JP5931326B2 - Activated carbon for electric double layer capacitors - Google Patents
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- JP5931326B2 JP5931326B2 JP2010037746A JP2010037746A JP5931326B2 JP 5931326 B2 JP5931326 B2 JP 5931326B2 JP 2010037746 A JP2010037746 A JP 2010037746A JP 2010037746 A JP2010037746 A JP 2010037746A JP 5931326 B2 JP5931326 B2 JP 5931326B2
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Description
本発明は、電気二重層キャパシタ用活性炭に関する。詳しくは、内部抵抗が小さく、高い出力密度を有し、耐久性にも優れた特性の電気二重層キャパシタ用活性炭に関する。 The present invention relates to activated carbon for electric double layer capacitors. Specifically, the present invention relates to activated carbon for electric double layer capacitors having a small internal resistance, a high output density, and excellent durability.
近年、地球環境対策の点から、自動車分野でも燃費のさらなる向上、排気ガスを更に浄化するための開発が行われている。この開発の取り組みの一環として、ハイブリッド自動車、電気自動車の技術開発が進められている。これらの技術開発に関連して駆動系パワーアシストあるいはエネルギー回生の用途に電気二重層キャパシタの実用化が注目されている。電気二重層キャパシタは、分極性電極と電解液の界面に形成される電気二重層に電荷を蓄積することを原理としており、鉛蓄電池、ニッケル水素二次電池等の二次電池と比べて大電流による急速充放電ができることが長所である。分極性電極の材料としては、界面が大きく、かつ導電性に優れる点から、通常、活性炭が用いられる。ハイブリッド自動車、電気自動車用途で求められる電気二重層キャパシタは、静電容量（Ｆ）のみならず、１００アンペアオーダーの大電流で繰り返し充電・放電が可能な高い出力（Ｗ）密度、即ち低い内部抵抗が求められている。 In recent years, from the viewpoint of global environmental measures, development for further improvement of fuel consumption and further purification of exhaust gas has been performed in the automobile field. As part of this development effort, technology development for hybrid and electric vehicles is underway. In connection with these technological developments, the practical use of electric double layer capacitors has attracted attention for applications such as drive system power assist or energy regeneration. The electric double layer capacitor is based on the principle that electric charge is stored in the electric double layer formed at the interface between the polarizable electrode and the electrolyte, and has a larger current than secondary batteries such as lead storage batteries and nickel metal hydride secondary batteries. It is an advantage that can be charged and discharged quickly. As a material for the polarizable electrode, activated carbon is usually used because it has a large interface and excellent conductivity. Electric double layer capacitors required for hybrid and electric vehicle applications are not only capacitance (F), but also high output (W) density that can be repeatedly charged and discharged with a large current of the order of 100 amps, that is, low internal resistance. Is required.
この様な問題点を解決しようとして、やしがらを炭化してなる活性炭であって、ＢＥＴ比表面積、平均細孔径及び細孔容積に着目し、これらを特定の数値範囲に制御してなる電気二重層キャパシタ用活性炭が知られている（特許文献１）。 In an attempt to solve such problems, activated carbon obtained by carbonizing coconut palms, focusing on the BET specific surface area, average pore diameter, and pore volume, and controlling them within a specific numerical range An activated carbon for a double layer capacitor is known (Patent Document 1).
特許文献１の発明を更に詳しく述べると、やしがらを炭化してなる活性炭であって、ＢＥＴ比表面積が２０００ｍ2／ｇ以上２５００ｍ2／ｇ以下であり、平均細孔径が１．９５ｎｍ（１９．５Å）以上２．２０ｎｍ（２２．０Å）以下であり、かつクランストンインクレー法で算出した細孔直径が５．０ｎｍ（５０Å）から３０．０ｎｍ（３００Å）間の細孔容積が０．０５ｃｍ3／ｇ以上０．１５ｃｍ3／ｇ以下であることを特徴とする電気二重層キャパシタ用活性炭である。 To describe the invention of Patent Document 1 in more detail, it is an activated carbon obtained by carbonizing coconut palm, having a BET specific surface area of 2000 m 2 / g to 2500 m 2 / g and an average pore diameter of 1.95 nm (19 0.5 Å) to 2.20 nm (22.0 Å) and the pore volume calculated by the Cranston inclay method is 5.0 nm (50 Å) to 30.0 nm (300 Å). an electric double layer activated carbon capacitor, wherein 05cm 3 / g or more 0.15 cm 3 / g or less.
特許文献１の発明は、電気二重層キャパシタ用活性炭に求められる多くの技術的課題を解決するものであるが、原料の多様化、内部抵抗の低下などに更なる課題が残されていた。 The invention of Patent Document 1 solves many technical problems required for activated carbon for electric double layer capacitors, but further problems remain such as diversification of raw materials and reduction of internal resistance.
係る課題に対処するものとして、やしがら炭の代わりに、石油系コークス原料を使用した発明が知られている（特許文献２）。特許文献２の発明は、比表面積及び平均細孔径を特許文献１の発明と重複部分を有する特定範囲に設定したうえに、細孔容積に着目してこれを０．８×１０-6〜２．０×１０-6ｍ3／ｇという大きな範囲に制御するものである。特定の比表面積、平均細孔径及び細孔容積からなる３物性の組合せを必須要件とするが、細孔容積の積算に当たり、細孔直径を考慮せずに、全細孔容積を発明の構成要件としたことに特徴があると見られる。
しかしながら、特許文献２の発明は電極の内部抵抗に影響を及ぼすクランストンインクレー法で算出した細孔直径が５．０ｎｍ（５０Å）から３０ｎｍ（３００Å）間の細孔容積についての言及はしていない。本発明者らの検討によれば、比表面積と細孔容積および平均細孔径がほぼ同一であってもクランストンインクレー法で算出した細孔直径が５．０ｎｍから３０ｎｍ間の細孔容積の多寡によって内部抵抗が変化することを確認している。
更に本発明者らは、賦活原料に含まれるカリウム、ナトリウムの量が変動すると内部抵抗に影響を及ぼすクランストンインクレー法で算出した細孔直径が５．０ｎｍから３０ｎｍ間の細孔容積量も変化することに着目して、細孔直径が５．０ｎｍから３０ｎｍ間の細孔容積量と、賦活前処理即ちアルカリ溶液への浸漬及び酸性溶液での洗浄の関係について鋭意検討をした。
その結果、賦活原料をアルカリ溶液に浸漬した後、水洗浄してカリウム、ナトリウム量を６００から２０００ｐｐｍに調整すると、賦活原料を酸性溶液で洗浄してカリウム、ナトリウム量を６００から２０００ｐｐｍに調整した場合に比べて、細孔直径が５．０ｎｍから３０ｎｍ間の細孔容積量が増える事実を見いだした。この原因については、まだ充分な技術的解析がなされていないが、アルカリ溶液への浸漬によってアルカリ成分が賦活原料の表面や気孔の内壁まで良好に分散していると推察することができる。
即ち、やしがらチャーに元々含まれるカリウムやナトリウムは、ヤシが成長する際に、根を通じて土中から吸収されヤシ組織の内部に蓄えられる。そのため、やしがらチャー固有のカリウムやナトリウムは、やしがらチャーの表面や気孔の内壁には殆ど存在してないと考えられる。一方、賦活原料をアルカリ溶液に浸漬した後、水洗浄をすると、賦活原料の表面や気孔の内壁にもアルカリが良好に分散され、賦活でガス化反応が促進され、細孔直径が５．０ｎｍから３０ｎｍ間の細孔容積量が増加すると考えられる。
In order to cope with such a problem, an invention using a petroleum coke raw material instead of coconut charcoal is known (Patent Document 2). In the invention of Patent Document 2, the specific surface area and the average pore diameter are set in a specific range having an overlapping portion with the invention of Patent Document 1, and this is set to 0.8 × 10 −6 to 2 with a focus on the pore volume. It is controlled within a large range of 0.0 × 10 −6 m 3 / g. A combination of three physical properties consisting of a specific specific surface area, average pore diameter, and pore volume is an essential requirement, but the total pore volume is considered a constituent requirement of the invention without considering the pore diameter when integrating the pore volume. It seems that there is a feature in that.
However, the invention of Patent Document 2 does not mention the pore volume between 5.0 nm (50 mm) and 30 nm (300 mm) calculated by the Cranston inclay method which affects the internal resistance of the electrode. Absent. According to the study by the present inventors, even when the specific surface area, the pore volume, and the average pore diameter are almost the same, the pore diameter calculated by the Cranston inclay method is a pore volume between 5.0 nm and 30 nm. It has been confirmed that the internal resistance changes depending on the number.
Furthermore, the present inventors also have a pore volume amount between 5.0 nm and 30 nm as calculated by the Cranston inclay method, which affects internal resistance when the amount of potassium and sodium contained in the activation raw material varies. Paying attention to the change, the inventors studied diligently about the relationship between the pore volume between 5.0 nm and 30 nm and the pretreatment for activation, that is, immersion in an alkaline solution and washing with an acidic solution.
As a result, when the activation raw material is immersed in an alkaline solution and then washed with water to adjust the potassium and sodium amounts from 600 to 2000 ppm, the activation raw material is washed with an acidic solution and the potassium and sodium amounts are adjusted from 600 to 2000 ppm. In comparison with the above, it was found that the pore volume increased between 5.0 nm and 30 nm. About this cause, although sufficient technical analysis has not been made yet, it can be inferred that the alkaline component is well dispersed to the surface of the activation raw material and the inner walls of the pores by immersion in the alkaline solution.
That is, potassium and sodium originally contained in coconut char are absorbed from the soil through the roots and stored in the palm tissue when the palm grows. Therefore, it is considered that potassium and sodium inherent to coconut char hardly exist on the surface of coconut char and the inner walls of the pores. On the other hand, when the activation raw material is immersed in an alkali solution and then washed with water, the alkali is well dispersed on the surface of the activation raw material and the inner walls of the pores, and the gasification reaction is promoted by activation, and the pore diameter is 5.0 nm. It is considered that the pore volume between 30 nm and 30 nm increases.
本発明は上記観点から生じたものであり、内部抵抗が小さく、高い出力密度を有し、耐久性にも優れた特性の電気二重層キャパシタ用活性炭を提供する。詳しくは、本発明は、体積当たりの出力密度が大きく、かつ、大電流下での充放電サイクルを繰り返したり、或いは一定電圧を長時間連続して印加した場合でも、出力密度の低下が少ない電気二重層キャパシタに適した活性炭を提供することを課題とする。 The present invention originates from the above viewpoint, and provides an activated carbon for an electric double layer capacitor having a low internal resistance, a high output density, and excellent durability. Specifically, the present invention provides an electric power with a small output density even when the output density per volume is large and the charge / discharge cycle under a large current is repeated or a constant voltage is applied continuously for a long time. It is an object to provide activated carbon suitable for a double layer capacitor.
本発明者らは、上記課題を解決すべく特許文献１の発明を基礎として鋭意研究を重ねた。その結果、クランストンインクレー法で算出した細孔直径が５．０ｎｍから３０．０ｎｍ間の細孔容積を数倍（中間値比較では４倍）大きく、かつＢＥＴ比表面積及び平均細孔径をやや大きめ（中間値比較では１〜２割）に制御した場合には、より一層良好な結果が得られるとの知見に基づき本発明を完成するに至った。 In order to solve the above-mentioned problems, the present inventors have made extensive studies based on the invention of Patent Document 1. As a result, the pore volume calculated by the Cranston inclay method is several times larger than the pore volume between 5.0 nm and 30.0 nm (4 times in the intermediate value comparison), and the BET specific surface area and the average pore diameter are slightly increased. The present invention has been completed based on the knowledge that even better results can be obtained when it is controlled to be larger (10 to 20% in the intermediate value comparison).
即ち、本発明の要旨とするところは、ＢＥＴ比表面積が２２００ｍ2／ｇ以上２７００ｍ2／ｇ以下であり、平均細孔径が２．２ｎｍ以上２．８ｎｍ以下であり、かつクランストンインクレー法で算出した細孔直径が５．０ｎｍから３０．０ｎｍ間の細孔容積が０．２０ｃｍ3／ｇ以上０．６０ｃｍ3／ｇ以下であることを特徴とする電気二重層キャパシタ用活性炭に存する。 That is, the gist of the present invention is that the BET specific surface area is 2200 m 2 / g or more and 2700 m 2 / g or less, the average pore diameter is 2.2 nm or more and 2.8 nm or less, and the Cranston inclay method is used. The activated carbon for an electric double layer capacitor is characterized in that the pore volume between the calculated pore diameters of 5.0 nm and 30.0 nm is 0.20 cm 3 / g or more and 0.60 cm 3 / g or less.
また、本発明の他の要旨は、活性炭中の含酸素官能基量が２重量％以下であり、かつ灰分が１重量％以下であることを特徴とする前記の電気二重層キャパシタ用活性炭に存する。 Another gist of the present invention resides in the activated carbon for an electric double layer capacitor, wherein the amount of oxygen-containing functional groups in the activated carbon is 2% by weight or less and the ash content is 1% by weight or less. .
また、本発明の他の要旨は、やしがら炭化物を水蒸気賦活してなる、前記の電気二重層キャパシタ用活性炭に存する。 Another gist of the present invention resides in the activated carbon for an electric double layer capacitor, which is obtained by steam activation of coconut palm.
また、本発明の他の要旨は、植物系材料を薬品賦活してなる活性炭を水洗または酸洗浄後、さらに水蒸気賦活することを特徴とする前記電気二重層キャパシタ用活性炭の製造方法に存する。 Another aspect of the present invention resides in the method for producing activated carbon for an electric double layer capacitor, wherein activated carbon obtained by chemical activation of a plant-based material is further subjected to water vapor activation after water washing or acid washing.
内部抵抗が小さく、高い出力密度を有し、耐久性にも優れた特性の電気二重層キャパシタ用活性炭を提供できる。原料炭として、やしがら炭化物が有効であり好ましいが、本発明が規定する必須要件物性を充足する限り、石油系又は石炭系原料も利用可能である。 An activated carbon for an electric double layer capacitor having a low internal resistance, a high output density, and excellent durability can be provided. As the raw coal, coconut carbide is effective and preferable, but petroleum-based or coal-based raw materials can be used as long as the essential physical properties defined by the present invention are satisfied.
以下、本発明を詳細に説明する。本発明の電気二重層キャパシタ用活性炭は、ＢＥＴ比表面積が２２００ｍ2／ｇ以上２７００ｍ2／ｇ以下であること、平均細孔径が２．２ｎｍ（２２Å）以上２．８ｎｍ（２８Å）以下であること、及びクランストンインクレー法で算出した細孔直径が５．０ｎｍ（５０Å）から３０．０ｎｍ（３００Å）の細孔容積が０．２０ｃｍ3／ｇ以上０．６０ｃｍ3／ｇ以下であることの各物性を充たすことが必須であって、好ましくは、活性炭中の含酸素官能基量が２重量％以下であり、かつ灰分が１重量％以下のものである。更に、非水系電解液中における対極リチウムでの自然電位が２．８５Ｖ以上３．０３Ｖ以下である物性を更に充たすものが好ましい。 Hereinafter, the present invention will be described in detail. The activated carbon for electric double layer capacitors of the present invention has a BET specific surface area of 2200 m 2 / g or more and 2700 m 2 / g or less, and an average pore diameter of 2.2 nm (22 mm) or more and 2.8 nm (28 mm) or less. And a pore volume calculated by the Cranston inclay method of 5.0 nm (50 mm) to 30.0 nm (300 mm) of a pore volume of 0.20 cm 3 / g or more and 0.60 cm 3 / g or less. It is essential to satisfy each physical property. Preferably, the amount of oxygen-containing functional groups in the activated carbon is 2% by weight or less and the ash content is 1% by weight or less. Furthermore, what further satisfies the physical property that the natural potential at the counter electrode lithium in the non-aqueous electrolyte solution is 2.85 V or more and 3.03 V or less is preferable.
これらの物性を充たす本発明の活性炭を分極性電極材料とする電気二重層キャパシタにおいては、活性炭の嵩密度が高く、かつ活性炭の細孔中に存在する電解液の電解質イオン、溶媒分子のイオン導電性が大きくなり、大電流での充放電であっても、十分に高い出力を発現することが可能である。また、活性炭に存在する含酸素官能基量を適切な量に調節し、かつ、非水系電解液中における活性炭電極の自然電位を適切な範囲に調節することにより、電気二重層キャパシタの耐久性をより向上させることが可能である。本発明は、好ましくは、やしがらを原料とした活性炭からこのような優れた特性を発現させることが出来るが、他の原料でも実施が可能である。他の原料については後述する。 In the electric double layer capacitor using the activated carbon of the present invention satisfying these physical properties as a polarizable electrode material, the bulk density of the activated carbon is high, and the electrolyte ions of the electrolyte existing in the pores of the activated carbon and the ionic conductivity of the solvent molecules Therefore, even when charging / discharging with a large current, a sufficiently high output can be expressed. In addition, by adjusting the amount of oxygen-containing functional groups present in the activated carbon to an appropriate amount, and adjusting the natural potential of the activated carbon electrode in the non-aqueous electrolyte to an appropriate range, the durability of the electric double layer capacitor can be improved. It is possible to improve further. The present invention can preferably exhibit such excellent characteristics from activated carbon made from coconut butter, but can also be implemented with other raw materials. Other raw materials will be described later.
本発明の電気二重層キャパシタ用活性炭は、活性炭の比表面積は大きすぎると嵩密度が低下して、単位体積あたりの静電容量が低下するので、窒素吸着法によるＢＥＴ法により求めたＢＥＴ比表面積は、２２００ｍ2／ｇ以上２７００ｍ2／ｇ以下であることを必須とし、好ましくは２３００ｍ2／ｇ以上２５００ｍ2／ｇ以下であり、より好ましくは２３５０ｍ2／ｇ以上２４５０ｍ2／ｇ以下である。比表面積がこの範囲を超えて小さすぎると、細孔のサイズと量が減少し、その結果、電極の内部抵抗が増加することとなり好ましくない。内部抵抗の増加は単位重量あたりの出力が低下につながるからである。
電極の内部抵抗に関連する要因としては、比表面積の他に平均細孔径や細孔直径が５．０ｎｍから３０．０ｎｍの細孔容積にも大きく影響されるので、本発明においては、これらの要因を総合的に勘案して高出力を図ることが好ましい。
また本発明の電気二重層キャパシタ用活性炭は、平均細孔径が２．２ｎｍ（２２Å）以上２．８ｎｍ（２８Å）以下であることを必須とする。平均細孔径が小さすぎると、大電流下における充放電時に細孔内での電解イオンの拡散抵抗によると思われる内部抵抗が増加するため高出力用途には適さず、他方、大きすぎると、活性炭の嵩密度が低下し、単位体積当たりの静電容量が低下するため好ましくない。好ましくは２．３ｎｍ（２３Å）以上２．７ｎｍ（２７Å）以下である。
In the activated carbon for electric double layer capacitor of the present invention, if the specific surface area of the activated carbon is too large, the bulk density decreases and the capacitance per unit volume decreases. Therefore, the BET specific surface area determined by the BET method by nitrogen adsorption method it is to mandatory to or less than 2200 m 2 / g or more 2700 m 2 / g, preferably not more than 2300 m 2 / g or more 2500 m 2 / g, more preferably not more than 2350m 2 / g or more 2450m 2 / g. When the specific surface area exceeds this range and is too small, the size and amount of the pores decrease, and as a result, the internal resistance of the electrode increases, which is not preferable. This is because an increase in internal resistance leads to a decrease in output per unit weight.
As a factor related to the internal resistance of the electrode, in addition to the specific surface area, the average pore diameter and the pore volume having a pore diameter of 5.0 nm to 30.0 nm are greatly affected. It is preferable to achieve a high output by comprehensively considering the factors.
The activated carbon for electric double layer capacitors of the present invention is required to have an average pore size of 2.2 nm (22 cm) or more and 2.8 nm (28 cm) or less. If the average pore diameter is too small, the internal resistance, which seems to be due to the diffusion resistance of electrolytic ions in the pores, increases during charging / discharging under a large current, so it is not suitable for high output applications. This is not preferable because the bulk density is reduced and the capacitance per unit volume is reduced. Preferably it is 2.3 nm (23 cm) or more and 2.7 nm (27 cm) or less.
更に、本発明の電気二重層キャパシタ用活性炭は、クランストンインクレー法で算出した細孔直径が５．０ｎｍ（５０Å）から３０．０ｎｍ（３００Å）間の細孔容積は、０．２０〜０．６０ｃｍ3／ｇであることを必須とする。細孔容積が大きすぎると電極の嵩密度が低下し、体積当たりの静電容量が小さくなるため好ましくない。また小さすぎると電極の内部抵抗が増加し、結果として出力密度が小さくなる。好ましくは０．２５〜０．５５ｃｍ3／ｇである。 Furthermore, the activated carbon for electric double layer capacitor of the present invention has a pore volume calculated by Cranston inclay method between 5.0 nm (50 Å) and 30.0 nm (300 細孔). It is essential to be 60 cm 3 / g. If the pore volume is too large, the bulk density of the electrode is lowered, and the electrostatic capacity per volume is reduced, which is not preferable. If it is too small, the internal resistance of the electrode increases, and as a result, the output density decreases. Preferably it is 0.25-0.55 cm < 3 > / g.
本発明の電気二重層キャパシタ用活性炭の原料は、やしがら炭であることが好ましいが、他の原料を使用することもできる。やしがら以外の活性炭原料としては、石油系ピッチ、石油コークス、タールピッチを紡糸した繊維、合成高分子、フェノール樹脂、フラン樹脂、ポリ塩化ビニル樹脂、ポリ塩化ビニリデン樹脂、ポリイミド樹脂、ポリアミド樹脂、液晶高分子、プラスチック廃棄物、廃タイヤ等多種多用のものが挙げられる。 The raw material of the activated carbon for electric double layer capacitors of the present invention is preferably coconut charcoal, but other raw materials can also be used. As activated carbon raw materials other than Yasugagara, petroleum pitch, petroleum coke, tar pitch fiber, synthetic polymer, phenol resin, furan resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyimide resin, polyamide resin, A wide variety of liquid crystal polymers, plastic wastes, waste tires and the like can be mentioned.
本発明の活性炭は、原料を炭化後、賦活することにより得られるが、賦活法は、ガス賦活法と薬品賦活法に大別される。
ガス賦活法は、薬品賦活が化学的な活性化であるのに対して、物理的な活性化ともいわれ、炭化された原料を高温で水蒸気、炭酸ガス、酸素、その他の酸化ガスなどと接触反応させることにより活性炭を生成する。
薬品賦活法は、原料に賦活薬品を均等に含浸させて、不活性ガス雰囲気中で加熱し、薬品の脱水および酸化反応により活性炭を得る方法である。使用される薬品としては、塩化亜鉛、りん酸、りん酸ナトリウム、塩化カルシウム、硫化カリウム、水酸化カリウム、水酸化ナトリウム、炭酸カリウム、炭酸ナトリウム、硫酸ナトリウム、硫酸カリウム、炭酸カルシウム等がある。
活性炭の製法に関しては特に制限されず、生成した活性炭が前記特性を満足する限り、上記方法に限られないが、これらの賦活法のうち、水蒸気賦活法で得られる活性炭が電気二重層キャパシタの耐久性に優れ、かつ製造コストも安いという特長を有するので水蒸気賦活法が有利である。また、活性炭の形状は、破砕状、粒状、顆粒、繊維、フェルト、織物、シート状等各種の形状があるが、いずれも本発明に使用することができる。
The activated carbon of the present invention can be obtained by activating the raw material after carbonization, and the activation methods are roughly classified into a gas activation method and a chemical activation method.
The gas activation method is also called physical activation while chemical activation is chemical activation, and the carbonized raw material is contacted with water vapor, carbon dioxide, oxygen, other oxidizing gases, etc. at high temperatures. To produce activated carbon.
The chemical activation method is a method in which an activated chemical is uniformly impregnated in a raw material, heated in an inert gas atmosphere, and activated carbon is obtained by dehydration and oxidation reaction of the chemical. Examples of chemicals used include zinc chloride, phosphoric acid, sodium phosphate, calcium chloride, potassium sulfide, potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium sulfate, potassium sulfate, and calcium carbonate.
The production method of the activated carbon is not particularly limited, and is not limited to the above method as long as the produced activated carbon satisfies the above characteristics. The water vapor activation method is advantageous because of its excellent properties and low manufacturing cost. The activated carbon has various shapes such as crushed, granular, granule, fiber, felt, woven fabric and sheet, and any of them can be used in the present invention.
本発明における水蒸気賦活法で得られる活性炭は、不活性雰囲気中で炭化処理（乾留）して得られた炭化物を、８００℃以上１３００℃以下、好ましくは８５０℃以上１２００℃以下、より好ましくは９００℃以上１１００℃以下で、３０体積％以上１００体積％以下の水蒸気ガス雰囲気を含む窒素、アルゴン、燃焼排ガス等の不活性ガス中で熱処理することにより得られる。
賦活原料として用いる炭化物、あるいは活性炭としては、水酸化ナトリウム溶液や水酸化カリウム溶液などのアルカリ溶液に浸漬し、水や塩酸、硝酸、硫酸など酸水溶液で洗浄してカリウム、ナトリウムの残有量を６００〜２０００ｐｐｍに調整するのが好ましく、より好ましくは８００〜１１００ｐｐｍである。
賦活前の炭化物、あるいは、賦活処理して得られた活性炭を、塩酸、硝酸、硫酸等の酸水溶液中で洗浄して、炭素中に含まれる金属不純物、灰分等を除去したものも本発明に含まれる。賦活処理後の活性炭を、窒素、アルゴン、ヘリウム、キセノン等の不活性雰囲気下で、５００〜２５００℃、好ましくは７００〜１５００℃で熱処理し、不要な表面官能基を除去したり、炭素の結晶性を高くし電気伝導性を増加させてもよい。粒状の活性炭の場合、電極の嵩密度の向上、内部抵抗の低減という点で、平均粒子径は３０μｍ以下が好ましく、より好ましくは７〜２０μｍである。
The activated carbon obtained by the steam activation method in the present invention is obtained by carbonizing a carbonized product (dry distillation) in an inert atmosphere at 800 ° C. or higher and 1300 ° C. or lower, preferably 850 ° C. or higher and 1200 ° C. or lower, more preferably 900. It is obtained by heat treatment in an inert gas such as nitrogen, argon, combustion exhaust gas or the like containing a water vapor gas atmosphere at 30 ° C. or higher and 1100 ° C. or lower and 30% by volume to 100% by volume.
Carbide or activated carbon used as an activation raw material is immersed in an alkaline solution such as sodium hydroxide solution or potassium hydroxide solution and washed with an aqueous acid solution such as water, hydrochloric acid, nitric acid, sulfuric acid, etc. It is preferable to adjust to 600-2000 ppm, More preferably, it is 800-1100 ppm.
The present invention also includes carbides before activation, or activated carbon obtained by activation treatment in an acid aqueous solution such as hydrochloric acid, nitric acid, sulfuric acid, etc. to remove metal impurities, ash, etc. contained in carbon. included. The activated carbon after the activation treatment is heat-treated at 500 to 2500 ° C., preferably 700 to 1500 ° C. in an inert atmosphere such as nitrogen, argon, helium, xenon, etc. to remove unnecessary surface functional groups, May increase the electrical conductivity. In the case of granular activated carbon, the average particle diameter is preferably 30 μm or less, more preferably 7 to 20 μm, in terms of improving the bulk density of the electrode and reducing internal resistance.
本発明の電気二重層キャパシタ用活性炭は、非水系電解液を用いた電気二重層キャパシタにおいて、該電解液中での自然電位が、Ｌｉ／Ｌｉ+を対極とした場合、２．８５Ｖ以上３．０３Ｖ以下であることが好ましく、より好ましくは、２．９０〜３．００Ｖである。自然電位が大きすぎると、例えば、活性炭を正極として組み立てた電気二重層キャパシタに２．５Ｖ以上の電圧を印加した場合、正極の充電後の電位が約４．３Ｖ（対Ｌｉ／Ｌｉ+）となり、電解液の酸化分解電位（４．３Ｖ以上）に達するので、その結果、電解液の分解反応が生じ、電気二重層キャパシタの耐久性が低下する。なお、自然電位が２．８５Ｖより小さいものは、上記の製法においては、通常得られない。
本発明における正極の炭素質電極の自然電位測定は、通常の電気化学的手法を用いて行われる。非水系電解液での電位測定は、水溶液での標準水素電極のような電位基準は厳密には定義されていないが、実際には、銀−塩化銀電極、白金電極、リチウム電極等の電極を用いて一般に広く行われており、本発明においても同様な方法で測定可能である。
The activated carbon for an electric double layer capacitor of the present invention is an electric double layer capacitor using a non-aqueous electrolyte, and the natural potential in the electrolyte is 2.85 V or more when Li / Li + is used as a counter electrode. The voltage is preferably 03 V or less, more preferably 2.90 to 3.00 V. If the natural potential is too large, for example, when a voltage of 2.5 V or higher is applied to an electric double layer capacitor assembled with activated carbon as the positive electrode, the potential after charging of the positive electrode is about 4.3 V (vs. Li / Li + ). As a result, the oxidative decomposition potential (4.3 V or higher) of the electrolytic solution is reached. As a result, a decomposition reaction of the electrolytic solution occurs, and the durability of the electric double layer capacitor decreases. In addition, what a natural potential is smaller than 2.85V cannot usually be obtained in said manufacturing method.
The natural potential measurement of the carbonaceous electrode of the positive electrode in the present invention is performed using a normal electrochemical technique. In the potential measurement with a non-aqueous electrolyte, the potential reference such as a standard hydrogen electrode in an aqueous solution is not strictly defined, but in reality, an electrode such as a silver-silver chloride electrode, a platinum electrode, or a lithium electrode is used. In general, it can be measured by the same method in the present invention.
活性炭中に含まれる含酸素官能基量は電気二重層キャパシタの耐久性に影響を及ぼすので、その量を適切な範囲に調節することが好ましい。本発明では、活性炭中の含酸素官能基量は２重量％以下が好ましく、より好ましくは０．１〜１重量％である。
本発明の含酸素官能基量は、昇温脱離法（真空中またはアルゴンガス、窒素ガス等の不活性ガス雰囲気中、常温〜９００℃、７℃／分）により、常温から９００℃までに活性炭から脱離した酸素量を含酸素官能基量として算出した。昇温中、キャリアガス中に含まれる一酸化炭素（ＣＯ）及び二酸化炭素（ＣＯ2）量を赤外線吸収スペクトルによる濃度分析計（ＵＲＡ−２０７ 島津製作所製）により定量し、発生したＣＯ量，ＣＯ2量から算出される酸素原子の重量合計を含酸素官能基量とした。
ここで、熱分解温度が１０００℃付近であることから、この酸素量は、活性炭中の含酸素官能基、すなわち、カルボキシル基、水酸基（フェノール基）、カルボニル基（ケトン類）等に相当している。活性炭中の含酸素官能基量が上記範囲を超えて多すぎると、電気二重層キャパシタの充放電時にセル内に含酸素官能基の分解または電解液との反応によると推定されるガス発生による電気抵抗の増加が生じ、キャパシタの耐久特性は低下するために好ましくない。また上記範囲より少なすぎると、電極作製時に電極用結着剤との親和性が低下し、結果として電極の嵩密度が低下するため、単位体積あたりの出力が低下するので好ましくない。
Since the amount of oxygen-containing functional groups contained in the activated carbon affects the durability of the electric double layer capacitor, it is preferable to adjust the amount to an appropriate range. In the present invention, the amount of oxygen-containing functional group in the activated carbon is preferably 2% by weight or less, more preferably 0.1 to 1% by weight.
The amount of the oxygen-containing functional group of the present invention is from room temperature to 900 ° C. by a temperature programmed desorption method (in a vacuum or in an inert gas atmosphere such as argon gas or nitrogen gas, from room temperature to 900 ° C., 7 ° C./min). The amount of oxygen desorbed from the activated carbon was calculated as the amount of oxygen-containing functional group. During the temperature increase, the amount of carbon monoxide (CO) and carbon dioxide (CO 2 ) contained in the carrier gas is quantified by a concentration analyzer (URA-207 manufactured by Shimadzu Corporation) using an infrared absorption spectrum, and the amount of generated CO, CO The total weight of oxygen atoms calculated from 2 amounts was defined as the oxygen-containing functional group amount.
Here, since the thermal decomposition temperature is around 1000 ° C., this amount of oxygen corresponds to oxygen-containing functional groups in activated carbon, that is, carboxyl groups, hydroxyl groups (phenol groups), carbonyl groups (ketones), and the like. Yes. If the amount of oxygen-containing functional groups in the activated carbon exceeds the above range and is too large, the electricity generated by gas generation is estimated to be due to decomposition of oxygen-containing functional groups in the cell or reaction with the electrolyte during charging / discharging of the electric double layer capacitor. An increase in resistance occurs and the durability characteristics of the capacitor deteriorate, which is not preferable. On the other hand, if it is less than the above range, the affinity with the electrode binder is reduced during electrode production, and as a result, the bulk density of the electrode is lowered.
本発明の活性炭を用いて電気二重層キャパシタを構成する場合について、以下に述べる。活性炭を主体とする分極性電極は、常法により形成され、主に活性炭とバインダーから構成されるが、電極に導電性を付与するために、さらに導電性物質を添加してもよい。
活性炭電極は、従来より知られている方法により成形することが可能である。例えば、活性炭とアセチレンブラックの混合物に、ポリテトラフルオロエチレンを添加・混合した後、プレス成形することにより成形体として得ることが出来る。また、活性炭に比較的軟化点の高い石炭ピッチをバインダーとして添加・混合後、成型したものを、不活性雰囲気中でバインダーの熱分解温度以上まで焼成して成型体を得ることもできる。さらに、導電剤、バインダーを用いず、活性炭のみを焼結して分極性電極とすることも可能である。電極は、薄い塗布膜、シート状または板状の成形体、さらには複合物からなる板状成形体のいずれであってもよい。
なお、バインダーとの混合に先立ち、活性炭を所望の粒状に粉砕することもできるが、活性炭を比較的大粒径のままバインダーと混合して一緒に粉砕し、混合スラリー又はドライな粉砕物として得ることもできる。
The case where an electric double layer capacitor is comprised using the activated carbon of this invention is described below. A polarizable electrode mainly composed of activated carbon is formed by a conventional method and is mainly composed of activated carbon and a binder, but a conductive substance may be further added to impart conductivity to the electrode.
The activated carbon electrode can be formed by a conventionally known method. For example, after adding and mixing polytetrafluoroethylene to a mixture of activated carbon and acetylene black, a molded product can be obtained by press molding. Further, a molded product obtained by adding and mixing a coal pitch having a relatively high softening point to activated carbon as a binder and then molding it may be fired to a temperature equal to or higher than the thermal decomposition temperature of the binder in an inert atmosphere. Furthermore, it is possible to sinter only activated carbon without using a conductive agent and a binder to form a polarizable electrode. The electrode may be a thin coating film, a sheet-shaped or plate-shaped molded body, or a plate-shaped molded body made of a composite.
Prior to mixing with the binder, the activated carbon can be pulverized into a desired granular form, but the activated carbon is mixed with the binder with a relatively large particle size and pulverized together to obtain a mixed slurry or a dry pulverized product. You can also.
活性炭電極に用いられる導電剤としては、アセチレンブラック、ケッチェンブラック等のカーボンブラック、天然黒鉛、熱膨張黒鉛、炭素繊維、酸化ルテニウム、酸化チタン、アルミニウム、ニッケル等の金属ファイバーからなる群より選ばれる少なくとも一種の導電剤が好ましい。少量で効果的に導電性が向上する点で、アセチレンブラック及びケッチェンブラックが特に好ましく、活性炭との配合量は、活性炭の嵩密度により異なるが多すぎると活性炭の割合が減り容量が減少するため、活性炭の５〜５０重量％、特に１０〜３０重量％程度が好ましい。 The conductive agent used for the activated carbon electrode is selected from the group consisting of carbon fibers such as acetylene black and ketjen black, natural graphite, thermally expanded graphite, carbon fiber, ruthenium oxide, titanium oxide, aluminum, nickel, and other metal fibers. At least one conductive agent is preferred. Acetylene black and ketjen black are particularly preferable in that the conductivity is effectively improved in a small amount, and the blending amount with activated carbon varies depending on the bulk density of the activated carbon, but if the amount is too large, the proportion of activated carbon decreases and the capacity decreases. The activated carbon content is preferably 5 to 50% by weight, particularly about 10 to 30% by weight.
バインダーとしては、ポリテトラフルオロエチレン、ポリフッ化ビニリデン、カルボキシセルロース、メチルセルロース、フルオロオレフィン共重合体架橋ポリマー、ポリビニルアルコール、ポリアクリル酸、ポリイミド、石油ピッチ、石炭ピッチ、フェノール樹脂のうち少なくとも１種類以上用いるのが好ましい。集電体は電気化学的及び化学的に耐食性があればよく、特に限定するものではないが、例えば、正極としてはステンレス、アルミニウム、チタン、タンタル等が挙げられ、負極では、ステンレス、ニッケル、アルミニウム、銅等が好適に使用される。 As the binder, at least one of polytetrafluoroethylene, polyvinylidene fluoride, carboxycellulose, methylcellulose, fluoroolefin copolymer crosslinked polymer, polyvinyl alcohol, polyacrylic acid, polyimide, petroleum pitch, coal pitch, and phenol resin is used. Is preferred. The current collector is not particularly limited as long as it has electrochemical and chemical corrosion resistance. Examples of the positive electrode include stainless steel, aluminum, titanium, tantalum, and the negative electrode includes stainless steel, nickel, and aluminum. Copper or the like is preferably used.
電解液は非水系電解液が好ましい。非水系電解液の溶質としては、Ｒ4Ｎ+、Ｒ4Ｐ+（ただし、ＲはＣnＨ2n+1で示されるアルキル基：ｎ＝１〜４）、トリエチルメチルアンモニウムイオン等で示される第４級オニウムカチオンと、ＢＦ4 -、ＰＦ6 -、ＣｌＯ4 -、ＳｂＦ6 -またはＣＦ3ＳＯ3 -なるアニオンとを組み合わせた塩、または、カチオンがリチウムイオンであるリチウム塩を用いる。リチウム塩としては、ＬｉＢＦ4、ＬｉＣｌＯ4、ＬｉＰＦ6、ＬｉＳｂＦ6、ＬｉＡｓＦ6、ＬｉＣＦ3ＳＯ3、ＬｉＣ（ＣＦ3ＳＯ2）3、ＬｉＢ（Ｃ6Ｈ5）4、ＬｉＣ4Ｆ9ＳＯ3、ＬｉＣ8Ｆ17ＳＯ3及びＬｉＮ（ＣＦ3ＳＯ2）2から選ばれる１つ以上の物質が好ましい。特に、電気伝導性、安定性、及び低コスト性という点から、カチオンとしてＲ4Ｎ+（ただし、ＲはＣnＨ2n+1で示されるアルキル基：ｎ＝１〜４）及びトリエチルメチルアンモニウムイオン、アニオンとして、ＢＦ4 -、ＰＦ6 -、ＣｌＯ4 -及びＳｂＦ6 -を組み合わせた塩が好ましい。 The electrolyte is preferably a non-aqueous electrolyte. Examples of the solute of the non-aqueous electrolyte include R 4 N + , R 4 P + (where R is an alkyl group represented by C n H 2n + 1 : n = 1 to 4), triethylmethylammonium ion, and the like. A salt obtained by combining a quaternary onium cation and an anion of BF 4 − , PF 6 − , ClO 4 − , SbF 6 − or CF 3 SO 3 − or a lithium salt in which the cation is a lithium ion is used. Examples of the lithium salt, LiBF 4, LiClO 4, LiPF 6, LiSbF 6, LiAsF 6, LiCF 3 SO 3, LiC (CF 3 SO 2) 3, LiB (C 6 H 5) 4, LiC 4 F 9 SO 3, One or more materials selected from LiC 8 F 17 SO 3 and LiN (CF 3 SO 2 ) 2 are preferred. In particular, from the viewpoint of electrical conductivity, stability, and low cost, R 4 N + (wherein R is an alkyl group represented by C n H 2n + 1 : n = 1 to 4) and triethylmethylammonium as cations As the ions and anions, salts in which BF 4 − , PF 6 − , ClO 4 − and SbF 6 − are combined are preferable.
これらの非水系電解液中の溶質濃度は電気二重層キャパシタの特性が十分引き出せるように、０．３〜２．０モル／リットルが好ましく、特に、０．７モル／リットル以上１．９モル／リットル以下の濃度では、高い電気伝導性が得られて好ましい。特に、−２０℃以下の低温で充放電するとき、２．０モル／リットル以上の濃度では、電解液の電気伝導性が低下し好ましくない。０．３モル／リットル以下では室温下、低温下とも電気伝導度が小さく好ましくない。電解液としてはテトラエチルアンモニウムテトラフルオロボレート（Ｅｔ4ＮＢＦ4）のプロピレンカーボネート溶液が好ましく、Ｅｔ4ＮＢＦ4の濃度としては０．５〜１．０モル／リットルが好ましい。 The concentration of the solute in these non-aqueous electrolytes is preferably 0.3 to 2.0 mol / liter, particularly 0.7 mol / liter or more and 1.9 mol / liter so that the characteristics of the electric double layer capacitor can be sufficiently extracted. A concentration of 1 liter or less is preferable because high electrical conductivity is obtained. In particular, when charging / discharging at a low temperature of −20 ° C. or less, a concentration of 2.0 mol / liter or more is not preferable because the electrical conductivity of the electrolytic solution is lowered. If it is 0.3 mol / liter or less, the electric conductivity is low and unfavorable at both room temperature and low temperature. As the electrolytic solution, a propylene carbonate solution of tetraethylammonium tetrafluoroborate (Et 4 NBF 4 ) is preferable, and the concentration of Et 4 NBF 4 is preferably 0.5 to 1.0 mol / liter.
非水系電解液の溶媒は特に限定するものではないが、プロピレンカーボネート、エチレンカーボネート、ブチレンカーボネート、ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネート、スルホラン、メチルスルホラン、γ−ブチロラクトン、γ−バレロラクトン、N−メチルオキサゾリジノン、ジメチルスルホキシド、及びトリメチルスルホキシドから選ばれる1種類以上からなる有機溶媒が好ましい。電気化学的及び化学的安定性、電気伝導性に優れる点から、プロピレンカーボネート、エチレンカーボネート、ブチレンカーボネート、ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネート、スルホラン、メチルスルホラン、γ−ブチロラクトンから選ばれる１種類以上の有機溶媒が特に好ましい。ただし、エチレンカーボネート等の高融点溶媒は、単独では低温下では固体となるため使用できず、プロピレンカーボネート等との低融点溶媒との混合溶媒とする必要がある。非水系電解液中の水分は、高い耐電圧が得られるように２００ｐｐｍ以下、さらには５０ｐｐｍ以下が好ましい。 The solvent of the non-aqueous electrolyte is not particularly limited, but propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, sulfolane, methyl sulfolane, γ-butyrolactone, γ-valerolactone, N- An organic solvent composed of one or more selected from methyl oxazolidinone, dimethyl sulfoxide, and trimethyl sulfoxide is preferable. One or more kinds selected from propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, sulfolane, methyl sulfolane, and γ-butyrolactone from the viewpoint of excellent electrochemical and chemical stability and electrical conductivity The organic solvent is particularly preferred. However, a high-melting-point solvent such as ethylene carbonate cannot be used alone because it becomes a solid at a low temperature, and must be a mixed solvent with a low-melting-point solvent such as propylene carbonate. The moisture in the non-aqueous electrolyte is preferably 200 ppm or less, and more preferably 50 ppm or less so that a high withstand voltage can be obtained.
以下、本発明を具体的な実施例を用いて更に詳細に説明するが、本発明はその要旨を超えない限り以下の実施例により限定されるのもではない。 Hereinafter, the present invention will be described in more detail using specific examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.
［実施例１］
<活性炭の製造>
カリウム＋ナトリウム含有量が７１００ｐｐｍのやしがら炭化物５０ｇをロータリーキルンに入れ水蒸気を含む窒素ガス雰囲気下で９００℃まで昇温し、水蒸気濃度５０容積％で５０分間賦活を行った（１次賦活）。この賦活で得られた活性炭のＢＥＴ比表面積は１４００ｍ2／ｇであった。その後、一旦、室温まで冷却後、常温の５重量％水酸化ナトリウム溶液に１時間浸漬した。その後、脱塩水で洗浄を行い、カリウム、ナトリウムの残存量を調整した。続いてこの活性炭を、前記同様に水蒸気雰囲気で昇温し、水蒸気濃度５０容積％で１０５分間賦活を行った（２次賦活）。この賦活炭を８０℃の１Ｎ−塩酸水溶液中に１時間浸漬し、その後、脱塩水で充分な洗浄を行った。この塩酸洗浄及び脱塩水による洗浄を２回繰り返した後、得られた賦活炭を空気中、１１５℃で２時間乾燥を行った。最後に、窒素ガスを流通させたロータリーキルンに入れ、９００℃で１時間焼成した。得られた熱処理品を粉砕した後に篩で分級して平均粒子径が約１０μｍの活性炭を得た。
[Example 1]
<Manufacture of activated carbon>
50 g of palm tree carbide having a potassium + sodium content of 7100 ppm was placed in a rotary kiln, heated to 900 ° C. in a nitrogen gas atmosphere containing water vapor, and activated for 50 minutes at a water vapor concentration of 50% by volume (primary activation). . The activated carbon obtained by this activation had a BET specific surface area of 1400 m 2 / g. Then, after cooling to room temperature, it was immersed in a 5 wt% sodium hydroxide solution at room temperature for 1 hour. Thereafter, washing with demineralized water was performed to adjust the residual amounts of potassium and sodium. Subsequently, the activated carbon was heated in a water vapor atmosphere in the same manner as described above, and activated for 105 minutes at a water vapor concentration of 50% by volume (secondary activation). This activated charcoal was immersed in a 1N hydrochloric acid aqueous solution at 80 ° C. for 1 hour, and then sufficiently washed with demineralized water. After repeating this hydrochloric acid washing and washing with demineralized water twice, the obtained activated charcoal was dried in air at 115 ° C. for 2 hours. Finally, it put into the rotary kiln which distribute | circulated nitrogen gas, and baked at 900 degreeC for 1 hour. The obtained heat-treated product was pulverized and classified with a sieve to obtain activated carbon having an average particle size of about 10 μm.
［実施例２〜４］及び［比較例１〜３］
実施例１において、活性炭原料及び賦活前処理条件を表１に示すように変更して、変更点以外は基本的に実施例１と同様の方法で活性炭を製造した。実施例４では、実施例１の１次賦活炭を原料とした。
[Examples 2 to 4] and [Comparative Examples 1 to 3]
In Example 1, the activated carbon raw material and activation pretreatment conditions were changed as shown in Table 1, and activated carbon was basically produced in the same manner as in Example 1 except for the changes. In Example 4, the primary activated charcoal of Example 1 was used as a raw material.
実施例１〜４及び比較例１〜３で得られた活性炭について、下記の方法で物性測定を行い、表２の結果を得た。最終製品である活性炭中のカリウム、ナトリウムの残存量は全て１００ｐｐｍ以下であった。
About the activated carbon obtained in Examples 1-4 and Comparative Examples 1-3, the physical property measurement was performed by the following method and the result of Table 2 was obtained. Residual amounts of potassium and sodium in the activated carbon as the final product were all 100 ppm or less.
＜活性炭の物性測定＞
（１）ＢＥＴ比表面積、全細孔容積、細孔分布
ソープトマチック１９９０型（カルロエルバ社製）を用い、活性炭粉末の液体窒素温度における各相対圧力下での窒素ガスの各平衡吸着量を測定して得られる活性炭の吸着等温線より算出した。
活性炭粉末の平均細孔径は、活性炭の細孔形状を円柱状に仮定し、上記の窒素ガスの吸着等温線から求めた全細孔容積とＢＥＴ比表面積から次の式で算出した。
平均細孔径（ｎｍ）＝
全細孔容積（ｃｍ3／ｇ）／比表面積（ｍ2／ｇ）×４０００
（２）カリウム、ナトリウム含有量
活性炭粉末１ｇを濃硝酸１０ｍｌと濃硫酸６ｍｌの混合物中で約１０分間煮沸して溶解させる。活性炭が完全に溶解するまで濃硝酸２ｍｌを添加し、煮沸する操作を繰り返す。この溶液について原子吸光法にてカリウムおよびナトリウム濃度を求め、活性炭中のカリウムおよびナトリウムの含有量を活性炭量に対する重量百分率として求めた。
（３）灰分
磁製ルツボに活性炭原料を入れ、空気中８１５℃で５時間以上加熱し、冷却後、残存した灰分の質量を測定し、ルツボに入れた活性炭量に対する重量百分率として求めた。
（４）含酸素官能基量
昇温脱離法（常温〜９００℃、７℃／分）により、常温から９００℃までに活性炭から脱離した酸素量として算出した。即ち、昇温中、キャリアガス中に含まれるＣＯ量、ＣＯ2量を赤外線吸収スペクトルによる濃度分析計（ＵＲＡ−２０７ 島津製作所製）により定量し、発生したＣＯ量、ＣＯ2量から算出される酸素原子の重量合計を活性炭量に対する重量百分率として求めた。
<Measurement of physical properties of activated carbon>
(1) BET specific surface area, total pore volume, pore distribution Measure each equilibrium adsorption amount of nitrogen gas under various relative pressures of activated carbon powder at liquid nitrogen temperature using Soptomatic 1990 type (manufactured by Carlo Elba) It calculated from the adsorption isotherm of the activated carbon obtained.
The average pore diameter of the activated carbon powder was calculated by the following formula from the total pore volume and BET specific surface area obtained from the above-mentioned nitrogen gas adsorption isotherm assuming that the activated carbon pore shape was cylindrical.
Average pore diameter (nm) =
Total pore volume (cm 3 / g) / specific surface area (m 2 / g) × 4000
(2) Potassium and sodium contents 1 g of activated carbon powder is dissolved by boiling for about 10 minutes in a mixture of 10 ml of concentrated nitric acid and 6 ml of concentrated sulfuric acid. Add 2 ml of concentrated nitric acid until the activated carbon is completely dissolved, and repeat the boiling operation. With respect to this solution, potassium and sodium concentrations were determined by atomic absorption, and the contents of potassium and sodium in the activated carbon were determined as a percentage by weight with respect to the amount of activated carbon.
(3) Ash content Activated carbon raw material was put into a porcelain crucible, heated in air at 815 ° C. for 5 hours or more, and after cooling, the mass of the remaining ash was measured and determined as a weight percentage with respect to the amount of activated carbon placed in the crucible.
(4) Amount of oxygen-containing functional group Calculated as the amount of oxygen desorbed from the activated carbon from room temperature to 900 ° C. by a temperature programmed desorption method (room temperature to 900 ° C., 7 ° C./min). That is, during the temperature rise, the amount of CO and CO 2 contained in the carrier gas is quantified by a concentration analyzer (URA-207 manufactured by Shimadzu Corporation) using an infrared absorption spectrum, and is calculated from the generated CO amount and CO 2 amount. The total weight of oxygen atoms was determined as a percentage by weight relative to the amount of activated carbon.
＜電気二重層キャパシタの作製＞
各例で得られた活性炭を用い、活性炭８０重量％、アセチレンブラック１０重量％、ポリテトラフルオロエチレン１０重量％からなる混合物を混練した後、錠剤成型器（日本分光社製）を用い、油圧プレスで直径１０ｍｍ、厚さ０．５ｍｍとなるように５０ｋｇｆ／ｃｍ2の圧力で加圧成型して円盤状の成型体を得、これを正極成型体とした。同様にして成型体を更に１枚作製し、これを負極成型体とした。
得られた２枚の成型体を１１０℃で２時間乾燥後、重量及び厚みを測定した。その後、０．１ｔｏｒｒ（１３．３Ｐａ）以下の真空中、３００℃で３時間乾燥した。乾燥した２枚の成型体を窒素ガス雰囲気中のドライボックス中に移した後、正・負極の成型体を、電解液である、１．３モル／リットル濃度のトリエチルメチルアンモニウムテトラフルオロボレート（Ｃ2Ｈ5）3ＣＨ3ＮＢＦ4）のプロピレンカーボネート溶液に真空含浸した。次に、ポリエチレン製セパレータを介して、電解液を含浸させた正極成型体及び負極成型体を対向させた後、２枚の白金電極板の間に挟んだ。これらを２枚のテフロン（登録商標）板で挟み固定した。このようにして作成した電極及び電解液をビーカーに入れ、電極を電解液に浸し、ビーカー型電気二重層キャパシタを得た。
得られた電気二重層キャパシタについて、下記の方法で初期性能評価を行い、表３の結果を得た。
<Production of electric double layer capacitor>
Using the activated carbon obtained in each example, a mixture of 80% by weight of activated carbon, 10% by weight of acetylene black and 10% by weight of polytetrafluoroethylene was kneaded, and then a hydraulic press using a tablet molding machine (manufactured by JASCO Corporation). And pressure-molding with a pressure of 50 kgf / cm 2 so as to have a diameter of 10 mm and a thickness of 0.5 mm to obtain a disk-shaped molded body, which was used as a positive electrode molded body. Similarly, another molded body was produced, and this was used as a negative electrode molded body.
The obtained two molded bodies were dried at 110 ° C. for 2 hours, and then the weight and thickness were measured. Then, it was dried at 300 ° C. for 3 hours in a vacuum of 0.1 torr (13.3 Pa) or less. After the two molded bodies were transferred to a dry box in a nitrogen gas atmosphere, the positive and negative molded bodies were converted to an electrolytic solution, 1.3 mol / liter concentration of triethylmethylammonium tetrafluoroborate (C 2 H 5 ) 3 CH 3 NBF 4 ) in propylene carbonate was vacuum impregnated. Next, the positive electrode molded body impregnated with the electrolytic solution and the negative electrode molded body were opposed to each other through a polyethylene separator, and then sandwiched between two platinum electrode plates. These were sandwiched and fixed between two Teflon (registered trademark) plates. The electrode thus prepared and the electrolytic solution were placed in a beaker, and the electrode was immersed in the electrolytic solution to obtain a beaker type electric double layer capacitor.
The obtained electric double layer capacitor was evaluated for initial performance by the following method, and the results shown in Table 3 were obtained.
＜電気二重層キャパシタの初期性能評価＞
（１）初期静電容量
得られたビーカー型電気二重層キャパシタを２５℃の恒温槽中で、充放電試験装置（北斗電工社製 ＨＪ１０１０型）にて２．８Ｖの電圧を印加後、電流密度１．１６ｍＡ／ｃｍ2の定電流で放電した。得られた放電曲線の２．４Ｖから１．０Ｖの間の勾配から、初期の静電容量（Ｆ）を求め、電極の重量と密度から、単位体積当たりの静電容量（Ｆ／ｃｍ3）を求めた。
（２）内部抵抗
得られたビーカー型電気二重層キャパシタに対して、２．８Ｖの電圧を印加 後、電流密度１１．６ｍＡ／ｃｍ2の定電流で放電し、得られた放電曲線の２ ．４Ｖから１．０Ｖの間において１次近似式を求め、放電開始時点の切片より 、電圧降下ΔＶ（Ｖ）を求め、
内部抵抗（Ω）＝電圧降下ΔＶ（Ｖ）／電流Ｉ（Ａ）
より、内部抵抗（Ω）を算出した。そして、この内部抵抗に電極面積０．８６５ｃｍ2を掛けて、単位面積当たりの内部抵抗（Ω・ｃｍ2）を算出した。
<Evaluation of initial performance of electric double layer capacitor>
(1) Initial capacitance After applying a voltage of 2.8 V with a charge / discharge test apparatus (HJ1010 type, manufactured by Hokuto Denko Co., Ltd.) in a thermostatic bath at 25 ° C. The battery was discharged at a constant current of 1.16 mA / cm 2 . The initial capacitance (F) is determined from the slope of the obtained discharge curve between 2.4 V and 1.0 V, and the capacitance per unit volume (F / cm 3 ) is determined from the weight and density of the electrode. Asked.
(2) Internal resistance After applying a voltage of 2.8 V to the obtained beaker type electric double layer capacitor, it was discharged at a constant current of 11.6 mA / cm 2 and 2. A linear approximation formula is obtained between 4 V and 1.0 V, and a voltage drop ΔV (V) is obtained from the intercept at the start of discharge.
Internal resistance (Ω) = Voltage drop ΔV (V) / Current I (A)
From this, the internal resistance (Ω) was calculated. Then, over the electrode area 0.865Cm 2 to the internal resistance was calculated internal resistance per unit area (Ω · cm 2).
表３より、電極材として本発明の活性炭を用いた電気二重層キャパシタは、内部抵抗が大幅に低いことが分かる。比較例１は、ＢＥＴ比表面積が１８００ｍ2／ｇ未満と小さいことに起因してか、静電容量は大きいものの内部抵抗が大きく実用上問題がある。比較例２，３は特許文献１に包含されるものであり、内部抵抗は改善されているが、まだ不充分である。
Table 3 shows that the internal resistance of the electric double layer capacitor using the activated carbon of the present invention as the electrode material is significantly low. In Comparative Example 1, the BET specific surface area is as small as less than 1800 m 2 / g. However, although the capacitance is large, the internal resistance is large and there is a problem in practical use. Comparative Examples 2 and 3 are included in Patent Document 1, and the internal resistance is improved, but it is still insufficient.
Claims (3)
（ａ）活性炭をアルカリ溶液に浸漬する工程と、
（ｂ）前記アルカリ溶液に浸漬した活性炭を酸洗浄する工程と、
（ｃ）前記洗浄後の活性炭を水蒸気賦活する工程と
を有する、方法。 A method for producing activated carbon for an electric double layer capacitor, comprising:
(A) immersing activated carbon in an alkaline solution;
(B) a step of acid cleaning the activated carbon immersed in the alkaline solution;
(C) A step of steam-activating the activated carbon after the washing.
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| JP2014036113A (en) * | 2012-08-08 | 2014-02-24 | Toyo Tanso Kk | Capacitor |
| JP6518589B2 (en) | 2012-10-08 | 2019-05-22 | マックスウェル テクノロジーズ インコーポレイテッド | Electrolyte for 3-volt ultracapacitors |
| US9799459B2 (en) | 2014-08-08 | 2017-10-24 | Corning Incorporated | High pore volume utilization carbon and electric double layer capacitor |
| JP6371787B2 (en) * | 2016-03-24 | 2018-08-08 | 関西熱化学株式会社 | Activated carbon, method for producing the same, and electric double layer capacitor using the activated carbon |
| WO2017201173A1 (en) | 2016-05-20 | 2017-11-23 | Avx Corporation | Nonaqueous electrolyte for an ultracapacitor |
| KR102635455B1 (en) | 2016-05-20 | 2024-02-13 | 교세라 에이브이엑스 컴포넌츠 코포레이션 | Ultracapacitor for use at high temperatures |
| WO2017201167A1 (en) | 2016-05-20 | 2017-11-23 | Avx Corporation | Electrode configuration for an ultracapacitor |
| WO2018003295A1 (en) * | 2016-06-27 | 2018-01-04 | 日本食品化工株式会社 | 5-hydroxymethyl-2-furfural production method |
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| JPS59105312A (en) * | 1982-12-09 | 1984-06-18 | 東洋紡績株式会社 | Wet type electric double layer capacitor |
| JP2000344507A (en) * | 1999-06-07 | 2000-12-12 | Kuraray Chem Corp | Powdery activated carbon, activated carbon sheet and electric double layer capacitor |
| JP4618929B2 (en) * | 2000-05-09 | 2011-01-26 | 三菱化学株式会社 | Activated carbon for electric double layer capacitors |
| WO2005076299A1 (en) * | 2004-02-03 | 2005-08-18 | Nisshinbo Industries, Inc. | Electric double layer capacitor |
| JP5018213B2 (en) * | 2006-06-14 | 2012-09-05 | カルゴンカーボンジャパン株式会社 | Phosphorus compound composite activated carbon for electric double layer capacitor and method for producing the same |
| JP2008141060A (en) * | 2006-12-04 | 2008-06-19 | Kansai Coke & Chem Co Ltd | Activated carbon and method of manufacturing the same |
| JP4618308B2 (en) * | 2007-04-04 | 2011-01-26 | ソニー株式会社 | Porous carbon material and method for producing the same, adsorbent, mask, adsorbing sheet, and carrier |
| JP5164418B2 (en) * | 2007-04-18 | 2013-03-21 | 株式会社キャタラー | Carbon material for electricity storage device electrode and method for producing the same |
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