JP4188585B2 - Electrolyte and lithium secondary battery - Google Patents

Description

【００１８】
係る電解質によれば、アジリジン化合物が上記の構造式に示されるものであり、これを有機電解液と混合することで容易にゲルが形成される。これにより、比較的安定したゲルからなる電解質を構成することが可能になる。
また、係る電解質を用いてリチウム二次電池を構成すれば、負極表面における電解質の分解反応を抑制することができる。
【００１９】
尚、本発明に係る電解質は、アジリジン化合物として、［化３］に示す構造式で表される化合物、又は上記［化２］に示す構造式で表される化合物と［化３］に示す構造式で表される化合物との混合物であってもよい。
また、下記［化４］〜［化５］に示すものを含んでいても良い。これらの化合物は、上記の［化２］及び／又は［化３］に示すものと同時に使用することが好ましい。
尚、［化４］におけるｎ₁は０〜１０の範囲が好ましく、［化５］におけるｎ₂は０〜１０の範囲が好ましい。
【００２０】
【化３】

【００２１】
【化４】

【００２２】
【化５】

【００２３】
また本発明の電解質は、先に記載の電解質であって、前記非プロトン溶媒が、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、γ−ブチロラクトン、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のうちの１種以上を含むものであることを特徴とする。
係る電解質によれば、上記の非プロトン溶媒を含んでいるので、アジリジン化合物とともに安定した電解質を形成することができ、電解質自体のイオン伝導度を向上させることが可能になる。
【００２４】
また本発明の電解質は、先に記載の電解質であって、前記リチウム塩が、ＬｉＰＦ₆、ＬｉＢＦ₄、ＬｉＳｂＦ₆、ＬｉＡｓＦ₆、ＬｉＣｌＯ₄、ＬｉＣＦ₃ＳＯ₃、Ｌｉ（ＣＦ₃ＳＯ₂）₂Ｎ、ＬｉＣ₄Ｆ₉ＳＯ₃、ＬｉＳｂＦ₆、ＬｉＡlＯ₄、ＬｉＡlＣl₄、ＬｉＮ（Ｃ_xＦ_2x+1ＳＯ₂）（Ｃ_yＦ_{2y 十 1}ＳＯ₂）（ただしｘ、ｙは自然数）のうちの１種以上を含むものであることを特徴とする。
【００２５】
係る電解質によれば、電解質材料中に上記のリチウム塩を含んでいるので、アジリジン化合物とともに安定したゲルを形成することができる。また、このリチウム塩が、初充電の際に、負極表面におけるアジリジン化合物を主成分とする被膜形成に寄与しているものと考えられる。
尚、電解質材料におけるリチウム塩の濃度は、０．５〜２．０モル／Ｌの範囲が好ましい。リチウム塩の濃度がこの範囲であれば、電解質のイオン伝導度が向上し、高率放電特性を改善することが可能になる。
【００２６】
また本発明の電解質は、先に記載の電解質であって、電解質材料中における前記アジリジン化合物の含有率が０．２質量％よりも多く、２０質量％以下の範囲であることを特徴とする。
アジリジン化合物の含有率が０．２質量％以下であると、有機電解液と共にゲルを形成することが困難になると共に、被膜形成によるものと推定される負極表面における電解質の分解反応を抑制する効果も得にくいものとなる。なお、０．５質量％以上とすることが、より好ましい。
一方、アジリジン化合物の含有率が２０質量％を越えると、リチウム塩がアジリジン化合物のアジリジン環によって強固に拘束されて、イオン伝導度が低下するので好ましくない。なお、１０質量％以下とすることがより好ましい。
ただし、ゲルの形成はアジリジン化合物の種類、有機電解液の組成、混合後のゲル形成時間等によっても左右される。また、被膜の形成も、アジリジン化合物の種類、有機電解液の組成、初充電時の充電条件等によっても左右される。したがって、実際のアジリジン化合物の含有率は、０．２質量％よりも多く、２０質量％以下の範囲内において、適宜調整することが好ましい。
【００２７】
本発明において、前記アジリジン化合物と前記有機電解液とによってゲルが形成されていることを特徴とすることができる。
これにより、薄型化や形状自由度の向上が可能なリチウム二次電池の形成が可能な電解質とすることができる。
【００２８】
係るゲルは、その一部又は全部が、前記リチウム塩に含まれるリチウムに複数の前記アジリジン環が配位することによって形成されていることを特徴とすることができる。
また、係るゲルは、その一部又は全部が、前記アジリジン環が開裂することにより形成された前記アジリジン化合物の重合体中に前記有機電解液が含浸されることによって形成されていることを特徴とすることができる。
なお、係るゲルは、その一部又は全部が、上記２つの形態のゲルが混合された状態で形成されていても良い。
【００２９】
また本発明のリチウム二次電池は、リチウムの吸蔵、放出が可能な正極及び負極と、電解質とを具備してなり、該電解質が請求項１ないし請求項８のいずれかに記載の電解質であることを特徴とする。
本発明によれば、電解質がゲル状態で、薄型化や形状自由度の向上を図ったリチウム二次電池とすることが可能である。また、負極表面における電解質の分解反応が抑制されたリチウム二次電池とすることが可能である。
【００３０】
さらに、本発明のリチウム二次電池は、前記負極の表面に、前記アジリジン化合物を主成分とする被膜が形成されていることを特徴とすることができる。
なお、「主成分」としたのは、皮膜形成時に、電解質材料中の他の成分を取り込む可能性等があるからである。
この場合、負極表面における電解質の分解反応が抑制され、電解質の分解によるガス発生や電解質自体の変質が低減され、リチウム二次電池の充放電容量の低下を防止し、サイクル特性を向上することが可能となり、更に電池の変形も防止可能となる。また、有機質被膜による電解質分解の抑制効果によって、リチウム二次電池の高温貯蔵特性が向上する。
【００３１】
さらに、本発明のリチウム二次電池は、リチウムの吸蔵、放出が可能な正極及び負極と、電解質とを具備してなり、前記負極の表面に、アジリジン化合物を主成分とする被膜が形成されていることを特徴とする。
なお、「主成分」としたのは、皮膜形成時に、電解質材料中の他の成分を取り込む可能性等があるからである。
この場合、負極表面における電解質の分解反応が抑制され、電解質の分解によるガス発生や電解質自体の変質が低減され、リチウム二次電池の充放電容量の低下を防止し、サイクル特性を向上することが可能となり、更に電池の変形も防止可能となる。また、有機質被膜による電解質分解の抑制効果によって、リチウム二次電池の高温貯蔵特性が向上する。
【００３２】
【発明の実施の形態】
以下、本発明の実施形態に係る電解質について説明する。
本実施形態の電解質は、１または２以上のアジリジン環を有するアジリジン化合物と、非プロトン性溶媒にリチウム塩が溶解されてなる有機電解液とが少なくとも混合された電解質材料を用いて形成されたものである。
【００３３】
電解質材料中のアジリジン化合物は、上記［化２］に示す構造式で表されるものを少なくとも含むものである。上記構造式中、Ｒ₁はＨ、ＣＨ₃、ＯＨのいずれかであり、Ｒ₂はＨまたはＣＨ₃のいずれか一方である。また、これらの混合物であっても良い。
【００３４】
アジリジン化合物は、上記［化２］に示す構造式で表される化合物や［化３］に示す構造式で表される化合物、又はこれらの混合物を単独で用いたり、［化２］及び／又は［化３］に示すものに［化４］〜［化５］に示すもののいずれか１種以上を混合したものを用いても良い。
［化２］及び／又は［化３］に示すものに［化４］〜［化５］に示すものを混合することにより、［化２］及び／又は［化３］単独の場合と比べて少量でゲル化させることができる。
尚、［化４］におけるｎ₁は０〜１０の範囲が好ましく、［化５］におけるｎ₂は０〜１０の範囲が好ましい。
ｎ₁またはｎ₂が上記の範囲より少ないと、電解質の流動性が高くなって固化しないので好ましくなく、上記の範囲を越えると分子量が巨大になり、有機電解液によってゲルが形成されにくくなるので好ましくない。
【００３５】
上記［化２］に示すアジリジン化合物は、炭素２つと窒素１つを骨格とする３つのアジリジン環に、Ｒ₂基がそれぞれ結合して構成されている。このアジリジン環が、リチウムと配位するか、あるいは開裂して別のアジリジン化合物とともに重合体を形成することによって、ゲルを形成することが可能である。
分子内におけるアジリジン環の数は１つあれば良いが、好ましくは２以上あった方がよい。分子中にアジリジン環が２以上あれば、リチウムイオンと配位する部分が増加し、後述する高次の網目構造を容易に形成することができる。
この［化２］〜［化５］に示すアジリジン化合物に、リチウムイオンを含有する有機電解液を混合することで容易にゲルが形成される。これにより、比較的安定したゲル状の電解質を構成することができる。
また、この［化２］〜［化５］に示すアジリジン化合物に、リチウムイオンを含有する有機電解液を混合してリチウム二次電池に用いると、初充電の際に、負極表面に［化２］〜［化５］に示すアジリジン化合物を主成分とする被膜を形成するものと推定される。
【００３６】
電解質材料中におけるアジリジン化合物の含有率は０．２質量％より大きく、２０質量％以下の範囲が好ましい。
アジリジン化合物の含有率が０．２質量％以下であると、有機電解液と共にゲルを形成することが困難になると共に、被膜形成によるものと推定される負極表面における電解質の分解反応を抑制する効果も得にくいものとなる。なお、０．５質量％以上とすることが、より好ましい。
一方、アジリジン化合物の含有率が２０質量％を越えると、リチウム塩がアジリジン化合物のアジリジン環によって強固に拘束されて、イオン伝導度が低下するので好ましくない。なお、１０質量％以下とすることがより好ましい。
【００３７】
なお、ゲルの形成はアジリジン化合物の種類や混合後のゲル形成時間等によっても左右される。また、被膜の形成も、アジリジン化合物の種類や初充電時の充電条件等によっても左右される。したがって、実際のアジリジン化合物の含有率は、目的が、ゲル形成、被膜形成、又はゲル及び被膜の双方の形成の何れにあるかを考慮して、０．２質量％より大きく、２０質量％以下の範囲内で、適宜調整することが好ましい。
【００３８】
有機電解液としては、非プロトン性溶媒にリチウム塩が溶解されてなるものが好ましい。
非プロトン性溶媒としては、エチレンカーボネート、ブチレンカーボネート、プロピレンカーボネート、γ−ブチロラクトン、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のうちの１種以上を含むものが好ましく、特にプロピレンカーボネート、エチレンカーボネート、ブチレンカーボネートのいずれか１つを必ず含むとともに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のいずれか１つを必ず含むことが好ましい。
電解質材料中にこれらの非プロトン溶媒がアジリジン化合物とともに含まれるので、リウムイオンの輸率を向上させて電解質自体のイオン伝導度を高めることができる。
【００３９】
また、リチウム塩としては、ＬｉＰＦ₆、ＬｉＢＦ₄、ＬｉＳｂＦ₆、ＬｉＡｓＦ₆、ＬｉＣｌＯ₄、ＬｉＣＦ₃ＳＯ₃、Ｌｉ（ＣＦ₃ＳＯ₂）₂Ｎ、ＬｉＣ₄Ｆ₉ＳＯ₃、ＬｉＳｂＦ₆、ＬｉＡlＯ₄、ＬｉＡlＣl₄、ＬｉＮ（Ｃ_xＦ_2x+1ＳＯ₂）（Ｃ_yＦ_{2 y 十 1}ＳＯ₂）（ただしｘ、ｙは自然数）のうちの１種以上を含むものが好ましく、特にＬｉＰＦ₆、ＬｉＢＦ₄のいずれか１つを含むものがより好ましい。
またこの他に、リチウム二次電池の非水電解液として従来から知られているものを用いることもできる。
電解質材料中にこれらのリチウム塩が含まれるので、電解質自体のイオン伝導度を高めることができる。
【００４０】
尚、電解質材料中のリチウム塩の濃度は、０．５〜２．０モル／Ｌの範囲が好ましい。濃度が０．５モル／未満だと、電解質のイオン伝導度が低下するので好ましくなく、濃度が２．０モル／Ｌを越えると、有機電解液とアジリジン化合物を混合したときに当該リチウム塩によると思われる沈殿が生じてしまうので好ましくない。リチウム塩の濃度が上記の範囲であれば、電解質のイオン伝導度が向上し、高率放電特性を改善することが可能になる。
【００４１】
本実施形態の電解質は、リチウム塩中のリチウムに対して複数のアジリジン環が配位することにより、ゲルを形成することが可能なものである。また、本実施形態の電解質は、前記アジリジン環が開裂することによってアジリジン化合物の重合体が形成され、この重合体中に前記有機電解液が含浸されることにより、ゲルを形成することが可能なものである。
【００４２】
図１に、リチウムに対してアジリジン環が配位することによりゲルが形成される様子を示す。図１に示すように、陽イオンであるリチウムイオンの周囲に、複数のアジリジン化合物の負の電荷を有するアジリジン環が接近し、静電気的な作用により配位結合が形成されている。更にこれらのアジリジン化合物の他のアジリジン環が、別のリチウムイオンに配位し、全体として高次の網目構造が形成されている。
このように、本実施形態に係る電解質は、リチウムイオンを介して複数のアジリジン化合物が網目構造を形成し、この網目構造の中に有機電解液が含浸された構造をとることが可能である。
【００４３】
また図２には、アジリジン環が開裂することによって重合体が形成される様子を示す。この構造はゲル状となった電解質の一部に見られる。図２に示すように、アジリジン化合物のアジリジン環が開裂して他のアジリジン化合物に結合している。このアジリジン環の開裂は、リチウムイオンあるいは当該アジリジン化合物または有機電解液に混入した水素イオンを触媒として進行したものと考えられる。
このように、本実施形態に係る電解質は、アジリジン環が開裂して高次の網目構造を有する重合体が形成され、この網目構造の重合体中に有機電解液が含浸された構造をとることができる。
【００４４】
本実施形態に係る電解質がゲルを形成している場合、アジリジン環がリチウムに配位した構造が大部分を占め、残りの部分がアジリジン環の開裂による重合体構造をとっているものと考えられる。
この場合、有機電解液は、アジリジン環とリチウムとの配位結合による網目構造中に含浸されるか、あるいはアジリジン環の開裂による網目構造の重合体の中に含浸されることにより保持される。
【００４５】
本実施形態の電解質は、上記の電極材料を所定の混合比で混合し、たとえば、１０〜７５℃の温度で２〜１５０時間放置することにより、ゲル状とされる。
本実施形態の電解質によれば、アジリジン化合物と有機電解液とを単に混合することにより、これらがゲル化して電解質を形成するので、重合反応が不十分になるおそれがなく、また重合開始剤等が不要になるためにガス発生等のおそれもなく、安定した電解質を得ることが可能になる。
【００４６】
また、本実施形態の電解質をリチウム二次電池に用いると、負極における電解質の分解反応が抑制される。これは、初充電の際に、負極表面にアジリジン化合物を主成分とする被膜が形成されるためであると推定される。
【００４７】
この皮膜の形成は、図１１に示すように進行するものと推定される。すなわち、図１１（ａ）に示すように、初充電開始前には、電解液（有機電解液）中にリチウムイオンとアジリジン化合物の全部又は一部が、高次の網目構造にまでは達しない程度のイオン架橋物（「Ｌｉ−アジリジン架橋物」と称する。）として存在しているものと考えられる。
このＬｉ−アジリジン架橋物は、ゲル形成の機構について、図１を用いて説明したのと同様に、アジリジン化合物の負の電荷を有するアジリジン環が、陽イオンであるリチウムイオンに配位して形成されているものと考えられる。
【００４８】
次に、図１１（ｂ）に示すように、充電を開始すると、陽イオンであるリチウムイオンが負極に引き寄せられることによって、Ｌｉ−アジリジン架橋物が負極表面に付着する。これにより、負極表面において、アジリジン化合物の密度増加が生じる。
【００４９】
次に、リチウムイオンがアジリジン環とのイオン架橋から解き放たれ、負極内に吸蔵される。すると、残されたアジリジン環が開裂し、重合反応が開始され、その結果図１１（ｃ）に示すように被膜が形成される。この生成した被膜は負の電荷を帯びているため、陽イオンのみを輸送する被膜となる。そのため、電解液が直接負極に接して分解することを防止することができる。
【００５０】
なお、初充電前に完全にゲル化した電解質では、被膜形成に足りるほどのＬｉ−アジリジン架橋物が存在せず、皮膜を形成しにくいものと考えられる。
そのため、電解質材料中のアジリジン化合物の含有率が高く、かつ、初充電前にゲル化反応が完全に進行している場合には、負極表面における電解質分解反応の抑制効果が得にくいものと考えられる。
【００５１】
次に、本実施形態のリチウム二次電池について説明する。
本実施形態のリチウム二次電池は、上記本実施形態に係る電解質と、リチウムを吸蔵・放出することが可能な正極及び負極とで基本的に構成される。
正極としては、ＬｉＭｎ₂Ｏ₄、ＬｉＣｏＯ₂、ＬｉＮｉＯ₂、ＬｉＦｅＯ₂、Ｖ₂Ｏ₅、ＴｉＳ、ＭｏＳ等、及び有機ジスルフィド化合物や有機ポリスルフィド化合物等のリチウムを吸蔵、放出が可能な正極活物質を含むものを例示できる。
また負極としては、可逆的にリチウムイオンを吸蔵・放出できるものが好ましく、例えば、人造黒鉛、天然黒鉛、黒鉛化炭素繊維、非晶質炭素等を含むものを例示できる。また金属リチウムも負極として使用できる。
正極及び負極の具体例として、上記の正極活物質または負極活物質と結着材と更に必要に応じて導電助材とを混合し、これらを金属箔若しくは金属網からなる集電体に塗布してシート状に成形したものを例示できる。
またこの他に、従来からリチウム二次電池の正極もしくは負極して知られているものを用いることもできる。
【００５２】
これらの正極と負極との間に上記の電解質を挟んで一体化することによりリチウム二次電池が形成される。電解質は、リチウムイオンの電解質として機能すると共にゲルを形成している場合、正極と負極を隔離するセパレータとしての機能を有する。また、従来のセパレータに電解質を含浸させて使用しても良い。
セパレータは、電解質がゲル化していない場合に必須であるが、多孔質のポリプロピレンフィルム、多孔質のポリエチレンフィルム等、公知のセパレータを適宜使用できる。
【００５３】
本実施形態のリチウム二次電池は、概略．３つのタイプに分けられる。
第１に、電解質がアジリジン化合物と有機電解液によりゲル化されているが、負極表面に皮膜が形成されていないタイプである。第２に、電解質はゲル化されていないが、負極表面にアジリジン化合物を主成分とする皮膜が形成されているタイプである。第３に、電解質がアジリジン化合物と有機電解液によりゲル化されていると共に、負極表面にアジリジン化合物を主成分とする皮膜が形成されているタイプである。
いずれのタイプとなるかは、電解質材料中のアジリジン化合物の種類や含有率、有機電解液の組成、初充電のタイミング等によって異なるが、アジリジン化合物の含有率が高いほど第１のタイプの電池を構成しやすい傾向がある。また、アジリジン化合物の含有率が比較的低い場合に第２のタイプの電池を構成しやすい傾向がある。また、アジリジン化合物の含有率が比較的高い電解質材料を用いて、初充電のタイミングを調整することにより、第３のタイプの電池を構成できる傾向がある。
なお、いずれのタイプのリチウム二次電池の場合にも、電解質材料中のアジリジン化合物は、電解質のゲル化若しくは粘性化、又は皮膜の形成に消費され、［化２］〜［化５］に示したそのままの形で残存することは少ないものと考えられる。
【００５４】
本実施形態のリチウム二次電池をゲルポリマー電池として製造する場合には、混合直後の電解質材料を電池容器等に注液し、電池極組み立て後に、電池内部でゲル化を進行させることが好ましい。
たとえば、渦巻き型電池の場合、図４に示すような正極と負極とをセパレータを介して渦巻状に巻回した素電池を作製し、これをアルミラミネート製の電池容器に挿入した後、電解質材料を電池容器に注液してから封止する。そして、ゲル化に必要な時間所定の温度で放置することで、ゲルポリマーリチウム二次電池とすることができる。
また、コイン型電池の場合、正極、セパレータ、パッキンを配置した正極ケースに、混合直後の電解質材料を注液する。つぎに負極、負極蓋で封口し、ゲル化に必要な時間所定の温度で放置することにより、ゲルポリマーリチウム二次電池とすることができる。
このように、ゲル化前の電解質材料を電池内部でゲル化させることにより、負極や正極の内面に浸透した電解質材料もゲル化できるので、優れた電池特性を得ることができる。
【００５５】
本実施形態のリチウム二次電池において、アジリジン化合物の被膜を負極に形成するには、後述の「化成」のように初期充電を行えばよい。ただし、この初期充電の際、電解質材料中に被膜形成に必要なアジリジン化合物が存在することが必要である。既にゲル形成に消費されたアジリジン化合物で皮膜形成をすることは困難であると思われるので、ゲル化していないアジリジン化合物が必要と考えられる。
したがって、本実施形態のリチウム二次電池を負極に皮膜が形成された電池として製造する場合には、たとえば、放置してもゲルを形成できない程度に比較的小さいアジリジン化合物含有率の電解質材料を用いることができる。
また、ゲル形成に充分な、比較的高いアジリジン化合物含有率の電解質材料を用いる場合、ゲル化が完全に終了する以前に、初期充電を行うことによって、負極に皮膜が形成された電池とすることができる。
【００５６】
本実施形態のリチウム二次電池によれば、電解質がゲル化しているタイプ（上記第１及び第２のタイプ）では、薄型化や形状自由度の向上を図ったリチウム二次電池とすることができる。また、負極表面に皮膜が形成されたタイプ（上記第２及び第３のタイプ）では、負極表面における電解質の分解反応が抑制されたリチウム二次電池とすることができる。
【００５７】
【実施例】
実験例１（試料１〜１０の電解質）
まず、ゲル形成化合物として、アジリジン化合物であるTAZM(trimethylolpropane-tri-β-aziridinylpropionate)を用意した。下記［化６］にTAZMの構造式を示す。このTAZMは、前記［化２］におけるＲ₁をＣＨ₃とし、Ｒ₂をＨとしたものである。
【００５８】
【化６】

【００５９】
上記のTAZMを、３種類の有機電解液にそれぞれ添加して十分に攪拌した後、種々の放置条件下に置くことによってTAZMを２．５〜１０質量％含有する試料１〜１０を得た。これらの試料１〜１０の外観を観察するとともにリチウムのイオン伝導度を測定した。結果を表１に示す。
尚、使用した有機電解液は、下記に示す３種類の組成の有機電解液である。
有機電解液１：EC：DMC：DEC=３：３：１(体積比)
有機電解液２：EC：DMC：DEC=３：３：１(体積比)+LiPF₆(1.0モル/Ｌ)
有機電解液３：EC：DMC：DEC=３：３：１(体積比)+LiPF₆(1.3モル/Ｌ)
また、ECはエチレンカーボネートの略称であり、DMCはジメチルカーボネートの略称であり、DECはジエチルカーボネートの略称である。
【００６０】
更に、放置条件は以下に示す３種類の条件とした。即ち、室温で１５時間放置する条件(室温・15時間放置)、室温で１５時間放置した後に５０℃で４時間放置する条件(50℃・4時間放置)、室温で１５０時間放置する条件(室温・150時間放置)である。
【００６１】
【表１】

【００６２】
表１に示すように、LiPF₆を全く含まない試料１〜４は、どの放置条件でもゲル化せず、液体のままであることが分かる。
また有機電解液２を含む試料５〜７においては、試料７が室温・15時間放置の条件でゲル化し、試料６が室温・150時間放置の条件でゲル化している。
また有機電解液３を含む試料８〜１０においては、試料９が50℃・4時間放置の条件でゲル化し、試料１０が室温・150時間放置の条件でゲル化している。
このように、リチウム塩を全く含まないものはゲル化することがなく、更にリチウム塩を含む場合はTAZMの濃度が高くなるにつれてゲル化しやすくなることが分かる。
なお、ゲル化した試料６、７、９，１０のイオン伝導度を測定したところ、いずれも２〜４ｍＳ/ｃｍの範囲であり、リチウム二次電池用の電解質として良好なイオン伝導度を示した。
【００６３】
実験例２（試料１１〜１２の電解質）
ゲル形成化合物として、アジリジン化合物である上記TAZMと、Me-TAZMを用意した。下記［化７］にMe-TAZMの構造式を示す。このMe-TAZMは、前記［化２］におけるＲ₁及びＲ₂をＣＨ₃としたものである。
【００６４】
【化７】

【００６５】
上記のTAZMまたはMe-TAZMを、上記の有機電解液２にそれぞれ添加して十分に攪拌した後、室温で１５時間放置することによって、TAZMまたはMe-TAZMを１０質量％含有する試料１1〜１2を得た。これらの試料１1〜１２のリチウムのイオン伝導度を測定した。結果を表２に示す。
【００６６】
【表２】

【００６７】
表２に示すように、試料１１及び１２はいずれも、室温・１５時間放置の条件でゲル化し、またイオン伝導度も２．５〜３ｍＳ/ｃｍの範囲であり、リチウム二次電池用の電解質として良好なイオン伝導度を示すことがわかる。
【００６８】
このように、アジリジン化合物(TAZMまたはMe-TAZM)に、リチウム塩と非プロトン溶媒を含む有機電解液を添加することにより、ゲル状でイオン伝導度に優れた電解質が得られることが分かる。
【００６９】
実験例３（試料７の電解質を備えたリチウム二次電池の放電曲線）
コイン型電池の正極ケースに正極、ポリプロピレン製多孔質セパレータ、パッキンを配置する。これに調整直後の電解質溶液（試料７）を注液する。つぎに負極、負極蓋で封口し、２４時間室温放置することでコイン型ポリマーリチウム二次電池とした。コイン型電池のサイズは直径２０mm、高さ１．６mm（ＣＲ２０１６サイズ）である。
充電条件は０．２Ｃの電流で電圧が４．２Ｖに達するまで定電流充電したあとに、４．２Ｖで９時間の定電圧充電、すなわち、定電流-定電圧充電で行った。
放電条件は、０．２Ｃの定電流で電圧が２．７５Ｖに達するまで放電、すなわち、定電流放電で行った。以後、この条件での１サイクル分の充放電作業を「化成」と称する。化成後に化成時と同じ条件で充放電した１サイクル目の放電曲線を図３に示す。
【００７０】
また、電解質溶液（試料７）に代えて、有機電解液２（比較例１）を使用した以外は上記と同様にして、比較のためのコイン型リチウム二次電池を作製し、上記の電池と同じ条件で充放電した。化成後の１サイクル目の放電曲線を図３に併せて示す。
【００７１】
図３に示すように、本発明に係る電解質を備えたリチウム二次電池は、従来の有機電解液を備えたリチウム二次電池に対し、電圧、放電容量が殆ど変わることがなく、良好な特性を示すことがわかる。
【００７２】
実験例４
（TAZM又はMe-TAZMを用いた電解質を備えたリチウム二次電池のレート特性）
ＬｉＣｏＯ₂を正極活物質とする正極と炭素を負極活物質とする負極を、ポリプロピレン製多孔質セパレータを介して渦巻状に巻回し、電池サイズ長さ６２mm、幅３５mm、厚さ３．６mmの図４に示すような素電池を作製し、これをアルミラミネート製の電池容器に挿入した。
この素電池を挿入した電池容器に、上記TAZMを１０質量％含有するように有機電解液に添加して十分に攪拌した直後の溶液を、所定量注液した。そして、注液後封止し、２４時間放置することで、試料１３のゲルポリマーリチウム二次電池とした。
同様に、上記素電池を挿入した電池容器に、上記Me-TAZMを１０質量％含有するように有機電解液に添加して十分に攪拌した直後の溶液を、所定量注液した。そして、注液後封止し、２４時間放置することで、試料１４のゲルポリマーリチウム二次電池とした。
なお、試料１３及び１４の調製で用いた有機電解液は、EC：DEC=３：７の混合溶媒に１．３モル/ＬのLiPF₆を溶解させたものを用いた。
また、TAZMやMe-TAZMを添加せずに、上記有機電解液をそのまま、素電池を挿入した電池容器に注液した以外は、上記ゲルポリマーリチウム二次電池と同様にして、比較例２のリチウム二次電池を作製した。
【００７３】
得られた各リチウム二次電池について、化成後、定電流−定電圧充電の後に定電流放電を行い、放電容量を測定するレート試験を行った。レート試験において、定電流−定電圧充電の条件は、０．５Ｃの電流で電圧が４．２Ｖに達するまで定電流充電したあとに、４．２Ｖで３時間の定電圧充電することとした。定電流放電の条件は、所定の定電流（放電レート）で電圧が２．７５Ｖに達するまで放電することとした。
試料１３、１４のゲルポリマーリチウム二次電池について、放電レートを０．２Ｃで行ったレート試験の結果を図５に示した。また、比較例２の有機電解液を用いたリチウム二次電池については、放電レートを０．２Ｃ、１．０Ｃ、２．０Ｃで行ったレート試験の結果を図５に併せて示した。
【００７４】
図５に示すように、試料１３及び１４の電解質を備えたリチウム二次電池は、比較例２の有機電解液を用いたリチウム二次電池よりも放電容量が若干低下するが、それでも十分な放電容量を有しており、TAZM又はMe-TAZMが電池内に存在しても、レート特性に悪影響を与えないことがわかった。
【００７５】
実験例５（TAZMを用いた電解質を備えたリチウム二次電池の特性）
ＬｉＣｏＯ₂を正極活物質とする正極と炭素を負極活物質とする負極を、ポリプロピレン製多孔質セパレータを介して渦巻状に巻回し、電池サイズ長さ６２mm、幅３５mm、厚さ３．６mmの図４に示すような素電池を作製し、これをアルミラミネート製の電池容器に挿入した。
この素電池を挿入した電池容器に、上記TAZMを２、５、７．５、１０質量％含有するように有機電解液に添加して十分に攪拌した直後の溶液を、所定量注液した。そして、注液後封止し、２４時間放置することでポリマーリチウム二次電池とした。
なお、有機電解液は、EC：DEC=３：７の混合溶媒に１．３モル/ＬのLiPF₆を溶解させたものを用いた。
また、TAZMを添加せずに、上記有機電解液をそのまま、素電池を挿入した電池容器に注液した以外は、上記ポリマーリチウム二次電池と同様にして、比較のためのリチウム二次電池（TAZMが０質量％）を作製した。
【００７６】
TAZMを用いたポリマーリチウム二次電池のゲル化の状態は、TAZMを２質量％含む場合では、室温で９６時間放置した後もゲル化することがなかった。また、TAZMを５質量％含む場合では、室温で９６時間放置することによりゲル化した。更にTAZMを７．５、１０質量％含む場合では、室温で２４時間放置することによりゲル化した。
【００７７】
得られた各リチウム二次電池について、化成後、実験例４の場合と同じ条件でレート試験を行った。放電レートを０．２Ｃ、０．５Ｃ、１．０Ｃで行った結果を図６に示す。
図６に示すように、放電レートが高くなると、TAZMの含有率が増加するにつれて放電容量の低下が大きくなっている。ただし、放電レートが０．５Ｃのときでも、TAZMを含む電池とTAZMを全く含まない電池との間では放電容量に大差があるわけではなく、本発明に係るリチウム二次電池も良好な特性を示すことがわかった。
すなわち、TAZMが電池内に存在しても、レート特性に悪影響を与えないことがわかった。
【００７８】
実験例６（TAZMを用いた電解質を備えたリチウム二次電池のリチウム塩濃度に応じた特性）
ＬｉＣｏＯ₂を正極活物質とする正極と炭素を負極活物質とする負極を、ポリプロピレン製多孔質セパレータを介して渦巻状に巻回し、電池サイズ長さ６２mm、幅３５mm、厚さ３．６mmの図４に示すような素電池を作製し、これをアルミラミネート製の電池容器に挿入した。
この素電池を挿入した電池容器に、上記TAZMを５質量％含有するように有機電解液に添加して十分に攪拌した直後の溶液を、所定量注液した。そして、注液後封止し、２４時間放置することでポリマーリチウム二次電池とした。
なお、有機電解液は、EC：DEC=３：７の混合溶媒に異なる濃度のLiPF₆を溶解させた３種類のものを用いた。LiPF₆の濃度は１．０、１．３、１．５モル/Ｌ(M)とした。
また、TAZMを添加せずに、EC：DEC=３：７の混合溶媒に１．３モル/Ｌ(M)のLiPF₆を溶解させた有機電解液をそのまま、素電池を挿入した電池容器に注液した以外は、上記ポリマーリチウム二次電池と同様にして、比較のためのリチウム二次電池（TAZMが０質量％）を作製した。
【００７９】
得られた各リチウム二次電池について、化成後、実験例４の場合と同じ条件でレート試験を行った。放電レートを０．２Ｃ、０．５Ｃ、１．０Ｃ、２．０Ｃで行った結果を図７に示す。
【００８０】
図７を見ると、放電レートが高くなると、LiPF₆の濃度が低下するにつれて放電容量の低下が大きくなっていることが分かる。
このように、本発明のリチウム二次電池の場合、リチウム塩の濃度を高めに設定することで、２Ｃもの高率放電においても比較的高めの放電容量を示すことがわかった。
【００８１】
実験例７（TAZOを用いた電解質）
ゲル形成化合物として、アジリジン化合物である［化８］に示すテトラメチロールメタン-トリ-β-アジリジニルプロピネート［tetramethylolmethane-tri-β-aziridinylpropionate］と、上記［化３］のＲ₂がＨである化合物とが、２５：７５の割合で混合した混合物（以下、TAZOと表記）を用意した。
これを有機電解液に添加して十分に攪拌した後、室温で放置することによって、TAZOを１、２、３、５、１０質量％含有する電解質を得た。
有機電解液としてはEC：DEC=３：７の混合溶媒に１．３モル/ＬのLiPF₆を溶解させたものを用いた。
その結果、TAZOを３、５、１０質量％含有する電解質は、室温で１５時間以内にゲル化した。また、TAZOを２質量％含有する電解質は、室温で３６時間放置後に柔らかいゲルとなった。また、TAZOを１質量％含有する電解質は、室温で４８時間放置後に粘調性液体となった。すなわち、TAZOを３質量％含有すれば、十分にゲル化が進行することがわかった。
次に、ゲル化後のTAZOを３質量％含有する電解質を、１００℃において１時間放置したところ、液化は見られなかった。このことから、TAZOを３質量％含有すれば安定したゲルを形成し、高温時液化しないことがわかった。
【００８２】
【化８】

【００８３】
実験例８
（TAZOを用いた電解質を備えたリチウム二次電池のレート特性）
ＬｉＣｏＯ₂を正極活物質とする正極と炭素を負極活物質とする負極を、ポリプロピレン製多孔質セパレータを介して渦巻状に巻回し、電池サイズ長さ６２mm、幅３５mm、厚さ３．６mmの図４に示すような素電池を作製し、これをアルミラミネート製の電池容器に挿入した。
この素電池を挿入した電池容器に、上記TAZOを３、４、５質量％含有するように有機電解液に添加して十分に攪拌した直後の溶液を、所定量注液した。そして、注液後封止し、２４時間放置することでゲルポリマーリチウム二次電池とした。
なお、実験例７と同様に、有機電解液は、EC：DEC=３：７の混合溶媒に１．３モル/ＬのLiPF₆を溶解させたものを用いた。
また、TAZOを添加せずに、上記有機電解液をそのまま、素電池を挿入した電池容器に注液した以外は、上記ゲルポリマーリチウム二次電池と同様にして、比較のためのリチウム二次電池を作製した。
【００８４】
得られた各リチウム二次電池について、化成後、実験例４の場合と同じ条件でレート試験を行った。放電レートを０．２Ｃ、０．５Ｃ、１．０Ｃ、２．０Ｃで行った結果を図８に示す。
【００８５】
図８に示すように、放電レートが２．０Ｃにおいて、TAZOを３、４、５質量％含有する電解質（３％ＴＡＺＯ、４％ＴＡＺＯ、５％ＴＡＺＯ）を備えたゲルポリマーリチウム二次電池の放電容量は、TAZOを含有しない有機電解液（液blank）を用いたリチウム二次電池よりも、TAZOの含有量が多い程低下する。
しかし、放電レートが１．０Ｃ以下では、各ゲルポリマーリチウム二次電池の放電容量の低下は小さく、実用上十分な放電容量であることがわかった。
特に、TAZOを３質量％含有する電解質（３％ＴＡＺＯ）を備えたゲルポリマーリチウム二次電池の放電容量は、TAZOを含有しない有機電解液（液blank）を用いたリチウム二次電池と比較して、放電レート１．０Ｃ以下においてほとんど遜色がなく、TAZOが電池内に存在しても、レート特性に悪影響を与えないことがわかった。
【００８６】
実験例９
（TAZOを用いた電解質を備えたリチウム二次電池のサイクル特性）
ＬｉＣｏＯ₂を正極活物質とする正極と炭素を負極活物質とする負極を、ポリプロピレン製多孔質セパレータを介して渦巻状に巻回し、電池サイズ長さ６２mm、幅３５mm、厚さ３．６mmの図４に示すような素電池を作製し、これをアルミラミネート製の電池容器に挿入した。
この素電池を挿入した電池容器に、上記TAZOを３質量％含有するように有機電解液に添加して十分に攪拌した直後の溶液を、所定量注液した。そして、注液後封止し、２４時間放置することでゲルポリマーリチウム二次電池とした。
なお、実験例７、８と同様に、有機電解液は、EC：DEC=３：７の混合溶媒に１．３モル/ＬのLiPF₆を溶解させたものを用いた。
また、TAZOを添加せずに、上記有機電解液をそのまま、素電池を挿入した電池容器に注液した以外は、上記ゲルポリマーリチウム二次電池と同様にして、比較のためのリチウム二次電池を作製した。
【００８７】
得られた各リチウム二次電池について、化成後、１Ｃの電流で電圧が４．２Ｖに達するまで定電流充電したあとに、４．２Ｖで２．５時間の定電圧充電する定電流-定電圧充電を行い、１．０Ｃの定電流で電圧が２．７５Ｖに達するまで放電する定電流放電を行う充放電サイクルを１００回繰り返し、各サイクル毎の放電容量を調べた。結果を図９に示す。
【００８８】
図９に示すように、TAZOを３質量％含有する電解質（３％ＴＡＺＯ）を備えたゲルポリマーリチウム二次電池の放電容量は、充放電サイクルを１００回繰り返しても、TAZOを含有しない有機電解液（液blank）を用いたリチウム二次電池と比較して遜色なく、TAZOが電池内に存在しても、サイクル特性に悪影響を与えないことがわかった。
なお、本実験例の３％ＴＡＺＯでは、化成前（初充電前）にゲル化がほぼ完全に終了しているため、化成時に負極表面上に皮膜が生成することはなかったものと考えられる。
【００８９】
実験例１０
（TAZOを用いた電解質を備えたリチウム二次電池の高温保存特性）
実験例９と同じ条件で、TAZOを３質量％含有する電解質（３％ＴＡＺＯ）を備えたゲルポリマーリチウム二次電池を作製した。また、実験例９と同じ条件で、TAZOを含有しない有機電解液（液blank）を用いたリチウム二次電池を作製した。
【００９０】
得られたリチウム二次電池について、化成後、以下の手順で実験を行った。
▲１▼１Ｃの電流で電圧が４．２Ｖに達するまで定電流充電したあとに、４．２Ｖで２．５時間の定電圧充電する定電流-定電圧充電を行い、満充電状態とした。
▲２▼８５℃の雰囲気に４時間放置した。
▲３▼▲２▼の電池を室温に戻した後、０．２Ｃの定電流で電圧が２．７５Ｖに達するまで放電する定電流放電を行い放電容量を調べた。この時の放電容量を「８５℃４ｈｒ保存容量」と称する。
▲４▼▲３▼の電池を▲１▼と同じ条件で再度満充電状態とした後、０．２Ｃの定電流で電圧が２．７５Ｖに達するまで放電する定電流放電を行い放電容量を調べた。この時の放電容量を「回復容量１」と称する。
▲５▼▲４▼の電池を▲１▼と同じ条件で再度満充電状態とした後、８５℃の雰囲気に２４時間放置した。
▲６▼▲５▼の電池を室温に戻した後、０．２Ｃの定電流で電圧が２．７５Ｖに達するまで放電する定電流放電を行い放電容量を調べた。この時の放電容量を「８５℃２４ｈｒ保存容量」と称する。
▲７▼▲６▼の電池を▲１▼と同じ条件で再度満充電状態とした後、０．２Ｃの定電流で電圧が２．７５Ｖに達するまで放電する定電流放電を行い放電容量を調べた。この時の放電容量を「回復容量２」と称する。
以上の結果を図１０に示す。
【００９１】
図１０に示すように、高温の雰囲気に曝した場合の保存容量は、TAZOを３質量％含有する電解質（３％ＴＡＺＯ）を備えたゲルポリマーリチウム二次電池と、TAZOを含有しない有機電解液（液blank）を用いたリチウム二次電池との間に有意の差は認められず、TAZOが電池内に存在しても、高温保存特性に悪影響を与えないことがわかった。
【００９２】
実験例１１
（電解質がゲル化していないリチウム二次電池のサイクル特性）
コイン型電池の正極ケースにＬｉＣｏＯ₂を正極活物質とする正極、ポリプロピレン製多孔質セパレータ、パッキンを配置する。
これにTAZMを０．２、０．５、１．０質量％、又はTAZOを０．２、０．５、１．０質量％含有するように有機電解液に添加して十分に攪拌した直後の溶液を注液する。
つぎに負極、負極蓋で封口し、コイン型リチウム二次電池とした。コイン型電池のサイズは直径２０mm、高さ１．６mm（ＣＲ２０１６サイズ）である。これを、２４時間室温で放置したが、いずれの電解質もゲル化しなかった。
なお、有機電解液は、EC：DEC=３：７の混合溶媒に１．３モル/ＬのLiPF₆を溶解させたものを用いた。
また、TAZM及びTAZOを添加せずに、上記有機電解液をそのまま、正極、セパレータ、パッキンを配置した正極ケースに注液した以外は、上記リチウム二次電池と同様にして、比較のためのリチウム二次電池（液blank）を作製した。
【００９３】
得られた各リチウム二次電池について、化成後、１Ｃの電流で電圧が４．２Ｖに達するまで定電流充電したあとに、４．２Ｖで２．５時間の定電圧充電する定電流-定電圧充電を行い、１．０Ｃの定電流で電圧が２．７５Ｖに達するまで放電する定電流放電を行う充放電サイクルを１００回繰り返し、各サイクル毎の放電容量を調べた。結果を図１２に示す。
【００９４】
図１２に示すように、TAZM又はTAZOを１．０質量％含有する電解質（１．０％ＴＡＺＭ、１．０％ＴＡＺＯ、）を備えたリチウム二次電池では、約５０サイクル目以降において、TAZM又はTAZOを含有しない有機電解液（液blank）を用いたリチウム二次電池より高い放電容量が得られることがわかった。これは、TAZM又はTAZOが存在することにより、負極表面に被膜が形成され、負極と電解質との反応が抑制されているためと考えられる。
また、TAZM又はTAZOを０．５質量％含有する電解質（０．５％ＴＡＺＭ、０．５０％ＴＡＺＯ）を備えたリチウム二次電池では、約５０サイクル目以降において、TAZM又はTAZOを含有しない有機電解液（液blank）を用いたリチウム二次電池とほぼ同様の放電容量が得られたが、TAZM又はTAZOを０．２質量％含有する電解質（０．２％ＴＡＺＭ、０．２％ＴＡＺＯ）を備えたリチウム二次電池では、全サイクルを通じて、TAZM又はTAZOを含有しない有機電解液（液blank）を用いたリチウム二次電池より低い放電容量しか得られなかった。これにより、サイクル特性向上の効果を得るためには、少なくとも０．２質量％よりも多くのTAZM、又は０．５質量％より多くのTAZOが必要であることがわかった。
【００９５】
実験例１２
（電解質がゲル化していないリチウム二次電池のサイクル特性）
ＬｉＣｏＯ₂を正極活物質とする正極と炭素を負極活物質とする負極を、ポリプロピレン製多孔質セパレータを介して渦巻状に巻回し、電池サイズ長さ６２mm、幅３５mm、厚さ３．６mmの図４に示すような素電池を作製し、これをアルミラミネート製の電池容器に挿入した。
この素電池を挿入した電池容器に、上記TAZMを０．２、０．５、１．０質量％、又はTAZOを０．５、１．０質量％含有するように有機電解液に添加して十分に攪拌した直後の溶液を、所定量注液した。そして、注液後封止し、２４時間放置することでリチウム二次電池としたが、何れの電解質もゲル化しなかった。
なお、有機電解液は、EC：DEC=３：７の混合溶媒に１．３モル/ＬのLiPF₆を溶解させたものを用いた。
また、TAZM及びTAZOを添加せずに、上記有機電解液をそのまま、素電池を挿入した電池容器に注液した以外は、上記リチウム二次電池と同様にして、比較のためのリチウム二次電池（液blank）を作製した。
【００９６】
得られた各リチウム二次電池について、化成後、１Ｃの電流で電圧が４．２Ｖに達するまで定電流充電したあとに、４．２Ｖで２．５時間の定電圧充電する定電流-定電圧充電を行い、１．０Ｃの定電流で電圧が２．７５Ｖに達するまで放電する定電流放電を行う充放電サイクルを１００回繰り返し、各サイクル毎の放電容量を調べた。結果を図１３に示す。
【００９７】
図１３に示すように、TAZMを０．５質量％若しくは１．０質量％含有する電解質（０．５％ＴＡＺＭ、１．０％ＴＡＺＭ）、又はTAZOを１．０質量％含有する電解質（１．０％ＴＡＺＯ）を備えたリチウム二次電池では、５サイクル目近くから後において、TAZM又はTAZOを含有しない有機電解液（液blank）を用いたリチウム二次電池より高い放電容量が得られることがわかった。これは、TAZM又はTAZOが適切な量存在することにより、負極表面に被膜が形成され、負極表面における電解質の分解反応が抑制されているためと考えられる。
一方、TAZMを０．２質量％含有する電解質（０．２％ＴＡＺＭ）、又はTAZOを０．５質量％含有する電解質（０．５％ＴＡＺＯ）を備えたリチウム二次電池では、１０サイクル目近くから後において、TAZM又はTAZOを含有しない有機電解液（液blank）を用いたリチウム二次電池より若干低い放電容量しか得られなかった。
これにより、少なくとも０．２質量％より多くの、好ましくは０．５質量％以上のTAZM、又は０．５質量％より多くの、好ましくは１．０質量％以上のTAZOを含有することによって、サイクル特性向上の効果を得られることがわかった。
なお、実験例１１よりも顕著なサイクル特性向上の効果が得られたのは、本実験例では図４に示す巻回したリチウム二次電池としたため、均一に電極間に圧力がかかったためと考えられる。
【００９８】
【発明の効果】
以上、詳細に説明したように、本発明の電解質は、アジリジン環を有するアジリジン化合物と、非プロトン性溶媒にリチウム塩が溶解されてなる有機電解液とが少なくとも混合された電解質材料を用いて形成されたものであり、アジリジン化合物と有機電解液とを単に混合することによってゲルが形成されるので、高温でも安定した電解質を得ることができる。
また、かかる電解質を用いたリチウム二次電池では、負極表面における電解質の分解反応が抑制され、優れたサイクル特性が得られるものである。
【図面の簡単な説明】
【図１】 本発明の実施形態である電解質の微細構造を示す模式図である。
【図２】 本発明の実施形態である電解質の微細構造を示す模式図である。
【図３】 試料７の電解質を備えたリチウム二次電池の化成後の１サイクル目の放電曲線である。
【図４】 素電池の斜視図である。
【図５】 試料１３及び１４の電解質を備えたリチウム二次電池の放電レートと放電容量との関係を示すグラフである。
【図６】 TAZMを０〜１０質量％含む電解質を備えたリチウム二次電池の放電レートと放電容量との関係を示すグラフである。
【図７】 １．０〜１．５モル／ＬのLiPF₆を含む有機電解液からなる電解質を備えたリチウム二次電池の放電レートと放電容量との関係を示すグラフである。
【図８】 TAZOを０〜5質量％含む電解質を備えたリチウム二次電池の放電レートと放電容量との関係を示すグラフである
【図９】 TAZOを3質量％含む電解質を備えたリチウム二次電池のサイクル特性を示すグラフである。
【図１０】 TAZOを3質量％含む電解質を備えたリチウム二次電池の高温保存特性を示すグラフである。
【図１１】 負極に被膜が形成される機構の説明図である。
【図１２】 TAZO又はTAZMを含むゲル化されていない電解質を備えたリチウム二次電池のサイクル特性を示すグラフである。
【図１３】 TAZO又はTAZMを含むゲル化されていない電解質を備えたリチウム二次電池のサイクル特性を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrolyte and a lithium secondary battery including the electrolyte. More specifically, the present invention relates to a so-called polymer electrolyte in which the electrolyte is gelled, a lithium secondary battery including the polymer electrolyte, and a lithium secondary battery in which the decomposition reaction of the electrolyte on the negative electrode surface is suppressed.
[0002]
[Prior art]
In order to meet the needs of portable electronic devices that are becoming smaller and lighter and having higher performance, further reduction in thickness and improvement in the degree of freedom of shape of lithium secondary batteries are required.
Therefore, recently, lithium secondary batteries have been provided in which the electrolyte of the lithium secondary battery is replaced with a so-called polymer electrolyte from a conventional organic electrolyte, thereby reducing the thickness and improving the degree of freedom of shape.
[0003]
Batteries using the above polymer electrolytes are roughly classified into two types, physical gel batteries and chemical gel batteries, depending on the manufacturing method.
A physical gel battery is prepared by adding an organic electrolyte to a polymer and heating it to dissolve the polymer to form a paste, which is then applied to the sheet-like positive electrode and the negative electrode on the coated paste. The unit cell is housed and sealed in a battery container, whereby the paste is cooled in the battery container to form a physical gel that is a gel polymer electrolyte.
A material that is easily swelled and gelled by the organic electrolyte at room temperature and is dissolved by the organic electrolyte at about 80 to 100 ° C. is selected as the polymer.
[0004]
For example, a chemical gel battery is formed by laminating a sheet-like positive electrode, a non-woven fabric, and a negative electrode to form an electrode group, and then storing the electrode group in a battery container and injecting an organic electrolyte and a polymerization initiator. A monomer having a group is injected. Thereby, a polymerization initiator and a monomer react and a chemical gel which is a gel-like polymer electrolyte is formed by polymerizing a monomer in a battery container.
As the monomer, a monomer that can swell with an organic electrolytic solution at room temperature and easily form a gel is selected.
[0005]
Since the above physical gel and chemical gel have an ionic conductivity of about 2 to 3 mS / cm, they can be applied as an electrolyte of a lithium secondary battery.
[0006]
On the other hand, in a lithium secondary battery, in particular, a negative electrode that has a base potential during charging tends to decompose the electrolyte. The decomposition of the electrolyte has a great influence on battery performance, particularly battery capacity, battery storage characteristics, cycle characteristics, low temperature characteristics, and the like.
Therefore, in order to develop high battery performance, it is important to suppress the decomposition reaction of the electrolyte on the negative electrode surface.
[0007]
In view of this, the electrolyte of the lithium secondary battery is selected in particular considering the reactivity with the negative electrode, and many solvents or combinations thereof that do not deteriorate the battery performance due to the decomposition reaction of the electrolyte on the negative electrode surface have been studied. Furthermore, the selection of the solvent takes into account the solubility of the supporting salt of the electrolytic solution, the reactivity with the positive electrode, the ion conductivity, the cost, and the like.
Specifically, the non-aqueous solvent for the lithium secondary battery includes organic carbonates such as ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, methyl propionate, butyl propionate, and ethyl propionate. A solvent is used individually or in combination of multiple types.
Further, many attempts have been made to improve the battery performance by adding a specific compound as an additive to the electrolyte so as to form a film on the negative electrode surface and suppressing the decomposition reaction of the electrolyte on the negative electrode surface.
[0008]
[Problems to be solved by the invention]
However, in the lithium secondary battery using the above physical gel, for example, when the temperature of the battery rises due to an external factor, the polymer polymer constituting the physical gel is dissolved and liquefied in the organic electrolytic solution, thereby There is a problem that the negative electrode is short-circuited and an internal short-circuit occurs.
[0009]
On the other hand, in a lithium secondary battery using the above chemical gel, unreacted polymerization initiator remains in the battery, adversely affecting the charge / discharge reaction of the battery, or accompanying the reaction between the polymerization initiator and the monomer. As a result, there is a problem that gas generation occurs in the battery, or further, the polymerization reaction of the monomer is insufficient, and the polymer electrolyte is not formed.
[0010]
In view of the above circumstances, the present invention provides an electrolyte that is surely present as a gel in a battery, has excellent heat resistance and does not dissolve even at high temperatures, and a lithium secondary battery including the electrolyte. Let it be 1 issue.
[0011]
On the other hand, as described above, attempts have been made to suppress the decomposition reaction of the electrolyte on the negative electrode surface by adding a specific compound as an additive to the electrolyte to form a film on the negative electrode surface. Depending on the additive, the film forming ability is not sufficient, or the film adversely affects the charge / discharge reaction, and the original voltage or current as a battery cannot be obtained in most cases.
For example, Japanese Patent Application Laid-Open No. 8-96852 discloses a battery using a negative electrode having metallic lithium or a material capable of doping and dedoping lithium, in which vinylene carbonate is contained in a non-aqueous solvent. However, when this vinylene carbonate was used for a battery having a carbonaceous material as a negative electrode, the film forming ability was not sufficient, and a sufficient improvement in battery characteristics could not be expected.
Furthermore, when vinylene carbonate is added, the amount of gas generated at the time of initial charge increases, and depending on the shape of the battery, the battery may be deformed due to an increase in the internal pressure of the battery. The cause of this gas generation is thought to be due to the simultaneous decomposition of the electrolyte during the formation of the initial charge film. This gas generation causes the electrolyte to deteriorate, which contributes to the deterioration of the battery characteristics. There was a possibility.
[0012]
In view of the above circumstances, a second object of the present invention is to provide a lithium secondary battery that can suppress the decomposition reaction of the electrolyte on the surface of the negative electrode without deteriorating the characteristics as a battery and that generates less gas. Let it be an issue.
[0013]
[Means for Solving the Problems]
As a result of studying the above problems, the present inventors have found that an organic electrolyte and an aziridine compound are stable by adding an aziridine compound having one or more aziridine rings to an organic electrolyte in which a lithium salt is dissolved. It was found to form a gel.
Further, it has been found that when an aziridine compound having one or two or more aziridine rings is added to an organic electrolytic solution in which a lithium salt is dissolved, an effect of suppressing the decomposition reaction of the electrolyte on the negative electrode surface is exhibited.
[0014]
  That is, the electrolyte of the present invention is at least mixed with an aziridine compound having one or more aziridine rings and an organic electrolyte obtained by dissolving a lithium salt in an aprotic solvent.Gel-formingFormed using electrolyte materialThe component that forms the gel is only lithium contained in the aziridine compound and the lithium salt.It is characterized by that.
[0015]
According to such an electrolyte, it is possible to form a gel simply by mixing an aziridine compound and an organic electrolyte. In this case, there is no possibility that the polymerization reaction becomes insufficient, and since there is no need for a polymerization initiator or the like, there is no risk of gas generation and the like, and an electrolyte that can stably maintain a gel state even at high temperatures can be obtained. .
Moreover, in the lithium secondary battery using such an electrolyte, the decomposition reaction of the electrolyte on the negative electrode surface can be suppressed. As a result, gas generation due to decomposition of the electrolyte and alteration of the electrolyte itself are reduced, it is possible to prevent a decrease in charge / discharge capacity of the lithium secondary battery, improve cycle characteristics, and further prevent deformation of the battery. . Also, the high temperature storage characteristics are improved.
This is presumed to be because a coating composed mainly of an aziridine compound is formed on the negative electrode surface at the initial stage of the initial charge. After that, even when the charging voltage increases due to the progress of charging, it is presumed that this coating suppresses the decomposition reaction of the electrolyte on the negative electrode surface.
[0016]
The electrolyte of the present invention is the electrolyte described above, wherein the aziridine compound includes at least one represented by the structural formula shown in the following [Chemical Formula 2].
However, in the following structural formula, R₁Is H, CH_Three, OH, and R₂Is H or CH_ThreeEither one of them. Moreover, these mixtures may be sufficient.
[0017]
[Chemical 2]

[0018]
According to such an electrolyte, the aziridine compound is represented by the above structural formula, and a gel is easily formed by mixing this with an organic electrolyte. This makes it possible to construct an electrolyte made of a relatively stable gel.
Moreover, if a lithium secondary battery is comprised using the electrolyte, the decomposition reaction of the electrolyte on the negative electrode surface can be suppressed.
[0019]
The electrolyte according to the present invention includes, as an aziridine compound, a compound represented by the structural formula represented by [Chemical Formula 3], or a compound represented by the structural formula represented by the above [Chemical Formula 2] and a structure represented by [Chemical Formula 3]. It may be a mixture with a compound represented by the formula.
In addition, the following [Chemical 4] to [Chemical 5] may be included. These compounds are preferably used simultaneously with those shown in the above [Chemical Formula 2] and / or [Chemical Formula 3].
In addition, n in [Chemical Formula 4]₁Is preferably in the range of 0 to 10, and n in [Chemical Formula 5]₂Is preferably in the range of 0-10.
[0020]
[Chemical 3]

[0021]
[Formula 4]

[0022]
[Chemical formula 5]

[0023]
The electrolyte of the present invention is the electrolyte described above, wherein the aprotic solvent is one or more of ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. It is characterized by including.
According to such an electrolyte, since the aprotic solvent is contained, a stable electrolyte can be formed together with the aziridine compound, and the ionic conductivity of the electrolyte itself can be improved.
[0024]
The electrolyte of the present invention is the electrolyte described above, wherein the lithium salt is LiPF.₆, LiBF_Four, LiSbF₆, LiAsF₆LiClO_Four, LiCF_ThreeSO_Three, Li (CF_ThreeSO₂)₂N, LiC_FourF₉SO_Three, LiSbF₆, LiAlO_Four, LiAlCl_Four, LiN (C_xF_{2x + 1}SO₂) (C_yF_{2y Ten 1}SO₂) (Where x and y are natural numbers).
[0025]
According to such an electrolyte, since the above lithium salt is included in the electrolyte material, a stable gel can be formed together with the aziridine compound. In addition, it is considered that this lithium salt contributes to the formation of a film mainly composed of an aziridine compound on the negative electrode surface during the initial charge.
The concentration of the lithium salt in the electrolyte material is preferably in the range of 0.5 to 2.0 mol / L. If the concentration of the lithium salt is within this range, the ionic conductivity of the electrolyte is improved, and the high rate discharge characteristics can be improved.
[0026]
The electrolyte of the present invention is the electrolyte described above, wherein the content of the aziridine compound in the electrolyte material is more than 0.2% by mass and 20% by mass or less.
When the content of the aziridine compound is 0.2% by mass or less, it becomes difficult to form a gel together with the organic electrolyte, and the effect of suppressing the decomposition reaction of the electrolyte on the negative electrode surface, which is presumed to be due to film formation It will be difficult to obtain. In addition, it is more preferable to set it as 0.5 mass% or more.
On the other hand, when the content of the aziridine compound exceeds 20% by mass, the lithium salt is strongly bound by the aziridine ring of the aziridine compound, and the ionic conductivity is lowered, which is not preferable. In addition, it is more preferable to set it as 10 mass% or less.
However, the formation of the gel depends on the type of the aziridine compound, the composition of the organic electrolyte, the gel formation time after mixing, and the like. In addition, the formation of the coating film also depends on the type of the aziridine compound, the composition of the organic electrolyte, the charging conditions at the first charging, and the like. Therefore, the actual content of the aziridine compound is preferably adjusted as appropriate within a range of more than 0.2% by mass and 20% by mass or less.
[0027]
In the present invention, a gel is formed by the aziridine compound and the organic electrolyte solution.
Thereby, it can be set as the electrolyte which can form a lithium secondary battery which can be reduced in thickness and an improvement in a shape freedom degree.
[0028]
Such a gel may be characterized in that a part or all of the gel is formed by coordination of a plurality of the aziridine rings with lithium contained in the lithium salt.
Further, the gel is characterized in that a part or all of the gel is formed by impregnating the organic electrolyte in a polymer of the aziridine compound formed by cleaving the aziridine ring. can do.
Note that part or all of the gel may be formed in a state where the two forms of the gel are mixed.
[0029]
The lithium secondary battery of the present invention comprises a positive electrode and a negative electrode capable of inserting and extracting lithium, and an electrolyte, and the electrolyte is the electrolyte according to any one of claims 1 to 8. It is characterized by that.
ADVANTAGE OF THE INVENTION According to this invention, it can be set as the lithium secondary battery which aimed at the thickness reduction and the improvement of the freedom degree of shape in the gel state of electrolyte. Further, a lithium secondary battery in which the decomposition reaction of the electrolyte on the negative electrode surface is suppressed can be obtained.
[0030]
Furthermore, the lithium secondary battery of the present invention may be characterized in that a coating containing the aziridine compound as a main component is formed on the surface of the negative electrode.
The “main component” is used because other components in the electrolyte material may be taken in at the time of film formation.
In this case, the decomposition reaction of the electrolyte on the negative electrode surface is suppressed, the gas generation due to the decomposition of the electrolyte and the alteration of the electrolyte itself are reduced, the decrease in charge / discharge capacity of the lithium secondary battery is prevented, and the cycle characteristics can be improved. In addition, the battery can be prevented from being deformed. Moreover, the high temperature storage characteristic of a lithium secondary battery improves by the inhibitory effect of the electrolyte decomposition | disassembly by an organic film.
[0031]
Furthermore, the lithium secondary battery of the present invention comprises a positive electrode and a negative electrode capable of occluding and releasing lithium, and an electrolyte, and a film mainly composed of an aziridine compound is formed on the surface of the negative electrode. It is characterized by being.
The “main component” is used because other components in the electrolyte material may be taken in at the time of film formation.
In this case, the decomposition reaction of the electrolyte on the negative electrode surface is suppressed, the gas generation due to the decomposition of the electrolyte and the alteration of the electrolyte itself are reduced, the decrease in charge / discharge capacity of the lithium secondary battery is prevented, and the cycle characteristics can be improved. In addition, the battery can be prevented from being deformed. Moreover, the high temperature storage characteristic of a lithium secondary battery improves by the inhibitory effect of the electrolyte decomposition | disassembly by an organic film.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the electrolyte according to the embodiment of the present invention will be described.
The electrolyte of the present embodiment is formed using an electrolyte material in which at least one aziridine compound having one or more aziridine rings and an organic electrolyte obtained by dissolving a lithium salt in an aprotic solvent are mixed. It is.
[0033]
The aziridine compound in the electrolyte material includes at least one represented by the structural formula shown in the above [Chemical Formula 2]. In the above structural formula, R₁Is H, CH_Three, OH, and R₂Is H or CH_ThreeEither one of them. Moreover, these mixtures may be sufficient.
[0034]
As the aziridine compound, a compound represented by the structural formula shown in the above [Chemical Formula 2], a compound represented by the structural formula shown in [Chemical Formula 3], or a mixture thereof may be used alone, or [Chemical Formula 2] and / or A mixture of any one or more of those shown in [Chemical 4] to [Chemical 5] with those shown in [Chemical 3] may be used.
By mixing the compounds shown in [Chemical Formula 4] to / or [Chemical Formula 3] with those shown in [Chemical Formula 2] and / or [Chemical Formula 3], compared with the case of [Chemical Formula 2] and / or [Chemical Formula 3] alone. It can be gelled with a small amount.
In addition, n in [Chemical Formula 4]₁Is preferably in the range of 0 to 10, and n in [Chemical Formula 5]₂Is preferably in the range of 0-10.
n₁Or n₂If the amount is less than the above range, it is not preferable because the fluidity of the electrolyte is increased and does not solidify, and if it exceeds the above range, the molecular weight becomes enormous and gel is hardly formed by the organic electrolyte, which is not preferable.
[0035]
The aziridine compound represented by the above [Chemical Formula 2] is bonded to three aziridine rings having two carbons and one nitrogen as a skeleton.₂Each group is formed by bonding. This aziridine ring can coordinate with lithium or be cleaved to form a polymer with another aziridine compound to form a gel.
The number of aziridine rings in the molecule may be one, but preferably two or more. If there are two or more aziridine rings in the molecule, the portion coordinated with lithium ions increases, and a higher-order network structure described later can be easily formed.
A gel is easily formed by mixing an organic electrolyte containing lithium ions with the aziridine compounds represented by [Chemical Formula 2] to [Chemical Formula 5]. Thereby, the comparatively stable gel-like electrolyte can be comprised.
Further, when an organic electrolyte containing lithium ions is mixed with the aziridine compounds shown in [Chemical Formula 2] to [Chemical Formula 5] and used in a lithium secondary battery, the chemical formula [Chemical Formula 2] is formed on the negative electrode surface during the initial charge. It is presumed that a film mainly composed of the aziridine compound represented by the formulas [Chemical Formula 5] is formed.
[0036]
The content of the aziridine compound in the electrolyte material is preferably larger than 0.2% by mass and 20% by mass or less.
When the content of the aziridine compound is 0.2% by mass or less, it becomes difficult to form a gel together with the organic electrolyte, and the effect of suppressing the decomposition reaction of the electrolyte on the negative electrode surface, which is presumed to be due to film formation It will be difficult to obtain. In addition, it is more preferable to set it as 0.5 mass% or more.
On the other hand, when the content of the aziridine compound exceeds 20% by mass, the lithium salt is strongly bound by the aziridine ring of the aziridine compound, and the ionic conductivity is lowered, which is not preferable. In addition, it is more preferable to set it as 10 mass% or less.
[0037]
The gel formation depends on the type of aziridine compound, the gel formation time after mixing, and the like. Further, the formation of the coating film also depends on the kind of the aziridine compound, the charging conditions at the time of initial charging, and the like. Therefore, the actual content of the aziridine compound is greater than 0.2% by mass and less than 20% by mass in consideration of whether the purpose is gel formation, film formation, or both gel and film formation. Within the range, it is preferable to adjust appropriately.
[0038]
The organic electrolyte is preferably one in which a lithium salt is dissolved in an aprotic solvent.
As the aprotic solvent, those containing at least one of ethylene carbonate, butylene carbonate, propylene carbonate, γ-butyrolactone, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate are preferable, and in particular, propylene carbonate, ethylene carbonate, butylene carbonate. It is preferable that any one of these is necessarily contained and any one of dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate is necessarily contained.
Since these aprotic solvents are contained in the electrolyte material together with the aziridine compound, it is possible to improve the transport number of the lithium ions and increase the ionic conductivity of the electrolyte itself.
[0039]
Moreover, as a lithium salt, LiPF₆, LiBF_Four, LiSbF₆, LiAsF₆LiClO_Four, LiCF_ThreeSO_Three, Li (CF_ThreeSO₂)₂N, LiC_FourF₉SO_Three, LiSbF₆, LiAlO_Four, LiAlCl_Four, LiN (C_xF_{2x + 1}SO₂) (C_yF_{2 y Ten 1}SO₂) (Where x and y are natural numbers) are preferred, especially LiPF₆, LiBF_FourThose containing any one of these are more preferred.
In addition, a conventionally known non-aqueous electrolyte for a lithium secondary battery can also be used.
Since these lithium salts are contained in the electrolyte material, the ionic conductivity of the electrolyte itself can be increased.
[0040]
The concentration of the lithium salt in the electrolyte material is preferably in the range of 0.5 to 2.0 mol / L. When the concentration is less than 0.5 mol / L, the ionic conductivity of the electrolyte is lowered, which is not preferable. When the concentration exceeds 2.0 mol / L, the lithium salt depends on the lithium salt when the organic electrolyte and the aziridine compound are mixed. This is not preferable because precipitation that appears to occur. If the concentration of the lithium salt is in the above range, the ionic conductivity of the electrolyte is improved, and the high rate discharge characteristics can be improved.
[0041]
The electrolyte of this embodiment can form a gel by coordinating a plurality of aziridine rings to lithium in a lithium salt. Further, the electrolyte of the present embodiment can form a gel by cleaving the aziridine ring to form a polymer of an aziridine compound and impregnating the polymer with the organic electrolyte. Is.
[0042]
FIG. 1 shows how a gel is formed by coordination of an aziridine ring to lithium. As shown in FIG. 1, aziridine rings having a negative charge of a plurality of aziridine compounds approach around a lithium ion that is a cation, and a coordination bond is formed by electrostatic action. Furthermore, other aziridine rings of these aziridine compounds are coordinated to another lithium ion, and as a whole, a higher-order network structure is formed.
Thus, the electrolyte according to the present embodiment can have a structure in which a plurality of aziridine compounds form a network structure via lithium ions, and the network structure is impregnated with an organic electrolyte.
[0043]
FIG. 2 shows a state in which a polymer is formed by cleavage of the aziridine ring. This structure is found in a part of the gel electrolyte. As shown in FIG. 2, the aziridine ring of the aziridine compound is cleaved and bonded to another aziridine compound. This cleavage of the aziridine ring is considered to proceed using lithium ions or hydrogen ions mixed in the aziridine compound or the organic electrolyte as a catalyst.
As described above, the electrolyte according to the present embodiment has a structure in which a polymer having a higher-order network structure is formed by cleavage of an aziridine ring, and an organic electrolyte is impregnated in the polymer of this network structure. Can do.
[0044]
When the electrolyte according to the present embodiment forms a gel, the structure in which the aziridine ring is coordinated to lithium occupies the majority, and the remaining part is considered to have a polymer structure by cleavage of the aziridine ring. .
In this case, the organic electrolytic solution is retained by being impregnated in a network structure by coordination bond between an aziridine ring and lithium, or by being impregnated in a polymer having a network structure by cleavage of an aziridine ring.
[0045]
The electrolyte of the present embodiment is made into a gel by mixing the electrode materials described above at a predetermined mixing ratio and leaving it at a temperature of 10 to 75 ° C. for 2 to 150 hours, for example.
According to the electrolyte of the present embodiment, by simply mixing the aziridine compound and the organic electrolyte solution, these are gelled to form an electrolyte, so that there is no fear that the polymerization reaction becomes insufficient, and the polymerization initiator or the like Therefore, a stable electrolyte can be obtained without the risk of gas generation.
[0046]
Moreover, when the electrolyte of this embodiment is used for a lithium secondary battery, the decomposition reaction of the electrolyte in the negative electrode is suppressed. This is presumably because a film mainly composed of an aziridine compound is formed on the negative electrode surface during the initial charge.
[0047]
The formation of this film is presumed to proceed as shown in FIG. That is, as shown in FIG. 11 (a), before starting the initial charge, all or a part of the lithium ions and the aziridine compound in the electrolytic solution (organic electrolytic solution) does not reach a high-order network structure. It is thought that it exists as an ionic cross-linked product of a certain degree (referred to as “Li-aziridine cross-linked product”).
This Li-aziridine cross-linked product is formed by coordinating the negatively charged aziridine ring of the aziridine compound to the lithium ion that is a cation, as described with reference to FIG. 1 regarding the mechanism of gel formation. It is thought that.
[0048]
Next, as shown in FIG. 11B, when charging is started, lithium ions, which are cations, are attracted to the negative electrode, so that a Li-aziridine cross-linked product adheres to the negative electrode surface. This causes an increase in the density of the aziridine compound on the negative electrode surface.
[0049]
Next, lithium ions are released from ionic crosslinking with the aziridine ring and occluded in the negative electrode. Then, the remaining aziridine ring is cleaved to start the polymerization reaction, and as a result, a film is formed as shown in FIG. Since the produced film is negatively charged, it becomes a film that transports only cations. Therefore, it can prevent that electrolyte solution contacts a negative electrode directly and decomposes | disassembles.
[0050]
In addition, in the electrolyte completely gelled before the first charge, there is no Li-aziridine cross-linked product sufficient for film formation, and it is considered that the film is difficult to form.
Therefore, when the content of the aziridine compound in the electrolyte material is high and the gelation reaction has completely proceeded before the initial charge, it is considered difficult to obtain the effect of suppressing the electrolyte decomposition reaction on the negative electrode surface. .
[0051]
Next, the lithium secondary battery of this embodiment will be described.
The lithium secondary battery of the present embodiment is basically composed of the electrolyte according to the present embodiment, and a positive electrode and a negative electrode capable of inserting and extracting lithium.
As the positive electrode, LiMn₂O_FourLiCoO₂, LiNiO₂LiFeO₂, V₂O_FiveExamples include those containing a positive electrode active material capable of occluding and releasing lithium, such as TiS, MoS, and organic disulfide compounds and organic polysulfide compounds.
Moreover, as a negative electrode, what can occlude / release lithium ion reversibly is preferable, for example, what contains artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, etc. can be illustrated. Metallic lithium can also be used as the negative electrode.
As specific examples of the positive electrode and the negative electrode, the above-described positive electrode active material or negative electrode active material, a binder, and further a conductive additive as necessary are mixed and applied to a current collector made of a metal foil or a metal net. Can be illustrated as a sheet.
In addition to this, what is conventionally known as a positive electrode or a negative electrode of a lithium secondary battery can also be used.
[0052]
A lithium secondary battery is formed by integrating the electrolyte between the positive electrode and the negative electrode. The electrolyte functions as a lithium ion electrolyte and, when a gel is formed, functions as a separator that separates the positive electrode and the negative electrode. Further, a conventional separator may be used by impregnating with an electrolyte.
The separator is essential when the electrolyte is not gelled, but a known separator such as a porous polypropylene film or a porous polyethylene film can be appropriately used.
[0053]
The lithium secondary battery of the present embodiment is schematically. There are three types.
First, the electrolyte is gelled with an aziridine compound and an organic electrolytic solution, but a film is not formed on the negative electrode surface. Second, the electrolyte is not gelled, but is a type in which a film mainly composed of an aziridine compound is formed on the negative electrode surface. Third, the electrolyte is gelled with an aziridine compound and an organic electrolytic solution, and a film mainly composed of an aziridine compound is formed on the negative electrode surface.
Which type will depend on the type and content of the aziridine compound in the electrolyte material, the composition of the organic electrolyte, the timing of the initial charge, etc., but the higher the aziridine compound content, the more the first type of battery. It tends to be easy to configure. Moreover, when the content rate of an aziridine compound is comparatively low, there exists a tendency which is easy to comprise a 2nd type battery. Moreover, there is a tendency that a third type battery can be configured by adjusting the timing of the initial charge using an electrolyte material having a relatively high content of the aziridine compound.
In any type of lithium secondary battery, the aziridine compound in the electrolyte material is consumed for the gelation or viscosity of the electrolyte or the formation of a film, as shown in [Chemical Formula 2] to [Chemical Formula 5]. However, it is considered that there is little remaining as it is.
[0054]
When the lithium secondary battery of the present embodiment is manufactured as a gel polymer battery, it is preferable to inject the electrolyte material immediately after mixing into a battery container or the like and advance gelation inside the battery after assembling the battery electrode.
For example, in the case of a spiral-type battery, a unit cell in which a positive electrode and a negative electrode are wound in a spiral shape through a separator as shown in FIG. 4 is manufactured and inserted into a battery container made of aluminum laminate, and then an electrolyte material. Is poured into the battery container and sealed. And it can be set as a gel polymer lithium secondary battery by leaving at predetermined temperature for the time required for gelatinization.
In the case of a coin-type battery, the electrolyte material immediately after mixing is injected into a positive electrode case in which a positive electrode, a separator, and packing are arranged. Next, it is sealed with a negative electrode and a negative electrode lid, and left at a predetermined temperature for a time required for gelation, whereby a gel polymer lithium secondary battery can be obtained.
In this way, by allowing the electrolyte material before gelation to gel within the battery, the electrolyte material that has penetrated into the inner surface of the negative electrode or the positive electrode can also be gelled, so that excellent battery characteristics can be obtained.
[0055]
In the lithium secondary battery of the present embodiment, in order to form the coating of the aziridine compound on the negative electrode, initial charging may be performed as in “chemical conversion” described later. However, at the time of this initial charging, it is necessary that an aziridine compound necessary for film formation is present in the electrolyte material. Since it seems difficult to form a film with an aziridine compound that has already been consumed for gel formation, an aziridine compound that is not gelled is considered necessary.
Therefore, when the lithium secondary battery of this embodiment is manufactured as a battery in which a film is formed on the negative electrode, for example, an electrolyte material having a relatively small aziridine compound content is used so that a gel cannot be formed even if left to stand. be able to.
Also, when using an electrolyte material with a relatively high aziridine compound content sufficient for gel formation, the battery should have a film formed on the negative electrode by performing initial charging before gelation is completely completed. Can do.
[0056]
According to the lithium secondary battery of the present embodiment, in the type in which the electrolyte is gelled (the first and second types), the lithium secondary battery can be thinned and the degree of freedom in shape can be improved. it can. Moreover, in the type (the said 2nd and 3rd types) with which the film | membrane was formed in the negative electrode surface, it can be set as the lithium secondary battery by which the decomposition reaction of the electrolyte in the negative electrode surface was suppressed.
[0057]
【Example】
Experimental Example 1 (Electrolyte of Samples 1 to 10)
First, TAZM (trimethylolpropane-tri-β-aziridinylpropionate), which is an aziridine compound, was prepared as a gel-forming compound. [Structure 6] below shows the structural formula of TAZM. This TAZM is the R in the above [Chemical 2].₁CH_ThreeAnd R₂Is H.
[0058]
[Chemical 6]

[0059]
Samples 1 to 10 containing 2.5 to 10% by mass of TAZM were obtained by adding the above TAZM to each of the three types of organic electrolytes and stirring sufficiently, and then placing them under various standing conditions. While observing the external appearance of these samples 1 to 10, the ionic conductivity of lithium was measured. The results are shown in Table 1.
In addition, the used organic electrolyte solution is an organic electrolyte solution having the following three types of compositions.
Organic electrolyte 1: EC: DMC: DEC = 3: 3: 1 (volume ratio)
Organic electrolyte 2: EC: DMC: DEC = 3: 3: 1 (volume ratio) + LiPF₆(1.0 mol / L)
Organic electrolyte 3: EC: DMC: DEC = 3: 3: 1 (volume ratio) + LiPF₆(1.3 mol / L)
EC is an abbreviation for ethylene carbonate, DMC is an abbreviation for dimethyl carbonate, and DEC is an abbreviation for diethyl carbonate.
[0060]
Furthermore, the leaving conditions were the following three conditions. That is, the conditions of leaving at room temperature for 15 hours (room temperature and 15 hours), leaving at room temperature for 15 hours and then leaving at 50 ° C for 4 hours (50 ° C and 4 hours), and leaving at room temperature for 150 hours (room temperature・ Leave for 150 hours).
[0061]
[Table 1]

[0062]
As shown in Table 1, LiPF₆It can be seen that Samples 1 to 4 that do not contain any of them do not gel under any standing conditions and remain liquid.
In Samples 5 to 7 containing the organic electrolyte 2, the sample 7 is gelled under the condition of being allowed to stand at room temperature for 15 hours, and the sample 6 is gelled under the condition of being allowed to stand at room temperature for 150 hours.
In Samples 8 to 10 containing the organic electrolyte 3, the sample 9 gels under the condition of being allowed to stand at 50 ° C. for 4 hours, and the sample 10 is gelled under the condition of being allowed to stand at room temperature for 150 hours.
Thus, it can be seen that the gel containing no lithium salt does not gel, and when the lithium salt is further contained, gelation tends to occur as the concentration of TAZM increases.
In addition, when the ionic conductivity of the gelled samples 6, 7, 9, and 10 was measured, all were in the range of 2 to 4 mS / cm, and showed good ionic conductivity as an electrolyte for a lithium secondary battery. .
[0063]
Experimental Example 2 (Electrolyte of Samples 11 to 12)
As the gel-forming compound, the above-mentioned TAZM, which is an aziridine compound, and Me-TAZM were prepared. [Structure 7] below shows the structural formula of Me-TAZM. This Me-TAZM is represented by R in [Chemical Formula 2].₁And R₂CH_ThreeIt is what.
[0064]
[Chemical 7]

[0065]
Samples 11 to 12 containing 10% by mass of TAZM or Me-TAZM by adding the above TAZM or Me-TAZM to the above-mentioned organic electrolyte solution 2 and stirring them well, and then allowing to stand at room temperature for 15 hours. Got. The ionic conductivity of lithium of these samples 11 to 12 was measured. The results are shown in Table 2.
[0066]
[Table 2]

[0067]
As shown in Table 2, the samples 11 and 12 both gelled at room temperature for 15 hours and have an ionic conductivity in the range of 2.5 to 3 mS / cm, and are electrolytes for lithium secondary batteries. As can be seen from FIG.
[0068]
As described above, it is understood that an electrolyte having a gel state and excellent ion conductivity can be obtained by adding an organic electrolytic solution containing a lithium salt and an aprotic solvent to an aziridine compound (TAZM or Me-TAZM).
[0069]
Experimental Example 3 (Discharge curve of a lithium secondary battery equipped with the electrolyte of Sample 7)
A positive electrode, a polypropylene porous separator, and a packing are disposed in a positive electrode case of a coin-type battery. The electrolyte solution (sample 7) just after adjustment is injected into this. Next, it was sealed with a negative electrode and a negative electrode lid, and allowed to stand at room temperature for 24 hours to obtain a coin-type polymer lithium secondary battery. The coin-type battery has a diameter of 20 mm and a height of 1.6 mm (CR2016 size).
The charging condition was constant current charging at a current of 0.2 C until the voltage reached 4.2 V, followed by constant voltage charging at 4.2 V for 9 hours, that is, constant current-constant voltage charging.
The discharge condition was a discharge at a constant current of 0.2 C until the voltage reached 2.75 V, that is, a constant current discharge. Hereinafter, the charge / discharge operation for one cycle under this condition is referred to as “chemical conversion”. The discharge curve of the 1st cycle charged / discharged on the same conditions as the time of formation after formation is shown in FIG.
[0070]
Further, a coin-type lithium secondary battery for comparison was produced in the same manner as described above except that the organic electrolyte solution 2 (Comparative Example 1) was used instead of the electrolyte solution (Sample 7). The battery was charged and discharged under the same conditions. The discharge curve of the first cycle after chemical conversion is also shown in FIG.
[0071]
As shown in FIG. 3, the lithium secondary battery including the electrolyte according to the present invention has almost the same voltage and discharge capacity as the lithium secondary battery including the conventional organic electrolyte, and has good characteristics. It can be seen that
[0072]
Experimental Example 4
(Rate characteristics of lithium secondary battery with electrolyte using TAZM or Me-TAZM)
LiCoO₂A positive electrode having a positive electrode active material and a negative electrode having carbon as a negative electrode active material are spirally wound through a polypropylene porous separator, and the battery size is 62 mm long, 35 mm wide, and 3.6 mm thick in FIG. A unit cell as shown was prepared and inserted into a battery container made of aluminum laminate.
A predetermined amount of the solution immediately after being added to the organic electrolyte solution and sufficiently stirred so as to contain 10% by mass of the TAZM was poured into the battery container in which the unit cell was inserted. And it sealed after liquid injection, and it was set as the gel polymer lithium secondary battery of the sample 13 by leaving it to stand for 24 hours.
Similarly, a predetermined amount of a solution immediately after being added to the organic electrolyte and sufficiently stirred so as to contain 10% by mass of the Me-TAZM was poured into a battery container in which the unit cell was inserted. And it sealed after liquid injection, and it was set as the gel polymer lithium secondary battery of the sample 14 by leaving it to stand for 24 hours.
The organic electrolyte used in the preparation of Samples 13 and 14 was 1.3 mol / L LiPF in a mixed solvent of EC: DEC = 3: 7.₆What was dissolved was used.
Further, in the same manner as in the gel polymer lithium secondary battery, except that the organic electrolyte was directly poured into a battery container in which a unit cell was inserted without adding TAZM or Me-TAZM. A lithium secondary battery was produced.
[0073]
About each obtained lithium secondary battery, after the chemical conversion, the constant current discharge after constant current-constant voltage charge was performed, and the rate test which measures discharge capacity was done. In the rate test, the constant current-constant voltage charging condition was a constant current charging at a current of 0.5 C until the voltage reached 4.2 V, and then a constant voltage charging at 4.2 V for 3 hours. The condition for the constant current discharge was to discharge at a predetermined constant current (discharge rate) until the voltage reached 2.75V.
For the gel polymer lithium secondary batteries of Samples 13 and 14, the results of the rate test performed at a discharge rate of 0.2 C are shown in FIG. Moreover, about the lithium secondary battery using the organic electrolyte solution of the comparative example 2, the result of the rate test done by the discharge rate 0.2C, 1.0C, and 2.0C was combined with FIG.
[0074]
As shown in FIG. 5, the lithium secondary battery provided with the electrolytes of Samples 13 and 14 has a slightly lower discharge capacity than the lithium secondary battery using the organic electrolyte solution of Comparative Example 2, but still has sufficient discharge. It has been found that even if TAZM or Me-TAZM is present in the battery, the rate characteristics are not adversely affected.
[0075]
Experimental Example 5 (Characteristics of lithium secondary battery with electrolyte using TAZM)
LiCoO₂A positive electrode having a positive electrode active material and a negative electrode having carbon as a negative electrode active material are spirally wound through a polypropylene porous separator, and the battery size is 62 mm long, 35 mm wide, and 3.6 mm thick in FIG. A unit cell as shown was prepared and inserted into a battery container made of aluminum laminate.
A predetermined amount of a solution immediately after stirring and adding to the organic electrolyte so as to contain 2, 5, 7.5, and 10% by mass of the TAZM was poured into the battery container in which the unit cell was inserted. And after pouring, it sealed, and it was set as the polymer lithium secondary battery by leaving it to stand for 24 hours.
The organic electrolyte is a 1.3 mol / L LiPF in a mixed solvent of EC: DEC = 3: 7.₆What was dissolved was used.
Further, a lithium secondary battery (for comparison) (for comparison) was prepared in the same manner as the polymer lithium secondary battery except that the organic electrolyte was directly poured into a battery container in which a unit cell was inserted without adding TAZM. TAZM was 0 mass%).
[0076]
When the polymer lithium secondary battery using TAZM contained 2% by mass of TAZM, it did not gel after being left at room temperature for 96 hours. Further, in the case where 5% by mass of TAZM was contained, gelation occurred by leaving it to stand at room temperature for 96 hours. Furthermore, in the case where TAZM was contained at 7.5% and 10% by mass, gelation occurred by leaving it at room temperature for 24 hours.
[0077]
About each obtained lithium secondary battery, the rate test was done on the same conditions as the case of Experimental example 4 after chemical conversion. FIG. 6 shows the results obtained at discharge rates of 0.2C, 0.5C, and 1.0C.
As shown in FIG. 6, as the discharge rate increases, the decrease in discharge capacity increases as the TAZM content increases. However, even when the discharge rate is 0.5 C, there is no great difference in discharge capacity between a battery containing TAZM and a battery containing no TAZM, and the lithium secondary battery according to the present invention also has good characteristics. I found out.
That is, it was found that even if TAZM is present in the battery, the rate characteristics are not adversely affected.
[0078]
Experimental Example 6 (Characteristics according to lithium salt concentration of a lithium secondary battery equipped with an electrolyte using TAZM)
LiCoO₂A positive electrode having a positive electrode active material and a negative electrode having carbon as a negative electrode active material are spirally wound through a polypropylene porous separator, and the battery size is 62 mm long, 35 mm wide, and 3.6 mm thick in FIG. A unit cell as shown was prepared and inserted into a battery container made of aluminum laminate.
A predetermined amount of the solution immediately after being added to the organic electrolyte so as to contain 5% by mass of the TAZM and sufficiently stirred was poured into a battery container into which the unit cell was inserted. And after pouring, it sealed, and it was set as the polymer lithium secondary battery by leaving it to stand for 24 hours.
The organic electrolyte is mixed with EC: DEC = 3: 7 in different concentrations of LiPF.₆Three types were used in which was dissolved. LiPF₆The concentration of was 1.0, 1.3, and 1.5 mol / L (M).
Further, without adding TAZM, 1.3 mol / L (M) of LiPF in a mixed solvent of EC: DEC = 3: 7₆Lithium secondary battery for comparison (TAZM is 0% by mass) in the same manner as the above polymer lithium secondary battery, except that the organic electrolyte solution in which the electrolyte is dissolved is directly poured into the battery container in which the unit cell is inserted. Was made.
[0079]
About each obtained lithium secondary battery, the rate test was done on the same conditions as the case of Experimental example 4 after chemical conversion. FIG. 7 shows the results obtained at discharge rates of 0.2C, 0.5C, 1.0C, and 2.0C.
[0080]
As shown in FIG. 7, when the discharge rate increases, LiPF₆It can be seen that the decrease in discharge capacity increases as the concentration of.
Thus, in the case of the lithium secondary battery of the present invention, it was found that a relatively high discharge capacity was exhibited even at a high rate discharge of 2C by setting the concentration of the lithium salt high.
[0081]
Experimental Example 7 (Electrolyte using TAZO)
As a gel-forming compound, tetramethylolmethane-tri-β-aziridinylpropionate shown in [Chemical Formula 8], which is an aziridine compound, and R in the above [Chemical Formula 3]₂A mixture (hereinafter referred to as TAZO) prepared by mixing a compound in which H is H with a ratio of 25:75 was prepared.
This was added to the organic electrolyte and stirred sufficiently, and then allowed to stand at room temperature to obtain an electrolyte containing TAZO in 1, 2, 3, 5, 10% by mass.
As an organic electrolyte, 1.3 mol / L LiPF in a mixed solvent of EC: DEC = 3: 7₆What was dissolved was used.
As a result, the electrolyte containing 3, 5, and 10% by mass of TAZO gelled within 15 hours at room temperature. The electrolyte containing 2% by mass of TAZO turned into a soft gel after standing at room temperature for 36 hours. Further, the electrolyte containing 1% by mass of TAZO became a viscous liquid after being left at room temperature for 48 hours. That is, it was found that the gelation sufficiently proceeds when 3% by mass of TAZO is contained.
Next, when an electrolyte containing 3% by mass of TAZO after gelation was allowed to stand at 100 ° C. for 1 hour, no liquefaction was observed. From this, it was found that if 3% by mass of TAZO was contained, a stable gel was formed and it did not liquefy at high temperatures.
[0082]
[Chemical 8]

[0083]
Experimental Example 8
(Rate characteristics of lithium secondary battery with electrolyte using TAZO)
LiCoO₂A positive electrode having a positive electrode active material and a negative electrode having carbon as a negative electrode active material are spirally wound through a polypropylene porous separator, and the battery size is 62 mm long, 35 mm wide, and 3.6 mm thick in FIG. A unit cell as shown was prepared and inserted into a battery container made of aluminum laminate.
A predetermined amount of the solution immediately after being added to the organic electrolyte solution and sufficiently stirred so as to contain 3, 4, and 5% by mass of the TAZO was poured into a battery container into which the unit cell was inserted. And after injecting, it sealed, and it was set as the gel polymer lithium secondary battery by leaving it to stand for 24 hours.
As in Experimental Example 7, the organic electrolyte was a 1.3 mol / L LiPF in a mixed solvent of EC: DEC = 3: 7.₆What was dissolved was used.
In addition, a lithium secondary battery for comparison was prepared in the same manner as the gel polymer lithium secondary battery except that the organic electrolyte was directly poured into a battery container in which a unit cell was inserted without adding TAZO. Was made.
[0084]
About each obtained lithium secondary battery, the rate test was done on the same conditions as the case of Experimental example 4 after chemical conversion. FIG. 8 shows the results obtained when the discharge rates were 0.2C, 0.5C, 1.0C, and 2.0C.
[0085]
As shown in FIG. 8, the gel polymer lithium secondary battery provided with an electrolyte (3% TAZO, 4% TAZO, 5% TAZO) containing 3, 4, and 5% by mass of TAZO at a discharge rate of 2.0C. The discharge capacity decreases as the TAZO content increases, compared to a lithium secondary battery using an organic electrolyte solution (liquid blank) that does not contain TAZO.
However, it was found that when the discharge rate was 1.0 C or less, the decrease in the discharge capacity of each gel polymer lithium secondary battery was small, and the discharge capacity was practically sufficient.
In particular, the discharge capacity of the gel polymer lithium secondary battery with an electrolyte containing 3% by mass of TAZO (3% TAZO) is compared with that of a lithium secondary battery using an organic electrolyte (liquid blank) that does not contain TAZO. Thus, it was found that there was almost no fading at a discharge rate of 1.0 C or less, and even if TAZO was present in the battery, the rate characteristics were not adversely affected.
[0086]
Experimental Example 9
(Cycle characteristics of lithium secondary battery with electrolyte using TAZO)
LiCoO₂A positive electrode having a positive electrode active material and a negative electrode having carbon as a negative electrode active material are spirally wound through a polypropylene porous separator, and the battery size is 62 mm long, 35 mm wide, and 3.6 mm thick in FIG. A unit cell as shown was prepared and inserted into a battery container made of aluminum laminate.
A predetermined amount of a solution immediately after being added to the organic electrolyte solution and sufficiently stirred so as to contain 3% by mass of the TAZO was poured into a battery container into which the unit cell was inserted. And after injecting, it sealed, and it was set as the gel polymer lithium secondary battery by leaving it to stand for 24 hours.
As in Experimental Examples 7 and 8, the organic electrolyte was 1.3 mol / L LiPF in a mixed solvent of EC: DEC = 3: 7.₆What was dissolved was used.
In addition, a lithium secondary battery for comparison was prepared in the same manner as the gel polymer lithium secondary battery except that the organic electrolyte was directly poured into a battery container in which a unit cell was inserted without adding TAZO. Was made.
[0087]
About each obtained lithium secondary battery, after forming, it was constant-current charged until the voltage reached 4.2 V at a current of 1 C, and then charged at a constant voltage of 4.2 V for 2.5 hours. Charging and discharging were conducted 100 times, and a constant current discharge was performed at a constant current of 1.0 C until the voltage reached 2.75 V, and the discharge capacity for each cycle was examined. The results are shown in FIG.
[0088]
As shown in FIG. 9, the discharge capacity of the gel polymer lithium secondary battery having an electrolyte containing 3% by mass of TAZO (3% TAZO) is an organic electrolysis that does not contain TAZO even if the charge / discharge cycle is repeated 100 times. Compared to lithium secondary batteries using liquid (liquid blank), it was found that even if TAZO is present in the battery, the cycle characteristics are not adversely affected.
In 3% TAZO of this experimental example, gelation was almost completely completed before the formation (before the first charge), so it is considered that no film was formed on the negative electrode surface during the formation.
[0089]
Experimental Example 10
(High-temperature storage characteristics of lithium secondary batteries with electrolyte using TAZO)
A gel polymer lithium secondary battery including an electrolyte containing 3% by mass of TAZO (3% TAZO) was produced under the same conditions as in Experimental Example 9. In addition, a lithium secondary battery using an organic electrolytic solution (liquid blank) not containing TAZO was produced under the same conditions as in Experimental Example 9.
[0090]
About the obtained lithium secondary battery, after chemical conversion, it experimented in the following procedures.
(1) After charging at a constant current until the voltage reached 4.2 V at a current of 1 C, constant current-constant voltage charging was performed at 4.2 V for 2.5 hours to obtain a fully charged state.
(2) It was left in an atmosphere at 85 ° C. for 4 hours.
After returning the battery of (3) and (2) to room temperature, a constant current discharge was performed at a constant current of 0.2 C until the voltage reached 2.75 V, and the discharge capacity was examined. The discharge capacity at this time is referred to as “85 ° C. 4 hr storage capacity”.
After the battery of (4) (3) is fully charged under the same conditions as in (1), the constant current discharge is performed until the voltage reaches 2.75 V at a constant current of 0.2 C, and the discharge capacity is examined. It was. The discharge capacity at this time is referred to as “recovery capacity 1”.
The batteries of (5) and (4) were again fully charged under the same conditions as in (1) and then left in an atmosphere of 85 ° C. for 24 hours.
After returning the battery of (6) (5) to room temperature, a constant current discharge was performed at a constant current of 0.2 C until the voltage reached 2.75 V, and the discharge capacity was examined. The discharge capacity at this time is referred to as “85 ° C. 24 hr storage capacity”.
After the battery of (7) and (6) is fully charged under the same conditions as in (1), a constant current discharge is performed at a constant current of 0.2 C until the voltage reaches 2.75 V, and the discharge capacity is examined. It was. The discharge capacity at this time is referred to as “recovery capacity 2”.
The above results are shown in FIG.
[0091]
As shown in FIG. 10, the storage capacity when exposed to a high-temperature atmosphere is as follows: a gel polymer lithium secondary battery having an electrolyte containing 3% by mass of TAZO (3% TAZO), and an organic electrolyte not containing TAZO No significant difference was observed with the lithium secondary battery using (liquid blank), and it was found that even if TAZO was present in the battery, the high-temperature storage characteristics were not adversely affected.
[0092]
Experimental Example 11
(Cycle characteristics of lithium secondary battery without electrolyte gel)
LiCoO for the positive electrode case of the coin-type battery₂A positive electrode using a positive electrode active material, a porous polypropylene separator, and a packing are disposed.
Immediately after adding TAZM to the organic electrolyte so as to contain 0.2, 0.5, 1.0% by mass of TAZM or 0.2, 0.5, 1.0% by mass of TAZ and sufficiently stirring Pour the solution.
Next, it was sealed with a negative electrode and a negative electrode lid to form a coin-type lithium secondary battery. The coin-type battery has a diameter of 20 mm and a height of 1.6 mm (CR2016 size). This was left for 24 hours at room temperature, but none of the electrolytes gelled.
The organic electrolyte is a 1.3 mol / L LiPF in a mixed solvent of EC: DEC = 3: 7.₆What was dissolved was used.
In addition, a lithium for comparison was made in the same manner as the above lithium secondary battery, except that the organic electrolyte was directly poured into a positive electrode case in which a positive electrode, a separator, and a packing were arranged without adding TAZM and TAZO. A secondary battery (liquid blank) was produced.
[0093]
About each obtained lithium secondary battery, after forming, it was constant-current charged until the voltage reached 4.2 V at a current of 1 C, and then charged at a constant voltage of 4.2 V for 2.5 hours. A charge / discharge cycle in which charging was performed and constant current discharging was performed at a constant current of 1.0 C until the voltage reached 2.75 V was repeated 100 times, and the discharge capacity for each cycle was examined. The results are shown in FIG.
[0094]
As shown in FIG. 12, in a lithium secondary battery including an electrolyte (1.0% TAZM, 1.0% TAZO) containing 1.0% by mass of TAZM or TAZO, after about 50th cycle, TAZM It was also found that a higher discharge capacity can be obtained than a lithium secondary battery using an organic electrolytic solution (liquid blank) that does not contain TAZO. This is presumably because the presence of TAZM or TAZO forms a coating on the negative electrode surface and suppresses the reaction between the negative electrode and the electrolyte.
In addition, in a lithium secondary battery equipped with an electrolyte containing 0.5% by mass of TAZM or TAZO (0.5% TAZM, 0.50% TAZO), an organic material that does not contain TAZM or TAZO after about 50 cycles. An almost same discharge capacity as that of a lithium secondary battery using an electrolytic solution (liquid blank) was obtained, but an electrolyte containing 0.2% by mass of TAZM or TAZO (0.2% TAZM, 0.2% TAZO). In the lithium secondary battery provided with the battery, only a discharge capacity lower than that of the lithium secondary battery using the organic electrolyte (liquid blank) not containing TAZM or TAZO was obtained throughout the entire cycle. Thus, it was found that at least 0.2% by mass of TAZM or 0.5% by mass of TAZO is necessary to obtain the effect of improving the cycle characteristics.
[0095]
Experimental Example 12
(Cycle characteristics of lithium secondary battery without electrolyte gel)
LiCoO₂A positive electrode having a positive electrode active material and a negative electrode having carbon as a negative electrode active material are spirally wound through a polypropylene porous separator, and the battery size is 62 mm long, 35 mm wide, and 3.6 mm thick in FIG. A unit cell as shown was prepared and inserted into a battery container made of aluminum laminate.
In a battery container in which this unit cell is inserted, the above-mentioned TAZM is added to the organic electrolyte so as to contain 0.2, 0.5, 1.0% by mass, or 0.5, 1.0% by mass of TAZO. A predetermined amount of the solution immediately after sufficiently stirring was injected. And after sealing, it was sealed and allowed to stand for 24 hours to make a lithium secondary battery, but neither electrolyte gelled.
The organic electrolyte is a 1.3 mol / L LiPF in a mixed solvent of EC: DEC = 3: 7.₆What was dissolved was used.
Further, a lithium secondary battery for comparison was prepared in the same manner as the lithium secondary battery, except that the organic electrolyte was directly poured into a battery container in which a unit cell was inserted without adding TAZM and TAZO. (Liquid blank) was produced.
[0096]
About each obtained lithium secondary battery, after forming, it was constant-current charged until the voltage reached 4.2 V at a current of 1 C, and then charged at a constant voltage of 4.2 V for 2.5 hours. A charge / discharge cycle in which charging was performed and constant current discharging was performed at a constant current of 1.0 C until the voltage reached 2.75 V was repeated 100 times, and the discharge capacity for each cycle was examined. The results are shown in FIG.
[0097]
As shown in FIG. 13, an electrolyte containing 0.5% by mass or 1.0% by mass of TAZM (0.5% TAZM, 1.0% TAZM), or an electrolyte containing 1.0% by mass of TAZO (1 The lithium secondary battery with 0.0% TAZO) has a higher discharge capacity than the lithium secondary battery using an organic electrolyte (liquid blank) that does not contain TAZM or TAZO after the fifth cycle. I understood. This is presumably because the presence of an appropriate amount of TAZM or TAZO forms a coating on the negative electrode surface and suppresses the decomposition reaction of the electrolyte on the negative electrode surface.
On the other hand, in the lithium secondary battery including the electrolyte containing 0.2% by mass of TAZM (0.2% TAZM) or the electrolyte containing 0.5% by mass of TAZO (0.5% TAZO), the 10th cycle From near to later, a discharge capacity slightly lower than that of a lithium secondary battery using an organic electrolyte (liquid blank) containing no TAZM or TAZO was obtained.
Thereby, by containing at least 0.2% by weight, preferably 0.5% by weight or more of TAZM, or more than 0.5% by weight, preferably 1.0% by weight or more of TAZO, It was found that the effect of improving the cycle characteristics can be obtained.
In addition, it is considered that the effect of improving the cycle characteristics more markedly than that of Experimental Example 11 was obtained because the wound lithium secondary battery shown in FIG. 4 was used in this Experimental Example, and pressure was applied uniformly between the electrodes. It is done.
[0098]
【The invention's effect】
As described above in detail, the electrolyte of the present invention is formed using an electrolyte material in which an aziridine compound having an aziridine ring and an organic electrolytic solution obtained by dissolving a lithium salt in an aprotic solvent are mixed at least. Since the gel is formed by simply mixing the aziridine compound and the organic electrolyte, a stable electrolyte can be obtained even at high temperatures.
Moreover, in the lithium secondary battery using such an electrolyte, the decomposition reaction of the electrolyte on the negative electrode surface is suppressed, and excellent cycle characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a fine structure of an electrolyte according to an embodiment of the present invention.
FIG. 2 is a schematic view showing a fine structure of an electrolyte according to an embodiment of the present invention.
3 is a discharge curve of the first cycle after the formation of a lithium secondary battery including the electrolyte of Sample 7. FIG.
FIG. 4 is a perspective view of a unit cell.
FIG. 5 is a graph showing a relationship between a discharge rate and a discharge capacity of a lithium secondary battery including the electrolytes of Samples 13 and 14.
FIG. 6 is a graph showing a relationship between a discharge rate and a discharge capacity of a lithium secondary battery including an electrolyte containing 0 to 10% by mass of TAZM.
FIG. 7: 1.0-1.5 mol / L LiPF₆It is a graph which shows the relationship between the discharge rate and discharge capacity of a lithium secondary battery provided with the electrolyte which consists of an organic electrolyte solution containing.
FIG. 8 is a graph showing the relationship between the discharge rate and the discharge capacity of a lithium secondary battery having an electrolyte containing 0 to 5% by mass of TAZO.
FIG. 9 is a graph showing cycle characteristics of a lithium secondary battery including an electrolyte containing 3% by mass of TAZO.
FIG. 10 is a graph showing high-temperature storage characteristics of a lithium secondary battery including an electrolyte containing 3% by mass of TAZO.
FIG. 11 is an explanatory diagram of a mechanism for forming a coating film on the negative electrode.
FIG. 12 is a graph showing cycle characteristics of a lithium secondary battery including a non-gelled electrolyte containing TAZO or TAZM.
FIG. 13 is a graph showing cycle characteristics of a lithium secondary battery including a non-gelled electrolyte containing TAZO or TAZM.

Claims (11)

An electrolyte formed by using an aziridine compound having one or more aziridine rings and an organic electrolyte obtained by dissolving a lithium salt in an aprotic solvent or at least a gel-forming electrolyte material mixed , An electrolyte characterized in that the component forming the gel is only lithium contained in the aziridine compound and the lithium salt . 2. The electrolyte according to claim 1, wherein the aziridine compound includes at least one represented by a structural formula represented by the following [Chemical Formula 1].
However, in the following structural formula, R ₁ is any _one of H, CH ₃ , and OH, and R ₂ is either one of H or CH ₃ .

The said aprotic solvent contains 1 or more types in ethylene carbonate, butylene carbonate, propylene carbonate, (gamma) -butyrolactone, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate, The Claim 1 or Claim 2 characterized by the above-mentioned. The electrolyte described. The lithium _{salt, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, LiClO 4, LiCF 3 SO 3, Li (CF 3 SO 2) 2 N, LiC 4 F 9 SO 3, LiSbF 6, LiAlO 4, LiAlCl 4 _{, LiN (C x F 2x +} 1 SO 2) (C y F 2y _{tens 1} SO ₂₎ (provided that x, y are natural numbers) according to claim 1 to claim, characterized in that it is intended to include one or more of 4. The electrolyte according to any one of 3. 5. The electrolyte according to claim 1, wherein the content of the aziridine compound in the electrolyte material is in a range of more than 0.2 mass% and 20 mass% or less. The electrolyte according to any one of claims 1 to 5, wherein a gel is formed by the aziridine compound and the organic electrolytic solution. The electrolyte according to claim 6, wherein a part or all of the gel is formed by coordination of a plurality of the aziridine rings with lithium contained in the lithium salt. 7. A part or all of the gel is formed by impregnating the organic electrolyte in a polymer of the aziridine compound formed by cleaving the aziridine ring. The electrolyte according to 1. A lithium secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, and an electrolyte, wherein the electrolyte is the electrolyte according to any one of claims 1 to 8. The lithium secondary battery according to claim 9, wherein a coating containing the aziridine compound as a main component is formed on a surface of the negative electrode. A lithium secondary battery comprising a positive electrode and a negative electrode capable of occluding and releasing lithium, and an electrolyte, wherein a film mainly composed of an aziridine compound is formed on a surface of the negative electrode.

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