JP4149042B2 - Non-aqueous electrolyte for secondary battery and non-aqueous electrolyte secondary battery - Google Patents

Description

【０００９】
式（１）中、Ｒ¹とＲ²は互いに同一であっても異なっていてもよく、炭素原子数が１〜７のアルキル基、不飽和結合を含む炭素原子数が２〜７の炭化水素基であり、Ｒ³とＲ⁴は互いに同一であっても異なっていてもよく、水素原子、炭素原子数が１〜７のアルキル基、不飽和結合を含む炭素原子数が２〜７の炭化水素基である。
【００１０】
上記一般式（１）で表される環状炭酸エステルは、Ｒ¹とＲ²に炭素原子数が１〜７のアルキル基を有し、Ｒ³とＲ⁴に水素あるいは炭素原子数が１〜７のアルキル基を有することが好ましい。
【００１１】
また、上記一般式（１）で表される環状炭酸エステルは、Ｒ¹とＲ²に炭素原子数が１〜４のアルキル基を有し、Ｒ³とＲ⁴の少なくとも一方に水素を有するものが特に好ましい。
【００１２】
さらに、上記一般式（１）で表される環状炭酸エステルは、Ｒ¹とＲ²にメチル基あるいはエチル基を有し、Ｒ³とＲ⁴に水素を有するものが最も好ましい。
また、本発明は前記非水溶媒が、下記一般式（２）で表される炭酸エステルをさらに含んでいる非水電解液を提供する。
【００１３】
【化４】

【００１４】
式中、Ｒ⁵は水素原子または炭素数１〜３のアルキル基を示し、Ｒ⁶は炭素原子数１〜３のアルキル基を示す。
さらに、これら上記の非水電解液に含まれる電解質が、リチウム塩である非水電解液を提供する。
【００１５】
さらにまた、本発明は、
負極活物質が黒鉛である負極と、
正極活物質としてリチウムと遷移金属の複合酸化物、炭素材料またはこれらの混合物のいずれかを含む正極と、
電解液として上記非水電解液とを
含むことを特徴とする非水電解液二次電池を提供する。
【００１６】
【発明の具体的説明】
以下、本発明に係る非水電解液およびこの非水電解液を用いた非水電解液二次電池について具体的に説明する。
【００１７】
本発明に係る非水電解液は、特定の環状炭酸エステルを含む非水溶媒と、電解質からなる。
環状炭酸エステル
本発明で用いられる環状炭酸エステルとして、下記一般式（１）で表されるものが使用される。
【００１８】
【化５】

【００１９】
式（１）中、Ｒ¹とＲ²は互いに同一であっても異なっていてもよく、炭素原子数が１〜７のアルキル基、不飽和結合を含む炭素原子数が２〜７の炭化水素基であり、Ｒ³とＲ⁴は互いに同一であっても異なっていてもよく、水素原子、炭素原子数が１〜７のアルキル基、不飽和結合を含む炭素原子数が２〜７の炭化水素基である。
【００２０】
本発明では、このような上記一般式（１）で表される環状炭酸エステルとして、 Ｒ¹とＲ²に炭素原子数が１〜７のアルキル基を有し、Ｒ³とＲ⁴に水素あるいは炭素原子数が１〜７のアルキル基を有することが好ましい。
【００２１】
また、上記一般式（１）で表される環状炭酸エステルは、Ｒ¹とＲ²に炭素原子数が１〜４のアルキル基を有し、Ｒ³とＲ⁴の少なくとも一方に水素を有するものが特に好ましい。
【００２２】
さらに、上記一般式（１）で表される環状炭酸エステルは、Ｒ¹とＲ²にメチル基あるいはエチル基を有し、Ｒ³とＲ⁴に水素を有するものが最も好ましい。
このような式（１）で表される環状炭酸エステルとしては、
4,4-ジメチル,5-メチレンエチレンカーボネート、4-メチル,4-エチル,5-メチレンエチレンカーボネート、4-メチル,4-プロピル, 5-メチレンエチレンカーボネート、4-メチル,4-ブチル,5-メチレンエチレンカーボネート、4,4-ジエチル,5-メチレンエチレンカーボネート、4-エチル,4-プロピル,5-メチレンエチレンカーボネート、4-エチル,4-ブチル,5-メチレンエチレンカーボネート、4,4-ジプロピル,5-メチレンエチレンカーボネート、4-プロピル,4-ブチル,5-メチレンエチレンカーボネート、4,4-ジブチル,5-メチレンエチレンカーボネート、4,4-ジメチル,5-エチリデンエチレンカーボネート、4-メチル,4-エチル,5-エチリデンエチレンカーボネート、4-メチル,4-プロピル, 5-エチリデンエチレンカーボネート、4-メチル,4-ブチル,5-エチリデンエチレンカーボネート、4,4-ジエチル,5-エチリデンエチレンカーボネート、4-エチル,4-プロピル,5-エチリデンエチレンカーボネート、4-エチル,4-ブチル,5-エチリデンエチレンカーボネート、4,4-ジプロピル,5-エチリデンエチレンカーボネート、4-プロピル,4-ブチル,5-エチリデンエチレンカーボネート、4,4-ジブチル,5-エチリデンエチレンカーボネート、4-メチル,4-ビニル,5-メチレンエチレンカーボネート、4-メチル,4-アリル,5-メチレンエチレンカーボネート、4-メチル,4-メトキシメチル,5-メチレンエチレンカーボネート、4-メチル,4-アクリルオキシメチル,5-メチレンエチレンカーボネート、4-メチル,4-アリルオキシメチル,5-メチレンエチレンカーボネート、などが挙げられる。
【００２３】
中でも特に好ましい化合物は、4,4-ジメチル,5-メチレンエチレンカーボネート（下記式（３））、及び4-メチル,4-エチル,5-メチレンエチレンカーボネート（下記式（４））である。
【化６】

【００２４】
このような環状炭酸エステルには、充電時における非水溶媒の還元反応を抑制し、充放電効率を改善する効果がある。
非水溶媒
本発明に係る二次電池用非水電解液では、上記（１）式で表される環状炭酸エステルを含む非水溶媒が使用される。
【００２５】
上記（１）式で表される環状炭酸エステルは、他の非水溶媒との混合物として使用することが好ましい。上記（１）式で表される環状炭酸エステルは、非水溶媒全体に対して0.001重量％以上、好ましくは0.01〜50重量％、さらに好ましくは0.1〜20重量％の量で含まれていることが望ましい。このような量で非水溶媒中に一般式（１）で表される環状炭酸エステルが含まれていると、充電時に起こる溶媒の還元分解反応を低く保つことができる。
【００２６】
本発明における非水溶媒は、上記式（１）で表される環状炭酸エステルとともに、下記一般式（２）で表される環状炭酸エステル及び／又は鎖状炭酸エステルを含んでいてもよい。
【００２７】
【化７】

【００２８】
式中、Ｒ⁵は水素原子または炭素数１〜３のアルキル基を示し、Ｒ⁶は炭素原子数１〜３のアルキル基を示す。
このような式（２）で表される環状炭酸エステルとしては、プロピレンカーボネート、1,2-ブチレンカーボネート、2,3-ブチレンカーボネート、1,2-ペンチレンカーボネート、2,3-ペンチレンカーボネートなどが挙げられる。
これらの中では、粘度及び凝固点の低いプロピレンカーボネートが好ましく使用される。また、これら環状炭酸エステルは2種以上混合して使用してもよい。
【００２９】
鎖状炭酸エステルとしては、ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネート、メチルプロピルカーボネート、メチルイソプロピルカーボネート、エチルプロピルカーボネートなどが挙げられる。またこれら鎖状炭酸エステルは２種以上混合して使用してもよい。
【００３０】
このような鎖状炭酸エステルが非水溶媒中に含まれていると、非水電解液の粘度を低くすることが可能となり、電解質の溶解度をさらに高め、常温または低温での電気伝導性に優れた電解液とすることできる。このため電池の充放電効率および負荷特性を改善することができる。
【００３１】
したがって、本発明の好ましい非水溶媒は、一般式（１）で表される環状炭酸エステルと、一般式（２）で表される環状炭酸エステル及び／又は前記鎖状炭酸エステルを含むものである。しかし、以下に記載する他の化合物の存在を排除するものではない。
電池特性の向上、たとえば電池の充放電効率の向上および負荷特性の改善の点から、前記したように、上記（１）式で表される環状炭酸エステルは、非水溶媒全体の０．００１重量％以上、好ましくは０．０１〜５０重量％、さらに好ましくは０．１〜２０重量％の量で含まれていることが望ましい。残余の量は、一般式（２）で表される環状炭酸エステル及び／又は前記鎖状炭酸エステルで占められることが好ましく、中でも一般式（２）で表される環状炭酸エステル、または一般式（２）で表される環状炭酸エステルおよび前記鎖状炭酸エステルで占められることがさらに好ましい。
即ち、一般式（２）で表される環状炭酸エステルと前記鎖状炭酸エステルの合計量は、非水溶媒全量の９９．９９９重量％以下、好ましくは５０〜９９．９９重量％、さらに好ましくは、８０〜９９．９重量％であることが望ましい。
非水溶媒中の、一般式（２）で表される環状炭酸エステルと鎖状炭酸エステルとの量比（一般式（２）で表される環状炭酸エステル：鎖状炭酸エステル）は、０：１００〜１００：０、好ましくは５：９５〜９５：５、特に好ましくは２０：８０〜８５：１５（いずれも重量比）である。
【００３２】
さらにまた本発明では、上記環状炭酸エステル、鎖状炭酸エステルの他に存在し得る化合物として、通常電池用非水溶媒として広く使用されている溶媒を使用することも可能であり、具体的には、ビニレンカーボネートなどの環内に二重結合を有する環状炭酸エステル、蟻酸メチル、蟻酸エチル、蟻酸プロピル、酢酸メチル、酢酸エチル、酢酸プロピル、プロピオン酸メチル、プロピオン酸エチルなどの鎖状エステル、リン酸トリメチルなどのリン酸エステル、ジメトキシエタンなどの鎖状エーテル類、テトラヒドロフランなどの環状エーテル類、 ジメチルホルムアミドなどのアミド類、メチル-N,N-ジメチルカーバメートなどの鎖状カーバメート類、γ-ブチロラクトンなどの環状エステル、スルホランなどの環状スルホン類、N-メチルオキサゾリジノンなどの環状カーバメート、N-メチルピロリドンなどの環状アミド、N,N-ジメチルイミダゾリドンなどの環状ウレアなどが挙げられる。
【００３３】
上記環状炭酸エステル、鎖状炭酸エステルの他に存在しうる他の化合物は、一般式（１）で表される環状炭酸エステル、一般式（２）で表される環状炭酸エステル及び鎖状炭酸エステルの合計量に対して、２０重量％以下で使用されることが望ましい。
【００３４】
電解質
本発明で使用される電解質としては、通常、非水電解液用電解質として使用されているものであれば、特に限定されることなく使用することができる。
【００３５】
具体的には、ＬiＰＦ₆、ＬiＢＦ₄、ＬiＣlＯ₄、ＬiＡｓＦ₆、ＬiＯＳＯ₂Ｒ¹¹、ＬiＮ(ＳＯ₂Ｒ¹²)(ＳＯ₂Ｒ¹³)、ＬiＣ(ＳＯ₂Ｒ¹⁴)(ＳＯ₂Ｒ¹⁵)(ＳＯ₂Ｒ¹⁶)、ＬiＮ(ＳＯ₂ＯＲ¹⁷)(ＳＯ₂ＯＲ¹⁸)［式中、Ｒ¹¹〜Ｒ¹⁸は、互いに同一であっても異なっていてもよく、炭素数１〜６のパーフルオロアルキル基である］、ＬiＳiＦ₆、ＬiＣ₄Ｆ₉ＳＯ₃、ＬiＣ₈Ｆ₁₇ＳＯ₃などのリチウム塩が好ましく使用される。これらのリチウム塩は単独で使用してもよく、また２種以上を混合して使用してもよい。
【００３６】
これらのうち、特に、ＬiＰＦ₆、ＬiＢＦ₄、ＬiＯＳＯ₂Ｒ¹¹、ＬiＮ(ＳＯ₂Ｒ¹²)(ＳＯ₂Ｒ¹³)、ＬiＣ(ＳＯ₂Ｒ¹⁴)(ＳＯ₂Ｒ¹⁵)(ＳＯ₂Ｒ¹⁶)、ＬiＮ(ＳＯ₂ＯＲ¹⁷)(ＳＯ₂ＯＲ¹⁸)が好ましい。
【００３７】
特に、このような電解質は、通常、0.1〜３モル／リットル、好ましくは0.5〜２モル／リットルの濃度で非水電解液中に含まれていることが望ましい。
以上のような本発明に係る二次電池用非水電解液は、リチウムイオン二次電池用の非水電解液として好適である。また本発明の非水電解液は、一次電池用の非水電解液としても用いることが出来る。
【００３８】
非水電解液二次電池
本発明に係る非水電解液二次電池は、負極と、正極と、前記の非水電解液を含んで構成されている。通常これに加えてセパレータが使用される。
【００３９】
本発明の好ましい非水電解液二次電池として、
負極活物質として金属リチウム、リチウム含有合金、リチウムイオンのドープ・脱ドーブが可能な炭素材料のいずれかを含む負極と、
正極活物質としてリチウムと遷移金属の複合酸化物、炭素材料またはこれらの混合物のいずれかを含む正極と、
セパレータと、
前記の非水電解液
とから構成されている非水電解液二次電池を挙げることができる。
【００４０】
このような非水電解液二次電池は、たとえば円筒型非水電解液二次電池に適用できる。円筒型非水電解液二次電池は、図１に示すように負極集電体9に負極活物質を塗布してなる負極1と、正極集電体10に正極活物質を塗布してなる正極2とを、非水電解液を注入されたセバレータ3を介して巻回し、巻回体の上下に絶縁板4を載置した状態で電池缶5に収納してなるものである。電池缶5には電池蓋7が封口ガスケット6を介してかしめることにより取り付けられ、それぞれ負極リード1 1および正極リード12を介して負極1あるいは正極2と電気的に接続され、電池の負極あるいは正極として機能するように構成されている。なおセパレータは多孔性の膜であり、微多孔性ポリマーフィルムが好ましく使用されるが、中でも多孔性ポリオレフィンフィルムが好ましい。多孔性ポリオレフィンフィルムとしては、多孔性ポリエチレンフィルム、多孔性ポリプロピレンフィルム、または多孔性のポリエチレンフィルムとポリプロピレンの多層フィルムを例示できる。
【００４１】
リチウムイオン二次電池では、通常電池の安全性を確保する手段として、リチウムイオン二次電池にシャットダウン性を有するセパレータの採用、ＰＴＣ素子、保護回路、電流遮断機構、安全弁などの工夫が提案ないし採用がされている。
【００４２】
この電池では、正極リード12は、電流遮断用薄板8を介して電池蓋7との電気的接続がはかられていてもよい。このような電池では、電池内部の圧力が上昇すると、電流遮断用薄板8が押し上げられ変形し、正極リード12が上記薄板8と溶接された部分を残して切断され、電流が遮断されるようなっている。
【００４３】
このような負極１を構成する負極活物質としては、金属リチウム、リチウム合金、リチウムイオンをドープ・脱ドープすることが可能な炭素材料のいずれかを用いることができるが、これらのうちで、リチウムイオンをドープ・脱ドープすることが可能な炭素材料を用いることが好ましい。このような炭素材料は、グラファイトであっても非晶質炭素であってもよく、活性炭、炭素繊維、カーボンブラック、メソカーボンマイクロビーズ等あらゆる炭素材料が用いられる。
【００４４】
本発明では、負極活物質として特に、Ｘ線解析で測定した（００２）面の面間隔（ｄ００２）が０．３４０ｎｍ以下の炭素材料が好ましく、特に、密度が１．７０ｇ／ｃｍ³以上である黒鉛またはそれに近い性質を有する高結晶性炭素材料が望ましく、このような炭素材料を使用すると、電池のエネルギー密度を高くすることができる。
【００４５】
正極2を構成する正極活物質としては、ＭoＳ₂、ＴiＳ₂、ＭnＯ₂、Ｖ₂Ｏ₅などの遷移金属酸化物および遷移金属硫化物、ＬiＣoＯ₂、ＬiＭnＯ₂、ＬiＭn₂Ｏ₄、ＬiＮiＯ₂などのリチウムと遷移金属とからなる複合酸化物が挙げられる。このうち、特にリチウムと遷移金属とからなる複合酸化物が好ましい。また、負極がリチウム金属またはリチウム合金である場合は、正極として炭素材料を用いることもできる。さらにまた、正極として、リチウムと遷移金属の複合酸化物と炭素材料との混合物を用いることもできる。
【００４６】
また、本発明に係る非水電解液二次電池は、図２に示すようなコイン型非水電解液二次電池にも適用することができる。
図２のコイン型非水電解液二次電池では、円盤状負極13、円盤状正極14、セバレータ15およびステンレスの板17が、負極13、セパレータ15、正極14、ステンレスの板17の順序に積層された状態で、電池缶16に収納され、電池缶(蓋)19がガスケット18を介してかしめることにより取り付けられている。負極13、セパレータ15、正極14としては、前記と同様のものが使用される。電池缶16、電池缶(蓋)19としては、電解液で腐食しにくいステンレスなどの材質のものが使用される。
【００４７】
なお、本発明に係る非水電解液二次電池は、電解液として以上説明した非水電解液を含むものであり、電池の形状などは図１および図２に示したものに限定されず、角型などであってもよい。
【００４８】
【発明の効果】
本発明の非水電解液は黒鉛などの高結晶性炭素を負極に用いた場合に起こる溶媒の還元分解反応を低く抑え、その結果本発明の非水電解液を用いた非水電解液二次電池は、充放電特性に優れ、低温における電池特性に優れる。また、本発明に係る二次電池用非水電解液は、リチウムイオン二次電池用の非水電解液として特に好適である。
【００４９】
【実施例】
以下、実施例を挙げて本発明を具体的に説明するが、本発明はこれら実施例により何ら限定されるものではない。
【００５０】
【実施例１】
＜非水電解液の調製＞
プロピレンカーボネート（ＰＣ）、ジエチルカーボネート（ＤＥＣ）を混合（混合重量比ＰＣ：ＤＥＣ＝５５：４５）した後、4,4-ジメチル,5-メチレンエチレンカーボネート（ＤＭＭＣ）をＰＣとＤＥＣとの混合溶媒９９重量部に対し、１重量部（１重量％）添加し、混合溶媒を調製した。次にＬiＰＦ₆１５．２g(１００mmol)を、前記混合溶媒に溶解し、電解質濃度が１．０mol/lとなるようにして、非水電解液を調製した。。
【００５１】
＜負極の作製＞
負極13は、以下のようにして作製した。
大阪ガス（株）製のメソカーボンマイクロビーズ(MCMB、焼成温度2800℃）の炭素粉末90重量部と結着剤のポリフッ化ビニリデン(PVDF)10重量部とを混合し、溶剤のN-メチルピロリドンに分散させ、負極合剤スラリー（ペースト状）を調製した。
【００５２】
この負極合剤スラリーを厚さ２０μｍの帯状銅箔製の負極集電体に塗布し、乾燥させた後、帯状の炭素負極を得た。このような負極合剤の厚さは２５μｍであった。さらに、この帯状電極を直径１５mmの円盤状に打ち抜いた後、圧縮成形し負極電極13とした。
＜正極の作製＞
正極14は、以下のようにして作製した。
【００５３】
本庄ケミカル（株）製のＬiＣoＯ₂（製品名：HLC-21、平均粒径８μｍ）微粒子91重量部と、導電材のグラファイト6重量部と、結着剤のポリフッ化ビニリデン3重量部とを混合して正極合剤を調製し、N-メチルピロリドンに分散させることにより、正極合剤スラリーを得た。
【００５４】
このスラリーを厚さ20μｍの帯状アルミニウム箔製正極集電体に塗布し、乾燥させ、圧縮成形して、帯状正極を得た。このような正極合剤の厚さは４０μｍであった。さらにこの帯状電極を直径１５mmの円盤状に打ち抜くことにより正極電極14とした。
＜電池の作製＞
このようにして得られた円盤状負極13、円盤状正極14、およびセパレータ15（厚さ25μｍ、直径19mmの微多孔性ポリプロピレンフィルム）を図２に示すようにステンレス製の２０３２サイズの電池缶16に、負極13、セパレータ15、正極14の順序で積層したのち、セパレータ15に前記非水電解液を注入した。その後、ステンレス製の板17（厚さ2.4mm、直径15.4mm）を収納した後、ポリプロピレン製のガスケット18を介して、電池缶（蓋）19をかしめることにより、電池内の気密性を保持し、直径20mm、高さ3.2mmのボタン型非水電解液二次電池を作製した。
＜放電容量の測定＞
こうして得られた非水電解液二次電池の放電容量を室温にて測定した。なお、本実施例では、負極にＬi+がドープされる電流方向を充電、脱ドープされる電流方向を放電とした。充電は、4.1V、１mA定電流定電圧充電方法で行い、充電電流が５０μＡ以下になった時点で終了とした。この充放電サイクルの充電容量と放電容量とから、次式により充放電効率を計算した。結果を表１に示す。
【００５５】
【数１】

【００５６】
【実施例２】
実施例１において、混合溶媒の重量比ＰＣ：ＤＥＣを５５：４５とし、4,4-ジメチル,5-メチレンエチレンカーボネートの代わりに4-エチル,4-メチル,5-メチレンエチレンカーボネート（ＥＭＭＣ）を使用した以外は実施例１と同様にして、電池の充放電効率を評価した。結果を表１に示す。
【００５７】
【実施例３】
実施例１において、4,4-ジメチル,5-メチレンエチレンカーボネートの添加量をＰＣとＤＥＣとの合計９９．５重量部に対し、０．５重量部（０．５重量％）にした以外は、実施例１と同様にして、電池の充放電効率を評価した。結果を表１に示す。
【００５８】
【実施例４】
実施例１において、4,4-ジメチル,5-メチレンエチレンカーボネートの添加量をＰＣとＤＥＣとの合計量９５重量部に対し、５重量部（５重量％）にした以外は、実施例１と同様
にして、電池の充放電効率を評価した。結果を表１に示す。
【００５９】
【比較例１】
実施例１において、4,4-ジメチル,5-メチレンエチレンカーボネートを添加しなかった以外は、実施例１と同様にして、電池の充放電効率を評価した。結果を表１に示す。
【００６０】
【表１】

【００６１】
【図面の簡単な説明】
【図１】本発明の非水電解液二次電池の一実施例を示す円筒型電池の概路断面図である。
【図２】本発明の非水電解液二次電池の一実施例を示すコイン電池の概略断面図である。
【符号の説明】
1,13・・・・負極
2,14・・・・正極
3,15・・・・セパレータ
4,11・・・・絶縁板
5,16・・・・電池缶
6・・・・封口ガスケット
7・・・・電池蓋
8・・・・電流遮断用薄板
9・・・・負極集電体
10・・・・正極集電体
11・・・・負極リード
12・・・・正極リード
17・・・・ステンレス製の板
18・・・・ガスケット
19・・・・電池缶(蓋)[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a novel non-aqueous electrolyte excellent in charge / discharge characteristics and a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte.
[0002]
TECHNICAL BACKGROUND OF THE INVENTION
Batteries using non-aqueous electrolytes are widely used as power sources for consumer electronic devices because they have high voltage and high energy density and are excellent in reliability such as storage.
[0003]
As such a battery, there is a nonaqueous electrolyte secondary battery, and a typical example thereof is a lithium ion secondary battery. In such a non-aqueous electrolyte secondary battery, carbonate having a high dielectric constant is known as a non-aqueous solvent for the non-aqueous electrolyte, and various carbonates have been proposed.
As an electrolyte for such a non-aqueous electrolyte secondary battery, a mixed solvent of a high dielectric constant solvent such as propylene carbonate and ethylene carbonate and a low viscosity solvent such as diethyl carbonate is usually added to LiBF ₄ , LiPF ₆ , LiClO _4. , LiAsF ₆ , LiCF ₃ SO ₃ , LiSiF _6, etc. mixed electrolytes are used.
On the other hand, research on electrodes has been advanced with the aim of increasing the capacity of batteries, and carbon materials capable of inserting and extracting lithium are used as negative electrodes of lithium ion secondary batteries. In particular, highly crystalline carbon such as graphite has characteristics such as a flat discharge potential, and is therefore used as a negative electrode for most of the lithium ion secondary batteries currently on the market.
[0004]
However, when highly crystalline carbon such as graphite is used for the negative electrode, if propylene carbonate or 1,2-butylene carbonate, which is a high dielectric constant solvent having a low freezing point, is used as a non-aqueous solvent for a non-aqueous electrolyte, The reductive decomposition reaction of lithium ions occurs, and the insertion reaction of lithium ions, which are active materials, into the graphite hardly proceeds and the function of the electrolytic solution is not achieved. As a result, there has been a problem that the initial charge / discharge efficiency is extremely deteriorated.
[0005]
For this reason, in addition to propylene carbonate as a non-aqueous solvent used in the electrolyte, high-dielectric constant solvent is solid at room temperature but is mixed with ethylene carbonate, which is less likely to cause reductive decomposition reaction continuously. Attempts have been made to suppress the reductive decomposition reaction of non-aqueous solvents. Furthermore, in order to improve the viscosity characteristics of non-aqueous solvents in addition to suppressing reductive decomposition reactions, the combination with low-viscosity solvents is devised, various additives are added, and the content of propylene carbonate in the electrolyte is reduced. It has been proposed to limit it. As a result, the charge / discharge characteristics and low-temperature characteristics of the battery have been improved, but this is not always satisfactory.
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the above problems, and even when highly crystalline carbon such as graphite is used for the negative electrode, reductive decomposition of the solvent is suppressed, and the battery has excellent charge / discharge efficiency and load characteristics. In addition, an object of the present invention is to provide a non-aqueous electrolyte that provides low-temperature characteristics, and to provide a secondary battery including the non-aqueous electrolyte.
[0007]
[Means for Solving the Problems]
The nonaqueous electrolytic solution according to the present invention is characterized by comprising a nonaqueous solvent containing a cyclic carbonate represented by the following general formula (1) and an electrolyte.
[0008]
[Chemical 3]

[0009]
In formula (1), R ¹ and R ² may be the same or different from each other, an alkyl group having 1 to 7 carbon atoms, and a hydrocarbon having 2 to 7 carbon atoms containing an unsaturated bond a group, R ³ and R ⁴ may be the being the same or different, a hydrogen atom, an alkyl group having a carbon number of 1 to 7 carbon atoms including an unsaturated bond of 2 to 7 carbon It is a hydrogen group .
[0010]
The cyclic carbonate represented by the general formula (1) has an alkyl group having 1 to 7 carbon atoms in R ¹ and R ² , and hydrogen or carbon atoms in R ³ and R ⁴ have 1 to 7 carbon atoms. It is preferable to have an alkyl group.
[0011]
The cyclic carbonate represented by the general formula (1) has an alkyl group having 1 to 4 carbon atoms in R ¹ and R ² and hydrogen in at least one of R ³ and R ^4. Is particularly preferred.
[0012]
Further, the cyclic carbonate represented by the general formula (1) is most preferably one having a methyl group or an ethyl group in R ¹ and R ² and hydrogen in R ³ and R ⁴ .
The present invention also provides a non-aqueous electrolyte in which the non-aqueous solvent further contains a carbonate ester represented by the following general formula (2).
[0013]
[Formula 4]

[0014]
In the formula, R ⁵ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R ⁶ represents an alkyl group having 1 to 3 carbon atoms.
Furthermore, the electrolyte contained in these non-aqueous electrolytes provides a non-aqueous electrolyte that is a lithium salt.
[0015]
Furthermore, the present invention provides:
A negative electrode whose negative electrode active material is graphite ;
A positive electrode including any of a composite oxide of lithium and a transition metal, a carbon material, or a mixture thereof as a positive electrode active material;
A non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte as an electrolyte is provided.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the non-aqueous electrolyte according to the present invention and the non-aqueous electrolyte secondary battery using the non-aqueous electrolyte will be specifically described.
[0017]
The nonaqueous electrolytic solution according to the present invention comprises a nonaqueous solvent containing a specific cyclic carbonate and an electrolyte.
Cyclic carbonic acid ester As the cyclic carbonic acid ester used in the present invention, those represented by the following general formula (1) are used.
[0018]
[Chemical formula 5]

[0019]
In formula (1), R ¹ and R ² may be the same or different from each other, an alkyl group having 1 to 7 carbon atoms, and a hydrocarbon having 2 to 7 carbon atoms containing an unsaturated bond a group, R ³ and R ⁴ may be the being the same or different, a hydrogen atom, an alkyl group having a carbon number of 1 to 7 carbon atoms including an unsaturated bond of 2 to 7 carbon It is a hydrogen group .
[0020]
In the present invention, as the cyclic ester carbonate represented by the above general formula (1), R ¹ and R ² have an alkyl group having 1 to 7 carbon atoms, and R ³ and R ⁴ have hydrogen or It is preferable to have an alkyl group having 1 to 7 carbon atoms.
[0021]
The cyclic carbonate represented by the general formula (1) has an alkyl group having 1 to 4 carbon atoms in R ¹ and R ² and hydrogen in at least one of R ³ and R ^4. Is particularly preferred.
[0022]
Further, the cyclic carbonate represented by the general formula (1) is most preferably one having a methyl group or an ethyl group in R ¹ and R ² and hydrogen in R ³ and R ⁴ .
As the cyclic carbonate represented by the formula (1),
4,4-dimethyl, 5-methyleneethylene carbonate, 4-methyl, 4-ethyl, 5-methyleneethylene carbonate, 4-methyl, 4-propyl, 5-methyleneethylene carbonate, 4-methyl, 4-butyl, 5- Methylene ethylene carbonate, 4,4-diethyl, 5-methylene ethylene carbonate, 4-ethyl, 4-propyl, 5-methylene ethylene carbonate, 4-ethyl, 4-butyl, 5-methylene ethylene carbonate, 4,4-dipropyl, 5-methylene ethylene carbonate, 4-propyl, 4-butyl, 5-methylene ethylene carbonate, 4,4-dibutyl, 5-methylene ethylene carbonate, 4,4-dimethyl, 5-ethylidene ethylene carbonate, 4-methyl, 4- Ethyl, 5-ethylidene ethylene carbonate, 4-methyl, 4-propyl, 5-ethylidene ethylene carbonate, 4-methyl, 4-butyl, 5-ethylidene ethylene carbonate, 4,4-die , 5-ethylidene ethylene carbonate, 4-ethyl, 4-propyl, 5-ethylidene ethylene carbonate, 4-ethyl, 4-butyl, 5-ethylidene ethylene carbonate, 4,4-dipropyl, 5-ethylidene ethylene carbonate, 4- Propyl, 4-butyl, 5-ethylidene ethylene carbonate, 4,4-dibutyl, 5-ethylidene ethylene carbonate, 4-methyl, 4-vinyl, 5-methylene ethylene carbonate, 4-methyl, 4-allyl, 5-methylene ethylene Carbonate, 4-methyl, 4-methoxymethyl, 5-methyleneethylene carbonate, 4-methyl, 4-acryloxymethyl, 5-methyleneethylene carbonate, 4-methyl, 4-allyloxymethyl, 5-methyleneethylene carbonate, etc. Is mentioned.
[0023]
Among them, particularly preferred compounds are 4,4-dimethyl, 5-methyleneethylene carbonate (the following formula (3)) and 4-methyl, 4-ethyl, 5-methyleneethylene carbonate (the following formula (4)).
[Chemical 6]

[0024]
Such a cyclic carbonate has the effect of suppressing the reduction reaction of the nonaqueous solvent during charging and improving the charge / discharge efficiency.
Nonaqueous solvent In the nonaqueous electrolyte solution for secondary batteries according to the present invention, a nonaqueous solvent containing a cyclic carbonate represented by the above formula (1) is used.
[0025]
The cyclic carbonate represented by the above formula (1) is preferably used as a mixture with another non-aqueous solvent. The cyclic carbonate represented by the above formula (1) is contained in an amount of 0.001% by weight or more, preferably 0.01 to 50% by weight, more preferably 0.1 to 20% by weight based on the whole non-aqueous solvent. Is desirable. When the cyclic carbonate represented by the general formula (1) is contained in the non-aqueous solvent in such an amount, the reductive decomposition reaction of the solvent that occurs during charging can be kept low.
[0026]
The non-aqueous solvent in the present invention may contain a cyclic carbonate and / or a chain carbonate represented by the following general formula (2) together with the cyclic carbonate represented by the above formula (1).
[0027]
[Chemical 7]

[0028]
Wherein, R ⁵ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R ⁶ represents an alkyl group having 1 to 3 carbon atoms.
Examples of the cyclic carbonate represented by the formula (2) include propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and the like. Is mentioned.
Among these, propylene carbonate having a low viscosity and a freezing point is preferably used. These cyclic carbonates may be used in combination of two or more.
[0029]
Examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, and ethyl propyl carbonate. These chain carbonate esters may be used in combination of two or more.
[0030]
When such a chain carbonate is contained in a non-aqueous solvent, it becomes possible to reduce the viscosity of the non-aqueous electrolyte, further increase the solubility of the electrolyte, and excellent electrical conductivity at room temperature or low temperature. It can be used as an electrolytic solution. For this reason, the charge / discharge efficiency and load characteristics of the battery can be improved.
[0031]
Therefore, the preferable non-aqueous solvent of this invention contains the cyclic carbonate represented by General formula (1), the cyclic carbonate represented by General formula (2), and / or the said chain carbonate. However, the presence of other compounds described below is not excluded.
From the viewpoint of improvement of battery characteristics, for example, improvement of charge / discharge efficiency of the battery and improvement of load characteristics, as described above, the cyclic carbonate represented by the above formula (1) is 0.001 weight of the whole non-aqueous solvent. % Or more, preferably 0.01 to 50% by weight, more preferably 0.1 to 20% by weight. The remaining amount is preferably occupied by the cyclic carbonate represented by the general formula (2) and / or the chain carbonate, and among them, the cyclic carbonate represented by the general formula (2) or the general formula ( More preferably, it is occupied by the cyclic carbonate represented by 2) and the chain carbonate.
That is, the total amount of the cyclic carbonate represented by the general formula (2) and the chain carbonate is 99.999% by weight or less of the total amount of the nonaqueous solvent, preferably 50 to 99.99% by weight, and more preferably. 80 to 99.9% by weight is desirable.
In the non-aqueous solvent, the quantitative ratio of the cyclic carbonate represented by the general formula (2) to the chain carbonate (cyclic carbonate represented by the general formula (2): chain carbonate) is 0: 100 to 100: 0, preferably 5:95 to 95: 5, particularly preferably 20:80 to 85:15 (all in weight ratio).
[0032]
Furthermore, in the present invention, it is also possible to use a solvent that is widely used as a nonaqueous solvent for batteries, as a compound that may exist in addition to the cyclic carbonate and chain carbonate, specifically, Cyclic carbonates having a double bond in the ring such as vinylene carbonate, chain esters such as methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, phosphoric acid Phosphate esters such as trimethyl, chain ethers such as dimethoxyethane, cyclic ethers such as tetrahydrofuran, amides such as dimethylformamide, chain carbamates such as methyl-N, N-dimethylcarbamate, γ-butyrolactone, etc. Cyclic esters, cyclic sulfones such as sulfolane, N-methyloxa Cyclic carbamates such as Rijinon, N- cyclic amides, such as methyl pyrrolidone, N, and cyclic ureas such as N- dimethylimidazolinium pyrrolidone.
[0033]
Other compounds that may be present in addition to the above cyclic carbonate ester and chain carbonate ester are the cyclic carbonate ester represented by the general formula (1), the cyclic carbonate ester represented by the general formula (2), and the chain carbonate ester. It is desirable to be used at 20% by weight or less based on the total amount.
[0034]
Electrolyte The electrolyte used in the present invention can be used without particular limitation as long as it is usually used as an electrolyte for a non-aqueous electrolyte.
[0035]
Specifically, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiOSO ₂ R ¹¹ , LiN (SO ₂ R ¹² ) (SO ₂ R ¹³ ), LiC (SO ₂ R ¹⁴ ) (SO ₂ R ¹⁵ ) ( SO ₂ R ¹⁶ ), LiN (SO ₂ OR ¹⁷ ) (SO ₂ OR ¹⁸ ) [wherein R ^{11 to} R ¹⁸ may be the same as or different from each other, and are perfluoro having 1 to 6 carbon atoms. Lithium salts such as LiSiF ₆ , LiC ₄ F ₉ SO ₃ , and LiC ₈ F ₁₇ SO ₃ are preferably used. These lithium salts may be used alone or in combination of two or more.
[0036]
Among these, LiPF ₆ , LiBF ₄ , LiOSO ₂ R ¹¹ , LiN (SO ₂ R ¹² ) (SO ₂ R ¹³ ), LiC (SO ₂ R ¹⁴ ) (SO ₂ R ¹⁵ ) (SO ₂ R ¹⁶ ) LiN (SO ₂ OR ¹⁷ ) (SO ₂ OR ¹⁸ ) is preferred.
[0037]
In particular, it is desirable that such an electrolyte is usually contained in the non-aqueous electrolyte at a concentration of 0.1 to 3 mol / liter, preferably 0.5 to 2 mol / liter.
The non-aqueous electrolyte for a secondary battery according to the present invention as described above is suitable as a non-aqueous electrolyte for a lithium ion secondary battery. The non-aqueous electrolyte of the present invention can also be used as a non-aqueous electrolyte for primary batteries.
[0038]
Nonaqueous Electrolyte Secondary Battery The nonaqueous electrolyte secondary battery according to the present invention includes a negative electrode, a positive electrode, and the nonaqueous electrolyte. Usually, in addition to this, a separator is used.
[0039]
As a preferred non-aqueous electrolyte secondary battery of the present invention,
A negative electrode including any one of metallic lithium, a lithium-containing alloy, and a carbon material that can be doped / dedoped with lithium ions as a negative electrode active material;
A positive electrode including any of a composite oxide of lithium and a transition metal, a carbon material, or a mixture thereof as a positive electrode active material;
A separator;
A non-aqueous electrolyte secondary battery composed of the non-aqueous electrolyte can be given.
[0040]
Such a non-aqueous electrolyte secondary battery can be applied to, for example, a cylindrical non-aqueous electrolyte secondary battery. As shown in FIG. 1, a cylindrical nonaqueous electrolyte secondary battery includes a negative electrode 1 obtained by applying a negative electrode active material to a negative electrode current collector 9 and a positive electrode obtained by applying a positive electrode active material to a positive electrode current collector 10. 2 is wound through a separator 3 injected with a non-aqueous electrolyte, and is housed in a battery can 5 with the insulating plates 4 placed on the upper and lower sides of the wound body. A battery lid 7 is attached to the battery can 5 by caulking through a sealing gasket 6, and electrically connected to the negative electrode 1 or the positive electrode 2 through the negative electrode lead 11 and the positive electrode lead 12, respectively, It is comprised so that it may function as a positive electrode. The separator is a porous film, and a microporous polymer film is preferably used. Among them, a porous polyolefin film is preferable. Examples of the porous polyolefin film include a porous polyethylene film, a porous polypropylene film, or a multilayer film of a porous polyethylene film and polypropylene.
[0041]
In lithium-ion secondary batteries, as a means to ensure the safety of ordinary batteries, the use of separators that have shutdown properties for lithium-ion secondary batteries, PTC elements, protection circuits, current interruption mechanisms, safety valves, etc. are proposed or adopted. Has been.
[0042]
In this battery, the positive electrode lead 12 may be electrically connected to the battery lid 7 via the current interrupting thin plate 8. In such a battery, when the pressure inside the battery rises, the current interrupting thin plate 8 is pushed up and deformed, and the positive electrode lead 12 is cut leaving a portion welded to the thin plate 8 to interrupt the current. ing.
[0043]
As the negative electrode active material constituting such anode 1, metal lithium, lithium alloys, can be used any of carbon materials capable of doping and dedoping lithium ions, among these, lithium It is preferable to use a carbon material that can be doped / undoped with ions. Such a carbon material may be graphite or amorphous carbon, and any carbon material such as activated carbon, carbon fiber, carbon black, and mesocarbon microbeads is used.
[0044]
In the present invention, a carbon material having a (002 ) plane spacing (d002) of 0.340 nm or less as measured by X-ray analysis is particularly preferable as the negative electrode active material, and in particular, the density is 1.70 g / cm ³ or more. A highly crystalline carbon material having graphite or a property close thereto is desirable, and when such a carbon material is used, the energy density of the battery can be increased.
[0045]
Examples of the positive electrode active material constituting the positive electrode 2 include transition metal oxides and transition metal sulfides such as MoS ₂ , TiS ₂ , MnO ₂ , and V ₂ O ₅ , LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , and LiNiO _2. And composite oxides of lithium and transition metals. Of these, composite oxides composed of lithium and a transition metal are particularly preferable. When the negative electrode is lithium metal or a lithium alloy, a carbon material can be used as the positive electrode. Furthermore, a mixture of a composite oxide of lithium and a transition metal and a carbon material can be used as the positive electrode.
[0046]
Moreover, the non-aqueous electrolyte secondary battery according to the present invention can also be applied to a coin-type non-aqueous electrolyte secondary battery as shown in FIG.
In the coin-type non-aqueous electrolyte secondary battery of FIG. 2, the disk-shaped negative electrode 13, the disk-shaped positive electrode 14, the separator 15 and the stainless steel plate 17 are laminated in the order of the negative electrode 13, the separator 15, the positive electrode 14, and the stainless steel plate 17. In this state, the battery can 16 is accommodated in a battery can 16 and a battery can (lid) 19 is attached by caulking through a gasket 18. As the negative electrode 13, the separator 15, and the positive electrode 14, the same ones as described above are used. The battery can 16 and the battery can (lid) 19 are made of a material such as stainless steel that is not easily corroded by the electrolytic solution.
[0047]
In addition, the non-aqueous electrolyte secondary battery according to the present invention includes the non-aqueous electrolyte described above as the electrolyte, and the shape of the battery is not limited to that shown in FIGS. It may be square.
[0048]
【The invention's effect】
The non-aqueous electrolyte solution of the present invention suppresses the reductive decomposition reaction of the solvent that occurs when highly crystalline carbon such as graphite is used for the negative electrode, and as a result, the non-aqueous electrolyte secondary solution using the non-aqueous electrolyte solution of the present invention. The battery has excellent charge / discharge characteristics and excellent battery characteristics at low temperatures. The non-aqueous electrolyte for secondary batteries according to the present invention is particularly suitable as a non-aqueous electrolyte for lithium ion secondary batteries.
[0049]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited at all by these Examples.
[0050]
[Example 1]
<Preparation of non-aqueous electrolyte>
After mixing propylene carbonate (PC) and diethyl carbonate (DEC) (mixing weight ratio PC: DEC = 55: 45), 4,4-dimethyl, 5-methyleneethylene carbonate (DMMC) is a mixed solvent of PC and DEC. 1 part by weight (1% by weight) was added to 99 parts by weight to prepare a mixed solvent. Then LiPF ₆ 15.2 g of (100 mmol), was dissolved in the mixed solvent, the electrolyte concentration is set to be 1.0 mol / l, to prepare a nonaqueous electrolyte. .
[0051]
<Production of negative electrode>
The negative electrode 13 was produced as follows.
90 parts by weight of carbon powder of mesocarbon microbeads (MCMB, calcining temperature 2800 ° C) manufactured by Osaka Gas Co., Ltd. and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder are mixed, and the solvent N-methylpyrrolidone To prepare a negative electrode mixture slurry (pasted).
[0052]
This negative electrode mixture slurry was applied to a negative electrode current collector made of a strip-shaped copper foil having a thickness of 20 μm and dried, and then a strip-shaped carbon negative electrode was obtained. The thickness of such a negative electrode mixture was 25 μm. Further, this strip electrode was punched into a disk shape having a diameter of 15 mm, and then compression molded to obtain a negative electrode 13.
<Preparation of positive electrode>
The positive electrode 14 was produced as follows.
[0053]
Mixing 91 parts by weight of LiCoO ₂ (product name: HLC-21, average particle size 8 μm) manufactured by Honjo Chemical Co., Ltd., 6 parts by weight of graphite as a conductive material, and 3 parts by weight of polyvinylidene fluoride as a binder A positive electrode mixture was prepared and dispersed in N-methylpyrrolidone to obtain a positive electrode mixture slurry.
[0054]
This slurry was applied to a positive electrode current collector made of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and compression molded to obtain a strip-shaped positive electrode. The thickness of such a positive electrode mixture was 40 μm. Further, this strip electrode was punched into a disk shape having a diameter of 15 mm to form a positive electrode 14.
<Production of battery>
The disk-shaped negative electrode 13, the disk-shaped positive electrode 14, and the separator 15 (microporous polypropylene film having a thickness of 25 μm and a diameter of 19 mm) thus obtained are made of stainless steel 2032 size battery can 16 as shown in FIG. Then, after laminating the negative electrode 13, the separator 15, and the positive electrode 14 in this order, the non-aqueous electrolyte was injected into the separator 15. After storing stainless steel plate 17 (thickness 2.4 mm, diameter 15.4 mm), the battery can (lid) 19 is caulked through a polypropylene gasket 18 to maintain the airtightness in the battery. Then, a button type non-aqueous electrolyte secondary battery having a diameter of 20 mm and a height of 3.2 mm was produced.
<Measurement of discharge capacity>
The discharge capacity of the nonaqueous electrolyte secondary battery thus obtained was measured at room temperature. In this example, the current direction in which the negative electrode is doped with Li + is charged, and the current direction in which the dedope is doped is discharge. Charging was performed by 4.1 V, 1 mA constant current constant voltage charging method, and was terminated when the charging current became 50 μA or less. From the charge capacity and discharge capacity of this charge / discharge cycle, the charge / discharge efficiency was calculated by the following equation. The results are shown in Table 1.
[0055]
[Expression 1]

[0056]
[Example 2]
In Example 1, the weight ratio of the mixed solvent PC: DEC was 55:45, and 4-ethyl, 4-methyl, 5-methyleneethylene carbonate (EMMC) was used instead of 4,4-dimethyl, 5-methyleneethylene carbonate. The charge / discharge efficiency of the battery was evaluated in the same manner as in Example 1 except that it was used. The results are shown in Table 1.
[0057]
[Example 3]
In Example 1, the addition amount of 4,4-dimethyl, 5-methyleneethylene carbonate was changed to 0.5 parts by weight (0.5% by weight) with respect to the total of 99.5 parts by weight of PC and DEC. In the same manner as in Example 1, the charge / discharge efficiency of the battery was evaluated. The results are shown in Table 1.
[0058]
[Example 4]
Example 1 is the same as Example 1 except that the amount of 4,4-dimethyl, 5-methyleneethylene carbonate added is 5 parts by weight (5% by weight) with respect to 95 parts by weight of the total amount of PC and DEC. Similarly, the charge / discharge efficiency of the battery was evaluated. The results are shown in Table 1.
[0059]
[Comparative Example 1]
In Example 1, the charge / discharge efficiency of the battery was evaluated in the same manner as in Example 1, except that 4,4-dimethyl, 5-methyleneethylene carbonate was not added. The results are shown in Table 1.
[0060]
[Table 1]

[0061]
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a cylindrical battery showing an embodiment of a non-aqueous electrolyte secondary battery of the present invention.
FIG. 2 is a schematic cross-sectional view of a coin battery showing an embodiment of the non-aqueous electrolyte secondary battery of the present invention.
[Explanation of symbols]
1,13 ... Negative electrode
2,14 ・ ・ ・ ・ Positive electrode
3,15 ... Separator
4,11 ... ・ ・ ・ Insulating plate
5,16 ... Battery can
6 ・ ・ ・ ・ Sealing gasket
7 ... Battery cover
8 ・ ・ ・ ・ Thin plate for current interruption
9 ... Negative electrode current collector
10 ... Positive electrode current collector
11 ... Negative lead
12 ... Positive lead
17 ... Stainless steel plate
18 ... Gasket
19 ... Battery can (lid)

Claims (11)

A non-aqueous electrolyte for a secondary battery having a negative electrode made of graphite, comprising a non-aqueous solvent containing a cyclic carbonate represented by the following general formula (1) and an electrolyte.

(In formula (1), R ¹ and R ² may be the same or different from each other, and are an alkyl group having 1 to 7 carbon atoms and a carbon atom having 2 to 7 carbon atoms including an unsaturated bond. A hydrogen group, R ³ and R ⁴ may be the same or different from each other, and are a hydrogen atom, an alkyl group having 1 to 7 carbon atoms, or a carbon atom number having 2 to 7 carbon atoms containing an unsaturated bond. It is a hydrocarbon group.) The cyclic carbonate represented by the general formula (1) has an alkyl group having 1 to 7 carbon atoms in R ¹ and R ² , and hydrogen or carbon atoms in R ³ and R ⁴ have 1 to 7 carbon atoms. The non-aqueous electrolyte for secondary batteries according to claim 1, which has an alkyl group of The cyclic carbonate represented by the general formula (1) has an alkyl group having 1 to 4 carbon atoms in R ¹ and R ² , and hydrogen in at least one of R ³ and R ^4. The nonaqueous electrolytic solution for a secondary battery according to claim 2. The cyclic carbonate represented by the general formula (1) has a methyl group or an ethyl group in R ¹ and R ² , and hydrogen in R ³ and R ⁴ , Nonaqueous electrolyte for secondary batteries. The non-aqueous electrolyte for a secondary battery according to claim 1, wherein the non-aqueous solvent further includes a cyclic carbonate represented by the following general formula (2).

(In the formula, R ⁵ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R ⁶ represents an alkyl group having 1 to 3 carbon atoms.)   The non-aqueous electrolyte for a secondary battery according to any one of claims 1 to 5, wherein the electrolyte is a lithium salt.   The nonaqueous electrolytic solution for a secondary battery according to claim 1, wherein the nonaqueous electrolytic solution is an electrolytic solution for a lithium ion secondary battery. A negative electrode whose negative electrode active material is graphite ;
A positive electrode including any of a composite oxide of lithium and a transition metal, a carbon material, or a mixture thereof as a positive electrode active material;
The nonaqueous electrolyte for secondary batteries according to any one of claims 1 to 7 as an electrolyte.
A non-aqueous electrolyte secondary battery comprising:   The nonaqueous electrolyte secondary battery according to claim 8, further comprising a separator. 10. The nonaqueous electrolyte secondary battery according to claim 8, wherein the graphite has an interplanar distance (d002) in the (002) plane measured by X-ray analysis of 0.340 nm or less.   The non-aqueous electrolyte secondary battery according to claim 8, wherein the separator is a porous polyolefin film.

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