JP2021028866A - Electrolyte solution and redox flow battery - Google Patents
Electrolyte solution and redox flow battery Download PDFInfo
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
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Abstract
Description
本発明は、電解液および該電解液を備えるレドックスフロー電池に関する。 The present invention relates to an electrolytic solution and a redox flow battery including the electrolytic solution.
大容量蓄電池としてレドックスフロー電池が知られている。一般に、レドックスフロー電池は、正極電極を備える正極室と、負極電極を備える負極室と、これら両電極室に挟まれるイオン交換膜からなる隔膜と、構成されており、両極室にそれぞれ電解液を供給し、充放電を行う。活物質として、酸化還元により価数が変化する金属イオンを含む水溶液系電解液を用いることが一般的である。例えば、鉄イオンを含む正極電解液と、クロムイオンを含む負極電解液とを用いる鉄―クロム系（Ｆｅ−Ｃｒ）レドックスフロー電池、マンガンイオンを含む正極電解液と、チタンイオンを含む負極電解液とを用いるマンガン―チタン系（Ｍｎ−Ｔｉ）レドックスフロー電池、バナジウムイオンを含む正負極電解液を用いる全バナジウム系（Ｖ−Ｖ）レドックスフロー電池等が挙げられる。その中で、特に、全バナジウム系（Ｖ−Ｖ）レドックスフロー電池の開発が世界中で広く進められている。 A redox flow battery is known as a large-capacity storage battery. Generally, a redox flow battery is composed of a positive electrode chamber provided with a positive electrode electrode, a negative electrode chamber provided with a negative electrode electrode, and a diaphragm composed of an ion exchange membrane sandwiched between the negative electrode chambers, and an electrolytic solution is placed in each of the polar chambers. Supply and charge / discharge. As the active material, it is common to use an aqueous electrolytic solution containing a metal ion whose valence changes by redox. For example, an iron-chromium (Fe-Cr) redox flow battery using a positive electrode electrolyte containing iron ions and a negative electrode electrolyte containing chromium ions, a positive electrode electrolyte containing manganese ions, and a negative electrode electrolyte containing titanium ions. Examples thereof include a manganese-titanium-based (Mn-Ti) redox flow battery using and a total vanadium-based (VV) redox flow battery using a positive and negative electrode electrolyte solution containing vanadium ions. Among them, in particular, the development of all vanadium-based (VV) redox flow batteries is being widely promoted all over the world.
なお、バナジウムイオンを含む電解液を用いたレドックスフロー電池では、充放電の際、バナジウムイオンの反応は以下の通りとされている。
正極：ＶＯ２＋＋Ｈ２Ｏ→ＶＯ２ ＋＋２Ｈ＋＋ｅ− (充電)
ＶＯ２＋＋Ｈ２Ｏ←ＶＯ２ ＋＋２Ｈ＋＋ｅ− (放電)
負極：Ｖ３＋＋ｅ−→Ｖ２＋ (充電)
Ｖ３＋＋ｅ−←Ｖ２＋ (放電)
In a redox flow battery using an electrolytic solution containing vanadium ions, the reaction of vanadium ions during charging and discharging is as follows.
Positive electrode: VO 2 + + H 2 O → VO 2 + + 2H + + e − (charging)
VO 2+ + H 2 O ← VO 2 + + 2H + + e - ( discharge)
The negative electrode: V 3+ + e - → V 2+ ( charging)
V 3+ + e − ← V 2+ (discharge)
しかしながら、レドックスフロー電池において、充放電を繰り返すと、クロスオーバーと呼ばれる活物質（特に金属イオン）、および溶媒が隔膜を介して移動する現象が生じる。クロスオーバーにより、正負極電解液中の活物質が混合することや、活物質の濃度および電解液量がアンバランスになることで、電気容量が著しく低下する。現状では、隔膜として広く用いられるイオン交換膜だけで、クロスオーバーを防ぐことが困難であるため、様々な工夫が試みられてきた。 However, in a redox flow battery, when charging and discharging are repeated, a phenomenon called crossover in which an active material (particularly a metal ion) and a solvent move through a diaphragm occurs. Due to the crossover, the active materials in the positive and negative electrode electrolytes are mixed, and the concentration of the active material and the amount of the electrolytic solution become unbalanced, so that the electric capacity is significantly reduced. At present, it is difficult to prevent crossover only with an ion exchange membrane widely used as a diaphragm, so various measures have been tried.
特許文献１によれば、同文献記載のレドックスフロー電池は、バナジウムイオンより高起電力を有する有機ラジカル正負活物質と、前記正負活物質を通さない孔径のイオン交換膜とを含むことにより、クロスオーバーの発生が抑えられたとされる。しかし、この方法は金属イオンが活物質として使用されるレドックスフロー電池には適さない。 According to Patent Document 1, the redox flow battery described in the same document contains an organic radical positive / negative active material having a higher electromotive force than vanadium ions and an ion exchange membrane having a pore size that does not allow the positive / negative active material to pass through. It is said that the occurrence of overcoating was suppressed. However, this method is not suitable for redox flow batteries in which metal ions are used as active materials.
特許文献２には、「隔膜で分離された正極セルおよび負極セルと、各セルに内蔵された正極および負極と、正極セルに正極用電解液を導入・排出する正極用タンクと、負極セルに負極用電解液を導入・排出する負極用タンクとを具える電解液流通型電池において、各タンク内の電解液の液面よりも低い位置で両タンクを接続する連通管と、連通管に設けられたバルブと、充電状態を検知する手段と、充電状態を検知する手段による検知結果に基づいて電池の充電状態が規定状態よりも低いときにバルブを開放して両タンクの電解液量を等しくするバルブ開閉機構と、を具えることを特徴とする電解液流通型電池。」が開示されている。この電解液流通型電池は、電解液の量を再バランスすることができるが、設備が複雑になり、コストが増加する。 Patent Document 2 describes "a positive electrode cell and a negative electrode cell separated by a diaphragm, a positive electrode and a negative electrode built in each cell, a positive electrode tank for introducing and discharging a positive electrode electrolyte solution into the positive electrode cell, and a negative electrode cell. In an electrolytic solution flow type battery including a negative electrode tank for introducing and discharging a negative electrode electrolytic solution, a communication pipe for connecting both tanks at a position lower than the liquid level of the electrolytic solution in each tank and a communication pipe are provided. When the charging state of the battery is lower than the specified state based on the detection results of the valve, the means for detecting the charging state, and the means for detecting the charging state, the valve is opened to equalize the amount of electrolyte in both tanks. An electrolyte flow type battery characterized by having a valve opening / closing mechanism and a valve opening / closing mechanism. ”Is disclosed. This electrolyte flow type battery can rebalance the amount of electrolyte, but the equipment becomes complicated and the cost increases.
本発明の目的は、上記の問題点を鑑みてなされたものであり、クロスオーバーによる電気容量の低下を抑制できる電解液およびそれを備えるレドックスフロー電池を提供することである。 An object of the present invention has been made in view of the above problems, and an object of the present invention is to provide an electrolytic solution capable of suppressing a decrease in electric capacity due to crossover and a redox flow battery including the same.
本発明者らは、上述した課題を解決するために鋭意検討を重ねた。その結果、アルカリ金属イオンと、バナジウムイオンと、を含む電解液をレドックスフロー電池に用いることで、バナジウムイオンのクロスオーバーが原因であるレドックスフロー電池容量の低下が抑制され、電池のサイクル寿命が向上することを見出し、本発明を完成するに至った。 The present inventors have made extensive studies to solve the above-mentioned problems. As a result, by using an electrolytic solution containing alkali metal ions and vanadium ions in the redox flow battery, the decrease in the redox flow battery capacity caused by the crossover of vanadium ions is suppressed, and the cycle life of the battery is improved. We have found that this is the case, and have completed the present invention.
本発明は以下[１]〜［８］の発明を含む。
[１] アルカリ金属イオンと、バナジウムイオンとを含み、前記アルカリ金属イオンの総濃度が０．３Ｍ〜２．０Ｍである電解液。
[２] 前記アルカリ金属イオンは、ナトリウムイオン、及びカリウムイオンから選ばれる少なくとも一種である、前項[１]に記載の電解液。
[３] 前記バナジウムイオンの濃度は１．０Ｍ〜４．０Ｍである、前項［１］または[２]に記載の電解液。
[４] 硫酸イオンを含む前項［１］〜［３］のいずれかに記載の電解液。
[５] 前記硫酸イオンの濃度は１．０Ｍ〜１０．０Ｍである、前項［４］に記載の電解液。
[６] さらに、フッ化物イオン、塩化物イオン、臭化物イオン、およびリン酸イオンからなる群から選ばれる少なくとも一種のアニオンを含有する前項［１］〜［５］のいずれかに記載の電解液。
[７] 前記アニオンの総濃度は０．０１Ｍ〜２．０Ｍである、前項［６］に記載の電解液。
[８] 前項［１］〜［７］のいずれかに記載の電解液を備えるレドックスフロー電池。
The present invention includes the following inventions [1] to [8].
[1] An electrolytic solution containing alkali metal ions and vanadium ions, wherein the total concentration of the alkali metal ions is 0.3M to 2.0M.
[2] The electrolytic solution according to the preceding item [1], wherein the alkali metal ion is at least one selected from sodium ion and potassium ion.
[3] The electrolytic solution according to the preceding item [1] or [2], wherein the vanadium ion concentration is 1.0 M to 4.0 M.
[4] The electrolytic solution according to any one of the above items [1] to [3], which contains sulfate ions.
[5] The electrolytic solution according to the preceding item [4], wherein the concentration of the sulfate ion is 1.0 M to 10.0 M.
[6] The electrolytic solution according to any one of the above items [1] to [5], further containing at least one anion selected from the group consisting of fluoride ions, chloride ions, bromide ions, and phosphate ions.
[7] The electrolytic solution according to the preceding item [6], wherein the total concentration of the anions is 0.01M to 2.0M.
[8] A redox flow battery comprising the electrolytic solution according to any one of the preceding items [1] to [7].
本発明によれば、レドックスフロー電池に用いると容量低下を抑制できる電解液、およびそれを備えるレドックスフロー電池を提供することができる。 According to the present invention, it is possible to provide an electrolytic solution capable of suppressing a decrease in capacity when used in a redox flow battery, and a redox flow battery including the same.
以下、本発明を実施するための形態について詳細に説明する。なお、本発明は、以下の実施形態に限定されるものではなく、その要旨の範囲内で変更して実施することができる。 Hereinafter, embodiments for carrying out the present invention will be described in detail. The present invention is not limited to the following embodiments, and can be modified and implemented within the scope of the gist thereof.
［電解液］
本実施形態に係る電解液は、アルカリ金属イオンと、バナジウムイオンとを含み、前記アルカリ金属イオンの総濃度が０．３Ｍ〜２．０Ｍである。ここで、濃度の単位として示すＭとは、体積モル濃度、即ちモル/リットル（ｍｏｌ／Ｌ）を意味する。以下も同様の意味を示す。また、本実施形態に係る電解液は、後述するようにレドックスフロー電池用の電解液として好ましく用いることができる。
[Electrolytic solution]
The electrolytic solution according to the present embodiment contains alkali metal ions and vanadium ions, and the total concentration of the alkali metal ions is 0.3M to 2.0M. Here, M shown as a unit of concentration means a volume molar concentration, that is, mol / liter (mol / L). The following has the same meaning. Further, the electrolytic solution according to the present embodiment can be preferably used as an electrolytic solution for a redox flow battery as described later.
[アルカリ金属イオン]
前記電解液中のアルカリ金属イオンは、リチウムイオン（Ｌｉ＋）、ナトリウムイオン（Ｎａ＋）、カリウムイオン（Ｋ＋）、ルビジウムイオン(Ｒｂ＋)、及びセシウムイオン（Ｃｓ＋）から選択される少なくとも一種である。その中で、経済上の観点で、ナトリウムイオン（Ｎａ＋）、及びカリウムイオン（Ｋ＋）が好ましく、ナトリウムイオン（Ｎａ＋）がより好ましい。このような電解液をレドックスフロー電池に用いると、電解液中のバナジウムイオンのクロスオーバーが原因である電池容量の低下が抑制できる。また、セル抵抗の上昇を抑える観点から、前記電解液中のアルカリ金属イオンの総濃度は０．３Ｍ〜２．０Ｍ、好ましくは０．３Ｍ〜１．５Ｍ、より好ましくは０．３Ｍ〜１．０Ｍ、さらに好ましくは０．４Ｍ〜０．８Ｍである。前記電解液に溶解して、アルカリ金属イオンを生じさせる原料としては、特に限定されるものではないが、取扱い安全上では、前記アルカリ金属イオンを含む塩が好ましい。電解液の安定性、およびイオン伝導性を向上する観点から、前記金属イオンのハロゲン塩、硫酸塩またはハロゲン塩と硫酸塩の混合物が特に好ましい。
[Alkali metal ion]
The alkali metal ion in the electrolytic solution is at least selected from lithium ion (Li + ), sodium ion (Na + ), potassium ion (K + ), rubidium ion (Rb + ), and cesium ion (Cs +). It is a kind. Among them, from an economic point of view, sodium ion (Na + ) and potassium ion (K + ) are preferable, and sodium ion (Na + ) is more preferable. When such an electrolytic solution is used in a redox flow battery, it is possible to suppress a decrease in battery capacity caused by a crossover of vanadium ions in the electrolytic solution. Further, from the viewpoint of suppressing an increase in cell resistance, the total concentration of alkali metal ions in the electrolytic solution is 0.3M to 2.0M, preferably 0.3M to 1.5M, and more preferably 0.3M to 1. It is 0M, more preferably 0.4M to 0.8M. The raw material that dissolves in the electrolytic solution to generate alkali metal ions is not particularly limited, but a salt containing the alkali metal ions is preferable from the viewpoint of handling safety. From the viewpoint of improving the stability of the electrolytic solution and the ionic conductivity, a halogen salt of the metal ion, a sulfate, or a mixture of a halogen salt and a sulfate is particularly preferable.
［バナジウムイオン］
前記電解液中のバナジウムイオンは、２価のバナジウムイオン（Ｖ２＋）、３価のバナジウムイオン（Ｖ３＋）、４価のバナジウムイオン（ＶＯ２＋）、および５価のバナジウムイオン（ＶＯ２ ＋）の少なくとも一種である。前記電解液に溶解して、このようなバナジウムイオンを生じさせる原料としては、水または酸性水溶液に溶解できるバナジウム塩が好ましい。水への溶解度が高いという観点から、酸化硫酸バナジウムがより好ましい。前記電解液中のバナジウムイオンの総濃度は、好ましくは１．０Ｍ〜４．０Ｍであり、この範囲内であれば、エネルギー密度を確保しつつ、バナジウムの沈殿物の発生が抑制される。より好ましくは１．０Ｍ〜３．０Ｍ、特に好ましくは１．０Ｍ〜２．５Ｍである。
[Vanadium ion]
Vanadium ions in the electrolytic solution, divalent vanadium ions (V 2+), 3-valent vanadium ions (V 3+), 4-valent vanadium ions (VO 2+), and pentavalent vanadium ions (VO 2 +) At least one of. As a raw material that dissolves in the electrolytic solution to generate such vanadium ions, a vanadium salt that can be dissolved in water or an acidic aqueous solution is preferable. Vanadium oxide sulfate is more preferable from the viewpoint of high solubility in water. The total concentration of vanadium ions in the electrolytic solution is preferably 1.0 M to 4.0 M, and if it is within this range, the generation of vanadium precipitates is suppressed while ensuring the energy density. It is more preferably 1.0M to 3.0M, and particularly preferably 1.0M to 2.5M.
［硫酸イオン］
本実施形態における電解液は、硫酸イオン（ＳＯ４ ２−）を含むことが好ましい。硫酸イオンが存在すると、バナジウムイオンはより安定に溶解する傾向がある。硫酸イオンの濃度は、好ましくは１．０Ｍ〜１０．０Ｍ、より好ましくは１．０Ｍ〜８．０Ｍ、さらに好ましくは２．０Ｍ〜６．０Ｍである。電解液に溶解して硫酸イオンを生じさせる原料としては、硫酸またはバナジウムの硫酸塩等が挙げられ、電解液を酸性に保つ点において好ましくは硫酸が挙げられる。
[Sulfate ion]
Electrolytic solution in this embodiment preferably contains a sulfate ion (SO 4 2-). In the presence of sulfate ions, vanadium ions tend to dissolve more stably. The concentration of sulfate ions is preferably 1.0 M to 10.0 M, more preferably 1.0 M to 8.0 M, and even more preferably 2.0 M to 6.0 M. Examples of the raw material that dissolves in the electrolytic solution to generate sulfate ions include sulfuric acid or vanadium sulfate, and sulfuric acid is preferable in terms of keeping the electrolytic solution acidic.
［硫酸イオン以外のアニオン］
本実施形態に係る電解液は、フッ化物イオン（Ｆ−）、塩化物イオン（Ｃｌ−）、臭化物イオン（Ｂｒ−）、およびリン酸イオン（ＰＯ４ ３−）からなる群から選ばれる少なくとも一種のアニオンをさらに含有することが好ましい。これらの中でも、塩化物イオン（Ｃｌ−）を含むことがより好ましい。前記アニオンをさらに含むことにより、電解液のイオン伝導度や金属イオンの反応性が高くなると考えられ、そのため、電池の内部抵抗が小さくなる。さらに、電解液中のバナジウムイオンの溶解度の向上が得られる。前記アニオンの総濃度は、好ましくは０．０１Ｍ〜２．０Ｍ、より好ましくは０．１Ｍ〜１．５Ｍ、さらに好ましくは０．１Ｍ〜１．０Ｍである。前記電解液に溶解して前記アニオンを生じさせる原料としては、前記アニオンを含む酸、バナジウム塩が好ましい。
[Anions other than sulfate ions]
Electrolytic solution according to the present embodiment, the fluoride ion (F -), chloride ion (Cl -) - at least one member selected from the group consisting of, and phosphate ions (PO 4 3-), bromide ion (Br) It is preferable to further contain the anion of. Among these, it is more preferable to contain chloride ion (Cl −). It is considered that the ionic conductivity of the electrolytic solution and the reactivity of the metal ions are increased by further containing the anion, and therefore the internal resistance of the battery is reduced. Further, the solubility of vanadium ions in the electrolytic solution can be improved. The total concentration of the anions is preferably 0.01M to 2.0M, more preferably 0.1M to 1.5M, and even more preferably 0.1M to 1.0M. As the raw material that dissolves in the electrolytic solution to generate the anion, an acid or vanadium salt containing the anion is preferable.
[レドックスフロー電池]
本実施形態に係るレドックスフロー電池は前記電解液を含むことを特徴とする。本発明のレドックスフロー電池は、公知の構成を採用することができる。
[Redox flow battery]
The redox flow battery according to the present embodiment is characterized by containing the electrolytic solution. The redox flow battery of the present invention can adopt a known configuration.
以下、実施例に基づいて本発明をより具体的に説明するが、本発明はこれら実施例に限定されるものではない。 Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to these Examples.
[実施例１]
（電解液の調製）
硫酸（Ｈ２ＳＯ４）濃度が４．０Ｍの硫酸水溶液１００ｍｌに、０．０３ｍｏｌの硫酸ナトリウム（Ｎａ２ＳＯ４）と、０．０９ｍｏｌの硫酸バナジウム（Ｖ２（ＳＯ４）３）と、０．１８ｍｏｌの酸化硫酸バナジウム（ＶＯＳＯ４）と、を添加して、溶液の体積が２００ｍｌになるように、純水を加え、撹拌して電解液を２００ｍｌ調製した。
[Example 1]
(Preparation of electrolyte)
0.03 mol of sodium sulfate (Na 2 SO 4 ), 0.09 mol of vanadyl sulfate (V 2 (SO 4 ) 3 ), and 0 in 100 ml of sulfuric acid aqueous solution having a sulfuric acid (H 2 SO 4) concentration of 4.0 M. .18 mol of vanadyl oxide sulfate (VOSO 4 ) and pure water were added so that the volume of the solution became 200 ml, and 200 ml of an electrolytic solution was prepared by stirring.
（充放電特性の測定）
実験に使用したレドックスフロー電池の模式図を図４に示す。電池セル２は、正極電極１０および負極電極２０として面積５０ｃｍ２（５ｃｍ×１０ｃｍ）の東洋紡（株）製カーボンフェルト（ＡＡＦ３０４ＺＳ）と、イオン交換膜としてＮａｆｉｏｎ（商標）２１２を用いた。正極電解液および負極電解液として、前記作製した電解液をそれぞれ５０ｍｌずつ用意し、正極セル１１および負極セル２１に、電解液を５０ｍｌ/ｍｉｎの流量で循環しながら、１０Ａの電流（電流密度０．２Ａ／ｃｍ２）で充放電を行った。最初に充電を行い、電圧が１．７５Ｖになったところで充電を停止し、次に放電を行い、電圧が１．０Ｖになったところで放電終了とした。この充放電をさらに４９サイクル（全部で５０サイクル）繰り返し、各サイクルの充電時間（ｈ）、放電時間（ｈ）、および充放電中のセル電圧（Ｖ）を測定した。充電時間の半分になる時点のセル電圧をＶ１、放電時間の半分になる時点のセル電圧をＶ２とした。そして、下記式の通り、第１０サイクル目（ｃｙｃ１０）のクーロン効率（％）と、セル抵抗（Ω・ｃｍ２）、および第１０サイクル目（ｃｙｃ１０）と第５０サイクル目（ｃｙｃ５０）の放電容量低減率(以下、放電容量低減率と称する)を求めた。
・充電容量（Ａｈ）＝充電電流×充電時間
・放電容量（Ａｈ）＝放電電流×放電時間
・クーロン効率(％)＝（[放電容量] ／[充電容量]）×１００
・セル抵抗（Ω・ｃｍ２）＝（Ｖ１−Ｖ２）／（２×電流密度）
・放電容量低減率(％)＝（1−[放電容量（ｃｙｃ５０）] ／[放電容量（ｃｙｃ１０）]）×１００
(Measurement of charge / discharge characteristics)
A schematic diagram of the redox flow battery used in the experiment is shown in FIG. For the battery cell 2, carbon felt (AAF304ZS) manufactured by Toyobo Co., Ltd. having an area of 50 cm 2 (5 cm × 10 cm) was used as the positive electrode 10 and the negative electrode 20, and Nafion (trademark) 212 was used as the ion exchange membrane. As the positive electrode electrolytic solution and the negative electrode electrolytic solution, 50 ml each of the prepared electrolytic solutions was prepared, and the electrolytic solution was circulated through the positive electrode cell 11 and the negative electrode cell 21 at a flow rate of 50 ml / min, and a current of 10 A (current density 0). Charging and discharging was performed at .2 A / cm 2). Charging was performed first, charging was stopped when the voltage reached 1.75 V, then discharging was performed, and discharging was terminated when the voltage reached 1.0 V. This charge / discharge was further repeated for 49 cycles (50 cycles in total), and the charge time (h), discharge time (h), and cell voltage (V) during charge / discharge of each cycle were measured. The cell voltage at the time when the charging time was halved was V 1 , and the cell voltage at the time when the discharging time was halved was V 2 . Then, as shown in the following equation, the Coulomb efficiency (%) in the 10th cycle (cyc10), the cell resistance (Ω · cm 2 ), and the discharge capacity in the 10th cycle (cyc10) and the 50th cycle (cyc50). The reduction rate (hereinafter referred to as the discharge capacity reduction rate) was determined.
-Charging capacity (Ah) = charging current x charging time-Discharging capacity (Ah) = discharging current x discharging time-Coulomb efficiency (%) = ([discharge capacity] / [charging capacity]) x 100
・ Cell resistance (Ω ・ cm 2 ) = (V 1 − V 2 ) / (2 × current density)
-Discharge capacity reduction rate (%) = (1- [Discharge capacity (cyc50)] / [Discharge capacity (cyc10)]) x 100
[実施例２〜５、比較例１、２]
添加した硫酸ナトリウムの量は表１に示す通りとした以外は実施例１と同様に２００ｍｌ電解液を作製し、充放電特性の測定を実施した。
[Examples 2 to 5, Comparative Examples 1 and 2]
A 200 ml electrolytic solution was prepared in the same manner as in Example 1 except that the amount of sodium sulfate added was as shown in Table 1, and the charge / discharge characteristics were measured.
[実施例６]
硫酸（Ｈ２ＳＯ４）濃度が４．０Ｍの硫酸水溶液１００ｍｌと、塩酸濃度が１０．０Ｍの塩酸水溶液１０ｍｌを混合して、混合水溶液を得た。前記混合水溶液に、０．０６ｍｏｌの硫酸ナトリウム（Ｎａ２ＳＯ４）と、０．０９ｍｏｌの硫酸バナジウム（Ｖ２（ＳＯ４）３）と、０．１８ｍｏｌの酸化硫酸バナジウム（ＶＯＳＯ４）と、を添加して、溶液の体積が２００ｍｌになるように、純水を加え、撹拌して電解液を２００ｍｌ調製した。そして、実施例１と同様に充放電特性の測定を実施した。
[Example 6]
A mixed aqueous solution was obtained by mixing 100 ml of a sulfuric acid aqueous solution having a sulfuric acid (H 2 SO 4 ) concentration of 4.0 M and 10 ml of a hydrochloric acid aqueous solution having a hydrochloric acid concentration of 10.0 M. In the mixed aqueous solution, 0.06 mol of sodium sulfate (Na 2 SO 4 ), 0.09 mol of vanadium sulfate (V 2 (SO 4 ) 3 ), and 0.18 mol of vanadyl oxide sulfate (VOSO 4 ) were added. Pure water was added so that the volume of the solution became 200 ml, and the mixture was stirred to prepare 200 ml of an electrolytic solution. Then, the charge / discharge characteristics were measured in the same manner as in Example 1.
上記実施例および比較例に、電解液を作製するため、使用された原料の量を表1にまとめた。各実施例および比較例の電解液組成と、充放電特性の測定結果を表２に示す。 Table 1 summarizes the amounts of raw materials used to prepare the electrolytic solution in the above Examples and Comparative Examples. Table 2 shows the electrolyte composition of each Example and Comparative Example and the measurement results of charge / discharge characteristics.
表２と図１、２から明らかなように、電解液中にアルカリ金属イオンとしてナトリウムイオンが０．３Ｍ含まれると、放電容量低減率が十分低くなり、さらに電解液中のナトリウムイオンの濃度が増加すると、放電容量の低減率がさらに低くなり、また、クーロン効率が高くなった。これらより、バナジウムイオンを含む電解液のクロスオーバーを抑制できることが確認された。一方で、図３に示すように、電解液中ナトリウムイオン量の増加と共に、セル抵抗の上昇も観察され、ひいてはセル抵抗による電力の消耗が高くなることが分かった。クロスオーバーの抑制と、セル抵抗上昇の抑制を両立する観点から、ナトリウムイオンの濃度は、０．３Ｍ〜２．０Ｍであり、特に０．３Ｍ〜１．０Ｍが好ましいことが分かった。 As is clear from Table 2 and FIGS. 1 and 2, when 0.3 M of sodium ions are contained as alkali metal ions in the electrolytic solution, the discharge capacity reduction rate becomes sufficiently low, and the concentration of sodium ions in the electrolytic solution becomes high. When it was increased, the reduction rate of the discharge capacity became lower and the Coulomb efficiency became higher. From these, it was confirmed that the crossover of the electrolytic solution containing vanadium ion can be suppressed. On the other hand, as shown in FIG. 3, as the amount of sodium ions in the electrolytic solution increased, an increase in cell resistance was also observed, and it was found that power consumption due to cell resistance increased. From the viewpoint of both suppressing the crossover and suppressing the increase in cell resistance, it was found that the sodium ion concentration was 0.3M to 2.0M, particularly preferably 0.3M to 1.0M.
実施例６では、硫酸イオン以外のアニオンとして、塩化物イオンをさらに含むことで、電解液のイオン伝導度およびバナジウムイオンの反応性が向上したと推定される。そのため、実施例２と比べ、バナジウムイオンのクロスオーバーが原因である放電容量の低下を抑制しながら、セル抵抗を低減させることができた。このような電解液は、特に高電流密度(充放電電流密度は１００ｍＡ／ｃｍ２以上)レドックスフロー電池には好適に利用できる。 In Example 6, it is presumed that the ionic conductivity of the electrolytic solution and the reactivity of vanadium ions were improved by further containing chloride ions as anions other than sulfate ions. Therefore, as compared with Example 2, the cell resistance could be reduced while suppressing the decrease in discharge capacity caused by the crossover of vanadium ions. Such an electrolytic solution can be particularly suitably used for a redox flow battery having a high current density (charge / discharge current density is 100 mA / cm 2 or more).
１ レドックスフロー電池
２ 電池セル
１０ 正極電極
１１ 正極セル
１２ 正極電解液タンク
１３ 正極往路配管
１４ 正極復路配管
１５ ポンプ
２０ 負極電極
２１ 負極セル
２２ 負極電解液タンク
２３ 負極往路配管
２４ 負極復路配管
２５ ポンプ
３０ 隔膜
1 Redox Flow Battery 2 Battery Cell 10 Positive Electrode 11 Positive Cell 12 Positive Electrode Tank 13 Positive Positive Outbound Piping 14 Positive Positive Return Piping 15 Pump 20 Negative Electrode 21 Negative Cell 22 Negative Electrode Tank 23 Negative Outbound Piping 24 Negative Return Piping 25 Pump 30 diaphragm
Claims (8)
A redox flow battery comprising the electrolytic solution according to any one of claims 1 to 7.
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| PCT/JP2018/046317 WO2019124300A1 (en) | 2017-12-19 | 2018-12-17 | Electrolyte solution and redox flow battery |
| TW107145622A TW201931658A (en) | 2017-12-19 | 2018-12-18 | Electrolytic solution and redox flow battery |
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| JP2014235946A (en) * | 2013-06-04 | 2014-12-15 | 旭化成イーマテリアルズ株式会社 | Electrolyte and redox flow battery |
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