JP4930852B2 - Electric double layer capacitor electrode manufacturing method, - Google Patents
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Abstract
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本発明は、電気２重層キャパシタ（以下、Electric Double Layer Capacitorを省略して「ＥＤＬＣ」ということがある。）電極の製造方法に関するものであり、詳しくは、ＥＤＬＣの電極において大きな表面積と高容量を実現するために、電極材料としてカーボンナノチューブを用いた電気２重層キャパシタ電極の製造方法に関する。 The present invention relates to a method of manufacturing an electric double layer capacitor (hereinafter referred to as “EDLC”, abbreviated to “Electric Double Layer Capacitor”) electrode. Specifically, the EDLC electrode has a large surface area and high capacity. In order to realize this, the present invention relates to a method of manufacturing an electric double layer capacitor electrode using carbon nanotubes as an electrode material.
近時、地球的規模で電力需要は著しく増大しているが、それを賄うための発電所の増設は難しく、とりわけ石化燃料を用いた火力発電所は、排出されるＣＯ２が地球温暖化現象のそしりを受け、一方、原子力発電所の建設も複雑な政治情勢も絡んで思うに任せないのが現状である。そこで太陽電池などの自然エネルギーに期待が集まるが、使用する時間帯と発電時間帯とが必ずしも一致しないために、安価でかつ大容量と長寿命の充電池が求められている。 Recently, it has been increasing on a global scale power demand significantly, difficult expansion of power plants to cover it, especially thermal power plants using fossil fuels, emissions are the CO 2 is global warming On the other hand, the current situation is not to leave it to the question of the construction of nuclear power plants and the complicated political situation. Therefore, expectation is gathered for natural energy such as solar cells. However, since the time zone to be used and the power generation time zone do not necessarily match, there is a need for a rechargeable battery that is inexpensive and has a large capacity and a long life.
また、増え続ける自動車においても環境保護の観点から、ハイブリット車や燃料電池自動車などが注目を集めているが、これらに使用されている二次電池には大電流による瞬間的な放電が求められると同時に、その長寿命化に加えて短時間充電も重要な要素であるところから、従来の二次電池ではこれらの要求に充分に応えることができないのが実状であった。 In addition, in an ever-increasing number of automobiles, hybrid vehicles and fuel cell vehicles are attracting attention from the viewpoint of environmental protection. However, secondary batteries used in these vehicles are required to be discharged instantly by a large current. At the same time, in addition to extending the life, short-time charging is also an important factor, and it has been the actual situation that conventional secondary batteries cannot sufficiently meet these requirements.
そこで従来から、電気エネルギーを蓄電するデバイスとして、化学電池や電気２重層キャパシタ（ＥＤＬＣ）が知られている。このＥＤＬＣは図１に示すように活性炭１０等の比表面積の大きな電極材料を用いた固体電極と、希硫酸などの電解液１２とを使用して、前記電極を対向するように設置し、電解液１２によって誘電体層を形成するものである（非特許文献１参照）。従来の通常型コンデンサは、絶縁物である誘電体を挟んだ電極に電圧を印加すると、双極子が配交することによって電荷が貯えられる構造であるが、電気２重層キャパシタでは、イオン性溶液中に一対の電極を浸して電気分解が起こらない程度の電圧をかけると（電気分解が起こるとコンデンサとして働かなくなる）、それぞれの電極の表面にイオンが吸着され、プラスとマイナスの電気が蓄えられる（充電）。また、外部に電気を放出すると正負のイオンは電極から離れて中和状態に戻る（放電）。 Therefore, chemical batteries and electric double layer capacitors (EDLC) are conventionally known as devices for storing electric energy. As shown in FIG. 1, the EDLC uses a solid electrode made of an electrode material having a large specific surface area such as activated carbon 10 and an electrolyte solution 12 such as dilute sulfuric acid, so that the electrodes are opposed to each other, A dielectric layer is formed by the liquid 12 (see Non-Patent Document 1). A conventional normal capacitor has a structure in which, when a voltage is applied to electrodes sandwiching a dielectric that is an insulator, charges are stored by crossing dipoles. In an electric double layer capacitor, an ionic solution is used. When a voltage is applied so that electrolysis does not occur by immersing a pair of electrodes in the electrode (it does not work as a capacitor when electrolysis occurs), ions are adsorbed on the surface of each electrode, and positive and negative electricity are stored ( charging). Further, when electricity is discharged to the outside, positive and negative ions are separated from the electrodes and return to a neutralized state (discharge).
即ち、従来から用いられる二次電池等においては充放電が化学反応の繰り返しであるため、１０００回も充放電を繰返した場合、必然的に電極や電解液が劣化して使用できなくなる。それに対し電気２重層キャパシタは、物理的な吸着・離脱で充放電を行うため、特に劣化するという現象は見られず、原理的にはその寿命は半永久的であるという特長を有している。 That is, in a conventionally used secondary battery or the like, charging and discharging are repeated chemical reactions. Therefore, when charging and discharging is repeated 1000 times, the electrodes and the electrolytic solution are inevitably deteriorated and cannot be used. On the other hand, the electric double layer capacitor is charged / discharged by physical adsorption / desorption, so that there is no particular phenomenon that it deteriorates, and in principle, its life is semi-permanent.
また、イオンの移動は化学反応に比較して物理的な吸着・離脱の方がはるかに早いために、電気２重層キャパシタは従来のバッテリにおいては到底及ぶことのできない、急速充放電が行えるという特長を有している。さらに、ユニットセル間の集電体を共通にするという構造を採用して、内部抵抗を下げることにより、数十ｋＷの大電流の充放電が秒単位で可能となるという特長もある。 In addition, since the movement of ions is much faster in physical adsorption / desorption than in chemical reactions, electric double-layer capacitors can perform rapid charge / discharge, which cannot be achieved with conventional batteries. have. Further, by adopting a structure in which the current collectors between the unit cells are shared, and reducing the internal resistance, there is a feature that charging and discharging of a large current of several tens of kW can be performed in seconds.
さらに、化学反応の場合は低温下においてはその能率が大きく低下するが、物理的吸着や離脱は低温下においてもその働きが大幅に低下することが少なく、最適な電極や電解液を選択することによって、従来のバッテリでは動作不能に陥る極低温過下（例えば−２５℃程度）においても充分に動作が可能である。 In addition, in the case of chemical reactions, the efficiency is greatly reduced at low temperatures, but physical adsorption and desorption are less likely to significantly reduce their functions even at low temperatures, and the optimum electrode and electrolyte should be selected. Therefore, the operation can be sufficiently performed even at an extremely low temperature (for example, about −25 ° C.) where the conventional battery becomes inoperable.
その他、従来のバッテリにおいては電極に鉛など環境保護の上で問題のある金属材料がより多く用いられているが、ＥＤＬＣの電極材料としては、活性炭粉末と樹脂とを焼成することによって得られる固体活性炭が用いられており、屋外への設置や廃棄等に際しても環境に悪影響を及ぼすという懸念が大幅に解消される。 In addition, in conventional batteries, more metal materials having problems in environmental protection such as lead are used for electrodes, but EDLC electrode materials are solids obtained by firing activated carbon powder and resin. Activated carbon is used, and the concern of adversely affecting the environment during outdoor installation or disposal is greatly eliminated.
このようにＥＤＬＣは従来タイプのバッテリでは及ばない多くの特性を有するところから、燃料電池から一定の電流を取り出して一旦ＥＤＬＣに貯めてバッファとして使用することにより、負荷変動を吸収するということも検討されている。一般に燃料電池で大電流の放電を実施すると、必然的に大型化や高コストが余儀なくされるが、燃料電池発電においてバッファ(負荷変動吸収)を持つということは、燃料電池定格容量の削減、高効率発電、負荷追従の高速化等の利点がある。特に家庭用など需要規模が小さいものほど負荷変動が激しくなるため、バッファの効果は大きくなるが、現状における燃料電池は高価であるところから、小さい燃料電池で瞬時に大電流を使用できることは極めて有効であり、システムの小型化においても期待されている。さらに、ハイブリット自動車や燃料電池車においては、加速時や発進の際にＥＤＬＣがアシストを行い、減速時にはエネルギーを回生して充電するシステムも検討され、位置エネルギーの回生などにも有効であり、ＥＤＬＣは短時間のエネルギー交換に有効なデバイスとしても注目されている。 As described above, EDLC has many characteristics that cannot be achieved with conventional batteries. Therefore, it is also considered to absorb load fluctuations by taking out a constant current from the fuel cell, storing it in the EDLC, and using it as a buffer. Has been. In general, when a large current discharge is performed in a fuel cell, the size and cost are inevitably increased.However, having a buffer (absorption of load fluctuation) in fuel cell power generation reduces the rated capacity of the fuel cell and increases the cost. There are advantages such as efficient power generation and faster load following. In particular, the smaller the demand scale, such as for home use, the more severe the load fluctuation, so the effect of the buffer increases. However, since current fuel cells are expensive, it is extremely effective to be able to use a large current instantaneously with a small fuel cell. It is also expected in the miniaturization of the system. In hybrid vehicles and fuel cell vehicles, EDLC assists when accelerating and starting, and a system that regenerates and recharges energy when decelerating has been studied. It is also effective for regenerating potential energy. Is attracting attention as a device effective for short-time energy exchange.
ＥＤＬＣの構成材料は、上記の如く一般的な二次電池と異なって重金属を使用していないために、燃料電池と同様に環境への負荷が低減されると共に、二次電池においては化学反応を伴うために安定電圧があり、燃料電池と並列にして使用する場合には電圧調整のための制御回路が必要となるが、ＥＤＬＣは安定電圧がなく、電圧が変動するために直接的の並列接続が可能であるところから、システムを簡素化するというメリットをも有している。 Unlike the general secondary battery, the constituent material of EDLC does not use heavy metals, so the burden on the environment is reduced as in the case of the fuel cell, and the chemical reaction in the secondary battery is reduced. Therefore, there is a stable voltage, and when it is used in parallel with the fuel cell, a control circuit for voltage adjustment is required, but EDLC does not have a stable voltage and the voltage fluctuates, so it is directly connected in parallel. Therefore, it has an advantage of simplifying the system.
ＥＤＬＣは、２枚の電極の間に電解液等を挟んだ通常のキャパシタ構造に似ているが、大きな容量を得るために大きな表面積の電極を使用しており、通常はフェノール樹脂等を炭化して作った活性炭を用いている。その表面積は１０００ｍ２／ｇ程度であるが、ＥＤＬＣで実際に電解液が入り込んで容量を形成している場合の表面積は、その１／３程度の７００ｍ２／ｇ程度と言われている。 EDLC is similar to a normal capacitor structure in which an electrolyte solution is sandwiched between two electrodes, but uses a large surface area electrode to obtain a large capacity, and usually carbonizes phenol resin or the like. Activated carbon made using The surface area is about 1000 m 2 / g, but it is said that the surface area in the case where the electrolytic solution actually enters in EDLC to form a capacity is about 1/3 of about 700 m 2 / g.
一方、電極材料として、大きな比表面積をもつカーボンナノチューブ（以下「ＣＮＴ」ということがある。）が知られているが、このカーボンナノチューブには、壁が１層でできているシングルウォールナノチューブ（以下「ＳＷＮＴ」ということがある。）と、複数層でできているマルチウォールナノチューブ（以下「ＭＷＮＴ」ということがある）とがあるが、対重量表面積を大きくするためには、ＳＷＮＴの方が有利であり、このＳＷＮＴの表面積を計算すると、約３０万ｍ２／ｇほどになる。 On the other hand, as an electrode material, a carbon nanotube having a large specific surface area (hereinafter also referred to as “CNT”) is known, and this carbon nanotube includes a single-wall nanotube (hereinafter referred to as “wall”). "SWNT") and multi-walled multi-wall nanotubes (hereinafter sometimes referred to as "MWNT"), but SWNT is more advantageous for increasing the surface area against weight. When the surface area of this SWNT is calculated, it is about 300,000 m 2 / g.
このように、ＥＤＬＣの大容量化には、ＣＮＴは充分に魅力的な大表面積を持つ材料ということができるために、ＣＮＴを電極に用いたＥＤＬＣの試みは既に数多く提案されているが、それら従来のＥＤＬＣは図２に示すように基板に垂直にＣＮＴを育成するものである（非特許文献１参照）。また、ＣＮＴを基板に最も密に接合させる手段としては、既に電着法が開示されている（非特許文献２及び３参照）。 Thus, for increasing the capacity of EDLC, since CNT can be said to be a material with a sufficiently attractive large surface area, many attempts of EDLC using CNT as an electrode have already been proposed. The conventional EDLC grows CNTs perpendicular to the substrate as shown in FIG. 2 (see Non-Patent Document 1). In addition, as a means for bonding CNTs most closely to a substrate, an electrodeposition method has already been disclosed (see Non-Patent Documents 2 and 3).
上記の各従来技術において開示されるＥＤＬＣによれば、ＣＮＴを電極基板に略垂直方向に付着接合するため、ＣＮＴ同士の間隔が充分に緻密にならず、全体として大きな表面積が得られない上に電極基板としての強度が不足するという問題があり、さらに基板とＣＮＴの接合強度を確保するために、電着に際して各種バインダーが用いられているが、結果として当該バインダーは導電性材料が直接基板に接触する妨げとなり、電気抵抗の上昇を招くという不都合が生じていた。 According to the EDLC disclosed in each of the above prior arts, since the CNTs are adhered and bonded to the electrode substrate in a substantially vertical direction, the intervals between the CNTs are not sufficiently dense, and a large surface area cannot be obtained as a whole. There is a problem that the strength as an electrode substrate is insufficient, and various binders are used for electrodeposition in order to secure the bonding strength between the substrate and the CNT. As a result, the conductive material is directly applied to the substrate. There was an inconvenience that the contact was hindered and the electrical resistance was increased.
そこで本発明者は、電極材料としてＣＮＴを使用し、比表面積を大にするために、ＣＮＴを密に形成することのできる電着法を詳細に検討した。その結果、ＣＮＴを電極基板に電着させる際に、バインダー材料を用いず、電極基板にその長手方向を略平行に付着接合させる電気二重層キャパシタの製造方法を提案した。この方法により得られる電気二重層キャパシタ電極用のＣＮＴは、単位重量換算で１５０，０００ｍ２/ｇ程度の比表面積をもち、高容量の電気二重層キャパシタが得られることが確認された（特許文献１参照）。
上記電気２重層キャパシタの最大の問題点は電気容量が小さいことであるが、本発明者が提案したように、ＣＮＴをバインダー材料を用いず、電極基板に対してその長手方向を略平行にして付着接合させることにより、ＥＤＬＣの電極で大きな表面積を実現した。しかしながら、この製造方法により電極を製造する際に、場合によってはＣＮＴが電極から剥離し、それが起因して容量の低下を招くという未解決課題があることが判明した。即ち本発明は、ＣＮＴをバインダー材料の不存在下において電極基板に接合させて電気二重層キャパシタを製造するに際し、電極基板とＣＮＴの強固な結合を実現して大きな表面積を保ちながら、高い容量を安定的に維持し得るＥＤＬＣを提供することを主たる目的とするものである。 The biggest problem of the electric double layer capacitor is that the electric capacity is small. However, as proposed by the present inventor, the CNT is not used as a binder material, and its longitudinal direction is made substantially parallel to the electrode substrate. By adhering and bonding, a large surface area was realized with the electrode of EDLC. However, when manufacturing an electrode by this manufacturing method, it has been found that there is an unresolved problem that CNT is peeled off from the electrode in some cases, which causes a decrease in capacity. That is, according to the present invention, when an electric double layer capacitor is manufactured by bonding CNTs to an electrode substrate in the absence of a binder material, a high capacity is achieved while maintaining a large surface area by realizing strong bonding between the electrode substrate and CNTs. The main object is to provide an EDLC that can be stably maintained.
本発明者は、上記課題を解決するために種々検討を重ねた結果、ＣＮＴを電極材料に用いたＥＤＬＣの安定した高容量を実現するために、ＣＮＴを電着法により電極基板に対して略平行に付着接合させ、その後熱処理を施すことにより、ＣＮＴを緻密にかつ強固に電極基板上に形成させることを見出し、本発明を完成した。 As a result of various studies to solve the above-mentioned problems, the present inventor has substantially reduced the CNT to the electrode substrate by electrodeposition in order to realize a stable high capacity of EDLC using CNT as an electrode material. The inventors have found that CNTs can be densely and firmly formed on an electrode substrate by adhering and bonding in parallel and then performing heat treatment, and the present invention has been completed.
即ち、本発明に基づく第１の発明による電気２重層キャパシタ電極の製造方法は、カーボンナノチューブを用いた電気２重層キャパシタ電極の製造方法において、該カーボンナノチューブを電着法により電極基板に付着接合する際、その長手方向を前記電極基板に対し略平行に付着接合させ、しかる後に熱処理することを構成上の特徴とするものである。 That is, the method for producing an electric double layer capacitor electrode according to the first invention based on the present invention is the method for producing an electric double layer capacitor electrode using carbon nanotubes, wherein the carbon nanotubes are adhered and bonded to an electrode substrate by electrodeposition. At this time, the longitudinal direction is adhered and bonded to the electrode substrate substantially in parallel, and then heat treatment is performed.
また、本発明に係る第２の発明による電気２重層キャパシタ電極の製造方法は、前記熱処理が、真空雰囲気下若しくは低酸素雰囲気下において、２００℃以上、前記電極基板の融点以下の温度域において施されることを特徴とするものである。 Further, in the method for manufacturing an electric double layer capacitor electrode according to the second invention of the present invention, the heat treatment is performed in a temperature range of 200 ° C. or higher and lower than the melting point of the electrode substrate in a vacuum atmosphere or a low oxygen atmosphere. It is characterized by that.
さらに、本発明に係る第３の発明による電気２重層キャパシタ電極の製造方法は、前記熱処理が、大気中において２００〜５５０℃の温度域において施されることを特徴とするものである。 Furthermore, the method for manufacturing an electric double layer capacitor electrode according to the third invention of the present invention is characterized in that the heat treatment is performed in a temperature range of 200 to 550 ° C. in the atmosphere.
本発明に係る第４の発明による電気２重層キャパシタ電極の製造方法は、前記電着法が電気泳動法であることを特徴とするものである。 According to a fourth aspect of the present invention, there is provided a method of manufacturing an electric double layer capacitor electrode, wherein the electrodeposition method is an electrophoresis method.
本発明方法によって得えられる電気２重層キャパシタ電極は、電極材料となるカーボンナノチューブの電着による金属基板への接合に際してバインダー材料を用いておらず、導電性材料が直接電極基板に接触しあうので、電気抵抗を極端に小さくすることができる。また、上記のように電極基板に平行に強く接合しているので、繊維状の導電性材料が基板に対して垂直に立つものが無く、表面積が大きく保たれているにも拘らずその厚みが極めて薄く、また、電着後の熱処理によりＣＮＴ同士やＣＮＴと電極基板とが強固に融着し、耐久性の高い電極が形成される。さらに、電極間の距離を相互に接触しない範囲に維持すれば、セパレータを不要とすることもできる。一方、上記のような電極構造とすることによって、イオン伝導が向上し、通常の電気２重層キャパシタより内部抵抗が極端に少なく、体積容量もより小さくすることが可能で、コンパクトな構造であるにも拘らず、安定した高容量の電気２重層キャパシタを比較的低価格で市場に提供することができる。 The electric double layer capacitor electrode obtained by the method of the present invention does not use a binder material for bonding to the metal substrate by electrodeposition of carbon nanotubes as the electrode material, and the conductive material directly contacts the electrode substrate. The electrical resistance can be made extremely small. In addition, since it is strongly bonded in parallel to the electrode substrate as described above, there is no fibrous conductive material that stands perpendicular to the substrate, and its thickness is maintained despite its large surface area. It is extremely thin, and the CNTs and the CNTs and the electrode substrate are firmly fused by the heat treatment after electrodeposition, so that a highly durable electrode is formed. Furthermore, if the distance between the electrodes is maintained in a range where they do not contact each other, a separator can be dispensed with. On the other hand, by adopting the electrode structure as described above, ion conduction is improved, the internal resistance is extremely smaller than that of a normal electric double layer capacitor, the volume capacity can be made smaller, and the structure is compact. Nevertheless, a stable and high-capacity electric double layer capacitor can be provided to the market at a relatively low price.
本発明の電気２重層キャパシタ電極の製造方法は、カーボンナノチューブを、バインダーを用いずに、電着法により、電極基板に略平行に堆積して付着接合し、その後熱処理することを構成上の特徴とするであるが、以下本発明の実施の形態について例示してさらに詳細に説明する。 The method for producing an electric double layer capacitor electrode of the present invention is characterized in that carbon nanotubes are deposited and adhered to an electrode substrate substantially in parallel by an electrodeposition method without using a binder, followed by heat treatment. However, embodiments of the present invention will be illustrated and described in further detail below.
本発明の電気２重層キャパシタ電極の製造方法において用いられる電極材料としてのカーボンナノチューブ即ちＣＮＴは、通常市販のカーボンナノチューブが好適に使用できるが、大きな表面積を得るためには、出来るだけ小さい粒径のものを集めることが有効である。その観点ではＣＮＴの筒径は通常１〜数ｎｍ程度であるから究極的に小さい径である。筒径１ｎｍ以下であると、通常ミクロ孔といって、電解液をその間に詰めることが困難となる。従って、筒径１ｎｍは、極限までに小さい粒径であって、かつ電解液をつめることができる限界である。即ち、ＣＮＴは大表面積のＥＤＬＣを得ることが出来る上で、現状においては究極の材料ということができる。そのほか、大表面積を得るためにはフラーレンも究極のサイズということができるが、絶縁体であるが故にＥＤＬＣには使用することができない。
また、本発明にかかるカーボンナノチューブは、直径が１〜１０ｎｍ、長さが３μｍ以下であることが好ましく、直径が１ｎｍ程度のＳＷＣＮＴが特に好ましい。そのほか、複数層でできているＭＷＮＴであれば層数の少ないＣＮＴが好ましく、また１０ｎｍを超えるものは、実験によると、金属面に接着しにくいので好ましくない。
As the carbon nanotube, that is, the CNT as an electrode material used in the method for producing an electric double layer capacitor electrode of the present invention, a commercially available carbon nanotube can be suitably used. However, in order to obtain a large surface area, the particle diameter is as small as possible. It is effective to collect things. From this point of view, the cylinder diameter of CNT is usually about 1 to several nm, so it is an extremely small diameter. If the tube diameter is 1 nm or less, it is usually called micropores, and it becomes difficult to fill the electrolyte between them. Therefore, the cylinder diameter of 1 nm is a limit that allows the electrolytic solution to be filled with a particle size that is as small as possible. That is, CNT can obtain an EDLC having a large surface area and can be said to be an ultimate material in the present situation. In addition, fullerene can be said to be the ultimate size in order to obtain a large surface area, but it cannot be used for EDLC because it is an insulator.
In addition, the carbon nanotube according to the present invention preferably has a diameter of 1 to 10 nm and a length of 3 μm or less, and SWCNT having a diameter of about 1 nm is particularly preferable. In addition, if the MWNT is made of a plurality of layers, CNTs having a small number of layers are preferable, and those exceeding 10 nm are not preferable because it is difficult to adhere to a metal surface according to experiments.
本発明において用いられるＣＮＴは、酸処理によりカルボキシル基、カルボニル基、α―ジケトン基、ケトン基、フェノール基、カルビノール基、ｏ−ヒドロキノイド基、ラクトン基などの官能基で修飾することができる。官能基と溶媒により帯電する電荷符号は異なるが、上記カルボキシル基の場合は、負電荷に帯電している。その帯電量と質量あるいはＣＮＴの曲がり具合などが原因で、ＣＮＴの直径や長さが大きくなると、基板である金属電極に接着し難くなるため、ＣＮＴの長さが３μｍを超えると上記の問題が現れるので好ましくない。また、ＣＮＴを電着させる前に、マイクロ波照射することにより、ＣＮＴに欠陥を導入することができる。ＣＮＴに欠陥を人工的に導入することにより、その後の官能基の修飾をし易くすることができる。 The CNT used in the present invention can be modified with a functional group such as a carboxyl group, a carbonyl group, an α-diketone group, a ketone group, a phenol group, a carbinol group, an o-hydroquinoid group, or a lactone group by acid treatment. . Although the charge code to be charged differs depending on the functional group and the solvent, the carboxyl group is negatively charged. If the diameter or length of the CNT increases due to the amount of charge and mass or the bending of the CNT, it becomes difficult to adhere to the metal electrode as the substrate. It is not preferable because it appears. Further, defects can be introduced into the CNTs by irradiating them with microwaves before electrodepositing the CNTs. By artificially introducing defects into the CNTs, subsequent functional group modification can be facilitated.
次いで、該ＣＮＴを強酸溶液に入れ、該溶液の入っている容器外側を冷却しながら超音波を印加し、バンドル化しているＣＮＴをほぐし、欠陥を持つＣＮＴをさらに切断して小サイズ化し、かつ、ＣＮＴに導電性の官能基を付与させることができる。この際、基板との電気伝導度の確保が重要であり、電気伝導度を良くするためには、上記強酸処理でつける官能基の選択は特に重要である。官能基としては、金属との相性が良いものであれば特に限定されないが、例えば、カルボキシル基、カルボニル基、α―ジケトン基、ケトン基、フェノール基、カルビノール基、ｏ−ヒドロキノイド基、ラクトン基などが好ましく採用される。 Next, the CNT is put into a strong acid solution, ultrasonic waves are applied while cooling the outside of the container containing the solution, the bundled CNTs are loosened, the defective CNTs are further cut and reduced in size, and A conductive functional group can be imparted to CNT. At this time, it is important to ensure electrical conductivity with the substrate, and in order to improve electrical conductivity, the selection of the functional group attached by the strong acid treatment is particularly important. The functional group is not particularly limited as long as it has good compatibility with the metal. For example, carboxyl group, carbonyl group, α-diketone group, ketone group, phenol group, carbinol group, o-hydroquinoid group, lactone A group or the like is preferably employed.
ＣＮＴの前処理工程においては、例えば、市販のＳＷＮＴ（住友商事製）7ｍｇに対してマイクロ波照射をするが、これは加熱にすることによってＣＮＴにダメージを与え、その後の酸処理で、切断やカルボキル基などの官能基の修飾がし易くするためである。次いで強酸（硫酸７５ｍｌ＋硝酸２５ｍｌ）に入れての酸処理に移るが、この際の酸処理は約５時間、外を氷で冷やしながら超音波を印加する。これで、バンドル化しているＣＮＴをほぐすと同時に、欠陥を持つＣＮＴをそこで切断し、小サイズ化することができる。次に、水洗を５時間程度行い、水酸化ナトリウムでアルカリ化し、ＣＮＴ表面に付いた官能基をイオン化する。その後、遠沈容器に入れて遠心分離を行い上部の液を採取する。下部の液に、長さ、あるいは質量の大きなＣＮＴが含まれているが、反対に上部の液には、長さ、あるいは質量の大きすぎない本発明に用いることのできるＣＮＴが含まれている。但し、どの程度の液を採取するかは、遠心分離機の回転速度、溶媒の粘性等の条件を適宜選定すればよく、その後上記の有機溶媒、例えば、ジメチルフォルムアミド（以下、ＤＭＦと記す）に分散させればよい。 In the CNT pretreatment step, for example, 7 mg of commercially available SWNT (manufactured by Sumitomo Corporation) is irradiated with microwaves, which causes damage to the CNTs by heating, followed by acid treatment, This is to facilitate modification of a functional group such as a carboxy group. Next, the process proceeds to acid treatment in a strong acid (75 ml of sulfuric acid + 25 ml of nitric acid). In this acid treatment, ultrasonic waves are applied while cooling the outside with ice for about 5 hours. As a result, the bundled CNTs can be loosened, and at the same time, the defective CNTs can be cut and reduced in size. Next, it is washed with water for about 5 hours, alkalized with sodium hydroxide, and functional groups attached to the CNT surface are ionized. Then, it is placed in a centrifuge container and centrifuged to collect the upper liquid. The lower liquid contains CNTs with a large length or mass, whereas the upper liquid contains CNTs that can be used in the present invention with a length or mass that is not too large. . However, the amount of liquid to be collected may be appropriately selected from conditions such as the rotational speed of the centrifuge and the viscosity of the solvent, and then the above organic solvent, for example, dimethylformamide (hereinafter referred to as DMF). What is necessary is just to disperse.
ＣＮＴの電着法による電極基板への付着接合させる工程においては、ＣＮＴを付着接合させる電極を正極とし、電極間距離を１ｍｍほどにして電圧を印加する。印加電圧はＣＮＴ濃度や溶媒に依存するが、１Ｖ〜５０Ｖ程度でも電着は起きる。水成分が残っている状態で高電圧を印加すると、両電極からの電気分解のため、水素、酸素の発生が起きて、電着が起きにくくなる傾向がある。したがって、好ましい印加電圧は１〜３０Ｖ程度の範囲である。 In the step of adhering and bonding the CNTs to the electrode substrate by the electrodeposition method, the electrode for adhering and bonding the CNTs is used as a positive electrode, and the voltage is applied with the distance between the electrodes being about 1 mm. Although the applied voltage depends on the CNT concentration and the solvent, electrodeposition occurs even at about 1V to 50V. When a high voltage is applied in a state where the water component remains, hydrogen and oxygen are generated due to electrolysis from both electrodes, and electrodeposition tends not to occur. Therefore, a preferable applied voltage is in the range of about 1 to 30V.
負極の材料としては金属であれば特に種類は問わないが、一方、被電着極である正極の金属種は、アルミニウムや銅のような金属、ＩＴＯなどの電気伝導性のある酸化物でも採用することが可能である。上記したように、電極基板（集電体とも言う）と大表面積を有する電極材料の間の電気的接合が重要な要素である。従来のＣＮＴ等を用いたＥＤＬＣでは、電極基板に直接垂直に育成する方法以外では、バインダーを用いている。また、ＣＮＴを用いたＥＤＬＣの場合、通常は電極基板に垂直にＣＮＴを成長させるため、電極間の間隔によっては、電極同士が接触してしまう可能性がある。 The material of the negative electrode is not particularly limited as long as it is a metal. On the other hand, the metal species of the positive electrode that is the electrodeposited electrode is also a metal such as aluminum or copper, or an electrically conductive oxide such as ITO. Is possible. As described above, an electrical connection between an electrode substrate (also called a current collector) and an electrode material having a large surface area is an important factor. In EDLC using conventional CNTs or the like, a binder is used except for a method of growing directly perpendicular to an electrode substrate. In addition, in the case of EDLC using CNTs, since CNTs are usually grown perpendicular to the electrode substrate, the electrodes may come into contact with each other depending on the distance between the electrodes.
本発明の方法においては、電着に際してバインダーを用いておらず、導電性材料が直接電極基板に接触しあうので、電気抵抗が小さくて済むのである。このように本発明の製造方法で得られる電気２重層キャパシタ電極は、バインダーを用いないところに特色があり、従って導電性材料が直接電極基板に接触しあうので、電気抵抗を小さくすることができ、また、上記したように電極基板に平行に強く接合しているので、繊維状に導電性材料が基板に垂直に立つものが無く、表面積が大きく保たれているにも拘らずその厚みが極めて薄く、電極基板を強固にし、電極間の距離を接触しない距離とすれば、セパレータを不要とすることもできるのである。また、かかる電極構造とすることによって、イオン伝導が向上し、通常の電気２重層キャパシタより内部抵抗が少なく、かつ体積容量も小さくした電気２重層キャパシタの提供が可能となる。 In the method of the present invention, no binder is used for electrodeposition, and the conductive material is in direct contact with the electrode substrate, so that the electrical resistance is small. As described above, the electric double layer capacitor electrode obtained by the manufacturing method of the present invention is characterized in that a binder is not used, and therefore, the conductive material directly contacts the electrode substrate, so that the electric resistance can be reduced. In addition, since it is strongly bonded in parallel to the electrode substrate as described above, there is no fiber-like conductive material standing perpendicular to the substrate, and its thickness is extremely high despite its large surface area. If the electrode substrate is thin, the electrode substrate is strong, and the distance between the electrodes is set so as not to contact, a separator can be dispensed with. Further, with such an electrode structure, it is possible to provide an electric double layer capacitor having improved ion conduction, lower internal resistance and smaller volume capacity than a normal electric double layer capacitor.
上記のようにしてＳＷＮＴを電極基板に電着させ、乾燥させて電極を得ることができる。メッキ部の面積は、１０×1０ｍｍ２であり、電子顕微鏡による観察から、厚みを求めると厚みは５μｍであった。また、ＣＮＴだけの重要増加は1ｍｇである。また、ＢＥＴ法で計測した表面積は、２６４０ｍ２／ｇであり、グラフェンシートから期待される表面積と一致した。つまり、ナノチューブの場合、先端が開放されると同時に内側も表面積として寄与していることが保証されている。 As described above, SWNT can be electrodeposited on an electrode substrate and dried to obtain an electrode. The area of the plated portion was 10 × 10 mm 2 , and the thickness was 5 μm when the thickness was determined from observation with an electron microscope. Moreover, the significant increase of only CNT is 1 mg. Moreover, the surface area measured by BET method was 2640 m < 2 > / g, and corresponded with the surface area anticipated from a graphene sheet. In other words, in the case of a nanotube, it is guaranteed that the inner side contributes to the surface area at the same time that the tip is opened.
このようにして作成したカーボンナノチューブを使用し、電着法で作成した電極を、低酸素雰囲気下、例えば、真空中（Ｐ＝１０―3 Torr）において、３５０℃に加熱して５時間の熱処理を行った。通常、電着したＣＮＴは、大気等の有酸素状態においては、５５０℃以上で燃焼してしまうため、熱処理はこの温度以下でなければならない。また、真空中や不活性ガス中での熱処理の場合においては、熱処理温度の上限は、使用する基板材料の融点や相変化温度等が重要となる。例えば、アルミニウムを基板として使用する場合は、６００℃以下という条件が必要となる。熱処理温度の下限は２００℃であるが、２００℃より低い温度で熱処理を行ってもＣＮＴの融着が見られず、熱処理による強度の向上は認められないため２００℃以上の温度が必要である。勿論、熱処理温度は高い方がその効果は顕著に現れる。 The electrode prepared by the electrodeposition method using the carbon nanotube thus prepared is heated to 350 ° C. in a low oxygen atmosphere, for example, in a vacuum (P = 10 −3 Torr) for 5 hours. Went. Usually, electrodeposited CNTs burn at 550 ° C. or higher in an aerobic state such as the atmosphere, so the heat treatment must be below this temperature. In the case of heat treatment in vacuum or inert gas, the upper limit of the heat treatment temperature is important for the melting point, phase change temperature, etc. of the substrate material used. For example, when aluminum is used as the substrate, the condition of 600 ° C. or lower is required. The lower limit of the heat treatment temperature is 200 ° C. However, even if the heat treatment is performed at a temperature lower than 200 ° C., the fusion of CNT is not observed, and the strength is not improved by the heat treatment. . Of course, the higher the heat treatment temperature, the more remarkable the effect.
通常、ナノサイズのカーボンナナノチューブでは、原子の活動が活発なため、接触したカーボンナノチューブでは比較的容易に融着（ＣＮＴとＣＮＴが接触しているところの原子の移動が起き易く、２本のＣＮＴが結合してしまう現象）がおきやすいことが知られており、例えば２００℃程度でもＣＮＴ同士の結合が起きることも知られている。まして、本発明にかかるＣＮＴは、マイクロ波処理、超音波環境下での酸処理を経ているため、ＣＮＴの端だけでなく、ＣＮＴの側面にも、ダメージ（炭素結合が切れている状態）が生じているので、活性状態の炭素が多くあることになる。従って、室温以上の高温時にＣＮＴ同士が接触すれば、容易にＣＮＴ同士の結合、即ち融着現象が現れるのである。 In general, since nano-sized carbon nanotubes are active in atoms, the contacted carbon nanotubes are relatively easily fused (the movement of atoms where CNTs and CNTs are in contact is likely to occur. It is known that the phenomenon of bonding of CNTs is likely to occur, for example, bonding of CNTs occurs even at about 200 ° C. Moreover, since the CNT according to the present invention has undergone microwave treatment and acid treatment under an ultrasonic environment, damage (carbon bonds are broken) not only on the end of the CNT but also on the side surface of the CNT. As a result, there is a lot of active carbon. Accordingly, if the CNTs come into contact with each other at a high temperature above room temperature, the bonding between the CNTs, that is, a fusion phenomenon easily appears.
ＣＮＴは、電着によって金属電極板とファンデアワールス力で結合している状態であるが、ＣＮＴ全体が金属電極と付いているのとは限らない。そこで、電解液を注入するとＣＮＴ同士の隙間、或いはＣＮＴ内部に電解液が入っていくが、その時ＣＮＴとＣＮＴの間、或いはＣＮＴと金属電極の間に入り込むと、ＣＮＴを引き剥がす方向に力が働く。そこで単純に積層しただけの状態では、ＣＮＴが剥がれる可能性があるが、熱処理によりＣＮＴ同士が融着しておれば、剥がれ難くなることは明らかである。このようにして、電解液を注入しても丈夫な電極膜が構成されることとなる。
［実施例］
CNT is in a state of being bonded to the metal electrode plate by van der Waals force by electrodeposition, but the entire CNT is not necessarily attached to the metal electrode. Therefore, when the electrolyte is injected, the electrolyte enters the gap between the CNTs or inside the CNT. At that time, if it enters between the CNTs or between the CNTs and the metal electrode, a force is applied in the direction of peeling off the CNTs. work. Thus, although the CNTs are simply stacked, the CNTs may be peeled off. However, if the CNTs are fused together by heat treatment, it is clear that the CNTs are hardly peeled off. In this way, a durable electrode film is formed even when the electrolytic solution is injected.
[Example]
以下、実施例を用いて本発明をさらに具体的に説明する。 Hereinafter, the present invention will be described more specifically with reference to examples.
市販のＳＷＮＴ（住友商事製：寸法詳細仕様：直径１〜２ｎｍ、長さ１〜３μｍ）７ｍｇを採取してガラス皿に平たく広げ、マイクロ波（５ＧＨｚ、約７００Ｗ）を３０分照射した。照射の途中、少し火花が見えるのが確認された。照射終了後、ガラス皿上のＳＷＮＴの重量を計測したところ約５ｍｇであった。このマイクロ波照射後のＳＷＮＴ５ｍｇを、強酸（硫酸７５ｍｌ＋硝酸２５ｍｌ）に入れ、約５時間、該溶液の入っている容器外側を氷で冷やしながら超音波発生器ＵＳ−１（アズワン社製）を使用して超音波を印加した。この酸処理により、バンドル化しているＣＮＴをほぐすと同時に、欠陥を持つＣＮＴをその場で切断して小サイズ化した。次に水洗を５時間程度行い、水酸化ナトリウムでアルカリ化し、ＣＮＴ表面に付いた官能基をイオン化した。その後さらに遠沈容器に入れて遠心分離を行い、その上部液を採取した。採取された上部液よりＣＮＴを取り出し、ジメチルフォルムアミド（以下、「ＤＭＦ」ということがある。）に分散させた。次いでアルミニウム電極基板を正極とし、負極もアルミニウム板として、電極間距離を１ｍｍほどに調整した状態で、数Ｖ、３０分間電圧を印加することによって、ＣＮＴの前処理および電着法による基板への付着接合の工程を完了した。得られたＣＮＴの平均長と電着された膜厚との関係を図３に示す。これによってＣＮＴの平均長がおよそ３μｍ以下で、５〜１００μｍ程度の膜厚の電着膜厚が得られることが確認された。 7 mg of commercially available SWNT (manufactured by Sumitomo Corporation: detailed dimensions: diameter 1 to 2 nm, length 1 to 3 μm) was collected and spread flat on a glass dish, and irradiated with microwaves (5 GHz, about 700 W) for 30 minutes. During the irradiation, it was confirmed that some sparks were visible. After the irradiation, the weight of SWNT on the glass dish was measured and found to be about 5 mg. Place 5 mg of SWNT after microwave irradiation in strong acid (75 ml of sulfuric acid + 25 ml of nitric acid) and use the ultrasonic generator US-1 (manufactured by ASONE) while cooling the outside of the container containing the solution with ice for about 5 hours. Then, ultrasonic waves were applied. By this acid treatment, the bundled CNTs were loosened, and at the same time, the defective CNTs were cut in situ to reduce the size. Next, it was washed with water for about 5 hours, alkalized with sodium hydroxide, and functional groups attached to the CNT surface were ionized. Thereafter, the mixture was further placed in a centrifuge container and centrifuged, and the upper liquid was collected. CNTs were taken out from the collected upper liquid and dispersed in dimethylformamide (hereinafter sometimes referred to as “DMF”). Next, with the aluminum electrode substrate as the positive electrode and the negative electrode as the aluminum plate, the voltage between the electrodes was adjusted to about 1 mm, and a voltage was applied for several minutes for 30 minutes. The process of adhesive bonding was completed. The relationship between the average length of the obtained CNTs and the electrodeposited film thickness is shown in FIG. Thus, it was confirmed that an electrodeposition film thickness of about 5 to 100 μm was obtained with an average length of CNT of about 3 μm or less.
上記の如くして得られたＣＮＴをアルミニウム基板に電着し、作成したＣＮＴ膜における熱処理温度の依存性を調べた。また、アルミニウムの電極（１０×１０ｍｍ２）上に、同様なプロセスでＣＮＴを電着させた。それぞれ電着したＣＮＴのみだけの重量は０．８５ｍｇから１．２５ｍｇまでのばらつきがあった。それぞれの成膜したサンプルを、真空（約１０−３Torr）中で、９段階の温度域において各条件について５個のＣＮＴ膜に熱処理を施した。上記の熱処理温度はそれぞれ１５０℃、２００℃、２５０℃、３００℃、３５０℃、４００℃、４５０℃、５００℃、５５０℃とし、ピーク温度に４時間保持した。この際いずれのサンプルも、７．５℃／分の昇温速度で昇温し、降温は、スイッチを切った後に一晩放置することによって自然に放冷した。上記各条件で熱処理を施した各５個のサンプルを、ＤＭＦの入ったビーカに浸し、更にそのＤＭＦ入りのビーカを、水を入れた超音波槽にビーカの概ねその半分が水中に浸るように設置した。その後、２００Ｗのパワーを加え、そのまま２時間超音波を印加して電着膜が剥がれるか否かを評価した。即ち、その後各サンプルを水洗して１５０℃で３時間乾燥した後、それぞれのサンプルについて重量変化を計測して、剥がれ落ちた分の対重量比を調べた結果は図４に示す通りであった。図４からも明らかなように、２００℃以上での熱処理を施した場合は、剥がれ落ちに対する充分な耐性を示してその効果が確認された。 CNTs obtained as described above were electrodeposited on an aluminum substrate, and the dependency of the heat treatment temperature on the prepared CNT film was examined. In addition, CNTs were electrodeposited on an aluminum electrode (10 × 10 mm 2 ) by the same process. The weight of each electrodeposited CNT alone varied from 0.85 mg to 1.25 mg. Each of the deposited samples was subjected to heat treatment in vacuum (about 10 −3 Torr) on five CNT films for each condition in a nine-step temperature range. The heat treatment temperatures were 150 ° C., 200 ° C., 250 ° C., 300 ° C., 350 ° C., 400 ° C., 450 ° C., 500 ° C., and 550 ° C., respectively, and held at the peak temperature for 4 hours. At this time, all the samples were heated at a temperature rising rate of 7.5 ° C./min, and the temperature was naturally allowed to cool by standing overnight after switching off. Each of the five samples heat-treated under the above conditions is immersed in a beaker containing DMF, and the beaker containing DMF is immersed in an ultrasonic bath containing water so that approximately half of the beaker is submerged in water. installed. Thereafter, a power of 200 W was applied, and an ultrasonic wave was applied as it was for 2 hours to evaluate whether or not the electrodeposition film was peeled off. That is, after each sample was washed with water and dried at 150 ° C. for 3 hours, the change in weight was measured for each sample, and the result of examining the weight ratio of the sample peeled off was as shown in FIG. . As is clear from FIG. 4, when heat treatment at 200 ° C. or higher was performed, the effect was confirmed with sufficient resistance against peeling off.
実施例１で得られたＣＮＴ膜を使用して、その熱処理時間依存性を調査した。実施例1と同様にして作成したＣＮＴ膜を各条件で５個ずつ用意し、３５０℃で、１時間、２時間、４時間、８時間、１０時間とそれぞれ熱処理を施した。得られた各サンプルについて実施例１と同様の条件で超音波を印加して、剥がれ落ちる割合を対重量比で求め、その結果を図５に示した。図５からも明らかなように２時間以上の熱処理を施すことによって、剥がれ落ちに対して充分な耐性効果があることが確認された。
（比較例１）
Using the CNT film obtained in Example 1, the heat treatment time dependency was investigated. Five CNT films prepared in the same manner as in Example 1 were prepared under each condition, and heat-treated at 350 ° C. for 1 hour, 2 hours, 4 hours, 8 hours, and 10 hours, respectively. For each of the obtained samples, an ultrasonic wave was applied under the same conditions as in Example 1, and the ratio of peeling off was determined by the weight ratio. The results are shown in FIG. As is clear from FIG. 5, it was confirmed that a heat resistance of 2 hours or more has a sufficient resistance effect against peeling off.
(Comparative Example 1)
実施例１と同様にして得られた電極で、熱処理していないＣＮＴ膜５個、熱処理したＣＮＴ膜５個のサンプルを用意し、これらのサンプルを電子顕微鏡で観察した結果、両者に特段の相違は認められなかった。次いでそれらのサンプルを、プロピレンカーボネート液を入れた小ガラスビン１０個の中にそれぞれ浸漬し、そのガラスビンを水が入った超音波槽に浸して、５時間に渡って超音波を印加してダメージを観察した。その結果、非熱処理品であっても２時間程度の処理では大きな変化は認められなかったが、５時間後の変化を観察すると、非熱処理品では２個ほど、少し剥がれているものが認められたが、熱処理が施されたサンプルにおいては、剥離が全く認められないことが確認された。 Samples of 5 CNT films that were not heat-treated and 5 heat-treated CNT films were prepared using electrodes obtained in the same manner as in Example 1, and these samples were observed with an electron microscope. Was not recognized. The samples were then immersed in 10 small glass bottles each containing propylene carbonate solution, the glass bottles were immersed in an ultrasonic bath containing water, and ultrasonic waves were applied for 5 hours to damage them. Observed. As a result, even if it was a non-heat-treated product, no significant change was observed in the treatment for about 2 hours. However, when the change after 5 hours was observed, about 2 non-heat-treated products were found to be slightly peeled off. However, it was confirmed that no peeling was observed in the heat-treated sample.
本発明方法によって得られる電気２重層キャパシタ電極は、カーボンナノチューブからなる電極材料の、金属基板に対する電着による接合に際してバインダー材料を用いておらず、導電性材料が直接電極基板に接触しあうので、電気抵抗を極めて少なくすることができる。また、上記のように電極基板に平行に強く接合しているので、繊維状の導電性材料が基板に対して垂直に立つものが無く、表面積が大きく保たれているにも拘らずその厚みが極めて薄く、また、電着後の熱処理によりＣＮＴ同士やＣＮＴと電極基板とが強固に融着し、耐久性の高い電極が形成される。さらに、電極間の距離を相互に接触しない範囲に維持すれば、セパレータを不要とすることもできる。一方、上記のような電極構造とすることによって、イオン伝導が向上し、通常の電気２重層キャパシタより内部抵抗が少なく、体積容量も小さくすることが可能で、コンパクトな構造であるにも拘らず、安定した高容量の電気２重層キャパシタを比較的低価格で市場に提供することができる。 The electric double layer capacitor electrode obtained by the method of the present invention does not use a binder material when the electrode material composed of carbon nanotubes is joined to the metal substrate by electrodeposition, and the conductive material directly contacts the electrode substrate. The electrical resistance can be extremely reduced. In addition, since it is strongly bonded in parallel to the electrode substrate as described above, there is no fibrous conductive material that stands perpendicular to the substrate, and its thickness is maintained despite its large surface area. It is extremely thin, and the CNTs and the CNTs and the electrode substrate are firmly fused by the heat treatment after electrodeposition, so that a highly durable electrode is formed. Furthermore, if the distance between the electrodes is maintained in a range where they do not contact each other, a separator can be dispensed with. On the other hand, by adopting the electrode structure as described above, the ion conduction is improved, the internal resistance is smaller than that of a normal electric double layer capacitor, the volume capacity can be reduced, and the compact structure is achieved. Thus, a stable and high-capacity electric double layer capacitor can be provided to the market at a relatively low price.
１０ 活性炭
１２ 電解液
10 Activated carbon 12 Electrolyte
Claims (1)
In the method of manufacturing an electric double layer capacitor electrode using carbon nanotubes, when the carbon nanotubes are adhered and bonded to an electrode substrate by electrophoresis , the longitudinal direction is adhered and bonded substantially parallel to the electrode substrate, and then vacuum is applied. A method for producing an electric double layer capacitor electrode , comprising performing heat treatment at 300 to 450 ° C. for 4 to 6 hours in an atmosphere .
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