JP3951404B2 - Electric double layer capacitor - Google Patents
Electric double layer capacitor Download PDFInfo
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- JP3951404B2 JP3951404B2 JP1281698A JP1281698A JP3951404B2 JP 3951404 B2 JP3951404 B2 JP 3951404B2 JP 1281698 A JP1281698 A JP 1281698A JP 1281698 A JP1281698 A JP 1281698A JP 3951404 B2 JP3951404 B2 JP 3951404B2
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- copolymer
- polymer electrolyte
- vinylidene fluoride
- double layer
- layer capacitor
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/13—Energy storage using capacitors
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- Electric Double-Layer Capacitors Or The Like (AREA)
- Organic Insulating Materials (AREA)
Abstract
Description
【0001】
【発明の属する技術分野】
本発明はポリマー電解質を使用した電気二重層キャパシタ、特にイオン伝導性とサイクル寿命に優れる電気二重層キャパシタに関する。
【0002】
【従来の技術】
近年、電気二重層キャパシタに液状である電解液を用いることによって生じうる漏液の対策、可燃性電解液の着火性低減対策、及び電池のフィルム状化による電子機器への組み込み性の向上とスペースの有効利用等の見地より、ポリマー電解質が提案されている。
【0003】
そのなかで、ポリエチレンオキシド系ポリマー電解質は電気化学的には安定であるが、有機電解液の溶媒の保持性が低い難点がある。
ポリフッ化ビニリデンをマトリックスとするポリマー電解質は電気化学的に安定であり、フッ素原子を含むのでポリマーが燃えにくい特徴があるが、ポリマー電解質の温度を上げると電解液がポリマーよりにじみ出る。これに対し、フッ化ビニリデン/ヘキサフルオロプロピレン共重合体を使用することによりこの問題を解決する試みもある。
さらに、従来のポリマー電解質使用電気二重層キャパシタは、充放電サイクル耐久性が液体電解質を用いた電気二重層キャパシタより劣る欠点がある。
【0004】
【発明が解決しようとする課題】
本発明は、特定のポリマー電解質を採用することにより、電解質の保持性がよく、安定でイオン伝導性が高く、充放電サイクル耐久性が優れた電気二重層キャパシタを提供することを目的とする。
【0005】
【課題を解決するための手段】
本発明は、炭素材料を主成分とする正極及び負極と電解質とを有する電気二重層キャパシタにおいて、前記電解質が、フッ化ビニリデン/パーフルオロ(アルキルビニルエーテル)共重合体、フッ化ビニリデン/テトラフルオロエチレン共重合体及びクロロトリフルオロエチレン/ビニレンカーボネート共重合体からなる群から選ばれる1種以上の共重合体をマトリックスとし、第4級アンモニウム塩又は第4級ホスホニウム塩からなる溶質と該溶質を溶解できる溶媒とからなる溶液を含有するポリマー電解質であることを特徴とする電気二重層キャパシタを提供する。
【0006】
本明細書においてA/B共重合体とは、Aに基づく重合単位とBに基づく重合単位とを含む共重合体を示す。そして、A/B共重合体はAに基づく重合単位とBに基づく重合単位のほかにこれらと共重合できる他の単量体に基づく重合単位を30重量%以下含んでもよい。また、本明細書では、炭素材料を主成分とする電極を金属集電体と一体化したものを電極体といい、これを正極側に用いる場合は正極体、負極側に用いる場合は負極体という。
【0007】
本発明においてポリマー電解質のマトリックスを形成する共重合体は、有機系電気二重層キャパシタ用電解液に対して安定であり、また熱安定性も高く、電気化学的にも不活性であるので好ましい。
【0008】
本発明においてポリマー電解質のマトリックスを形成する共重合体の分子量は1万〜100万が好ましい。分子量が100万を超えると溶解粘度が著しく高く、第4級アンモニウム塩溶液又は第4級ホスホニウム塩溶液との均一混合が困難となったり、該溶液の保持量が少なくなってポリマー電解質の電気伝導度が低下するので好ましくない。一方、1万未満であると、ポリマー電解質の機械的強度が低下するので好ましくない。特に好ましくは3万〜50万が採用される。
【0009】
本発明において、ポリマー電解質のマトリックスとしてフッ化ビニリデン/パーフルオロ(アルキルビニルエーテル)共重合体又はフッ化ビニリデン/テトラフルオロエチレン共重合体を採用する場合、該共重合体中のフッ化ビニリデンに基づく重合単位は40〜99重量%であることが好ましい。
【0010】
フッ化ビニリデンに基づく重合単位が99重量%を超えると結晶性が高くなり、柔軟性が低下して成形加工性が低下しやすい。フッ化ビニリデンに基づく重合単位が40重量%未満であると、柔軟性が高くなりすぎて強度が低下しやすい。フッ化ビニリデンに基づく重合単位が60〜97重量%であるとより好ましい。
【0011】
クロロトリフルオロエチレン/ビニレンカーボネート共重合体の場合は、ビニレンカーボネートに基づく重合単位が5〜60重量%含まれることが好ましい。ビニレンカーボネートに基づく重合単位が5重量%未満であるとポリマーの結晶性が高くなり、柔軟性が低下し成形加工性が低下したり、電解液がポリマー中に侵入しにくくなったり、ポリマー電解質の電気伝導度が低くなったりしやすい。60重量%を超えると、ポリマー電解質の柔軟性が高くなりすぎ、強度が低下しやすい。ビニレンカーボネートに基づく重合単位が10〜40重量%であるとより好ましい。
【0012】
本発明におけるフッ化ビニリデン/パーフルオロ(アルキルビニルエーテル)共重合体において、パーフルオロ(アルキルビニルエーテル)に基づく重合単位としては、例えばパーフルオロ(プロピルビニルエーテル)に基づく重合単位、パーフルオロ(エチルビニルエーテル)に基づく重合単位、パーフルオロ(ブチルビニルエーテル)に基づく重合単位等が挙げられる。
【0013】
本発明におけるフッ化ビニリデン/テトラフルオロエチレン共重合体は、2元共重合体でもよいが、プロピレン、ブテン又はイソブチレンに基づく重合単位を含む3元共重合体であることが好ましい。特にプロピレンに基づく重合単位を含むフッ化ビニリデン/テトラフルオロエチレン/プロピレン共重合体が好ましい。このとき、プロピレン、ブテン又はイソブチレンに基づく重合単位は、共重合体中に3〜30重量含まれることが好ましい。プロピレン、ブテン又はイソブチレンに基づく重合単位を含むことにより、前記共重合体はゴム状とすることも樹脂状とすることもできる。マトリックスとしての強度の点からは樹脂状であることが好ましい。
【0014】
本発明におけるポリマー電解質のマトリックスにおいて、必要に応じて添加される他の単量体に基づく重合単位の重量比、共重合体の分子量等は、ポリマー電解質フィルムを形成するための有機溶媒へのマトリックスの溶解性又は分散性、第4級アンモニウム塩又は第4級ホスホニウム塩溶液とマトリックスとの混和性及び該溶液の保持性、ポリマー電解質の集電体金属への接着性、強度、成形性、ハンドリング性、マトリックスの入手の容易性等により適宜選定できる。
【0015】
本発明の電気二重層キャパシタに使用される第4級アンモニウム塩又は第4級ホスホニウム塩としてはR1 R2 R3 R4 N+ 又はR1 R2 R3 R4 P+ (ただし、R1 、R2 、R3 、R4 は炭素数1〜6のアルキル基で、それぞれ同じでも異なっていてもよい)で表される第4級アンモニウムカチオン又は第4級ホスホニウムカチオンと、BF4 -、PF6 -、ClO4 -、CF3 SO3 -等のアニオンとからなる塩が好ましい。
【0016】
第4級アンモニウム塩又は第4級ホスホニウム塩を溶解し、ポリマー電解質中に含有される有機溶媒としては、プロピレンカーボネート、ブチレンカーボネート、ジエチルカーボネート等のカーボネート類、γ−ブチロラクトン等のラクトン類、スルホラン、又はこれらの混合溶媒が好ましく使用できる。
【0017】
本発明における第4級アンモニウム塩又は第4級ホスホニウム塩は、前記溶媒に0.1〜2.0mol/lの濃度で溶解することが好ましい。この範囲を逸脱すると、イオン伝導度が低下し、ポリマー電解質の電気伝導度が低下する。より好ましくは0.2〜1.0mol/lが採用される。
【0018】
本発明では、マトリックス中に前記第4級アンモニウム塩溶液又は第4級ホスホニウム塩溶液が均一に分布したポリマー電解質を使用するが、ポリマー電解質中の前記溶液の含有量は30〜90重量%が好ましい。30重量%未満であるとポリマー電解質の電気伝導度が低くなるので好ましくない。90重量%を超えるとポリマー電解質が固体又はゲルの状態で保てなくなるので好ましくない。特には40〜65重量%が好ましい。
【0019】
本発明におけるポリマー電解質は種々の方法で作製できる。例えば、マトリックスを形成する共重合体を有機溶媒に溶解又は均一に分散させ、第4級アンモニウム塩又は第4級ホスホニウム塩を溶媒に溶解させた溶液と混合する(以下、この溶液をポリマー電解質形成用混合液という)。この混合液をガラス板上にバーコータ又はドクターブレードによる塗布、キャスト又はスピンコートした後、乾燥して主として前記共重合体を溶解又は分散させた有機溶媒を除去し、ポリマー電解質フィルムを得る。乾燥時に第4級アンモニウム塩又は第4級ホスホニウム塩の溶液に用いた溶媒が一部蒸発する場合は、該フィルムに新たにその溶媒を含浸させるか又はフィルムをその溶媒蒸気に暴露して所望の組成にする。
【0020】
前記共重合体を溶解又は分散させる有機溶媒としては、テトラヒドロフラン(以下、THFという)、メチルエチルケトン、メチルイソブチルケトン、トルエン、キシレン、N−メチルピロリドン、アセトン、アセトニトリル、ジメチルカーボネート、酢酸エチル、酢酸ブチル等が使用できるが、乾燥により選択的にこの有機溶媒を除去するため、THF、アセトン等の沸点100℃以下の揮発性の有機溶媒が好ましい。
【0021】
また、本発明では、前記共重合体を有機溶媒に溶解又は分散させずに多孔質フィルム状に形成し、炭素材料を含んでなる正極及び負極の間に挟み、その後に第4級アンモニウム塩溶液又は第4級ホスホニウム塩溶液をフィルムに含浸させてもよい。
【0022】
本発明の電気二重層キャパシタの電極の炭素材料としては、電気化学的に不活性な高比表面積の材料であれば使用できるが、比表面積が大きい活性炭粉末を主成分とするのが好ましい。また、活性炭粉末以外に、カーボンブラック、ポリアセン等の高比表面積の材料も好ましく使用できる。これらの炭素材料の比表面積としては500〜2500m2 /gが好ましい。
【0023】
本発明における電極は、抵抗を低くするために導電材としてカーボンブラックや黒鉛等を含んでもよい。導電材は電極中に3〜20重量%含まれることが好ましい。
【0024】
本発明における電極体は、炭素材料をポリテトラフルオロエチレン等のバインダとともに有機溶媒等の混練助剤の存在下で混練した後、シート状に成形し、例えば導電性接着剤を介して金属集電体に接合して金属集電体と一体化して得ることができる。また、炭素材料とポリフッ化ビニリデン等のバインダと有機溶媒とを混合してスラリとなし、金属集電体に塗工した後乾燥して金属集電体と一体化した電極体を得てもよい。このようにして得られた電極体の電極層にはポリマー電解質形成用混合液を含浸させるか塗布すると、電極層の内部までポリマー電解質が浸透するので好ましい。
また、炭素材料とポリマー電解質形成用混合液を混合してスラリとなし、金属集電体に塗工して電極体を形成してもよい。
【0025】
本発明において、金属集電体としては、アルミニウム又はアルミニウム合金が好ましい。特に純度が99.9%以上で、銅の含有量が0.015重量%以下であるアルミニウムが好ましい。金属集電体は表面が粗面化されていると分極性電極との密着性が高まるので好ましい。表面の粗面化は化学エッチングや交流エッチングにより行うことが好ましい。
【0026】
本発明におけるポリマー電解質は、電極間に配置されてセパレータの役割も有する。フィルム状のポリマー電解質はそのまま使用してもよいが、必要に応じてポリマー電解質を多孔質補強材料により保持してもよい。多孔質補強材料としては、例えば不織布、網、ガラス繊維マット、多孔質ポリプロピレンシート、多孔質ポリテトラフルオロエチレンシート等が使用できる。なかでも耐熱性が高く、含水率の低いガラス繊維マット、多孔質ポリテトラフルオロエチレンシート等が好ましく挙げられる。
【0027】
本発明の電気二重層キャパシタは、例えば一対の帯状の電極体を正極体及び負極体とし、間に帯状のセパレータを介在させて巻回して素子とし、有底円筒型ケースに収容し、有機電解液を該素子に含浸させ、正極端子と負極端子を有する蓋体により封口することにより得られる。このとき、ケース材質はアルミニウムであることが好ましい。
【0028】
また、例えば矩形の複数枚の電極体を同数枚の正極体及び負極体とし、間にセパレータを介在させて交互に積層して素子とし、前記複数枚の正極体及び負極体からはそれぞれリードを取り出して有底角型アルミニウムケースに収容し、有機電解液を前記素子に含浸させた後、正極端子と負極端子を有する蓋体を取り付け、レーザー溶接等により封口することにより角型電気二重層キャパシタを構成してもよい。
【0029】
【実施例】
[例1]
アルゴン雰囲気中で、フッ化ビニリデン/CF2 =CFOCF2 CF2 CF3 共重合体(フッ化ビニリデンに基づく重合単位とCF2 =CFOCF2 CF2 CF3 に基づく重合単位とが重量比で89/11であり、THFを溶媒とする極限粘度が1.4dl/g)10重量部をTHF32重量部に撹拌しながら60℃に加温して溶解させた。この溶液を溶液1とする。次にプロピレンカーボネートに(C2 H5 )3 (CH3 )NBF4 を1mol/lの濃度でアルゴン雰囲気中で溶解させた。これを溶液2とする。
【0030】
21重量部の溶液1に5重量部の溶液2を加え、60℃に加熱し撹拌した。この溶液をガラス板上にバーコータにて塗布し、60℃で30分乾燥して厚さ100μmの透明なポリマー電解質フィルムを得た。このフィルムの組成は、共重合体、プロピレンカーボネート、(C2 H5 )3 (CH3 )NBF4 が重量比で50/44.3/5.7であった。
このフィルムをガラス板より剥離し、交流インピーダンス法で電気伝導度を25℃、アルゴン雰囲気中で測定した。電気伝導度は8×10-4S/cmであった。
【0031】
純度99.8重量%以上であり、かつ銅の含有量が0.05重量%未満のアルミニウム箔に対して交流2段エッチングを行い、両面を粗面化した。得られたアルミニウム箔は厚さ19μmで、粗面化層の片側あたりの厚さは1.8μmであった。表面を2万倍で電子顕微鏡観察すると海綿状であり、平均孔径0.1μmのエッチング孔が1cm2 あたりに約70億個存在した。引っ張り破断強度は箔幅1cmあたり1.7kgであった。このアルミニウム箔を集電体とした。
【0032】
活性炭粉末を11重量部、導電材としてカーボンブラックを1.5重量部、フッ化ビニリデン/CF2 =CFOCF2 CF2 CF3 共重合体を6重量部、溶液2を11重量部、及びTHF70重量部をアルゴン雰囲気中で混合し、撹拌しながら加温してスラリを得た。このスラリを上記のアルミニウム箔2枚にバーコータにて塗布し、乾燥させて有効電極面積1cm×1cmの正極体及び負極体とした。
【0033】
上記ポリマー電解質フィルムを1.5cm角に成形し、これを介して正極と負極を対向させ、厚さ1.5mmで3cm角の2枚のポリテトラフルオロエチレン背板で挟み締め付け、その外側を外装フィルムで覆うことにより電気二重層キャパシタ素子を作製した。この操作もすべてアルゴン雰囲気中で行った。
【0034】
[例2(参考例)]
フッ化ビニリデン/CF2 =CFOCF2 CF2 CF3 共重合体のかわりにフッ化ビニリデン/ヘキサフルオロアセトン共重合体(フッ化ビニリデンに基づく重合単位とヘキサフルオロアセトンに基づく重合単位とが重量比で88/12であり、ジメチルアセトアミドを溶媒としてゲル浸透クロマトグラフィ(以下、GPCという)で測定して算出した数平均分子量は96000)を用いたほかは例1と同様にして電気二重層キャパシタを作製した。
【0035】
[例3]
フッ化ビニリデン/CF2 =CFOCF2 CF2 CF3 共重合体のかわりにクロロトリフルオロエチレン/ビニレンカーボネート共重合体(クロロトリフルオロエチレンに基づく重合単位とビニレンカーボネートに基づく重合単位とが重量比で62/38であり、数平均分子量は105000)を用いたほかは例1と同様にして電気二重層キャパシタを作製した。
【0036】
[例4(参考例)]
フッ化ビニリデン/CF2 =CFOCF2 CF2 CF3 共重合体のかわりにフッ化ビニリデン/クロロトリフルオロエチレン共重合体(フッ化ビニリデンに基づく重合単位とクロロトリフルオロエチレンに基づく重合単位とが重量比で56/44であり、ガラス転移温度が−5℃で、ASTM D746の試験法に基づいて測定した脆化温度は−64℃)を用いたほかは例1と同様にして電気二重層キャパシタを作製した。
【0037】
[例5(比較例)]
フッ化ビニリデン/CF2 =CFOCF2 CF2 CF3 共重合体のかわりにフッ化ビニリデン/ヘキサフルオロプロピレン共重合体(フッ化ビニリデンに基づく重合単位とヘキサフルオロプロピレンに基づく重合単位とが重量比で61/39であり、GPCによる分子量が10万であり、ガラス転移温度が5℃で、示差熱分析測定装置を用い、窒素ガス雰囲気中で加熱速度10℃/分の条件で測定したところ融点なし)を用いたほかは例1と同様にして電気二重層キャパシタを作製した。
【0038】
[例6]
フッ化ビニリデン/CF2 =CFOCF2 CF2 CF3 共重合体のかわりにフッ化ビニリデン/テトラフルオロエチレン/プロピレン共重合体(フッ化ビニリデンに基づく重合単位とテトラフルオロエチレンに基づく重合単位とプロピレンに基づく重合単位とが重量比で53/32/15であり、GPCによる分子量が15万)を用いたほかは例1と同様にして電気二重層キャパシタを作製した。
【0039】
[評価]
例1〜6で作製した電気二重層キャパシタ素子を用い、25℃にて20mAで上限電圧を2.8Vとして定電流充電を30分行った後、1mAにて0Vまで定電流放電して静電容量を求めた。また、10mAにて定電流放電して放電直後の電圧低下値より直流抵抗を求めた。初期性能を測定後、2.8Vにて10mAで10分の充電と5mAでの定電流放電を2000回繰り返し、容量維持率と抵抗上昇率を求め、充放電サイクル耐久性を評価した。結果を表1に示す。
【0040】
【表1】
【0041】
【発明の効果】
本発明による電気二重層キャパシタは、ポリマー電解質が第4級アンモニウム塩又は第4級ホスホニウム塩を溶質とする溶液の保持性に優れるため良好な電気伝導度を保ちつつ、かつポリマー電解質と電極の炭素材料との密着性がよいので、充放電サイクル耐久性に優れる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric double layer capacitor using a polymer electrolyte, and more particularly to an electric double layer capacitor excellent in ion conductivity and cycle life.
[0002]
[Prior art]
In recent years, countermeasures for leaks that may occur due to the use of liquid electrolytes in electric double layer capacitors, measures for reducing the ignitability of flammable electrolytes, and improving the ease of incorporation into electronic devices by making batteries into a film and space Polymer electrolytes have been proposed from the standpoint of effective utilization of the.
[0003]
Among them, the polyethylene oxide polymer electrolyte is electrochemically stable, but has a drawback that the solvent retention of the organic electrolyte is low.
Polymer electrolytes using polyvinylidene fluoride as a matrix are electrochemically stable and contain fluorine atoms, so that the polymer is difficult to burn. However, when the temperature of the polymer electrolyte is raised, the electrolyte oozes out from the polymer. On the other hand, there is an attempt to solve this problem by using a vinylidene fluoride / hexafluoropropylene copolymer.
Furthermore, the conventional electric double layer capacitor using a polymer electrolyte has a disadvantage that the charge / discharge cycle durability is inferior to that of an electric double layer capacitor using a liquid electrolyte.
[0004]
[Problems to be solved by the invention]
It is an object of the present invention to provide an electric double layer capacitor that employs a specific polymer electrolyte, has good electrolyte retention, is stable, has high ion conductivity, and has excellent charge / discharge cycle durability.
[0005]
[Means for Solving the Problems]
The present invention, in the electric double layer capacitor having a positive electrode and a negative electrode and an electrolyte mainly composed of carbon material, the electrolyte, vinylidene fluoride / perfluoro (alkyl vinyl ether) copolymer, full Kka vinylidene / tetrafluoroethylene 1 or more copolymers selected from the group consisting of ethylene copolymer及 beauty chlorotrifluoroethylene / vinylene carbonate copolymer as a matrix, solute and solute comprising a quaternary ammonium salt or quaternary phosphonium salt Provided is an electric double layer capacitor characterized by being a polymer electrolyte containing a solution comprising a solvent capable of dissolving
[0006]
In this specification, the A / B copolymer refers to a copolymer containing a polymer unit based on A and a polymer unit based on B. The A / B copolymer may contain 30% by weight or less of polymer units based on other monomers that can be copolymerized with the polymer units based on A and polymer units based on B. Further, in this specification, an electrode body in which an electrode mainly composed of a carbon material is integrated with a metal current collector is referred to as an electrode body, and when used on the positive electrode side, a positive electrode body, and when used on the negative electrode side, a negative electrode body. That's it.
[0007]
In the present invention, the copolymer that forms the matrix of the polymer electrolyte is preferable because it is stable with respect to the electrolyte for an organic electric double layer capacitor, has high thermal stability, and is electrochemically inactive.
[0008]
In the present invention, the molecular weight of the copolymer forming the polymer electrolyte matrix is preferably 10,000 to 1,000,000. When the molecular weight exceeds 1,000,000, the dissolution viscosity is remarkably high, and uniform mixing with a quaternary ammonium salt solution or a quaternary phosphonium salt solution becomes difficult, or the retained amount of the solution decreases and the electric conductivity of the polymer electrolyte is reduced. This is not preferable because the degree is lowered. On the other hand, if it is less than 10,000, the mechanical strength of the polymer electrolyte is lowered, which is not preferable. Particularly preferably, 30,000 to 500,000 is employed.
[0009]
In the present invention, when a vinylidene fluoride / perfluoro (alkyl vinyl ether) copolymer or a vinylidene fluoride / tetrafluoroethylene copolymer is employed as the matrix of the polymer electrolyte, polymerization based on the vinylidene fluoride in the copolymer The unit is preferably 40 to 99% by weight.
[0010]
When the polymerization unit based on vinylidene fluoride exceeds 99% by weight, the crystallinity becomes high, the flexibility is lowered, and the moldability is liable to be lowered. When the polymerization unit based on vinylidene fluoride is less than 40% by weight, the flexibility becomes too high and the strength tends to decrease. More preferably, the polymerized units based on vinylidene fluoride is 60 to 97% by weight.
[0011]
In the case of a chlorotrifluoroethylene / vinylene carbonate copolymer, it is preferable that 5 to 60% by weight of polymer units based on vinylene carbonate is contained. If the polymerization unit based on vinylene carbonate is less than 5% by weight, the crystallinity of the polymer becomes high, the flexibility is lowered and the molding processability is lowered, the electrolytic solution is less likely to enter the polymer, the polymer electrolyte Electric conductivity is likely to be low. If it exceeds 60% by weight, the flexibility of the polymer electrolyte becomes too high and the strength tends to decrease. More preferably, the polymerized units based on vinylene carbonate is 10 to 40% by weight.
[0012]
In the vinylidene fluoride / perfluoro (alkyl vinyl ether) copolymer in the present invention, examples of the polymer unit based on perfluoro (alkyl vinyl ether) include polymer units based on perfluoro (propyl vinyl ether), perfluoro (ethyl vinyl ether), and the like. Polymer units based on perfluoro (butyl vinyl ether) and the like.
[0013]
The vinylidene fluoride / tetrafluoroethylene copolymer in the present invention may be a binary copolymer, but is preferably a ternary copolymer containing polymer units based on propylene, butene or isobutylene. In particular, a vinylidene fluoride / tetrafluoroethylene / propylene copolymer containing a polymer unit based on propylene is preferred. At this time, it is preferable that 3-30 weight% of polymer units based on propylene, butene, or isobutylene are contained in the copolymer. By including polymerized units based on propylene, butene or isobutylene, the copolymer can be rubbery or resinous. From the viewpoint of strength as a matrix, it is preferably in the form of a resin.
[0014]
In the matrix of the polymer electrolyte in the present invention, the weight ratio of polymerized units based on other monomers added as necessary, the molecular weight of the copolymer, etc. are the matrix in the organic solvent for forming the polymer electrolyte film. Solubility or dispersibility, miscibility of quaternary ammonium salt or quaternary phosphonium salt solution with matrix and retention of the solution, adhesion of polymer electrolyte to current collector metal, strength, formability, handling It can be selected as appropriate depending on the properties and the availability of the matrix.
[0015]
The quaternary ammonium salt or quaternary phosphonium salt used in the electric double layer capacitor of the present invention is R 1 R 2 R 3 R 4 N + or R 1 R 2 R 3 R 4 P + (where R 1 , R 2 , R 3 , and R 4 are alkyl groups having 1 to 6 carbon atoms, which may be the same or different from each other), and BF 4 − , A salt composed of an anion such as PF 6 − , ClO 4 − and CF 3 SO 3 — is preferred.
[0016]
Examples of the organic solvent in which the quaternary ammonium salt or quaternary phosphonium salt is dissolved and contained in the polymer electrolyte include carbonates such as propylene carbonate, butylene carbonate and diethyl carbonate, lactones such as γ-butyrolactone, sulfolane, Alternatively, a mixed solvent thereof can be preferably used.
[0017]
The quaternary ammonium salt or quaternary phosphonium salt in the present invention is preferably dissolved in the solvent at a concentration of 0.1 to 2.0 mol / l. If it deviates from this range, the ionic conductivity decreases and the electrical conductivity of the polymer electrolyte decreases. More preferably, 0.2 to 1.0 mol / l is employed.
[0018]
In the present invention, the polymer electrolyte in which the quaternary ammonium salt solution or the quaternary phosphonium salt solution is uniformly distributed in the matrix is used, and the content of the solution in the polymer electrolyte is preferably 30 to 90% by weight. . If it is less than 30% by weight, the electric conductivity of the polymer electrolyte is lowered, which is not preferable. If it exceeds 90% by weight, the polymer electrolyte cannot be kept in a solid or gel state, which is not preferable. In particular, 40 to 65% by weight is preferable.
[0019]
The polymer electrolyte in the present invention can be produced by various methods. For example, a copolymer forming a matrix is dissolved or uniformly dispersed in an organic solvent, and mixed with a solution in which a quaternary ammonium salt or a quaternary phosphonium salt is dissolved in a solvent (hereinafter, this solution is formed as a polymer electrolyte). Called mixed liquid). This mixed solution is applied on a glass plate by a bar coater or a doctor blade, cast or spin coated, and then dried to remove an organic solvent in which the copolymer is mainly dissolved or dispersed, thereby obtaining a polymer electrolyte film. If the solvent used in the solution of the quaternary ammonium salt or quaternary phosphonium salt partially evaporates during drying, the film is newly impregnated with the solvent or the film is exposed to the solvent vapor to obtain the desired Make composition.
[0020]
Examples of the organic solvent for dissolving or dispersing the copolymer include tetrahydrofuran (hereinafter referred to as THF), methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, N-methylpyrrolidone, acetone, acetonitrile, dimethyl carbonate, ethyl acetate, butyl acetate, and the like. However, in order to selectively remove the organic solvent by drying, a volatile organic solvent having a boiling point of 100 ° C. or lower such as THF or acetone is preferable.
[0021]
In the present invention, the copolymer is formed into a porous film without being dissolved or dispersed in an organic solvent, sandwiched between a positive electrode and a negative electrode containing a carbon material, and then a quaternary ammonium salt solution. Alternatively, the film may be impregnated with a quaternary phosphonium salt solution.
[0022]
As the carbon material of the electrode of the electric double layer capacitor of the present invention, any material having an electrochemically inactive high specific surface area can be used. However, it is preferable to use activated carbon powder having a large specific surface area as a main component. In addition to the activated carbon powder, materials having a high specific surface area such as carbon black and polyacene can be preferably used. The specific surface area of these carbon materials is preferably 500 to 2500 m 2 / g.
[0023]
The electrode in the present invention may contain carbon black, graphite or the like as a conductive material in order to reduce resistance. The conductive material is preferably contained in the electrode in an amount of 3 to 20% by weight.
[0024]
In the electrode body in the present invention, a carbon material is kneaded in the presence of a kneading aid such as an organic solvent together with a binder such as polytetrafluoroethylene, and then formed into a sheet shape, for example, a metal current collector via a conductive adhesive. It can be obtained by joining to the body and integrating with the metal current collector. Alternatively, a carbon material, a binder such as polyvinylidene fluoride, and an organic solvent may be mixed to form a slurry, which may be applied to a metal current collector and then dried to obtain an electrode body integrated with the metal current collector. . When the electrode layer of the electrode body thus obtained is impregnated or coated with the polymer electrolyte forming mixed solution, it is preferable because the polymer electrolyte penetrates into the electrode layer.
Alternatively, a carbon material and a polymer electrolyte forming mixed solution may be mixed to form a slurry, which may be applied to a metal current collector to form an electrode body.
[0025]
In the present invention, the metal current collector is preferably aluminum or an aluminum alloy. Particularly preferred is aluminum having a purity of 99.9% or more and a copper content of 0.015% by weight or less. It is preferable that the metal current collector has a rough surface because adhesion with the polarizable electrode is increased. The roughening of the surface is preferably performed by chemical etching or AC etching.
[0026]
The polymer electrolyte in the present invention is disposed between the electrodes and also serves as a separator. Although the film-like polymer electrolyte may be used as it is, the polymer electrolyte may be held by a porous reinforcing material as necessary. As the porous reinforcing material, for example, a nonwoven fabric, a net, a glass fiber mat, a porous polypropylene sheet, a porous polytetrafluoroethylene sheet, or the like can be used. Of these, glass fiber mats and porous polytetrafluoroethylene sheets having high heat resistance and low water content are preferred.
[0027]
The electric double layer capacitor of the present invention has, for example, a pair of band-shaped electrode bodies as a positive electrode body and a negative electrode body, wound with a band-shaped separator interposed therebetween to form an element, accommodated in a bottomed cylindrical case, and organic electrolysis It is obtained by impregnating the device with a liquid and sealing with a lid having a positive electrode terminal and a negative electrode terminal. At this time, the case material is preferably aluminum.
[0028]
In addition, for example, a plurality of rectangular electrode bodies are made into the same number of positive electrode bodies and negative electrode bodies, and are alternately stacked with separators interposed therebetween to form elements, and leads are respectively connected from the plurality of positive electrode bodies and negative electrode bodies. After taking out and storing in a square aluminum case with a bottom, impregnating the element with an organic electrolyte, a lid having a positive electrode terminal and a negative electrode terminal is attached and sealed by laser welding etc. May be configured.
[0029]
【Example】
[Example 1]
In an argon atmosphere, a vinylidene fluoride / CF 2 = CFOCF 2 CF 2 CF 3 copolymer (a polymer unit based on vinylidene fluoride and a polymer unit based on CF 2 = CFOCF 2 CF 2 CF 3 in a weight ratio of 89 / 11 and an intrinsic viscosity of 1.4 dl / g using THF as a solvent was dissolved in 32 parts by weight of THF while stirring at 60 ° C. with stirring. This solution is designated as Solution 1. Next, (C 2 H 5 ) 3 (CH 3 ) NBF 4 was dissolved in propylene carbonate at a concentration of 1 mol / l in an argon atmosphere. This is Solution 2.
[0030]
5 parts by weight of Solution 2 was added to 21 parts by weight of Solution 1, heated to 60 ° C. and stirred. This solution was applied onto a glass plate with a bar coater and dried at 60 ° C. for 30 minutes to obtain a transparent polymer electrolyte film having a thickness of 100 μm. The composition of this film was 50 / 44.3 / 5.7 in terms of weight ratio of copolymer, propylene carbonate, and (C 2 H 5 ) 3 (CH 3 ) NBF 4 .
This film was peeled off from the glass plate, and the electrical conductivity was measured at 25 ° C. in an argon atmosphere by the AC impedance method. The electric conductivity was 8 × 10 −4 S / cm.
[0031]
AC two-stage etching was performed on an aluminum foil having a purity of 99.8% by weight or more and a copper content of less than 0.05% by weight to roughen both surfaces. The obtained aluminum foil was 19 μm thick, and the thickness of one side of the roughened layer was 1.8 μm. When the surface was observed with an electron microscope at a magnification of 20,000, it was spongy, and about 7 billion etching holes with an average pore diameter of 0.1 μm existed per 1 cm 2 . The tensile strength at break was 1.7 kg per 1 cm foil width. This aluminum foil was used as a current collector.
[0032]
11 parts by weight of activated carbon powder, 1.5 parts by weight of carbon black as a conductive material, 6 parts by weight of vinylidene fluoride / CF 2 = CFOCF 2 CF 2 CF 3 copolymer, 11 parts by weight of Solution 2, and 70 parts by weight of THF The parts were mixed in an argon atmosphere and heated with stirring to obtain a slurry. This slurry was applied to the two aluminum foils with a bar coater and dried to obtain a positive electrode body and a negative electrode body having an effective electrode area of 1 cm × 1 cm.
[0033]
The polymer electrolyte film is formed into a 1.5 cm square, the positive electrode and the negative electrode are opposed to each other, sandwiched between two 1.5 mm thick 3 cm square polytetrafluoroethylene back plates, and the outside is packaged. An electric double layer capacitor element was produced by covering with a film. This operation was also performed in an argon atmosphere.
[0034]
[Example 2 (Reference example) ]
Instead of vinylidene fluoride / CF 2 = CFOCF 2 CF 2 CF 3 copolymer, vinylidene fluoride / hexafluoroacetone copolymer (polymerized units based on vinylidene fluoride and polymer units based on hexafluoroacetone in weight ratio) The electric double layer capacitor was fabricated in the same manner as in Example 1 except that the number average molecular weight calculated by measuring by gel permeation chromatography (hereinafter referred to as GPC) using dimethylacetamide as a solvent was 886,000. .
[0035]
[Example 3]
Instead of vinylidene fluoride / CF 2 = CFOCF 2 CF 2 CF 3 copolymer, chlorotrifluoroethylene / vinylene carbonate copolymer (polymer unit based on chlorotrifluoroethylene and polymer unit based on vinylene carbonate in weight ratio) The electric double layer capacitor was manufactured in the same manner as in Example 1 except that the number average molecular weight was 105000).
[0036]
[Example 4 (Reference example) ]
Instead of vinylidene fluoride / CF 2 = CFOCF 2 CF 2 CF 3 copolymer, vinylidene fluoride / chlorotrifluoroethylene copolymer (polymerized units based on vinylidene fluoride and polymerized units based on chlorotrifluoroethylene are weight The electrical double layer capacitor was the same as in Example 1 except that the ratio was 56/44, the glass transition temperature was −5 ° C., and the embrittlement temperature was −64 ° C. measured according to ASTM D746. Was made.
[0037]
[Example 5 (comparative example) ]
Instead of vinylidene fluoride / CF 2 = CFOCF 2 CF 2 CF 3 copolymer, vinylidene fluoride / hexafluoropropylene copolymer (polymerized units based on vinylidene fluoride and polymer units based on hexafluoropropylene in weight ratio) 61/39, GPC molecular weight is 100,000, glass transition temperature is 5 ° C., using a differential thermal analysis measuring device, measured in a nitrogen gas atmosphere at a heating rate of 10 ° C./min, no melting point ) Was used in the same manner as in Example 1 to produce an electric double layer capacitor.
[0038]
[Example 6]
Instead of vinylidene fluoride / CF 2 = CFOCF 2 CF 2 CF 3 copolymer, vinylidene fluoride / tetrafluoroethylene / propylene copolymer (polymerized units based on vinylidene fluoride, polymerized units based on tetrafluoroethylene and propylene) An electric double layer capacitor was produced in the same manner as in Example 1 except that the polymer unit based on the weight ratio was 53/32/15 and the molecular weight by GPC was 150,000).
[0039]
[Evaluation]
Using the electric double layer capacitor element produced in Examples 1 to 6, constant current charging was performed for 30 minutes at 25 mA and 20 mA at an upper limit voltage of 2.8 V. The capacity was determined. In addition, a constant current discharge was performed at 10 mA, and a direct current resistance was obtained from a voltage drop value immediately after the discharge. After the initial performance was measured, 10 minutes of charging at 2.8 V and 10 minutes of charging and constant current discharging at 5 mA were repeated 2000 times to determine the capacity retention rate and the rate of resistance increase, and the charge / discharge cycle durability was evaluated. The results are shown in Table 1.
[0040]
[Table 1]
[0041]
【The invention's effect】
The electric double layer capacitor according to the present invention is excellent in retention of a solution in which a polymer electrolyte is a quaternary ammonium salt or a quaternary phosphonium salt. Excellent adhesion to the material, resulting in excellent charge / discharge cycle durability.
Claims (4)
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