the metal can hardly swells even if gas is generated at the time of the first charge, so that the degree of change in the battery thickness before and after the first charge could not be evaluated.
[0162]
(Charge / discharge cycle characteristics)
For each secondary battery, as an initial charge / discharge step, a constant current / constant voltage charge was performed for 15 hours at a room temperature of 0.2 C (square: 124 mA, cylindrical: 360 mA) to 4.2 V for 15 hours, and then at a room temperature of 0.2 C And discharged to 3.0V.
[0163]
Next, as charge / discharge cycle characteristics, a charge / discharge test was performed at a charge / discharge rate of 1 C, a charge end voltage of 4.2 V, and a discharge end voltage of 3.0 V, and after charge / discharge was repeated 500 times in an environment at a temperature of 20 ° C. The discharge capacity retention ratio (the capacity of the first discharge was defined as 100%) was determined.
[0164]
(Low temperature discharge characteristics)
For each secondary battery, as a first charge / discharge step, constant-current / constant-voltage charging was performed at room temperature to 0.2 V at 4.2 V for 15 hours, and then discharged at room temperature to 0.2 V at 3.0 V.
[0165]
Next, the discharge capacity was measured at a low temperature by discharging under an environment of a temperature of −20 ° C. and a discharge rate of 1 C and a discharge end voltage of 3.0 V. The discharge capacity at low temperature was expressed assuming that the discharge capacity when discharged under the same conditions at room temperature was 100%, and the result was defined as the discharge capacity retention rate at -20 ° C.
[0166]
[Table 4]

[0167]
In the prismatic nonaqueous electrolyte secondary batteries of Example 23 and Comparative Example 11, the change rate of the battery thickness before and after the first charge is smaller than that of Example 23 because the outer body is a metal can. Also in this case, Example 23 shows a better value than Comparative Example 11 containing no sultone compound. In addition, it is apparent that the addition of the sultone compound improved the capacity retention after 500 cycles and the -20 ° C discharge capacity retention in both the square and cylindrical shapes.
[0168]
(Method of detecting PRS and VC)
Further, with respect to the secondary battery of Example 17, after the initial charge / discharge step, the circuit was opened for 5 hours or more and the potential was sufficiently settled, and then the Ar concentration was 99.9% or more and the dew point was −50 ° C. It was disassembled in the following glove box and the electrode group was taken out. The electrode group was placed in a centrifuge tube, and dimethylsulfoxide (DMSO) -d₆, And sealed, taken out of the glove box, and centrifuged. Then, in the glove box, the electrolytic solution and the DMSO-d were passed through the centrifuge tube.₆Was collected. About 0.5 ml of the mixed solvent was placed in a 5 mmφ NMR sample tube, and NMR measurement was performed. The apparatus used for the NMR measurement is JNM-LA400WB manufactured by JEOL Ltd.¹H, observation frequency is 400 MHz, dimethyl sulfoxide (DMSO) -d₆The residual proton signal slightly contained therein was used as an internal reference (2.5 ppm). The measurement temperature was 25 ° C.¹In the HNMR spectrum, a peak corresponding to EC was observed at around 4.5 ppm, and a peak corresponding to VC was observed at around 7.7 ppm. On the other hand, the peak corresponding to PRS is close to 5.1 ppm (P₁), Around 7.05 ppm (P₂) And around 7.2 ppm (P₃) Was observed. From these results, it was confirmed that VC and PRS were contained in the nonaqueous solvent present in the secondary battery of Example 17 after the initial charge / discharge step.
[0169]
The observation frequency was set to 100 MHz, and dimethyl sulfoxide (DMSO) -d₆(39.5 ppm) as internal reference substance¹³When the CNMR measurement was performed, a peak corresponding to EC was observed at around 66 ppm, a peak corresponding to VC was observed at around 133 ppm, and peaks corresponding to PRS were observed at around 74 ppm, around 124 ppm, and around 140 ppm. It was confirmed that VC and PRS were contained in the non-aqueous solvent present in the secondary battery of Example 17 after the discharging step.
[0170]
further,¹In the HNMR spectrum, the ratio of the NMR integrated intensity of VC to the NMR integrated intensity of EC and the ratio of the NMR integrated intensity of PRS to the NMR integrated intensity of EC were determined. In each case, it could be confirmed that the number was smaller than that before assembling the secondary battery.
[0171]
The present invention is not limited to the above-described embodiment, and is similarly applicable to combinations of other types of positive electrodes, negative electrodes, separators, and containers.
[0172]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery in which the amount of gas generated during initial charging is reduced, and which has practical low-temperature discharge characteristics and a long charge-discharge cycle life.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a thin non-aqueous electrolyte secondary battery as an example of a non-aqueous electrolyte secondary battery according to the present invention.
FIG. 2 is a partial cross-sectional view of the thin non-aqueous electrolyte secondary battery of FIG. 1 cut along a short side direction.
FIG. 3 is a partially cutaway perspective view showing a rectangular non-aqueous electrolyte secondary battery as an example of the non-aqueous electrolyte secondary battery according to the present invention.
FIG. 4 is a partial cross-sectional view showing a cylindrical non-aqueous electrolyte secondary battery which is an example of the non-aqueous electrolyte secondary battery according to the present invention.
FIG. 5 is a graph showing the PRS contained in the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery of Example 17.¹FIG. 4 is a characteristic diagram showing an HNMR spectrum.
[Explanation of symbols]
1. The container body,
2 ... electrode group,
3: Positive electrode,
4 ... negative electrode,
5 ... separator,
6 ... lid plate,
7 ... external protective layer,
8 ... internal protective layer,
9 ... metal layer,
10 ... Positive terminal,
11 ... Negative electrode terminal.

Claims (5)

A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode including a carbonaceous material capable of inserting and extracting lithium ions, and a non-aqueous electrolyte including a non-aqueous solvent,
The non-aqueous solvent contains ethylene carbonate (EC), a chain carbonate containing at least methyl ethyl carbonate (MEC), and a sultone compound having at least one double bond in a ring. Electrolyte secondary battery. When the proportions of ethylene carbonate (EC), the chain carbonate and the sultone compound with respect to the total volume of the non-aqueous solvent are x (vol%), y (vol%), and z (vol%), The non-aqueous electrolyte secondary battery according to claim 1, wherein y and z satisfy 20 ≦ x ≦ 50, 40 ≦ y ≦ 80, and 0 <z ≦ 10, respectively. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous solvent further includes vinylene carbonate (VC). The proportions of ethylene carbonate (EC), chain carbonate, sultone compound and vinylene carbonate (VC) with respect to the total volume of the nonaqueous solvent are x (vol%), y (vol%), z (vol%) and w, respectively. (Volume%), the x, y, z, and w satisfy 20 ≦ x ≦ 50, 40 ≦ y ≦ 80, 0 <z ≦ 10, and 0 <w ≦ 10, respectively. The non-aqueous electrolyte secondary battery according to claim 3. 2. The chain carbonate according to claim 1, wherein the chain carbonate is composed of methyl ethyl carbonate (MEC), or is composed of MEC with at least one of diethyl carbonate (DEC) and dimethyl carbonate (DMC). 3. A nonaqueous electrolyte secondary battery according to any one of claims 1 to 4.

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