JP2006147374A - Method of operating vanadium redox flow battery system - Google Patents

Method of operating vanadium redox flow battery system Download PDF

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JP2006147374A
JP2006147374A JP2004336720A JP2004336720A JP2006147374A JP 2006147374 A JP2006147374 A JP 2006147374A JP 2004336720 A JP2004336720 A JP 2004336720A JP 2004336720 A JP2004336720 A JP 2004336720A JP 2006147374 A JP2006147374 A JP 2006147374A
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electrode electrolyte
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Naohiro Inui
直浩 乾
Mitsuyasu Ogawa
光靖 小川
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Kansai Electric Power Co Inc
Sumitomo Electric Industries Ltd
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Sumitomo Electric Industries Ltd
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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
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of operating a redox flow battery system having high battery efficiency. <P>SOLUTION: In the method of operating the vanadium redox flow battery conducting charge discharge by supplying a positive electrode electrolyte and a negative electrode electrolyte to a cell, charge and discharge are conducted so that the charging depth of the positive electrode electrolyte becomes 75% or below. By lowering the charging depth of the positive electrode electrolyte, current efficiency can be enhanced. At this point, by setting the charging depth of the negative electrode electrolyte slightly high, high electromotive force can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

本発明は、バナジウムイオンを含む正負極電解液をセルにそれぞれ供給して充放電を行うレドックスフロー電池システムの運転方法に関するものである。特に、電池効率を高くすることができるバナジウムレドックスフロー電池システムの運転方法に関するものである。   The present invention relates to a method for operating a redox flow battery system in which positive and negative electrode electrolytes containing vanadium ions are supplied to a cell and charged and discharged. In particular, the present invention relates to a method of operating a vanadium redox flow battery system that can increase battery efficiency.

従来、負荷平準化用途や瞬低・停電対策用途などに、レドックスフロー電池を利用することが提案されている。特に、電解液としてバナジウム(V)イオンを含む溶液を利用するバナジウムレドックスフロー電池は、1.起電力が高く、2.エネルギー密度が大きく、3.電解液が単一元素系であるため、正極電解液と負極電解液とを混合しても、充電により再生することができる、といった多くの利点を有している。   Conventionally, it has been proposed to use a redox flow battery for load leveling applications, voltage sag and power failure countermeasure applications. In particular, the vanadium redox flow battery that uses a solution containing vanadium (V) ions as the electrolyte is 1. High electromotive force, 2. High energy density, 3. Since the electrolyte is a single element system, Even if the electrolytic solution and the negative electrode electrolytic solution are mixed, there are many advantages that they can be regenerated by charging.

このようなバナジウムレドックスフロー電池の運転技術において、特許文献1では、充放電開始初期における電極の劣化防止を目的として、充電終了時、正極活物質(5価バナジウムイオン)が90％以下になるように運転を行うことを開示している。また、電池反応の副反応などにより発生するガス量を低減し、運転の効率を向上させる技術として、特許文献2、特許文献3に記載のものがある。特許文献2に記載される技術は、待機中に自己放電電力量に相当する電力量を常時補充充電し、負極活性物質中の2価バナジウムイオンが94％以下になるように上記補充充電を行うものである。特許文献3に記載される技術は、価数バランスが3.41〜3.60価となるように電解液を再生するものである。   In such a vanadium redox flow battery operation technique, in Patent Document 1, the positive electrode active material (pentavalent vanadium ions) is 90% or less at the end of charging for the purpose of preventing deterioration of the electrode at the beginning of charge / discharge. It is disclosed that driving is performed. In addition, there are technologies described in Patent Document 2 and Patent Document 3 as techniques for reducing the amount of gas generated due to a side reaction of the battery reaction and improving the operation efficiency. The technique described in Patent Document 2 always replenishes the amount of power corresponding to the self-discharge power amount during standby, and performs the replenishment charge so that the divalent vanadium ions in the negative electrode active material are 94% or less. Is. The technique described in Patent Document 3 regenerates the electrolyte so that the valence balance becomes 3.41 to 3.60.

特開平8-138718号公報Japanese Unexamined Patent Publication No. 8-138718 特開2003-157884号公報Japanese Patent Laid-Open No. 2003-157884 特開2003-157883号公報Japanese Patent Laid-Open No. 2003-157883

しかし、上記従来の技術でも、電流効率が低くなる場合があり、電流効率の低下により電池効率の低下を招くため、更なる改善が求められている。   However, even in the above conventional technique, the current efficiency may be lowered, and the battery efficiency is lowered due to the decrease in the current efficiency. Therefore, further improvement is demanded.

特許文献1では、長期的な使用に関する評価が不十分であり、また、負極側の発生ガスについて検討されていない。そこで、特許文献2では、負極側の充電深度が94％以下となるように補充充電を行うと共に、負極側の充電深度と正極側の充電深度とのバラツキを少なくして、ガスの発生を低減し、結果として電圧効率の低下を低減している。しかし、本発明者らが更に検討したところ、正極活物質がある一定量より多くなると、即ち、正極電解液の充電深度がある一定値よりも高くなると、正極活物質が隔膜(イオン交換膜)を通過し易くなり、電流効率が低下するとの知見を得た。   In Patent Document 1, evaluation on long-term use is insufficient, and the generated gas on the negative electrode side is not examined. Therefore, in Patent Document 2, supplementary charging is performed so that the charging depth on the negative electrode side is 94% or less, and variation in the charging depth on the negative electrode side and the charging depth on the positive electrode side is reduced, thereby reducing gas generation. As a result, a decrease in voltage efficiency is reduced. However, when the present inventors further examined, when the positive electrode active material exceeds a certain amount, that is, when the charge depth of the positive electrode electrolyte becomes higher than a certain value, the positive electrode active material is separated from the diaphragm (ion exchange membrane). It has been found that the current efficiency is lowered and the current efficiency is lowered.

また、上記従来の技術では、大きな起電力が望まれる場合に対応できないことがある。   In addition, the above conventional technique may not be able to cope with a case where a large electromotive force is desired.

セルに一定の電力(MW；単位時間当たりの放電量)を維持しておくよりも、電力量(MWh)を優先する場合、充電深度が低い領域まで使用することがある。このような運転を行うと、起電力が平均すると小さくなってしまい、所望の起電力が得られないことがある。上記従来の技術では、このような要求に対応するための手法について検討されていない。   When priority is given to the amount of power (MWh) rather than maintaining constant power (MW; amount of discharge per unit time) in the cell, the cell may be used up to an area where the charging depth is low. When such an operation is performed, the average electromotive force becomes small, and a desired electromotive force may not be obtained. In the above conventional technique, a technique for meeting such a demand has not been studied.

従って、本発明の主目的は、電流効率の低下を低減して、電池効率を向上させることができるバナジウムレドックスフロー電池システムの運転方法を提供することにある。また、本発明の他の目的は、更に大きな起電力を得ることができるバナジウムレドックスフロー電池システムの運転方法を提供することにある。   Accordingly, a main object of the present invention is to provide a method of operating a vanadium redox flow battery system that can reduce the decrease in current efficiency and improve the battery efficiency. Another object of the present invention is to provide a method for operating a vanadium redox flow battery system capable of obtaining a larger electromotive force.

本発明は、電流効率の改善を図るべく、正極電解液の充電深度を上げ過ぎないように充放電を行うことを規定する。   In the present invention, in order to improve current efficiency, it is specified that charging / discharging is performed so as not to increase the charging depth of the positive electrode electrolyte.

即ち、本発明は、セルに正極電解液及び負極電解液を供給して充放電を行うバナジウムレドックスフロー電池の運転方法であって、正極電解液の充電深度が75％以下となるように充放電を行うことを特徴とする。   That is, the present invention is a method for operating a vanadium redox flow battery in which charging and discharging is performed by supplying a positive electrode electrolyte and a negative electrode electrolyte to a cell, and charging and discharging are performed so that the charging depth of the positive electrode electrolyte is 75% or less. It is characterized by performing.

上記正極電解液の充電深度の制御に加えて、更に、負極電解液のみを充電深度が高い領域で使用することで、本発明は、大きな起電力を得ることができる。具体的には、正極電解液の充電深度を75％以下とし、負極電解液の充電深度が75％以上95％以下となるように充放電を行う。   In addition to controlling the charge depth of the positive electrode electrolyte, the present invention can obtain a large electromotive force by using only the negative electrode electrolyte in a region where the charge depth is high. Specifically, charging and discharging are performed so that the charging depth of the positive electrode electrolyte is 75% or less and the charging depth of the negative electrode electrolyte is 75% or more and 95% or less.

特許文献3では、価数バランスが3.41〜3.60価となるように電解液を再生することで、ガスの発生が少なく、電池効率に優れることを開示している。特に、3.45価以上3.5価未満となるように再生することで、電池効率及び液エネルギー密度に優れることが記載されている。しかし、特許文献3では、充放電条件について開示されていない。そこで、本発明者らは、電池効率の更なる向上を図るべく、種々の価数バランスで充放電試験を行った結果、価数バランスが3.5価よりも小さい領域で充放電を行うと電池効率に優れることがわかった。そして、電池効率は、電流効率の変動に影響され、電流効率は、価数バランスに影響されることがわかった。価数バランスは、次の数式1により定義される。   Patent Document 3 discloses that by regenerating the electrolyte so that the valence balance becomes 3.41 to 3.60, gas generation is reduced and battery efficiency is excellent. In particular, it is described that the battery efficiency and the liquid energy density are excellent by regenerating so as to have a valence of 3.45 or more and less than 3.5. However, Patent Document 3 does not disclose charge / discharge conditions. Therefore, the present inventors conducted a charge / discharge test with various valence balances in order to further improve the battery efficiency. As a result, when the charge / discharge is performed in a region where the valence balance is less than 3.5 valences, the battery efficiency is improved. It was found to be excellent. And it turned out that battery efficiency is influenced by the fluctuation | variation of current efficiency, and current efficiency is influenced by a valence balance. The valence balance is defined by Equation 1 below.

Figure 2006147374
Figure 2006147374

従来、電流効率は、価数バランスに影響されず、一定であると考えられていた。しかし、本発明者が実測試験を行った結果、上記のように価数バランスが3.5よりも小さいほど、電流効率に優れることがわかった。そして、価数バランスを3.5価よりも小さくすることは、負極電解液の充電深度に対して、相対的に正極電解液の充電深度を小さくすることになる。ここで、特許文献3にも記載されるように、充放電においても価数バランスが小さくなるほど、また、正極電解液の充電深度と負極電解液の充電深度とのばらつきが大きくなるほど、ガスの発生量が増加する傾向にあった。しかし、本発明者が調べたところ、電流効率は低下しておらず、むしろ上昇しており、ガス発生量の増加は、電流効率に対する影響が無視できる程度のレベルであることがわかった。そこで、本発明では、電流効率をよくするべく、充放電を行う際、正極電解液の充電深度を低くすることを規定する。   Conventionally, the current efficiency was considered to be constant without being affected by the valence balance. However, as a result of the actual measurement test conducted by the present inventor, it was found that the current efficiency is better as the valence balance is smaller than 3.5 as described above. And making the valence balance smaller than 3.5 valences makes the charging depth of the positive electrode electrolyte relatively smaller than the charging depth of the negative electrode electrolyte. Here, as described in Patent Document 3, as the valence balance decreases in charge and discharge, and the variation between the charge depth of the positive electrode electrolyte and the charge depth of the negative electrode electrolyte increases, gas generation occurs. The amount tended to increase. However, as a result of investigation by the present inventor, it was found that the current efficiency did not decrease, but rather increased, and that the increase in the amount of gas generated was at a level where the influence on the current efficiency was negligible. Therefore, in the present invention, in order to improve current efficiency, it is specified that the charge depth of the positive electrode electrolyte is lowered when charging and discharging are performed.

正極電解液の充電深度を小さくするには、正極電解液において正極活物質である5価バナジウムイオンの割合を少なくすることである。正極電解液の充電深度が高くなると、具体的には75％超となると、5価バナジウムイオンが隔膜を通り抜ける量が増加することがわかった。この理由を調べたところ、隔膜は、活物質の透過を完全に遮断できず、また、隔膜を透過する速度がバナジウムイオンの価数によって異なり、5価バナジウムイオンが他の価数のバナジウムイオンよりも格段に大きいためであると考えられる。そこで、本発明では、5価バナジウムイオンが隔膜を透過して電流効率が低下することを低減するべく、正極電解液の充電深度を75％以下とする。正極電解液の充電深度は、小さいほど電流効率の低下を低減することができるため、下限を特に設けない。75％を超えない範囲で、所望の電池容量が確保できるように適宜選択するとよい。実用的には、10％程度以上が適当である。   In order to reduce the depth of charge of the positive electrode electrolyte, it is necessary to reduce the proportion of pentavalent vanadium ions as the positive electrode active material in the positive electrode electrolyte. It was found that the amount of pentavalent vanadium ions passing through the diaphragm increases when the charging depth of the positive electrode electrolyte is increased, specifically, when it exceeds 75%. When this reason was investigated, the diaphragm cannot completely block the permeation of the active material, and the speed of permeation through the diaphragm varies depending on the valence of the vanadium ion, and the pentavalent vanadium ion is different from the vanadium ion of other valences. It is thought that this is because it is much larger. Therefore, in the present invention, the charging depth of the positive electrode electrolyte is set to 75% or less in order to reduce the reduction in current efficiency due to permeation of pentavalent vanadium ions through the diaphragm. The smaller the charging depth of the positive electrode electrolyte, the lower the current efficiency can be reduced. It may be selected as appropriate so that a desired battery capacity can be secured within a range not exceeding 75%. Practically, about 10% or more is appropriate.

正極電解液の充電深度とは、正極電解液中の全活物質中における5価バナジウムイオンの濃度のことであり、次の数式2で表わされる。また、後述する負極電解液の充電深度とは、負極電解液中の全活物質中における2価バナジウムイオンの濃度のことであり、次の数式3で表わされる。
正極：5価バナジウムイオン/(5価バナジウムイオン+4価バナジウムイオン)
… 数式2
負極：2価バナジウムイオン/(2価バナジウムイオン+3価バナジウムイオン)
… 数式3 The charge depth of the positive electrode electrolyte is the concentration of pentavalent vanadium ions in all active materials in the positive electrode electrolyte, and is expressed by the following formula 2. Further, the charging depth of the negative electrode electrolyte described later is the concentration of divalent vanadium ions in all active materials in the negative electrode electrolyte, and is expressed by the following mathematical formula 3.
Positive electrode: pentavalent vanadium ion / (pentavalent vanadium ion + tetravalent vanadium ion)
… Formula 2
Negative electrode: divalent vanadium ion / (divalent vanadium ion + trivalent vanadium ion)
… Formula 3

充電深度は、充放電によって変動し、充電末が最も高い値となる。従って、本発明では、正極電解液の充電末充電深度が75％以下になるように制御する。また、充電深度は、開放電圧(非通電時の電圧、正極電解液の電位−負極電解液の電位で求められる)と一定の関係があり、充電末において開放電圧を測定することで調べることができる。開放電圧の測定は、通常運転時に充放電を行うセル(主セル)と別にモニタ用セルを設けておき、このモニタ用セルの電解液を分析することで容易に行うことができる。なお、開放電圧により充電深度を求める場合、予め充電深度と開放電圧との関係データを得ておく。   The charge depth varies depending on charge / discharge, and the end of charge is the highest value. Therefore, in the present invention, the control is performed so that the depth of charge at the end of charging of the positive electrode electrolyte is 75% or less. In addition, the depth of charge has a certain relationship with the open-circuit voltage (the voltage at the time of non-energization, the potential of the positive electrode electrolyte-the potential of the negative electrode electrolyte), and can be examined by measuring the open-circuit voltage at the end of charging. it can. The open circuit voltage can be easily measured by providing a monitoring cell separately from a cell (main cell) that performs charging / discharging during normal operation and analyzing the electrolyte in the monitoring cell. In addition, when calculating | requiring the charge depth by an open circuit voltage, the relationship data of a charge depth and an open circuit voltage are acquired previously.

上記のように正極電解液の充電深度を上げすぎないようにすることで、電流効率の向上を図ることができる。更に、正極電解液の充電深度が低い領域であっても、負極電解液のみ充電深度が高い領域とすることで、電池システム全体では、開放電圧が増加するため、高い起電力を得ることができるとの知見を得た。   As described above, the current efficiency can be improved by preventing the charging depth of the positive electrode electrolyte from being increased too much. Furthermore, even in a region where the charging depth of the positive electrode electrolyte is low, by setting only the negative electrode electrolyte to a region where the charging depth is high, the open voltage increases in the entire battery system, so that a high electromotive force can be obtained. And gained knowledge.

従来、鉄イオン及びクロムイオンなどといった二元素を用いたレドックスフロー電池において充電深度と起電力とは、充電深度の増加に対応して起電力も増加するといういわゆる線形関係にあるが、充電深度がある一定の値よりも大きくなると、起電力が急激に大きくなる(非線形関係になる)ことが知られている。しかし、バナジウムイオン溶液を電解液に用いたバナジウムレドックスフロー電池において上記充電深度と起電力との関係は確認されていなかった。そこで、本発明者らは、バナジウムレドックスフロー電池について、充電深度と起電力との関係を調べたところ、ある充電深度以上となると、起電力が急激に大きくなることがわかった。即ち、バナジウムレドックスフロー電池においても充電深度と起電力との関係が非線形関係となる領域が存在し、このような非線形関係の領域にあるときに同電池を利用すれば、大きな起電力を得ることができる。そこで、本発明では、大きな起電力を得るべく、負極側において2価バナジウムイオンを多めにしておくことを規定する。具体的には、負極電解液の充電深度を75％以上とする。   Conventionally, in a redox flow battery using two elements such as iron ions and chromium ions, the charging depth and the electromotive force have a so-called linear relationship in which the electromotive force increases in response to the increase in the charging depth. It is known that the electromotive force suddenly increases (becomes a non-linear relationship) when the value exceeds a certain value. However, in the vanadium redox flow battery using the vanadium ion solution as the electrolyte, the relationship between the charging depth and the electromotive force has not been confirmed. Therefore, the present inventors examined the relationship between the charging depth and the electromotive force for the vanadium redox flow battery, and found that the electromotive force rapidly increased when the charging depth exceeded a certain charging depth. That is, even in the vanadium redox flow battery, there is a region where the relationship between the charging depth and the electromotive force is non-linear, and a large electromotive force can be obtained if the battery is used in such a non-linear region. Can do. Therefore, in the present invention, in order to obtain a large electromotive force, it is prescribed that a large amount of divalent vanadium ions is kept on the negative electrode side. Specifically, the charging depth of the negative electrode electrolyte is set to 75% or more.

負極電解液の充電深度は、高いほど好ましく、特に80％以上とすることが望まれる。しかし、高すぎると活物質の供給不足になる、即ち、拡散抵抗が増加して、総合的に効率が低下するため、上限を95％とする。より好ましくは、90％以下である。   The charging depth of the negative electrode electrolyte is preferably as high as possible, and is particularly desired to be 80% or more. However, if it is too high, there will be insufficient supply of the active material, that is, diffusion resistance will increase and overall efficiency will decrease, so the upper limit is made 95%. More preferably, it is 90% or less.

本発明運転方法に利用するバナジウムレドックスフロー電池システムは、レドックスフロー電池用のセル(主セル)と、セルに供給/排出される各極の電解液をそれぞれ貯留するタンクと、セルと各タンクとを連結する電解液の輸送路(配管)とを具える構成が挙げられる。その他、各タンクから電解液をセルに供給し易いようにポンプを具えていてもよい。また、公知のレドックスフロー電池システムを利用してもよい。レドックスフロー電池用セルは、イオン交換膜からなる隔膜を介して正極セルと負極セルとを具える。電解液としては、1.起電力が高く、2.エネルギー密度が大きく、3.電解液が単一元素系であるため正極電解液と負極電解液とが混合しても充電によって再生することができるといった多くの利点を有しているバナジウムイオン溶液を利用する。   The vanadium redox flow battery system used in the operation method of the present invention includes a cell for a redox flow battery (main cell), a tank for storing an electrolyte solution of each electrode supplied / discharged to the cell, a cell and each tank, And an electrolyte transportation path (pipe) for connecting the two. In addition, you may provide the pump so that electrolyte solution may be easily supplied to a cell from each tank. Moreover, you may utilize a well-known redox flow battery system. The redox flow battery cell includes a positive electrode cell and a negative electrode cell through a diaphragm made of an ion exchange membrane. As the electrolyte, 1. High electromotive force 2. High energy density 3. Since the electrolyte is a single element system, it can be regenerated by charging even if the cathode electrolyte and anode electrolyte are mixed Vanadium ion solutions are used that have many advantages such as being able to.

本発明運転方法では、正極電解液の充電深度を制御して充放電を行うことで、電流効率を向上させることができ、引いては電池効率を向上することができるという優れた効果を奏し得る。特に、負極電解液の充電深度をも制御することで、大きな起電力を得ることができる。   In the operation method of the present invention, the charging efficiency of the cathode electrolyte can be controlled to perform charging / discharging so that the current efficiency can be improved, and in turn, the battery efficiency can be improved. . In particular, a large electromotive force can be obtained by controlling the charging depth of the negative electrode electrolyte.

以下、本発明の実施の形態を説明する。   Embodiments of the present invention will be described below.

価数バランスが異なる電解液を用いてバナジウムレドックフロー電池の充放電を行い、電流効率、電圧効率、電池効率を測定した。   The vanadium redock flow battery was charged / discharged using electrolytes having different valence balances, and current efficiency, voltage efficiency, and battery efficiency were measured.

用いた電解液は、正極電解液が4価バナジウムイオン(V+4)/5価バナジウムイオン(V+5)の硫酸水溶液であり、負極電解液が3価バナジウムイオン(V+3)/2価バナジウムイオン(V+2)の硫酸水溶液である。各電解液量は、同量とし、価数バランスが3.3価〜3.7価となるように各極の電解液のバナジウムイオン濃度を調整した。 The electrolyte used was a sulfuric acid aqueous solution of a tetravalent vanadium ion (V +4 ) / 5 valent vanadium ion (V +5 ), while the negative electrode electrolyte was a trivalent vanadium ion (V +3 ) / 2. This is a sulfuric acid aqueous solution of valent vanadium ions (V +2 ). The amount of each electrolytic solution was the same, and the vanadium ion concentration of the electrolytic solution of each electrode was adjusted so that the valence balance was 3.3 to 3.7.

次にこの試験に用いたレドックスフロー電池システムの概要を説明する。図1は、レドックスフロー電池の動作原理図である。このシステムは、イオンが透過可能なイオン交換膜からなる隔膜101により正極セル100Aと負極セル100Bとに分離されたセル100を具える。正極セル100Aに正極電極102、負極セル100Bに負極電極103を内蔵している。正極セル100Aには、正極電解液を供給/排出する正極電解液用のタンク104Aが導管106Aを介して接続されている。負極セル100Bも同様に、負極電解液を供給/排出する負極電解液用のタンク104Bが導管106Bを介して接続されている。導管106A、106Bには、電解液を循環させるためのポンプ105A、105Bを具える。このような構成により、各電極102、103にそれぞれ正極電解液、負極電解液が供給されて、イオンの価数変化反応に伴って充放電を行う。   Next, an outline of the redox flow battery system used in this test will be described. FIG. 1 is an operation principle diagram of a redox flow battery. This system includes a cell 100 separated into a positive electrode cell 100A and a negative electrode cell 100B by a diaphragm 101 made of an ion exchange membrane through which ions can permeate. A positive electrode 102 is incorporated in the positive electrode cell 100A, and a negative electrode 103 is incorporated in the negative electrode cell 100B. A positive electrode electrolyte tank 104A for supplying / discharging the positive electrode electrolyte is connected to the positive electrode cell 100A via a conduit 106A. Similarly, in the negative electrode cell 100B, a tank 104B for negative electrode electrolyte that supplies / discharges the negative electrode electrolyte is connected via a conduit 106B. The conduits 106A and 106B include pumps 105A and 105B for circulating the electrolytic solution. With such a configuration, the positive electrode electrolyte and the negative electrode electrolyte are supplied to the electrodes 102 and 103, respectively, and charging / discharging is performed in accordance with the ion valence change reaction.

試験条件を以下に示す。本試験では、以下に示すような仕様の小型の電池システムを利用した。
(電池仕様)
電極の反応面積：9cm2
電解液：バナジウムイオン(1.7mol/l)と硫酸(2.6mol/l)からなる電解液
正負極とも20cc
電解液の流量：5.4cc/min Test conditions are shown below. In this test, a small battery system having the following specifications was used.
(Battery specifications)
Electrode reaction area: 9cm 2
Electrolyte: Electrolyte composed of vanadium ions (1.7 mol / l) and sulfuric acid (2.6 mol / l)
20cc for both positive and negative electrodes
Electrolyte flow rate: 5.4cc / min

(充電方法)
電流密度70mA/cm2で定電流充電を行う。上限充電電圧:1.55(V/セル)に達したところで充電を終了する。
(放電方法)
電流密度70mA/cm2で定電流放電を行う。下限放電電圧:1.0(V/セル)に達したところで放電を終了する。
上記のようにいずれの価数バランスにおいても、充電末電圧及び放電末電圧を一定にして電流効率、電圧効率、電池効率を測定した。 (Charging method)
Constant current charging is performed at a current density of 70 mA / cm 2 . Charging is terminated when the upper limit charging voltage reaches 1.55 (V / cell).
(Discharge method)
Constant current discharge is performed at a current density of 70 mA / cm 2 . The discharge is terminated when the lower limit discharge voltage reaches 1.0 (V / cell).
As described above, in any valence balance, the current efficiency, voltage efficiency, and battery efficiency were measured with the end-of-charge voltage and end-of-discharge voltage kept constant.

(評価方法)
上記仕様の電池を用いて3サイクルの充放電を行い、電流効率、電圧効率、電池効率を測定した。また、充電末において正極電解液の充電深度、負極電解液の充電深度をそれぞれ測定した。充電深度の測定は、主セルと別にモニタ用セルを設けておき、このモニタ用セルの電解液を分析して、開放電圧を測定し、予め求めた関係データを利用することで求めた。
電流効率は、放電電気量(C)/充電電気量(C)、電圧効率は、放電電圧(V)/充電電圧(V)、電池効率は、放電電流(A)×放電電圧(V)×放電時間(h)/充電電流(A)×充電電圧(V)×充電時間(h)で表わされる。
試験結果を図2に示す。また、各価数バランスにおける充電終了時の充電深度を表1に示す。 (Evaluation methods)
The battery having the above specifications was charged and discharged for 3 cycles, and the current efficiency, voltage efficiency, and battery efficiency were measured. Moreover, the charge depth of the positive electrode electrolyte and the charge depth of the negative electrode electrolyte were measured at the end of charging. The depth of charge was determined by providing a monitoring cell separately from the main cell, analyzing the electrolyte in the monitoring cell, measuring the open circuit voltage, and using the relationship data determined in advance.
Current efficiency is discharge electricity (C) / charge electricity (C), voltage efficiency is discharge voltage (V) / charge voltage (V), battery efficiency is discharge current (A) x discharge voltage (V) x It is expressed by discharge time (h) / charge current (A) × charge voltage (V) × charge time (h).
The test results are shown in FIG. Table 1 shows the charging depth at the end of charging in each valence balance.

Figure 2006147374
Figure 2006147374

図2に示すように電池効率は、価数バランスが3.5価よりも小さい領域で優れていることがわかる。従来、電池効率は、価数バランスが3.5価であるとき、最も優れていると考えられていた。しかし、図2に示すように、価数バランスが3.5価のとき、電池効率が約96％であるのに対し、同3.5価よりも小さい領域では、電池効率が98％超となっており、電池効率が上昇していることがわかる。この電池効率の変動は、電流効率の変動に伴っていることが図2からわかる。これらのことから、電流効率を向上させることが、電池効率の向上に寄与すると言える。そして、表1から、電流効率は、正極電解液の充電深度が低い方が好ましいことがわかる。具体的には、75％以下が好ましいと言える。   As shown in FIG. 2, the battery efficiency is excellent in the region where the valence balance is smaller than 3.5. Traditionally, battery efficiency was considered best when the valence balance was 3.5. However, as shown in FIG. 2, when the valence balance is 3.5, the battery efficiency is about 96%, whereas in the region smaller than 3.5, the battery efficiency is over 98%. It can be seen that the battery efficiency is increasing. It can be seen from FIG. 2 that this change in battery efficiency is accompanied by a change in current efficiency. From these facts, it can be said that improving current efficiency contributes to improving battery efficiency. From Table 1, it can be seen that the current efficiency is preferably lower in the depth of charge of the positive electrode electrolyte. Specifically, it can be said that 75% or less is preferable.

更に、価数バランスを3.1〜3.3価以下に変化させて同様に充放電を行ったところ、価数バランスが小さくなるほど、即ち、正極電解液の充電深度が小さくなるほど、電流効率が上昇し、それに伴い電池効率も向上することが確認された。この結果から、正極電解液の充電深度を小さくするほど、電流効率の低下を低減できることが確認されたが、実用的に使用するには、上記価数バランスが3.3価程度が好ましい。   Furthermore, when charging and discharging were performed in the same manner by changing the valence balance to 3.1 to 3.3 or less, the current efficiency increased as the valence balance decreased, that is, the charging depth of the positive electrode electrolyte decreased. Along with this, it was confirmed that the battery efficiency was also improved. From this result, it was confirmed that the decrease in current efficiency can be reduced as the charging depth of the positive electrode electrolyte is reduced. However, for practical use, the valence balance is preferably about 3.3.

以上の試験結果から、正極電解液の充電深度が75％以下となるように充放電を行うことで、電流効率の向上、引いては電池効率を向上することができることが確認された。   From the above test results, it was confirmed that by performing charging / discharging so that the charging depth of the positive electrode electrolyte solution is 75% or less, it is possible to improve current efficiency and thereby improve battery efficiency.

上記試験により、正極電解液の充電深度が低くなるように充放電を行うことで、電池効率の向上が図れることがわかった。次に、負極電解液の充電深度に注目してみる。上記実施例1で用いた電池システムと同様の小型の電池システムを利用して、負極電解液の充電深度が種々の値となるように充放電を行い、負極電解液の充電深度と起電力との関係を調べてみた。   From the above test, it was found that the battery efficiency can be improved by charging and discharging so that the charging depth of the positive electrode electrolyte is lowered. Next, attention is paid to the charging depth of the negative electrode electrolyte. Using a small battery system similar to the battery system used in Example 1 above, charging and discharging were performed so that the charging depth of the negative electrode electrolyte had various values, and the charging depth and electromotive force of the negative electrode electrolyte were I examined the relationship.

用いた電解液は、正極電解液が4価バナジウムイオン(V+4)/5価バナジウムイオン(V+5)の硫酸水溶液であり、負極電解液が3価バナジウムイオン(V+3)/2価バナジウムイオン(V+2)の硫酸水溶液である。各電解液量は、同量とし、価数バランスが3.45価となるように各極の電解液のバナジウムイオン濃度を調整した。充電方法及び放電方法は、上記試験と同様とした。充電深度の測定は、主セルと別にモニタ用セルを設けておき、このモニタ用セルの電解液を分析して、開放電圧を測定することで求めた。試験結果を図3に示す。 The electrolyte used was a sulfuric acid aqueous solution of a tetravalent vanadium ion (V +4 ) / 5 valent vanadium ion (V +5 ), while the negative electrode electrolyte was a trivalent vanadium ion (V +3 ) / 2. This is a sulfuric acid aqueous solution of valent vanadium ions (V +2 ). The amount of each electrolytic solution was the same, and the vanadium ion concentration of the electrolytic solution of each electrode was adjusted so that the valence balance was 3.45. The charging method and discharging method were the same as in the above test. The depth of charge was determined by providing a monitoring cell separately from the main cell, analyzing the electrolyte in the monitoring cell, and measuring the open circuit voltage. The test results are shown in FIG.

図3に示すように負極電解液の充電深度と起電力(開放電圧)とは、充電深度がある値までは線形関係にあり、同充電深度がある値以上となると、具体的には、75％以上となると、起電力が非常に大きくなって非線形関係となることがわかる。従って、負極電解液の充電深度と起電力とが非線形関係にある領域において電池システムを使用すると、大きな起電力が得られることがわかる。図3に示すように負極電解液の充電深度が高いほど大きな起電力が得られているが、95％を超えると、活物質の供給不足となり易い。従って、負極電解液の充電深度は、特に80〜90％が好ましいと言える。なお、負極電解液の充電深度が85％のとき、正極電解液の充電深度は75％であった。   As shown in FIG. 3, the charging depth of the negative electrode electrolyte and the electromotive force (open voltage) are in a linear relationship up to a certain charging depth, and when the charging depth exceeds a certain value, specifically, 75 It can be seen that when the ratio is greater than or equal to%, the electromotive force becomes very large, resulting in a nonlinear relationship. Therefore, it can be seen that a large electromotive force can be obtained when the battery system is used in a region where the charging depth of the negative electrode electrolyte and the electromotive force are in a non-linear relationship. As shown in FIG. 3, the higher the depth of charge of the negative electrode electrolyte, the larger the electromotive force is obtained. However, when it exceeds 95%, the supply of the active material tends to be insufficient. Therefore, it can be said that the charging depth of the negative electrode electrolyte is particularly preferably 80 to 90%. When the depth of charge of the negative electrode electrolyte was 85%, the depth of charge of the positive electrode electrolyte was 75%.

また、価数バランスを3.5価に調整した電解液で正極電解液の充電深度を放電終了時:10％、充電終了時:60％となるように充放電を行ったところ(負極電解液の充電深度の変化:10〜60％)、平均起電力は1.369Vであった。これに対し、価数バランスを3.35価に調整した電解液を利用して同様に、正極電解液の充電深度を放電終了時:10％、充電終了時:60％となるように充放電を行ったところ(負極電解液の充電深度の変化：40〜90％)、平均起電力は、1.414Vであり、起電力が約3％上昇していた。   In addition, when the charge depth of the positive electrode electrolyte was 10% at the end of discharge: 60% at the end of charge: 60% with the electrolyte having the valence balance adjusted to 3.5 (charge of the negative electrode electrolyte) Depth change: 10-60%), the average electromotive force was 1.369V. On the other hand, using an electrolyte whose valence balance is adjusted to 3.35, charge / discharge is similarly performed so that the charge depth of the positive electrode electrolyte is 10% at the end of discharge and 60% at the end of charge. As a result (change in the charging depth of the negative electrode electrolyte: 40 to 90%), the average electromotive force was 1.414 V, and the electromotive force increased by about 3%.

負極電解液の充電深度が大きくなるにつれて、起電力が大きくなる原因を調べるべく、負極電解液の充電深度と負極電解液の電位との関係を調べてみた。その結果を図4に示す。   In order to investigate the cause of the increase in electromotive force as the depth of charge of the negative electrode electrolyte increases, the relationship between the depth of charge of the negative electrode electrolyte and the potential of the negative electrode electrolyte was examined. The results are shown in FIG.

電解液の開放電圧は、正極電解液の電位から負極電解液の電位を引いたもので表わされる。即ち、開放電圧＝正極電解液の電位−負極電解液の電位となる。このとき、図4に示すように、負極電解液の充電深度が大きくなるにつれて、負極電解液の電位が小さくなる、即ち、電位の絶対値が大きくなっていることがわかる。従って、上記式により求められる開放電圧は、負極電解液の電位が小さくなる、即ち、電位の絶対値が大きくなるほど、大きな値をとることがわかる。   The open circuit voltage of the electrolytic solution is expressed by subtracting the potential of the negative electrode electrolyte from the potential of the positive electrode electrolyte. That is, the open circuit voltage = the potential of the positive electrode electrolyte−the potential of the negative electrode electrolyte. At this time, as shown in FIG. 4, it can be seen that as the charging depth of the negative electrode electrolyte increases, the potential of the negative electrode electrolyte decreases, that is, the absolute value of the potential increases. Therefore, it can be seen that the open-circuit voltage obtained by the above formula takes a larger value as the potential of the negative electrode electrolyte decreases, that is, as the absolute value of the potential increases.

本発明は、負荷平準化や瞬低対策などとして利用されているバナジウムレドックスフロー電池システムの運転に利用することが好適である。特に、大きな起電力が望まれている場合に好適である。   The present invention is preferably used for the operation of a vanadium redox flow battery system that is used for load leveling, a measure for instantaneous voltage drop, and the like. This is particularly suitable when a large electromotive force is desired.

バナジウムレドックスフロー電池システムの動作原理を示す説明図である。It is explanatory drawing which shows the operating principle of a vanadium redox flow battery system. 価数バランスと電流効率、電圧効率、電池効率との関係を示すグラフである。It is a graph which shows the relationship between a valence balance, current efficiency, voltage efficiency, and battery efficiency. 負極電解液の充電深度と開放電圧との関係を示すグラフである。It is a graph which shows the relationship between the charge depth of a negative electrode electrolyte solution, and an open circuit voltage. 負極電解液の充電深度と負極電解液の電位との関係を示すグラフである。It is a graph which shows the relationship between the charge depth of a negative electrode electrolyte, and the electric potential of a negative electrode electrolyte.

符号の説明Explanation of symbols

100 セル 100A 正極セル 100B 負極セル 101 隔膜 102 正極電極
103 負極電極 104A 正極電解液タンク 104B 負極電解液タンク
105A,105B ポンプ 106A,106B 導管 100 cells 100A positive electrode cell 100B negative electrode cell 101 diaphragm 102 positive electrode
103 Negative electrode 104A Positive electrolyte tank 104B Negative electrolyte tank
105A, 105B Pump 106A, 106B Conduit

Claims (2)

セルに正極電解液及び負極電解液を供給して充放電を行うバナジウムレドックスフロー電池の運転方法であって、
正極電解液の充電深度が75％以下となるように充放電を行うことを特徴とするバナジウムレドックスフロー電池の運転方法。 A method for operating a vanadium redox flow battery that charges and discharges by supplying a positive electrode electrolyte and a negative electrode electrolyte to a cell,
A method for operating a vanadium redox flow battery, wherein charging and discharging are performed so that the charge depth of the positive electrode electrolyte is 75% or less. 更に、負極電解液の充電深度が75％以上95％以下となるように充放電を行うことを特徴とする請求項1に記載のバナジウムレドックスフロー電池の運転方法。   2. The method for operating a vanadium redox flow battery according to claim 1, wherein charging and discharging are performed such that the charging depth of the negative electrode electrolyte is 75% or more and 95% or less.
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