JP2017092303A - Active carbon for electrode for high potential capacitor, manufacturing method thereof, and electric double-layer capacitor with the active carbon - Google Patents
Active carbon for electrode for high potential capacitor, manufacturing method thereof, and electric double-layer capacitor with the active carbon Download PDFInfo
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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
Abstract
Description
本発明は、高電圧充電に対応可能な電気二重層キャパシタの電極材料としての活性炭、その製造方法及び当該活性炭を備えた電気二重層キャパシタに関するものである。 TECHNICAL FIELD The present invention relates to activated carbon as an electrode material of an electric double layer capacitor that can handle high voltage charging, a method for producing the same, and an electric double layer capacitor including the activated carbon.
近年、電気二重層キャパシタは、大電流充放電が可能で、長寿命かつ高温安定性に優れるため、例えばハイブリッド自動車等の蓄電デバイスとして注目されている。電気二重層キャパシタは、活性炭などの多孔質炭素電極内の細孔と電解液の界面に形成される電気二重層に電荷を蓄えるコンデンサである。 In recent years, an electric double layer capacitor is attracting attention as a power storage device such as a hybrid vehicle because it can charge and discharge a large current, has a long life and is excellent in high-temperature stability. An electric double layer capacitor is a capacitor that stores electric charge in an electric double layer formed at the interface between a pore in a porous carbon electrode such as activated carbon and an electrolytic solution.
電気二重層キャパシタに蓄電されるエネルギー（Ｅ）は、充電電圧（Ｖ）の二乗と電気二重層容量（Ｃ）の積に比例する（Ｅ＝ＣＶ２／２）。従って、エネルギー密度の向上には充電電圧（Ｖ）の向上及び電気二重層容量（Ｃ）の増加が有効と考えられる。しかしながら、３Ｖ以上の電圧で充電すると電極や電解液の電気分解が始まることで容量が低下し、電気二重層キャパシタの劣化が促進されるため、高電圧化は困難であった。
Energy charged in the electric double layer capacitor (E) is proportional to the product of the square and the electric double layer capacity of the charging voltage (V) (C) (E =
そこで、連通した均一なマクロ孔が形成された板状の多孔質フェノール樹脂を有機溶媒に浸漬、次いで加圧して得られたブロックを炭化・賦活することにより、３Ｖ以上の高電圧充電に対する耐久性に優れた電気二重層キャパシタの電極用活性炭が提案されている（例えば、特許文献１，２参照）。 Therefore, by immersing a plate-like porous phenolic resin with uniform macropores in communication in an organic solvent and then pressurizing and activating the resulting block, it is durable against high-voltage charging of 3V or higher. An activated carbon for an electrode of an electric double layer capacitor excellent in the above has been proposed (for example, see Patent Documents 1 and 2).
しかしながら、上記特許文献１に記載された活性炭では、連通マクロ孔を有していることにより、体積当たりの静電容量という点では不利であると考えられる。また、上記特許文献２に記載された活性炭では、実施例の比表面積は１３９０〜１９３０ｍ２／ｇであり、キャパシタの性能向上の観点からはさらなる比表面積の増加が望まれる。
However, it is considered that the activated carbon described in Patent Document 1 is disadvantageous in terms of capacitance per volume because it has communicating macropores. Moreover, in the activated carbon described in the said
そこで、本発明は、３．０Ｖ以上、特に好ましくは３．０Ｖを超える高電圧充放電に対しても優れたキャパシタ性能をもたらし得る電気二重層キャパシタ（以下、「高電位キャパシタ」という。）の電極用活性炭、その製造方法、及び当該活性炭を用いた電気二重層キャパシタを提供することを目的とする。 Therefore, the present invention is an electric double layer capacitor (hereinafter referred to as “high potential capacitor”) capable of providing excellent capacitor performance even for high voltage charge / discharge of 3.0 V or more, particularly preferably over 3.0 V. It aims at providing the activated carbon for electrodes, its manufacturing method, and the electric double layer capacitor using the said activated carbon.
上記の目的を達成するために、本発明では、高電位キャパシタの電極用活性炭について、より高い比表面積を有するとともに、３．０Ｖ以上、特に好ましくは３．０Ｖを超える高電圧充放電に対して最適化された細孔径を有するようにした。 In order to achieve the above object, in the present invention, the activated carbon for an electrode of a high potential capacitor has a higher specific surface area, and for high voltage charge / discharge exceeding 3.0V, particularly preferably exceeding 3.0V. Optimized pore size.
すなわち、ここに開示する高電位キャパシタの電極用活性炭は、比表面積が、２５００ｍ２／ｇ以上であり、ミクロ孔の細孔径が、１．１ｎｍ以上１．５ｎｍ以下であることを特徴とする。 That is, the activated carbon for electrodes of the high potential capacitor disclosed herein is characterized by having a specific surface area of 2500 m 2 / g or more and a micropore diameter of 1.1 nm or more and 1.5 nm or less.
比表面積が２５００ｍ２／ｇより大きいことにより、電気二重層キャパシタの電極材料として使用したときに、電解液中のイオンの吸着量が増大し、電気二重層キャパシタの容量増加に寄与することができる。 When the specific surface area is greater than 2500 m 2 / g, when used as an electrode material for an electric double layer capacitor, the amount of ions adsorbed in the electrolyte increases, which can contribute to an increase in the capacity of the electric double layer capacitor. .
活性炭の細孔は、一般に、直径５０ｎｍ以上のマクロ孔、直径２ｎｍ以上５０ｎｍ未満のメソ孔、直径２ｎｍ未満のミクロ孔に分類される。電気二重層キャパシタでは、活性炭のミクロ孔に吸着保持されるイオン量が容量に大きく寄与する。 The pores of the activated carbon are generally classified into macropores having a diameter of 50 nm or more, mesopores having a diameter of 2 nm or more and less than 50 nm, and micropores having a diameter of less than 2 nm. In the electric double layer capacitor, the amount of ions adsorbed and held in the micropores of the activated carbon greatly contributes to the capacity.
高電圧下では、一般に電解液の分解がキャパシタの容量低下・劣化の一因であるところ、上記ミクロ孔の細孔径は、電解液のイオン及び溶媒分子の直径の合計値近傍から少し大きいサイズであるから、このような細孔を有することにより、電解液中のイオンのうち活性炭の細孔に吸着保持されるイオンの量を最大限増加させることができる。また、上記細孔径のサイズよりも小さな細孔径を有する細孔やそのエッジ部分は、電解液の分解反応の活性点となり得るところ、そのような小さな細孔の量を低減させることにより、分解反応の抑制に寄与することができる。さらに、電解液の分解反応により生じる分解生成物は、細孔に溜まって細孔を塞ぎ、イオンの吸着を阻害するところ、細孔のサイズを上記細孔径のサイズとすることにより、イオン及び溶媒の移動経路を確保することができ、容量の低下を抑制することができる。 Under high voltage, the decomposition of the electrolytic solution is generally one of the causes of the capacity reduction / degradation of the capacitor. Therefore, the pore size of the micropores is slightly larger than the total value of the electrolyte ion and solvent molecule diameters. Therefore, by having such pores, the amount of ions that are adsorbed and held in the pores of the activated carbon among the ions in the electrolytic solution can be maximized. In addition, pores having a pore diameter smaller than the above-mentioned pore size and edge portions thereof can be active sites for the decomposition reaction of the electrolytic solution. By reducing the amount of such small pores, the decomposition reaction It can contribute to suppression of the above. Furthermore, the decomposition product generated by the decomposition reaction of the electrolytic solution accumulates in the pores, blocks the pores, and inhibits the adsorption of ions. By setting the pore size to the size of the pore diameter, ions and solvents Can be secured, and a decrease in capacity can be suppressed.
また、好ましい態様では、本発明に係る高電位キャパシタの電極用活性炭は、平均粒径が、１０μｍ以上２０μｍ以下の略球状粒子であり、前記比表面積が、２８００ｍ２／ｇ以上３０００ｍ２／ｇ未満である。これにより、効果的に細孔径を制御することができる。なお、本明細書において「平均粒径」とは、レーザー散乱回析式粒度分布測定を用いて測定したメディアン径（Ｄ５０）をいう。また、本明細書において「略球状」とは、真球状及び球状に近い形状を含んでおり、粒子の長径と短径の比（アスペクト比）が１．３以下のものをいう。 In a preferred embodiment, the activated carbon for an electrode of the high potential capacitor according to the present invention is a substantially spherical particle having an average particle diameter of 10 μm or more and 20 μm or less, and the specific surface area is 2800 m 2 / g or more and less than 3000 m 2 / g. It is. Thereby, the pore diameter can be controlled effectively. In the present specification, “average particle diameter” refers to the median diameter (D 50 ) measured using laser scattering diffraction particle size distribution measurement. Further, in the present specification, “substantially spherical” means a shape including a true spherical shape and a shape close to a spherical shape, and the ratio of the major axis to the minor axis (aspect ratio) of the particles is 1.3 or less.
また、本発明に係る高電位キャパシタの電極用活性炭は、電気二重層キャパシタに好適に用いることができる。これにより、高容量であり且つ高電圧下での充放電可能なキャパシタをもたらすことができる。 Moreover, the activated carbon for electrodes of a high potential capacitor according to the present invention can be suitably used for an electric double layer capacitor. As a result, a capacitor having a high capacity and capable of being charged and discharged under a high voltage can be provided.
好ましい態様において、上記電気二重層キャパシタにおける電解液に含まれる電解質は、テトラエチルアンモニウムテトラフルオロホウ酸（ＴＥＡ）である。これにより、３．０Ｖ以上、特に好ましくは３．０Ｖを超える高電圧下においても、容量の低下が抑制された、ＴＥＡ電解質を用いた電気二重層キャパシタをもたらすことができる。 In a preferred embodiment, the electrolyte contained in the electrolytic solution in the electric double layer capacitor is tetraethylammonium tetrafluoroboric acid (TEA). As a result, it is possible to provide an electric double layer capacitor using a TEA electrolyte in which a decrease in capacity is suppressed even under a high voltage of 3.0 V or more, particularly preferably over 3.0 V.
ここに開示する高電位キャパシタの電極用活性炭の製造方法は、略球状のフェノール樹脂粒子を、不活性ガス雰囲気下、６００℃以上９００℃以下に加熱して炭化させる炭化工程と、上記炭化工程により得られた炭化物を、アルカリ性条件下、６００℃以上９００℃以下に加熱して賦活させる賦活工程とを備えたことを特徴とする。これにより、活性炭の比表面積を低下させることなく、活性炭の細孔のうち、小さすぎる細孔や大きすぎる細孔の生成を抑えつつ、細孔径を効果的に制御することができる。 The method for producing activated carbon for electrodes of a high potential capacitor disclosed herein includes a carbonization step in which substantially spherical phenol resin particles are carbonized by heating to 600 ° C. or more and 900 ° C. or less in an inert gas atmosphere, and the carbonization step described above. And an activation step of activating the activated carbide by heating to 600 ° C. or more and 900 ° C. or less under alkaline conditions. Thereby, the pore diameter can be effectively controlled while suppressing the generation of pores that are too small or pores among the pores of the activated carbon without reducing the specific surface area of the activated carbon.
以上述べたように、本発明によると、活性炭の細孔に吸着保持するイオン量を効果的に増大させ、電気二重層キャパシタの容量を増大させるとともに、３．０Ｖ以上、特に好ましくは３．０Ｖを超える高電圧下での安定した充放電が可能な電気二重層キャパシタをもたらすことができる。 As described above, according to the present invention, the amount of ions adsorbed and retained in the pores of the activated carbon is effectively increased, the capacity of the electric double layer capacitor is increased, and 3.0 V or more, particularly preferably 3.0 V. It is possible to provide an electric double layer capacitor capable of stable charging and discharging under a high voltage exceeding.
以下、本発明の実施形態を図面に基づいて詳細に説明する。以下の好ましい実施形態の説明は、本質的に例示に過ぎず、本発明、その適用物或いはその用途を制限することを意図するものでは全くない。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its application.
−活性炭の製造方法−
図１に、本発明の一実施形態に係る活性炭の製造工程を示す。
-Manufacturing method of activated carbon-
In FIG. 1, the manufacturing process of the activated carbon which concerns on one Embodiment of this invention is shown.
＜原料＞
原料４は、活性炭の原料として一般的に用いられる、例えばピッチ等の炭素材料や、フェノール樹脂、ポリイミド樹脂、ポリアクリロニトリル樹脂などの樹脂材料等を用いることができる。
<Raw material>
As the
原料４の形状は、略球状、特に真球状の粒子であることが好ましい。これにより、粒子同士の接触面積が小さくなり且つ電極内に均一に分散可能であるから、より多くの細孔に電解液のイオンを吸着保持することができる。このとき、粒子の平均粒径は、活性炭の比表面積の増加、分散性向上の観点から、好ましくは１μｍ以上５０μｍ以下、より好ましくは５μｍ以上３０μｍ以下、特に好ましくは１０μｍ以上２０μｍ以下である。
The shape of the
＜炭化工程＞
上記原料４を、例えば、図２に示す装置１内のステンレス管２中に配置されたＮｉ管３に入れ、電気炉５により、不活性ガス雰囲気下、加熱する（図１、Ｓ１）。
<Carbonization process>
The
不活性ガスは、具体的には例えば、窒素、二酸化炭素、ヘリウム、アルゴン、又はこれらのガスを主成分として他のガスとの混合したガスである。 Specifically, the inert gas is, for example, nitrogen, carbon dioxide, helium, argon, or a gas obtained by mixing these gases as a main component with another gas.
室温から炭化温度までの昇温速度は、炭化速度を制御しつつ、作業効率の観点から、好ましくは１℃／分以上２０℃／分以下、より好ましくは３℃／分以上１５℃／分以下、特に好ましくは５℃／分以上１０℃／分以下である。 The heating rate from room temperature to the carbonization temperature is preferably 1 ° C./min to 20 ° C./min, more preferably 3 ° C./min to 15 ° C./min from the viewpoint of work efficiency while controlling the carbonization rate. Particularly preferably, it is 5 ° C./min or more and 10 ° C./min or less.
炭化温度は、後述する賦活工程において活性炭のミクロ孔の形成を促進させつつ、過度に大きな孔とならないようこれらの径を制御する観点から、好ましくは５００℃以上１０００℃以下、より好ましくは６００℃以上９００℃以下、特に好ましくは６００℃以上８００℃以下である。なお、５００℃未満の炭化温度では、形成される細孔の分布の不均一性が増す傾向がある。また、１０００℃を超える炭化温度では、炭化が進み、細孔の形成が難しくなる傾向がある。 The carbonization temperature is preferably 500 ° C. or more and 1000 ° C. or less, more preferably 600 ° C. from the viewpoint of controlling these diameters so as not to become excessively large pores while promoting the formation of micropores of activated carbon in the activation step described later. The temperature is 900 ° C. or lower, particularly preferably 600 ° C. or higher and 800 ° C. or lower. In addition, when the carbonization temperature is less than 500 ° C., the nonuniformity of the distribution of the formed pores tends to increase. Further, at a carbonization temperature exceeding 1000 ° C., carbonization proceeds and the formation of pores tends to be difficult.
炭化時間は、後述する賦活工程において活性炭のミクロ孔の形成を促進させつつ、過度に大きな孔とならないようこれらの径を制御する観点から、好ましくは０．５時間以上２時間以下、より好ましくは０．７時間以上１．５時間以下、特に好ましくは０．８時間以上１．２時間以下である。なお、０．５時間未満の炭化時間では、所定温度での熱処理効果が得られにくく、また２時間を超える炭化時間では、製造時間が長くなりすぎるため不利である。 The carbonization time is preferably from 0.5 hours to 2 hours, more preferably from the viewpoint of controlling these diameters so as not to become excessively large pores while promoting the formation of micropores of activated carbon in the activation step described below. It is 0.7 hours or more and 1.5 hours or less, particularly preferably 0.8 hours or more and 1.2 hours or less. Note that if the carbonization time is less than 0.5 hours, it is difficult to obtain the heat treatment effect at a predetermined temperature, and if the carbonization time exceeds 2 hours, the production time becomes too long, which is disadvantageous.
＜賦活工程＞
上記炭化工程Ｓ１において得られた炭化物に対して、アルカリ剤を添加・混合し、得られた混合物４’を、図３に示すように、カーボンフェルト６を設置した装置１’により、不活性ガス雰囲気下において、加熱する（図１、Ｓ２）。
<Activation process>
An alkaline agent is added to and mixed with the carbide obtained in the carbonization step S1, and the resulting
アルカリ剤は、アルカリ金属化合物を用いることができ、具体的には例えば、水酸化カリウム（ＫＯＨ）、水酸化ナトリウム等の水酸化物、炭酸カリウム、炭酸ナトリウム等の炭酸塩などを用いることができる。特に、活性炭の細孔径を制御する観点から、水酸化カリウム（ＫＯＨ）を用いることが好ましい。 As the alkali agent, an alkali metal compound can be used. Specifically, for example, hydroxides such as potassium hydroxide (KOH) and sodium hydroxide, carbonates such as potassium carbonate and sodium carbonate, and the like can be used. . In particular, potassium hydroxide (KOH) is preferably used from the viewpoint of controlling the pore diameter of the activated carbon.
室温から賦活温度までの昇温速度は、活性炭の細孔径の制御及び作業効率の観点から、好ましくは１℃／分以上２０℃／分以下、より好ましくは３℃／分以上１５℃／分以下、特に好ましくは５℃／分以上１０℃／分以下である。 The rate of temperature increase from room temperature to the activation temperature is preferably 1 ° C./min or more and 20 ° C./min or less, more preferably 3 ° C./min or more and 15 ° C./min or less, from the viewpoint of controlling the pore diameter of the activated carbon and working efficiency. Particularly preferably, it is 5 ° C./min or more and 10 ° C./min or less.
賦活温度は、活性炭の細孔径１．０ｎｍ未満のミクロ孔の形成を抑制しつつ、細孔径１．１ｎｍ〜１．５ｎｍのミクロ孔の形成を促進させる観点から、好ましくは５００℃以上１０００℃以下、より好ましくは５５０℃以上９５０℃以下、特に好ましくは６００℃以上９００℃以下である。なお、賦活温度が５００℃未満の場合、賦活反応の進行が遅く賦活時間が長くなるため不利である。また、賦活温度が１０００℃を超えると賦活反応が速くなりすぎるため、比較的均一な細孔の形成が困難となる。 The activation temperature is preferably 500 ° C. or more and 1000 ° C. or less from the viewpoint of promoting the formation of micropores having a pore diameter of 1.1 nm to 1.5 nm while suppressing the formation of micropores having a pore diameter of less than 1.0 nm of activated carbon. More preferably, it is 550 to 950 ° C., particularly preferably 600 to 900 ° C. In addition, when activation temperature is less than 500 degreeC, since progress of activation reaction is slow and activation time becomes long, it is disadvantageous. On the other hand, if the activation temperature exceeds 1000 ° C., the activation reaction becomes too fast, and it becomes difficult to form relatively uniform pores.
賦活時間は、活性炭の細孔径１．０ｎｍ未満のミクロ孔の形成を抑制させつつ、細孔径１．１ｎｍ〜１．５ｎｍのミクロ孔の形成を促進させる観点から、好ましくは０．５時間以上２時間以下、より好ましくは０．７時間以上１．５時間以下、特に好ましくは０．８時間以上１．２時間以下である。なお、賦活温度が０．５時間未満では、十分に賦活反応が進行しない傾向がある。また、賦活温度が２時間を超えると、二次的な賦活反応により比較的均一な細孔の形成が困難となる傾向がある。 The activation time is preferably 0.5 hours or more from the viewpoint of promoting the formation of micropores having a pore diameter of 1.1 nm to 1.5 nm while suppressing the formation of micropores having a pore diameter of less than 1.0 nm of activated carbon. It is not more than time, more preferably not less than 0.7 hours and not more than 1.5 hours, particularly preferably not less than 0.8 hours and not more than 1.2 hours. In addition, when activation temperature is less than 0.5 hour, there exists a tendency for activation reaction not to fully advance. Moreover, when activation temperature exceeds 2 hours, there exists a tendency for formation of a comparatively uniform pore by the secondary activation reaction to become difficult.
＜洗浄・濾過・乾燥工程＞
賦活工程後の賦活物を、活性炭の製造方法として一般的な方法で、洗浄・濾過・乾燥させる（図１、Ｓ３）。具体的には例えば、水で洗浄後、例えば塩酸や硝酸などの酸で洗浄、濾過し、得られた固形物を乾燥する。これにより賦活工程で使用した余剰のアルカリ剤を取り除くことができる。
<Washing, filtration and drying process>
The activated product after the activation process is washed, filtered, and dried by a general method for producing activated carbon (FIG. 1, S3). Specifically, for example, after washing with water, it is washed with an acid such as hydrochloric acid or nitric acid and filtered, and the resulting solid is dried. Thereby, the excess alkaline agent used at the activation process can be removed.
＜官能基除去処理工程＞
上記乾燥物に対し、活性炭の製造方法として一般的な方法で、官能基除去処理を施す（図１、Ｓ４）。具体的には例えば、水素ガスなどの非酸化性雰囲気下、加熱処理する。これにより、上記洗浄・濾過・乾燥工程で得られた乾燥物表面に存在し、電解液の分解反応の活性点となり得る、例えば（水酸基などの）官能基を効果的に除去することができる。
<Functional group removal treatment process>
The dried product is subjected to functional group removal treatment by a general method for producing activated carbon (FIG. 1, S4). Specifically, for example, heat treatment is performed in a non-oxidizing atmosphere such as hydrogen gas. Thereby, for example, functional groups (such as hydroxyl groups) present on the surface of the dried product obtained in the washing, filtering and drying steps and serving as an active site for the decomposition reaction of the electrolytic solution can be effectively removed.
−活性炭の物性−
＜比表面積＞
本実施形態に係る活性炭は、細孔径１．０ｎｍ未満の細孔の形成を抑制しているにも拘わらず、高い比表面積を有しており、後述するαＳ比表面積は、好ましくは２５００ｍ２／ｇ以上、より好ましくは２７００ｍ２／ｇ以上、特に好ましくは２８００ｍ２／ｇ以上３０００ｍ２／ｇ未満である。これにより、電気二重層キャパシタの電極材料として使用したときに、電解液中のイオンの吸着量が増大し、電気二重層キャパシタの容量増加に寄与することができる。また、３．０Ｖ以上、特に好ましくは３．０Ｖを超える高電圧下においても高い静電容量を発現することができる。
-Physical properties of activated carbon-
<Specific surface area>
The activated carbon according to the present embodiment has a high specific surface area even though the formation of pores having a pore diameter of less than 1.0 nm is suppressed, and the α S specific surface area described below is preferably 2500 m 2. / G or more, more preferably 2700 m 2 / g or more, particularly preferably 2800 m 2 / g or more and less than 3000 m 2 / g. Thereby, when it uses as an electrode material of an electric double layer capacitor, the adsorption amount of the ion in electrolyte solution increases, and it can contribute to the capacity | capacitance increase of an electric double layer capacitor. Further, a high capacitance can be exhibited even under a high voltage of 3.0 V or higher, particularly preferably higher than 3.0 V.
＜細孔容量＞
また、本実施形態に係る活性炭は、高い細孔容量を有しており、後述するαＳ法により得られるミクロ孔の細孔容量は、好ましくは１．４ｃｍ３／ｇ以上２．５ｃｍ３／ｇ以下、より好ましくは１．５ｃｍ３／ｇ以上２．０ｃｍ３／ｇ以下、特に好ましくは１．６ｃｍ３／ｇ以上１．９ｃｍ３／ｇ以下である。これにより、電気二重層キャパシタの電極材料と使用したときに、電解液中のイオンの吸着量が増大し、電気二重層キャパシタの容量増加に寄与することができる。また、３．０Ｖ以上、特に好ましくは３．０Ｖを超える高電圧下においても高い静電容量を発現することができる。
<Pore volume>
Also, the activated carbon according to the present embodiment has a high pore volume, pore volume of micropores obtained by alpha S method described below is preferably 1.4 cm 3 / g or more 2.5 cm 3 / g or less, more preferably 1.5 cm 3 / g or more 2.0 cm 3 / g, particularly preferably at most 1.6 cm 3 / g or more 1.9 cm 3 / g. Thereby, when it uses with the electrode material of an electrical double layer capacitor, the adsorption amount of the ion in electrolyte solution increases, and it can contribute to the capacity | capacitance increase of an electrical double layer capacitor. Further, a high capacitance can be exhibited even under a high voltage of 3.0 V or higher, particularly preferably higher than 3.0 V.
＜細孔径＞
以下、本実施形態に係る活性炭の細孔径について検討する。
<Pore diameter>
Hereinafter, the pore diameter of the activated carbon according to the present embodiment will be examined.
ここに、電気二重層キャパシタに用いられる電解液としては、メチルエチルピロリジニウムテトラフルオロホウ酸（ＭＥＰＹ／ＢＦ４）やテトラエチルアンモニウムテトラフルオロホウ酸（ＴＥＡ／ＢＦ４）などの電解質が、プロピレンカーボネート（ＰＣ）などの溶媒に溶解したもの等が用いられる。これらのイオン及び溶媒分子の大きさは、分子軌道計算によれば、ＭＥＰＹ：０．５０ｎｍ、ＴＥＡ：０．５５ｎｍ、ＢＦ４ −：０．２３ｎｍ、ＰＣ：０．５５ｎｍであることが知られている。 Here, electrolytes used for electric double layer capacitors include electrolytes such as methyl ethyl pyrrolidinium tetrafluoroborate (MEPY / BF 4 ) and tetraethylammonium tetrafluoroborate (TEA / BF 4 ), propylene carbonate. Those dissolved in a solvent such as (PC) are used. The sizes of these ions and solvent molecules are known to be MEPY: 0.50 nm, TEA: 0.55 nm, BF 4 − : 0.23 nm, PC: 0.55 nm according to molecular orbital calculations. Yes.
例えば、ＭＥＰＹが活性炭の細孔に取り込まれるには、ＭＥＰＹは溶媒とともに細孔内に取り込まれるため、少なくともＭＥＰＹとＰＣとを合計した大きさである１．０５ｎｍ以上の細孔であることが必要である。同様にＴＥＡとＰＣでは１．１０ｎｍ、ＢＦ４ −とＰＣでは０．７８ｎｍ以上の細孔であることが必要である。このことから、例えば１．０ｎｍ未満の大きさの細孔は少なくともＭＥＰＹ又はＴＥＡイオンを取り込むことができないため、電気二重層キャパシタの電極用活性炭では不要と考えられる。さらに、このような小さすぎる細孔は、電極の容量として寄与しないばかりか、電解液の分解反応の活性点となり得るため、高電圧下での分解反応を抑制する観点からも、できる限りこのような細孔の数が低減されることが望ましい。 For example, in order for MEPY to be taken into the pores of activated carbon, MEPY is taken into the pores together with the solvent, so it is necessary that the pores have a size of at least 1.05 nm, which is the total size of MEPY and PC. It is. Similarly, it is necessary that the pores are 1.10 nm for TEA and PC, and 0.78 nm or more for BF 4 − and PC. For this reason, for example, pores having a size of less than 1.0 nm cannot take at least MEPY or TEA ions, and thus it is considered unnecessary for activated carbon for electrodes of electric double layer capacitors. Furthermore, such a too small pore not only contributes to the capacity of the electrode, but can also serve as an active site for the decomposition reaction of the electrolytic solution. Therefore, from the viewpoint of suppressing the decomposition reaction under a high voltage as much as possible. It is desirable that the number of fine pores be reduced.
また、高電圧下での分解反応により生じた分解生成物が細孔近傍に堆積し、細孔径が縮小されることによりイオンを取り込めなくなることも、キャパシタ性能の劣化の一因である。従って、分解生成物が堆積しても、イオン及び溶媒が出入り可能な細孔径として約１．１ｎｍ以上の細孔径を有することが効果的である。 In addition, decomposition products generated by the decomposition reaction under a high voltage accumulate in the vicinity of the pores, and the pore diameter is reduced, so that ions cannot be taken in, which is one cause of deterioration of the capacitor performance. Therefore, it is effective to have a pore diameter of about 1.1 nm or more as a pore diameter through which ions and solvents can enter and exit even when decomposition products are deposited.
さらに、細孔径が大きすぎる場合には、細孔に取り込まれたイオンが細孔に保持されることなく細孔外へ放出される可能性が高まるおそれがある。 Furthermore, when the pore diameter is too large, there is a possibility that ions taken into the pore are likely to be released out of the pore without being retained in the pore.
以上のことから、本実施形態に係る活性炭の細孔径は、好ましくは１．０ｎｍより大きく２．０ｎｍ未満、より好ましくは１．１ｎｍ以上１．５ｎｍ以下、特に好ましくは、１．１ｎｍ以上１．４ｎｍ以下である。 From the above, the pore diameter of the activated carbon according to the present embodiment is preferably greater than 1.0 nm and less than 2.0 nm, more preferably 1.1 nm or more and 1.5 nm or less, and particularly preferably 1.1 nm or more and 1. 4 nm or less.
これにより、電解液中のイオンのうち活性炭の細孔に吸着保持されるイオンの量を最大限増加させることができる。また、上記細孔径のサイズよりも小さな細孔径を有する細孔の量を低減させることにより、３．０Ｖ以上、特に好ましくは３．０Ｖを超える高電圧下においても、分解反応の抑制に寄与することができ、キャパシタの劣化を抑制することができる。さらに、細孔のサイズを上記細孔径のサイズとすることにより、３．０Ｖ以上、特に好ましくは３．０Ｖを超える高電圧下においてもイオン及び溶媒の移動経路を確保することができ、容量の低下を抑制することができる。 Thereby, the amount of ions adsorbed and held in the pores of the activated carbon among the ions in the electrolytic solution can be maximized. Further, by reducing the amount of pores having a pore size smaller than the size of the pore size, it contributes to the suppression of the decomposition reaction even under a high voltage of 3.0 V or more, particularly preferably more than 3.0 V. And deterioration of the capacitor can be suppressed. Furthermore, by setting the size of the pores to the size of the above-mentioned pore diameter, it is possible to ensure the movement path of ions and solvents even under a high voltage of 3.0 V or more, particularly preferably more than 3.0 V. The decrease can be suppressed.
＜まとめ＞
以上述べたように、本実施形態に係る高電位キャパシタの電極用活性炭の製造方法によれば、活性炭の比表面積を低下させることなく、活性炭の細孔のうち、静電容量の発現に寄与しない小さすぎる細孔や大きすぎる細孔の生成を抑えつつ、細孔径を効果的に制御することができる。そうして、３．０Ｖ以上、特に好ましくは３．０Ｖを超える高電圧下においても、高い静電容量を発現する高電位キャパシタをもたらし得る。
<Summary>
As described above, according to the method for producing activated carbon for electrodes of the high potential capacitor according to the present embodiment, without reducing the specific surface area of the activated carbon, it does not contribute to the expression of capacitance among the pores of the activated carbon. The pore diameter can be effectively controlled while suppressing the generation of pores that are too small or too large. Thus, it is possible to provide a high-potential capacitor that develops a high capacitance even under a high voltage of 3.0 V or more, particularly preferably over 3.0 V.
−キャパシタの製造方法−
電気二重層キャパシタの構造に制限はなく、金属製ケースに収容したコイン型、アルミラミネートフィルムに収容したラミネート型、集電体両面に電極層を形成した一対の帯状電極体の間にセパレータを介して捲回し有底円筒型容器に収容させた円筒型、集電体両面に活性炭シートを貼り付けた活性炭シート電極をセパレータを介して複数交互に積層し有底角型容器に収容させた積層型など公知の構造とすることができる。本実施形態においては、コイン型のセルの作製手順を説明する。
-Capacitor manufacturing method-
There are no restrictions on the structure of the electric double layer capacitor. A coin is housed in a metal case, a laminate is housed in an aluminum laminate film, and a separator is interposed between a pair of strip electrode bodies in which electrode layers are formed on both sides of the current collector. A cylindrical type that is rolled and housed in a bottomed cylindrical container, and a stacked type in which a plurality of activated carbon sheet electrodes with activated carbon sheets pasted on both sides of the current collector are alternately stacked via a separator and accommodated in a bottomed rectangular container For example, a known structure can be used. In this embodiment, a procedure for manufacturing a coin-type cell will be described.
＜混練工程＞
上述のごとく調製した活性炭と、導電補助剤と、バインダ材とを混練機により混練する（図４、Ｓ１１）。
<Kneading process>
The activated carbon prepared as described above, the conductive auxiliary agent, and the binder material are kneaded with a kneader (FIG. 4, S11).
導電補助剤は、活物質としての活性炭の導電性を良好にするものであれば特に限定されず、公知の導電補助剤を使用できる。例えば、黒鉛、カーボンブラック（アセチレンブラック、ケッチェンブラック（ＫＢ）、その他のファーネスブラック、チャンネルブラック、サーマルランプブラックなど）等の炭素材料が挙げられる。混練物中における導電補助剤の混合割合は、電極の導電性向上の観点から、好ましくは５〜１５質量％、より好ましくは６〜１４質量％、特に好ましくは７〜１３質量％である。 A conductive auxiliary agent will not be specifically limited if the electroconductivity of the activated carbon as an active material is made favorable, A well-known conductive auxiliary agent can be used. Examples thereof include carbon materials such as graphite and carbon black (acetylene black, ketjen black (KB), other furnace blacks, channel blacks, thermal lamp blacks, and the like). The mixing ratio of the conductive auxiliary agent in the kneaded product is preferably 5 to 15% by mass, more preferably 6 to 14% by mass, and particularly preferably 7 to 13% by mass from the viewpoint of improving the conductivity of the electrode.
バインダ材は、活性炭や導電補助剤同士、またこれらの電極材料と後述する集電体とを結合させるものである。バインダ材は、上述の結合が可能なものであればよく、例えば、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）等のフッ素樹脂、ポリエチレン、ポリプロピレン、ポリエチレンテレフタレート、芳香族ポリアミド、カルボキシメチルセルロース（ＣＭＣ）などのセルロース誘導体、スチレン・ブタジエンゴム（ＳＢＲ）、イソプレンゴム、ブタジエンゴム、ポリアセチレン等が挙げられる。混練物中におけるバインダ材の混合割合は、活性炭、導電補助剤及び集電体間の接着性向上の観点から、好ましくは５〜４０質量％、より好ましくは７〜３５質量％、特に好ましくは１０〜３２質量％である。 The binder material binds activated carbon and conductive auxiliary agents, and these electrode materials and a current collector described later. The binder material may be any material as long as the above-described bonding is possible. For example, fluororesin such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, carboxymethyl cellulose Examples thereof include cellulose derivatives such as (CMC), styrene / butadiene rubber (SBR), isoprene rubber, butadiene rubber, polyacetylene and the like. The mixing ratio of the binder material in the kneaded material is preferably 5 to 40% by mass, more preferably 7 to 35% by mass, and particularly preferably 10 from the viewpoint of improving the adhesion between the activated carbon, the conductive additive and the current collector. It is -32 mass%.
混練機は、例えば、加圧式ニーダー、押し出し機、プラネタリーミキサーなど公知の混練機やミキサーを用いることができる。 As the kneader, for example, a known kneader or mixer such as a pressure kneader, an extruder, or a planetary mixer can be used.
＜圧延及び乾燥工程＞
上記混練工程で得られた混練物をカレンダロールなどの公知の圧延機で圧延することによって、シート状に成形する（図４、Ｓ１２）。
<Rolling and drying process>
The kneaded product obtained in the kneading step is rolled into a sheet by a known rolling machine such as a calender roll (FIG. 4, S12).
圧延により成形された活性炭シートは水を含むので、乾燥により水分を除去する（図４、Ｓ１３）。活性炭シートからの水の除去は、圧延して成形した後で乾燥してもよいし、圧延と同時に乾燥して水の一部又は全部を除去してもよい。具体的には例えば、真空中好ましくは１００℃〜１５０℃の温度に６時間〜２４時間加熱し、乾燥させる。これにより、充放電に伴う残留水分のガス化に起因するキャパシタの破損を防止することができる。 Since the activated carbon sheet formed by rolling contains water, the moisture is removed by drying (FIG. 4, S13). The removal of water from the activated carbon sheet may be dried after rolling and forming, or may be dried simultaneously with the rolling to remove a part or all of the water. Specifically, for example, it is heated in a temperature of preferably 100 ° C. to 150 ° C. for 6 hours to 24 hours and dried. Thereby, damage to the capacitor due to gasification of residual moisture accompanying charge / discharge can be prevented.
＜打ち抜き工程＞
そして、得られたシート状の圧延物を、例えば円形の打抜き型を用いてディスク状に打抜く（図４、Ｓ１４）。
<Punching process>
Then, the obtained sheet-like rolled product is punched into a disk shape using, for example, a circular punching die (FIG. 4, S14).
得られたディスク体の質量及び厚さを測定した後、そのディスク体を、例えば黒鉛系の導電性接着剤などを用いて集電体に貼り付け、電極を得る。 After measuring the mass and thickness of the obtained disk body, the disk body is attached to a current collector using, for example, a graphite-based conductive adhesive to obtain an electrode.
なお、集電体としては、導電性に優れ且つ電気化学的に耐久性のある材料であればよく、例えばアルミニウム、チタン、タンタルなどの金属やステンレス鋼などが通常用いられる。 The current collector may be any material that is excellent in conductivity and electrochemically durable. For example, metals such as aluminum, titanium, and tantalum, and stainless steel are usually used.
＜コインセル組立工程＞
上述のごとく得られた電極を、不活性ガス雰囲気下、電解液を用いて、コインセルを組み立てる（図４、Ｓ１５）。
<Coin cell assembly process>
A coin cell is assembled from the electrode obtained as described above using an electrolyte in an inert gas atmosphere (FIG. 4, S15).
電解液は、電気二重層キャパシタの内部に含有させるものであり、電解質と溶媒とを含む。 The electrolytic solution is contained in the electric double layer capacitor and includes an electrolyte and a solvent.
電解液に含有される電解質としては、カチオンとアニオンとを含む塩であって、例えば、カチオンは、テトラエチルアンモニウム（ＴＥＡ）、トリエチルメチルアンモニウム、メチルエチルピロリジニウム（ＭＥＰＹ）、スピロ−（１、１’）−ビピロリジニウム、ジエチルメチル−２−メトキシエチルアンモニウム（ＤＥＭＥ）、１、３−ジアルキルイミダゾリウム、１，２，３−トリアルキルイミダゾリウム、１−エチル−３−メチルイミダゾリウム（ＥＭＩ）、１，２−ジメチル−３−プロピルイミダゾリウム（ＤＭＰＩ）等であり、アニオンは、ＢＦ４−、ＰＦ６−、ＣｌＯ４−、ＡｌＣｌ４−又はＣＦ３ＳＯ３−であるものを採用することができる。
The electrolyte contained in the electrolytic solution is a salt containing a cation and an anion. For example, the cation includes tetraethylammonium (TEA), triethylmethylammonium, methylethylpyrrolidinium (MEPY), spiro- (1, 1 ′)-bipyrrolidinium, diethylmethyl-2-methoxyethylammonium (DEME), 1,3-dialkylimidazolium, 1,2,3-trialkylimidazolium, 1-ethyl-3-methylimidazolium (EMI), 1,2-dimethyl-3-propyl imidazolium (DMPI), etc., anion, BF 4-, PF 6-, ClO 4-, be employed as a 3-
電解液の溶媒としては、プロピレンカーボネート（ＰＣ）、エチレンカーボネート（ＥＣ）、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、アセトニトリル（ＡＮ）、プロピオニトリル、γ−ブチロラクトン（ＢＬ）、ジメチルホルムアミド（ＤＭＦ）、テトラヒドロフラン（ＴＨＦ）、ジメトキシエタン（ＤＭＥ）、ジメトキシメタン（ＤＭＭ）、スルホラン（ＳＬ）、ジメチルスルホキシド（ＤＭＳＯ）、エチレングリコール、プロピレングリコール、メチルセルソルブなどの有機溶媒などが挙げられる。これらは単独で使用してもよく、２種以上を任意の割合で混合して使用してもよい。 Solvents for the electrolyte include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), acetonitrile (AN), propionitrile, γ-butyrolactone (BL), dimethylformamide ( Examples thereof include organic solvents such as DMF), tetrahydrofuran (THF), dimethoxyethane (DME), dimethoxymethane (DMM), sulfolane (SL), dimethyl sulfoxide (DMSO), ethylene glycol, propylene glycol, and methyl cellosolve. These may be used alone or in combination of two or more at any ratio.
電解液中の電解質の濃度は、電気二重層キャパシタの十分な容量発現の観点から、好ましくは０．３〜２．０ｍｏｌ／Ｌ、より好ましくは０．５〜１．７ｍｏｌ／Ｌ、特に好ましくは０．７〜１．５ｍｏｌ／Ｌである。 The concentration of the electrolyte in the electrolytic solution is preferably 0.3 to 2.0 mol / L, more preferably 0.5 to 1.7 mol / L, particularly preferably from the viewpoint of sufficient capacity development of the electric double layer capacitor. 0.7 to 1.5 mol / L.
−コインセルのキャパシタ性能−
＜静電容量＞
本実施形態に係る電気二重層キャパシタは、高電圧下においても高い静電容量を示し、後述する充放電試験により得られるミクロ孔の単位体積当たりの静電容量が、好ましくは３Ｆ／ｃｍ３以上２０Ｆ／ｃｍ３以下、より好ましくは５Ｆ／ｃｍ３以上１５Ｆ／ｃｍ３以下、特に好ましくは９Ｆ／ｃｍ３以上１４．５Ｆ／ｃｍ３以下である。これにより、３．０Ｖ以上、特に好ましくは３．０Ｖを超える高電圧下においても、高いキャパシタ性能をもたらすことができる。
-Capacitor performance of coin cell-
<Capacitance>
The electric double layer capacitor according to this embodiment exhibits a high capacitance even under a high voltage, and the capacitance per unit volume of micropores obtained by a charge / discharge test described later is preferably 3 F / cm 3 or more. 20F / cm 3 or less, more preferably 5F / cm 3 or more 15F / cm 3 or less, particularly preferably not more than 9F / cm 3 or more 14.5F / cm 3. As a result, high capacitor performance can be achieved even under a high voltage of 3.0 V or more, particularly preferably over 3.0 V.
＜容量維持率＞
本実施形態に係る電気二重層キャパシタは、高電圧下においても高い容量維持率を示し、後述する耐久試験により得られる容量維持率が、好ましくは５５％以上９５％以下、より好ましくは６５％以上９０％以下、特に好ましくは７５％以上８５％以下である。これにより、３．０Ｖ以上、特に好ましくは３．０Ｖを超える高電圧下においても、高いキャパシタ性能をもたらすことができる。
<Capacity maintenance rate>
The electric double layer capacitor according to the present embodiment exhibits a high capacity maintenance ratio even under a high voltage, and a capacity maintenance ratio obtained by an endurance test described later is preferably 55% or more and 95% or less, more preferably 65% or more. It is 90% or less, particularly preferably 75% or more and 85% or less. As a result, high capacitor performance can be achieved even under a high voltage of 3.0 V or more, particularly preferably over 3.0 V.
本実施形態に係る電気二重層キャパシタは、高電圧下においても高い静電容量及び容量維持率を示し、ハイブリッド自動車などの蓄電デバイスとして有用である。 The electric double layer capacitor according to the present embodiment exhibits high capacitance and capacity retention even under a high voltage, and is useful as a power storage device such as a hybrid vehicle.
次に、具体的に実施した実施例について説明する。 Next, specific examples will be described.
表１に、実施例１，２及び比較例１，２の活性炭の調製条件及び各物性値について示す。 In Table 1, it shows about the preparation conditions and each physical-property value of the activated carbon of Examples 1, 2 and Comparative Examples 1, 2.
−活性炭の調製−
［実施例１］
＜炭化工程＞
原料４として市販の粒状フェノール樹脂（平均粒径１７μｍ）を、図２に示す装置１のステンレス管２中に設置されたＮｉ管３中に入れ、窒素ガス気流下（２００ｍＬ／分）、５℃／分で室温から６００℃まで昇温した。その後、６００℃の温度で１時間保持し、炭化物を得た。
-Preparation of activated carbon-
[Example 1]
<Carbonization process>
Commercially available granular phenolic resin (average particle size 17 μm) as
＜賦活工程＞
次に、炭化物を室温まで冷却後、炭化物が入ったＮｉ管３内に、炭化物に対して質量比が４となるようにＫＯＨを添加した。そして、図３に示すようにカーボンフェルトを設置して、５℃／分で室温から８００℃まで昇温した。その後８００℃の温度で１時間保持し、賦活物を得た。
<Activation process>
Next, after cooling the carbide to room temperature, KOH was added into the
＜洗浄・濾過・乾燥工程＞
賦活物を室温まで冷却後、イオン交換水、次いで塩酸で洗浄後、濾過して得られた固形物を乾燥した。
<Washing, filtration and drying process>
The activated product was cooled to room temperature, washed with ion-exchanged water and then hydrochloric acid, and then the solid obtained by filtration was dried.
＜官能基除去工程＞
上記固形物を、Ｈ２ガス５０ｍＬ／分、及びＡｒガス２００ｍＬ／分の気流下、６００℃の温度で２４時間加熱することにより、活性炭表面の官能基除去処理を行い、実施例１の活性炭Ｅ１を得た。
<Functional group removal step>
The above solid matter was heated for 24 hours at a temperature of 600 ° C. under an air flow of 50 mL / min of H 2 gas and 200 mL / min of Ar gas, thereby performing functional group removal treatment on the activated carbon surface, and activated carbon E1 of Example 1 Got.
［実施例２］
表１に示すように、賦活温度を９００℃とした以外は、実施例１と同様の条件により活性炭Ｅ２を調製した。
[Example 2]
As shown in Table 1, activated carbon E2 was prepared under the same conditions as in Example 1 except that the activation temperature was 900 ° C.
［比較例１］
表１に示すように、賦活温度を７００℃とした以外は、実施例１と同様の条件により活性炭Ｃ１を調製した。
[Comparative Example 1]
As shown in Table 1, activated carbon C1 was prepared under the same conditions as in Example 1 except that the activation temperature was 700 ° C.
［比較例２］
表１に示すように、賦活温度を９００℃とするとともに、ＫＯＨ量を炭化物に対して質量比が６となるようにした以外は、実施例１と同様の条件により活性炭Ｃ２を調製した。
[Comparative Example 2]
As shown in Table 1, activated carbon C2 was prepared under the same conditions as in Example 1 except that the activation temperature was 900 ° C. and the mass ratio of KOH was 6 with respect to the carbide.
−活性炭の物性−
実施例１，２及び比較例１，２の活性炭について、比表面積、ミクロ孔の細孔容量、及びミクロ孔の細孔径について、窒素ガスを用いて測定した吸着等温線よりαＳ法（K. Kaneko，C. Ishii，M. Ruike，H. Kuwabara，“Origin of Superhigh Surface Area and Microcrystalline Graphitic Structures of Activated Carbons”，Carbon，30，(1992) 1075-1088）にて算出した。結果を表１に示す。
-Physical properties of activated carbon-
With respect to the activated carbons of Examples 1 and 2 and Comparative Examples 1 and 2, the specific surface area, the micropore pore volume, and the micropore pore diameter were measured by the α S method (K. Kaneko, C. Ishii, M. Ruike, H. Kuwabara, “Origin of Superhigh Surface Area and Microcrystalline Graphitic Structures of Activated Carbons”, Carbon, 30, (1992) 1075-1088). The results are shown in Table 1.
表１に示すように、実施例１，２に係る活性炭Ｅ１，Ｅ２では、細孔径が１．１０ｎｍ以上１．５０ｎｍ以下となり、電解液のイオンの吸着・保持に有効であると考えられる。また、このように、静電容量の発現に寄与しない細孔径１．００ｎｍ未満の細孔の形成を抑制しているにも拘わらず、２８００ｍ２／ｇ以上の比表面積を有し、十分な細孔容量を有しており、電気二重層キャパシタの電極用活性炭として有用であると考えられる。 As shown in Table 1, in the activated carbons E1 and E2 according to Examples 1 and 2, the pore diameter is 1.10 nm or more and 1.50 nm or less, which is considered to be effective for adsorption / retention of ions in the electrolytic solution. In addition, it has a specific surface area of not less than 2800 m 2 / g and is sufficiently fine despite the suppression of the formation of pores having a pore diameter of less than 1.00 nm that does not contribute to the development of capacitance. It has a pore capacity and is considered useful as an activated carbon for electrodes of electric double layer capacitors.
−コインセルの作製−
実施例１，２及び比較例１，２の活性炭及び表２に示す電解液を用いて、コインセルを作製した。表３にコインセルの構成を示す。
-Production of coin cell-
Coin cells were produced using the activated carbons of Examples 1 and 2 and Comparative Examples 1 and 2 and the electrolyte solution shown in Table 2. Table 3 shows the configuration of the coin cell.
［実施例３］
＜混練工程＞
表３に示すように、実施例１の活性炭Ｅ１と、ケッチェンブラック（ＫＢ）と、カルボキシメチルセルロース（ＣＭＣ）とスチレン・ブタジエンゴム（ＳＢＲ）とポリテトラフルオロエチレン（ＰＴＦＥ）とを、質量比で８：１：１：１：２の割合となるように、混練機に入れ、混練を行った。
[Example 3]
<Kneading process>
As shown in Table 3, the activated carbon E1 of Example 1, Ketjen Black (KB), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE) in mass ratio. The mixture was placed in a kneader so as to have a ratio of 8: 1: 1: 1: 2 and kneaded.
＜圧延・乾燥工程＞
その後上記混練物を圧延し、真空下１２０℃の温度で１２時間加熱し、乾燥させた。
<Rolling / drying process>
Thereafter, the kneaded product was rolled, heated at 120 ° C. under vacuum for 12 hours, and dried.
＜打抜き工程＞
そして、円形の打抜き型を用いて直径１２ｍｍのディスク状に打抜き、ディスク体を得た。得られたディスク体の質量及び厚さを測定した後、アルミニウムシート製集電体に貼り付け、電極を得た。
<Punching process>
Then, using a circular punching die, it was punched into a disk shape having a diameter of 12 mm to obtain a disk body. After measuring the mass and thickness of the obtained disc body, it was attached to an aluminum sheet current collector to obtain an electrode.
＜コインセル作製＞
得られた電極を用いて、Ａｒ雰囲気下、表２に示す電解液Ｍを使用して、ＣＲ２０３２型コインセルを組み立てた。
<Coin cell production>
Using the obtained electrode, a CR2032-type coin cell was assembled using the electrolytic solution M shown in Table 2 under an Ar atmosphere.
［実施例４］
表３に示すように、実施例２の活性炭Ｅ２を用いた以外は実施例３と同様の条件によりコインセルを作製した。
[Example 4]
As shown in Table 3, coin cells were produced under the same conditions as in Example 3 except that the activated carbon E2 of Example 2 was used.
［比較例３］
表３に示すように、比較例１の活性炭Ｃ１を用いた以外は実施例３と同様の条件によりコインセルを作製した。
[Comparative Example 3]
As shown in Table 3, coin cells were produced under the same conditions as in Example 3 except that the activated carbon C1 of Comparative Example 1 was used.
［比較例４］
表３に示すように、比較例２の活性炭Ｃ２を用いた以外は実施例３と同様の条件によりコインセルを作製した。
[Comparative Example 4]
As shown in Table 3, coin cells were produced under the same conditions as in Example 3 except that the activated carbon C2 of Comparative Example 2 was used.
［実施例５］
表３に示すように、電解液Ｔを用いた以外は実施例３と同様の条件によりコインセルを作製した。
[Example 5]
As shown in Table 3, coin cells were produced under the same conditions as in Example 3 except that the electrolytic solution T was used.
［実施例６］
表３に示すように、電解液Ｔを用いた以外は実施例４と同様の条件によりコインセルを作製した。
[Example 6]
As shown in Table 3, coin cells were produced under the same conditions as in Example 4 except that the electrolytic solution T was used.
［比較例５］
表３に示すように、電解液Ｔを用いた以外は比較例３と同様の条件によりコインセルを作製した。
[Comparative Example 5]
As shown in Table 3, coin cells were produced under the same conditions as in Comparative Example 3 except that the electrolytic solution T was used.
［比較例６］
表３に示すように、電解液Ｔを用いた以外は比較例４と同様の条件によりコインセルを作製した。
[Comparative Example 6]
As shown in Table 3, coin cells were produced under the same conditions as in Comparative Example 4 except that the electrolytic solution T was used.
−充放電試験−
＜静電容量＞
実施例３〜６及び比較例３〜６のコインセルについて、静電容量を測定するため、充放電試験を行った。まず、電圧値を２．７Ｖとし、充放電レート０．５ｍＡ／ｃｍ２で１００サイクルの充放電試験後，さらに５ｍＡ／ｃｍ２で１００サイクルの充放電試験を行い、静電容量（終止容量）を算出した。そして、電圧値を３．０Ｖ、及び３．３Ｖとして、同様の充放電試験を行い、静電容量（終止容量）を算出した。表３、図５及び図６に、ミクロ孔単位体積当たりの静電容量（Ｆ／ｃｍ３）を示す。
−Charge / discharge test−
<Capacitance>
About the coin cell of Examples 3-6 and Comparative Examples 3-6, in order to measure an electrostatic capacitance, the charging / discharging test was done. First, the voltage value was set to 2.7 V, and after 100 cycles of charge / discharge tests at a charge / discharge rate of 0.5 mA / cm 2 , 100 cycles of charge / discharge tests were further conducted at 5 mA / cm 2 to determine the capacitance (end capacity). Was calculated. And the voltage value was set to 3.0V and 3.3V, the same charging / discharging test was done, and the electrostatic capacitance (end capacity) was computed. In Table 3, FIG.5, and FIG.6, the electrostatic capacitance per micropore unit volume (F / cm < 3 >) is shown.
表３及び図５に示すとおり、電解液Ｍを用いた場合、２．７〜３．３Ｖのいずれの電圧値においても、細孔径１．１６ｎｍ又は１．３０ｎｍの活性炭Ｅ１又はＥ２で、静電容量は最大となることが判った（実施例３，４）。一方、細孔径１．００ｎｍの活性炭Ｃ１では、活性炭Ｅ１，Ｅ２に比べ、静電容量が大きく低下することが判った（比較例３）。また、細孔径１．６２ｎｍの活性炭Ｃ２においても、活性炭Ｅ１，Ｅ２に比べて、静電容量が減少することが判った（比較例４）。 As shown in Table 3 and FIG. 5, when the electrolytic solution M is used, the activated carbon E1 or E2 having a pore diameter of 1.16 nm or 1.30 nm is used for any voltage value of 2.7 to 3.3 V. It was found that the capacity was maximized (Examples 3 and 4). On the other hand, in the activated carbon C1 having a pore diameter of 1.00 nm, it was found that the capacitance was greatly reduced as compared with the activated carbons E1 and E2 (Comparative Example 3). Moreover, it turned out that electrostatic capacitance reduces also in activated carbon C2 with a pore diameter of 1.62 nm compared with activated carbon E1 and E2 (comparative example 4).
表３及び図６に示すとおり、電解液Ｔを用いた場合、２．７Ｖ印加時には細孔径１．１６ｎｍの活性炭Ｅ１で静電容量は最大となり（実施例５）、一方で３．０Ｖ、３．３Ｖ印加時には、細孔径１．３０ｎｍの活性炭Ｅ２で静電容量は最大となった（実施例６）。また、いずれの電圧値においても、細孔径１．００ｎｍ又は１．６２ｎｍの活性炭Ｃ１又はＣ２を用いた場合には、静電容量の低下が見られた（比較例５，６）。特に活性炭Ｃ２では３．３Ｖ印加時に静電容量の大きな低下が見られた（比較例６）。 As shown in Table 3 and FIG. 6, when the electrolytic solution T is used, when 2.7 V is applied, the activated carbon E1 having a pore diameter of 1.16 nm maximizes the capacitance (Example 5), while 3.0 V, 3 When 3 V was applied, the capacitance was maximized with activated carbon E2 having a pore diameter of 1.30 nm (Example 6). Moreover, in any voltage value, when activated carbon C1 or C2 having a pore diameter of 1.00 nm or 1.62 nm was used, a decrease in capacitance was observed (Comparative Examples 5 and 6). In particular, activated carbon C2 showed a large decrease in capacitance when 3.3 V was applied (Comparative Example 6).
＜容量維持率＞
コインセルの静電容量の容量維持率として、上述の充放電試験で得られた上記終止容量と、上記充放電レート５ｍＡ／ｃｍ２で１００サイクル充放電試験を行った中で得られた最大静電容量との比を容量維持率（％）とした。表３、図７及び図８に結果を示す。
<Capacity maintenance rate>
As the capacity retention rate of the electrostatic capacity of the coin cell, the maximum electrostatic capacity obtained during the 100-cycle charge / discharge test performed at the above-mentioned final capacity obtained in the above-mentioned charge / discharge test and the above-mentioned charge / discharge rate of 5 mA / cm 2 The ratio with the capacity was defined as the capacity maintenance rate (%). The results are shown in Table 3, FIG. 7 and FIG.
表３及び図７に示すとおり、電解液Ｍを用いた場合、２．７〜３．３Ｖのいずれの電圧値においても、細孔径１．１６ｎｍ、１．３０ｎｍ又は１．６２ｎｍの活性炭Ｅ１，Ｅ２，Ｃ２で、７５％以上の高い容量維持率を示すことがわかった（実施例３，４、比較例４）。一方、細孔径１．００ｎｍの活性炭Ｃ１では、他の活性炭に比べ、容量維持率は大きく低下することが判った（比較例３）。 As shown in Table 3 and FIG. 7, when the electrolytic solution M is used, activated carbon E1, E2 having a pore diameter of 1.16 nm, 1.30 nm, or 1.62 nm at any voltage value of 2.7 to 3.3 V. , C2 was found to exhibit a high capacity retention rate of 75% or more (Examples 3 and 4, Comparative Example 4). On the other hand, in the activated carbon C1 having a pore diameter of 1.00 nm, it was found that the capacity retention rate was greatly reduced as compared with other activated carbon (Comparative Example 3).
表３及び図８に示すとおり、電解液Ｔを用いた場合、２．７Ｖ、３．０Ｖ印加時には細孔径１．６２ｎｍの活性炭Ｃ２で容量維持率は最大となったが（比較例６）、一方で３．３Ｖ印加時には、細孔径１．３０ｎｍの活性炭Ｅ２で容量維持率は最大となり（実施例６）、細孔径１．６２ｎｍの活性炭Ｃ２では容量維持率は低下した（比較例６）。また、いずれの電圧値においても、細孔径１．００ｎｍの活性炭Ｃ１では、容量維持率の大きな低下が見られた（比較例５）。 As shown in Table 3 and FIG. 8, when the electrolytic solution T was used, the capacity retention rate was the maximum with activated carbon C2 having a pore diameter of 1.62 nm when 2.7 V and 3.0 V were applied (Comparative Example 6). On the other hand, when 3.3 V was applied, the capacity retention ratio was maximized with activated carbon E2 having a pore diameter of 1.30 nm (Example 6), and the capacity retention ratio was decreased with activated carbon C2 having a pore diameter of 1.62 nm (Comparative Example 6). Further, at any voltage value, the activated carbon C1 having a pore diameter of 1.00 nm showed a large decrease in capacity retention rate (Comparative Example 5).
＜考察＞
電解液Ｍ，Ｔを用いた場合、上述のごとく、カチオンであるＭＥＰＹ，ＴＥＡと溶媒分子ＰＣの大きさの合計値は各々１．０５ｎｍ，１．１０ｎｍとなる。例えばカソード電極では、上記カチオンが活性炭の細孔内に吸着・保持されて静電容量が発現する。カチオンの移動には溶媒分子ＰＣの移動が伴うところ、少なくとも上記１．０５ｎｍ，１．１０ｎｍ未満の細孔径を有する細孔には、各々のカチオンは吸着・保持されにくく、容量が発現し難いと考えられる。実際、図５〜図８に示すように、細孔径１．００ｎｍの活性炭Ｃ１では、他の活性炭に比べて、静電容量及び容量維持率ともに大きな数値の低下が確認された。このことは、活性炭Ｃ１では細孔径が小さすぎるために、カチオンが細孔内に吸着・保持され難く、容量が発現し難い上に、細孔のエッジ部分が電解液の分解反応の活性点となり得るため、容量維持率の低下につながったものと考えられる。
<Discussion>
When the electrolytic solutions M and T are used, as described above, the total sizes of the cations MEPY and TEA and the solvent molecules PC are 1.05 nm and 1.10 nm, respectively. For example, in the cathode electrode, the cation is adsorbed and held in the pores of the activated carbon to develop a capacitance. The movement of the cation is accompanied by the movement of the solvent molecule PC, and at least the pores having a pore diameter of less than 1.05 nm and 1.10 nm are difficult to adsorb and retain each cation, and the capacity is difficult to express. Conceivable. In fact, as shown in FIGS. 5 to 8, the activated carbon C1 having a pore diameter of 1.00 nm was confirmed to have a large decrease in both the capacitance and the capacity retention rate compared to other activated carbons. This is because activated carbon C1 has too small a pore size, so that cations are hardly adsorbed and retained in the pores, capacity is hardly developed, and the edge portion of the pore becomes an active point for the decomposition reaction of the electrolyte. Therefore, it is thought that the capacity maintenance rate was reduced.
また、いずれの電解液を用いた場合も、細孔径１．６２ｎｍの活性炭Ｃ２では、静電容量が低下する傾向が見られた。これは、細孔径が大きくなるにつれて、カチオンの吸着量だけでなく流出量も増加するため、細孔内に保持されるカチオン量が減少したことが一因と考えられる。 Moreover, even when any electrolyte solution was used, the activated carbon C2 having a pore diameter of 1.62 nm tended to have a reduced capacitance. This is thought to be due to a decrease in the amount of cations retained in the pores, as not only the adsorption amount of cations but also the outflow amount increases as the pore diameter increases.
電解液Ｍを用いた場合において、静電容量及び容量維持率のいずれにおいても印加電圧の変化、すなわち高電圧化に対しても同一の活性炭については大きな数値の変化は確認されなかった。このことは、カチオンのＭＥＰＹが高電圧印加時においても分解されにくいことが一因であると考えられる。 When the electrolytic solution M was used, no significant change in numerical value was confirmed for the same activated carbon even when the applied voltage was changed, that is, when the voltage was increased, in both the capacitance and the capacity retention ratio. This is considered to be partly because the cationic MEPY is not easily decomposed even when a high voltage is applied.
電解液Ｔを用いた場合において、３．０Ｖ以上の高電圧下において、細孔径１．３０ｎｍの活性炭Ｅ２で、静電容量が最大となった。一方、電解液Ｍの場合には、活性炭Ｅ１，Ｅ２で大きな差が確認されなかった。このことは、ＴＥＡイオンがＭＥＰＹイオンよりも少し大きいことに起因していると考えられる。 In the case where the electrolytic solution T was used, the capacitance was maximized with activated carbon E2 having a pore diameter of 1.30 nm under a high voltage of 3.0 V or higher. On the other hand, in the case of the electrolytic solution M, a large difference was not confirmed between the activated carbons E1 and E2. This is thought to be due to the fact that TEA ions are slightly larger than MEPY ions.
本発明は、活性炭の細孔に吸着保持するイオン量を効果的に増大させ、電気二重層キャパシタの容量を増大させるとともに、高電圧下での安定した充放電が可能な電気二重層キャパシタをもたらすことができるので、極めて有用である。 The present invention effectively increases the amount of ions adsorbed and held in the pores of activated carbon, increases the capacity of the electric double layer capacitor, and provides an electric double layer capacitor that can be stably charged and discharged under a high voltage. Can be very useful.
１ 装置
１’ 装置
２ ステンレス管
３ Ｎｉ管
４ 原料
４’ 混合物
５ 電気炉
６ カーボンフェルト
DESCRIPTION OF SYMBOLS 1 Apparatus 1 '
Claims (5)
ミクロ孔の細孔径が、１．１ｎｍ以上１．５ｎｍ以下である
ことを特徴とする高電位キャパシタの電極用活性炭。 The specific surface area is 2500 m 2 / g or more,
An activated carbon for an electrode of a high potential capacitor, wherein the micropore has a pore diameter of 1.1 nm to 1.5 nm.
平均粒径が、１０μｍ以上２０μｍ以下の略球状粒子であり、
前記比表面積が、２８００ｍ２／ｇ以上３０００ｍ２／ｇ未満である
ことを特徴とする高電位キャパシタの電極用活性炭。 In claim 1,
Are substantially spherical particles having an average particle size of 10 μm or more and 20 μm or less,
The activated carbon for an electrode of a high potential capacitor, wherein the specific surface area is 2800 m 2 / g or more and less than 3000 m 2 / g.
電解液に含まれる電解質は、テトラエチルアンモニウムテトラフルオロホウ酸である
ことを特徴とする電気二重層キャパシタ。 In claim 3,
An electric double layer capacitor, wherein the electrolyte contained in the electrolytic solution is tetraethylammonium tetrafluoroborate.
略球状のフェノール樹脂粒子を、不活性ガス雰囲気下、６００℃以上９００℃以下に加熱して炭化させる炭化工程と、
上記炭化工程により得られた炭化物を、アルカリ性条件下、６００℃以上９００℃以下に加熱して賦活させる賦活工程とを備えた
ことを特徴とする高電位キャパシタの電極用活性炭の製造方法。 A method for producing activated carbon for an electrode of a high potential capacitor according to claim 2,
A carbonization step in which substantially spherical phenol resin particles are carbonized by heating to 600 ° C. or more and 900 ° C. or less in an inert gas atmosphere;
A method for producing activated carbon for an electrode of a high potential capacitor, comprising: an activation step of activating the carbide obtained by the carbonization step by heating to 600 ° C. to 900 ° C. under alkaline conditions.
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| CN112384473A (en) * | 2018-07-20 | 2021-02-19 | 株式会社可乐丽 | Carbonaceous material, method for producing same, electrode active material for electrochemical device, electrode for electrochemical device, and electrochemical device |
| WO2023109408A1 (en) * | 2021-12-17 | 2023-06-22 | 宁波中车新能源科技有限公司 | Electric double layer capacitor |
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