JP4128807B2 - Nonaqueous electrolyte secondary battery and electrolyte used therefor - Google Patents

Description

【００１０】
（式（１）中、Ｒ¹〜Ｒ⁶はそれぞれ独立に、水素原子、ハロゲン原子、炭素数１〜６のアルキル基または炭素数１〜６のアセチル基）で表されるγ―ブチロラクトン誘導体を含み、前記添加剤が、式（２）：
【００１１】
【化４】

【００１２】
（式（２）中、Ｒ⁷〜Ｒ⁸はそれぞれ独立で、水素原子、ハロゲン原子、炭素数１〜３のアルキル基、フェニル基または水酸基であり、結合手Ｘは、共有結合、炭素数１〜３のアルキレン基または第２級アミノ基）で表される２個のピリジン環を有する化合物からなる非水電解質二次電池に関する。Ｒ¹〜Ｒ⁶は同一でも異なってもよい。また、Ｒ⁷〜Ｒ⁸は同一でも異なってもよい。
【００１３】
前記２個のピリジン環を有する化合物は、２，２’−ビピリジン、４，４’−ビピリジン、４，４’−ジメチル−２，２’−ビピリジン、２，２’−ジピリジルアミン、２，２’−ジピコリルアミンおよび３，３’−ジピコリルアミンよりなる群から選ばれた少なくとも１種であることが好ましい。
前記非水電解質に含まれる２個のピリジン環を有する化合物の量は、前記非水溶媒１００体積部あたり０．０１〜０．５体積部である。
【００１４】
前記γ―ブチロラクトン誘導体は、γ−ブチロラクトン、γ−バレロラクトンおよびα−メチル−γ−ブチロラクトンよりなる群から選ばれた少なくとも１種であることが好ましい。
前記γ―ブチロラクトン誘導体の量は、前記非水溶媒全体の３０体積％以上である。
前記正極は、リチウム含有遷移金属酸化物からなり、前記負極は、黒鉛からなることが好ましい。
【００１５】
高温保存時における電池のインピーダンスの増大は、主に正極のインピーダンスの増大に起因する。一方、非水電解質に２個のピリジン環を有する化合物を含ませることにより、正極上でのγ―ブチロラクトン誘導体の酸化反応が著しく抑制され、被膜形成による正極のインピーダンス増大を抑制することができる。よって、高温環境下での保存後においても優れた充放電特性を有する電池を提供することができる。
γ―ブチロラクトン誘導体の酸化反応が著しく抑制される理由は、２個のピリジン環を有する化合物がγ―ブチロラクトン誘導体よりも優先的に分解して正極上に被膜を形成するためと考えられる。
【００１６】
【発明の実施の形態】
本発明で用いる非水電解質は、高温環境下での保存特性、特に保存後の高率放電特性を向上させたものであり、式（１）：
【００１７】
【化５】

【００１８】
（式（１）中、Ｒ¹〜Ｒ⁶はそれぞれ独立に、水素原子、ハロゲン原子、炭素数１〜６のアルキル基または炭素数１〜６のアセチル基）で表されるγ―ブチロラクトン誘導体を含有する非水溶媒、前記非水溶媒に溶解した溶質および式（２）：
【００１９】
【化６】

【００２０】
（式（２）中、Ｒ⁷〜Ｒ⁸はそれぞれ独立で、水素原子、ハロゲン原子、炭素数１〜３のアルキル基、フェニル基または水酸基であり、結合手Ｘは、共有結合、炭素数１〜３のアルキレン基または第２級アミノ基）で表される添加剤としての２個のピリジン環を有する化合物からなる。
【００２１】
式（１）で表されるγ―ブチロラクトン誘導体としては、γ−ブチロラクトン、γ−バレロラクトン、α−メチル−γ−ブチロラクトン、γ−カプロラクトン、α−メチレン−γ−ブチロラクトン、γ−ヘキサノラクトン、γ−ノナノラクトン、γ−オクタノラクトン、γ−メチル−γ−デカノラクトン等を用いることができる。これらは単独で用いてもよく、２種以上を組み合わせて用いてもよい。これらのうちでは、γ−ブチロラクトン、γ−バレロラクトンおよびα−メチル−γ−ブチロラクトンよりなる群から選ばれた少なくとも１種を用いることが特に好ましい。
【００２２】
前記非水溶媒は、耐酸化性および耐還元性の観点から、環状炭酸エステル、鎖状炭酸エステル、γ−ブチロラクトン誘導体以外の環状カルボン酸エステルおよび鎖状カルボン酸エステルよりなる群から選ばれる少なくとも１種を含むことができる。これらは単独で用いてもよく、２種以上を組み合わせて用いてもよい。
【００２３】
環状炭酸エステルとしては、エチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ブチレンカーボネート（ＢＣ）、ビニレンカーボネート（ＶＣ）などを用いることができる。これらは単独で用いてもよく、２種以上を組み合わせて用いてもよい。これらのうちでは、特にエチレンカーボネート、プロピレンカーボネートおよびビニレンカーボネートが好ましい。
【００２４】
鎖状炭酸エステルとしては、ジエチルカーボネート（ＤＥＣ）、ジメチルカーボネート（ＤＭＣ）、エチルメチルカーボネート（ＥＭＣ）などを用いることができる。これらは単独で用いてもよく、２種以上を組み合わせて用いてもよい。
【００２５】
鎖状カルボン酸エステルとしては、メチルアセテート（ＭＡ）、エチルアセテート（ＥＡ）、メチルプロピオネート（ＭＰ）、メチルブチレート（ＭＢ）、エチルブチレート（ＥＢ）、ブチルアセテート（ＢＡ）、ｎ−プロピルアセテート（ＰＡ）、イソブチルプロピオネート（ｉｓｏ−ＢＰ）などを用いることができる。これらは単独で用いてもよく、２種以上を組み合わせて用いてもよい。これらのうちでは、特にメチルアセテート、エチルアセテートおよびメチルプロピオネートが好ましい。
【００２６】
式（２）で表される２個のピリジン環を有する化合物としては、２，２’−ビピリジン、４，４’−ビピリジン、４，４’−ジメチル−２，２’−ビピリジン、２，２’−ジピリジルアミン、２，２’−ジピコリルアミン、３，３’−ジピコリルアミン等を用いることができる。これらは単独で用いてもよく、２種以上を組み合わせて用いてもよい。これらのうちでは、特に２，２’−ビピリジンおよび４，４’−ビピリジンが好ましい。
【００２７】
非水電解質に含まれる２個のピリジン環を有する化合物の量は、非水溶媒１００体積部あたり０．０１〜０．５体積部、さらには０．０５〜０．２体積部であることが好ましい。２個のピリジン環を有する化合物の量が非水溶媒１００体積部あたり０．０１体積部未満では、γ−ブチロラクトン誘導体の正極上での酸化分解を抑制するのに充分な２個のピリジン環を有する化合物由来の被膜が正極表面に形成されない。また、２個のピリジン環を有する化合物の量が非水溶媒１００体積部あたり０．５体積部を超えると、電池容量の低下を引き起こす。
【００２８】
γ−ブチロラクトン誘導体の量は、非水溶媒全体の３０体積％以上、さらには５０体積％以上であることが好ましい。非水溶媒中におけるγ−ブチロラクトン誘導体の含有量が３０体積％未満になると、電解液の導電率、特に低温における導電率が低下する。
【００２９】
環状炭酸エステルの量は、非水溶媒全体の１０〜６０体積％、さらには２０〜４０体積％であることが好ましい。非水溶媒中における環状炭酸エステルの含有量が１０体積％未満になると、非水溶媒の誘電率が低下して溶質が溶媒に溶解しにくくなる。また、非水溶媒中における環状炭酸エステルの含有量が６０体積％を超えると、電解液の導電率、特に低温における導電率が低下する。
【００３０】
鎖状炭酸エステルの量は、非水溶媒全体の１０〜８０体積％であることが好ましい。非水溶媒中における鎖状炭酸エステルの含有量が１０体積％未満になると、セパレータが電解液で濡れにくくなることがある。また、非水溶媒中における鎖状炭酸エステルの含有量が８０体積％を超えると、非水溶媒の誘電率が低下して溶質が溶媒に溶解しにくくなる。
【００３１】
非水溶媒に溶解させる溶質には、少なくともＬｉＰＦ₆を用いることが好ましい。ＬｉＰＦ₆は単独で用いてもよく、非水電解質二次電池で通常に用いられているＬｉＰＦ₆以外の溶質と組み合わせて用いてもよい。具体的には、ＬｉＣｌＯ₄、ＬｉＡｓＦ₆、ＬｉＢＦ₄、ＬｉＣＦ₃ＳＯ₃、ＬｉＮ（ＣＦ₃ＳＯ₂）₂、ＬｉＮ（Ｃ₂Ｆ₅ＳＯ₂）₂、ＬｉＮ（ＣＦ₃ＳＯ₂）（Ｃ₄Ｆ₉ＳＯ₂）、ＬｉＣ（ＣＦ₃ＳＯ₂）₃、ＬｉＢ［Ｃ₆Ｆ₃（ＣＦ₃）₂-３，５］₄等から選ばれる１種以上を用いることができる。特にＬｉＰＦ₆とＬｉＢＦ₄とを組み合わせて用いることが好ましい。
【００３２】
本発明の非水電解質二次電池の正極には、通常の非水電解質二次電池で用いられている正極材料を用いることができる。正極材料は、本願発明では特に限定されない。電池容量を向上させ、エネルギー密度を高める観点から、正極材料は、リチウムと１種以上の遷移金属とを含有する複合酸化物（リチウム含有遷移金属複合酸化物）を主体とすることが好ましい。例えばＬｉ_xＭＯ₂（式中、Ｍは１種以上の遷移金属を表し、ｘは電池の充放電状態により異なり、通常０．０５≦ｘ≦１．１０である）で表されるリチウム含有遷移金属複合酸化物を主体とする活物質が好適である。Ｌｉ_xＭＯ₂において、遷移金属Ｍには、Ｃｏ、ＮｉおよびＭｎよりなる群から選ばれる少なくとも１種を用いることが好ましい。上記の他、リチウム含有遷移金属複合酸化物としては、Ｌｉ_xＭｎ₂Ｏ₄などを用いることもできる。
【００３３】
本発明の非水電解質二次電池の負極には、通常の非水電解質二次電池で用いられている負極材料を用いることができる。負極材料は、本願発明では特に限定されない。負極材料には、金属リチウム、リチウムをドープ・脱ドープすることが可能な材料等を用いることができる。リチウムをドープ・脱ドープすることが可能な材料としては、熱分解炭素、コークス（ピッチコークス、ニードルコークス、石油コークス等）、黒鉛、ガラス状炭素、有機高分子化合物焼成体（フェノール樹脂、フラン樹脂等を適当な温度で焼成して炭素化したもの）、炭素繊維、活性炭素等の炭素材料や、ポリアセチレン、ポリピロール、ポリアセン等のポリマー、Ｌｉ_4/3Ｔｉ_5/3Ｏ₄等のリチウム含有遷移金属酸化物、ＴｉＳ₂等のリチウム含有遷移金属硫化物等が挙げられる。これらのうちでは、炭素材料が好ましく、特に（００２）面の面間隔が０．３４０ｎｍ以下である黒鉛を用いることが、電池のエネルギー密度を向上させる上で好ましい。
【００３４】
正極材料は、結着剤、導電剤等と混練され、得られた正極合剤から正極が作製される。前記結着剤および導電剤には、従来公知のものがいずれも使用可能である。また、負極材料は、結着剤等と混練され、得られた負極合剤から負極が作製される。前記結着剤には、従来公知のものがいずれも使用可能である。
【００３５】
本発明は、あらゆる形状の電池に適用することができる。本発明は、例えば円筒型、角型、コイン型、ボタン型等の電池に適用することができ、大型の電池にも適用することができる。正極および負極の形態は電池の形状に応じて変更される。
【００３６】
【実施例】
《実施例１》
（ｉ）正極
Ｌｉ₂ＣＯ₃とＣｏ₃Ｏ₄とを混合し、９００℃で１０時間焼成してＬｉＣｏＯ₂を合成した。次いで、１００重量部のＬｉＣｏＯ₂に、導電剤としてアセチレンブラックを３重量部、結着剤としてポリ四フッ化エチレンを７重量部、カルボキシメチルセルロースの１重量％水溶液を１００重量部添加し、攪拌・混合し、ペースト状の正極合剤を得た。次いで、厚さ３０μｍのアルミニウム箔の集電体の両面に前記正極合剤を塗布し、乾燥後、圧延ローラーを用いて圧延を行い、所定寸法に裁断して、正極とした。正極にはアルミニウム製正極リードを溶接した。
【００３７】
（ii）負極
鱗片状黒鉛を平均粒径が約２０μｍになるように粉砕・分級した。得られた鱗片状黒鉛１００重量部に、結着剤としてスチレン／ブタジエンゴムを３重量部、カルボキシメチルセルロースの１重量％水溶液を１００重量部添加し、攪拌・混合し、ペースト状の負極合剤を得た。次いで、厚さ２０μｍの銅箔の集電体の両面に前記負極合剤を塗布し、乾燥後、圧延ローラーを用いて圧延を行い、所定寸法に裁断して、負極とした。負極にはニッケル製負極リードを溶接した。
【００３８】
（iii）非水電解質
後述の表１に示した組成の非水溶媒に、１．５モル／リットルの濃度でＬｉＰＦ₆を溶解し、さらに表１に示した２個のピリジン環を有する化合物を前記非水溶媒１００体積部あたり０．１体積部添加して、非水電解質を調製した。
なお、表１において、ＥＣはエチレンカーボネートを示し、ＥＭＣはエチルメチルカーボネートを示し、ＧＢＬはγ−ブチロラクトンを示し、ＶＣはビニレンカーボネートを示す。
【００３９】
（iv）電池の組み立て
図１に作製した電池の右半分断面正面図を示す
上記で作製した帯状の正極２と負極３とを、厚さ２５μｍの微多孔性ポリエチレン樹脂製セパレータ１を介して渦巻状に巻回し、極板群を得た。極板群の下にポリエチレン樹脂製底部絶縁板６を装着し、内面をニッケルメッキした鉄製電池ケース７内に極板群を収容した。電池ケース７の内定面には負極リード５の他端をスポット溶接した。極板群上面にポリエチレン樹脂製上部絶縁板８を載置してから、電池ケース７の開口部の所定位置に溝入れした。次いで、所定量の非水電解質を電池ケース７内に注入し、極板群に電解質を含浸させた。一方、ポリプロピレン樹脂製ガスケット９を周縁部に装着したステンレス鋼製の封口板１０を準備した。封口板１０の下面には正極リード４の他端をスポット溶接した。その後、電池ケース７の開口部に前記ガスケット９を介して封口板１０を装着し、封口板１０の周縁部に電池ケース７の上縁部をかしめ、電池を完成した。完成した非水電解質二次電池１〜１４は、直径１８ｍｍ、総高６５ｍｍの円筒型であった。
【００４０】
（ｖ）電池の評価
完成した各電池の充放電を環境温度２０℃で行った。充電過程では、上限電圧を４．２Ｖに設定して、最大電流１０５０ｍＡで２時間３０分間の定電流・定電圧充電を行った。放電過程では、放電電流１５００ｍＡ、放電終止電圧３．０Ｖで定電流放電を行った。充放電後の電池を再度充電し、充電状態の電池を環境温度６０℃で１０日間保存した。保存後の電池を環境温度２０℃で放冷後、放電電流３００ｍＡ、放電終止電圧３．０Ｖで定電流放電を行った。次いで、上限電圧を４．２Ｖに設定して、最大電流１０５０ｍＡで２時間３０分間の定電流・定電圧充電を行い、放電電流１５００ｍＡ、放電終止電圧３．０Ｖで定電流放電を行った。
上記操作で得られた保存後の電池の放電電流１５００ｍＡ時の放電容量Ｃ₁₅₀₀と放電電流３００ｍＡ時の放電容量Ｃ₃₀₀を
計算式１：Ｐ_h（％）＝（Ｃ₁₅₀₀／Ｃ₃₀₀）×１００
に代入することにより、保存後の電池の高率放電特性Ｐ_hを求めた。結果を表１に示す。
【００４１】
【表１】

【００４２】
表１からわかるように、電池７および電池１４は、非水電解質が２個のピリジン環を有する化合物を含まないため、高率放電特性Ｐ_hがそれぞれ６０％および７５％であった。それに対し、２個のピリジン環を有する化合物を非水溶媒１００体積部あたり０．１体積部添加した非水電解質を用いた電池１〜６および電池８〜１３では、高率放電特性Ｐ_hが５〜２５％も向上した。また、高率放電特性Ｐ_hの向上の程度は、非水溶媒におけるγ−ブチロラクトン（ＧＢＬ）の含有率が高いほど顕著であった。これらの結果から、非水溶媒にＧＢＬを用いた場合には、高温保存による電池のインピーダンスが通常は著しく増大するが、２個のピリジン環を有する化合物を非水電解質に含ませることにより、インピーダンスの増大を抑制でき、高率放電特性Ｐ_hの向上を図れることが示された。
【００４３】
《実施例２》
次に、非水電解質に含ませる２個のピリジン環を有する化合物の量を検討した。２個のピリジン環を有する化合物を非水溶媒に添加した場合、電池の不可逆容量が増大するため、２個のピリジン環を有する化合物の量が多すぎると、電池容量が低下すると考えられる。また、２個のピリジン環を有する化合物は耐酸化性および耐還元性が低いため、余剰の２個のピリジン環を有する化合物が高温では酸化または還元分解されてガス発生量が増大するおそれがある。
【００４４】
非水溶媒としてＥＣ／ＥＭＣ／ＧＢＬ／ＶＣ＝０／０／１００／２（体積比）を用いた。また、非水溶媒には溶質として１．５モル／リットルの濃度でＬｉＰＦ₆を溶解した。２個のピリジン環を有する化合物としては２，２’−ビピリジンを用いた。前記非水溶媒１００体積部あたりの２個のピリジン環を有する化合物の添加量ΔＶ_hは、表２に示すように０．００１〜５体積部の範囲で変化させた。上記以外は実施例１と同様にして電池１５〜２０を作製した。なお、電池１５、１９および２０は参考例の電池である。
【００４５】
完成した各電池の高率放電特性Ｐ_hを実施例１と同様に評価した。また、各電池の不可逆容量および高温保存時のガス発生量を求めた。得られた結果を表２に示す。
【００４６】
【表２】

【００４７】
表２に示すように、２，２’−ビピリジンの添加量ΔＶ_hが非水溶媒１００体積部あたり０．００1体積部の電池１５では、高率放電特性Ｐ_hの向上は認められなかった。これは、インピーダンスの増大を抑制する被膜が正極表面に充分に形成されなかったためと考えられる。一方、２，２’−ビピリジンの添加量ΔＶ_hが非水溶媒１００体積部あたり１体積部および５体積部の電池１９および電池２０の場合、２，２’−ビピリジンが過剰であるため、不可逆容量および高温保存時のガス発生量が増大した。電池２０の高率放電特性Ｐ_hの大きな低下は、発生したガスが電極間に残ることによる反応面積の低下によるものと考えられる。よって、２，２’−ビピリジンの添加量ΔＶ_hが非水溶媒１００体積部あたり０．０１〜０．５体積部の範囲が、良好な高率放電特性を示し、かつ、不可逆容量とガス発生量の著しい増大が認められない好適範囲である。
【００４８】
《実施例３》
次に、非水溶媒に含ませるγ−ブチロラクトンの量を検討した。用いた非水溶媒の組成を表３に示す。また、非水溶媒には、溶質として１．５モル／リットルの濃度でＬｉＰＦ₆を溶解し、さらに２，２’−ビピリジンを添加した。前記非水溶媒１００体積部あたりの２，２’−ビピリジンの添加量ΔＶ_hは０．２体積部とした。上記以外は実施例１と同様にして電池２１〜２３を作製した。なお、電池２３は参考例の電池である。次いで、完成した各電池の高率放電特性Ｐ_hを実施例１と同様に評価した。得られた結果を表３に示す。
【００４９】
【表３】

【００５０】
表３に示すように、γ−ブチロラクトンの量が非水溶媒全体の３０体積％以上の電池２１および２２では、実施例１の電池８と同程度の高率放電特性Ｐ_hが得られた。一方、γ−ブチロラクトンの量が非水溶媒全体の３０体積％未満の電池２３では、電解液の導電率の低下により、高率放電特性Ｐ_hが低下した。以上より、γ−ブチロラクトンの量は非水溶媒全体の３０体積％以上が好適範囲であることが理解できる。
【００５１】
《実施例４》
次に、γ−ブチロラクトンの代わりにγ−バレロラクトン（ＧＶＬ）またはα−メチル−γ−ブチロラクトン（ＡＭＧＢＬ）を含む表４に示す非水溶媒を用いたこと以外、実施例１の電池８と同様の構成の電池２４および２５を作製した。すなわち、非水溶媒には、溶質として１．５モル／リットルの濃度でＬｉＰＦ₆を溶解し、さらに前記非水溶媒１００体積部あたり０．１体積部の２，２’−ビピリジンを添加した。なお、電池２５は参考例の電池である。完成した各電池の高率放電特性Ｐ_hを実施例１と同様に評価した。得られた結果を表４に示す。
【００５２】
【表４】

【００５３】
表４の結果から、γ−ブチロラクトン以外のγ−ブチロラクトン誘導体を用いた場合にも、γ−ブチロラクトンを用いた場合と同程度の高率放電特性Ｐ_hが得られることが理解できる。
【００５４】
なお、本実施例では、γ―ブチロラクトン誘導体および２個のピリジン環を有する化合物として上記化合物を含む非水電解質について記載したが、上記以外のγ−ブチロラクトン誘導体や２個のピリジン環を有する化合物を用いた場合についても同様の効果が得られている。従って、本発明はここに記載の実施例に限定されるものではない。
【００５５】
【発明の効果】
本発明によれば、高温環境下における保存特性、特に保存後の高率放電特性に優れた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】図１は、本発明の非水電解質二次電池の一例の右半分断面正面図である。
【符号の説明】
１ セパレータ
２ 正極
３ 負極
４ 正極リード
５ 負極リード
６ 底部絶縁板
７ 電池ケース
８ 上部絶縁板
９ ガスケット
１０ 封口板[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
In recent years, electronic devices such as personal computers and mobile phones have been rapidly reduced in size and weight and are cordless, and secondary batteries having high energy density are required as power sources for driving these electronic devices. Under such circumstances, lithium ion secondary batteries using lithium as an active material are currently commercialized as batteries having high voltage and high energy density. In a lithium ion secondary battery, for example, a porous film made of lithium cobaltate (LiCoO ₂ ) as a positive electrode, a carbon material such as graphite as a negative electrode, a nonaqueous solvent in which a lithium salt is dissolved in a nonaqueous electrolyte, and polyethylene as a separator Is used.
[0003]
In lithium ion secondary batteries with high energy density, in order to obtain good battery characteristics including reliability, not only the characteristics of the positive electrode and the negative electrode but also the characteristics of the non-aqueous electrolyte responsible for the transfer of lithium ions are important. . As the non-aqueous solvent constituting the non-aqueous electrolyte, a mixed solvent combining a high dielectric constant solvent having a high solubility of a solute and a low viscosity solvent having a high ability to transfer ions generated by dissociation of the solute is usually used. It is used. For example, a non-aqueous electrolyte composed of a mixed solvent containing a cyclic carbonate that is a high dielectric constant solvent and a chain carbonate that is a low viscosity solvent, and a solute such as lithium hexafluorophosphate (LiPF ₆ ) dissolved in the solvent is high. Widely used because of its conductivity and wide electrochemical window.
[0004]
Ethylene carbonate (EC), propylene carbonate (PC), etc. are used for the cyclic carbonate which is a high dielectric constant solvent, and dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) are used for the chain carbonate. ) Etc. are used.
However, ethylene carbonate and propylene carbonate have problems such as solidification at low temperatures and a marked decrease in ionic conductivity. In order to solve this problem, a nonaqueous electrolyte secondary battery including a nonaqueous solvent mainly containing γ-butyrolactone (GBL) as a high dielectric constant solvent has been studied (Japanese Patent Laid-Open No. 12-235868).
[0005]
[Problems to be solved by the invention]
However, as described in JP-A-11-9706, when LiBF ₄ is used as a solute in a non-aqueous electrolyte containing γ-butyrolactone, the non-aqueous electrolyte is positive or negative at the current operating voltage of a lithium ion secondary battery. It tends to be oxidatively and reductively decomposed on the negative electrode. For this reason, especially when the battery is stored in a high temperature environment, the battery is severely self-discharged, which has a serious problem with respect to long-term reliability.
[0006]
Even when LiPF ₆ having high oxidation resistance is used as a solute, when a charged battery is stored in a high temperature environment, the electrode surface has high impedance due to the reaction between the nonaqueous electrolyte and the positive electrode or the negative electrode. A film is formed. With this coating, the characteristics (particularly high rate discharge characteristics and low temperature characteristics) of the battery after storage are significantly deteriorated. Therefore, it is important to suppress the increase in impedance of the battery during high-temperature storage in order to put the nonaqueous electrolyte secondary battery into practical use.
[0007]
[Means for Solving the Problems]
In view of the above, an object of the present invention is to provide a non-aqueous electrolyte secondary battery excellent in storage characteristics in a high-temperature environment, in particular, high-rate discharge characteristics after storage.
As a result of extensive studies by the present inventors, by using a non-aqueous electrolyte in which a compound having two pyridine rings and a solute such as LiPF ₆ are dissolved in a non-aqueous solvent containing a γ-butyrolactone derivative, The present inventors have found that a nonaqueous electrolyte secondary battery having excellent storage characteristics in a high temperature environment can be obtained.
[0008]
That is, the present invention comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises a non-aqueous solvent, a solute dissolved in the non-aqueous solvent, and an additive, and the non-aqueous solvent is represented by the formula (1) :
[0009]
[Chemical Formula 3]

[0010]
(In formula (1), R ^{1 to} R ⁶ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms or an acetyl group having 1 to 6 carbon atoms) a γ-butyrolactone derivative represented by And the additive is of formula (2):
[0011]
[Formula 4]

[0012]
(In the formula (2), R ^{7 to} R ⁸ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 3 carbon atoms, a phenyl group or a hydroxyl group, and the bond X is a covalent bond, having 1 carbon atom. for non-aqueous electrolyte secondary battery comprising a compound having two pyridine ring represented by to 3 alkylene group or a 2 Kyua amino group). R ^{1 to} R ⁶ may be the same or different. R ^{7 to} R ⁸ may be the same or different.
[0013]
The compounds having two pyridine rings are 2,2′-bipyridine, 4,4′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, 2,2′-dipyridylamine, 2,2 It is preferably at least one selected from the group consisting of '-dipicolylamine and 3,3'-dipicolylamine.
The amount of a compound having two pyridine rings contained in the nonaqueous electrolyte, Ru 0.01-0.5 parts by volume der per the nonaqueous solvent 100 parts by volume.
[0014]
The γ-butyrolactone derivative is preferably at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, and α-methyl-γ-butyrolactone.
The amount of the γ- butyrolactone derivatives, Ru der 30% by volume or more of the total non-aqueous solvent.
The positive electrode is preferably made of a lithium-containing transition metal oxide, and the negative electrode is preferably made of graphite.
[0015]
The increase in the impedance of the battery during high temperature storage is mainly due to the increase in the impedance of the positive electrode. On the other hand, by including a compound having two pyridine rings in the nonaqueous electrolyte, the oxidation reaction of the γ-butyrolactone derivative on the positive electrode is remarkably suppressed, and an increase in the impedance of the positive electrode due to film formation can be suppressed. Therefore, a battery having excellent charge / discharge characteristics even after storage in a high temperature environment can be provided.
The reason why the oxidation reaction of the γ-butyrolactone derivative is remarkably suppressed is considered to be because the compound having two pyridine rings decomposes preferentially over the γ-butyrolactone derivative and forms a film on the positive electrode.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The non-aqueous electrolyte used in the present invention has improved storage characteristics in a high-temperature environment, particularly high-rate discharge characteristics after storage. Formula (1):
[0017]
[Chemical formula 5]

[0018]
(In formula (1), R ^{1 to} R ⁶ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms or an acetyl group having 1 to 6 carbon atoms) a γ-butyrolactone derivative represented by Nonaqueous solvent contained, solute dissolved in the nonaqueous solvent and formula (2):
[0019]
[Chemical 6]

[0020]
(In the formula (2), R ^{7 to} R ⁸ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 3 carbon atoms, a phenyl group or a hydroxyl group, and the bond X is a covalent bond, having 1 carbon atom. a compound having two pyridine rings as an additive represented by to 3 alkylene group or a 2 Kyua amino group).
[0021]
Examples of the γ-butyrolactone derivative represented by the formula (1) include γ-butyrolactone, γ-valerolactone, α-methyl-γ-butyrolactone, γ-caprolactone, α-methylene-γ-butyrolactone, γ-hexanolactone, γ-nonanolactone, γ-octanolactone, γ-methyl-γ-decanolactone, and the like can be used. These may be used alone or in combination of two or more. Among these, it is particularly preferable to use at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, and α-methyl-γ-butyrolactone.
[0022]
The non-aqueous solvent is at least one selected from the group consisting of a cyclic carbonate ester, a chain carbonate ester, a cyclic carboxylic acid ester other than a γ-butyrolactone derivative, and a chain carboxylate ester from the viewpoint of oxidation resistance and reduction resistance. Species can be included. These may be used alone or in combination of two or more.
[0023]
As the cyclic carbonate, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), or the like can be used. These may be used alone or in combination of two or more. Of these, ethylene carbonate, propylene carbonate, and vinylene carbonate are particularly preferable.
[0024]
As the chain carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or the like can be used. These may be used alone or in combination of two or more.
[0025]
Examples of chain carboxylic acid esters include methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP), methyl butyrate (MB), ethyl butyrate (EB), butyl acetate (BA), n- Propyl acetate (PA), isobutyl propionate (iso-BP), etc. can be used. These may be used alone or in combination of two or more. Of these, methyl acetate, ethyl acetate and methyl propionate are particularly preferable.
[0026]
Examples of the compound having two pyridine rings represented by the formula (2) include 2,2′-bipyridine, 4,4′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, 2,2 '-Dipyridylamine, 2,2'-dipicolylamine, 3,3'-dipicolylamine and the like can be used. These may be used alone or in combination of two or more. Of these, 2,2′-bipyridine and 4,4′-bipyridine are particularly preferable.
[0027]
The amount of the compound having two pyridine rings contained in the non-aqueous electrolyte is 0.01 to 0.5 volume part, further 0.05 to 0.2 volume part per 100 volume parts of the non-aqueous solvent. preferable. When the amount of the compound having two pyridine rings is less than 0.01 parts by volume per 100 parts by volume of the nonaqueous solvent, two pyridine rings sufficient to suppress oxidative decomposition of the γ-butyrolactone derivative on the positive electrode are formed. The film derived from the compound is not formed on the positive electrode surface. On the other hand, when the amount of the compound having two pyridine rings exceeds 0.5 parts by volume per 100 parts by volume of the non-aqueous solvent, the battery capacity is reduced.
[0028]
The amount of the γ-butyrolactone derivative is preferably 30% by volume or more, more preferably 50% by volume or more of the whole non-aqueous solvent. When the content of the γ-butyrolactone derivative in the non-aqueous solvent is less than 30% by volume, the electrical conductivity of the electrolytic solution, particularly the electrical conductivity at a low temperature is lowered.
[0029]
The amount of the cyclic carbonate is preferably 10 to 60% by volume, more preferably 20 to 40% by volume, based on the whole nonaqueous solvent. When the content of the cyclic carbonate in the non-aqueous solvent is less than 10% by volume, the dielectric constant of the non-aqueous solvent decreases and the solute becomes difficult to dissolve in the solvent. On the other hand, when the content of the cyclic carbonate in the non-aqueous solvent exceeds 60% by volume, the conductivity of the electrolytic solution, particularly, the conductivity at a low temperature is lowered.
[0030]
The amount of the chain carbonate is preferably 10 to 80% by volume of the whole non-aqueous solvent. When the content of the chain carbonate in the non-aqueous solvent is less than 10% by volume, the separator may be difficult to wet with the electrolytic solution. On the other hand, when the content of the chain carbonate in the non-aqueous solvent exceeds 80% by volume, the dielectric constant of the non-aqueous solvent decreases and the solute becomes difficult to dissolve in the solvent.
[0031]
It is preferable to use at least LiPF ₆ as the solute dissolved in the non-aqueous solvent. LiPF ₆ may be used alone or in combination with a solute other than LiPF ₆ that is normally used in non-aqueous electrolyte secondary batteries. Specifically, LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiB [C ₆ F ₃ (CF ₃ ) _{2 -3, 5} ] ₄ or the like can be used. In particular, it is preferable to use LiPF ₆ and LiBF ₄ in combination.
[0032]
As the positive electrode of the nonaqueous electrolyte secondary battery of the present invention, a positive electrode material used in a normal nonaqueous electrolyte secondary battery can be used. The positive electrode material is not particularly limited in the present invention. From the viewpoint of improving battery capacity and increasing energy density, the positive electrode material is preferably composed mainly of a composite oxide (lithium-containing transition metal composite oxide) containing lithium and one or more transition metals. For example, a lithium-containing transition represented by Li _x MO ₂ (wherein M represents one or more transition metals, x varies depending on the charge / discharge state of the battery, and is generally 0.05 ≦ x ≦ 1.10.) An active material mainly composed of a metal composite oxide is suitable. In Li _x MO ₂ , the transition metal M is preferably at least one selected from the group consisting of Co, Ni and Mn. In addition to the above, Li _x Mn ₂ O ₄ can also be used as the lithium-containing transition metal composite oxide.
[0033]
For the negative electrode of the nonaqueous electrolyte secondary battery of the present invention, a negative electrode material used in a normal nonaqueous electrolyte secondary battery can be used. The negative electrode material is not particularly limited in the present invention. As the negative electrode material, metallic lithium, a material that can be doped / undoped with lithium, and the like can be used. Materials that can be doped / undoped with lithium include pyrolytic carbon, coke (pitch coke, needle coke, petroleum coke, etc.), graphite, glassy carbon, and fired organic polymer compound (phenol resin, furan resin). Etc.), carbon materials such as carbon fiber and activated carbon, polymers such as polyacetylene, polypyrrole and polyacene, and lithium-containing transitions such as Li _4/3 Ti _5/3 O ₄ Examples thereof include metal oxides and lithium-containing transition metal sulfides such as TiS ₂ . Among these, a carbon material is preferable, and it is particularly preferable to use graphite having a (002) plane spacing of 0.340 nm or less in order to improve the energy density of the battery.
[0034]
The positive electrode material is kneaded with a binder, a conductive agent, and the like, and a positive electrode is produced from the obtained positive electrode mixture. Any conventionally known binder and conductive agent can be used. The negative electrode material is kneaded with a binder or the like, and a negative electrode is produced from the obtained negative electrode mixture. Any conventionally known binder can be used as the binder.
[0035]
The present invention can be applied to batteries of any shape. The present invention can be applied to, for example, a cylindrical battery, a rectangular battery, a coin battery, a button battery, etc., and can also be applied to a large battery. The form of a positive electrode and a negative electrode is changed according to the shape of a battery.
[0036]
【Example】
Example 1
(I) The positive electrode Li ₂ CO ₃ and Co ₃ O ₄ were mixed and baked at 900 ° C. for 10 hours to synthesize LiCoO ₂ . Next, 3 parts by weight of acetylene black as a conductive agent, 7 parts by weight of polytetrafluoroethylene as a binder, and 100 parts by weight of a 1% by weight aqueous solution of carboxymethylcellulose are added to 100 parts by weight of LiCoO ₂ and stirred. By mixing, a paste-like positive electrode mixture was obtained. Next, the positive electrode mixture was applied to both surfaces of a current collector of aluminum foil having a thickness of 30 μm, dried, then rolled using a rolling roller, and cut into a predetermined size to obtain a positive electrode. An aluminum positive electrode lead was welded to the positive electrode.
[0037]
(Ii) The negative electrode flaky graphite was pulverized and classified so that the average particle diameter was about 20 μm. To 100 parts by weight of the obtained flake graphite, 3 parts by weight of styrene / butadiene rubber as a binder and 100 parts by weight of a 1% by weight aqueous solution of carboxymethylcellulose are added, stirred and mixed, and a paste-like negative electrode mixture is prepared. Obtained. Next, the negative electrode mixture was applied to both surfaces of a copper foil current collector with a thickness of 20 μm, dried, then rolled using a rolling roller, and cut into a predetermined size to obtain a negative electrode. A negative electrode lead made of nickel was welded to the negative electrode.
[0038]
(Iii) Nonaqueous electrolyte A compound having two pyridine rings shown in Table 1 is prepared by dissolving LiPF ₆ at a concentration of 1.5 mol / liter in a nonaqueous solvent having a composition shown in Table 1 described later. A non-aqueous electrolyte was prepared by adding 0.1 part by volume per 100 parts by volume of the non-aqueous solvent.
In Table 1, EC represents ethylene carbonate, EMC represents ethyl methyl carbonate, GBL represents γ-butyrolactone, and VC represents vinylene carbonate.
[0039]
(Iv) Battery assembly The belt-like positive electrode 2 and negative electrode 3 produced as described above, showing a front view of the right half section of the battery produced in FIG. 1, are spirally wound through a microporous polyethylene resin separator 1 having a thickness of 25 μm. The electrode plate group was obtained. A polyethylene resin bottom insulating plate 6 was mounted under the electrode plate group, and the electrode plate group was housed in an iron battery case 7 whose inner surface was nickel-plated. The other end of the negative electrode lead 5 was spot welded to the inner surface of the battery case 7. After placing the polyethylene resin upper insulating plate 8 on the upper surface of the electrode plate group, it was grooved at a predetermined position of the opening of the battery case 7. Next, a predetermined amount of non-aqueous electrolyte was injected into the battery case 7, and the electrode plate group was impregnated with the electrolyte. On the other hand, a stainless steel sealing plate 10 with a polypropylene resin gasket 9 attached to the periphery was prepared. The other end of the positive electrode lead 4 was spot welded to the lower surface of the sealing plate 10. Thereafter, the sealing plate 10 was attached to the opening of the battery case 7 through the gasket 9, and the upper edge of the battery case 7 was caulked to the peripheral edge of the sealing plate 10 to complete the battery. The completed nonaqueous electrolyte secondary batteries 1 to 14 were cylindrical with a diameter of 18 mm and a total height of 65 mm.
[0040]
(V) Evaluation of Battery Each completed battery was charged and discharged at an environmental temperature of 20 ° C. In the charging process, the upper limit voltage was set to 4.2 V, and constant current / constant voltage charging was performed for 2 hours 30 minutes at a maximum current of 1050 mA. In the discharge process, constant current discharge was performed at a discharge current of 1500 mA and a discharge end voltage of 3.0 V. The charged / discharged battery was recharged, and the charged battery was stored at an environmental temperature of 60 ° C. for 10 days. The battery after storage was allowed to cool at an environmental temperature of 20 ° C., and then a constant current discharge was performed at a discharge current of 300 mA and a discharge end voltage of 3.0 V. Next, the upper limit voltage was set to 4.2 V, constant current / constant voltage charging was performed for 2 hours 30 minutes at a maximum current of 1050 mA, and constant current discharging was performed at a discharge current of 1500 mA and a discharge end voltage of 3.0 V.
The calculation operation and the discharge capacity C ₁₅₀₀ at the time of discharging current 1500mA of battery after storage was obtained by the discharge current 300mA when the discharge capacity C ₃₀₀ Formula _{1: P h (%) =} (C 1500 / C 300) × 100
By substituting was determined high rate discharge property P _h of the battery after storage. The results are shown in Table 1.
[0041]
[Table 1]

[0042]
As can be seen from Table 1, the battery 7 and the battery 14, since the non-aqueous electrolyte does not contain a compound having two pyridine rings, high rate discharge property P _h was 60% and 75%, respectively. In contrast, the two batteries 1-6 to a compound having a pyridine ring with a non-aqueous solvent 0.1 parts by volume of the added non-aqueous electrolyte per 100 parts by volume of and a battery 8-13, high-rate discharge characteristic P _h Improved by 5-25%. The degree of improvement of high rate discharge property P _h, the content of γ- butyrolactone in the nonaqueous solvent (GBL) was higher significantly. From these results, when GBL is used as the non-aqueous solvent, the impedance of the battery due to high-temperature storage is usually remarkably increased, but by adding a compound having two pyridine rings to the non-aqueous electrolyte, the impedance can be reduced. the increase can be suppressed, it was shown that thereby improving the high rate discharge property P _h.
[0043]
Example 2
Next, the amount of the compound having two pyridine rings to be included in the nonaqueous electrolyte was examined. When a compound having two pyridine rings is added to a non-aqueous solvent, the irreversible capacity of the battery is increased. Therefore, if the amount of the compound having two pyridine rings is too large, the battery capacity is considered to decrease. In addition, since a compound having two pyridine rings has low oxidation resistance and reduction resistance, the compound having an excess of two pyridine rings may be oxidized or reductively decomposed at a high temperature to increase the amount of gas generated. .
[0044]
EC / EMC / GBL / VC = 0/0/100/2 (volume ratio) was used as a non-aqueous solvent. In addition, LiPF ₆ was dissolved in the nonaqueous solvent as a solute at a concentration of 1.5 mol / liter. 2,2′-bipyridine was used as the compound having two pyridine rings. The addition amount ΔV _h of the compound having two pyridine rings per 100 parts by volume of the non-aqueous solvent was varied in the range of 0.001 to 5 parts by volume as shown in Table 2. Except for the above, batteries 15 to 20 were produced in the same manner as in Example 1. The batteries 15, 19 and 20 are reference batteries.
[0045]
The finished high-rate discharge characteristics P _h of each battery was evaluated in the same manner as in Example 1. Moreover, the irreversible capacity | capacitance of each battery and the gas generation amount at the time of high temperature storage were calculated | required. The obtained results are shown in Table 2.
[0046]
[Table 2]

[0047]
As shown in Table 2, in the battery 15 in which the addition amount ΔV _{h of} 2,2′-bipyridine was 0.001 part by volume per 100 parts by volume of the nonaqueous solvent, no improvement in the high rate discharge characteristic P _h was observed. This is considered because the film which suppresses an increase in impedance was not sufficiently formed on the positive electrode surface. On the other hand, in the case of the battery 19 and the battery 20 in which the addition amount ΔV _{h of} 2,2′-bipyridine is 1 part by volume and 5 parts by volume per 100 parts by volume of the non-aqueous solvent, 2,2′-bipyridine is excessive, and therefore irreversible. Increased volume and gas generation during high temperature storage. Greater reduction in high rate discharge property P _h of the battery 20, the generated gas is considered to be due to reduction of the reaction area due to remain between the electrodes. Therefore, when the addition amount ΔV _{h of} 2,2′-bipyridine is in the range of 0.01 to 0.5 parts by volume per 100 parts by volume of the nonaqueous solvent, good high rate discharge characteristics are exhibited, and the irreversible capacity and gas generation This is a preferable range in which no significant increase in the amount is observed.
[0048]
Example 3
Next, the amount of γ-butyrolactone included in the nonaqueous solvent was examined. Table 3 shows the composition of the nonaqueous solvent used. In the non-aqueous solvent, LiPF ₆ was dissolved as a solute at a concentration of 1.5 mol / liter, and 2,2′-bipyridine was further added. The addition amount ΔV _h of 2,2′-bipyridine per 100 parts by volume of the non-aqueous solvent is 0. The volume was 2 parts. Batteries 21 to 23 were produced in the same manner as Example 1 except for the above. The battery 23 is a reference battery. Were then evaluated high rate discharge property P _h of each battery was completed in the same manner as in Example 1. The obtained results are shown in Table 3.
[0049]
[Table 3]

[0050]
As shown in Table 3, the amount of γ- butyrolactone in the battery 21 and 22 of more than 30% by volume of the total non-aqueous solvent, the high-rate discharge characteristics P _h substantially equal to that of the battery 8 of Example 1 were obtained. On the other hand, in the battery 23 in which the amount of γ-butyrolactone was less than 30% by volume of the whole non-aqueous solvent, the high rate discharge characteristic _Ph was lowered due to the decrease in the conductivity of the electrolytic solution. From the above, it can be understood that the preferable amount of γ-butyrolactone is 30% by volume or more of the entire non-aqueous solvent.
[0051]
Example 4
Next, the battery 8 of Example 1 was used except that the nonaqueous solvent shown in Table 4 containing γ-valerolactone (GVL) or α-methyl-γ-butyrolactone (AMGBL) was used instead of γ-butyrolactone. Batteries 24 and 25 having the structure described above were produced. That is, in the non-aqueous solvent, LiPF ₆ was dissolved as a solute at a concentration of 1.5 mol / liter, and 0.1 part by volume of 2,2′-bipyridine was further added per 100 parts by volume of the non-aqueous solvent. The battery 25 is a reference battery. The finished high-rate discharge characteristics P _h of each battery was evaluated in the same manner as in Example 1. Table 4 shows the obtained results.
[0052]
[Table 4]

[0053]
The results in Table 4, .gamma. even when using butyrolactone other .gamma.-butyrolactone derivatives, .gamma.-butyrolactone can be seen that the high rate discharge property P _h can be obtained in the same extent as if using.
[0054]
In this example, a non-aqueous electrolyte containing the above compound as a γ-butyrolactone derivative and a compound having two pyridine rings was described. However, other γ-butyrolactone derivatives and compounds having two pyridine rings were used. Similar effects are also obtained when used. Accordingly, the present invention is not limited to the embodiments described herein.
[0055]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte secondary battery excellent in the storage characteristic in a high temperature environment, especially the high rate discharge characteristic after a preservation | save can be provided.
[Brief description of the drawings]
FIG. 1 is a right half cross-sectional front view of an example of a nonaqueous electrolyte secondary battery of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Separator 2 Positive electrode 3 Negative electrode 4 Positive electrode lead 5 Negative electrode lead 6 Bottom insulating plate 7 Battery case 8 Upper insulating plate 9 Gasket 10 Sealing plate

Claims (8)

Consisting of a positive electrode, a negative electrode and a non-aqueous electrolyte,
The non-aqueous electrolyte comprises a non-aqueous solvent, a solute dissolved in the non-aqueous solvent, and an additive,
The non-aqueous solvent has the formula (1):

(In formula (1), R ^{1 to} R ⁶ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms or an acetyl group having 1 to 6 carbon atoms) represented by a γ-butyrolactone derivative. Including
The additive is represented by the formula (2):

(In the formula (2), R ^{7 to} R ⁸ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 3 carbon atoms, a phenyl group or a hydroxyl group, and the bond X is a covalent bond, having 1 carbon atom. Ri Do from a compound having two pyridine ring represented by to 3 alkylene group or a 2 Kyua amino group),
The amount of the compound having two pyridine rings contained in the nonaqueous electrolyte is 0.01 to 0.5 parts by volume per 100 parts by volume of the nonaqueous solvent,
The amount of the γ- butyrolactone derivative, the nonaqueous solvent entire 30 vol% der Ru nonaqueous electrolyte secondary battery.   The compound having two pyridine rings is 2,2′-bipyridine, 4,4′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, 2,2′-dipyridylamine, 2,2 The nonaqueous electrolyte secondary battery according to claim 1, which is at least one selected from the group consisting of '-dipiconylamine and 3,3′-dipiconylamine. The non-aqueous electrolyte secondary battery according to claim 1 or 2 , wherein the γ-butyrolactone derivative is at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, and α-methyl-γ-butyrolactone. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the positive electrode is made of a lithium-containing transition metal oxide, and the negative electrode is made of graphite. Consisting of a non-aqueous solvent, a solute dissolved in the non-aqueous solvent and an additive,
The non-aqueous solvent has the formula (1):

(In formula (1), R ^{1 to} R ⁶ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms or an acetyl group having 1 to 6 carbon atoms) represented by a γ-butyrolactone derivative. Including
The additive is represented by formula (2):

(In the formula (2), R ^{7 to} R ⁸ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 3 carbon atoms, a phenyl group or a hydroxyl group, and the bond X is a covalent bond, having 1 carbon atom. Ri Do from a compound having two pyridine ring represented by to 3 alkylene group or a 2 Kyua amino group),
The amount of the compound having two pyridine rings contained in the nonaqueous electrolyte is 0.01 to 0.5 parts by volume per 100 parts by volume of the nonaqueous solvent,
The γ- butyrolactone amount of derivative is 30% by volume or more der Ru nonaqueous electrolyte secondary battery electrolyte of the entire nonaqueous solvent. The compound having two pyridine rings is 2,2′-bipyridine, 4,4′-bipyridine, 4,4′-dimethyl-2,2′-bipyridine, 2,2′-dipyridylamine, 2,2 The electrolyte solution for a non-aqueous electrolyte secondary battery according to claim 5, which is at least one selected from the group consisting of '-dipicolylamine and 3,3'-dipicolylamine. The electrolysis for nonaqueous electrolyte secondary battery according to claim 5 or 6 , wherein the γ-butyrolactone derivative is at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, and α-methyl-γ-butyrolactone. liquid. An electrolyte for a non-aqueous electrolyte secondary battery comprising a positive electrode including a lithium-containing transition metal oxide, a negative electrode including graphite, and a non-aqueous electrolyte,
Consisting of a non-aqueous solvent, a solute dissolved in the non-aqueous solvent and an additive,
The non-aqueous solvent has the formula (1):

(In formula (1), R ^{1 to} R ⁶ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms or an acetyl group having 1 to 6 carbon atoms) represented by a γ-butyrolactone derivative. Including
The additive is represented by the formula (2):

(In the formula (2), R ^{7 to} R ⁸ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 3 carbon atoms, a phenyl group or a hydroxyl group, and the bond X is a covalent bond, having 1 carbon atom. Ri Do from a compound having two pyridine ring represented by to 3 alkylene group or a 2 Kyua amino group),
The amount of the compound having two pyridine rings contained in the nonaqueous electrolyte is 0.01 to 0.5 parts by volume per 100 parts by volume of the nonaqueous solvent,
The γ- butyrolactone amount of derivative is 30% by volume or more der Ru nonaqueous electrolyte secondary battery electrolyte of the entire nonaqueous solvent.

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