JP3826452B2 - Polymer electrolyte and its production method - Google Patents

Description

【００１０】
この架橋構造は無定形高分子のイオン導電率を大きく低下させることなく機械的特性を向上させるために手段として非常に有効である。しかしながら、このような手段でも十分な成果を得るには至っていない。
【００１１】
一方、複合体膜の構成有機高分子ＰＥＯの分子量を１００００以下にすることによって室温近傍の温度領域でイオン導電率を向上させることができるが、この場合には成膜性が著しく低下し、フィルム化が困難となる。
【００１２】
また、イオン導電率を向上させるためにアルカリ金属塩の含有濃度を高くした場合には、複合体膜のガラス転移点Ｔｇも上がってしまい、そのためにイオン導電性が低下してしまう。このようにキャリア体の密度の増加と導電率の増加を同時に達成することはできない。
【００１３】
他の高分子電解質としては、上述のＰＥＯおよびアルカリ金属塩を用いた複合体膜の類似化合物で、化学式（３）
【化３】

で示されるように、側鎖にＰＥＯ構造を有するアクリル系およびメタクリル系の有機高分子が知られている。また、化学式（４）
【化４】

で示されるように、側鎖にＰＥＯ構造を有し、主鎖として−Ｐ＝Ｎ−からなるポリホスファゼン系の有機高分子や、化学式（５）
【化５】

で示されるように、側鎖にＰＥＯ構造を有し、主鎖として−Ｓｉ−Ｏ−からなるシロキサン系の有機高分子が知られている。
【００１４】
これらの有機高分子とアルカリ金属塩からなる高分子電解質のイオン導電率は〜１０^−５Ｓｃｍ^−１程度であり、ＰＥＯとアルカリ金属塩からなる複合体膜に比べてやや改善されているが、実用上はまだ不十分である。また、成膜性や可撓性も十分なものとはなっていない。
【００１５】
一方、前述のような有機高分子と金属塩とからなる高分子（固体）電解質以外に、有機高分子と金属塩とさらに金属塩を溶解する有機溶媒とからなる高分子電解質が開発されている。言い換えると前述の高分子電解質に有機溶媒をさらに膨潤させたものである。なお、この際、有機溶媒を膨潤しても高分子自体が溶解してしまうことがないように、活性放射線、光、電子戦、加熱などによって架橋させるなどの改良も施されている。
【００１６】
これらは一般に有機溶媒を含まない高分子（固体）電解質に比べて、導電率は〜１０^−３Ｓ／ｃｍ程度と非常に高いものが得られる。さらに、有機溶媒は高分子中に膨潤され、高分子ゲルを形成するようになるため、圧力をかけても液体成分が染み出ることもなく、比較的良好な膜性を有する。
【００１７】
しかしながら、従来の有機溶媒と金属塩からなる電解液に比べ、その導電率は低く、さらに機械的強度の高いものが求められているのが実情である。
【００１８】
本発明の課題は、このような従来技術の問題点を解決しようとするものであり、室温付近でも高いイオン導電性を発揮し、かつ成膜性、機械的強度、柔軟性にも優れた高分子電解質を得ることである。
【００１９】
【課題を解決するための手段】
本発明者らは５員環状カーボネート基を官能基とする構造を側鎖の一部として有する有機高分子が本発明の課題を解決する材料として有望と考えた。
すなわち、前記有機高分子は５員環状カーボネート官能基を含有するために、従来技術に比べて高密度でキャリアイオンを含有させることができ、さらにその官能基が主鎖よりもより快活なセグメント運動する側鎖部にあるために、低温状態でも結晶化しにくく、そのため無定形状態を保持することによる十分なセグメント運動を確保することができる特長を有することを知見した。
【００２０】
そして、この５員環状カーボネート基を官能基とする構造を側鎖の一部として有する有機高分子を高分子電解質の構成材料として使用することにより、本発明の課題が達成できることを見い出し、本発明を完成させるに至った。
【００２１】
また、本発明は、５員環状カーボネート基を官能基とする構造を側鎖の一部として有する有機高分子とアルカリ金属塩とからなる高分子（固体）電解質に有機溶媒を少量加えたことを特徴とする高分子電解質である。
【００２２】
本発明において使用する有機高分子としては、化学式（１）
【化１】

で示されるポリ［４−（１−プロペニルオキシメチル）−１，３−ジオキサン−２−オン］（通称ポリ（プロペニル−プロピレンカーボネート−エーテル）、以下ＰＰｐＰＣＥと略す）を使用する。
【００２３】
ポリ（プロペニル−プロピレンカーボネート−エーテル）は、例えばカチオン重合法や配位重合法などを用いることにより容易に得ることができる。このような５員環状カーボネート基を官能基とする構造を側鎖の一部として有する有機高分子を用いることにより、高分子電解質中にキャリアイオンを高濃度で含有させた状態においても高イオン伝導性を実現でき、さらに良好な成膜性をおよび可撓性を同時に実現することができる。
【００２４】
さらに、有機溶媒を少量これに膨潤させることにより、成膜性を低下させることなく、より一層の高伝導性を実現することができる。
【００２５】
本発明の５員環状カーボネート基を官能基とする構造を側鎖の一部として有する有機高分子の平均分子量は、低すぎると固体とならず、成膜が低下してしまい、また高すぎても有機溶媒に溶けにくくなり、さらに柔軟性が低下する。そこで、本発明の有機高分子の平均分子量は１０^３〜１０^６の範囲とすることが望ましい。
【００２６】
また、本発明において使用する５員環状カーボネート基を官能基とする構造を側鎖の一部として有する有機高分子を単独で用いるだけでなく、これらと相溶性のある他の高分子とブレンドすることにより得られるポリマーブレンドを使用することもできる。
【００２７】
このような他の高分子としては、例えばＰＥＯや化学式（２）〜（５）で示される有機高分子、ポリアクリロニトリル（ＰＡＮ）、ポリメタクリル酸メチル（ＰＭＭＡ）などの従来から高分子電解質に用いられてきた有機高分子、また５員環状カーボネート基を官能基とする構造を有する類似高分子や鎖状カーボネート基を介し、直鎖または分岐メチレンにより結合した有機高分子などを使用することができる。ブレンドの割合としては、必要な導電率やフィルムの柔軟性などに応じて適宜選択することができる。
【００２８】
本発明における高分子電解質を構成する金属塩としては従来の高分子電解質に用いられているものも使用可能であり、例えばリチウム塩ではＬｉＢｒ、ＬｉＩ、ＬｉＳＣＮ、ＬｉＢＦ_４、ＬｉＡｓＦ₆、ＬｉＣＩＯ_４、ＬｉＣＦ_３ＳＯ_３、ＬｉＰＦ_６、ＬｉＮ（ＣＦ_３ＳＯ_２）_２、ＬｉＣ（ＣＦ_３ＳＯ_２）_３などが挙げられる。また、これらのリチウム塩のアニオンと、リチウム塩以外のアルカリ金属塩、例えばカリウム、ナトリウムなどの塩を使用することもできる。この場合、塩としては複数の塩を同時に使用してもよい。
【００２９】
高分子電解質を構成する金属塩と有機高分子の比率は、使用する金属塩の種類や有機高分子の誘導体の種類などにより異なるが、有機高分子の全構成モノマーユニット当たりの金属塩の分子比（モル比）を［塩の金属イオン］／［ｍｏｎｏｍｅｒ ｕｎｉｔ］で表した場合に
［塩の金属イオン］／［ｍｏｎｏｍｅｒ ｕｎｉｔ］＝０．０２〜０．８
の範囲とすることが好ましい。この比が低すぎると導電率が低下してしまい、高すぎると塩の析出による成膜性が低下する。
【００３０】
本発明の高分子電解質は、常法により製造することができるが、好ましくは、以上のような有機高分子と金属塩とを、溶媒に均一に溶解させることによって得られる。
【００３１】
一般に、本発明の高分子電解質は膜の形態で使用するが、成膜する方法は常法によることができる。例えば、有機系のキャスト溶媒に有機高分子と金属塩とを溶解し、この溶液を平坦な基板に広げ、溶媒を蒸発させることにより複合体フィルムを得るというキャスト法により成膜することができる。この場合、キャスト溶媒としては高分子および金属塩ともに溶解させることができる溶媒、例えばジメチルホルムアミド（ＤＭＦ）やＮ−メチルピロリドン（ＮＭＰ）、プロピレンカーボネート（ＰＣ）など適度に極性を有する有機溶媒を適宜しようすることができる。
【００３２】
また、本発明の有機溶媒を膨潤した高分子電解質は常法によって得ることができる。例えば、前述の手法によって得られた高分子電解質フィルムを有機溶媒中に浸し、所定量の有機溶媒を含んだ時点で引き上げる様な方法や、キャスト溶媒を完全に蒸発させず、適当量の溶媒を残存させた状態で使用する方法などが挙げられる。
【００３３】
ここに用いる有機溶媒としては、前記のキャスト溶媒として用いたものや、一般的にリチウム系の非水電解液として用いられているような、エチレンカーボネート（ＥＣ）、ジメトキシエタン（ＤＭＥ）、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、メチルエチルカーボネート（ＭＥＣ）など適宜使用することが可能であり、さらにこれら有機溶媒を同時に複数使用することも可能である。
【００３４】
有機溶媒の含有量に関しては必ずしも限定されるものではないが、含有量が高くなるほど導電率も高くなる傾向が見られるものの、ある量以上含有されると膜性（自己支持性）が低下し、粘着体の様相を呈するようになる。したがって、使用目的に合致する膜性と導電率とにより選択することが可能となる。なお、有機高分子の平均分子量が高くなるほど、有機溶媒の含有量が高くなっても膜性の低下が抑えられる傾向が見られることから、本発明の有機溶媒を含む高分子電解質の場合には高分子の平均分子量が高いほど導電率が高いものが得られる。
【００３５】
本発明の高分子電解質は、５員環状カーボネート基を官能基とする構造を側鎖の一部として有する有機高分子を含有するので、キャリアイオンとなる金属塩を高濃度で高分子電解質中に含有させることが可能となる。したがって、高イオン導電性と成膜性および可撓性を同時に実現することが可能となる。
【００３６】
【発明の実施の形態】
以下、本発明の実施の形態について説明する。
実施例１
［ポリ（プロペニル−プロピレンカーボネート−エーテル）（ＰＰｐＰＣＥ）の合成］
三方活せんを付した３００ｍｌのガラス反応容器にジクロロメタン１００ｍｌ、プロペニル−プロピレンカーボネート−エーテル２０ｇを秤取し、−７８℃に冷却する。これに０．１ｍｏｌ／リットルの濃度のＢＦ_３Ｏ（Ｃ_２Ｈ_５）_２のジクロロメタン溶液を２．５ｍｌ加える。３時間の反応の後、反応溶液に冷却したエタノールを添加して重合を停止させ、大量の冷却したエタノールに反応溶液を注いで生成した白色の高分子を沈澱させる。エタノールで十分に洗浄し、減圧乾燥によって高分子を精製する。
【００３７】
その結果、収率はほぼ１００％で所期の有機高分子を得た。この有機高分子をＦＴ−ＩＲおよびＣＤＣｌ_３中^１Ｈ−ＮＭＲで同定し、確認した。
【００３８】
またこの有機高分子の平均分子量はモノマーの仕込み濃度、反応時間で抑制することが比較的容易であり、種々の条件で作製した有機高分子の平均分子量はゲルパーミエーションクロマトグラフィー（ＧＰＣ）により測定したが、その結果平均分子量は１×１０^３〜１×１０^６程度であった。
【００３９】
［高分子固体電解質フィルムの作製］
上記方法で得られた有機高分子ＰＰｐＰＣＥを十分に脱水したＤＭＦ中に添加し、十分に撹拌して均一溶液とし、さらに撹拌しながらＬｉＣｌＯ_４を有機高分子の全構成モノマーに対して、［Ｌｉ^＋］／［ｍｏｎｏｍｅｒ ｕｎｉｔ］＝０．７となるように加え、さらに完全に溶解するまでしばらく撹拌を続ける。その後、孔径０．４５μｍのフィルターを通し、不溶物を除去し、キャスト法により成膜した。すなわち、溶液を底面が平滑なテフロン製シャーレに移し入れ、窒素雰囲気下、４０〜６０℃の温度範囲で設定された恒温器中で溶媒を蒸発させ、さらに真空加熱下で溶媒を完全に除去し、乾燥させ、高分子電解質フィルムを得た。
【００４０】
こうして得られた高分子電解質フィルムは可撓性に富んだ無色〜淡黄色のフィルムであり、その膜厚は目的に応じ、適宜作製することができるが、導電率を評価するものとしては５０〜１５０μｍのものを用いた。
【００４１】
［イオン導電率の評価］
上記方法で得られた高分子電解質フィルムのイオン導電率の評価を次のように行った。
すなわち、高分子電解質フィルムを白金電極あるいはリチウム金属電極で圧着し、数時間、９０℃で加熱保存することによって、電極／フィルム／電極の各接触が十分に保たれるようにする。その後、定電圧複素インピーダンス法により得られた半円弧部からイオン導電率を解析的に算出した。
【００４２】
なお、これらの測定は温度可変式の恒温装置の中に評価セルを入れ、任意の温度で約１時間要して定常状態にした後に行った。この場合、得られる複数個の疑似半円弧成分を電極を白金、リチウム金属に代え、またそれらの電極面積を代えることにより高分子固体電解質中のイオン導電に寄与する抵抗部を帰属した。
【００４３】
このとき測定で用いた交流振幅電圧は３０〜１００ｍＶ程度に設定し、交流の周波数帯域は１０^−２〜１０^７Ｈｚで行った。上記のようにして−１０〜９０℃の領域で求められた導電率の温度依存性について図１に示す。
【００４４】
図１の結果から、本発明の高分子電解質フィルムは従来のＰＥＯおよび他の有機高分子とアルカリ金属塩との複合体フィルムに比べて、室温近傍の温度領域における導電率が著しく高いことが確認できた。また、成膜性、機械的強度および柔軟性も十分なものであった。
【００４５】
実施例２〜５
ＬｉＣｌＯ_４の添加量を図２のように変える以外は実施例１と同様にして、ＰＰｐＰＣＥによる高分子電解質を作製し、−１０〜９０℃の領域で求められた導電率依存性について図１に示す。
【００４６】
図１から明らかなように、ＬｉＣｌＯ_４の添加量が［Ｌｉ^＋］／［ｍｏｎｏｍｅｒ ｕｎｉｔ］＝０．３以下の低濃度の場合、導電率は低いという傾向がある。
【００４７】
一方、［Ｌｉ^＋］／［ｍｏｎｏｍｅｒ ｕｎｉｔ］＝０．５〜１．０で得られた高分子電解質フィルムは柔軟性に富んだ、良好なフィルムであり、導電率は著しく増加する傾向を示す。さらに、ＬｉＣｌＯ_４の添加量が［Ｌｉ^＋］／［ｍｏｎｏｍｅｒ ｕｎｉｔ］＝１．０よりも多くなると、キャスト溶媒を完全に除去して得られたフィルムは金属塩の析出による懸濁がおこり、金属塩と有機高分子が相溶したものが得られない。さらに、この懸濁した状態のフィルムは、導電率が低下してしまうだけでなく、柔軟性および機械的強度が著しく低下する。
【００４８】
したがって、この系では［Ｌｉ^＋］／［ｍｏｎｏｍｅｒ ｕｎｉｔ］＝０．１〜１．０の範囲であることが好ましく、さらに好ましくは［Ｌｉ^＋］／［ｍｏｎｏｍｅｒ ｕｎｉｔ］＝０．５〜１．０であることが望ましい。
【００４９】
実施例６〜１３
実施例１に示したＬｉＣｌＯ_４の代わりに図２に示したリチウム、ナトリウム又はカリウムなどのアルカリ金属塩を用いて、それぞれのもので［Ｍ^＋］／［Ｏ−ＣＯ−Ｏ ｕｎｉｔ］になるように塩を添加した高分子電解質を作製し、３０℃における導電率を求めた。この結果を図２に示し、ここに実施例１のＬｉＣｌＯ_４の結果も合わせて示す。
【００５０】
図２から明らかなように、アルカリ金属塩を代えても得られた高分子固体電解質の導電率が極度に低下することなく、従来の高分子固体電解質のイオン導電率と比較して、室温（３０℃）においても高い値を示す。なお、いずれも成膜性の低下は見られなかった。
【００５１】
実施例１４〜１６
実施例１のＰＰｐＰＣＥにＬｉＣｌＯ_４を［Ｌｉ^＋］／［ｍｏｎｏｍｅｒ ｕｎｉｔ］＝０．７となるように含有させた高分子電解質にプロピレンカーボネート（ＰＣ）を添加したものを作製した。ＰＣの添加量はＰＰｐＰＣＥとＬｉＣｌＯ_４とからなる高分子電解質の重量に対して０．１倍、０．５倍及び１．０倍となるようにし、−１０〜９０℃の領域で求められた導電率の温度依存性について測定した結果を図３に示す。
【００５２】
図３から明らかなように、ＰＣの添加量が多くなるにしたがって、導電率は高くなるとともに、低温側での導電率の低下も小さくなる。しかしながら、添加量が多くなると高温で固体状態を保持できず、溶解してしまい、流動性をもってしまう。したがって、使用目的とする温度領域と膜の状態とに合う状態で、ＰＣの添加量が多い方が望ましい。
【００５３】
【発明の効果】
本発明によれば、従来の高分子固体電解質と比較して、室温付近でも高いイオン導電性を発揮し、かつ成膜性、機械的強度及び柔軟性にも優れた高分子固体電解質を得ることが可能となる。
【図面の簡単な説明】
【図１】 ＰＰｐＰＣＥ／ＬｉＣｌＯ_４系高分子固体電解質における塩濃度を変化された時の導電率の温度依存性を示す図である。
【図２】 ＰＰｐＰＣＥ系高分子固体電解質におけるアルカリ金属塩毎の導電率を示す図である。
【図３】 ＰＰｐＰＣＥ系高分子固体電解質におけるｐＰＣ含有量を変化させた場合の導電率の温度依存性を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ion conductive polymer electrolyte and a method for producing the same. More specifically, the present invention exhibits high ionic conductivity by containing an alkali metal ion-based conductive carrier such as lithium ion, and has high film forming properties, mechanical strength, and flexibility. The present invention relates to a molecular electrolyte and a method for producing the same.
[0002]
[Prior art]
When an all-solid battery is configured using a solid electrolyte, the leakage of contents in the battery, which is one of the problems of conventional batteries, is eliminated, and the safety and reliability of the battery are improved. The battery can be thinned and stacked. For this reason, solid electrolytes are attracting attention as materials for electrochemical devices such as batteries.
[0003]
By the way, as a characteristic requested | required as a solid electrolyte, generally (a) that ion conductivity is high and there is no electronic conductivity,
(B) Excellent film formability so that it can be molded thinly;
(C) excellent flexibility;
Etc.
[0004]
The types of solid electrolytes can be broadly divided into two types, those made of inorganic materials and those made of organic materials. Among these, solid electrolytes made of inorganic materials have relatively high ionic conductivity, but because they are crystalline, they have poor mechanical strength and are difficult to process into flexible films. If you do it, you are significantly disadvantaged.
[0005]
In contrast, polymer electrolytes made of organic polymers can be formed into flexible thin films, and the molded thin films are given superior mechanical properties due to the inherent flexibility of the polymers. It becomes possible to do. Therefore, a thin film made of a polymer electrolyte can be flexibly adapted to a volume change that occurs in an ion-electron exchange reaction process between an electrode and a polymer electrolyte. For these reasons, polymer electrolytes are promising as electrolyte materials for high energy density batteries, particularly thin batteries. In addition, since it can be made more flame retardant than conventional non-aqueous electrolytes based on organic solvents, it is considered promising as being able to greatly contribute to ensuring safety when the battery is enlarged.
[0006]
As such a polymer electrolyte, polyethylene oxide having a polyether structure [(—CH ₂ CH ₂ O—) _n , n is an integer of 1 or more: hereinafter abbreviated as PEO], and an alkali metal such as a Li salt or a Na salt It is known that a complex with a salt exhibits high alkali metal ion conductivity. Theoretical studies on ion transmission mechanisms and molecular structures in various polymer electrolytes including this complex, or batteries, etc. Research on application to electrochemical devices is actively underway.
[0007]
By the way, the ionic conductivity in polymer electrolytes is that the alkali metal ions in the polymer matrix selectively ionize in the amorphous part of the polymer matrix and interact with the coordinating atoms in the polymer. It is believed to be achieved by diffusing and moving along the electric field. For example, in a composite film composed of PEO and an alkali metal salt, ion transmission is shown by molecular chain segmental motion due to heat while interacting with alkali metal ions and oxygen in the ether bond portion having a high dielectric constant in the main chain. It is thought that it will become.
[0008]
[Problems to be solved by the invention]
However, polymer electrolytes generally have a problem of low ionic conductivity near room temperature compared to solid electrolytes made of inorganic materials. Furthermore, when trying to improve the ionic conductivity, there is a problem that the film formability and flexibility are lowered.
[0009]
For example, in the case of a composite film of PEO and an alkali metal salt, when the molecular weight of the constituent organic polymer is about 10,000, the film formability is excellent, and the ion conductivity is 10 ⁻³ to 10 ⁻⁴ Scm ⁻ at 100 ° C. or higher. ^It has a relatively high value of about ¹ . However, since this composite film is crystalline, the conductivity rapidly decreases at a temperature of 60 ° C. or less, and exhibits a very low value of about 10 ⁻⁷ Scm ⁻¹ or less at room temperature. For this reason, it becomes impossible to incorporate as a normal battery material in which the so-called room temperature is used. Therefore, as shown in chemical formula (2), attempts have been made to suppress the crystallinity of the composite film by reacting diisocyanate or forming ester crosslinks in order to urethane-crosslink the terminal hydroxyl groups of PEO. .
[Chemical 2]

[0010]
This cross-linked structure is very effective as a means for improving the mechanical properties without greatly reducing the ionic conductivity of the amorphous polymer. However, sufficient results have not yet been obtained by such means.
[0011]
On the other hand, by setting the molecular weight of the organic polymer PEO of the composite film to 10,000 or less, the ionic conductivity can be improved in the temperature range near room temperature. It becomes difficult.
[0012]
Moreover, when the content concentration of the alkali metal salt is increased in order to improve the ionic conductivity, the glass transition point Tg of the composite film is also increased, so that the ionic conductivity is lowered. Thus, an increase in the density of the carrier body and an increase in conductivity cannot be achieved simultaneously.
[0013]
Another polymer electrolyte is a compound compound similar to the composite film using PEO and alkali metal salt described above, which has the chemical formula (3)
[Chemical 3]

As shown, acrylic and methacrylic organic polymers having a PEO structure in the side chain are known. In addition, chemical formula (4)
[Formula 4]

As shown, a polyphosphazene-based organic polymer having a PEO structure in the side chain and -P = N- as the main chain, or a chemical formula (5)
[Chemical formula 5]

As shown, a siloxane-based organic polymer having a PEO structure in the side chain and composed of -Si-O- as the main chain is known.
[0014]
The ionic conductivity of the polymer electrolyte composed of these organic polymer and alkali metal salt is about 10 ⁻⁵ Scm ^−1, which is slightly improved as compared with the composite film composed of PEO and alkali metal salt. It is still insufficient for practical use. Further, the film formability and flexibility are not sufficient.
[0015]
On the other hand, in addition to the polymer (solid) electrolyte composed of an organic polymer and a metal salt as described above, a polymer electrolyte composed of an organic polymer, a metal salt, and an organic solvent that dissolves the metal salt has been developed. . In other words, an organic solvent is further swollen in the aforementioned polymer electrolyte. At this time, improvements such as crosslinking by actinic radiation, light, electronic warfare, heating, etc. have been made so that the polymer itself does not dissolve even when the organic solvent is swollen.
[0016]
In general, these have a conductivity as high as about 10 ⁻³ S / cm as compared with a polymer (solid) electrolyte containing no organic solvent. Furthermore, since the organic solvent swells in the polymer and forms a polymer gel, the liquid component does not exude even when pressure is applied, and has a relatively good film property.
[0017]
However, in reality, there is a demand for a material having a lower electrical conductivity and higher mechanical strength than an electrolytic solution comprising a conventional organic solvent and a metal salt.
[0018]
An object of the present invention is to solve such problems of the prior art, exhibit high ionic conductivity even near room temperature, and high film formation, mechanical strength, and flexibility. It is to obtain a molecular electrolyte.
[0019]
[Means for Solving the Problems]
The present inventors considered that an organic polymer having a structure having a 5-membered cyclic carbonate group as a functional group as a part of the side chain is promising as a material for solving the problems of the present invention.
That is, since the organic polymer contains a 5-membered cyclic carbonate functional group, it can contain carrier ions at a higher density than in the prior art, and the functional group is more vigorous than the main chain. It has been found that since it is in the side chain portion, it is difficult to crystallize even in a low temperature state, and therefore, it has a feature that a sufficient segment motion can be secured by maintaining an amorphous state.
[0020]
And it has been found that the object of the present invention can be achieved by using, as a constituent material of a polymer electrolyte, an organic polymer having a structure having a 5-membered cyclic carbonate group as a functional group as a part of a side chain. It came to complete.
[0021]
Further, the present invention is that a small amount of an organic solvent is added to a polymer (solid) electrolyte composed of an organic polymer having a structure having a 5-membered cyclic carbonate group as a functional group as part of a side chain and an alkali metal salt. It is a featured polymer electrolyte.
[0022]
The organic polymer used in the present invention includes a chemical formula (1)
[Chemical 1]

[4- (1-propenyloxymethyl) -1,3-dioxan-2-one] (commonly called poly (propenyl-propylene carbonate-ether), hereinafter abbreviated as PPpPCE).
[0023]
Poly (propenyl-propylene carbonate-ether) can be easily obtained by using, for example, a cationic polymerization method or a coordination polymerization method. By using an organic polymer having such a structure having a five-membered cyclic carbonate group as a functional group as a part of the side chain, high ion conduction can be achieved even in a state where carrier ions are contained at a high concentration in the polymer electrolyte. In addition, it is possible to realize excellent film forming properties and flexibility at the same time.
[0024]
Furthermore, by swelling a small amount of the organic solvent, even higher conductivity can be realized without lowering the film formability.
[0025]
The average molecular weight of the organic polymer having a structure having a five-membered cyclic carbonate group as a functional group as a part of the side chain of the present invention is too low to form a solid, resulting in reduced film formation and too high. However, it becomes difficult to dissolve in an organic solvent, and the flexibility is further reduced. Therefore, the average molecular weight of the organic polymer of the present invention is preferably in the range of 10 ³ to 10 ⁶ .
[0026]
In addition, an organic polymer having a structure having a 5-membered cyclic carbonate group as a functional group as a part of the side chain used in the present invention is not only used alone, but also blended with other polymers compatible with these. It is also possible to use polymer blends obtained by this.
[0027]
As such other polymers, for example, PEO, organic polymers represented by chemical formulas (2) to (5), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA) and the like have been conventionally used for polymer electrolytes. Organic polymers that have been used, similar polymers having a structure having a 5-membered cyclic carbonate group as a functional group, and organic polymers that are linked by linear or branched methylene via a chain carbonate group can be used. . The blend ratio can be appropriately selected according to the required conductivity, the flexibility of the film, and the like.
[0028]
As the metal salt constituting the polymer electrolyte in the present invention, those used in conventional polymer electrolytes can be used. For example, LiBr, LiI, LiSCN, LiBF ₄ , LiAsF ₆ , LiCIO ₄ , LiCF can be used for lithium salts. ₃ SO ₃ , LiPF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _{3 and the} like. In addition, anions of these lithium salts and alkali metal salts other than lithium salts, such as potassium and sodium salts, can also be used. In this case, a plurality of salts may be used simultaneously as the salt.
[0029]
The ratio of metal salt to organic polymer constituting the polyelectrolyte varies depending on the type of metal salt used and the type of organic polymer derivative, but the molecular ratio of metal salt per unit monomer unit of the organic polymer. (Molar ratio) expressed as [salt metal ion] / [monomer unit] [salt metal ion] / [monomer unit] = 0.02 to 0.8
It is preferable to set it as the range. If this ratio is too low, the electrical conductivity will decrease, and if it is too high, the film formability due to salt precipitation will decrease.
[0030]
The polymer electrolyte of the present invention can be produced by a conventional method, but is preferably obtained by uniformly dissolving the organic polymer and metal salt as described above in a solvent.
[0031]
In general, the polymer electrolyte of the present invention is used in the form of a film, but the method of forming a film can be a conventional method. For example, a film can be formed by a casting method in which an organic polymer and a metal salt are dissolved in an organic casting solvent, this solution is spread on a flat substrate, and the solvent is evaporated to obtain a composite film. In this case, as the casting solvent, a solvent that can dissolve both the polymer and the metal salt, for example, an organic solvent having a moderate polarity such as dimethylformamide (DMF), N-methylpyrrolidone (NMP), and propylene carbonate (PC) is appropriately used. Can be used.
[0032]
The polymer electrolyte swollen with the organic solvent of the present invention can be obtained by a conventional method. For example, a method in which the polymer electrolyte film obtained by the above-mentioned method is immersed in an organic solvent and pulled up when it contains a predetermined amount of organic solvent, or an appropriate amount of solvent is not evaporated without completely evaporating the cast solvent. The method of using it in the state left | survived is mentioned.
[0033]
As the organic solvent used here, ethylene carbonate (EC), dimethoxyethane (DME), dimethyl carbonate, which is used as the above casting solvent, or generally used as a lithium-based nonaqueous electrolytic solution, is used. (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC) and the like can be used as appropriate, and a plurality of these organic solvents can be used simultaneously.
[0034]
The content of the organic solvent is not necessarily limited, but although the conductivity tends to increase as the content increases, the film property (self-supporting) decreases when the content exceeds a certain amount, It appears to be an adhesive body. Therefore, it is possible to select the film according to the purpose of use and the conductivity. In addition, in the case of the polymer electrolyte containing the organic solvent of the present invention, as the average molecular weight of the organic polymer increases, a decrease in film properties tends to be suppressed even when the content of the organic solvent increases. The higher the average molecular weight of the polymer, the higher the conductivity.
[0035]
Since the polymer electrolyte of the present invention contains an organic polymer having a structure having a five-membered cyclic carbonate group as a functional group as part of the side chain, a metal salt serving as a carrier ion is contained in the polymer electrolyte at a high concentration. It can be contained. Therefore, it is possible to simultaneously realize high ion conductivity, film formability and flexibility.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
Example 1
[Synthesis of poly (propenyl-propylene carbonate-ether) (PPpPCE)]
100 ml of dichloromethane and 20 g of propenyl-propylene carbonate-ether are weighed in a 300 ml glass reaction vessel equipped with a three-way cell and cooled to -78 ° C. To this, 2.5 ml of a dichloromethane solution of BF ₃ O (C ₂ H ₅ ) _{2 having} a concentration of 0.1 mol / liter is added. After the reaction for 3 hours, cooled ethanol is added to the reaction solution to stop the polymerization, and the white polymer produced by pouring the reaction solution into a large amount of cooled ethanol is precipitated. Wash the polymer thoroughly with ethanol and purify the polymer by drying under reduced pressure.
[0037]
As a result, the desired organic polymer was obtained with a yield of almost 100%. This organic polymer was identified and confirmed by ¹ H-NMR in FT-IR and CDCl ₃ .
[0038]
The average molecular weight of the organic polymer is relatively easy to suppress by the monomer concentration and reaction time, and the average molecular weight of the organic polymer prepared under various conditions is measured by gel permeation chromatography (GPC). As a result, the average molecular weight was about 1 × 10 ³ to 1 × 10 ⁶ .
[0039]
[Preparation of polymer solid electrolyte film]
The organic polymer PPpPCE obtained by the above method is added to sufficiently dehydrated DMF, sufficiently stirred to obtain a homogeneous solution, and further stirred, LiClO ₄ is added to all constituent monomers of the organic polymer [Li ⁺ ] / [Monomer unit] = 0.7 and continue stirring for a while until complete dissolution. Then, the insoluble matter was removed through a filter having a pore diameter of 0.45 μm, and a film was formed by a casting method. That is, the solution was transferred to a Teflon petri dish with a smooth bottom, the solvent was evaporated in a thermostat set in a temperature range of 40 to 60 ° C. in a nitrogen atmosphere, and the solvent was completely removed under vacuum heating. And dried to obtain a polymer electrolyte film.
[0040]
The polymer electrolyte film thus obtained is a flexible, colorless to light yellow film, and its film thickness can be appropriately prepared according to the purpose. The thing of 150 micrometers was used.
[0041]
[Evaluation of ionic conductivity]
The ionic conductivity of the polymer electrolyte film obtained by the above method was evaluated as follows.
That is, the polymer electrolyte film is pressure-bonded with a platinum electrode or a lithium metal electrode, and is stored by heating at 90 ° C. for several hours, so that each electrode / film / electrode contact is sufficiently maintained. Thereafter, the ionic conductivity was analytically calculated from the semicircular arc portion obtained by the constant voltage complex impedance method.
[0042]
These measurements were performed after placing the evaluation cell in a temperature-controlled thermostat and taking a steady state at an arbitrary temperature for about 1 hour. In this case, the resistance part which contributes to the ionic conduction in the polymer solid electrolyte was assigned by replacing the electrodes of the obtained pseudo semicircular arc components with platinum or lithium metal and changing the electrode area.
[0043]
At this time, the AC amplitude voltage used in the measurement was set to about 30 to 100 mV, and the AC frequency band was 10 ⁻² to 10 ⁷ Hz. FIG. 1 shows the temperature dependence of the conductivity obtained in the region of −10 to 90 ° C. as described above.
[0044]
From the results shown in FIG. 1, it is confirmed that the polymer electrolyte film of the present invention has a remarkably high conductivity in the temperature range near room temperature, compared to the composite film of the conventional PEO and other organic polymers and alkali metal salts. did it. In addition, the film formability, mechanical strength and flexibility were sufficient.
[0045]
Examples 2-5
A polymer electrolyte by PPpPCE was prepared in the same manner as in Example 1 except that the addition amount of LiClO ₄ was changed as shown in FIG. 2, and the conductivity dependency obtained in the region of −10 to 90 ° C. was shown in FIG. Show.
[0046]
As is clear from FIG. 1, when the added amount of LiClO ₄ is a low concentration of [Li ⁺ ] / [monomer unit] = 0.3 or less, the conductivity tends to be low.
[0047]
On the other hand, the polymer electrolyte film obtained with [Li ⁺ ] / [monomer unit] = 0.5 to 1.0 is a good film rich in flexibility, and the conductivity tends to increase remarkably. Furthermore, when the amount of LiClO ₄ added exceeds [Li ⁺ ] / [monomer unit] = 1.0, the film obtained by completely removing the casting solvent is suspended due to precipitation of the metal salt, A solution in which a salt and an organic polymer are compatible cannot be obtained. Furthermore, this suspended film not only has a reduced electrical conductivity, but also has a marked decrease in flexibility and mechanical strength.
[0048]
Therefore, in this system, it is preferable that [Li ⁺ ] / [monomer unit] = 0.1 to 1.0, and more preferably [Li ⁺ ] / [monomer unit] = 0.5 to 1.0. It is desirable that
[0049]
Examples 6-13
Instead of LiClO ₄ shown in Example 1, an alkali metal salt such as lithium, sodium or potassium shown in FIG. 2 is used, so that each becomes [M ⁺ ] / [O—CO—O unit]. A polymer electrolyte in which salt was added to was prepared, and the conductivity at 30 ° C. was determined. This result is shown in FIG. 2, and the result of LiClO ₄ of Example 1 is also shown here.
[0050]
As is clear from FIG. 2, the conductivity of the obtained polymer solid electrolyte is not extremely lowered even when the alkali metal salt is changed, and compared with the ionic conductivity of the conventional polymer solid electrolyte, the room temperature ( Even at 30 ° C., a high value is exhibited. In all cases, no decrease in film formability was observed.
[0051]
Examples 14-16
A PPpPCE of Example 1 was prepared by adding propylene carbonate (PC) to a polymer electrolyte containing LiClO _{4 such} that [Li ⁺ ] / [monomer unit] = 0.7. The amount of PC added was 0.1 times, 0.5 times and 1.0 times the weight of the polymer electrolyte composed of PPpPCE and LiClO _4, and was determined in the range of −10 to 90 ° C. The results of measuring the temperature dependence of the conductivity are shown in FIG.
[0052]
As is clear from FIG. 3, as the amount of PC added increases, the conductivity increases and the decrease in conductivity on the low temperature side also decreases. However, when the addition amount increases, the solid state cannot be maintained at a high temperature and is dissolved and has fluidity. Therefore, it is desirable that the amount of PC added is large in a state that matches the intended temperature range and the state of the film.
[0053]
【The invention's effect】
According to the present invention, it is possible to obtain a solid polymer electrolyte that exhibits high ionic conductivity even near room temperature and is excellent in film formability, mechanical strength, and flexibility as compared with conventional solid polymer electrolytes. Is possible.
[Brief description of the drawings]
FIG. 1 is a graph showing the temperature dependence of conductivity when the salt concentration is changed in a PPpPCE / LiClO ₄ polymer solid electrolyte.
FIG. 2 is a graph showing the conductivity of each alkali metal salt in a PPpPCE polymer solid electrolyte.
FIG. 3 is a graph showing the temperature dependence of electrical conductivity when the pPC content in a PPpPCE polymer solid electrolyte is changed.

Claims (6)

In a polymer electrolyte comprising an organic polymer having a structure having a 5-membered cyclic carbonate group as a functional group as a part of a side chain and a metal salt,
A polymer electrolyte, wherein the organic polymer is represented by the chemical formula (1).

  The polymer electrolyte according to claim 1, wherein the metal salt is an alkali metal salt.   The constituent ratio between the metal salt and the organic polymer is such that the molar ratio of metal ions per monomer of all constituents of the organic polymer ([metal ion] / [monomer unit]) is 0.02 to 0.80. The polymer electrolyte according to claim 1.   The polymer electrolyte according to claim 1, comprising a polymer electrolyte and an organic solvent in which the electrolyte is soluble.   5. The organic solvent in which the electrolyte is soluble has at least one oxygen atom or nitrogen atom in its structure, and these organic solvents are single or plural kinds of mixed solvents. Polymer electrolyte. A method for producing a polymer electrolyte, comprising dissolving an organic polymer represented by the chemical formula (2) and an alkali metal salt in an organic casting solvent to form a film by a casting method.

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