JP2020149858A - Positive electrode material for redox battery and redox battery including the same - Google Patents

Abstract

To provide a positive electrode material for a redox battery which achieves both low resistance and long life.SOLUTION: A positive electrode material for a redox battery according to the present invention is made of carbonaceous fiber, the number of bonded oxygen atoms is 0.2 to 0.6% of the total number of carbon atoms on the surface of the electrode material, and the BET specific surface area determined from the amount of nitrogen adsorbed is 0.5 m2/g or more. Further, the carbonaceous fiber contains active particles bound by a binder, and the active particles and the binder are less than 20% of the total amount of the electrode material.SELECTED DRAWING: None

Description

本発明は、水溶液系電解液によるレドックス電池の正極に使用され、炭素質繊維からなる電極材、または炭素質繊維とそれに結着された活性粒子からなる電極材、及びそれを備えたレドックス電池に関するものである。 The present invention relates to an electrode material made of carbonaceous fibers or an electrode material made of carbonaceous fibers and active particles bound thereto, which is used as a positive electrode of a redox battery using an aqueous electrolyte solution, and a redox battery provided with the same. It is a thing.

従来、電極は電池の性能を左右するものとして重点的に開発されている。電極には、それ自体が活物質とならず、活物質の電気化学的反応を促進させる反応場として働くタイプのものがあり、このタイプには導電性や耐薬品性などから炭素材料がよく用いられる。特に電力貯蔵用に開発が盛んなレドックス電池の電極には、耐薬品性があり、導電性を有し、かつ通液性のある炭素質繊維の不織布等が用いられている。 Conventionally, electrodes have been mainly developed as having an influence on the performance of a battery. There is a type of electrode that does not become an active material by itself but acts as a reaction field that promotes the electrochemical reaction of the active material. Carbon materials are often used for this type because of its conductivity and chemical resistance. Be done. In particular, carbonaceous fiber non-woven fabrics having chemical resistance, conductivity, and liquid permeability are used for electrodes of redox batteries, which are being actively developed for power storage.

レドックス電池は、正極に鉄の塩酸水溶液、負極にクロムの塩酸水溶液を用いたタイプから、起電力の高いバナジウムの硫酸水溶液を両極に用いるタイプに替わり、高エネルギー密度化されたが、最近さらに活物質濃度を高める開発が進み、一段と高エネルギー密度化が進んでいる。 Redox batteries have changed from a type that uses an aqueous solution of iron hydrochloric acid for the positive electrode and an aqueous solution of chromium hydrochloric acid for the negative electrode to a type that uses an aqueous solution of vanadium sulfuric acid with high electromotive force for both electrodes, and the energy density has been increased. Development to increase the concentration of substances is progressing, and the energy density is further increasing.

レドックス電池の主な構成は、図１に示すように電解液（正極電解液、負極電解液）を貯える外部タンク６，７と電解槽ＥＣとからなる。電解槽ＥＣでは、相対する集電板１、１の間にイオン交換膜３が配置されている。レドックス電池では、ポンプ８，９にて活物質を含む電解液を外部タンク６，７から電解槽ＥＣに送りながら、電解槽ＥＣに組み込まれた電極５上で電気化学的なエネルギー変換、すなわち充放電が行われる。 As shown in FIG. 1, the main configuration of the redox battery is composed of external tanks 6 and 7 for storing electrolytic solutions (positive electrode electrolytic solution, negative electrode electrolytic solution) and an electrolytic cell EC. In the electrolytic cell EC, the ion exchange membrane 3 is arranged between the opposing current collector plates 1 and 1. In the redox battery, while the electrolytic solution containing the active material is sent from the external tanks 6 and 7 to the electrolytic cell EC by the pumps 8 and 9, electrochemical energy conversion, that is, charging is performed on the electrode 5 incorporated in the electrolytic cell EC. Discharge is performed.

一般に、充放電の際には、電解液を外部タンクと電解槽との間で循環させるため、電解槽は図１に示すような液流通型構造をとる。該液流通型電解槽を単セルと称し、これを最小単位として単独もしくは多段積層して用いられる。液流通型電解槽における電気化学反応は、電極表面で起こる不均一相反応であるため、一般的には二次元的な電解反応場を伴うことになる。電解反応場が二次元的であると、電解槽の単位体積当たりの反応量が小さいという難点がある。 Generally, during charging and discharging, the electrolytic cell is circulated between the external tank and the electrolytic cell, so that the electrolytic cell has a liquid flow type structure as shown in FIG. The liquid flow type electrolytic cell is referred to as a single cell, and is used alone or in multiple stages with this as the smallest unit. Since the electrochemical reaction in the liquid flow type electrolytic cell is a heterogeneous phase reaction that occurs on the electrode surface, it generally involves a two-dimensional electrolytic reaction field. If the electrolytic reaction field is two-dimensional, there is a drawback that the amount of reaction per unit volume of the electrolytic cell is small.

そこで、単位面積当りの反応量、すなわち電流密度を増すために電気化学反応場の三次元化が行われるようになった。図２は、三次元電極を有する液流通型電解槽の分解斜視図である。該電解槽では、相対する二枚の集電板１，１間にイオン交換膜３が配設され、イオン交換膜３の両側にスペーサ２によって集電板１，１の内面に沿った電解液の流路４ａ，４ｂが形成されている。該流通路４ａ，４ｂの少なくとも一方には炭素質繊維の不織布等よりなる電極材５が配設されており、このようにして三次元電極が構成されている。なお、集電板１には電解液の液流入口１０と液流出口１１とが設けられている。 Therefore, the electrochemical reaction field has come to be three-dimensionalized in order to increase the reaction amount per unit area, that is, the current density. FIG. 2 is an exploded perspective view of a liquid flow type electrolytic cell having a three-dimensional electrode. In the electrolytic cell, an ion exchange membrane 3 is arranged between two opposing current collector plates 1, 1, and an electrolytic solution along the inner surface of the current collector plates 1, 1 is provided by spacers 2 on both sides of the ion exchange membrane 3. Flow paths 4a and 4b are formed. An electrode material 5 made of a non-woven fabric of carbonaceous fibers or the like is disposed in at least one of the flow passages 4a and 4b, and a three-dimensional electrode is formed in this way. The current collector plate 1 is provided with a liquid inlet 10 and a liquid outlet 11 for the electrolytic solution.

正極電解液にオキシ硫酸バナジウム、負極電解液に硫酸バナジウムの各々硫酸酸性水溶液を用いたレドックス型電池の場合、放電時には、Ｖ^２＋を含む電解液が負極側の液流路４ａに供給され、正極側の流路４ｂにはＶ^５＋（実際には酸素を含むイオン）を含む電解液が供給される。負極側の流路４ａでは、三次元電極５内でＶ^２＋が電子を放出しＶ^３＋に酸化される。放出された電子は外部回路を通って正極側の三次元電極内でＶ^５＋をＶ^４＋（実際には酸素を含むイオン）に還元する。この酸化還元反応に伴って負極電解液中のＳＯ_４ ^２−が不足し、正極電解液ではＳＯ_４ ^２−が過剰になるため、イオン交換膜３を通ってＳＯ_４ ^２−が正極側から負極側に移動し電荷バランスが保たれる。あるいは、Ｈ^＋がイオン交換膜を通って負極側から正極側へ移動することによっても電荷バランスを保つことができる。充電時には放電と逆の反応が進行する。 In the case of a redox type battery in which vanadium oxysulfate is used as the positive electrode electrolyte and vanadium sulfate is used as the negative electrode electrolytic solution, the electrolytic solution containing V ²⁺ is supplied to the liquid flow path 4a on the negative electrode side during discharge, and the positive electrode is positive. An electrolytic solution containing V ⁵⁺ (actually an ion containing oxygen) is supplied to the side flow path 4b. In the flow path 4a on the negative electrode side, V ²⁺ emits electrons in the three-dimensional electrode 5 and is oxidized to V ³⁺ . The emitted electrons reduce V ⁵⁺ to V ⁴⁺ (actually oxygen-containing ions) in the three-dimensional electrode on the positive electrode side through an external circuit. The redox reaction SO ₄ ^2-of the negative electrode electrolytic solution is insufficient with the, for SO ₄ ^2-becomes excessive in the positive electrolyte, negative electrode SO ₄ ^2-is from the positive electrode side through the ion-exchange membrane 3 It moves to the side and the charge balance is maintained. Alternatively, the charge balance can be maintained by moving H ⁺ from the negative electrode side to the positive electrode side through the ion exchange membrane. When charging, the reaction opposite to discharging proceeds.

レドックス電池用電極材には、特に以下に示す性能が要求される。 The electrode materials for redox batteries are particularly required to have the following performances.

１）目的とする反応以外の副反応を起こさないこと（反応選択性が高いこと）、具体的には電流効率（η_I）が高いこと。
２）電極反応活性が高いこと、具体的にはセル抵抗（Ｒ）が小さいこと。すなわち電圧効率（η_V）が高いこと。
３）上記１）、２）に関連する電池エネルギー効率（η_E）が高いこと。
η_E＝η_I×η_V
４）繰返し使用に対する劣化が小さいこと（高寿命）、具体的には電池エネルギー効率（η_E）の低下量が小さいこと。 1) Do not cause side reactions other than the desired reaction (high reaction selectivity), specifically, high current efficiency (η _I ).
2) The electrode reaction activity is high, specifically, the cell resistance (R) is small. That is, the voltage efficiency (η _V ) is high.
3) High battery energy efficiency (η _E ) related to 1) and 2) above.
η _E = η _I × η _V
4) Small deterioration due to repeated use (long life), specifically, small decrease in battery energy efficiency (η _E ).

そして、セル抵抗（Ｒ）に関しては、炭素質繊維集合体等の電極材と集電板との接触抵抗、及び電極材を構成する炭素質繊維間の接触抵抗が寄与する割合が大きく、これらの接触抵抗やその経時変化が、電池エネルギー効率やその経時変化に及ぼす影響は大きい。 As for the cell resistance (R), the contact resistance between the electrode material such as the carbonaceous fiber aggregate and the current collector plate and the contact resistance between the carbonaceous fibers constituting the electrode material contribute to a large proportion. The contact resistance and its change with time have a great influence on the battery energy efficiency and its change with time.

例えば特許文献１には、電池のトータルエネルギー効率を高め得るＦｅ−Ｃｒ電池の電極材として、結晶性の高い特定の擬黒鉛微結晶構造を有する炭素質材料が開示されている。具体的には、Ｘ線広角解析より求めた＜００２＞面間隔が、平均３．７０Å以下であり、またｃ軸方向の結晶子の大きさが平均９．０Å以上の擬黒鉛微結晶を有し、かつ全酸性官能基量が少なくとも０．０１ｍｅｑ／ｇである炭素質材料をレドックス電池の電極材として用いることが提案されている。 For example, Patent Document 1 discloses a carbonaceous material having a specific pseudographite microcrystal structure with high crystallinity as an electrode material of an Fe—Cr battery capable of increasing the total energy efficiency of the battery. Specifically, there are pseudographite microcrystals in which the <002> plane spacing obtained by X-ray wide-angle analysis is 3.70Å or less on average, and the crystallite size in the c-axis direction is 9.0Å or more on average. However, it has been proposed to use a carbonaceous material having a total acidic functional group amount of at least 0.01 meq / g as an electrode material for a redox battery.

また、特許文献２には、電池のエネルギー効率を高め、かつ充放電サイクル寿命を改善する鉄−クロム系レドックス電池等の電界層用電極として、ポリアクリロニトリル系繊維を原料とする炭素質繊維で、Ｘ線広角解析より求めた＜００２＞面間隔が３．５０〜３．６０Åの擬黒鉛結晶構造を有し、炭素質材料表面の結合酸素原子数が炭素原子数の１０〜２５％となるような炭素質材をレドックス電池の電極材として用いることが提案されている。 Further, Patent Document 2 describes a carbonaceous fiber made of polyacrylonitrile fiber as a raw material as an electrode for an electric field layer of an iron-chromium redox battery or the like that enhances the energy efficiency of the battery and improves the charge / discharge cycle life. It has a pseudographite crystal structure with a <002> plane spacing of 3.50 to 3.60Å determined by X-ray wide-angle analysis, and the number of bonded oxygen atoms on the surface of the carbonaceous material is 10 to 25% of the number of carbon atoms. It has been proposed to use a carbonaceous material as an electrode material for a redox battery.

特開昭６０−２３２６６９号公報Japanese Unexamined Patent Publication No. 60-232669 特開平５−２３４６１２号公報Japanese Unexamined Patent Publication No. 5-234612

しかしながら、特許文献１や２の技術では、炭素質材料表面と電解液との間に有効な濡れ性を発現させるために、全酸性官能基量が０．０１ｍｅｑ／ｇ以上か、あるいは炭素質材料表面の結合酸素原子数が全炭素原子数の１０％以上必要である。よって、炭素質材料表面の官能基が多すぎて、単繊維間の接触抵抗が高くなり、その結果、セル抵抗が高くなり、高い電池エネルギー効率を得られないことが判明した。 However, in the techniques of Patent Documents 1 and 2, the total amount of acidic functional groups is 0.01 meq / g or more, or the carbonaceous material is used in order to develop effective wettability between the surface of the carbonaceous material and the electrolytic solution. The number of bonded oxygen atoms on the surface must be 10% or more of the total number of carbon atoms. Therefore, it has been found that there are too many functional groups on the surface of the carbonaceous material and the contact resistance between the single fibers becomes high, and as a result, the cell resistance becomes high and high battery energy efficiency cannot be obtained.

そこで、本発明の目的は、かかる事情に鑑み、電池エネルギー効率を高めることができ、かつ繰返し使用しても劣化が小さい電極材を提供することにある。 Therefore, an object of the present invention is to provide an electrode material which can improve battery energy efficiency and has little deterioration even after repeated use in view of such circumstances.

上記課題を解決し得た本発明に係る電極材の構成は以下の通りである。
１．炭素質繊維からなるレドックス電池用正極電極材において、電極材表面の結合酸素原子数が電極材表面の全炭素原子数の０．２〜０．６％であり、かつ、窒素吸着量から求められるＢＥＴ比表面積が０．５ｍ^２／ｇ以上である電極材。
２．前記炭素質繊維に結着材により結着された活性粒子を含み、前記活性粒子及び前記結着材が電極材総量の２０％未満である、１に記載の電極材。
３．１または２に記載の電極材を備えたレドックス電池。
４．１または２に記載の電極材を備えたバナジウム系レドックス電池。 The configuration of the electrode material according to the present invention that has solved the above problems is as follows.
1. 1. In a positive electrode material for a redox battery made of carbonaceous fiber, the number of bound oxygen atoms on the surface of the electrode material is 0.2 to 0.6% of the total number of carbon atoms on the surface of the electrode material, and it is obtained from the amount of nitrogen adsorbed. An electrode material having a BET specific surface area of 0.5 m ² / g or more.
2. 2. The electrode material according to 1, wherein the electrode material contains active particles bound to the carbonaceous fiber by a binder, and the active particles and the binder are less than 20% of the total amount of the electrode material.
A redox battery comprising the electrode material according to 3.1 or 2.
A vanadium-based redox battery comprising the electrode material according to 4.1 or 2.

本発明の電極材は、上記構成により、電池のエネルギー効率を高めることができ、かつ繰返し使用しても劣化が小さい。 With the above configuration, the electrode material of the present invention can improve the energy efficiency of the battery and has little deterioration even after repeated use.

本発明の電極材は、レドックス電池、特に、バナジウム系レドックス電池の正極に用いられることが好ましい。バナジウム系のレドックス電池では、鉄−クロム系電解液に比べ活物質と電極材表面の反応速度が速く、電極材の接触抵抗は電極材との反応にともなう抵抗（反応抵抗）に比べて相対的に高くなる傾向にある。したがって電極材を構成する繊維間の接触抵抗が特に問題となりやすいので、上記作用効果を有する本発明の炭素電極材が特に有用なものとなる。 The electrode material of the present invention is preferably used for the positive electrode of a redox battery, particularly a vanadium-based redox battery. In vanadium-based redox batteries, the reaction rate between the active material and the surface of the electrode material is faster than that of the iron-chromium-based electrolyte, and the contact resistance of the electrode material is relative to the resistance (reaction resistance) associated with the reaction with the electrode material. Tends to be higher. Therefore, the contact resistance between the fibers constituting the electrode material tends to be a problem, and the carbon electrode material of the present invention having the above-mentioned action and effect is particularly useful.

図１はレドックス電池の概略図である。FIG. 1 is a schematic view of a redox battery. 図２は本発明に好適に用いられる三次元電極を有する液流通型電解槽の分解斜視図である。FIG. 2 is an exploded perspective view of a liquid flow type electrolytic cell having a three-dimensional electrode preferably used in the present invention.

本発明の電極材は炭素質繊維から、または炭素質繊維とこれに結着材により結着された活性粒子からなる。炭素質繊維は、取扱いや加工性、製造性等の点から不織布としての形状（炭素質繊維不織布）が好ましく用いられるが、別の形状でもよい。上記不織布は、焼成（炭化）前の不融化あるいは耐炎化された短繊維を開繊し、カードにかけ、幾層かに重ねられたレイヤーからなるウェブをまず作成し、さらにニードルパンチ加工機にかけることで、好適に作製される。 The electrode material of the present invention consists of carbonaceous fibers or active particles bonded to the carbonaceous fibers by a binder. The carbonaceous fiber preferably has a shape as a non-woven fabric (carbonaceous fiber non-woven fabric) from the viewpoint of handling, processability, manufacturability, etc., but may have a different shape. The non-woven fabric is made by opening infusible or flame-resistant short fibers before firing (carbonization), applying them to a curd, first creating a web consisting of several layers, and then applying it to a needle punching machine. Therefore, it is suitably produced.

本発明の電極材に用いられる炭素質繊維不織布の目付量は、隔膜と集電板に挟まれた充填状態の厚みを２〜３ｍｍで使用する場合、１００〜１０００ｇ／ｍ^２が好ましく、特に１００〜６００ｇ／ｍ^２が望ましい。また片面に凹溝加工が施されたものが通液性から好んで用いられる。その場合の溝幅、溝深さは少なくとも０．３ｍｍ、特に０．５ｍｍ以上が望ましい。該炭素質繊維不織布の厚みは、上記充填状態の厚みより少なくとも大きいこと、好ましくは充填状態の厚みの１．５倍程度である。しかしながら、厚みが厚すぎると圧縮応力で膜を突き破ってしまうので、圧縮応力を１ｋｇｆ／ｃｍ^２以下に設計するのが好ましい。 The basis weight of the carbonaceous fiber non-woven fabric used for the electrode material of the present invention is preferably 100 to 1000 g / m ² when the thickness of the packed state sandwiched between the diaphragm and the current collector plate is 2 to 3 mm, and particularly 100. ~ 600 g / m ² is desirable. In addition, one with a concave groove on one side is preferably used because of its liquid permeability. In that case, the groove width and groove depth are preferably at least 0.3 mm, particularly 0.5 mm or more. The thickness of the carbonaceous fiber nonwoven fabric is at least larger than the thickness in the filled state, preferably about 1.5 times the thickness in the filled state. However, if the thickness is too thick, the film will be pierced by the compressive stress, so it is preferable to design the compressive stress to be 1 kgf / cm ² or less.

なお、上記の炭素質繊維の平均繊維径は５〜２０μｍ程度が好ましく、平均長さは３０〜１００ｍｍ程度が好ましい。 The average fiber diameter of the carbonaceous fibers is preferably about 5 to 20 μm, and the average length is preferably about 30 to 100 mm.

炭素質繊維不織布は、電池の中に圧接されて組み込まれ、その薄い隙間を粘度の高い電解液が流れるため、脱落を防止して形態保持するためには引張強度を０．１ｋｇ／ｃｍ以上にすることが望ましい。また集電板との接触抵抗を良くするために、隔膜、集電板に挟まれた充填層の密度を０．０５ｇ／ｃｍ^３以上に、電極面に対する反発力を０．１ｋｇｆ／ｃｍ^２以上にすることが好ましい。 The carbonaceous fiber non-woven fabric is pressure-welded and incorporated into the battery, and the highly viscous electrolytic solution flows through the thin gaps. Therefore, in order to prevent the carbonaceous fiber non-woven fabric from falling off and maintain its shape, the tensile strength should be 0.1 kg / cm or more. It is desirable to do. In addition, in order to improve the contact resistance with the current collector plate, the density of the packing layer sandwiched between the diaphragm and the current collector plate should be 0.05 g / cm ³ or more, and the repulsive force against the electrode surface should be 0.1 kgf / cm ² or more. Is preferable.

このような炭素質繊維不織布は、不織布構造が特定の空隙と圧縮特性を持つことが前提となる。特定の空隙と圧縮特性は前段階のニードルパンチの条件を制御することによって得られる。すなわち、ニードルパンチの密度を１５０〜３００本／ｃｍ^２、好ましくは、２００〜３００本／ｃｍ^２にし、ニードルパンチの針を不融化繊維あるいは耐炎化繊維が交互に絡みやすく、繊維間の接触、特に交差する繊維間の接触が多くなるもの、例えばＳＢ＃４０（Ｆｏｓｔｅｒ Ｎｅｅｄｌｅ社）にすることが好ましい。 Such a carbonaceous fiber nonwoven fabric is premised on the nonwoven fabric structure having specific voids and compressive properties. Specific voids and compression properties are obtained by controlling the conditions of the needle punch in the previous step. That is, the density of the needle punch is set to 150 to 300 / cm ² , preferably 200 to 300 / cm ² , and the needles of the needle punch are easily entangled with infusible fibers or flame resistant fibers alternately, so that the fibers come into contact with each other. In particular, it is preferable to use SB # 40 (Foster Needle), for example, which increases the contact between intersecting fibers.

本発明の電極材は、上記で説明した炭素質繊維に活性粒子が結着されていてもよい。 In the electrode material of the present invention, active particles may be bound to the carbonaceous fibers described above.

活性粒子は、電極材において、反応活性を得ると共に、導電性を高めるためのものである。従来公知のものを用いることができる。 The active particles are for obtaining reaction activity and increasing conductivity in the electrode material. Conventionally known ones can be used.

結着材は、炭素質繊維と活性粒子とを結着させるバインダーの役割を担うものである。ここでは、電極材として製造された後、つまり、炭化後の結着材を指す。
本発明に用いられる結着材の種類は、炭素質繊維と活性粒子とを結着し得るものであれば良く、具体的には、本発明の電極材作製時における炭化時に結着性を示すものであれば特に限定されない。このような例として、例えば、コールタールピッチ、石炭系ピッチ等のピッチ類；フェノール樹脂、ベンゾオキサジン樹脂、エポキシド樹脂、フラン樹脂、ビニルエステル樹脂、メラニン−ホルムアルデヒド樹脂、尿素−ホルムアルデヒド樹脂、レソルシノール−ホルムアルデヒド樹脂、シアネートエステル樹脂、ビスマレイミド樹脂、ポリウレタン樹脂、ポリアクリロニトリル等の樹脂；フルフリルアルコール；アクリロニトリル−ブタジエンゴム等のゴムなどが挙げられる。これらは市販品を用いても良い。 The binder serves as a binder that binds the carbonaceous fibers and the active particles. Here, it refers to a binder material after being manufactured as an electrode material, that is, after carbonization.
The type of binder used in the present invention may be any as long as it can bind carbonaceous fibers and active particles, and specifically, it exhibits binding properties during carbonization during the production of the electrode material of the present invention. It is not particularly limited as long as it is a thing. Examples of such are pitches such as coal tar pitch and coal pitch; phenol resin, benzoxazine resin, epoxide resin, furan resin, vinyl ester resin, melanin-formaldehyde resin, urea-formaldehyde resin, resorcinol-formaldehyde. Examples thereof include resins such as resins, cyanate ester resins, bismaleimide resins, polyurethane resins and polyacrylonitrile; furfuryl alcohols; rubbers such as acrylonitrile-butadiene rubber. Commercially available products may be used for these.

本発明の電極材が、炭素質繊維に活性粒子が結着材により結着されている場合、活性粒子及び前記結着材が電極材総量の２０％未満が好ましい。２０％未満であることにより、電池エネルギー効率を高めて低抵抗化に寄与でき、また、電極材の繰返しの使用に対する劣化を抑えられ、長寿命化に寄与できる。 When the electrode material of the present invention has active particles bound to carbonaceous fibers by a binder, the active particles and the binder are preferably less than 20% of the total amount of the electrode material. When it is less than 20%, the energy efficiency of the battery can be increased and the resistance can be reduced, the deterioration of the electrode material due to repeated use can be suppressed, and the life can be extended.

（電極材の特性）
本発明の電極材は、炭素電極材表面の結合酸素原子数が炭素電極材表面の全炭素原子数の０．２％〜０．６％である。以下、上記全炭素原子数に対する結合酸素原子数の比をＯ／Ｃで略記する場合がある。Ｏ／Ｃは、Ｘ線光電子分光法（ＸＰＳ）や蛍光Ｘ線分析法などの表面分析にて測定できる。Ｏ／Ｃが０．２％〜０．６％の電極材を用いることにより、高耐久性が得られ、低抵抗も維持できる。これに対し、Ｏ／Ｃが大きい電極材を用いると、耐久性を高められず、寿命が低下することがある。 (Characteristics of electrode material)
In the electrode material of the present invention, the number of bonded oxygen atoms on the surface of the carbon electrode material is 0.2% to 0.6% of the total number of carbon atoms on the surface of the carbon electrode material. Hereinafter, the ratio of the number of bound oxygen atoms to the total number of carbon atoms may be abbreviated as O / C. O / C can be measured by surface analysis such as X-ray photoelectron spectroscopy (XPS) and fluorescent X-ray analysis. By using an electrode material having an O / C of 0.2% to 0.6%, high durability can be obtained and low resistance can be maintained. On the other hand, if an electrode material having a large O / C is used, the durability cannot be improved and the life may be shortened.

更に本発明の電極材は、窒素吸着量から求められるＢＥＴ比表面積が０．５ｍ²／ｇ以上を満足する。ＢＥＴ比表面積が０．５ｍ²／ｇ未満になると、所望とする低抵抗が得られなくなる。なおＢＥＴ比表面積の上限は、上記観点からは特に限定されないが、耐酸化性などを考慮すると、おおむね、１５０ｍ²／ｇ以下であることが好ましい。 Further, the electrode material of the present invention satisfies a BET specific surface area of 0.5 m ² / g or more, which is determined from the amount of nitrogen adsorbed. If the BET specific surface area is less than 0.5 m ² / g, the desired low resistance cannot be obtained. The upper limit of the BET specific surface area is not particularly limited from the above viewpoint, but it is preferably about 150 m ² / g or less in consideration of oxidation resistance and the like.

本発明の電極材の目付量は、集電板１とイオン交換膜３に挟まれたスペーサ２の厚み（以下、「スペーサ厚み」と言う）を０．３〜３ｍｍで使用する場合、５０〜５００ｇ／ｍ²が好ましく、１００〜４００ｇ／ｍ²がより好ましい。目付を上記範囲内に制御することで、通液性を確保しつつ、イオン交換膜３の破損を防止することができる。特に、近年では低抵抗化の観点から、イオン交換膜３の厚みは薄くなる傾向にあり、イオン交換膜３へのダメージを軽減する処置及び使用方法は極めて重要である。また上記の観点から、本発明の電極材として、片面に平坦加工が施された不織布や紙を基材として使用することもより好ましい。平坦加工方法は、公知の任意の方法を適用でき、例えばスラリーを炭素質繊維の片面に塗布、乾燥する方法；ＰＥＴなどの平滑なフィルム上で含侵、乾燥するなどの手法が挙げられる。 The basis weight of the electrode material of the present invention is 50 to 50 when the thickness of the spacer 2 sandwiched between the current collector plate 1 and the ion exchange membrane 3 (hereinafter referred to as "spacer thickness") is 0.3 to 3 mm. preferably ^{500g / m 2, 100~400g / m} 2 is more preferable. By controlling the basis weight within the above range, it is possible to prevent damage to the ion exchange membrane 3 while ensuring liquid permeability. In particular, in recent years, from the viewpoint of reducing resistance, the thickness of the ion exchange membrane 3 tends to be thin, and treatment and usage methods for reducing damage to the ion exchange membrane 3 are extremely important. From the above viewpoint, it is more preferable to use a non-woven fabric or paper having a flat surface processed on one side as a base material as the electrode material of the present invention. Any known method can be applied to the flattening method, and examples thereof include a method of applying a slurry to one side of a carbonaceous fiber and drying it; a method of impregnating and drying it on a smooth film such as PET.

本発明の電極材の厚みは、少なくともスペーサ厚みより大きいことが好ましい。例えば炭素質繊維に不織布等のように密度の低いものを用い、これに本発明の電極材に用いられる黒鉛粒子や結着性の炭素質材料を坦持した場合、スペーサ厚みの１．５〜６．０倍が好ましい。しかしながら、厚みが厚すぎるとシート状物の圧縮応力によりイオン交換膜３を突き破ってしまうことがあるので、本発明の電極材の圧縮応力が９．８Ｎ／ｃｍ²以下のものを使用するのが好ましい。本発明の電極材の目付量・厚みに応じて、圧縮応力などを調整するために、本発明の電極材を２層や３層など積層して用いることも可能である。或は、別の形態の電極材との組み合わせも可能である。 The thickness of the electrode material of the present invention is preferably at least larger than the spacer thickness. For example, when a carbonaceous fiber having a low density such as a non-woven fabric is used and graphite particles or a binding carbonaceous material used for the electrode material of the present invention are carried therein, the spacer thickness is 1.5 to 1.5 to. 6.0 times is preferable. However, if the thickness is too thick, the ion exchange membrane 3 may be pierced by the compressive stress of the sheet-like material. Therefore, it is recommended to use the electrode material of the present invention having a compressive stress of 9.8 N / cm ² or less. preferable. In order to adjust the compressive stress and the like according to the basis weight and thickness of the electrode material of the present invention, it is also possible to use the electrode material of the present invention in a laminated manner such as two layers or three layers. Alternatively, it can be combined with another form of electrode material.

（電極材の製造方法）
次に、炭素質繊維からなる電極材を製造する方法を説明する。レドックス電池に好適な内部構造、表面特性を有する炭素質繊維は、緊張下２００〜３００℃の初期空気酸化を経たポリアクリロニトリル、等方性ピッチ、メソフェーズピッチ、セルロースなど、あるいはフェノール、ポリパラフェニレンベンゾビスオキサゾール（ＰＢＯ）などを原料にして、不活性雰囲気下１０００〜３０００℃で焼成（炭化）した擬黒鉛結晶構造を有する炭素材料を、乾式酸化処理することによって得られる。炭素質繊維に活性粒子を結着させる場合には、炭化前に活性粒子を結着材で添着させればよい。 (Manufacturing method of electrode material)
Next, a method for producing an electrode material made of carbonaceous fiber will be described. Carbonized fibers having an internal structure and surface properties suitable for redox batteries include polyacrylonitrile, isotropic pitch, mesophase pitch, cellulose, etc., which have undergone initial air oxidation at 200 to 300 ° C. under tension, or phenol, polyparaphenylene benzo. It is obtained by dry oxidation treatment of a carbon material having a pseudo-graphite crystal structure that is fired (carbonized) at 1000 to 3000 ° C. in an inert atmosphere using bisoxazole (PBO) or the like as a raw material. When the active particles are bound to the carbonaceous fiber, the active particles may be bound with a binder before carbonization.

上記において、炭化温度は原料により結晶性が異なるので温度には限定されず、原料に応じて最適化するのが好ましい。乾式酸化については公知の方法でよいが、材料の機械的強度を考慮すると酸化後の重量収率にして９０〜９６％に調整することが望ましい。しかし処理法はこれに限定されるものではなく、例えばこの乾式酸化処理の代わりに電解酸化をおこなっても同様な効果が得られる。さらに、本発明ではその後に不活性雰囲気下９００〜２０００℃、好ましくは９００〜１５００℃で焼成（炭化）することで含酸性官能基を一部除去し、濡れ性を維持しつつ、接触抵抗が低い表面を得ることができる。 In the above, the carbonization temperature is not limited to the temperature because the crystallinity differs depending on the raw material, and it is preferable to optimize the carbonization temperature according to the raw material. A known method may be used for dry oxidation, but it is desirable to adjust the weight yield after oxidation to 90 to 96% in consideration of the mechanical strength of the material. However, the treatment method is not limited to this, and the same effect can be obtained even if electrolytic oxidation is performed instead of this dry oxidation treatment, for example. Further, in the present invention, the acid-containing functional groups are partially removed by firing (carbonizing) at 900 to 2000 ° C., preferably 900 to 1500 ° C. in an inert atmosphere thereafter, and the contact resistance is increased while maintaining the wettability. A low surface can be obtained.

（電池）
本発明の電極材は、レドックス電池の正極に用いられる。当該レドックス電池は、前述のように、例えば間隙を介した状態で対向して配設された一対の集電板間に隔膜が配設され、該集電板と隔膜との間に少なくとも一方に電極材が圧接挟持され、電極材は活物質を含んだ水溶液からなる電解液を含んだ構造を有する電解槽を備える。 (battery)
The electrode material of the present invention is used for the positive electrode of a redox battery. In the redox battery, as described above, for example, a diaphragm is arranged between a pair of current collector plates arranged so as to face each other with a gap between them, and at least one of the current collector plates and the diaphragm is provided. The electrode material is pressure-welded and sandwiched, and the electrode material includes an electrolytic cell having a structure containing an electrolytic solution composed of an aqueous solution containing an active material.

水溶液系電解液としては、前述の如きバナジウム系電解液の他、鉄−クロム系、チタン−マンガン−クロム系、クロム−クロム系、鉄−チタン系などが挙げられるが、バナジウム系電解液が好ましい。本発明の炭素電極材集合体は、特に、粘度が２５℃にて０．００５Ｐａ・ｓ以上であるバナジウム系電解液、あるいは１．５ｍｏｌ／ｌ以上のバナジウムイオンを含むバナジウム系電解液を使用するレドックス電池に用いるのが有用である。 Examples of the aqueous electrolytic solution include iron-chromium-based, titanium-manganese-chromium-based, chromium-chromium-based, iron-titanium-based, and the like, in addition to the vanadium-based electrolytic solution as described above, but vanadium-based electrolytic solution is preferable. .. The carbon electrode material aggregate of the present invention uses, in particular, a vanadium-based electrolytic solution having a viscosity of 0.005 Pa · s or more at 25 ° C. or a vanadium-based electrolytic solution containing vanadium ions of 1.5 mol / l or more. It is useful to use for redox batteries.

〔実施例〕
以下に実施例及び比較例を挙げて、本発明をより詳細に説明する。なお、本発明は、以下の実施例に限定されるものではない。以下において、％は特に断りのない限り「質量％」を意味する。 〔Example〕
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples. In the following,% means "mass%" unless otherwise specified.

実施例及び比較例では、以下の項目を測定した。測定方法の詳細は以下の通りである。 In the examples and comparative examples, the following items were measured. The details of the measurement method are as follows.

１．電極材表面の全炭素原子数に対する電極材表面の結合酸素原子数Ｏ／Ｃ
ＥＳＣＡまたはＸＰＳと略称されているＸ線光電子分光法の測定には、アルバック・ファイ５８０１ＭＣの装置を用いた。
まず、試料をサンプルホルダー上にＭｏ板で固定し、予備排気室にて十分に排気した後、測定室のチャンバーに投入した。線源にはモノクロ化ＡｌＫα線を用い、出力は１４ｋＶ、１２ｍＡ、装置内真空度は１０-8ｔｏｒｒとした。
全元素スキャンを行って表面元素の構成を調べ、検出された元素および予想される元素についてナロースキャンを実施し、存在比率を評価した。
全表面炭素原子数に対する表面結合酸素原子数の比を百分率（％）で算出し、Ｏ／Ｃを算出した。 1. 1. Number of bound oxygen atoms on the surface of the electrode material O / C with respect to the total number of carbon atoms on the surface of the electrode material
The ULVAC-PHI 5801MC device was used for the measurement of X-ray photoelectron spectroscopy, which is abbreviated as ESCA or XPS.
First, the sample was fixed on the sample holder with an Mo plate, sufficiently exhausted in the preliminary exhaust chamber, and then charged into the chamber of the measurement chamber. A monochrome AlKα ray was used as the radiation source, the output was 14 kV, 12 mA, and the degree of vacuum inside the apparatus was 10-8 torr.
All element scans were performed to examine the composition of surface elements, and narrow scans were performed on the detected and expected elements to evaluate the abundance ratio.
The ratio of the number of surface-bonded oxygen atoms to the total number of surface carbon atoms was calculated as a percentage (%), and O / C was calculated.

２．ＢＥＴ比表面積
試料を約１００ｍｇ採取し、１２０℃で１２時間真空乾燥して９０ｇを秤量し、比表面積・細孔分布測定装置Ｇｅｍｉｎｉ２３７５（Ｍｉｃｒｏｍｅｒｉｔｉｃｓ社製）を使用してＢＥＴ比表面積を測定した。具体的には液体窒素の沸点（−１９５．８℃）における窒素ガスの吸着量を相対圧が０．０２〜０．９５の範囲で測定し、試料の吸着等温線を作成した。相対圧０．０２〜０．１５の範囲の結果に基づき、ＢＥＴ法により重量あたりのＢＥＴ比表面積（単位：ｍ²／ｇ）を求めた。 2. 2. About 100 mg of a BET specific surface area sample was collected, vacuum dried at 120 ° C. for 12 hours, weighed 90 g, and the BET specific surface area was measured using a specific surface area / pore distribution measuring device Gemini2375 (manufactured by Micromeritics). Specifically, the amount of nitrogen gas adsorbed at the boiling point (-195.8 ° C.) of liquid nitrogen was measured in the range of relative pressure of 0.02 to 0.95, and an adsorption isotherm of the sample was prepared. Based on the results in the range of relative pressure 0.02 to 0.15, the BET specific surface area per weight (unit: m ² / g) was determined by the BET method.

３．電極特性
後記する方法で得られた各電極材を、上下方向（通液方向）に１０ｃｍ、幅方向に１ｃｍの電極面積１０ｃｍ^２に切り出し、図１のセルを組み立てた。このセルを正極に用いた。負極には、後述の比較例１の電極材を上記と同様に切り出してセルに組み立てたものを用いた。この正極および負極を有するレドック電池を用いて、定電流密度で充放電を繰り返し、電極特性の測定を行った。正極電解液には２ｍｏｌ／ｌのオキシ硫酸バナジウムの３ｍｏｌ／ｌ硫酸水溶液を用い、負極電解液には２ｍｏｌ／ｌの硫酸バナジウムの３ｍｏｌ／ｌ硫酸水溶液を用いた。電解液量はセル、配管に対して大過剰とした。液流量は毎分６．２ｍｌとし、３０℃で測定を行った。 3. 3. Electrode characteristics Each electrode material obtained by the method described later was cut into an electrode area of 10 cm ² having an electrode area of 10 cm in the vertical direction (liquid flow direction) and 1 cm in the width direction, and the cell of FIG. 1 was assembled. This cell was used as the positive electrode. As the negative electrode, the electrode material of Comparative Example 1 described later was cut out in the same manner as described above and assembled into a cell. Using this reddock battery having a positive electrode and a negative electrode, charging and discharging were repeated at a constant current density, and electrode characteristics were measured. A 3 mol / l sulfuric acid aqueous solution of 2 mol / l vanadium oxysulfate was used as the positive electrode electrolytic solution, and a 3 mol / l sulfuric acid aqueous solution of 2 mol / l vanadium sulfate was used as the negative electrode electrolytic solution. The amount of electrolyte was too large for the cell and piping. The liquid flow rate was 6.2 ml per minute, and the measurement was performed at 30 ° C.

（ａ）電流効率：η_Ｉ
充電に始まり、放電で終わる１サイクルのテストにおいて、電流密度を電極幾何面積当たり４０ｍＡ／ｃｍ^２（４００ｍＡ）として、１．７Ｖまでの充電に要した電気量をＱ_１クーロン、１．０Ｖまでの定電流放電、およびこれに続く１．２Ｖでの定電圧放電で取りだした電気量をそれぞれＱ_２、Ｑ_３クーロンとし、数式１で電流効率η_Ｉ を求める。 (A) Current efficiency: η _I
Beginning in charge, the 1-cycle test of ending the discharge, the current density of the electrode geometry area per 40mA ^/ cm 2 (400mA), the amount of electricity required to charge up to 1.7V _{Q 1} coulombs, up to 1.0V Let Q ₂ and Q ₃ Coulomb be the amounts of electricity taken out by the constant current discharge and the subsequent constant voltage discharge at 1.2 V, and calculate the current efficiency η _I by Equation 1.

（ｂ）セル抵抗：Ｒ
負極液中のＶ^３＋をＶ^２＋に完全に還元するのに必要な理論電気量Ｑ_ｔｈに対して、放電により取りだした電気量の比を充電率とし、数式２で充電率を求める。 (B) Cell resistance: R
The V ³⁺ in negative electrode solution on the theoretical quantity of electricity Q _th required to completely reduce the V ^2+, the electric quantity ratios began taking by discharge and charging rate, determine the charging rate in Equation 2.

充電率が５０％のときの電気量に対応する充電電圧Ｖ_Ｃ５０、放電電圧Ｖ_Ｄ５０を電気量−電圧曲線からそれぞれ求め、数式３より電極幾何面積に対するセル抵抗Ｒ（Ω・ｃｍ^２ ）を求める。 The charge voltage _VC50 and the discharge voltage V _D50 corresponding to the amount of electricity when the charge rate is 50% are obtained from the amount of electricity-voltage curve, respectively, and the cell resistance R (Ω · cm ² ) with respect to the geometric area of the electrode is obtained from Equation 3. ..

（ｃ）電圧効率：η_Ｖ
上記の方法で求めたセル抵抗Ｒを用いて数式４の簡便法により電圧効率η_Ｖを求める。 (C) Voltage efficiency: η _V
Using the cell resistance R obtained by the above method, the voltage efficiency η _V is obtained by the simple method of Equation 4.

ここで、Ｅは充電率５０％のときのセル開回路電圧１．４３２Ｖ（実測値）、Ｉは定電流充放電における電流値０．４Ａである。 Here, E is the cell open circuit voltage 1.432V (measured value) when the charging rate is 50%, and I is the current value 0.4A in constant current charging / discharging.

（ｄ）エネルギー効率：η_Ｅ
前述の電流効率η_Ｉと電圧効率η_Ｖを用いて、数式５によりエネルギー効率η_Ｅを求める。 (D) Energy efficiency: η _E
Using the above-mentioned current efficiency η _I and voltage efficiency η _V , the energy efficiency η _E is obtained by Equation 5.

（ｅ）充放電サイクルの経時変化
（ａ）、（ｂ）、（ｃ）、（ｄ）の測定後、続いて同セルを用い、４０ｍＡ／ｃｍ^２の定電流密度でセル電圧１．０〜１．７Ｖ間で充放電を繰り返し実施する。規定サイクル経過後、再び（ａ）、（ｂ）、（ｃ）、（ｄ）の測定を行い、η_Ｅ及びその初期からの変化量Δη_Ｅを求める。 (E) Changes over time in the charge / discharge cycle After measuring (a), (b), (c), and (d), the cell is subsequently used, and the cell voltage is 1.0 to 1.0 at a constant current density of 40 mA / cm ^2. Charging and discharging are repeated between 1.7V. After the lapse of the specified cycle, the measurements (a), (b), (c), and (d) are performed again to obtain η _E and the amount of change Δη _E from the initial stage.

レドックス電池等の電解槽用電極の特性は、主に上記のような電流効率η_Ｉ、電圧効率η_Ｖ（セル抵抗Ｒ）およびエネルギー効率η_Ｅ（η_Ｉとη_Ｖとの積）とこれらの効率の充放電サイクル安定性（寿命）で表される。 The characteristics of the electrodes for electrolytic cells such as redox batteries are mainly the above-mentioned current efficiency η _I , voltage efficiency η _V (cell resistance R) and energy efficiency η _E (product of η _I and η _V ). It is expressed by the charge / discharge cycle stability (life) of efficiency.

（実施例１）
平均繊維径１６μｍのポリアクリロニトリル繊維を空気中２００〜３００℃で耐炎化した後、該耐炎化繊維の短繊維（長さ約８０ｍｍ）を用いてフェルト針ＳＢ＃４０（Ｆｏｓｔｅｒ Ｎｅｅｄｌｅ社）、パンチング密度２５０本／ｃｍ^２でフェルト化して目付量６００ｇ／ｍ^２、厚み５．０ｍｍの不織布を作成した。次に、窒素ガス中で１０℃／分の昇温速度で１５００℃まで昇温し、この温度で１時間保持し炭化を行って冷却し、空気中７００℃で重量収率９５％になるまで処理し、炭素質繊維不織布を得た。さらに、窒素ガス中で１０℃／分の昇温速度で１３００℃まで昇温し、この温度で１時間保持した。 (Example 1)
After making polyacrylonitrile fibers with an average fiber diameter of 16 μm flame-resistant in air at 200 to 300 ° C., felt needle SB # 40 (Foster Needle) and punching density using the short fibers (length of about 80 mm) of the flame-resistant fibers. A non-woven fabric having a grain size of 600 g / m ² and a thickness of 5.0 mm was prepared by felting at 250 lines / cm ² . Next, the temperature is raised to 1500 ° C. in nitrogen gas at a heating rate of 10 ° C./min, held at this temperature for 1 hour, carbonized and cooled, and the weight yield is 95% at 700 ° C. in air. The treatment gave a carbonized fiber non-woven fabric. Further, the temperature was raised to 1300 ° C. in nitrogen gas at a heating rate of 10 ° C./min, and the temperature was maintained at this temperature for 1 hour.

（実施例２）
平均繊維径１６μｍのポリアクリロニトリル繊維を空気中２００〜３００℃で耐炎化した後、該耐炎化繊維の短繊維（長さ約８０ｍｍ）を用いてフェルト針ＳＢ＃４０（Ｆｏｓｔｅｒ Ｎｅｅｄｌｅ社）、パンチング密度２５０本／ｃｍ^２でフェルト化して目付量６００ｇ／ｍ^２、厚み５．０ｍｍの不織布を作成した。次に、窒素ガス中で１０℃／分の昇温速度で１５００℃まで昇温し、この温度で１時間保持し炭化を行って冷却し、空気中７００℃で重量収率９５％になるまで処理し、炭素質繊維不織布を得た。さらに、窒素ガス中で１０℃／分の昇温速度で１１００℃まで昇温し、この温度で１時間保持した。 (Example 2)
After making polyacrylonitrile fibers with an average fiber diameter of 16 μm flame-resistant in air at 200 to 300 ° C., felt needle SB # 40 (Foster Needle) and punching density using the short fibers (length of about 80 mm) of the flame-resistant fibers. A non-woven fabric having a grain size of 600 g / m ² and a thickness of 5.0 mm was prepared by felting at 250 lines / cm ² . Next, the temperature is raised to 1500 ° C. in nitrogen gas at a heating rate of 10 ° C./min, held at this temperature for 1 hour, carbonized and cooled, and the weight yield is 95% at 700 ° C. in air. The treatment gave a carbonized fiber non-woven fabric. Further, the temperature was raised to 1100 ° C. in nitrogen gas at a heating rate of 10 ° C./min, and the temperature was maintained at this temperature for 1 hour.

（実施例３）
平均繊維径１６μｍのポリアクリロニトリル繊維を空気中２００〜３００℃で耐炎化した後、該耐炎化繊維の短繊維（長さ約８０ｍｍ）を用いてフェルト針ＳＢ＃４０（Ｆｏｓｔｅｒ Ｎｅｅｄｌｅ社）、パンチング密度２５０本／ｃｍ^２でフェルト化して目付量６００ｇ／ｍ^２、厚み５．０ｍｍの不織布を作成した。次に、窒素ガス中で１０℃／分の昇温速度で１５００℃まで昇温し、この温度で１時間保持し炭化を行って冷却し、空気中７００℃で重量収率９５％になるまで処理し、炭素質繊維不織布を得た。さらに、窒素ガス中で１０℃／分の昇温速度で９００℃まで昇温し、この温度で１時間保持した。 (Example 3)
After making polyacrylonitrile fibers with an average fiber diameter of 16 μm flame-resistant in air at 200 to 300 ° C., felt needle SB # 40 (Foster Needle) and punching density using the short fibers (length of about 80 mm) of the flame-resistant fibers. A non-woven fabric having a grain size of 600 g / m ² and a thickness of 5.0 mm was prepared by felting at 250 lines / cm ² . Next, the temperature is raised to 1500 ° C. in nitrogen gas at a heating rate of 10 ° C./min, held at this temperature for 1 hour, carbonized and cooled, and the weight yield is 95% at 700 ° C. in air. The treatment gave a carbonized fiber non-woven fabric. Further, the temperature was raised to 900 ° C. in nitrogen gas at a heating rate of 10 ° C./min, and the temperature was maintained at this temperature for 1 hour.

（実施例４）
実施例１で作製した不織布に対して、活性粒子として粒径５μｍ、ＢＥＴ比表面積１０ｍ^２／ｇの膨張黒鉛粒子を用い、結着材としてＪＦＥケミカル社製コールタールピッチＭＣＰ２５０のピッチ類を用い、これらを湿式で添着した。乾燥後の活性粒子は９ｇ／ｍ^２、結着材は２６ｇ／ｍ^２であった。炭化からの処理は実施例２と同様に行った。 (Example 4)
For the non-woven fabric produced in Example 1, expanded graphite particles having a particle size of 5 μm and a BET specific surface area of 10 m ² / g were used as active particles, and pitches of coal tar pitch MCP250 manufactured by JFE Chemical Co., Ltd. were used as binders. These were wet-coated. The amount of active particles after drying was 9 g / m ² , and the amount of binder was 26 g / m ² . The treatment from carbonization was carried out in the same manner as in Example 2.

（実施例５）
実施例１で作製した不織布に対して、活性粒子として粒径０．０４μｍ、ＢＥＴ比表面積１８００ｍ^２／ｇのカーボンブラック粒子を用い、結着材としてＪＦＥケミカル社製コールタールピッチＭＣＰ２５０のピッチ類を用い、これらを湿式で添着した。乾燥後の活性粒子は５ｇ／ｍ^２、結着材は３１ｇ／ｍ^２であった。炭化からの処理は実施例２と同様に行った。 (Example 5)
For the non-woven fabric produced in Example 1, carbon black particles having a particle size of 0.04 μm and a BET specific surface area of 1800 m ² / g were used as active particles, and pitches of coal tar pitch MCP250 manufactured by JFE Chemical Co., Ltd. were used as binders. These were used and adhered wet. The active particles after drying were 5 g / m ² , and the binder was 31 g / m ² . The treatment from carbonization was carried out in the same manner as in Example 2.

（実施例６）
実施例１で作製した不織布に対して、活性粒子として粒径０．０４μｍ、ＢＥＴ比表面積１８００ｍ^２／ｇのカーボンブラック粒子を用い、結着材としてＪＦＥケミカル社製コールタールピッチＭＣＰ２５０のピッチ類を用い、これらを湿式で添着した。乾燥後の活性粒子は１０ｇ／ｍ^２、結着材は６２ｇ／ｍ^２であった。炭化からの処理は実施例２と同様に行った。 (Example 6)
For the non-woven fabric produced in Example 1, carbon black particles having a particle size of 0.04 μm and a BET specific surface area of 1800 m ² / g were used as active particles, and pitches of coal tar pitch MCP250 manufactured by JFE Chemical Co., Ltd. were used as binders. These were used and adhered wet. Active particles after drying 10 g / ^{m 2,} binder was 62 g / ^{m 2.} The treatment from carbonization was carried out in the same manner as in Example 2.

（比較例１）
平均繊維径１６μｍのポリアクリロニトリル繊維を空気中２００〜３００℃で耐炎化した後、該耐炎化繊維の短繊維（長さ約８０ｍｍ）を用いてフェルト針ＳＢ＃４０（Ｆｏｓｔｅｒ Ｎｅｅｄｌｅ社）、パンチング密度２５０本／ｃｍ^２でフェルト化して目付量６００ｇ／ｍ^２、厚み５．０ｍｍの不織布を作成した。次に、窒素ガス中で１０℃／分の昇温速度で１５００℃まで昇温し、この温度で１時間保持し炭化を行って冷却し、空気中７００℃で重量収率９５％になるまで処理し、炭素質繊維不織布を得た。 (Comparative Example 1)
After making polyacrylonitrile fibers with an average fiber diameter of 16 μm flame-resistant in air at 200 to 300 ° C., felt needle SB # 40 (Foster Needle) and punching density using the short fibers (length of about 80 mm) of the flame-resistant fibers. A non-woven fabric having a grain size of 600 g / m ² and a thickness of 5.0 mm was prepared by felting at 250 lines / cm ² . Next, the temperature is raised to 1500 ° C. in nitrogen gas at a heating rate of 10 ° C./min, held at this temperature for 1 hour, carbonized and cooled, and the weight yield is 95% at 700 ° C. in air. The treatment gave a carbonized fiber non-woven fabric.

（比較例２）
平均繊維径１６μｍのポリアクリロニトリル繊維を空気中２００〜３００℃で耐炎化した後、該耐炎化繊維の短繊維（長さ約８０ｍｍ）を用いてフェルト針ＳＢ＃４０（Ｆｏｓｔｅｒ Ｎｅｅｄｌｅ社）、パンチング密度２５０本／ｃｍ^２でフェルト化して目付量６００ｇ／ｍ^２、厚み５．０ｍｍの不織布を作成した。次に、窒素ガス中で１０℃／分の昇温速度で１５００℃まで昇温し、この温度で１時間保持し炭化を行って冷却し、炭素質繊維不織布を得た。 (Comparative Example 2)
After making polyacrylonitrile fibers with an average fiber diameter of 16 μm flame-resistant in air at 200 to 300 ° C., felt needle SB # 40 (Foster Needle) and punching density using the short fibers (length of about 80 mm) of the flame-resistant fibers. A non-woven fabric having a grain size of 600 g / m ² and a thickness of 5.0 mm was prepared by felting at 250 lines / cm ² . Next, the temperature was raised to 1500 ° C. in nitrogen gas at a heating rate of 10 ° C./min, held at this temperature for 1 hour, carbonized and cooled to obtain a carbonaceous fiber non-woven fabric.

（比較例３）
平均繊維径１６μｍのポリアクリロニトリル繊維を空気中２００〜３００℃で耐炎化した後、該耐炎化繊維の短繊維（長さ約８０ｍｍ）を用いてフェルト針ＳＢ＃４０（Ｆｏｓｔｅｒ Ｎｅｅｄｌｅ社）、パンチング密度２５０本／ｃｍ^２でフェルト化して目付量６００ｇ／ｍ^２、厚み５．０ｍｍの不織布を作成した。次に、窒素ガス中で１０℃／分の昇温速度で１５００℃まで昇温し、この温度で１時間保持し炭化を行って冷却し、空気中７００℃で重量収率９５％になるまで処理し、炭素質繊維不織布を得た。さらに、窒素ガス中で１０℃／分の昇温速度で７００℃まで昇温し、この温度で１時間保持した。 (Comparative Example 3)
After making polyacrylonitrile fibers with an average fiber diameter of 16 μm flame-resistant in air at 200 to 300 ° C., felt needle SB # 40 (Foster Needle) and punching density using the short fibers (length of about 80 mm) of the flame-resistant fibers. A non-woven fabric having a grain size of 600 g / m ² and a thickness of 5.0 mm was prepared by felting at 250 lines / cm ² . Next, the temperature is raised to 1500 ° C. in nitrogen gas at a heating rate of 10 ° C./min, held at this temperature for 1 hour, carbonized and cooled, and the weight yield is 95% at 700 ° C. in air. The treatment gave a carbonized fiber non-woven fabric. Further, the temperature was raised to 700 ° C. in nitrogen gas at a heating rate of 10 ° C./min, and the temperature was maintained at this temperature for 1 hour.

（比較例４）
実施例１で作製した不織布に対して、活性粒子として粒径０．０４μｍ、ＢＥＴ比表面積１８００ｍ^２／ｇのカーボンブラック粒子を用い、結着材としてＪＦＥケミカル社製コールタールピッチＭＣＰ２５０のピッチ類を用い、これらを湿式で添着した。乾燥後の活性粒子は５ｇ／ｍ^２、結着材は３１ｇ／ｍ^２であった。炭化からの処理は比較例１と同様に行った。 (Comparative Example 4)
For the non-woven fabric produced in Example 1, carbon black particles having a particle size of 0.04 μm and a BET specific surface area of 1800 m ² / g were used as active particles, and pitches of coal tar pitch MCP250 manufactured by JFE Chemical Co., Ltd. were used as binders. These were used and adhered wet. The active particles after drying were 5 g / m ² , and the binder was 31 g / m ² . The treatment from carbonization was carried out in the same manner as in Comparative Example 1.

（比較例５）
実施例１で作製した不織布に対して、活性粒子として粒径０．０４μｍ、ＢＥＴ比表面積１８００ｍ^２／ｇのカーボンブラック粒子を用い、結着材としてＪＦＥケミカル社製コールタールピッチＭＣＰ２５０のピッチ類を用い、これらを湿式で添着した。乾燥後の活性粒子は５ｇ／ｍ^２、結着材は３１ｇ／ｍ^２であった。炭化からの処理は比較例２と同様に行った。 (Comparative Example 5)
For the non-woven fabric produced in Example 1, carbon black particles having a particle size of 0.04 μm and a BET specific surface area of 1800 m ² / g were used as active particles, and pitches of coal tar pitch MCP250 manufactured by JFE Chemical Co., Ltd. were used as binders. These were used and adhered wet. The active particles after drying were 5 g / m ² , and the binder was 31 g / m ² . The treatment from carbonization was carried out in the same manner as in Comparative Example 2.

（比較例６）
実施例１〜３で作製した不織布に対して、活性粒子として粒径０．０４μｍ、ＢＥＴ比表面積１８００ｍ^２／ｇのカーボンブラック粒子を用い、結着材としてＪＦＥケミカル社製コールタールピッチＭＣＰ２５０のピッチ類を用い、これらを湿式で添着した。乾燥後の活性粒子は５ｇ／ｍ^２、結着材は３１ｇ／ｍ^２であった。炭化からの処理は比較例３と同様に行った。 (Comparative Example 6)
For the non-woven fabrics produced in Examples 1 to 3, carbon black particles having a particle size of 0.04 μm and a BET specific surface area of 1800 m ² / g were used as active particles, and a pitch of coal tar pitch MCP250 manufactured by JFE Chemical Co., Ltd. was used as a binder. Classes were used and these were wetted. The active particles after drying were 5 g / m ² , and the binder was 31 g / m ² . The treatment from carbonization was carried out in the same manner as in Comparative Example 3.

（比較例７）
実施例１で作製した不織布に対して、活性粒子として粒径０．０４μｍ、ＢＥＴ比表面積１８００ｍ^２／ｇのカーボンブラック粒子を用い、結着材としてＪＦＥケミカル社製コールタールピッチＭＣＰ２５０のピッチ類を用い、これらを湿式で添着した。乾燥後の活性粒子は３３ｇ／ｍ^２、結着材は２０７ｇ／ｍ^２であった。炭化からの処理は実施例２と同様に行った。 (Comparative Example 7)
For the non-woven fabric produced in Example 1, carbon black particles having a particle size of 0.04 μm and a BET specific surface area of 1800 m ² / g were used as active particles, and pitches of coal tar pitch MCP250 manufactured by JFE Chemical Co., Ltd. were used as binders. These were used and adhered wet. Active particles after drying 33 g / ^{m 2,} binder was 207 g / ^{m 2.} The treatment from carbonization was carried out in the same manner as in Example 2.

以上の実施例、比較例で得られた炭素質繊維不織布の目付、厚み、ＢＥＴ比表面積、ＸＰＳ分析によるＯ／Ｃ比を、製造条件とともに表１に示す。 Table 1 shows the basis weight, thickness, BET specific surface area, and O / C ratio by XPS analysis of the carbonaceous fiber nonwoven fabrics obtained in the above Examples and Comparative Examples together with the production conditions.

上記の全ての処理物をスペーサ厚２．０ｍｍで電極性能（充放電サイクルの２サイクル目と１００サイクル目）の測定を行った結果、表１のようになった。 Table 1 shows the results of measuring the electrode performance (second cycle and 100th cycle of the charge / discharge cycle) of all the above-mentioned processed products with a spacer thickness of 2.0 mm.

表１の結果から明らかなように、実施例１〜６の炭素質繊維不織布は、電圧効率が高く、エネルギー効率に優れていた。しかも長期間使用時における繊維間の接触抵抗の増加、すなわち導電性の低下を抑制でき、長期間の充放電サイクル時のエネルギー効率の経時変化も抑制される。 As is clear from the results in Table 1, the carbonaceous fiber nonwoven fabrics of Examples 1 to 6 had high voltage efficiency and excellent energy efficiency. Moreover, an increase in contact resistance between fibers during long-term use, that is, a decrease in conductivity can be suppressed, and a change over time in energy efficiency during a long-term charge / discharge cycle is also suppressed.

これに対し、含酸性官能基の制御がされていない、または不十分な比較例１、３、４、６では、電圧効率が低くてかつ長期間のエネルギー効率の変化も大きく、また含酸性官能基の付与処理がされていない比較例２と５では電圧効率が極端に低くなっていた。炭素質繊維に対して添加物が多い比較例７では、液の流れが悪く、電圧効率が低く、長期的にも脱落などでエネルギー効率の変化が大きくなっていた。 On the other hand, in Comparative Examples 1, 3, 4, and 6 in which the acidic functional group is not controlled or insufficiently controlled, the voltage efficiency is low, the energy efficiency changes significantly over a long period of time, and the acidic functional group is not controlled. In Comparative Examples 2 and 5 in which the grouping process was not performed, the voltage efficiency was extremely low. In Comparative Example 7 in which the amount of additives was large with respect to the carbonaceous fiber, the flow of the liquid was poor, the voltage efficiency was low, and the change in energy efficiency was large due to dropping off even in the long term.

本発明によれば、低抵抗化と長寿命化を両立する電極材を提供でき、レドックス電池の正極電極材として有用である。本発明の電極材は、フロータイプおよびノンフロータイプのレッドクスフロー電池や、リチウム、キャパシタ、燃料電池のシステムと複合化されたレドックス電池などに好適に用いられる。 According to the present invention, it is possible to provide an electrode material having both low resistance and long life, which is useful as a positive electrode material for a redox battery. The electrode material of the present invention is suitably used for flow type and non-flow type redox flow batteries, redox batteries combined with lithium, capacitor, and fuel cell systems.

１…集電板、２…スペーサ、３…イオン交換膜、４ａ，ｂ…通液路、５…電極
材、６…正極液タンク、７…負極液タンク、８，９…ポンプ、１０…液流入口、
１１…液流出口 1 ... current collector plate, 2 ... spacer, 3 ... ion exchange membrane, 4a, b ... liquid passage, 5 ... electrode material, 6 ... positive electrode liquid tank, 7 ... negative electrode liquid tank, 8, 9 ... pump, 10 ... liquid Inlet,
11 ... Liquid outlet

Claims (4)

炭素質繊維からなるレドックス電池用正極電極材において、
電極材表面の結合酸素原子数が電極材表面の全炭素原子数の０．２〜０．６％であり、かつ、
窒素吸着量から求められるＢＥＴ比表面積が０．５ｍ^２／ｇ以上である電極材。 In the positive electrode material for redox batteries made of carbonaceous fiber
The number of bonded oxygen atoms on the surface of the electrode material is 0.2 to 0.6% of the total number of carbon atoms on the surface of the electrode material, and
An electrode material having a BET specific surface area of 0.5 m ² / g or more, which is determined from the amount of nitrogen adsorbed. 前記炭素質繊維に結着材により結着された活性粒子を含み、
前記活性粒子及び前記結着材が電極材総量の２０％未満である、請求項１に記載の電極材。 Contains active particles bound to the carbonaceous fiber by a binder,
The electrode material according to claim 1, wherein the active particles and the binder are less than 20% of the total amount of the electrode material. 請求項１または２に記載の電極材を備えたレドックス電池。 A redox battery comprising the electrode material according to claim 1 or 2. 請求項１または２に記載の電極材を備えたバナジウム系レドックス電池。 A vanadium-based redox battery comprising the electrode material according to claim 1 or 2.